Skip to main content
Staff of the Hitachi, Ltd. Industrial Systems Group, Transportation Systems Division who developed the hybrid drive technology (standing in front of the first electric locomotive manufactured in Japan).
Today, railroads are considered to be very energy efficient transportation systems. However, compared with electric trains, the diesel trains that run on non-electrified lines have low energy efficiency, and their exhaust gases contain large quantities of nitrogen oxides (NOx) and other hazardous substances. Nevertheless, considering the construction costs of electric lines and other above-ground equipment, in practical terms it would be difficult to electrify the non-electrified segments of the Japanese railway network, which are mostly local branch lines. Presently, there are approximately 3,000 diesel railcars running in Japan, and they account for less than 6 percent of the nation's total rolling stock.
The energy efficiency of electric trains has been greatly increased through the introduction of electrical regenerative brakes, which feed energy generated from braking back into the electric lines for use by other trains.
Capturing the braking energy generated by diesel trains—which run on engine power—is more difficult, and that has been one of the main reasons for their relatively poor energy efficiency.
To solve this problem, Hitachi has been jointly working, since 2001, on the commercialization of a hybrid drive system with the East Japan Railway Co. (JR East).
One easy way to understand this approach is to imagine trains that carry their own electric power plants. The system's basic configuration is to use the diesel engine to produce electricity and then use that electricity to drive the motor. Lithium-ion batteries are placed in between the generator and the motor, enabling the reuse of energy generated from braking, just as in hybrid cars.
Of course, this configuration has different problems than those associated with hybrid cars. To eliminate noise inside train stations, the engines are stopped and the motor runs on batteries alone until a speed of 25 km per hour is reached. For that reason, the batteries must be charged when the trains arrive at train stations. To make this possible, Hitachi has developed battery charge management control technologies that make detailed assessments based on such factors as train running speed and the slope of the railway tracks.
Hybrid Drive System Electricity Control
The hybrid drive system starts the train using batteries, and recharges the batteries using electricity from braking and from the engine while the train is running.
Kiha E200 operating on the Koumi Line
JR East's Kiha E200 hybrid railcar series, the world's first in commercial use, have been in operation on the Koumi Line in Nagano, Japan since the summer of 2007.
Compared with conventional diesel trains running on the same line, the Kiha E200 railcars reduce fuel consumption by 10 percent and emissions of harmful substances by 60 percent. Hitachi will continue striving to improve efficient electricity control technologies to further reduce the environmental impact from railways.
(Published in July 2008)