Cylinder Deactivation for Engine Knock Control
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Solution Overview
Problem
Spark ignited internal combustion engines face challenges in controlling knock events, especially under high load operations with lower octane fuels, which often require spark retard, resulting in reduced engine torque and fuel economy.
Innovation Solution
Implementing individual cylinder valve deactivation mechanisms to transiently deactivate cylinders with higher knocking rates, adjusting the cylinder pattern based on knock occurrence, and reactivating them when cooled, allowing for advanced spark timing and reduced spark retard.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spark timing is retarded to control knock, then knock is reduced, but engine torque output and fuel economy deteriorate
Solution Approach 1:
The engine is divided into multiple cylinders with independent control. Individual cylinders are selectively deactivated based on their knock propensity, allowing knock control in specific cylinders while maintaining optimal spark timing in others, thereby preserving overall engine torque output.
Solution Approach 2:
Different cylinders are treated differently based on their individual knock characteristics. Cylinders prone to knock are deactivated or operated with retarded spark timing, while cylinders less prone to knock operate with advanced spark timing for optimal efficiency, creating local quality variations in spark timing and deactivation status.
2Reliability
If spark timing is retarded to control knock, then knock is reduced, but fuel economy deteriorates
Solution Approach 1:
The engine operation is segmented into active and deactivated cylinders. By deactivating only the cylinders most prone to knock rather than retarding spark timing across all cylinders, the system minimizes the fuel penalty while maintaining effective knock control where needed.
Solution Approach 2:
The system dynamically adjusts spark timing and cylinder deactivation status based on real-time knock sensor feedback and cylinder temperature estimates. This allows the engine to operate with advanced spark timing (better fuel economy) when knock is not present, and switch to retarded timing or deactivation only when knock occurs.
3Reliability
If cylinders are deactivated to control knock, then knock is reduced and fuel economy improves, but device complexity increases
Solution Approach 1:
The cylinder deactivation mechanism serves multiple functions: it controls knock by cooling prone cylinders, improves fuel economy by reducing pumping losses, and enables dynamic adjustment of effective engine displacement. This multi-functionality justifies the added complexity.
Solution Approach 2:
The system uses knock sensors to provide real-time feedback on cylinder knock events, which feeds back to the control system to dynamically adjust spark timing and cylinder deactivation status. This closed-loop feedback mechanism automates the complex control decisions, reducing the need for manual intervention and simplifying operation.
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 approach effectively reduces the fuel penalty associated with knock control by minimizing spark retard, improving engine torque output and fuel economy by operating active cylinders closer to MBT and reducing knock occurrences.
Implementation Method 1
Due to the deactivation, the cylinder may start cooling, reducing its propensity for further knock events
Data Source
AI summary
Methods and systems are provided for using selective cylinder deactivation for knock control with reduced fuel penalty. Cylinders with heavier knock and/or more borderline limited spark may be transiently deactivated until they are sufficiently cool. While reactivating the cylinders following cooling, other cylinders that are knocking, hot, or borderline spark limited may be deactivated.