Active control of one or more EGR loops

Active control of one or more exhaust gas recirculation loops is provided to manage and EGR fraction in the charge flow to produce desired operating conditions and/or provide diagnostics in response to at least one of an oxygen concentration and a NOx concentration in the charge flow and in the exhaust flow.

BACKGROUND

The present application is generally related to control of one or more exhaust gas recirculation (EGR) loops. In order to meet the stringent emissions limits for light duty vehicles, engine out NOx emissions levels must be reduced substantially when compared with current single path high pressure EGR systems. Current single loop high pressure EGR systems are limited to their NOx reduction performance by high particular matter (PM) and hydrocarbon (HC) emissions, which increase exponentially as the EGR fraction increases. Dual path high pressure and low pressure EGR systems promise the capability of further reduced NOx emission levels, but at substantially lower HC and PM emissions. Due to the increased complexity of these systems, minor changes in component performance can have drastic impacts on the actual EGR fraction of the intake air. Therefore, further improvements in this technological area are needed.

SUMMARY

Active control of one or more EGR loops of an internal combustion engine system is provided. Other aspects include unique methods, techniques, systems, devices, kits, assemblies, equipment, and/or apparatus related to control of one or more EGR loops.

Further aspects, embodiments, forms, features, benefits, objects, and advantages shall become apparent from the detailed description and figures provided herewith.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

Feedback based control strategies are proposed herein to provide capabilities of meeting the desired exhaust gas recirculation ratios or fractions in the charge flow to produce a desire operating result. In certain aspects, systems and methods for feedback based control of single loop or multiple loop EGR systems are provided. Implementation of a multiple loop EGR system may be desirable in meeting low engine out NOx emissions levels while keeping PM and HC emissions to a minimum. Due to the complexity of multiple loop EGR systems, for example, open loop control (such as those based on look-up tables corresponding to various operating parameters) does not provide the level of controls sensitivity required for operation with fluctuating operating parameters. In one form, the control approaches described herein vastly improve the controls sensitivity, and are able to account for various fluctuations in operating parameters including cooler efficiency, flow restrictions, valve position, and other parameters.

In one embodiment of a system10such as shown inFIG. 1, various sensors are inserted into the intake system14of the engine12, and can record with a controller50a variety of parameters related to the incoming charge flow30, which includes intake air flow16and any recirculated exhaust gas flow from one or both of high pressure EGR system32and low pressure EGR system34. The monitored parameters may include oxygen concentration by an oxygen sensor18, NOx concentration by a NOx sensor20, temperature by a temperature sensor22, and/or other parameters such as mass air flow of the charge air and intake manifold pressure, and parameters suitable for calculating the charge flow, such as with a speed-density approach. In addition, the parameters of the engine out exhaust gas24such as oxygen concentration from oxygen sensor26and NOx concentration from engine out NOx sensor28may also be monitored. The composition of the charge flow30including intake air flow16can then be compared with the composition of the engine out exhaust gas24in order to quantify the amount of exhaust gas24being re-circulated through the engine12. The feedback based control system10can then be used to modify parameters such as a position of low pressure EGR valve36, a position of high pressure EGR valve38, a position or opening amount of a variable geometry (VG) turbine40, a position of an intake air throttle42, a position of an exhaust throttle44, etc. in order to achieve a desired ratio of recirculated exhaust gas to the charge flow30, i.e. the EGR fraction. Additionally, these controls can be used to blend both high pressure and low pressure EGR flows in order to achieve the desired EGR fractions in the charge flow30.

Amongst other benefits, a feedback based control system10will provide improved EGR control when compared with an open loop look-up based system, and aging of the system will have a reduced impact on the ability of the system to meet requested EGR fraction.

In one form, the system10includes a dual path EGR system containing a low pressure loop34and a more traditional high pressure loop32. In the high pressure loop32, exhaust gas is removed from the flow of engine exhaust gas24upstream of the turbine40, and is passed through a heat exchanger60(e.g. a cooler)cooled by an engine coolant supply line62. This recirculated exhaust gas is then blended with compressed intake air flow16compressed by compressor41, and is then combined with fuel in the engine12during the combustion process. In the low pressure EGR loop34, exhaust gas is removed from the flow of exhaust gas24downstream of the turbine40, and is passed through a heat exchanger64(e.g. a cooler) cooled by an engine coolant supply line66. This recirculated exhaust gas is then blended with the intake air flow16upstream of the compressor41. The blended feed is then compressed in the compressor41, and is combined with fuel in the engine12during the combustion process. In one form, both the high pressure and low pressure EGR loops32,34are equipped with variable position valves38,36, respectively, used to meter the amount of exhaust gas blended into the intake air flow16.

