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Why certify safety-related systems in trains?
Regioflexx, Wabtec’s latest-generation integrated brake control system for main line applications has received safety concept approval by TÜV SÜD and found 100% compliant in design phase with all relevant EN standards by DB Systemtechnik. By choosing to use certified components, car builders and operators facilitate full-train certification, particularly when it comes to safety-critical elements like brakes. With Regioflexx, a fully certified state-of-the-art solution, Wabtec is supporting the rail industry both by boosting safety and also by making the full-train certification process easier and more efficient.
Some decades ago, a new train was a co-design exercise between a railway administration, a car builder, and various equipment suppliers. Thankfully, things have changed since the Technical Specification of Interoperability (TSI) came into force, along with the associated harmonized EN standards.
Ever since the introduction of the TSI, operators must implement TSI-compliant trains, and new trains delivered by car builders must demonstrate TSI compliance. This implies full train certification, which is of course made much easier when all the building blocks have already been certified, particularly safety components like brakes.
At Wabtec, we took a major leap forward years ago when we introduced Metroflexx, a new generation of integrated brake control for mass transit. Metroflexx is now part of our standard product catalog, and is in service in several regions of the world. Metroflexx safety certification was successfully performed by TÜV SÜD.
The natural next step was to extend this brake control concept to main line applications; so in 2018, we began developing Regioflexx. From the earliest stages, it was clear to us that Regioflexx would require a robust certification process right from the design stage, both for safety and TSI compliance. We worked with TÜV SÜD for safety certification and DB Systemtechnik for TSI and EN standards compliance verification.
Regioflexx: an innovative design concept
Regioflexx is a fully integrated device in which electronics and pneumatics are both located in a small, light, and versatile box. It includes all the usual brake control functions, monitoring and communication with the train.
Regioflexx features two fully independent electronic units, one SIL 2 performing the usual Brake Control Unit (BCU) control function, and one SIL4 providing monitoring of the SIL2 unit, as well as advanced functions. The SIL2 BCU controls the service brake and Wheel Slide Protection (WSP) with two independent EP unit channels. The benefit of this design is that in the event of a single failure, at least half of the braking effort is still guaranteed. This contributes to the train’s highest Guaranteed Emergency Brake Rate (GEBR).
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AR: Auxiliary Reservoir; BC1 & BC2: Brake Cylinder pressure 1 & 2
The safety unit (SIL4) ensures continuous storage of a pilot pressure proportional to the vehicle load. This pilot pressure is always available to perform weighted emergency brake. In addition, Regioflexx implements innovative SIL4 functions, including WSP safety timer smart management and traditional pneumatic valves emulation (e.g. distributor valves, average load valves and multistage valves). It also uses vehicle deceleration compensation, wheel rotation monitoring and holding brake.
A robust certification and validation methodology
Wabtec implemented a robust process to obtain certification. We began by identifying railway market limitations, pneumatic components tolerances and duties from their maintenance activities, before focusing on improvements to reduce or remove these limitations. The next steps were concept definition and approval of the safety concept by the safety assessor (TÜV SÜD). The concept was also approved by an independent assessor (DB Systemtechnik) regarding compliance with applicable standards. We then proceeded to design and validation of the prototype, then the pre-series, before carrying out final assessments, and on-train tests and revenue service.
TÜV SÜD fully analyzed the system and assessed safety level compliance in line with EN 50126 series standards. Compliance was confirmed, and the Regioflexx safety concept approval was granted by TÜV SÜD.
DB Systemtechnik assessed Regioflexx’s compliance with the following system standards:
- TSI Loc & Pass
- EN 16185-1 (XMU brake system)
- EN 15595 (WSP)
- EN 15734-1 (high-speed train brake system)
- EN 14198
In addition, compliance with the following product standards was verified:
- EN 15611 (Relay valves)
- EN 15355 (Distributor valve)
3,782 different clauses were reviewed, and not a single non-compliance issue was identified. We are now starting a review of the Notified National Technical Rules (NNTR)for a few key European countries with DB Systemtechnik.
Conclusion of the assessment by Dr. Stefan Dörsch (DB ST)
Based on the investigations carried out so far and under realization of the agreed additions (integration in the documentation), DB Systemtechnik GmbH states as a preliminary conclusion that the design of the RegioFlexx brake system was created in accordance with the requirements of the above-mentioned regulations (TSI LOC&PAS:2014, EN 16185-1:2015, EN 15595:2019, EN 15734:2013 and EN 14198:2019).
The evaluation of the functional safety, in particular the specified safety levels of the various functions of RegioFlexx is not included in the review of DB Systemtechnik GmbH. It is part of an independent inspection by TÜV SÜD Rail GmbH.