Irish Railway Record Society

The Class 2900 DMU is a four-car Diesel Mechanical Multiple Unit (DMMU) and the four-car composition is formed of two independent 2-car semi-units.  Each semi-unit contains all propulsion and control equipment necessary to power and propel the train and therefore there is full redundancy of operational and power supply equipment on-board.

The unit is designed primarily to cater for the needs of high density commuter traffic on the commuter corridors serving Dublin, however on-board equipment has been specified to permit the train to operate on longer distance journeys when required on specials and Friday Only relief trains.

The trains are manufactured by CAF SA (Construcciones Y Auxiliar de Ferrocarriles) and structural design of the train is based upon CAF’s experience of manufacturing the Class 332 Heathrow Express and Class 333 Northern Spirit EMUs in partnership with Siemens Transportation Systems.

The Class 2900 DMU was specified to a very high fire rating BS 6853 1999 category 1b to enable the trains to run for limited periods underground. This requirement is cognoscent of IE’s desire to construct an underground commuter interchange station at Spencer Dock.  It is believed that the Class 2900 DMU will be the first diesel train in the world to comply with the requirements of BS 6853 Category 1b.

The unit was designed to meet the requirements of the Rail Vehicle Accessibility Requirements RVAR 1999 published by HM Government UK.  The Rail Vehicle Accessibility Regulations prescribe a wide range of requirements for mobility and sensory impaired customers from design of livery, to interior fixtures and fittings and suitable toilet facilities for wheelchair users.  The RVAR regulations are not mandatory in Ireland, however they are widely used by railway administrations across Europe as a code of “Best Practice”.

The train consists of DM1+MDT+MT+DM2:

COMPATIBILITY

The Class 2900s can be formed into a maximum of a 10 car consist by coupling together with another 2900 and any other existing type of IE DMU or; one Class 2900 DMU and a mixture of any other type of IE DMUs up to a 10 car formation.  In an emergency, a 10-car DMU composition is capable of rescuing another failed 10-car unit composition in a worst case of being crush laden and on the most severe incline on IE’s track network. 

It should be noted that given independent provision of power and propulsion equipment on each car within a consist, the likelihood of this occurring is very remote, however if the risk exists, no matter how small, then it must be mitigated.  Imagine trying to provide a reasonable explanation to a crush laden GAA special as to why they will miss part or all of their exciting cup final because the train service for which they have paid good money has failed and cannot be rescued!

The Class 2900s will not be compatible with NIR Translink’s new CAF built Regional DMUs due to differences in auto-coupler height on each respective unit, however rescue is possible using any existing IE & NIR Translink locomotive type.  All Class 2900s will carry an emergency adapter coupler, which adapts to the differing heights of the auto-coupler and conventional shackle coupler fitted to locomotives.

Each cab car is fitted with flexible air-pipe couplings enabling the locomotive to supply the train with air for the brake pipe and main reservoir supply throughout the train formation.

DRIVER’S CAB

The Class 2900 is uniquely identifiable by its full width driving cab and this design enables considerable enhancements in the cab area for the driver.  Externally, the cab features split screen windows and a full width destination indicator.  The cab face is manufactured from a single Phenolic moulding and this is mechanically fixed to the bodyshell structure.  A Phenolic material was used in place of the more conventional Glass Reinforced Polyester (GRP) due to arduous requirements of fire specification BS 6853 Category 1b. 

Unlike existing DMUs, the Class 2900 is fitted with external cab access doors on both sides of the cab and each door portal is fitted with recessed handrails on either side of the access door.  Cab doors are fitted with a droplight to permit the driver to carry out the mandatory pre-departure look down the train before departing the station.  This window is generous enough to permit exchange of signalling tokens on lines not yet fitted with CTC equipment.

The cab may also be accessed from the saloon through a controlled access cab to saloon door for reasons of security.  The cab to saloon door forms part of a fire barrier between the cab and saloon and therefore is not fitted with glazing.  The door is fitted with a spyglass to enable the train crew to identify the person seeking access to the cab.

