Variable geometry turbocharger feed forward control system and method

Abstract

A variable geometry turbocharger control method and system for an engine air system with a variable geometry turbocharger having adjustable vanes. 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 vane positions of the variable geometry turbocharger. An inverse engine observer model can generate the desired variable geometry turbocharger vane positions. The method can include generating feedback actuator commands in generating the desired variable geometry turbocharger vane positions. The correction factors can include fresh air, EGR and/or turbine mass flow correction factors.

We claim: 
     
         1 . A variable geometry turbocharger control method for an engine having an air system with a variable geometry turbocharger having adjustable vanes; 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 turbocharger vane position based on setpoint commands, the monitored engine parameters, the model corrections and the engine state estimates;   adjusting positions of the vanes of the variable geometry turbocharger based on the desired turbocharger vane position.   
     
     
         2 . The variable geometry turbocharger control method of  claim 1 ; wherein the generating a desired turbocharger vane position step is performed using an inverse engine model, the inverse engine model comprising an inverse of the engine observer model. 
     
     
         3 . The variable geometry turbocharger 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 turbocharger vane position.   
     
     
         4 . The variable geometry turbocharger control method of  claim 1 ; wherein the air system further comprises an intake manifold, an exhaust manifold and an exhaust gas recirculation (EGR) cooler, exhaust gasses from the engine flowing through the exhaust manifold and into the EGR cooler or the variable geometry turbocharger;
 and exhaust gasses from the EGR cooler flowing through the intake manifold and into the engine, the method further comprising:   calculating a desired EGR rich mass flow;   calculating a desired exhaust manifold pressure; and   calculating a desired turbine mass flow through the variable geometry turbocharger based on the desired exhaust manifold pressure; and   determining the desired turbocharger vane position based on the desired turbine mass flow.   
     
     
         5 . The variable geometry turbocharger control method of  claim 4 ; wherein calculating a desired EGR rich mass flow comprises:
 calculating a desired intake manifold EGR rich mass fraction;   calculating a desired rich mass flow into the engine cylinders; and   calculating the desired EGR rich mass flow based on the product of the desired intake manifold EGR rich mass fraction and the desired rich mass flow into the engine cylinders.   
     
     
         6 . The variable geometry turbocharger control method of  claim 5 ; wherein calculating a desired intake manifold EGR rich mass fraction comprises:
 calculating a desired intake manifold diluent rich mass fraction based on a desired engine rich fuel-to-air ratio and a desired engine diluent-to-air ratio.   
     
     
         7 . The variable geometry turbocharger control method of  claim 6 ; wherein the air system further comprises an EGR valve controlling flow through the EGR cooler, the EGR valve having a maximum valve open position, the method further comprising:
 calculating a desired EGR valve position;   when the desired EGR valve position is less than the maximum valve open position, calculating a minimum exhaust manifold pressure based on the desired EGR rich mass flow and a desired intake manifold rich pressure; and   when the desired EGR valve position is not less than the maximum valve open position, calculating the minimum exhaust manifold pressure based on a desired EGR mass flow and a current intake manifold pressure.   
     
     
         8 . The variable geometry turbocharger control method of  claim 4 ; wherein calculating a desired exhaust manifold pressure comprises;
 calculating an unlimited desired exhaust manifold pressure based on a desired intake manifold pressure and a previous desired exhaust manifold pressure.   
     
     
         9 . The variable geometry turbocharger control method of  claim 8 ; further comprising:
 limiting the unlimited desired exhaust manifold pressure to the maximum of the calculated unlimited desired exhaust manifold pressure, the minimum exhaust manifold pressure for necessary EGR mass flow, and a minimum exhaust manifold pressure for engine performance.   
     
     
         10 . The variable geometry turbocharger control method of  claim 8 ; further comprising:
 limiting the unlimited desired exhaust manifold pressure to the minimum of the calculated unlimited desired exhaust manifold pressure, a maximum exhaust manifold pressure for engine delta pressure protection, and a maximum exhaust manifold pressure for engine component protection.   
     
     
         11 . The variable geometry turbocharger control method of  claim 4 ; wherein calculating a desired turbine mass flow comprises:
 calculating an exhaust manifold pressure error as the difference between the calculated desired exhaust manifold pressure and the calculated exhaust manifold pressure from the engine observer model;   calculating a closed loop turbine mass flow based on the exhaust manifold pressure error;   determining a feed forward turbine mass flow based on the difference between a mass flow out of the engine cylinders and an EGR mass flow determined by the engine observer model; and   calculating the desired turbine mass flow based on the closed loop turbine mass flow and the feed forward turbine mass flow.   
     
