System and method for detecting exhaust air leaks

Abstract

The present disclosure relates to systems and methods for detecting exhaust air leaks. Methods and systems are provided for distinguishing exhaust air leaks from a catalyst monitor sensor that has degraded to have a slow response. In one example, a pressure near an exhaust system particulate filter that is less than a threshold pressure may indicate an exhaust air leak, and in response to the indication of an exhaust air leak, a threshold for monitoring the catalyst monitor sensor response may be adjusted. In this way, the effect of the exhaust air leak on the catalyst monitor output may be taken into account so that subsequent monitoring of the threshold catalyst continues to be accurately performed in the presence of the exhaust air leak.

Description

Technical Field

[0001] The present description generally relates to methods and systems for distinguishing a degraded catalyst from an exhaust air leak. Background Art

[0002] The engine exhaust system utilizes an emission control device to treat the exhaust of the internal combustion engine in order to reduce the amount of particulate emissions released into the atmosphere. The emission control device includes a catalytic converter, such as a three-way catalytic converter (TWC) that can reduce NOx and other pollutants. The emission control device may further include a particulate filter (PF) positioned downstream of the TWC to collect particulate matter (such as carbon particles from incomplete combustion). Exhaust gas sensors may be coupled to the emission control device to monitor exhaust gas flow and control the air-fuel ratio (AFR) of the exhaust gas close to stoichiometry. The exhaust gas sensor may include various oxygen sensors, such as oxygen sensors coupled to the upstream and downstream of the catalytic converter. Other sensors may include temperature sensors and pressure sensors. Exhaust gas regulation requires regular execution of on-board diagnostic routines to ensure that the various emission control devices and associated sensors are operating.

[0003] An example method for diagnosing an emission control device catalyst is shown by Santillo et al. in U.S. Patent No. 9,359,967. Therein, during feedback engine air-fuel ratio control, in response to a downstream catalyst exhaust sensor, degradation of the catalyst can be indicated in response to a catalyst transfer function determined within a specified frequency range, the range being based on the exhaust sensor output. In other words, catalyst degradation can be determined after a small air-fuel ratio change that is otherwise routinely used to improve catalyst efficiency. In other methods, catalyst degradation is determined based on the exhaust sensor output after a directed significant perturbation.

[0004] However, the inventors have recognized potential problems with such systems. As an example, the method of U.S. Patent No. 9,359,967 relies on fully functional exhaust sensor measurements to assess potential degradation of the catalyst. While other on-board diagnostic routines may indicate whether an exhaust sensor is functional or degraded, such routines typically assess the output of the same sensor during selected conditions. However, because the output of the catalyst exhaust sensor itself is significantly affected by air-fuel ratio disturbances, there may be situations where the sensor is determined to be degraded when it is functional. For example, if there is an exhaust air leak upstream of the exhaust sensor, the output of the sensor may inadvertently reflect a slow sensor response even if the sensor is not degraded. Because the catalyst upstream of the diagnosis relies on the output of the sensor, sensor state errors may result in significant errors in the catalyst state. For example, an inaccurate assessment of a slow sensor response may result in an erroneous pass of a catalyst monitor, leading to emissions problems. Summary of the invention

[0005] In one example, the above problem may be solved by a method for an engine, comprising: adjusting a diagnostic threshold of an oxygen sensor coupled downstream of an exhaust catalyst in response to a measured pressure at a particulate filter coupled downstream of the oxygen sensor. In this way, the effect of exhaust air leakage at the downstream particulate matter filter may be used to evaluate the functionality of the upstream oxygen sensor and adjust the execution of an on-board diagnostic routine.

[0006] As an example, in response to meeting an entry condition for monitoring an exhaust oxygen sensor coupled downstream of an exhaust catalyst, a pressure associated with a particulate matter filter coupled downstream of the oxygen sensor may be evaluated. If the pressure indicates an exhaust air leak, such as may occur when the pressure measured upstream of or across the filter is below a threshold pressure, a threshold for oxygen sensor monitoring (also referred to herein as CMS monitoring) may be adjusted (e.g., lowered). The output of the oxygen sensor is then compared to the adjusted threshold to perform the monitor. Once the sensor monitor is reliably performed, a catalyst monitor dependent on the output of the sensor may be evaluated.

[0007] In this way, exhaust air leaks that may corrupt the output of an oxygen sensor may be timely and reliably identified based on the output of a pressure sensor coupled to a downstream particulate matter filter. By reliably identifying exhaust air leaks, degraded sensor responses due to the effects of exhaust air leaks may be better distinguished from actual degraded sensor responses. By adjusting diagnostic thresholds for an oxygen sensor monitor based on the pressure response at a downstream particulate matter filter, the reliability of the oxygen sensor monitor may be improved. The reliability of a catalyst monitor that uses the output of the oxygen sensor may then be improved.

[0008] It should be understood that the above summary is provided to introduce selected concepts in a simplified form, which will be further described in the detailed description. This is not meant to identify key or important features of the claimed subject matter, the scope of which is solely defined by the appended claims. In addition, the claimed subject matter is not limited to embodiments that address any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A schematic diagram of a vehicle system having an emissions control device including a particulate filter with a bypass is shown.

[0010] Figure 2 Emission control devices such as Figure 1 A schematic diagram of an emission control device including a catalyst control system having a feedback loop.

[0011] Figure 3 A graph is shown illustrating the effect of significant upstream exhaust air leakage on the CMS voltage response during a deceleration fuel cut-off event.

[0012] Figure 4 A graph is shown illustrating the effect of a small upstream exhaust air leak on the CMS voltage response during a deceleration fuel cut-off event.

[0013] Figure 5 A graph is shown illustrating the effect of upstream exhaust leakage on the GPF inlet pressure sensor response during a deceleration fuel cut-off event.

[0014] Figure 6 A flow chart illustrating an example method for diagnosing an exhaust air leak and adjusting a voltage threshold for a CMS monitor in response to an indication of an exhaust air leak is shown.

[0015] Figure 7 A flow chart is shown illustrating an example method for adjusting execution of a threshold catalyst monitor in response to results of a CMS monitor.

[0016] Figure 8 A prophetic example of engine operation for diagnosing an exhaust air leak and adjusting each of the CMS monitor and the catalyst monitor is shown. DETAILED DESCRIPTION

[0017] The following description relates to systems and methods for improving the reliability of oxygen sensor monitors and catalyst monitors that use the output of oxygen sensors. The methods enable oxygen sensor responses due to a degraded oxygen sensor to be distinguished from similar responses due to an upstream exhaust air leak. The systems and methods described herein may be implemented in a vehicle that includes an engine, such as Figure 1 The engine system depicted may include an emission control device such as Figure 2 A device having an exhaust catalyst coupled upstream of a particulate matter filter. Large exhaust air leaks may cause the output of the exhaust gas sensor to respond more slowly, such as Figure 3 As shown, the exhaust gas sensor may be mistaken for a degraded exhaust gas sensor. However, a small exhaust air leak may not cause such a dramatic change in the exhaust gas sensor response and may therefore be more difficult to identify, such as Figure 4 By monitoring the pressure at the particulate filter of the exhaust system or the pressure across the particulate filter of the exhaust system, the pressure shows different responses to exhaust air leakage (such as Figure 5 Further, in response to the diagnosed exhaust air leak, the diagnostic threshold for the oxygen sensor (CMS) monitor may be appropriately adjusted, such as Figure 6 Then, based on the output of the CMS monitor, the threshold of the catalyst monitor can be adjusted, such as Figure 7 shown. Figure 8 Example engine operation and implementation of an onboard exhaust system monitor are shown in FIG.

[0018] Now go to Figure 1, which schematically shows one cylinder of a multi-cylinder engine 10, which can be included in a propulsion system of a vehicle system 5. In some examples, the vehicle system 5 can be a hybrid vehicle with multiple torque sources that can be used for one or more wheels 55. In other examples, the vehicle system 5 is a conventional vehicle with only an engine or an electric vehicle with only (one or more) motors. In the example shown, the vehicle system 5 includes an engine 10 and a motor 52. The motor 52 can be a motor or a motor / generator (M / G). When one or more clutches 56 are engaged, the crankshaft 140 of the engine 10 and the motor 52 is connected to the wheel 55 via the transmission 54. In the depicted example, the first clutch 56 is disposed between the crankshaft 140 and the motor 52, and the second clutch 56 is disposed between the motor 52 and the transmission 54. The controller 12 can send a signal to the actuator of each clutch 56 to engage or release the clutch so as to connect or disconnect the crankshaft 140 with the motor 52 and the components connected to the motor 52, and / or connect or disconnect the motor 52 with the transmission 54 and the components connected to the transmission 54. The transmission 54 may be a gearbox, a planetary gear system, or another type of transmission.The powertrain may be configured in a variety of ways, including as a parallel, series, or series-parallel hybrid vehicle.

[0019] The electric machine 52 receives power from the traction battery 58 to provide torque to the wheels 55. The electric machine 52 may also be operated as a generator to provide power to charge the battery 58, such as during braking operations.

[0020] Generator 10 may be controlled at least in part by a control system including controller 12 and by input from a vehicle operator 130 via an input device 132. In this example, input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Combustion chamber (e.g., cylinder) 14 of engine 10 may include combustion chamber wall 136 having a piston 138 positioned therein. In some embodiments, the face of piston 138 within cylinder 14 may have a bowl. Piston 138 may be coupled to crankshaft 140 so that reciprocating motion of the piston is converted into rotational motion of the crankshaft. Crankshaft 140 may be coupled to at least one drive wheel of the vehicle via an intermediate transmission system. Further, a starter motor (not shown) may be coupled to crankshaft 140 via a flywheel to enable a starting operation of engine 10.

[0021] Combustion chamber 14 may receive intake air from intake manifold 146 via intake passages 142 and 144, and may exhaust combustion gases via exhaust manifold 148. As such, intake passages 142 and 144 are fluidly coupled to intake manifold 146. Intake manifold 146 and exhaust manifold 148 may selectively communicate with combustion chamber 14 via respective intake valves 150 and exhaust valves 156. In some embodiments, combustion chamber 14 may include two or more intake valves and / or two or more exhaust valves.

[0022] The intake valve 150 and the exhaust valve 156 may be controlled by the controller 12 via respective electric variable valve actuators 152 and 154. Alternatively, the variable valve actuators 152 and 154 may be electro-hydraulic or any other conceivable mechanism for achieving valve actuation. During some conditions, the controller 12 may change the signal provided to the variable valve actuator to control the opening and closing of the respective intake valves and exhaust valves. The positions of the intake valve 150 and the exhaust valve 156 may be determined by respective valve position sensors (not shown). In alternative embodiments, one or more of the intake valve and the exhaust valve may be actuated by one or more cams, and one or more of the cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and / or variable valve lift (VVL) systems may be used to change the valve operation. For example, the cylinder 14 may alternatively include an intake valve controlled via electronic valve actuation and an exhaust valve controlled via cam actuation including CPS and / or VCT.

