SYSTEM AND METHOD FOR DETERMINING ENGINE EXHAUST COMPOSITION

• US 20120053821A1
• Filed: 06/24/2011
• Published: 03/01/2012
• Est. Priority Date: 08/24/2010
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Wolfe, Kathryn, Burleigh, Darrell W.
• Granted Patent: US 8,762,026 B2
• Time in Patent Office: Days
• US Class Current: 701/105
• CPC Class Codes: F01N 2560/025 for measuring or detecting O2, e.g. lambda sensors
• CPC Class Codes: F01N 2900/0412 using pre-calibrated maps, tables or charts
• CPC Class Codes: F01N 2900/0416 using the state of a sensor, e.g. of an exhaust gas sensor
• CPC Class Codes: F01N 2900/0601 being estimated
• CPC Class Codes: F01N 2900/08 said parameters being related to the engine
• CPC Class Codes: F01N 2900/1402 Exhaust gas composition
• CPC Class Codes: F01N 9/00 Electrical control of exhaust gas treating apparatus monitoring or diagnostic devices for exhaust-gas treatment apparatus F01N11/00; conjoint electrical control of two or more combustion engine functions F02D43/00
• CPC Class Codes: F02B 2275/14 Direct injection into combustion chamber
• CPC Class Codes: F02D 2200/0602 Fuel pressure
• CPC Class Codes: F02D 41/401 Controlling injection timing F02D41/402 takes precedence
• CPC Class Codes: F02D 41/403 with pilot injections
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An engine assembly includes a controller and at least one data storage medium storing a database. The database includes empirically-derived NOx values based on engine equivalence ratio and engine speed at predetermined reference conditions. The controller is configured to retrieve a NOx value from the database that corresponds to a measured value of the equivalence ratio and a measured value of the engine speed, and to modify the NOx value to compensate for differences between the reference conditions and the actual operating conditions of the engine assembly.

Claims

1. An engine assembly comprising:

an engine being configured such that the engine selectively generates exhaust gas, and being characterized by an engine speed having a selectively variable engine speed value, an equivalence ratio having a selectively variable equivalence ratio value, and variable operating conditions each having a respective selectively variable operating condition value;

an exhaust system including a conduit defining a passage and being operatively connected to the engine such that the exhaust gas enters the passage;

a data storage medium storing a first database having, for a plurality of different combinations of engine speed value and equivalence ratio value, a respective estimated amount of oxides of nitrogen (NOx) in the exhaust gas for when the variable operating condition values are at predetermined reference values;

a controller operatively connected to the engine and configured to monitor the engine speed, the equivalence ratio, and the variable operating conditions to obtain a measured engine speed value, a measured equivalence ratio value, and measured variable operating condition values;

wherein the controller is configured to retrieve from the first database a reference NOx value that corresponds to the measured engine speed value and the measured equivalence ratio value; and

wherein the controller is configured to modify the reference NOx value using the variable operating condition values to compensate for variation between the measured variable operating condition values and the predetermined reference values.

2. The engine assembly of claim 1, wherein the engine includes an engine cylinder and a fuel injector configured to selectively inject fuel into the cylinder;

wherein one of variable operating conditions is injection timing having a selectively variable injection timing value; and

wherein the predetermined reference value for injection timing is the best torque timing at which the engine achieves the maximum torque output at the other predetermined reference values.

3. The engine assembly of claim 2, wherein the controller is configured to determine a timing variation value;

said timing variation value being based on the difference between best torque timing and a measured injection timing value;

wherein the data storage medium stores a second database containing, for each of a plurality of timing variation values, a respective injection timing correction factor value; and

wherein the controller is configured to retrieve from the second database the injection timing correction factor value that corresponds to the determined timing variation value.

4. The engine assembly of claim 3, wherein the engine assembly is configured such that the fuel injector injects fuel into the cylinder during a plurality of injection events;

wherein each of the injection events has a respective measured injection timing value;

wherein each of the injection events has a respective mass of fuel injected into the cylinder;

wherein the controller is configured to determine a respective fuel weight for each of the injection events;

wherein the fuel weight for an injection event is the mass of fuel injected into the cylinder during the injection event divided by the total mass of fuel injected during all of the plurality of injection events;

wherein the controller is configured to retrieve from the second database a respective timing correction factor value for each of the measured injection timing values;

wherein the controller is configured to, for each of the injection events, multiply the respective timing correction factor value by the respective fuel weight to obtain a respective weighted timing correction factor value; and

wherein the controller is configured to add the respective weighted timing correction factor values to determine a final injection timing correction factor value.

