Dynamic Skip Fire Engine Control for Torque Precision
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Solution Overview
Problem
Existing engine control systems face challenges in efficiently varying engine displacement and torque output to meet operational demands, particularly in achieving fine control over engine displacement and reducing pumping losses, while maintaining thermodynamic efficiency.
Innovation Solution
The implementation of dynamic skip fire engine control, which involves making firing decisions on a cylinder-by-cylinder basis, using accumulators to determine firing and skipping patterns, and gradually ramping firing densities to manage transitions between different effective firing densities, allowing for immediate changes in torque output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional variable displacement control deactivates a group of cylinders substantially simultaneously, then engine displacement is reduced, but control precision of effective displacement is coarse and cannot achieve fractional displacement
Solution Approach 1:
The system dynamically adjusts firing decisions on a cylinder-by-cylinder basis rather than deactivating fixed groups of cylinders. The controller makes real-time decisions about which cylinders to fire or skip based on accumulated values, enabling continuous variation of effective displacement rather than discrete steps. This dynamic approach achieves fine control precision while maintaining relatively simple control logic.
2Measurement precision
If skip fire engine control selectively skips firing of certain cylinders, then effective displacement is reduced with finer control, but transitions between different firing densities cause torque fluctuations
Solution Approach 1:
The controller prepares for transitions by gradually adjusting the accumulation rate before changing firing density. When transitioning between different effective displacement levels, the system modifies the accumulation value incrementally across multiple cycles rather than making abrupt changes. This preliminary adjustment of accumulation parameters smooths the transition process and minimizes torque fluctuations while maintaining the ability to achieve precise fractional displacement control.
3Loss of energy
If engine displacement is reduced to improve fuel efficiency, then pumping losses are reduced, but torque output decreases
Solution Approach 1:
The system changes the parameter of effective displacement continuously rather than in fixed steps. By controlling which individual cylinders fire on each cycle and adjusting the accumulation rate dynamically, the engine can operate at any effective displacement between 0 and 100% of total capacity. This enables the engine to reduce pumping losses by operating at lower effective displacements during light load conditions while maintaining the capability to deliver full torque when needed, thus resolving the trade-off between energy efficiency and power output.
Data Source
AI summary
A variety of engine controllers and methods are described for controlling engines operating in a cylinder output level modulation mode. In one aspect transitions between different effective firing fractions are managed by gradually ramping an effective firing density. In another, when an engine transitions to a multi-level skip fire firing density that has more than one possible high/low/skip sequence, the phase of the high/low pattern is set relative to the phase of the firing pattern to ensure that a preferred high/low/skip sequence is generated. In another aspect, rapid large torque changes can be implemented in part by immediately changing the operational high/low fraction in response to a command to increase or reduce the desired engine torque.