Volvo debuts new VN series tractors
Oct 1, 2002 12:00 PM
Volvo Trucks North America spent $190 million and three years creating its new VN series heavy tractors that were introduced to dealers and the trade press on August 20, 2002. The new tractors follow the previous VN series, which made their debut only in 1996.
While derived from the previous VN, the new tractors are substantially different from their predecessors with more than 1,000 completely redesigned parts. In addition, 1,500 pounds has been taken out of the chassis weight without compromising structural integrity or safety. This was done primarily to counter the additional weight of engines with exhaust gas recirculation. For instance, a new gear reduction starter is 29 pounds lighter than traditional starters, and the tail lamp bar has been integrated into the rear frame cross member, saving 10 pounds. Volvo has adopted the new front air suspension system from Hendrickson that is 125 pounds lighter than earlier front axles suspensions. Also related to the front axle, the power steering system is 10 pounds lighter than the system used on earlier Volvo tractors. All brackets for component mounting were evaluated through months of shaker tests to ensure that they were stronger and lighter than those used before.
Volvo also redesigned the aerodynamics of the VN to produce a cleaner profile to help regain some of the fuel efficiency lost to the new engine designs. An effort was made to reduce drag coefficients on every surface of the vehicle, Volvo says.
The original VN series had been designed knowing that new engine technology would be required in 2004. This date was prior to the consent agreement with the Environmental Protection Agency. However, Volvo decided to design a new truck rather than modify the older design to accommodate anticipated changes in engines. The alternative would have been to make a new engine and associated components fit into a chassis designed for different engines, under an old hood design with a grille opening too small to meet the cooling requirements of engines that meet the October 2002 emission standards, says Susan Alt, Volvo's vice-president of marketing. “Sure, you can make the new engines fit in the old chassis, but what are the effects downstream?” she asks.
The new VN began with a series of two-dimensional sketches that soon developed into three-dimensional computer-aided designs. These conceptual designs were then narrowed to potential models for feasibility evaluation. Two models were constructed for wind tunnel testing at the Volvo research center in Sweden. Two full-scale clay models were made for design review at Volvo's technical center in Greensboro, North Carolina.
After a final design was selected, prototypes were run through barrier tests, shaker tests, full-scale wind tunnel evaluations, and the Swedish impact tests. Numerous changes resulted. For instance, wind tunnel texts showed that the lower edge of the bumper was too sharp, adversely affecting airflow under the truck. Additional studies, including evaluation of race car bumpers, resulted in softening the shape of the bumper edge. The new bumper design helps manage airflow under the truck as well as drawing excess heat from the engine compartment. Other changes include the chassis fairings that not only lower drag, but also cut total vehicle weight by 105 pounds. The fairings, which cover the battery box, toolbox, and other frame-mounted equipment, can be removed completely without using any tools.
In finishing the design, Volvo repackaged the entire chassis, repositioning the cab over the front axle. This results in a shorter wheelbase, and, in some instances, reduced the gap between tractor and trailer by 12 inches. Closing the gap between tractor and trailer reduces drag on the entire combination by eliminating air turbulence behind the tractor.
Another aerodynamic and aesthetic change is the positioning of headlamps. Instead of using traditional automotive headlamps, Volvo engineers used lamps of a size proportionate to the size of a heavy truck and stacked them vertically within the lines of the flared fenders. Drawing on race car technology, the flared fenders smooth airflow across the vehicle and help increase fresh air intake to the engine. An additional benefit of the flared fenders is reduction of road spray onto other vehicles.
The new VN series is designed to use Volvo VE D12 series 12-liter engines or Cummins ISX 15-liter power plants. To meet the October 2002 emission standards, the Volvo VE D12 uses V-Pulse technology to achieve the exhaust gas recirculation needed to reduce combustion temperature and lower oxides of nitrogen levels. The system introduces up to 30% of exhaust gas into the intake stream without the use of a variable geometry turbocharger. The Cummins engines use exhaust gas recirculation with a variable geometry turbocharger. Both emission technologies result in higher engine coolant temperature, because a higher percentage combustion heat, normally allowed to escape with the exhaust, is rejected through the cooling system. Recommended oil change interval for the October-compliant VE D12 is unchanged from previous versions.
To deal with this increased operating temperature and reduce heat buildup in the engine compartment, Volvo designed new mountings and installed a high performance fan for maximum cooling. The radiator has a pivot design that allows the core to be cleaned without dumping the coolant. In addition, the hood on the new VN has two air intakes, one on each side to help balance intake airflow and to help dissipate heat. Also the oil fill tube and oil check dipstick along with components that require routine maintenance are positioned on the cool side of the engine away from the hot exhaust gas recirculation components.
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