First Volvo hybrid trucks in

Volvo subsidiary Mack has developed a hybrid powertrain for heavy trucks in the United States.

The Mack truck is the first of a number of hybrid vehicles that Volvo Group plans to present during the coming year.

The hybrid powertrain is in a fuel-tanker truck developed in co-operation with the US Air Force.

Diesel-powered hybrid vehicles combine the power from an electric motor with that from a diesel engine.

The advantages of hybrid technology include improved fuel economy, lower emissions, reduced noise levels, lower operating costs and longer service intervals for engines and brake systems.

The Mack vehicle is a "mild hybrid".

This means that the hybrid engine assists at start-up and then recycles the energy released in braking - energy that is stored in batteries and reused instead of diesel fuel.

The goal for the Volvo Group is to develop a full hybrid system able to launch a heavy-duty truck solely with electrical power.

In a full hybrid system, the engine is not operated at idle, which reduces fuel consumption and noise levels from, for example, rubbish trucks.

A likely commercial use for full hybrid technology is a rubbish truck based on a Mack platform.

With a market share of more than 70 per cent, Mack is the leading maker of refuse trucks in North America.

"Hybrids offer the potential to reduce fuel consumption by 20 to 25 per cent," says Volvo CEO Leif Johansson.

"This is an extensive reduction and the possibilities within hybrid technology are highly promising and exciting."

The cost to develop the hybrid refueller was borne mostly by the US Government, through a US$1.2 million ($1.72 million) grant from the Department of Defence.

"We believe this technology shows promise for urban vehicles such as refuse trucks for many of the same reasons that the air force is interested in the refueller - reduced cost of operations and emissions without loss of performance," said Guy Rini, programme manager for the Mack hybrid project.