Method for open loop and closed loop control of an exhaust gas recirculation system

Abstract

Method for an engine (10), comprising: Estimating an exhaust gas recirculation (EGR) mass flow rate based on a differential pressure sensor output when an engine load is below a threshold; Estimating the EGR mass flow rate based on an intake carbon dioxide sensor output when the engine load is above the threshold, and independent of the differential pressure sensor output; and Setting an ignition timing based on the estimated EGR mass flow rate.

Description

Area

[0001] The present description generally relates to methods and systems for controlling an exhaust gas recirculation system of a vehicle engine. Background / Summary

[0002] Engine control systems utilize exhaust gas recirculation (EGR) mechanisms to control exhaust emissions and improve fuel economy. EGR mechanisms may include an EGR system that recirculates a portion of the exhaust gas from the exhaust passage to the intake passage via an EGR passage. The EGR systems utilize a delta pressure (DP) sensor at an orifice located downstream of an EGR valve in the EGR passage to provide an estimate of EGR mass flow. The estimated EGR mass flow is then used to determine a degree of pre-ignition.

[0003] However, under certain engine operating conditions, such as high-load conditions and / or when manifold absolute pressure (MAP) is greater than a threshold pressure, differential pressure at the port is modulated due to pulsating exhaust gas flow. Therefore, the DP sensor may output a higher voltage due to the root mean square of the exhaust gas pulsations. In other words, exhaust pulsation may cause the DP sensor to output a higher voltage than the actual voltage. Therefore, EGR mass flow may be estimated higher than the actual flow during high-load conditions. Since spark advance is based on the estimated EGR mass flow, typically one degree of spark advance for each percent of estimated EGR, an overestimation of EGR mass, for example, can lead to potential ignition knock (due to excessively advanced spark timing).Therefore, it may be necessary to retard the ignition timing to reduce knocking, which can result in reduced fuel economy and reduced power.

[0004] DE 10 2014 105 274 A1 discloses systems for estimating exhaust gas recirculation mass and air mass during steady-state and transient operating conditions. DE 10 2004 016 936 A1 discloses a system for testing exhaust gas recirculation operation in an internal combustion engine.

[0005] The inventors have recognized the above-mentioned problems. Accordingly, in one example, some of the above problems may be at least partially addressed by a method for an engine comprising: estimating an exhaust gas recirculation (EGR) mass flow rate based on a differential pressure sensor output when an engine load is below a threshold; estimating the EGR mass flow rate based on an intake carbon dioxide sensor output when the engine load is above the threshold and independent of the differential pressure sensor output; and adjusting spark timing based on the estimated EGR mass flow rate. In this way, more accurate EGR flow rate estimates may be made at various load conditions. Consequently, more accurate spark advance may be scheduled, reducing the likelihood of spark knock.

[0006] As one example, the EGR system may be operated in an open-loop control mode during certain engine operating conditions, such as when an engine load is above a threshold load and / or when a MAP is above a threshold pressure. In the open-loop control mode, the EGR mass flow rate is estimated independently of the DP sensor output, but rather based on feedforward-mapping intake carbon dioxide data based on engine speed and load; and a degree of spark advance is scheduled based on the EGR mass flow rate estimated based on carbon dioxide levels in the intake. Further, during the open-loop mode, an EGR valve is not controlled based on the DP sensor output, but rather is maintained in a fully open position or a near-fully open position based on the threshold load.

[0007] During engine operating conditions below the threshold, the EGR system may operate in a closed-loop control mode. In the closed-loop control mode, the EGR mass flow rate is estimated based on the DP sensor output, and the degree of pre-ignition is scheduled based on the DP sensor-based EGR mass flow rate estimate. Furthermore, during the closed-loop control mode, the EGR valve is controlled based on the DP sensor output. For example, the EGR valve is adjusted based on a deviation between an actual DP sensor output and a desired DP sensor output.

[0008] In this way, by switching between open-loop and closed-loop control of the EGR system, more accurate EGR flow estimations can be performed. Consequently, more accurate ignition advance can be scheduled, which can lead to reduced ignition knock. This can reduce undue ignition retardation, resulting in improved fuel economy and improved power performance. Therefore, by using open-loop control and closed-loop control of the EGR system based on boost and intake manifold pressure, the technical effects of more accurate EGR flow estimation, more accurate ignition advance, and reduced ignition knock can be achieved, and thus, fuel economy can be improved.

[0009] It should be understood that the above summary is provided to introduce, in simplified form, a selection of concepts further described in the detailed description. It is not intended to identify critical or essential features of the claimed subject matter, the scope of which is defined solely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any disadvantages noted above or in any part of the present disclosure. Short description of the drawings Fig. Figure 1 shows a schematic diagram of a twin-turbocharged engine system incorporating a high-pressure EGR system. Fig. Figure 2 shows an example speed-load map illustrating open and closed loop EGR control modes. Fig. 3 shows an example control block diagram illustrating example open loop and closed loop EGR control. Fig. 4 shows a flowchart illustrating an example method for switching between closed loop and open loop EGR control modes. Fig. 5 shows a flowchart illustrating an example method for closed loop EGR control. Fig. 6 illustrates an exemplary EGR system operation according to the present disclosure. Detailed description

[0010] The following description relates to systems and methods for open loop and closed loop control of an EGR system in an engine system (such as the engine system of Fig. 1) based on boost and / or intake manifold pressure to improve EGR mass flow estimation in areas with high exhaust pulsations. Specifically, the EGR system can be Fig. 2, the EGR system may operate in a closed-loop feedback mode at engine operating conditions below a threshold load, and when the engine is operating at loads above the threshold load, the EGR system may operate in an open-loop feedforward mode. In some examples, the EGR system may additionally or alternatively operate in the closed-loop feedback mode when a manifold absolute pressure (MAP) is below a threshold pressure, and when the MAP is above the threshold pressure, the EGR system may operate in the closed-loop feedforward mode. An example of the open-loop feedforward mode and the closed-loop feedback mode is shown in a block diagram in Fig. 3. A control system, such as the control of Fig. 1, may be configured to perform a control routine, such as the exemplary routine of Fig. 4 for switching the EGR system operation between open loop and closed loop modes and the example routine of Fig. 5 for operating the EGR system in the closed loop mode. An exemplary open and closed loop control of the EGR system according to the present disclosure is shown in Fig. 6 shown.

[0011] Referring to Fig. 1 shows a schematic representation of an exemplary turbocharged engine system 100 including a multi-cylinder internal combustion engine 10 and twin 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 herein, other engine configurations, such as an engine with a single turbocharger or an engine without a turbocharger, may be used without departing from the scope of the present disclosure.

[0012] The engine system 100 may be controlled at least in part by a controller 12 and by inputs 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, keep-alive 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 anticipated but not specifically listed.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 (various examples of which are described herein). Additional actuators, such as a plurality of 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 commands or code programmed therein that correspond to one or more routines. In other words, the controller 12 receives signals from the various sensors from. Fig. 1, including the DP sensor 217, the intake carbon dioxide sensor 220, the manifold air pressure (MAP) sensor 182 and the intake oxygen sensor 168, and utilizes the various actuators of Fig. 1, such as an engine actuator for the high-pressure EGR valve 210, ignition timing, etc., to adjust engine operation based on the received signals and commands stored in a memory of the controller. Example control routines are described herein with respect to the Fig. 3 to 5.

