METHOD AND SYSTEM FOR DIAGNOSIS OF AN EXHAUST GAS RECIRCULATION SYSTEM

Abstract

A method of operating an engine, comprising: when a commanded EGR flow changes, dynamically setting an upper and lower EGR limit based on the commanded EGR flow; indicating degradation of the EGR system based on a ratio of an accumulated difference between a measured EGR flow and one between the upper and lower EGR limits to an accumulated commanded EGR flow relative to a threshold, the threshold being based on exhaust NOx levels; and Adjust EGR flow based on impairment indication.

Description

Area

[0001] This description generally relates to methods and systems for on-board diagnostics of components of an exhaust gas recirculation (EGR) system. General state of the art / brief description

[0002] Engine systems can utilize the recirculation of exhaust gas from an engine exhaust system to an engine intake system, a process known as exhaust gas recirculation (EGR), to reduce regulated emissions. An EGR valve can be controlled to achieve a desired intake air dilution for given engine operating conditions. Typically, the amount of low-pressure EGR (LP EGR) and / or high-pressure EGR (HP EGR) passed through the EGR system is measured and adjusted based on engine speed, temperature, and load during engine operation to maintain desirable engine combustion stability while providing emissions and fuel efficiency benefits. EGR effectively cools the combustion chamber temperature, thereby reducing NOx formation. EGR also reduces an engine's pumping work and increases the compression ratio, resulting in increased fuel efficiency.A diagnostic procedure may need to be performed periodically or opportunistically to monitor the operation of the EGR system.

[0003] Various approaches are provided for diagnosing an EGR system. In one example, as shown in US 5,508,926 A, Wade discloses a method for detecting restrictions in the EGR system during steady-state engine operations. The air pressure in the engine intake manifold is monitored over a test period while an amount of EGR (determined based on engine operating conditions) is delivered to the intake manifold. Changes in the monitored air pressure are filtered by a lag filtering process including a dynamic filter coefficient. The filtered air pressure is then compared to a dynamic threshold to determine the presence of a restriction in the EGR system. Further prior art is known from documents US 6,802,302 B1 and EP 2 562 406 A1.

[0004] However, the inventors of the present invention have recognized potential problems with such systems. For example, by relying on a single dynamic threshold when diagnosing the EGR system, it may not be possible to distinguish between degradations in the EGR system that result in insufficient EGR flow and those that result in excessive EGR flow. Wade's approach may also fail to detect undesirable EGR flow that occurs when EGR is not requested. As another example, Wade's approach is limited to steady-state conditions. However, it may be desirable to also perform EGR diagnostics during transient engine operating conditions to reduce tailpipe emissions.

[0005] In one example, the problems described above may be at least partially solved by a method for an engine, comprising: when a commanded EGR flow changes, dynamically adjusting an upper and lower EGR limit based on the commanded EGR flow, indicating degradation of the EGR system based on a ratio of an accumulated difference between a measured EGR flow and one of the upper and lower EGR limits to an accumulated commanded EGR flow relative to a threshold, the threshold being based on exhaust NOx levels, and adjusting the EGR flow based on the indication of degradation.In this way, EGR system diagnostics can be effectively performed during both steady-state and transient engine operating conditions by dynamically updating an EGR tolerance band based on the requested EGR flow and appropriately adjusting a threshold for detecting EGR system degradation based on emission levels.

[0006] For example, an EGR system diagnostic routine may be executed periodically or opportunistically during a vehicle drive cycle. As engine operating conditions change, a commanded EGR flow may be varied to match the changing EGR demand. A dynamic EGR tolerance band may also be calculated, with the tolerance band having a lower limit and a higher limit, each based on the commanded EGR flow. In one example, the tolerance band may be calculated as a function of the commanded EGR flow and using a multiplier whose value changes with the change (e.g., magnitude of change and rate of change) in the EGR flow, such as based on whether an increase and decrease in the commanded EGR flow rate occurs.An actual EGR flow rate is measured via an EGR flow sensor, such as a pressure sensor (either an absolute pressure sensor or a delta pressure sensor). If the measured EGR flow rate is above the commanded flow rate, a difference between the higher limit of the tolerance band and the measured EGR flow rate can be estimated to obtain a mass flow error. If the measured EGR flow rate is below the commanded flow rate, a difference between the lower limit of the tolerance band and the measured EGR flow rate can be estimated to obtain the mass flow error. If EGR flow is detected during conditions where no EGR is commanded (i.e., the commanded EGR flow rate is zero), a difference between a fixed (upper) EGR limit and the measured EGR flow rate can be estimated to obtain the mass flow error.The mass flow error and the commanded EGR mass flow may be accumulated over a period of time (also referred to herein as the test period). The ratio of the accumulated mass flow error to the accumulated commanded EGR mass flow may then be compared to a threshold. Different thresholds may be applied to diagnose insufficient EGR flow, undesirable EGR flow, and excessive EGR flow, while considering acceptable limits for tailpipe emissions in each case. EGR system degradation may be indicated, and a diagnostic code may be set if the ratio is above the specified threshold. If degradation in the EGR system is indicated, further supply of EGR may be temporarily disabled by closing the EGR valve.In one example where the diagnostic approach is used to investigate a high pressure (HP) EGR system, EGR delivered via a low pressure (LP) EGR system may be increased in response to a degradation of the HP EGR system.

[0007] In this way, undesirable tailpipe emissions caused by the degraded EGR system can be reduced by dynamically adjusting an EGR tolerance band based on the commanded EGR flow and varying the threshold for detecting EGR system degradation based on emission standards. By selecting different thresholds for the diagnostic process based on the commanded EGR flow rate relative to the measured EGR flow rate, an EGR system degradation resulting in insufficient EGR flow can be distinguished from one resulting in excessive EGR flow and treated appropriately. By estimating undesirable EGR flow based on accumulated intake air flow (when no EGR has been commanded), leaks in an EGR valve can be detected.The technical effect of dynamically calculating the tolerance band for an EGR mass flow error estimate, taking into account changes in EGR flow, is to reduce erroneous indications of EGR system degradation due to transport delays between a delivered and commanded EGR flow rate. By enabling EGR system diagnostics to be performed reliably and accurately, the overall fuel efficiency and emissions benefits of EGR can be extended over a wider range of engine operating conditions.

[0008] It should be understood that the foregoing summary is provided to introduce, in simplified form, a selection of concepts further described in the detailed description. It is not intended to identify important or essential features of the claimed subject matter, the scope of which is defined solely in the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that overcome any disadvantages noted above or in any part of this disclosure. Brief description of the drawings Fig. 1 shows a schematic representation of an exemplary engine system that includes an exhaust gas recirculation (EGR) system. Fig. Figure 2 shows a flowchart illustrating a method that can be implemented for general diagnosis of the EGR system, including during insufficient EGR flow. Fig. Figure 3 shows a flowchart illustrating a method that may be implemented to diagnose the EGR system during excessive EGR flow. Fig. Figure 4 shows a flowchart illustrating a method that may be implemented to diagnose the EGR system during undesirable EGR flow. Fig. Figure 5 shows an example diagnosis of the EGR system during insufficient EGR flow. Fig. Figure 6 shows an example diagnosis of the EGR system during an undesired EGR flow. Fig. Figure 7 shows an example diagnosis of the EGR system during excessive EGR flow. Fig. 8 shows an example of detection of an impairment of the EGR system based on the diagnosis of the EGR system. Detailed description

[0009] The following description relates to systems and methods for on-board diagnostics of an exhaust gas recirculation (EGR) system. An exemplary turbocharged engine system including a low-pressure EGR system and a high-pressure EGR system is described in Fig. 1. An engine controller may be configured to perform a control sequence, such as the exemplary sequences of Fig. 2, Fig. 3 and Fig. 4 to perform on-board diagnostics of the EGR system during insufficient, excessive, and undesirable EGR flow. Examples of diagnostic procedures for detecting HD EGR system degradation are described in Fig. 5-8 shown.

