Exhaust Lambda Compensation Using NOx Feedback to Limit Breakthrough
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Solution Overview
Problem
Traditional oxygen sensor-based controls in vehicle exhaust systems struggle to effectively control nitrogen oxides (NOx) breakthrough emissions, leading to inefficiencies and higher costs in aftertreatment systems.
Innovation Solution
Implementing an NOx sensor and control algorithm that integrates NOx concentration measurements when the mid-TWC oxygen sensor control error is within a threshold voltage, calculating lambda compensation based on these measurements to adjust the air/fuel ratio and reduce NOx breakthrough.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional oxygen sensor-based controls are used to manage exhaust treatment, then the control system is simple and cost-effective, but NOx breakthrough emissions cannot be effectively controlled
Solution Approach 1:
The patent combines oxygen sensor-based control with NOx sensor-based control into a unified control system. The NOx sensor output is integrated with the oxygen sensor signal through a gain factor, creating a composite control signal that leverages both sensor types to achieve effective NOx control while maintaining system simplicity
Solution Approach 2:
The patent implements feedback control by continuously monitoring NOx sensor output and using it to adjust the air/fuel ratio control strategy. The integrated NOx signal provides real-time feedback on NOx emissions, enabling dynamic adjustment of the catalyst operation to prevent NOx breakthrough
2Reliability
If a large catalyst is provided to tolerate NOx emissions from oxygen sensor-based control, then NOx breakthrough is tolerated, but the aftertreatment system cost increases
Solution Approach 1:
The patent applies preliminary action by proactively adjusting the air/fuel ratio to maintain optimal catalyst operation before NOx breakthrough occurs. The control system uses NOx sensor feedback to make preemptive adjustments to fueling strategy, preventing the catalyst from becoming saturated with NOx rather than tolerating breakthrough after it happens
3Reliability
If NOx sensor is integrated with oxygen sensor control, then NOx breakthrough is reduced, but the control algorithm complexity increases
Solution Approach 1:
The patent changes control parameters by introducing a gain factor that scales the NOx sensor output to be compatible with oxygen sensor control signals. This parameter transformation allows the NOx signal to be integrated into the existing control framework without requiring a complete redesign of the control algorithm
Solution Approach 2:
The patent uses an intermediary approach by introducing a gain factor as a mediator between the NOx sensor output and the control system. This gain factor translates the NOx sensor signal into a form that can be effectively combined with oxygen sensor signals, facilitating integration without direct complex interaction between sensor systems
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
Significantly reduces NOx emissions by accurately compensating for oxygen sensor errors and integrating NOx sensor data to optimize the air/fuel ratio, enhancing the efficiency of NOx control in vehicle exhaust systems.
Implementation Method 1
The TWC is configured to oxidize carbon monoxide (CO) and unburnt hydrocarbons (HC) to produce carbon dioxide (CO2) and water (H2O)
Implementation Method 2
reduce nitrogen oxides (NOx) to nitrogen (N2)
Implementation Method 3
one or more oxygen (O2) sensors disposed proximate to a three-way catalytic converter (TWC) in an exhaust system of the vehicle, the one or more O2 sensors each being configured to measure an O2 level of exhaust gas
Implementation Method 4
a nitrogen oxides (NOx) sensor configured to measure an NOx level of the exhaust gas downstream of the TWC
Data Source
AI summary
An engine control system includes one or more oxygen (O2) sensors disposed proximate to a three-way catalytic converter (TWC) in an exhaust system of the vehicle, a nitrogen oxides (NOx) sensor configured to measure an NOx level of the exhaust gas downstream of the TWC, and a controller. The controller is programmed to determine a downstream O2 sensor control error, compare the O2 sensor control error to a predetermined threshold voltage, enable an NOx control logic if the O2 sensor control error is less than the predetermined threshold voltage, monitor the NOx sensor and integrate a measured NOx concentration for a predetermined time threshold or NOx flow threshold, determine a lambda compensation based on the integrated NOx concentration, and adjust an air/fuel ratio of the engine based on the lambda compensation to reduce NOx breakthrough.