[0013] The engine system 100 may receive intake air via an intake passage 140. As shown in Fig. 1, the intake passage 140 may include an air filter 156 and an air intake 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.

[0014] 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, as indicated 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, as indicated at 144. Accordingly, the engine system 100 includes a low-pressure AIS (LP AIS) system 191 upstream of the compressors 122 and 132 and a high-pressure AIS (HP AIS) system 193 downstream of the compressors 122 and 132.

[0015] A forced crankcase ventilation (PCV) line 198 may connect a crankcase (not shown) to the second intake passage branch 144 such that gases in the crankcase are vented from the crankcase in a controlled manner. Furthermore, evaporative emissions from a fuel vapor tank (not shown) may be vented into the intake passage through a fuel vapor purge line 195 for connecting the fuel vapor tank to the second intake passage branch 144.

[0016] The first portion of the total intake air may be compressed via a compressor 122, where it may be provided to the intake manifold 160 via an intake air passage 146. Therefore, the intake passages 142 and 146 form a first branch of the engine's air intake system. Likewise, a second portion of the total intake air may be compressed via the compressor 132, where it may be provided to the intake manifold 160 via an intake air passage 148. Therefore, the intake passages 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 combined via a common intake passage 149 before reaching intake manifold 160, where the intake air may be provided to the engine. In some examples, intake manifold 160 may include an intake manifold pressure sensor 182 for estimating manifold pressure (MAP) and / or an intake manifold temperature sensor 183 for estimating manifold air temperature (MCT), both of which communicate with controller 12. In the depicted example, intake passage 149 also includes an air cooler 154 and a throttle 158. The position of throttle 158 may be adjusted by the control system via a throttle actuator 157 communicatively coupled to controller 12. As shown, the throttle 158 may be disposed in the intake passage 149 downstream of the air cooler 154 and may be configured to adjust the flow of an intake gas stream entering the engine 10.

[0017] As in Fig. 1, a compressor bypass valve (CBV) 152 may be disposed in a CBV 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 (EPCBVs). The CBVs 152 and 155 may be controlled to allow the release of pressure in the intake system when the engine is boosted. An upstream end of the CBV passage 150 may be coupled to the intake passage 144 upstream of the compressor 132, and a downstream end of the CBV passage 150 may be coupled to the intake passage 148 downstream of the compressor 132. Likewise, an upstream end of the CBV passage 151 may be coupled to the intake passage 142 upstream of the compressor 122, and a downstream end of the CBV passage 151 may be coupled to the intake passage 146 downstream of the compressor 122.Depending on the position of each CBV, air compressed by the corresponding compressor can be recirculated into the intake passage upstream of the compressor (e.g., intake passage 144 for compressor 132 and intake passage 142 for compressor 122). For example, CBV 152 can open to recirculate compressed air upstream of compressor 132, and / or CBV 155 can open to recirculate compressed air upstream of compressor 122 to release pressure into the intake system during selected conditions to reduce the effects of compressor surge loading. CBVs 155 and 152 can be controlled either actively or passively by the control system.

[0018] As illustrated, a compressor inlet pressure (CIP) sensor 196 is disposed in the intake passage 142, and an HP AIS pressure sensor 169 is disposed in the intake passage 149. However, in further anticipated embodiments, the sensors 196 and 169 may be disposed at other locations within the LP AIS and HP AIS, respectively.

[0019] The engine 10 may include a plurality of cylinders 14. In the depicted example, the engine 10 includes six cylinders arranged in a V-configuration. Specifically, the six cylinders are arranged on two banks 13 and 15, with each bank including three cylinders. In alternative 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 alternative configurations, such as a V, inline, horizontally opposed, etc. Each cylinder 14 may be configured with a fuel injector 166. In the depicted example, the fuel injector 166 is a direct in-cylinder fuel injector. However, in further examples, the fuel injector 166 may be configured as a port fuel injector.

[0020] Intake air provided to each cylinder 14 (also referred to herein as combustion chamber 14) via a common intake passage 149 may be used for fuel combustion, and combustion products may then be exhausted via bank-specific exhaust passages. In the illustrated example, a first bank 13 of cylinders of engine 10 may exhaust combustion products via a common exhaust passage 17, and a second bank 15 of cylinders may exhaust combustion products via a common exhaust passage 19.

[0021] The position of intake and exhaust valves of each cylinder 14 may be controlled via hydraulically actuated lifters coupled to valve tappets or via mechanical pistons using cam plates. In this example, at least the intake valves of each cylinder 14 may be controlled by cam actuation using a cam actuation system. Specifically, the intake valve cam actuation system 25 may include one or more cams and may use variable cam timing or 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.

[0022] Combustion products expelled by the engine 10 via the exhaust passage 17 may be directed through an exhaust turbine 124 of the turbocharger 120, which in turn may provide mechanical work to the compressor 122 via a shaft 126 to provide compression to the intake air. Alternatively, some or all of the exhaust gases flowing through the exhaust passage 17 may bypass the turbine 124 via a turbine bypass passage 123 controlled by a wastegate 128. The position of the wastegate 128 may be controlled by an actuator (not shown) commanded by the controller 12. As a non-limiting example, the controller 12 may adjust the position of the wastegate 128 via a pneumatic actuator controlled by a solenoid valve.For example, the solenoid valve may receive a signal to facilitate actuation of the wastegate 128 via the pneumatic actuator based on the difference in air pressure between the intake passage 142 located upstream of the compressor 122 and the intake passage 149 located downstream of the compressor 122. In further examples, other suitable approaches besides a solenoid valve may be used to actuate the wastegate 128.

[0023] Likewise, combustion products expelled from the engine 10 via the exhaust passage 19 may be directed through the exhaust turbine 134 of the turbocharger 130, which in turn may provide mechanical work to the compressor 132 via the shaft 136 to provide compression to the intake air flowing through the second branch of the engine intake system. Alternatively, some or all of the exhaust gases flowing through the exhaust passage 19 may bypass the turbine 134 via a turbine bypass passage 133 controlled by the wastegate 138. The position of the wastegate 138 may be controlled by an actuator (not shown) commanded by the controller 12. As a non-limiting example, the controller 12 may adjust the position of the wastegate 138 via a solenoid valve controlling a pneumatic actuator.For example, the solenoid valve may receive a signal to facilitate actuation of the wastegate 138 via the pneumatic actuator based on the difference in air pressure between the intake passage 144 located upstream of the compressor 132 and the intake passage 149 located downstream of the compressor 132. In further examples, other suitable approaches besides a solenoid valve may be used to actuate the wastegate 138.

[0024] In some examples, exhaust turbines 124 and 134 may be configured as variable geometry turbines, wherein controller 12 may adjust the position of the turbine impeller blades (or vanes) to vary the amount of energy obtained from the exhaust stream and transferred to their respective compressor. Alternatively, exhaust turbines 124 and 134 may be configured as variable nozzle turbines, wherein controller 12 may adjust the position of the turbine nozzle to vary the amount of energy obtained from the exhaust stream and transferred 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.Combustion products expelled by the cylinders via exhaust passage 19 may be directed to the atmosphere via an exhaust passage 180 downstream of the turbine 134, while combustion products expelled via exhaust passage 17 may be directed to the atmosphere via an exhaust passage 170 downstream of the turbine 124. The exhaust passages 170 and 180 may include one or more exhaust aftertreatment devices, such as a catalyst, and one or more exhaust gas sensors. For example, the exhaust passage 170 may be configured as shown in FIG. Fig. 1, an emissions control device 129 located downstream of the turbine 124, and the exhaust passage 180 may include an emissions control device 127 located downstream of the turbine 134. The emissions control devices 127 and 129 may be selective catalytic reduction (SCR) devices, three-way catalysts (TWC), NOx traps, various other emissions control devices, or combinations thereof. Further, in some embodiments, the emissions 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 within a particular air / fuel ratio.

