Motorcycle Frame Crossmember Overlap for Rigidity
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Solution Overview
Problem
Existing motorcycle vehicle body frames for all-terrain travel exhibit poor resistance to longitudinal and lateral loads, leading to the need for heavy and thick connecting portions, which compromises the frame's rigidity and weight.
Innovation Solution
The vehicle body frame design features a crossmember positioned between the upper end portions of pivot plates, with the crossmember overlapping the joint portions between the main frame sections and pivot plates, and includes a damper mounting portion above the main frame sections' upper surface line, a reinforcing frame section, and an engine hanger positioned below the crossmember, enhancing rigidity while preventing excessive weight and thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the connecting portions are made large, heavy and thick to improve resistance against loads, then the strength and rigidity are improved, but the weight of the frame increases
Solution Approach 1:
The crossmember is positioned to overlap the joint portion between the main frame section and pivot plate in the longitudinal direction, creating a three-dimensional arrangement where the crossmember extends rearwardly beyond the joint portion. This spatial repositioning allows the crossmember to participate in load-bearing in addition to its lateral function, improving strength without increasing material thickness.
Solution Approach 2:
The crossmember serves multiple functions simultaneously: it provides lateral support between pivot plates, acts as a load-bearing element through its overlap with the joint portion, and serves as a mounting structure for the damper. This multi-functionality allows the same component to contribute to both lateral and longitudinal load resistance without requiring additional separate structural elements.
2Ease of manufacture
If the crossmember is arranged at a relatively upper position to accommodate damper mounting, then the damper mounting is facilitated, but the input from the damper becomes relatively large
Solution Approach 1:
The crossmember acts as an intermediary structure that transfers damper forces to the pivot plates and main frame section. By positioning the crossmember to overlap the joint portion, it creates a favorable force transmission path that converts vertical damper inputs into moments about the joint, reducing the direct lateral force input while maintaining mounting feasibility.
3Stability of the object's composition
If the crossmember overlaps the joint portion between main frame section and pivot plate, then the rigidity of joint portions is improved, but the device complexity increases
Solution Approach 1:
The crossmember is designed to perform multiple functions: providing lateral support between pivot plates, overlapping the joint portion to enhance rigidity in the longitudinal direction, and serving as a damper mounting structure. This multi-functionality is achieved through a single component design rather than requiring multiple separate elements, thereby limiting the increase in overall structural complexity.
Data Source
AI summary
A vehicle body frame of a motorcycle includes a head pipe, a pair of main frame sections extending rearwardly from the head pipe, a pair of pivot plates joined to end portions of the main frame sections, and a crossmember arranged between the pivot plates. In such vehicle body frame, the crossmember is arranged between upper end portions of the pivot plates such that the upper end portions of the pivot plates are sandwiched between the crossmember and rear end portions of main frame sections so that at least a portion of the crossmember overlaps a joint portion between the main frame sections and the pivot plates as viewed in a side view. Such structure of the vehicle body frame ensures the rigidity of connecting portions where the crossmember is connected to pivot plates without making the vehicle body frame heavy and thick.