Sweden's AB Volvo (VOLVY), one of the world's largest truck makers, on Friday unveiled a new hybrid engine technology that it said will cut fuel consumption in heavy vehicles by up to 35 percent.

The hybrid vehicles are expected to be launched in 2009, and will feature a diesel engine supported by electric batteries charged by energy released from the brakes, Volvo said. The electric engine will reduce both fuel emissions and noise levels, making the vehicles more suitable for city traffic, the company which also makes buses said at a news conference in Stockholm.

"There is a growing interest in the market to reduce fuel consumption," Volvo Chief Executive Leif Johansson said. "We now have a technology that is interesting from a commercial viewpoint ... for a hybrid market for heavy vehicles."

The hybrid technology will be used in serially produced buses, trucks and heavy machinery by 2009, with sales expected to reach around 10,000 a year, Volvo said.

The new engines will be most effective during city driving with a lot of stops and starts, where some of the energy released from the brakes will be used to charge up the electric engine. When the batteries are fully charged, a bus or truck will be able to run solely on electric power, allowing them to drive silently through city neighborhoods, the company said.

During city driving, fuel consumption will be reduced by up to 35 percent. However, the price of the vehicles is expected to be about 35 percent higher than for those with traditional engines.

Volvo, whose truck brands include Mack Trucks and Renault, said potential customers should still benefit from their investment in one to two years from the purchase date, depending on oil price developments and the emergence of alternative fuels.

The Goteborg-based company, which sold its car division to U.S.-based Ford Motor Co. in 1999, employs about 81,000 people in 25 countries.