BY BILL SIURU, PHD, PE
BAE Systems’ HybriDrive series propulsion systems are currently powering more than
3000 Daimler, New Flyer, Alexander
Dennis and Irisbus Iveco transit buses
in cities around the world. They have
transported more than a billion passengers in cities such as New York, San
Francisco, Toronto, Ottawa, Houston,
Seattle, London and Oxford, U.K.
There are also between 6000 and
7000 hybrid-electric urban buses that
have been delivered or ordered from
several manufacturers, including BAE
Systems and ISE Corp.
More recently, BAE Systems has
developed a heavy-duty parallel hybrid
propulsion system for Class 6, 7 and
8 vocational trucks. According to the
company, its series hybrid system
was designed to meet the demands of
urban transit bus duty cycles that are
designed to be compatible with auto-
matic and automated manual trans-
missions. Operating as a generator
driven by the engine, the electrical
energy is used to charge the battery.
Additional charging is also achieved
through regenerative braking. When
additional power is needed, such as
for accelerating and hill climbing, elec-
tricity from the battery pack is supplied
to the motor-generator, whose output
augments the output of the engine.
With BAE Systems’ new HybriDrive parallel system, a mechanical connection is estab-
lished between the engine and the rear axle. This system is designed for applications with
duty cycles that have higher operating speeds and less frequent stops and starts, such as
Class 6, 7 and 8 vocational trucks.
BAE Systems Adds
characterized by low average speeds
and frequent stop-and-go operation.
In contrast, the new HybriDrive parallel system is designed for applications
with duty cycles that have higher
operating speeds and less frequent
stops and starts.
An electric motor-generator is inte-
grated between the transmission and
the engine in the HybriDrive parallel
system. The system architecture is
There is no mechanical connection
between the engine and rear axle in BAE
Systems’ HybriDrive series hybrid system.
The engine drives a generator that supplies power to
an electric motor, which drives the rear wheels.