The drivers cab is fitted with a wrap around style desk and unlike the cantilevered driver’s seat in the Class 2600, 2700 & 2800 DMUs, this cab features a pedestal seat mounted on a sliding base permitting the access and egress to/from the cab.  The 2900s were designed for one-person operation, however a drop down seat is provided on the second persons side if required for driver training etc.  The train controls have been designed around the driver with the notch controller, braking and signalling equipment immediately in front of the driver. The main and auxiliary engine and air conditioning switches are on the cab wall on the driver’s left while the fuel gauges, electrical current indicators are above the driver’s window. The Train Diagnostics & Management System (TDMS) is on a monitor left of the driving position. The cab air-conditioning (separate from that of the saloons) is controlled from a panel in the centre of the desk console. The main equipment circuit breakers are clearly visible through a window in the electrical cubicle immediately behind the driver. The systems emergency isolation switches are visible through a window in the electrical cubicle at the second person’s position.

Given the change in the environment and the trend towards warmer weather, it was decided that the cab should be fitted with air-conditioning. Railtrack Group Standards specify that the cab must be fitted with air-conditioning independent of the saloon due to the risks associated with fire and smoke should they occur in the passenger saloon or in the cab.  Therefore, all cabs are fitted with an independent air-conditioning unit and the driver regulates the desired temperature. The air-conditioning unit also serves as a demister for the driver’s windows although these are also embedded with a windscreen-heating filament.

WINDSCREENS

Practically all railway administrations suffer from the epidemic of stone throwing and this is particularly acute in summer months.  IE is no exception and therefore, the design of the windscreen has been specified to have high impact resistance and complies with the requirements of BS857, GM/RT 2456, UIC section 2.7 and GM/RT 1261 section 6.2.  Anti-spall coatings where applied conform to BR 566 (type 1 windscreen).  The windscreen is laminated featuring a number of glass layers and sandwiched between them is an inter-layer which holds the glass in suspension in event of it being shattered.  The inner most layer is coated with an anti-spall material, preventing crystalline dust becoming air-borne and contaminating the eyes of persons in the cab.

SAFETY EQUIPMENT

All cabs are fitted with a Geismar Track Circuit short-circuit bar.  In case of an incident, this secondary protection is placed between the running rails to ensure that signals protecting the train within its block are automatically set to danger.  A First-Aid kit is also fitted together with an AFFF (aqueous film forming foam) fire extinguisher and a secure location is provided for the driver’s bag.

PASSENGER ACCESS DOORS

The passenger saloon layout features 2 entrance vestibules located at 1/3^rd & 2/3^rd positions as per Class 2600 & 2800 units, each vestibule is fitted with bi-parting sliding pocket doors which are simple design and engineered to provide very high reliability.    Door leafs are fitted with electrically actuated leading edge detection and this is designed to sense any obstacles in the path of a closing door. 

Doors are pneumatically operated with control and actuation equipment supplied by IFE of Austria and the door leafs are manufact-ured by CAF SA at its Zaragoza plant.  CAF has a long history of manufacturing doors for both its own projects and for reputable door suppliers in the Rail Industry.  In the event of a door failure, the driver is automatically notified by a message displayed on the TDMS screen in the cab, which specifies the location of the door failure along the train.

IE has noted that particularly with its Mark lll push-pull stock, passengers tend to congregate around vestibules at times of peak traffic and the standing capacity for passengers is not fully utilised because passengers do not stand along the aisle within the car.  The 2900 design has overcome this problem by providing a much larger vestibule with plenty of room for standing and permits flow of passengers to and from seated areas.  The unit is fitted with sufficient handrails to enable all passengers on a crush-laden train to have a safe handhold within their reach.

SEATING

Seats were specified to meet the requirements of Fire Specification BS6853 Category 1b and this is essential given the trend in vandalism right across the industry of attempting to set fire to trains even when in service.  Seating is arranged in a 2+2 format and both unidirectional and bay seating is provided.  Unidirectional seats are fitted with a seat back table enabling refreshments to be served on longer journeys.  All saloon seating is provided by FAINSA S.A. supplied from FAINSA’s plant near Barcelona.

