DOHC Engine Cylinder Head Compact Design via Rocker Arm Layout
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Solution Overview
Problem
DOHC-type internal combustion engines face challenges in downsizing the cylinder head due to the need for a large space between intake and exhaust valves, which restricts further miniaturization.
Innovation Solution
The engine design includes rocker arms with support portions disposed orthogonally around the plug hole between intake and exhaust valves, allowing for closer valve placement and reduced rocker arm length, along with commonalized rocker arm shapes and different support hole diameters to enhance assembly efficiency and prevent misassembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If support portions of rocker arms are disposed around the plug hole between intake and exhaust valves, then valve placement can be closer and cylinder head can be downsized, but rocker arm length must be reduced which may affect operation efficiency
Solution Approach 1:
The support portions of the rocker arms are disposed in a direction orthogonal to the axes of the camshafts, utilizing the vertical space around the plug hole. This dimensional reconfiguration allows the valves to be placed closer together horizontally while the rocker arms maintain adequate length by extending vertically around the plug hole, thus resolving the contradiction between compact valve placement and sufficient rocker arm length.
2Ease of manufacture
If rocker arms of the same shape are used for both intake and exhaust sides, then manufacturing efficiency is improved, but assembly complexity increases due to potential misassembly
Solution Approach 1:
While the overall shapes of the rocker arms are made the same for manufacturing efficiency, asymmetric features are introduced: the support holes have different diameters (first and fourth support portions have one diameter, second and third have another), and the rocker arms are disposed on opposite sides of the plug hole. This asymmetric detailing prevents misassembly while maintaining the benefits of standardized manufacturing.
3Reliability
If support holes of different diameters are used in rocker arms, then misassembly is prevented, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs parameter changes by specifying two distinct diameter values for the support holes (first and fourth support portions have a first diameter, second and third have a second diameter). This parameter differentiation provides a simple, robust method to prevent misassembly through physical incompatibility, while the actual precision requirements remain conventional for hole drilling operations.
Data Source
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AI summary
In a DOHC-type internal combustion engine in which a pair of intake valves and a pair of exhaust valves are disposed around a plug hole, and two pairs of rocker arms are respectively interposed between intake-side and exhaust-side camshafts and the intake valves and the exhaust valves, first and second support portions of one pair of the rocker arms are disposed between the intake valves and the exhaust valves in a direction orthogonal to axes of the intake-side and exhaust-side camshafts and around the plug hole, and the third and fourth support portions of an other pair of the rocker arms are disposed outside a region between the intake valves and the exhaust valves in the direction orthogonal to the axes of the intake-side and exhaust-side camshafts.