The system consists of a generator, an electric motor, and an energy storage system. A diesel engine that turns the generator operates independent of the electric drive motor, allowing it to run at nearly consistent speed for optimum efficiency. The system uses no mechanical transmission, a major maintenance item on traditional diesel buses.

The optional accessory power system in the new configuration can further improve efficiency and reduce maintenance by eliminating alternators and their associated pulleys and belts. The system can produce up to 27 kW of electricity to run vehicle accessories and to enable the bus to be operated for brief periods in zero-emission mode, with the engine off. It also combines the starter and generator to eliminate the starter motor and flywheel, making the system simpler and lighter and further reducing maintenance requirements.

Buses equipped with the new hybrid system also will use a lithium-ion energy storage system that increases battery life and reduces vehicle weight, improving fuel economy and reducing emissions. The battery system is self-monitoring and easy to service for further savings in maintenance costs.

Applied in the Daimler Buses Orion VII NG (Next Generation) bus, the BAE hybrid system uses an inline configuration and features:

• ± 200 kW peak Li-ion battery pack with A123Systems cells;

• ± 200 kW propulsion control system;

• 160 kW (215 hp) continuous, 200 kW (268 hp) peak traction motor;

• 200 kW integrated starter/generator;

• 6.7-liter 280 hp@ 2,300 rpm diesel engine; and

• 28 VDC and 208 3-phase AC auxiliary power system.

Applied in the double-decker Enviro400 from Alexander Dennis, the BAE hybrid system uses a transverse configuration and features:

• ± 200 kW peak Li-ion battery pack with A123Systems cells;

• 320 kW continuous propulsion control system

• 120 kW (160 hp) continuous, 175 kW (235 hp peak) motor with 425 Nm continuous, 650 Nm for 4 minutes, 900 Nm peak;

• 145 kW generator, including starter; and

• 4.5-liter 185 hp ISBe Euro 4 engine with SCR.

More than 1,500 buses powered by the HybriDrive system transport more than a million passengers daily in cities such as New York, San Francisco, Toronto, and London. To date, these buses have logged more than 70 million miles of revenue service. BAE Systems provides the systems for buses built by Alexander Dennis Limited, Daimler Buses North America, and New Flyer Industries.

Separately at APTA, Engineered Machined Products Inc. (EMP) announced that it is collaborating with BAE Systems on next-generation thermal management solutions for the hybrid municipal transit bus market.

EMP has developed a robust custom cooling system for hybrid electronics and motors specifically for BAE Systems’ needs. The cooling system introduces fully-controllable, long-life electric fans along with brushless electric water and oil pumps.