Piston Pin DLC Coating for Low-Friction Engine Motion Transfer
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Solution Overview
Problem
Current motion transmission devices in heat engines face increased risks of seizure and excessive wear due to higher mechanical loads and thermal loads, particularly at the piston/piston pin contact, especially under WLTP cycle conditions, despite the use of low-friction coatings and low viscosity oils.
Innovation Solution
The implementation of a mechanical motion transmission device with surface coatings on the piston pin and piston hole featuring a low coefficient of friction, specifically using DLC type coatings with varying hydrogen content and structure, such as a-C:H and ta-C families, to reduce friction and wear, and a gradient hardness profile for optimal adhesion and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If engine displacement is increased to achieve higher power under WLTP cycles, then engine power is improved, but mechanical loads and thermal loads at piston/piston pin contact increase significantly, leading to increased seizure risk
Solution Approach 1:
The patent applies parameter changes by modifying the surface properties of the piston pin through DLC coating with specific hydrogen content (20-30% atomic hydrogen) and thickness (1-3 micrometers). This changes the friction and wear parameters of the contact surface, allowing higher engine power to be achieved while maintaining acceptable seizure risk through the low-friction coating interface.
Solution Approach 2:
The patent uses composite materials by combining the piston pin substrate (steel or aluminum) with a DLC coating layer. This composite structure provides both the mechanical strength of the base material and the low-friction, wear-resistant properties of the carbon-based coating, enabling the system to handle higher loads while reducing seizure risk.
2Use of energy by moving object
If low-viscosity oils are used to reduce fuel consumption, then fuel efficiency is improved, but oil degradation accelerates under high load conditions, leading to excessive wear
Solution Approach 1:
The DLC coating on the piston pin provides self-lubricating properties, reducing dependence on the lubricating oil's viscosity and film strength. The coating itself acts as a solid lubricant, allowing the system to use low-viscosity oils for reduced friction and fuel consumption while the coating protects against wear even when the oil degrades under high load conditions.
3Use of energy by moving object
If oil supply to the piston is interrupted at lightly loaded operating points to improve efficiency, then energy efficiency is improved, but lubrication gaps create risks of piston pin seizure
Solution Approach 1:
The DLC coating provides continuous self-lubrication regardless of oil supply status. During periods when oil supply is interrupted at lightly loaded operating points, the low-friction coating maintains adequate lubrication through its inherent solid lubricant properties, preventing seizure while allowing the system to achieve energy efficiency improvements from oil pump control.
4Loss of energy
If DLC coating is applied to the piston pin to reduce friction, then friction is reduced, but excessive wear still occurs under high load conditions with degraded oil
Solution Approach 1:
The patent optimizes the DLC coating parameters including hydrogen content (20-30% atomic hydrogen), thickness (1-3 micrometers), and deposition conditions to achieve a coating that simultaneously provides low friction and high wear resistance. This specific parameter range creates a coating structure that maintains its integrity and lubricating properties even when the oil is degraded, preventing both excessive wear and friction loss.
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
This solution significantly reduces friction and wear, allowing for increased engine performance, compact architectures, and extended oil pump control range, while maintaining stable friction coefficients across different lubrication conditions and temperatures.
Implementation Method 1
contact between two surface coatings with a low coefficient of friction... the aC:H family with an atomic hydrogen content of between 20% and 30% covers the piston pin... the other surface coating being based on amorphous carbon of the DLC type of the ta-C family
Data Source
Figure 1~2a
Figure 2b~3
Figure 4a~4b
AI summary
The invention mainly relates to a mechanical device (9) for transmitting movement for a combustion engine, comprising: - a connecting rod (10) comprising a connecting rod big end (13) intended to cooperate with a crank pin of a crankshaft and a connecting rod small end (12) having an internal bore (18); - a piston (16) comprising a pin hole (22); and - a piston pin (15) inserted into said pin hole (22) of said piston (16) and into said internal bore (18) of the connecting rod small end (12) in order to provide a rotary link between said connecting rod (10) and said piston (16), characterised in that the piston pin (15) is covered with a surface coating (14a) with a low friction coefficient and the pin hole (22) of said piston (16) or an insert interposed between said piston pin (15) and said pin hole (22) is covered with a layer of a surface coating (14b) with a low friction coefficient.