Rack Bushing Design for Steering Assembly Load Management
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Solution Overview
Problem
Existing rack bushings for rack and pinion steering assemblies are either expensive and heavy due to machined metal components or inadequate in withstanding high side loads when made of molded plastic, and they often have design features that create stress risers.
Innovation Solution
A rack bushing with a generally annular main body and cylindrical surfaces, featuring axially extending channels and bores to support the rack and maintain sealing integrity, made from cost-effective, high-strength materials like glass-filled polyphenylene sulfide, which is injection molded for reduced weight and stress resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If machined or cast metal rack bushings with inner liners and outer rubber O-rings are used, then the bushing can withstand high side loads, but the cost and manufacturing complexity increase
Solution Approach 1:
The patent uses glass-filled polyphenylene sulfide, a composite material that combines the strength needed to withstand side loads with the cost-effectiveness of molded plastic manufacturing. The glass fibers reinforce the plastic matrix to achieve metal-like mechanical properties while maintaining injection molding compatibility.
Solution Approach 2:
The invention replaces the multi-component mechanical assembly (metal bushing with inner liner and outer O-ring) with a single molded plastic component. The integrated design eliminates the need for separate parts and assembly steps while maintaining the necessary load-bearing and sealing functions.
2Ease of manufacture
If molded plastic rack bushings are used, then the manufacturing cost decreases, but the ability to withstand high side loads is reduced
Solution Approach 1:
The patent uses glass-filled polyphenylene sulfide, a composite material that combines the strength needed to withstand side loads with the cost-effectiveness of molded plastic manufacturing. The glass fibers reinforce the plastic matrix to achieve metal-like mechanical properties while maintaining injection molding compatibility.
Solution Approach 2:
The invention changes the material parameters by using glass-filled polyphenylene sulfide instead of conventional plastic. This material has enhanced mechanical properties including higher strength, stiffness, and load-bearing capacity, allowing the molded bushing to withstand high side loads during steering operation.
3Weight of moving object
If axially extending voids with rectangular cross sections (metal savers) are included in the rack bushing, then the overall weight is reduced, but stress risers are created at the corners
Solution Approach 1:
The patent replaces rectangular voids with circular cross-sectional voids (bores) in the rack bushing. The circular geometry eliminates sharp corners and stress concentration points, distributing stresses more uniformly around the void perimeter while still achieving weight reduction through material removal.
Data Source
AI summary
The invention contemplates a rack bushing and a rack and pinion steering assembly for use in a vehicle that includes such a rack bushing. The steering assembly may include a housing having a tubular rack portion with a tubular end, a rack mounted in the tubular rack portion and extending out of the tubular end, and a rack bushing mounted in the rack portion around the rack. The rack bushing includes a generally annular main body portion having a generally cylindrical inner surface centered about the axis and supporting the rack, an outer surface centered about the axis and including a generally cylindrical main surface adapted to engage the tubular end of the housing, and a first end and an opposed second end. The rack bushing may include a plurality of bores extending within the main body axially from the first end a portion of the way toward the second end. The rack bushing may also include a plurality of channels extending parallel to the axis, recessed in, and spaced circumferentially around the outer surface.