Dual Three-Way Catalytic Converter Lambda Control
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Solution Overview
Problem
The existing LIN/BIN lambda probe system for gasoline engines operates in a narrow conversion window, leading to emissions breakthroughs due to deviations in lambda values from the setpoint, especially with modern engines having dynamic operation and numerous manipulated variables, resulting in unstable catalytic converter conditions.
Innovation Solution
The method involves operating two three-way catalytic converters in different oxygen states, with the first converter in a low-oxygen range for NOx reduction and the second in an oxygen-rich range for complete HC and CO conversion, using an NOx sensor as an NH3 sensor for control and secondary air for precise lambda management, and a binary lambda probe for controlling the second converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single three-way catalytic converter is operated at lambda=1.000, then ideal conversion conditions are achieved, but the system is highly sensitive to deviations and causes emissions breakthroughs
Solution Approach 1:
The patent divides a single catalytic converter into two separate catalytic converters with different functions. The first catalytic converter is operated in a slightly rich range (lambda < 1.000) optimized for NOx reduction, while the second catalytic converter is operated in a slightly lean range (lambda > 1.000) optimized for HC and CO oxidation. This segmentation allows each converter to operate in its optimal conversion window, reducing sensitivity to lambda deviations and preventing emissions breakthroughs.
2Reliability
If the catalytic converter is operated in a narrow conversion window at lambda=1.000, then conversion efficiency is maximized, but small deviations lead to emissions breakthroughs
Solution Approach 1:
The patent applies different operational conditions to different parts of the exhaust gas treatment system. The first catalytic converter is operated in a slightly rich range (lambda < 1.000) with optimized conditions for NOx reduction, while the second catalytic converter is operated in a slightly lean range (lambda > 1.000) with optimized conditions for HC and CO oxidation. This local differentiation of operational parameters allows each converter to tolerate larger deviations from its setpoint without causing emissions breakthroughs.
3Reliability
If larger catalytic converters with higher storage capacity are used, then emissions breakthroughs are avoided, but system volume and complexity increase
Solution Approach 1:
The patent segments the catalytic converter system into two smaller converters with distinct functions rather than using one large converter. The first converter handles NOx reduction in rich conditions, while the second converter handles HC and CO oxidation in lean conditions. This segmentation achieves reliable emissions control with smaller overall volume by allowing each converter to operate in its optimal conversion window with reduced storage capacity requirements.
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
This approach provides stable exhaust gas aftertreatment, reduces emissions, allows for smaller catalytic converter volumes, and simplifies diagnosis, achieving robust control and lower emissions even in dynamic driving cycles.
Implementation Method 1
operating a first three-way catalytic converter arranged in the exhaust gas tract of the engine in a slightly low-oxygen range
Implementation Method 2
operating a second three-way catalytic converter arranged downstream thereof in the exhaust gas tract of the engine in a slightly oxygen-rich range
Implementation Method 3
blowing secondary air into the exhaust gas tract between the two three-way catalytic converters
Data Source
AI summary
A method for exhaust gas aftertreatment in a gasoline engine and an exhaust gas aftertreatment system are provided. In the method, two catalytic converters arranged in the exhaust gas tract of the gasoline engine are operated in different states. A first three-way catalytic converter is operated in a slightly low-oxygen range, and a second three-way catalytic converter is operated in a slightly oxygen-rich range. Secondary air is furthermore blown into the exhaust gas tract between the two three-way catalytic converters. It is thereby possible to reduce the output of emissions of the gasoline engine to a great extent. An exhaust gas aftertreatment system is likewise explained.