Systems and methods for operating an engine including a secondary air system

A method for monitoring a secondary airflow (SAIR) system in an engine includes determining degradation of the SAIR system adding a SAIR to downstream of an engine cylinder exhaust based on a comparison of the SAIR before and after a shutdown of a SAIR pump, the SAIR calculated from a fuel injection amount, an exhaust air-fuel ratio, and an engine intake airflow. In this way, SAIR at the exhaust manifold can be monitored utilizing existing onboard sensors and technology, thereby maintaining OBD and emissions monitoring, reducing engine emissions, and maintaining costs.

FIELD

The present description relates generally to methods and systems for operating a secondary air system in an engine.

Injection of secondary airflow (SAIR) is a vehicle emissions reduction strategy whereby air is delivered into the exhaust stream of a vehicle engine to increase combustion of hydrocarbon fuel in the engine exhaust. When SAIR is reduced, for example, due to problems with the SAIR system, combustion of exhaust hydrocarbons can decrease, resulting in increased vehicle emissions. Conventional OBD engine systems monitor SAIR by measuring SAIR directly within the SAIR system. For example, SAIR may be measured by a mass air flow (MAF) sensor and/or a pressure sensor positioned within the SAIR system.

However, the inventors herein have recognized potential issues with such systems. In particular, these conventional engine systems do not include confirmation of the SAIR being delivered to the engine exhaust stream where the SAIR fluidly contacts and reacts with the uncombusted hydrocarbon fuel. Furthermore, in cases where the engine cylinders are arranged in cylinder banks, SAIR delivery issues and resulting emissions increases cannot be determined by conventional engine systems on a per cylinder bank basis. As an example, in cases where problems with delivery of SAIR occur downstream of the SAIR MAF or SAIR pressure sensor, a decrease in SAIR to the engine exhaust stream may not be detected, leading to increased engine emissions.

In one example, the issues described above may be addressed by a method for monitoring a secondary airflow (SAIR) system in an engine, including determining degradation of the SAIR system adding a SAIR to downstream of an engine cylinder exhaust based on a comparison of the SAIR before and after a shutdown of a SAIR pump, the SAIR calculated from a fuel injection amount, an exhaust air-fuel ratio, and an engine intake airflow. In this way, SAIR at the exhaust manifold can be monitored utilizing existing onboard sensors and technology, thereby maintaining OBD and emissions monitoring, reducing engine emissions, and maintaining costs.

DETAILED DESCRIPTION

The following description relates to systems and methods operating an engine system including a secondary airflow (SAIR) system. In one example, the SAIR system is fluidly coupled between an air intake and an exhaust manifold of an engine of a vehicle, as illustrated inFIGS.1and2. An amount of the SAIR at the exhaust manifold can be estimated from measurements of the intake air and fuel flow delivered to the engine, and the air-to-fuel ratio (AFR) at the engine exhaust before and after shutdown of the SAIR system, as illustrated by the methods ofFIGS.4and5.FIGS.3and7show plots comparing measured SAIR upstream of the exhaust with calculated SAIR at the engine exhaust. A timeline for operating the engine system ofFIGS.1and2according to the methods ofFIGS.4and5is illustrated inFIG.6.

Turning now to the figures,FIG.1shows an engine system100that may be included in a vehicle5, the engine system100including a partial view of a single cylinder130of an internal combustion engine10. Internal combustion engine10may be a multi-cylinder engine. Cylinder (e.g., combustion chamber)130includes a coolant sleeve114and cylinder walls132, with a piston136positioned therein and connected to a crankshaft140. Cylinder130is shown communicating with an intake manifold44via an intake valve4and an intake port22and with an exhaust manifold48via an exhaust valve8and an exhaust port86. Intake passage42may include an air filter191for filtering intake air passing through the intake passage. A throttle62including a throttle plate64may be provided in an intake passage downstream from air filter191and upstream of intake manifold44for varying a flow rate and/or pressure of intake air provided to the engine cylinders130. A MAF sensor120may be coupled to the intake passage42between air filter191and throttle62for providing a MAF signal to controller12. A MAP sensor122may be coupled to intake manifold44downstream of throttle62for providing respective MAP signal to controller12.

As further described herein with reference toFIGS.2-6, the engine may be configured to inject secondary airflow (SAIR) into the exhaust manifold48to increase conversion of certain emissions during various engine operating conditions. As depicted inFIG.1, the SAIR system220may be fluidly coupled to the intake passage42downstream of the air filter191and upstream from the throttle62by way of SAIR intake passage90. SAIR system220may deliver SAIR to the exhaust manifold48by way of SAIR exhaust passage92. SAIR exhaust passage92is fluidly coupled to the exhaust manifold48downstream from exhaust port86and upstream of exhaust gas sensor128and emission control device178. The SAIR system220may additionally or alternatively include other configurations for delivering SAIR to the exhaust manifold48. In one example, the SAIR system220may be fluidly coupled to the intake manifold44downstream of throttle62by way of SAIR intake passage90, whereby SAIR system220may deliver compressed air to the exhaust manifold48. In another example, the SAIR system220may include an external air pump that delivers air directly from the atmosphere to the exhaust manifold48. In another example, the SAIR system220may include means for delivering air to the exhaust manifold48by way of EGR passage81when the EGR valve80closed.

In the depicted view, intake valve4and exhaust valve8are located at an upper region of cylinder130, and may be coupled to a cylinder head18. Intake valve4and exhaust valve8may be controlled by a controller12using respective cam actuation systems including one or more cams. The cam actuation systems may utilize one or more of variable displacement engine (VDE), cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and/or variable valve lift (VVL) systems to vary valve operation. In the depicted example, intake valve4is controlled by an intake cam151, and exhaust valve8is controlled by an exhaust cam153. The intake cam151may be actuated via an intake valve timing actuator101and the exhaust cam153may be actuated via an exhaust valve timing actuator103according to set intake and exhaust valve timings, respectively. In some examples, the intake valve and exhaust valve may be deactivated via the intake valve timing actuator101and exhaust valve timing actuator103, respectively. The position of intake cam151and exhaust cam153may be determined by camshaft position sensors155and157, respectively.

In some examples, the intake and/or exhaust valve may be controlled by electric valve actuation. For example, cylinder130may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation, including CPS and/or VCT systems. In still other examples, the intake and exhaust valves may be controlled by a common valve actuator or actuation system or a variable valve timing actuator or actuation system. The various valve control systems may be used to vary a timing, open duration, and lift of intake valve4and exhaust valve8.

An exhaust passage135can receive exhaust gases from other cylinders of engine10in addition to cylinder130. An exhaust gas sensor128is shown coupled to exhaust passage135upstream of an emission control device178. Exhaust gas sensor128may be selected from among various suitable sensors for providing an indication of an exhaust gas air-fuel ratio (AFR), such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx sensor, a HC sensor, or a CO sensor, for example. Emission control device178may be a three-way catalyst, a NOx trap, various other emission control devices, or combinations thereof.

External exhaust gas recirculation (EGR) may be provided to the engine via a high pressure EGR system83, delivering exhaust gas from a zone of higher pressure in exhaust passage135to a zone of lower pressure in intake manifold44, downstream of throttle62, via an EGR passage81. An amount of EGR provided to intake manifold44may be varied by controller12via an EGR valve80. For example, controller12may be configured to actuate and adjust a position of EGR valve80to adjust the amount of exhaust gas flowing through EGR passage81. EGR valve80may be adjusted between a fully closed position, in which exhaust gas flow through EGR passage81is blocked, and a fully open position, in which exhaust gas flow through the EGR passage is enabled. As an example, EGR valve80may be continuously variable between the fully closed position and the fully open position. As such, the controller may increase a degree of opening of EGR valve80to increase an amount of EGR provided to intake manifold44and decrease the degree of opening of EGR valve80to decrease the amount of EGR provided to intake manifold44. As an example, EGR valve80may be an electronically actuated solenoid valve. In other examples, EGR valve80may be positioned by an incorporated stepper motor, which may be actuated by controller12to adjust the position of EGR valve80through a range of discreet steps (e.g., 52 steps), or EGR valve80may be another type of flow control valve. Further, EGR may be cooled via passing through an EGR cooler85within EGR passage81. EGR cooler85may reject heat from the EGR gases to engine coolant, for example.

Under some conditions, the EGR system may be used to regulate a temperature of the air and fuel mixture within the combustion chamber. Further, EGR may be desired to attain a desired engine dilution, thereby increasing fuel efficiency and emissions quality, such as emissions of nitrogen oxides. As an example, EGR may be requested at low-to-mid engine loads. Thus, it may be desirable to measure or estimate the EGR mass flow. EGR sensors may be arranged within EGR passage81and may provide an indication of one or more of mass flow, pressure, and temperature of the exhaust gas, for example. Additionally, EGR may be desired after emission control device178has attained its light-off temperature. An amount of EGR requested may be based on engine operating conditions, including engine load, engine speed, engine temperature, etc. For example, controller12may refer to a look-up table having the engine speed and load as the input and output a desired amount of EGR corresponding to the input engine speed-load. In another example, controller12may determine the desired amount of EGR (e.g., desired EGR flow rate) through logic rules that directly take into account parameters such as engine load, engine speed, engine temperature, etc. In still other examples, controller12may rely on a model that correlates a change in engine load with a change in a dilution requirement, and further correlates the change in the dilution requirement with a change in the amount of EGR requested. For example, as the engine load increases from a low load to a mid-load, the amount of EGR requested may increase, and then as the engine load increases from a mid-load to a high load, the amount of EGR requested may decrease. Controller12may further determine the amount of EGR requested by taking into account a best fuel economy mapping for a desired dilution rate. After determining the amount of EGR requested, controller12may refer to a look-up table having the requested amount of EGR as the input and a signal corresponding to a degree of opening to apply to the EGR valve (e.g., as sent to the stepper motor or other valve actuation device) as the output.

