Eccentric Worm Reducer Support for Backlash and Rattle Control
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Solution Overview
Problem
Conventional worm reduction gears in electric power steering systems experience gear rattle noise due to backlash between the worm tooth and wheel tooth, which is not effectively reduced, especially when tooth flanks wear out, and require increased dimensional accuracy and assembly precision to mitigate this issue.
Innovation Solution
A worm reduction gear design incorporating a radial ball bearing or sliding bearing with an eccentric guide member and a dual elastic urging mechanism, including a torsion coil spring and leaf spring, to apply preload and restrict rotation, thereby reducing backlash and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional worm reduction gear with a pair of rolling bearings is used, then the structure is simple and easy to manufacture, but backlash exists between the worm tooth and wheel tooth causing gear rattle noise
Solution Approach 1:
The patent replaces the conventional fixed rolling bearing support with a dynamic support system using a swingable guide member and elastic urging members. This allows the worm to dynamically adjust its position to eliminate backlash while maintaining ease of manufacture through standardized elastic components.
Solution Approach 2:
The patent changes the support parameter from rigid fixed positioning to flexible elastic positioning. The elastic urging members provide variable preload forces that can compensate for dimensional errors and wear, eliminating gear rattle noise while keeping the structure manufacturable.
2Object-generated harmful factors
If dimensional accuracy and assembly precision are increased to reduce backlash, then gear rattle noise is reduced, but manufacturing cost and complexity increase
Solution Approach 1:
The patent changes the approach from controlling dimensional parameters to controlling force parameters. The elastic urging members apply preload forces that compensate for dimensional variations and assembly errors, eliminating the need for high manufacturing precision while reducing gear rattle noise.
Solution Approach 2:
The elastic urging members automatically adjust to compensate for wear and dimensional errors over time. The system self-regulates the preload force to maintain zero backlash without requiring precision control or adjustment mechanisms.
3Object-generated harmful factors
If a preload mechanism is added to eliminate backlash, then gear rattle noise is reduced, but the axial dimension increases
Solution Approach 1:
The patent nests the elastic urging members and guide member within the existing bearing support structure. The guide member swings within the guide holding portion, and the elastic members are positioned between existing components, eliminating the need for additional axial space while providing the necessary preload.
Solution Approach 2:
The patent transitions from axial preload application to radial preload application. The elastic urging members apply forces in the radial direction through the swingable guide member, achieving backlash elimination without increasing axial dimension.
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 effectively reduces axial dimension and minimizes gear rattle noise at the meshing portion between the worm tooth and wheel tooth, absorbing dimensional and assembly errors without increasing manufacturing costs or precision requirements.
Implementation Method 1
a torsion coil spring 23 is provided between the preload pad 22 and the holder 19. By the torsion coil spring 23, the tip end portion of the worm 14 is elastically pressed toward the worm wheel 13
Implementation Method 2
The worm 14 is rotatably supported inside the worm accommodation portion 16 by a pair of rolling bearings 18a and 18b such as deep-groove-type ball bearings
Data Source
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AI summary
A holder member (36) includes a holder-side holding surface (40) for internally fitting and holding a rolling bearing (18c) on a tip end side and a holder-side held surface (42) eccentric to a center axis of the holder-side holding surface (40). A guide member (37) is internally fitted and held into a guide holding portion (25) of a housing (12a) and includes a guide-side holding surface (48) for internally fitting and holding the holder member (36) to be capable of swinging about a center axis of the holder-side held surface (42). A first elastic urging member elastically urges a tip end portion of a worm (14) toward a worm wheel side by elastically urging the holder member (36) in a direction to rotate with respect to the guide member (37). Therefore, a structure which can more effectively suppress generation of gear rattle noise at a meshing portion between a wheel tooth and a worm tooth can be realized.