[0010] Fig. 1 schematically illustrates aspects of an exemplary engine system 100 including an engine 10. In the illustrated embodiment, the engine 10 is a supercharged engine coupled to a turbocharger 13 including a compressor 114 driven by a turbine 116. The exhaust turbine 116 may be configured as a variable geometry turbine (VGT). Specifically, fresh air is introduced into the engine 10 along an intake passage 42 via an air cleaner 112 and flows to the compressor 114. The compressor may be any suitable intake air compressor, such as an engine-driven or drive-shaft-driven supercharger compressor. In the engine system 10, the compressor is a turbocharger compressor mechanically coupled to the turbine 116 via a shaft 19, with the turbine 116 driven by expanding engine exhaust gases.A wastegate actuator 92 may be actuated to open to vent at least a portion of the exhaust pressure from upstream of the turbine via the wastegate 90 to a location downstream of the turbine. By reducing the exhaust pressure upstream of the turbine, the turbine speed may be reduced, which in turn may help reduce compressor surge and overboosting issues.

[0011] The compressor 114 may be coupled to a throttle valve 20 through a charge-air cooler (CAC) 17. The throttle valve 20 is coupled to an engine intake manifold 22. From the compressor, the compressed air charge flows through the charge-air cooler 17 and the throttle valve to the intake manifold. A compressor recirculation passage (not shown) may be provided for compressor surge control. In particular, boost pressure may be vented from the intake manifold downstream of the CAC 17 and upstream of the throttle valve 20 into the intake passage 42 to reduce compressor surge, such as upon driver permission. By flowing charge air from upstream of an intake throttle inlet to upstream of the compressor inlets, boost pressure may be rapidly reduced, thereby accelerating boost control.

[0012] One or more sensors may be coupled to an inlet of compressor 114. For example, a temperature sensor 55 may be coupled to the inlet for estimating a compressor inlet temperature, and a pressure sensor 56 may be coupled to the inlet for estimating a compressor inlet pressure. As another example, a humidity sensor 57 may be coupled to the inlet for estimating a humidity of an air charge entering the compressor. Still other sensors may include, for example, air-fuel ratio sensors, etc. In other examples, one or more of the compressor inlet conditions (such as humidity, temperature, pressure, etc.) may be inferred based on engine operating conditions.Furthermore, when exhaust gas recirculation (EGR) is enabled, the sensors can estimate a temperature, pressure, humidity, and air-fuel ratio of the air charge mixture, including fresh air, recirculated compressed air, and residual exhaust gases taken in at the compressor inlet.

[0013] In some examples, intake manifold 22 may include an intake manifold pressure sensor 124 for estimating a manifold pressure (MAP) and / or an intake airflow sensor 126 for estimating a mass air flow (MAF) within intake manifold 22. Intake manifold 22 is coupled to a series of combustion chambers 30 through a series of intake valves (not shown). The combustion chambers are further coupled to an exhaust manifold 36 via a series of exhaust valves (not shown). In the embodiment shown, a single exhaust manifold 36 is shown. However, in other embodiments, the exhaust manifold may include a plurality of exhaust manifold sections. Configurations including a plurality of exhaust manifold sections may allow wastewater from different combustion chambers to be routed to different locations in the engine system.

[0014] In one embodiment, each of the exhaust and intake valves may be electronically actuated or controlled. In another embodiment, each of the exhaust and intake valves may be cam-actuated or controlled. Regardless of whether electronically actuated or cam-actuated, the timing of the opening and closing of the exhaust and intake valves may be adjusted as required for the desired combustion and emissions control performance. One or more fuels, such as gasoline, alcohol-fuel blends, diesel, biodiesel, compressed natural gas, etc., may be delivered to the combustion chambers 30 via an injector 66. The fuel may be delivered to the combustion chambers via direct injection, port injection, throttle body injection, or any combination thereof. Combustion within the combustion chambers may be initiated via spark ignition and / or compression ignition.

[0015] As in Fig. 1, exhaust gas is directed from one or more exhaust manifold sections to drive the turbine 116. The combined flow from the turbine and the wastegate then flows through an emission control device 170. In general, one or more emission control devices 170 may include one or more exhaust aftertreatment catalysts configured to catalytically treat the exhaust stream and thereby reduce an amount of one or more substances in the exhaust stream. For example, an exhaust aftertreatment catalyst may be configured to x from the exhaust gas stream when the exhaust gas stream is lean, and the stored NO x to reduce when the exhaust flow is rich. In further examples, an exhaust aftertreatment catalyst may be configured to reduce NO x to disproportionate or NO xusing a reductant. In still further examples, an exhaust aftertreatment catalyst may be configured to oxidize hydrocarbon and / or carbon monoxide residues in the exhaust stream. Different exhaust aftertreatment catalysts with such functionality may be disposed in washcoats or elsewhere in the exhaust aftertreatment stages, either separately or together. In some embodiments, the exhaust aftertreatment stages may include a regenerable soot filter configured to trap and oxidize soot particulates in the exhaust stream. The treated exhaust from emissions control 170 may be exhausted, in whole or in part, to the atmosphere via an exhaust passage 102 after passing through a muffler 172.

[0016] A portion of the exhaust gas from the exhaust passage 102 may be recirculated to the intake manifold 22 via an exhaust gas recirculation (EGR) system 140, which includes a low-pressure exhaust gas recirculation (LP EGR) delivery system 142 and a high-pressure exhaust gas recirculation (HP EGR) delivery system 140. The low-pressure exhaust gas recirculation (LP EGR) delivery passage 180 may be coupled to the exhaust passage 102 at a location upstream of the emissions control device 170. A portion of the exhaust gas from the exhaust pipe 102 may be discharged as LP EGR from downstream of the turbocharger turbine 116 into the engine intake manifold 22 upstream of a turbocharger compressor 114. The opening of an EGR valve 52 can be regulated to control the flow of exhaust gas from the exhaust passage 102 via the EGR passage 180 to the intake manifold 22. The EGR valve 52 can be opened to admit a controlled amount of exhaust gas to the compressor inlet for desired combustion and emission control performance.A portion of the exhaust gas from exhaust passage 102 may be discharged from upstream of a turbocharger turbine 116 into the engine intake manifold 22 downstream of a turbocharger compressor 114 via an HP EGR passage 182. An EGR cooler 184 may be coupled to the HP EGR passage 182 for cooling the exhaust gas before it is discharged to the intake manifold. An HP EGR valve assembly 190 may be coupled to the HP EGR passage for regulating the flow of exhaust gas from the exhaust passage 102 via the EGR passage 182 to the intake manifold 22. The valve assembly 190 may include an EGR valve 192 with an EGR valve position sensor and two 100 mm orifices 193. A delta pressure sensor 194 may be coupled across the valve assembly 190 and the HP EGR delivery passage 182. The EGR flow rate across the HP EGR passage 182 may be estimated based on inputs from the EGR valve position sensor and the delta pressure sensor 194.

[0017] EGR valve 52 may also be part of a valve assembly coupled to LP EGR passage 180 (similar to HP EGR valve assembly 190). Valves 52 and 192 may be configured as continuously variable valves. However, in an alternative example, EGR valves 52 and 192 may be configured as an on / off valve. One or more sensors may be coupled to EGR passages 180 and 182 to provide details regarding the composition and condition of the EGR. For example, a temperature sensor 197 may be provided to determine a temperature of the EGR, an absolute pressure sensor 198 may be provided to determine a pressure of the EGR, a humidity sensor may be provided to determine a humidity or water content of the EGR, and an air-fuel ratio sensor may be provided to estimate an air-fuel ratio of the EGR.Alternatively, EGR conditions may be inferred by one or more temperature, pressure, humidity, and air-fuel ratio sensors 55-57 coupled to the compressor inlet. In one example, air-fuel ratio sensor 57 is an oxygen sensor.

[0018] The amount of low-pressure EGR (LP EGR) and / or high-pressure EGR (HP EGR) directed through the EGR system 140 may be requested to achieve a desired engine dilution, thereby improving fuel efficiency and emissions quality. A requested EGR amount may be based on engine operating conditions, including engine load, engine speed, engine temperature, etc. For example, the controller may refer to a lookup table having engine speed and load as input and a signal as output corresponding to a degree of opening to be commanded to the EGR valve, where the degree of opening provides a dilution amount corresponding to the input engine speed / load.In another example, the controller may rely on a model that correlates the change in engine load with a change in engine dilution demand and further correlates the change in engine dilution demand with a change in EGR demand. For example, as the engine load increases from a low load to a medium load, the EGR demand may increase, and as the engine load then increases from a medium load to a high load, the EGR demand may decrease. A diagnostic procedure may need to be performed periodically or opportunistically to monitor the operation of the EGR system to reduce the possibility that EGR system degradation will result in undesirable emissions quality. For example, the diagnostic procedure may be performed once per trip.

