Robust EGR control for counteracting exhaust back-pressure fluctuation attributable to soot accumulation in a diesel particulate filter

1. A method for counteracting the effect of soot accumulation in a diesel particulate filter (DPF) in an exhaust system of a diesel engine on the control of exhaust gas recirculation (EGR) through an EGR system of the engine by a control system of the engine, the method comprising:

in the control system,

a) processing certain data to select a data value for present EGR volumetric efficiency that is based on a predetermined relationship between certain parameters associated with operation of the engine,

b) processing the selected data value for present EGR volumetric efficiency and certain other data, including data that accounts for present soot accumulation in the DPF, to develop a data value indicative of present total mass flow through the engine during engine operation, and

c) processing the data value indicative of present total mass flow through the engine and still other data to develop flow control data for controlling flow of exhaust gas through the EGR system, and

in the EGR system,

using the flow control data for controlling flow of exhaust gas.

2. A method as set forth in claim 1 wherein step a) comprises processing certain data to select a data value for present EGR volumetric efficiency that is based a relationship of EGR flow being proportional to the square root of the difference between pressure in an exhaust manifold of the engine and pressure in an intake manifold of the engine.

3. A method as set forth in claim 1 wherein step a) comprises processing certain data to select a data value for present EGR volumetric efficiency that is based on a relationship of the sum of EGR flow and mass airflow into the engine being a constant at any given combination of EGR flow and mass airflow.

4. A method as set forth in claim 1 wherein step a) comprises processing data values for present engine speed and present indicated engine torque according to a map containing data values for EGR volumetric efficiency, each of which is correlated with a set of data values for engine speed and indicated engine torque, to select from the map a data value for present EGR volumetric efficiency that is correlated with the data value for present engine speed and the data value for present indicated engine torque.

5. A method as set forth in claim 4 wherein step b) comprises processing a data value for present pressure drop across the DPF according to a multiplier map containing data values for a multiplier, each of which is correlated with a data value for pressure drop across the DPF, to select from the multiplier map a data value for the multiplier that is correlated with the data value for present pressure drop across the DPF, multiplying the selected data value for present EGR volumetric efficiency by the data value for the selected multiplier to develop a data value for the product of the multiplication, and using the data value for the product of the multiplication as the data value for the data accounting for present soot accumulation in the DPF.

6. A method as set forth in claim 5 wherein step c) comprises

i) multiplying the data value indicative of present total mass flow through the engine and a data value for desired EGR percentage to develop a data value for desired EGR mass flow,

ii) processing the data value for desired EGR mass flow and a data value indicative of present pressure drop across an EGR valve in the EGR system according to a valve control map containing data values for an amount of opening for the EGR valve, each of which is correlated with a set of data values for desired EGR mass flow and pressure drop across the EGR valve, to select from the valve control map a data value for amount of opening correlated with the data value for desired EGR mass flow and the data value indicative of present pressure drop across the EGR valve, and

in the EGR system, causing the EGR valve to be open in an amount correlated with the selected data value for the amount of opening.

7. A method as set forth in claim 6 wherein the data value for desired EGR percentage is developed by processing data values for present engine speed and present indicated engine torque according to an EGR percentage map containing data values for desired EGR percentage, each of which is correlated with a set of data values for engine speed and indicated engine torque, to select from the EGR percentage map a data value for desired EGR percentage that is correlated with the data values for present engine speed and present indicated engine torque.

8. A method as set forth in claim 5 wherein step c) comprises

i) multiplying the data value for the product of the multiplication and a data value for desired mass airflow through the engine to develop a data value for corrected desired mass airflow through the engine,

ii) processing the data value for corrected desired mass airflow through the engine and a data value indicative of actual mass airflow through the engine to develop a data value for a mass airflow error signal,

iii) processing the data value for the mass airflow error signal through a proportional-integral-derivative control function to develop a data value for an amount of opening of an EGR valve in the EGR system, and

in the EGR system, causing the EGR valve to be open in an amount correlated with the data value for the amount of opening of the EGR valve.