Cylinder130can have a compression ratio, which is a ratio of volumes when piston136is at bottom dead center to top dead center. Conventionally, the compression ratio is in a range of 9:1 to 10:1. However, in some examples where different fuels are used, the compression ratio may be increased. This may happen, for example, when higher octane fuels or fuels with higher latent enthalpy of vaporization are used. The compression ratio may also be increased if direct injection is used due to its effect on engine knock. The compression ratio may also be increased if pre-chamber ignition increases knock resistance due to faster combustion.

As a non-limiting example, cylinder130is shown including a fuel injector66. Fuel injector66is shown coupled directly to cylinder130for injecting fuel directly therein in proportion to a pulse-width of a signal FPW received from controller12via an electronic driver168. In this manner, fuel injector66provides what is known as direct injection (hereafter also referred to as “DI”) of fuel into cylinder130. In another example, fuel injector66may be a port injector providing fuel into the intake port upstream of cylinder130. Further, whileFIG.1shows fuel injected to the cylinder via a single injector, the engine may alternatively be operated by injecting fuel via multiple injectors, such as one direct injector and one port injector. For example, both port and direct injectors may be included in a configuration that is known as port fuel and direct injection (PFDI). In such a configuration, controller12may vary a relative amount of injection from each injector. In this way, controller12may control and determine, based on engine and vehicle operating conditions, a fuel injection flow rate, to each jthengine cylinder130.

Fuel may be delivered to fuel injector66from a high pressure fuel system180including one or more fuel tanks, fuel pumps, and a fuel rail. Alternatively, fuel may be delivered by a single stage fuel pump at a lower pressure. Further, while not shown, the fuel tanks may include a pressure transducer providing a signal to controller12. Fuel tanks in fuel system180may hold fuel with different fuel qualities, such as different fuel compositions. These differences may include different alcohol content, different octane, different heats of vaporization, different fuel blends, and/or combinations thereof, etc. One example of fuels with different heats of vaporization includes gasoline as a first fuel type with a lower heat of vaporization and ethanol as a second fuel type with a greater heat of vaporization. In another example, the engine may use gasoline as a first fuel type and an alcohol-containing fuel blend, such as E85 (which is approximately 85% ethanol and 15% gasoline) or M85 (which is approximately 85% methanol and 15% gasoline), as a second fuel type. Other feasible substances include water, methanol, a mixture of ethanol and water, a mixture of water and methanol, a mixture of alcohols, etc. In this way, air and fuel are delivered to cylinder130, which may produce a combustible air-fuel mixture.

Fuel may be delivered by fuel injector66to cylinder130during a single cycle of the cylinder. Further, the distribution and/or relative amount of fuel delivered from fuel injector66may vary with operating conditions. Furthermore, for a single combustion event, multiple injections of the delivered fuel may be performed per cycle. The multiple injections may be performed during a compression stroke, intake stroke, or any appropriate combination thereof.

In the example shown inFIG.1, cylinder130includes a pre-chamber igniter192coupled to cylinder head18for initiating combustion. In some examples, the pre-chamber igniter192may be coupled to a mounting surface different than the cylinder head18, such as a cylinder block or other portion of the cylinder. In one example, the pre-chamber igniter192is the only ignition device of the cylinder130. As such, there are no other ignition devices in the engine10other than the pre-chamber igniter192corresponding to each cylinder130.

An ignition system88may produce an ignition spark in pre-chamber igniter192in response to a spark advance signal SA from controller12under select operating modes. A timing of signal SA may be adjusted based on engine operating conditions and a driver torque demand. For example, spark may be provided at maximum brake torque (MBT) timing to maximize engine power and efficiency. Controller12may input engine operating conditions, including engine speed, engine load, and exhaust gas AFR, into a look-up table, which may output the corresponding MBT timing for the input engine operating conditions. In other examples, spark may be retarded from MBT to prevent an occurrence of knock. In still other examples, spark may be retarded from MBT to reduce engine torque, such as due to a decrease in driver-demanded torque or a transmission gear shift event, or to provide a torque reserve.

Engine10may be controlled at least partially by controller12and by input from a vehicle operator113via an accelerator pedal116and an accelerator pedal position sensor118and via a brake pedal117and a brake pedal position sensor119. The accelerator pedal position sensor118may send a pedal position signal (PP) to controller12corresponding to a position of accelerator pedal116, and the brake pedal position sensor119may send a brake pedal position (BPP) signal to controller12corresponding to a position of brake pedal117. Controller12is shown inFIG.1as a microcomputer, including a microprocessor unit102, input/output ports104, an electronic storage medium for executable programs and calibration values shown as a read-only memory106in this particular example, random access memory108, keep alive memory110, and a data bus. Storage medium read-only memory106can be programmed with computer readable data representing instructions executable by microprocessor unit102for performing the methods and routines described herein as well as other variants that are anticipated but not specifically listed.

Controller12may receive various signals from sensors coupled to engine10, in addition to those signals previously discussed, including a measurement of inducted mass air flow (MAF) from a mass air flow sensor46, an engine coolant temperature signal (ECT) from an ECT sensor112coupled to coolant sleeve114, signal UEGO from exhaust gas sensor128, which may be used by controller12to determine the AFR of the exhaust gas, an exhaust gas temperature signal (EGT) from a temperature sensor158coupled to exhaust passage135, an ECD temperature sensor179coupled to the ECD178, a profile ignition pickup signal (PIP) from a Hall effect sensor120(or other type) coupled to crankshaft140, a throttle position (TP) from a throttle position sensor coupled to throttle62, and an manifold absolute pressure signal (MAP) from a MAP sensor122coupled to intake manifold44. An engine speed signal, RPM, may be generated by controller12from signal PIP. The manifold pressure signal MAP from the manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold44. Furthermore, controller12may send and receive a SAIR signal to and from SAIR system220for operating the SAIR system220responsive to operating conditions, as further described with reference toFIGS.2-6. In one example, the SAIR signal may indicate when a SAIR pump is switched ON or OFF. In another example, the controller12may transmit a SAIR signal to toggle the SAIR pump222ON/OFF status and/or adjust a position of one or more SAIR flow control valves226and228. In another non-limiting example, controller12may receive a SAIR signal from SAIR flow sensor224, indicating a flow rate of SAIR.

Based on input from one or more of the above-mentioned sensors, controller12may adjust one or more actuators, such as fuel injector66, throttle62, pre-chamber igniter192, the intake/exhaust valves and cams, etc. The controller12may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on instructions or code programmed therein corresponding to one or more routines, an example of which is described with respect toFIGS.4and5.

In some examples, vehicle5may be a hybrid vehicle with multiple sources of torque available to one or more vehicle wheels160. In other examples, vehicle5is a conventional vehicle with only an engine. In the example shown inFIG.1, the vehicle includes engine10and an electric machine161. Electric machine161may be a motor or a motor/generator and thus may also be referred to herein as an electric motor. Electric machine161receives electrical power from a traction battery170to provide torque to vehicle wheels160. Electric machine161may also be operated as a generator to provide electrical power to charge battery170, for example, during a braking operation.

Crankshaft140of engine10and electric machine161are connected via a transmission167to vehicle wheels160when one or more clutches166are engaged. In the depicted example, a first clutch166is provided between crankshaft140and electric machine161, and a second clutch166is provided between electric machine161and transmission167. Controller12may send a signal to an actuator of each clutch166to engage or disengage the clutch, so as to connect or disconnect crankshaft140from electric machine161and the components connected thereto, and/or connect or disconnect electric machine161from transmission167and the components connected thereto. Transmission167may be a gearbox, a planetary gear system, or another type of transmission. The powertrain may be configured in various manners including as a parallel, a series, or a series-parallel hybrid vehicle.

As described above,FIG.1shows only one cylinder of a multi-cylinder engine. As such, each cylinder may similarly include its own set of intake/exhaust valves, fuel injector(s), igniter, etc. It will be appreciated that engine10may include any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Further, each of these cylinders can include some or all of the various components described and depicted byFIG.1with reference to cylinder130. Further still, the multiple cylinders may be arranged and/or organized into one or more banks of cylinders, whereby each bank of cylinders is arranged in a separate line parallel to the crankshaft. Arranging engine cylinders in banks can aid in reducing a size of the engine, and in reducing engine vibration.

Turning now toFIG.2, it illustrates another schematic of the engine system100including engine10, SAIR system220and controller12. Components of the engine system100previously introduced inFIG.1are numbered identically in this figure and subsequent figures. Several elements of engine10, such as EGR system83, ignition system88, transmission167, and the like (as shown inFIG.1), are omitted inFIG.2for clarity; however, engine system100may include all of the elements of engine10, as shown inFIG.1. Furthermore, engine system100may be included as part of a vehicle system, such as vehicle5, ofFIG.1.

Engine system100may include multiple cylinders130arranged into one or more cylinder banks. In particular, the two cylinder banks216and218of four cylinders130are shown in the example of engine system100. In other examples, engine system100may include more than two cylinder banks, each bank having more or less than four cylinders130. As described previously with reference toFIG.1, intake air entering intake passage42is filtered through air filter191before passing through throttle62to intake manifold44of engine10. MAF sensor46may be fluidly coupled at intake passage42between SAIR intake passage90and throttle62to measure a flow rate of air entering the intake manifold, Qair,intake. In other words, Qair,intakedoes not include the SAIR, QSAIR, directed to SAIR intake passage90.

