Disc Brake Master Cylinder Bladder Venting for Air-Free Refilling

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Solution Overview

Problem

Air bubbles form in brake fluid systems due to improper orientations during fluid checking and refilling, leading to undesirable braking performance and frequent rebleeding, especially in vertically stored bikes.

Innovation Solution

A disc brake master cylinder assembly with a bladder member and a vent hole in the bladder cap member allows air to enter and exit the bladder member, preventing air accumulation by expanding or contracting in response to fluid displacement during operation, and a hold down plate secures the bladder member to inhibit fluid leaks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the master cylinder reservoir is oriented in certain positions for checking and refilling brake fluid, then the rider can easily access and maintain the brake fluid level, but air bubbles form and accumulate in the reservoir causing braking performance issues

Engineering Contradiction:

Improveaccessibility for brake fluid checking and refillingVSAvoidbraking performance consistency

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The invention extracts the air removal function from the traditional closed reservoir system by adding a vent hole in the bladder cap. This allows air bubbles to be actively removed from the reservoir during maintenance operations, resolving the contradiction between easy access and reliable braking by enabling air-free fluid refilling without changing the reservoir orientation.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The vent hole is positioned and configured to allow air bubbles to escape before they can contaminate the brake fluid system. By providing a predetermined air escape path during the refilling process, the system prevents air accumulation that would otherwise require brake bleeding, maintaining braking reliability while preserving ease of operation.

Inventive Principle:

Principle #10Preliminary action

2Volume of stationary object

If the bike is stored vertically or upside down, then storage space is optimized, but air enters the brake caliper and hose and accumulates in the master cylinder reservoir

Engineering Contradiction:

Improvestorage space efficiencyVSAvoidair introduction into brake system

Core Design Contradiction:

Volume of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The bladder member acts as an intermediary that physically separates the brake fluid from the vent hole. During vertical or upside-down storage, the bladder can deform to seal against the reservoir walls, preventing air from entering through the vent hole while still allowing the vent hole to function normally when the bike is in operating position. This resolves the contradiction between storage efficiency and prevention of air contamination.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If the vent hole is positioned to allow air escape during operation, then air bubbles can be purged from the system, but the vent hole may allow air entry during storage

Engineering Contradiction:

Improveair purging capabilityVSAvoidair contamination during storage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The bladder member is designed to dynamically change its shape and position based on the orientation and operational state of the master cylinder. During operation, the bladder allows the vent hole to remain open for air purging. During storage, the bladder deforms to seal the vent hole, preventing air contamination. This dynamic adaptation resolves the contradiction between air purging capability and storage protection.

Inventive Principle:

Principle #15Dynamics

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 system effectively prevents air introduction into the brake line, maintaining a leakproof and air-free brake fluid system, reducing the need for frequent rebleeding and ensuring consistent braking performance.

Implementation Method 1

a vent hole provided in a sidewall of the bladder cap member, wherein the vent hole is configured to allow direct communication of outside air within the bladder member

Methodology Applied

Scientific EffectAir pressure differential: Pressure Gradient

Implementation Method 2

air bubbles can float to the top of the master cylinder reservoir

Methodology Applied

Scientific EffectAir buoyancy: Archimedes' Principle (Buoyancy)

Implementation Method 3

a hold down plate provided on the bladder member and secured to the bladder cap member

Methodology Applied

Scientific EffectMechanical fastening: Mechanical Fastener

Data Source

PatentUS20260070628A1Air purging disc brake master cylinder assembly

Publication Date: 2026.03.12 FOX FACTORY INC

AI summary

An air purging disc brake master cylinder assembly is provided. A master cylinder reservoir housing is oriented vertically relative to the disc brake master cylinder assembly. A bladder cap member is secured to a bladder member and the bladder member is received within the master cylinder reservoir housing. A bleed threaded aperture is provided in the bladder cap member in order to allow accumulated air bubbles in the master cylinder reservoir housing to escape to the atmosphere. A vent hole is also provided in the bladder cap member allowing direct communication of outside air within the bladder member.