System for estimating NOx content of exhaust gas produced by an internal combustion engine

• US 6,697,729 B2
• Filed: 04/08/2002
• Issued: 02/24/2004
• Est. Priority Date: 04/08/2002
• Status: Expired due to Fees

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Incorporated
• Inventors: Wright, John F.
• Primary Examiner(s): WOLFE JR, WILLIS RAY
• Application Number:
  US10/118,416
• Publication Number:
  US 20030191575A1
• Time in Patent Office: 687 Days
• Field of Search: 701/100, 701/101, 701/102, 701/103, 701/104, 701/105, 701/106, 701/108, 701/109, 123/478, 123/480, 123/568.12, 123/568.21, 123/568.25, 123/568.26, 605/99, 606/02, 606/052, 602/74, 602/76, 602/84, 602/85, 602/86, 73/232, 73/233.1, 73/233.2, 700/29, 700/30, 700/31, 700/266, 700/299
• US Class Current: 701/104
• CPC Class Codes: F01N 9/005 using models instead of sensors to determine operating characteristics of exhaust systems, e.g. calculating catalyst temperature instead of measuring it directly
• CPC Class Codes: F02B 29/0406 Layout of the intake air cooling or coolant circuit
• CPC Class Codes: F02B 37/00 Engines characterised by provision of pumps driven at least for part of the time by exhaust
• CPC Class Codes: F02D 41/0072 Estimating, calculating or determining the EGR rate, amount or flow sensors in EGR systems F02M26/45
• CPC Class Codes: F02D 41/1446 the characteristics being exhaust temperatures
• CPC Class Codes: F02D 41/1462 with determination means using an estimation
• CPC Class Codes: F02M 26/05 High pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust system upstream of the turbine and reintroduced into the intake system downstream of the compressor
• CPC Class Codes: F02M 26/23 Layout, e.g. schematics
• CPC Class Codes: F02M 26/33 controlling the temperature of the recirculated gases
• CPC Class Codes: F02M 26/47 the characteristics being temperatures, pressures or flow rates
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A system for estimating NOx content of exhaust gas produced by an internal combustion engine includes a control computer operable to estimate an exhaust temperature corresponding to temperature of exhaust gas produced by the engine, to determine an EGR fraction corresponding to a fractional amount of recirculated exhaust gas present in an air charge supplied to the engine, and to estimate an emissions index, corresponding to a fuel rate normalized, mass-based NOx concentration of the exhaust gas produced by the engine, as a function of the exhaust temperature and the EGR fraction. The control computer is further operable to determine a mass flow rate of fresh air entering the intake manifold and a fuel mass flow rate, and estimate the NOx content by volume of the exhaust gas produced by the engine as a function of charge mass flow value, the fuel mass flow value and the emissions index value.

Claims

1. System for estimating NOx content of exhaust gas produced by an internal combustion engine, comprising:

means for determining exhaust temperature corresponding to temperature of exhaust gas produced by the engine;

an exhaust gas recirculation structure configured to controllably route exhaust gas produced by the engine to an intake manifold of the engine;

means for determining an EGR fraction corresponding to a fractional amount of recirculated exhaust gas present in an air charge supplied to the engine; and

a control computer estimating a fuel rate normalized, mass-based NOx concentration of the exhaust gas produced by the engine as a function of said exhaust temperature and said EGR fraction.

2. The system of claim 1 wherein said control computer is operable to estimate said fuel rate normalized, mass-based NOx concentration of the exhaust gas produced by the engine according to the function:

3. The system of claim 1 further including a fuel system responsive to a fueling signal to supply fuel to the engine;

and wherein said means for determining exhaust temperature corresponding to temperature of exhaust gas produced by the engine includes;

a temperature sensor producing a temperature signal indicative of air temperature within said intake manifold;

a pressure sensor producing a pressure signal indicative of air pressure within said intake manifold;

an engine speed sensor producing a speed signal indicative of rotational speed of the engine; and

means for determining a charge mass flow rate corresponding to a mass flow rate of said air charge supplied to the engine;

and wherein said control computer is operable to produce said fueling signal as a function of a fuel mass flow rate and a start-of-injection value, said control computer determining said exhaust temperature as a function of said temperature signal, said pressure signal, said speed signal, said charge mass flow rate, said fuel mass flow rate and said start-of-injection value.

4. The system of claim 1 wherein said exhaust gas recirculation structure includes a flow restriction mechanism having an inlet fluidly coupled to an exhaust manifold of the engine and an outlet fluidly coupled to said intake manifold.

5. The system of claim 4 wherein said means for determining an EGR fraction corresponding to a fractional amount of recirculated exhaust gas present in an air charge supplied to the engine includes:

a first pressure sensor producing a first pressure signal indicative of air pressure within said intake manifold;

a second pressure sensor producing a second pressure signal indicative of a pressure differential across said flow restriction mechanism; and

means for determining an effective flow area of said exhaust gas through said exhaust gas recirculation structure;

and wherein said control computer is operable to determine said EGR fraction as a function of said first pressure signal, said second pressure signal, said effective flow area and said exhaust temperature.

6. The system of claim 1 further including:

means for determining a fresh air mass flow rate corresponding to a mass flow rate of fresh air supplied to the engine; and

a fuel system responsive to a fueling signal to supply fuel to the engine;

wherein said control computer is operable to produce said fueling signal as a function of a fuel mass flow rate, said control computer estimating a NOx content by volume of exhaust gas produced by the engine as a function of said fuel rate normalized, mass-based NOx concentration of the exhaust gas produced by the engine, said fresh air mass flow rate and said fuel mass flow rate.