Fuel system180may deliver fuel to fuel injectors66(e.g., direct fuel and/or port fuel injectors) included at each cylinder130.FIG.2shows fuel injection lines coupling fuel system180and cylinders130of cylinder bank218. Although not depicted for clarity, engine system100further includes fuel injection lines coupling fuel system180to cylinders13of cylinder bank216. As described with reference toFIG.1, the controller12may control and determine, based on engine and vehicle operating conditions, a fuel injection flow rate, Qinj,j, to each jthengine cylinder130of each ithcylinder bank (e.g., for the case of 2 cylinder banks, each with 4 cylinders, i=2 and j=4). In particular, fuel may be injected in proportion to a pulse-width of a signal FPW received from controller12by way of an electronic driver168, and the fuel injection rate at each cylinder may be varied depending on engine operating conditions.

Intake air is delivered to each cylinder130of each cylinder bank216and218of engine10by way of intake manifold44. In one example, intake manifold44may divide and deliver the intake air evenly to each cylinder bank216and218, and/or to each cylinder130. Cylinder combustion products, including unreacted air, uncombusted fuel hydrocarbons, and the like are exhausted from the cylinders130by way of exhaust manifolds246and248. As depicted inFIG.2, each exhaust manifold246and248corresponds to one of the cylinder banks216and218, respectively. Furthermore, an exhaust gas sensor286and288is coupled upstream of an emission control device276and278, corresponding to each exhaust manifold246and278, respectively. The exhaust gas sensors286and288may correspond to exhaust gas sensor128, and may include one or more various suitable sensors for providing an indication of an exhaust gas air-fuel ratio (AFR), such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx sensor, a HC sensor, or a CO sensor, for example. Emission control devices276and278may correspond to emission control device178, and may include a three-way catalyst, a NOx trap, various other emission control devices, or combinations thereof.

A portion of the intake air may be diverted from intake passage42to SAIR system220by way of SAIR intake passage90. SAIR system220can include SAIR pump222, SAIR flow sensor224, and one or more SAIR flow control valves226and228positioned in SAIR exhaust passages296and298, respectively. The SAIR exhaust passages296and298ofFIG.2may be fluidly coupled to exhaust manifolds246and248, respectively, and may correspond to SAIR exhaust passage92. Furthermore, SAIR system220can include one or more flow control valves226and228and one or more SAIR exhaust passages296and298, each of the SAIR exhaust passages296and298fluidly coupled to one of the exhaust manifolds246and248. Each of the exhaust manifolds246and248correspond to the one of the cylinder banks216and218. SAIR flow control valves226and228may further act as check valves, preventing exhaust gases from flowing upstream from the SAIR exhaust passages296and298and past SAIR flow control valves226and228.

Accordingly SAIR may be diverted from the intake passage42and delivered to the one or more exhaust manifolds246and248during a condition when SAIR pump222is turned on and when one or more of the SAIR flow control valves226and228are open. Furthermore, SAIR flow rate, QSAIR,measmay be measured and/or inferred by SAIR flow sensor224and communicated to controller12. SAIR flow sensor224may include a SAIR MAF sensor that directly measures the SAIR mass flow rate. In another example, SAIR flow sensor may include an orifice and one or more pressure sensors for indicating SAIR flow based on a pressure drop measured across the orifice. SAIR pump222and SAIR flow control valves226and228are conductively coupled to the controller12, whereby the controller12may turn SAIR pump222on or off, and/or adjust a position of one or both of SAIR flow control valves226and228, responsive to various engine operating conditions. Adjusting a position of one or both of SAIR flow control valves226and228includes moving one or both of SAIR flow control valves226and228to a more open position and/or to a more closed position. In one example, adjusting one or both of SAIR flow control valves226and228to a more open position includes fully opening one or both of SAIR flow control valves226and228; similarly, adjusting one or both of SAIR flow control valves226and228to a more closed position includes fully closing one or both of SAIR flow control valves226and228. As such, controller12can direct and distribute SAIR evenly or unevenly to each of the exhaust manifolds246and248by adjusting positions of the SAIR flow control valves226and228.

In one example, controller12may startup SAIR system220to deliver SAIR to the engine exhaust manifolds246and248following a cold start engine event during a cold start condition, the cold start condition including when a temperature of one or more of the ECDs276and278, TECD,j(j index refers to corresponding to the jthcylinder bank), is less than a threshold ECD temperature, TECD,TH. As an example, TECD,THmay include temperatures less than 200 degrees Fahrenheit. In another example, the cold start condition may further include when an engine temperature, Tengine, is less than a threshold engine temperature, Tengine,TH, and when an engine status has been switched from OFF to ON. In one example, Tengine,THmay include temperatures less than 40 degrees Fahrenheit. In a further example the cold start condition may further include prior to when a threshold post-engine start duration, ΔtSTART,TH, following an engine start (e.g., engine status switching from OFF to ON) has elapsed.

When the cold start condition is satisfied, fuel combustion at the engine cylinders130may be less efficient, resulting in higher amounts of uncombusted fuel exhausted from the engine at the exhaust manifolds246and248, which can give rise to higher emissions. Furthermore, when an ECD temperature is less than the threshold ECD temperature, the ability of the ECD to remove pollutants, including uncombusted fuel hydrocarbons, may be reduced. Furthermore, when a duration following an engine start event, ΔtSTART, is less than the threshold post-engine start duration, ΔtSTART,TH, emissions of uncombusted fuel can be higher. As such, when one or more of the engine status is ON and Tengine<Tengine,TH, TECD,j<TECD,TH, and ΔtSTART<ΔtSTART,TH, the cold start condition may be satisfied, and controller12may startup SAIR system220by switching SAIR pump222ON and opening one or more of SAIR flow control valves226and228.

Conversely, the cold start condition is not met when one or more of Tengineincreases above Tengine,THwhile the engine is ON (the engine is no longer under cold start conditions), TECD,j>TECD,TH(the emission control device is greater than the threshold ECD temperature), and ΔtSTART<ΔtSTART,THis met (the threshold post-engine start duration after an engine start event is exceeded). Thus, responsive to the cold start condition not being met, the controller12shutdown the SAIR system220by closing one or more of the SAIR flow control valves226and228and switching OFF SAIR pump222.

Controller12may measure a SAIR flow rate with the SAIR flow sensor224positioned within the SAIR system220. In the example ofFIG.2, SAIR flow sensor224is positioned upstream from the SAIR flow control valves226and228and downstream from SAIR pump222. As such, flow rate measurement with the SAIR flow sensor224may not reliably detect when SAIR is not being delivered to (or when SAIR flow is partially blocked or diverted from) the exhaust manifolds246and248, in the case of a malfunction in the SAIR system (e.g., a faulty SAIR pump222, stuck SAIR flow control valve226or228, a blockage in the SAIR system220, a leak in the SAIR system, and the like). In one example, a leak in the SAIR system220downstream from the SAIR flow sensor may appear non-faulty to the SAIR flow sensor224as SAIR is moving past the SAIR flow sensor224but may be at least partially diverted before reaching the exhaust manifold.

An estimate of the total SAIR delivered to the exhaust manifolds246and248, and the SAIR at each of the exhaust manifolds246and248(e.g., SAIR on a per cylinder bank basis) may be back calculated from the fuel injection flow rate to each cylinder bank, Qinj,j, the air-to-fuel ratio, AFR (measured by exhaust gas sensors286and288), and the intake air flow rate, Qair,intake(measured by MAF sensor46). As shown in equation (1), an estimate for the amount of air in each exhaust manifold246and248may be back calculated from the measured AFRJ(AFR in exhaust manifold corresponding to jthcylinder bank) and the fuel flow delivered, Qinj,j(fuel injection flow rate to the jthcylinder bank).
Qair,j=Qinj,j*AFRJ[mass/cycle]  (1)
Qair,j=Qinj,j*λj*AFRSTOICH[mass/cycle]  (2)
Qinj,j=ΣiQinj,j,i[mass/cycle]  (3)

Here, Qair,jrepresents the sum of the SAIR flow rate delivered to the exhaust manifold (corresponding to the jthcylinder bank) and the residual air flow rate exhausted from the jthbank of cylinders following cylinder combustion. In the case where the exhaust gas sensor286or288measures, λ, the ratio of the actual AFR to the stoichiometric AFR, AFRSTOICH, Qair,jis given by equation (2). In general, the amount of fuel and oxygen consumed by combustion is negligible relative to the total amount of fuel and oxygen exhausted. As such, equations (1) and (2) are able to provide reliable estimates for the SAIR flow rate. Furthermore, Qinj,jmay be calculated from equation (3), where the fuel injection flow rate to the jthcylinder bank, Qinj,j, is determined by summing the fuel injection flow rates to each ithcylinder in the jthbank, Qinj,j,i. The units for Qair,jand Qinj,jare in mass units per cycle, where a cycle refers to a 4-stroke cylinder cycle, and 720 crank degrees of revolution.