[0025] The engine system 100 may further 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 loops (not shown) for providing low-pressure EGR (LP EGR).

[0026] In the illustrated example, engine system 100 may include an HP-EGR system 206. In the illustrated example, engine system 100 may be equipped with an HP-EGR system on only one bank of the V-engine. HP-EGR system 206 routes a desired portion of exhaust gas from common exhaust passage 17 upstream of turbine 124 to intake manifold 160 downstream of intake throttle 158. Alternatively, HP-EGR system 206 may be disposed between exhaust passage 17 and intake passage 193 downstream of compressor 122. The amount of HP-EGR provided to intake manifold 160 may be varied by controller 12 via EGR valve 210 coupled within HP-EGR passage 208. For example, the controller 12 may adjust a position of the EGR valve 210 by providing a control signal (e.g.an electrical signal (such as voltage or current) to an EGR valve actuator, such as a motor, which may be a DC motor, to provide a desired amount of EGR HP. In the embodiment shown in . Fig. 1, the HP-EGR system 206 includes an EGR cooler 212 located upstream of the EGR valve 210. The EGR cooler 212 may reject heat from the recirculated exhaust gas, for example, to the engine coolant.

[0027] Further, a differential pressure (DP) sensor 217 may be disposed within the EGR passage. The DP sensor 217 may provide an indication of pressure and / or temperature and / or concentration of the exhaust gas. In one example, an output of the DP sensor 217 may be used with an output of the MAP sensor 182 to estimate an EGR mass flow rate. For example, the DP sensor 217 may detect a pressure drop across an EGR flow control orifice 219 located downstream of the EGR valve 210, which, in combination with the MAP, may provide an indication of the amount of EGR. As such, the DP sensor 217 may provide the controller 12 with a differential pressure signal DP at the EGR orifice. In some examples, sensor 217 may include a manifold absolute pressure (MAP) sensing element and a differential pressure (DP) sensing element, as well as a manifold temperature sensing element.In some examples, the flow control orifice 219 may be located upstream of the EGR valve 210 or downstream of the EGR valve 210 as shown. In some examples, an additional sensor may sense EGR valve position to sense EGR valve flow area changes based on commands from the controller 12, thus providing feedback control for valve position control.

[0028] The engine system 100 may also include a second high-pressure EGR loop (not shown) for recirculating at least a portion of the exhaust gas from the exhaust passage 19 upstream of the turbine 134 to the intake passage 148 downstream of the compressor 132 or to the intake manifold 160 downstream of the intake throttle 158. EGR flow through the HP EGR loop 208 may be controlled via the HP EGR valve 210.

[0029] The EGR valve 210 may be configured to adjust an amount and / or rate of exhaust gas diverted through the respective EGR passages to achieve a desired EGR dilution percentage of the intake charge entering the engine. As a specific example, during engine operation at lower load conditions below a threshold load, the EGR valve 210 may be controlled based on a feedback control mechanism to achieve a desired EGR mass flow rate. For example, when the engine load is below the threshold, an output from the DP sensor 217 may be used to estimate an actual EGR mass flow rate (i.e., EGR mass flow rate at a given time). Based on engine operating conditions (e.g., engine speed and engine load), a desired EGR mass flow rate may be determined.The engine controller may then determine a deviation between the actual and desired EGR mass flow rates and adjust the EGR valve 210 based on the deviation. Further, a degree of spark advance may be scheduled based on the actual EGR mass flow rate determined based on the DP sensor output. In some examples, a deviation between an actual (or measured) DP sensor output and a desired DP sensor output may be used by the controller to adjust the EGR valve 210.

[0030] In this way, during operation at loads below the threshold load, feedback from the DP sensor can be used to control the EGR valve to provide a desired EGR mass flow rate. In other words, the EGR system operates in a closed-loop mode with feedback from the DP sensor during engine operation below the threshold load.

[0031] However, during operation at higher loads above the threshold load, pulsating exhaust flow may cause the DP sensor to indicate a higher EGR mass flow rate than the actual EGR mass flow rate. For example, due to the root mean square of the exhaust pulsations, the DP sensor may output a higher voltage than the actual voltage. Consequently, the DP sensor may indicate a higher EGR mass flow rate than the actual EGR mass flow rate. Therefore, to improve the accuracy of the EGR flow estimation when the engine is operating at higher loads above the threshold, the actual EGR mass flow rate at a given time may be determined independently of the DP sensor output, but rather derived from an output of an intake carbon dioxide sensor 220.For example, a map correlating intake carbon dioxide levels with EGR percentage at various speed and load conditions may be stored within a controller's memory. EGR mass flow may then be determined based on the intake carbon dioxide concentration measured by the intake carbon dioxide sensor and the engine airflow measured by a MAF sensor. The degree of pre-ignition is then determined based on the EGR flow estimated from the intake carbon dioxide sensor.

[0032] Furthermore, during engine operation at loads above the threshold, due to exhaust pulsation corrupting the DP sensor output discussed above, the engine controller may not adjust the EGR valve based on the DP sensor output, but rather an open loop control mechanism of the EGR system may be used. That is, the EGR valve may be maintained at an open loop position when the engine is operating above the threshold load, and the actual EGR mass flow rate is estimated based on the intake carbon dioxide sensor. In one example, the open loop position may be a fully open position of the EGR valve 210. In another example, the open loop position may be based on the threshold load. For example, at the threshold load, the controller may adjust the EGR valve to a threshold load position to provide a desired EGR flow rate.Then, as long as the load remains at or above the threshold load, the EGR valve can be held at the threshold load position and the actual EGR mass flow rate can be estimated based on the mapped intake carbon dioxide values.

[0033] In some examples, the threshold load may be based on a fully open position of the EGR valve 210. In such cases, the threshold load position may be the fully open position. In some examples, the threshold load position may be a nearly fully open position.

[0034] In the illustrated example, the intake carbon dioxide sensor is located at a junction of the intake passage 149 and the HP-EGR passage 208. However, in other embodiments, the intake carbon dioxide sensor may be located within the intake passage 149 downstream of the throttle 158. The intake carbon dioxide sensor may be any suitable sensor for providing an indication of carbon dioxide concentration in the intake charge.

[0035] In this way, during operation at loads at or above the threshold, feedback from the DP sensor may not be used to control the EGR valve; rather, the EGR valve may be held at a specific position corresponding to the threshold load, or the EGR valve may be fully open, and the EGR flow rate estimation for scheduling ignition may be based on mapped intake carbon dioxide values. In other words, during engine operation above the threshold load, the EGR system operates in an open-loop mode without feedback from the DP sensor, but rather based on intake carbon dioxide sensor output.

