Model-based diagnostic method and system for a selective reduction catalyst device in a vehicle

A control system for a vehicle having an engine and a selective catalytic reduction (SCR) device which receives exhaust gas from the engine and reduces a level of nitrogen oxide (NOx) gasses in the exhaust gas, the control system comprising:

• a NOx sensor positioned downstream of the SCR device;
• a first controller having an SCR model which provides estimated levels of NOx gasses in the SCR device, wherein the first controller compares the estimated level of NOx gasses from the SCR model to actual levels of NOx gasses as measured by the downstream NOx sensor, and automatically updates the SCR model when the estimated and the actual levels of NOx gasses differ from each other;
• and
• a second controller which determines an updating frequency of the SCR model, wherein the updating frequency indicates how frequently the SCR model has been automatically updated by the first controller over a calibrated duration, and which evaluates the updating frequency of the SCR model conducted by the first controller and executes a control action when the updating frequency is evaluated by the second controller as exceeding at least one calibrated threshold.

A method of diagnosing performance of an exhaust system in a vehicle having an engine, a nitrogen oxide (NOx) sensor, a first controller, and a second controller, the exhaust system including a selective catalytic reduction (SCR) device, the method comprising:

• measuring an actual level of NOx gasses downstream of the SCR device;
• estimating a level of NOx gasses using an SCR model and the first controller;
• comparing the estimated level of NOx gasses from the SCR model to the actual level of NOx gasses from the NOx sensor using the first controller;
• updating the SCR model via the first controller when the estimated and the actual level of NOx gasses differ from each other;
• determining an updating frequency of the SCR model, wherein the updating frequency indicates how frequently the SCR model has been automatically updated by the first controller over a calibrated duration;
• using the second controller to diagnose a performance of the exhaust system by automatically evaluating an updating frequency of the SCR model conducted by the first controller with respect to at least one calibrated threshold;
• and
• executing a control action when the updating frequency is evaluated by the second controller as exceeding the at least one calibrated threshold.