Variable Compression Ratio Engine Linkage Mechanism
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Solution Overview
Problem
Existing engines with variable compression ratios require additional joints in the linkage between the crankshaft and piston, increasing manufacturing complexity, potential failure points, and friction, while also limiting the maximum cylinder volume for expansion, thereby reducing efficiency.
Innovation Solution
A compression ratio varying mechanism that uses a first link connected to the piston, a second link connected to the crankpin, and a third control link connected to both, with a lever arm and control shaft to adjust the TDC position of the piston, minimizing additional joints and maintaining the BDC position, thus optimizing expansion volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a variable compression ratio mechanism is implemented using traditional multi-linkage designs, then the compression ratio can be varied to improve fuel efficiency, but the number of additional joints in the linkage increases manufacturing complexity and potential failure points
Solution Approach 1:
The compression ratio variation function is segmented between the variable crank radius mechanism and the adjustable piston offset mechanism, allowing each component to perform a specific function with fewer joints. The piston offset mechanism uses a simple adjustable linkage with minimal joints to achieve the desired compression ratio variation.
Solution Approach 2:
The piston offset adjustment mechanism is extracted as a separate, simplified subsystem from the traditional multi-linkage compression ratio mechanism. This extraction allows for a dedicated, low-complexity adjustment system that works in conjunction with the variable crank radius to achieve compression ratio variation without requiring a complex integrated linkage system.
2Adaptability or versatility
If traditional variable compression ratio mechanisms are used, then compression ratio can be adjusted, but the maximum cylinder volume for expansion is reduced, limiting overall efficiency
Solution Approach 1:
The mechanism dynamically adjusts the piston offset position during operation to vary the compression ratio while maintaining the maximum expansion volume. By making the piston offset adjustable rather than fixed, the system can optimize compression for different operating conditions without permanently reducing the cylinder volume available for expansion.
Solution Approach 2:
The system changes the geometric parameters of the piston position (offset distance and angle) to achieve compression ratio variation. By modifying these parameters through adjustable linkage positioning rather than changing the fundamental cylinder geometry, the maximum expansion volume is preserved while still achieving variable compression ratios.
3Adaptability or versatility
If multiple additional joints are added to the linkage system, then compression ratio variability is achieved, but friction and potential failure points increase
Solution Approach 1:
The function is segmented between the variable crank radius (which provides inherent compression ratio variation) and a simplified piston offset mechanism. This segmentation allows the majority of the compression ratio control to come from the crank mechanism with fewer additional joints, while the offset mechanism provides fine-tuning capability with minimal additional complexity.
Solution Approach 2:
The variable crank radius mechanism serves dual purposes: it provides the primary compression ratio variation and simultaneously drives the piston through the simplified offset linkage. This self-service approach reduces the need for additional independent control linkages and their associated joints, thereby improving reliability.
Data Source
AI summary
A compression ratio varying mechanism of an engine includes an upper link connected to the piston, and a lower link connected to the crankshaft and to the upper link. A control link is connected to the lower end of the upper link and/or to the upper end of the lower link. A lever arm is connected to a lever control shaft, and is controlled in its orientation thereby. The control link is connected to the lever arm, and is substantially the same length as the lever arm. The crankpin offset, the length of the lower link, and the position of the lever control shaft are such that the position of the connection between the control link and the upper and lower links coincides with the position of the lever control shaft at the Bottom Dead Center position of the piston and crankshaft.