Torsion Bar Groove Design for Consistent Active Length
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Solution Overview
Problem
Existing torsion bars in power steering assemblies exhibit significant length variation due to manufacturing stackups, leading to variations in torsional stiffness and tactile feel, which is undesirable.
Innovation Solution
A torsion bar design featuring a central portion with a non-circular cross-section and splined end portions, along with annular grooves, which reduces active length variation by simplifying the manufacturing process and eliminating the need for costly machinery, allowing for a more precise and consistent spring rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional torsion bar design with splined end portions pressed into mating components is used, then the torsion bar can be manufactured with standard processes, but the active length varies significantly (up to 3.0 millimeters) due to manufacturing stackup
Solution Approach 1:
The patent applies preliminary action by pre-forming the annular groove at the desired location on the torsion bar before assembly. This groove serves as a predetermined stop feature that defines the exact insertion depth of the torsion bar into the mating component, eliminating the variability caused by bore depth tolerances and assembly gaps. The groove is machined to precise dimensions to ensure consistent active length across all parts.
Solution Approach 2:
The patent replaces complex, expensive precision machining operations with simpler, more cost-effective processes. Instead of requiring costly machinery to achieve tight tolerances on bore depths and assembly gaps, the solution uses a simple annular groove feature that can be manufactured with standard machining processes, significantly reducing manufacturing cost while improving consistency.
2Manufacturing precision
If precise control of active length is implemented through complex manufacturing processes, then length variation is reduced, but manufacturing cost and complexity increase
Solution Approach 1:
The patent extracts the source of variability (the need for precise control of insertion depth) by removing the dependence on bore depth tolerances and assembly gaps. The annular groove feature isolates the critical dimension to a single, easily controllable feature on the torsion bar itself, eliminating the stackup of multiple tolerances that would otherwise require complex manufacturing and assembly processes.
3Manufacturing precision
If tolerance specifications for hole depths and assembly gaps are tightened to reduce variation, then active length consistency improves, but manufacturing cost increases
Solution Approach 1:
The annular groove is pre-formed on the torsion bar at the exact location where the active length should terminate. This preliminary feature acts as a mechanical stop that prevents over-insertion during assembly, ensuring that the active length is consistently defined regardless of variations in bore depth or assembly gap tolerances. This eliminates the need for tight tolerance specifications on these other features.
Data Source
AI summary
A method of manufacturing a torsion bar includes cutting a stock torsion bar material to a desired torsion bar length to form the torsion bar. The method also includes forming a first end portion by removing material from the torsion bar to form a first annular groove extending circumferentially about the torsion bar. The method further includes forming a second end portion by removing material from the torsion bar to form a second annular groove extending circumferentially about the torsion bar.