Variable Valve Mechanism Abnormality Diagnosis via Exhaust Gas Pressure
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Solution Overview
Problem
Variable valve mechanisms in diesel engines that open the exhaust valve during the intake stroke face challenges in accurately diagnosing abnormalities, leading to decreased engine performance, fuel efficiency, and deteriorated exhaust emissions.
Innovation Solution
An abnormality diagnosis device and method that utilize intake air amount detection, exhaust gas pressure detection, and temperature sensors to calculate and estimate the exhaust gas returning amount, determining the variable valve mechanism's abnormality based on differences and thresholds, while considering engine speed and fuel supply conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the exhaust valve is opened during the intake stroke in the second mode to improve combustion stability and startability, then engine performance and emission control are improved, but the difficulty of detecting and measuring abnormalities in the variable valve mechanism increases
Solution Approach 1:
The patent introduces an intermediary estimation method that uses exhaust gas pressure as a mediator to indirectly measure the exhaust gas returning amount. Instead of directly measuring the complex valve mechanism behavior, the system uses exhaust gas pressure (which is easier to measure) as an intermediary parameter to infer the exhaust gas returning amount, thereby solving the difficulty of detecting abnormalities in the variable valve mechanism during second mode operation
Solution Approach 2:
The patent replaces direct mechanical measurement of the variable valve mechanism with a pressure-based measurement system. By substituting the complex mechanical detection of valve timing and exhaust gas return with pressure sensor measurements, the system achieves easier and more reliable abnormality detection while maintaining the ability to monitor combustion stability and emission control parameters
2Temperature
If the variable valve mechanism operates in the second mode to increase temperature inside the combustion chamber during cold start, then startability and combustion stability are improved, but the accuracy of abnormality diagnosis decreases
Solution Approach 1:
The patent implements a feedback mechanism where the estimated exhaust gas returning amount (based on exhaust gas pressure) is continuously compared with the actual exhaust gas returning amount (calculated from intake air amount differences). This feedback loop allows the system to detect abnormalities in the variable valve mechanism during second mode operation, maintaining diagnosis accuracy even when combustion chamber temperature is increased for cold start conditions
Solution Approach 2:
The patent changes the measurement parameter from direct mechanical valve timing measurement to exhaust gas pressure measurement. By using pressure as a parameter that reflects exhaust gas returning amount, the system can maintain measurement precision during second mode operation where temperature variations would otherwise interfere with abnormality detection. The parameter change allows accurate diagnosis while preserving the temperature increase needed for cold start performance
3Power
If the exhaust valve opening timing is varied to control overlap amount for high engine speed, then engine performance is improved, but the complexity of diagnosing variable valve mechanism abnormalities increases
Solution Approach 1:
The patent extracts the essential diagnostic function from the complex variable valve mechanism control system. By separating the exhaust gas returning amount estimation (based on exhaust gas pressure) from the complex valve timing control, the system achieves simplified abnormality detection. This extraction allows the diagnosis system to focus on a single measurable parameter (exhaust gas pressure) rather than monitoring multiple valve timing parameters, thereby reducing device complexity while maintaining engine performance optimization
Data Source
AI summary
Abnormality diagnosis device for a variable valve mechanism configured to open an exhaust valve even during an intake stroke and capable of selecting a first mode wherein the exhaust valve only opens during an exhaust stroke, or a second mode wherein the exhaust valve opens during both an exhaust stroke and an intake stroke. The abnormality diagnosis by the device determines the mechanism is abnormal when a difference between an exhaust gas returning amount calculated to recirculate from an exhaust passage into a cylinder in the second mode based on intake air amounts in the first and second modes, and an exhaust gas returning amount estimated to recirculate from an exhaust passage in the second mode based on an exhaust gas pressure, exceeds a diagnosis threshold value. The higher an exhaust gas pressure is, the larger an exhaust gas returning amount is estimated to be.