Methods and systems for an inlet oxygen sensor

Abstract

Methods for a power engine, comprising: with EGR flow Modulating a reference voltage at an intake manifold oxygen sensor (172) via a control unit; and Estimating EGR dilution in the presence of drain and Crankcase ventilation hydrocarbons based on a sensor output received by the control unit during modulation and Setting the position of an EGR valve (204) via the control unit based on the estimated amount of exhaust and crankcase ventilation hydrocarbons.

Description

[0001] The present application generally relates to a gas constituent sensor included in an intake system of an internal combustion engine.

[0002] Engine systems may utilize the recirculation of exhaust gas from an engine exhaust system to an engine intake system (the intake passage), a process known as exhaust gas recirculation (EGR), to reduce regulated emissions. An EGR system may include various sensors to measure and / or control EGR. As one example, the EGR system may include an intake gas constituent sensor, such as an oxygen sensor, which may be used during non-EGR conditions to determine the oxygen content of the 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. An example of such an intake oxygen sensor is shown by Matsubara et al. in US Pat. No. 6,742,379 B2.The EGR system may additionally or optionally include an exhaust gas oxygen sensor coupled to the exhaust manifold to estimate a combustion air-fuel ratio.

[0003] Document DE 10 2014 111 476 A1 discloses a fuel control system for a vehicle that includes a pressure compensation module that compensates an intake oxygen signal based on an intake pressure signal and generates a compensated intake oxygen signal. A blowby estimation module generates an estimated blowby flow. A purge flow estimation module estimates the purge flow based on the compensated intake oxygen signal and the estimated blowby flow. A fuel control estimation module also reduces the fueling for the fuel injectors of an engine of the vehicle based on the purge flow with the aim of estimating HC inputs from the ACF purge and the crankcase ventilation into the intake gas mixture.

[0004] DE 10 2014 218 971 A1 discloses methods and systems for estimating PCV flow to an engine based on the output of an exhaust gas oxygen sensor, wherein, during DFSO conditions, a sensor reference voltage is modulated initially with an open throttle and then with the throttle closed. With the throttle open, the resulting pumping current changes are associated with the atmospheric humidity, and with the throttle closed, with the HC content of the crankcase gases. Thus, PCV flow leakage at the piston valves in an engine, as well as an estimate of the ambient humidity, are derived based on the sensor outputs during modulation with the intake throttle open and closed.

[0005] Document DE 10 2012 204 992 A1 discloses a control system for an engine, the control system comprising a first and a second module. The first module determines an oxygen concentration in an intake manifold of the engine. The second module regulates a flow of exhaust gas recirculation (EGR) into the intake manifold based on the determined oxygen concentration. In a homogeneous charge compression ignition (HCCI) engine, the second module can also deactivate an HCCI combustion mode of the HCCI engine based on the oxygen concentration. However, no differentiation is made here between inert gases in the sense of charge dilution from the EGR and the HC or humidity influences.

[0006] Due to the location of the oxygen sensor downstream of an intercooler in the high-pressure air intake system, the sensor itself may be sensitive to the presence of fuel vapor and other reductants and oxidizers, such as oil mist. During boosted engine operation, for example, purge air may be received at the compressor inlet location. Hydrocarbons picked up from purge air, crankcase ventilation (PCV), and / or rich EGR, for example, may consume oxygen on the catalytic sensor surface and reduce the oxygen concentration detected by the sensor. In some cases, the reductants may also react with the sensing element of the oxygen sensor. The reduction in oxygen at the sensor may be misinterpreted as a diluent when the change in oxygen is used to estimate EGR.Consequently, the sensor measurements may be confounded by the different sensitivities, reducing the accuracy of the sensor and consequently the measurement and / or control of the EGR.

[0007] In one example, some of the above issues may be addressed by a method for an engine comprising: upon EGR flow, modulating a reference voltage at an intake manifold oxygen sensor via a controller; estimating an amount of purge and crankcase ventilation hydrocarbons in the EGR based on sensor output received from the controller during the modulating; and adjusting a position of an EGR valve via the controller based on the estimated amount of purge and crankcase ventilation hydrocarbons in the EGR. In this way, an EGR estimate provided by the intake oxygen sensor may be corrected for purge and / or PCV content.

[0008] During EGR conditions, when purge and / or crankcase ventilation (PCV) are enabled, the purge and / or crankcase gas hydrocarbons may react with oxygen at the sensor to produce water and carbon dioxide. Thus, when EGR is flowing and purge and PCV are enabled, a reference voltage applied to the intake manifold oxygen sensor may alternate between a higher reference voltage and a lower reference voltage. The lower voltage may be a nominal voltage, such as 450 mV, which does not allow dissociation of water or carbon dioxide molecules, while the higher voltage may be at or above a threshold voltage, such as at or above 800 mV, which allows dissociation of the products of the reacting hydrocarbons (i.e., water and carbon dioxide).By comparing a pumping current output by the sensor with the higher and lower voltages, the change in oxygen concentration can be used to derive a total amount of purge and PCV hydrocarbons contained in the air charge. Purging can then be selectively inhibited, for example, by closing a purge valve. The reference voltage can then be modulated again between the higher and lower reference voltages. A difference between the pumping currents output by the sensor at the higher and lower reference voltages can be used, in the absence of purge air, to derive a PCV content of the air charge. The total amount of purge and PCV hydrocarbons in the air charge (estimated with purge enabled) and the PCV content of the air charge (estimated with purge inhibited) can then be used to calculate the purge content of the air charge.The controller can then correct an EGR estimate based on the learned purge and PCV content and use the corrected EGR estimate for more accurate EGR flow control.

[0009] In this way, by applying a higher reference voltage to an intake manifold oxygen sensor during purge and crankcase ventilation conditions, the effect of ingested hydrocarbons on the sensor's output can be canceled. Furthermore, by comparing the sensor's output at the higher reference voltage to a sensor output at a lower nominal reference voltage, a purge and PCV content of the air charge can be determined. By correcting the EGR estimated by the intake manifold oxygen sensor for purge and PCV hydrocarbon content, the sensor output can be corrupted by purge air or crankcase gas hydrocarbons. By improving the accuracy of the EGR dilution estimate in the presence of purge air or crankcase gases, EGR control can be improved.

[0010] It should be understood that the above summary is provided to introduce, in simplified form, a selection of the concepts 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 clearly defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that eliminate all of the disadvantages noted above or in any part of this disclosure.

[0011] The figures show: Fig. 1-2 are schematic diagrams of a power machine system. Fig. Figure 3 is a graph illustrating the effect of purge air on the oxygen concentration estimated by an intake manifold oxygen sensor. Fig. 4 illustrates a flowchart for setting a reference voltage applied to an intake manifold sensor when sensing EGR flow in the presence of purge or crankcase hydrocarbons. Fig. 5 illustrates a flow chart for estimating a purge or crankcase content of the EGR flow.

