Overhaul ML700: Krefeld maintenance depot makes first ICE 4 fit for service

More than 115 ICE 4s are now in service with DB – and a new one is added every three weeks. With a total of 137 vehicles to be delivered by 2024, the ICE 4 represents the backbone of the long-distance fleet and is thus an important building block for the "expansion of fleet and maintenance depot" in the context of the "Strong rail" umbrella strategy. In order to cope with the maintenance requirements, extensive measures are planned at DB Fahrzeuginstandhaltung. The most extensive of these is the expansion of the Cottbus maintenance depot. By the beginning of 2024, a first new maintenance hall will be built there specifically for the ICE 4 multiple units. Until then, the ICE 4 multiple units will be overhauled solely at the Krefeld maintenance depot.

New technology – new challenges

The employees at the Krefeld maintenance depot have a wealth of experience and routinely carry out the extensive overhauls on all ICE series. They have already dealt intensively with the new 412 series and its technical innovations in advance in order to be optimally prepared for the work. The long 12- and 13-car ICE 4 multiple units still pose a special challenge for the maintenance depot’s infrastructure: In order to be able to work on the 346-metre-long multiple units on only 170-metre-long processing tracks, a special maintenance concept was developed for the series. Thus, the 12-car ICE 4 is processed in three carpools of four individual cars each. With the help of a sophisticated schedule, the train is thus worked on at several processing tracks in parallel and in raised or lowered wagon condition.

Full programme for the new fleet

The "ML700" is the most extensive maintenance level (ML). The programme includes the scheduled replacement of major components such as bogies, couplings, nose cones, air supply systems, brake components, toilet modules and driver's cabin air conditioning systems. According to the manufacturer's specifications, extensive maintenance work is also carried out on interior doors, galley components and safety equipment. In addition, wear parts such as relays, contactors and fan modules in the passenger compartment air-conditioning systems will be replaced, and work will be carried out on the traction and high-voltage equipment. In short: the ICE 4 undergoes a wide-ranging complete inspection and general overhaul, so that it is once again reliably available for passenger transport.

Always good for a surprise

The vehicles "ML700-ready" this year are the first from the ICE 4 series. Seven pre-series trains were used for the necessary test and certification runs by the manufacturer as well as a one-year trial run before the ICE 4 was put into service. These pre-series trains have one or two technical features in store that are not always fully described in the maintenance and spare parts documentation, but only come to light in the course of work on the vehicle. For example, the staff in Krefeld were confronted with incompatible installation locations or additional conversion measures that were necessary.

In addition to the already extremely extensive planned work, the vehicles also surprise with unplanned findings after a mileage of approx. 3 million kilometres, i.e. unscheduled work such as the removal of graffiti damage and traces of corrosion.

Put through its paces

Once all scheduled and unscheduled work has been completed, the final functional check is carried out in the form of the recommissioning or commissioning of the vehicle.

In the first step, each individual wagon is put through its paces before it is allowed to leave the processing hall. Together with experts from the manufacturer Siemens, the relevant test scopes were defined and a test system called "Vehicle Test Unit" (VTU) was used as standard. This system makes it possible to test wagon functions such as interior lighting, reserve indicators, exterior doors as well as air-conditioning, fan and brake functions directly at the processing track.

In the second step, the tested individual wagons are assembled into two six-car half-trains. These are then connected on the neighbouring tracks by means of a complex, newly developed connection system to form a block train. The innovative connection system not only enables the train of a 346-metre-long, 12-car ICE 4 on the 200-metre track length, but also offers completely new automation approaches through the diverse interfaces.

Successful concept with a sustainable contribution

Due to the high demand for replacement components during a vehicle overhaul, the reconditioning of these components also plays an essential role. As the leading expert in component reconditioning, DB Fahrzeuginstandhaltung makes a decisive contribution to the sustainability of rail vehicle maintenance and to coping with the rapid growth in traffic. The goal for the overhaul of the ICE 4 is also to have as many components as possible undergo technical refurbishment. Under the leadership of the "Cross-Functional Team ICE 4", all spare parts have been examined together with the product management experts. Wheelsets, bogies, couplings, brake components, air supply parts, air-conditioning units and electronics are refurbished in the respective maintenance depots throughout Germany and then reused.

Initial successes motivate the employees from Krefeld even further: during the first "ML700" overhaul this year, they were able to beat the planned overhaul time. The multiple unit left the factory ahead of schedule and was thus available to passenger traffic again more quickly. And the next ICE 4 is already in the works – true to the motto: "After the train is before the train."