Motorcycle Frame Bracket Structure for Rigidity and Weight Reduction
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Solution Overview
Problem
Existing motorcycle frame structures face challenges in achieving a balance between strength and rigidity, particularly in aluminum twin-spar frames, where the use of hollow cast products and sand cores leads to stress concentration and reduced strength, and the opening of the frame's cross-section for weight reduction compromises rigidity.
Innovation Solution
A motorcycle frame structure featuring a head frame and tank rails with downward-extending bracket portions that include front and side wall portions forming a space at the rear, allowing for core-less molding and improved torsional and lateral rigidity while maintaining longitudinal rigidity, and accommodating components like wiring lines within closed spaces on the tank rails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the cross section of the frame is opened to simplify the mold and reduce weight, then the molding process is simplified and weight is reduced, but the balance between strength and rigidity deteriorates
Solution Approach 1:
The bracket portion is divided into multiple wall portions (first wall portion, second wall portion, third wall portion) that form a segmented hollow structure. This segmentation allows the mold to be simplified while maintaining structural integrity, as each wall portion can be formed independently yet collectively provides the necessary strength and rigidity.
Solution Approach 2:
The bracket portion has different wall thickness distributions in different regions - the first wall portion has a first thickness, the second wall portion has a second thickness, and the third wall portion has a third thickness. This local quality variation optimizes both manufacturing ease and structural performance in different areas of the same component.
2Shape
If sand cores are used to create hollow structures in aluminum casting, then hollow structures are achieved, but stress concentration and reduced strength occur
Solution Approach 1:
The sand core is completely removed from the molding process. The hollow structure is achieved without any core material, eliminating the source of stress concentration and potential defects that cores introduce during casting and subsequent removal.
Solution Approach 2:
Instead of using a core to create the hollow space from the inside out, the invention inverts the approach by forming the hollow structure through the mold cavity design itself, where the hollow space is defined by the absence of material rather than the presence of a core.
3Weight of moving object
If the frame structure is made lighter by opening the cross section, then weight is reduced, but rigidity deteriorates
Solution Approach 1:
The bracket portion utilizes a composite wall structure with varying thicknesses in different regions, creating a composite-like effect within a single aluminum casting. This allows weight reduction in non-critical areas while maintaining adequate thickness in load-bearing regions, achieving both lightness and rigidity.
Solution Approach 2:
The bracket portion extends in multiple dimensions with wall portions arranged in different spatial orientations. This three-dimensional configuration provides structural rigidity through geometric arrangement rather than relying solely on material quantity, enabling weight reduction while maintaining stability.
Data Source
AI summary
There is provided a motorcycle frame structure including a head frame which extends rearward from a head pipe, and tank rails which are welded to the head frame and extends rearward. The head frame includes first bracket portions extending downward. The tank rails include second bracket portions extending downward. An engine is suspended by the first bracket portions and the second bracket portions. Each of the first bracket portions includes a front wall portion extending in a width direction of a motorcycle, and a pair of side wall portions extending rearward from both ends of the front wall portion so as to form a first space opened to a rear side.