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EuroBrake 2022: Rail brake systems and testing session overview

The Rail brake systems and testing session will take place on Tuesday May 17th and will be chaired by Stefan Dörsch of DB Systemtechnik GmbH and co-chaired by Roberto Tione of Wabtec.

Topics and speakers for the session include:

Electro-mechanical brake device, novel solution for the migration of the safety functions

Matteo Frea, Wabtec

The electro-mechanical brake is a novel concept of friction brake based on a force’s generator that is driven by purely electro-mechanical components instead of pneumatic or hydraulic components.

The sustainability topic is addressed, being the electro-mechanical brake, a sub-system designed to support the transition from traditional train architecture to the novel “air-less train” concept. The brake system, together with the suspension system, are the main consumers of compressed air. This air is not only compressed but also filtered and dried by a component’s family called AGTU (air generation and treatment unit). The AGTU components, typically compressors and air dryers, are well known to have intrinsic limitations in terms of energy efficiency, electrical consumption, for the heavy weight, the maintenance duty and to be one of the main sources of acoustic noise.

On the other hand, however, the compressed air is the traditional way used by the train to store the braking energy and to actuate the friction brake, that is the ultimate safety brake methodology associated to the emergency brake. To support the transition from the air-based train to the air-less train, the braking system shall revolutionize its technological solutions without any compromise on the “safety assessment” associated to the “braking performances”.

The high-level challenges addressed by this research are:

  • Design a brake system that does not require compressed air/oil being compatible with the air-less train concept with consequent improvements: - Energy efficiency (i.e. electrical consumption) - Acoustic noise - Suspended weight - Simplified brake architecture with the removal of pneumatic piping - Maintenance associated to compressor and air dryer

  • Design an electro-mechanical brake capable to respect the railway safety requirements, for all the market segments (mass transit, regional, high speed, etc…) in terms of: - Brake performances - Safety integrity levels associated to: - the way to store the braking energy - the way to permanently monitor the effective storage of braking energy

The high-level needs of the railway community, addressed by this development, are confirmed by the European projects Shift2Rail and by the upcoming ERJU program, highlighting the demand of sustainable, silent and green solutions.

The methodology starts from a novel interpretation of the “postulates” of the railway braking system:

  1. The traditional way to apply the friction-brake is filling a brake cylinder.

  2. The traditional way to store the braking energy is cumulating compressed air into a reservoir.

  3. The traditional way to make sure that the braking energy is still available is monitoring the pressure inside the reservoir.

The migration of the postulate n°1, towards an air-less system, leads to the design of an electro-mechanical system based on electrical motor/s and mechanical solutions to convert the rotational motion into a linear motion.

The migration of the second postulate, towards an air-less system, leads to the scouting of a technology to cumulate energy. The batteries, which may seem like the obvious solution, do not offer sufficient guarantees in terms of safety, if the target is to achieve a safety integrity level 4 for the emergency brake application even in degraded condition (e.g. no electricity by the pantograph).

The postulate n°3 is the one making the difference, leading to the selection of alternative way to store the braking energy based on cumulating the kinetic energy in a rotating element.

  • The inertia of the rotating element is comparable to the volume of the air reservoir

  • The monitoring of its rotational speed is comparable to the monitoring of the pressure inside the air reservoir. The techniques to safely measure a rotational speed are far more consolidated than the technologies to ensure the effective availability of power from a battery.

The first phase of the research aims to ensure the feasibility of the solution mentioned above, the capability of the electro-mechanical actuator to convert kinetic energy into mechanical energy for brake application and/or into electrical power for the brake control unit.

This is main scientific challenge. After that, the research and development process will be carried out like a braking device integrating mechanic, electronic and software according to applicable standards.


The results achieved so far at demonstrator level, are highly promising and show the feasibility of the concept, in relation to the main scientific challenges: kinetic energy storage and electrical energy recovery.

