Tapered Sector Gear Variable Ratio Steering
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Solution Overview
Problem
Recirculating-ball style steering systems with tapered sector gears are not compatible with variable ratio racks, leading to interference issues and inability to adjust mesh load effectively.
Innovation Solution
A recirculating-ball style steering system incorporating a variable ratio rack meshing with a tapered sector gear, where the involute teeth of the sector gear have helical meshing lines with decreasing leads radially outward, allowing for adjustable meshing load by longitudinal adjustment of the sector gear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a tapered sector gear is used with a variable ratio rack, then the precision and adjustability of gear mesh load is improved, but interference issues occur at the lower end of the tooth taper and gap issues occur at the upper end of the tooth taper
Solution Approach 1:
The patent modifies the geometric parameters of the sector gear teeth by introducing a specific taper angle (α) that ranges from 5 to 15 degrees. This parameter change allows the teeth to be tapered while maintaining compatibility with variable ratio racks, resolving both the interference issues at the lower end and gap issues at the upper end of the tooth taper. The controlled taper enables precise mesh load adjustment without compromising meshing reliability.
2Ease of manufacture
If straight non-tapered sector teeth are used, then manufacturing is simpler, but mesh load setting becomes cumbersome and expensive with no ability for future adjustments
Solution Approach 1:
The patent introduces adjustability to the sector gear assembly by enabling longitudinal movement of the sector gear along its shaft. This dynamic adjustment capability allows the mesh load to be modified after assembly and throughout the vehicle's service life. The tapered teeth geometry works in conjunction with this adjustability mechanism, providing both ease of manufacture and future adaptability for mesh load optimization.
3Ease of operation
If variable ratio steering is implemented, then mechanical advantage is increased at maximum turning positions, but the complexity of the rack gear geometry increases
Solution Approach 1:
The patent applies the principle of local quality by introducing taper only to the sector gear teeth while keeping the rack teeth geometry relatively simple. The tapered portion is localized to specific regions of the teeth, allowing variable ratio steering functionality to be achieved without overly complicating the overall gear system. This selective application of complexity provides the desired steering control characteristics while managing manufacturing and design complexity.
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
Enables variable ratio steering, precise and cost-effective initial gear mesh load setting, and future adjustments, eliminating interference and gap issues between tapered sector gears and variable ratio racks.
Implementation Method 1
The ball bearings are used to reduce friction and unwanted excess clearance between the worm gear and the ball-nut rack.
Implementation Method 2
The recirculating-ball style gearbox provides a mechanical advantage from the steering wheel to the steerable road wheels.
Data Source
AI summary
A recirculating-ball style gearbox for a vehicle steering system is provided. The gearbox has a rack with rack-teeth that are capable of providing variable ratio steering, where the rack-teeth are in mesh with the involute-teeth of a tapered sector gear. The involute-teeth of the sector gear have arrays of helical meshing lines extending across the meshing surfaces of the teeth, wherein the array of helical meshing lines have leads that decrease in length moving radially outward across the meshing surfaces.