[0012] The present description relates to methods and a system for using an intake manifold sensor to sense an amount of EGR flow to an engine system, such as the engine systems according to the Fig. 1-2. A reference voltage applied to the sensor may be adjusted based on the presence of purge or crankcase ventilation hydrocarbons. A controller may be configured to execute a control routine, such as the routine following the Fig. 4-5, to determine an amount of purge and / or crankcase hydrocarbons ingested into an engine and adjust EGR flow accordingly. Both a sensor output and an EGR dilution estimated by the sensor can be adjusted to compensate for the effect of purge and / or crankcase hydrocarbons on the sensor output ( Fig. 3). This increases the accuracy of EGR estimation by an intake oxygen sensor.

[0013] 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. As a non-limiting example, engine system 100 may be included as part of a propulsion system for a passenger vehicle. Engine system 100 may receive intake air via an intake passage 140. Intake passage 140 may include an air cleaner 156 and an EGR throttle valve 230. Engine system 100 may be a split engine system in which intake passage 140 branches downstream of EGR throttle valve 230 into first and second parallel intake passages, each of which includes a turbocharger compressor.Specifically, at least a portion of the intake air is directed to a compressor 122 of the turbocharger 120 via a first parallel inlet passage 142 and at least another portion of the intake air is directed to a compressor 132 of the turbocharger 130 via a second parallel inlet passage 144 of the inlet passage 140.

[0014] The first portion of the total intake air compressed by the compressor 122 may be delivered to the intake manifold 160 via a first parallel branched intake passage 146. In this way, the intake passages 142 and 146 form a first parallel branch of the engine's air intake system. Similarly, a second portion of the total intake air may be compressed via the compressor 132 and may be delivered to the intake manifold 160 via the second parallel branched intake passage 148. Consequently, the intake passages 144 and 148 form a second parallel branch of the engine's air intake system. As shown in Fig. 1, the intake air from the intake ports 146 and 148 may be recombined via a common intake port 149 before reaching the intake manifold 160 where the intake air may be provided to the engine.

[0015] A first EGR throttle valve 230 may be positioned in the engine intake upstream of the first and second parallel intake passages 142 and 144, while a second air intake throttle valve 158 may be positioned in the engine intake downstream of the first and second parallel intake passages 142 and 144 and downstream of the first and second parallel branched intake passages 146 and 148, e.g., in the common intake passage 149.

[0016] 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), each of which is in communication with a controller 12. Intake passage 149 may include a charge air cooler (CAC) 154 and / or a throttle valve (such as a second throttle valve 158). The position of throttle valve 158 may be adjusted by the control system via a throttle actuator (not shown) communicatively coupled to controller 12. An antisurge valve 152 may be provided to selectively bypass the compressor stages of turbochargers 120 and 130 via bypass passage 150.As an example, the anti-surge valve 152 may be open to allow flow through the bypass passage 150 when the inlet air pressure upstream of the compressors reaches a threshold.

[0017] The intake manifold 160 may further include an intake gas oxygen sensor 172. In one example, the oxygen sensor is a UEGO sensor. As elaborated herein, the intake gas oxygen sensor may be configured to provide an estimate regarding the oxygen content of the fresh air received in the intake manifold. Additionally, as EGR flows, a change in oxygen concentration at the sensor may be used to infer an amount of EGR and used for precise control of EGR flow. In the depicted example, the oxygen sensor 162 is positioned upstream of the throttle body 158 and downstream of the charge air cooler 154. However, in alternative embodiments, the oxygen sensor may be positioned upstream of the CAC. A pressure sensor 174 may be positioned adjacent to the oxygen sensor to estimate an intake pressure at which an output of the oxygen sensor is received.Because the oxygen sensor output is influenced by intake pressure, a reference oxygen sensor output may be learned from a reference intake pressure. In one example, the reference intake pressure is throttle inlet pressure (TIP), where pressure sensor 174 is a TIP sensor. In alternative examples, the reference intake pressure is manifold pressure (MAP), as sensed by MAP sensor 182.

[0018] 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 in two banks 13 and 15, with each bank containing 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 equally spaced and arranged in alternative configurations, such as 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-into-cylinder fuel injector. However, in other examples, the fuel injector 166 may be configured as a port-based fuel injector.

[0019] The intake air supplied to each cylinder 14 (also referred to herein as a combustion chamber 14) via the common intake passage 149 may be used for fuel combustion, with the products of combustion then being exhausted via row-specific parallel exhaust passages. In the illustrated example, a first bank 13 of cylinders of the engine 10 may exhaust the products of combustion via a first parallel exhaust passage 17, and a second bank 15 of cylinders may exhaust the products of combustion via a second parallel exhaust passage 19. Both the first and second parallel exhaust passages 17 and 19 may further include a turbocharger turbine.Specifically, the products of combustion exhausted via exhaust passage 17 may be directed through the 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 the turbine bypass passage 123, as controlled by a wastegate valve 128. Similarly, the products of combustion exhausted via 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 a shaft 136 to provide compression to the intake air flowing through the second branch of the engine's intake system.Alternatively, some or all of the exhaust gas flowing through the exhaust passage 19 may bypass the turbine 134 via a turbine bypass passage 133, as controlled by a wastegate valve 138.

[0020] 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 level of energy received from the exhaust flow and transferred 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 level of energy received from the exhaust flow and transferred to their respective compressor. For example, the control system may be configured to independently vary the blade or nozzle position of exhaust turbines 124 and 134 via respective actuators.

[0021] The exhaust gases in the first parallel exhaust passage 17 may be directed to the atmosphere via the branched parallel exhaust passage 170, while the exhaust gases in the second parallel exhaust passage 19 may be directed to the atmosphere via the branched parallel exhaust passage 180. 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.

[0022] The engine 10 may further include one or more exhaust gas recirculation (EGR) passages or loops for recirculating at least a portion of the exhaust gas from the exhaust manifold to the intake manifold. These may include high-pressure EGR loops for providing high-pressure EGR (HP EGR) and low-pressure EGR loops for providing low-pressure EGR (LP EGR). In one example, HP EGR may be provided in the absence of boost provided by the 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.

[0023] In the depicted example, engine 10 may include a low-pressure EGR loop 202 to recirculate at least some exhaust gas from first branched parallel exhaust passage 170 downstream of turbine 124 to first parallel intake passage 142 upstream of compressor 122. In some embodiments, a second low-pressure EGR loop (not shown) may similarly be provided to recirculate at least some exhaust gas from second branched parallel exhaust passage 180 downstream of turbine 134 to second parallel intake passage 144 upstream of compressor 132. The LP-EGR loop 202 may include both an LP-EGR valve 204 for controlling an EGR flow (i.e., a recirculated exhaust gas amount) through the loops and an EGR cooler 206 for reducing a temperature of the exhaust gas flowing through the EGR loop before being recirculated to the engine intake.Under certain conditions, the EGR cooler 206 may also be used to heat the exhaust gas flowing through the LP EGR loop 202 before the exhaust gas enters the compressor to prevent water droplets from impacting the compressors.

