Motorcycle Frame Weld Bead Stress Reduction
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Solution Overview
Problem
The existing frame structures for motorcycles experience stress concentration and load issues at the welded portions between the head frame and tank rails due to bending loads, and the rectangular-tube shape restricts continuous welding over high-curvature corner portions, leading to weak weld beads on the upper surface.
Innovation Solution
The frame structure features a head frame with arm portions and tank rails having convex, arc-shaped upper surfaces, allowing weld beads to be positioned on side surfaces, enabling continuous welding from upper to side surfaces, and incorporating fillet welding with angled torches for precise welding in tight spaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the joint portion and tank rail are formed in rectangular-tube shape with fillet welding, then joint strength is improved, but stress concentration occurs on the upper surface and welding cannot be continuous over corner portions
Solution Approach 1:
The patent applies curvature by forming the upper surface of the arm portion and the front end portion of the tank rail as convex surfaces with arc-shaped cross sections, replacing the rectangular-tube shape with curved surfaces. This eliminates the corner portions where stress concentration occurs and allows continuous welding from the upper surface to the side surface, with the weld bead end position located on the side surface where stress does not concentrate.
2Ease of manufacture
If rectangular-tube shape is used for joint portion, then manufacturing is simplified, but continuous welding over corner portions with high curvature is not possible
Solution Approach 1:
The patent replaces the rectangular-tube shape with convex surfaces having arc-shaped cross sections. This curved geometry eliminates the high-curvature corner portions that prevent continuous welding, allowing the welding torch to move continuously from the upper surface to the side surface without abrupt angle changes, thereby achieving both manufacturing simplicity and welding continuity.
3Ease of operation
If weld bead end portion is positioned on the upper surface, then welding operation is simplified, but load is likely to be applied to the welded portion due to stress concentration
Solution Approach 1:
The curved surface design allows the welding operation to proceed smoothly from the upper surface to the side surface without abrupt angle changes. The weld bead end portion is naturally positioned on the side surface where stress does not concentrate, thereby maintaining welding operation ease while significantly improving welded portion reliability by avoiding stress concentration.
Data Source
AI summary
There is provided a frame structure for a saddle-ridden type vehicle. A pair of tank rails are jointed to a head frame and extend rearward of a vehicle body from the head frame. The head frame includes a head pipe portion and a pair of arm portions being continuous with the head pipe portion and extending rearward of the vehicle body. Each of upper surfaces of at least one of rear end portions of the arm portions and front end portions of the tank rails are formed into a convex surface having an arc-shaped cross section. The rear end portions of the arm portions and the front end portions of the tank rails are respectively welded to each other so that end portions of weld beads are positioned at side surfaces thereof.