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Siemens series hybrid drive system Elfa reduces fuel consumption in buses by about one-third

City buses equipped with the new Siemens series hybrid drive system Elfa consume one-third less fuel than conventional buses, according to the company. Rather than powering the rear axle via an automatic transmission, as usually, the diesel engine in the Elfa system drives a generator that uses power electronics to supply electricity to one or more drive motors.

In the Elfa system from Siemens, the electric motors act as generators during braking and thus feed electricity back into the batteries. This power can then be subsequently used to drive the vehicle, which means at times the bus can run fully electrically and without producing any emissions. The vehicle range depends on battery capacity and can vary between a few hundred meters and several kilometers.

In combination with a clever power management system, Elfa not only reduces fuel consumption but also noise, since the diesel engine doesn’t provide acceleration and therefore operates only at quiet and economical engine speeds. As a result, fuel consumption falls by around one-third.

Buses with Elfa drives are now being used in a number of cities worldwide, including a test fleet of double-deckers in London. Hamburg, meanwhile, is planning to introduce buses with an Elfa hybrid drive equipped with a fuel cell system rather than a diesel engine. This new drive technology is also targeted for other commercial vehicles that make frequent stops, such as garbage trucks or light delivery trucks. The Elfa system forms part of the Siemens environmental portfolio, which generated around €28 billion in sales for the company in fiscal year 2010.



Sounds good.
Make them run on Nat Gas as well as diesel (or both).
Then increase the battery size and have recharging at fixed points (terminii etc.)
Even without the charge points, you would be ahead, especially if you used Nat Gas (and buses should be large enough to fit the bulky tanks, unlike cars).


There are a lot of school systems that could use a 30% reduction in fuel costs. Not to mention city buses.

George Furey

Good to see someone finally found a good way to apply diesel locomotive technology to buses. Now you have a simplified engine that can be tuned to run optimally at a set RPM with varying loads.

Mahonj, can you elaborate on efficiency advantage of CNG? It is my understanding that diesels run more efficiently, especially at low RPM when compared to a spark ignited engine.


George, some engines run a diesel engine using mostly natural gas, with a small amount of diesel to initiate the combustion.

Series hybrid makes more sense for a bus than a power split, as it would have to deal with high torque levels. And you can replace the 6 litre engine with one less than half the size.

You'd also be able to top up the batteries at each bus stop or even once per route.

George Furey

"George, some engines run a diesel engine using mostly natural gas, with a small amount of diesel to initiate the combustion."

@3PeaceSweet: I was not aware of this. Sounds like a great way to get diesel-like efficiency while also reducing emissions.

Also I agree, series hybrid (a-la diesel locomotive) when applied to buses, definitely makes sense when compared to a power split architecture.

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