System and method for operating an exhaust gas recirculation valve based on a temperature difference of the valve

Abstract

Method for an engine (10), comprising: Adjusting an exhaust gas recirculation valve (EGR valve, 121) based on an estimate of the EGR flow, wherein the EGR flow is estimated based on a pressure difference across the EGR valve (121) and a set valve passage cross-section, wherein the set valve passage cross-section is based on a first temperature difference between a stem and a body of the EGR valve (121).

Description

Area

[0001] This description generally relates to methods and systems for an exhaust gas recirculation system of an internal combustion engine. Background / Summary

[0002] Engine systems may utilize the recirculation of exhaust gas from an engine exhaust system to an engine intake system (intake passage), a process known as exhaust gas recirculation (EGR), to reduce regulated emissions and improve fuel economy. An EGR system, such as a low-pressure EGR system, may include various sensors for measuring and / or controlling EGR. As an example, an engine intake system may include an intake gas constituent sensor, such as an oxygen sensor, that may be used during non-EGR conditions to determine the oxygen content of fresh intake air. During EGR conditions, the sensor may be used to divert EGR based on a change in oxygen concentration due to the addition of EGR as a diluent.

[0003] DE 10 2014 216 251 A1 describes methods and systems for improving the accuracy of a differential valve pressure (DPOV)-based EGR flow measurement during low valve lift conditions by learning the errors in the lift of the EGR valve and / or a transfer function of the flow of the EGR valve.

[0004] DE 600 11 315 T2 describes compression-ignition internal combustion engines with exhaust gas recirculation systems and, in particular, methods for limiting fuel delivery in order to avoid visible soot or smoke development in diesel engines with turbochargers with exhaust gas recirculation systems (EGR).

[0005] US 2013 / 0 061 831 A1 describes a system and method for measuring EGR flow rate for an engine having an EGR valve with a selectable EGR valve position and a venturi sensor arranged to provide a differential pressure measurement relative to recirculated exhaust gas, comprising determining an effective EGR valve area based on the EGR valve position, determining a weighting factor based on the effective area, calculating a first EGR flow estimate based on the effective area, and calculating a second EGR flow estimate based on the differential pressure measurement of the venturi sensor. A final EGR flow rate is determined based on the weighting factor, the first EGR flow estimate, and the second EGR flow estimate.

[0006] An example of an intake oxygen sensor is shown by Matsubara et al. in US Pat. No. 6,742,379 B2. The accuracy of EGR estimates using the intake oxygen sensor may be reduced during boosted engine operation and under scavenging conditions when hydrocarbons flow through the intake system. EGR flow may then be estimated using alternative EGR sensors. For example, the EGR system may also include a differential pressure over valve (DP) sensor positioned around an EGR valve to estimate EGR flow based on a pressure differential across the EGR valve and a flow area of ​​the EGR valve. EGR flow estimates may then be used to adjust a position of the EGR valve and, therefore, adjust an amount of EGR delivered to the engine.

[0007] For example, an EGR valve flow area may change when the EGR valve temperature changes due to changes in the EGR temperature. Specifically, thermal expansion or contraction of the EGR valve may cause a change in the EGR valve flow area. This change in the EGR valve flow area may impact EGR flow estimation and thus EGR control based on measurements from a DPOV system including the DP sensor. The present inventors have recognized that errors in EGR flow estimates using the DPOV method may increase with increasing temperature differences between a stem and body of the EGR valve.

[0008] In one example, the problems described above may be addressed by a method for adjusting an exhaust gas recirculation (EGR) valve based on an EGR flow estimate, wherein the EGR flow is estimated based on a pressure differential across the EGR valve and an adjusted valve flow area, wherein the adjusted valve flow area is based on a first temperature difference between a stem and a body of the EGR valve. In this way, changes in the flow area of ​​the EGR valve due to thermal expansion or contraction may be determined, and subsequently, EGR flow estimates may be corrected based on the adjusted valve flow area, thereby increasing the accuracy of EGR flow estimates and resulting engine control.

[0009] As an example, a second temperature difference between a stem and a body of the EGR valve may be determined when the EGR valve is closed. The difference between the second temperature difference of the EGR valve stem and body and the first temperature difference between the EGR valve stem and body may be used to provide a change in the EGR valve flow area. The change in the EGR valve flow area may be used to correct EGR valve area estimates. Corrected EGR valve area estimates may be used for subsequent EGR flow estimates.

[0010] It should be understood that the above summary is intended to introduce, in a simplified form, a selection of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any of the disadvantages noted above or elsewhere in this disclosure.

[0011] None of the aforementioned prior art documents discloses the inventive approach using a first temperature difference between a stem and a body of the EGR valve to estimate an EGR flow according to the features of the claims. Short description of the drawings Fig. 1 is a schematic diagram of an example engine system including an intake oxygen sensor and an exhaust gas recirculation system. Fig. 2 is a flowchart of a method for estimating EGR flow with an intake oxygen sensor or differential pressure sensor based on engine operating conditions. Fig. 3 is a flowchart of a method for indicating soot accumulation at an EGR valve and determining a corrected EGR valve passage area based on soot accumulation. Fig. Figure 4 is a graph illustrating changes in EGR flow estimates using an intake oxygen sensor and differential pressure sensor under varying engine operating conditions. Fig. 5 is a flowchart of a method for learning changes in an EGR valve passage area due to changes in a temperature difference between an EGR valve stem and body. Fig. 6 is a flowchart of a method for learning a temperature difference between an EGR valve stem and body in an EGR valve closed position. Detailed description

[0012] The following description relates to systems and methods for determining changes in the flow area of ​​an exhaust gas recirculation (EGR) valve for EGR flow estimations. In one example, the changes in the flow area of ​​the EGR valve may be due to soot accumulation on the EGR valve and / or a change in the temperature difference between a stem and a body of the EGR valve. A turbocharged internal combustion engine, as in Fig. 1, may include an intake oxygen sensor positioned in an intake passage of the engine and a DP sensor positioned in an EGR passage. The DP sensor and the intake oxygen sensor may each be used to provide estimates of EGR flow through a low-pressure EGR system. The EGR flow may be regulated by an EGR valve that, when open, allows exhaust gas recirculation to an intake passage from downstream of a turbine to upstream of a compressor. As shown in Fig. 4, EGR flow may be estimated using the intake oxygen sensor and / or the DP sensor based on engine operating conditions. When the EGR valve is open and EGR is flowing through the EGR passage, a pressure differential across the EGR valve and the size of the EGR valve opening may be used to determine the size of the EGR flow. A position sensor may be used to determine EGR valve lift and thus estimate the area of ​​the EGR valve opening, and the DP sensor may provide the differential pressure across the EGR valve. As shown in the Fig. 5 and Fig. As described in Figure 6, the accuracy of the EGR valve opening estimate can be increased by accounting for thermal expansion of the EGR valve due to high EGR temperatures. Overall, measurements from an EGR valve position sensor and a DP sensor can be used to provide an EGR air mass estimate. However, over time, soot can accumulate on the EGR valve, which can reduce the effective flow area of ​​the valve opening. Without a method for estimating soot accumulation, EGR flow estimates can become increasingly inaccurate as soot accumulates on the EGR valve.

[0013] As in Fig. 2, the determination of whether to use DPOV intake oxygen sensor measurements (from a DPOV system that includes a DP sensor via an EGR valve) to estimate EGR flow rates may be based on engine operating parameters, such as scavenging, boost, and intake air mass. Fig. The method described in Figure 3 provides a technique for estimating soot accumulation at the EGR valve, thereby providing more accurate estimates of EGR flow. Using an intake oxygen sensor, EGR flow can be estimated by comparing the oxygen content of intake air when the EGR valve is open to a baseline level when the EGR valve is closed. As soot accumulates, the EGR flow estimate obtained from the intake oxygen sensor can be compared to the EGR flow estimate obtained from the DP and position sensors (also referred to herein as the DPOV system). Fig. Figure 3 further illustrates how the difference between the EGR flow estimates obtained from the oxygen sensor and the DP and position sensors can then be used to determine an estimate of soot accumulation at the EGR valve. By accounting for changes in the effective valve passage area due to soot accumulation, subsequent EGR flow estimates based on the DP and position sensors can be adjusted based on the determined soot accumulation.

[0014] Fig. 1 shows a schematic representation of an exemplary turbocharged engine system 100 including a multi-cylinder internal combustion engine 10 and dual turbochargers 120 and 130, which may be identical. As a non-limiting example, the engine system 100 may be included as part of a propulsion system for a passenger vehicle. Although not illustrated here, other engine configurations, such as a single-turbocharged engine, may be used without departing from the scope of the present disclosure.

[0015] The engine system 100 may be controlled at least partially by a controller 12 and by input from a vehicle operator 190 via an input device 192. In this example, the input device 192 includes an accelerator pedal and a pedal position sensor 194 for generating a proportional pedal position signal PP. The controller 12 may be a microcomputer including a microprocessor unit, input / output ports, an electronic storage medium for executable programs and calibration values ​​(e.g., a read-only memory chip), random access memory, maintain memory, and a data bus. The read-only memory storage medium may be programmed with computer-readable data representing non-transitory instructions executable by the microprocessor to perform the routines described herein, as well as other variations that are expected but not specifically recited.The controller 12 may be configured to receive information from a plurality of sensors 165 and send control signals to a plurality of actuators 175 (examples of which are described herein). Other actuators, such as various additional valves and throttles, may be coupled to various locations in the engine system 100. The controller 12 may 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 according to one or more routines. Example control routines are described herein with reference to FIG. Fig. 2-3 and 5-6.

[0016] The engine system 100 may receive intake air via the intake passage 140. As in Fig. 1, the intake duct 140 may include an air filter 156 and an air induction system (AIS) throttle 115. The position of the AIS throttle 115 may be adjusted by the control system via a throttle actuator 117 communicatively coupled to the controller 12.

[0017] At least a portion of the intake air may be directed to a compressor 122 of the turbocharger 120 via a first branch of the intake passage 140, shown at 142, and at least a portion of the intake air may be directed to a compressor 132 of the turbocharger 130 via a second branch of the intake passage 140, shown at 144. Accordingly, the engine system 100 includes a low-pressure AIS system (LP-AIS) 191 upstream of the compressors 122 and 132 and a high-pressure AIS system (HP-AIS) 193 downstream of the compressors 122 and 132.

[0018] A positive crankcase ventilation (PCV) line 198 (e.g., a pressure-side pipe) may couple a crankcase (not shown) to the second intake passage branch 144 so that gases in the crankcase may be vented from the crankcase in a controlled manner. Furthermore, evaporative emissions from a fuel vapor canister (not shown) may be vented into the intake passage through a fuel vapor purge line 195 that couples the fuel vapor canister to the second intake passage branch 144.

[0019] The first portion of the total intake air may be compressed by a compressor 122, from where it may be supplied to the intake manifold 160 via the intake port 146. Thus, the intake ports 142 and 146 form a first branch of the engine's air intake system. Similarly, a second portion of the total intake air may be compressed by the compressor 132, from where it may be supplied to the intake manifold 160 via the intake port 148. Thus, the intake ports 144 and 148 form a second branch of the engine's air intake system. As shown in Fig. 1, intake air from intake passages 146 and 148 may be recombined via a common intake passage 149 before reaching intake manifold 160, from where the intake air may be delivered to the engine. In some examples, intake manifold 160 may include an intake manifold pressure sensor 182 for estimating a manifold air pressure (MAP) and / or an intake manifold temperature sensor 183 for estimating a manifold charge temperature (MCT), each in communication with controller 12. In the depicted example, intake passage 149 further includes a charge air cooler (CAC) 154 and a throttle valve 158. The position of throttle valve 158 may be adjusted by the control system via a throttle actuator 157 communicatively coupled to controller 12.As shown, the throttle valve 158 may be disposed in the intake passage 149 downstream of the CAC 154 and configured to adjust the flow of an intake gas stream entering the engine 10.

