Rack Bar Support Mechanism for Steering Weight Reduction
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Solution Overview
Problem
The existing rack and pinion steering apparatuses face challenges with weight increase due to thickened rack bars for enhanced bending strength, leading to potential bad steering feel and increased weight, as well as stress concentration and buckling issues from point contact engagement between pinion and rack gears.
Innovation Solution
A rotation-linear motion conversion apparatus with a pinion shaft, rack bar, and support part that includes rolling elements, where the pinion and rack gears are formed as spur gears with a tilted pitch surface, and a support mechanism that prevents perpendicular movement of the rack bar, reducing weight and improving engagement stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the rack bar is thickened to increase bending strength, then the strength is improved, but the weight of the apparatus is increased
Solution Approach 1:
The invention introduces a support surface extending in the longitudinal direction of the rack bar and support parts that engage with this surface, adding a dimensional constraint along the length of the rack bar. This distributes the load-bearing function across multiple points along the longitudinal axis, allowing the rack bar to maintain strength while reducing its cross-sectional thickness and overall weight.
Solution Approach 2:
The support mechanism divides the rack bar into multiple supported sections along its longitudinal direction, with support parts positioned at different locations. This segmentation of support functions allows the rack bar to be thinner between support points while maintaining overall structural integrity and buckling resistance.
2Strength
If the tooth width of the rack gear is increased to enhance strength, then the strength is improved, but the width of the rack bar is increased and weight is increased
Solution Approach 1:
The invention extends the support surface in the longitudinal direction of the rack bar and positions support parts along this length, creating a distributed support system. This longitudinal dimensioning of support allows the rack gear to have sufficient strength with reduced tooth width, as the distributed support compensates for the reduced gear thickness.
3Device complexity
If the pinion gear and rack gear engage with point contact to allow tilted pinion shaft, then the compactness is improved, but the stress concentration increases and steering feel deteriorates
Solution Approach 1:
By introducing a support surface extending in the longitudinal direction and support parts distributed along this surface, the invention creates a new dimensional framework for load distribution. This allows the tilted pinion-rack configuration to maintain point contact engagement simplicity while the longitudinal support distribution reduces stress concentration by providing multiple support points along the engagement length.
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 reduces the weight of the rack bar, enhances steering feel by distributing stress, and maintains strength against buckling loads, resulting in a more efficient and lightweight steering system.
Implementation Method 1
a plurality of rolling elements that are provided between the support part and the rack bar and roll on the support surface
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
This rotation-linear motion conversion apparatus (10) includes: a pinion shaft (20) in which a pinion gear (22) is formed; a rack bar (30) in which a rack gear (32) that engages with the pinion gear (22) and a support surface (31) along a longitudinal direction are formed; and a support part (40) that supports the rack bar (30) movably along the support surface (31). The support part (40) prevents a movement of the rack bar (30) in a direction X perpendicular to a surface (30a) in which the rack gear (32) is formed.