Lean-Rich Engine Control via Downstream NOx Sensor
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Solution Overview
Problem
Existing engine control systems struggle to effectively manage the transition between lean and rich operation states in a gasoline engine, leading to inefficient emission control from three-way catalysts, particularly due to differences in oxygen concentration and NOx detection timing.
Innovation Solution
A method involving a limited current type NOx sensor with NH3 interference, placed downstream of the three-way catalyst, detects changes in oxygen concentration and NOx levels to actively control the engine's operation state, switching between lean and rich modes based on these detections to minimize emission deterioration regardless of exhaust air flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a binary oxygen sensor is used to detect rich/lean atmosphere for engine control switching, then the control system can switch between lean and rich operation states, but the detection timing is delayed and cannot accurately reflect real-time emission conditions downstream of the catalyst
Solution Approach 1:
The patent introduces a limited current type NOx sensor as an intermediary device placed downstream of the three-way catalyst. This sensor detects both NOx concentration and oxygen concentration in the exhaust gas, providing direct feedback on the actual emission conditions and atmospheric state after catalyst treatment. The sensor output is processed to generate switching signals that directly control engine operation state transitions, eliminating the delay inherent in upstream binary sensor detection.
2Reliability
If the engine operation state is switched based on upstream oxygen sensor detection, then lean and rich operation states can be maintained, but emission deterioration occurs during transition periods when the catalyst atmosphere is not properly controlled
Solution Approach 1:
The patent implements a feedback control mechanism where the limited current type NOx sensor continuously monitors the atmospheric conditions downstream of the three-way catalyst. The sensor output signal is fed back to the control device, which adjusts the engine operation state (lean or rich) to maintain optimal catalyst performance. This closed-loop feedback ensures that emission deterioration is minimized by keeping the catalyst in its appropriate atmospheric state during operation transitions.
Solution Approach 2:
The control device switches the engine operation state in advance based on predictions of upcoming transitions, rather than waiting for sensor detection of actual atmospheric changes. By anticipating transition needs and preparing the engine state beforehand, the system prevents emission deterioration from occurring during transition periods, ensuring the catalyst is already in the correct atmospheric condition when transitions occur.
3Measurement precision
If the limited current type NOx sensor is used to detect both NOx and oxygen concentration, then accurate real-time detection is achieved, but the sensor output must be carefully processed to distinguish between NOx and oxygen signals
Solution Approach 1:
The patent employs dynamic signal processing where the control device adjusts processing parameters based on real-time operating conditions. The switching determination is made by dynamically evaluating sensor outputs against predefined criteria that account for the relationship between NOx and oxygen concentrations. This dynamic approach allows accurate distinction between NOx and oxygen signals while adapting to changing engine operating states, maintaining measurement precision without requiring overly complex fixed processing algorithms.
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 effectively suppresses emission deterioration from the three-way catalyst to the downstream side by precisely timing the engine's operation state changes, improving overall emission control regardless of exhaust air flow rates.
Implementation Method 1
locating, on a downstream side with respect to the three way catalyst in the exhaust path, a limited current type NOx sensor having NH3 interference and also capable of detecting a change in an oxygen concentration on the downstream side
Implementation Method 2
Pd and Pt have a function of oxidizing HC and CO in an exhaust gas to generate carbon dioxide (CO2) and water (H2O). Ceria has a function of causing absorption and elimination of oxygen (O2). In the TWC, when HC and CO are oxidized, necessary oxygen is released from ceria
Implementation Method 3
Pd and Rh have a function of reducing NOx in an exhaust gas to generate nitrogen (N2)
Implementation Method 4
Ceria has a function of causing absorption and elimination of oxygen (O2). When NOx is reduced, generated oxygen is absorbed into (stored in) ceria
Data Source
AI summary
In a method of performing active control between a lean operation state and a rich operation state on a vehicle engine including a three way catalyst in an exhaust path, on a downstream side with respect to the three way catalyst in the exhaust path, a limited current type NOx sensor having NH3 interference and also capable of detecting a change in an oxygen concentration on the downstream side is disposed, and an operation state of the vehicle engine is switched between a lean operation state and a rich operation state at a timing when a detection of a change in an oxygen concentration in an exhaust air flowing out from the three way catalyst or a detection of NOx or NH3 is performed first by the NOx sensor.