[0023] Fuel injector 166 is shown coupled directly to combustion chamber 14 for injecting fuel directly into combustion chamber 14 in proportion to the pulse width of signal FPW-1 received from controller 12 via electronic driver 168. In this manner, fuel injector 166 provides what is known as direct injection of fuel into combustion chamber 14. It will be appreciated that the fuel injector could be mounted in the side of the combustion chamber or in the top of the combustion chamber, for example.

[0024] Fuel injector 170 is shown coupled directly to intake manifold 146 for injecting fuel directly into intake manifold 146 in proportion to the pulse width of signal FPW-2 received from controller 12 via electronic driver 171. In this manner, fuel injector 170 provides what is known as port injection of fuel into intake manifold 146. Fuel may be delivered to fuel injectors 166 and 170 via fuel system 8, which may include fuel tanks, fuel pumps, and a fuel rail. It will be appreciated that engine 10 may include one or more of port fuel injection and direct injection.

[0025] As described above, some engine embodiments may include operating the engine in a deceleration fuel cut-off (DFSO) mode to improve fuel economy and reduce brake wear. When operating the engine in DFSO mode, the engine operates without fuel injection, while the engine continues to rotate and pump air through the cylinders. In particular, fuel injection to one or more cylinders 14 via fuel injector 166 and / or fuel injector 170 is disabled, while intake air can continue to be pumped from the intake manifold through the cylinders to the exhaust manifold via the operating intake and exhaust valves through the cylinders. DFSO entry conditions may be based on multiple vehicle and engine operating conditions. Specifically, a combination of one or more of vehicle speed, vehicle acceleration, engine speed, engine load, throttle position, pedal position, transmission gear position, and various other parameters may be used to determine whether the engine is about to enter DFSO. In one example, the DFSO entry condition may be met when the vehicle is decelerating (e.g., the vehicle speed is decreasing). In another example, the DFSO entry condition may be based on an engine speed below a threshold. In yet another example, the DFSO entry condition may be based on an engine load below a threshold and / or a continuously decreasing engine load. In yet another example, DFSO conditions may be based on an accelerator pedal position indicating unrequested torque. For example, during a tip-out where the operator releases the accelerator pedal (e.g., input device 132), DFSO entry conditions may be met and DFSO may be requested. Additionally or alternatively, entry into DFSO may be determined based on a command signal to stop fuel injection.

[0026] Ignition system 188 can provide an ignition spark to combustion chamber 14 via spark plug 192 in response to spark advance signal SA from controller 12, under select operating modes. Although spark ignition components are shown, in some embodiments, combustion chamber 14 or one or more other combustion chambers of engine 10 may be operated in a compression ignition mode with or without an ignition spark.

[0027] Intake passage 144 or intake manifold 146 may include throttle 162 having throttle plate 164. In this particular example, the position of throttle plate 164, or throttle opening, may be varied by controller 12 via a signal provided to an electric motor or actuator (a device commonly referred to as electronic throttle control (ETC)) included with throttle 162. In this manner, throttle 162 may be operated to vary the intake air provided to combustion chamber 14 and other engine cylinders. The position of throttle plate 164 may be provided to controller 12 via throttle position signal TP. Intake passage 142 may include a mass air flow sensor 122 for providing a MAF signal to controller 12, and intake manifold 146 may include a manifold absolute pressure sensor 124 for providing a MAP signal to controller 12.

[0028] Engine 10 may further include a compression device such as a turbocharger or supercharger including at least one compressor 174 arranged along intake passage 144. For a turbocharger, compressor 174 may be at least partially driven by a turbine 176 arranged along exhaust passage 158 (e.g., via shaft 180). If the engine includes a supercharger, compressor 174 may be at least partially driven by engine 10 and / or an electric machine, and may not include a turbine. A compression device (e.g., a turbocharger or supercharger) allows controller 12 to vary the amount of compression provided to one or more cylinders of the engine.

[0029] In some embodiments, engine 10 may include an exhaust gas recirculation (EGR) system including a low pressure (LP) EGR and / or high pressure (HP) EGR passage (not shown) for recirculating exhaust gas. One example of an EGR system includes a low pressure (LP) EGR system, in which EGR may be delivered from downstream of a turbine 176 of a turbocharger to upstream of a compressor 174 of a turbocharger. In a high pressure (HP) EGR system, EGR may be delivered from upstream of a turbine 176 of a turbocharger to downstream of a compressor 174 passage of a turbocharger. In both the LP EGR system and the HP EGR system, the amount of EGR provided to intake manifold 146 may be varied by controller 12 via corresponding LP EGR valves and HP EGR valves (not shown). Further, an EGR sensor (not shown) may be disposed in corresponding LP EGR and / or HP EGR passages and may provide an indication of one or more of a pressure, temperature, and concentration of the exhaust gas. Alternatively, EGR flow may be controlled by a value calculated based on signals from a MAF sensor (upstream), MAP (intake manifold), MAT (manifold gas temperature), and a crank speed sensor. Further, EGR flow may be controlled based on an exhaust O2 sensor 128 and / or an intake oxygen sensor (not shown). Under some conditions, the EGR system may be used to regulate the temperature of the air and fuel mixture within the combustion chamber and / or the temperature near the particulate filter 72.

[0030] It should be understood that in several embodiments, the exhaust passage 158 may include a bypass passage 173 having an inlet positioned upstream of the turbine 176. A flow control valve referred to as a wastegate valve 172 may be disposed in the bypass passage. By adjusting the position (e.g., degree of opening) of the wastegate valve 172, the amount of exhaust gas that bypasses the turbine 176 may be controlled. The position of the wastegate valve may be controlled via a wastegate actuator (not shown, and the wastegate actuator may be hydraulic, pneumatic, electrical, or mechanical in nature) in response to a signal from the controller 12. For example, the controller 12 may receive an operator request for increased engine torque, and may increase boost pressure to meet the torque request. One way to increase boost pressure is to increase the amount of exhaust gas that passes through the turbine 176. To increase the amount of exhaust gas passing through turbine 176, the controller may send a signal to the wastegate actuator to change the wastegate valve to a first position, or maintain the first position (e.g., fully closed), such that no exhaust gas may travel through bypass passage 173, and all exhaust gas passes through turbine 176. Conversely, to reduce boost pressure, the controller may send a command signal to the wastegate actuator to cause the wastegate valve to assume or maintain a second position (e.g., fully open) to allow a percentage of exhaust gas traveling from exhaust passage 158 to flow through wastegate valve 172 through bypass passage 173, thereby bypassing turbine 176, until the bypass passage is reconnected to exhaust passage 158 downstream of turbine 176. It should be appreciated that the wastegate valve may assume a plurality of intermediate positions between the first (e.g., fully closed) and second (e.g., fully open) positions (in response to controller 12 sending a signal to the wastegate actuator to change the position of the wastegate valve) such that a variable amount of exhaust gas may travel through the bypass passage, thereby bypassing turbine 176.

[0031] Similarly, it should be understood that the compressor 174 may include a recirculation passage (not shown) at both ends of the compressor. The recirculation passage may be used to recirculate (warm) compressed air from the compressor outlet back to the compressor inlet. In some embodiments, the compressor recirculation system may alternatively or additionally include a recirculation passage for recirculating (cooled) compressed air from the compressor outlet downstream of the charge air cooler (not shown) to the compressor inlet or compressor bypass for dispersing the compressed air to the atmosphere. A flow control valve referred to as a compression recirculation valve (not shown) may be included between the intake passage 142 and the recirculation passage. Depending on the position of the wastegate valve, the amount of intake air recirculated may be controlled. The position of the compression recirculation valve (CRV) may be controlled via a CRV actuator (not shown, and the CRV actuator may be hydraulic, pneumatic, electrical or mechanical in nature) in response to a signal from the controller 12. The CRV may be a continuously variable valve, in which the position of the valve may be continuously changed from a fully closed position to a fully open position. In some embodiments, the compressor recirculation valve may typically be partially open during boost engine operation to provide some surge margin. Herein, the partially open position may be a default valve position. Increasing the opening of the compression recirculation valve may include actuating (or energizing) a solenoid of the valve.

[0032] Emission control device (ECD) 70 is shown arranged along exhaust passage 158 downstream of exhaust manifold 148 and downstream of exhaust gas sensor 128. Exhaust gas sensor 128 is shown coupled to exhaust passage 158 upstream of emission control device (ECD) 70. Exhaust gas sensor 128 may be any suitable sensor for providing an indication of exhaust gas air / fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide range exhaust gas oxygen) sensor, a two-state oxygen sensor or EGO sensor, a HEGO (heated EGO) sensor, a NOx sensor, an HC sensor, or a CO sensor.

[0033] In this example, the ECD 70 includes a three-way catalytic converter (TWC) 71, but it should be understood that any type of catalyst or catalytic converter may be used without departing from the scope of the present disclosure. The ECD 70 may also include a particulate filter (PF) 72, but it should be understood that the PF 72 may be any type of particulate filter, including but not limited to a diesel particulate filter (DPF) or a gasoline particulate filter (GPF). The ECD 70 further includes a downstream exhaust oxygen sensor, which is also referred to herein as a catalyst monitor sensor (CMS) 13, which may be any type of exhaust gas sensor, including an oxygen sensor or a HEGO sensor. The CMS 13 is coupled downstream of the TWC 71 and may be used to evaluate the state of the catalyst during execution of the catalyst monitor. A pressure sensor 15 and a temperature sensor 16 are also included in the ECD 70. In the depicted embodiment, the pressure sensor 15 is positioned upstream of the PF 72 (or coupled to the inlet of the PF), and the temperature sensor 16 is positioned downstream of the PF 72, but it should be understood that the temperature sensor 16 may be positioned downstream of the PF 72 without departing from the scope of the present disclosure. Figure 1 One or more of the sensors shown are omitted and / or relocated. For example, pressure sensor 15 may be a differential pressure sensor coupled across the inlet and outlet of the PF. In some embodiments, in addition to components configured to filter exhaust, PF 72 may include one or more catalytic materials. For example, PF 72 may be coated with a wash-coat including one or more catalytic materials. For example, such a configuration may be employed for embodiments in which engine 10 is spark ignited. In some embodiments, TWC 71 and PF 72 may be separate components including separate housings positioned away from each other (e.g., as shown, TWC is upstream of PF). Bypass passage 19 may be coupled to exhaust passage 158 directly upstream and downstream of PF 72, and therefore positioned around PF 72. Exhaust control valve (e.g., bypass valve) 17 is positioned within bypass passage 19. Reference is made below to Figure 2 An example detailed ECD configuration is provided. However, it should be understood that ECD 70 is provided as a non-limiting example, and in other embodiments, the ECD may include other components in addition to or in place of TWC 71 and / or PF 72, including but not limited to a lean NOx trap, an SCR catalyst, an oxidation catalyst, or an alternative gas treatment device. For example, in some embodiments, an alternative catalyst or exhaust aftertreatment device may be positioned upstream of PF 72 in place of TWC 71.

