Ball Nut-Pulley Coupling Structure for Low-Vibration Power Steering
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Solution Overview
Problem
Existing power assisted steering systems face challenges in easily coupling a ball nut and a nut pulley, leading to complex manufacturing processes, increased weight, and reduced rigidity, which can result in vibration and discomfort for drivers.
Innovation Solution
A power assisted steering device is designed with a rack bar featuring an outer circumferential screw groove and a ball nut with an inner screw groove, allowing easy coupling via balls, and a nut pulley made from materials like poly acetal or polyphenylene sulfide, with a large diameter portion and pulley fastening portions for enhanced coupling and reduced weight, along with a torque sensor and motor control for steering assistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional coupling methods are used between ball nut and nut pulley, then coupling strength is sufficient, but manufacturing process becomes complex and weight increases
Solution Approach 1:
The coupling structure is divided into a ball nut with an outer circumferential coupling groove and a nut pulley with an inner circumferential coupling groove. The groove structures are segmented into multiple portions (first, second, third grooves) that can be independently formed and assembled, simplifying the manufacturing process while maintaining coupling strength.
Solution Approach 2:
The coupling groove structures are nested within the ball nut and nut pulley bodies. The inner circumferential coupling groove of the nut pulley fits into the outer circumferential coupling groove of the ball nut, creating a nested arrangement that reduces overall complexity while ensuring strong coupling.
2Strength
If traditional materials and structures are used for ball nut and nut pulley, then rigidity is sufficient, but weight increases and vibration occurs
Solution Approach 1:
The ball nut and nut pulley are designed with varying local qualities - the coupling groove portions have specific structural characteristics for strength, while other portions are optimized for weight reduction. The groove structures have different depths and configurations in different locations to balance rigidity and weight requirements.
Solution Approach 2:
The invention employs composite structural design combining metallic components (ball nut, rack bar) with polymeric materials (nut pulley made from POM, PA, PC, PI, PBT, PPS, or PF). This composite approach reduces overall weight while maintaining necessary rigidity and coupling strength through the integrated groove structures.
3Ease of manufacture
If simplified coupling structure is used between ball nut and nut pulley, then manufacturing is easier and weight is reduced, but coupling reliability may be compromised
Solution Approach 1:
The coupling grooves are designed with dynamic characteristics that allow for easy assembly while ensuring reliable coupling under operational loads. The groove configurations enable the components to be easily coupled during manufacturing, while the structural design ensures reliability during steering operations through proper load distribution.
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
This configuration simplifies manufacturing, reduces weight and vibration, enhances rigidity, and provides improved comfort and convenience for drivers by facilitating easy coupling between the ball nut and nut pulley, while maintaining necessary steering assistance.
Implementation Method 1
a ball nut having an inner circumferential screw groove, corresponding to the outer circumferential screw groove, formed in an inner circumferential surface to be rotatably coupled to the rack bar via a ball
Data Source
AI summary
A power assisted steering device comprises a rack bar having an outer circumferential screw groove formed on an outer circumferential surface of the rack bar; a ball nut having an inner circumferential screw groove corresponding to the outer circumferential screw groove of the rack bar and formed on an inner circumferential surface of the ball nut to be rotatably coupled to the rack bar via balls, and a nut fastening portion formed on an outer circumferential surface; and a nut pulley coupled to the outer circumferential surface of the ball nut and having a pully fastening portion coupled to the nut fastening portion and formed on an inner circumferential surface of the nut pulley.