[0036] While the above example describes switching between open-loop and closed-loop operation of the EGR system in response to load, the inventors have further identified that exhaust gas pulsations cause DP sensor measurement deviations when manifold absolute pressure (MAP) determined based on MAP sensor 182 is above a threshold pressure (such as 26 inches Hg). Therefore, EGR system operation may switch between closed-loop and open-loop operation in response to MAP. Accordingly, in one example, during engine operation below the threshold load and / or when MAP is below the threshold pressure, the EGR system may operate in closed-loop (regulatory) mode; and during engine operation above the threshold load and / or when MAP is above the threshold pressure, the EGR system may operate in open-loop (control) mode.

[0037] Therefore, by switching between open-loop and closed-loop EGR system operation, the impact of exhaust gas pulsation on EGR flow estimation can be reduced. Therefore, more accurate EGR flow estimates can be obtained, leading to more accurate spark advance planning. This can reduce ignition knock, resulting in improved fuel economy and power.

[0038] Further, although the example presented herein shows a boosted engine system, it should be noted that switching between open loop and closed loop operation of the EGR system to reduce the impact of exhaust pulsation on the EGR flow rate estimation may be applied in other engine configurations, such as a naturally aspirated engine, without departing from the scope of the present disclosure.

[0039] An example graph showing engine speed along the X-axis and engine load along the Y-axis, indicating areas of open loop and closed loop operation of the EGR system, is shown in Fig. 2. In particular, Fig. 2 the operation of the EGR system in the open loop mode at loads above the threshold 202 and the operation of the EGR system in the closed loop mode at loads below the threshold 202. While the Fig. 2 shows areas of open-loop and closed-loop EGR system control in a speed-load map, it should be noted that EGR system operation may additionally or alternatively be based on MAP, as briefly discussed above. For example, the EGR system may operate in open-loop mode when the engine load is above threshold load 202 and / or when MAP (determined, for example, based on MAP sensor 182) is above a threshold pressure; otherwise, the EGR system may operate in closed-loop mode. Details of operating the EGR system in open-loop mode and closed-loop mode and switching between the two modes are further described below with respect to the Fig. 3 to 6.

[0040] Although the above examples illustrate estimating EGR mass flow rate during open-loop control mode based on the intake carbon dioxide sensor, it should be understood that in some examples, an intake oxygen sensor 168 may be used for EGR mass flow estimation. In the illustrated example, the intake oxygen sensor is located downstream of the air cooler 154. However, in other embodiments, the sensor 168 may be located at a junction of the intake passages 146, 148, and 149 and upstream of the air cooler 154, or at another location along the intake passage 149, such as downstream of the throttle 158. The intake oxygen sensor (IAO2) 168 may be any suitable sensor for providing an indication of the oxygen concentration of the intake charge, such as a linear oxygen sensor, intake UEGO (universal or wide range exhaust gas oxygen) sensor, dual-stage oxygen sensor, etc.Controller 12 may estimate the percentage dilution of EGR flow based on feedback from intake oxygen sensor 168. In some examples, the controller may then adjust one or more of EGR valve 121, AIS throttle 115, or other actuators to achieve a desired EGR dilution percentage of the intake charge.

[0041] The engine system 100 may include various sensors 165 in addition to those mentioned above. As shown in Fig. 1, the common intake passage 149 may include a throttle intake pressure (TIP) sensor 172 for estimating a throttle intake pressure (TIP) and / or a throttle intake temperature sensor 173 for estimating a throttle air temperature (TCT), each in communication with the controller 12. Further, although not shown herein, each of the intake passages 142 and 144 may include a mass air flow sensor, or alternatively, the mass air flow sensor may be disposed in a common passage 140.

[0042] With reference now to Fig. 3 is an exemplary method 300 for closed loop and open loop operation of an EGR system, such as the EGR system 206 in Fig. 1, shown in block diagram form. Specifically, at loads above a threshold, method 300 includes operating the EGR system in an open-loop mode (control mode) 330, where an EGR flow rate estimate is based on mapped intake carbon dioxide levels; and at loads below the threshold, operating the EGR system in a closed-loop mode 320 (regulatory mode) based on a pressure feedback mechanism for EGR flow rate control by controlling the EGR valve through a PID controller.

[0043] If the engine load is below the threshold, the controller determines a desired EGR percentage of fresh airflow (%EGR) based on the engine speed and load. Then, at 306, the controller determines a desired EGR mass (DES EM) based on the engine air mass (as determined from MAP and speed density calculations or a mass airflow sensor).

[0044] Next, at 308, a desired differential pressure (DES DP) may be determined based on the desired EGR mass and the measured MAP from block 310. Block 310 may include the calculated MAP based on pressures determined by a DP sensor located on the intake manifold, such as sensor 217 in Fig. 1, may be detected. Next, at 312, a desired DP sensor voltage (DES VOLTAGE) may be calculated based on DES DP. Then, at 313, an error signal (ERROR) may be calculated based on DES VOLTAGE from block 312 and an actual DP sensor voltage (block 314) from the DP sensor. A PID controller, shown at block 316, may then determine an actuation signal based on the calculated ERROR signal. The actuation signal may be used to adjust EGR flow by controlling the EGR valve, such as EGR valve 210, through the PID controller. For example, by providing the actuation signal to an engine actuator, such as actuator 340, a position of the EGR valve may be adjusted to a desired position to provide the desired EGR mass (DES EM) to the engine. The actuation signal can be, for example, a duty cycle or a voltage signal.

[0045] Furthermore, during closed loop control, an actual EGR flow rate may be estimated based on the actual DP sensor voltage, and a degree of pre-ignition may be scheduled based on the actual EGR flow rate based on the actual DP sensor voltage.

[0046] In this way, during closed-loop mode, the EGR flow rate may be adjusted based on a pressure feedback mechanism from the DP sensor, which includes controlling the EGR flow rate through the EGR valve based on a deviation calculated between the desired sensor voltage and the actual sensor voltage. In some examples, a deviation between the actual EGR mass flow rate determined based on the actual sensor voltage and the desired EGR mass flow rate (DESEM) may be used to provide feedback control of the EGR valve.

[0047] When the engine load is above the threshold, the EGR system may be operated in the open loop control mode indicated at 330. During the open loop mode, the controller may set the EGR valve to a fully open position and, as indicated at 332, the actual EGR mass flow rate may be estimated based on intake carbon dioxide values ​​obtained by a carbon dioxide sensor / analyzer located within the intake manifold, such as the one shown in Fig. 1. For example, intake carbon dioxide levels may be mapped to EGR percentage at various speed and load conditions and stored in a lookup table or map in a controller memory. An EGR percentage may then be calculated based on the measured / estimated intake carbon dioxide levels. Subsequently, the actual EGR mass flow rate may be determined as a function of the EGR percentage and the engine air mass. Then, at 334, a degree of spark advance may be scheduled based on the actual EGR mass flow rate.

[0048] In one example, in response to a load change from a first load below a threshold to a second load above the threshold, a transition may occur from closed-loop EGR flow control to open-loop EGR flow control, wherein during the transition, the EGR valve is placed in a fully open position. Further, during the transition, while the EGR valve is being opened, the EGR valve may be assumed to be in a fully open position, and the EGR mass flow rate may be estimated based on intake carbon dioxide levels measured by the carbon dioxide sensor located within the intake manifold. For example, a lookup table mapping intake carbon dioxide values ​​to EGR percentage for open-loop control may be stored in memory of the controller.When estimating intake carbon dioxide values, the controller can estimate the EGR percentage based on the lookup table. The estimated EGR mass flow rate can then be calculated based on the estimated EGR percentage, and a degree of spark advance can be scheduled based on the estimated EGR mass. In this way, during high-load conditions, by estimating EGR flow rate based on intake carbon dioxide values ​​and independently of the DP sensor output, deviations in the EGR flow rate estimate due to exhaust pulsations affecting the DP sensor output can be reduced.