Next, an estimate for SAIR delivered to the exhaust manifold may be determined by subtracting the intake airflow, Qair,intake, from the sum over each jthcylinder bank of each Qair,j, as indicated by equation (4). Furthermore, assuming the intake air, Qair,intake, is apportioned equally amongst each jthcylinder bank, the SAIR delivered to each exhaust manifold corresponding to the jthcylinder bank, QSAIR,j, can be determined as represented by equation (5). Further still, an estimate of SAIR on a per cylinder basis within each bank may be calculated by dividing QSAIR,jby the number of cylinders in the jthbank, Ij, as shown in equation (6).
QSAIR=ΣjQair,j−Qair,intake[mass/cycle]  (4)
QSAIR,j=Qair,j−Qair,intake,j=Qair,intake/J[mass/cycle]  (5)
QSAIR,j,cylinder=QSAIR,j/Ij[mass/cycle]  (6)

In equation (5), j is the total number of cylinder banks, and Qair,intake,jrepresents the intake air flow rate delivered to the jthcylinder bank. In equation (6), Ijrepresents the total number of cylinders130in the jthcylinder bank. Furthermore, conversion to units of [mass/time] can be executed by multiplying by engine speed and a factor of revolutions per cycle, as represented by equation (7).
QSAIR,j[mass/min]=QSAIR,j[mass/cycle]*½[cycle/revolutions]*Engine Speed [rpm]  (7)

The SAIR can also be expressed as a percentage of the total exhaust flow, either across all cylinder banks (equation (8)), or by cylinder bank (equation (9)). In equation (9), it is assumed that the intake air flow, Qair,intake, is divided evenly across the intake manifolds corresponding to the j cylinder banks.
%QSAIR=(QSAIR/ΣjQair,j)*100=[QSAIR/(QSAIR+Qair,intake)]*100  (8)
%QSAIR,j=(QSAIR,j/Qair,j)*100=[QSAIR,j/(QSAIR,jQair,intake/j)]*100  (9)

Turning now toFIG.3, it illustrates two data plots310and320, comparing estimated SAIR flow rates, QSAIR(QSAIRsummed over all cylinder banks,314,324), QSAIR,1(QSAIRdirected to a first cylinder bank,316,326), and QSAIR,2(QSAIRdirected to a second cylinder bank,318,328), calculated from equations (4) and (5), along with a measured flow rate, QSAIR,meas(312,322) (e.g., measured with SAIR flow sensor224). Plot310illustrates engine operating conditions from a time between 0 to 12 s when SAIR is being delivered to the exhaust manifolds, and operating conditions after a time of 12 s when the SAIR is not being delivered to the exhaust manifolds. In other words, between 0 to 12 s, a first condition may be satisfied, including when a SAIR pump is ON and one or more of the SAIR flow control valves is adjusted to a more open position. The first condition may further include when a cold start condition is satisfied, including when the engine status is ON and Tengine<Tengine,TH, TECD,j<TECD,TH, and ΔtSTART<ΔtSTART,THFurthermore, after 12 s the first condition may not be satisfied, and a second condition may be satisfied, including when the SAIR pump is OFF, and all of the SAIR flow control valves are closed. The second condition may further include when the cold start condition is not satisfied, including when the engine status is OFF and Tengine>Tengine,TH, TECD,j>TECD,TH, and ΔtSTART>ΔtSTART,TH.

Both plots310and320illustrate that, in spite of substantial noise factors influencing the estimated data, there is reasonable agreement between the estimated and measured values of SAIR, QSAIRand QSAIR,measOne example noise factor may include the influence of lost fuel. Lost fuel includes fuel that does not evaporate and excludes fuel that is combusted in the air-fuel mixture. Accordingly, the lost fuel (non-evaporated fuel) is included and accounted for in the measured fuel injection flow rates, Qinj,j, but is not measured as part of the exhaust air-fuel mixture by the exhaust gas sensors128(e.g., AFR measurement). Accordingly, the Qair,jcalculated from equations (2) and (3) can deviate from the true air flow rate. Furthermore, the amount of lost fuel can vary depending on engine operating conditions such as engine temperature and soak time, whereby an amount of lost fuel increases with colder ambient temperatures and/or longer soak times. Thus, as engine operating conditions vary, noise factors such as lost fuel can fluctuate, causing variability in the QSAIR,jcalculated from Qair,j(equations (4)-(6)). Herein, the soak time refers to the duration of time in which a vehicle engine status is OFF and which precedes a successful vehicle start (a successful vehicle start is defined as a vehicle start that does not result in a stall). In one example, when the soak-time is greater than a threshold soak time, the corresponding engine start is designated as a cold start. As one example, the threshold soak time may include 12 hours.

Owing to the substantial noise in the estimated data, indication of a normally functioning SAIR system can be indicated by changes in the estimated QSAIRand QSAIR,j. For example, the change in QSAIR, ΔQSAIR(ΔQSAIR=|QSAIR1−QSAIR2|), can be compared with a threshold change, ΔQSAIR,TH(ΔQSAIR,THrefers to a threshold SAIR difference). Here, QSAIR1and QSAIR2denote an estimated SAIR flow rate, QSAIR(summed over each cylinder bank, j), corresponding to when the first condition is satisfied and when the second condition is satisfied, respectively. In other words, ΔQSAIRmay refer to a change in estimated SAIR flow rate before and after SAIR shutdown. In another example, ΔQSAIRmay also refer to a change in estimated SAIR flow rate before and after SAIR startup. In a further example, ΔQSAIRmay also refer to a change in estimated SAIR flow rate between a first condition (e.g., when the controller12takes action to startup the SAIR system220and direct SAIR to the exhaust manifold) and a second condition (e.g., when the controller12takes action to shut down the SAIR system220and stop directing SAIR to the exhaust manifold).

In one example, the duration when the first condition is satisfied and the duration when the second condition is satisfied may not be sequentially consecutive in time, whereby the second duration follows the first duration in uninterrupted succession. As an example, the duration when the first condition is satisfied and the duration when second condition is satisfied may be separated by an intervening interval of time therebetween. Furthermore, the duration when the second condition is satisfied may occur prior to the duration when the first condition is satisfied, or, the duration when the first condition is satisfied may occur prior to the duration when the second condition is satisfied. In another example, the first duration and the second duration may preferably be sequentially consecutive in time because noise factors may be reduced. For instance, the influence of lost fuel on the calculated Qsair,jand QSAIRmay be reduced since the amount of lost fuel during the first duration and the second duration may be more similar when the first duration and the second duration are sequentially consecutive in time. In the example illustrated by the plots ofFIG.3, ΔQSAIRcorresponds to before and after shutdown of the SAIR system at a time of 12 s. When ΔQSAIR>ΔQSAIR,TH, the SAIR system is functioning normally; conversely, when ΔQSAIR<ΔQSAIR,TH, the SAIR system may be faulty.

In one example, QSAIR1and QSAIR2may be determined by averaging the measured data for QSAIR1and QSAIR2over a threshold duration prior to and after the SAIR system being shutdown. In one example, the threshold duration may include five seconds. In one example, QSAIR1may be calculated by averaging the measured data for QSAIR1over the threshold duration just prior to an engine shutdown event; QSAIR2may be calculated by averaging the measured data for QSAIR2over the threshold duration just after the engine shutdown event. In another example, the averaging may exclude data measured during a deadband duration just prior to and just after the engine shutdown event in order to reduce the variability arising from the transient effects of the engine shutdown event. Accordingly, QSAIR1may be calculated by averaging the measured data for QSAIR1over the threshold duration just prior to the deadband duration before an engine shutdown event; QSAIR2may be calculated by averaging the measured data for QSAIR2over the threshold duration just after the deadband duration following the engine shutdown event.

Furthermore, ΔQSAIR,THmay be a predetermined based on a set point SAIR. For example, ΔQSAIR,THmay include 50% of the desired SAIR. In this way, ΔQSAIR,THmay vary with engine operating conditions. For example, at higher engine loads (e.g., higher Qin), the exhaust may contain higher levels of uncombusted fuel; thus, the desired SAIR may be higher to aid in oxidizing the higher amounts of uncombusted fuel in the exhaust. In another example, ΔQSAIR,THmay be determined based on emissions data that correlates SAIR with exhaust emissions. In other words, ΔQSAIR,THmay be chosen to aid in maintaining exhaust emissions below a threshold level. Additionally or alternatively, ΔQSAIR,THmay be determined based on tolerances and sensitivities, and measurement ranges of the measurement sensors such as the exhaust gas sensors, manifold pressure sensors, SAIR flow sensors, and the like. For instance, ΔQSAIR,THmay be higher when the measurement error for the sensors is higher. In one example, when the ECD temperature is lower and/or the vehicle engine soak time is longer, ΔQSAIR,THmay be reduced since underdelivering SAIR by more than ΔQSAIR,j,THincreases a probability of exceeding emissions thresholds.

In another example, the change (e.g., before and after shutdown of the SAIR system, or before and after startup of the SAIR system) in QSAIR,j, ΔQSAIR,j, can be compared with a threshold change, ΔQSAIR,TH,j(ΔQSAIR,j=|QSAIR1,j−QSAIR2,j|). QSAIR,jrefers to the SAIR directed to the jthengine cylinder bank. When ΔQSAIR,j>ΔQSAIR,j,TH, the SAIR system is functioning normally; conversely, when ΔQSAIR,j<ΔQSAIR,j,TH, the SAIR system may be faulty. In one example, QSAIR1,jand QSAIR2,jmay be determined by averaging the QSAIR1,jand QSAIR2,jdata over the threshold duration (e.g., prior to and after the SAIR system being shut down or prior to and after the SAIR system being started up). Furthermore, ΔQSAIR,j,THmay be a predetermined based on a set point SAIR corresponding to the jthbank. For example, ΔQSAIR,j,THmay include 50% of the desired SAIR for the jthbank. In this way, ΔQSAIR,j,THmay vary with engine operating conditions, and may also be determined on a per cylinder bank basis, to account for differences in fuel injection flow rates, compression ratio, and the like between each cylinder bank.

