Worm Reducer Holder Preload to Prevent Backlash Rattle
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Solution Overview
Problem
The existing worm gear reducers in electric power steering devices suffer from backlash-induced rattling noises due to dimensional and assembly errors, leading to unwanted displacement of the worm tip-end portion during steering wheel direction changes, which is not adequately addressed by existing elastic biasing mechanisms.
Innovation Solution
A worm gear reducer design incorporating a holder, pad, and elastic member configuration that applies a preload with opposing components to stabilize the worm tip-end portion, preventing displacement in directions perpendicular to the biasing and axial directions during rotational changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the worm tip-end portion is elastically biased toward the worm wheel side to suppress teeth rattling noise, then the rattling noise is reduced, but the worm tip-end portion may be forcefully displaced in the third direction (perpendicular to both biasing direction and axial direction) when changing rotational direction
Solution Approach 1:
The patent introduces a holder as an intermediary component between the worm and the housing. The holder has pressing surfaces that contact the worm tip-end portion and are pressed by elastic members, mediating the biasing force application. This allows the worm to be elastically biased toward the worm wheel while the holder constrains displacement in the third direction through its structure and pressing mechanisms.
Solution Approach 2:
The patent applies different mechanical properties to different parts of the worm assembly. The tip-end portion of the worm is made with a different material or structure than the base portion, allowing it to be more compliant and accept elastic biasing. The holder also has localized pressing surfaces and elastic members that apply force only where needed, creating local quality variations to solve the contradiction.
2Ease of manufacture
If dimensional errors and assembly errors are present in the worm gear reducer components, then manufacturing is easier and cost is reduced, but backlash occurs at the engaging portion between wheel teeth and worm teeth
Solution Approach 1:
The patent changes the mechanical parameters of the worm tip-end portion by making it more compliant (different material or structure). This allows the system to tolerate dimensional and assembly errors in other components while maintaining proper tooth engagement. The compliant tip-end portion can adapt to variations in tooth spacing and positioning, reducing backlash without requiring high-precision manufacturing throughout the entire assembly.
Solution Approach 2:
The elastic members are pre-installed in the holder to apply a preliminary biasing force to the worm tip-end portion. This preliminary action ensures that the worm is already positioned correctly relative to the worm wheel before operation begins, compensating for potential backlash caused by dimensional and assembly errors in the gear components.
3Object-affected harmful factors
If the worm tip-end portion is made compliant to accept elastic biasing, then teeth rattling noise is suppressed, but the worm may be forcefully displaced in directions other than the biasing direction during rotational changes
Solution Approach 1:
The holder serves as a mediator that allows the worm tip-end portion to be compliant for noise suppression while preventing unwanted displacement. The holder's structure with pressing surfaces and elastic members provides controlled compliance in the biasing direction while maintaining stability in perpendicular directions, resolving the contradiction between compliance and displacement control.
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
Stabilizes the worm tip-end portion, effectively reducing backlash-related rattling noises and ensuring smooth operation by maintaining alignment between the worm and worm wheel teeth.
Implementation Method 1
the tip-end portions of protrusions 64a, 64b of the pad elastic pressure plates 54 elastically press the holder-pressed surfaces 52
Implementation Method 2
a torsion coil spring 115 is provided between the pad 114 and the holder 110. The torsion coil spring 115 elastically pressing the pad 114 toward the worm wheel 102 side
Data Source
Figure 1
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AI summary
Portions with respect to a third direction perpendicular to both a first direction which is a biasing direction of an elastic member 21 and a second direction which is an axial direction of the worm housing 23, on side surfaces of the other side with respect to the second direction of two pad elastic pressure plates 54, come in contact with two holder-pressed surfaces 52 of a holder 19, and by elastically pressing the two holder-pressed surfaces 52 toward the other side in the second direction, apply a preload to contact portions between a holder-engaging portion 41 of the holder 19 and a pad-engaging portion of a pad 20. The portions with respect to the third direction of the two pad elastic pressure plates 54 come in surface contact with or in line contact at at least two locations with respect to the third direction with the two holder-pressed surfaces 52.