[0049] Further, in response to a load change from the second load above the threshold to a first load below the threshold, a transition from open-loop EGR flow control to closed-loop EGR flow control occurs, wherein during the transition to closed-loop EGR flow control, the EGR valve is moved from a fully open position to a more closed position. The actuation signal to move the EGR valve to a more closed position is based on a desired EGR flow determined based on the current speed and load condition. However, to schedule spark advance during the transition period in which the EGR valve is moved to the more closed position, the EGR flow may be determined based on intake carbon dioxide levels, and spark advance may be adjusted based on the intake carbon dioxide levels.Upon completing the transition, spark advance may be scheduled based on the EGR mass flow rate determined based on the DP sensor output.

[0050] In this way, the operation of the EGR system can be switched between an open loop mode and a closed loop mode based on load to obtain a more accurate estimate of the EGR mass flow rate.

[0051] Although the above example illustrates EGR system operation based on load, in one example, when the load is below the threshold and / or when a MAP (based on an output from a MAP sensor, such as sensor 182 in Fig. 1) is below a threshold pressure, operate in closed-loop mode; and when the load is above the threshold and / or when the MAP is above the threshold pressure, the EGR system may operate in open-loop mode. In one example, the threshold pressure may be 26 inches Hg.

[0052] With reference now to Fig. 4, a flowchart illustrating an exemplary method 400 for operating an EGR system, such as the EGR system 206 in Fig. 1, comprising an EGR valve, such as valve 210 in Fig. 1, in an engine, such as engine 10 in Fig. 1. Specifically, method 400 illustrates switching between closed loop and open loop operation of the EGR system. Although method 400 illustrates closed loop and open loop operation of the EGR system with respect to the Fig. 1, it should be noted that method 400 and the remainder of the methods encompassed herein are applicable to other engine systems, such as a naturally aspirated engine, without departing from the scope of the present disclosure. Furthermore, instructions for executing method 400 and the remainder of the methods encompassed herein may be provided by a controller, such as the controller illustrated in Fig. 1, based on commands stored in a memory of the controller and in conjunction with the sensors of the engine system, such as those described above with reference to Fig. 1. The controller can utilize motor actuators of the engine system to adjust engine operation according to the procedures described below.

[0053] Method 400 begins at 402. At 402, method 400 includes estimating and / or measuring engine operating conditions. These may include, for example, engine speed and load, driver torque request (based on throttle pedal position), boost, MAP, MAF, BP, engine temperature, EGR mass flow rate, air-fuel ratio, etc. Based on engine operating conditions and torque request, the vehicle controller may make one or more engine actuator adjustments. The actuator adjustments made may include, for example, spark timing, EGR valve opening, variable cam timing (VCT), AFR, throttle opening, etc.

[0054] Next, at 404, method 400 includes determining whether an engine load is greater than a threshold load. In some examples, additionally or alternatively, it may be determined whether MAP is greater than a threshold pressure. In one example, the threshold may correspond to a load in the higher load range. For example, the threshold load may be 9 bar mean brake power (BMEP). In another example, the threshold may be based on a fully open position of the EGR valve. At the threshold load and above, due to exhaust pulsations in the turbocharged engine, a differential pressure (DP) sensor, such as sensor 217 in Fig. 1, which is used to estimate an EGR mass flow rate, may output a higher voltage, resulting in a higher EGR flow rate estimate than the actual EGR flow rate. Therefore, when the engine is operating at or above the threshold engine load, the EGR system may operate in an open loop mode that does not rely on the DP sensor output for EGR flow rate estimation, but rather, the EGR flow rate is calculated based on an intake carbon dioxide sensor, such as sensor 220 in Fig. 1, as discussed below. Further, in the exemplary method 400 discussed herein, the EGR valve may be maintained in a fully open position when operating in the open loop mode.

[0055] Accordingly, if the engine load is greater than the threshold, method 400 proceeds to 406. At 406, method 400 includes determining whether the EGR valve is fully open. For example, when operating at a first engine load below a threshold prior to a transition from the first engine load to a second engine load at or above the threshold, the engine may operate in closed-loop mode for EGR flow control. Consequently, prior to the transition, the EGR valve position may be adjusted based on feedback from the DP sensor to provide a desired EGR flow rate. Therefore, the EGR valve may not be fully open prior to the transition, and when the load transitions from the first load to the second load, the EGR valve may not be fully open.Accordingly, if it is determined that the EGR valve is not fully open at a time when the load is above the threshold, method 400 proceeds to 408.

[0056] At 408, method 400 includes positioning the EGR valve to a fully open position. For example, positioning the EGR valve to the fully open position may include positioning the EGR valve from a less open position to a middle, more open position, and finally to a fully open position. The transition from the less open position to the fully open position may include one or more middle more open positions. In some examples, such as when an EGR valve opening value at the less open position is greater than a threshold opening value, the EGR valve may transition from the less open position to the fully open position with no middle more open positions. Further, ignition during positioning may be scheduled based on EGR flow estimated from mapped intake carbon dioxide values.When the EGR valve is placed in the fully open position, method 400 proceeds to 412.

[0057] Returning to 406, if it is determined that the EGR valve is fully open, method 400 proceeds to 410. At 410, method 400 includes maintaining the EGR valve in the fully open position. The EGR valve may be maintained in the fully open position as long as the load remains at or above the threshold.

[0058] Although in this example method 400, the EGR valve is placed in a fully open position, it should be noted that in some examples, when the load increases above the threshold, the EGR valve may be opened to a threshold load position, which may not be a fully open position, and may be maintained in the threshold load position as long as the load remains above the threshold. For example, the threshold load position may be a nearly fully open position.

[0059] Next, method 400 proceeds to 412. At 412, method 400 includes estimating EGR mass flow rate (414) based on mapped intake carbon dioxide values ​​and independent of DP sensor output while maintaining the EGR valve in the fully open position. That is, the EGR system is operated in an open loop feedforward mode, wherein the EGR valve is maintained in the fully open position until the load drops below the threshold, and while the EGR valve is in the fully open position, the EGR mass flow rate is estimated based on an output from the carbon dioxide sensor, engine load and engine speed, and mass airflow. For example, the EGR mass flow rate may be estimated based on a lookup table that maps intake carbon dioxide values ​​to EGR percentages based on engine speed and engine load.Based on the estimated EGR percentage from the mapped carbon dioxide values ​​and the mass airflow, the EGR mass flow rate may be estimated. Further, at 414, method 400 includes disabling the EGR system diagnostics (416) during EGR operation in the open loop mode.

[0060] Upon estimating the EGR mass flow rate, method 400 proceeds to 418. At 418, method 400 includes scheduling ignition based on the estimated EGR mass. In this way, by switching to open-loop feedforward control of EGR flow when the engine is operating at or above the load threshold and scheduling ignition based on an estimated EGR flow from the mapped intake carbon dioxide values ​​rather than the DP sensor output, potential ignition knock may be reduced. Consequently, unwarranted ignition retardation may be reduced, which may lead to improved fuel economy and performance.