In certain forms, in a single EGR path operation of system10, the position of, for example, the high pressure EGR valve38position is commanded based on a look-up table as a function of engine operating parameters, and the high pressure EGR fraction is estimated based on the position from the look-up table. In the system illustrated in connection withFIG. 1, the oxygen and/or NOx concentration of the charge flow30in the intake is measured by sensors18and/or20and compared with the oxygen and/or NOx concentration of the exhaust gas measured by sensors26and/or28in order to quantify the actual EGR fraction in the charge flow. These measurements can then be used to modify the position(s) of high pressure valve38and/or low pressure EGR valve36in order to adjust an oxygen concentration in the charge flow to a desired oxygen concentration by achieving the desired EGR fraction based on engine operating conditions, thus resulting in closed loop control of EGR flow.

In an alternative embodiment where the total EGR flow is comprised both of a high pressure EGR fraction and a low pressure EGR fraction, one can utilize existing controls strategies as described above for estimating the high pressure EGR fraction from a look-up table based on valve position and engine operating parameters. The oxygen sensor18or NOx sensor20installed in the intake system14can then provide closed loop feedback control of the low pressure EGR valve36and thus the low pressure EGR fraction in order to control the total EGR fraction of the charge flow30.

The system as shown inFIG. 1also provides potential benefits for on-board diagnostics (OBD) capabilities of the EGR system. The EGR flow through one or both the high pressure and low pressure EGR loops32,34can be estimated by monitoring various operating parameters of the EGR system including but not limited to temperature, pressure, etc., and determining an estimate of the EGR fraction from look up tables. By utilizing oxygen sensor18or NOx sensor20installed in the intake system14, the total EGR fraction of the charge air flow can be directly calculated since the intake air flow is known from mass air flow sensor52and the oxygen concentration and NOx concentration in the fresh air of the intake flow is known. OBD can compare this calculated actual value of the total EGR fraction to the estimated EGR fraction based on indirect measurements and look up tables in order to check the EGR flow path for potential leaks.

The use of an oxygen sensor18and/or NOx sensor20in the intake system14also provides opportunities for periodic recalibration or correction of measurements of the mass air flow sensor52. The EGR fraction in the intake system14can be measured by determining an oxygen concentration in intake system14and an oxygen concentration in the exhaust flow24, and by assuming the oxygen amount in the inlet air is at atmospheric, one can calculate the EGR fraction in the charge flow30. The rate of intake air flow16to the engine12is then calculated from the difference between the charge flow30through the intake system14and the determined EGR fraction. This calculation of intake air flow16can be used to correct the fresh air intake flow rate sensed by the mass air flow sensor52in order to account for sensor drift.

Referring toFIG. 2, a flow diagram for one embodiment of a procedure100is illustrated. Procedure100starts at102in response to, for example, a key-on event. Procedure100includes an operation104to operate engine12with a dual loop EGR system, such as engine12including an intake system14with a compressor41and an exhaust system with a turbine40, a high pressure EGR loop32connecting the exhaust system upstream of the turbine40to the intake system14downstream of the compressor41, and a low pressure EGR loop34connecting the exhaust system downstream of the turbine40to the intake system14upstream of the compressor41.

Procedure100further include an operation106to recirculate exhaust gas through the dual loop EGR system. For example, exhaust gas can be recirculated to the intake system14through both the high pressure EGR loop32and the low pressure EGR loop34to combine with the intake air flow16and provide charge flow30to an intake manifold of the engine that includes an EGR fraction. Procedure100further includes an operation108to determine a desired oxygen concentration in charge flow30, an operation110to determine at least one of an oxygen concentration and a NOx concentration in the charge flow30, and an operation112to determine at least one of an oxygen concentration and a NOx concentration in the exhaust gas24.

Procedure100also includes an operation114to adjust the EGR fraction in response to the at least one of the oxygen concentration and the NOx concentration in the charge flow30and in the exhaust gas24to adjust an actual oxygen concentration in the charge flow30toward the desired oxygen concentration. Procedure100can return to operation108, or end at116with a key-off event or other event indicating operating conditions are not suitable for procedure100.

In one embodiment, procedure100includes adjusting the EGR fraction includes controlling a position of control valve36.38in at least one of the low pressure EGR loop34and the high pressure EGR loop32. In another embodiment, the procedure includes cooling recirculated exhaust gas with the heat exchanger60(e.g. a cooler) in the high pressure EGR loop32and the heat exchanger64(e.g. a cooler) in the low pressure EGR loop34.

