Variable Compression Ratio Engine Control via Dynamic Cylinder Pressure
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Solution Overview
Problem
Existing variable compression ratio internal combustion engines face challenges in setting an appropriate allowable cylinder pressure that varies with the engine compression ratio, leading to unnecessary weight and size increases in the link mechanism and actuator due to inconsistent torque transmission.
Innovation Solution
A control method that adjusts the allowable cylinder pressure based on the attenuation rate, converting the operation amount of the driving source according to the engine compression ratio and transmitting it to the control mechanism, thereby setting a lower allowable cylinder pressure as the attenuation rate becomes smaller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the allowable cylinder pressure is set to a large value to protect components, then component protection is improved, but the weight and size of the link mechanism and actuator increase
Solution Approach 1:
The patent applies dynamics by making the allowable cylinder pressure variable rather than constant. The control device dynamically adjusts the allowable cylinder pressure based on the current compression ratio and attenuation rate, allowing the system to adapt to changing operational conditions. This resolves the contradiction by enabling component protection at high pressures when needed while allowing weight optimization when the attenuation rate is favorable
Solution Approach 2:
The patent changes the parameter of allowable cylinder pressure from a fixed design value to a variable parameter that depends on the compression ratio and attenuation rate. By establishing a relationship where allowable pressure is determined by these operational parameters, the system can optimize both component protection and mechanism size/weight based on real-time conditions
2Reliability
If the allowable cylinder pressure is maintained at a large value irrespective of attenuation rate, then component protection is improved, but the cylinder pressure is unnecessarily restricted when attenuation rate is large
Solution Approach 1:
The control device dynamically adjusts the allowable cylinder pressure based on the attenuation rate, which varies with compression ratio. When the attenuation rate is large (favorable mechanical advantage), the system allows higher cylinder pressures to maximize engine output. When the attenuation rate is small, the allowable pressure is reduced appropriately. This dynamic adjustment resolves the contradiction between component protection and performance optimization
3Reliability
If the link mechanism and actuator are designed for large input load when attenuation rate is small, then reliability is improved, but weight and size increase
Solution Approach 1:
The patent changes the design approach from static over-design to dynamic parameter adjustment. Instead of designing the link mechanism and actuator for the worst-case scenario (small attenuation rate with large pressure), the system dynamically determines the allowable pressure based on the current attenuation rate. This allows the mechanism to be optimized for actual operating conditions rather than maximum theoretical loads, reducing unnecessary weight and size while maintaining reliability
Data Source
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AI summary
The present invention has: a variable compression ratio mechanism (10) for changing an engine compression ratio according to the rotational position of a control shaft (14); a driving motor (20) that rotationally drives a rotary shaft (23); and a linking mechanism (21) for mechanically linking the control shaft (14) with the rotary shaft (23). The linking mechanism (21) has a reduction ratio (attenuation ratio) that is the ratio of the rotational amount of the rotary shaft (23) and the rotational amount of the control shaft (14), and that changes according to the rotational position of the control shaft (14). Permissible in-cylinder pressure is set, which is a permissible limit pressure in a combustion chamber of an internal combustion engine. The permissible in-cylinder pressure at an engine compression ratio where the reduction ratio becomes low is set lower than that at an engine compression ratio where the reduction ratio becomes high.