Variable Compression Ratio Engine Linkage Mechanism
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Solution Overview
Problem
Miller cycle internal combustion engines with high compression ratios face limitations in achieving maximum power at high loads and high engine speeds, where they become spark limited, preventing efficient operation.
Innovation Solution
The internal combustion engine features a linkage system with a rotatably connected lower connecting rod that adjusts the compression stroke length, allowing for a variable compression ratio by rotating the second end of the lower connecting rod relative to the crankshaft and control shaft, enabling shorter compression strokes at high loads and high engine speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Miller cycle engine uses high compression ratio, then fuel economy is improved at low loads and low engine speeds, but the engine becomes spark limited and cannot achieve maximum power at high loads and high engine speeds
Solution Approach 1:
The patent implements a variable compression ratio mechanism that dynamically adjusts the compression ratio based on operating conditions. The lower connecting rod can rotate relative to the control shaft, changing the compression stroke length. At low loads and speeds, the system maintains a high compression ratio (e.g., 16:1) for optimal fuel economy. At high loads and speeds, the compression ratio is reduced (e.g., to 10:1 or lower) to prevent spark limitation and enable maximum power output. This dynamic adjustment resolves the contradiction between fuel economy and power output.
2Power
If compression stroke length is reduced in Miller cycle engine, then compression ratio is reduced to prevent spark limitation, but fuel economy gains are lost
Solution Approach 1:
The variable compression ratio mechanism allows the engine to maintain high compression ratio during normal operation for fuel economy, and only reduce compression stroke length when high power output is required. The lower connecting rod rotation mechanism enables smooth transition between compression ratios, allowing the engine to optimize for fuel economy during most operating conditions while retaining the capability to deliver maximum power when needed.
Solution Approach 2:
The system changes the compression ratio parameter dynamically based on operating conditions. By adjusting the compression stroke length through lower connecting rod rotation, the engine can switch between high compression ratio mode (for fuel economy) and low compression ratio mode (for power output), resolving the contradiction between these two performance goals.
3Device complexity
If standard Otto cycle is used with equal compression and expansion stroke lengths, then mechanical simplicity is maintained, but fuel economy potential of Atkinson/Miller cycle cannot be achieved
Solution Approach 1:
The patent introduces a control shaft and lower connecting rod mechanism that adds complexity only when needed. The lower connecting rod can rotate relative to the control shaft to vary compression stroke length, enabling Miller cycle operation for improved fuel economy. When high power output is required, the mechanism can revert to equal stroke lengths, maintaining compatibility with standard Otto cycle operation. This dynamic capability allows the engine to achieve fuel economy benefits while retaining mechanical simplicity when necessary.
Data Source
AI summary
An internal combustion engine includes a crankshaft rotatably supported by an engine block, and rotatable about a crank axis. A control shaft is rotatably supported by the engine block, and rotatable about a control axis. A link rod is rotatably connected to the crankshaft. A lower connecting rod includes a first end rotatably connected to the link rod, and a second end rotatably connected to the control shaft. An upper connecting rod is rotatably connected to the link rod and a piston. The second end of the lower connecting rod and the control shaft are rotatably connected at a location offset from the control axis to define an eccentric connection relative to the control axis. Rotation of the control shaft about the control axis rotates the second end of the lower connecting rod about the control axis to adjust a compression stroke length of the piston.