NOx Sensor Dynamic Monitoring via Pump Current Gradient
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Solution Overview
Problem
Conventional NOx sensor monitoring procedures are inadequate for dynamic monitoring, especially when NOx sensors are positioned downstream of a SCR catalyst or nitrogen oxide storage catalyst, as they lack precise and dynamic NOx emission models, limiting the ability to assess sensor dynamics and detect issues like electrode damage or diffusion barrier failures.
Innovation Solution
A procedure using an oxygen ion-conducting NOx sensor with a layer structure and multiple electrodes, where the temporal course of the pump current is evaluated during self-diagnosis, allowing for dynamic monitoring by assessing the gradient of the pump current, enabling detection of impaired sensor dynamics and potential electrode or diffusion barrier issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a NOx sensor is positioned downstream of an SCR catalyst or nitrogen oxide storage catalyst, then the sensor can function in the exhaust aftertreatment system, but dynamic monitoring of the sensor becomes impossible due to lack of accurate NOx emission models
Solution Approach 1:
The patent changes the monitoring approach from evaluating static integral values to evaluating dynamic temporal profiles and gradients of the pumping current. This parameter transformation enables differentiation between sensor aging and actual sensor failures even in positions downstream of SCR catalysts where NOx conversion occurs.
2Ease of operation
If conventional monitoring methods using integral evaluation are used, then the monitoring procedure is simple, but dynamic sensor impairments such as electrode damage or diffusion barrier failures cannot be detected
Solution Approach 1:
The patent introduces dynamic evaluation by analyzing the temporal profile and gradient of the pumping current during self-diagnosis. This transforms the static integral evaluation into a dynamic assessment that can detect rapid changes in sensor response, enabling identification of electrode damage, diffusion barrier failures, and other dynamic sensor impairments.
3Measurement precision
If the temporal profile and gradient of pump current are evaluated, then dynamic sensor impairments can be detected, but the monitoring procedure becomes more complex
Solution Approach 1:
The patent utilizes the existing self-diagnosis functionality of the NOx sensor and enhances it by evaluating temporal characteristics of the pumping current. The control unit performs the additional analysis using standard processing capabilities, avoiding the need for external diagnostic equipment or complex additional hardware, thus implementing self-service monitoring.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables effective dynamic monitoring of NOx sensors, even in positions where traditional methods fail, by evaluating the time course and gradient of the pump current, allowing for the detection of sensor impairments such as a poisoned electrode or damaged diffusion barrier, and is suitable for use with existing motor vehicles.
Implementation Method 1
gas components to be determined and/or oxygen are first removed from a chamber of the sensor by electrochemical pumping processes. In a further step, oxygen is selectively introduced into a chamber of the sensor by electrochemical pumping processes
Implementation Method 2
NOx sensors (NOx measuring probes) based on the Nernst principle are known for measuring the NOx concentration in a sample gas
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a method for monitoring a NOx sensor (10) having an oxygen-ion-conducting solid electrolyte and having at least one cavity (12), wherein at least one cavity (12) of the NOx sensor is flooded with a defined oxygen concentration during a self-diagnosis of the NOx sensor. The gradient of a pump current resulting therefrom is evaluated and, in the case of a deviation in comparison with reference values, possibly impaired dynamics of the NOx sensor are inferred.