[0020] As in Fig. 1, a compressor bypass valve (CBV) 152 may be disposed in a CBV (compressor bypass valve) passage 150, and a CBV 155 may be disposed in a CBV passage 151. In one example, the CBVs 152 and 155 may be electronic pneumatic CBVs (EPCBV). The CBVs 152 and 155 may be controlled to provide intake system depressurization when the engine is boosted. An upstream end of the CBV passage 150 may be coupled to the intake passage 148 downstream of the compressor 132, and a downstream end of the CBV passage 150 may be coupled to the intake passage 144 upstream of the compressor 132. Similarly, an upstream end of a CBV passage 151 may be coupled to the inlet passage 146 downstream of the compressor 122, and a downstream end of the CBV passage 151 may be coupled to the inlet passage 142 upstream of the compressor 122.Depending on a position of each CBV, the air compressed by the corresponding compressor may be recirculated to the intake port upstream of the compressor (e.g., intake port 144 for compressor 132 and intake port 142 for compressor 122). For example, CBV 152 may open to recirculate compressed air upstream of compressor 132, and / or CBV 155 may open to recirculate compressed air upstream of compressor 122 to relieve pressure in the intake system during selected conditions and thus reduce the effects of compressor surge loading. CBVs 155 and 152 may be controlled either actively or passively by the control system.

[0021] As shown, a compressor inlet pressure (CIP) sensor 196 is disposed in intake passage 142, and an HP AIS pressure sensor 169 is disposed in intake passage 149. However, in other anticipated embodiments, sensors 196 and 169 may be disposed at other locations within the LP AIS and HP AIS, respectively. Among other functions, CIP sensor 196 may be used to determine a pressure downstream of an EGR valve 121.

[0022] The internal combustion engine 10 may include a plurality of cylinders 14. In the example shown, the engine 10 includes six cylinders arranged in a V-configuration. More specifically, the six cylinders are arranged on two banks 13 and 15, with each bank containing three cylinders. In other examples, the engine 10 may include two or more cylinders, such as 3, 4, 5, 8, 10, or more cylinders. These various cylinders may be evenly split and arranged in other configurations, such as a V, inline, or horizontally opposed configuration, etc. Each cylinder 14 may be configured with a fuel injector 166. In the example shown, the fuel injector 166 is a direct-in-cylinder fuel injector. However, in other examples, the fuel injector 166 may also be configured as a port fuel injector.

[0023] Intake air supplied to each cylinder 14 (also referred to herein as combustion chamber 14) via a common intake port 149 may be used for fuel combustion, and combustion products may then be exhausted via bank-specific exhaust ports. In the example shown, a first bank 13 of cylinders of engine 10 may exhaust combustion products via a common exhaust port 17, and a second bank 15 of cylinders may exhaust combustion products via a common exhaust port 19.

[0024] The position of the intake and exhaust valves of each cylinder 14 may be controlled via hydraulically actuated lifters coupled to valve pushrods or via mechanical cup systems utilizing cam lobes. In this example, at least the intake valves of each cylinder 14 may be controlled by cam actuation using a cam actuation system. In particular, the intake valve cam actuation system 25 may include one or more cams and may utilize variable cam timing or variable cam lift for intake and / or exhaust valves. In alternative embodiments, the intake valves may be controlled by electric valve actuation. Likewise, the exhaust valves may be controlled by cam actuation systems or electric valve actuation. In yet another alternative embodiment, the cams may be non-adjustable.

[0025] Combustion products expelled by engine 10 via exhaust passage 17 may be directed through exhaust turbine 124 of turbocharger 120, which in turn may provide mechanical work to compressor 122 via shaft 126 to provide compression of the intake air. Alternatively, some or all of the exhaust gas flowing through exhaust passage 17 may bypass turbine 124 via turbine bypass passage 123, as controlled by wastegate 128. The position of wastegate 128 may be controlled by an actuator (not shown) in a manner determined by controller 12. As a non-limiting example, controller 12 may adjust the position of wastegate 128 via a pneumatic actuator controlled by a solenoid valve.For example, the solenoid valve may receive a signal to enable actuation of the wastegate 128 via the pneumatic actuator based on the difference in air pressures between the inlet passage 142 located upstream of the compressor 122 and the inlet passage 149 located downstream of the compressor 122. In other examples, other suitable approaches other than a solenoid valve may be used to actuate the wastegate 128.

[0026] Likewise, combustion products expelled by engine 10 via exhaust passage 19 may be directed through exhaust turbine 134 of turbocharger 130, which in turn may provide mechanical work to compressor 132 via shaft 136 to provide compression of the intake air flowing through the second branch of the engine intake system. Alternatively, some or all of the exhaust gas flowing through exhaust passage 19 may bypass turbine 134 via turbine bypass passage 133, as controlled by wastegate 138. The position of wastegate 138 may be controlled by an actuator (not shown) in a manner determined by controller 12. As a non-limiting example, controller 12 may adjust the position of wastegate 138 via a solenoid valve controlling a pneumatic actuator.For example, the solenoid valve may receive a signal to enable actuation of the wastegate 138 via the pneumatic actuator based on the difference in air pressures between the inlet passage 144 located upstream of the compressor 132 and the inlet passage 149 located downstream of the compressor 132. In other examples, other suitable approaches other than a solenoid valve may be used to actuate the wastegate 138.

[0027] In some examples, exhaust turbines 124 and 134 may be configured as variable geometry turbines, where controller 12 may adjust the position of the turbine impeller blades (or vanes) to vary the energy level received from the exhaust flow and applied to their respective compressor. Alternatively, exhaust turbines 124 and 134 may be configured as variable nozzle turbines, where controller 12 may adjust the position of the turbine nozzle to vary the energy level received from the exhaust flow and applied to their respective compressor. For example, the control system may be configured to independently vary the vane or nozzle position of exhaust turbines 124 and 134 via respective actuators.

[0028] Combustion products expelled by the cylinders via exhaust port 19 may be directed to the atmosphere via exhaust port 180 downstream of turbine 134, while combustion products expelled via exhaust port 17 may be directed to the atmosphere via exhaust port 170 downstream of turbine 124. Exhaust ports 170 and 180 may include one or more exhaust aftertreatment devices, such as a catalyst and one or more exhaust gas sensors. For example, exhaust port 170 may be configured as shown in Fig. 1, the exhaust passage 180 may include an emission control device 129 located downstream of the turbine 124, and the exhaust passage 180 may include an emission control device 127 located downstream of the turbine 134. The emission control devices 127 and 129 may be selective catalytic reduction (SCR) devices, three-way catalysts (TWC), NOx traps, various other emission control devices, or combinations thereof. Further, in some embodiments, the emission control devices 127 and 129 may be periodically regenerated during operation of the engine 10, for example, by operating at least one cylinder of the engine at a particular air / fuel ratio.

[0029] Further, engine system 100 may include one or more exhaust gas recirculation (EGR) systems for recirculating at least a portion of the exhaust gas from the exhaust manifold to the intake manifold. These may include one or more high-pressure EGR systems for providing high-pressure EGR (HP EGR) and one or more low-pressure EGR circuits for providing low-pressure EGR (LP EGR). In one example, HP EGR may be provided in the absence of boost provided by turbochargers 120, 130, while LP EGR may be provided in the presence of turbocharger boost and / or when the exhaust gas temperature is above a threshold. In still other examples, both HP EGR and LP EGR may be provided simultaneously.

[0030] In the illustrated example, engine system 100 may include a low-pressure (LP) EGR system 108. LP EGR system 108 routes a desired portion of the exhaust gas from exhaust passage 170 to intake passage 142. In the illustrated embodiment, EGR in an EGR passage 197 is routed from downstream of turbine 124 to intake passage 142 at a mixing point located upstream of compressor 122. The amount of EGR supplied to intake passage 142 may be varied by controller 12 via EGR valve 121 coupled in LP EGR system 108. In the illustrated embodiment, Fig. 1, the LP-EGR system 108 includes an EGR cooler 113 positioned upstream of the EGR valve 121. The EGR cooler 113 may transfer heat from the recirculated exhaust gas to, for example, engine coolant. The LP-EGR system may include a Differential Pressure Over Valve (DP) sensor 125. In one example, EGR flow may be estimated based on the DPOV system, which includes the DP sensor 125 detecting a pressure difference between an upstream region of the EGR valve 121 and a downstream region of the EGR valve 121.The EGR flow determined by the DPOV system (e.g., LP EGR flow) may be further based on an EGR temperature detected by an EGR temperature sensor 135 located downstream of the EGR valve 121 and an EGR valve opening area detected by an EGR valve lift sensor 131. In another example, the EGR flow may be determined based on outputs from an EGR measurement system including an intake oxygen sensor 168 (referred to herein as the IAO2 sensor), a mass air flow sensor (not shown), a manifold absolute pressure (MAP) sensor 182, and a manifold temperature sensor 183. In some examples, both EGR measurement systems (i.e., the DPOV system including the differential pressure sensor 125 and the EGR measurement system including the intake oxygen sensor 168) may be used to determine, monitor, and adjust EGR flow.

[0031] In an alternative embodiment, the engine system may include a second LP EGR system (not shown) that directs a desired portion of the exhaust gas from the exhaust port 180 to the intake port 144. In another alternative embodiment, the engine system may include both of the LP EGR systems described above (one directing exhaust gas from the exhaust port 180 to the intake port 144 and another directing exhaust gas from the exhaust port 170 to the intake port 142).

[0032] In another embodiment, the engine system 100, although in Fig. 1, may further include a high pressure EGR system that may direct a desired portion of the exhaust gas from the common exhaust passage 17 upstream of the turbine 124 to the intake manifold 160 downstream of the intake throttle 158.

[0033] The EGR valve 121 may include a body and a stem (not shown), wherein the stem is movable within the body of the EGR valve 121 such that the opening of the EGR valve 121 can be adjusted based on the relative position of the stem and the body. The EGR valve 121 may be configured to adjust an amount and / or rate of exhaust gas redirected through the EGR passage to achieve a desired EGR dilution percentage of the intake charge entering the engine, wherein an intake charge with a higher EGR dilution percentage has a greater ratio of recirculated exhaust gas to air than an intake charge with a lower EGR dilution percentage. It is understood that in addition to the EGR valve position, the AIS throttle position of the AIS throttle 115 and other actuators can also affect the EGR dilution percentage of the intake charge.For example, a position of the AIS throttle may increase the pressure drop across the LP EGR system, allowing more flow of LP EGR into the intake system. This may increase the EGR dilution percentage, whereas a lower LP EGR flow into the intake system may decrease the EGR dilution percentage (e.g., percentage of EGR). Accordingly, EGR dilution of the intake charge may be controlled by controlling EGR valve position and / or AIS throttle position, among other parameters. Thus, by adjusting the EGR valves 121 and / or the AIS throttle 115, an amount (or rate) of EGR flow and, subsequently, a percentage of EGR in the air mass (e.g., the air charge entering the intake manifold) may be adjusted.