[0019] If the measured EGR flow is above the commanded EGR flow, an EGR system degradation may be indicated for the HP EGR system 144 based on a first accumulated difference between a measured EGR flow and an upper limit of a tolerance band accumulated over a duration, distance, or movement of the vehicle. Thus, a first ratio of the first accumulated difference to an accumulated commanded EGR mass flow may be estimated over the duration, and an EGR system degradation resulting in excessive EGR flow may be indicated in response to the first ratio being above a first threshold.If the measured EGR flow is below the commanded EGR flow, degradation of the EGR system may be indicated based on a second accumulated difference between a measured EGR flow and a lower limit of the tolerance band accumulated over the duration, distance, or movement of the vehicle. Similarly, a second ratio of the second accumulated difference to the accumulated commanded EGR mass flow may be estimated over the duration, and degradation in the EGR system resulting in insufficient EGR flow may be indicated in response to the second ratio being above a second threshold. Each of the upper and lower limits of the tolerance band may be dynamically adjusted based on a function of the commanded EGR flow, a fixed error margin, and a multiplier, where the multiplier is determined depending on the commanded EGR flow.The first threshold may be different from the second threshold. In one example, the first threshold may be higher than the second threshold. Dynamically adjusting the upper and lower limits of the tolerance band allows for compensation for transient flow changes within the threshold where an overshoot may occur. This allows for easy calibration to mitigate expected errors related to the transport delay between the time EGR flow is commanded and the time it can be delivered by controlling the valve.

[0020] If no EGR flow is commanded and the measured EGR flow is above the commanded non-EGR flow, a third accumulated difference between the measured EGR flow and an error limit may be estimated for the HP EGR system 144 over the duration; a third ratio of the third accumulated difference to the accumulated commanded intake air mass flow accumulated over the duration may then be estimated, and EGR system degradation may be indicated in response to the third ratio being above a third threshold. The third threshold may be different from each of the first and second thresholds. In one example, the third threshold may be lower than the second threshold.Each of the first threshold, the second threshold, and the third threshold may be based on a measured exhaust emission component level, including one of an exhaust NOx level and an exhaust particulate matter level. In this way, by detecting EGR system degradation based on one of the first threshold, the second threshold, and the third threshold, undesirable emissions that cause an increase in NOx level and / or particulate matter level caused by EGR system degradation may be reduced. Details regarding the diagnostic operations for the HP EGR system 144 are provided with respect to FIG. Fig. 2, Fig. 3 and Fig. 4. A similar diagnostic process may also be performed for the LP EGR system 142. In the case of LP EGR, the EGR mass flow may be measured based on inputs from one or more of the temperature, pressure, humidity, and air-fuel ratio sensors 55-57 coupled to the compressor inlet. Additionally, an exhaust pressure sensor may be coupled to the LP EGR discharge passage 180 to estimate the EGR flow rate using the Delta Pressure Over Valve (DPOV) method.

[0021] The engine system 100 may further include a control system 14. As shown, the control system 14 receives information from a plurality of sensors 16 (various examples of which are described herein) and sends control signals to a plurality of actuators 18 (various examples of which are described herein). For example, the sensors 16 may include the MAP sensor 124, the MAF sensor 126, the exhaust gas temperature sensor 128, the exhaust gas pressure sensor 129, the EGR temperature sensor 197, the EGR absolute pressure sensor 198, the EGR delta pressure sensor 194, the compressor inlet temperature sensor 55, the compressor inlet pressure sensor 56, the compressor inlet humidity sensor 57, a crankshaft sensor, a pedal position sensor, and an engine coolant temperature sensor. Other sensors, such as additional pressure, temperature, air-fuel ratio, and composition sensors, may be coupled to various locations in the engine system 100.The actuators 18 may include, for example, the throttle 20, the LP EGR valve 52, the HP EGR valve 192, the wastegate valve 92, and the fuel injector 66. The control system 14 may include a controller 12. The controller 12 may receive input data from the various sensors, process the input data, and trigger various actuators in response to the processed input data based on an instruction or code programmed therein according to one or more sequences. For example, the controller may derive a flow rate of EGR flowing through the EGR passage 182 based on inputs from the delta pressure sensor 194 and the absolute pressure sensor 198, and may perform a diagnostic sequence in response to a difference between a commanded EGR flow rate and the measured flow rate to monitor the operation of the HP EGR system 144.In response to the indication of a degradation in the HP EGR system 144, the controller may send a signal to an actuator of the HP EGR valve 192 to close the valve to interrupt further EGR flow.

[0022] In this way, the system Fig. 1 provides a vehicle engine system comprising: an intake manifold and an exhaust manifold, a turbocharger comprising an exhaust turbine and an intake compressor, a low-pressure exhaust gas recirculation (LP-EGR) system comprising a first EGR passage having a first EGR valve for recirculating exhaust gas from downstream of the turbine in the exhaust manifold to upstream of the compressor in the intake manifold, a high-pressure exhaust gas recirculation (HP-EGR) system comprising a second EGR passage having a second EGR valve for recirculating exhaust gas from upstream of the turbine in the exhaust manifold to downstream of the compressor in the intake manifold, a temperature sensor, an absolute pressure sensor, and a differential pressure sensor coupled to each of the LP-EGR and HP-EGR systems.The engine system further includes a controller with computer-readable instructions stored on non-transitory memory for: accumulating a difference between the measured EGR flow and one of an upper limit and a lower limit over a duration of vehicle movement in response to a measured EGR flow via the HP EGR system being above or below a commanded EGR flow, the upper and lower limits being dynamically adjusted depending on the commanded EGR flow, accumulating the commanded EGR flow over the duration, indicating degradation of the HP EGR system in response to a ratio of the accumulated difference to the accumulated commanded EGR flow being above the threshold, and actuating the second EGR valve to a closed position in response to the indication while increasing an opening of the first EGR valve.

[0023] Fig. 2 illustrates an exemplary method 200 used to examine the HP EGR system (such as the HP EGR system 144 of Fig. 1). The method may enable identification of, for example, a deterioration of the EGR system that results in insufficient EGR flow. The exemplary method 200 and the remaining methods included herein may be performed for on-board diagnostics of each of the LP EGR and the HP EGR systems. Instructions for performing the method 200 and the remaining methods may be executed by a controller based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the engine system, such as those described above with reference to Fig. 1. The controller may use motor actuators of the engine system to adjust engine operation according to the methods described below.

[0024] At 202, the process includes estimating and / or measuring engine operating conditions. Evaluated conditions may include, for example, engine temperature, engine load, driver torque demand, boost demand, manifold air flow, manifold air pressure, engine speed, throttle position, exhaust pressure, exhaust air-fuel ratio, ambient conditions, including ambient temperature, pressure, and humidity, etc.

[0025] At 204, the process includes determining whether EGR is requested for engine operations. EGR may be requested to achieve a desired engine dilution, thereby improving fuel efficiency and emissions quality. EGR may be desired after the exhaust catalyst has reached its appropriate light-off temperature. A requested EGR amount may be based on engine operating conditions, including engine load as estimated via a pedal position sensor, engine speed as estimated via a crankshaft acceleration sensor, engine temperature as estimated via an engine coolant temperature sensor, etc.

[0026] If it is determined that EGR is desired for optimal engine operations, the requested EGR amount (commanded EGR amount) may be determined at 206. For example, control may refer to a lookup table having engine speed and load as input and a signal as output corresponding to a degree of opening to be applied to the EGR valve, where the degree of opening provides an amount of dilution corresponding to the input engine speed / load. In another example, control may determine the EGR amount through a determination that directly considers parameters such as engine load, engine speed, engine temperature, etc. In still other examples, control may rely on a model that correlates the change in engine load with a change in engine dilution demand and further correlates the change in engine dilution demand with a change in EGR demand.For example, as engine load increases from low load to medium load, EGR request may increase, and then as engine load increases from medium load to high load, EGR request may decrease. Control may further determine the requested EGR amount considering a best fuel efficiency distribution for a desired dilution rate. Further, internal EGR (residual EGR) may be achieved from intake / exhaust valve opening overlap (such as VCT-CAM control). Control may also determine a ratio of EGR to be delivered as HP EGR relative to EGR to be delivered as LP EGR. In one example, the amount of EGR delivered as HP EGR may be increased during boosted engine operating conditions, while the amount of EGR delivered as LP EGR may be increased during naturally aspirated engine operating conditions.