7. The system of claim 6 wherein said control computer is operable to estimate said NOx content by volume of exhaust gas produced by the engine in units of parts-per-million.

8. The system of claim 6 wherein said control computer is operable to estimate said NOx content by volume of exhaust gas according to the function:

9. The system of claim 6 wherein said means for determining exhaust temperature corresponding to temperature of exhaust gas produced by the engine includes:

a temperature sensor producing a temperature signal indicative of air temperature within said intake manifold;

a pressure sensor producing a pressure signal indicative of air pressure within said intake manifold; and

an engine speed sensor producing a speed signal indicative of rotational speed of the engine;

and wherein said control computer is operable to produce said fueling signal further as a function of a start-of-injection value, said control computer determining said exhaust temperature as a function of said temperature signal, said pressure signal, said speed signal, said charge mass flow rate, said fuel mass flow rate and said start-of-injection value.

10. The system of claim 6 wherein said exhaust gas recirculation structure includes a flow restriction mechanism having an inlet fluidly coupled to an exhaust manifold of the engine and an outlet fluidly coupled to said intake manifold.

11. The system of claim 10 wherein said means for determining an EGR fraction corresponding to a fractional amount of recirculated exhaust gas present in an air charge supplied to the engine includes:

a first pressure sensor producing a first pressure signal indicative of air pressure within said intake manifold;

a second pressure sensor producing a second pressure signal indicative of a pressure differential across said flow restriction mechanism; and

means for determining an effective flow area of said exhaust gas through said exhaust gas recirculation structure;

and wherein said control computer is operable to determine said EGR fraction as a function of said first pressure signal, said second pressure signal, said effective flow area and said exhaust temperature.

12. A method of estimating NOx content of exhaust gas produced by an internal combustion engine, the method comprising the steps of:

determining an exhaust temperature corresponding to temperature of exhaust gas produced by the engine;

determining an EGR fraction corresponding to a fractional amount of recirculated exhaust gas present in an air charge supplied to the engine; and

estimating a fuel rate normalized, mass-based NOx concentration of the exhaust gas produced by the engine as a function of said exhaust temperature and said EGR fraction.

13. The method of claim 12 wherein the estimating step includes estimating said fuel rate normalized, mass-based NOx concentration of the exhaust gas produced by the engine according to the function:

14. The method of claim 12 wherein the step of determining an EGR fraction includes:

determining a first pressure indicative of air pressure within an intake manifold of the engine;

determining a second pressure indicative of a pressure differential across a flow restriction mechanism disposed between an exhaust manifold of the engine and said intake manifold;

determining an effective flow area of said flow restriction mechanism; and

estimating said EGR fraction as a function of said first pressure, said second pressure, said effective flow area and said exhaust temperature.

15. The method of claim 12 wherein the step of determining exhaust temperature includes:

determining an intake temperature indicative of air temperature within an intake manifold of the engine;

determining an intake pressure indicative of air pressure within said intake manifold;

determining an engine speed indicative of rotational speed of the engine;

determining a charge mass flow rate corresponding to a mass flow rate of air charge supplied to the engine;

determining a fuel mass flow rate corresponding to a mass flow rate of fuel supplied to the engine;

determining a start-of-injection value corresponding to a start of injection of fuel into the engine; and

estimating said exhaust temperature as a function of said intake temperature, said intake pressure, said engine speed, said charge mass flow rate, said fuel mass flow rate and said start-of-injection value.

16. The method of claim 12 further including the steps of:

determining a fresh air mass flow rate corresponding to a mass flow rate of fresh air supplied to the engine;

determining a fuel mass flow rate corresponding to a mass flow rate of fuel supplied to the engine; and

estimating a NOx content by volume of exhaust gas produced by the engine as a function of said fuel rate normalized, mass-based NOx concentration of the exhaust gas produced by the engine, said fresh air mass flow rate and said fuel mass flow rate.

17. The method of claim 16 wherein the step of estimating a NOx content by volume of exhaust gas includes estimating said NOx content by volume of exhaust gas produced by the engine in units of parts-per-million.

18. The method of claim 16 wherein the step of estimating a NOx content by volume of exhaust gas includes estimating said NOx content by volume of exhaust gas according to the function:

19. The method of claim 16 wherein the step of determining an EGR fraction includes:

determining a first pressure indicative of air pressure within an intake manifold of the engine;

determining a second pressure indicative of a pressure differential across a flow restriction mechanism disposed between an exhaust manifold of the engine and said intake manifold;

determining an effective flow area of said flow restriction mechanism; and

estimating said EGR fraction as a function of said first pressure, said second pressure, said effective flow area and said exhaust temperature.

20. The method of claim 16 wherein the step of determining exhaust temperature includes:

determining an intake temperature indicative of air temperature within an intake manifold of the engine;

determining an intake pressure indicative of air pressure within said intake manifold;

determining an engine speed indicative of rotational speed of the engine;

determining a start-of-injection value corresponding to a start of injection of fuel into the engine; and

estimating said exhaust temperature as a function of said intake temperature, said intake pressure, said engine speed, said charge mass flow rate, said fuel mass flow rate and said start-of-injection value.