Rack Bushing Support Geometry for Stable Steering Feel
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Solution Overview
Problem
Existing rack bushings in steering devices of rack-and-pinion type cause torque variation and potential damage due to contact between rack gear teeth and the bushing's inner circumference, leading to unstable steering feel and increased backlash.
Innovation Solution
A rack bushing design with a hollow cylindrical bushing main body and annular elastic members, featuring three support surfaces and an offset elastic member attachment groove, allowing the steering rack to move without contact with the bushing's inner circumference, reducing reaction forces and preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the annular portion surrounds the steering rack all around in the place with the formed rack gear, then the steering rack is supported in axial directions, but the tip of rack gear teeth contacts the inner circumferential surface of the annular portion causing torque variation and unstable steering feel
Solution Approach 1:
The patent applies local quality by providing support surfaces only at specific locations on the inner circumferential surface rather than a continuous annular portion. The support surfaces are positioned at locations that do not interfere with rack gear teeth movement, providing localized support where needed while avoiding contact with the gear teeth tips.
Solution Approach 2:
The continuous annular portion is segmented into discrete support surfaces. Instead of having a complete circular support structure, the patent divides it into specific support points that provide necessary support while leaving gaps that prevent interference with the rack gear teeth operation.
2Strength
If the O-ring reduces the diameter of the bushing main body, then the steering rack is supported with intended stiffness, but the inner circumferential surface contacts the tip of rack gear teeth causing damage and backlash
Solution Approach 1:
The patent applies local quality by providing support surfaces only at specific locations on the inner circumferential surface rather than a continuous annular portion. The support surfaces are positioned at locations that do not interfere with rack gear teeth movement, providing localized support where needed while avoiding contact with the gear teeth tips.
Solution Approach 2:
The elastic member acts as an intermediary that provides the necessary radial force to maintain bushing stiffness without requiring the O-ring to reduce the bushing diameter. This intermediary mechanism achieves the stiffness requirement while preventing direct contact between the bushing inner surface and gear teeth.
3Stability of the object's composition
If the steering rack is prevented from movement in axial direction by contact with rack gear teeth, then movement is restricted, but torque variation occurs resulting in unstable steering feel
Solution Approach 1:
The patent provides support surfaces at specific locations that allow the steering rack to move freely in the axial direction while providing support at positions that prevent unwanted lateral movement. This selective support maintains position stability without restricting necessary axial movement.
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 design ensures stable steering feel by allowing axial movement without inner contact, reducing torque variation and protecting the bushing from damage, thus maintaining consistent performance over time.
Implementation Method 1
an elastic member having an annular shape and arranged around an axis of the bushing main body so as to be located between a housing for attachment of the rack bushing and the bushing main body
Data Source
AI summary
A clearance is created between an inner circumference of a bushing main body (2) which surrounds a rack (5) across a row of rack gear teeth (50) and an outer circumference of the rack (5), and two supporting surfaces (21A, 21B) which face each other with a bushing main body axis O therebetween and a supporting surface (21C) which faces a back surface of the rack (5), each extending along an x-axis direction, are formed on the inner circumference of the bushing main body (2). The rack (5) in a neutral state is supported by the two supporting surfaces (21A, 21B) so as to be displaceable along a z-axis direction, and the rack (5) in operation is stably supported by the three supporting surfaces (21A-21C) at three places. A groove bottom position of an annular elastic member attachment groove (24), which is formed on an outer circumference of the bushing main body (2), is offset toward the support surface (21B) only in an area on a support surface (21B) side from the bushing main body axis O, and therefore an elastic ring (3) attached to the elastic member attachment groove (24), protrudes above an outer circumferential surface of the bushing main body (2), but only in the area on the support surface (21B) side from the bushing main body axis O.