[0027] At 208, the controller may send a signal to the HP EGR valve and / or LP EGR valve to open the valve(s) to supply the commanded amount of EGR through the HP EGR and / or LP EGR passage. The opening of the EGR valve(s) may be adjusted based on the commanded EGR amount. For example, the HP EGR valve opening may be increased with an increase in the commanded HP EGR amount, while the LP EGR valve opening may be increased with an increase in the commanded LP EGR amount.

[0028] At 210, the EGR mass flow rate (flow rate of exhaust gas flowing through the HP EGR passage) may be estimated based on inputs from one or more EGR sensors, such as an EGR delta pressure sensor and an EGR (absolute) pressure sensor coupled to the EGR system (such as EGR delta pressure sensor 194 and EGR pressure sensor 198 of Fig. 1). Alternatively, the EGR flow rate may be derived by one or more temperature, pressure, humidity, and air-fuel ratio sensors coupled to the compressor inlet. In one example, the measured EGR flow rate may be accumulated for a predetermined period of time and compared to the commanded EGR flow rate accumulated over the same period of time.

[0029] At 212, the process includes determining whether the accumulated measured HP EGR flow rate is less than the accumulated commanded HP EGR flow rate. Alternatively, the accumulated commanded EGR flow rate may be compared to a flow rate threshold.

[0030] If it is determined that the commanded measured EGR flow rate is below the commanded EGR flow rate, or if the accumulated commanded EGR flow rate is below the flow rate threshold, it can be inferred that the actual EGR flow is insufficient relative to the commanded EGR flow. EGR flow that is lower than commanded is undesirable, as it can lead to higher emissions and an increase in fuel consumption. Thus, the accumulated commanded EGR flow rate can be used to determine when sufficient EGR has been commanded to execute an EGR system diagnostic routine. For example, the diagnostic sequence may be initiated when the difference between the accumulated measured HP EGR flow rate and the accumulated commanded HP EGR flow rate is high enough to exceed an emissions level threshold during a cycle of an emissions test (such as FTP).Thus, an EGR diagnostic procedure for insufficient HD EGR flow may be performed to detect a deterioration in the EGR system, as discussed below.

[0031] At 214, a dynamic error tolerance band (for insufficient EGR flow) having an upper limit and a lower limit based on the commanded EGR flow rate may be determined. A fixed error margin may be used to determine the upper and lower limits of the tolerance band. The limits of the tolerance bands may be calculated based on a measured linear flow distance from an expected EGR mass flow (dependent on a commanded EGR mass flow). An additional multiplier may be used to adjust the tolerance band during a change in EGR flow direction, such as during an increase or decrease in the commanded EGR flow rate based on engine operating conditions. For example, the additional multiplier may be used during an increase in the commanded EGR flow to increase the upper limit, thereby increasing the tolerance band.As another example, the additional multiplier can be used during a decrease in commanded EGR flow to lower the lower limit, thereby increasing the tolerance band. The multiplier provides increased error tolerance in the direction of the changing flow, while a fixed error margin can be used during steady flow. By adjusting the tolerance band during changes in EGR flow direction, false detections of EGR system degradation due to transport delays between a commanded and measured EGR flow rate or due to PID control inaccuracies can be reduced. The upper limit of the tolerance band for insufficient EGR flow can be calculated based on Equation 1, while the lower limit of the tolerance band can be calculated based on Equation 2, where: Tlo1=Mcmd.−Serr Thi1=Mcmd.+(Mcmd.−Mexp.)∗Mmult.+Serr where T lo1 the lower limit of the tolerance band is Mcmd. is the commanded EGR mass flow, S err is the fixed error margin, T hi1 the higher limit of the tolerance band is Mexp. is the expected EGR mass flow and Multi. is a multiplier for the EGR mass flow. The mass flow multiplier can be based on the commanded EGR flow. The expected EGR mass flow (Mexp.) is a filtered version of the commanded EGR mass flow (Mcmd.).

[0032] At 216, the mass flow error between the lower limit of the tolerance band and the measured EGR flow rate over a drive cycle (or other test period) may be determined. At 218, an accumulated mass flow error over the current drive cycle, as given by Equation 3, may be determined as follows: Emf1=∑(Tlo1−Mmd.) where E mf1 is the accumulated mass flow error over the current drive cycle, T lo1 is the lower limit of the tolerance band and mmd. the measured EGR mass flow.

[0033] At 220, an accumulated commanded mass flow over the current drive cycle, as given by Equation 4, may be determined as follows: Ecmd=∑Mcmd. where E cmd is the accumulated commanded mass flow over the current drive cycle and Mcmd. is the commanded EGR mass flow.

[0034] At 222, a ratio of the accumulated mass flow error to the accumulated commanded mass flow can be estimated as shown in Equation 5: Eratio1=∑(Tlo−Mmd.)∑Mcmd. where E ratio1 is the first error rate of the accumulated mass flow to the accumulated commanded mass flow. The first error rate may be compared to a first threshold, threshold_1. At 224, the process includes determining whether the first error rate is above the first threshold. The first threshold may represent a point in the drive cycle where emissions levels above the target may occur. In other words, degradation of the EGR system resulting in undesirable emissions may be confirmed if the ratio increases above the first threshold during a point in the drive cycle.

[0035] If it is confirmed that the error rate is above the first threshold, it may be inferred that the EGR system is not impaired, and the emissions level may remain within the target range. At 226, the controller may indicate that the EGR system is not impaired and may maintain the current EGR valve position to deliver the commanded amount of EGR.

[0036] However, if it is determined at 228 that the failure rate is above the first threshold, a degradation of the HP EGR system may be indicated by setting a diagnostic code (flag). The HP EGR valve may be closed to interrupt EGR flow through the degraded system. In one example, the HP EGR valve may be closed when a degradation is detected in the HP EGR system, while the opening of the LP EGR valve may be increased to provide engine dilution via LP EGR.

[0037] If it is determined at 212 that the measured EGR flow rate is not less than the commanded EGR flow rate, or the accumulated commanded EGR flow rate is less than the flow rate threshold, the process includes determining at 230 whether the accumulated measured EGR flow rate is greater than the accumulated commanded EGR flow rate.

[0038] If it is determined that the measured EGR flow rate is above the commanded EGR flow rate, it may be inferred that the actual EGR flow is excessive relative to the commanded EGR flow. EGR flow that is higher than commanded may be undesirable, as it may result in undesirable engine dilution and higher than desired emissions levels. Thus, at 234, an EGR diagnostic routine for excessive EGR flow may be executed to detect a deterioration in the EGR system. The details of the EGR diagnostic routine for excessive EGR flow are described with respect to Fig. 3. If it is determined that the measured EGR flow rate is not above the commanded EGR flow rate, it may be inferred that the measured EGR flow rate is substantially equal to the commanded EGR flow rate. At 232, EGR delivery may continue with the EGR valve maintained in the open position without initiating a diagnostic operation. If it is determined at 204 that EGR is not desired for engine operations, the process includes determining at 236 whether EGR flow is detected in the HP EGR passage based on inputs from one or more EGR pressure sensors. If it is determined that EGR flow is detected even if EGR is not commanded, it may be inferred that a leak may exist in the EGR system, and at 240, a diagnostic for undesired EGR flow may be initiated. The details of the EGR diagnostic procedure for an undesired EGR flow are described in relation to Fig. 4. If no undesired current is detected, the EGR valve at 238 may be held in the closed position and the EGR system diagnostics may not be initiated.

[0039] Fig. 5 shows an example diagnostic sequence 500 for a high-pressure EGR system during insufficient EGR flow. A diagnostic sequence, such as the example sequence 200 of Fig. 2, can be used to detect EGR system degradation that results in the measured (actual) EGR flow rate being below the commanded EGR flow rate. The first trace 502 shows a change in EGR flow rate (in g / s) over time. Line 504 shows a commanded EGR flow rate (determined based on engine operating parameters), while line 510 shows a measured EGR flow rate (determined based on inputs from EGR system pressure sensors). In this example, the measured EGR flow rate is essentially zero, indicating insufficient EGR flow relative to the commanded EGR flow.

