Steering System Ball Screw Nut Alignment
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Solution Overview
Problem
Conventional electric power steering systems face issues with smooth operation and axial alignment of the ball screw mechanism due to deformation of the ball screw nut during press-fitting and misalignment caused by loose fitting with small clearance between the ball screw nut and driven pulley.
Innovation Solution
A steering system with an aligning structure using elastic members and grooves on the driven pulley and ball screw nut to apply a biasing force for precise axial alignment, reducing radial load on the ball screw nut and preventing deformation, ensuring smooth operation and accurate coaxial alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the ball screw nut is press-fitted into the driven pulley, then the fixation strength is improved, but the ball screw nut deforms and the groove on its inner peripheral surface deforms, adversely affecting smooth rolling of balls
Solution Approach 1:
The patent introduces a resin layer as an intermediary substance between the ball screw nut and the driven pulley. This resin layer acts as a mediator that transmits the pressing force uniformly across the contact surface, preventing localized stress concentrations that would cause deformation of the ball screw nut grooves, while still achieving sufficient fixation strength through the adhesive and compressive properties of the resin material.
Solution Approach 2:
The patent changes the physical state and distribution of force by introducing a compliant resin layer that can deform elastically under compression. This parameter change allows the force transmission mechanism to transition from rigid direct contact to flexible distributed contact, maintaining groove precision while achieving secure fixation through the resin's mechanical properties.
2Manufacturing precision
If the ball screw nut is loosely fitted with very small clearance, then the groove deformation is prevented, but the axis of the driven pulley and the axis of the ball screw nut are easily misaligned
Solution Approach 1:
The resin layer serves as a compensating intermediary that fills the clearance between the ball screw nut and driven pulley. This intermediary material allows for minor dimensional variations and misalignments while maintaining intimate contact and force transmission, effectively compensating for clearance issues without requiring extremely tight tolerances on the ball screw nut itself.
Solution Approach 2:
The resin layer provides beforehand cushioning by being pre-formed with properties that accommodate dimensional variations. The compliant nature of the resin anticipates and absorbs potential misalignment issues, providing a buffer that maintains proper alignment and force distribution even when clearance exists between components.
3Reliability
If press-fitting is used to fix the ball screw nut, then the fixation reliability is improved, but the balls may come into direct contact with the driven pulley, adversely affecting smooth operation
Solution Approach 1:
The resin layer acts as a protective intermediary that prevents direct contact between the balls and the driven pulley. This intermediary substance fills the space between the ball screw nut outer periphery and the driven pulley inner periphery, ensuring that balls remain contained within the groove and cannot escape to contact the pulley surface, thereby eliminating the harmful effect while maintaining fixation reliability.
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 maintains smooth operation of the ball screw mechanism, prevents distortion of the ball screw nut, and ensures accurate coaxial alignment of the driven pulley and ball screw nut, enhancing the system's durability and reducing vibration and noise.
Implementation Method 1
a plurality of elastic members 63 each having a pair of base parts 63a, 63b extending in the axial direction and a spring part 63c formed between the base parts and being elastically deformable in the radial direction
Data Source
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AI summary
A steering system is provided in which smooth operation of a ball screw mechanism can be maintained and a driven pulley and a ball screw nut can be coaxially aligned accurately. The driven pulley (44) is disposed around an outer periphery of a rack shaft (12) coaxially therewith, and is fitted onto the ball screw nut (51) so as to be integrally rotatable with an aligning structure (48) interposed therebetween. The aligning structure (48) includes locking grooves (61) formed on an inner peripheral surface of the driven pulley (44), mounting grooves (62) formed on an outer peripheral surface of the ball screw nut (51) and radially opposed to the respective locking grooves (61), and elastic members (63). Each elastic member (63) has a pair of base parts (63a, 63b) and a spring part (63c) integrally formed between the base parts (63a, 63b), is disposed in the corresponding mounting groove (62) with the base parts (63a, 63b) spaced apart from circumferential side surfaces (62b, 62c), and is disposed between the mounting groove (62) and the corresponding locking groove (61) such that the spring part (63c) is locked on inner surfaces (61a, 61b) of the locking groove (61) in a radially compressed manner.