Resin Gear Grease Composition for Low-Torque Electric Power Steering
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Solution Overview
Problem
There is a need for a grease composition that provides improved low friction characteristics under low speed and low load conditions during operation not assisted by Electric Power Steering (EPS), and a reduction gear mechanism that retains the grease on the resin worm wheel to reduce steering torque and enhance durability.
Innovation Solution
A grease composition is developed that includes a diurea compound as a thickener and a chained hydrocarbon polymer, along with polyolefin and montan waxes, which is used to lubricate resin and metal components, and a reduction gear mechanism with a resin driven gear having a tooth surface roughness of 0.5 μm or more to retain the grease and reduce friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional grease composition is used, then the lubrication is adequate under normal driving conditions, but the friction characteristics are insufficient under low speed and low load conditions during operation not assisted by EPS
Solution Approach 1:
The grease composition uses a composite thickener system combining lithium soap and polyurea compounds, which provides different lubrication mechanisms for different operating conditions. The lithium soap component handles high load conditions while the polyurea component provides excellent low-speed lubrication, achieving adaptability across all operating conditions through material composition
Solution Approach 2:
The invention modifies the chemical composition parameters of the grease by incorporating specific polyurea compounds with controlled molecular structures and ratios. This parameter change enables the grease to maintain optimal viscosity and film strength across varying temperatures and loads, improving friction characteristics under low speed and low load conditions while maintaining performance under normal conditions
2Reliability
If the tooth surface roughness is increased to retain grease, then the grease retention is improved, but the steering torque increases due to higher friction
Solution Approach 1:
The invention applies different surface roughness characteristics to different functional areas of the gear teeth. The tooth surfaces have controlled roughness (Ra 0.2-0.8 μm) that provides adequate grease retention, while the grease composition itself is formulated with specific viscosity and adhesion properties that ensure smooth operation. This local optimization of surface quality combined with tailored grease properties resolves the contradiction between retention and friction
3Reliability
If the tooth surface roughness is increased to retain grease, then the durability is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The invention specifies a broad but controlled range for tooth surface roughness (Ra 0.2-0.8 μm) that balances grease retention and manufacturing feasibility. This parameter range is achieved through standard machining and finishing processes, avoiding the need for ultra-precise manufacturing while ensuring adequate grease retention for improved durability
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 grease composition effectively reduces steering torque and improves lubrication under various conditions, including low speed and high load, while the reduction gear mechanism enhances durability and maintains low friction coefficients.
Implementation Method 1
a grease composition for lubricating resins, comprising; a base oil, as a thickener, a diurea compound... a chained hydrocarbon polymer... capable of reducing the steering torque during the operation not assisted by EPS
Implementation Method 2
as a thickener, a diurea compound represented by the following formula (I)... capable of improving low friction characteristics under the conditions of a low speed and a low load
Implementation Method 3
another grease composition for lubricating resins... is characterized by comprising a polyolefin wax and a wax from montanic acid derivatives... capable of maintaining good sliding lubrication between the resin member and the metal member
Data Source
AI summary
The invention provides a grease composition for lubricating resins which contains a base oil, a diurea compound represented by formula (I) as a thickener: R1—NHCONH—R2—NHCONH—R3 (I) (wherein R2 represents a bivalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R1 and R3 each independently represent a straight-chain or branched alkyl group having 8 to 22 carbon atoms), and a chained hydrocarbon polymer having a weight-average molecular weight of 20,000 to 300,000.