Skip Fire Engine Control via Lookup Tables
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Solution Overview
Problem
Skip fire engine control technologies face challenges in commercial adoption due to noise, vibration, and harshness (NVH) issues, which affect the engine's operational smoothness and efficiency, limiting their widespread use despite potential for improved fuel economy.
Innovation Solution
The implementation of skip fire engine controllers that utilize look-up tables and state machines to determine the timing and sequence of engine firings, incorporating an accumulator to track requested but uncommanded firing portions, and adjust firing fractions dynamically to mitigate NVH problems, allowing for finer control of engine displacement.
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) issues worsen
Solution Approach 1:
The patent applies dynamics by making the firing sequence adaptive and variable rather than fixed. The controller dynamically adjusts which cylinders fire on which cycles based on real-time operating conditions, engine speed, and load requirements. This dynamic control allows the system to optimize fuel efficiency through selective cylinder deactivation while simultaneously managing NVH characteristics by varying the firing pattern to avoid consistent vibration patterns.
Solution Approach 2:
The patent utilizes periodic action through the use of predetermined firing sequences that repeat over specific cycles. The system implements periodic firing patterns where cylinders are selectively activated and deactivated in repeating sequences, allowing the engine to maintain smooth operation while achieving fuel savings. The periodic nature of these sequences helps regularize the combustion events to reduce vibration and noise.
2Use of energy by moving object
If fixed set of cylinders is deactivated during low-load conditions, then thermodynamic efficiency is improved, but operational flexibility is reduced
Solution Approach 1:
The patent transforms the static cylinder deactivation strategy into a dynamic system where any cylinder can be deactivated at any time based on operating conditions. Rather than fixing specific cylinders for deactivation, the system continuously evaluates which cylinders should be inactive to optimize both efficiency and flexibility across varying load conditions.
Solution Approach 2:
The patent changes the parameter of cylinder activation status from a fixed configuration to a variable state that can be adjusted in real-time. The system modifies which cylinders are active or inactive based on changing operational requirements, allowing the engine to adapt its effective displacement and firing patterns to match varying load demands while maintaining thermodynamic efficiency.
3Adaptability or versatility
If selective skipping of cylinder firings is implemented, then effective displacement control is improved, but engine smoothness deteriorates
Solution Approach 1:
The patent applies periodic action by implementing predetermined repeating firing sequences that regulate the skip-fire pattern. These periodic sequences ensure that cylinder deactivations follow a structured rhythm rather than occurring randomly, which helps maintain engine smoothness while still achieving variable effective displacement control.
Solution Approach 2:
The system uses feedback mechanisms to monitor engine operation and adjust the skip-fire sequencing in real-time. By continuously evaluating engine speed, load, and vibration characteristics, the controller can modify the firing patterns to maintain smooth operation while achieving the desired effective displacement control through selective cylinder deactivation.
Data Source
AI summary
A variety of skip fire engine controllers and control methods are described that utilize look-up tables, state machines, or other data structures to determine the sequence or ordering of skip-fire firings. In one aspect, a skip fire engine controller utilizes a look-up table to determine when firings are appropriate to deliver a desired engine output. In some embodiments, a firing timing controller tracks a value indicative of the portion of a firing that has been requested, but not yet directed and such information is utilized in the determination of the timing of the firings. The accumulator value is particularly useful when transitioning between different requested firing fractions.