Enhancing the safety and the availability of wheel slide protection function for railways applications

Pierre Debernardi, Wabtec

In the European railways market, the Wheel Slide Protection (WSP) function is regulated by the EN 15595 standard. This standard defines the basic features of the Wheel Slide Protection function and introduces the requirements for a watchdog (safety timer) functionality that prevents unwanted and extended reduction of brake effort, especially (but not exclusively), during an emergency braking activation.

The typical WSP architectures developed according to this standard perform this safety timer function by means of an electronic hardware timer that counts the time during which the WSP electro-pneumatic valves are energized by the WSP control software, and forces the de-energization of these valves, thus disabling the WSP control function, when this time exceeds a given threshold. Once the timer has expired and has triggered the de-energization of the WSP valves, this state can be changed, and WSP control can be re-enabled, only if specific conditions are fulfilled, such as that the train has come to a full stop.

These architectures, although widely deployed by all brake system suppliers for all the types of rolling stock, have in the recent years generated concerns about their safety integrity, because of the potential for the WSP control software to spuriously interrupt the hardware timer counting or to unduly reset the hardware timer after its triggering and before the system reaches a true “safe state”.

This paper describes a solution to enhance the safety, yet improving the availability, of the WSP function by means of an electronic system developed with adequate Safety Integrity Level (SIL) that can be introduced in the traditional WSP architecture, offering an additional and independent safety barrier against a potentially unsafe behaviour of the WSP control software.

The present paper describes the use of a supervising device, named WSP Supervisor, arranged to monitor the behaviour of the associated WSP system and, through direct or indirect actions on the timer devices of said WSP system, to increase its overall safety level, so that it can reach the expected safety integrity for a brake system during the emergency braking phase.

The WSP Supervisor is arranged to:

  • acquire the instantaneous linear speeds of the associated train axles and compare such instantaneous speeds with the linear reference speed of the railway vehicle

  • monitor the state of the braking pressure available to the brake actuators

Based on the above-mentioned inputs, the WSP Supervisor determines, for each axle in sliding phase, whether the WSP control software is working in a safe manner or not, depending on pre-determined operating conditions, and to cut-off the WSP control software when it is deemed to be working in an unsafe manner.

Moreover, the WSP Supervisor can maintain or increase the preloaded time value for the safety timer associated with each axle when the WSP control software is deemed to be working properly, with the aim of fully “using” the available adhesion between wheel and rail to improve the braking performance.

To guarantee an adequate safety integrity of the brake system especially during the emergency braking phase, the WSP Supervisor shall be developed with a Safety Integrity Level (SIL) 4 according to the standards EN50128/EN50657 and EN50129 respectively for its software and hardware.

This invention introduces a high safety integrity calculator in traditional WSP architectures, that are typically designed to reach a maximum SIL2 integrity level, and revolutionize the way in which the WSP safety timer is performed, moving from a “non-intelligent”, purely hardware-based, safety timer to an intelligent safety timer function that has the technologies and the means to maximize the performance adapting the safety timer to the real conditions of the train (axle inertia) and the rail (available adhesion).

This invention will bring the following benefits for future beneficiaries:

  • Increased safety of the braking system, with reduced efforts in the Train Acceptance and Homologation phases

  • Ensure an optimized availability of the WSP function, thus reducing the occurrence of wheel flats, with consequent wheel re-profiling

  • Possibility to integrate the WSP Supervisor into existing WSP systems, with minimal integration and installation constraints

On a risk-based approach to automatic brake testing in freight rail

Raphael Pfaff, FH Aachen & RailCrowd GmbH

Brake testing in freight trains is time consuming and, in most cases, executed manually. Current approaches aim to replicate the manual process, which leads to technical challenges that need to be solved on a wagon individual basis. By assessing past accidents, we find indications that the brake rigging is not frequently involved in malfunctions of brake systems and propose a different sensor set. This sensor set does not require individualisation on the wagon system and is thus suitable for reducing the system cost.

