Steering Device Inner Shaft Spline Surface Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The telescopic mechanism in steering devices experiences performance degradation due to issues with the smooth insertion of the inner shaft into the outer shaft, leading to changes in sliding force and potential damage or marking on the shaft surfaces, which can affect the steering feeling and generate abnormal sounds.
Innovation Solution
A steering device design featuring an outer shaft with a spline hole portion and an inner shaft with a synthetic resin surface on the first spline shaft portion and a metal surface on the second spline shaft portion, where the distance between the center axis and the surface of the second spline shaft portion is smaller than that of the first, allowing for smooth insertion and reduced contact damage, thereby stabilizing the sliding force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the inner shaft is inserted into the outer shaft during manufacturing, then the steering device can be assembled, but the inner shaft may be damaged or marked, leading to performance degradation
Solution Approach 1:
The patent applies local quality by providing a synthetic resin coating only on specific portions of the inner shaft - specifically on the first spline shaft portion that engages with the outer shaft, while leaving the second spline shaft portion (with smaller diameter) uncoated. This localized coating provides protection where needed during insertion while maintaining smooth engagement surfaces.
Solution Approach 2:
The inner shaft is segmented into two distinct portions: a first spline shaft portion with larger diameter and synthetic resin coating, and a second spline shaft portion with smaller diameter and metal surface. This segmentation allows different surface treatments for different functional requirements - protection during assembly versus smooth engagement during operation.
2Ease of operation
If the inner shaft and outer shaft are spline-fitted, then the telescopic mechanism functions, but rattling and abnormal sounds occur due to clearance
Solution Approach 1:
The patent changes the surface parameters of the spline engagement interface by coating the first spline shaft portion with synthetic resin. This material change reduces friction and eliminates clearance between the mating spline surfaces, thereby preventing rattling and abnormal sounds while maintaining the telescopic movement function.
Solution Approach 2:
The patent uses composite materials by combining metal (inner shaft base material) with synthetic resin (coating material) on the first spline shaft portion. This composite structure provides both the structural strength of metal and the surface properties of synthetic resin that eliminate clearance and prevent abnormal sounds during spline engagement.
3Reliability
If the shaft surface is damaged or marked, then the sliding force changes, but the telescopic movement becomes unstable
Solution Approach 1:
The patent applies preliminary action by pre-coating the first spline shaft portion with synthetic resin before the insertion process. This preventive coating protects the shaft surface from damage and marking during the insertion operation, thereby maintaining surface integrity and ensuring stable sliding force throughout the telescopic movement.
Data Source
AI summary
A steering device includes: an outer shaft around a center axis and includes an inner space with a spline hole portion; and an inner shaft at least a part of which is disposed in the inner space. The inner shaft includes a first spline shaft portion including a synthetic resin surface and includes a shaft portion that is adjacent to one side of the first spline shaft portion, includes one end of the inner shaft in the inner space, and includes a synthetic resin surface. A distance between the center axis and the surface of the shaft portion is smaller than a distance between the center axis and the surface of the first spline shaft portion. The spline hole portion and the first spline shaft portion are spline-fitted to each other, and the outer and inner shafts are relatively movable in the axial direction.