Engine Air/Fuel Ratio Control Using Dynamic Gain Adjustment
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Solution Overview
Problem
Conventional air/fuel ratio control devices for internal combustion engines face challenges in stabilizing feedback control due to non-linear interactions among controlling constants, leading to hunting or insufficient following, which destabilizes the control of the average air/fuel ratio on the upstream side of the catalyst.
Innovation Solution
A control device that includes a catalyst, upstream and downstream air/fuel ratio sensors, and a conversion means to calculate controlling constants using a target average air/fuel ratio as a common index, allowing for stable and accurate control of the air/fuel ratio by optimizing the combination of controlling constants based on operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple controlling constants are simultaneously controlled to improve air/fuel ratio control accuracy, then control precision improves, but non-linear interactions cause hunting or insufficient following that destabilizes control
Solution Approach 1:
The patent dynamically adjusts the gain values of proportional and integral terms based on the operating region (rich side, lean side, or near-stoichiometric) of the air/fuel ratio. By making the controlling constants variable rather than fixed, the system adapts to different operating conditions, preventing non-linear interactions that cause hunting or insufficient following while maintaining high control accuracy across various regions.
Solution Approach 2:
The patent changes the parameters (gain values) of the feedback control system based on the detected air/fuel ratio region. When the air/fuel ratio is on the rich side, different gain values are applied compared to when it is on the lean side or near stoichiometric. This parameter adaptation resolves the contradiction by optimizing control characteristics for each operating region, ensuring both accuracy and stability.
2Speed
If upstream O2 sensor is placed close to combustion chamber to enable early feedback control, then response speed improves, but sensor is exposed to high temperature and toxic substances causing output fluctuation
Solution Approach 1:
The patent introduces a downstream O2 sensor as an intermediary element that indirectly provides feedback information about the air/fuel ratio. Instead of relying solely on the upstream sensor exposed to harsh conditions, the downstream sensor (located after the catalyst where conditions are milder) serves as a mediator to verify and supplement the feedback control, reducing the impact of upstream sensor fluctuations while maintaining fast response through the dual-sensor approach.
Data Source
AI summary
Provided is a control device for an internal combustion engine, which can enable stable and fine control of an average air/fuel ratio of an exhaust gas on the upstream side of a catalyst. The control device for an internal combustion engine includes: a catalytic converter; an upstream O2 sensor to the upstream of the catalyst; a downstream O2 sensor to the downstream of the catalyst; a first air/fuel ratio feedback control unit for controlling the air/fuel ratio of the exhaust gas based on an output value of the upstream O2 sensor and a controlling constant group; a second air/fuel ratio feedback control unit for calculating a target average air/fuel ratio AFAVEobj based on the output value of the upstream O2 sensor and an output target value VR2; and a conversion unit for calculating at least two controlling constants by using the target average air/fuel ratio AFAVEobj as a common index.