Air-Fuel Ratio Sensor Control for Internal Combustion Engine
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Solution Overview
Problem
Air-fuel ratio sensors in internal combustion engines face challenges in accurately detecting absolute air-fuel ratios, especially when they are not at the stoichiometric ratio, due to variations in production processes and aging, leading to inconsistent output currents.
Innovation Solution
A control system with an air-fuel ratio sensor that includes a reference cell and a pump cell, where the reference cell's output current changes with air-fuel ratio, and a pump current control device to maintain a constant voltage, allowing for accurate detection of air-fuel ratios by controlling the pump current and detecting the pump current as the sensor output current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-cell type air-fuel ratio sensor is used, then the device complexity is reduced, but the measurement precision deteriorates because the output current varies with sensor differences and aging, making accurate detection of absolute air-fuel ratios difficult
Solution Approach 1:
The sensor is divided into two independent cells: a reference cell that detects oxygen concentration in exhaust gas and a pump cell that actively pumps oxygen. This segmentation allows each cell to have specialized functions, with the reference cell providing stable detection and the pump cell enabling active control, thereby improving measurement precision without excessive complexity increase
Solution Approach 2:
A solid electrolyte layer is introduced as an intermediary between the reference electrode and pump electrode. This electrolyte layer enables selective oxygen ion transport while electrically isolating the two cells, allowing the reference cell and pump cell to operate independently yet cooperatively, which resolves the contradiction between simplified structure and precise measurement
2Measurement precision
If the pump cell pumps oxygen actively according to pump current, then the measurement precision improves by enabling detection of absolute air-fuel ratios, but the device complexity increases due to the need for pump current control and voltage application mechanisms
Solution Approach 1:
The reference cell and pump cell are merged into a single integrated sensor unit sharing common components (electrolyte layer, electrodes, housing). This merging allows the complex pump control functionality to be combined with the reference detection function, achieving precise absolute air-fuel ratio measurement while managing overall device complexity through integration rather than separate systems
Solution Approach 2:
The system changes the operating parameter of the pump cell by applying controlled voltage to drive oxygen pumping. By dynamically adjusting the pump voltage based on reference cell feedback, the system achieves precise control over oxygen transfer, enabling accurate absolute air-fuel ratio detection while managing complexity through parameter-based control rather than mechanical complexity
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 accurate detection of air-fuel ratios even when they are not stoichiometric, improving the precision of engine control and reducing variations caused by sensor differences and aging.
Implementation Method 1
a solid electrolyte layer which can pass oxygen ions and two electrodes which are provided on both side surfaces of the layer
Implementation Method 2
the detected voltage (electromotive force) changes in accordance with a concentration of oxygen in exhaust gas in a measured gas chamber
Implementation Method 3
the other cell (pump cell) pumps oxygen in and pumps it out with respect to the exhaust gas in the measured gas chamber, in accordance with a pump current
Data Source
AI summary
This control device for an internal combustion engine is equipped with: an air/fuel ratio sensor provided to the exhaust passage of an internal combustion engine; and an engine control device that controls the internal combustion engine on the basis of the sensor output current of the air/fuel ratio sensor. The air/fuel ratio sensor is equipped with: a gas chamber to be measured, into which exhaust gas flows; a reference cell for which the reference cell output current varies according to the air/fuel ratio of the exhaust gas inside the gas chamber to be measured; and a pump cell that, according to the pump current, pumps oxygen into or out of the exhaust gas in the gas chamber to be measured. The reference cell is configured so that the applied voltage, at which the reference cell output current reaches zero, varies according to the air/fuel ratio of the exhaust gas in the gas chamber to be measured. The applied voltage in the reference cell is fixed at a constant voltage, said constant voltage being set to a voltage different to the voltage at which the reference cell output current reaches zero when the air/fuel ratio of the exhaust gas in the gas chamber to be measured is the stoichiometric air/fuel ratio.