Variable Valve Recess Depth for Engine Clearance
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Solution Overview
Problem
In internal combustion engines with variable compression ratio and valve train mechanisms, securing a large minimum distance between valves and pistons to avoid interference leads to decreased output torque, fuel economy, and increased engine size, while also worsening fuel consumption and thermal efficiency.
Innovation Solution
A control system with mechanisms to detect and adjust the piston TDC position and valve operational characteristics to maintain a calculated 'limit distance' that prevents interference, even during unexpected operation, allowing for optimal fuel economy and performance while keeping engine size compact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the minimum distance between the valve and piston is secured larger to avoid interference, then the reliability of avoiding valve-piston interference is improved, but the effective compression ratio lowers leading to decreased output torque and fuel economy
Solution Approach 1:
The patent applies dynamics by making the valve recess depth variable rather than fixed. The control unit adjusts the depth of the valve recess formed in the piston crown surface based on detected valve lift amounts and timing, allowing the system to dynamically optimize the distance between the valve and piston for each operating condition, thereby maintaining reliability while improving compression ratio and performance.
Solution Approach 2:
The patent changes the geometric parameter of the valve recess depth based on operating conditions. By varying the valve recess depth according to detected valve lift characteristics, the system optimizes the compression ratio and combustion chamber geometry for each operating point, resolving the contradiction between safety clearance and performance.
2Reliability
If the depth of valve recess formed in piston crown surface is increased to avoid valve interference, then the minimum distance between valve and piston is improved, but the S/V ratio of the combustion chamber deteriorates worsening fuel consumption
Solution Approach 1:
The system dynamically adjusts the valve recess depth based on real-time detection of valve lift characteristics. This allows the combustion chamber geometry to be optimized for each operating condition, maintaining adequate valve-piston clearance while preserving favorable surface-to-volume ratio for efficient combustion and low fuel consumption.
Solution Approach 2:
The valve recess depth parameter is varied according to operating conditions rather than being fixed. This parameter change allows optimization of both the minimum valve-piston distance and the combustion chamber S/V ratio, preventing deterioration of fuel consumption characteristics.
3Reliability
If the depth of valve recess is increased to avoid valve interference, then the clearance between valve and piston is improved, but the surface area of the combustion chamber increases decreasing thermal efficiency
Solution Approach 1:
The valve recess depth is dynamically controlled based on detected valve operational characteristics. This dynamic adjustment ensures that the combustion chamber surface area is minimized for each operating condition, maintaining thermal efficiency while preventing valve-piston interference.
Solution Approach 2:
By changing the valve recess depth parameter according to operating conditions, the system optimizes the combustion chamber surface area to minimize heat loss while ensuring adequate clearance between the valve and piston, thereby maintaining high thermal efficiency.
Data Source
AI summary
A control system is provided with a piston TDC (top dead center) position variable mechanism and a valve operational characteristics variable mechanism. An actual distance between the valve and the piston of closest approach is calculated based on the actual operation states of these mechanisms. In addition, a limit distance of closest approach necessary to avoid interference between the valve and the piston is set, and, the piston TDC position variable mechanism and the valve operational characteristics variable mechanism are controlled to be driven to increase the actual distance.