Variable Compression Ratio Engine Control Method
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Solution Overview
Problem
Existing internal combustion engines with variable compression ratio mechanisms face challenges in maintaining optimal response speed and power consumption due to differing response rates between high and low compression ratio variations, leading to deteriorated performance and increased power consumption when varying the compression ratio.
Innovation Solution
The control method for the internal combustion engine sets a higher response speed for the low compression ratio side than the high compression ratio side, and uses threshold values to limit the variation amount of the target compression ratio, ensuring the actual compression ratio follows the target value, thereby reducing power consumption and maintaining efficient engine performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the variation amount of the target compression ratio is limited in accordance with the high compression ratio side (lower response speed), then the deviation between target and actual compression ratio is suppressed and power consumption is decreased, but the response speed toward the low compression ratio side is unnecessarily limited and response is deteriorated
Solution Approach 1:
The patent segments the compression ratio control into two distinct modes: high compression ratio mode with limited variation amount (first variation amount threshold) and low compression ratio mode with larger variation amount (second variation amount threshold). This segmentation allows each mode to have optimized control parameters suited to its response characteristics, resolving the contradiction between stability and response speed.
Solution Approach 2:
The patent dynamically adjusts the variation amount threshold based on the current compression ratio state. When the compression ratio is high, a stricter threshold is applied; when low, a more permissive threshold is applied. This dynamic adjustment enables the system to maintain control stability while maximizing response speed according to the operating condition.
2Adaptability or versatility
If the target compression ratio is repeatedly varied from high to low and back, then the engine adapts to varying load conditions, but the power consumption of the motor increases due to frequent adjustments
Solution Approach 1:
The patent calculates and sets the target compression ratio in advance based on predicted engine load conditions, rather than reacting to sudden load changes. This preliminary action reduces the frequency of compression ratio adjustments and allows the system to maintain optimal compression ratio for anticipated conditions, thereby reducing motor power consumption while maintaining adaptability.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the actual compression ratio and comparing it with the target compression ratio. The control unit adjusts the motor output based on the deviation between actual and target values, ensuring that compression ratio changes only occur when necessary and are executed efficiently, thus reducing unnecessary power consumption.
3Speed
If the response speed toward low compression ratio side is set higher than high compression ratio side, then the response speed is optimized for each direction, but the control complexity increases
Solution Approach 1:
The patent applies different control characteristics (variation amount thresholds) to different local states of the system: high compression ratio state receives one control parameter set, while low compression ratio state receives another. This local differentiation optimizes response speed for each state without requiring a completely complex control system, as the differentiation is based on simple state recognition.
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A variable compression ratio mechanism (5) is a multi-link piston crank mechanism constituted by a plurality of links linking a piston 4 and a crank shaft (6). A combustion load is acted in a direction pressing the piston (4) in a downward direction. Accordingly, a response speed at a variation of a compression ratio toward a low compression ratio side is higher than a response speed at a variation of the compression ratio toward a high compression ratio side. Therefore, the response speed toward the low compression ratio side is set to be higher than the response speed toward the high compression ratio side. With this, the variation toward the low compression ratio side is varied at the response speed higher than that of the high compression ratio side without corresponding to the response speed on the high compression ratio side. Accordingly, it is possible to suppress the deterioration of the response.