[0040] As in Fig. As discussed in Figure 2, a (dynamic) fault tolerance band with an upper and a lower limit for insufficient EGR flow may be calculated based on the commanded EGR flow, a fixed error margin, and a multiplier to examine the EGR system. Line 506 shows the upper limit of the tolerance band, and line 508 shows the lower limit of the tolerance band. As the commanded EGR flow is decreased, the lower limit 508 may be further decreased (via a multiplier) to increase the fault tolerance, thus reducing false detection of EGR system degradation due to transport delays. Likewise, as the commanded EGR flow is increased, the upper limit 506 may be increased accordingly. The difference between the lower limit 508 of the tolerance band and the measured EGR flow 510 can be calculated and accumulated over a test period t1 to determine the accumulated mass flow error.Line 514 shows the change in the accumulated mass flow error (g / s) over time. The commanded EGR mass flow may also be accumulated over the test period t1 to determine the accumulated commanded EGR mass flow. Thus, the test period t1 may be determined by the time it takes for the accumulated commanded EGR mass flow to result in an emissions level above the threshold in one cycle of an emissions test (such as FTP). To determine a failure rate, a ratio of the accumulated mass flow error to the accumulated commanded EGR mass flow may be calculated. Line 516 shows a change in the failure rate over time. The dashed line 517 shows a ratio threshold above which the EGR system may be indicated to be degraded.Line 518 shows a flag (a diagnostic code) that can be set to indicate EGR system degradation when the failure rate rises to threshold 517. As can be seen in this example, at the end of the test period, at time t1, the flag can be set when the failure rate rises to threshold 517, thereby indicating EGR system degradation. The HP EGR valve can be actuated to a closed position in response to the degradation indication, and further HP EGR supply can be interrupted.

[0041] Fig. 3 illustrates an exemplary method 300 that may be used for diagnosing the EGR system (such as the EGR system 140 of Fig. 1) may be implemented during excessive EGR flow (measured EGR flow rate higher than commanded). Method 300 may be part of the example method 200 described in Fig. 2 and may be performed at step 234 of method 200.

[0042] At 302, the controller may retrieve the actual EGR mass flow rate (flow rate of exhaust gas flowing through the HP EGR passage) based on inputs from one or more EGR sensors, such as an EGR delta pressure sensor and an EGR pressure sensor, coupled to the EGR system. Alternatively, the EGR flow rate may be derived based on inputs from the one or more temperature, pressure, humidity, and air-fuel ratio sensors coupled to the compressor inlet. The controller may determine the commanded EGR amount based on engine operating conditions, such as engine speed, engine load, engine temperature, etc. The controller may determine the HP EGR flow rate based on a calculation using a lookup table, where the input is one or more of engine speed, engine load, and engine temperature, and the output is the EGR flow rate.Alternatively, the controller may make a logical determination (e.g., regarding EGR flow rate) based on logical rules that are a function of parameters such as engine speed, engine load, and engine temperature. The controller may then generate a control signal that is sent to the high-pressure EGR valve.

[0043] At 304, a dynamic error tolerance band having an upper and lower limit for excessive EGR flow may be determined based on the commanded EGR flow rates. A fixed error margin may be used to determine the upper and lower limits of the tolerance band. The boundaries of the tolerance bands may be calculated based on a measured linear flow distance from an expected EGR mass flow (dependent on a commanded EGR mass flow). An additional multiplier may be used to adjust the tolerance band during a change in EGR flow direction, such as during an increase or decrease in the commanded EGR flow rate based on engine operating conditions. The multiplier provides increased error tolerance in the direction of the changing flow, while a fixed error tolerance may be used during steady flow.By adjusting the tolerance band during EGR flow direction changes, false detections of EGR system degradation due to transport delays between a commanded and measured EGR flow rate or due to PID control inaccuracies can be reduced. The upper limit of the tolerance band for excessive EGR flow can be calculated based on Equation 6, while the lower limit of the tolerance band can be calculated based on Equation 7, where: . Tlo2=Mcmd.−Serr Thi2=Mcmd.+(Mcmd.−Mexp.)∗Mmult.−Serr where T lo2 the lower limit of the tolerance band is Mcmd. is the commanded EGR mass flow, S err is the fixed error margin, T hi2 the upper limit of the tolerance band is Mexp. is the expected EGR mass flow and Multi ⋅ is a multiplier for the EGR mass flow based on the commanded EGR flow. The expected EGR mass flow (Mexp ⋅) is a filtered version of the commanded EGR mass flow (Mcmd ⋅).

[0044] At 306, the mass flow error between the upper limit of the tolerance band and the measured EGR flow rate over a drive cycle (test period) may be determined. At 308, an accumulated mass flow error over the current drive cycle, as given by Equation 8, may be determined as follows: Emf2=∑(Mmd ⋅−Tlo2) where E mf2 is the accumulated mass flow error over the current drive cycle, T lo2 the lower limit of the tolerance band and Mmd ⋅ the measured EGR mass flow.

[0045] At 310, an accumulated commanded mass flow over the current drive cycle, as indicated by Equation 4 (as previously introduced in step 220 of method 200), may be determined as follows: Ecmd=∑Mmd ⋅ where E cmd is the accumulated commanded mass flow over the current drive cycle and Mcmd ⋅ is the commanded EGR mass flow.

[0046] At 312, a ratio of the accumulated mass flow error to the accumulated commanded mass flow may be estimated as shown in Equation 9 as follows: Eratio2=∑(Mmd ⋅−Tlo2)∑Mcmd ⋅ where E ratio2is the second error rate of the accumulated mass flow to the accumulated commanded mass flow. The second error rate may be compared to a second threshold, threshold_2. At 314, the process includes determining whether the second error rate is above the second threshold. The second threshold may represent the point in the drive cycle at which higher than desired emission levels may occur. In other words, degradation of the EGR system resulting in undesirable emissions may be confirmed if the ratio increases above the second threshold during a point in the drive cycle.

[0047] If the error rate is confirmed to be above the second threshold, it may be inferred that the EGR system is not degraded. At 316, the controller may indicate that the EGR system is not degraded and may maintain the current EGR valve position to deliver the commanded amount of EGR.

[0048] However, if it is determined at 318 that the failure rate is above the second threshold, a degraded HP EGR may be indicated by setting a diagnostic code (a flag). The HP EGR valve may be closed to interrupt HP EGR flow through the degraded system.

[0049] Fig. 7 shows an example diagnostic 700 of a high-pressure EGR system during excessive EGR flow. A diagnostic flow, such as the example flow 300 of Fig. 3, can be used to detect EGR system degradation that results in the measured (actual) EGR flow rate being above the commanded EGR flow rate. The first trace, line 701, shows a change in EGR flow rate (in g / s) over time, as determined based on engine operating conditions. In the second trace, line 710 shows a measured EGR flow rate as estimated based on inputs from EGR system pressure sensors. In this example, the measured EGR flow rate is substantially above the commanded EGR flow rate, indicating excessive EGR flow relative to the commanded EGR flow.

[0050] As in Fig. 3, a dynamic error tolerance band with an upper and a lower limit for excessive EGR flow may be calculated based on the commanded EGR flow rates to investigate the EGR system. Line 706 shows the upper limit of the tolerance band, and line 708 shows the lower limit of the tolerance band. The difference between the upper limit of the tolerance band 708 and the measured EGR flow 710 may be calculated and accumulated over a test period t1 to determine the accumulated mass flow error. Line 714 shows the change in the accumulated mass flow error (g / s) over time. The commanded EGR mass flow may also be accumulated over the test period t1 to determine the accumulated commanded EGR mass flow. To determine an error rate, a ratio of the accumulated mass flow error to the accumulated commanded EGR mass flow can be calculated.Line 716 shows a change in the failure rate over time. The dashed line 717 shows a ratio threshold above which it may be indicated that the EGR system is degraded. Line 718 shows a flag (a diagnostic code) that can be set to indicate EGR system degradation when the failure rate increases to threshold 717. As can be seen in this example, at the end of the test period, at time t1, the flag can be set when the failure rate increases to threshold 717, thereby indicating EGR system degradation. The EGR valve may be actuated to a closed position in response to the degradation indication, and further EGR supply may be discontinued.