[0034] In the depicted embodiment, CMS 13 is a HEGO (heated exhaust gas oxygen) sensor that can monitor the air-fuel ratio of the exhaust gas exiting TWC71. It should be understood that another suitable type of exhaust gas sensor can be used to monitor the catalyst. Pressure sensor 15 can be positioned upstream of PF 72, and the output of pressure sensor 15 can provide an indication of the exhaust back pressure level from PF 72 to vehicle controller 12, which can further be an indication of the soot load on the filter. For example, if PF 72 has a higher soot load, there may be an increased back pressure upstream of PF 72. Pressure sensor 15 can be one of an absolute pressure sensor coupled to the inlet of PF 72 and a differential pressure sensor coupled to each of the inlet and outlet of PF 72. Additionally, a first low threshold exhaust back pressure can be determined, which indicates a "clean" (e.g., minimum soot load) filter, and a second low threshold exhaust back pressure can be determined, which indicates a degraded (e.g., cracked or leaking) filter. In one example, the first low threshold exhaust back pressure and the second low threshold exhaust back pressure can be exactly the same. For example, a PF 72 without soot loading may cause exhaust back pressure upstream of the PF to be at a first low threshold exhaust back pressure. If the output of pressure sensor 15 indicates that the pressure back pressure is below the first low threshold exhaust back pressure, the controller may determine that the PF may be ruptured or degraded.

[0035] Temperature sensor 16 may be positioned downstream of PF 72 to monitor the temperature of the particulate filter. In particular, the output from temperature sensor 16 may provide an indication of exhaust temperature to controller 12. In some examples, the exhaust temperature may be a temperature near the outlet of PF 72, or it may be the temperature of the particulate filter itself. It should be appreciated that a temperature sensor may additionally or alternatively be placed upstream of the particulate filter to monitor the temperature gradient of an exothermic reaction occurring in the particulate filter, for example, during regeneration. In yet another example, temperature sensor 16 may be positioned within PF 72.

[0036] The controller 12 Figure 1 1 is shown as a microcomputer that includes a microprocessor (CPU) 106, input / output ports (I / O) 108, an electronic storage medium (e.g., computer readable) for executable programs and calibration values, shown in this particular example as a read-only memory (ROM) 110, a random access memory (RAM) 112, a keep-alive memory (KAM) 114, and a data bus. The storage medium read-only memory 10 is capable of being programmed with computer readable data representing instructions executable by the microprocessor unit 106 for performing the methods described herein as well as other variants that are anticipated but not specifically listed. As described above, Figure 1One cylinder of a multi-cylinder engine is shown, and it should be understood that each cylinder may similarly include its own set of intake / exhaust valves, fuel injectors, spark plugs, etc.

[0037] Controller 12 may receive various signals from sensors coupled to engine 10, in addition to those previously discussed, including measurements of exhaust and / or PF 72 temperatures from temperature sensor 16, measurements of pressure near the inlet of PF 72 (e.g., exhaust back pressure) from pressure sensor 15, the degree of operator demanded torque from pedal position sensor 134, and air-fuel ratio of the exhaust gas downstream of TWC 71 from catalyst monitor sensor 13. Controller 12 may also receive signals including: measurements of intake mass air flow (MAF) from mass air flow sensor 122; engine coolant temperature (ECT) from temperature sensor 116 coupled to cooling sleeve 118; a surface ignition pick-off signal (PIP) from a Hall effect sensor 120 (or other type) coupled to crankshaft 140; throttle position (TP) or throttle opening from a throttle position sensor; and a manifold absolute pressure signal MAP from pressure sensor 124, which may be used to provide an indication of vacuum or pressure in the intake manifold. Engine speed signal RPM may be generated by controller 12 from signal PIP. Note 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 give an indication of engine torque. Further, along with the detected engine speed, this sensor can provide an estimate of charge (including air) being inducted into the cylinder. In one example, Hall effect sensor 120 (which also serves as an engine speed sensor) may produce a predetermined number of equally spaced pulses every and every revolution of the crankshaft. Controller 12 generates a pulse signal from the engine speed sensor. Figure 1 The various sensors receive signals (e.g., CMS 13, pressure sensor 15, temperature sensor 16, pedal position sensor 134, etc.), and use Figure 1 The controller may control various actuators (eg, valve actuator 17 of the bypass valve, throttle plate 164, spark plug 192, etc.) to adjust engine operation based on received signals and instructions stored in the memory of the controller.

[0038] In one example, the controller may reference a raw gas soot model (stored in the controller's memory and according to instructions stored on the memory) to estimate the amount of soot carried in the exhaust gas exiting the cylinder of the engine and entering the particulate filter. The raw gas soot model may use multiple sensor inputs to estimate the soot carried. In one example, the output of the engine coolant temperature sensor 116 may provide an indication of the engine temperature, and the output of the exhaust gas sensor 128 may provide an indication of the air-fuel ratio. Based on these sensor inputs, the controller may use the raw gas soot model to estimate the amount of soot carried in the exhaust gas. For example, when the engine is operating near the stoichiometric air-fuel ratio and the engine coolant temperature is above the "warm-up" threshold temperature, the controller may determine that a reduced amount of soot is carried in the exhaust gas. In response to data from the raw gas soot model, the controller may use the estimated raw gas soot level (e.g., the soot level in the exhaust gas) to update the PF soot storage model. In one example, the controller may use the PF soot storage model to estimate the amount of soot stored in the PF 72. For example, the controller may estimate a reduced amount of soot stored in the PF when the PF was recently regenerated during DFSO or when exhaust backpressure at the PF (as may be indicated by pressure sensor 15 ) is below an upper threshold exhaust backpressure indicative of a loaded PF.

[0039] Now go to Figure 2 , which shows an example vehicle exhaust system 200, the example vehicle exhaust system 200 includes Figure 1 Therefore, previously in Figure 1 Similar components are described in Figure 2 In one example, the exhaust system 200 may be included in Figure 1 The exhaust system 200 includes an exhaust manifold 148 having a plurality of exhaust runners 210, 212, and 214 (eg, channels) from the engine cylinders (eg, Figure 1 Exhaust from cylinders 14) flows from the exhaust runners 210, 212, and 214. The exhaust runners converge to form a short, narrow exhaust runner convergence conduit 216 that feeds the exhaust into the collection area 206 upstream of the ECD 70. The convergence conduit 216 can be connected to the exhaust gas collector 206. Figure 1 The exhaust passage 158 is the same or similar. Thus, the ECD 70 is configured to Figure 1 The engine 10 receives exhaust gas.

[0040] The ECD 70 includes a TWC 71 positioned upstream of the PF 72. The TWC 71 may include a catalyst canister 218 positioned within an ECD body 219. The catalyst canister 218 is specifically positioned adjacent to an exhaust runner converging conduit 216 and a PF 72 described below and positioned downstream of the exhaust runner converging conduit 216 and upstream of the PF 72. The catalyst canister 218 may include a catalyst brick 220 inserted between mounting pads 222 positioned between the catalyst brick and an upper wall 224 of the ECD body 219 and between the catalyst brick and a lower wall 226 of the ECD body. Figure 2 As shown, the catalyst brick 220 is positioned in close proximity to the exhaust manifold 148. This close-coupled configuration can facilitate a rapid rise in temperature of the catalyst brick 220 to its light-off temperature. When the light-off temperature is reached, exhaust species in the exhaust gas can be effectively converted to desired inert gases before the exhaust gas is discharged into the tailpipe and atmosphere.

[0041] It should be understood that ECD 70 is provided as a non-limiting example, and that many additions and modifications may be made to the ECD without departing from the scope of the present disclosure. For example, in other embodiments, ECD 70 may include two or more catalyst bricks. One or more of the multiple catalyst bricks may include two or more different cell densities. The variation in cell density between the multiple catalyst bricks may be the same, or may vary between at least two of the catalyst bricks. Further, the average cell density between the multiple catalyst bricks may be the same, or may vary between at least two of the catalyst bricks. Other features may or may not be shared between the multiple catalyst bricks, including but not limited to length, catalyst brick base material, catalyst material, and oxygen storage material (if included).

[0042] Exhaust gas sensor 128 is shown positioned at an upstream region of the ECD adjacent exhaust runner conduit 216. As previously described, exhaust gas sensor 128 may be, but is not limited to, a linear oxygen sensor or a universal or wide-range exhaust gas oxygen (UEGO) sensor, a two-state oxygen sensor (EGO), a heated EGO (HEGO) sensor, a NOx sensor, an HC sensor, or a CO sensor. Figure 2In the depicted example, the exhaust gas sensor 128 includes an internal electrode (not shown) encapsulated within a metal shield 246. Exhaust flow originating from the exhaust runners 210, 212, and 214 flows through the exhaust runner converging duct 216 and is detected by the electrodes of the exhaust gas sensor 128. After flowing into the metal shield 246 via openings 248 arranged longitudinally along the bottom of the metal shield 246, the exhaust flow is detected by the electrodes. The sensor housing 250 allows the exhaust gas sensor 128 to be located within the ECD body 219 and couples the electrodes to a control system (e.g., Figure 1 Controller 12 of the ECD 70). Readings from exhaust gas sensor 128 may be used to control operational aspects of ECD 70 as described below.

[0043] The CMS 13 shown is positioned downstream of the TWC 71, which may be configured similarly to the exhaust gas sensor 128. As described in further detail below, readings from the exhaust gas sensor 128 and the CMS 13 may be used to control aspects of the operation of the ECD 70. For example, the difference between the readings from each sensor may indicate the amount of oxygen stored in the TWC 71. It should be understood that the relative positioning of the exhaust gas sensor 128 and the TWC 71 is non-limiting, and the sensor and / or catalyst may be placed elsewhere. In other embodiments, three or more exhaust gas sensors may be included in the ECD 70 - for example, in addition to the exhaust gas sensors 128 and 13, a third exhaust gas sensor is positioned downstream of the PF 72 described below.

[0044] The pressure sensor 15 is shown positioned between the TWC 71 and the PF 72, and is configured to measure the pressure of the exhaust gas flowing through the ECD 70 at a position upstream of the PF 72. As shown therein, the pressure sensor 15 is positioned along the lower wall 226 and is inserted between the TWC 71 and the particulate filter described below. It should be understood that this positioning is non-limiting and that the pressure sensor 15 can be positioned elsewhere in the ECD 70. For example, one or more pressure sensors can be positioned upstream of the catalyst brick 220 or downstream of the particulate filter. In other embodiments, the pressure sensor 15 can be omitted from the ECD 70, where the exhaust pressure is inferred based on one or more engine operating parameters.

[0045] Figure 2Embodiments also include a temperature sensor 16 that is configured to measure the temperature of the exhaust gas flowing through the ECD. As shown, the temperature sensor 16 is positioned along the lower wall 226 and is located after the PF 72 (directly downstream of the PF 72). It should be understood that this positioning is non-limiting and the temperature sensor 16 can be positioned elsewhere in the ECD 70. For example, one or more temperature sensors 16 can be positioned upstream of the catalyst brick 220 or upstream of the particulate filter to measure the temperature gradient across the particulate filter. In this way, the heat release across the particulate filter can be characterized and monitored, such as during the filter regeneration process. Alternatively, the temperature sensor 16 can be omitted from the ECD 70, where the exhaust temperature is inferred based on one or more engine operating parameters.

