Multilayer Coolant Pipe Structure for Fire Resistance and Flexibility
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Solution Overview
Problem
Conventional pipes for low temperature and low pressure cooling circuits in vehicles face challenges in meeting requirements for resistance to cooling fluids, mechanical flexibility, vibration damping, and fire resistance, particularly in adhering to the UL94 V-0 standard, with thermoplastic materials showing insufficient flexibility and vibration resistance.
Innovation Solution
A multilayer pipe structure comprising an internal layer of ethylene-propylene copolymers for fluid resistance and flexibility, an external layer of ethylene-vinyl acetate copolymers with a flame-retardant filler for fire resistance, and an intermediate connecting layer to enhance adhesion between the internal and external layers, ensuring compliance with UL94 V-0 standards and maintaining mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If thermoplastic materials are used for the outer layer to achieve fire resistance, then fire resistance is improved, but flexibility and vibration resistance deteriorate
Solution Approach 1:
The patent uses a composite material for the outer layer consisting of ethylene-vinyl acetate copolymer (EVA) as the base polymer and hydroxylated polyether polyol as an additive. This composite formulation achieves UL94 V-0 fire resistance while maintaining the flexibility and vibration damping properties required for automotive cooling hoses. The specific combination of EVA with vinyl acetate content of 28-33% and the polyether polyol additive creates a material that balances fire resistance with mechanical flexibility.
Solution Approach 2:
The patent specifies precise parameter ranges for the outer layer material: vinyl acetate content of 28-33%, hydroxylated polyether polyol content of 3-8 parts by weight per 100 parts of EVA, and viscosity of 100-500 Pas at 25°C. By optimizing these parameters, the material achieves fire resistance meeting UL94 V-0 standards while maintaining sufficient flexibility for complex hose shapes and vibration damping capabilities.
2Object-affected harmful factors
If multiple concentric layers are used to meet resistance and fire requirements, then fire resistance and chemical resistance are improved, but device complexity increases
Solution Approach 1:
The hose is divided into functional segments: an inner layer for chemical resistance to coolant, an intermediate layer for adhesion and reinforcement, and an outer layer for fire resistance. Each layer is optimized for its specific function, with the outer layer using EVA-based composite material to achieve UL94 V-0 fire resistance while the inner layer provides chemical resistance to glycol-based coolants.
Solution Approach 2:
The patent combines multiple functions into the outer layer material itself. The EVA-based composite provides both fire resistance (meeting UL94 V-0) and mechanical flexibility in a single material formulation, eliminating the need for additional fire-resistant layers that would increase complexity. The hydroxylated polyether polyol additive contributes to both fire resistance and maintenance of flexibility.
3Object-affected harmful factors
If the outer layer material is made fire-resistant with high filler content, then fire resistance is improved, but flexibility deteriorates
Solution Approach 1:
The patent uses hydroxylated polyether polyol with specific parameters: viscosity of 100-500 Pas at 25°C, and content of 3-8 parts by weight per 100 parts of EVA. These parameter optimizations ensure the outer layer achieves UL94 V-0 fire resistance while maintaining flexibility. The polyether polyol acts as a plasticizer that reduces the brittleness that would otherwise result from fire-retardant additives.
Solution Approach 2:
The outer layer is formulated as a composite of EVA copolymer and hydroxylated polyether polyol. This composite material inherently provides fire resistance through the EVA structure while the polyether polyol component maintains flexibility. The synergistic interaction between these two components achieves fire resistance without the need for traditional fire-retardant fillers that would compromise flexibility.
Data Source
Figure 1~2
AI summary
The invention relates to a pipe (1) for the transport of a fluid, in particular a coolant, for a vehicle, the pipe (1) having a multilayer structure and comprising: - an inner layer (10) defining an internal passage for the circulation of the fluid, the inner layer (10) being formed of a first material comprising an elastomer selected from ethylene-propylene copolymers, - an outer layer (16) formed of a second material comprising: - an elastomer selected from ethylene-vinyl acetate copolymers in a proportion of at least 50 parts per cent, and - a flame retardant filler in a proportion of at least 50 parts per cent, and - an intermediate bonding layer (12) arranged between the inner layer (10) and the outer layer (16) and comprising a mixture of an ethylene-propylene copolymer with an ethylene-vinyl acetate copolymer or a polyacrylate or an ethylene acrylate copolymer.