Torque Transmission Joint With Variable Rigidity Coupling

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Solution Overview

Problem

Existing torque-transmission systems, such as those in electric power steering devices, face challenges in smoothly transmitting torque between drive and driven shafts with mismatched central axes and often generate abnormal noises due to backlash in spline engagement parts.

Innovation Solution

A torque-transmission joint with a coupling having convex and concave portions on its circumferential surfaces, where the circumferential rigidity of axial end portions is lower than the intermediate portion, allowing for elastic deformation and oscillation to align the shafts, and a preload mechanism to prevent noise by elastically pressing the worm towards the worm wheel.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the central axes of the drive shaft and driven shaft are mismatched, then torque transmission becomes difficult, but making the coupling rigid prevents accommodation of axis misalignment

Engineering Contradiction:

Improvetorque transmission smoothnessVSAvoidcoupling rigidity

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The coupling employs different rigidity characteristics in different regions: the axial end portions have lower circumferential rigidity to allow elastic deformation and accommodate axis misalignment, while the axially intermediate portion maintains higher rigidity for stable torque transmission. This local differentiation of mechanical properties resolves the contradiction between needing flexibility for alignment and rigidity for transmission stability.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The coupling transitions from a static rigid structure to a dynamic elastic structure that can oscillate and adapt to axis misalignment. The varying circumferential rigidity enables the coupling to dynamically adjust its shape during operation, allowing the axial end portions to deform elastically while the intermediate portion maintains structural integrity for torque transmission.

Inventive Principle:

Principle #15Dynamics

2Object-affected harmful factors

If elastic members are used to press the worm towards the worm wheel to suppress gear-tooth striking sound, then meshed part noise is reduced, but abnormal noise occurs at the coupled part between output shaft and worm

Engineering Contradiction:

Improvegear-tooth striking soundVSAvoidabnormal noise at coupled part

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The coupling applies local quality differentiation by having the axial end portions with lower circumferential rigidity specifically at the regions that contact the drive shaft and driven shaft. This localized softness allows these end portions to elastically deform and oscillate, absorbing shocks and preventing abnormal noise at the coupled parts, while the stiffer intermediate portion ensures proper worm engagement.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The elastic axial end portions act as beforehand cushioning elements that absorb and dampen shocks before they can propagate to the coupled parts. By designing the coupling with lower rigidity at the axial ends, the patent preemptively cushions the impact between the spline engagement parts and the worm, preventing abnormal noise generation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Stability of the object's composition

If circumferential rigidity is increased throughout the coupling to prevent oscillation, then alignment stability improves, but torque transmission smoothness deteriorates due to inability to accommodate misalignment

Engineering Contradiction:

Improvealignment stabilityVSAvoidtorque transmission smoothness

Core Design Contradiction:

Stability of the object's compositionVSEase of operation

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

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 enables smooth torque transmission between mismatched shafts while preventing abnormal noises by ensuring proper alignment and contact without strong collisions, enhancing durability and reducing manufacturing costs.

Implementation Method 1

the circumferential rigidity of both axial end portions of each coupling-side convex portion is lower than circumferential rigidity of an axially intermediate portion, so that both axial end portions are elastically deformed

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Implementation Method 2

a preload mechanism configured to elastically press the worm towards the worm wheel

Methodology Applied

Scientific EffectElastic pressing: Elasticity

Data Source

PatentUS10738834B2Joint for torque transmission and worm reduction gear

Publication Date: 2020.08.11 NSK LTD

AI summary

Circumferential rigidity of both axial end portions of each coupling-side convex portion is lower than circumferential rigidity of an axially intermediate portion of each coupling-side convex portion. The drive-side concave-convex portion is engaged with a half portion on the other axial side of the coupling-side concave-convex portion. The driven-side concave-convex portion is engaged with a half portion on one axial side of the coupling-side concave-convex portion.