Rack Assist EPS Ball Nut Rotational Support
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Solution Overview
Problem
Rack assist type electric power steering apparatuses experience rattling noise and resistance due to vibrations from the operation of the ball nut and rack bar, as well as impact loads from the road surface, leading to potential damage and safety issues with the steering wheel.
Innovation Solution
The apparatus includes a ball nut coupled to the rack bar via balls on a screw thread, a nut pulley on the ball nut's outer surface, and a rotational support member between the ball nut and the rack housing, which supports the nut pulley and reduces vibrations and impact loads through a power transmission structure with a screw thread and rolling members.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a ball nut and rack bar are used in the steering system, then the steering assist power can be effectively transmitted, but rattling noise and resistance occur due to vibrations and impact loads
Solution Approach 1:
The patent introduces a rotational support member as an intermediary component between the ball nut and rack housing. This support member includes a bearing that mediates the interaction between the rotating ball nut and the stationary rack housing, reducing direct contact and friction. The intermediary bearing absorbs vibrations and impact loads, preventing them from being directly transmitted to the rack bar and tie rods, thereby eliminating rattling noise and resistance while maintaining effective power transmission.
2Ease of operation
If the ball nut rotates to slide the rack bar, then steering motion is achieved, but the ball nut and nut pulley may be deformed or damaged due to vibration and impact
Solution Approach 1:
The patent implements beforehand cushioning by pre-installing a bearing within the rotational support member that is positioned to receive and cushion impact loads before they can reach the ball nut and nut pulley. The bearing acts as a protective buffer that absorbs shock and vibration during steering operations, preventing deformation or damage to the ball nut and nut pulley while allowing smooth steering motion to occur.
3Speed
If a bearing is mounted on the outer circumferential surface of the ball nut, then rotation is supported, but the bearing and other components can be damaged by impact from the road surface
Solution Approach 1:
The patent applies the nesting principle by placing the bearing inside a protective rotational support member that is coupled between the ball nut and the rack housing. The bearing is nested within the support member structure, which provides an additional layer of protection against impact loads from the road surface. This nested configuration allows the bearing to support rotation efficiently while the outer support member absorbs and distributes impact forces, preventing damage to the bearing and other components.
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 effectively eliminates rattling noise and resistance, reduces the risk of damage to the ball nut and nut pulley, and enhances driving reliability by mitigating vibrations and impact loads.
Implementation Method 1
a ball nut (310) that is coupled to the rack bar (306) by means of balls
Implementation Method 2
a ball nut (310) that is coupled to the rack bar (306) by means of balls connected to a screw thread (306a, 310a)
Implementation Method 3
A bearing (340) for supporting the rotation of the ball nut (310) is mounted on the outer circumferential surface of the ball nut (310)
Data Source
AI summary
The present invention provides a rack assist type electric power steering apparatus that may include: a ball nut configured to be coupled to the outer circumferential side of a rack bar through balls that are coupled to a screw thread formed on the inner circumferential surface; a nut pulley configured to be coupled to the outer circumferential surface of the central portion of the ball nut in the axial direction; and a rotational support member configured to be coupled between the outer circumferential surface of the ball nut and the rack housing while supporting both side ends of the nut pulley.