Scavenging Control for Internal Combustion Engine Emission
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Solution Overview
Problem
Scavenging in internal combustion engines leads to a rich combustion air-fuel ratio in the cylinder, causing the air-fuel ratio sensor output to deviate, resulting in inefficient exhaust gas purification and potential emission deterioration, especially as the exhaust purification catalyst deteriorates over time.
Innovation Solution
An internal combustion engine equipped with a supercharger, variable valve timing mechanism, downstream and upstream air-fuel ratio sensors, and a scavenging control device that adjusts valve overlap to maintain a target air-fuel ratio, switching between rich and lean settings based on sensor readings and catalyst oxygen storage to optimize scavenging and prevent emission deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If scavenging is increased to improve intake air amount and torque, then the turbine speed is raised and intake air pressure is increased, but the combustion air-fuel ratio becomes rich and exhaust emission deteriorates
Solution Approach 1:
The patent changes the parameter of air-fuel ratio control by switching between feedback control (using sensor output) and open-loop control (ignoring sensor output) based on scavenging detection. This allows the system to maintain proper air-fuel ratio management even when scavenging causes sensor reading deviations, thereby preventing exhaust emission deterioration while preserving the benefits of scavenging for intake air amount.
Solution Approach 2:
The patent uses feedback from the air-fuel ratio sensor to detect scavenging conditions and triggers a control mode switch. When scavenging is detected (indicated by abnormal sensor readings), the system transitions from feedback control to open-loop control, preventing the rich air-fuel ratio condition that causes emission deterioration while maintaining adequate intake air supply.
2Measurement precision
If feedback control is used to maintain target air-fuel ratio based on sensor output, then the air-fuel ratio is controlled precisely, but during scavenging the sensor output deviates and actual exhaust air-fuel ratio becomes leaner causing purification efficiency to fall
Solution Approach 1:
The patent inverts the normal control logic by detecting scavenging conditions through air-fuel ratio sensor readings and then switching to open-loop control mode. This inversion allows the system to recognize when feedback control becomes unreliable due to scavenging-induced sensor deviations and automatically transition to a mode that prevents purification efficiency deterioration.
Solution Approach 2:
The system uses feedback from the air-fuel ratio sensor not for direct control during scavenging, but for detecting scavenging conditions. This feedback mechanism triggers the switch to open-loop control, ensuring that the actual exhaust air-fuel ratio remains appropriate for catalyst purification even when sensor readings are deviated during scavenging events.
3Object-generated harmful factors
If the upper limit of scavenging amount is reduced to prevent emission deterioration, then exhaust emission is protected, but the scavenging amount becomes insufficient for meeting torque requests
Solution Approach 1:
The patent implements dynamic control mode switching between feedback and open-loop control based on real-time detection of scavenging conditions. This dynamic approach allows the system to permit larger scavenging amounts when needed for torque production while preventing emission deterioration through appropriate control mode selection, rather than imposing a fixed conservative limit on scavenging amount.
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 solution effectively suppresses exhaust emission deterioration during scavenging without excessively limiting the scavenging amount, ensuring efficient exhaust gas purification and maintaining sufficient scavenging to meet torque requests, even as the catalyst deteriorates.
Implementation Method 1
a catalyst arranged in an exhaust passage and able to store oxygen
Implementation Method 2
a downstream side air-fuel ratio sensor arranged at a downstream side of the catalyst in an exhaust flow direction and able to detect an air-fuel ratio of outflowing exhaust gas flowing out from the catalyst
Implementation Method 3
Hydrogen is faster in speed of diffusion compared with other components in the exhaust gas in the diffusion-regulating layer of the air-fuel ratio sensor, so reaches the electrode surface of the air-fuel ratio sensor faster than these other components
Data Source
AI summary
The internal combustion engine comprises a supercharger, a variable valve timing mechanism able to change a valve overlap amount, a catalyst arranged in an exhaust passage and able to store oxygen, a downstream side air-fuel ratio sensor arranged at a downstream side of the catalyst in an exhaust flow direction and able to detect an air-fuel ratio of outflowing exhaust gas flowing out from the catalyst, and a scavenging control device able to control a scavenging amount by controlling the valve overlap amount by the variable valve timing mechanism. The scavenging control device reduces the valve overlap amount when an air-fuel ratio detected by the downstream side air-fuel ratio sensor changes from less than a lean judged air-fuel ratio leaner than a stoichiometric air-fuel ratio to the lean judged air-fuel ratio or more during scavenging.