In another example, a difference in SAIR directed to the exhaust of two cylinder banks, ΔQSAIR,j,j+1(ΔQSAIR,j,j+1=|QSAIR,j−QSAIR,j+|), can be compared, both before and after shutdown (or before and after startup) of the SAIR system. When ΔQSAIR,j,j+1<ΔQSAIR,j,j+1,TH(ΔQSAIR,j,j+1,THrefers to a threshold bank-bank SAIR difference), the SAIR system is functioning normally; conversely, when ΔQSAIR,j,j+1>ΔQSAIR,j,j+1,TH, the SAIR system may be faulty. In one example, QSAIR,jand QSAIR,j+1may be determined by averaging the QSAIR,jand QSAIR,j+1data, respectively, over the threshold duration prior to and/or after the SAIR system being shutdown.

Furthermore, ΔQSAIR,i,j+1,THmay be a predetermined based on a set point SAIR corresponding to the jthand (j+1)thbank. For example, ΔQSAIR,j,j+1,TH may include50% of the desired SAIR,j for the jthbank or (j+1)thbank. In this way, ΔQSAIR,j,j+1,THmay vary with engine operating conditions and may account for differences in operating conditions between the jthand (j+1)thcylinder bank.

ΔQSAIR,j,THand ΔQSAIR,j,j+1,THmay be determined based on engine operating conditions, as described above for ΔQSAIR,TH. For instance, ΔQSAIR,j,TH(or ΔQSAIR,j,j+1,TH) may be a predetermined based on a set point SAIR. For example, ΔQSAIR,j,TH(or ΔQSAIR,j,j+1,TH) may include 50% of the desired SAIR. In this way, ΔQSAIR,j,TH(or ΔQSAIR,j,j+1,TH) may vary with engine operating conditions. For example, at higher engine loads (e.g., higher Qinj), the exhaust may contain higher levels of uncombusted fuel; thus, the desired SAIR may be higher to aid in oxidizing the higher amounts of uncombusted fuel in the exhaust. In another example, ΔQSAIR,j,TH(or ΔQSAIR,j,j+1,TH) may be determined based on emissions data that correlates SAIR with exhaust emissions. In other words, ΔQSAIR,j,TH(or ΔQSAIR,j,j+1,TH) may be chosen to aid in maintaining exhaust emissions below a threshold level. Additionally or alternatively, ΔQSAIR,j,TH(or ΔQSAIR,j,j+1,TH) may be determined based on tolerances and sensitivities, and measurement ranges of the measurement sensors such as the exhaust gas sensors, manifold pressure sensors, SAIR flow sensors, and the like. For instance, ΔQSAIR,j,TH(or ΔQSAIR,j,j+1,TH) may be higher when the measurement error for the sensors is higher. In one example, when the ECD temperature is lower and/or the vehicle engine soak time is longer, ΔQSAIR,j,TH(or ΔQSAIR,j,j+1,TH) may be reduced since underdelivering SAIR by more than ΔQSAIR,j,THincreases a probability of exceeding emissions thresholds.

In another example, a sum of the estimated SAIR across all cylinder banks, QSAIR=, ΣQSAIR,j, may be compared with QSAIR,meas. When ΔQSAIR,mease,est=QSAIR,meas−ΣQSAIR,jis greater than a threshold difference, ΔQSAIR,mease,est,TH, a substantial portion of the SAIR delivered by SAIR pump may not be delivered to the exhaust manifold, indicating a faulty SAIR system. QSAIR,meas−ΣQSAIR,jmay be compared both before and after shutdown, and ΔQSAIR,mease,estmay be dependent on the values of ΔQSAIR,mease,estbefore and after shutdown.

The plot310shows QSAIRestimates for a non-faulty SAIR system. As such ΔQSAIR>ΔQSAIR,TH, ΔQSAIR,j>ΔQSAIR,j,TH(for both cylinder banks), and ΔQSAIR,j,j+1<ΔQSAIR,j,j+1,TH. In contrast, plot320shows QSAIRestimates for a faulty SAIR system. In particular, the change in QSAIR,2(ΔQSAIR,2=|QSAIR1,2−QSAIR2,2|) before and after the SAIR shutdown at 12 s is much lower than the corresponding change to QSAIR,1, (ΔQSAIR,1=|QSAIR1,1−QSAIR2,1|). As such, ΔQSAIR,2<ΔQSAIR,2,THand ΔQSAIR1,1,2<ΔQSAIR1,i,j+1,TH, indicating a faulty SAIR system, specifically, a faulty SAIR system corresponding to cylinder bank 2. For example, a SAIR flow control valve delivering SAIR to the exhaust of cylinder bank 2 may be stuck in a closed position. Furthermore, ΔQSAIR,mease,est, =QSAIR,meas−ΣQSAIR,jmay be greater than a threshold difference, ΔQSAIR,mease,est,TH, because a substantial portion of the SAIR delivered by SAIR pump is not be delivered to the exhaust manifold.

In another example, a SAIR ratio, QSAIR,ratio12=QSAIR1/QSAIR2, of the estimated SAIR before shutdown of the SAIR system to the estimated SAIR after shutdown of the SAIR system may be calculated to determine if the SAIR system is faulty. Utilizing a SAIR flow ratio, QSAIR,ratio12, may advantageously aid in reducing an influence of noise factors in diagnosing the SAIR system. For the case where QSAIR,ratio12is less than a lower threshold SAIR ratio, QSAIR,ratio,TH,lower, a faulty SAIR system is indicated. QSAIR,ratio12<QSAIR,ratio,TH,lowermay be caused by a one or more of a lower than expected QSAIR1and a higher than expected QSAIR2. A lower than expected QSAIR1(SAIR flow during the first condition when the SAIR system is ON) may be caused by one or more of a blockage in the SAIR system, a leak in the SAIR system, or a stuck SAIR flow control valve in a more closed position, that lowers SAIR flow, QSAIR1, to the exhaust manifold. A higher than expected QSAIR2(SAIR flow during the second condition when the SAIR system is OFF) may be caused by one or more of a stuck SAIR flow control valve in a more open position, and a faulty SAIR pump that doesn't shut OFF, that prevents stopping of the SAIR flow to the exhaust manifold.

In another example, a SAIR ratio, QSAIR,ratio12=QSAIR1/QSAIR2, of the estimated SAIR before shutdown of the SAIR system to the estimated SAIR after shutdown of the SAIR system may be compared with an upper threshold SAIR ratio, QSAIR,ratio,TH,upper. For the case where QSAIR,ratio12>QSAIR,ratio,TH,upper, a faulty SAIR system is indicated. QSAIR,ratio12>QSAIR,ratio,TH,uppermay be caused by a higher than expected QSAIR1. A higher than expected QSAIR1(SAIR flow during the first condition when the SAIR system is ON) may be caused by a faulty SAIR pump that is operating at a higher than expected pump speed and that raises SAIR flow, QSAIR1, to the exhaust manifold. In another example, the SAIR ratio may be applied on a cylinder bank basis. In other words, a SAIR ratio by cylinder bank, QSAIR,ratio12,j=QSAIR1,j/QSAIR2,jmay be compared with upper and lower threshold SAIR ratios, QSAIR,ratio,TH,upper,jand QSAIR,ratio,TH,lower,j, respectively, corresponding to the jthcylinder bank. When QSAIR,ratio12,j<QSAIR,ratio,TH,lower,jor when QSAIR,ratio12,j>QSAIR,ratio,TH,upper,j, a faulty SAIR system corresponding to SAIR flow at the jthcylinder bank may be indicated. Conditions giving rise to when QSAIR,ratio12,j<QSAIR,ratio,TH,lower,jor when QSAIR,ratio12,j>QSAIR,ratio,TH,upper,j, may be as described above for QSAIR,ratio12<QSAIR,ratio,TH,lowerand QSAIR,ratio12>QSAIR,ratio,TH,upper, but as applied on a per jthcylinder bank basis. Furthermore, the SAIR ratio may further include a ratio comparing SAIR flows from two different cylinder banks. For example, QSAIR,ratio12,j,j+1=QSAIR1,j/QSAIR2,j+1, may be compared with thresholds, QSAIR,ratio,j,j+1,TH,lowerand QSAIR,ratio,j,j+1,TH,upperto diagnose a faulty SAIR system.

Turning now toFIG.7, it illustrates data plots700and710. Similar to data plot310, data plot700compares estimated total SAIR flow rate708, estimated SAIR flow rate704for a first cylinder bank, and estimated SAIR flow rate706for a second cylinder bank, with the measured total SAIR flow rate702(e.g., measured with SAIR flow sensor224). In contrast, during the same time period, data plot710compares estimated SAIR flow rates as a percentage of total exhaust flow, % QSAIR,1(% QSAIRdirected to a first cylinder bank,714), and QSAIR,2(QSAIRdirected to a second cylinder bank,716), calculated from equation (9), along with a measured % SAIR flow rate, % QSAIR,meas(712) (e.g., % QSAIR,meas=QSAIR,meas/(QSAIR,meas+Qair,intake), QSAIR,measmeasured with SAIR flow sensor224). Plot710illustrates engine operating conditions from a time between 0 to about 15 s when SAIR is being delivered to the exhaust manifolds, and operating conditions after a time of 15 s when the SAIR is not being delivered to the exhaust manifolds. In other words, between 0 to 15 s, a first condition may be satisfied, including when a SAIR pump is ON and one or more of the SAIR flow control valves is adjusted to a more open position. The first condition may further include when a cold start condition is satisfied, including when the engine status is ON and Tengine<Tengine,TH, TECD,j<TECD,TH, and ΔtSTART<ΔtSTART,TH. Furthermore, after 15 s the first condition may not be satisfied, and a second condition may be satisfied, including when the SAIR pump is OFF, and all of the SAIR flow control valves are closed. The second condition may further include when the cold start condition is not satisfied, including when the engine status is OFF and Tengine>Tengine,TH, TECD,j>TECD,TH, and ΔtSTART>ΔtSTART,TH.

