Pulley Creep Prevention via Localized Knurling Geometry
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Solution Overview
Problem
Pulley apparatuses with synthetic resin pulleys and metal outer rings experience creep due to differing linear expansion coefficients, leading to potential deformation and reduced processing precision, and existing solutions either deform during heat treatment or require large processing areas, making them inefficient.
Innovation Solution
A pulley apparatus with a rolling bearing featuring a locking groove on the outer ring with regulated concave and convex sections, and trapezoidal protrusions on the pulley, which are formed during injection molding to prevent creep by ensuring proper engagement and maintaining contact force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If knurling is formed around the entire outer circumferential surface of the outer ring to prevent creep, then the adhesion between the pulley and outer ring is improved, but the outer ring deforms during heat treatment due to residual strain
Solution Approach 1:
The outer circumferential surface is segmented into multiple regions: a locking groove region with knurling for creep prevention, and a cylindrical surface region without knurling for maintaining processing precision. This segmentation allows each region to serve its specific function without interfering with the other.
Solution Approach 2:
Knurling is applied locally only to the locking groove region where creep prevention is needed, rather than the entire outer circumferential surface. This localized application maintains processing precision in the cylindrical surface region while still providing sufficient creep prevention in the locking groove region.
2Reliability
If concave grooves with large width difference in axial direction are formed to prevent creep, then the engagement with synthetic resin is improved, but the processing area on the outer circumferential surface becomes large
Solution Approach 1:
Instead of forming concave grooves that extend deeply in the axial direction (which would require large processing area), the invention uses moderate-depth knurling in a localized locking groove region. This partial action provides sufficient creep prevention through the knurled surface engagement without requiring excessive processing area.
3Strength
If the difference in width dimension of concave groove or inclination angle is increased to prevent creep, then the engagement strength is improved, but the outer ring deforms during heat treatment due to residual strain
Solution Approach 1:
The outer circumferential surface is divided into a locking groove region with knurling for engagement strength and a cylindrical surface region without knurling for maintaining processing precision. This segmentation allows strong engagement in the locking groove region without deforming the cylindrical surface region during heat treatment.
Solution Approach 2:
Knurling with appropriate depth and pattern is applied locally to the locking groove region to provide sufficient engagement strength, while the cylindrical surface region maintains its original precision. The localized knurling creates residual strain only in the locking groove region, preventing deformation of the entire outer ring.
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
Effectively prevents creep between the synthetic resin pulley and metal outer ring, maintaining structural integrity and processing precision while reducing the risk of deformation and looseness.
Implementation Method 1
knurling is formed on the bottom surface of the locking groove... so as to engage with the protrusions... which prevents creep
Data Source
AI summary
Construction is achieved by which it is possible definitely prevent the occurrence of creep between a pulley 2b and an outer ring 7f. Trapezoidal shaped concave sections are formed such that the angle of intersection θ between the inside surfaces 23 on both sides of each concave section 17a of knurling 19a of the outer ring 7f is within the range 45°≦θ≦120°. Moreover, the depth h in the radial direction of the concave sections 17a and the diameter D of the circumscribed circle of the tip end surfaces 22 of the convex sections 18a are regulated so as to satisfy the relationship 0.004D≦h≦0.015D, and the length L in the circumferential direction of the bottom surface 21 of the concave sections 17a is regulated within the range 0.01D≦L≦0.03D.