[0051] Fig. 4 illustrates an exemplary method 400 used for diagnosing the HD EGR system (such as the HD EGR system 144 of Fig. 1) during undesired EGR flow (EGR flow detected when no EGR is commanded). Method 400 may be part of the exemplary method 200 described in Fig. 2 and may be performed at step 240 of method 200.

[0052] At 402, the controller may retrieve the actual EGR mass flow rate (flow rate of exhaust gas flowing through the HP EGR passage) based on inputs from one or more EGR sensors, such as an EGR delta pressure sensor and an EGR absolute pressure sensor, coupled to the EGR system. Alternatively, the EGR flow rate may be derived by the one or more temperature, pressure, humidity, and air-fuel ratio sensors coupled to the compressor inlet. EGR may flow through the EGR passage due to a degradation, such as due to EGR valve leakage or when the EGR valve is stuck in an open position, even when no EGR delivery is commanded. The controller may also determine the intake air mass flow based on inputs from an intake air flow sensor (such as sensor 125 of Fig. 1) determine.

[0053] At 404, a fixed EGR limit for undesirable EGR flow may be determined based on emissions control regulations. The fixed EGR limit may be a constant value, and an EGR flow above the fixed EGR limit for a predetermined period of time may result in an undesirable emission level. The fixed EGR limit may differ from a dynamically adjusted upper and lower EGR threshold band used for diagnosing the EGR system for insufficient and excessive EGR flow. The fixed EGR limit for undesirable EGR flow may be calculated based on Equation 10 as follows: T3=Mcmd ⋅+Serr where T3 is the fixed EGR limit and S err is the fixed margin of error.

[0054] At 406, the mass flow error between the fixed EGR limit and the measured intake air mass flow over a drive cycle (test period during which no EGR flow is commanded) may be determined. If no EGR flow is desired, using the accumulated air flow results in a maximum reference value of a possible measured EGR mass flow for the error rate calculation. At 408, an accumulated mass flow error over the current drive cycle, as given by Equation 11, may be determined as follows: Emf3=∑(Mmd ⋅−T3) where E mf3 is the accumulated mass flow error over the current drive cycle, T3 is the fixed EGR limit and Mmd ⋅ the measured EGR mass flow.

[0055] At 410, an intake air mass flow over the current drive cycle, as given by Equation 12, may be determined as follows: Eaf=∑Maf ⋅ where E afis the accumulated commanded intake air mass flow over the current drive cycle and Mmf ⋅ is the intake air mass flow.

[0056] At 412, a ratio of the accumulated mass flow error to the accumulated intake air mass flow may be estimated as shown in Equation 13 as follows: Eratio3=∑(Mmd ⋅−T3)∑Maf ⋅ where E ratio3is the third error rate of the accumulated mass flow to the accumulated intake air mass flow. The third error rate may be compared to a third threshold, threshold_3. At 414, the process includes determining whether the third error rate is above the third threshold. The third threshold may represent the point in the drive cycle at which higher than desired emission levels may occur due to the undesirable EGR flow. In other words, an EGR system degradation (such as EGR valve leakage) resulting in undesirable emissions may be confirmed if the ratio increases above the third threshold during a point in the drive cycle.

[0057] If it is confirmed that the failure rate is above the third threshold, it may be inferred that the HP EGR system is not impaired, and the emission level may remain within acceptable limits. At 416, the controller may indicate that the HP EGR system is not impaired, and the current EGR valve position may be maintained in the closed position. However, if it is determined at 418 that the failure rate is above the third threshold, HP EGR impairment may be indicated by setting a diagnostic code (e.g., a flag). The HP EGR valve may be maintained in the closed position to prevent further EGR flow through the impaired system.

[0058] Fig. 6 shows an example diagnosis 600 of a high-pressure EGR system during an undesired EGR flow. A diagnostic sequence, such as the example sequence 400 of Fig. 4, can be used to detect EGR system degradation leading to undesirable EGR flow when no EGR is commanded. The first trace, line 604, shows the commanded EGR flow rate (in g / s) over time, as determined based on engine operating conditions. In this example, the commanded EGR flow rate is zero because no EGR is desired. Line 608 shows a measured EGR flow rate, as estimated based on inputs from EGR system pressure sensors. In this example, the measured EGR flow rate is non-zero, indicating undesirable EGR flow relative to the commanded HP EGR flow.

[0059] As in Fig. 4, a fixed EGR limit, line 606, may be calculated for undesirable EGR flow based on emissions control regulations to evaluate the EGR system. The difference between the measured EGR flow 608 and the fixed EGR limit 606 may be calculated and accumulated over a test period t1 to determine the accumulated mass flow error. Line 614 shows the change in the accumulated mass flow error (g / s) over time. The intake air mass flow may also be accumulated over the test period t1 to determine the accumulated intake air mass flow. A ratio of the accumulated mass flow error to the accumulated intake air mass flow may be calculated to determine an error rate. Line 616 shows a change in the error rate over time. The dashed line 617 shows a ratio threshold above which it can be indicated that the EGR system is impaired.Line 618 shows a flag (a diagnostic code) that can be set to indicate a degradation of the EGR system when the failure rate rises to threshold 617. As can be seen in this example, at the end of the test period, at time t1, the flag can be set when the failure rate rises to threshold 617, thereby indicating a degradation (such as a leak in the EGR valve) of the HP EGR system. The HP EGR valve can be held in the closed position in response to the degradation indication to disable future HP EGR delivery.

[0060] Fig. 8 shows an exemplary operating sequence 800, which includes a diagnostic sequence of the HD-EGR system Fig.1. A similar diagnostic sequence can also be performed for a low-pressure EGR system. A degradation of the high-pressure EGR system resulting in undesirable, excessive, or insufficient EGR flow can be indicated after the diagnostic sequence. The horizontal (x-) axis represents time, and the vertical markers t1-t4 represent significant points in the engine exhaust system's operation.

[0061] The first trace, line 802, shows a change in engine load over time, as estimated via inputs from a pedal position sensor. The second trace, line 804, shows an exhaust gas temperature, as estimated via inputs from an exhaust gas temperature sensor. The third trace, line 806, shows a commanded EGR flow rate, as estimated based on engine operating parameters such as engine speed, engine load, and engine temperature. The fourth trace, line 808, shows a position of the HP EGR valve. The fifth trace, line 810, shows a measured EGR flow rate, as estimated based on inputs from EGR system pressure sensors. The sixth trace, line 814, shows an error rate from an accumulated EGR mass flow error and an accumulated commanded EGR mass flow.The accumulated EGR mass flow error includes a difference between a boundary of a tolerance band and the measured EGR flow rate accumulated over a diagnostic test period. The accumulated commanded EGR mass flow may also be estimated taking into account the EGR mass flow over the test period. The dashed line 815 denotes an error rate threshold above which it may be determined that the EGR system is impaired. The threshold 815 may be based on a measured exhaust emission level, including one of an exhaust NOx level and an exhaust particulate matter level. Thus, the EGR diagnostic threshold may differ if the measured EGR flow is below the commanded EGR flow, if the measured EGR flow is above the commanded EGR flow, or if the measured EGR flow is above the commanded non-EGR flow.The seventh trace, line 818, shows the position of a marking indicating a deterioration of the EGR system.

[0062] Before time t1, the engine is shut down and the vehicle is not being propelled using engine torque. At time t1, the engine starts from idle in response to an operator torque demand after a period of inactivity. The controller may determine, based on operating conditions, including engine load, engine speed, and engine temperature, that EGR is undesirable for engine operations between time t1 and t2. Thus, the EGR valve is held in the closed position between time t1 and t2 to disable EGR flow. As can be seen in this example, no undesirable EGR flow exists between t1 and t2; thus, no EGR system diagnostics are run and the flag is not set.

[0063] However, if there is a deterioration in the EGR system (such as a leak in the EGR valve), as indicated by dashed line 811, undesirable EGR flow may occur. If undesirable EGR flow is detected, a diagnostic sequence may be initiated. EGR deterioration may be indicated in response to a non-zero measured EGR flow based on the error rate (dashed line 812) of the accumulated difference between the non-zero measured EGR flow and a fixed EGR limit to an accumulated intake air flow being above threshold 815. The accumulated difference and the accumulated intake air flow may be estimated between time t1 and t2.If the error rate (line 812) reaches threshold 815 at time t2, an EGR system degradation causing undesirable EGR flow may be indicated, and consequently, as shown by dashed line 816, the flag (the set diagnostic code) may be set at time t2. In response to the indication of an EGR system degradation causing undesirable EGR flow, the EGR valve may be maintained in the closed position to disable future EGR flow.

