Exhaust fluid dosing control system and method

1. A dosing control system for an exhaust system, the exhaust system having an exhaust flow port configured and disposed to receive exhaust flow from an internal combustion engine, and a selective catalytic reduction (SCR) apparatus disposed in downstream flow communication with the exhaust flow port, the dosing control system comprising:

a reductant tank operable to contain a reductant solution comprising urea;

an injector disposed in operable communication between the reductant tank and the SCR apparatus, and being operable to inject the reductant solution into an exhaust flow upstream of the SCR apparatus;

a first NOx sensor disposed to sense NOx emissions in the exhaust flow upstream of the SCR apparatus;

a second NOx sensor disposed to sense NOx emissions in the exhaust flow downstream of the SCR apparatus; and

a control module disposed and configured to be in signal communication with the first and second NOx sensors and to be in operable communication with the injector, the control module comprising a processing circuit responsive to executable instructions which when executed by the processing circuit is operable to set an original dosing level and decrease a dosing of the reductant solution injected by the injector based on a determination from signals received from the first and second NOx sensors that a reduction in a conversion efficiency of the SCR apparatus below a defined level of conversion efficiency has occurred;

wherein the processing circuit of the control module is responsive to executable instructions which when executed by the processing circuit is configured to facilitate one of:

a passive control process for decreasing the dosing of the reductant solution by a defined amount in response to signals from the first and second NOx sensors being indicative of the conversion efficiency of the SCR apparatus having fallen below a defined level of conversion efficiency, wherein in the passive control process the controller is configured to: execute a diagnostic test of the conversion efficiency of the SCR apparatus after a defined period of time that the engine has been running; decrease the dosing of the reductant solution by a defined amount if the conversion efficiency of the SCR apparatus is determined by the control module to be below a defined level of conversion efficiency; maintain the decreased dosing level for an existing ignition cycle of the engine; and, save to a memory the decreased dosing level for use in a next ignition cycle of the engine;

or;

an intrusive control process for decreasing the dosing of the reductant solution by a defined amount in response to signals from the first and second NOx sensors being indicative of the conversion efficiency of the SCR apparatus having fallen below a defined level of conversion efficiency, wherein in the intrusive control process, the processing circuit of the control module is responsive to executable instructions which when executed by the processing circuit is configured to: execute a diagnostic test of the conversion efficiency of the SCR apparatus after a defined period of time that the engine has been running; decrease the dosing of the reductant solution by a defined amount if the conversion efficiency of the SCR apparatus is determined by the control module to be below a defined level of conversion efficiency; maintain the decreased dosing level for an existing ignition cycle of the engine; save to a memory the decreased dosing level for use in a next ignition cycle of the engine; and, resort back to the original dosing level for use in a next diagnostic test.

2. The dosing control system of claim 1 , wherein:

the control module comprises a processing circuit responsive to executable instructions which when executed by the processing circuit facilitates a downward adjustment of the dosing of the reductant solution in response to signals from the first and second NOx sensors being indicative of the reduction in the conversion efficiency of the SCR apparatus.

3. The dosing control system of claim 2 , wherein the processing circuit is further responsive to executable instructions to decrease the dosing of the reductant solution according to at least one of: a look up table; a mathematical function; or, a multiplier.

4. The dosing control system of claim 2 , wherein the processing circuit is further responsive to executable instructions to downwardly adjust the dosing of the reductant solution in response to the conversion efficiency of the SCR apparatus falling below a defined level of conversion efficiency.

5. The dosing control system of claim 4 , wherein the defined level of conversion efficiency is 70%.

6. The dosing control system of claim 1 , wherein:

the processing circuit is configured to facilitate only one of: the passive control process; or, the intrusive control process.

7. The dosing control system of claim 1 , wherein:

in response to the processing circuit being configured to facilitate either of the passive control process or the intrusive control process, the defined level of conversion efficiency is 70%, the defined period of time is 15 minutes, and the defined amount is 10%.

8. A method for delivering an exhaust fluid reductant solution to an exhaust flow upstream of a selective catalytic reduction (SCR) apparatus disposed in flow communication with an internal combustion engine, the method comprising:

determining a NOx conversion efficiency of the SCR apparatus;

based on the NOx conversion efficiency being determined to have decreased below a defined level of conversion efficiency, decreasing by a defined amount the dosing of the reductant solution to be injected into the exhaust flow upstream of the SCR apparatus; and

injecting the decreased dosing of the reductant solution into the exhaust flow upstream of the SCR apparatus;

executing a diagnostic test of the conversion efficiency of the SCR apparatus after a defined period of time that the engine has been running;

decreasing the dosing of the reductant solution by a defined amount if the conversion efficiency of the SCR apparatus is determined by the diagnostic test to be below a defined level of conversion efficiency;

maintaining the decreased dosing level for an existing ignition cycle of the engine; and

either saving to a memory the decreased level of dosing for use in a next ignition cycle of the engine, or resorting back to the original level of dosing for use in a next ignition cycle of the engine.