[0046] PF 72 is shown positioned within ECD body 219 downstream of TWC 71. PF 72 may be inserted between mounting pads 222 positioned between the particulate filter and upper wall 224 and between the particulate filter and lower wall 226 of the ECD body. PF 72 may be configured to capture particulate matter, such as soot mixed with exhaust gas, as it flows through PF 72. As soot and / or other particulate matter accumulates in PF 72, back pressure in the particulate filter may increase, which may adversely affect engine operation and reduce fuel economy. Therefore, PF 72 may be regenerated periodically so that soot stored in PF 72 may be burned (e.g., incinerated). In some examples, PF 72 may be passively or actively regenerated in response to a soot storage level in the filter exceeding a threshold soot level (as may be indicated by the output of pressure sensor 15 exceeding a threshold pressure). For embodiments where ECD 70 is used in conjunction with a spark-ignition engine, PF 72 may be a gasoline particulate filter (GPF), and exhaust from the spark-ignition engine may be hot enough to burn (e.g., incinerate) soot stored in PF 72. However, in some examples, the spark-ignition engine may be operated primarily under stoichiometric conditions, in which case a sufficient amount of gaseous oxygen is not available to burn soot stored in PF 72, and active regeneration may be initiated. As previously described, PF 72 may be any type of particulate filter, including but not limited to a gasoline particulate filter (GPF) or a diesel particulate filter (DPF).

[0047] Bypass valve 17 is shown disposed in bypass passage 19 coupled about PF 72, wherein filter bypass flow (e.g., exhaust gas) bypasses only PF 72 and does not bypass additional emission control devices or TWC 71 positioned downstream of PF 72. As such, bypass passage 19 may be coupled to a first ECD passage 217 directly upstream of PF 72 and a second ECD passage 219 directly downstream of PF 72. In one example, in response to a request to increase the amount of gasoline-burned exhaust gas that bypasses PF 72, ( Figure 1 Controller 12 may send a control signal to the actuator of bypass valve 17 to increase the opening of bypass valve 17 so that an increased flow of burnt exhaust gas may enter bypass passage 19. In this way, the amount of burnt exhaust gas flowing through PF 72 may be reduced because a greater proportion of the total amount of burnt exhaust gas travels through bypass passage 19 and around PF 72. Conversely, when controller sends a control signal to the actuator of bypass valve 17 to decrease the amount of opening of bypass valve 17, a reduction in the flow of exhaust gas through particulate filter bypass passage 19 may be achieved, which will cause an increase in the flow of burnt exhaust gas through PF 72. After the exhaust gas passes through PF 72 or bypass passage 19, the exhaust gas continues through tail pipe 208 toward the atmosphere. In an alternative embodiment, the exhaust gas may continue through 208 to further exhaust treatment downstream.

[0048] Figure 2 Further included is a schematic diagram of the internal and external feedback control loops for the engine's catalyst control system 272, which may provide feedback to a vehicle controller (such as may be included in Figure 1 The catalyst control system 272 is shown as receiving information from the exhaust oxygen sensor and providing information to the engine's fuel injectors such as fuel injector 166 and / or fuel injector 170 ( Figure 1 As shown), the exhaust gas oxygen sensor may include exhaust gas sensor 128 positioned upstream of emission control device 70, and CMS 13 positioned downstream of TWC 71. Other sensors such as pressure sensors, temperature sensors, air-fuel ratio sensors, and composition sensors may be coupled to various locations in the vehicle system. Catalyst control system 272 may receive input data from various sensors, process the input data, and apply actuators in response to the input data processed based on instructions or code programmed therein corresponding to one or more routines. Catalyst control system 272 may be configured to have instructions stored in a non-volatile memory that cause the catalyst control system 272 to execute a control routine via one or more actuators based on information received via one or more sensors. Reference herein Figure 7 and Figure 8 An example control routine is described.

[0049] The catalyst control system 272 regulates the air-fuel ratio (AFR) to a desired air-fuel ratio close to stoichiometry and fine-tunes the regulation based on the deviation of the HEGO voltage from a predetermined HEGO voltage set point. The inner loop controller 207 uses the UEGO (e.g., upstream exhaust gas sensor) 128 for higher bandwidth feedback control, while the outer loop controller 205 uses the HEGO sensor (e.g., CMS) 13 for lower bandwidth control. The control can be controlled by an engine controller such as Figure 1 Controller 12 implements a catalyst control system 272 .

[0050] The inner loop controller 207 may include a proportional integral derivative (PID) controller that regulates the engine AFR by generating an appropriate fuel command (e.g., fuel pulse width). Summing junction 276 combines the fuel command from the inner loop controller 207 and the command from the feedforward controller 274. The combined command is delivered to the fuel injectors (such as Figure 1 The exhaust gas sensor 128 provides a feedback signal to the inner loop controller 207, and the UEGO feedback signal is proportional to the oxygen content of the feed gas or the engine exhaust between the engine 10 and the TWC 71. The outer loop controller 205 generates a UEGO reference signal (e.g., a desired air-fuel ratio) provided to the inner loop controller 207. The UEGO reference signal is combined with the UEGO feedback signal at the converging pipe 216. The inner loop controller 207 then uses the error or difference signal provided by the converging pipe 216 to adjust the fuel command so that the actual AFR in the combustion chamber of the engine approaches the desired AFR. The HEGO sensor (e.g., CMS) 13 provides feedback to the outer loop controller 205. The HEGO feedback signal can be used to adjust the UEGO reference signal or air-fuel ratio reference signal provided to the inner loop controller 207 via the converging pipe 216. Additionally, the outer loop controller 205 operates to improve catalyst efficiency by applying a low amplitude air-fuel ratio square wave at the catalyst input. The square wave allows the exhaust composition entering the catalyst to be altered in order to replenish oxygen and CO in the catalyst, thereby improving hydrocarbon oxidation and NOx reduction.

[0051] Because the CMS 13 is positioned far downstream of the TWC 71, the CMS 13 may be used for feedback control as well as input to diagnose whether a threshold catalyst level of exhaust gas exiting the TWC 71 is exceeded. The threshold catalyst level may be defined as an upper threshold limit of emissions permitted to exit the TWC 71. In one example, in the rare event of a double failure, the downstream CMS 13 may be expected to diagnose the presence of the threshold catalyst level even during conditions where the downstream CMS 13 is erroneous due to low response. In such cases, accurately distinguishing between a normal distribution of catalyst output and the threshold catalyst level may be challenging. As Figure 6 to Figure 7 As stated, the output of the pressure sensor upstream of the PF can be advantageously used to diagnose conditions where the CMS monitor response can be disrupted. By adjusting the thresholds of the CMS monitor during such conditions, the reliability of the CMS monitor can be improved, and in turn, the reliability of the catalyst monitor that depends on the output of the CMS can be improved.

[0052] therefore, Figure 1 and Figure 2 The components of the present invention provide an engine system, which includes: an engine; an exhaust passage including an exhaust catalyst; an upstream oxygen sensor coupled upstream of the exhaust catalyst; a downstream oxygen sensor coupled downstream of the exhaust catalyst; a particulate filter coupled downstream of a second oxygen sensor; a pressure sensor coupled to the particulate filter; and a controller having computer-readable instructions stored on a non-volatile memory, the computer-readable instructions being used to: in response to satisfying an entry condition for a first monitor for a downstream oxygen sensor, compare an output of the pressure sensor to a threshold pressure; and in response to the output of the pressure sensor being higher than the threshold pressure, increase the threshold of the first monitor; execute the first monitor; and in response to the output of the downstream oxygen sensor exceeding the increased threshold after executing the first monitor, indicate degradation of the downstream oxygen sensor.

[0053] It should be understood that various aspects of the vehicle exhaust system 200 and the ECD 70 may be modified without departing from the scope of the present disclosure. For example, the relative positioning, geometry, and dimensions (e.g., length, width, height) of various components of the exhaust system 200 (e.g., TWC 71, PF 72, exhaust gas sensor 128, catalyst monitor sensor 13, pressure sensor 15, and temperature sensor 16) may be adjusted. In some embodiments, two or more exhaust gas sensors, two or more pressure sensors, and / or two or more temperature sensors may be provided, while in other embodiments, the temperature sensor 16 may be omitted from the exhaust system 200. In some embodiments, two or more ECDs may be provided in a cascaded form, such that a first ECD (e.g., including a catalyst and / or a particulate filter) may be followed by a second ECD positioned downstream of the first ECD, wherein the second ECD may or may not include the same components as the first ECD. Further, alternatively or in addition to the TWC 71 and / or PF 72, the ECD 70 may be modified to include other emission control devices, such as a NOx trap, an SCR catalyst, and the like.

[0054] Now go to Figure 3 , which shows a graph 300 showing the CMS voltage response (eg, Figure 1 and Figure 2As shown, graph 300 compares the voltage response of the downstream CMS (due to a deceleration fuel cut-off event) for both a nominal (e.g., no leak) exhaust system at curve 302 and an exhaust system having a significant air leak upstream of the sensor at curve 304. At time 0, fuel delivery to the cylinders of the engine is stopped due to DFSP. It should be understood that a higher voltage output from the HEGO sensor corresponds to rich exhaust and a lower voltage output from the HEGO sensor corresponds to lean exhaust. During DFSO, the exhaust is converted from a rich exhaust mixture to a leaner exhaust mixture because no combustion occurs during DFSO and intake air continues to be pumped through the engine and exhaust system, saturating the catalyst with oxygen. In this particular example, at voltages above ~0.3V, the sensor response in the case of an exhaust air leak appears to be slower than the sensor response in the case of no exhaust air leak. In particular, the transition rate (304) of the leaky exhaust system from high voltage to low voltage appears slowed compared to the transition rate (302) of the exhaust system without the leak, and can therefore be erroneously classified by the CMS OBD monitor as slow response degradation rather than an exhaust air leak. In addition, the degraded sensor response may erroneously lead to a false pass result for a threshold catalyst (TC) OBD monitor when an actual degraded catalyst is present. In particular, the TC monitor may assess the performance of the catalyst based on the output 304 of the catalyst monitor sensor, and if the TC monitor threshold is not adjusted or is adjusted incorrectly, the sensor response can be misleading for an exhaust air leak (if present). For example, if sensor degradation is erroneously detected from an air leak and the threshold is incorrectly modified for the catalyst monitor, the determined catalyst performance may be incorrect.

[0055] Now go to Figure 4 , which shows a graph 400 showing the CMS voltage response (eg, Figure 1 and Figure 2 As shown, graph 400 compares the voltage response of the CMS (due to a deceleration fuel cut-off event) for a nominal (e.g., no leak) exhaust system at curve 402 and an exhaust system having a small air leak upstream of the catalyst monitor sensor at curve 404. Figure 4 The slow response of the CMS to a small upstream exhaust air leak is not as Figure 3 As shown in FIG. 1 , the slow CMS response to a significant upstream exhaust air leak is evident. As a result, simply monitoring the CMS response may not be a robust and reliable diagnostic method for identifying exhaust air leaks.

