Mid-power Spring Brake Actuator Fuse-Collar Design
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Solution Overview
Problem
Mid-power spring brake actuators experience undesired full power spring expansion upon connecting shaft failure, which can lead to unsafe conditions.
Innovation Solution
The design includes a parking piston with a collar and juncture section that promotes failure at a predetermined location, limiting the travel of the connecting shaft upon interconnection failure, using an undercut feature and secure connections like threads or press-fitting to retain the collar on the shaft, preventing excessive spring expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a connecting shaft is used to connect the parking brake release actuator and service brake apply actuator, then the mid-power spring brake actuator can achieve proper brake actuation, but upon connecting shaft failure the brake actuator spring can expand fully causing unsafe conditions
Solution Approach 1:
The parking piston is segmented into distinct sections: a collar section that receives the connecting shaft, a juncture section with predetermined failure locations, and a piston head section. This segmentation allows the failure to be contained to a specific section while retaining other functional sections to limit the spring expansion and maintain safety.
Solution Approach 2:
The juncture section is designed with predetermined failure locations (such as undercuts or reduced cross-section areas) that are intended to fail before other critical components. This preliminary failure action redirects the force to limit the connecting shaft travel and prevents the brake actuator spring from expanding beyond safe limits.
2Reliability
If the parking piston is designed with a collar and juncture section to limit connecting shaft travel upon failure, then safety is improved, but the piston structure becomes more complex
Solution Approach 1:
The collar, juncture section, and piston head are merged into a single integrated parking piston component. This merging allows the safety function to be built into the existing piston structure without requiring separate limiting components, thereby reducing overall system complexity while maintaining the safety function.
Solution Approach 2:
The juncture section has locally different properties (reduced cross-section, undercuts, or weakened material) compared to the collar and piston head sections. This local quality change creates a predetermined failure location that is weaker than other parts, allowing controlled failure to occur at this specific location while the rest of the piston maintains its structural integrity to limit shaft travel.
Data Source
AI summary
A mid-power spring brake actuator includes first, second, and third actuator housing portions, with the first actuator housing portion interposed between the second and third housing portions. A parking brake release actuator is received within the third housing portion, and a connecting shaft is attached at a first end to the parking brake release actuator and extends through a dividing wall defined by the first housing portion. A service brake apply actuator is received within at least one of the first and second housing portions. Between the dividing wall defined by the first housing portion and a second end of the connecting shaft, a brake actuator spring is provided, and a service brake actuation chamber is interposed between the brake actuator spring and the service brake apply actuator. A parking or emergency brake de-actuation chamber is defined between the parking brake release actuator and the first housing portion. Travel of the connecting shaft as a result of force applied by the brake actuator spring upon failure of an interconnection between the connecting shaft and the parking brake release actuator is limited so as to avoid undesired or unsafe power spring expansion or release beyond the rated power spring stroke.