[0034] The internal combustion engine 10 may further include one or more oxygen sensors positioned within the common intake passage 149. Thus, the one or more oxygen sensors may be referred to as intake oxygen sensors. In the illustrated embodiment, an intake oxygen sensor 168 is positioned upstream of the throttle body 158 and downstream of the CAC 154. However, in other embodiments, the intake oxygen sensor 168 may be located elsewhere along the intake passage 149, such as upstream of the CAC 154. The intake oxygen sensor (IAO2) 168 may be a variable voltage (VVs) oxygen sensor or any suitable sensor for providing an indication of the oxygen concentration and EGR concentration of the intake charge air (e.g., the air flowing through the common intake passage 149).In one example, the inlet oxygen sensors 168 may be an inlet oxygen sensor that includes a heating element as a sensing element. During operation, the pumping current of the inlet oxygen sensor may indicate an amount of oxygen in the gas stream.

[0035] A pressure sensor 172 may be positioned adjacent to the oxygen sensor for estimating an intake pressure at which an oxygen sensor output is received. Since the oxygen sensor output is influenced by intake pressure, a reference oxygen sensor output may be learned at a reference intake pressure. In one example, the reference intake pressure is throttle inlet pressure (TIP), with pressure sensor 172 being a TIP sensor. In other examples, the reference intake pressure is manifold pressure (MAP) sensed by MAP sensor 182.

[0036] The engine system 100 may include various sensors 165 in addition to those mentioned above. As in Fig. 1, the common intake passage 149 may include a throttle inlet temperature sensor 173 for estimating throttle air temperature (TCT). Although not shown here, the intake passages 142 and 144 may each further include a mass air flow sensor, or alternatively, the mass air flow sensor may be located in the common passage 140.

[0037] A humidity sensor 189 may be included in only one of the parallel inlet channels. As in Fig. 1, the humidity sensor 189 is positioned in the intake passage 142 (e.g., non-PCV and non-purge bank of the intake passage) upstream of the CAC 154 and an outlet of the LP EGR passage 197 into the intake passage 142 (e.g., intersection between the LP EGR passage 197 and the intake passage 142 where LP EGR enters the intake passage 142). The humidity sensor 189 may be configured to estimate a relative humidity of the intake air. In one embodiment, the humidity sensor 189 is a UEGO sensor configured to estimate the relative humidity of the intake air based on the sensor's output at one or more voltages. Because purge air and PCV air can interfere with the humidity sensor readings, the purge port and PCV port are positioned in a different intake port than the humidity sensor.

[0038] The intake oxygen sensor 168 can be used to estimate an intake oxygen concentration and derive an amount of EGR flow through the engine based on a change in the intake oxygen concentration when the EGR valve 121 opens. Specifically, a change in the sensor's output when the EGR valve 121 opens is compared to a reference point at which the sensor is operating without EGR (the zero point). Based on the change (e.g., decrease) in the amount of oxygen from the time of operation without EGR, an EGR flow supplied to the engine at that time can be calculated. For example, when a reference voltage (Vs) is applied to the sensor, a pumping current (Ip) is output by the sensor.The change in oxygen concentration can be proportional to the change in the pumping current (delta Ip output) output by the sensor in the presence of EGR relative to the sensor output in the absence of EGR (zero point). Further EGR control can be performed based on a deviation of the estimated EGR flow from the expected (or target) EGR flow.

[0039] A zero point estimation of the intake oxygen sensor 168 may be performed under idle conditions where intake pressure fluctuations are minimal and when no PCV or purge air is admitted to the low-pressure intake system. Furthermore, idle adjustment may be performed periodically, such as at each initial idle after an engine start, to compensate for the effect of sensor aging and part-to-part variability on the sensor output.

[0040] Alternatively, intake oxygen sensor zero estimation can be performed under engine non-fueling conditions, such as during overrun fuel cut (SFC). Performing the adjustment under SFC conditions can reduce sensor reading fluctuations due to EGR valve leakage, in addition to reducing noise factors such as those achieved during idle adjustment.

[0041] Thus, the system of Fig. 1 provides a system for an engine comprising: a turbocharger having an intake compressor and an exhaust turbine, a low-pressure exhaust gas recirculation (low-pressure EGR) passage coupled between an exhaust passage downstream of the exhaust turbine and the intake passage upstream of the intake compressor, the low-pressure EGR passage including an EGR valve and a DPOV system for measuring EGR flow, an intake oxygen sensor disposed in an intake of the engine downstream of the low-pressure EGR passage, and a controller with computer-readable instructions for indicating flow area degradation of the EGR valve based on a difference between a first EGR flow estimate based on an output of the DP sensor and a second EGR flow estimate based on an output of the intake oxygen sensor during engine operation with scavenging disabled, boost disabled, and air mass below a threshold.The intake oxygen sensor may be further positioned in an intake manifold of the engine, and the computer-readable instructions further include instructions for setting a third EGR flow estimate, the third EGR flow estimate based on the output of the DP sensor during engine operation when purge is enabled and / or boost is enabled and / or the air mass is greater than the threshold, based on the difference between the first EGR flow estimate and the second EGR flow estimate.

[0042] Fig. 2 shows a flowchart of a method 200 for estimating EGR flow in a low-pressure EGR system using an intake oxygen sensor (for example, the one shown in Fig. 1 shown IAO2 168) and / or a DP sensor (for example the one shown in Fig. 1) of a DPOV system based on engine operating conditions. Instructions for performing method 200 may be stored in a memory of an engine controller, such as the memory of Fig. 1. Further, method 200 may be performed by the controller. The controller may estimate the EGR mass flow rate using a DP sensor that measures the pressure differential across the EGR valve and a valve position sensor (such as the EGR valve lift sensor 131). As previously explained, as soot accumulates on the EGR valve, the EGR mass flow rate estimate using the DPOV method described above may become increasingly inaccurate. Thus, under some conditions, an IAO2 sensor may be used to estimate EGR mass flow rate to provide an EGR mass flow rate estimate with increased accuracy. The IAO2 sensor may also be used to determine an estimate of soot accumulation on the EGR valve.Because the IAO2 sensor measurements may be subject to large errors under certain engine operating conditions (e.g., during boosted engine operation, with intake air mass above a threshold), the IAO2 sensor may not be usable at all times. Thus, method 200 further includes determining when to use the IAO2 sensor to estimate EGR mass flow. Furthermore, method 200 includes comparing an EGR flow estimate obtained from the IAO2 sensor with that from a DPOV system. This may provide an accurate EGR flow estimate from the DPOV system with improved accuracy of the DPOV system input of the EGR valve flow area.Method 200 begins at 202, and the controller (e.g., controller 12) estimates and / or measures engine operating conditions based on engine load, intake air mass, manifold pressure, a position of the EGR valve, a position of a purge valve, etc.

[0043] Method 200 proceeds to 204, where control determines whether EGR is enabled based on feedback from a position sensor (e.g., EGR valve lift sensor 131) about the position of the EGR valve. In another example, control may determine that EGR is enabled based on EGR flow being greater than zero. In this way, EGR flow may be enabled when EGR flows through the low-pressure EGR passage (e.g., EGR passage 197) from the exhaust port to the intake port. If control determines that the EGR valve is closed and EGR is disabled, then method 200 proceeds to 206, where control detects an intake air oxygen (IAO2) sensor (e.g., the one shown in Fig. 1) to measure intake air oxygen content. The IAO2 sensor is configured to apply a base reference voltage (V0) across a pumping electrode pair that pumps oxygen from or into an internal cavity and generates a pumping current that can be used to infer the oxygen content (i.e., the partial pressure of O2) in the intake airstream. In one embodiment, the IAO2 sensor may be a variable voltage (VVs) oxygen sensor. If control determines that EGR is enabled at 204, then control proceeds to 208 to determine whether scavenging and boosting are disabled.

[0044] At 208 and 214, control determines whether purge and boost are off and whether intake air mass is below a threshold to determine whether to use outputs from the IAO2 sensor or the DP and EGR valve position sensors to estimate EGR flow. At 208, control determines whether purge and boost are off. If the engine is not boosted, the IAO2 sensor may provide a more accurate estimate of EGR flow than the DP sensor using the DPOV method. However, if the EGR estimation is performed using outputs from the IAO2 sensor under conditions where fuel canister purge and / or crankcase ventilation is enabled (for example, PCV flow is enabled), an output from the IAO2 sensor may be corrupted by the additional hydrocarbons flowing to the sensor.Thus, the DP sensor can provide a more accurate estimate of EGR flow under boosted engine conditions. The IAO2 sensor output can be corrupted primarily under boosted conditions due to ingested hydrocarbons reacting with ambient oxygen at the intake sensor sensing element. This reduces the (local) oxygen concentration measured by the sensor. Since the sensor output and the change in oxygen concentration are used to infer EGR dilution of the intake air charge, the reduced oxygen concentration measured by the intake oxygen sensor in the presence of purge air and / or PCV may be erroneously interpreted as additional diluent.Thus, if control determines at 208 that either purge or boost is enabled, then method 200 proceeds to 210, and control estimates the EGR mass flow rate using the DPOV system, which includes a delta pressure (DP) sensor (e.g., delta pressure sensor 125) and a position sensor (e.g., EGR valve lift sensor 131). The EGR mass flow rate may be proportional to the cross-sectional area of ​​the EGR valve opening and the differential pressure across the EGR valve (as determined by the DP sensor). An estimate of the cross-sectional area (e.g., flow area) of the EGR valve opening may be calculated using the displacement of the EGR valve (e.g., valve lift) provided by the position sensor, a known flow area of ​​the EGR valve, and a valve lift correction factor.The known flow area of ​​the EGR valve is a standard cross-sectional area of ​​the valve perpendicular to the direction of EGR flow through the valve. The valve lift correction factor can increase the accuracy of the cross-sectional area estimate by accounting for thermal effects on EGR valve expansion. For example, this thermal compensation method may include using a specific difference between the EGR valve stem and body temperatures to estimate a change in the known (or expected) EGR valve flow area, as described below with reference to FIG. Fig. 5 and Fig. 6. The estimation of the cross-sectional area of ​​the EGR valve opening (e.g., the EGR valve passage area perpendicular to the flow direction through the valve), along with the estimated pressure differential across the EGR valve as provided by the DP sensor, may be used to estimate the EGR mass flow rate (also referred to herein as the DPOV method). After estimating the EGR mass flow rate, at 212, the controller then adjusts engine operation based on the estimated EGR mass flow rate. For example, if the estimated EGR mass flow rate is below a desired rate, the controller may command the EGR valve to open wider and allow more exhaust gases to be recirculated to the intake passage (e.g., to the common intake passage 149). The desired EGR rate may be determined by the controller based on engine operating conditions, such as engine load and engine speed.

[0045] If the controller determines at 208 that scavenging and boosting are off, then at 214 the controller determines whether the intake air mass is greater than a threshold based on feedback from a mass air flow sensor in the engine air intake passage. Estimating EGR flow based on the output of the IAO2 sensor may include multiplying the sensor output by an air mass-based factor to convert the output to an EGR flow or an EGR flow percentage. Thus, in one example, the threshold air mass may be based on an air mass at which an error in the EGR flow estimate using the IAO2 sensor increases beyond an acceptable amount (or increases beyond an error in estimating EGR flow using the DPOV method).When calculating the EGR mass estimate using the IAO2 sensor and mass flow, the EGR mass estimate is influenced by the accuracy of the air mass measurement. The relative air flow error in the EGR mass flow estimate can be smaller at lower air mass flows. The threshold air mass flow can be selected so that the air mass flow error is small compared to the EGR mass flow estimate.

