Skip Fire Engine Control for Pumping Loss Reduction
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Solution Overview
Problem
Internal combustion engines operate at suboptimal thermodynamic efficiency due to varying loads, leading to inefficient air and fuel delivery, increased pumping losses, and rapid switching between displacement modes, which affects fuel efficiency and control.
Innovation Solution
Implementing a skip fire variable displacement mode where selected combustion events are skipped, using feedback control and adaptive predictive controllers to optimize air and fuel delivery, and dynamically determining chamber firings to maintain optimal efficiency and reduce vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the engine operates at partial throttle to control power output, then the power delivery matches the desired load, but the thermodynamic efficiency decreases due to reduced compression and increased pumping losses
Solution Approach 1:
The engine operation is segmented into active cycles and skipped cycles. During skipped cycles, the throttle remains open (reducing pumping losses) while no combustion occurs. This segmentation allows the engine to deliver reduced power without maintaining partial throttle conditions during all cycles, thereby reducing overall pumping losses while matching power demand.
Solution Approach 2:
The engine employs periodic combustion events rather than continuous combustion in all cylinders. By alternating between active and skipped cycles in a periodic pattern, the engine can maintain lower average power output while keeping the throttle open more often, reducing the periodic pumping losses associated with sustained partial throttle operation.
2Power
If the engine operates at partial throttle to reduce power output, then the power delivery matches the desired load, but the compression ratio decreases reducing thermodynamic efficiency
Solution Approach 1:
The engine cycles are segmented into active and skipped phases. During skipped cycles, the throttle is opened to maintain high compression ratios and optimal thermodynamic conditions, even though no combustion occurs. This allows the engine to achieve reduced power output while maintaining high compression ratios during active cycles, preserving thermodynamic efficiency.
3Speed
If the engine rapidly switches between displacement modes to respond to load changes, then the engine response is fast, but the control stability deteriorates and fuel efficiency decreases
Solution Approach 1:
The engine uses periodic patterns of active and skipped cycles rather than rapid, irregular switching. This periodic approach provides predictable, stable operation while still enabling relatively fast response to load changes. The regular pattern allows the control system to anticipate and prepare for mode transitions, improving stability compared to erratic switching.
Solution Approach 2:
The engine control system incorporates feedback mechanisms that monitor operating conditions and adjust the pattern of active and skipped cycles accordingly. This feedback control allows the engine to respond to load changes while maintaining stable operation, preventing the control instability that would result from rapid, uncontrolled switching between displacement modes.
Data Source
Figure 1A~1B
Figure 2(a)~2(c)
Figure 3
AI summary
A variety of methods and arrangements for improving the fuel efficiency of internal combustion engines are described. Generally, an engine is controlled to operate in a skip fire variable displacement mode. Feedback control is used to dynamically determine the working cycles to be skipped to provide a desired engine output. In some embodiments a substantially optimized amount of air and fuel is delivered to the working chambers during active working cycles so that the fired working chambers can operate at efficiencies close to their optimal efficiency. In some embodiments, the appropriate firing pattern is determined at least in part using predictive adaptive control. By way of example, sigma delta controllers work well for this purpose. In some implementations, the feedback includes feedback indicative of at least one of actual and requested working cycle firings. In some embodiments, the appropriate firings are determined on a firing opportunity by firing opportunity basis. Additionally, in some embodiments, an indicia of the current rotational speed of the engine is used as a clock input for a controller used to selectively cause the skipped working cycles to be skipped.