A further challenge is the identification of the wagons in a rake as well as their order in the rake. Based on the wagon 4.0 approach, a communication architecture is presented that offers a cost-efficient yet safe solution to this problem. Similar to the above, it relies on proven open protocols and low power hardware in attempt to reduce hardware cost while improving overall safety. From this technological and operational basis, an algorithm for rake setup and brake test is developed that reduces risks currently not covered in brake test procedures.

Swedish tests of ll-brake blocks under winter conditions - winter 2020–2021

Tore Vernersson, Chalmers Railway Mechanics

The Swedish Transport Agency arranged testing of LL brake blocks in the northern part of Sweden. The tests were performed from January through to April 2021, using a train built-up by one locomotive and five (mostly) unloaded (empty) test wagons. The locomotive was unbraked during the tests. Two sets of five wagons were used, where one wagon set was equipped with organic composite blocks and one set was equipped with sinter blocks. Both wagon sets had a detailed sensor instrumentation on three of the wagons during the test campaign.

During the test campaign, four stop braking tests per day were performed from 100 km/h. Three different locomotive driver instructions were employed that prescribed the brake applications to be performed in-between the stop braking tests and one aim was to investigate braking performance for these instructions. The first instruction is denoted “normal” brake conditioning and the brakes are then applied for 13 s every 10 minutes with main brake pipe pressure lowered by 0.6 bar. The “enhanced” brake conditioning is that the brakes are applied for 10 s every 15 minutes with main brake pipe pressure lowered by 1.0 bar. The third one is denoted “provocative” brake conditioning which means that no brake applications are performed for some prolonged periods between stop braking tests.

A total of 127 stop braking cycles were performed by the instrumented test train, 78 stops with organic composite LL-blocks and 49 with sinter LL-blocks. For organic composite brake blocks and braking with loaded wagons (15 tonnes axle load), very strong braking action was found, which resulted in locking-up of wheel axles and formation of wheel tread damage in the form of wheel flats. Because of this, tests with loaded wagons were only performed on the first day of testing and all remaining tests were performed with unloaded wagons. The wheel flats were machined by an angle grinder so that acceptable levels of wheel-rail contact forces were achieved, although it can be presumed that some test wagons had somewhat increased vibration levels for the remainder of the test campaign.

For organic composite blocks and unloaded wagons with an axle load of 6.5 tonnes it is found for perfectly bedded-in blocks that the stopping distances when using the normal brake instructions are the shortest, followed by the ones for the enhanced instructions, and the longest are found to result when employing the provocative driver instructions. No extremely long stopping distances (longest stopping distance is 910 m) are resulting, which can be compared to a nominal braking distance (based on information in UIC leaflet 544-1) for the train being 850 m. Ice and snow were present on the blocks during testing to a high degree for all three driver instructions, often in such amounts that the actual blocks could not be seen.

For sinter blocks and unloaded wagons with an axle load of 6.5 tonnes it is found for not perfectly bedded-in blocks that they behave rather well when employing normal brake instructions; in fact, the performance is somewhat better than for “enhanced driver instructions”. This finding is the same as for the organic composite blocks. Braking employing the provocative instructions causes occurrences of substantially prolonged braking distances, with longest stopping distance 1100 m that can be compared to the nominal braking distance 850 m. For one such stop, two wagons more or less lost their braking abilities as an effect of massive amounts of ice and snow, that had accumulated between blocks and wheels, fell off at the test. The stopping distance for the train under these conditions was 1550 m, which constitute more than a doubling of the braking distance as compared to the shortest stopping distances registered. The sinter blocks are not very well bedded-in at the tests; the degree of bedding-in is between about 60% and 100% for the test wagons. One effect of a low degree of bedding-in is that it seems to help keeping the brake blocks frictionally active, a conclusion drawn from the fact that they are less prone to high reductions in friction and the related low block temperatures at tests. One reason for the weaker braking for the sinter brake blocks as compared to the organic composite blocks is that the time until the friction force reaches a significant level, after the brake is applied, is almost the double.

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