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Hybrid technology enters the real world

01 Jul 2007

Fuel savings of up to 20% are anticipated during tests of a power car and three DMUs fitted with a prototype hybrid battery-diesel system which reuses braking energy for acceleration

THIS MONTH East Japan Railway will put into revenue service its initial production series of three battery-diesel hybrid DMUs, which will begin carrying passengers on the Koumi Line between Kobuchizawa and Komoro.

The single-car units have 331 kW diesel engines and 15·2 kWh lithium-ion batteries, and manufacturer Hitachi expects deployment on the arduous commuter duties with frequent station stops will bring significant fuel savings and a cut in particulates of up to 60%.

Meanwhile, testing is now underway with 'Hayabusa', a much more powerful hybrid vehicle which Hitachi says is Europe's first battery-assisted diesel-electric power car. Hitachi's hybrid drive has been installed in a British HST power car to allow realistic trials of the prototype technology, which the Japanese firm and its development partners Brush Traction, Network Rail and Porterbrook Leasing anticipate could reduce fuel consumption by 20% and slash the most harmful engine emissions by half.

The technology

The key to the system is an onboard energy management system, which forms an interface between the diesel engine and a high energy density lithium-ion battery bank which can be charged from either the engine or from energy regenerated during braking.

The hybrid train uses battery power alone to accelerate from a stand, with power fed from the battery through a DC to AC inverter to the newly-installed Hitachi 300 kW AC traction motors, which have replaced the previous DC motors. The peak power available is 1 MW, with the energy management system blending in power from the vehicle's existing Paxman Valenta diesel engine as the speed reaches 30 km/h. The management system ensures the engine runs at its most efficient speed, with excess power not required for traction being diverted to the charge the battery. The management system automatically draws on the battery if more power is needed at any point, perhaps on an adverse gradient or for further acceleration.

To reduce emissions the engine can be switched off when it is not needed, such as when standing in a station, and will start up as the train approaches 30 km/h.

The key to reducing energy consumption is the use of the battery to store energy from braking, which would otherwise be lost. During braking the traction motors act as generators, with kinetic energy converted to electricity, rectified and the resulting DC used to charge the battery rather than being dissipated as heat. Allowing for energy losses in charging and discharging, Hitachi expects that around 80% of the regenerated braking energy will be recovered for the next powering cycle.


Power car No 43 089, now named after the Japanese word for falcon, and a MkIII TGS coach were donated to the project by Porterbrook in November 2005. Modification of the vehicles was undertaken by Brush Traction in Loughborough.

The 48 high energy density 1 kWh lithium-ion modules weigh around 20 kg each, and limitations on weight distribution meant the 1 tonne battery bank could not be installed in the power car. As a result, the battery is located in custom-designed racks in the adjacent coach. Future new-build vehicles would have the batteries incorporated into the design from the start, allowing the modules to be distributed throughout the train and reducing the weight of the supporting structures.

Hitachi is expecting to see a 20% cut in fuel consumption from the prototype, but higher savings could be made with production vehicles, as the use of battery power for acceleration means that a new-build vehicle could have a smaller diesel engine, cooler group and fuel tanks, resulting in an overall reduction in vehicle weight despite the battery.

Further weight reductions are expected as battery technology advances, driven by demand from the automotive industry Hitachi supplies the batteries for Toyota's Prius hybrid car. 'The weight saving is marginal today, but might be significant in a couple of years', said a Hitachi engineer at the launch. Battery life is currently estimated at eight to 10 years, but this is also expected to improve as the mass-market automotive technology matures. 'This is cutting-edge for rail, but exploits mass-market technology', explained Jon Shaw, Hitachi Europe's Safety & Approvals Manager.

Head of Project & Operations Keith Jordan drew a comparison with the silicon chip market, where rapid technological progress brought huge increases in capabilities at the same time as costs fell.

During May the project partners undertook initial trials of the HST at speeds of up to 96 km/h on the Great Central Railway, a heritage line which can offer exclusive use of a double-track main line for testing. From September Hayabusa will undergo six months of extensive trials as part of Network Rail's New Measurement Train (RG 7.03 p441). It is paired with a conventional HST power car to allow direct comparisons of performance and energy efficiency, and use in the NMT will require it to operate at up to 200 km/h to run between passenger trains. Network Rail Chief Engineer Andrew McNaughton said that NMT operations are similar to those of a train in regular inter-city passenger service, which will enable Hitachi to gather realistic performance data. 'The duty cycle of NMT is very onerous, which is why we think it makes a good test bed.'

Future prospects

The current project is focused on research for the future, with the production of a demonstrator train showing Hitachi's commitment to the technology, and willingness to support and develop it further.

Train operators are following the research with interest, but no orders are currently planned. Hitachi has the InterCity Express Programme (RG 2.07 p77) in mind, and McNaughton points out that 'there is a whole swathe of ex-British Rail suburban EMUs coming up for renewal,' offering one possibility for applying the technology to inner-suburban services in the future. McNaughton said that the potential for faster acceleration offers an opportunity to increase capacity on the network. 'Accelerating just a bit quicker helps to increase capacity, and we are very positive about anything to increase capacity.'

The HST is the first use of Hitachi's hybrid system in Europe, and the most powerful yet tried. However, experience has been gathered from the E991 prototype New Energy Train Series, a single-car unit with a roof-mounted 19 kWh battery which has been on test in Japan since 2003. Derived from a Series E231 EMU, the 100 km/h vehicle has demonstrated a 20% reduction in fuel consumption compared to a standard JR East DMU. There was a 2% to 5% cut in fuel consumption through the ability to switch the engine off at stations, which also reduces noise and pollution. Hydrocarbon, NOx carbon monoxide and particulates were cut by 50%

One strength of the system is that it is independent of the power source. JR East's 100 km/h NE Train was built as a battery-assisted DMU, then was converted last year to use two underfloor 65 kW fuel cells (RG 12.06 p758).

As well as being suitable for incorporation into vehicles powered by diesel or fuel cells, the hybrid system can be used on electrified lines where the fixed equipment is not designed for regeneration. Hitachi suggests it could bring benefits on high speed lines built using French technology, such as Britain's Channel Tunnel Rail Link, which are not currently able to benefit from regeneration. The use of battery energy storage is also seen as a possibility for Britain's extensive 750 V DC third-rail network, where the costs of adapting existing hardware for regeneration may be high.

'This hybrid HST power car is a fantastic demonstration of the advances in hybrid battery-diesel technology', Hitachi Europe General Manager Alistair Dormer told guests at the launch on May 3. 'Hitachi is very proud to unveil this technology which will demonstrate energy and emissions savings today, but more importantly unlocks the future potential for the application of rapidly-improving battery hybrid-powered traction technology to future generations of rail vehicles in the UK.'

  • CAPTION: Executive General Manager of Hitachi Europe's Rail Group, Chiaki Ueda (left), unveiled the nameplate to mark the start of testing on May 3
  • CAPTION: 'Hayabusa' makes use of the same battery technology found in Toyota's Prius hybrid car
  • CAPTION: Network Rail will use the hybrid power car in its New Measurement Train to provide a rigorous assessment of the concept on the main line. The power car will remain permanently coupled to the trailer coach behind, which houses the battery racks
  • CAPTION: Porterbrook Leasing is providing an unrefurbished Paxman Valenta-engined power car as part of the trial to enable comparisons to be made in traffic with Hayabusa