Transmission Gear Fluid Composition for Copper Corrosion Control
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Solution Overview
Problem
Lubricants containing sulfurized additives, such as thiadiazole, provide good load carrying capacity but cause unacceptable copper corrosion, failing performance in copper corrosion tests like ASTM D130-19 when tested for extended periods.
Innovation Solution
A lubricating composition comprising one or more base oils, at least 0.35 weight percent of a thiadiazole additive, and one or more substituted tris-aryl phosphites with a specific para-to-ortho substitution ratio, which reduces copper tarnishing and maintains high load carrying capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If sulfurized additives such as thiadiazole are included in the lubricant to achieve good load carrying capacity, then extreme pressure and antiwear performance are improved, but copper corrosion performance deteriorates leading to unacceptable copper corrosion
Solution Approach 1:
The patent introduces substituted tris-aryl phosphites as intermediary compounds that react with sulfurized additives to form protective films on copper surfaces. These phosphite compounds (with specific para-to-ortho substitution ratios between 0.5 and 2.0) act as mediators between the sulfurized additive and copper components, preventing direct corrosive interaction while maintaining the load-carrying benefits of sulfurized additives through controlled reaction products.
Solution Approach 2:
The lubricant composition creates a composite protective system by combining sulfurized thiadiazole additives with substituted tris-aryl phosphites. This composite approach allows the sulfurized component to provide extreme pressure protection while the phosphite component provides copper corrosion inhibition, with their interaction forming a synergistic protective film that addresses both requirements simultaneously.
2Reliability
If a minimum amount of thiadiazole additive is included to achieve acceptable failure load stage in FZG wear scar testing, then antiwear performance is improved, but copper corrosion performance deteriorates when tested for extended periods at high temperatures
Solution Approach 1:
The substituted tris-aryl phosphites are included in the lubricant composition to preemptively counteract the copper corrosion that would otherwise be caused by sulfurized additives during extended high-temperature operation. The phosphites react with sulfurized compounds before they can reach and corrode copper surfaces, creating a protective barrier in advance of any harmful interaction.
Solution Approach 2:
The phosphite compounds serve as intermediary substances that intercept sulfurized additive molecules and redirect their reactivity away from copper surfaces. The specific molecular structure (with controlled para-to-ortho substitution ratios) enables these intermediaries to preferentially react with sulfurized species, forming stable complexes or protective films that prevent the sulfurized additives from attacking copper components during thermal stress.
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 composition achieves a copper tarnishing rating of no higher than 3B after 168 hours at 150°C and a failure load stage of 7 or higher in FZG testing, while maintaining effective load carrying capacity.
Implementation Method 1
one or more substituted tris-aryl phosphites... which forms a sulfurized reaction product
Data Source
AI summary
A gear fluid composition for lubricating a driveline including a thiadiazole additive and select substituted aryl-phosphite compounds to achieve good antiwear and copper corrosion performance.