Rail Brake Actuator Safety Unit for Controlled Emergency Braking
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Solution Overview
Problem
Current electromechanical braking systems for railway applications face challenges in cost-effectively achieving emergency braking while maintaining safety integrity level SIL=4, as they struggle to store energy proportionally to the current weight and control the emergency braking force gradient, leading to increased risks of wheel flats and passenger safety concerns.
Innovation Solution
An electromechanical service and emergency braking actuator that includes a safety unit with a SIL≥3 safety integrity level, which calculates and adjusts the emergency braking force based on predetermined deceleration values and real-time weight signals, ensuring the emergency braking force is applied within a controlled gradient, and integrates an energy storage mechanism to store energy sufficient for at least one emergency braking event.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a control unit is developed according to safety integrity level SIL≥3, then emergency braking safety is improved, but design, validation, and certification costs increase by approximately an order of magnitude
Solution Approach 1:
The control system is segmented into two distinct units: a service braking control unit with lower complexity (SIL≤2) and a safety unit with higher integrity (SIL≥3). This segmentation allows the expensive safety-critical functions to be isolated to only the necessary emergency braking control, while service braking operates under less stringent and therefore less costly requirements.
Solution Approach 2:
The safety-critical emergency braking control functions are extracted from the general service braking control unit and placed into a dedicated safety unit. This extraction ensures that only the minimal necessary functions require SIL≥3 certification, reducing overall system complexity and cost while maintaining required safety levels.
2Reliability
If emergency braking energy storage means are provided, then emergency braking capability is improved, but the actuator size and complexity increase
Solution Approach 1:
The emergency braking energy storage means are merged with the service braking energy storage means into a single integrated energy storage system. This consolidation eliminates duplicate components and reduces the overall actuator volume while ensuring sufficient energy is available for both service and emergency braking operations.
Solution Approach 2:
The energy storage system is designed to serve multiple functions: it provides energy for both service braking and emergency braking operations. This multi-functionality reduces the need for separate dedicated emergency braking energy storage, thereby reducing overall actuator size and complexity.
3Reliability
If the emergency braking force is increased to ensure safety, then passenger safety is improved, but the risk of wheel flats increases
Solution Approach 1:
The emergency braking force application is made dynamic through gradient control. The safety unit controls the release of stored energy to apply braking force in a controlled gradient manner rather than instantaneously, adapting the force application rate to prevent wheel flats while still achieving the required safety deceleration levels.
Solution Approach 2:
The system incorporates feedback control where the safety unit monitors the braking force application and adjusts the energy release from storage means to maintain the desired braking force gradient. This feedback mechanism ensures the braking force increases at a controlled rate that prevents wheel flats while achieving safe deceleration.
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 enables cost-effective emergency braking with improved safety by ensuring the emergency braking force is proportional to the current weight and applied with a controlled gradient, enhancing passenger safety and reducing the risk of wheel flats, while simplifying the design and construction of the safety unit compared to traditional service braking control units.
Implementation Method 1
The emergency braking energy storage means comprise a mechanical means for storing potential mechanical energy, the mechanical means for storing potential mechanical energy being by way of non-exclusive example a helical spring.
Data Source
AI summary
An electromechanical service and emergency braking actuator for a railway vehicle is described, comprising a safety unit arranged to regulate a first emergency braking control signal so as to indicate to first emergency braking energy release means to release the energy stored in first emergency braking energy storage means when an emergency braking request signal indicates a request for an emergency braking and a first electrical signal of actual braking force does not indicate, within a predetermined maximum delay time, a force value coinciding with a further emergency braking force value calculated by said safety unit or a force value that does not fall, within a predetermined maximum delay time, in a predetermined tolerance range including the additional emergency braking force value calculated by said safety unit. Electromechanical braking systems are also described.