Straddled Vehicle Cross Member Positioning for Airflow and Rigidity
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Solution Overview
Problem
The existing two-wheeled vehicles face challenges with smooth airflow in the intake passage due to obstructions from frame members, which also result in relatively low rigidity of the body frame.
Innovation Solution
A straddled vehicle design that includes a cross member connecting the right and left seat frames, positioned more rearward than the air cleaner, with fastening portions that support the side covers without obstructing airflow, enhancing both airflow and frame rigidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If frame members are positioned inside the intake passage to connect seat frames, then body frame rigidity is improved, but airflow smoothness deteriorates due to obstructions
Solution Approach 1:
The cross member is positioned in the longitudinal dimension (rearward of air cleaner, forward of inlet ports) rather than occupying the transverse airflow path, allowing rigidity reinforcement without blocking airflow. This spatial repositioning resolves the contradiction by changing the dimensional arrangement of the structural element.
Solution Approach 2:
The cross member is designed with through-holes that segment its structure, allowing airflow to pass through the member itself. This segmentation enables the member to simultaneously provide structural reinforcement and maintain airflow continuity, resolving the contradiction between rigidity and airflow smoothness.
2Object-affected harmful factors
If cross member is positioned forward of inlet ports, then airflow smoothness is improved, but body frame rigidity deteriorates due to insufficient reinforcement
Solution Approach 1:
The cross member utilizes the longitudinal dimension for positioning (between air cleaner and inlet ports) rather than occupying the transverse airflow path, enabling it to provide rearward support for rigidity enhancement while maintaining clear airflow passage. This dimensional arrangement simultaneously achieves both airflow smoothness and structural reinforcement.
3Device complexity
If bolts are positioned to overlap inlet ports in rear view, then seat frame connection is simplified, but airflow intake is obstructed
Solution Approach 1:
The bolts are extracted from the airflow path by positioning them forward of the inlet ports, removing the obstruction to airflow intake. This repositioning maintains the simplified connection function while eliminating the harmful effect of blocking air entry into the intake passage.
Data Source
AI summary
A straddled vehicle, including a cross member connecting right and left seat frames, a seat above the cross member and right and left seat frames, left and right side covers, a rear fender, an intake passage formed below the seat, between the left and right side covers and above the rear fender, an air cleaner located in a front part of the intake passage, left and right inlet ports located in a rear part of the intake passage, first and second fastening portions respectively fastening the right and left side cover to the right and left seat frames or to the rear fender. In a rear view of the vehicle, the cross member is convex upward and does not overlap the right or left inlet port, and the first and second fastening portions are located outside the intake passage, or are located inside the intake passage but does not overlap the right or left inlet port.