Straddled Vehicle Exhaust Catalyst Positioning
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Solution Overview
Problem
Straddled vehicles with single-cylinder four-stroke engine units face challenges in maintaining catalyst durability due to low exhaust pipe rigidity and vibration, requiring complex supporting structures to prevent catalyst vibration.
Innovation Solution
The catalyst is positioned closer to the line connecting the downstream end of the cylinder exhaust passage member and the upstream end of the silencer, reducing path length and utilizing the silencer's support structure, and using a multi-walled pipe upstream of the catalyst to maintain exhaust gas temperature, while also employing upstream and downstream catalysts for enhanced purification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the catalyst is provided on the exhaust pipe upstream of the silencer to improve purification performance, then the purification performance of the catalyst is improved, but the structure of the exhauster becomes complicated to secure durability against vibrations
Solution Approach 1:
The patent positions the catalyst in the left-right direction (orthogonal to the up-down vibration direction) by having the exhaust pipe extend in the left-right direction from the cylinder exhaust passage. This dimensional repositioning moves the catalyst away from the high-vibration up-down path while maintaining its upstream location for effective purification, thus simplifying the supporting structure needed.
Solution Approach 2:
The exhaust pipe is designed with different extension directions in different sections: it extends in the up-down direction initially, then bends to extend in the left-right direction toward the silencer. This local variation in orientation allows the catalyst to be positioned in a low-vibration zone (left-right direction) while maintaining the upstream position for purification performance.
2Volume of moving object
If the exhaust pipe is made narrower to reduce size, then the exhauster size is reduced, but the rigidity of the exhaust pipe becomes lower making it more susceptible to vibrations
Solution Approach 1:
The exhaust pipe employs different cross-sectional dimensions at different locations: it has a smaller cross-section in the upstream portion where size reduction is critical, and a larger cross-section in the downstream portion where rigidity is needed to resist vibrations. This local variation in dimensions reconciles the conflicting requirements of compact size and sufficient rigidity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration improves catalyst purification performance while simplifying the exhauster structure by reducing vibrations and maintaining exhaust gas temperature, thus enhancing durability and efficiency.
Implementation Method 1
using a multi-walled pipe upstream of the catalyst to maintain exhaust gas temperature
Implementation Method 2
a single-combustion-chamber main catalyst provided in the single-combustion-chamber exhaust pipe member, the single-combustion-chamber main catalyst purifying the exhaust gas
Data Source
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AI summary
An object is to provide a straddled vehicle including a single-cylinder four-stroke engine unit including a horizontal cylinder member, in which the purification performance of a catalyst purifying exhaust gas is improved while the structure of an exhauster is simplified. It is assumed that the straddled vehicle 1 is viewed in an up-down direction. The upstream end 35a of a silencer 35 is provided one of leftward and rightward of the downstream end 31 b of a cylinder exhaust passage member 31. A main catalyst 39 is arranged so that the center of the downstream end is on the one of the leftward and rightward of the center of the upstream end. The main catalyst 39 is provided to at least partially overlap a quadrangle S10 which is formed of a side S11 which passes the downstream end 31 b of the cylinder exhaust passage member 31 and is parallel to a cylinder axis Cy1, a side S12 which passes the downstream end 31b of the cylinder exhaust passage member 31 is parallel to a crankshaft axis Cr1, a side S13 which passes the upstream end 35a of the silencer 35 and is parallel to the cylinder axis Cy1, and a side S14 which passes the upstream end 35a of the silencer 35 is parallel to the central axis of the crankshaft axis Cr1.