     
         12 . The variable geometry turbocharger control method of  claim 1 ; wherein the air system further comprises an exhaust manifold, an intake manifold and a low pressure turbine, exhaust gasses from the engine flowing through the exhaust manifold and into the intake manifold or the variable geometry turbocharger; and exhaust gasses from the variable geometry turbocharger flowing through the low pressure turbine, and wherein determining the desired turbocharger vane position comprises:
 determining a desired turbine mass flow;   initializing a current desired vane position;   finding a turbine interstage pressure between the variable geometry turbocharger and the low pressure turbine for the current desired vane position that produces the same or closest to the same mass flows through the variable geometry turbocharger and the low pressure turbine;   comparing the desired turbine mass flow to a modeled mass flow through the variable geometry turbocharger and the low pressure turbine for the found turbine interstage pressure;   adjusting the current desired vane position based on the comparison between the desired turbine mass flow and the modeled mass flow through the variable geometry turbocharger and the low pressure turbine; and   repeating the finding, comparing and adjusting steps to determine the desired turbocharger vane position.   
     
     
         13 . The variable geometry turbocharger control method of  claim 12 ; wherein generating model corrections based on the observer error comprises:
 generating a turbine mass flow correction factor based on the difference between a modelled exhaust manifold pressure from the engine observer model and a measured exhaust manifold pressure from the plurality of sensors; and   wherein the turbine mass flow correction factor is used to correct the mass flows through the variable geometry turbocharger and the low pressure turbine used in finding the turbine interstage pressure.   
     
     
         14 . The variable geometry turbocharger control method of  claim 1 ; wherein generating model corrections based on the observer error comprises:
 generating a turbine mass flow correction factor based on the difference between a modelled exhaust manifold pressure from the engine observer model and a measured exhaust manifold pressure from the plurality of sensors.   
     
     
         15 . A variable geometry turbocharger control system for an engine having an air system with a variable geometry turbocharger having adjustable vanes; 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 vanes of the variable geometry turbocharger are adjusted based on the actuator commands.   
     
     
         16 . The variable geometry turbocharger control system of  claim 15 , wherein the engine observer, the comparator, the observer controller, and the inverse engine model are run on an electronic control unit of the engine. 
     
     
         17 . The variable geometry turbocharger control system of  claim 15 , further comprising a feedback controller for generating feedback actuator commands based on the setpoint commands and the engine state estimates, the positions of the vanes of the variable geometry turbocharger being adjusted based on the actuator commands and the feedback actuator commands. 
     
     
         18 . The variable geometry turbocharger control system of  claim 15 , wherein the air system further comprises an intake manifold, an exhaust manifold, an exhaust gas recirculation (EGR) cooler, and a low pressure turbine, exhaust gasses from the engine flowing through the exhaust manifold and into the EGR cooler or the variable geometry turbocharger, exhaust gasses from the EGR cooler flowing through the intake manifold and back into the engine, and exhaust gasses from the variable geometry turbocharger flowing through the low pressure turbine; the control system further comprising:
 a turbine mass flow module for calculating a desired turbine mass flow based on a desired EGR mass flow and a desired exhaust manifold pressure;   wherein the desired turbine mass flow is used in calculating the actuator commands.   
     
     
         19 . The variable geometry turbocharger control system of  claim 18 , further comprising:
 an interstage pressure search module for finding an interstage pressure between the variable geometry turbocharger and the low pressure turbine for a current turbocharger vane position that provides the same or closest to the same mass flow through the variable geometry turbocharger and the low pressure turbine;   a vane position adjustment module for adjusting the current turbocharger vane position based on a comparison between the desired turbine mass flow and the modeled mass flow through the variable geometry turbocharger and the low pressure turbine for the interstage pressure found by the interstage pressure search module;   wherein the adjusted turbocharger vane position found by the vane position adjustment module is used in calculating the actuator commands.   
     
     
         20 . The variable geometry turbocharger control system of  claim 19 ; wherein:
 the observer controller generates a turbine mass flow correction factor based on the difference between the modelled and measured exhaust manifold pressures; and   the turbine mass flow correction factor is used by the interstage pressure search module.