9. A method as set forth in claim 8 wherein the data value for desired mass airflow through the engine is developed by processing data values for present engine speed and present indicated engine torque according to a desired mass airflow map containing data values for desired mass airflow, each of which is correlated with a set of data values for engine speed and indicated engine torque, to select from the desired mass airflow map a data value for desired mass airflow that is correlated with the data values for present engine speed and present indicated engine torque.

10. A diesel engine comprising:

an exhaust system comprising a diesel particulate filter (DPF) for trapping diesel particulate matter (DPM) in exhaust gas passing through the exhaust system;

an EGR system for recirculating some exhaust gas through the engine;

and a control system for controlling flow of exhaust gas through the EGR system in consequence of the processing of data by the control system wherein the control system

a) processes certain data to select a data value for present EGR volumetric efficiency that is based on a predetermined relationship between certain parameters associated with operation of the engine,

b) processes the selected data value for present EGR volumetric efficiency and certain other data, including data that accounts for present soot accumulation in the DPF, to develop a data value indicative of present total mass flow through the engine during engine operation, and

c) processes the data value indicative of present total mass flow through the engine and still other data to develop flow control data for controlling flow of exhaust gas through the EGR system, and

d) controls the flow of exhaust gas through EGR system in accordance with the flow control data.

11. An engine as set forth in claim 10 wherein the control system comprises a map containing data values for EGR volumetric efficiency, each of which is correlated with a set of data values for engine speed and indicated engine torque, and processes data values for present engine speed and present indicated engine torque to select from the map a data value for present EGR volumetric efficiency that is correlated with the data value for present engine speed and the data value for present indicated engine torque.

12. An engine as set forth in claim 11 wherein the control system comprises a multiplier map containing data values for a multiplier, each of which is correlated with a data value for pressure drop across the DPF, processes a data value for present pressure drop across the DPF to select from the multiplier map a data value for the multiplier that is correlated with the data value for present pressure drop across the DPF, multiplies the selected data value for present EGR volumetric efficiency by the data value for the selected multiplier to develop a data value for the product of the multiplication, and uses the data value for the product of the multiplication as the data value for the data accounting for present soot accumulation in the DPF.

13. An engine as set forth in claim 12 wherein

the EGR system comprises an EGR valve that controls flow through the EGR system, and

the control system comprises a valve control map containing data values for an amount of opening of the EGR valve, each of which is correlated with a set of data values for desired EGR mass flow and pressure drop across the EGR valve, and

i) multiplies the data value indicative of present total mass flow through the engine and a data value for desired EGR percentage to develop a data value for desired EGR mass flow;

ii) processes the data value for desired EGR mass flow and a data value indicative of present pressure drop across the EGR valve to select from the valve control map a data value for amount of opening correlated with the data value for desired EGR mass flow and the data value indicative of pressure drop across the EGR valve; and

iii) causes the EGR valve to be open in an amount correlated with the selected data value for the amount of opening.

14. An engine as set forth in claim 13 wherein the control system comprises an EGR percentage map containing data values for desired EGR percentage, each of which is correlated with a set of data values for engine speed and indicated engine torque, develops a data value for desired EGR percentage by processing data values for present engine speed and present indicated engine torque to select from the EGR percentage map a data value for desired EGR percentage that is correlated with the data values for present engine speed and present indicated engine torque.

15. An engine as set forth in claim 12 wherein the EGR system comprises an EGR valve that controls flow through the EGR system, and the control system

i) multiplies the data value for the product of the multiplication and a data value for desired mass airflow through the engine to develop a data value for corrected desired mass airflow through the engine;

ii) processes the data value for corrected desired mass airflow through the engine and a data value indicative of actual mass airflow through the engine to develop a data value for a mass airflow error signal;

iii) processes the data value for the mass airflow error signal through a proportional-integral-derivative control function to develop a data value for an amount of opening of an EGR valve in the EGR system; and

iv) causes the EGR valve to be open in an amount correlated with the data value for the amount of opening of the EGR valve.

16. An engine as set forth in claim 15 wherein the control system comprises a desired mass airflow map containing data values for desired mass airflow, each of which is correlated with a set of data values for engine speed and indicated engine torque, and develops the data value for desired mass airflow through the engine by selecting from the desired mass airflow map a data value for desired mass airflow that is correlated with the data values for present engine speed and present indicated engine torque.

