Skip Fire Transition Control for Engine NVH Reduction
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Solution Overview
Problem
Skip fire engine operation often results in undesirable noise, vibration, and harshness (NVH) characteristics during transitions between different firing fractions, as existing methods struggle to smoothly adjust engine parameters to maintain desired torque and efficiency.
Innovation Solution
Implementing gradual changes in commanded firing fractions, using techniques such as linear slew rates and delayed adjustments, in conjunction with spark retard and air pumping through skipped cylinders, to track manifold filling dynamics and minimize torque mismatches and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If skip fire engine control is used to vary displacement, then fuel efficiency is improved, but noise, vibration and harshness (NVH) characteristics deteriorate
Solution Approach 1:
The patent implements dynamic adjustment of firing fractions based on real-time engine operating conditions. The controller continuously monitors parameters such as manifold pressure, engine speed, and load requirements to dynamically switch between different firing fractions (e.g., 1/3, 2/3, 1/2 of cylinders firing), allowing the engine to adaptively optimize fuel efficiency while managing NVH through condition-based selection of appropriate firing patterns
Solution Approach 2:
The system varies multiple engine parameters simultaneously during skip fire operation, including firing fraction, spark timing, and air-fuel ratio. By coordinating these parameter changes, the patent achieves smoother transitions between different firing modes and reduces NVH. For example, when transitioning from higher to lower firing fractions, the system adjusts spark timing and air management to maintain stable combustion and reduce vibration
2Speed
If abrupt changes in firing fraction are implemented, then response speed is improved, but torque delivery and NVH characteristics deteriorate
Solution Approach 1:
The controller performs preliminary adjustments to manifold pressure and air-fuel ratio before actually changing the firing fraction. When a transition is detected, the system first prepares the air management system by adjusting throttle position or EGR rates to match the upcoming firing fraction change. This preliminary action ensures that when the firing fraction changes, the air charge is already appropriately configured, preventing torque shocks and maintaining smooth delivery
Solution Approach 2:
The patent implements cushioning mechanisms to buffer the effects of abrupt firing fraction changes. This includes using EGR (exhaust gas recirculation) as a buffer medium to gradually adjust air charges, and implementing rate-limited transitions where the firing fraction changes in controlled steps rather than instantly. The cushioning effect absorbs the shock of transition and prevents torque fluctuations and NVH spikes
3Productivity
If transitions between firing fractions are accelerated, then productivity is improved, but NVH and vibration increase
Solution Approach 1:
The system uses feedback from manifold pressure sensors, crankshaft position sensors, and vibration monitors to dynamically adjust transition rates. When the manifold pressure differential between cylinders exceeds a threshold or vibration levels increase during transition, the controller automatically slows down the firing fraction change rate. This feedback mechanism allows the system to achieve high productivity when conditions permit while preventing NVH and vibration when physical constraints are approached
Data Source
AI summary
Methods and arrangements are described for controlling transitions between firing fractions during skip fire operation of an engine in order to help smooth the transitions. Generally, firing fractions transitions are implemented gradually, preferably in a manner that relatively closely tracks manifold filling dynamics. In some embodiments, the commanded firing fraction is altered each firing opportunity. Another approach contemplates altering the commanded firing fraction by substantially the same amount each firing opportunity for at least a portion of the transition. These approaches work particularly well when the commanded firing fraction is provided to a skip fire controller that includes an accumulator functionality that tracks the portion of a firing that has been requested, but not delivered, or vice versa. In various embodiments, commanded firing fraction changes are delayed relative to initiation of the change in throttle position to help compensate for inherent delays associated with changing the manifold air pressure.