Adura Systems, a Menlo Park, Calif. company that is developing an engine and electronics platform for plug-in hybrid buses and delivery vehicles, has raised an additional bridge atop its first funding round.

The company hasn’t disclosed the amount of either investment, and is also quiet on the specifics of its technology. So far, it has only said that its technology can greatly improve fuel efficiency, while saving on maintenance costs.

The investor in the first round, New Frontier Renewable Energy, provided the bridge. According to VentureWire, Adura is looking for $10 million more.