As a parallel hybrid, the bus can be powered by the electric motor or the diesel engine independently and well as by both engines simultaneously. As a result, the bus could be equipped with a smaller, 5-liter diesel engine compared with the 9-liter engine in the diesel version of the Volvo 7700. The bus’s performance is enhanced, but fuel consumption is reduced.

“Another major benefit with Volvo’s hybrid technology is that the diesel engine will be turned off at bus stops and traffic lights,” says Maurice Brown, Volvo Bus’s product manager for city buses in Europe. “The bus starts moving driven by the electric motor and when the bus reaches 15-20 kph, the diesel engine starts up automatically feeding in the mechanical power until driven by the diesel engine only.”

This solution is a major benefit for the environment in cities. Passengers, pedestrians and fellow road-users, are spared from noise and exhaust fumes.

The hybrid system

Wide range of uses

Hybrid technology is well suited for vehicles with many starts and stops, perfect for buses in heavy city traffic. The advantage with the parallel hybrid technology, that Volvo has chosen, is that the buses also operate well in suburban traffic with less frequent halts at bus stops. The reason is the mechanical coupling between the diesel engine and the driveshaft. With this, the inefficiency in converting from mechanical power to electrical and back again is avoided.

“It is highly important for our customers that the buses also save fuel outside the most densely populated areas,” says Maurice Brown. “Many of the large operators need to move the bus around to different areas during the bus’s lifetime and this does not work with a technology that is suited only for the most extreme city traffic.”

Volvo 7700 Hybrid