Engine Valve Timing Control for Knock Suppression
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Solution Overview
Problem
Internal combustion engines experience knocking due to spontaneous combustion of the air-fuel mixture at low-rotation, high-load states, exacerbated by increased air-fuel mixture temperature from internal EGR, and reducing exhaust valve opening timing to mitigate this leads to increased exhaust gas loss.
Innovation Solution
A valve opening/closing timing control apparatus with a phase adjustment mechanism that adjusts the relative rotational phase of the exhaust valve to reduce overlap with the intake valve, using an electrically powered actuator to displace the phase in both advancing and retarding directions, allowing the exhaust valve to open at the original timing while minimizing overlap and maintaining efficient exhaust pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the exhaust valve opening timing is advanced to reduce overlap and mitigate internal EGR effects, then knocking is suppressed, but exhaust gas loss increases due to premature valve opening
Solution Approach 1:
The valve timing control is segmented into two independent phases: overlap control (adjusting intake valve closing timing) and exhaust valve opening timing control. This allows the overlap to be reduced to suppress knocking while maintaining the exhaust valve opening timing at the original position to prevent exhaust gas loss.
Solution Approach 2:
Different timing adjustments are applied to different valves based on their specific functional requirements. The intake valve timing is adjusted to control overlap and reduce internal EGR effects, while the exhaust valve timing is maintained to preserve expansion pressure and prevent exhaust loss.
2Power
If the overlap amount is increased to improve low-rotation, high-load performance, then engine power is enhanced, but air-fuel mixture temperature rises causing knocking
Solution Approach 1:
The valve timing is made dynamically adjustable through the phase adjustment mechanism, allowing the overlap amount to be optimized for different operating conditions. At low-rotation, high-load states, the overlap is reduced to prevent knocking while maintaining engine power.
Solution Approach 2:
The overlap amount is changed as a controllable parameter through independent adjustment of intake and exhaust valve timing. By reducing the overlap parameter, the air-fuel mixture temperature is controlled to prevent knocking while preserving engine performance.
Data Source
AI summary
A control unit for an internal combustion engine is configured for suppressing knocking phenomenon with reduction of overlap, while maintaining an opening timing of an exhaust valve at the time of low-rotation, high-load state. A valve opening/closing timing control apparatus includes a phase adjustment mechanism configured to vary a relative rotational phase between a driving side rotary body rotatable in synchronism with a crankshaft of the internal combustion engine and a driven side rotary body rotatable together with an exhaust cam shaft. After an opening timing of the exhaust valve, an advancing operation is effected for displacing the relative rotational phase in the advancing direction relative to the opening timing.