Fresh air flow and exhaust gas recirculation control system and method

Abstract

A fresh air and exhaust gas control method and system for an engine air system with an air throttle and exhaust gas recirculation (EGR) valve. The method includes monitoring engine parameters; generating engine state estimates using an engine observer model; generating measured engine states based on the monitored engine parameters; computing observer error based on the differences between the measured and modeled engine states; generating model correction factors; and generating commands for adjusting the air throttle and EGR valve. An inverse engine observer model can generate the desired air throttle and EGR valve positions. The method can include generating feedback actuator commands in generating the desired air throttle and EGR valve positions. The correction factors can include fresh air, EGR and/or turbine mass flow correction factors.

We claim: 
     
         1 . A fresh air and exhaust gas control method for an engine having an air system with an air throttle and an exhaust gas recirculation (EGR) valve; the control method comprising:
 monitoring parameters of the engine using a plurality of sensors;   modeling the air system and generating engine state estimates using an engine observer model;   generating measured engine states based on the monitored engine parameters from the plurality of sensors;   computing an observer error based on the differences between the measured engine states and the engine state estimates;   generating model corrections based on the observer error, the model corrections being input to the engine observer model;   generating a desired air throttle position and a desired EGR valve position based on setpoint commands, the monitored engine parameters, the model corrections and the engine state estimates;   adjusting the air throttle based on the desired air throttle position; and   adjusting the EGR valve based on the desired EGR valve position.   
     
     
         2 . The fresh air and exhaust gas control method of  claim 1 ; wherein the generating a desired air throttle position and a desired EGR valve position step is performed using an inverse engine model, the inverse engine model comprising an inverse of the engine observer model. 
     
     
         3 . The fresh air and exhaust gas control method of  claim 1 ; further comprising:
 generating feedback actuator commands based on the setpoint commands and the engine state estimates; and   using the feedback actuator commands in generating the desired air throttle position and the desired EGR valve position.   
     
     
         4 . The fresh air and exhaust gas control method of  claim 1 ; wherein the aft system further comprises a charge air cooler and an engine intake manifold coupled to the air throttle, intake air to the engine flowing through the charge air cooler, the air throttle and the engine intake manifold; and the method further comprising:
 estimating a pressure difference across the charge air cooler;   estimating a temperature difference across the charge air cooler; and   estimating an air throttle mass flow as part of the engine state estimates based on the pressure and temperature differences across the charge air cooler.   
     
     
         5 . The fresh air and exhaust gas control method of  claim 4 ; wherein estimating a pressure difference across the charge air cooler comprises:
 estimating a compressor outlet pressure;   estimating an intake manifold pressure; and   estimating an air intake pressure at a location between the charge air cooler and the air throttle by starting at the previous value of the air intake pressure and searching a percentage of the range between the compressor outlet pressure and the intake manifold pressure for the air intake pressure that makes the charge air cooler mass flow and the air throttle mass flow the same or closest to the same.   
     
     
         6 . The fresh air and exhaust gas control method of  claim 1 ; wherein the air system further comprises an EGR cooler coupled to the EGR valve, recirculated exhaust gasses from the engine flowing through the EGR cooler, the EGR valve and the engine intake manifold; and the method further comprising;
 estimating a pressure difference across the EGR cooler;   estimating a temperature difference across the EGR cooler;   estimating an EGR valve mass flow as part of the engine state estimates based on the pressure and temperature differences across the EGR cooler.   
     
     
         7 . The fresh air and exhaust gas control method of  claim 6 ; wherein estimating a pressure difference across the EGR cooler comprises:
 estimating an exhaust manifold pressure;   estimating an intake manifold pressure; and   estimating an EGR internal pressure at a location between the EGR cooler and the EGR valve by starting at the previous value of the EGR internal pressure and searching a percentage of the range between the exhaust manifold pressure and the intake manifold pressure for the EGR internal pressure that makes the EGR cooler mass flow and the EGR valve mass flow the same or closest to the same.   
     
     
         8 . The fresh air and exhaust gas control method of  claim 4 ; wherein the air system further comprises an EGR cooler coupled to the EGR valve, recirculated exhaust gasses from the engine flowing through the EGR cooler, the EGR valve and the engine intake manifold; and the method further comprising;
 estimating a pressure difference across the EGR cooler;   estimating a temperature difference across the EGR cooler;   estimating an EGR valve mass flow as part of the engine state estimates based on the pressure and temperature differences across the EGR cooler.   
     
     
         9 . The fresh air and exhaust gas control method of  claim 8 ; wherein estimating a pressure difference across the charge air cooler comprises:
 estimating a compressor outlet pressure;   estimating an intake manifold pressure;   estimating an air intake pressure at a location between the charge air cooler and the air throttle by starting at the previous value of the air intake pressure and searching a percentage of the range between the compressor outlet pressure and the intake manifold pressure for the air intake pressure that makes the charge air cooler mass flow and the air throttle mass flow the same or closest to the same; and wherein estimating a pressure difference across the EGR cooler comprises:   estimating an exhaust manifold pressure;   estimating an EGR internal pressure at a location between the EGR cooler and the EGR valve by starting at the previous value of the EGR internal pressure and searching a percentage of the range between the exhaust manifold pressure and the intake manifold pressure for the EGR internal pressure that makes the EGR cooler mass flow and the EGR valve mass flow the same or closest to the same.   
     