[0061] In one example, switching from closed-loop control to open-loop feedforward control of EGR flow may be performed in response to MAP reaching or exceeding the threshold pressure. In one example, the threshold pressure may be based on a MAP at which the EGR valve is fully open. In another example, the threshold pressure may be a predetermined value, such as 26 inches Hg.

[0062] Returning to 404, if it is determined that the load is not greater than the threshold, method 400 proceeds to 420. At 420, method 400 includes determining whether EGR flow control is operating in open loop mode. For example, EGR flow control may be determined to be operating in open loop mode if the EGR valve is not adjusted in response to DP sensor output and if EGR flow estimation is based on mapped intake carbon dioxide values ​​and not DP sensor output. In some examples, additionally or alternatively, EGR flow control may be determined to be operating in open loop mode if an open loop indicator flag is established.

[0063] If the answer at 420 is YES, method 400 proceeds to 422. For example, when operating at a third engine load at or above the threshold prior to a transition from the third engine load to a fourth engine load below the threshold, the engine may operate in the open loop mode for EGR flow control. Therefore, when the load transitions from the third load to the fourth load, EGR flow control may occur in the open loop mode. Accordingly, if it is determined that EGR flow control is operating in the open loop mode when the load is below the threshold, method 400 proceeds to 422. At 422, method 400 includes determining a desired EGR flow based on current engine speed and engine load.

[0064] Upon determining the desired EGR flow rate, method 400 proceeds to 424. At 424, method 400 includes positioning the EGR valve from the fully open position to a desired opening position, where the desired opening position is based on the desired EGR flow rate. For example, the desired opening position may be a less open position, and therefore the EGR valve may be closed from the fully open position to a less open position. During positioning, the EGR system may continue to operate in open loop mode until the desired EGR valve position is reached. Accordingly, during positioning, ignition may be scheduled based on EGR estimation of mapped intake carbon dioxide levels.

[0065] Next, upon setting the EGR valve to the desired position, method 400 proceeds to 426. At 426, the EGR flow control is operated in a closed loop feedback mode. Operating in the closed loop feedback mode includes adjusting the EGR valve based on feedback from the DP sensor to provide an estimate of actual EGR flow, and adjusting ignition based on the actual EGR flow estimate from the DP sensor output. Details of operating the EGR system in a closed loop configuration are discussed with respect to Fig. 5 further elaborated.

[0066] With reference now to Fig. 5, a flowchart illustrating an example method 500 for operating the EGR system in a closed loop mode is shown.

[0067] At 502, method 500 includes determining a desired exhaust gas recirculation percentage (EGR%) based on engine speed and load. Next, at 504, method 500 includes calculating a desired EGR flow rate (DESEM) based on the desired EGR percentage and engine airflow (as determined from MAP and speed density calculations or a mass airflow sensor). The desired EGR flow rate may be calculated according to the following formula: Desired EGR flow rate (DESEM) = engine air flow * EGR% / (1 - EGR%)

[0068] Next, at 506, the method includes measuring or estimating an actual EGR flow rate based on output from a DP sensor such as sensor 217 in Fig. 1. For example, a differential pressure at the EGR flow control port, such as port 219 in Fig. 1, determined from the DP sensor output. The actual EGR flow can then be determined as a function of differential pressure and MAP, for example, based on the square root of the product. Ignition is then scheduled based on the actual EGR flow.

[0069] Next, at 510, method 500 includes determining a deviation between the actual EGR flow rate and the desired EGR flow rate. In one example, a proportional-integral-derivative (PID) controller may be used to calculate the deviation. Various other control architectures may be used, such as proportional control or proportional-integral control, or various other controls, including feedback and feedforward combined control action.

[0070] Next, at 512, method 500 includes adjusting an EGR valve, such as valve 210 in Fig. 1, based on the deviation. For example, an actuation signal based on a calculated ERROR signal. The actuation signal can be used to adjust the EGR flow rate by controlling the EGR valve. Specifically, the actuation signal can be sent by the controller to a DC motor actuator, such as actuator 340 in Fig. 3, which controls the EGR valve.

[0071] In this way, the EGR system can operate in a closed loop feedback mode during engine operation at loads below the threshold.

[0072] With reference now to Fig. 6 is an exemplary Fig. which illustrates an EGR flow control. In particular, Fig. 6 switching between an open loop control and a closed loop control of an EGR system, such as the EGR system 206 in Fig. 1, comprising an EGR valve, such as EGR valve 210 in Fig. 1, in response to load according to the present disclosure.

[0073] The sequence of Fig. 6 can be executed by executing commands in the system of Fig. 1 according to the procedure of Fig. 4 in cooperation with the procedure of Fig. 5. Vertical markers at times t0 to t4 represent times of interest during the sequence.

[0074] In particular, the first curve from the top in Fig. 6 represents load over time, and the load increases in the direction of the Y-axis arrow. Trace 604 represents a change in load, and the horizontal line 602 represents a threshold load.

[0075] The second curve from the top in Fig. 6 represents an EGR system control mode. Lane 606 represents operation of the EGR system in an open loop mode or a closed loop mode.

[0076] The third curve from the top in Fig. Trace 6 represents EGR valve position over time, and EGR valve opening increases in the direction of the Y-axis arrow. Trace 608 represents an actual change in EGR valve opening.

[0077] The fourth curve from the top in Fig. 6 represents a status of EGR system diagnostics. Lane 610 represents the status of EGR system diagnostics.

[0078] At t0 and between t0 and t1, the engine may be operating at a load below the threshold. Accordingly, the EGR system may be operating in a closed-loop mode. Consequently, the EGR valve may be controlled based on feedback from a DP sensor, such as sensor 217 in Fig. 1. That is, as in Fig. 3, the EGR valve may be adjusted during closed-loop control based on a deviation between an actual DP sensor voltage and a desired DP sensor voltage, where the desired DP sensor voltage is based on a desired EGR flow rate estimated as a function of engine mass air flow and desired EGR percentage at current speed and load conditions. Further, when the load is below the threshold and the EGR system is operating in closed-loop mode, an actual EGR flow rate may be calculated based on the actual DP sensor voltage, and ignition may be scheduled based on the determined actual EGR flow rate. Further, during time points at t0 and between t0 and t1, EGR system diagnostics may be performed if input conditions are met.

[0079] At t1, the engine load reaches the threshold. In response to the load reaching the threshold, the EGR system may switch from the closed-loop control mode to the open-loop control mode between t1 and t2. Switching to open-loop control includes positioning the EGR valve from a less open position to a fully open position. In some examples, switching to open-loop control includes positioning the EGR valve to a threshold load position, which may be a fully open position or not a fully open position. Switching to open-loop control further includes estimating actual EGR flow rate based on intake carbon dioxide values ​​and not DP sensor output (e.g., DP sensor voltage).Specifically, EGR flow during switching while the EGR valve is opened may be estimated based on a map that maps intake carbon dioxide levels at different engine speed and load with EGR percentage. The intake carbon dioxide levels may be estimated based on an output from a carbon dioxide sensor, such as sensor 220 in FIG. Fig. 1, can be measured. Furthermore, ignition can be scheduled during switching to the open loop control mode while the EGR valve is placed in the fully open position based on the actual EGR flow rate estimated based on mapped intake carbon dioxide values.

[0080] At t2 and between t2 and t3, the engine load remains above the threshold. This operates the EGR system based on open-loop control. Operating the EGR system in the open-loop control mode includes maintaining the EGR valve in a fully open position and estimating the actual EGR flow rate based on mapped intake carbon dioxide values. In some examples, the EGR valve may be maintained in the threshold load position. Further, during open-loop control, ignition is scheduled based on the actual EGR flow rate, which is estimated based on mapped intake carbon dioxide values.

