Cam Follower Roller Assembly with WS2 Coating
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Solution Overview
Problem
Existing cam follower assemblies face challenges with high frictional losses and wear, especially under increased load conditions, and require significant oil flow for lubrication, which is undesirable for cost savings and potential oil-free operations.
Innovation Solution
A cam follower assembly with a tungsten (IV) sulfide (WS2) coating on the radially outer and inner surfaces of the shaft and roller, which acts as a solid lubricant, reducing friction and wear, and can operate reliably even without continuous oil flow, combined with a diamond-like carbon (DLC) coating for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a sliding contact system is used between cam and rocker arm, then the structure is simple, but frictional losses are large and wear is increased
Solution Approach 1:
The patent replaces the sliding contact mechanical system with a rolling contact system by introducing a roller follower. This substitution transforms the friction mechanism from sliding friction to rolling friction, significantly reducing frictional losses and wear while maintaining structural simplicity.
2Loss of energy
If roller follower assemblies are used to reduce friction, then friction between cam and rocker arm is reduced, but wear problems persist
Solution Approach 1:
The patent applies a composite coating system consisting of multiple layers with different functions: a base coat providing wear resistance, an intermediate layer for adhesion, and a top layer of tungsten disulfide (WS2) providing low friction. This composite structure simultaneously achieves both friction reduction and wear resistance.
Solution Approach 2:
The patent changes the surface properties of the roller follower by applying coatings with specific material properties. The tungsten disulfide coating provides a low friction coefficient, while the composite structure ensures wear resistance, thereby improving reliability under high load conditions.
3Loss of energy
If DLC coating is applied on pin surface, then friction is reduced, but the improvements are not sufficient for meeting industry requirements
Solution Approach 1:
The patent enhances the DLC coating by creating a multi-layer composite structure. The base DLC layer provides low friction, while additional layers including tungsten disulfide and other materials are added to improve wear resistance under high load conditions, meeting industry requirements that single-layer DLC cannot satisfy.
4Reliability
If black oxide coating is combined with DLC coating, then wear resistance is improved, but the black oxide coating peels off after certain period
Solution Approach 1:
The patent replaces the problematic black oxide coating with a specifically designed composite coating system. The new structure uses an intermediate adhesion layer that chemically bonds to both the substrate and the top wear-resistant layer, preventing peeling while maintaining wear resistance. The coating layers are designed with appropriate thickness ratios and material compatibility.
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 WS2 coating significantly reduces the required oil flow rate and ensures reliable operation under high loads and varying lubrication conditions, extending the service life and maintaining low friction coefficients, even in oil-free scenarios.
Implementation Method 1
Tungsten (IV) sulfide (WS2) is a solid lubricant which despite being in the solid phase, is able to reduce friction between two surfaces sliding against each other without the need for a large amount of liquid lubrication medium
Implementation Method 2
The high pressure/load acting on the assembly may press the lubricant out of the pores or spaces and thus improves the lubrication
Data Source
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AI summary
The invention starts from a cam follower roller assembly comprising a body (12), a shaft (14, 28) mounted on the body (12), and a roller (16, 30) rotatably mounted on said shaft (14, 28), wherein at least a radially outer surface (14b) of the shaft (14, 28) and/or at least a radially inner surface (16a) of a bore of the roller (16, 30) are coated with an antifriction and/or wear resistance coating. It is proposed that said antifriction coating comprises tungsten (IV) sulfide (WS2).