Comparison of the plot710with the plots710, (and plots310and320) show that expressing the SAIR flow as a percentage of the exhaust flow, % QSAIRmay additionally or alternatively be utilized to diagnose faults in the SAIR system220. Furthermore, expressing the estimated SAIR flow as % QSAIRmay aid in reducing the influence of noise factors, including lost fuel, as indicated by the smaller amplitude signal fluctuations in the trend lines of plot710, as compared with the data plots inFIG.3. Threshold-based criteria for diagnosing a faulty SAIR system can be analogously described for % QSAIRand % QSAIR,jvalues as described above for QSAIRand QSAIR,jwith reference to the plots ofFIG.3. The data plots700and710illustrate QSAIRand % QSAIRestimates, respectively, for a non-faulty SAIR system. As such, with reference to data plot710, A % QSAIR>A % QSAIR,TH, Δ % QSAIR,j>Δ % QSAIR,j,TH(for both cylinder banks), and Δ % QSAIR,i,j+1<Δ % QSAIR,j,j+1,TH. Here, Δ % QSAIR=%−% QSAIR2|, Δ % QSAIR1,j−% QSAIR2,j|, and Δ % QSAIR,j,j+1=|% QSAIR,j−% QSAIR,j+1|. Furthermore, Δ % QSAIR,THmay be described and determined analogously to ΔQSAIR,TH, Δ % QSAIR,j,THmay be described and determined analogously to ΔQSAIR,j,TH, and Δ % QSAIR,j,j+1,TH(bank-bank percent SAIR difference) may be described and determined analogously to ΔQSAIR,j,j+1,TH. In contrast, a faulty SAIR system may be indicated by one or more of when Δ % QSAIR<Δ % QSAIR,TH, Δ % QSAIR,j<Δ % QSAIR,j,TH(for both cylinder banks), and Δ % QSAIR,j,j+1<Δ % QSAIR,j,j+1,TH.

Turning now toFIGS.4and5, flow charts representing methods400and500are shown for operating an engine system200, including an engine10and SAIR system220of a vehicle5. The methods ofFIGS.4and5are directed to determining degradation of a SAIR system adding a SAIR to downstream of an engine cylinder exhaust based on a comparison of the SAIR determined from a fuel injection amount, an exhaust air-fuel ratio, and an engine intake airflow, both before and after shutdown of the SAIR pump. Furthermore, the degradation of the SAIR system can be determined on a per cylinder bank basis so that a fault in the SAIR system may be indicated as corresponding to one or more particular cylinder banks. Instructions for carrying out the methods400and500may be executed by a controller12based on instructions stored on a memory of the controller12and in conjunction with signals received from sensors of the engine, such as the sensors described above with reference toFIGS.1and2. The controller12may employ engine actuators of the engine10to adjust engine operation, according to the methods described below.

At410, method400includes estimating and/or measuring engine operating conditions. The engine operating conditions may include, for example, engine ON/OFF status, SAIR pump ON/OFF status, QSAIR,meas, AFRj, Qinj,j, Qair,intake, % opening position of SAIR flow control valves, Tengine, TECD, ΔtSTART, and the like. The engine operating conditions may be measured by one or more sensors communicatively coupled to the controller12or may be inferred based on available data. For example, the engine temperature may be measured by an engine coolant temperature sensor, such as ECT sensor112ofFIG.1, and the ECD temperature may be measured by an ECD temperature sensor. As yet another example, the accelerator pedal position may be measured by an accelerator pedal position sensor, such as accelerator pedal position sensor118ofFIG.1, and the brake pedal position may be measured by a brake pedal position sensor, such as brake pedal position sensor119ofFIG.1. Together, the accelerator pedal position and the brake pedal position may indicate a demanded amount of engine torque.

Next, method400continues at420where the controller12determines if a first condition is satisfied. The first condition being satisfied includes when a SAIR pump is ON. The first condition may further include when one or more of the SAIR flow control valves226and228are open. Furthermore, the first condition may further include when a cold start engine event has occurred (e.g., and a cold start condition is satisfied), including when the engine status is ON and Tengine<Tengine,TH. Furthermore, the cold start condition may further include when TECD,j<TECD,THand/or when ΔΔtSTART<ΔtSTART,TH. For the case where the first condition is satisfied, method400continues at422,424, and426, where the controller12measures the fuel injection flow, Qinj,j,i, for each ithcylinder in each jthcylinder bank, λjat the exhaust manifold for each jthcylinder bank, and Qair,intake, respectively, corresponding to when the first condition is satisfied. As described earlier, Qinj,j,i, λj, and Qair,intakemay be determined by averaging measured data received from signals and sensors (e.g., FPW signal from driver168, exhaust gas sensors128,286and288, and MAF sensor46). In particular, the measured data may be averaged over a threshold duration during conditions when the first condition is satisfied. Averaging the measure data over the threshold duration may aid in reducing an influence of noise factors, and can increase the reliability of the method400. Next, method400continues at428where the controller12calculates QSAIR1and QSAIR1,j(e.g., QSAIRand QSAIR,jwhen the first condition is satisfied), from equations (1) through (6).

Returning to420, for the case where the first condition is not satisfied, method400continues at430where the controller12determines if a second condition is satisfied. The second condition being satisfied includes when a SAIR pump is OFF. The second condition may further include when one or more of the SAIR flow control valves226and228are fully closed. Furthermore, the second condition may further include when a cold start engine event has ended (e.g., and when a cold start condition is not satisfied), including when the engine status is ON and Tengine>Tengine,TH. Furthermore, the cold start condition not being satisfied may further include when TECD,j>TECD,THand/or when ΔΔtSTART>ΔtSTART,TH. For the case where the second condition is satisfied, method400continues at432,434, and436, where the controller12measures the fuel injection flow, Qinj,j,i, for each ithcylinder in each jthcylinder bank, λjfor each jthcylinder bank, and Qair,intake, respectively, corresponding to when the second condition is satisfied. As described earlier, Qinj,j,i, λj, and Qair,intakemay be determined by averaging measured data received from signals and sensors (e.g., FPW signal from driver168, exhaust gas sensors128,286and288, and MAF sensor46). In particular, the measured data may be averaged over threshold duration when the second condition is satisfied. Averaging the measure data over the threshold duration may aid in reducing an influence of noise factors, and can increase the reliability of the method400. Next, method400continues at438where the controller12calculates QSAIR2and QSAIR2,j(e.g., QSAIRand QSAIR,jwhen the second condition is satisfied), from equations (1) through (6).

After428and438, method400continues at440, where the controller12determines if a SAIR system degradation condition is satisfied, as shown inFIG.5. Turning now toFIG.5, method500begins at520where the controller12determines if ΔQSAIR<ΔQSAIR,TH, whereby ΔQSAIRrefers to a difference between QSAIR1(QSAIRduring the first condition) and QSAIR2(QSAIRduring the second condition). For the case where ΔQSAIR<ΔQSAIR,TH, method500continues to524where the controller12indicates degradation at the SAIR system. In one example, ΔQSAIR,THmay include a percentage of QSAIR,meas, such as 80% of QSAIR,meas. In another example, QSAIR1,THmay depend on QSAIR,measand the number of cylinders130. For example, if the number of cylinders is I, ΔQSAIR,THmay be (1−1/I)*QSAIR,meas; as such, for the case of a 4-cylinder engine, ΔQSAIR,TH=0.75*QSAIR,meas.

For the case where ΔQSAIR>ΔQSAIR,TH, method500continues to530where the controller12determines if ΔQSAIR,j<ΔQSAIR,j,TH, whereby ΔQSAIR,jrefers to a difference between QSAIR1,j(QSAIR,jduring the first condition) and QSAIR2,j(QSAIR,jduring the second condition). For the case where ΔQSAIR,j<ΔQSAIR,j,TH, method500continues to534where the controller12indicates degradation at the SAIR system, in particular, degradation at the SAIR system corresponding to the jthcylinder bank.

For the case where ΔQSAIR,j>ΔQSAIR,j,TH, method500continues to540where the controller12determines if ΔQSAIR1,j,j+1>ΔQSAIR1,j,j+1,TH, whereby ΔQSAIR1,j,j+1refers to a difference between QSAIR1,j(QSAIR,jduring the first condition) and QSAIR1,j+1(QSAIR,j+during the first condition). For the case where ΔQSAIR1,j,j+1>ΔQSAIR1,j,j+1,TH, method500continues to544where the controller12indicates degradation at the SAIR system, in particular, degradation at the SAIR system corresponding to the (j+1)thcylinder bank. In one example, ΔQSAIR1,j,j+1>ΔQSAIR1,j,j+1,THmay indicate that the SAIR flow control valve directing SAIR to the exhaust manifold downstream of the (j+1)thcylinder bank is faulty; for example, the valve may not be opening, resulting in low or no SAIR to the exhaust manifold downstream of the (j+1)thcylinder bank. At540, the controller12may evaluate ΔQSAIR1,j,j+1for each combination of pairs of cylinder banks, j and j+1 in the engine10.