[0081] In this way, under high-load conditions (e.g., above 9 bar BMEP), deviations in the actual EGR flow estimate, which occur due to exhaust pulsations that cause the DP sensor to output a higher voltage than the actual voltage, can be reduced by estimating the actual EGR flow based on intake carbon dioxide values ​​rather than the DP sensor output. Consequently, excessive pre-ignition due to overestimation of the actual EGR flow by the DP sensor output can be reduced. This can reduce ignition knock.

[0082] At t3, the engine load drops below the threshold. In response to the engine load dropping below the threshold, the EGR system operation is switched to closed-loop control. Accordingly, at t3 and between t3 and t4, a desired EGR flow rate is calculated based on engine speed and load conditions, and the EGR valve is adjusted to a first desired position to provide the desired EGR flow rate. For example, as discussed above with respect to Fig.3, the first desired position may be based on a desired sensor voltage determined from a desired differential pressure, where the desired differential pressure is determined using a graphical representation from a desired EGR flow rate. The desired EGR flow rate may be calculated as a function of a desired EGR percentage and engine airflow, where the desired EGR percentage is based on engine speed and load. Upon calculating the desired sensor voltage, a control signal is sent to an actuator of the EGR valve to adjust the EGR valve from the fully open position to the first desired position. The control signal may be, for example, a voltage level or a duty cycle.

[0083] Further, adjusting the EGR valve from the fully open position to the first target position includes adjusting the EGR valve from the fully open position to the target position. For example, if the first target position is a more closed position, the EGR valve may be adjusted from the fully open position to a middle, less closed position and then adjusted to the more closed position. The transition from the fully open position to the more closed (or less open) position may include one or more middle, less closed (or more open) positions.Furthermore, the actual EGR flow rate is calculated based on intake carbon dioxide values ​​during the shift from the fully open position to the first target position until the first target position is reached, and the ignition is scheduled based on the actual EGR flow rate calculated based on intake carbon dioxide values.

[0084] In summary, during the transition from the open-loop control mode to the closed-loop control mode, the EGR valve is adjusted from the fully open position to the first target position, where the first target position is estimated based on the target differential pressure sensor voltage for the target EGR flow rate at current speed and load conditions. Furthermore, during the transition until the EGR valve is adjusted to the first target position, the actual EGR flow rate is estimated from the intake carbon dioxide values, and ignition is scheduled based on the actual EGR flow rate estimated from the intake carbon dioxide values.

[0085] Furthermore, between t1 and t4, if the EGR flow estimation is based on the intake carbon dioxide sensor and the EGR system is operating in an open loop mode, EGR system diagnostics cannot be performed (e.g., EGR valve, DP sensor, or EGR cooler diagnostics cannot be performed).

[0086] Next, at t4, the EGR valve is in the first desired position. Furthermore, the engine load remains below the threshold at t4 and beyond t4. Accordingly, at t4 and beyond t4, the EGR system operates in closed-loop control mode, and therefore, the actual EGR flow rate is calculated based on the DP sensor output, and ignition is scheduled based on the EGR flow rate calculated based on the DP sensor output. Furthermore, between t4 and beyond, the EGR valve position is adjusted based on a deviation between the actual DP sensor voltage and the desired DP sensor voltage, where the desired DP sensor voltage is based on a desired EGR flow rate at current speed and load conditions. In other words, during closed-loop control, feedback from the DP sensor is used to control the EGR valve position.

[0087] In this way, by switching the operation of the EGR system between an open-loop control mode and a closed-loop control mode depending on engine load conditions, more accurate EGR flow estimation can be performed. Consequently, more accurate ignition scheduling can be performed. This can, for example, reduce ignition knock due to excessive ignition advance or excessive EGR flow estimation. Therefore, ignition retardation measures to counteract ignition knock can be reduced, leading to improved fuel economy and efficiency.

[0088] While the present example illustrates switching between open-loop and closed-loop operation of the EGR system in response to load, EGR system operation may switch between closed-loop and open-loop operation in response to manifold absolute pressure (MAP). Accordingly, in one example, the EGR system may operate in closed-loop mode during engine operation below the threshold load and / or when MAP is below the threshold pressure; and during engine operation above the threshold load and / or when MAP is above the threshold pressure, the EGR system may operate in open-loop mode.Furthermore, the EGR system operation in the closed loop mode and open loop mode and the transition between the two modes as discussed herein may be applied to various engine configurations, such as a boosted engine with high pressure and / or low pressure EGR and a naturally aspirated engine.

[0089] In one example, a method for an engine includes estimating an exhaust gas recirculation (EGR) mass flow rate based on a differential pressure sensor output when an engine load is below a threshold, estimating the EGR mass flow rate based on an intake carbon dioxide sensor output when the engine load is above the threshold, and independent of the differential pressure sensor output; and adjusting spark timing based on the estimated EGR mass flow rate. In a first example of the method, an EGR valve is in a fully open position when the engine load is above the threshold. A second example of the method optionally includes the first example and further includes turning off EGR system diagnostics when the engine load is above the threshold.A third example of the method optionally includes one or more of the first and second examples, and further includes, during a first transition from a first load below the threshold to a second load above the threshold, estimating the exhaust gas recirculation mass flow rate independently of the differential pressure sensor output and based on the intake carbon dioxide sensor output. A fourth example of the method optionally includes one or more of the first through third examples, and further includes the case where an EGR valve is placed in a fully open position during the transition.A fifth example of the method optionally includes one or more of the first through fourth examples, and further includes, during a second transition from the second load above the threshold to the first load below the threshold, estimating the exhaust gas recirculation mass flow rate independently of the differential pressure sensor output and based on the intake carbon dioxide sensor output. A sixth example of the method optionally includes one or more of the first through fifth examples, and further includes the case where an EGR valve is closed from a fully open position to a less open position, the less open position based on a desired EGR flow rate at the second load. A seventh example of the method optionally includes one or more of the first through sixth examples, and further includes the case where the EGR is high pressure EGR (HP EGR).An eighth example of the method optionally includes one or more of the first through seventh examples, and further includes the case where the engine is a V-engine; and the case where HP-EGR occurs on only one bank of the engine.

[0090] In another example, a method for an engine, in response to manifold absolute pressure increasing above a threshold pressure, includes setting the EGR valve to a fully open position; and timing the spark based on an intake carbon dioxide sensor output. In a first example of the method, timing the spark based on the intake carbon dioxide sensor output includes determining an EGR percentage based on mapped data, the mapped data correlating the EGR percentage with the intake carbon dioxide sensor output at different engine speed and load conditions; determining an EGR flow rate based on the EGR percentage and the engine air mass; and scheduling a degree of spark advance based on the EGR flow rate.A second example of the method optionally includes the first example and further includes, in response to the MAP falling below the threshold pressure, moving the EGR valve from the fully open position to a desired position, the desired position based on engine speed and load; and adjusting spark based on an output from a differential pressure (DP) sensor that measures differential pressure at an opening in an EGR passage. A third example of the method optionally includes one or more of the first and second examples and further includes where the desired position is a more closed position; and where a degree of opening of the EGR valve in the more closed position is based on engine speed and load.A fourth example of the method optionally includes one or more of the first through third examples, and further includes where adjusting spark based on the differential pressure (DP) sensor output comprises: determining an EGR flow rate based on the differential pressure sensor output; and scheduling a degree of spark advance based on the EGR flow rate. A fifth example of the method optionally includes one or more of the first through fourth examples, and further includes, when the MAP is above the threshold pressure, maintaining the EGR valve in the fully open position; and when the MAP is below the threshold pressure, controlling the EGR valve based on a deviation between the DP sensor output and a desired sensor output, wherein the desired sensor output is based on a desired EGR flow rate at current engine speed and load.

