The first of 84 low-floor Class ET422 EMUs for the Rhein-Ruhr S-Bahn are taking shape at Hennigsdorf and Salzgitter. Harry Hondius reports

THIS MONTH is due to see the start of deliveries of a new generation of S-Bahn trainsets for DB Regio, to work services in the Rhein-Ruhr region.

In 2005 DB AG ordered 84 four-car Class ET422 units for delivery between March 2008 and October 2010, with an option for a further 72 sets. The price is €4·4m a set, or €21 316 per m2. The first eight units are due to start test running between April and July of this year. They will be based at Essen, where the depot has been enlarged and adapted at a cost of €3·3m.

The ET422s are being supplied by a consortium of Bombardier Transportation and Alstom LHB. As the project leader, Bombardier is responsible for construction of the underframe, floor and cabs, the electrical equipment, bogie development and the production of the intermediate articulation bogies. The firm will also assemble 26 units at Hennigsdorf. Alstom LHB is responsible for the rest of the mechanical work, including the production of all car bodies and the powered end bogies and the assembly of the remaining 58 sets. Each firm will be responsible for commissioning the trainsets that it assembles.

The ET422 is a further development of the ET423 S-Bahn EMU, of which 462 units have already been supplied by the same consortium. The new units will be able to run in multiple with their older siblings, and to be coupled mechanically to classes ET420, 424, 425 and 426.

The principal new elements are a steel-reinforced nose meeting the crashworthiness requirements of prEN 15227, the first DB trainset to be so equipped, a new brake system and magnetic track brakes on the central articulation bogie. The carbody is a welded aluminium design with a reinforced steel front section bolted to it.

The Bombardier-designed bogies have conical rubber/metal springs supported by vertical shock absorbers as the primary suspension, which also control the axle guidance. The secondary air suspensions have internal rubber/metal auxiliary springs. Traction forces are transmitted by a kingpin, which connects with the bogie frame at a low level through a central longitudinal link. Torsion stabilisers and a horizontal shock absorber complete the suspension. Yaw dampers are mounted between the bogie frame and carbody.

Transverse-mounted TSA motors drive each axle through a Voith double-reduction helical gearbox. The drive assembly is suspended at the inner side from the bogie frame at two points and on the axle side a quill shaft rests on the wedge packet coupling which drives the axle. The articulation bogie is of a similar pattern, but here a longitudinal link connects with the main articulation and each carbody has its own yaw damper on each side of the bogie.

The electrical traction package is fed by one pantograph but otherwise incorporates full redundancy. The equipment is housed above the end bogies. An oil-cooled transformer transforms the 15 kV AC to 900 V, which then feeds the DC intermediate circuit through a four-quadrant converter. The intermediate circuit feeds a single IGBT inverter pack, which provides a VVVF three-phase AC supply to the four traction motors in parallel. All of the equipment is liquid-cooled.

Auxiliary inverters and batteries are placed under the floor of the middle coaches. Each car has its own heating, ventilation and cooling unit on the roof. A direct 370 V 16·7 Hz connection powers the warm water train heating system.

The main traction control package uses Bombardier's Mitrac technology. Up to three units can be driven from one cab through the train bus, which is linked between sets using the Scharfenberg automatic couplers. Each unit has its own information and diagnostics system connected to the vehicle bus.

Service braking is electro-dynamic, with full regeneration back to the 15 kV supply. Electro-pneumatic brakes on 10 axles can be automatically blended in parallel with the dynamic brake should the deceleration be insufficient. There is only one brake compressor. Spring-applied parking brakes are fitted on eight of the 12 axles.

It is interesting to compare the ET422 with the Stadler Flirt 4/10, of which 35 have been ordered by private operators for regional services in Germany, including some in the Rhein-Ruhr area (RG 2.05 p97). The Flirt is 5 m longer but 140 mm narrower, with only four out of 10 axles powered. It has smaller doors, with 146 mm of door width per m of car length, against 228 mm for the ET422. The Flirt has more seats, 219 against 176, but room for fewer standing passengers, giving a total capacity of 457 against 560 for the ET422. The weights per seat are similar, but the Flirt has a higher power-to-weight ratio of 16 kW/t and a higher top speed of 160 km/h.

Table I. Technical data for DB class ET422 EMUs
Gauge mm 1 435
Platform level mm 960
Minimum radius m 100
Maximum gradient % 4
Maximum speed km/h 140
Buffing load kN 1 500
Axle arrangement Bo' (Bo)'(2)'(Bo)' Bo’
Overall car body length mm 68 350
Overall width mm 3 020
Height above rail mm 4 273
Empty weight tonnes 113
Maximum axleload tonnes 18·1
Floor height at entrance mm 995
Floor height in saloons mm 1 025
Doors per side 12 x 1 300
Door width/m of car length mm 228
Seat spacing mm 1 650
Inter-car gangway width mm 400
Wheelbase end bogies mm 2 200
Wheelbase articulation bogies mm 2 700
Wheel diameter new/used mm 850/780
Bogie centres mm 15 140 + 2 x 15 460 + 15 140
Continuous rating kW 8 x 200
Maximum motor speed rev/min 6 000
Gearing 1:6·333
Auxiliary inverters
3 x 400 V AC, 60 Hz 95 kVA
110 V DC 13 kW
110 V DC/24 V DC 0·5 KW
first class 16
second class 160
Standees (at 4/m²) 340
Total 516
Specific power kW/t 14 3
Specific weight kg/m2 553
Weight per seat kg 636

Table II. Main suppliers for ET422
Carbody and bogies
Alstom LHB/Bombardier
Transformers ABB Sécheron
Traction motors TSA
Electronic controls Bombardier
Traction inverters Bombardier
Static inverters ABB
Air-conditioning Liebherr
Wheel flange lubrification Delimon
Pantograph Schunk
Gears/final drives Voith
Brakes Knorr-Bremse