Disc Brake Adjuster Piston Transition for Lower Stress Concentration
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Solution Overview
Problem
Air disc brakes for heavy vehicles face piston failure due to high loads at stepped transitions between threaded and non-threaded regions, leading to premature wear and increased manufacturing complexity.
Innovation Solution
An adjuster mechanism with an outer piston featuring a progressive transition from a female thread to a non-threaded region, minimizing stress raisers and simplifying manufacturing, along with a torque limiting clutch and one-way clutch for smooth operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a stepped transition is used between female thread and non-threaded region of the piston, then manufacturing is simplified, but stress concentrations occur leading to piston failure under high loads
Solution Approach 1:
The patent applies curvature by replacing the stepped transition with a tapered transition region where the diameter gradually changes from the threaded portion to the non-threaded portion. This curved/tapered geometry eliminates the abrupt angular discontinuity of the stepped design, distributing stress more evenly and preventing stress concentration at sharp corners, thereby improving piston reliability while maintaining manufacturing simplicity.
2Device complexity
If a single extendible piston is used to account for wear, then device complexity is reduced, but load on the piston increases leading to heightened failure risk
Solution Approach 1:
The tapered transition region in the single piston design serves to strengthen the piston structure at its most vulnerable point, enabling it to withstand the full braking load without failing. This structural reinforcement allows the single piston system to reliably handle high loads that would otherwise require a more complex multi-piston arrangement, thus maintaining low device complexity while achieving high reliability.
3Ease of manufacture
If a stepped transition is used in the piston design, then manufacturing process is simpler, but premature failure occurs due to stress raisers at the transition
Solution Approach 1:
The tapered transition region eliminates the sharp corners inherent in stepped designs, creating a smooth gradual transition that prevents stress concentration. This curved geometry distributes mechanical stresses evenly throughout the piston structure during repeated braking cycles, preventing fatigue failure and significantly extending the piston's service life while remaining simple to manufacture.
Data Source
AI summary
An adjuster mechanism for a disc brake. The adjuster mechanism may include an outer piston and an inner piston. The outer piston may define a bore having a female thread, a non-threaded region, and a transition region. The non-threaded region may have a greater diameter than a minor diameter of the female thread. The minor diameter of the female thread in the transition region may progressively increase until it meets a major diameter of the female thread.