Rack Bar Dummy Teeth Forming for End Portion Strength
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Solution Overview
Problem
Existing rack bars in power steering systems have insufficient strength, durability, and steering force transmission efficiency near the axial end portions due to inadequate material distribution during the formation process, leading to smaller rack teeth that compromise strength and efficiency.
Innovation Solution
A hollow rack bar design with obliquely arranged rack teeth and dummy teeth, where the dummy teeth are shallower and provide extra material to support the formation of stronger rack teeth, ensuring consistent strength and efficiency across the entire rack toothed portion by using a specialized teeth forming die with corresponding transfer portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If rack teeth are formed over the whole area of the central recess portion including end portions, then the rack teeth at end portions become smaller due to insufficient material supply, but this reduces strength and durability at critical locations
Solution Approach 1:
The patent introduces dummy teeth at the end portions of the rack bar before the actual rack teeth formation. These dummy teeth are formed first to redirect material flow, ensuring that sufficient material is supplied to the rack teeth at end portions during the subsequent forming process. This preliminary action prevents material deficiency and ensures consistent rack teeth dimensions and strength throughout the entire rack bar.
Solution Approach 2:
The dummy teeth act as an intermediary element that mediates the material flow between the central recess portion and the rack teeth at end portions. By introducing these dummy teeth, the patent creates a intermediate structure that guides and redistributes the metal material, ensuring adequate material supply to the critical end portion rack teeth without directly modifying the rack teeth formation process itself.
2Reliability
If the contact face area of rack teeth is increased to improve steering force transmission efficiency, then more material is required at end portions, but the available material is insufficient
Solution Approach 1:
The dummy teeth are formed in advance at the end portions to establish proper material flow paths before the rack teeth formation. This preliminary structure ensures that when material is supplied during rack teeth formation, it is properly distributed to provide sufficient quantity for large contact face areas, thereby enabling high steering force transmission efficiency without material deficiency.
Solution Approach 2:
The patent applies local quality by creating different structures at different locations: dummy teeth at the end portions and actual rack teeth in the central portion. This localized differentiation ensures that material is properly distributed to where it is most needed (end portions with dummy teeth), allowing sufficient material quantity for large contact faces while maintaining overall structural integrity.
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
The solution ensures sufficient strength, durability, and steering force transmission efficiency with the pinion gear even at the end portions of the rack bar, enhancing the overall performance by distributing material effectively through the use of dummy teeth and a tailored forming process.
Implementation Method 1
a teeth forming die 300 is brought into abutment with this central recess portion 230... A material of the central recess portion 230 is caused to project into recess portions of the teeth forming die 430
Data Source
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AI summary
A rack bar (200) includes a shaft portion (210), a rack toothed portion (220) provided on the shaft portion (210), and a dummy toothed portion. The rack toothed portion (220) includes a plurality of rack teeth (221) provided side by side in an axial direction (C) of the shaft portion (210), each of the rack teeth (221) including a contact face (223) arranged obliquely relative to the axial direction (C) to contact the pinion gear (13a). The dummy toothed portion includes at least one dummy tooth (222) provided on at least one side of the rack toothed portion (220) in the axial direction (C) such that the dummy tooth (222) is arranged parallel to and next to the rack teeth (221). The dummy tooth (222) is designed such that a whole height of the dummy tooth is smaller than a whole height of each of the rack teeth (221).