NH3 Sensor Rationality Diagnostic via Downstream NOx Monitoring

Solution Overview

Problem

Detecting a failed NH3 sensor in selective catalytic reduction (SCR) systems is challenging, particularly when positioned downstream of a reductant injector and part of the total SCR catalyst, impacting emission control.

Innovation Solution

A method involving a controller with modules to diagnose the NH3 sensor, interpreting upstream NH3 and downstream NOx composition values, determining an NH3 sensor rationality threshold, and assessing sensor health based on these values to identify sensor failures, using equations to set thresholds and account for NOx conversion efficiency and cross-sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an NH3 sensor is positioned downstream of a reductant injector and SCR catalyst to enable system control, then the sensor can provide feedback for SCR system operation, but detecting sensor failure becomes challenging and unreliable

Engineering Contradiction:

Improvesensor failure detection reliabilityVSAvoidsensor failure detection difficulty

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The patent introduces a downstream NOx sensor as an intermediary to indirectly assess the health of the upstream NH3 sensor. By measuring NOx conversion efficiency downstream and comparing it with upstream NH3 levels, the system can detect NH3 sensor failures without directly testing the sensor itself. This intermediary measurement approach resolves the difficulty of detecting failures in the challenging downstream position.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements a feedback mechanism where downstream NOx measurements are fed back to evaluate upstream NH3 sensor performance. The control module continuously monitors the relationship between upstream NH3 composition and downstream NOx conversion, using this feedback loop to detect when the NH3 sensor is providing erroneous readings. This feedback approach enables reliable failure detection despite the sensor's challenging position.

Inventive Principle:

Principle #23Feedback

2Reliability

If the NH3 sensor is relied upon for SCR system control, then system control depends on accurate sensor readings, but sensor failure significantly impacts control accuracy and emission estimates

Engineering Contradiction:

ImproveSCR system control reliabilityVSAvoidemission control impact

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent implements a feedback mechanism where downstream NOx measurements are fed back to evaluate upstream NH3 sensor performance. The control module continuously monitors the relationship between upstream NH3 composition and downstream NOx conversion, using this feedback loop to detect when the NH3 sensor is providing erroneous readings. This feedback approach enables reliable failure detection despite the sensor's challenging position.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent introduces a downstream NOx sensor as an intermediary to indirectly assess the health of the upstream NH3 sensor. By measuring NOx conversion efficiency downstream and comparing it with upstream NH3 levels, the system can detect NH3 sensor failures without directly testing the sensor itself. This intermediary measurement approach resolves the difficulty of detecting failures in the challenging downstream position.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS9429062B2Method and algorithm for performing an NH3 sensor rationality diagnostic

Publication Date: 2016.08.30 CUMMINS INC

AI summary

An example method includes interpreting an NH3 composition value at a position upstream of a selective reduction catalyst (SCR) element fluidly disposed in the exhaust conduit of an engine, interpreting a NOx composition value at a position downstream of the SCR element, and determining an NH3 sensor rationality threshold in response to the upstream NH3 composition value. The method further includes determining an NH3 sensor health value as indicating a sensor failure in response to the downstream NOx composition value exceeding the NH3 sensor rationality threshold.