[0056] Now go to Figure 5 , which shows a graph 500 showing the effect of upstream exhaust leakage on a pressure sensor (eg, Figure 1 and Figure 2 It should be noted that the pressure sensor is positioned on the particulate filter (e.g., Figure 1 and Figure 2 PF 72 of the embodiment. As shown, graph 500 compares the pressure response of the pressure sensor of a nominal (e.g., no leak) exhaust system at curve 502 and an exhaust system with an air leak upstream of the pressure sensor at curve 504. As shown, the exhaust air leakage causes a negative change in the pressure sensor response compared to the pressure sensor response for the nominal, non-leaking exhaust system. In one example, a leaking exhaust system can reduce the sensor response 504 for the leaking exhaust system to below a pressure threshold 506. In one example, pressure threshold 506 can represent the exhaust back pressure corresponding to a "clean" filter. In other examples, pressure threshold 506 can be a low pressure threshold, which can be lower than the "clean" filter pressure threshold. In this way, more than one threshold can be used to assess the potential degradation of the exhaust system and / or the particulate filter. When the output of the pressure sensor is lower than pressure threshold 506, this can indicate a leak in the exhaust system and / or a particulate filter that has otherwise degraded.

[0057] Now go to Figure 6 , which shows a flow chart illustrating an example method 600 for diagnosing an exhaust air leak and adjusting a threshold for a CMS monitor. The CMS monitor is a method for evaluating a catalyst monitor sensor (e.g., Figure 1 and Figure 2 In one example, adjusting the threshold for the CMS monitor for the catalyst monitor sensor includes adjusting a rich-to-lean voltage threshold for the CMS monitor. In other examples, adjusting the rich-to-lean voltage threshold for the CMS monitor includes reducing the rich-to-lean voltage threshold used to calculate a slew rate during a DFSO event to determine a CMS response rate.

[0058] Instructions for implementing method 600 and the remaining methods included herein may be provided by a controller (e.g., Figure 1 The controller 12 and / or Figure 2 The controller 272) is based on instructions stored in the controller's memory and in conjunction with instructions from the vehicle system (e.g., Figure 1The vehicle system 5) sensors such as those mentioned above Figure 1 and Figure 2 The controller may use engine actuators of the engine system to adjust engine operation according to the methods described below.

[0059] Method 600 begins at 602, where the routine includes estimating and / or measuring current engine operating conditions. Current engine operating conditions may include, but are not limited to, air-fuel ratio (e.g., the air-fuel ratio of combusted exhaust gas exiting engine cylinders), particulate filter bypass valve (e.g., Figure 1 and Figure 2 The current operating conditions evaluated may include the position of the bypass valve 17 shown, the duration since the last particulate filter regeneration, the engine speed and engine load, the engine coolant temperature, the degree of actuation (or position) of the accelerator pedal, and the exhaust temperature and pressure near the particulate filter. Other conditions include MAP, MAF, boost pressure, etc. The current operating conditions evaluated may also include the current particulate filter soot load, which may be modeled based on the level of raw gas soot. The raw gas soot level may be modeled based on one or more of the engine coolant temperature, torque, air-fuel ratio, and engine speed. Additional engine operating conditions may include pressures and temperatures measured at the exhaust system.

[0060] In one example, the combustion air-fuel ratio can be measured by an exhaust gas sensor (e.g. Figure 1 to Figure 2 The output of the exhaust gas sensor 128 or the catalyst monitor sensor 13 is indicated. In this way, the controller (for example, Figure 1 The controller 12 may determine whether the engine is running leaner than stoichiometry (λ greater than 1) or richer than stoichiometry (λ less than 1). In another example, the controller may be further capable of inferring the presence of a threshold catalyst (or threshold catalyst state) by determining a magnitude of a frequency domain transfer function of the catalyst within a particular frequency range corresponding to the square wave input. An engine temperature above an engine temperature threshold may indicate that the engine is warm and not in a cold start condition. The controller 12 may receive a pressure sensor at the particulate filter (e.g., Figure 1 to Figure 2 The output of a pressure sensor 15) may be indicative of the degree of soot loading on the particulate filter, as will be further described below.

[0061] It should be understood that raw gas smoke or exhaust smoke can be the amount of smoke carried in the exhaust gas leaving the engine and entering the exhaust system. Ambient and other engine operating conditions may also be included due to their impact on raw gas smoke. An example of a typical operating condition that can generate raw gas with a smoke level lower than the first smoke level threshold is when the engine coolant temperature is higher than the threshold engine temperature (e.g., when the engine is warm), when the air-fuel ratio is close to the stoichiometric air-fuel ratio, and when the engine is not operating in compression injection mode. Conversely, an example of an operating condition that can generate raw gas with a smoke level higher than the first smoke level threshold is when the engine coolant temperature is lower than the threshold engine temperature (e.g., during a cold start), and / or when the air-fuel ratio is rich.

[0062] In one example, a PF soot model may estimate soot every and every 100ms, while a slower calibratable timer determines how often the soot estimated by the model is accumulated and added to the measured soot load value. The timer may be executed while the engine is running and the PF, such as a gasoline particulate filter, is not in regeneration mode. For example, the timer may be calibrated to execute as slowly as every and every 6 minutes, and thus an additional accumulator may be used to capture soot generated during transient operating conditions. The transient accumulator may be reset at the same frequency as the above timer, but with a delay. Soot from the soot model may be accumulated independently and added to the last measured soot load value. When the measured soot load value is available, the accumulated soot load from the model is cleared (e.g., set to zero).

[0063] Under certain engine operating conditions, the PF soot load cannot be accurately determined based on the measured differential pressure across the PF. For example, the PF soot load measurement may not be sufficiently accurate at low exhaust volume flow rates due to the degraded accuracy of the pressure sensor under low exhaust flow conditions. Additionally, the PF soot load may be inaccurate during transients due to the higher time constant of the sensor and / or unstable fluid dynamics in the exhaust system. Therefore, during these conditions, the estimate of the PF soot loading is independent of the soot load based on the measured differential pressure across the PF. Instead, a PF soot model is used to estimate the soot load based on engine speed and load, and then the PF soot model is corrected for engine / ambient conditions. The corrected PF soot model output is then added to the most recent measurement of the soot load from the differential pressure occurring under conditions other than those described above.

[0064] At 604, the routine includes determining whether the output of a pressure sensor near the particulate filter is lower than a first threshold pressure. The first threshold pressure may be a low threshold pressure corresponding to a degraded particulate filter. In one example, the degraded particulate filter may be a cracked particulate filter resulting in a significant pressure loss from the exhaust system to the atmosphere. Due to the significant pressure loss, the pressure at the particulate filter may be less than the first threshold pressure. The first threshold pressure reference Figure 5 for discussion. If the pressure sensor output is less than the first threshold pressure, the routine proceeds to 606, where the routine includes indicating potential degradation of the particulate filter. The routine then proceeds to 608, where the routine includes notifying an operator of potential particulate filter degradation and limiting engine operation. For example, a diagnostic code may be set, and a malfunction indicator light (MIL) may be illuminated on a display panel of the vehicle to notify the operator, maintaining the code and MIL until the filter is replaced or repaired. In this way, the method may indicate the state of the particulate filter based on the pressure measured at the particulate filter; and limit the engine load based on the indicated state. In one example, the indicated state may be a particulate filter or housing that is cracked or otherwise significantly degraded. The routine then ends.

[0065] If the PF pressure sensor output is not less than the first threshold pressure, the routine proceeds to 610 where the routine includes determining whether the PF pressure sensor output is less than a second threshold pressure. It should be noted here that the second threshold pressure may be greater than the first threshold pressure. In one example, the second threshold pressure may be a pressure at a particulate filter corresponding to an upstream exhaust air leak, where a portion of the exhaust pressure may be lost to the atmosphere upstream of the PF, thereby partially reducing the pressure upstream of the particulate filter.

[0066] If the PF pressure sensor output is not less than the second threshold, then the routine proceeds to 612 where the routine includes maintaining the nominal threshold for the CMS monitor. In some embodiments, the threshold for the CMS monitor may include a rich-to-lean response rate of the CMS during a DFSO event, such as Figure 3 In one example, a nominal rich to lean CMS response can be calculated as follows: interpolation can be used between CMS measurement data points to obtain a fully functional CMS to determine when the CMS output exceeds a rich limit threshold (e.g., 0.6 volts in one example), and additional interpolation can be used to determine when the CMS output exceeds a lean limit threshold (e.g., 0.2 volts in one example) during DFSO. The slope between the rich limit threshold and the lean limit threshold can determine the nominal CMS response rate, and this data can be stored in the controller's memory.

[0067] At 614, the routine includes determining whether CMS monitor entry conditions have been met. In one example, the CMS monitor entry conditions may include the engine operating in DFSO mode. DFSO Entry Conditions and Operation Reference Figure 1 The description is not repeated herein and therefore will not be repeated here. Additional entry conditions may include determining whether a threshold duration or distance of travel has elapsed since the last repetition of the CMS monitor. In another example, because the CMS monitor needs to be executed in anticipation of the catalyst monitor, the entry condition may be satisfied when a threshold duration or distance of travel has elapsed since the last repetition of the catalyst monitor. In this way, a CMS (e.g., oxygen sensor) monitor may be initiated in response to satisfying the corresponding monitor entry condition.

[0068] If the CMS monitor entry conditions are not met, the routine waits at 616 until the CMS monitor entry conditions are met. When the CMS monitor entry conditions are met, the routine advances to 618 where the routine includes launching the CMS monitor. In one example, running the CMS monitor includes measuring an actual rich to lean response rate of the CMS during DFSO. In particular, this may include determining a transition rate or response rate of the CMS between a time when a rich limit threshold is reached and a time when a lean limit threshold is reached. In other examples, the CMS monitor may include invoking an air fuel ratio oscillation and monitoring a sensor response.

[0069] At 620, the routine includes comparing the actual CMS output (e.g., response rate) to the nominal response rate of the CMS to determine if the actual CMS output is greater than the nominal response rate. In some embodiments, this includes comparing the rich-to-lean response rate of the CMS to the nominal rich-to-lean response rate of a fully functional CMS as previously described. In other examples, this may include comparing sensor responses during air-fuel ratio oscillations. If the CMS response rate is less than the nominal threshold, then the routine proceeds to 622, where the routine includes indicating that the CMS has passed the monitor and that the CMS is functional. In this example, there is no indication of an exhaust air leak and the CMS is functional. The routine then proceeds to 624, where the routine includes running as Figure 7 The threshold catalyst (TC) monitor described above. If the CMS response rate is greater than the nominal threshold, then the routine proceeds to 626 where the routine indicates that the CMS has failed the CMS monitor and that the CMS may be degraded. In some examples, CMS degradation includes the CMS operating at a slow response rate. In this example, there is no indication of an exhaust air leak, but the CMS may be diagnosed as having a slow response due to an error at the sensor. The method then proceeds to 624 where it is performed Figure 7However, in response to the slow response of the sensor, it is possible to Figure 7 The described adjustment is used for the threshold value of the TC monitor. The method then ends.