In another embodiment, procedure100includes determining the EGR fraction of the charge flow30in response to the at least one of the oxygen concentration and the NOx concentration in the charge flow30, the at least one of the oxygen concentration and the engine out NOx concentration in the exhaust gas24, and at least one of an oxygen concentration and a NOx concentration in the intake air flow16, A portion of the EGR fraction from the high pressure EGR loop32can be estimated in response to a position of the high pressure EGR control valve38of the high pressure EGR loop32and engine operating parameters. A target EGR fraction can be determined and a position of the control valve36in the low pressure EGR loop34is controlled to adjust the EGR fraction toward the target EGR fraction.

In another embodiment, mass air flow sensor52in the intake system14is upstream of the connection with the low pressure EGR loop32and is operable to measure the intake air flow16in the intake system14. In yet another embodiment, adjusting the EGR fraction includes operating at least one of intake throttle42, exhaust throttle44, and a variable geometry inlet to the turbine40.

Referring now toFIG. 3, a flow diagram of another embodiment procedure200is provided. After start, procedure200includes an operation202to operate engine12with a dual loop EGR system including high pressure EGR loop32and low pressure EGR loop34. Procedure200continues at operation204to recirculate exhaust gas to the intake system through at least one of the high pressure EGR loop32and the low pressure EGR loop34to combine with an intake air flow and provide a charge flow to an intake manifold of engine12. Procedure200continues at operation206to determine a charge flow30to the engine12; at operation208to determine one of an oxygen concentration and a NOx concentration in the charge flow30; and at operation210to determine one of an oxygen concentration and an engine out NOx concentration in the exhaust gas24.

Procedure200continues at operation212to determine an EGR fraction of the charge flow30from the one of the oxygen concentration and the NOx concentration in the charge flow30, the one of the oxygen concentration and engine out NOx concentration in the exhaust gas24, and one of an oxygen concentration and a NOx concentration in the intake air flow16. At operation214procedure200determines an intake air flow from the difference between the charge flow and the EGR fraction. Procedure200continues at operation216to correct an intake air flow measurement from mass air flow sensor52(MAF) in intake system14in response to a deviation of the intake air flow measurement from the intake air flow determined from the difference between the charge flow and the EGR fraction.

In one embodiment of procedure200, exhaust gas is recirculated through both of the high pressure EGR loop32and the low pressure EGR loop34.

Referring now toFIG. 4, a flow diagram of another embodiment procedure300is shown. After start, procedure300includes an operation302to operate engine12with a dual loop EGR system including high pressure EGR loop32and low pressure EGR loop34. Procedure300continues at operation304to recirculate exhaust gas to the intake system through at least one of the high pressure EGR loop32and the low pressure EGR loop34to combine with an intake air flow and provide a charge flow to an intake manifold of engine12. Procedure300continues at operation306to determine a charge flow30to the engine12; at operation308to determine an EGR fraction estimate in the charge flow30; at operation310to determine one of an oxygen concentration and an engine out NOx concentration in the charge flow30; and at operation312to determine one of an oxygen concentration and an engine out NOx concentration in the exhaust gas24.

Procedure300continues at operation314to determine an EGR fraction of the charge flow30from the one of the oxygen concentration and the NOx concentration in the charge flow30, the one of the oxygen concentration and engine out NOx concentration in the exhaust gas24, and one of an oxygen concentration and a NOx concentration in the intake air flow16. At operation316procedure300includes diagnosing the at least one of the high pressure EGR loop and the low pressure EGR loop in response to a deviation of the EGR fraction estimate from the EGR fraction.

In an embodiment of any of procedures100,200,300, determining one of the oxygen concentration and the NOx concentration in the charge flow includes measuring the oxygen concentration with a first oxygen sensor in the intake system downstream of the connection of the high pressure EGR loop with the intake system and determining one of the oxygen concentration and the engine out NOx concentration in the exhaust gas includes measuring the oxygen concentration with a second oxygen sensor in the exhaust system.

In another embodiment of any of procedures100,200,300, determining one of the oxygen concentration and the NOx concentration in the charge flow includes measuring the NOx concentration with a first NOx sensor in the intake system downstream of the connection of the high pressure EGR loop with the intake system, and determining one of the oxygen concentration and the engine out NOx concentration in the exhaust gas includes measuring the engine out NOx concentration with a second NOx sensor in the exhaust system.