Variable Volume Boot for CV Joint Pressure Management
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Solution Overview
Problem
Constant velocity joints face issues with pressure changes due to thermal cycling, leading to premature boot failure and contamination, as traditional venting methods can result in undesirable pressure imbalances and leakage of lubricants.
Innovation Solution
An articulated joint with a selectively deformable boot that adjusts its volume in response to pressure changes, using a radial shaft seal and scraper to manage pressure equalization and prevent lubricant loss and contaminant ingress, eliminating the need for a vent valve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a vent valve or vent hole is used to release internal pressure, then pressure build-up is prevented, but grease or lubricant leaks and contaminants enter the joint chamber
Solution Approach 1:
The boot is designed as a flexible membrane that can deform elastically in response to pressure changes. When internal pressure increases during operation, the boot expands outward to accommodate the pressure without requiring a vent valve. This flexible shell approach maintains sealing integrity while accommodating pressure variations, preventing both lubricant leakage and contaminant ingress.
Solution Approach 2:
The system allows the boot to change its physical state by deforming elastically in response to pressure parameter changes. The boot transitions between compressed and expanded states naturally in response to thermal cycling and pressure variations, eliminating the need for mechanical venting components that would compromise the seal.
2Reliability
If the joint is sealed without a vent valve, then lubricant leakage and contaminant entry are prevented, but thermal cycling creates excessive pressure that deforms the boot beyond desirable limits
Solution Approach 1:
The boot is designed as an elastic flexible shell that can accommodate pressure changes through controlled deformation. The material and geometric design allow the boot to expand and contract within safe stress limits during thermal cycling, maintaining sealing integrity while preventing structural failure from excessive deformation.
Solution Approach 2:
The boot's elastic properties provide a cushioning effect that absorbs pressure fluctuations before they can cause damage. The flexible material acts as a buffer, gradually accommodating pressure changes during thermal cycling rather than allowing sudden, damaging deformations.
3Stress or pressure
If a one-way valve is used to vent internal pressure, then pressure build-up during heating is relieved, but negative pressure develops during cooling that stresses the boot excessively
Solution Approach 1:
The elastic boot acts as a two-way pressure accommodation system, expanding during heating and contracting during cooling without creating excessive negative pressure. The flexibility allows the boot to naturally equalize pressure changes in both directions, eliminating the need for one-way valves that create problematic vacuum conditions during cooling.
Solution Approach 2:
The boot's elastic properties enable it to self-regulate pressure changes during thermal cycling without requiring external venting mechanisms. The material naturally expands and contracts in response to temperature and pressure changes, providing automatic pressure equalization that protects against both over-pressurization and vacuum conditions.
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 effectively manages pressure changes within the joint chamber, reducing lubricant loss and contaminant entry, while minimizing stress on the boot, thereby extending its lifespan and maintaining the integrity of the joint.
Implementation Method 1
During operation, a CV joint may create excess internal pressure in the inner chamber of the joint. This is usually the result of temperature, which may be generated during operation.
Implementation Method 2
The boot is selectively deformable in response to an increase in pressure in a joint chamber to increase the volume of the joint chamber
Implementation Method 3
A radial shaft seal is interposed between a small end of the boot and the second rotational member in a channel formed in a small end of the boot
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
An articulated joint includes a first rotational member and a second rotational member coupled with and positioned generally coaxial to the first rotational member. The joint also includes a boot. The boot is selectively deformable in response to an increase in pressure in a joint chamber to increase the volume of the joint chamber. The volume of the joint chamber is selectively changed due to, at least in part, relative movement of the boot end to the second rotational member.