Three-Segment Intermediate Shaft for Controlled Crash Collapse
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Solution Overview
Problem
Existing intermediate shaft assemblies with only two coaxial shafts have limited collapse capability during a vehicle crash, which may not meet the requirements for modern vehicles.
Innovation Solution
A three-segment intermediate shaft assembly with an upper shaft releasably fixed for controlled movement relative to an intermediate shaft during normal conditions and a lower shaft fixed against movement, using a polymeric material to secure the assembly during normal operation, which shears under excessive axial force to allow telescopic collapse during abnormal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If only two coaxial shafts are used in the intermediate shaft assembly, then the structure is simpler, but the collapse capacity during crashes is limited
Solution Approach 1:
The intermediate shaft assembly is divided into three separate coaxial shaft segments (first shaft, second shaft, third shaft) that can collapse relative to each other. This segmentation allows the assembly to achieve greater total collapse capacity compared to a two-shaft design, while each individual shaft maintains a manageable size and structural integrity.
Solution Approach 2:
The three shaft segments are arranged in a nested configuration where the second shaft is positioned within the first shaft, and the third shaft is positioned within the second shaft. This nesting arrangement enables telescopic collapse motion while maintaining a compact overall structure when not collapsed, effectively solving the space efficiency problem.
2Reliability
If the shafts are fixed against movement during normal operation, then stability is improved, but collapse capability during crashes is reduced
Solution Approach 1:
The connection between shaft segments transitions from a fixed rigid state during normal operation to a movable telescopic state during crash conditions. The polymeric material provides a dynamic response: it maintains rigid fixation under normal loads but allows controlled telescopic movement when subjected to excessive crash forces, thereby protecting the driver while maintaining steering stability during normal use.
Solution Approach 2:
The mechanical properties of the polymeric material change based on the applied load parameters. Under normal operating conditions, the material exhibits high strength and rigidity to maintain shaft stability. Under crash conditions with excessive axial forces, the material's effective strength decreases as it deforms and allows telescopic movement, thereby changing the system's response from rigid to compliant.
3Ease of operation
If polymeric material is used to fix the lower shaft, then controlled movement is achieved during normal operation, but the material must be designed to shear under excessive load
Solution Approach 1:
The polymeric material is strategically positioned at specific locations where it provides localized flexibility and controlled movement. The material's properties are optimized for the specific function of allowing slight relative movement between shaft segments during normal operation, while maintaining sufficient strength to prevent unintended disassembly. The local placement and formulation of the polymeric material enable differentiated behavior in different operational contexts.
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 assembly provides enhanced axial collapse capacity during crashes, minimizing driver injury by allowing telescopic movement of the shafts, while maintaining stability during normal operation.
Implementation Method 1
The polymeric material is configured to shear under a predetermined axial load to allow the lower shaft to move along the axis relative to the intermediate shaft during an abnormal operating condition
Data Source
AI summary
An I-shaft assembly includes an upper shaft extending along an axis between a first upper end and a first lower end bounding a first hollow bore. An intermediate shaft extends along the axis between a second upper end and a second lower end bounding a second hollow bore. The second upper end is disposed in the first hollow bore. A lower shaft extends along the axis between a third upper end and a third lower end disposed in the second hollow bore. The upper shaft is releasably fixed for controlled movement along the axis relative to the intermediate shaft, and the lower shaft is releasably fixed against movement along the axis relative to the intermediate shaft during a normal operating condition. The upper shaft moves along the axis relative to the intermediate shaft and the lower shaft moves along the axis relative to the intermediate shaft during an abnormal operating condition.