[0024] The engine 10 may further include a first high-pressure EGR loop 208 for recirculating at least some exhaust gas from the first parallel exhaust passage 17 upstream of the turbine 124 to the intake manifold 160 downstream of the intake throttle 158. Similarly, the engine may include a second high-pressure EGR loop (not shown) for recirculating at least some exhaust gas from the second parallel exhaust passage 18 upstream of the turbine 134 to the second branched parallel intake passage 148 downstream of the compressor 132. EGR flow through the HP EGR loops 208 may be controlled via an HP EGR valve 210.

[0025] A PCV port 102 may be configured to deliver the crankcase ventilation gases (the crankcase gases) along the second parallel intake passage 144 to the engine intake manifold. In some embodiments, the flow of PCV air through the PCV port 102 may be controlled by a dedicated PCV port valve. Similarly, a purge port 104 may be configured to deliver purge gases from a fuel system canister along the passage 144 to the engine intake manifold. In some embodiments, the flow of purge air through the purge port 104 may be controlled by a dedicated purge port valve.

[0026] A humidity sensor 232 and a pressure sensor 234 may be included in only one of the parallel intake passages (shown here in the first parallel intake air passage 142, but not the second parallel intake passage 144) downstream of the EGR throttle valve 230. Specifically, the humidity sensor and the pressure sensor may be included in the intake passage that does not receive the PCV or purge air. The humidity sensor 232 may be configured to estimate a relative humidity of the intake air. In one embodiment, the humidity sensor 232 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 confound the humidity sensor readings, the purge port and PCV port are positioned in a different intake passage than the humidity sensor. Pressure sensor 234 may be configured to estimate intake air pressure. Some embodiments may also include a temperature sensor in the same parallel intake passage downstream of EGR throttle valve 230.

[0027] As such, the intake oxygen sensor 172 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 204 opens. Specifically, a change in the sensor's output when the EGR valve opens is compared to a reference point where the sensor is operating without EGR (the zero point). Based on the change (e.g., decrease) in the amount of oxygen from the time when operating without EGR, the EGR flow currently provided to the engine can be calculated. For example, upon applying a reference voltage (Vs) to the sensor, a pumping current (Ip) is output by the sensor. The change in oxygen concentration can be proportional to the change in pumping current (delta Ip) output by the sensor in the presence of EGR relative to the sensor output in the absence of EGR (the zero point).Based on a deviation of the estimated EGR flow from the expected (or target) EGR flow, further EGR control may be performed.

[0028] During idle conditions, when intake pressure fluctuations are minimal and no PCV of purge air is being drawn into the low-pressure intake system, a zero-point estimation of the intake oxygen sensor can be performed. In addition, an idle adjustment can be performed periodically, such as at each initial idle after an engine start, to compensate for the effects of sensor aging and component-to-component variability on the sensor output.

[0029] Alternatively, intake oxygen sensor zero estimation can be performed during engine defueling conditions, such as during deceleration fuel shutoff (DFSO). Performing the adjustment during DFSO conditions can reduce sensor reading variations due to EGR valve leakage, in addition to reducing noise factors such as those obtained during idle adjustment.

[0030] In Fig. 1, 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 a direct-acting mechanical cup system 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. Specifically, the intake valve cam actuation system 25 may include one or more cams and may utilize variable cam timing or variable cam lift for the intake and / or exhaust valves. In alternative embodiments, the intake valves may be controlled by electric valve actuation. Similarly, the exhaust valves may be controlled by cam actuation systems or electric valve actuation.

[0031] The engine system 100 may be controlled at least in part by a control system 15 including a controller 12 and input from a vehicle operator via an input device (not shown). The control system 15 is shown receiving information from a plurality of sensors 16 (various examples of which are described herein) and sending control signals to a plurality of actuators 81. As one example, the sensors 16 may include a humidity sensor 232, an intake air pressure sensor 234, a MAP sensor 182, an MCT sensor 183, a TIP sensor 174, and an intake air oxygen sensor 172. In some examples, the common intake passage 149 may further include a throttle inlet temperature sensor for estimating a throttle air temperature (TCT).In other examples, one or more of the EGR passages may include pressure, temperature, and air-fuel ratio sensors for determining EGR flow characteristics. As another example, actuators 81 may include fuel injector 166, HP EGR valves 210 and 220, LP EGR valves 204 and 214, throttle valves 158 and 230, and wastegate valves 128, 138. Other actuators, such as various additional valves and throttle bodies, may be coupled to various locations in engine system 100. 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 respect to FIG. Fig. 4-5 described.

[0032] In Fig. 2 is another exemplary embodiment 200 of the engine according to Fig. 1. The previously Fig. 1 are numbered similarly and are not introduced again here for the sake of brevity.

[0033] Embodiment 200 depicts a fuel tank 218 for supplying fuel to the engine's fuel injectors. A fuel pump (not shown) immersed in fuel tank 218 may be configured to pressurize the fuel supplied to the injectors of engine 10, such as injector 166. The fuel may be pumped into the fuel tank from an external source through a fuel door (not shown). Fuel tank 218 may contain multiple fuel blends, including fuel with a range of alcohol concentrations, such as various gasoline-ethanol blends, including E10, E85, gasoline, etc., and combinations thereof. A fuel level sensor 219 located in fuel tank 218 may provide an indication of the fuel level to controller 12.As illustrated, fuel level sensor 219 may include a float connected to a variable resistor. Alternatively, other types of fuel level sensors may be used. One or more other sensors may be coupled to fuel tank 218, such as a fuel tank pressure sensor 220 for estimating fuel tank pressure.

[0034] The vapors generated in the fuel tank 218 may be routed via a line 31 to a fuel vapor canister 22 before being vented into the engine inlet 23. These may contain, for example, the daily and refueling fuel tank vapors. The canister may be filled with a suitable adsorbent, such as activated charcoal, to temporarily capture the fuel vapors (including vaporized hydrocarbons) generated in the fuel tank. Then, during later engine operation, when the venting conditions are met, such as when the canister is saturated, the fuel vapors from the canister may be vented into the engine inlet by opening a canister vent valve 112 and a canister vent valve 114.

[0035] The canister 22 includes a vent opening 27 to direct the gases from the canister 22 to the atmosphere when storing or capturing fuel vapors from the fuel tank 218. The vent opening 27 may also allow fresh air to be drawn into the fuel vapor canister 22 when venting the stored fuel vapors to the engine intake 23 via the vent lines 90 or 92 (depending on the boost level) and the vent valve 112. While this example shows the vent opening 27 communicating with fresh, unheated air, various modifications may also be used. The vent opening 27 may include a canister vent valve 114 to adjust the flow of air and vapors between the canister 22 and the atmosphere. The vent valve may be used during fuel vapor storage operations (e.g.,During emptying operations (e.g., during refueling of the fuel tank and while the engine is not running), the vent valve may be open so that the air from which the fuel vapor has been removed can be forced out to the atmosphere after passing through the canister. Similarly, during emptying operations (e.g., during canister regeneration and while the engine is running), the vent valve may be open to allow a flow of fresh air to remove the fuel vapors stored in the canister.