The luggage racks fitted to the Class 2900s are identical to the racks fitted in the Heathrow Express featuring an aluminium frame and glazed base finished in an attractive green colour.  In keeping with the recommendations made after the Ladbroke Grove inquiry, end stops have been fitted to all luggage racks.  The purpose of the end stops is to prevent luggage from catapulting along the train in case of a collision.

  INTERIOR FINISH

The saloon sidewalls are manufactured from a Phenolic material and finished in white.  All surfaces are easily cleaned and both permanent marker and paint graffiti can easily be removed using solvents without damage to the surface finish.  The ceiling panels are manufactured from aluminium and two longitudinal rows of fluorescent lighting are provided along the length of the saloon.

The down lighters for the saloon lighting are made from folded aluminium and fresh air supplied from the air-conditioning system is fed through the down lighters.  All saloons are finished in white, with end walls, draught-screens and interior door leaf surfaces are finished in blue and designed to provide a marked contrast with internal fixtures and fittings for the benefit passengers with visual impairments. 

For the same reasons, all handholds and handrails are finished in an attractive yellow and are textured to provide improved grip over conventional handrails. It is important to note that persons suffering from visual impairments may not be able to recognise the edges of handrails if they are metal finished such as bright drawn aluminium tubing.

Air-conditioning equipment is supplied by MERAK S.A. and each car is fitted with one roof mounted air-conditioning module.  The air-conditioning system is divided into two separate identical circuits and if one circuit fails, the other will continue to supply conditioned air to the saloon at a marginally reduced rate.  This is one of many examples of redundancy in systems fitted throughout the train in order to mitigate the potential for a single point failure.  In the unlikely event of a complete system failure, four emergency hopper windows are fitted per car to ensure continued supply of fresh-air.

Saloon windows are supplied by Percy Lane UK and feature two types of glazing.  The majority of windows are fitted with laminated glass composed of an outer and inner layer of glass and an interlayer to hold the glass in suspension should it become broken.  Two emergency escape windows are provided per car and these are fitted with weakened tempered safety glass and in emergency this can be broken to enable emergency egress by using a hammer.

  EMERGENCY EQUIPMENT

All cars are fitted with emergency break glass hammers and these are interlocked with the emergency communication handle to prevent them from being stolen.  Two emergency communication handles are fitted per car at 1/3^rd and 2/3^rds along the car and when triggered these automatically apply the train brakes.  The handles latch in position and can only be reset using an IE security key.  When triggered the TDMS screen in the cab identifies the car in which the handle was actuated and a red light is illuminated mid-way along the body side of the car at cant-rail height.

One fire extinguisher is fitted per car and this is protected from misuse behind a locked door.  In emergency, there is a breakable panel within the glazed portion of the door to enable retriev-al of the fire extinguisher.  When removed from its position the driver is automatically notified by a message on the in-cab TDMS screen.

Two consoles are fitted per car, one in each vestibule.  In case of a passenger needing to communicate directly with the driver, they shall break a small perspex cover and depress a button; upon doing so, they are in immediate two-way contact with the Driver.  The Driver is also immediately notified of which Two-way Communication point has been activated by a message displayed on the in-cab TDMS screen.

IE continues to suffer a high rate of vandalism on its commuter and DART trains especially off-peak when trains are lightly loaded.  In an effort to curb this, IE has specified the fitting of Closed Circuit Television (CCTV) on all 2900 units.  A number of cameras are discretely mounted in all cars and images are recorded from all cameras on a down-loadable hard disk for use in prosecution for vandalism and other social demeanours.  The driver can also view images from all CCTV cameras when the train is stationary or travelling below 5km/hr and this will be particularly useful for when an incident arises on-board or simply to encourage passengers to move down aisles during times of peak loading.

