Coupled Steering Shaft Assembly for Misalignment-Tolerant Power Transfer
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Solution Overview
Problem
Conventional power steering assemblies face issues with radial and angular misalignments, leading to increased wear on seals, reduced efficiency, and high torsional stiffness, which results in premature fatigue and malfunction of input shafts, requiring special tooling for each platform and causing side loads due to mounting errors.
Innovation Solution
A steering shaft assembly with a mid-coupler that includes inwardly-angled surfaces and extensions to engage with the output shaft and screw mechanism, allowing lateral movement to maintain power transfer despite misalignments, and utilizing a modified Oldham coupling for two-axis adjustments to accommodate misalignments and reduce stress on components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional power steering assemblies use a rigid connection between input shaft and output shaft, then torque transmission is efficient, but misalignments cause increased wear on seals and reduced reliability
Solution Approach 1:
The coupling between input shaft and output shaft is segmented into multiple components: input shaft, output shaft, and a mid-coupler with Oldham coupling mechanism. This segmentation allows each component to perform its specific function while accommodating misalignments, resolving the contradiction between reliable seal operation and structural complexity.
Solution Approach 2:
The mid-coupler acts as an intermediary element between the input shaft and output shaft. It includes Oldham coupling mechanisms that mediate the torque transmission while compensating for radial and angular misalignments, protecting the seals from excessive wear caused by misalignment stresses.
2Manufacturing precision
If conventional systems use high radial stiffness in input shaft to maintain precision, then positioning accuracy is improved, but mounting errors cause side loads and premature fatigue
Solution Approach 1:
The stiffness characteristics of the coupling system are changed by introducing the Oldham coupling mechanism. While the input shaft maintains its high radial stiffness for positioning accuracy, the Oldham coupling provides compliance in radial and angular directions, allowing the system to accommodate mounting errors without imposing damaging side loads on the input shaft.
Solution Approach 2:
The coupling system transitions from a static rigid connection to a dynamic compliant connection. The Oldham coupling mechanisms allow for dynamic adjustment and accommodation of misalignments while maintaining torque transmission, enabling the input shaft to operate within its precision parameters without suffering from mounting error-induced side loads.
3Adaptability or versatility
If conventional assemblies require special tooling for each platform to accommodate various piston travel lengths, then customization for different applications is achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The mid-coupler and Oldham coupling mechanisms are designed as universal components that can accommodate different piston travel lengths and platform requirements. The modular design allows the same basic coupling structure to be adapted to various applications by adjusting parameters such as coupling length or mounting positions, eliminating the need for completely different tooling for each platform.
Solution Approach 2:
The coupling system accommodates variations in piston travel length by utilizing dimensional adjustments in the coupling structure. The Oldham coupling mechanisms can be configured with different dimensions or spacing to match various platform requirements, allowing a single design family to serve multiple applications without requiring special tooling for each platform.
4Device complexity
If conventional systems combine rotary valve and recirculating ball screw shaft into a single unit, then device complexity is reduced, but torque transmission causes increased wear on internal seals
Solution Approach 1:
The mid-coupler serves as an intermediary that decouples the torque transmission path from the internal seal environment. By positioning the Oldham coupling mechanisms externally and using the mid-coupler as a mediator, torque is transmitted to the output shaft without directly loading the internal seals of the combined rotary valve and ball screw unit, thereby improving seal durability while maintaining assembly integration.
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 solution effectively reduces stresses on input shaft and control valve components, minimizes backlash, and provides high torsional stiffness, improving reliability and accessibility across various vehicle platforms by accommodating radial and angular misalignments, thus enhancing the overall performance and longevity of the power steering system.
Implementation Method 1
an elongated torsion bar joined to an input shaft and to an output shaft. The elongated torsion bar transfers torque applied to the input shaft
Implementation Method 2
Rotation of the output shaft is typically converted by a recirculating ball screw into linear movement of a piston
Implementation Method 3
The mid-coupler includes an inner diameter that is greater than an outer diameter of the output shaft, such that the mid-coupler can move laterally to maintain the smooth transfer of power
Data Source
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AI summary
An improved steering shaft assembly is provided. The steering shaft assembly further includes an output shaft that is rotatable with respect to the input shaft. The output shaft includes a rotary valve portion and a longitudinal portion. The steering shaft assembly further includes a torsion bar coupled to the input shaft and coupled to the output shaft distal from the input shaft. The steering shaft assembly further includes a mid-coupler extending around about the longitudinal portion of the output shaft and adapted to cooperate with the rotary valve portion of the output shaft. The steering shaft assembly further includes a screw mechanism extending about the longitudinal portion of the output shaft and adapted to cooperate with the mid-coupler. The screw mechanism is adapted to move laterally relative to the output shaft to maintain transfer of power from between output shaft and the screw mechanism despite misalignments therebetween.