[0036] The fuel vapors released from the canister 22, for example, during a purge operation, may be routed to the engine intake manifold 160 via the purge line 28. The flow of vapors along the purge line 28 may be regulated by the canister purge valve 112, which is coupled between the fuel vapor canister and the engine intake. The amount and rate of vapors released through the canister purge valve may be determined by the duty cycle of an associated canister purge valve solenoid (not shown). As such, the duty cycle of the canister purge valve solenoid may be controlled by the vehicle's powertrain control module (PCM), such as the controller 12, in response to engine operating conditions, e.g., B. including the engine speed-load conditions, an air-fuel ratio, a canister load, etc.

[0037] An optional canister check valve (not shown) may be included in purge line 28 to prevent intake manifold pressure from causing gases to flow in the opposite direction of the purge flow. As such, the check valve may be necessary if the canister purge valve timing is not precisely timed or if the canister purge valve itself may be forced open by high intake manifold pressure. An estimate of manifold absolute pressure (MAP) may be obtained from MAP sensor 174 coupled to intake manifold 160 and communicated to controller 12. Alternatively, MAP may be derived from alternative engine operating conditions, such as mass air flow (MAF) as measured by a MAF sensor coupled to the intake manifold.

[0038] The purge hydrocarbons may be routed to the intake manifold 160 via either a boost path 92 or a vacuum path 90, based on engine operating conditions. Specifically, during conditions when the turbocharger 120 is operating to provide a boosted air charge to the intake manifold, the increased pressure in the intake manifold causes the one-way valve 94 in the vacuum path 90 to close while the one-way valve 96 in the boost path 92 is opened. As a result, the purge air is routed via the boost path 92 into the air intake passage 140 downstream of the air cleaner 156 and upstream of the charge air cooler 154. Here, the purge air is introduced upstream of the intake air sensor 172.In some embodiments, as shown, a venturi 98 may be positioned in the boost path so that the purge air is directed to the inlet as it passes through the venturi and channel 99. This allows the purge air flow to be advantageously utilized for creating negative pressure.

[0039] During conditions when engine 10 is operating without boost, the increased vacuum in the intake manifold causes one-way valve 94 in the vacuum path to open while one-way valve 96 in the boost path to close. As a result, purge air is routed via vacuum path 90 to intake manifold 160 downstream of throttle valve 158. Here, the purge air is introduced downstream of intake air sensor 172.

[0040] The PCV hydrocarbons may also be routed to the intake manifold 160 via either a boost-side PCV hose 252 or a vacuum-side PCV hose 254 based on engine operating conditions. Specifically, the crankcase gases from the engine cylinders 14 flow past the piston rings, entering the crankcase 255. During conditions when the turbocharger 120 is operating to provide a boosted air charge to the intake manifold, the increased pressure in the intake manifold causes the one-way valve 256 in the vacuum-side PCV hose 254 to close. As a result, during boosted engine operation, the PCV gases flow in a first direction (arrow 262), being received downstream of the intake oxygen sensor in the engine intake.Specifically, the PCV air is directed via the boost-side PCV hose 252 into the air intake passage 140 downstream of the air cleaner 156 and upstream of the charge air cooler 154. The PCV flow may be directed to the intake passage after passing through a boost-side oil separator 260. The boost-side oil separator may be integrated into the cam cover or may be an external component. Consequently, during boosted conditions, the PCV gases are introduced upstream of the intake oxygen sensor 172, therefore affecting the output of the oxygen sensor 172.

[0041] In comparison, during conditions when the engine 10 is operating without boost, the increased vacuum in the intake manifold causes the one-way valve 256 in the vacuum-side PCV hose 254 to open. As a result, during non-boosted engine operation, the PCV gases flow in a second direction (arrow 264) different from the first direction, being received downstream of the intake oxygen sensor in the engine intake. In the depicted example, the second direction of PCV flow during non-boosted engine operation is opposite to the first direction of PCV flow during boosted engine operation (compare arrows 262 and 264). Specifically, during non-boosted operation, the PCV air is directed directly into the intake manifold 160 via the vacuum-side PCV hose 254 downstream of the throttle body 158.Here, the PCV air is introduced downstream of the intake oxygen sensor 172 and therefore does not affect the output of the oxygen sensor 172. Consequently, due to the specific engine configuration, the PCV and purge air hydrocarbons are ingested into the engine intake manifold upstream of the intake oxygen sensor during boosted engine operation and downstream of the intake oxygen sensor during unboosted conditions.

[0042] As previously discussed, the intake air oxygen sensor can be used to measure the amount of EGR in the intake air charge as a function of the amount of change in oxygen content due to the addition of EGR as a diluent. Consequently, as more EGR is introduced, the sensor may output an indication or pumping current corresponding to a lower oxygen concentration. During estimation, a nominal reference voltage (e.g., at 450 mV) or Nernst voltage is applied to the sensor, and an output (e.g., a pumping current output by the sensor upon application of the lower reference voltage) is detected. Based on the sensor's output relative to a sensor zero point (i.e., the sensor output at the no-EGR conditions), a change in oxygen concentration is learned, and intake dilution with EGR is derived.

[0043] However, if the EGR estimation is performed during conditions when purge and / or crankcase ventilation are enabled, a sensor output will be corrupted. As such, the purge air and / or crankcase ventilation hydrocarbons may be ingested along the boost path 92 and PCV hose 252 on the boost side during boosted engine operating conditions when the purge valve 112 is open and / or the PCV valve 256 is closed. The sensor output may be corrupted primarily due to the ingested hydrocarbons reacting with ambient oxygen at the intake sensor sensing element. This reduces the (local) oxygen concentration indicated by the sensor.Because the sensor output and the change in oxygen concentration are used to infer EGR dilution of the intake air charge, the reduced oxygen concentration indicated by the intake oxygen sensor in the presence of purge air and / or PCV may be misinterpreted as additional diluent. This impacts EGR estimation and subsequent EGR control. Specifically, EGR may be overestimated.

[0044] Fig. 3 illustrates this variation in the intake sensor display. Specifically, plot 300 represents an oxygen concentration estimated by the intake manifold oxygen sensor along the y-axis and a purge hydrocarbon content (purge HC content) along the x-axis at a given EGR level. As the amount of purge HCs ingested into the low-pressure intake system increases, such as when a purge valve is released during purge conditions, the hydrocarbons react with oxygen at the intake oxygen sensor sensing element. The oxygen is consumed, releasing water and carbon dioxide. As a result, the estimated oxygen concentration is decreased, even though an amount of EGR flow may remain constant.This reduction in oxygen concentration estimated by the oxygen sensor can be inferred as increased dilution (or replacement of oxygen by EGR). Consequently, the controller can infer that a greater amount of EGR flow is available than actually exists. If the effect of the hydrocarbons is not corrected, a controller may reduce EGR flow in response to an incorrect indication of the increased EGR dilution, degrading EGR control. As such, PCV and purge hydrocarbons are recognized as flowing (directly) into the intake manifold during unboosted conditions. Consequently, during unboosted conditions, purge and PCV flow is received downstream of the intake oxygen sensor and therefore does not confound the sensor readings.However, during boosted conditions, the PCV and purge flow is received upstream of the intake oxygen sensor in the low-pressure air intake system. As a result, only during boosted conditions is the sensor output confounded by the purge and PCV flow.