[0070] If at 610, the GPF sensor output is less than the second threshold, the routine proceeds to 628, where the routine includes indicating that an exhaust air leak may exist in the exhaust system upstream of the GPF. In response to the indication of an exhaust air leak, the CMS OBD monitor threshold may be adjusted based on the indication of the air leak at 630. In response to the indication of the exhaust air leak, a diagnostic threshold (e.g., a response rate or a threshold slope) of the CMS monitor may be adjusted (e.g., reduced) to account for the exhaust air leak. As an example, adjusting the diagnostic threshold (of the CMS monitor) includes reducing the diagnostic threshold in response to the measured pressure exceeding the second threshold, the diagnostic threshold further increasing as the difference between the measured pressure and the second threshold increases. For example, the threshold may be further reduced as the indication of the exhaust air leak increases. In this way, adjusting the diagnostic threshold of the oxygen sensor monitor in response to the measured pressure of the GPF includes adjusting the threshold in response to the measured pressure exceeding the threshold. In one example, the threshold is calibrated based on the soot load at the filter. It should be understood that the threshold compared to the output of the pressure sensor to assess the state of the sensor is different from the threshold compared to the output of the pressure sensor to assess the degradation of the particulate filter. In this way, by adjusting the thresholds of the CMS monitor in response to an indication of an exhaust air leak, the controller can more reliably distinguish between an actual slow response of the CMS and an exhaust air leak that manifests itself as a slow CMS response. As a result, a more robust CMS diagnostic is provided, which can also provide more specific diagnostic information to a service technician. In one example, in response to an indication of an exhaust air leak upstream of the GPF, the routine can include reducing a rich-to-lean voltage threshold used to calculate a transition rate during a DFSO event in order to determine a CMS response rate. In this way, a slow CMS response rate can be identified under nominal (e.g., no exhaust air leak) conditions as well as when an exhaust leak is present. In one example, in response to a large air leak, the threshold can be adjusted more than when a small air leak is detected.

[0071] At 632, the routine includes determining whether the CMS monitor entry conditions have been met as described above with reference to 614. If the CMS monitor entry conditions have not been met, the routine waits at 616. When the CMS monitor entry conditions are met, the routine proceeds to 634 where the routine includes running the CMS monitor. In one example, running the CMS monitor includes measuring an actual rich to lean response rate of the CMS during DFSO. In particular, this may include determining a transition rate or response rate of the CMS between the time a rich limit threshold is reached and the time a lean limit threshold is reached.

[0072] At 636, the routine includes comparing the actual CMS output (e.g., response rate) to the adjusted response rate of the CMS (as determined at 630) to determine if the actual CMS output is greater than the adjusted response rate. The adjusted response rate here is lower than the unadjusted nominal response rate used at 620. In some embodiments, this includes comparing the rich-to-lean response rate of the CMS to the adjusted rich-to-lean response rate as previously described. If the CMS response rate is less than the adjusted threshold, then the routine proceeds to 622 where the routine includes indicating that the CMS has passed the monitor and that the CMS is functional. In this example, the exhaust system exhibits an exhaust air leak but the CMS is functional. The routine can then proceed to 624 where the routine includes running as Figure 7 The threshold catalyst (TC) monitor described above. If the CMS response rate is greater than the adjusted threshold, then the routine proceeds to 626 where the routine indicates that the CMS failed the CMS monitor, then the CMS may be degraded. In this example, the exhaust system exhibits both exhaust air leakage and a CMS with a low response due to CMS degradation. Here, the CMS may be degraded to have a low response rate. The method then proceeds to 624 where the TC monitor is performed, where the TC monitor threshold is adjusted in response to the indication of CMS sensor degradation.

[0073] Now go to Figure 7 , which shows a flow chart illustrating an example method 700 for performing a threshold catalyst (TC) monitor, which is to determine the exhaust catalyst (such as Figure 1 and Figure 2 It should be understood that the method 700 can be used as a diagnosis of whether the TWC 71) is deteriorated. Figure 6 The TC monitor may be performed as part of method 600, wherein after the CMS monitor is completed, the TC monitor may be performed.

[0074] HEGO sensors (e.g. Figure 1 and Figure 2 The CMS 13) implements a TC monitor to identify threshold catalysts (e.g. Figure 1 and Figure 2The presence of a TWC 71). In one example, a threshold catalyst may exhibit a maximum allowable emission level leaving the catalyst and may provide an indication of catalyst degradation. In some embodiments, the TC monitor may identify the presence of a threshold catalyst by determining the magnitude of a frequency domain transfer function of the catalyst within a specific frequency range corresponding to a square wave input. Among them, a simplified model of the catalyst utilizing system gain, time delay, and an integrator may be used. The system gain and time delay may be a function of engine parameters such as air mass flow rate and may be determined using a lookup table stored in a memory of the controller. In one example, the nominal system gain and time delay may be initially calibrated using a new catalyst, and as the catalyst ages, a scaling gain may be used to adjust the system gain to represent aging. Once the scaling gain has been determined, a calibrated nominal value may be determined for determining whether a threshold catalyst exists. Further details regarding the TC monitor will be discussed below.

[0075] Diagnostic routine 700 begins at 702, where the routine includes estimating and / or measuring engine operating conditions. Current engine operating conditions may include, but are not limited to, air-fuel ratio (e.g., the air-fuel ratio of combusted exhaust gas exiting engine cylinders), particulate filter bypass valve (e.g., Figure 1 and Figure 2 The current vehicle conditions may include the position of the bypass valve 17 shown, the duration since the last particulate filter regeneration, the engine speed and engine load, the engine coolant temperature, the degree of actuation (or position) of the accelerator pedal, and the exhaust gas temperature and pressure adjacent to the particulate filter. The current vehicle conditions may also include the current particulate filter soot load, which may be modeled based on the level of the raw gas soot. The raw gas soot level may be modeled based on one or more of the engine coolant temperature, torque, air-fuel ratio, and engine speed. Additional engine operating conditions may include whether the CMS monitor ( Figure 6 The controller may also determine whether an exhaust air leak is detected during a previous CMS monitor and whether a CMS threshold is adjusted in response to an indication of an exhaust air leak. Further, the controller may also determine whether the CMS was diagnosed as having a low response during a previous CMS monitor.

[0076] At 704, the routine includes determining whether the TC monitor entry conditions have been met. In some embodiments, the outer loop feedback controller may be enabled (e.g., Figure 2As described above, the TC monitor is continuously executed. As a result, execution of the TC monitor may not be limited to steady state conditions or specific operating events (such as DFSO or cold start). In some examples, the TC monitor entry conditions may include one or more of engine temperature above a threshold temperature, exhaust temperature above a threshold temperature, catalyst ignition, engine speed above a threshold speed, and engine load above a threshold load. In addition, the TC monitor entry conditions may be met if a threshold distance or duration of vehicle travel has passed since the last repetition of the TC monitor. If the threshold catalyst monitor entry conditions are not met, then the routine proceeds to 706, where the routine includes continuing engine operation to meet the torque demand. The routine then ends.

[0077] If the TC monitor entry conditions are met, then the routine proceeds to 708 where the routine determines ( Figure 6 If the CMS monitor has not been completed since the previous TC monitor, the routine proceeds to 710, where the routine includes running or completing Figure 6 After the CMS monitor has been run, the method determines whether the CMS has passed the CMS monitor at 712. In one example, the CMS may have passed the CMS monitor when the actual CMS response rate is within a nominal threshold (when no exhaust leak is indicated in response to a particulate filter pressure being above a threshold) or when the actual CMS response rate is within an adjusted threshold (when an exhaust air leak is indicated in response to a particulate filter pressure being less than a threshold).

[0078] If the CMS fails the CMS monitor, the routine proceeds to 714 where the routine includes adjusting one or more TC monitor thresholds. Adjusting the thresholds includes increasing or decreasing the nominal threshold levels depending on the type of catalyst monitoring algorithm utilized. It should be appreciated that the catalyst model may utilize variables such as system gain and time delay, which may be a function of engine operating parameters such as air mass flow rate and may be determined using a lookup table or algorithm. In one example, the output of the modeling may be responsive to, for example, a change in the output of the modeling may be made during execution of the catalyst monitoring algorithm. Figure 6 In this way, both the CMS monitor and the catalyst monitor may be running simultaneously, however, if the CMS monitor indicates that the catalyst monitor thresholds need to be adjusted (after the catalyst monitor has been running), the catalyst monitor data may be changed or adjusted after the fact while maintaining the accuracy and reliability of the monitor results.

[0079] The method then proceeds to 716 where a TC monitor is executed. In some examples, each of the first (e.g., CMS) monitor and the second (e.g., TC) monitor may include oscillating the air-fuel ratio between a rich stoichiometric air-fuel ratio and a lean stoichiometric air-fuel ratio. The TC monitor may be used to monitor the effectiveness of the catalyst in reducing tailpipe emissions. That is, hydrocarbon (HC), NOx, and CO emissions may be monitored relative to a threshold value, which may be adjusted using a correction factor for aging of the catalyst. In one non-limiting example, operating the TC monitor may include the following steps:

[0080] 1) Estimated scaling gain (indicative of catalyst aging)

[0081] 2) Use an algorithm or lookup table to convert the measured HEGO output voltage into an equivalent normalized air-fuel ratio

[0082] 3) Apply a frequency domain bandpass filter to the Catalyst input (e.g. Figure 1 and Figure 2 exhaust gas sensor 128) and catalyst output (e.g., Figure 1 and Figure 2 CMS 13) Both

[0083] 4) Apply a low pass or moving average filter to the band pass filtered input and output signals (which allows the input and output signals to be out of phase)

[0084] 5) Calculate the model error between the measured output and the modeled output through a predetermined catalyst model consisting of system gain, integrator and time delay

[0085] 6) Use the calculated model error and an integrator with a calibrated estimator gain to update the magnitude estimate of the catalyst frequency domain transfer function at a specified input frequency

[0086] 7) Calculate the estimate maturity metric to ensure that enough estimate time has passed to make a threshold catalyst monitor determination

[0087] 8) Once the maturity metric is met, the magnitude estimate is compared to a predetermined threshold to determine if a threshold catalyst is present.

[0088] At 718, the routine includes determining whether the result of the TC monitor is greater than the adjusted threshold determined at 714. In particular, the result of the TC monitor can determine whether emissions above a threshold emission level are passing through the catalyst (e.g., whether the catalyst is degraded). If the output of the TC monitor is greater than the adjusted threshold, then the threshold catalyst monitor may not be passed, and the catalyst may be indicated as degraded at 722. In some examples, degradation of the catalyst may be displayed as one or more emission levels leaving the catalyst exceeding an allowable threshold. In other examples, indicating degradation of the catalyst may include indicating catalyst aging. In response to an indication of a degraded catalyst, the routine may proceed to 730, where the routine may include setting a diagnostic code, illuminating a MIL light, and limiting engine operation. In other examples, in response to an indication of degradation of the catalyst, the controller may send a command signal to reduce the amplitude of air-fuel ratio oscillations.

