Grease Composition for Electric Power Steering Stick-Slip
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Solution Overview
Problem
Existing greases for electric power steering devices with steel-resin sliding areas tend to lose lubrication over time, leading to increased friction and stick-slip issues, which affect steering performance and fuel efficiency.
Innovation Solution
A grease composition incorporating a saturated aliphatic amide compound, boron nitride, glycerin fatty acid partial ester, and a metal soap-based thickener, which maintains low friction and prevents oil film breakdown, reducing stick-slip occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional greases are used in electric power steering devices, then initial low friction is achieved, but the grease is gradually removed from the sliding area over time leading to oil film breakdown and stick-slip
Solution Approach 1:
The patent uses a composite grease formulation combining lithium hydroxystearate thickener with specific additives (polyethylene glycol monolaurate and boron nitride) to create a multi-functional lubricant that resists removal while maintaining low friction over extended periods
Solution Approach 2:
The patent modifies the chemical composition parameters of the grease by specifying exact proportions of thickener (2-15 mass%), polyethylene glycol monolaurate (1-10 mass%), and boron nitride (0.1-5 mass%), creating a optimized formulation that balances adhesion, low friction, and long-term stability
2Productivity
If grease is used to reduce friction at the steel-resin sliding area, then transmission efficiency is improved, but the grease eventually breaks down causing stick-slip and steering resistance
Solution Approach 1:
The patent introduces polyethylene glycol monolaurate as an intermediary substance that mediates between the grease base and the steel-resin sliding interface, providing consistent lubrication and preventing direct contact that would lead to stick-slip
Solution Approach 2:
The patent applies boron nitride particles specifically at the sliding interface area to provide localized low-friction properties, while the lithium hydroxystearate thickener provides bulk grease structure, creating different functional zones within the grease system
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 maintains low friction and prevents oil film breakdown, enhancing the durability and performance of electric power steering devices by reducing stick-slip and improving lubricity over extended periods.
Implementation Method 1
A boron nitride having cleavage properties reduces the coefficient of friction at the steel-resin sliding area
Implementation Method 2
the saturated aliphatic amide compound and the glycerin fatty acid partial ester adsorb to the sliding surface
Data Source
Figure 1
AI summary
Provided are both a grease composition for an electric power steering device and an electric power steering device. The grease composition can keep a sufficiently low coefficient of friction in a sliding area between a steel and a resin over a long period, is less susceptible to being removed from the sliding area, does not cause break down of an oil film, and thus can minimize the occurrence of stick-slips. A grease composition for an electric power steering device, containing a synthetic hydrocarbon oil which exhibits a density of 0.75 to 0.95 g/cm3 at 15°C, a saturated aliphatic amide compound, boron nitride, a glycerin fatty acid partial ester, and a metal soap-based thickener; and an electric power steering device using the grease composition.