[0045] As in Fig. 4, to reduce the effect of hydrocarbons on the intake oxygen sensor, the EGR estimation can be performed at a higher reference voltage when the purge and / or PCV are enabled. By changing the reference voltage or Nernst voltage of the intake oxygen sensor, the sensor switches from reacting the hydrocarbons with the ambient oxygen at the sensor to dissociating the products of the reaction (water and carbon dioxide). At a defined elevated reference voltage that is higher than the nominal reference voltage, e.g., at or above 800 mV, the sensor cancels out the effect of the hydrocarbons and displays the oxygen reading only due to the dilution effect (of the EGR) and not due to the effect of the hydrocarbons in the purge and PCV air. In addition, as described in Fig. 5, the reference voltage can be modulated between the higher voltage and the lower voltage in the presence and absence of HCs from the purge and PCV air to estimate purge and PCV content in the intake air charge. The EGR flow estimated by the intake sensor can then be corrected to account for the effect of the purge and PCV hydrocarbons. As such, this improves the accuracy of the EGR control.

[0046] It is recognized that in alternative examples, the intake oxygen sensor may be operated at the higher reference voltage at all times to eliminate the effect of hydrocarbons on the EGR measurement.

[0047] In Fig. 4 shows a routine 400 for adjusting the reference voltage applied to the intake manifold oxygen sensor based on purge and / or crankcase ventilation conditions being met. This approach allows the effect of purge and PCV air hydrocarbons to be canceled, improving the accuracy of the EGR estimation.

[0048] At 402, the routine includes estimating and / or measuring engine operating conditions. These include, for example, engine speed, torque request, boost, EGR, required engine dilution, engine temperature, BP, MAP, etc. At 404, it may be determined whether EGR is enabled. In one example, EGR may be enabled based on engine speed-load conditions at which EGR benefits may be achieved. For example, EGR may be enabled when engine speed is above a threshold speed (e.g., above an idle speed) and when engine load is above a threshold load (e.g., above a minimum load). If EGR is not enabled, the routine may end.

[0049] At 406, it may be determined whether the canister purge conditions and / or the crankcase ventilation (PCV) conditions have been met. The canister purge conditions may be met when a canister charge is greater than a threshold, the engine is running, the engine is in a boosted state, and a purge valve is open. The PCV conditions may be met when the engine is operating boosted and a PCV valve 256, which couples the crankcase to the intake manifold along the vacuum-side PCV hose, is closed. During these conditions, PCV flow may be received along the boosted-side PCV hose 252.Specifically, a PCV valve (or check valve) 256 closes on the vacuum side below the boost, directing purge flow from the positive pressure in the crankcase to the lower (~atmospheric) pressure in the low-pressure intake system. If the purge air is received as such in the intake air charge, the purge hydrocarbons (purge HCs) may be ingested along with the exhaust gas residue in the EGR. Likewise, if the PCV is open, the PCV hydrocarbons may be ingested into the intake air charge. These hydrocarbons may react with oxygen at the sensing element of the intake oxygen sensor, producing carbon dioxide and water. The resulting reduction in oxygen concentration leads to a misinterpretation of engine dilution.

[0050] If the purge air or PCV is not enabled, then the routine at 408 includes applying a lower reference voltage (V 1 ) to the intake manifold oxygen sensor. For example, a nominal voltage, such as 450 mV, may be applied. The lower reference voltage may be a voltage that does not cause the dissociation of the hydrocarbon-oxygen reaction products (water and carbon dioxide). As elaborated below, the controller may then adjust the EGR flow to the engine based on an output from the sensor at the lower reference voltage.

[0051] If, by comparison, purge or the PCV is enabled, then at 410, in response to ingesting purge or crankcase hydrocarbons during EGR flow, the routine includes increasing a reference voltage applied to the intake manifold oxygen sensor. The controller may then adjust EGR flow to the engine based on an output of the sensor at the increased reference voltage. The increased reference voltage (V 2) applied to the intake oxygen sensor may be a voltage at which an effect of the ingested hydrocarbons on the sensor is canceled. Specifically, the higher voltage may be a voltage that enables the dissociation of the hydrocarbon-oxygen reaction products water and carbon dioxide. In one example, the higher reference voltage may be at or above a threshold voltage, such as at or above 800 mV. As elaborated below, the controller may then adjust the EGR flow to the engine based on an output of the sensor at the increased reference voltage.

[0052] Upon applying the higher reference voltage in the presence of purge and PCV air at 410, or upon applying the lower reference voltage in the absence of purge and PCV air at 408, the routine proceeds to 412, where an EGR flow to the engine intake is estimated based on the sensor output. Estimating the EGR flow includes estimating an oxygen concentration based on an output of the sensor (at the higher voltage if the higher voltage was applied, or at the lower voltage if the lower voltage was applied). The routine then estimates an engine dilution based on the estimated oxygen concentration relative to a zero point. The zero point reflects an oxygen concentration estimated by the oxygen sensor in the absence of any EGR.The sensor zero point may be learned during an idle trim (during selected engine idle conditions) or a deceleration fuel cut trim (during selected engine unfueled conditions). As the amount of EGR dilution of the intake air charge increases, more intake oxygen may be replaced by the EGR and a corresponding decrease in the intake oxygen sensor output may occur. Consequently, an amount of EGR flow may be estimated based on the change in oxygen concentration estimated by the oxygen sensor. In one example, the sensor output at either the higher or lower reference voltage is a pumping current (Ip), with the EGR estimate based on a change in the sensor output at the applied voltage relative to the zero point (previously estimated upon application of the same reference voltage).

[0053] Next, at 414, the routine includes estimating a PCV and / or purge air charge content (including EGR flow) based on the oxygen sensor output. As in Fig. 5, the controller may modulate the sensor reference voltage (by decreasing the reference voltage applied to the oxygen sensor from the higher voltage to the lower voltage) and estimate an amount of purge and / or crankcase hydrocarbons ingested into the air charge and EGR flow based on the output of the sensor at the increased reference voltage relative to the output of the sensor at the decreased reference voltage.

[0054] At 416, the routine may correct the EGR flow to the engine (estimated at 412) based on the estimated amount of purge and crankcase ventilation hydrocarbons. For example, an amount of dilution corresponding to the purge or crankcase hydrocarbon content may be reduced from the EGR flow estimate.

[0055] At 418, a position of an EGR valve may be adjusted based on the corrected EGR flow. For example, the controller may adjust the position of an EGR valve coupled to a low-pressure EGR passage, where the passage recirculates exhaust gas residue from a location downstream of an exhaust turbine to a location upstream of an intake compressor. The EGR flow may be adjusted based on a difference between the corrected EGR flow and a desired EGR flow. Consequently, an opening of the EGR valve may be increased if the corrected EGR flow is less than the desired EGR flow, or decreased if the corrected EGR flow is greater than the desired EGR flow. Additionally, the EGR flow can be adjusted relative to the intake air flow to maintain a fixed percentage of EGR flow relative to the intake air flow.

