Worm Shaft Biasing Mechanism for Miniaturized Electric Power Steering
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Solution Overview
Problem
The existing electric power steering devices with worm reduction gears face challenges in miniaturization due to inherent backlash and noise issues, primarily caused by dimensional errors and abrasion, which require additional components to mitigate these problems, thereby increasing the axial dimension of the worm shaft.
Innovation Solution
The electric power steering device incorporates a biasing mechanism using inclined cylindrical face portions and an elastic member to bias the worm gear towards the worm wheel, allowing the worm shaft to oscillate and reduce backlash, thereby minimizing the axial dimension of the worm shaft and enhancing miniaturization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the worm shaft is made longer to accommodate additional components for minimizing backlash, then the backlash is reduced, but the axial dimension of the worm shaft increases
Solution Approach 1:
The patent combines the backlash minimization function with the existing tip side bearing support structure. The biasing means is integrated into the tip side bearing assembly, merging two functions (support and backlash control) into a single compact unit, thereby avoiding axial length increase
Solution Approach 2:
The tip side bearing assembly is designed to serve multiple functions: supporting the worm shaft rotation and simultaneously providing backlash minimization through the integrated biasing means. This multi-functionality eliminates the need for separate axial space for backlash control components
2Reliability
If additional components are added to minimize backlash and suppress noise, then the operational efficiency is improved, but the device complexity increases
Solution Approach 1:
The biasing means is merged with the tip side bearing assembly, combining backlash control and noise suppression functions with the existing support structure. This integration reduces the number of separate components while maintaining enhanced operational efficiency and noise suppression
3Weight of moving object
If the worm reduction gear is miniaturized, then the weight and size of the electric power steering device are reduced, but the backlash and noise issues become more pronounced
Solution Approach 1:
The biasing means is integrated into the compact tip side bearing assembly, allowing effective backlash and noise control within the miniaturized worm reduction gear structure. This merging enables small-sized design without sacrificing reliability
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 reduces the axial dimension of the worm shaft, minimizes backlash, and suppresses gear rattling noise, facilitating the miniaturization of the worm reduction gear while maintaining operational efficiency.
Implementation Method 1
an annular bush 12 made of an elastic material is internally fitted and fixed to an inner ring configuring the tip side bearing 9
Data Source
AI summary
A slide member (26) is externally fitted to an outer peripheral surface of an outer ring (20) configuring a tip side bearing (9a) for supporting a tip portion of a worm shaft (6a) so as to be displaceable in an axial direction. A first inclined cylindrical face portion (32) which is an inclined surface disposed on an outer peripheral surface of the slide member (26), and a second inclined cylindrical face portion (30) which is an inclined surface disposed on an inner peripheral surface of a guide member (28) internally fitted and fixed to a holding hole (10a) of a housing (3a) are fitted to each other so as to be slidable in an inclined direction of the respective inclined cylindrical face portions (32, 30). An elastic ring (29) which biases a bearing holding member (26) against to one side in the axial direction is disposed. This realizes a structure which can shorten an axial dimension of a tip side portion of the worm shaft in an electric power steering device including biasing means for minimizing backlash in a meshing portion of a worm reduction gear.