All cars are fitted with a high technology Customer Information System manufactured by IKUSI of Donostia/San Sebastian.  Cab fronts are fitted with a full-width destination Indicator using high intensity Light Emitting Diodes (LEDs) and these include an ambient lighting detector that varies the brightness of the LED’s depending on brightness of the day.  The size of the Destination Indicator was maximised taking into account the needs of the partially sighted and white LEDs were used on cab end displays.  Red was not permitted on the grounds of safety, for there is the possibility of mistaking the red LEDs for a signal displaying a red aspect.

All cars are fitted with two external destination indicators per-side and these are located adjacent to the door vestibules.  One Indicator per car is configured to display information in English and the other displays information in Gaelic.  Both signs alternate between displaying the train’s final destination and its next station stop.  Red LEDs are used for body side destination indicators.

There are two LED destination indicators fitted in the saloon of all cars and these integrated into the bulkhead at the car ends.  The internal destination indicators alternate between displaying next station and destination station in both Gaelic and English languages.  Additionally, all cars are fitted with an audio system, which is configured to automatically announce the following information:

Regular passengers sometimes complain that they hear the same announcements day in day out throughout their journey.  However, it should be noted that the purpose of audio and visual PIS announcements is to communicate with passengers who suffer sensory impairments and those who are unfamiliar with the network, e.g. Tourists and the occasional traveller.  The CIS system is fitted with automatic attenuation enabling the volume of the announcements to be adjusted to the ambient background noise in the passenger saloon.

Two toilet modules are fitted per four-car unit, one in the MT car referred to as a standard toilet and a second one in the MDT car, referred to as the Disabled Toilet.  Both toilet systems are supplied as a complete module by CMC S.A. and are “dropped “ into the unit during fit-out through the aperture in the roof for the air-conditioning system.  Each module is fitted with a combined vacuum and pressure toilet and waste is discharged into a retention tank located in the module. 

IE has implemented learnings from failures of toilet systems on its De-Dietrich and particularly its Class 2700 DMUs in a concerted effort to provide reliable on-board toilet systems.  It should be noted that IE is not alone in having suffered poor reliability with closed circuit toilet systems and the same experiences have been repeated across most European railway administrations.

IE has made a conscious effort to provide suitable on-board toilet facilities for sensory and mobility impaired passengers especially those confined to wheelchairs.   IE has specified that the disabled toilet should meet the requirements of the Rail Vehicle Accessibility Regulations 1999 and the supplier has discharged its responsibility in meeting this requirement.  In summary, all surfaces are colour contrasted, there is full wheelchair access, and door control buttons are designed for use by those with physical impairments. 

Additionally, emergency voice communication is fitted at two points, one at normal wheelchair height, and the second at floor level; therefore if a user should become distressed or need help, they can contact the driver directly.  Finally, IE has also taken account the need to provide for its very young passengers and to meet their needs, baby-changing facilities are provided in both toilets.

  DESIGNATED WHEELCHAIR USER’S AREA

The MDT car within the unit formation is designated specifically for wheelchair users.  Two wheelchair positions are provided adjacent to the disabled toilet and both locations are fitted with foldaway tables for refreshments and a call for aid button.  The call for aid button is only enabled by a member of IE staff when a wheelchair passenger is present and this is considered prudent, otherwise the feature would be open to abuse and become a nuisance to train crew.

Wheelchair positions are fitted with inertia reel safety belts for safely restraining wheelchairs and occupants; the belts secured against opportunist vandalism and misuse when not required.  One manual wheelchair ramp is fitted per train and when in use, it securely attaches to the tread plate in the door portal to prevent it from moving from its desired position.  The wheelchair ramp is securely stored on-board the MDT car and is protected against opportunist vandalism.

The choice on engine for delivering tractive was made taking into account the need to meet EU environmental standard Euro 2, this standard quantifies the maximum permissible exhaust discharge such as carbon and its oxides, sulphur and as nitrous oxides.  On this basis, a diesel engine manufactured by MAN was chosen and one unit is fitted per car. 

