Skip Fire Engine Controller Firing Fraction Management
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Skip fire engine control systems face challenges in mitigating noise, vibration, and harshness (NVH) issues, which has limited their widespread adoption despite potential fuel economy benefits, due to the generation of undesirable vibrations and rough engine operation.
Innovation Solution
The implementation of an engine controller that dynamically determines firing sequences, using a first-order sigma delta converter and cyclic pattern generators to minimize low-frequency vibrations, and adjust engine parameters to ensure smooth transitions and desired output, while avoiding firing fractions that exacerbate NVH.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If skip fire engine control is implemented to improve fuel economy, then fuel efficiency is improved, but noise, vibration and harshness (NVH) increases
Solution Approach 1:
The system dynamically adjusts the firing fraction based on real-time engine operating conditions rather than using fixed skip fire patterns. The controller continuously monitors engine parameters and modifies the proportion of fired cylinders to optimize both fuel economy and NVH characteristics for each specific operating point
Solution Approach 2:
The invention changes the firing fraction parameter continuously within a range (e.g., 0.8-1.0) rather than using discrete fixed patterns. This continuous parameter adjustment allows the system to navigate through operating spaces that balance fuel efficiency and vibration generation, selecting optimal firing fractions for each condition
2Device complexity
If fixed skip fire firing patterns are used to simplify control, then device complexity is reduced, but transitions between patterns cause vibration spikes
Solution Approach 1:
The system transitions from static fixed patterns to dynamic continuous adjustment of firing fractions. This allows smooth, progressive changes in the firing pattern rather than abrupt switches between discrete patterns, eliminating vibration spikes associated with pattern transitions
Solution Approach 2:
The controller anticipates transitions by continuously adjusting the firing fraction toward the target value rather than switching abruptly. This preliminary gradual adjustment prepares the engine for the transition, smoothing the overall behavior and preventing sudden vibration changes
3Use of energy by moving object
If low firing fractions are used to maximize fuel economy, then fuel efficiency is improved, but engine roughness and NVH increase
Solution Approach 1:
The system optimizes the firing fraction parameter within a constrained range (e.g., 0.8-1.0) rather than using very low fractions. This parameter optimization balances the fuel economy benefits of reduced firing with the smoothness requirement, selecting the highest possible firing fraction that maintains acceptable NVH and roughness characteristics
Data Source
AI summary
Engine controllers and methods are described that facilitate skip fire control of an internal combustion engine. An engine controller determines a skip fire firing fraction and (as appropriate) associated engine settings that are suitable for delivering a requested output. The engine controller selects an operational firing fraction from a set of available firing fractions. A firing controller then directs cylinder firings in a skip fire manner that delivers the selected operational firing fraction. The firing controller includes an accumulator that helps smooth transitions between different firing fractions.