Plastic Worm Gear Tooth Surface Structuring for Lubrication

Solution Overview

Problem

Plastic worm gears with smaller diameters experience insufficient lubrication, leading to potential failure and unwanted self-locking issues, particularly in applications like window adjusting drives, due to the limitations of standard and high-viscosity greases.

Innovation Solution

A plastic gear with a structured tooth surface, featuring an average peak-to-valley height of 1.5 μm to 15 μm, specifically designed to create a grease depot, allowing standard lubricating grease to remain effective throughout the service life, thereby ensuring adequate lubrication and controlling self-locking.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the diameter of the plastic worm wheel is reduced to minimize installation space, then the volume of installation space is minimized, but insufficient lubrication on the teeth occurs leading to gear failure

Engineering Contradiction:

Improveinstallation space volumeVSAvoidgear reliability

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The tooth surface is given a specific local quality through structuring with defined roughness parameters (Ra 0.4-1.6 μm, Rz 1.5-15 μm). This local surface structuring creates grease retention zones that ensure adequate lubrication even in compact gear designs, resolving the contradiction between small size and reliable lubrication.

Inventive Principle:

Principle #3Local quality

2Reliability

If high-viscosity special greases are used to improve lubrication, then lubrication behavior is partially improved, but self-locking capability is reduced leading to unwanted automatic opening

Engineering Contradiction:

Improvelubrication adequacyVSAvoidself-locking capability

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

Instead of changing the grease viscosity parameter, the invention changes the surface roughness parameters (Ra 0.4-1.6 μm, Rz 1.5-15 μm) to optimize grease retention. This allows the use of standard low-viscosity greases that maintain self-locking capability while the surface structuring ensures adequate lubrication through improved grease depot formation.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If the tooth surface is made smooth through injection molding, then manufacturing precision is achieved, but grease retention is insufficient leading to lubrication failure

Engineering Contradiction:

Improvetooth surface smoothnessVSAvoidlubrication retention

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The tooth surface is given a specific local quality through structuring with defined roughness parameters (Ra 0.4-1.6 μm, Rz 1.5-15 μm). This local surface structuring creates grease retention zones that ensure adequate lubrication even in compact gear designs, resolving the contradiction between small size and reliable lubrication.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The tooth surface is structured to have micro-scale porosity and roughness features that act as grease depots. This porous surface structure (with Rz 1.5-15 μm) allows the surface to retain lubricating grease throughout the service life, transforming the smooth injection-molded surface into a grease-retentive structure.

Inventive Principle:

Principle #31Porous materials

4Ease of operation

If standard grease is used to maintain self-locking, then self-locking capability is preserved, but insufficient lubrication leads to gear failure in compact designs

Engineering Contradiction:

Improveself-locking capabilityVSAvoidlubrication sufficiency

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

Instead of changing the grease viscosity parameter, the invention changes the surface roughness parameters (Ra 0.4-1.6 μm, Rz 1.5-15 μm) to optimize grease retention. This allows the use of standard low-viscosity greases that maintain self-locking capability while the surface structuring ensures adequate lubrication through improved grease depot formation.

Inventive Principle:

Principle #35Parameter changes

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 structured surface design ensures consistent lubrication and optimal self-locking performance, reducing installation space requirements and eliminating the drawbacks of high-viscosity greases, with peak results between 5 μm and 10 μm average roughness for window regulator drives.

Implementation Method 1

the surface of at least one tooth, preferably of all teeth, is structured in such a way that a grease depot is formed from the tooth surface

Methodology Applied

Scientific EffectSurface roughness:

Implementation Method 2

Standard series lubricating grease which has been used until now remains in this grease depot for the entire service life

Methodology Applied

Scientific EffectGrease retention:

Data Source

PatentEP2031277B1Plastic cog wheel, drive with a plastic wheel and method for producing same

Publication Date: 2012.02.15 ROBERT BOSCH GMBH

Figure 1~2

AI summary

The invention relates to a plastic gear (6), in particular a worm gear, with teeth (9, 10) arranged side by side in the circumferential direction. According to the invention, the surface (12, 14) of at least one of the teeth (8, 9) is structured to form a grease deposit. Furthermore, the invention relates to a transmission (3) and a method for introducing a grease-depositing structure into a surface (12, 14) of at least one tooth (8, 9) of a plastic gear (6).