The engine is a 12-litre 6-cylinder in-line block with turbo-charger and inter-cooling, model NO. D 2876 LUH 01. It develops 294kW / approx 400 Horsepower at 2000 rpm and is well proven in the rail industry on RENFE TRD DMUs and SNCF TER DMUs.  It is also fitted in marine applications rated for 700 hp and even in racing trucks up rated to an astounding 1000 hp.

  ENGINE TURBO-CHARGER

The turbo-charger may be thought of as two fans coupled back to back, each independently housed from the other, but coupled on a common shaft.  Exhaust gases piped from the engine outlet to one fan drive one side of the turbo-charger; the exhaust gases cause the fan to rotate at high speed. This drives the second fan (on common shaft) and this fan is connected between engine fresh air intake and the engine fresh air inlet. 

The effect of the turbo charger is to drive more air into the engine than it would otherwise naturally draw itself, and thus combustion within the cylinders is more efficient. One consequence of forcing more air into the engine is that the air becomes hotter and expands; therefore, the improvement gained by using a turbo-charger is partially negated. To overcome this, an intercooler is fitted between the turbo-charger and this cools the pressurised air to reduce the air and therefore increase its volume.  Simply put, more air can be forced into the engine combustion chamber.

HYDRO-DYNAMIC TRANSMISSION

The Class 2900 is the first IE DMU to be fitted with a VOITH hydraulic torque converter and includes an integral hydro-dynamic brake.  The model fitted is the VOITH T211 re.3 with Integral Hydrodynamic Retarder model NO. KB190.  The VOITH T211 well proven in service and is fitted to DMUs across the world.

The Hydro-Dynamic Transmission is essentially an automatic gearbox fitted between the output of the engine and the mechanical drive to the wheels.  Unlike a car, it does not have separate gears that are meshed together manually. 

Imagine two sets of blades (similar to those at the front of an aeroplane jet engine) positioned to face each other and separated by a small gap. One set of blades is connected by a drive shaft to the engine (we will call these the input blades) and the other set of blades (output blades) connected to the mechanical drive to the wheels.   These are enclosed in a box and the box is filled with oil. 

When the engine is revved, it causes the input blades to rotate, which in turn starts to move the oil around, just like a fan moving air.  When the oil is forced to move, it contacts the output blades and forces them to turn too.  Since these are mechanically coupled to the trains wheel sets, the vehicle is propelled forwards.  By varying the flow of oil, the train’s speed can be varied.

This is very similar to the explanation above.  Imagine that the train is travelling at speed and you want to apply a brake.  The engine is in neutral so it is no longer moving oil around and causing the second set of blades to turn.  In fact now the opposite is happening, the blades mechanically coupled to the wheel sets are now being driven by the trains momentum and causes the oil to move around quickly.

Now instead of the train trying to drive the engine, the oil is re-routed into a smaller turbine away from the blades connected to the engine.  The oil is forced onto the blades of an extremely in-efficient turbine and the energy it possesses is lost as heat.  The heat is rejected through a cooling circuit to a fan-cooled radiator on the vehicle underframe.  While travelling on a 2900 DMU, when the train starts to brake there is a whirring sound, this is the hydrodynamic retarder at work.  Hydrodynamic retarders reduce consumption of brake pads on trains four-fold and consequently the emission of brake dust to atmosphere is minimised.

TRANSMISSION SYSTEM

The MAN traction engine and VOITH hydrodynamic drive are bolted together to form a single traction engine and gearbox unit.  A Cardan Shaft featuring a universal joint at each end and a spline permits the length of the Cardan Shaft to vary slightly and its purpose is to connect the output from the gearbox to the powered bogie.  Variation in length of the shaft is needed in order to permit the bogie to rotate when negotiating curves and turnouts.

The powered bogie consists of two axles each fitted with a mechanical gearbox and these are coupled together with a small Cardan Shaft.  The inner most axle and gearbox is coupled to the output Cardan Shaft from the MAN and VOITH traction engine and gearbox arrangement.