5. The engine assembly of claim 4, wherein the controller is configured to multiply the weighted timing correction factor by a decay term if an injection event is a pilot injection.

6. The engine assembly of claim 3, wherein the engine assembly is configured such that the fuel injector injects fuel into the cylinder during a plurality of injection events;

wherein the engine assembly includes a fuel rail that is operatively connected to the fuel injector and characterized by a rail pressure;

wherein the controller is configured to determine a single timing variation value that applies to all of the injection events based on the start of injection of the earliest injection event, the actual fuel mass flow rate during the injection events, the average fuel mass flow rate during the injection events, and the rail pressure; and

wherein the controller retrieves from the second database the timing correction factor value that corresponds to the single timing variation value.

7. The engine assembly of claim 2, wherein the variable operating conditions include at least one of amount exhaust gas recirculation, intake manifold temperature, barometric pressure, coolant temperature, oxygen mass fraction, oxygen concentration, and humidity.

8. The engine assembly of claim 1, further comprising a reductant injector configured to inject reductant into the exhaust system;

and

wherein the controller controls the amount of reductant injected by the reductant injector based on the modified reference NOx value.

9. A method of estimating the amount of oxides of nitrogen in the exhaust of an engine, the engine being characterized by an engine speed having a selectively variable engine speed value, an equivalence ratio having a selectively variable equivalence ratio value, and variable operating conditions each having a respective selectively variable operating condition value, the method comprising:

monitoring the engine speed, the equivalence ratio, and the variable operating conditions to obtain a measured engine speed value, a measured equivalence ratio value, and measured variable operating condition values;

accessing a first database having, for a plurality of different combinations of engine speed value and equivalence ratio value, a respective estimated amount of oxides of nitrogen (NOx) in the exhaust gas for when the variable operating condition values are at predetermined reference values;

retrieve from the first database a reference NOx value that corresponds to the measured engine speed value and the measured equivalence ratio value; and

modifying the reference NOx value using the variable operating condition values to compensate for variation between the measured variable operating condition values and the predetermined reference values.

10. The method of claim 9, wherein the engine includes an engine cylinder and a fuel injector configured to selectively inject fuel into the cylinder;

wherein one of variable operating conditions is injection timing having a selectively variable injection timing value; and

wherein the predetermined reference value for injection timing is the best torque timing at which the engine achieves the maximum torque output at the other predetermined reference values.

11. The method of claim 10, further comprising determining a timing variation value;

said timing variation value being based on the difference between best torque timing and a measured injection timing value;

accessing a second database to obtain an injection timing correction factor value that corresponds to the timing variation value; and

retrieving from the second database the injection timing correction factor value that corresponds to the determined timing variation value.

12. The method of claim 11, wherein the engine is configured such that the fuel injector injects fuel into the cylinder during a plurality of injection events;

wherein each of the injection events has a respective measured injection timing value;

wherein each of the injection events has a respective mass of fuel injected into the cylinder; and

wherein the method further comprises determining a respective fuel weight for each of the injection events;

wherein the fuel weight for an injection event is the mass of fuel injected into the cylinder during the injection event divided by the total mass of fuel injected during all of the plurality of injection events;

retrieving from the second database a respective timing correction factor value for each of the measured injection timing values;

for each of the injection events, multiplying the respective timing correction factor value by the respective fuel weight to obtain a respective weighted timing correction factor value; and

adding the respective weighted timing correction factors values to determine a final injection timing correction factor value.

13. The method of claim 12, further comprising multiplying the weighted timing correction factor by a decay term if an injection event is a pilot injection.

14. The method of claim 11, wherein the engine is configured such that the fuel injector injects fuel into the cylinder during a plurality of injection events;

wherein the engine includes a fuel rail that is operatively connected to the fuel injector and characterized by a rail pressure; and

wherein the method further comprises determining a single timing variation value that applies to all of the injection events based on the start of injection of the earliest injection event, the actual fuel mass flow rate during the injection events, the average fuel mass flow rate during the injection events, and the rail pressure; and

retrieving from the second database the timing correction factor value that corresponds to the single timing variation value.

15. The engine assembly of claim 11, wherein the variable operating conditions include at least one of amount exhaust gas recirculation, intake manifold temperature, barometric pressure, coolant temperature, and humidity.

16. The engine assembly of claim 9, wherein the engine includes a reductant injector configured to inject reductant into an exhaust system;

and

controlling the amount of reductant injected by the reductant injector based on the modified reference NOx value.