Worm Reducer Bearing Support to Suppress Backlash and Chatter
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Solution Overview
Problem
The existing worm reducers in steering devices experience backlash and chattering due to dimensional and assembly errors, which are exacerbated by the expansion of synthetic resin outer wheel elements, leading to increased friction and displacement of the worm tip end portion, necessitating a solution to prevent orthogonal displacement and reduce friction at the worm teeth and wheel teeth engagement.
Innovation Solution
A worm reducer design incorporating a housing, worm wheel, worm, support bearing, elastic biasing means, and elastic holding means, where the elastic biasing means elastically biases the support bearing toward the worm wheel, and the elastic holding means, composed of leaf springs or an elastic ring, holds the outer ring from both sides orthogonal to the biasing direction, preventing the worm tip end from displacing orthogonally and maintaining alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If dimensional errors and assembly errors are present in the worm reducer parts, then manufacturing and assembly are easier, but backlash and chattering occur at the engagement area between worm teeth and wheel teeth
Solution Approach 1:
The patent applies elastic biasing force to dynamically adjust the engagement parameters between worm teeth and wheel teeth, compensating for dimensional and assembly errors. This changes the operational state from rigid fixed-position engagement to elastic adaptive engagement, eliminating backlash and chattering while maintaining ease of manufacture
Solution Approach 2:
The invention introduces dynamic elastic deformation capability to the worm or worm wheel structure, allowing the engagement area to adaptively adjust during operation. This dynamic adjustment compensates for manufacturing tolerances and prevents chattering, resolving the contradiction between ease of manufacture and reliability
2Weight of moving object
If the outer wheel element made of synthetic resin is used to reduce weight, then the weight of the worm wheel is reduced, but the outer wheel element expands due to water absorption or heat, leading to increased friction at the engagement area
Solution Approach 1:
The elastic biasing mechanism compensates for the dimensional changes caused by thermal expansion or water absorption of the synthetic resin outer wheel element. By dynamically adjusting the engagement parameters, the system maintains optimal friction levels despite material expansion, preserving both weight reduction and low friction characteristics
3Reliability
If the tip end portion of the worm is elastically biased toward the worm wheel to suppress chattering, then chattering is reduced, but the tip end portion may displace in a direction orthogonal to the biasing direction
Solution Approach 1:
The elastic biasing structure allows controlled dynamic displacement in the biasing direction while maintaining stability in orthogonal directions through the constraint mechanism. This dynamic design suppresses chattering through elastic deformation while preventing unwanted orthogonal displacement, resolving the contradiction between reliability and stability
4Reliability
If a large gap is provided between the outer circumferential surface of the large diameter portion of the worm and the inner circumferential surface of the bush to allow displacement, then the worm tip can displace to suppress backlash, but the worm tip may displace excessively in directions other than the biasing direction
Solution Approach 1:
The elastic biasing mechanism provides controlled dynamic displacement capability in the biasing direction to suppress backlash, while the constraint mechanism limits displacement in orthogonal directions. This creates an anisotropic displacement characteristic that maintains reliability through backlash elimination while preserving stability by preventing excessive orthogonal displacement
Solution Approach 2:
The patent creates different mechanical properties in different directions: high compliance in the biasing direction to allow backlash compensation, and high stiffness in orthogonal directions to maintain stability. This local quality differentiation resolves the contradiction between reliability and stability
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 design effectively suppresses backlash and chattering by ensuring the worm tip end remains aligned with the worm wheel, reducing friction and maintaining efficient torque transmission, even under changes in rotational direction.
Implementation Method 1
an elastic biasing means which elastically biases the support bearing toward the worm wheel
Implementation Method 2
a helical torsion spring 110 is provided between the pad 109 and the holder 106. By elastically pressing the pad 109 toward the worm wheel 15 side
Implementation Method 3
The inner ring of the support bearing 17 supporting the tip end side of the worm 16 is externally fitted to a large diameter portion 107 of the worm 16 with a clearance fit while interposing a bush 108 made of synthetic resin therebetween
Data Source
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AI summary
A structure capable of preventing the tip end portion of the worm from being displaced in a direction orthogonal to the biasing direction is provided for the worm reducer comprising a means for elastically biasing the tip end portion of the worm toward the worm wheel side. The support bearing 17 supports the tip end portion of the worm 16 is elastically biased toward the worm wheel 15 side by the elastic biasing means 81, and the support bearing 17 is elastically held by the elastic holding means 82 from both sides in the second direction orthogonal to the first direction parallel to the biasing direction by the elastic biasing means 81 and to the center axis of the worm housing portion 22.