Variable Compression Ratio Engine Control for Combustion Pressure
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Solution Overview
Problem
The variable compression ratio mechanism in internal combustion engines with a multi-link type piston crank mechanism faces challenges in managing combustion pressure, particularly in the middle compression ratio region, where the permissible combustion pressure is lower than in other regions, leading to a risk of exceeding maximum permissible values during acceleration.
Innovation Solution
A control method that sets a target compression ratio lower than the regular value for acceleration requests and restricts maximum combustion pressure in the middle compression ratio region, using engine controller signals to adjust valve timing and compression ratio, and limiting intake pressure to prevent excessive combustion pressure through wastegate and throttle valve adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the target compression ratio is set lower than the regular value during acceleration, then the engine response to acceleration request is improved, but the combustion pressure in the middle compression ratio region may exceed permissible values causing mechanical problems
Solution Approach 1:
The control device changes the target compression ratio parameter dynamically based on engine operation conditions. During acceleration requests, the target compression ratio is set lower than the regular value to improve response speed, while during deceleration or steady state, the regular target compression ratio is used. This parameter change approach allows the system to optimize performance while managing combustion pressure risks through controlled transitions.
Solution Approach 2:
The control device implements periodic monitoring and adjustment of the compression ratio based on detected engine operation conditions. When acceleration is detected, the system transitions to a lower target compression ratio regime, and when deceleration or steady state is detected, it transitions back to the regular target compression ratio. This periodic control action ensures that the variable compression ratio mechanism operates within safe pressure limits while maintaining acceleration performance.
2Productivity
If the variable compression ratio mechanism varies compression ratio quickly in response to acceleration request, then the engine performance is improved, but the combustion pressure may have a maximum value exceeding permissible value in middle compression ratio region
Solution Approach 1:
The control device performs preliminary detection of acceleration requests and proactively adjusts the target compression ratio before the combustion pressure problem occurs. By detecting the acceleration request early and setting the lower target compression ratio in advance, the system prepares the variable compression ratio mechanism to operate in a safer compression ratio range, preventing the combustion pressure from exceeding permissible values during the transition.
Solution Approach 2:
The control device continuously detects engine operation conditions including acceleration requests and uses this feedback to dynamically adjust the target compression ratio. The feedback mechanism allows the system to respond to changing operating conditions in real-time, ensuring that the compression ratio is optimized for performance while staying within mechanical tolerance limits. The control device monitors the engine state and adjusts the compression ratio target accordingly to maintain reliability.
Data Source
AI summary
An internal-combustion engine includes a variable compression ratio mechanism for changing a mechanical compression ratio, and a variable valve timing mechanism for changing the valve timing of an intake valve. When acceleration is demanded, a target compression ratio is set to a lower compression ratio than the target value in a normal condition, and the valve timing is set to the advance angle side. Since the allowable combustion pressure decreases in a prescribed intermediate compression ratio region, if an actual compression ratio exists in the prescribed intermediate compression ratio region in the course of a compression ratio change accompanying acceleration, the variable compression ratio mechanism restricts the intake pressure by increasing a degree of opening of a wastegate valve or reducing a degree of opening of a throttle valve, for example.