[0056] In some embodiments, the controller may also adjust an engine operating parameter based on the sensor output at the increased reference voltage. Similarly, the controller may also adjust one or more engine operating parameters based on the amount of purge and crankcase ventilation hydrocarbons (estimated at 414). The adjusted engine operating parameters include, for example, spark timing, fuel injection timing, and / or fuel injection amount.

[0057] In one example, during a first EGR condition, a controller may estimate EGR based on an intake manifold oxygen sensor operating at a higher reference voltage, while during a second EGR condition, the controller may estimate EGR based on the intake manifold oxygen sensor operating at a lower reference voltage. The first EGR condition may include hydrocarbons being received from a fuel system canister and / or an engine crankcase in an engine intake, while the second EGR condition may include no hydrocarbons being received in the engine intake. The higher reference voltage may be a voltage at which an effect of the hydrocarbons on the sensor is canceled, while the lower reference voltage is a voltage at which an effect of the hydrocarbons on the sensor is not canceled.As such, during both the first and second EGR conditions, an EGR valve may be adjusted based on the estimated EGR relative to a desired EGR flow to provide a fixed percentage of EGR relative to the intake air flow.

[0058] Here, estimating EGR during the first condition includes estimating a first oxygen concentration of the intake air charge based on an output of the sensor at the higher reference voltage and deriving an EGR dilution of the intake air charge based on the first oxygen concentration with respect to a zero point of the sensor estimated at the higher reference voltage. Estimating EGR during the second condition includes estimating a second oxygen concentration of the intake air charge based on an output of the sensor at the lower reference voltage and deriving an EGR dilution of the intake air charge based on the second oxygen concentration with respect to a zero point of the sensor estimated at the lower reference voltage. The EGR estimated during the first EGR condition at the higher reference voltage may be a first EGR amount.The controller may further apply the lower reference voltage to the sensor during the first EGR condition, estimate a second EGR amount based on the intake manifold oxygen sensor operating at a lower reference voltage, and derive an amount of hydrocarbons ingested during the first EGR condition based on a difference between the first EGR amount and the second EGR amount.

[0059] In another example, an engine system includes an engine including an intake manifold and a crankcase; a turbocharger having an intake compressor, an exhaust turbine, and an intercooler; an intake throttle coupled to the intake manifold downstream of the intercooler; and a canister configured to receive fuel vapors from a fuel tank, the canister coupled to the intake manifold. The engine system further includes an EGR system including a passage for recirculating exhaust gas residues from a location downstream of the turbine via an EGR valve to a location upstream of the compressor; an oxygen sensor coupled to the intake manifold downstream of the intercooler and upstream of the intake throttle; and a controller having computer-readable instructions.The controller may be configured to adjust a reference voltage applied to the oxygen sensor based on either the purge conditions or the crankcase ventilation conditions being met, estimate intake EGR dilution based on an output of the oxygen sensor, and adjust an opening of the EGR valve based on the estimated intake EGR dilution. Here, adjusting the reference voltage in response to either the purge conditions or the crankcase ventilation conditions being met includes applying a higher reference voltage at which an effect of the ingested hydrocarbons is cancelled, and applying a lower reference voltage in response to neither the purge conditions nor the crankcase ventilation conditions being met.The controller may further include instructions for setting the higher reference voltage based on an amount of purge hydrocarbons or crankcase ventilation hydrocarbons ingested into the intake manifold, wherein the reference voltage is increased as the amount increases.

[0060] In Fig. 5 shows a routine 500 for modulating a reference voltage applied to an intake manifold oxygen sensor to estimate a purge and / or crankcase ventilation content of the air charge supplied to the engine, including the purge content of the flowing EGR. The approach allows an EGR estimate to be corrected for purge and PCV hydrocarbon content, improving the accuracy of the EGR estimate. The routine of Fig. 5 may be performed as such during boosted engine operation when PCV flow and purge flow are received upstream of an intake oxygen sensor, and their effect on the EGR estimate may be learned and compensated for.

[0061] At 501, it may be confirmed that the engine is operating with boost. For example, it may be confirmed that the engine is operating at a boost pressure higher than a threshold. At 502, it may be determined whether EGR is enabled. For example, it may be determined whether engine speed-load conditions are above a threshold where engine dilution may provide fuel economy and emissions benefits. It may also be determined whether the EGR valve is open. If EGR is not enabled, the routine may end.

[0062] At 504, it may be determined whether the combustion air-fuel ratio is at or about stoichiometry. If not, at 506, engine operating parameters may be adjusted to operate the engine at stoichiometry. For example, an intake throttle and / or the EGR valve may be adjusted to operate the engine at stoichiometry. By ensuring the exhaust gas is stoichiometric before proceeding further with the routine, the effects of rich or lean exhaust gas on the intake oxygen sensor output are reduced.

[0063] At 508, it is determined whether the crankcase ventilation (PCV) is enabled. In one example, the PCV may be enabled during boosted engine operation if a PCV valve in the vacuum-side PCV hose is closed. During this condition, the PCV may be supplied upstream of an intake oxygen sensor used to estimate EGR flow. If the PCV is enabled for supply upstream of the intake oxygen sensor, it may be determined at 516 whether purge is also enabled. For example, it may be determined whether canister purge conditions have been met and whether a canister purge valve is open.

[0064] If both purge air and the PCV are enabled for supply upstream of the intake oxygen sensor, then at 521 the routine includes measuring an intake oxygen sensor output corresponding to a combination of the EGR flow, the PCV flow, and the purge flow at a nominal reference voltage, with the sensor output adjusted with respect to ambient humidity. Here, the nominal reference voltage is a first, lower reference voltage. Next, at 522, while EGR is flowing, the routine includes modulating a reference voltage of an intake manifold oxygen sensor. Modulating the oxygen sensor reference voltage includes alternating between applying the first, lower reference voltage and a second, higher reference voltage. The first voltage is a voltage (e.g.,450 mV) at which the effect of the purge and PCV hydrocarbons on the sensor is not canceled, while the second voltage (e.g., 800 mV or higher) is a voltage at which the effect of the hydrocarbons is canceled.

[0065] At 524, the routine includes estimating an amount (the total amount) of purge and crankcase ventilation hydrocarbons in the EGR based on the sensor output during modulation. Specifically, the total purge and PCV content in the EGR is estimated based on a difference (also referred to herein as delta Ip) between a first pumping current output by the sensor upon application of the first reference voltage and a second pumping current output by the sensor upon application of the second reference voltage.

