Diagnostic methods for selective catalytic reduction (SCR) exhaust treatment system

Abstract

In an internal combustion engine system having an exhaust aftertreatment system including a selective catalytic reduction (SCR) catalyst, diagnostic methods involve the intrusive perturbation of a target surface coverage parameter theta to determine the state of health of the SCR catalyst or an ammonia concentration sensor. An adaptive learning block adapts the target theta based on the use of NH3 sensing feedback from a mid-brick positioned ammonia concentration sensor to pull in system variation. A further diagnostic monitors the amount of adaptation and when the adaptive learning excessively learns, the diagnostic assumes that some system-level degradation must have occurred and the diagnostic will notify the overall emissions control monitor.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of U.S. provisional application Ser. No. 61 / 108,172 filed Oct. 24, 2008 entitled “DIAGNOSTIC METHODS FOR SELECTIVE CATALYTIC REDUCTION (SCR) EXHAUST TREATMENT SYSTEM and EXHAUST GAS TREATMENT SYSTEM AND METHODS FOR OPERATING THE SAME” (attorney Docket No. DP-318283), the disclosure of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD[0002]The present invention relates generally to diagnostics and more particularly to diagnostic methods for selective catalytic reduction (SCR) based engine exhaust treatment systems.BACKGROUND OF THE INVENTION[0003]The relevant background includes the fields of exhaust gas treatment systems and diagnostics therefore. As to the former field of endeavor, there have been a variety of exhaust gas treatment systems developed in the art to minimize emission of undesirable constituent components of engine exhaust gas. It is known to reduce NOx emissions us...

AI Technical Summary

Benefits of technology

The invention provides a method and system for diagnosing the health of a selective catalytic reduction (SCR) catalyst in an internal combustion engine. The method involves introducing a reductant into the exhaust gas stream and measuring the operating characteristic of the exhaust gas treatment system. By perturbing the target theta parameter and measuring the NH3 concentration level, a healthy SCR catalyst exhibits a relatively small magnitude perturbation in the NH3 sensed feedback, while a degraded SCR catalyst exhibits a much larger magnitude. The method can also determine when NH3 sensing feedback-based adaptive learning for adjusting the target theta values excessively learns, resulting in a fault or error. The technical effects of the invention include improved diagnosis of SCR catalyst health and detection of faults or errors in the system.

Problems solved by technology

However, for an SCR catalyst that has lost ammonia storage capability, the NH3 sensed feedback exhibits a much larger magnitude, indicating degraded SCR catalyst performance.

Otherwise, where the NH3 concentration does not track the target theta perturbation, the NH3 sensor is unhealthy.

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