[0089] If the result of the TC monitor is less than the adjustment threshold determined at 714, the routine proceeds to 720 where the routine includes indicating that the emissions pass the threshold catalyst monitor and the catalyst is not degraded. The routine then ends.

[0090] If the CMS passes the monitor at 712, the routine proceeds to 724 where the routine includes maintaining nominal thresholds. In one example, this may include maintaining nominal thresholds for the catalyst model, and variables such as system gain and time delay may not be determined as a function of engine operating parameters such as air mass flow rate and may not be determined using a lookup table or algorithm. In one example, the output of the modeling may be responsive to, as may be performed in the Figure 6 The routine may be adjusted when an exhaust air leak has been indicated or an indication of a degraded CMS is present. In response to an indication of a CMS by a monitor, the air mass flow rate may be used without adjustment when determining the modeling output, and the correction factor may not be used to determine the model error to compensate for the degraded CMS. Because exhaust air leaks may exist with a functioning CMS, in some embodiments, the thresholds for the TC monitor may be adjusted to reflect exhaust air leak conditions.

[0091] At 726, the TC monitor may be performed using a nominal threshold, and at 728, the routine includes comparing the output (e.g., result) of the TC monitor to the nominal threshold established at 724. If the result of the TC monitor determines that a threshold catalyst is present (e.g., TC monitor output>nominal threshold), then the threshold catalyst monitor may not be passed, and the catalyst may be indicated as degraded at 722. In particular, emissions exiting the catalyst may have exceeded an allowable threshold. In response to an indication of a degraded catalyst, the routine may proceed to 730, where the routine may include one or more of setting a diagnostic code, illuminating a MIL light, and limiting engine operation.

[0092] If the result of the TC monitor is less than the nominal threshold at 724 , the routine proceeds to 720 where the routine includes indicating that the emission level passes the threshold catalyst monitor and the catalyst is not degraded. The routine then ends.

[0093] Now go to Figure 8 , which shows that the engine (such as Figure 110 ), the predictive operation map 800 includes monitoring the pressure of the adjacent filter and diagnosing the exhaust air leakage based on the pressure relative to the threshold. Further, the map 800 includes adjusting the CMS monitor threshold in response to the indication of the exhaust air leakage. Additionally, the subsequent threshold catalyst monitor input can be adjusted in response to the results of the catalyst monitor sensor diagnosis and whether the exhaust air leakage is diagnosed. The map 800 includes various engine parameters along the vertical axis and the time elapsed along the horizontal axis. The map 800 depicts the accelerator pedal position (PP) at curve 802, which is an indication of the operator torque demand. The map 800 further depicts the engine temperature relative to the warm engine threshold temperature at 803 at curve 804, depicts whether the engine is operated in DFSO mode at 806, and depicts whether the CMS OBD monitor or TC OBD monitor is executed at curve 808. Map 800 also depicts particulate filter (PF) soot load at curve 810 relative to an upper soot load threshold at 809 and a lower soot load threshold 811, and depicts pressure 812 at the PF relative to an upper threshold pressure 813, a clean threshold pressure 814, and a degraded threshold pressure 815. It should be understood that the clean threshold pressure 814 can correspond to the pressure at the PF for a clean (e.g., no soot load) filter, below which the clean threshold pressure 814 can indicate an upstream exhaust air leak. Further, the degraded threshold pressure 815 can correspond to the pressure at the PF for a degraded PF, below which the degraded threshold pressure 815 can indicate a cracked filter housing or a filter housing with a significant leak. An exhaust air leak diagnostic marker is shown at 818, and a HEGO sensor (e.g., Figure 1 to Figure 2 The output of the CMS sensor 13 is shown at 826. The measured catalyst output relative to the modeled catalyst threshold at 828 and the catalyst degradation diagnostic flag at 830 is shown at 829. The modeled catalyst output is shown at 829.

[0094] Prior to time t1, the operator requests torque, as indicated by increasing actuation of the accelerator pedal (curve 802). As a result, the engine temperature increases (curve 804). The engine can be operated with a rich air-fuel ratio, and therefore the exhaust gas can pass through a particulate filter (PF) so that particulate matter can be loaded onto the filter. As a result, the soot load of the PF can increase (curve 810). As the soot load in the PF continues to increase, the pressure at the PF can increase in a corresponding manner (curve 812). Because there is a torque demand, the engine is not operated with DFSO. The output 820 of the HEGO sensor (e.g., a CMS positioned downstream of the catalyst) remains approximately at the stoichiometric ratio (819). The measured output of the catalyst (curve 826) remains below the modeled catalyst output threshold (828).

[0095] At time t1, as indicated by steady actuation of the accelerator pedal (curve 802), the operator ceases to request acceleration and requests steady torque from the engine. As a result, the engine is still not operating in DFSO (curve 806). As the engine continues to operate, the engine temperature (curve 804) increases above the warm engine threshold temperature 803, and the soot load of the PF continues to increase toward the upper soot load threshold 809 (curve 810). The pressure 812 at the PF may also continue to increase toward the upper threshold pressure 813.

[0096] At time t2, there is a decrease in the actuation of the accelerator pedal (curve 502). This may be the result of the operator de-throttled. In response to meeting the DFSO condition at time t2, the engine enters the DFSO mode (curve 806), and fuel is no longer delivered to the cylinders of the engine. The engine operation in the DFSO mode lasts for a duration D1 (e.g., from time t2 to time t4). In the depicted example, the exhaust temperature reaches the regeneration temperature, and as a result, the PF is passively regenerated during the DFSO, thereby causing a decrease in the soot load in the PF (curve 810). In particular, as the soot in the PF is incinerated, the soot load of the PF moves away from the upper soot load threshold 809 toward the lower soot load threshold 811. When the engine is operated in the DFSO mode, the pressure at the PF also decreases (curve 812). In particular, the pressure of the PF moves away from the upper threshold pressure 813 toward the cleaning threshold pressure 814. Entry conditions for the CMS monitor may be met at time t2 , but diagnostics may not be initiated until time t3 (eg, after determining the pressure at the particulate filter and determining the presence or absence of an exhaust air leak).

[0097] Between time t2 and time t3, the pressure at the PF decreases below the clean threshold pressure 814, but does not fall below the degraded threshold pressure 815. In response to the pressure falling below the threshold at the PF, the controller may infer that there is an exhaust air leak upstream of the PF and the CMS sensor. Because an air leak may corrupt the output of the CMS and any monitors that rely on the output of the CMS, to improve the reliability of those monitors, the controller may first communicate the status of the exhaust air leak to the CMS monitor. In one example, the exhaust air leak may be an exhaust air leak upstream of the PF that causes the exhaust system pressure to be lost to the atmosphere, thereby reducing the pressure within the PF to below the clean threshold pressure 814. At time t3, the execution conditions for performing a catalyst monitor sensor diagnostic (e.g., a CMS monitor) are met, and the CMS monitor is therefore activated. As previously described, the entry conditions for performing a catalyst monitor sensor diagnostic may include the engine being operated in DFSO mode. Additional entry conditions may include determining whether the pressure at the particulate filter is within one or more thresholds and whether an exhaust air leak has been identified.

[0098] The CMS OBD monitor operates from time t3 to time t4, wherein the CMS monitor includes measuring an actual rich-to-lean response rate of the CMS during DFSO. Specifically, this may include determining a transition rate (e.g., response rate, slope) of the CMS between a time when a rich limit threshold is reached and a time when a lean limit threshold is reached. The response rate of the HEGO sensor output 820 shows a slow response, but since an exhaust air leak was previously identified, the threshold for the transition rate is reduced from an upper transition rate threshold 823 (e.g., maximum slope) to a medium transition rate threshold 821. Because the CMS response rate is not less than the medium transition rate threshold 821, the CMS is not immune to slow response degradation. For illustrative purposes, an exhaust system without an exhaust air leak and with a fully functional HEGO sensor will exhibit a transition rate during DFSO according to curve 824 (small dashed line), and an exhaust system with an exhaust air leak and a slow-responding HEGO sensor will exhibit a lower transition rate during DFSO according to curve 825 (long dashed line). Between t3 and t4 , the measured catalyst level ( 826 ) exiting the catalyst is lower than the modeled catalyst output 828 .

[0099] At time t4, there is a tip-in (802), and thus DFSO ends (806). At this time, the CMS OBD monitor also ends, and thus there is a flag indicating an exhaust air leak (818). The output of the HEGO sensor may increase back to stoichiometry as engine load increases. At time t5, the entry conditions for executing the threshold catalyst (TC) monitor are met, and thus the monitor is enabled. In some embodiments, when the outer loop feedback controller (such as reference Figure 2 ), the TC monitor may be continuously executed when the engine is in a state of being ...

[0100] The TC monitor is executed from time t5 to time t6 (808). Between t3 and t4, in response to an earlier indication of exhaust air leakage during execution of the CMS monitor, the modeling output for the threshold catalyst can be adjusted. In one example, this can include adjusting a system gain and / or time delay variable used to model the catalyst, which can be a function of an engine operating parameter (such as air mass flow rate). It should be understood that parameters such as air mass flow rate can be affected by air leakage from the exhaust system to the atmosphere, and adjusting the variables in response to an indication of air leakage based on such parameters will provide a more accurate and robust diagnosis of the threshold catalyst level. Due to the indication of exhaust air leakage, the modeling output for the threshold catalyst can be adjusted downward during the diagnosis between t5 and t6 (dashed line portion 829), resulting in the catalyst output exceeding the adjusted modeling catalyst output. As a result, when the TC monitor ends at time t6, the catalyst can be marked as degraded (curve 830).

[0101] In this way, the possibility of false pass results when executing the TC monitor can be reduced by first determining whether an exhaust air leak exists based on the output of the PF pressure sensor. By adjusting the threshold for the CMS monitor based on the result of the leak, a slow response of the downstream oxygen sensor due to sensor degradation can be better distinguished from a slow response of the downstream oxygen sensor due to an exhaust air leak. Also by adjusting the threshold for the TC monitor to account for the slow response of the CMS due to the exhaust air leak, inaccuracies at the monitor that relies on the output of the CMS can be reduced. In this way, a more robust exhaust diagnostic can be provided, the results of which are not corrupted by the presence of an exhaust air leak. The technical effect of using the pressure indication at the particulate filter downstream of the catalyst to identify the exhaust air leak is that the higher sensitivity of the pressure response at the particulate filter can be fully utilized to identify even a small pressure difference caused by an exhaust air leak, regardless of the size of the leak. Further, if an exhaust air leak exists, the threshold for the catalyst monitor sensor diagnosis can be adjusted in time to achieve the distinction between a true slow response of the catalyst monitor sensor and an exhaust air leak, which may similarly show itself as a slowed CMS response. In summary, the possibility of false pass of the threshold catalyst monitor can be reduced, thereby improving engine emissions compliance.

