Steering Shaft Stake Retention Without Slip Joint Lockup
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Solution Overview
Problem
Current stake processes for retaining intermediate shafts in vehicle steering systems often result in slip joints locking up during assembly, failing to meet ergonomic and load requirements, such as holding 2.5 times the mass of the column with less than a 60 N breakaway load.
Innovation Solution
A steering shaft assembly design featuring a male shaft with splines terminating at 90-degree angles and a female shaft with stakes located in an end region of reduced thickness, providing a retention feature that prevents locking up and meets high pull-apart load requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional stake processes are used to retain the male shaft in the female tube, then the shafts can be retained during shipping and handling, but the slip joint locks up when pushed in from full extension, exceeding the breakaway collapse requirement
Solution Approach 1:
The female shaft is designed with a reduced thickness end region specifically at the stake location, while maintaining full thickness in the splined portion. This localized geometric modification allows the stakes to be formed through the wall without compromising the structural integrity of the splined connection, enabling the male shaft to push through and collapse the stakes during assembly while still providing retention during shipping and handling
2Reliability
If stakes are used to retain the male shaft inside the female tube, then separation during shipping and handling is prevented, but the stake pull apart requirements increase (e.g., holding 2.5 times the mass of the column with less than 60 N breakaway load)
Solution Approach 1:
The stakes are formed by displacing material to create a specific geometric profile with controlled dimensions and orientation. By adjusting the stake geometry parameters (length, diameter, angle, depth) during the forming process, the retention strength and breakaway characteristics can be optimized to meet the specified requirements of holding 2.5 times the column mass with less than 60 N breakaway load
3Ease of manufacture
If the female shaft has uniform thickness throughout, then manufacturing is simpler, but stakes cannot be effectively formed without compromising the splined portion structural integrity
Solution Approach 1:
The female shaft is designed with a reduced thickness end region specifically at the stake location, while maintaining full thickness in the splined portion. This localized geometric modification allows the stakes to be formed through the wall without compromising the structural integrity of the splined connection, enabling the male shaft to push through and collapse the stakes during assembly while still providing retention during shipping and handling
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.