NOx Trap Purging with Dual-Mode Oxygen Sensor Feedback
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Solution Overview
Problem
Current nitrogen oxide (NOx) trap purging processes are not reliable enough to maintain high storage efficiency, leading to incomplete purging and increased pollutant emissions, as they rely on oxygen sensor switching criteria which does not guarantee complete trap emptying, and are sensitive to initial conditions and engine variations.
Innovation Solution
A method for purging NOx traps that includes a step to detect the need for purging when the NOx mass reaches a threshold, followed by a purge entry delay, allowing purging to continue in two modes: a standard mode based on oxygen probe richness switching, and a reinforced mode that extends purging duration if the delay is prolonged, ensuring complete emptying of the trap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If purging is stopped based on oxygen sensor switching criterion, then fuel consumption is reduced, but trap emptying is incomplete and storage efficiency decreases
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring the richness signal from the oxygen sensor downstream of the trap during purging. The purging process is dynamically adjusted based on this feedback, extending the duration until the richness signal switches from rich to lean, ensuring complete trap emptying while optimizing fuel consumption.
Solution Approach 2:
The purging duration is made dynamic rather than fixed. The system adapts the purging duration based on real-time trap state and sensor feedback, extending purging when needed to ensure complete emptying and reducing it when the trap is sufficiently cleared, thereby optimizing both completeness and fuel efficiency.
2Reliability
If purging duration is extended to ensure complete trap emptying, then storage efficiency is maintained, but fuel consumption increases
Solution Approach 1:
The system uses feedback from the oxygen sensor to determine the optimal purging duration. Purging continues only as long as necessary to achieve complete trap emptying, with the richness signal serving as the termination criterion. This prevents unnecessary extended purging while ensuring storage efficiency is maintained.
Solution Approach 2:
The system changes the operating parameter (air-fuel ratio) dynamically during purging. By adjusting the richness of the mixture and monitoring its effect on the trap contents via the oxygen sensor, the system optimizes the balance between purging effectiveness and fuel consumption.
3Reliability
If purging is triggered immediately when NOx mass reaches threshold, then trap efficiency is maintained, but engine operation disruptions increase
Solution Approach 1:
The system prepares for purging in advance by monitoring NOx mass accumulation and pre-conditioning the system. When the threshold is approached, the system gradually transitions toward rich mixture operation, allowing smooth purging initiation that minimizes disruption to engine operation while maintaining trap efficiency.
4Reliability
If purging duration is extended for prolonged entry delay, then residual NOx mass is reduced, but fuel consumption increases
Solution Approach 1:
The oxygen sensor provides continuous feedback during extended purging following prolonged entry delay. This feedback allows the system to terminate purging as soon as the trap is sufficiently cleared, preventing unnecessary fuel consumption while ensuring residual NOx mass is reduced to acceptable levels.
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 maintains high storage efficiency close to maximum levels, reducing residual NOx mass in the trap and minimizing pollutant emissions by ensuring thorough purging, even under varying engine conditions.
Implementation Method 1
During normal engine operation in lean mixture, it stores nitrogen oxide molecules from combustion in the engine with a certain efficiency, called storage efficiency
Implementation Method 2
The trap is then purged: the NOx molecules that were stored in the trap during the lean-mixture phase are reduced to harmless species by the action of the fuel delivered to the trap along with the engine's combustion gases
Data Source
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AI summary
Method for purging a nitrogen oxides trap, said trap being able to store nitrogen oxides emitted by a motor vehicle internal combustion engine in a lean-burn normal mode of operation of the engine and able, under the action of fuel from the engine in a rich-burn engine mode of operation to reduce same, said method comprising:- a step (300) in which a need to purge the trap is detected when the mass of nitrogen oxides (MNOx) stored in the trap reaches a threshold (Ms); and - a step (800, 1100) of purging the nitrogen oxides under the action of fuel from the engine, beginning after a start-purge time (T) following on from the step (300) of detecting the need to purge; characterized in that the purge step (800, 1100) can be carried out in at least two distinct modes: - a first mode of purging the nitrogen oxides, in which mode the purge step (800) is stopped on a switch-over criterion from a richness signal from an oxygen probe downstream of the trap; and, - an enhanced nitrogen oxides purge second mode in which the purge step (1100) is stopped after a predetermined extended purging time.