17. A system for counteracting the effect of soot accumulation in a diesel particulate filter (DPF) in an exhaust system of a diesel engine on the control of exhaust gas recirculation (EGR) through an EGR system of the engine, the system comprising:

a processor for processing data and performing a control function based on a result of data processing, wherein the processor

a) processes certain data to select a data value for present EGR volumetric efficiency that is based on a predetermined relationship between certain parameters associated with operation of the engine,

b) processes the selected data value for present EGR volumetric efficiency and certain other data, including data that accounts for present soot accumulation in the DPF, to develop a data value indicative of present total mass flow through the engine during engine operation, and

c) processes the data value indicative of present total mass flow through the engine and still other data to develop flow control data for controlling flow of exhaust gas through the EGR system, and

d) controls flow of exhaust gas through the EGR system based on the flow control data.

18. A system as set forth in claim 17 wherein the processor comprises and executes an algorithm for controlling EGR flow that is based a relationship of EGR flow being proportional to the square root of the difference between pressure in an exhaust manifold of the engine and pressure in an intake manifold of the engine.

19. A system as set forth in claim 17 wherein the processor comprises and executes an algorithm for controlling EGR flow that is based on a relationship of the sum of EGR flow and mass airflow into the engine being a constant at any given combination of EGR flow and mass airflow.

20. A system as set forth in claim 17 wherein the processor processes data values for present engine speed and present indicated engine torque according to a map containing data values for EGR volumetric efficiency, each of which is correlated with a set of data values for engine speed and indicated engine torque, by selecting from the map a data value for present EGR volumetric efficiency that is correlated with the data value for present engine speed and the data value for present indicated engine torque.

21. A system as set forth in claim 20 wherein the processor processes a data value for present pressure drop across the DPF according to a multiplier map containing data values for a multiplier, each of which is correlated with a data value for pressure drop across the DPF, by selecting from the multiplier map a data value for the multiplier that is correlated with the data value for present pressure drop across the DPF, multiplies the selected data value for present EGR volumetric efficiency by the data value for the selected multiplier to develop a data value for the product of the multiplication, and uses the data value for the product of the multiplication as the data value for the data accounting for present soot accumulation in the DPF.

22. A system as set forth in claim 21 wherein the processor multiplies the data value indicative of present total mass flow through the engine and a data value for desired EGR percentage to develop a data value for desired EGR mass flow, processes the data value for desired EGR mass flow and a data value indicative of present pressure drop across an EGR valve in the EGR system according to a valve control map containing data values for an amount of opening for the EGR valve, each of which is correlated with a set of data values for desired EGR mass flow and pressure drop across the EGR valve, by selecting from the valve control map a data value for amount of opening correlated with the data value for desired EGR mass flow and the data value indicative of present pressure drop across the EGR valve, and causes the EGR valve to be open in an amount correlated with the selected data value for the amount of opening.

23. A system as set forth in claim 22 wherein the processor develops a data value for desired EGR percentage by processing data values for present engine speed and present indicated engine torque according to an EGR percentage map containing data values for desired EGR percentage, each of which is correlated with a set of data values for engine speed and indicated engine torque, by selecting from the EGR percentage map a data value for desired EGR percentage that is correlated with the data values for present engine speed and present indicated engine torque.

24. A system as set forth in claim 21 wherein the processor multiplies the data value for the product of the multiplication and a data value for desired mass airflow through the engine to develop a data value for corrected desired mass airflow through the engine, processes the data value for corrected desired mass airflow through the engine and a data value indicative of actual mass airflow through the engine to develop a data value for a mass airflow error signal, processes the data value for the mass airflow error signal through a proportional-integral-derivative control function to develop a data value for an amount of opening of an EGR valve in the EGR system, and causes the EGR valve to be open in an amount correlated with the data value for the amount of opening of the EGR valve.

25. A system as set forth in claim 24 wherein the processor develops a data value for desired mass airflow through the engine by processing data values for present engine speed and present indicated engine torque according to a desired mass airflow map containing data values for desired mass airflow, each of which is correlated with a set of data values for engine speed and indicated engine torque, by selecting from the desired mass airflow map a data value for desired mass airflow that is correlated with the data values for present engine speed and present indicated engine torque.