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 reduced compression and increased pumping losses, especially at partial throttle, and existing variable displacement engines struggle to maintain efficiency and responsiveness.
Innovation Solution
Implementing a skip fire variable displacement mode where selected combustion events are skipped, allowing other working cycles to operate at optimal efficiency, using a firing control unit with a drive pulse generator and sequencer to dynamically calculate and sequence cylinder firings, and potentially utilizing a sigma-delta control circuit to synchronize with engine speed.
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 and inactive cylinders. By shutting down selected cylinders during low-load conditions, the engine reduces the number of pumping cycles, thereby minimizing pumping losses while maintaining adequate power output from the remaining active cylinders.
Solution Approach 2:
The engine dynamically adjusts the number of active cylinders based on the required power output. This variable displacement operation allows the engine to optimize thermodynamic efficiency by matching the number of active cylinders to the load demand, reducing pumping losses when full power is not required.
2Power
If the engine operates at partial throttle, then the power output is controlled, but the compression ratio decreases reducing thermodynamic efficiency
Solution Approach 1:
By segmenting the engine into active and inactive cylinders, the active cylinders can operate at higher compression ratios since they are not constrained by partial throttle conditions. The inactive cylinders effectively remove their constraint, allowing the active cylinders to maintain optimal compression for thermodynamic efficiency.
Solution Approach 2:
The engine changes the operating parameters by varying the number of active cylinders based on load conditions. This allows the active cylinders to operate at optimal compression ratios and thermodynamic conditions, rather than being forced to operate at suboptimal partial throttle settings.
3Loss of energy
If variable displacement mode shuts down cylinders to improve efficiency, then fuel efficiency improves, but the engine responsiveness and power delivery are reduced
Solution Approach 1:
The engine dynamically transitions between different numbers of active cylinders based on real-time power demands. This allows rapid adjustment of power output while maintaining fuel efficiency during low-load conditions, and quickly restoring full power capability when high load is required.
Solution Approach 2:
The engine control system uses feedback from power demand sensors to dynamically adjust the number of active cylinders. This feedback mechanism ensures that the engine maintains optimal fuel efficiency during low-load operation while being able to quickly respond to increases in power demand by activating additional cylinders.
Data Source
AI summary
A variety of methods and arrangements for controlling the operation of an internal combustion engine in a skip fire variable displacement mode are described. Generally, an engine is controlled to operate in a skip fire variable displacement mode. In one aspect, the spark timing associated with each fired working cycle is based at least in part on the firing history of the fired working chamber.