For the case where ΔQSAIR1,j,j+1<ΔQSAIR1,j,j+1,TH, method500continues to550where the controller12determines if ΔQSAIR2,i,j+1>ΔQSAIR2,j,j+1,TH, whereby ΔQSAIR2,j,j+1refers to a difference between QSAIR2,j(QSAIR,jduring the second condition) and QSAIR2,j+1(QSAIR2,j+1during the second condition). For the case where ΔQSAIR1,j,j+1>ΔQSAIR2,j,j+1,TH, method500continues to554where the controller12indicates degradation at the SAIR system, in particular, degradation at the SAIR system corresponding to the (j)thcylinder bank. In one example, ΔQSAIR2,j,j+1>ΔQSAIR2,j,j+1,THmay indicate that both the SAIR pump and the SAIR flow control valve directing SAIR to the exhaust manifold downstream of the (j)thcylinder bank is faulty; for example, the valve may not be closing and the SAIR pump may remain ON (despite being switched OFF) resulting non-zero SAIR to the exhaust manifold downstream of the (j)thcylinder bank. At540, the controller12may evaluate ΔQSAIR2,j,j+1for each combination of pairs of cylinder banks, j and j+1 in the engine10.

After550, for the case where ΔQSAIR2,j,j+1<ΔQSAIR2,j,j+1,TH, and following524,534,544, and554, method500returns to method400after440. For the case where SAIR system degradation condition is satisfied, method500continues to444where the controller12generates an indication at the vehicle5notifying the operator of the degraded SAIR system. Returning to440, for the case where the SAIR system degradation condition is not satisfied, method500continues to448where the controller12generates an indication at the vehicle5notifying the operator of the non-faulty SAIR system. In one example, the controller12may notify the operator of a degraded or not degraded SAIR system by generating one or more of an audio, visual, and a haptic indication at an instrument panel or dashboard of the vehicle (not shown inFIG.1). After444and448, method400ends.

In this manner, a method for monitoring a secondary airflow (SAIR) system in an engine includes, determining a degradation of the SAIR system adding a SAIR to downstream of an engine cylinder exhaust based on a comparison of the SAIR before and after a shutdown of a SAIR pump, the SAIR calculated from a fuel injection amount, an exhaust air-fuel ratio, and an engine intake airflow. In a first example, the method further includes determining the degradation of the SAIR system responsive to a difference between the SAIR before the shutdown of the SAIR pump and the SAIR after the shutdown of the SAIR pump being less than a threshold SAIR difference. In a second example, optionally including the first example, the method further includes determining the degradation of a the SAIR system responsive to a difference between the SAIR corresponding to a first bank of engine cylinders and the SAIR corresponding to a second bank of engine cylinders being greater than a threshold bank-bank SAIR difference. In a third example, optionally including one or more of the first and second examples, the method further includes determining the degradation of a SAIR valve directing the SAIR to a first bank of engine cylinders responsive to a difference between the SAIR from the first bank of engine cylinders before the shutdown of the SAIR pump and the SAIR from the first bank of engine cylinders after the shutdown of the SAIR pump being less than a threshold first bank SAIR difference. In a fourth example, optionally including one or more of the first through third examples, the method further includes measuring the exhaust air-fuel ratio downstream of the engine cylinder exhaust with an exhaust gas sensor, and calculating an exhaust airflow in the engine cylinder exhaust based on the exhaust air-fuel ratio and the fuel injection amount. In a fifth example, optionally including one or more of the first through fourth examples, the method further includes calculating the SAIR from a difference between the exhaust airflow in the engine cylinder exhaust and the engine intake airflow. In a sixth example, optionally including one or more of the first through fifth examples, the method further includes measuring the exhaust air-fuel ratio in an exhaust from each cylinder bank of the engine, calculating an exhaust airflow from each cylinder bank of the engine from the exhaust air-fuel ratio and the fuel injection amount delivered to each cylinder bank, and calculating the SAIR at the exhaust from each cylinder bank from a difference between the exhaust airflow from each cylinder bank and the intake airflow. In a seventh example, optionally including one or more of the first through sixth examples, the method further includes turning on the SAIR pump responsive to a cold start condition being met, including when a cold start engine event has occurred, and shutting down the SAIR pump responsive to the cold start condition not being met, the cold start condition not being met including when an engine temperature increases above a threshold engine temperature. In an eighth example, optionally including one or more of the first through seventh examples, the method further includes, wherein the cold start condition not being met further includes when a threshold duration following the cold start engine event is exceeded.

In another representation, optionally including one or more of the first through eighth examples, the method further includes calculating a percent SAIR from a ratio of the calculated SAIR to the exhaust airflow in the engine cylinder exhaust, and determining a degradation of the SAIR system based on a difference between the percent SAIR before the shutdown of the SAIR pump and the percent SAIR after the shutdown of the SAIR pump being less than a threshold percent SAIR difference. In another representation, optionally including one or more of the first through eighth examples, the method further includes determining a degradation of the SAIR system based on a SAIR ratio being less than a lower threshold SAIR ratio, the SAIR ratio calculated from the SAIR before the shutdown of the SAIR pump divided by the SAIR after shutdown of the SAIR pump. In another representation, optionally including one or more of the first through eighth examples, the method further includes determining a degradation of the SAIR system based on a SAIR ratio being greater than an upper threshold SAIR ratio, the SAIR ratio calculated from the SAIR before the shutdown of the SAIR pump divided by the SAIR after shutdown of the SAIR pump.

In this manner, a method for an engine includes turning on a secondary airflow (SAIR) pump to direct intake air to a SAIR system responsive to a first condition being met, turning off the SAIR pump responsive to a second condition being met, and determining a degradation of the SAIR system based on a comparison of a SAIR flow rate at an exhaust manifold during the first condition and during the second condition, the SAIR flow rate calculated from a fuel injection amount, an exhaust air-fuel ratio, and an engine intake airflow. In a first example, the method further includes, wherein the first condition includes when the engine is cold started. In a second example, optionally including the first example, the method further includes, wherein the second condition includes when an engine temperature exceeds a threshold engine temperature. In a second example, optionally including the first example, the method further includes, wherein the second condition includes when an engine temperature exceeds a threshold engine temperature. In a third example, optionally including one or more of the first and second examples, the method further includes, wherein the second condition includes when a threshold duration following the engine being cold started elapses. In a third example, optionally including one or more of the first and second examples, the method further includes indicating the degradation of the SAIR system responsive to a difference between the SAIR during the second condition and the SAIR during the first condition being less than a threshold SAIR difference.

In another representation, optionally including one or more of the first through third examples, the method further includes, wherein the comparison of the SAIR flow rate at the exhaust manifold during the first condition and during the second condition includes determining a difference between the SAIR flow rate during the first condition and the SAIR flow rate during the second condition. In another representation, optionally including one or more of the first through third examples, the method further includes, wherein the comparison of the SAIR flow rate at the exhaust manifold during the first condition and during the second condition includes determining a SAIR ratio, the SAIR ratio calculated by dividing the SAIR flow rate during the first condition by the SAIR flow rate during the second condition.

Turning now toFIG.6, it illustrates a timeline600for operating an engine system200, including an engine10and SAIR system220of a vehicle5, according to the methods400and500. In the example ofFIG.6, engine10includes two cylinder banks, however, in other examples engine10may include fewer or more cylinder banks. Similarly, in the example ofFIG.6, engine system200includes two exhaust manifolds and a SAIR system220with two SAIR flow control valves, however, in other examples engine system200may include fewer or more exhaust manifolds and SAIR flow control valves. Trend lines are shown for a first condition status610, a second condition status620, QSAIR,1630and QSAIR,2636, QSAIR, SAIR degradation condition status650, SAIR pump status660, SAIR valve positions670and680, engine (ON/OFF) status690, Tengine692, TECD1696, and TECD2698(TECD1refers to the ECD in the exhaust downstream from cylinder bank 1 and TECD2refers to the ECD in the exhaust downstream from the cylinder bank 2). Also shown are threshold values for ΔQSAIR,TH642, ΔQSAIR,j,TH631, ΔQSAIR1,j,j+1,TH632, ΔQSAIR2,j,j+1,TH633, Tengine,TH695, TECD,TH699, and Δtstart,TH691.

For clarity, the example timeline600depicts smooth (e.g. flat) trend lines for the calculated QSAIR,1, QSAIR,2, and QSAIR, however, in other examples the values for QSAIR,1, QSAIR,2, and QSAIRmay fluctuate (as illustrated inFIG.3) since AFRj, Qinj,j, and Qair,intakemay fluctuate during engine operation as engine operating conditions such as engine load, engine speed, torque, and the like, also change.

At time t=0, the engine is cold started, and the engine status switches from OFF to ON. Responsive to the cold engine start, Tengine<Tengine,TH, TECD1<TECD,TH, and TECD2<TECD,TH, the controller12switches ON the SAIR pump and opens both of the SAIR flow control valves to direct SAIR to the exhaust manifolds downstream from both cylinder banks. Thus, at time t=0, the first condition is satisfied and the second condition is not satisfied. Responsive to the first condition being satisfied, controller12measures Qinj,j, Qair,intake, and λj, and begins estimating QSAIR1,1, QSAIR1,2and QSAIR1(QSAIR1refers to QSAIRwhen the first condition is satisfied) from equations (1) to (6). The calculated values QSAIR1,1, QSAIR1,2, and QSAIR1are at higher levels between times t=0 and t1. Between times t=0 and t1, Tengine, TECD1, and TECD2begin to increase as the vehicle5is operated and the engine10warms up. From time t=0 to time t1, a difference between QSAIR1,1and QSAIR1,2, ΔQSAIR1,1,2is less than a threshold difference, ΔQSAIR1,j,j+1,TH634. As such, the SAIR degradation condition is not satisfied.