[0102] A method for an engine includes adjusting a diagnostic threshold of an oxygen sensor coupled to a downstream exhaust catalyst in response to a measured pressure at a particulate filter coupled to the oxygen sensor downstream. In a first example of the method, the method further includes, wherein the measured pressure at the particulate filter includes one of a measured inlet pressure of the particulate filter and a differential pressure across the particulate filter. A second example of the method optionally includes the first example, and further includes, wherein the adjustment in response to the measured pressure includes an adjustment in response to the measured pressure exceeding a first threshold, the first threshold being calibrated based on a soot load at the filter, the method further includes, in response to the measured pressure exceeding a second threshold that is higher than the first threshold, indicating that the particulate filter is degraded. A third example of the method optionally includes one or more of the first example and the second example, and further includes, wherein the adjustment includes increasing the diagnostic threshold in response to the measured pressure exceeding the first threshold, the diagnostic threshold further increasing as the difference between the measured pressure and the first threshold increases. A fourth example of the method optionally includes one or more of the first to third examples, and further includes indicating an exhaust air leak in response to the measured pressure exceeding the first threshold. The fifth example of the method optionally includes one or more of the first to fourth examples, and further includes, wherein the diagnostic threshold is a first diagnostic threshold for an oxygen sensor monitor, and the method further includes: in response to meeting a corresponding monitor entry condition, enabling the oxygen sensor monitor; in response to the measured output of the oxygen sensor exceeding the first diagnostic threshold, indicating degradation of the oxygen sensor; and in response to the indication of degradation of the oxygen sensor, adjusting the second diagnostic threshold for the catalyst monitor. The sixth example of the method optionally includes one or more of the first to fifth examples, and further includes wherein indicating degradation of the oxygen sensor includes indicating a slow sensor response. The seventh example of the method optionally includes one or more of the first to sixth examples, and further includes enabling the catalyst monitor in response to meeting a corresponding monitor entry condition; in response to the measured output of the oxygen sensor exceeding the second diagnostic threshold, indicating degradation of the catalyst; and in response to the indication of degradation of the catalyst, reducing the peak-to-peak air-fuel ratio during air-fuel ratio oscillations. The eighth example of the method optionally includes one or more of the first to seventh examples, and further includes wherein indicating degradation of the catalyst includes indicating catalyst aging.

[0103] In another example, a method for an engine includes: indicating an air leak in an exhaust passage based on a measured pressure at a particulate filter coupled downstream of an exhaust catalyst; adjusting a threshold for an oxygen sensor monitor in response to the indication of air leak, the oxygen sensor coupled downstream of the catalyst; and indicating a degraded sensor response based on an oxygen sensor output relative to the threshold during an air-fuel ratio oscillation. In a first example of the method, the method further includes where the threshold is a first threshold and the air-fuel ratio oscillation is a first air-fuel ratio oscillation, the method further includes: adjusting a second threshold for a catalyst monitor in response to the indication of degraded sensor response; and indicating catalyst aging based on an oxygen sensor output relative to the second threshold during a second air-fuel ratio oscillation. The second example of the method optionally includes the first example, and further includes indicating a state of the filter based on the measured pressure; and limiting engine load based on the indication. The third example of the method optionally includes one or more of the first and second examples, and further includes where the indication includes: indicating an air leak in the exhaust passage in response to the measured pressure being above a first threshold pressure; and indicating a degraded state of the filter in response to the measured pressure being above a second threshold pressure, the second threshold pressure being higher than the first threshold pressure, the first threshold pressure being calibrated as a function of filter soot load and engine speed. A fourth example of the method optionally includes one or more of the first to third examples, and further includes wherein the adjusting includes: increasing the first threshold in response to an indication of an air leak; and increasing the second threshold in response to an indication of a degraded sensor response. A fifth example of the method optionally includes one or more of the first to fourth examples, and further includes wherein the measured pressure includes one of a filter inlet pressure and a differential pressure across the filter.

[0104] A system for a hybrid vehicle including an engine system, comprising: an engine; an exhaust passage including an exhaust catalyst; an upstream oxygen sensor coupled upstream of the exhaust catalyst; a downstream oxygen sensor coupled downstream of the exhaust catalyst; a particulate filter coupled downstream of a second oxygen sensor; a pressure sensor coupled to the particulate filter; and a controller having computer readable instructions stored on a non-transitory memory for: in response to meeting an entry condition for a first monitor for a downstream oxygen sensor, comparing an output of the pressure sensor to a threshold pressure; and in response to the output of the pressure sensor being above the threshold pressure, increasing a threshold of the first monitor; executing the first monitor; and after executing the first monitor, in response to the output of the downstream oxygen sensor exceeding the increased threshold, indicating degradation of the downstream oxygen sensor. In a first example of the system, the system further includes wherein the controller includes further instructions for: in response to meeting an entry condition for a second monitor for the catalyst, increasing a threshold of the first monitor in response to an indication of degradation of the downstream oxygen sensor; executing the second monitor; and after executing the second monitor, in response to the output of the downstream oxygen sensor exceeding the increased threshold, indicating degradation of the catalyst. The second example of the system optionally includes the first example, and further includes one of an absolute pressure sensor coupled to the inlet of the filter and a differential pressure sensor coupled to each of the inlet and outlet of the filter. The third example of the system optionally includes one or more of the first example and the second example, and further includes one of the first monitor and the second monitor, and further includes one of the second monitor and the second monitor, and further includes one of the first monitor and the second monitor, and further includes one of the first monitor and the second monitor, and further includes one of the first monitor and the second monitor, and further includes one of the first monitor and the second monitor, and further includes one of the first monitor and the second monitor, and further includes one of the first monitor and the second monitor, and further includes one of the first monitor and the second monitor, and further includes one of the second ...

[0105] In another representation, a method for an engine includes determining each of an air leak in an exhaust passage upstream of an exhaust oxygen sensor and a state of an exhaust particulate filter based on output of a pressure sensor coupled to the particulate filter, an oxygen sensor coupled downstream of an exhaust catalyst, the particulate filter coupled downstream of the oxygen sensor.

[0106] Note 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 performed 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 order shown, in parallel, or omitted in some cases. Similarly, the order of processing is not necessary to achieve the features and advantages of the example embodiments described herein, but the depicted processing order is provided for ease of illustration and description. One or more of the actions, operations, and / or functions shown can be repeatedly performed according to the specific strategy used. Further, the described actions, operations, and / or functions can graphically represent the code in the non-transitory memory of the computer-readable storage medium to be programmed into the engine control system, wherein the described actions are performed by executing instructions in a system including various engine hardware components in conjunction with an electronic controller.

[0107] 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. For example, the above technology can 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 disclosed herein, and other features, functions, and / or properties.

[0108] The appended claims particularly point out certain combinations and subcombinations believed to be 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 combinations 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 presenting new claims in this or a related application. Such claims, whether broader, narrower, equal to, or different in scope from the original claims, are also deemed to be included in the subject matter of the present disclosure.

Claims

1. A method for an engine, comprising: adjusting a diagnostic threshold of an oxygen sensor coupled downstream of an exhaust catalyst in response to a measured pressure at a particulate filter coupled downstream of the oxygen sensor; as well as In response to an indication of degradation of the catalyst, a peak-to-peak air-fuel ratio during an air-fuel ratio oscillation is reduced, wherein the degradation of the catalyst is responsive to a measured output of the oxygen sensor. 2 . The method of claim 1 , wherein the measured pressure at the particulate filter comprises one of a measured inlet pressure of the particulate filter and a differential pressure across the particulate filter.

3. The method of claim 1 , wherein the adjusting in response to the measured pressure comprises adjusting in response to the measured pressure exceeding a first threshold, the first threshold being calibrated based on soot loading at the particulate filter, the method further comprising indicating particulate filter degradation in response to the measured pressure exceeding a second threshold that is higher than the first threshold. 4 . The method of claim 3 , wherein the adjusting comprises increasing the diagnostic threshold in response to the measured pressure exceeding the first threshold, the diagnostic threshold further increasing as the difference between the measured pressure and the first threshold increases. The method of claim 3 , further comprising indicating an exhaust air leak in response to the measured pressure exceeding the first threshold.

6. The method of claim 1 , wherein the diagnostic threshold is a first diagnostic threshold for an oxygen sensor monitor, the method further comprising: activating the oxygen sensor monitor in response to corresponding monitor entry conditions being met; responsive to a measured output of the oxygen sensor exceeding the first diagnostic threshold, indicating degradation of the oxygen sensor; as well as In response to the indication of degradation of the oxygen sensor, a second diagnostic threshold for a catalyst monitor is adjusted. The method of claim 6 , wherein indicating degradation of the oxygen sensor comprises indicating a slow sensor response.

8. The method according to claim 6, further comprising: The catalyst monitor is enabled in response to corresponding monitor entry conditions being met. 9 . The method of claim 8 , wherein indicating degradation of the catalyst comprises indicating catalyst aging.

10. An engine system, comprising: engine; an exhaust passage including an exhaust catalyst; an upstream oxygen sensor coupled upstream of the exhaust catalyst; a downstream oxygen sensor coupled downstream of the exhaust catalyst; a particulate filter coupled downstream of the downstream oxygen sensor; a pressure sensor coupled to the particulate filter; as well as A controller having computer readable instructions stored on a non-transitory memory, the computer readable instructions being for: In response to an entry condition of a first monitor for the downstream oxygen sensor being met, comparing the output of the pressure sensor to a threshold pressure; and responsive to the output of the pressure sensor being above the threshold pressure, increasing a threshold of the first monitor; executing the first monitor; as well as After the execution of the first monitor, in response to the output of the downstream oxygen sensor exceeding the elevated threshold, degradation of the downstream oxygen sensor is indicated.

11. The system of claim 10, wherein the controller includes further instructions for: In response to satisfying an entry condition of a second monitor for the catalyst, responsive to said indication of degradation of said downstream oxygen sensor, increasing a threshold of said first monitor; executing the second monitor; and After the execution of the second monitor, in response to the output of the downstream oxygen sensor exceeding the elevated threshold, degradation of the catalyst is indicated. 12 . The system of claim 10 , wherein the pressure sensor is one of an absolute pressure sensor coupled to an inlet of the particulate filter and a differential pressure sensor coupled to each of the inlet and outlet of the particulate filter.

13. The system of claim 11 , wherein executing each of the first monitor and the second monitor includes oscillating an air-fuel ratio between a richer air-fuel ratio and a leaner air-fuel ratio, and wherein the controller includes further instructions for: In response to the indication of degradation of the catalyst, a magnitude of the air-fuel ratio oscillations is reduced.

14. The system of claim 12, wherein the threshold pressure is a first threshold pressure, and wherein the controller includes further instructions for: comparing the output of the pressure sensor to a second threshold pressure that is higher than the first threshold pressure; responsive to the output of the pressure sensor exceeding the second threshold pressure, indicating degradation of the particulate filter; and In response to the indication, engine load is limited until an operator input is received indicating replacement of the particulate filter.

Images