Die-Forged Rack Bar with Face Width-Enlarged Portions
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Solution Overview
Problem
Conventional rack bars for rack-and-pinion type steering devices have insufficiently wide rack teeth due to limited material plastic flow in die forging, making it difficult to form teeth wider than the circular cross section.
Innovation Solution
A rack bar formed by die forging with face width-enlarged portions and burr-removed portions, where the face width-enlarged portions protrude outwardly from the circular cross section, and burr-removed portions are strategically positioned to enhance material flow and prevent defective formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rack teeth are formed within the circular cross section of the rack bar, then the manufacturing process is simple, but the face width of the rack teeth cannot be sufficiently ensured
Solution Approach 1:
The invention transitions from forming rack teeth only within the circular cross-section to creating face width-enlarged portions that extend radially outward from the circular cross-section. This dimensional expansion allows the rack teeth to have a larger face width than the original circular material cross-section, resolving the contradiction between manufacturing simplicity and sufficient face width.
Solution Approach 2:
The invention applies local quality by creating face width-enlarged portions at specific locations (both ends of the rack teeth) rather than uniformly expanding the entire rack bar. This localized enlargement maintains manufacturing efficiency while achieving the required face width for proper gear engagement.
2Productivity
If die forging is used to form rack teeth, then production efficiency is high, but the plastic flow of material cannot sufficiently be developed limiting tooth width
Solution Approach 1:
The invention incorporates preliminary action by designing the die forging process to include cavities that guide material flow toward the face width-enlarged portions. The burr-forming cavities are strategically positioned to direct excess material toward the rack teeth regions, ensuring sufficient plastic flow development during the forging process itself, thereby achieving both high productivity and adequate tooth width.
3Quantity of substance
If burrs are formed during die forging, then material flow is enhanced, but defective formation occurs at the face width-enlarged portions
Solution Approach 1:
The invention converts the harmful effect of burrs (which cause defective formation) into a beneficial process feature. By intentionally designing burr-forming cavities in the dies, the excess material that would otherwise cause defects is channeled to form burrs that actually enhance material flow into the face width-enlarged portions. The burrs are then controlled and removed in a subsequent step, leaving the desired enlarged portions without defects.
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 design ensures a larger face width dimension for the rack teeth, improving the contact gear ratio and processing convenience, while preventing defective formation and reducing production costs.
Implementation Method 1
a pair of face width-enlarged portions respectively provided at both ends that the rack teeth have in a face width direction, the face width-enlarged portions being formed such that the material flows plastically at the time of die forging
Data Source
AI summary
Rack bar 10 for transmitting a steering operation to steered wheels while converting a rotational movement of a pinion shaft rotatably connected to a steering wheel into an axial movement, the rack bar being formed by conducting a die forging process on a material having an approximately circular cross section. A pair of face width-enlarged portions 15 is provided at both ends that rack teeth 14 have in face width direction. With this, it becomes possible to ensure face width dimension W of rack teeth 14 larger than outer shape S of a circular cross section of rack main body 13 (material), which results in an improvement of a contact gear ratio between the pinion teeth and the rack teeth.