Steering Shaft Resin Tooth Layer for Thermal Backlash Control
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Solution Overview
Problem
The expansion coefficient difference between resin and metal in steering shafts results in gaps and rattle sounds due to thermal expansion and contraction, leading to backlash and noise during vehicle travel.
Innovation Solution
A steering shaft design with a resin layer comprising thick and thin film parts, where thin film parts contact tooth surfaces without gaps, reducing thermal expansion and minimizing backlash.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a resin layer with uniform thickness is provided on all first tooth parts, then the manufacturing process is simple, but gaps are generated between the resin layer and second tooth parts after thermal cycling, causing backlash and rattle sound
Solution Approach 1:
The resin layer is designed with different thicknesses in different regions: thin film parts (0.01-0.06mm) at positions contacting second tooth parts, and thick film parts (0.06-0.2mm) at other positions. This local differentiation ensures that thin film parts maintain contact without gaps after thermal cycling, preventing backlash and rattle sounds, while thick film parts accommodate thermal expansion of the resin material.
2Temperature
If the resin layer thickness is increased to accommodate thermal expansion, then the resin layer can maintain contact at high temperature, but gaps are generated at room temperature, increasing backlash
Solution Approach 1:
The patent applies different thickness values of the same resin material to different functional regions: thin film parts (0.01-0.06mm) where contact is critical to prevent gaps at room temperature, and thick film parts (0.06-0.2mm) where thermal expansion accommodation is needed at high temperature. This resolves the contradiction by optimizing thickness for each specific thermal condition.
3Reliability
If thin film parts are provided at multiple positions, then gaps are minimized and backlash is reduced, but the manufacturing precision requirement increases
Solution Approach 1:
The patent specifies a concrete thickness range for thin film parts (0.01-0.06mm) and thick film parts (0.06-0.2mm), providing clear manufacturing parameters. By defining these specific parameter ranges, the patent makes the manufacturing process controllable and repeatable, reducing the actual precision difficulty while achieving the goal of minimizing gaps and backlash.
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 design effectively reduces backlash and rattle sounds by minimizing thermal expansion-induced gaps, enhancing steering shaft performance and reducing weight.
Implementation Method 1
Resin has a linear expansion coefficient higher than that of metal. Thus, at high temperature in the steering shaft disclosed in Patent Literature 1, the resin layer part provided on the tooth surface of each first tooth part expands and contacts both the tooth surface of the first tooth part and the tooth surface of the corresponding second tooth part. Thereafter, the resin layer part contracts when the steering shaft returns to room temperature.
Data Source
AI summary
A steering shaft includes an inner shaft including first tooth parts, an outer shaft including second tooth parts, and a resin layer. The resin layer includes a plurality of thick film parts and at least four thin film parts. Each thick film part is disposed with a gap from one of the second tooth parts, and each thin film part contacts both one of the first tooth parts and one of the second tooth parts. At a section orthogonal to a central axis of the inner shaft, the thickness of each thin film part is smaller than the thickness of each thick film part.