[0046] If the intake air mass at 214 is below the threshold, then the IAO2 sensor may provide a more accurate estimate of the EGR mass flow than the DPOV system. Thus, control may proceed to 216 and estimate the EGR flow using the IAO2 sensor. As shown in Fig. 1, the intake oxygen sensor may apply a reference voltage that may produce an output in the form of a pumping current (Ip), which may be used to determine the oxygen concentration of the ambient gas in the common intake passage 149. The controller may then estimate an EGR concentration in the intake air based on a change in the intake oxygen concentration when the EGR valve is open and EGR (e.g., EGR valve 121) is on, versus a reference point where the EGR valve is closed and EGR is off. In other words, based on the change (e.g., decrease) in oxygen concentration determined when EGR is operating versus a time when EGR is not operating, the controller may estimate the EGR flow. Then, at 218, the controller may adjust engine operation based on the estimated EGR mass flow rate.For example, if the estimated EGR mass flow rate is less than a desired rate, the controller may open the EGR valve further and allow more exhaust gases to be recirculated to the intake passage (e.g., to the common intake passage 149). Furthermore, the controller may direct more exhaust gas through the EGR passage 197. The desired EGR rate may be determined by the controller based on engine operating conditions, such as engine load and engine speed.

[0047] Alternatively, if the intake air mass is above the threshold, EGR mass flow estimates using the IAO2 sensor may be compromised. As discussed above, the EGR mass flow estimation controller may convert the EGR concentration estimated by the IAO2 sensor into an EGR mass flow by multiplying the intake air mass flow by the ratio of EGR concentrations to intake air. In other words, the magnitude of errors in EGR flow estimation may be increased by multiplying by higher air mass values. Thus, EGR flow estimates become increasingly less accurate at larger air masses. If intake air mass amounts at 214 are above the threshold, then the EGR mass flow estimate using the DPOV method may be more accurate than using the IAO2 sensor.Thus, if control determines at 214 that the intake air mass is above the threshold, then control may estimate the EGR mass flow rate using the DPOV system at 210. Then, at 212, control may adjust engine operation based on the estimated EGR mass flow rate. For example, if the estimated EGR mass flow rate is below the desired rate, control may command the EGR valve to open wider and allow more exhaust gases to be recirculated to the intake passage (e.g., to the common intake passage 149). The desired rate may be adjusted based on engine operating parameters, such as engine load, engine temperature, etc., as shown in FIG. Fig. 1 described in more detail.

[0048] As described above, control may estimate the EGR mass flow rate using the IAO2 sensor as long as purge and boost are off and the intake air mass is below a threshold. Otherwise, the DPOV system may be used to estimate the EGR mass flow rate. Thus, in one example, under non-boosting engine conditions, the IAO2 may provide a more accurate estimate of the EGR mass flow rate than the DPOV system. After estimating the EGR mass flow rate using either the IAO2 sensor or the DPOV system, control may then adjust engine operation based on the estimated EGR flow rate at 218 or 212, respectively. In one embodiment, control may adjust engine operation by increasing or decreasing the amount of EGR by opening or closing the EGR valve to match the desired EGR flow rate.If the estimated EGR mass flow rate is less than the desired rate, the controller may command the EGR valve to open further to allow more EGR. On the other hand, if the estimated EGR is greater than the desired EGR, the controller may command the EGR valve to close further, thereby reducing EGR flow.

[0049] Referring again to method 200, after adjusting engine operation based on the estimated EGR flow using the IAO2 sensor at 218, control then proceeds to 220 and determines whether it is time to learn the EGR valve area. Learning the EGR valve area may be a method for increasing the accuracy of EGR mass flow estimates when it may not be desirable to use the IAO2 sensor, such as during boosted engine operating conditions, and the DPOV system may be used instead. As described in Fig. 3, valve area learning may include correcting an EGR valve flow area estimate by comparing two EGR flow estimates, one obtained from outputs of the IAO2 sensor and the other obtained from outputs of the DPOV system. Because valve area learning requires a measurement by the IAO2 sensor, it may only occur under non-boosted engine conditions, when purge is also disabled, and when the intake air mass is below a threshold. Controller may determine when valve area learning occurs based on preset time intervals between valve area learning instances. In one embodiment, the time interval between valve area learning instances may be a number of engine cycles.Thus, when a preset number of engine cycles have passed since the last EGR valve area learning operation, the controller may determine that it is time to initiate another valve area learning sequence. However, as noted above, valve area learning may only occur while the engine is operating under non-boosted conditions and the intake air mass is below a threshold. In another embodiment, the time interval between valve area learning operations may be a duration of engine usage. In another embodiment, the time interval may be a period of time.Thus, it is important to note that during engine operation, EGR valve area learning may occur multiple times, each operation generating a correction factor for estimating the effective flow area through the EGR valve, and each valve error correction may update a correction determined during a previous valve area learning operation.

[0050] If control determines it is time to learn the EGR valve area (e.g., the EGR valve flow area), then method 200 proceeds to 224, and control estimates the EGR mass flow rate using the DPOV system (through the DPOV method described above) and compares it to the EGR flow rate estimate obtained from the IAO2 sensor. The difference between the two estimates may be used to correct expected EGR valve flow area estimates (based on the EGR valve lift sensor and any other lift corrections) and to indicate an amount of soot accumulation on the EGR valve, as described below with reference to Fig. 3. In particular, EGR flow estimates obtained using the IAO2 sensor may be lower than EGR flow estimates obtained using the DPOV system due to soot accumulation on the EGR valve. The soot may block portions of the EGR valve opening and reduce the effective flow area through the valve. The reduced flow area may result in lower EGR mass flow rates at the common intake port 149, where the oxygen sensor may be located. The difference between the two EGR mass flow estimates may then be used by the controller to determine a corrected EGR valve flow area. For a further description of how the controller determines the corrected EGR valve flow area, see Fig. 3. If the difference between the two EGR mass flow estimates is greater than a threshold, the controller may indicate that soot has accumulated on the EGR valve.

[0051] If control determines at 220 that a preset time interval has not been reached since the last valve area learning operation, then control continues at 222 engine operation without performing EGR valve offset learning. Then, a correction factor for the flow area through the EGR valve from a previous valve offset learning operation may be used for engine control when using the DPOV method to determine EGR flow.

[0052] Method 200 may further include a method for an engine that includes indicating soot accumulation at an exhaust gas recirculation (EGR) valve based on a difference in EGR flow estimated under a first condition when the engine is not boosted using an intake oxygen sensor and a pressure sensor coupled across the EGR valve. The difference in EGR flow is a difference between a first EGR flow estimated based on an output of the intake oxygen sensor under the first condition and a second EGR flow estimated using the pressure sensor across the EGR valve under the first condition, wherein the pressure sensor is a differential pressure over valve (DPOV) (DP sensor).The method may further include estimating the second EGR flow based on an output of the DP sensor and a flow area of ​​the EGR valve, wherein the flow area of ​​the EGR valve is estimated based on a known cross-section of the EGR valve and an EGR valve position based on an output of an EGR valve position sensor. The first condition further includes purge being disabled and air mass to the engine being below a threshold. Thus, when the engine is not boosted, purge being disabled, and air mass to the engine being below a threshold, method 200 further includes adjusting engine operation based on the estimated EGR flow associated with the intake oxygen sensor and not the pressure sensor coupled via the EGR valve.Further, the method 200 includes determining a change in EGR valve flow area based on the difference in EGR flow, an expected EGR valve flow area, and a first EGR flow estimated with the intake oxygen sensor under the first condition, wherein the expected EGR valve flow area is based on an output of an EGR valve position sensor and an EGR valve lift correction, wherein the EGR valve lift correction is learned during an EGR valve end stop and thermal compensation learning routine.

[0053] An indication of soot accumulation at the EGR valve may be obtained based on the change in the effective EGR valve flow area. Method 200 may include indicating soot accumulation at the EGR valve based on the change in the EGR valve flow area increasing above the threshold. In another example, the method may further include indicating soot accumulation at the EGR valve based on a rate of change in the EGR valve flow area increasing above a threshold rate.

[0054] Further, method 200 may include determining a corrected EGR valve flow area based on the determined change in EGR valve flow area and the expected EGR valve flow area, and under a second condition where EGR flow is estimated using the DP sensor, estimating the EGR flow based on the output of the DP sensor and the corrected EGR valve flow area. The second condition includes at least one of the engine being boosted, purge being enabled, and / or the engine air mass being greater than a threshold.

[0055] Now on Fig. 3, a method 300 for indicating soot accumulation at an EGR valve and determining a corrected EGR valve flow area is shown. Instructions for performing method 300 may be stored in a memory of an engine controller, such as the memory shown in Fig. 1. Furthermore, the method 300 can be executed by the controller.

[0056] Method 300 may continue from step 224 in method 200. Thus, method 300 begins at 302 where control estimates the EGR mass flow rate using the IAO2 sensor and the EGR valve DPOV system. As described above with reference to Fig. 2, the controller may calculate the EGR mass flow (e.g., the EGR flow or flow percentage) by comparing the intake oxygen concentrations estimated by the oxygen sensor when the EGR valve is open and EGR is enabled (e.g., EGR valve 121 is enabled) to a reference point where the EGR valve is closed and EGR is disabled. The controller may estimate the EGR mass flow using the DPOV system based on estimates of the pressure differential across the EGR valve and the flow area through the valve opening. A DP sensor may provide the pressure differential across the EGR valve. A position sensor coupled to the EGR valve may provide the displacement (e.g., lift) of the EGR valve.The flow area through the EGR valve may then be estimated based on the position of the EGR valve, a known flow area of ​​the valve, and a compensation (e.g., correction) based on the expansion and / or contraction of the EGR valve due to thermal effects (e.g., due to a temperature differential between the EGR valve stem and body), as described below with reference to FIG. Fig. 5 and Fig. 6 is described in more detail.

[0057] After the controller estimates the EGR mass flow at 302 using the IAO2 sensor and the DPOV system, it then adjusts the DPOV EGR estimate for a delay to the IAO2 sensor location at 304. In other words, the delay may be a measurement delay due to the different locations of the IAO2 sensor and the EGR valve relative to each other. As shown in Fig. 2, the DPOV EGR flow estimate may differ from the EGR flow estimate by the IAO2 sensor. This difference may be caused, at least in part, by the IAO2 sensor and the DPOV system measuring different exhaust gases, or it could be the result of a systematic error in one of the measurement systems. If soot accumulation on the EGR valve reduces the effective flow area of ​​the EGR valve, the DPOV system may systematically overestimate EGR flow. One goal of method 300 is to estimate a systematic error in the DPOV measurement system and learn a valve area correction factor that can be used to provide more accurate estimates of the EGR valve flow area and, therefore, EGR flow estimates.To assess the accuracy of the DPOV system by comparing its EGR mass flow estimate with that of the IAO2 sensor, it is important that the IAO2 sensor and the DPOV system measure the same exhaust gases at the same time. As shown in . Fig. 1, exhaust gas must travel a distance from the EGR passage 197 to the common intake passage 149. Thus, it takes time for exhaust gas leaving the EGR valve in the EGR passage to reach the IAO2 sensor located in the common intake passage. Measuring the same exhaust gases at both the EGR valve and the IAO2 sensor may require a time delay adjustment of the DPOV and / or IAO2 EGR estimates. Thus, control may delay the DPOV flow estimate to the IAO2 EGR estimate to account for the time it takes for exhaust gas to flow from the EGR valve to the intake oxygen sensor. In this way, the resulting EGR flow estimates from the DPOV sensor (of the DPOV system) and the IAO2 sensor may reflect an EGR flow estimate for the same EGR gas.