[0066] At 526, purge may be selectively disabled. Specifically, the purge valve may be closed while the PCV valve is held open. Next, at 528, the routine includes re-modulating the intake oxygen sensor reference voltage. Thus, while the initial modulation of the reference voltage (at 522) is performed with purge on, the subsequent modulation of the reference voltage is performed with purge off. At 530, an amount of crankcase ventilation hydrocarbons in the EGR is distinguished from an amount of purge hydrocarbons in the EGR based on the intake oxygen sensor output during the re-modulation.The distinguishing includes distinguishing based on a first difference between the first and second pumping currents output by the sensor during modulating and a second difference between the first and second pumping currents output by the sensor during re-modulating. Here, the first difference estimated during modulating indicates a total amount of purge and crankcase ventilation hydrocarbons in the EGR, while the second difference estimated during re-modulating indicates a crankcase ventilation content of the total amount of purge and crankcase ventilation hydrocarbons in the EGR. Consequently, by comparing the delta Ip contained with purge on to the delta Ip contained with purge off, a PCV content of the EGR can be determined.Then, based on the total amount of hydrocarbons estimated at 524, an EGR purge content can be calculated.

[0067] For example, the intake oxygen sensor may nominally operate at a lower reference voltage of 450 mV while measuring EGR, with the output referred to as iao2_ip_nominal. The reference voltage may be periodically changed to a higher reference voltage to measure dilution by canceling the effect of purge and PCV hydrocarbons. This measurement at the higher reference voltage may be referred to as iao2_ip_hi_vs. By taking the difference between the measurements at the nominal reference voltage and the higher reference voltage, the combined effect of PCV and purge hydrocarbons (iao2_hc_meas) can be estimated as: iao2_hc_meas = iao2_ip_nominal - iao2_ip_hi_vs.

[0068] To further separate the hydrocarbon effect of purge and PCV, the above voltage modulation is first repeated with purge on to obtain the hydrocarbon effect as: iao2_hc_meas_tot = iao2_hc_meas (with purge on), where iao2_hc_meas_tot is the total amount of measured PCV and purge hydrocarbons. Then, the measurement is repeated with purge off to estimate the PCV content as: iao2_hc_meas_pcv = iao2_hc_meas (with purge off).

[0069] The hydrocarbon impact of the purge air is then defined as: iao2_hc_meas_purge = iao2_hc_meas_tot - iao2_hc_meas_pcv calculated.

[0070] If back in Fig. 5 only either the PCV or purge is enabled while EGR is enabled, modulating may be used to derive the hydrocarbon contribution of this parameter to EGR. For example, if the PCV is not enabled at 508 and purge is enabled at 510, then at 534 the routine includes measuring an intake oxygen sensor output corresponding to a combination of the EGR flow and the purge flow (and no PCV flow) at the nominal (first) reference voltage, with the sensor output adjusted with respect to ambient humidity. Then, at 536, the reference voltage may be modulated, and at 538, the purge content of the EGR may be estimated based on the difference in pumping currents (Delta Ip) output by the intake oxygen sensor at the higher and lower reference voltages.

[0071] The pumping current at the higher reference voltage can be determined, for example, as Ip_hi_Vs. Then, a sensor output (or pumping current) corresponding to the EGR flow can be calculated as: Ip_egr=(Ip_hi_Vs−lp_epr_purge)*K where K is a conversion factor of the pumping current (Ip) to the EGR at the higher reference voltage, and where the purge content (Ip_purge) is defined as: lp_purge=lp_egr_purge−lp_egr is found out.

[0072] Alternatively, if the PCV is enabled at 508 and purge is not enabled at 516, then the routine includes measuring, at 517, an intake oxygen sensor output corresponding to a combination of the EGR flow and the PCV flow (and no purge flow) at the (first) nominal reference voltage, with the sensor output adjusted with respect to ambient humidity. Then, at 518, the reference voltage may be modulated, and at 520, the PCV content of the EGR may be estimated based on the difference in pumping currents (Delta Ip) output by the intake oxygen sensor at the higher and lower reference voltages.

[0073] The pumping current at the higher reference voltage can be determined, for example, as Ip_hi_Vs. Then, a sensor output (or pumping current) corresponding to the EGR flow can be calculated as: Ip_egr=(lp_hi_Vs−lp_egr_PCV)*K where K is a conversion factor of the pumping current (Ip) to the EGR at the higher reference voltage and where the PCV content (Ip_PCV) is defined as: Ip_PCV=Ip_egr_PCV−Ip_egr is found out.

[0074] As in Fig. 4, once the PCV and / or purge content have been accurately determined, the controller can correct the EGR flow estimate based on the PCV and / or purge content and adjust the EGR valve accordingly to provide a desired EGR flow. By compensating the EGR estimate determined using the intake manifold oxygen sensor for the effect of purge and PCV hydrocarbons, EGR control can be improved.

[0075] In one example, during a first EGR condition where both a purge valve and a PCV valve are open, a controller may change an intake manifold oxygen sensor reference voltage between a first, lower voltage and a second, higher voltage and estimate a total purge and PCV hydrocarbon content in the EGR based on the sensor output. During a second EGR condition where the purge valve is closed and the PCV valve is open, the controller may change the intake manifold oxygen sensor reference voltage between the first and second voltages and distinguish a purge hydrocarbon content from a PCV hydrocarbon content based on the sensor output.Here, the second, higher voltage is a voltage at which an effect of the PCV and purge hydrocarbons is canceled, while the first voltage is a voltage at which the effect is not canceled. Estimating the total content of the purge and PCV hydrocarbons in the EGR based on the sensor output during the first EGR condition includes estimating a total content based on a first difference between a first pumping current output by the sensor at the first voltage and a second pumping current output by the sensor at the second voltage.Distinguishing a purge hydrocarbon content from a PCV hydrocarbon content based on the sensor output during the second EGR condition includes estimating the PCV hydrocarbon content based on a second difference between a first pumping current output by the sensor at the first voltage and a second pumping current output by the sensor at the second voltage, and estimating the purge hydrocarbon content based on a difference between the total content estimated during the first EGR condition and the PCV hydrocarbon content estimated during the second EGR condition.

[0076] In another example, an engine system includes: an engine including an intake manifold and a crankcase coupled to the intake manifold via a PCV valve; a turbocharger having an intake compressor, an exhaust turbine, and an intercooler; and an intake throttle coupled to the intake manifold downstream of the intercooler. The system may further include a fuel vapor canister configured to receive fuel vapors from a fuel tank, the canister coupled to the intake manifold via a purge valve; and an EGR system including a passage for recirculating exhaust gas residues from a location downstream of the turbine to a location upstream of the compressor via an EGR valve. An oxygen sensor may be coupled to the intake manifold downstream of the intercooler and upstream of the intake throttle.An engine controller may be configured with computer-readable instructions to: adjust a reference voltage applied to the oxygen sensor based on either the purge conditions or the crankcase ventilation conditions being met; estimate an intake EGR dilution based on an output of the oxygen sensor during the adjusting; and estimate a purge and crankcase ventilation hydrocarbon content of the intake EGR dilution based on the output of the oxygen sensor and further based on an opening of both the PCV valve and the purge valve. The controller may further include instructions to adjust an opening of the EGR valve based on the estimated intake EGR dilution and the estimated purge and crankcase ventilation hydrocarbon content of the intake EGR dilution.Adjusting may include correcting the estimated intake EGR dilution based on the estimated purge and crankcase ventilation hydrocarbon content of the intake EGR dilution and adjusting the opening of the EGR valve to bring the corrected EGR dilution to a desired EGR dilution.