[0064] At time t2, EGR is required for engine operations in response to an increase in engine temperature. The commanded amount of EGR is determined by the controller based on engine operating parameters such as engine temperature, engine load, and engine speed. The opening of the EGR valve is adjusted to allow a commanded amount of EGR to the intake manifold. Between times t2 and t3, the measured (actual) amount of EGR delivered is substantially equal to the commanded amount of EGR. Thus, between times t2 and t3, no EGR diagnostics are performed, and the flag may be held in the off position.

[0065] However, if excessive EGR flow is detected, such as when the measured EGR flow is substantially above the commanded EGR flow (as shown by dashed line 811), a diagnostic sequence may be initiated to indicate a degradation in the EGR system causing the excessive EGR flow. If the measured EGR flow is above the commanded EGR flow, an error rate (as shown by dashed line 813) may be estimated from the accumulated difference between the measured EGR flow and an upper EGR limit of a tolerance band to the accumulated commanded EGR flow. The ratio may then be compared to threshold 815, and at time t3, degradation of the EGR system may be indicated in response to the ratio being above threshold 815.In response to the indication of an EGR system degradation causing excessive EGR flow, the flag may be set at time t3 and the EGR valve may be actuated to a closed position, thereby disabling future EGR flow.

[0066] At time t3, there is an increase in the amount of EGR commanded for engine operations in response to a reduction in engine load. The EGR valve opening is increased to supply the increased amount of EGR. However, between time t3 and t4, it is observed that there is no significant increase in EGR flow (relative to the EGR flow between t2 and t3), even when the EGR valve opening is increased. Thus, in response to the insufficient EGR flow at time t3, a diagnostic sequence is initiated. If the measured EGR flow is lower than the commanded EGR flow, an error rate 814 is estimated from the accumulated difference between the measured EGR flow and a lower EGR limit of the tolerance band to the accumulated commanded EGR flow.The ratio is then compared to threshold 815, and at time t4, an EGR system degradation is indicated in response to the ratio being above threshold 815. The flag is set at time t4 in response to the indication of the EGR system degradation causing insufficient EGR flow. Furthermore, in response to detecting the EGR system degradation at time t4, the EGR valve is actuated to a closed position to interrupt exhaust flow through the degraded EGR system. After time t4, the flag remains set, and EGR remains disabled.

[0067] An example engine method includes: when a commanded EGR flow changes, dynamically adjusting an upper and lower EGR limit based on the commanded EGR flow, indicating degradation of the EGR system based on a ratio of an accumulated difference between a measured EGR flow and one of the upper and lower EGR limits to an accumulated commanded EGR flow relative to a threshold, wherein the threshold is based on exhaust NOx levels, and adjusting the EGR flow based on the indication of degradation. In any preceding example, dynamically adjusting additionally or optionally includes selecting each of the upper and lower EGR limits depending on the commanded EGR flow, a fixed error margin, and a multiplier, wherein the multiplier is determined depending on the commanded EGR flow.In any or all of the preceding examples, the threshold additionally or optionally includes a first threshold when the measured EGR flow is above the commanded EGR flow, and a second, different threshold when the measured EGR flow is below the commanded EGR flow. In any or all of the preceding examples, indicating based on the ratio additionally or optionally includes indicating based on the ratio of the accumulated difference between the measured EGR flow and the upper EGR limit to the accumulated commanded EGR flow when the measured EGR flow is above the commanded EGR flow.In any or all of the preceding examples, indicating based on the ratio additionally or optionally further includes indicating based on the ratio of the accumulated difference between the measured EGR flow and the lower EGR limit to the accumulated commanded EGR flow when the measured EGR flow is below the commanded EGR flow. In any or all of the preceding examples, indicating additionally or optionally includes comparing the ratio to the first threshold when the measured EGR flow is above the commanded EGR flow, and indicating degradation of the EGR system in response to the ratio being above the first threshold.In any or all of the preceding examples, indicating additionally or optionally further includes comparing the ratio to the second threshold when the measured EGR flow is below the commanded EGR flow, and indicating degradation of the EGR system in response to the ratio being above the second threshold. In any or all of the preceding examples, adjusting the EGR flow additionally or optionally includes actuating an EGR valve to a closed position to interrupt EGR flow. Any or all of the preceding examples includeadditionally or optionally include indicating EGR degradation based on an error rate of an accumulated difference from the non-zero measured EGR flow and a fixed EGR limit to an accumulated intake air flow being above a third threshold in response to a non-zero measured EGR flow when the commanded EGR flow does not include EGR flow, and discontinuing EGR flow in response to the indication of the degradation, wherein the third threshold is based on exhaust NOx levels, wherein the fixed EGR limit is different from the dynamically adjusted upper and lower EGR limits.In any or all of the preceding examples, the engine is additionally or optionally coupled in a vehicle and wherein the accumulated difference between the measured EGR flow and one of the upper and lower EGR limits, the accumulated difference between the non-zero measured EGR flow and the EGR limit, and the accumulated intake air flow are accumulated over a duration or distance of vehicle travel, and wherein the EGR flow includes a high pressure EGR flow from upstream of an exhaust turbine to downstream of an intake compressor.

[0068] Another example method for an engine includes indicating degradation of the EGR system based on a first accumulated difference between the measured EGR flow and an upper limit accumulated over a duration when the measured EGR flow is above the commanded EGR flow, and indicating degradation of the EGR system based on a second accumulated difference between the measured EGR flow and a lower limit accumulated over the duration when the measured EGR flow is below the commanded EGR flow, wherein each of the upper limit and the lower limit is dynamically adjusted based on the commanded EGR flow. Any preceding example further additionally or optionally includes closing an EGR valve in response to indicating to discontinue EGR flow.In any of the preceding examples, indicating additionally or optionally includes estimating a first ratio of the first accumulated difference to an accumulated commanded EGR mass flow over the duration, and indicating degradation of the EGR system in response to the first ratio being above a first threshold. In any of the preceding examples, indicating further additionally or optionally includes estimating a second ratio of the second accumulated difference to an accumulated commanded EGR mass flow accumulated over the duration, and indicating degradation of the EGR system in response to the second ratio being above the second threshold that is different from the first threshold.In any or all of the preceding examples, the indicating further additionally or optionally includes, when the commanded EGR flow does not include EGR flow and the measured EGR flow is above the commanded non-EGR flow, estimating a third accumulated difference from the measured EGR flow and an error margin over the duration, estimating a third ratio of the third accumulated difference to the accumulated commanded intake air mass flow accumulated over the duration, and indicating degradation of the EGR system in response to the third ratio being above a third threshold that is different from the first and second thresholds.In any or all of the preceding examples, each of the first threshold, the second threshold, and the third threshold are additionally or optionally based on a measured exhaust emission component level, including one of an exhaust NOx level and an exhaust particulate matter level. In any or all of the preceding examples, the upper limit and the lower limit are additionally or optionally continuously varied depending on the commanded EGR flow, and wherein the error limit is a fixed error limit.

