Drum Brake Clearance Adjuster With Force-Limited Ratchet
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Solution Overview
Problem
Existing parking brake systems of the drum-in-hat type face challenges in maintaining a minimum operating clearance between shoes and drum, especially after repeated actuations that do not involve wear, and require a simpler, less bulky design with fewer components.
Innovation Solution
A device with an extensible strut assembly and a ratchet mechanism that adjusts the clearance between shoes and a drum, using a piston, support, toothed ring, and sliding guide, where the ratchet mechanism allows extension only when the braking force is below a threshold, preventing further extension when the force exceeds it, thus maintaining a minimum clearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the pawl engages multiple teeth on the star wheel during high braking force, then the shoe is pressed onto the friction surface, but the minimum operating clearance is canceled and drum rotation is prevented
Solution Approach 1:
The patent applies the Dynamics principle by making the strut extensible rather than fixed. The strut can dynamically adjust its length based on operating conditions - extending when wear occurs to maintain clearance, and remaining stable when high braking forces are applied. This dynamic adaptability resolves the contradiction by allowing the system to respond differently to wear conditions versus high-force braking conditions.
Solution Approach 2:
The patent implements Parameter changes by modifying the physical state of the strut from rigid to extensible. By changing the structural parameter of the clearance adjustment mechanism, the system can accommodate both wear compensation (requiring extension) and high-force braking (requiring stability) without compromising the minimum operating clearance.
2Reliability
If a yielding member is used to limit the effect of operating force on the expandable strut, then the maximum adjustment is limited during a single application, but the structure becomes more complex
Solution Approach 1:
The patent applies the Self-service principle by designing the strut to automatically respond to operating conditions without requiring additional yielding members or complex limiting mechanisms. The extensible strut inherently provides the necessary adjustment while self-regulating based on the forces applied during braking operations, thereby maintaining reliability without increasing structural complexity.
3Adaptability or versatility
If the strut is made extensible to adjust shoe distance, then clearance adjustment is possible, but the number of components and bulkiness increases
Solution Approach 1:
The patent applies the Merging principle by integrating the clearance adjustment function directly into the existing strut component rather than adding separate adjustment mechanisms. The strut combines both its primary support function and the clearance adjustment function, thereby providing adaptability without significantly increasing the number of components or bulkiness.
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 maintains a minimum operating clearance between shoes and drum even after repeated actuations without wear, simplifies manufacturing, reduces bulkiness, and minimizes the number of components, addressing the limitations of existing solutions.
Implementation Method 1
The sliding guide (13) comprises a ratchet mechanism (14) which acts on the toothed ring (10) so as to turn the toothed ring (10) when the sliding guide (13) slides with respect to the extensible strut assembly (7) and when it exceeds a predetermined idle stroke (15) of the ratchet mechanism (14) with respect to the toothed ring (10)
Implementation Method 2
an elastic element (31) arranged between the lever assembly (11) and the shoe (3), said elastic element (31) storing and releasing a mechanical energy to enable said lever assembly (11) to rotate about the lever pin (12)
Data Source
AI summary
A device for adjusting the clearance of a drum brake capable of avoiding the canceling of the minimum operating clearance also in case of repeated brakes without the wear of the shoes, and arranged between two shoes which cooperate with a braking surface of a drum.