[0058] As an example, the controller may take simultaneous measurements from both the DPOV system and the IAO2 sensor. In one embodiment, the controller may then apply a preset time delay correction factor to the IAO2 sensor measurement. The delay correction factor may be based on an estimated time for exhaust gases to flow from the EGR valve to the common intake port, which may be based on airflow rates. In another embodiment, the controller may apply a preset time delay correction factor to the DPOV system measurement. The delay correction factor may be based on an estimated time for exhaust gases to flow from the EGR valve to the common intake port, which may be based on airflow rates. For example, during transient operation, the EGR valve and the delta pressure across the EGR valve (DP) change.The EGR mass flow calculated for a given event must be compared with the EGR mass flow measured by the IAO2 sensor. To be able to compare the same EGR flows, the DPOV measurement of the EGR flow is delayed by the time it takes for the EGR measurement in question to reach the IAO2 sensor.

[0059] In another example, control may delay the EGR flow estimate using the IAO2 sensor from the DPOV system EGR flow estimate. In other words, the EGR measurement at the IAO2 sensor may occur at a time shortly after the DP and position sensor measurements at the EGR valve. The EGR flow estimate made by the IAO2 sensor may be slightly delayed to account for the time it takes for exhaust gases to flow from the EGR valve to the intake exhaust gas sensor. Thus, control may determine two EGR mass flow rate estimates that are separated in time but based on measurements of the same exhaust gases. The exact time between the two measurements may be determined by control based on intake air flow, pressure (boost pressure), and temperature. Thus, at faster flows, the duration of the delay between the two measurements may be shorter than at slower flows.

[0060] In another example, control may record multiple measurements from both the DPOV system and the IAO2 sensor over a period of EGR operation under non-boosted engine conditions. Then, control may determine the amount of time it takes for exhaust gases to flow from the EGR valve to the intake oxygen sensor based on the estimated air flow. Next, control may determine which measurements taken by the DPOV system and the IAO2 sensor correspond to the same measured exhaust gases. For a given DPOV measurement, control may first determine the time the measurement was taken, add the time it takes for exhaust gases to flow to the intake oxygen sensor, and then determine which IAO2 sensor measurement occurred at the later time. Control may then use these two measurements to obtain two estimates of EGR mass flow.

[0061] Continuing to 306, control may determine an EGR flow error based on the difference between the IAO2 and DPOV EGR flow estimates. An assumption in step 306 may be that the EGR flow estimate indicated by the IAO2 sensor is more accurate than the flow indicated by the DPOV system. Thus, the IAO2 EGR flow estimate is treated as the actual estimated EGR flow. As discussed above, this is a reasonable assumption under non-boosted engine conditions when intake air flows are below a threshold flow. The EGR flow estimate obtained from the DPOV system may have lower accuracy due to soot accumulation on the EGR valve. In this case, the EGR flow estimate obtained from the IAO2 sensor may be less than that obtained from the DPOV system. The EGR flow error would be the IAO2 EGR flow estimate subtracted from the DPOV EGR flow estimate.After estimating the EGR flow error, at 310, the controller determines the change in EGR valve flow area based on the EGR flow error. The controller may divide the EGR flow error by the IAO2 EGR flow estimate, resulting in a percentage error in the DPOV EGR flow estimate. Then, multiplying the percentage error in the DPOV EGR flow estimate by the EGR valve flow area (e.g., an expected or known EGR valve flow area) may result in an estimate of the change in EGR valve flow area due to soot accumulation. The EGR valve flow area may be the same EGR valve flow area estimate used in the DPOV EGR flow calculation. In another embodiment, the controller may estimate the EGR valve flow area after making the EGR flow estimate.Based on the change in EGR valve flow area, the controller may then determine the corrected EGR valve flow area at 312. The corrected EGR valve flow area may be the difference between the estimated flow area obtained from the EGR valve position sensor (e.g., the EGR valve lift sensor) and the estimated change in valve flow area. As shown in FIG. Fig. As explained in Figure 2, soot accumulation at the EGR valve can reduce the valve's flow area and cause the EGR flow estimated by the IAO2 sensor to be lower than that estimated by the DPOV system. Thus, the change in the valve's flow area can be directly related to the amount of soot accumulation at the EGR valve and can be used to indicate the amount of soot at the EGR valve.

[0062] After learning the EGR valve area at 312, method 300 then proceeds to 314, and control uses the corrected EGR valve flow area for subsequent DPOV EGR flow estimates and adjusts the EGR based on the corrected EGR flow estimate. If control uses the corrected EGR valve flow area to estimate EGR flow, and that flow is different from the desired flow, then control may adjust engine operation to adjust the EGR flow to the desired rate. If the EGR flow is less than the desired rate, then in one example, control may command the EGR valve to open wider and allow more exhaust gases to be recirculated to the intake passage. Additionally, control may increase the amount of exhaust gases entering the EGR passage 197.The desired flow rate may be based on engine operating parameters, such as engine load, engine speed, engine temperature, exhaust gas temperature, etc., as measured by multiple engine sensors. Thus, when the controller uses outputs from the DPOV system to estimate EGR flow, it may use the corrected EGR valve flow area. As shown in . Fig. 2, control may continuously update the corrected EGR valve flow area based on new EGR flow estimates based on measurements from the IAO2 sensor. As engine operation continues, soot accumulation at the EGR valve continues. If soot has accumulated to a sufficient extent, the DPOV EGR flow accuracy will also continue to decrease. The difference between the desired EGR flow and the actual EGR flow may also be greater at higher soot levels due to the inaccuracy of EGR flow estimates. At 316, control determines whether the EGR valve flow area error is greater than a threshold. In one example, the EGR valve flow area error may be a difference between the actual EGR valve flow area (based on the EGR valve position sensor output) and the corrected EGR valve flow area.In another example, the EGR valve flow area error may be based on the EGR flow error. If the controller determines that the EGR valve error is greater than the threshold, then it proceeds to 320 to indicate EGR valve degradation and / or initiate a valve cleaning routine.

[0063] In one embodiment, the threshold EGR valve error may be based on the difference between the EGR valve area error and the last determined EGR valve area error. As in Fig. 2, the controller may continuously update the EGR valve area error based on new estimates of EGR flow from the IAO2 sensor. Thus, if the EGR valve area error is greater than the last determined EGR valve area error by more than a threshold value, the controller may indicate EGR valve degradation and / or initiate a valve cleaning routine. In another embodiment, the threshold EGR valve error may be based on the difference between the EGR valve area error and a raw estimate of the EGR valve flow area based solely on the EGR valve position and a known area of ​​the valve without using EGR valve flow error correction. The raw estimate of the EGR valve flow area may be an initial estimate of the valve flow area made prior to any soot accumulation and valve area learning.The controller may archive the raw estimate for the duration of engine operation. The raw estimate may also be generated each time the DPOV system is used to estimate the valve area, and then the EGR valve flow error correction may be applied thereafter. In other words, the area may first be determined by the EGR valve position and a known area of ​​the valve. Then, the EGR valve error may be applied to correct the area estimate. The controller may compare the EGR valve area estimate before the valve error correction with the EGR valve area estimate after the valve area error correction. If the difference between the two valve area estimates is greater than a threshold, then the controller may continue to 320.The threshold may also be considered a threshold amount of soot accumulation at the EGR valve, as the change in EGR valve area may be directly related to soot accumulation at the EGR valve. In another embodiment, the threshold may be based on the rate of change in the EGR valve area estimate. If the rate of change in the valve passage area, as estimated by the EGR error, increases above a threshold, then control may proceed to 320.

[0064] At 320, the controller may indicate EGR valve degradation. The indication may be provided to the user via a user feedback display, such as an instrument panel light switch. Additionally, or alternatively, the controller may initiate a valve cleaning routine that may be used to reduce the amount of soot at the EGR valve. In yet another example, indicating EGR valve degradation may include setting a diagnostic code.

[0065] If control determines at 316 that the EGR valve area error is not greater than a threshold, then control continues to 318 and continues EGR valve operation without indicating EGR valve degradation and / or initiating a valve cleaning routine.

[0066] Method 300 includes estimating a change in EGR valve flow area due to soot accumulation. In one example, the determined change in EGR flow area may be used to correct the EGR flow estimated using the DPOV method. Further, the method may include indicating EGR valve degradation and / or initiating an EGR valve cleaning routine when soot accumulation has reached a threshold, as determined based on an EGR valve area error, a change in EGR valve flow area, and / or a rate of change of the EGR valve flow area and / or the EGR flow error.

[0067] Fig. 3 includes a method for an engine, comprising: under selected conditions, comparing a first exhaust gas recirculation (EGR) flow estimated based on an intake oxygen sensor output with a second EGR flow estimated based on a pressure differential across an EGR valve, and indicating soot deposition at the EGR valve based on the comparison. Comparing the first EGR flow with the second EGR flow includes learning an EGR valve flow area error based on a difference between the first EGR flow and the second EGR flow. Indicating soot accumulation at the EGR valve includes indicating degradation of the EGR valve due to soot based on the learned flow area error increasing above a threshold.Further, during subsequent engine operation, when EGR flow is estimated based on the pressure differential across the EGR valve, the method may include adjusting the EGR flow estimate based on the learned flow area error. The pressure differential across the EGR valve may be measured by a differential pressure over valve (DP) sensor coupled across the EGR valve. Indicating soot accumulation at the EGR valve includes setting a diagnostic code and / or initiating an EGR valve cleaning routine and / or alerting a vehicle operator that the EGR valve is degraded and requires service. The selected conditions may include the engine not being boosted, purge being disabled, and air mass being less than a threshold.Indicating soot deposits includes initiating a cleaning routine and / or warning a vehicle operator that the EGR valve is compromised and / or setting a diagnostic code.

[0068] Determining the adjusted valve flow area is further based on a second change in flow area due to EGR valve soot accumulation. The method may include determining the second change in flow area based on a difference in EGR flow estimated using an intake oxygen sensor and a pressure sensor coupled via the EGR valve under a first condition when the engine is not boosted. Determining the second change in flow area is further based on an expected EGR valve flow area and a first EGR flow estimated using the intake oxygen sensor under the first condition, wherein the expected EGR valve flow area is based on an output of an EGR valve position sensor and an EGR valve lift correction, wherein the EGR valve lift correction is learned during an EGR valve end stop and thermal compensation learning routine.The method may further include indicating soot accumulation at the EGR valve based on the second passage area change increasing above the threshold.

[0069] Now on Fig. 4, a graph is shown illustrating how EGR flow may be estimated under varying engine conditions. In particular, a graph 400 shows changes in EGR flow measured at plot 402 by an EGR valve DPOV system and at curve 404 by an IAO2 sensor. Furthermore, the graph 400 shows an EGR valve flow error at curve 406, an estimated soot deposit amount on an EGR valve at 408, an intake air mass flow at curve 410, a boosted condition of the engine at curve 412, and a purge condition at curve 414. The EGR valve flow error is essentially the difference between the EGR flow estimates from the DPOV system and the IAO2 sensor, as in the method in Fig. 3. Thus, the EGR valve flow error is the error in the DPOV EGR flow estimation based on the difference between the EGR flow estimates from the IAO2 sensor and the DPOV system. Soot deposition can be derived from the EGR flow error, as described by the method in Fig. 3. In particular, the EGR flow error may be used to estimate an EGR flow area error because the EGR flow error may be caused by a change in the EGR valve flow area due to soot accumulation. The EGR flow area error may then be used to infer a soot accumulation amount. Intake air mass may be measured by a mass air flow sensor. The operating status of boost and purge may be regulated by a controller (e.g., controller 12). Thus, the controller may determine purge levels based on the position of a purge valve in the purge passage (e.g., in fuel vapor purge line 195). The controller may determine boost levels by the operating status of the turbines, compressors, or commands sent to the turbocharger.

