Variable Compression Ratio Engine Speed Control
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Solution Overview
Problem
The existing methods for controlling internal combustion engine rotation speed, particularly during idle conditions, face challenges due to response delays from throttle valve adjustments and ignition timing retardation, which deteriorate convergence and impact fuel economy.
Innovation Solution
Implementing a control system that combines feedback control of intake air quantity and mechanical compression ratio to converge the actual and target rotation speeds, with the selection of control targets based on the magnitude of the deviation between them.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If intake air quantity is adjusted using a throttle valve, then rotation speed control is achieved, but response delay occurs due to the throttle valve being spaced apart from the cylinder
Solution Approach 1:
The patent introduces a variable compression ratio mechanism as an intermediary control element between the throttle valve and the cylinder. This mechanism directly affects the compression ratio based on the deviation between actual and target rotation speeds, providing a faster response pathway that compensates for the throttle valve's inherent delay. The control unit calculates the deviation and adjusts the compression ratio accordingly, creating a mediating control action that bridges the gap caused by the throttle valve's distance from the cylinder.
2Ease of operation
If ignition timing is retarded to allow advance control, then rotation speed control is achieved, but fuel economy performance deteriorates due to increased retard amount relative to MBT
Solution Approach 1:
The patent changes the control parameter from ignition timing adjustment to variable compression ratio adjustment. Instead of retarding ignition timing to create control headroom, the system directly modifies the compression ratio parameter based on the deviation between actual and target rotation speeds. This parameter change eliminates the need for proactive ignition timing retardation, allowing the ignition timing to remain closer to the optimal MBT position and thereby improving fuel economy while maintaining control flexibility.
3Device complexity
If only intake air quantity control is used, then system simplicity is maintained, but convergence of rotation speed deviation is deteriorated due to response delay
Solution Approach 1:
The patent merges two control mechanisms: the traditional intake air quantity control via throttle valve and the newly introduced variable compression ratio control. The control unit calculates the deviation between actual and target rotation speeds and determines the appropriate compression ratio based on this deviation. By combining these two control actions, the system maintains the simplicity of the existing throttle valve control while adding the convergence-enhancing capability of compression ratio adjustment, thereby improving reliability without significantly increasing overall system complexity.
Data Source
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AI summary
It is an object to quickly reduce a deviation between a target rotation speed and an actual rotation speed in rotation speed control by changing an intake air quantity and changing a mechanical compression ratio. There is provided electronically controllable throttle valve 23 capable of changing the intake air quantity, and variable compression ratio mechanism 30 capable of changing the mechanical compression ratio. ECU 40 is configured to calculate a deviation between the target idle rotation speed and the actual rotation speed during idle operation, select either one or both of the intake air quantity and the mechanical compression ratio as control targets in accordance with magnitude of the deviation, and reduce the deviation by changing the selected either one or both of the intake air quantity and the mechanical compression ratio.