COOLING SYSTEM

All cars are fitted with a number of radiator units with hydraulically driven fans manufact-ured by BEHR GmbH. Their function is to:

ELECTRONIC CONTROL & DIAGNOSTICS

A Controller Area Network (CAN) CAN-Bus system is fitted in order to electronically control and match the needs of various systems including, engine, transmission and braking.  This is an industrial computer which takes inputs from for example the drivers traction and brake controllers to control engine fuel injection, hydrodynamic traction state and braking requirements, depending on the demand made.

IE’s philosophy is to fit separate traction systems and on-board power generation in order to minimise the consequences of a single piece of equipment failing in-service and to provide sufficient redundancy of critical on-board equipment.  In order to achieve this a separate Cummins Engine and LETAG generator are coupled to form a diesel powered generator set and are fitted to an underframe-mounted raft.  The generator set specification is:

  Diesel Power Unit: 

Cummins 6B5.9GR diesel engine providing 54kW at 1,500rpm.

 Generator: LETAG 3 phase synchronous generator Model 50EXR-225M.2.4M.

UNDERFRAME FIRE PROTECTI

Given the provision of two internal combustion engines on all underframes, automatic fire detection and extinguishing system is fitted.  This comprises of a detection circuit above each engine, a discharge circuit and a pressurised Aqueous Film Forming Foam fire extinguisher bottle.

If a fire is detected, the driver is notified of the incident and is instructed to stop the train.  Once it is travelling at under 5km/hr, the AAAF fire extinguisher discharges to eliminate the source of the fire.  It should be noted that it is not common practice in the rail industry to discharge an underframe mounted fire suppression system when the train is at speed, since most of the foam will be blown away from the source of the fire due to the wind generated by the vehicles speed.  The fire system is supplied by Kidde Graviner UK.

BRAKE SYSTEM

Sab-Wabco S.A of Madrid supplied the standard two-pipe air automatic braking system with associated valve and actuation equipment.  The friction brake applies onto two self-ventilated discs mounted on each axle and it is “blended” with the dynamic brake (VOITH retarder) so to achieve smooth continuous and jerk free braking using the retarder and friction brake. 

As a rule, the dynamic brake brakes the train completely until it decelerates to approximately 20km/hr at which point the dynamic brake becomes ineffective due to the low speed.  The friction brake and dynamic brake are blended together until at very low speeds the dynamic brake is switched out and the friction brakes arrests the train.  It is critical to achieve a smooth and imperceptible blending of the friction and dynamic brakes; otherwise, passengers would notice a perceptible jerk when both systems are blended.

One spring applied and air-released parking brake is fitted per axle. A variable rate sanding system is fitted which applies sand under every fourth axle in both directions of travel.

BODYSHELL CRASH-WORTHINESS

The Class 2900 DMU was designed to meet the requirements of Railtrack Group Standard GM/RT2100 and in doing so, it achieves current rail-industry best practice relating to crash worthiness.  All bodyshells are designed with integral crumple zones in the first and last metre of each car.  In the event of a collision, the crumple zone “crumples” and in doing so, it absorbs collision energy. 

The rest of the bodyshell is designed to act as a “survivable space” for persons on-board should a collision occur.  All vehicle ends are fitted with anti-climbers on the headstock (where buffers are fitted on conventional stock).  In a collision, the couplers are design-ed to shear away for a given loading, and this permits the anti-climbers to engage with each other.  They are called anti-climbers because when they engage, they prevent vehicles from climbing on top of each other or telescoping.

BOGIES

CAF S.A. has a core competence in designing and manufacturing bogies to meet the requirements of Railtrack Group Standards and UIC Standards.  It has also developed powered and trailer bogies featuring tilt technologies and automatic gauge changing at speeds of up to 50km/hr.

CAF’s centre of expertise for bogie design and manufacture is its Beasain facility in the Basque Country.  It has a significant range of facilities enabling full in-house production of bogies including:

Plasma Cutter      This machine uses gas in its plasma state operating up to 10 times hotter than the sun to cut thick metal plate for example 12mm within a protective bath of water.

Electric Arc Furnace CAF manufactures it’s own steel and the steel furnace has a capacity for a charge of 40 tonnes of steel.