     
         10 . The fresh air and exhaust gas control method of  claim 1 ; wherein the air system further comprises a charge air cooler and an engine intake manifold coupled to the air throttle, intake air to the engine flowing through the charge air cooler, the air throttle and the engine intake manifold; and wherein the generating model corrections step comprises:
 generating a fresh air mass flow correction term based on a pressure error at the engine intake manifold.   
     
     
         11 . The fresh air and exhaust gas control method of  claim 1 ; wherein the air system further comprises an EGR cooler and an engine intake manifold coupled to the EGR valve, recirculated exhaust gasses from the engine flowing through the EGR cooler, the EGR valve and the engine intake manifold; and wherein the generating model corrections step comprises:
 generating an EGR mass flow correction term based on a difference between the modelled and measured mass flows through the EGR cooler.   
     
     
         12 . The fresh air and exhaust gas control method of  claim 1 ; further comprising:
 calculating a desired intake manifold diluent mass fraction based on a desired diluent-to-air ratio setpoint, an engine speed and a number of cylinders in the engine;   calculating a desired EGR mass flow based on the desired intake manifold diluent mass fraction; and   calculating the desired EGR valve position based on the desired EGR mass flow;   calculating a desired intake manifold pressure based on the desired diluent-to-air ratio setpoint and the number of cylinders in the engine;   calculating a desired air throttle mass flow based on the desired intake manifold pressure; and   calculating the desired air throttle position based on the desired air throttle mass flow.   
     
     
         13 . The fresh air and exhaust gas control method of  claim 1 ; further comprising:
 calculating a desired intake manifold diluent mass fraction based on a desired diluent-to-air ratio setpoint, an engine speed and a number of cylinders in the engine;   calculating an intake manifold EGR mass fraction and a closed loop EGR mass flow based on the desired intake manifold diluent mass fraction;   calculating a maximum air throttle mass flow and a maximum EGR valve mass flow;   calculating a desired intake manifold pressure based on the desired diluent-to-air ratio setpoint and the number of cylinders in the engine;   calculating a maximum intake manifold mass flow based on the intake manifold EGR mass fraction, the closed loop EGR mass flow, the maximum air throttle mass flow and the maximum EGR valve mass flow;   calculating a desired intake manifold mass flow in based on the maximum intake manifold mass flow and the desired intake manifold pressure;   calculating a desired air throttle mass flow and a desired EGR valve mass flow based on the intake manifold EGR mass fraction, the closed loop EGR mass flow and the desired intake manifold mass flow in;   calculating the desired EGR valve position based on the desired EGR valve mass flow; and   calculating the desired air throttle position based on the desired air throttle mass flow.   
     
     
         14 . A fresh air and exhaust gas control system for an engine having an air system with an air throttle and an exhaust gas recirculation (EGR) valve; the control system comprising:
 a plurality of sensors for monitoring engine parameters of the engine;   an engine observer for modeling the air system and generating engine state estimates;   a comparator for generating measured engine states based on the engine parameters from the plurality of sensors, and computing an observer error based on the differences between the measured engine states and the engine state estimates;   an observer controller for generating model corrections based on the observer error, the model corrections being input to the engine observer; and   an inverse engine model for generating actuator commands based on setpoint commands, the engine parameters from the plurality of sensors, the model corrections and the engine state estimates;   wherein the positions of the air throttle and the EGR valve are adjusted based on the actuator commands.   
     
     
         15 . The fresh air and exhaust gas control system of  claim 14 , wherein the engine observer, the comparator, the observer controller, and the inverse engine model are run on an electronic control unit of the engine. 
     
     
         16 . The fresh air and exhaust gas control system of  claim 14 , further comprising a feedback controller for generating feedback actuator commands based on the setpoint commands and the engine state estimates, the positions of the air throttle and the EGR valve being adjusted based on the actuator commands and the feedback actuator commands. 
     
     
         17 . The fresh air and exhaust gas control system of  claim 14 , wherein the air system further comprises a charge air cooler and an engine intake manifold coupled to the air throttle, intake air to the engine flowing through the charge air cooler, the air throttle and the engine intake manifold; and
 the engine state estimates generated by the engine observer include an air throttle mass flow estimate, the air throttle mass flow estimate being based on pressure and temperature differences across the charge air cooler.   
     
     
         18 . The fresh air and exhaust gas control system of  claim 17 ; wherein the air system further comprises an EGR cooler coupled to the EGR valve, recirculated exhaust gasses from the engine flowing through the EGR cooler, the EGR valve and the engine intake manifold; and
 the engine state estimates generated by the engine observer include an EGR valve mass flow estimate, the EGR valve mass flow estimate being based on pressure and temperature differences across the EGR cooler.   
     
     
         19 . The fresh air and exhaust gas control system of  claim 14 ; wherein the air system further comprises a charge air cooler and an engine intake manifold coupled to the air throttle, intake air to the engine flowing through the charge air cooler, the air throttle and the engine intake manifold; and
 the observer controller generates a fresh air mass flow correction term based on a difference between the modelled and measured intake manifold pressures.   
     
     
         20 . The fresh air and exhaust gas control system of  claim 14 ; wherein the air system further comprises an EGR cooler and an engine intake manifold coupled to the EGR valve, recirculated exhaust gasses from the engine flowing through the EGR cooler, the EGR valve and the engine intake manifold; and
 the observer controller generates an EGR mass flow correction term based on a difference between the modelled and measured EGR cooler mass flows.