Rack-Driven Steering Ball Nut Structure for Vibration Durability
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Solution Overview
Problem
Conventional electric power-assisted steering devices have complex structures and numerous components in the ball circulation system of the ball nut and rack bar, leading to increased costs, assembly processes, and frequent failures due to vibrations and impact loads, which deteriorate driving stability and durability.
Innovation Solution
A rack-driven power-assisted steering device with a simplified structure featuring a rack bar with an outer screw groove, a ball nut with an inner screw groove, a ball circulation path, and an end cap with a ball return hole, along with a supporting member to reduce the number of parts and enhance stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional ball circulation structure with multiple components is used, then the steering device can transfer driving force effectively, but the structure becomes complicated and costs increase
Solution Approach 1:
The patent combines multiple separate components (ball circulation path, end cap, and supporting member) into an integrated structure. The end cap is coupled to both ends of the ball circulation path, and the supporting member provides axial support, creating a unified assembly that reduces part count while maintaining functional integrity and reliability.
Solution Approach 2:
The end cap serves multiple functions: it closes the ball circulation path, provides mounting points for the supporting member, and contributes to the structural integrity of the ball nut assembly. The supporting member simultaneously provides axial support and anchors the end cap, demonstrating multi-functionality that reduces overall component count.
2Reliability
If multiple components are equipped in the ball circulation structure, then the steering function is complete, but the assembly process becomes lengthy and costs increase
Solution Approach 1:
By integrating the ball circulation path, end cap, and supporting member into a coordinated assembly, the patent reduces the number of separate assembly operations. The supporting member is coupled to the ball nut while providing axial support for the end cap, allowing for simplified assembly sequencing and reduced assembly time.
3Ease of operation
If conventional components are used in the ball nut and rack bar, then the steering mechanism functions properly, but frequent failures occur due to vibrations and impact loads
Solution Approach 1:
The supporting member is positioned to provide axial support to the end cap before impact loads or vibrations occur during operation. This pre-positioned support structure absorbs and mitigates the effects of reverse impact loads from the road and vibrations from ball nut rotation, preventing component failure before it occurs.
Solution Approach 2:
The ball circulation structure integrates multiple materials and components (ball nut, end cap, supporting member, balls) into a composite system where each element contributes specific properties. The supporting member provides rigid axial support while the ball circulation mechanism provides smooth motion, creating a composite structure that resists both vibrations and impact loads.
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 design reduces costs and assembly processes while increasing driving stability and durability by minimizing component failures from vibrations and impact loads, thereby improving the overall performance of the steering system.
Implementation Method 1
a ball circulation path axially formed through the ball nut between the inner circumferential surface and the outer circumferential surface
Implementation Method 2
having an outer circumferential screw groove formed in an outer circumferential surface thereof, a ball nut having an inner circumferential screw groove formed in an inner circumferential surface thereof
Implementation Method 3
an end cap having a ball return hole to circulate a ball along the ball circulation path
Data Source
AI summary
A rack-driven electric power assisted steering device includes a rack bar which axially slides in a rack housing and has an outer circumferential screw groove formed at the outer circumferential surface thereof; a ball nut which has an inner circumferential screw groove formed at the inner circumferential surface thereof and corresponding to the outer circumferential screw groove of the rack bar, and has a ball circulation passage formed between the inner and outer circumferential surfaces thereof, the ball circulation passage passing through the ball nut in the axial direction; end caps coupled to ends of the ball circulation passage, each of the end caps having a ball return hole provided to circulate balls through the ball circulation passage, the outer circumferential screw groove, and the inner circumferential screw groove; and a support member coupled to the inner circumferential surface of the ball nut while axially supporting the end caps.