[0070] As mentioned above with reference to the Fig. 2 and Fig. 3, both a DPOV system and an IAO2 sensor can be used to estimate the EGR mass flow in a turbocharged engine. Both the DPOV system and the IAO2 sensor can fail due to sensor errors under conditions such as boost, scavenging, etc., as described in Fig. 2, can only be used to estimate EGR mass flow estimates under certain operating conditions. Thus, EGR flow estimates from the DPOV system and the IAO2 sensor may have different levels of accuracy depending on the engine operating conditions. For example, when the intake air mass is above a threshold, the DPOV system may provide more accurate EGR flow estimates than the IAO2 sensor. However, under non-boosted engine operating conditions, when purge is disabled and when the intake air mass is below a threshold, the IAO2 sensor measurements may provide more accurate EGR mass flow estimates than the DPOV system. The controller may determine whether the EGR flow estimate from the DPOV system or the IAO2 sensor is more accurate based on the engine operating conditions.In another embodiment, control may use a combination of the EGR flow estimates to estimate EGR flow. Thus, if control determines that purge and boost are disabled and intake air mass is below a threshold, control may use EGR estimates by the IAO2 sensor to correct and increase the accuracy of EGR flow estimates by the DPOV system. By utilizing IAO2 measurements when the engine is operating under select operating conditions (e.g., non-boost, purge deactivated, low intake air mass conditions), EGR mass flow estimates may be improved under all vehicle operating conditions.This is particularly useful because, as soot accumulation at the EGR valve increases, EGR flow estimates by the DPOV system can become increasingly inaccurate due to the reduction in the valve passage area caused by the soot. By using the IAO2 sensor as a reference point, the EGR rate estimates by the DPOV system can be corrected to account for the reduced EGR valve passage area due to soot accumulation. If soot accumulation reaches a critical threshold, a valve cleaning routine can be initiated, or an indication of soot deposition can be reported to the vehicle operator.

[0071] Starting before time t1, boost is on (plot 412) (e.g., the engine is being boosted), while scavenging is off (plot 414) and the intake air mass is below a threshold T1 (plot 410). Because boost is on, no EGR flow estimates are made by the IAO2 sensor (plot 404), as seen by the absence of plot 404 before time t1. The EGR valve flow error may be at a first level E1 (plot 406). The first level E1 may be an EGR valve flow error estimated from a previous valve area learning event. The soot deposition may be at a first level S1 corresponding to the EGR valve flow area error level E1. At time t1, boosting is switched off, but intake air mass peaks occur above the threshold T1.Thus, the controller continues to use the DPOV system to estimate EGR mass flow without considering the outputs from the IAO2 sensor. Since measurements from the IAO2 sensor are not being taken, no new valve area learning can occur, and thus no new estimates of EGR valve flow error or soot deposition can occur. Thus, the EGR valve flow area error and soot deposition remain the same before and after t1 at levels E1 and S1, respectively.

[0072] At time t2, purge is enabled, and the intake air mass falls below threshold T1. The IAO2 sensor measurements continue to be ignored by the controller, and thus the EGR valve flow error and soot deposition estimates remain unchanged. At time t3, the intake air mass rises above threshold T1, and boost is enabled. Purge also remains enabled. The controller continues to ignore IAO2 sensor measurements, and the soot deposition estimate remains at the first level S1, and the EGR valve flow area error remains at E1. It is important to note that the three engine operating parameters (intake air mass, boost, and purge) can be at or above a threshold in any combination.However, as long as either boost or purge is on, or the intake air mass is above T1, the IAO2 sensor measurements continue to be unused by the controller, and the soot deposition and EGR valve flow error estimates remain unchanged.

[0073] At time t4, the intake air mass falls below threshold T1, and both purge and boost are turned off. Thus, at time t4, the controller may estimate the EGR flow using the output of the IAO2 sensor (at curve 404). At this time, EGR mass flow estimates are obtained from both the IAO2 sensor and the DPOV system. The controller may compare the two EGR flow estimates and estimate an EGR valve flow error, as in the method in Fig. 3. Since the IAO2 sensor may not have been used to estimate EGR flow prior to time t4, an amount of soot may have accumulated on the EGR valve, as seen at the peak in curve 408 from the first level S1 to a higher, second level S2. The soot deposition may cause inaccuracies in the EGR flow estimates, particularly in the estimation of the EGR valve flow area, by the DPOV system. Accordingly, at curve 406, the EGR valve flow error at time t4 increases from a first error E1 to a higher, second error E2.

[0074] From time t4 to time t5, boost and scavenging remain off, and the intake air mass remains below T1. EGR mass flow estimates based on the IAO2 sensor output continue to be performed during this time, but they may differ from the DPOV EGR mass flow estimates. This may be due to soot accumulation at the EGR valve increasing from time t4 to time t5. Thus, as soot accumulation at the EGR valve increases, the difference between the EGR mass flow estimates between the DPOV system and the IAO2 sensor may increase. As can be seen in curves 406 and 408 from time t4 to time t5, soot accumulation steadily increases, as does the EGR valve flow error. Then, at time t5, the controller corrects the EGR valve area estimate, as in the method in Fig. 3. Due to the correction, the EGR mass flow estimated by the DPOV system becomes more accurate and more closely approximates the estimate obtained from the IAO2 sensor. Thus, at time t5, the EGR valve flow error decreases from a higher level E4 to a lower level similar to E1. Meanwhile, soot deposition continues to increase. Although soot deposition continues to increase, at time t5, the controller uses the IAO2 sensor measurements as a reference point to correct the EGR valve flow estimates using the DPOV system. In particular, the controller may use the difference between the EGR flow estimates by the IAO2 sensor and the DPOV system to derive an error in the EGR valve flow area estimates.Since the EGR valve flow area is used to estimate the DPOV system EGR flow, errors in the EGR valve flow area due to soot accumulation can cause errors in the DPOV system EGR flow estimates. Thus, differences between EGR flow estimates by the IAO2 sensor and the DPOV system can be attributed to errors in the EGR valve flow area estimates due to soot accumulation on the EGR valve. Accordingly, the EGR valve flow error can be used to derive an EGR valve flow area error. By accounting for changes in the EGR valve flow area due to soot accumulation on the EGR valve, the accuracy of the DPOV EGR flow estimates can be increased.

[0075] Moving forward in time to time t6, the intake air mass increases above threshold T1. As seen in curve 404, at time t6, the controller no longer uses output from the IAO2 sensor for EGR flow estimates. The DPOV system continues to take measurements (curve 402), and the controller uses the corrected EGR valve flow area estimated from the EGR flow error at time t5 to estimate the EGR mass flow. Thus, the EGR valve flow error remains constant past time t6 because no new IAO2 sensor measurements are used for comparison to the DPOV system estimates. Likewise, soot may continue to accumulate on the EGR valve past time t6, but without accurate IAO2 measurements, the controller may not be able to measure and / or estimate soot levels. Thus, soot levels estimated by the control system, as can be seen in curve 408, remain constant after time t6.

[0076] At time t7, the intake air mass decreases below threshold T1 while boost and scavenging remain off. Thus, the controller may estimate EGR flow based on outputs from the IAO2 sensor at time t7. The EGR mass flow estimates from the IAO2 sensor may be lower than the estimates from the DPOV system. Accordingly, the EGR valve flow error increases from a similar level to E1 to a higher level E3 due to the disparity between the two EGR mass flow estimates. Controller-estimated soot accumulation increases from a lower level S3 to a higher level S4 due to the difference between the EGR flow estimates from the IAO2 sensor and the DPOV sensor.From time t7 to time t8, the EGR mass flow estimates from the DPOV system and the IAO2 sensor diverge due to increased soot accumulation on the EGR valve and thus a higher error in the EGR valve area estimate from the DPOV system. The EGR valve flow error steadily increases until the controller corrects the EGR valve area estimate at time t8, as in the procedure in . Fig. 3, just as it did at time t5. With the EGR valve area corrected, the EGR mass flow estimate by the DPOV system more closely matches the IAO2 sensor estimate. The EGR valve flow error decreases to a lower level similar to that of E1. Meanwhile, soot accumulation continues to increase. Thus, at time t5 and time t8, control initiates valve area learning and corrects the EGR valve area estimate from the DPOV system so that the EGR mass flow estimate from the DPOV system more closely matches the estimate from the IAO2 sensor.

[0077] Further at time t9, the soot accumulation reaches a threshold value T2. As in the procedure in Fig. 3, the controller may indicate to a vehicle operator at time t9 that the EGR valve is degraded, or it may initiate a valve cleaning routine in response to soot accumulation reaching threshold T2. If the controller indicates to a vehicle operator that the EGR valve is degraded, soot accumulation may continue to increase past time t9. However, if the controller initiates a valve cleaning routine, soot may be removed from the EGR valve, and soot levels may decrease to a lower level S5, similar to that of S1. Past time t9, the intake air mass remains below threshold T1, and boost and scavenging remain off. Thus, IAO2 sensor measurements continue to be used to estimate EGR mass flow, and soot accumulates at the EGR valve.Accordingly, the EGR valve flow error increases, and the EGR mass flow estimates from the DPOV system and IAO2 sensor may differ from each other.

[0078] Graph 400 illustrates how the controller may estimate EGR mass flow rates depending on engine operating conditions. In one embodiment, the controller may estimate EGR mass flow using the DPOV system alone when the intake air mass is above a threshold and / or boost is enabled and / or purge is enabled. Under conditions where the intake air mass is below a threshold, boost is off, and purge is disabled, the controller may use the IAO2 sensor to estimate EGR mass flow due to the increased accuracy of the IAO2 sensor under these conditions.

[0079] In other embodiments, the controller may estimate EGR flow using both the IAO2 sensor and the EGR valve DPOV system; however, the controller may then decide which estimate to use based on a relative accuracy of each measurement, where the relative accuracy is based on engine operating conditions, such as boost level, purge level, and / or air mass. The controller may compare the EGR mass flow estimates by the DPOV system with those by the IAO2 sensor to assess an error magnitude in the EGR flow estimates by the DPOV system. The controller may then correct the EGR flow estimates by the DPOV system based on the IAO2 sensor estimates. The error in the EGR mass flow estimates by the DPOV system may increase during engine use because soot may accumulate on the EGR valve.Soot accumulation can affect EGR valve flow area estimates and thus EGR flow estimates. By using the IAO2 sensor measurements as a comparison reference, the EGR mass flow estimates can be corrected by the DPOV system by accounting for the reduced EGR valve flow area resulting from soot accumulation. When soot accumulation reaches a threshold soot level, the controller can further signal that the EGR valve has been compromised and / or initiate a valve cleaning routine to remove soot from the EGR valve.

[0080] Now on Fig. 5, a method 500 is provided for learning changes in EGR valve flow area due to changes in a temperature difference between an EGR valve stem and body. As the temperature difference between the body and stem of the EGR valve increases, the flow area of ​​the EGR valve may change due to thermal expansion or contraction, thereby increasing the error in the EGR valve flow area and thus in the resulting EGR flow estimate using the DPOV method. More accurate estimates of the EGR valve flow area may increase the accuracy of EGR flow estimates using the DPOV system. Thus, the method 500 may provide a means for more accurate EGR flow estimation using the DPOV system. As previously discussed with the Fig. 2 and Fig. 3, the DPOV system may estimate an EGR flow based on a pressure differential across the EGR valve (e.g., EGR valve 121) and a flow area through the EGR valve. The EGR valve flow area may be estimated based on the position of the EGR valve (as determined by a lift sensor) and a known flow area of ​​the valve. Method 500 provides a correction factor for estimating the EGR valve flow area based on thermal expansion of the EGR valve. Instructions for performing method 500 may be stored in a memory of an engine controller, such as the memory described in Fig. 1. Furthermore, the method 500 can be executed by the controller.