9. The method of claim 8 , wherein the determining a NOx conversion efficiency of the SCR apparatus comprises:

sensing a first level of NOx emissions in the exhaust flow upstream of the SCR apparatus;

sensing a second level of NOx emissions in the exhaust flow downstream of the SCR apparatus; and

via a processing circuit, determining from the sensed first and second levels of NOx emissions a NOx conversion efficiency of the SCR apparatus.

10. The method of claim 8 , wherein:

the defined level of conversion efficiency is 70%, the defined period of time is 15 minutes, and the defined amount is 10%.

11. The method of claim 8 , wherein the decreasing by a defined amount the dosing of the reductant solution to be injected into the exhaust flow upstream of the SCR apparatus comprises adjusting the dosing of the reductant solution according to at least one of: a look up table; a mathematical function; or, a multiplier.

12. The method of claim 8 , wherein:

the step of either saving to a memory the decreased level of dosing for use in a next ignition cycle of the engine, or resorting back to the original level of dosing for use in a next ignition cycle of the engine, comprises only one of: saving to a memory the decreased level of dosing for use in a next ignition cycle of the engine; or, resorting back to the original level of dosing for use in a next ignition cycle of the engine.

13. A vehicle, comprising:

an internal combustion engine;

an exhaust system comprising an exhaust flow port configured and disposed to receive exhaust flow from the engine, and a selective catalytic reduction (SCR) apparatus disposed in downstream flow communication with the exhaust flow port; and

a dosing control system comprising:

a reductant tank operable to contain a reductant solution comprising urea;

an injector disposed in operable communication between the reductant tank and the SCR apparatus, and being operable to inject the reductant solution into an exhaust flow upstream of the SCR apparatus;

a first NOx sensor disposed to sense NOx emissions in the exhaust flow upstream of the SCR apparatus;

a second NOx sensor disposed to sense NOx emissions in the exhaust flow downstream of the SCR apparatus; and

a control module disposed and configured to be in signal communication with the first and second NOx sensors and to be in operable communication with the injector, the control module comprising a processing circuit responsive to executable instructions which when executed by the processing circuit is operable to decrease a dosing of the reductant solution injected by the injector based on a determination from signals received from the first and second NOx sensors that a reduction in a conversion efficiency of the SCR apparatus below a defined level of conversion efficiency has occurred;

wherein the processing circuit of the control module is responsive to executable instructions which when executed by the processing circuit is configured to facilitate one of:

a passive control process for decreasing the dosing of the reductant solution by a defined amount in response to signals from the first and second NOx sensors being indicative of the conversion efficiency of the SCR apparatus having fallen below a defined level of conversion efficiency, wherein in the passive control process the controller is configured to: execute a diagnostic test of the conversion efficiency of the SCR apparatus after a defined period of time that the engine has been running; decrease the dosing of the reductant solution by a defined amount if the conversion efficiency of the SCR apparatus is determined by the control module to be below a defined level of conversion efficiency; maintain the decreased dosing level for an existing ignition cycle of the engine; and, save to a memory the decreased dosing level for use in a next ignition cycle of the engine;

or;

an intrusive control process for decreasing the dosing of the reductant solution by a defined amount in response to signals from the first and second NOx sensors being indicative of the conversion efficiency of the SCR apparatus having fallen below a defined level of conversion efficiency, wherein in the intrusive control process, the processing circuit of the control module is responsive to executable instructions which when executed by the processing circuit is configured to: execute a diagnostic test of the conversion efficiency of the SCR apparatus after a defined period of time that the engine has been running; decrease the dosing of the reductant solution by a defined amount if the conversion efficiency of the SCR apparatus is determined by the control module to be below a defined level of conversion efficiency; maintain the decreased dosing level for an existing ignition cycle of the engine; save to a memory the decreased dosing level for use in a next ignition cycle of the engine; and, resort back to the original dosing level for use in a next diagnostic test.

14. The vehicle of claim 13 , wherein:

the processing circuit is configured to facilitate only one of: the passive control process; or, the intrusive control process.