Rack Bushing Support Geometry to Prevent Steering Torque Variation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing rack bushings in steering devices of rack-and-pinion type can cause torque variation and damage due to contact between the inner circumference of the bushing and the tip of the rack gear teeth, leading to unstable steering feel and potential backlash.
Innovation Solution
A rack bushing design with a bushing main body having first and second support surfaces facing each other and a third support surface opposite the rack gear, allowing the steering rack to move in the row direction of the rack gear teeth while being stably supported in three places, and an elastic member attachment groove with an offset groove bottom to reduce reaction force and prevent contact with the rack gear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the annular portion of the rack bushing surrounds the steering rack all around in the place with the formed rack gear, then the steering rack is supported with stiffness, but the tip of any rack gear tooth may contact the inner circumferential surface of the annular portion causing torque variation and potential damage
Solution Approach 1:
The annular portion is divided into multiple arcuate-section portions (first, second, third) that are spaced apart angularly, creating gaps between them. This segmentation allows the rack gear teeth to move without contacting the bushing inner surface while maintaining support stiffness through the distributed arcuate sections.
Solution Approach 2:
The arcuate-section portions are strategically positioned at specific angular locations to provide support only where needed, rather than surrounding the steering rack completely. This local support approach prevents contact damage while maintaining adequate stiffness for steering operation.
2Strength
If the O-ring reduces the diameter of the bushing main body to support the steering rack with stiffness, then the steering rack is supported axially, but contact between the inner circumferential surface and rack gear tooth tip may occur causing torque variation
Solution Approach 1:
Instead of using a continuous O-ring that reduces the entire circumference of the bushing main body, the support function is segmented into multiple discrete arcuate-section portions. These portions provide localized support and radial positioning without creating a continuous contact surface that would interfere with rack gear tooth movement.
Solution Approach 2:
The arcuate-section portions act as intermediaries between the bushing main body and the steering rack, providing support and positioning functions without creating harmful contact points. The gaps between arcuate sections allow the rack gear teeth to pass through without contacting the bushing inner surface.
3Manufacturing precision
If the steering rack is prevented from movement in the axial direction of the pressure pad to reduce backlash, then steering precision is improved, but torque variation occurs due to contact with the rack gear teeth causing unstable steering feel
Solution Approach 1:
The segmented arcuate-section portions provide support and positioning without creating continuous contact points. This allows the steering rack to be supported precisely in the axial direction while avoiding the torque variation that would result from contact between the rack gear teeth and the bushing inner surface.
Data Source
Figure 1
Figure 2(A)~2(C)
Figure 3(A)~3(E)
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.