[0081] Method 500 begins at 502, where the controller estimates and / or measures engine operating parameters. Engine operating parameters may be estimated based on feedback from multiple sensors and may include: engine temperature, engine speed and load, intake air mass, manifold pressure, etc.

[0082] Control then proceeds to 504 and determines whether it is time for EGR valve thermal compensation learning. Valve thermal compensation learning may include estimating a change in EGR valve flow area based on a change in the temperature difference between a stem and a body of the EGR valve, as described further below. Control may determine the timing of thermal compensation learning based on how much time has passed since the last thermal compensation learning event. Thus, control may initiate valve thermal compensation learning when a preset amount of time has passed since the last thermal compensation learning event. The preset amount of time may be a number of engine cycles, an engine usage period, or a period of time.Thus, if the preset amount of time has not passed since the last thermal compensation learning event, then control may determine that thermal compensation is not required and may proceed to 506. At 506, control may use a previously determined EGR valve area correction from a previous thermal compensation learning event for DPOV EGR estimates. This previously determined EGR valve area correction may then be used in the methods of . Fig. 2-3 can be used to more accurately estimate EGR flow using the DPOV method.

[0083] If the preset amount of time has passed since the last heat compensation learn event, then the controller may determine that it is time for heat compensation learning and proceed to 508. At 508, the controller estimates the temperature difference between the stem and body of the EGR valve based on the EGR temperature. Specifically, the temperature difference between the stem and body of the EGR valve may be stored in the controller's memory as a function of the EGR temperature. The relationship between the EGR valve stem and body temperature difference and the EGR temperature may be based on factory testing. The EGR temperature may be estimated by a temperature sensor (e.g., EGR temperature sensor 135) either upstream or downstream of the EGR valve. The temperature registered by the temperature sensor may be adjusted depending on the position of the temperature sensor relative to the EGR valve.Exhaust gas may cool as it flows through an exhaust passage (e.g., EGR passage 197), and thus the temperature registered by a sensor downstream of the EGR valve may be lower than the actual temperature of the exhaust gas as it passes through the EGR valve. Conversely, an upstream temperature sensor may register an exhaust gas temperature that is higher than the temperature at the EGR valve. The extent of the exhaust gas temperature change from the position of the EGR valve to the temperature sensor may be predetermined by factory testing and based on EGR flow. Thus, the exhaust gas temperature registered by the temperature sensor may be modified to represent the exhaust gas temperature at the EGR valve.When estimating EGR temperature, the controller can estimate the temperature difference between the EGR valve stem and body using a known relationship between the EGR temperature and the EGR valve stem and body temperature difference. The resulting temperature difference can then be modified based on EGR flow. In this way, the temperature difference between the EGR valve stem and body can be based on EGR temperature and EGR flow.

[0084] Then, at 510, the controller may determine the temperature difference between the EGR valve stem and body in an EGR valve closed position ( Δ T ESL ), which is essentially the same EGR temperature used to determine the Δ T vlvat 508. Specifically, at 508, the difference between the stem and body temperature of the EGR valve at a current EGR temperature is determined. Whenever the EGR valve closes (e.g., closes completely so that no EGR flows through the EGR passage), the controller may store the temperature difference between the stem and body of the EGR valve as a function of the EGR temperature, as described further below with reference to Fig. 6. Therefore, the control can have a body and shaft temperature difference that corresponds to the same EGR temperature at which Δ T vlv estimated at 508, retrieve (for example, look up).

[0085] Method 500 may then proceed to 512, and control may determine the change in EGR valve flow area based on the difference between Δ T vlv and Δ T ESLand a thermal expansion coefficient. In particular, the controller can determine the difference between T vlv and Δ T ESL Multiply by a coefficient of thermal expansion to obtain an estimate of the change in the EGR valve passage area. In one example, the coefficient of thermal expansion may be predetermined based on the type of material the EGR valve is made of.

[0086] After determining the change in EGR valve flow area, control may continue to 514 and determine a corrected EGR valve flow area for use in subsequent DPOV EGR flow estimations. Thus, the corrected EGR valve flow area may be determined based on the change in EGR valve flow area. As previously described in Fig. 2, the EGR valve flow area can be determined using the EGR valve position (as determined by an EGR valve lift sensor) and a known EGR valve flow area. However, due to thermal expansion of the EGR valve, the EGR valve flow area may differ from the flow area determined using the EGR valve position and known area. Thus, by utilizing the change in valve flow area due to thermal expansion of the EGR valve, the accuracy of the EGR valve flow area estimation can be increased and can more closely match the actual flow area through the EGR valve and thus the effective EGR flow through the valve. Therefore, when determining the EGR valve passage area, the control system can take into account both the effects of thermal expansion of the valve and the extent of soot accumulation on the valve.Thus, the controller may estimate a first EGR valve area correction factor based on the thermal expansion of the EGR valve. Furthermore, the controller may determine a second EGR valve area correction factor based on soot deposition on the EGR valve. By incorporating the two EGR valve area correction factors, the controller may determine an overall EGR valve flow area correction factor. Thus, the accuracy of the EGR valve area estimates may be increased and may subsequently be used to provide more accurate DPOV EGR flow estimates, as previously described in [ ]. Fig. 2. In particular, the EGR valve area estimate and the pressure differential across the EGR valve, as measured by the DP sensor, can be used to derive an EGR rate.

[0087] In this way, a method for an engine may include adjusting an exhaust gas recirculation (EGR) valve based on an estimate of EGR flow, wherein the EGR flow is based on a pressure differential across the EGR valve and an adjusted valve flow area, wherein the adjusted valve flow area is based on a first temperature difference between a stem and a body of the EGR valve. The pressure differential across the EGR valve may be estimated using a pressure sensor across the EGR valve, wherein the pressure sensor is a differential pressure-over-valve (DP) sensor, and wherein the adjusted valve flow area is further based on a known cross-section of the EGR valve and an EGR valve position, wherein the EGR valve position is measured using an EGR valve position sensor (such as a lift sensor).The adjusted valve flow area is adjusted based on a known flow area of ​​the EGR valve and an output of an EGR valve position sensor. The method may further comprise determining the adjusted valve flow area based on a first change in the flow area based on the first temperature difference between the stem and the body of the EGR valve and a thermal expansion coefficient of the EGR valve. The method may further comprise: during each EGR valve closing event, determining a second temperature difference between the stem and the body of the EGR valve in an EGR valve closed position; and storing the determined second temperature difference in the EGR valve closed position in a memory of a controller.The first change in the passage area is further based on a difference between the first temperature difference between the stem and the body of the EGR valve and the second temperature difference between the stem and the body of the EGR valve in the EGR valve closed position. The method may further include estimating the first temperature difference based on a temperature and a flow rate of EGR gas flowing through the EGR valve.

[0088] In another example, a method for an engine may further include determining an EGR valve lift correction based on a change in a temperature difference of a stem and a body of the EGR valve between the open and closed valves, wherein the temperature difference of the stem and the body of the EGR valve is based on an EGR temperature measured proximate the EGR valve and EGR flow.

[0089] In another example, a method for an engine includes estimating an exhaust gas recirculation (EGR) flow based on a pressure differential across an EGR valve and a total valve flow area, learning a first valve flow area correction factor based on a first temperature differential between a stem and a body of the EGR valve, and adjusting the total valve flow area based on the first learned valve flow area correction factor. Learning the first valve flow area correction factor includes storing the learned first valve flow area correction factor in a memory of a controller and repeating the learning of the first valve flow area correction factor after a duration, wherein the duration includes a duration of engine operation and / or a number of engine cycles.Learning the first valve passage area correction factor includes estimating the first temperature difference between the stem and the body of the EGR valve based on EGR flow and a temperature of the exhaust gas flowing through the EGR valve. Learning the first valve passage area correction factor includes estimating the first temperature difference between the stem and the body of the EGR valve based on EGR flow and a temperature of the exhaust gas flowing through the EGR valve. Learning the first valve passage area correction factor includes multiplying the difference between the first temperature difference and the second temperature difference by a thermal expansion coefficient of the EGR valve, wherein the thermal expansion coefficient is a thermal expansion coefficient of one valve lift per degree of temperature difference between the stem and the body of the EGR valve.The method for an engine further includes learning a second valve flow correction factor based on a difference between a first EGR flow estimated based on an intake oxygen sensor output and a second EGR flow estimated based on the pressure differential across the EGR valve during engine operation with purge disabled, boost disabled, and mass flow below a threshold, and further includes adjusting the total valve flow area based on the first learned valve flow correction factor and the second valve flow correction factor. Estimating EGR flow includes estimating EGR flow based on the pressure differential across the EGR valve and the total valve flow area under a first condition where engine purge and / or boost are enabled and intake air mass is above a threshold.The method further includes estimating the EGR flow based on an output of an intake oxygen sensor and not the pressure differential across the EGR valve under a second condition where engine purge and boost are off and the intake air mass is below the threshold.

[0090] In another example, a system for an engine includes: a turbocharger having an intake compressor and an exhaust turbine, a low-pressure exhaust gas recirculation (low-pressure EGR) passage coupled between an exhaust passage downstream of the exhaust turbine and the intake passage upstream of the intake compressor, the low-pressure EGR passage including an EGR valve and a DP sensor for estimating EGR flow, an intake oxygen sensor disposed in an intake of the engine downstream of the low-pressure EGR passage, and a controller with computer-readable instructions for adjusting the EGR valve based on the EGR flow estimated based on an output of the DP sensor and an adjusted valve flow area,wherein the adjusted valve flow area is based on a first temperature difference between a stem and a body of the EGR valve and a second temperature difference between the stem and the body of the EGR valve at a closed position of the EGR valve. Furthermore, the intake oxygen sensor is positioned in an intake manifold of the engine, wherein the adjusted valve flow area is further based on a difference between a first EGR flow estimated from an output of the DP sensor and a second EGR flow estimated from an output of the intake oxygen sensor when the engine is operating with boost and purge disabled and the air mass below a threshold. Furthermore, the engine system may include a temperature sensor positioned near the EGR valve in the low-pressure EGR passage, wherein the first and second temperature differences are based on an output of the temperature sensor and the EGR flow.

[0091] Now on Fig. 6, a method 600 is shown for estimating the temperature difference between the EGR valve stem and body in a valve closed position (referred to herein, for example, as end-stop learning). The method 600 provides a means for estimating a temperature difference between the EGR valve stem and body when the EGR valve is closed ( ΔT ESL ) is available. As previously with the procedure of Fig. 5, can thus ( ΔT ESL ) to improve the accuracy of the estimated change in EGR valve flow area due to thermal expansion of the EGR valve.

[0092] Method 600 begins at 602, and the controller estimates and / or measures engine operating conditions. Engine operating parameters may be estimated based on feedback from multiple sensors and may include engine temperature, engine speed and load, intake air mass, manifold pressure, EGR valve position, etc.

[0093] Based on the engine operating conditions, control may then determine whether the EGR valve is closing at 604. In particular, control may determine whether the EGR valve is closing based on the position of the EGR valve provided by a position sensor (e.g., EGR valve lift sensor 131). In one embodiment, control may continuously monitor the EGR valve, so it may proceed to 608 at each valve closing event. If control determines that the valve is not closing, then control may proceed to 606. In another embodiment, control may not proceed to 608 at each valve closing event; instead, control may proceed to 608 only if the EGR valve closes and a duration has elapsed. Otherwise, control may proceed to 606. The duration may be a number of valve closing events, a time interval, a number of engine cycles, etc.Thus, even if control detects that the valve is closing, control may instead proceed to 606 if the duration has not elapsed. At 606, the EGR valve position may be modulated based on a desired EGR flow determined by engine operating parameters (e.g., engine temperature, exhaust gas temperature, intake air mass, etc.).