Wheel Forging & Heat Treatment Wheels are forged to shape from steel billets and are cold rolled.

Axle Forging and Heat Treatment  Axles are forged from longitudinal rectangular shaped steel billets into a round cross section before they are precision machined to form the profile of the axle and its journals.

Casting CAF also has a casting facility for the casting of complex parts such as brake hangers.

Bogie Frames These are fabricated from sheet steel cut to profile on a plasma cutter and assembled in jigs.  Both manual and robot welding is used in the fabrication of bogies.

BOGIE FRAME

Two types of bogie frame are fitted and both are of UIC design.  A common bogie frame deign is used for the powered and trailer bogies and they differ only in respect to equipment fitted and hangers for Track Circuit Assistors (TCAs).   The bogie frame is an open “H-Frame” permitting access at each end of the bogie for maintenance purposes.

Suspension The purpose of a suspension is two-fold:

First, to ensure safety, it must keep the wheelset in contact with the rail at all times in worst case of vehicle loading, track condition and through-out the vehicles operational range of speed.

Secondly, it must provide a reasonable level of comfort for passengers and isolate sensitive equipment from shock loading.

Primary Suspension In general, the primary suspension is responsible for maintaining the wheelset in contact with the track and it “checks” the high magnitude shock loading due to the wheelset negotiating varying track conditions and varying speed.

The primary suspension comprises of a radial arm and axle box attached to the bogie frame with metalastic elements.  This permits the wheel set to move up and down relative to the bogie and a spring and damper arrangement check this movement.

The metalastic element permits limited bogie self-steering and this reduces flange wear and flange squeal when negotiating tight curves. The axle box permits a very small amount of lateral play, essential for negotiating turnouts, track joints and curved track.

Secondary Suspension The secondary suspension comprises of two air bags regulated by check valves to determine the volume and pressure of air within the bag.  The check valves are fitted with a rod between them and the body shell their purpose is to regulate suspension height and levelling to compensate for canted track at station stops etc. 

The secondary suspension is relatively soft in comparison to the primary suspension and it’s main duty of to achieve a high level of comfort on-board.  In case of an air bag failing, there is a secondary rubber element within the bag to provide continued damping at a marginally reduced rate.  The secondary suspension also provides some level of bogie rotational stiffness and is carefully designed to prevent derailment on curved track.

Braking Installations Two axle mounted brake discs are fitted per wheel set and brake callipers are hung from the transverse structure of the bogie known as the “transom”.  This is the best possible arrangement for braking given the heat generated between the pads and discs during braking.

Body to Bogie Connection As mentioned above, a secondary air suspension is fitted between the bogie frame and the body however this is much too soft to be able to transfer tractive and braking forces between body shell and bogie and vice-versa.  The main body-bogie connection is the centre-pin and it is fitted with an end cap to retain the bogies to the train when being lifted or in event of collision. 

The centre pin must allow for some relative movement between bogie and body especially when starting from rest or coming to rest.  Additional metalastic elements are fitted within rods between centre-pin and transom and these dampen out shock loads generated by starting and stopping inertia and furthermore contribute to the overall suspension system of the vehicle.  A lateral number of lateral and vertical dampers provide additional control in this area.

Bogie Mounted Traction Equipment One power bogie is fitted per car and this is mechanically driven from a Cardan Shaft fitted between the engine & torque converter and the bogie final drive.  Toothed gears within an oil filled gearbox mechanically drive the wheel-sets on the bogie. 

The gearboxes on both axles are mechanically coupled by a smaller Cardan-shaft and thus if one wheelset slips or slides, it automatically causes the coupled wheelset to slide too!  To prevent this from happening wheel slip-slide protection is incorporated and provision is made for sanding.  From the above explanation, it is clear that the train is mechanically driven hence it is described as a Diesel Mechanical Multiple unit.

Track Circuit Assistors Two Track Circuit Assistors (TCA) have been fitted per four-car unit, one under the leading bogie at each cab end.  The TCA fitted is manufactured by AEA Technology (formerly BR Research) and is proven in application for over 10 years in Britain. All Diesel Multiple Units in operation in IÈ lines have been fitted with a TCA.