[0091] In another example, a method for an engine includes, during a first condition, operating an EGR valve based on a deviation between a desired DP sensor output and a measured DP sensor output and adjusting spark timing based on the measured DP sensor output; and during a second condition, operating the EGR valve independently of the DP sensor output and adjusting spark timing based on an intake carbon dioxide sensor voltage. In a first example of the method, the first condition includes an engine load below a threshold and the second condition includes an engine load above the threshold, wherein the threshold load is based on the EGR valve in a fully open position.A second example of the method optionally includes the first example and further includes, during a first transition event from the first condition to the second condition, setting the EGR valve to the fully open position while adjusting spark timing based on an assumed fully open EGR valve position and the intake carbon dioxide sensor voltage; and wherein operating the EGR valve independent of the DP sensor output includes operating the EGR valve in the fully open position.A third example of the method optionally includes one or more of the first and second examples, and further includes, during a second transition event from the second condition to the first condition, setting the EGR valve from a fully open position to a less open position based on a desired EGR while adjusting spark timing based on the assumed fully open EGR valve position and the intake carbon dioxide sensor voltage; and turning off EGR system diagnostics during the second condition and during the first and second transition events. A fourth example of the method optionally includes one or more of the first through third examples, and further includes when the first condition includes manifold absolute pressure (MAP) below a threshold pressure and the second condition includes MAP above the threshold pressure.

[0092] It should be noted that exemplary control and estimation routines encompassed 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 executed by the control system, including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various illustrated actions, operations, and / or functions may be performed in the illustrated sequence, in parallel, or in some cases, omitted.Likewise, the processing order is not 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 actions, operations, and / or functions may be performed repeatedly depending on the specific strategy employed. Further, the described actions, operations, and / or functions may graphically represent code to be programmed into non-transitory memory of the computer-readable storage medium in the engine control system, wherein the described actions are performed by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.

[0093] It is understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not intended to be limiting, as various variations are possible. For example, the above technology may be applied to V-6, I-4, I-6, V-12, counter-rotating four piston engines, 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.

[0094] The following claims specifically point out certain combinations and sub-combinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims are to be construed as encompassing the inclusion of one or more such elements, neither requiring nor excluding two or more such elements. Further combinations and sub-combinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by submitting new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope with respect to the original claims, are also to be considered within the subject matter of the present disclosure.

Claims

[1] A method for an engine (10) comprising: Estimating an exhaust gas recirculation (EGR) mass flow rate based on a differential pressure sensor output when an engine load is below a threshold; Estimating the EGR mass flow rate based on an intake carbon dioxide sensor output when the engine load is above the threshold and independent of the differential pressure sensor output; and Setting ignition timing based on the estimated EGR mass flow rate. [2] The method of claim 1, wherein an EGR valve (210) is in a fully open position when the engine load is above the threshold. [3] The method of claim 2, further comprising disabling an EGR system diagnostic (416) when the engine load is above the threshold. [4] The method of claim 1, further comprising, during a first transition from a first load below the threshold to a second load above the threshold, estimating the EGR mass flow rate independently of the differential pressure sensor output and based on the intake carbon dioxide sensor output. [5] The method of claim 4, wherein during the transition an EGR valve (210) is placed in a fully open position. [6] The method of claim 1, further comprising, during a second transition from the second load above the threshold to the first load below the threshold, estimating the EGR mass flow rate independently of the differential pressure sensor output and based on the intake carbon dioxide sensor output. [7] The method of claim 6, wherein an EGR valve (210) is closed from a fully open position to a less open position, the less open position being based on a desired EGR mass flow rate at the second load. [8] The method of claim 1, wherein the EGR is high pressure EGR (HP EGR). [9] The method of claim 8, wherein the engine (10) is a V-engine; and wherein the HP EGR occurs on only one bank of the engine (10). [10] Method for an engine (10), comprising: in response to a manifold absolute pressure (MAP) rising above a threshold pressure, Setting an EGR valve (210) to a fully open position; and Adjusting the ignition based on an intake carbon dioxide sensor output. [11] The method of claim 10, wherein adjusting the ignition based on the intake carbon dioxide sensor output comprises: Determining an EGR percentage based on mapped data, wherein the mapped data correlates the EGR percentage with the intake carbon dioxide sensor output at various engine speed and load conditions; Determining an EGR mass flow rate based on the EGR percentage and the engine air mass; and Scheduling a degree of spark advance based on EGR mass flow. [12] The method of claim 10, further comprising: in response to the MAP falling below the threshold pressure, Setting the EGR valve (210) from the fully open position to a desired position, the desired position being based on engine speed and load; and Adjusting the ignition based on a differential pressure sensor output that measures the differential pressure at an orifice in an EGR passage (208). [13] The method of claim 12, wherein the desired position is a more closed position; and wherein a degree of opening of the EGR valve (210) in the more closed position is based on engine speed and load. [14] The method of claim 12, wherein adjusting the ignition based on the differential pressure sensor output comprises: Determining an EGR mass flow rate based on the differential pressure sensor output; and Scheduling a degree of spark advance based on EGR mass flow. [15] The method of claim 12, further comprising, when the MAP is above the threshold, maintaining the EGR valve (210) in the fully open position; and when the MAP is below the threshold, controlling the EGR valve (210) based on a deviation between the differential pressure sensor output and a desired differential pressure sensor output, wherein the desired differential pressure sensor output is based on a desired EGR mass flow rate at current engine speed and load. [16] Method for an engine (10), comprising: during a first condition, operating an EGR valve (210) based on a deviation between a desired differential pressure sensor output and a measured differential pressure sensor output and adjusting the ignition timing based on the measured differential pressure sensor output; and during a second condition, operating the EGR valve (210) independently of the differential pressure sensor output and adjusting the ignition timing based on an intake carbon dioxide sensor voltage. [17] The method of claim 16, wherein the first condition comprises an engine load below a threshold load and the second condition comprises the engine load above the threshold load, the threshold load being based on the EGR valve (210) in a fully open position. [18] The method of claim 17, further comprising, during a first transition event from the first condition to the second condition, placing the EGR valve (210) in the fully open position while adjusting spark timing based on an assumed fully open EGR valve position and the intake carbon dioxide sensor voltage; and wherein operating the EGR valve (210) independent of the differential pressure sensor output comprises operating the EGR valve (210) in the fully open position. [19] The method of claim 18, further comprising, during a second transition event from the second condition to the first condition, positioning the EGR valve (210) from a fully open position to a less open position based on a desired EGR while adjusting spark timing based on the assumed fully open EGR valve position and the intake carbon dioxide sensor voltage; and disabling EGR system diagnostics (416) during the second condition and during the first and second transition events. [20] The method of claim 16, wherein the first condition comprises manifold absolute pressure (MAP) below a threshold pressure and the second condition comprises MAP above the threshold pressure.

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