[0077] In this way, during conditions when hydrocarbons from purge and crankcase ventilation are ingested into the intake manifold, a higher reference voltage can be applied to the intake manifold oxygen sensor. The higher voltage dissociates the products of the hydrocarbons reacting with oxygen at the sensor, canceling the effect of the ingested hydrocarbons on the sensor output. This improves the reliability of the EGR dilution estimated based on the sensor output. Additionally, the reference voltage can be modulated between the higher voltage and a nominal voltage when purge air is enabled and disabled to distinguish the purge content of ingested hydrocarbons from the PCV content.By correcting the EGR dilution estimate to account for PCV and purge content, the accuracy of EGR estimation using an intake oxygen sensor is increased, which improves engine EGR control.

Claims

[1] A method for a prime mover, comprising: with EGR flow Modulating a reference voltage at an intake manifold oxygen sensor (172) via a control unit; and Estimating EGR dilution in the presence of drain and Crankcase ventilation hydrocarbons based on a sensor output received by the control unit during modulation and Adjusting a position of an EGR valve (204) via the control unit based on the estimated amount of purge and crankcase ventilation hydrocarbons. [2] The method of claim 1, wherein modulating the reference voltage of the oxygen sensor (172) comprises alternating between applying a first, lower reference voltage and a second, higher reference voltage. [3] The method of claim 2, wherein EGR flows while the engine (10) is operating under boost, and wherein during modulation, a purge valve (112) coupling a fuel system canister (22) to an intake manifold (160) is opened and a crankcase PCV valve (256) coupling the intake manifold (160) along a vacuum side crankcase hose is closed. [4] The method of claim 3, wherein estimating based on sensor output during modulating comprises estimating based on a difference between a first pumping current output by the oxygen sensor (172) upon application of a first reference voltage and a second pumping current output by the oxygen sensor (172) upon application of the second reference voltage. [5] The method of claim 4, further comprising closing the purge valve (112) to allow PCV flow, re-modulating the reference voltage, and distinguishing an amount of crankcase ventilation hydrocarbons in the EGR from an amount of purge hydrocarbons in the EGR based on sensor output during the re-modulating. [6] The method of claim 5, wherein the distinguishing comprises based on a first difference between the first and second pumping currents output by the oxygen sensor (172) during modulating and a second difference between the first and second pumping currents output by the oxygen sensor (172) during re-modulating. [7] The method of claim 6, wherein the first difference estimated during modulating indicates a total amount of purge and crankcase ventilation hydrocarbons in the EGR, and wherein the second difference estimated during re-modulating indicates a crankcase ventilation content of the total amount of purge and crankcase ventilation hydrocarbons in the EGR. [8] The method of claim 7, further comprising correcting EGR flow to the engine based on the estimated amount of purge and crankcase ventilation hydrocarbons. [9] The method of claim 1, wherein routing EGR comprises routing low pressure EGR from downstream of an exhaust turbine (124) to upstream of an intake compressor (122). [10] The method of claim 9, wherein directing EGR further comprises directing low pressure EGR at a fixed rate relative to the intake air flow. [11] The method of claim 1, further comprising adjusting one or more engine operating parameters based on the estimated amount of purge and crankcase ventilation hydrocarbons in the EGR. [12] The method of claim 11, wherein the one or more engine operating parameters comprise EGR flow, fuel injection amount, fuel injection timing, and spark ignition timing. [13] The method of claim 1, further comprising estimating EGR flow to an intake manifold (160) based on sensor output during modulating. [14] A method for a prime mover, comprising: during a first EGR condition, wherein both a purge valve (112) and a PCV valve (256) are opened via a control unit, alternating a reference voltage of an intake manifold oxygen sensor (172) between a first, lower voltage and a second, higher voltage by means of the control unit, and Estimating a total content of purge and PCV hydrocarbons in the EGR based on sensor output by means of the control unit; during a second EGR condition, wherein the purge valve (112) is closed and the PCV valve (256) is open, alternating the reference voltage of the intake manifold oxygen sensor (172) between the first and second voltages and distinguishing a purge hydrocarbon content from a PCV hydrocarbon content by means of the controller based on sensor output; Adjusting a position of an EGR valve (204) via the control unit based on the estimated amount of purge and crankcase ventilation hydrocarbons in the EGR. [15] The method of claim 14, wherein both the first and second EGR conditions comprise boosted engine operation, wherein the second, higher voltage is a voltage at which an effect of the PCV and purge hydrocarbon content is cancelled, and wherein the first, lower voltage is a voltage at which the effect is not cancelled. [16] The method of claim 14, wherein estimating a total content of purge and PCV hydrocarbons in the EGR based on sensor output during the first EGR condition comprises estimating a total content based on a first difference between a first pumping current output by the sensor at the first voltage and a second pumping current output by the sensor at the second voltage. [17] The method of claim 16, wherein distinguishing a purge hydrocarbon content from a PCV hydrocarbon content based on sensor output during the second EGR condition comprises estimating the PCV hydrocarbon content based on a second difference between a first pumping current output by the sensor at the first voltage and a second pumping current output by the sensor at the second voltage, and estimating the purge hydrocarbon content based on a difference between the total content estimated during the first EGR condition and the PCV hydrocarbon content estimated during the second EGR condition. [18] A power machine system (100) comprising: an engine (10) including an intake manifold (160), a crankcase coupled to the intake manifold (160) via a PCV valve (256); a turbocharger (120) with an inlet compressor (122), an exhaust turbine (124) and an intercooler; an intake throttle valve coupled to the intake manifold (160) downstream of the charge air cooler; a canister (22) configured to receive fuel vapors from a fuel tank (218), the canister (22) coupled to the intake manifold (160) via a purge valve (112); an EGR system including a passage for recirculating exhaust gas residues from a location downstream of the turbine (124) via an EGR valve (204) to a location upstream of the compressor (122); an oxygen sensor (172) coupled to the intake manifold (160) downstream of the charge air cooler and upstream of the intake throttle valve; and a controller with computer-readable instructions to: Setting a reference voltage applied to the oxygen sensor (172) based on either the emptying conditions or the Crankcase ventilation conditions are met; Estimating an intake EGR dilution based on an output of the oxygen sensor (172) during the adjustment by means of a control unit; and Estimating a purge and crankcase ventilation hydrocarbon content of the intake EGR dilution based on the output of the oxygen sensor (172) and further based on opening both the PCV valve (256) and the purge valve (112); Adjusting an opening of the EGR valve (204) based on the estimated intake EGR dilution and the estimated purge and crankcase ventilation hydrocarbon content of the intake EGR dilution. [19] The engine system of claim 18, wherein adjusting comprises correcting the estimated intake EGR dilution based on the estimated purge and crankcase ventilation hydrocarbon content of the intake EGR dilution and adjusting the opening of the EGR valve (204) to bring the corrected EGR dilution to a desired EGR dilution.

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