The TCA functions similarly to an induction motor.  The current in the track circuit acts as one induction loop and the second induction loop is formed by the TCA loop fitted under the bogie.  The presence of the TCA induces a current to flow between the wheel and the rail and its purpose is to breakdown any oxide layer or light contamination on the railhead that would otherwise prevent a track circuit from being made.

The TCA can operate successfully in conjunction with sanding equipment providing that the flow rate and volumetric output of sand are optimised to suit the TCA.

COUPLERS

Coupling systems for the 2900s are supplied by VOITH Gmbh from its Radenton-Scharfenberg facility in the UK and all units are equipped with three types of coupling systems.  These are:

Auto-Coupler  Auto-Couplers are fitted to cab cars and these are compatible with existing Scharfenberg and Dellner Auto-couplers fitted across the existing IE DMU fleet.  The purpose of the Auto-Coupler is to automatically provide the following couplings:

Mechanical Coupling-Uncoupling between units

Apart from direct coupling, the auto-coupler absorbs traction and buffing forces and limited “rough shunting” forces without damage.  Additionally, in the event of a collision the Auto-Coupler serves two purposes:

Low Energy Collision and/or Derailment               The Auto-coupler maintains the train in one formation and prevents individual units from de-coupling.

High Energy Collision and/or Derailment              In this case the Auto-Coupler is designed to shear away for a given load and by doing this it enables the anti-climbers of adjacent vehicles to engage.  It is vital that the auto-Coupler shears to enable engagement of anti-climbers since this is the primary defence against cars telescoping over one another in a collision scenario.

Co-incidentally, the 1m crumple zones at the end of the cars “crumple” and by doing this they absorb collision energy away from the main bodyshell. 

Semi-Permanent Coupler  IE’s philosophy is the run DMUs as fixed formation trains and therefore semi-permanent couplers fitted between intermediate cars.  These are bolted together using special high tensile steel bolts.  Cars within a unit formation are only coupled-uncoupled when individual cars need heavy maintenance, unscheduled repair, refurb-ishment and/or overhaul and therefore; the use of semi-permanent couplers is appropriate.

Semi-permanent couplers provide mechanical coupling only and all electrical and pneumatic connections are made independently of the coupler.  The functionality of the semi-permanent coupler in low energy and high-energy collisions is identical to the auto-coupler.

Emergency Adaptor Coupler  One emergency coupler is fitted per unit. It is stored in a purpose built equipment box mounted on the underframe of the MDT car.  Its purpose is to provide mechanical coupling between the unit and any existing IE/NIR locomotive for rescue purposes only. The pneumatic “Brake Pipe” and “Main Reservoir” couplings are made separately through flexible pipes fitted with “Glad-Hands” and these are located on the right side of the headstock (buffer-beam) on cab cars.

The emergency adaptor coupler comprises of three individual parts and must be “pinned” together before being fitted between the rescue locomotive and the failed unit.  The reason it comprises of three separate parts is to enable one person to carry it from its underframe storage position to the appropriate end of the vehicle.  This is a critical requirement given that the trains are designed to permit “One-Person-Operation” and that it should be possible to carry each part safely walking in the cess or on ballast for a distance of approximately 50 metres.

  SPECIFICATIONS

NOTE OF THANKS

A special word of thanks is due to Sr. Fernando Fuentes, Class 2900 Project Manager CAF S.A, who has very kindly provided official CAF SA photographs for this article.

DEDICATION

The Authors wish to dedicate this article in memory of Brendan Tighe and his father Tommy Tighe affectionately known to all as “Railway Tommy”.  Both have made invaluable contributions to Irish Railways throughout their respective careers and many of the innovative and safety features on the Class 2900 Units are a direct result of Brendan’s untiring work on the project.  May they rest in peace.

Copyright © 2004 by Irish Railway Record Society Limited
Revised: January 07, 2004 .