[0094] However, if the EGR valve closes at 604 and the duration has elapsed, then the controller may determine the temperature difference between the EGR valve stem and body based on the EGR temperature provided by a temperature sensor (e.g., EGR temperature sensor 135). For example, the controller may look up the temperature difference between the EGR valve stem and body as a function of EGR temperature and / or EGR flow and then use the temperature difference as ΔT ESLWhen the EGR valve closes, the calculated delta temperature is used as the value to be saved ΔT ESL After determining ΔT ESL At 608, control can go to 610 and the parameters determined at 608 ΔT ESL and EGR temperature values ​​in the controller memory (for example, in a lookup table). This allows access to the values ​​stored in the controller ΔT ESL - Values ​​are accessed to use them with ΔT VLV -works to determine a thermal expansion correction for EGR valve passage area estimates, as in the method of Fig. 5 described.

[0095] In this way, a method may include estimating EGR flow based on outputs from a DPOV system and an intake oxygen sensor. Both the DPOV system, including a delta pressure (DP) sensor and an EGR valve position sensor, and an intake oxygen sensor may be used to output separate EGR mass flow estimates. Under engine operating conditions where purge is disabled, boost is off, and intake air mass is below a threshold, the intake oxygen sensor may be used to output an EGR mass flow estimate.The EGR mass air flow estimate determined from the intake oxygen sensor output may then be compared to an EGR flow estimate based on outputs from the DPOV system to determine a soot deposit amount at the EGR valve, thereby providing an EGR mass air flow estimate with increased accuracy. The DPOV system may estimate the EGR mass flow based on the pressure differential across the valve measured by the DP sensor and the EGR valve opening area (for EGR flow). The EGR valve opening area may be estimated based on the valve position provided by a position sensor (for example, the EGR valve lift sensor), a known valve flow area, and a thermal expansion correction factor that accounts for valve expansion under a current EGR temperature.The flow area (e.g., the opening for the EGR flow) of the valve can change depending on the temperature difference between the stem and the valve body. Thus, the area of ​​the EGR valve opening can be modified based on a change between the temperature difference between the stem and the EGR valve body when the EGR valve is closed and open, and a thermal expansion coefficient.

[0096] In this way, the technical impact of determining a corrected EGR flow area based on soot accumulation at the EGR valve (as determined by comparing EGR flow estimates from the intake oxygen sensor and the DPOV system) and thermal expansion or contraction of the EGR valve (as determined by the temperature difference between the stem and body of the EGR valve) is to determine a more accurate EGR flow estimate to increase the accuracy of EGR control and additional engine control. Furthermore, the extent of soot deposition at an EGR valve can be estimated and used to initiate a valve cleaning routine or trigger a signal to a vehicle operator when the soot level reaches a threshold.By using the EGR flow rate based on the oxygen sensor as a reference point, EGR flow estimates by the DPOV system can be more accurate by accounting for the reduced flow area caused by soot deposition on the EGR valve. A further technical impact is achieved by adjusting the EGR flow rate based on a temperature difference between the EGR valve stem and body when the valve is open and closed. The valve opening can change depending on the temperature difference between the stem and body of the valve. Thus, the area of ​​the EGR valve opening can be modified based on a change between the temperature difference between the EGR valve stem and body when the EGR valve is closed and open, and a thermal expansion coefficient.The EGR flow can then be adjusted to more closely match a target EGR flow so that engine efficiency can be increased.

[0097] In another embodiment, a method for an engine includes, under selected conditions, comparing a first exhaust gas recirculation (EGR) flow estimated based on an output of an intake oxygen sensor with a second EGR flow estimated based on a pressure differential across an EGR valve; and indicating soot deposition on the EGR valve based on the comparison.

[0098] In yet another embodiment, a method for an engine includes, under selected conditions, learning an EGR valve flow area error based on a difference between EGR flow estimates via an intake oxygen sensor and a DPOV (DP) sensor coupled across the EGR valve; and indicating EGR valve degradation due to soot based on the learned flow area. Further, during subsequent engine operation when EGR is estimated with a DP sensor, the method includes adjusting the DPOV EGR estimate based on the learned flow area error.

[0099] It should be noted that the exemplary control and estimation routines included herein may be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-volatile memory and may be performed by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The particular routines described herein may represent one or more of a number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Thus, various illustrated acts, operations, and / or functions may be performed in the order illustrated, in parallel, or in some cases, omitted.Likewise, the order of processing is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but 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. Furthermore, the described acts, operations, and / or functions may graphically represent code to be programmed into the non-volatile 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.

[0100] It is understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be interpreted in a limiting sense, as numerous variations are possible. For example, the above technology may be applied to V-6, I-4, I-6, V-12, horizontally opposed four, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and / or characteristics disclosed herein.

[0101] The following claims particularly point out 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 should be construed as encompassing the inclusion of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by presenting new claims in this or a related application. Such claims, whether their scope is broader, narrower, the same, or different with respect to the original claims, are also considered to be included within the subject matter of the present disclosure.

Claims

[1] A method for an engine (10) comprising: Adjusting an exhaust gas recirculation valve (EGR valve, 121) based on an estimate of the EGR flow, wherein the EGR flow is estimated based on a pressure difference across the EGR valve (121) and an adjusted valve passage area, wherein the adjusted valve passage area is based on a first temperature difference between a stem and a body of the EGR valve (121). [2] The method of claim 1, wherein the pressure differential across the EGR valve (121) is estimated with a pressure sensor (172) across the EGR valve (121), wherein the pressure sensor (172) is a differential pressure over valve (DP) sensor, and wherein the adjusted valve passage area is further based on a known cross-section of the EGR valve (121) and an EGR valve position, wherein the EGR valve position is measured with an EGR valve position sensor. [3] The method of claim 1, wherein the adjusted valve flow area is adjusted based on a known flow area of ​​the EGR valve and an output of an EGR valve position sensor, and further comprising determining the adjusted valve flow area based on a first change in the flow area based on the first temperature difference between the stem and the body of the EGR valve (121) and a thermal expansion coefficient of the EGR valve (121). [4] The method of claim 3, further comprising, at each closing event of the EGR valve (121), determining a second temperature difference between the stem and the body of the EGR valve (121) in an EGR valve closed position and storing the determined second temperature difference in the EGR valve closed position in a memory of a controller (12), and wherein the first change in the passage area is further based on a difference between the first temperature difference between the stem and the body of the EGR valve (121) and the second temperature difference between the stem and the body of the EGR valve (121) in the EGR valve closed position. [5] The method of claim 3, further comprising estimating the first temperature difference based on a temperature and a flow rate of EGR gas flowing through the EGR valve (121). [6] The method of claim 3, wherein determining the adjusted valve passage area is further based on a second change in passage area due to EGR valve soot accumulation, and further comprising determining the second change in passage area based on a difference in estimated EGR flow under a first condition when the engine (10) is not boosted, with an intake oxygen sensor (168) and with a pressure sensor (172) coupled across the EGR valve (121). [7] The method of claim 6, wherein determining the second change in flow area is further based on an expected EGR valve flow area and a first EGR flow estimated under the first condition with the intake oxygen sensor (168), the expected EGR valve flow area being based on an output of an EGR valve position sensor and an EGR valve lift correction, the EGR valve lift correction being learned during an EGR valve end stop and heat compensation learning routine. [8] The method of claim 6, further comprising indicating soot accumulation at the EGR valve (121) based on the second change in flow area increasing above the threshold. [9] Method for an engine (10), comprising: Estimating an exhaust gas recirculation (EGR) flow based on a pressure difference across an EGR valve and a total valve passage area, the latter consisting of at least a first valve passage area and at least a second valve passage area; Learning a first valve passage area correction factor based on a first temperature difference between a stem and a body of the EGR valve (121); and Adjust the total valve passage area based on the first learned valve passage area correction factor. [10] The method of claim 9, wherein learning the first valve passage area correction factor comprises storing the learned first valve passage area correction factor in a memory of a controller (12) and repeating the learning of the first valve passage area correction factor after a duration, wherein the duration comprises a duration of engine operation and / or a number of engine cycles. [11] The method of claim 9, wherein learning the first valve passage area correction factor comprises estimating the first temperature difference between the stem and the body of the EGR valve (121) based on EGR flow and a temperature of the exhaust gas flowing through the EGR valve (121). [12] The method of claim 9, wherein learning the first valve passage area correction factor comprises determining a difference between the first temperature difference between the stem and the body of the EGR valve (121) and a second temperature difference between the stem and the body of the EGR valve (121) in an EGR valve closing position, the second temperature difference in the EGR valve closing position being learned at each EGR valve closing event. [13] The method of claim 12, wherein learning the first valve passage area correction factor comprises multiplying the difference between the first temperature difference and the second temperature difference by a thermal expansion coefficient of the EGR valve (121), wherein the thermal expansion coefficient is a thermal expansion coefficient of one valve lift per degree of temperature difference between the stem and the body of the EGR valve. [14] The method of claim 9, further comprising learning a second valve passage area correction factor based on a difference between a first EGR flow estimated based on an output of an intake oxygen sensor (168) and a second EGR flow estimated based on the pressure differential across the EGR valve (121) during engine operation with purge disabled, boost disabled, and mass flow below a threshold. [15] The method of claim 14, further comprising adjusting the total valve passage area based on the first learned valve passage area correction factor and the second valve passage area correction factor. [16] The method of claim 9, wherein estimating EGR flow comprises estimating EGR flow based on the pressure differential across the EGR valve (121) and the total valve flow area under a first condition where engine purge and / or boost is / are enabled and intake air mass is above a threshold. [17] The method of claim 16, further comprising estimating the EGR flow based on an output of an intake oxygen sensor and not the pressure differential across the EGR valve (121) under a second condition where engine purge and boost are off and the intake air mass is below the threshold. [18] System for an engine (10), comprising: a turbocharger (120, 130) with an intake compressor and an exhaust turbine (124, 134); a low-pressure exhaust gas recirculation (LOW-PRESSURE EGR) passage coupled between an outlet passage (17, 19) downstream of the exhaust turbine (124) and the inlet passage (140, 142, 144, 146, 148, 149) upstream of the intake compressor, the low-pressure EGR passage including an EGR valve (121) and a differential pressure over valve (DP) sensor for measuring EGR flow; an intake oxygen sensor (168) disposed in an inlet of the engine (10) downstream of the low-pressure EGR passage; and a controller (12) having computer-readable instructions for adjusting the EGR valve (121) based on the EGR flow estimated based on an output of the DP sensor and an adjusted valve flow area, wherein the adjusted valve flow area is based on a first temperature difference between a stem and a body of the EGR valve (121) and a second temperature difference between the stem and the body of the EGR valve (121) in a closed position of the EGR valve (121). [19] The system of claim 18, wherein the intake oxygen sensor (168) is further positioned in an intake manifold of the engine (10), and wherein the adjusted valve flow area is further based on a difference between a first EGR flow estimate based on an output of the DP sensor and a second EGR flow estimate based on an output of the intake oxygen sensor during engine operation when boost and scavenging are disabled and air mass is below a threshold. [20] The system of claim 18, further comprising a temperature sensor positioned proximate the EGR valve (121) in the low-pressure EGR passage, and wherein the first and second temperature differences are based on an output of the temperature sensor and EGR flow.

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