Intermediate Shaft Stake Retention to Prevent Slip-Joint Locking
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Solution Overview
Problem
Current stake-based retention systems for intermediate shafts in vehicle steering systems face challenges in maintaining torque transmission while preventing separation during shipping, handling, and assembly, particularly under increased load requirements, which can lead to locking up or high stroke loads, compromising ergonomic assembly and assembly efficiency.
Innovation Solution
A steering shaft assembly featuring a male shaft with splines terminating at 90-degree angles and a female shaft with a splined portion and a thinner end region, where stakes are formed within the end region to provide a retention feature, preventing locking and enhancing pull-apart resistance without deforming the female shaft, using a two-piece stake forming tool to ensure consistent stake formation and reduced tool wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stakes are used to retain the male shaft inside the female tube to prevent separation, then the shafts are retained securely during shipping and handling, but the stakes cause the slip joint to lock up when pushed in from full extension, exceeding the breakaway collapse requirement
Solution Approach 1:
The patent applies local quality by creating a thinner end region specifically at the stake formation zone of the female shaft, while maintaining normal thickness in the splined portion. This localized thickness reduction allows stakes to be formed without deforming the splines, enabling the male shaft to slide freely during assembly while still providing secure retention when needed
2Strength
If increased stake pull apart requirements are imposed to meet assembly requirements, then the shafts are held more securely, but the stakes create high stroke loads that prevent ergonomic assembly and may result in a no build situation
Solution Approach 1:
The thinner end region concentrates the stake formation activity in a specific zone that is isolated from the splined portion. This allows the stakes to provide high holding capacity (meeting 2.5x mass requirements) while the 90-degree spline ends ensure smooth engagement that limits breakaway loads to under 60N, satisfying both strength and force requirements simultaneously
3Reliability
If traditional stake formation processes are used on the female shaft, then retention features are created, but the stakes may deform the female shaft or fail to provide consistent retention under increased load requirements
Solution Approach 1:
The patent creates a dedicated end region with reduced thickness specifically for stake formation, separating this function from the splined portion. This localized approach allows stakes to be formed consistently without deforming the female shaft splines, ensuring reliable retention while maintaining the integrity and shape of the splined engagement surfaces
Data Source
AI summary
A steering shaft assembly includes a male shaft having a plurality of splines formed thereon, each of the splines terminating at a spline end, wherein each of the spline ends form an angle of about 90 degrees relative to a longitudinal direction of the splines. The steering shaft assembly also includes a female shaft including a plurality of stakes located proximate an end of the female shaft, the stakes retaining the male shaft at an interface between the stakes and the spline ends.