THROUGH its 2020 Action Programme for Climate Protection, which was adopted in 2014, Germany’s federal government has reaffirmed its commitment to reducing greenhouse gas emissions to 40% below 1990 levels by 2020. While greenhouse gas emissions from transport continue to grow in the European Union (EU), Germany has been relatively successful at stabilising the situation and transport emissions fell by 2% between 1990 and 2014, but further reductions will be needed to support the federal government’s goals.
Germany’s rail industry is seeking technical solutions that could be widely deployed to achieve a significant reduction in emissions from diesel engines. In the Erzgebirge (Ore Mountains) of Saxony, German Rail (DB) and its partners in the EcoTrain consortium are exploring how equipping diesel multiple units with lithium-ion batteries could enable electric operation on non-electrified regional lines.
EcoTrain partners include the technical universities of Dresden and Chemnitz, the Dresden-based Fraunhofer Institute, and DB RegioNetz Verkehrs Erzgebirgsbahn, a subsidiary of DB Regio which operates the 217km Erzgebirge Diesel Network. The four-line regional network serves 68 stations and features challenging gradients, which reach up to 4‰, with trains climbing up to 450m in height. Speeds typically range from 60-80km/h, with trains reaching 120km/h on the Chemnitz - Flöha line.
The €15m project, which is funded jointly by DB and the federal Ministry of Transport and Digital Infrastrucutre (BMVI), involves converting one of Erzgebirgsbahn’s 13 Siemens class 642 Desiro Classic DMUs to bi-mode (diesel and electric) configuration as a prototype for conversion of the remaining 13 trains. Siemens supplied 234 class 642 sets to DB from 1999 onwards and the Desiro Classic DMU is used by various other operators in Germany as well as in Austria, Denmark, Greece, Romania, Hungary, and the United States. All of the DB sets are due to have their drive systems modernised in the coming years and a hybrid solution could be considered as an alternative to conventional diesel power packs.
The class 642 is a two-car articulated train with two diesel engines (275kW and 315kW), each operating with a hydro-mechanical gearbox with five gears and a torque converter. Each engine and gearbox is mounted in the power pack in the high-floor section at the outer end of each car.
Hybrid drive train
By hybridising the drive train of the class 642, EcoTrain seeks to reduce both emissions and operating and maintenance costs. The project also aims to cut fuel consumption by 30% compared with conventional DMUs.
In determining the final hybrid drive configuration for EcoTrain, 11 different variations were evaluated and the consortium considered serial, parallel and power-split hybrid drives. This considered both the technical criteria for the conversion as well as the specific operating conditions of the Erzgebirge Diesel Network. The evaluation concluded that a serial hybrid drive with a diesel engine and distributed energy accumulators would be the optimum configuration for this application.
Using this drive design, Fraunhofer IVI evaluated the energetic properties of the drive train and dimensioned it using the IVIsion simulation tool. This has been used extensively in similar projects and includes modules for data processing, calculation of drive systems, and evaluation of calculation results.
The EcoTrain prototype will be fitted with a single 390kW diesel engine with a start-stop system, which shuts the engine down during braking and station stops. Electric traction motors have an output of 250kW for acceleration and 280kW for deceleration, driving the wheels via a reduction gear and final drive.
To allow the integration of electric traction motors and energy storage unit into the drive system, EcoTrain will replace the mechanical transmission of the class 642 with electric transmission. Using a generator, the diesel engine feeds the intermediate traction circuit that supplies the traction motors and all auxiliaries. When braking, the traction motors recover energy to lithium-ion batteries installed in the space previously occupied by the second diesel engine. The vehicle can be charged externally via a transformer mounted in the roof, which can be linked to shore supply cables. At a later stage a pantograph will also be installed to facilitate charging through the 15kV 16.7Hz overhead electrification system.
The IVIsion simulations showed that a 100kWh high-power (HP) energy storage unit would meet all driving requirements, but after considering economic and lifecycle factors it was decided to install a 150kWh HP storage unit on the EcoTrain prototype.
Knorr-Bremse has designed and supplied the train’s ESRA modular electronic braking system, which replaces the original MRP system. The company has also supplied an oil-free air supply system and a TSI-compliant sanding unit. Knorr-Bremse says the main challenge for this element of the project was to synchronise the brake control unit with both the existing and new vehicle interfaces. Re-engineering of the brake control system was partially based on the original vehicle documentation and this process had to ensure smooth communication with systems that remained unchanged.
An onboard Energy Efficiency Module (EEM) developed by Fraunhofer IVI manages the interface between the hybrid traction system and the vehicle control system and ensures operation of the train is energy-efficient. The EEM will monitor parameters including the current condition of the vehicle and the drive system as well as route and environmental factors. To manage the hybrid drive effectively, the EEM will also need to be able to determine future power and energy demands.
The module will incorporate data on timetable and current schedule conditions and charging infrastructure and will recommend a power split between diesel and electric power, providing the driver with a driving strategy to optimise performance and ensure energy-efficient operation.
The train management system will automatically determine when the train switches between diesel and electric traction, with all electric-drive used when approaching and departing from stations. This will reduce both particulate emissions and noise in urban areas.
To further improve energy efficiency, the HVAC system has been replaced with a CO2 system with heat pump function.
With fundamental changes to the vehicle architecture, the train is heavier than a standard class 642. DB says it cannot readily compensate for the extra mass without sacrificing seat capacity, and this is not considered an acceptable compromise. EcoTrain will therefore seek to compensate for the added weight of the revised traction system by reducing the mass of conventional components such as wheelsets. DB Systemtechnik has adapted the bogies to accommodate the additional weight of the revised traction system and batteries and the suspension system has also been adapted.
Installation of the hybrid drive system began in June 2016 and the prototype train is due to be ready for testing by September, with authorisation by the Federal Railway Authority envisaged by early 2018. The remaining 12 trains are due to be converted to hybrid configuration by 2021, and if the EcoTrain project is successful, DB may consider offering rebuilt class 642 trains in future tenders for regional contracts elsewhere in Germany.