CV Joint Boot Rubber Blend for Cold and Oil Resistance

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Solution Overview

Problem

Existing flexible boots for constant velocity universal joints face challenges in maintaining heat resistance, cold resistance, oil resistance, and ozone resistance, particularly under severe environmental conditions, with chloroprene rubber (CR) failing to meet dynamic ozone and air heat aging resistance, and hydrogenated nitrile rubber (HNBR) compromising cold resistance when improving oil resistance.

Innovation Solution

A flexible boot for a constant velocity universal joint is formed using a rubber material blended with 50 to 80 parts by weight of HNBR having an acrylonitrile content of 15 to 21 wt% and 20 to 50 parts by weight of EPDM, ensuring an elastic recovery rate of 18% or more at -40 °C, with swelling of 100% or less in IRM 903 oil immersion tests.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If chloroprene rubber (CR) is used for heat resistance, then grease resistance is improved, but dynamic ozone resistance and air heat aging resistance deteriorate

Engineering Contradiction:

Improvegrease resistanceVSAvoiddynamic ozone resistance and air heat aging resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent uses a composite rubber material consisting of HNBR (30-70 parts by weight) and EPDM (30-70 parts by weight) to combine the heat resistance and grease resistance of HNBR with the ozone resistance of EPDM, resolving the contradiction between grease resistance and ozone/heat aging resistance

Inventive Principle:

Principle #40Composite materials

2Temperature

If EPDM is increased to improve cold resistance, then cold resistance is improved, but oil resistance deteriorates

Engineering Contradiction:

Improvecold resistanceVSAvoidoil resistance

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The patent optimizes the compositional parameters of the rubber material by controlling the weight ratio of HNBR to EPDM between 30:70 and 70:30, and adjusting the acrylonitrile content in HNBR to 15-21 wt%, achieving a balance between cold resistance and oil resistance through parameter optimization

Inventive Principle:

Principle #35Parameter changes

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 solution provides a boot that satisfies heat, cold, and ozone resistance while maintaining oil resistance, suitable for high-speed and high-temperature conditions, with improved durability and sealability.

Implementation Method 1

the rubber material having an elastic recovery rate of 18% or more at -40 °C in a TR test

Methodology Applied

Scientific EffectElastic recovery: Elastic Recovery

Implementation Method 2

the rubber material preferably swells by 100% or less in an immersion test with IRM 903 oil

Methodology Applied

Scientific EffectOil resistance:

Data Source

PatentEP4339491B1Flexible boot for constant-velocity universal joint and constant-velocity universal joint

Publication Date: 2025.12.31 NTN CORP

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Figure 3

AI summary

A flexible boot for a constant velocity universal joint includes: attachment portions to a mating member at both ends; and a bent portion provided between the attachment portions and absorbing deformation caused by operation of a constant velocity universal joint. The flexible boot is made of a rubber material obtained by blending 50 to 80 parts by weight of HNBR having an acrylonitrile content of 15 to 21 wt% and 20 to 50 parts by weight of EPDM, the rubber material having an elastic recovery rate of 18% or more at -40 °C in a TR test.