At time t1, the threshold duration, Δtstart,TH691is exceeded, the engine status remains ON, Tengineincreases beyond Tengine,TH, and both TECD1and TECD2increase beyond TECD,TH, each (individually or in combination) signaling end of the engine cold start event. Responsive to the end of the cold start event at time t1, controller12switches OFF the SAIR pump, and closes the SAIR flow control valves. As such, at time t1, the first condition is no longer satisfied, and the second condition is satisfied. Controller12continues to measure Qinj,j, Qair,intake, and λj, and estimates QSAIR2,1, QSAIR2,2and QSAIR2(QSAIR2refers to QSAIRwhen the second condition is satisfied) from equations (1) to (6). Responsive to the SAIR pump being switched OFF and closing of the SAIR flow control valves, the calculated values of QSAIR2,1, QSAIR2,2, and QSAIR2decrease to a lower level at time t1.

At time t1, the change in QSAIR, ΔQSAIR644is greater than a threshold change in QSAIR, ΔQSAIR,TH642. Furthermore, a change in QSAIR,1630, ΔQSAIR,1is greater than a threshold change in QSAIR,1, ΔQSAIR,j,TH631; similarly, a change in QSAIR,2636, ΔQSAIR,2is greater than a threshold change in QSAIR2, ΔQSAIR,j,TH631. Furthermore, a difference between QSAIR2,1and QSAIR2,2, ΔQSAIR2,1,2is less than a threshold difference, ΔQSAIR2,j,j+1,TH633. Accordingly, the controller12determines that the SAIR degradation condition is not satisfied.

At time t2, the engine is switched OFF, and Tengine, TECD1, and TECD2all begin to decrease, eventually decreasing below their respective threshold temperatures between times t2and t3, Tengine,THand TECD,TH, respectively, as the engine and the exhaust stream cool. Between time t2and time t3, the second condition remains satisfied, and QSAIR2,1, QSAIR2,2and QSAIR2remain at lower levels since the SAIR pump remains OFF and the SAIR flow control valves remain closed.

At time t3, the engine is cold started, and the engine status switches from OFF to ON. Responsive to the cold engine start, Tengine<Tengine,TH, TECD1<TECD,TH, and TECD2<TECD,TH, the controller12switches ON the SAIR pump and opens both of the SAIR flow control valves to direct SAIR to the exhaust manifolds downstream from both cylinder banks. Thus, at time t=0, the first condition is satisfied and the second condition is not satisfied. Between times t3and t4, Tengine, TECD1, and TECD2begin to increase as the vehicle5is operated and the engine10warms up. Responsive to the first condition being satisfied, controller12measures Qinj,j, Qair,intake, and λj, and begins estimating QSAIR1,1, QSAIR1,2and QSAIR1. The calculated values QSAIR1,1, QSAIR1,2, and QSAIR1increase. In particular, QSAUD1,1increases to a higher level (similar to between times t=0 and t1), however, QSAIR1,2just slightly increases, and QSAIR1between times t3and t4is lower than QSAIR1between times t=0 and t1.

At time t3, the change in QSAIR, ΔQSAIR644is less than the threshold change in QSAIR, ΔQSAIR,TH642. Furthermore, a change in QSAIR,1630, ΔQSAIR,1is greater than the threshold change in QSAIR,1, ΔQSAIR,j,TH631(ΔQSAIR,j,THrefers to a threshold jthbank SAIR difference); however, a change in QSAIR,2636, ΔQSAIR,2is less than the threshold change in QSAIR2, ΔQSAIR,j,TH631. Furthermore, a difference between QSAIR1,1and QSAIR1,2, ΔQSAIR1,1,2is greater than a threshold difference, ΔQSAIR,j,j+1,TH633. Accordingly, responsive to one or more of ΔQSAIR<ΔQSAIR,TH, ΔQSAIR,2<ΔQSAIR,2,TH, and ΔQSAIR1,1,2>tΔQSAIR1,i,j+1,TH, the controller12determines that the SAIR degradation condition is satisfied. In particular, the controller12may generate an indication to the vehicle operator that the second cylinder bank is degraded. In the example of timeline600, at time t3, because QSAIR,2did not increase to a higher level with then SAIR pump was turned ON and when the SAIR flow control valves were opened, there may be a faulty SAIR flow control valve directing SAIR to the exhaust manifold downstream of the 2nd cylinder bank.

Between times t3and t4, Tengine, TECD1, and TECD2continue to increase as the vehicle5is operated and the engine10warms up. Furthermore, the first condition remains satisfied (and the second condition is not satisfied), and the values of QSAIR1,1, QSAIR1,2and QSAIR1are maintained.

Next, at time t4, the threshold duration since the engine cold start, Δtstart,TH691is exceeded, the engine status remains ON, Tengineincreases beyond Tengine,TH, and both TECD1and TECD2increase beyond TECD,TH, each (individually or in combination) signaling end of the engine cold start event. Responsive to the end of the cold start event at time t4, controller12switches OFF the SAIR pump, and closes the SAIR flow control valves. As such, at time t4, the first condition is no longer satisfied, and the second condition is satisfied. Controller12continues to measure Qinj,j, Qair,intake, and λj, and estimates QSAIR2,1, QSAIR2,2and QSAIR2from equations (1) to (6). Responsive to the SAIR pump being switched OFF and closing of the SAIR flow control valves, the calculated values of QSAIR2,1, QSAIR2,2, and QSAIR2all decrease to a lower level at time t4.

At time t4, the change in QSAIR, ΔQSAIR644is less than a threshold change in QSAIR, ΔQSAIR,TH642. Furthermore, a change in QSAIR,1630, ΔQSAIR,1is greater than a threshold change in QSAIR,1, ΔQSAIR,j,TH631; however, a change in QSAIR,2636, ΔQSAIR,2is less than a threshold change in QSAIR2, ΔQSAIR,j,TH631. Furthermore, a difference between QSAIR2,1and QSAIR2,2, ΔQSAIR2,1,2is less than a threshold difference, ΔQSAIR1,j,j+1,TH633. Responsive to one or more of ΔQSAIR<ΔQSAIR,TH, and ΔQSAIR,2<ΔQSAIR,j,TH, the controller12determines that the SAIR degradation condition remains satisfied. At time t5, the engine is switched OFF, and Tengine, TECD1, and TECD2all begin to decrease, eventually decreasing below their respective threshold temperatures after time t5, Tengine,THand TECD,TH, respectively, as the engine and the exhaust stream cool. After time t5, the second condition remains satisfied, and QSAIR2,1, QSAIR2,2and QSAIR2remain at lower levels since the SAIR pump remains OFF and the SAIR flow control valves remain closed.

In this manner, an engine system includes an engine cylinder, a secondary airflow (SAIR) pump, and a controller, including executable instructions stored in non-transitory memory thereon to, determine a degradation of a SAIR system delivering a SAIR downstream of an exhaust of the engine cylinder based on a comparison of the SAIR before and after a shutdown of a SAIR pump, the SAIR calculated from a fuel injection amount, an exhaust air-fuel ratio, and an engine intake airflow. In a first example of the engine system, the executable instructions further include, indicating the degradation of the SAIR system responsive to a difference between the SAIR before the shutdown of the SAIR pump and the SAIR after the shutdown of the SAIR pump being less than a threshold SAIR difference. In a second example, optionally including the first example, the engine system further includes first and second banks of engine cylinders, wherein the executable instructions further include, indicating the degradation of the SAIR system responsive to a difference between the SAIR from the first bank of engine cylinders and the SAIR from the second bank of engine cylinders being less than a threshold bank-bank SAIR difference. In a third example, optionally including one or more of the first and second examples, the engine system further includes first and second exhaust gas sensors, wherein the first and second exhaust gas sensors are positioned downstream of an exhaust from the first bank of engine cylinders and an exhaust from the second bank of engine cylinders, respectively, and wherein the executable instructions further include measuring the exhaust air-fuel ratio downstream from the first and second bank of engine cylinders with the first and second exhaust gas sensors, respectively. In a fourth example, optionally including one or more of the first through third examples, the engine system further includes first and second SAIR valves, wherein each of the first and second SAIR valves are positioned downstream from the SAIR pump and upstream of the first and second exhaust gas sensors, respectively, and wherein the executable instructions further include, indicating the degradation of at one of the first and second SAIR valves responsive to the difference between the SAIR from the first bank of engine cylinders and the SAIR from the second bank of engine cylinders being less than the threshold bank-bank SAIR difference. In a fifth example of the engine system, optionally including one or more of the first through fourth examples, the executable instructions further include, indicating the degradation of the first SAIR valve responsive to a difference between the SAIR from the first bank of engine cylinders before shutdown of the SAIR pump and the SAIR from the first bank of engine cylinders after shutdown of the SAIR pump being less than a threshold first bank SAIR difference.

In another representation of the engine system, optionally including one or more of the first through fifth examples, the executable instructions further include, wherein the comparison of the SAIR before and after the shutdown of the SAIR pump includes determining a SAIR ratio, the SAIR ratio calculated by dividing the SAIR before shutdown of the SAIR pump by the SAIR after shutdown of the SAIR pump. In another representation of the engine system, optionally including one or more of the first through fifth examples, the executable instructions further include, wherein the comparison of the SAIR before and after the shutdown of the SAIR pump includes determining a difference between a percent SAIR before the shutdown of the SAIR pump and a percent SAIR after shutdown of the SAIR pump, the percent SAIR calculated by determining the SAIR downstream of an engine cylinder exhaust divided by the exhaust airflow downstream of the engine cylinder exhaust.

In this way, a technical effect of monitoring and diagnosing a SAIR system, including determining the SAIR at the exhaust manifold can be achieved utilizing existing onboard sensors and technology, thereby maintaining OBD and emissions monitoring, reducing engine emissions, and maintaining vehicle manufacturing expenses.