[0069] In yet another example, an engine system of a vehicle includes: an intake manifold and an exhaust manifold, a turbocharger including an exhaust turbine and an intake compressor, a low-pressure exhaust gas recirculation (LP-EGR) system including a first EGR passage having a first EGR valve for recirculating exhaust gas from downstream of the turbine in the exhaust manifold to upstream of the compressor in the intake manifold, a high-pressure exhaust gas recirculation (HP-EGR) system including a second EGR passage having a second EGR valve for recirculating exhaust gas from upstream of the turbine in the exhaust manifold to downstream of the compressor in the intake manifold, a temperature sensor, an absolute pressure sensor, and a differential pressure sensor coupled to each of the LP-EGR system and the HP-EGR system,and a controller having computer-readable instructions stored on non-volatile memory for: accumulating a difference between the measured EGR flow and one of an upper limit and a lower limit over a duration of vehicle movement in response to a measured EGR flow across the HP EGR system being above or below a commanded EGR flow, the upper and lower limits being dynamically adjusted depending on the commanded EGR flow, accumulating the commanded EGR flow over the duration, indicating degradation of the HP EGR system in response to a ratio of the accumulated difference to the accumulated commanded EGR flow being above the threshold, and actuating the second EGR valve to a closed position in response to the indication,while an opening of the first EGR valve is increased. In any or all of the preceding examples, the accumulated difference additionally or optionally includes an accumulated difference between the measured EGR flow and the upper limit when the EGR flow is above the commanded flow, and an accumulated difference between the measured EGR flow and the lower limit when the EGR flow is below the commanded flow, and wherein the threshold is based on an exhaust emission level. In any or all of the preceding examples, the measured EGR flow is additionally or optionally based on input from the absolute pressure sensor and the differential pressure sensor, and wherein the commanded EGR flow is based on an engine temperature, as estimated via an engine coolant temperature sensor, an engine load, as estimated via a pedal position sensor, and an engine speed, as estimated via a crankshaft acceleration sensor.

[0070] In this way, unintended emissions due to EGR system degradation can be reduced by adjusting the EGR system degradation detection threshold based on EGR flow conditions. By estimating undesired EGR flow when no EGR flow is commanded, degradations such as leaks in the EGR system can be detected. The technical effect of dynamically calculating the EGR mass flow error tolerance band, including increasing the tolerance limit in the direction of EGR flow change, is to reduce erroneous indications of EGR system degradation due to transport delays between a delivered and commanded EGR flow rate.By distinguishing between problems with undesirable, excessive, and insufficient EGR flow, appropriate measures can be taken to mitigate the specific cause of the impairment. By enabling EGR system diagnostics to be performed reliably and accurately, the overall fuel economy and emissions benefits of the system can be extended across a wider range of engine operating conditions.

[0071] It should be noted that the example control and estimation procedures included herein may be used with various engine and / or vehicle system configurations. The control methods and procedures disclosed herein may be stored as executable instructions in non-transitory memory and executed by the control system, including the controller in combination with the various sensors, actuators, and other engine hardware. The specific procedures described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Accordingly, various illustrated acts, operations, and / or functions may be performed in the illustrated sequence or in parallel, or in some cases, may be omitted.Likewise, the processing order is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but rather is provided for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may be performed repeatedly depending on the particular strategy employed. Further, the described acts, operations, and / or functions may graphically represent code to be programmed into the non-transitory memory of the computer-readable storage medium in the engine control system, wherein the described acts are performed by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.

[0072] It is understood that the designs and operations disclosed herein are exemplary in nature, and these specific embodiments are not to be considered limiting, as numerous variations are possible. For example, the above technology may be applied to V-6, I-4, I-6, V-12, horizontally opposed 4-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various systems and configurations, and other features, functions, and / or characteristics disclosed herein.

[0073] The following claims particularly set forth certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims are to be construed as including one or more such elements and 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 amending the present claims or by filing new claims in this or a related application.Such claims, whether broader, narrower, equal, or different in scope than the original claims, are further considered to be included within the subject matter of the present disclosure.

Claims

[1] A method of operating an engine, comprising: when a commanded EGR flow changes, dynamically setting an upper and lower EGR limit based on the commanded EGR flow; indicating degradation of the EGR system based on a ratio of an accumulated difference between a measured EGR flow and one between the upper and lower EGR limits to an accumulated commanded EGR flow relative to a threshold, the threshold being based on exhaust NOx levels; and Adjust EGR flow based on impairment indication. [2] The method of claim 1, wherein the dynamically adjusting includes selecting each of the upper and lower EGR limits depending on the commanded EGR flow, a fixed error margin, and a multiplier, the multiplier being determined depending on the commanded EGR flow. [3] The method of claim 1, wherein the threshold includes a first threshold when the measured EGR flow is above the commanded EGR flow and a second, different threshold when the measured EGR flow is below the commanded EGR flow. [4] The method of claim 3, wherein indicating based on the ratio includes indicating based on the ratio of the accumulated difference between the measured EGR flow and the upper EGR limit to the accumulated commanded EGR flow when the measured EGR flow is above the commanded EGR flow. [5] The method of claim 4, wherein indicating based on the ratio further includes indicating based on the ratio of the accumulated difference between the measured EGR flow and the lower EGR limit to the accumulated commanded EGR flow when the measured EGR flow is below the commanded EGR flow. [6] The method of claim 4, wherein indicating includes comparing the ratio to the first threshold when the measured EGR flow is above the commanded EGR flow, and indicating degradation of the EGR system in response to the ratio being above the first threshold. [7] The method of claim 6, wherein indicating further includes comparing the ratio to the second threshold when the measured EGR flow is below the commanded EGR flow, and indicating degradation of the EGR system in response to the ratio being above the second threshold. [8] The method of claim 1, wherein adjusting the EGR flow includes actuating an EGR valve to a closed position to interrupt the EGR flow. [9] The method of claim 1, further comprising indicating EGR degradation based on an error ratio of an accumulated difference of a non-zero measured EGR flow and a fixed EGR limit to an accumulated intake air flow being above a third threshold in response to a non-zero measured EGR flow when the commanded EGR flow does not include EGR flow, and discontinuing EGR flow in response to the indication of the degradation, wherein the third threshold is based on exhaust NOx levels, wherein the fixed EGR limit is different from the dynamically adjusted upper and lower EGR limits. [10] The method of claim 9, wherein the engine is coupled in a vehicle and wherein the accumulated difference between the measured EGR flow and one of the upper and lower EGR limits, the accumulated difference between the non-zero measured EGR flow and the EGR limit, and the accumulated intake air flow are accumulated over a duration or a distance of vehicle travel, and wherein the EGR flow includes a high pressure EGR flow from upstream of an exhaust turbine to downstream of an intake compressor. [11] A method of operating an engine, comprising: Indicating degradation of the EGR system based on a first accumulated difference between the measured EGR flow and a first upper limit accumulated over the duration when the measured EGR flow is above the commanded EGR flow; Indicating an impairment of the EGR system based on a second accumulated difference between the measured EGR flow and a second lower limit, accumulated over the duration when the measured EGR flow is below the commanded EGR flow, wherein each of the upper limit and the lower limit is dynamically adjusted based on the commanded EGR flow. [12] The method of claim 11, wherein the first limit and the second limit are continuously varied depending on the commanded EGR flow. [13] Vehicle engine system, comprising: an intake manifold and an exhaust manifold; a turbocharger comprising an exhaust turbine and an intake compressor; a low-pressure exhaust gas recirculation (LP-EGR) system comprising a first EGR passage with a first EGR valve for recirculating exhaust gas from downstream of the turbine in the exhaust manifold to upstream of the compressor in the intake manifold; a high pressure exhaust gas recirculation (HP EGR) system including a second EGR passage with a second EGR valve for recirculating exhaust gas from upstream of the turbine in the exhaust manifold to downstream of the compressor in the intake manifold; a temperature sensor, an absolute pressure sensor, and a differential pressure sensor coupled to each of the LP EGR and HP EGR systems; and a controller having computer-readable instructions stored in non-volatile memory for the following: in response to a measured EGR flow through the HP EGR system being above or below a commanded EGR flow, Accumulating a difference between the measured EGR flow and one of an upper limit and a lower limit over a duration of vehicle movement, wherein the upper and lower limits are dynamically adjusted depending on the commanded EGR flow; Accumulating the commanded EGR flow over the duration; Indicating a degradation of the HD EGR system in response to a ratio of the accumulated difference to the accumulated commanded EGR flow being above the threshold; and Actuating the second EGR valve to a closed position in response to the indication while increasing an opening of the first EGR valve. [14] The system of claim 13, wherein the accumulated difference includes an accumulated difference between the measured EGR flow and the upper limit when the EGR flow is above the commanded flow, and an accumulated difference between the measured EGR flow and the lower limit when the EGR flow is below the commanded flow, and wherein the threshold is based on an exhaust emission level. [15] The system of claim 13, wherein the measured EGR flow is based on an input from the absolute pressure sensor and the differential pressure sensor, and wherein the commanded EGR flow is based on an engine temperature as estimated via an engine coolant temperature sensor, an engine load as estimated via a pedal position sensor, and an engine speed as estimated via a crankshaft acceleration sensor.

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