Dana Corporation's Commercial Vehicle Systems group proposes a new single drive axle concept aimed at generating maximum fuel economy while maintaining the weight capacity of a traditional tandem drive axle combination. The proposal makes use of the new Dana Spicer S21-170DE high entry single drive axle and the Dana Spicer R21BS tag axle. The system is being demonstrated in a special technology vehicle that includes an Eaton Roadranger UltraShift automated transmission with experimental fuel-saving calibrations in the operational software.
Single drive axles provide enhanced fuel economy, because they eliminate the energy losses associated with inter-axle drivelines and rear axle gear assemblies, says Leo Wenstrup, Dana's senior product manager for drive axle systems. A single drive axle in combination with a tag axle eliminates the extra weight and complexity of traditional tandem drivers and saves more than 200 lb when compared to the installed weight of a 40,000 lb drive tandem. Equipping the axles with wide-base single tires can save an additional 400 lb and improve fuel economy with reduced rolling resistance.
In addition to saving weight, the single drive plus tag combination should reduce maintenance costs, Wenstrup says. Using a single gear set reduces lubrication requirements by 14 pints. It also eliminates the need for trailing axle gear set maintenance and servicing an inter-axle driveline. A single axle also eliminates the potential for vibration damage to an inter-axle drive line, he says.
Improving traction
Two objections typically arise to using a single drive in combination with a tag axle. The first objection suggests that single drive with an auxiliary axle can result in loss of traction. Dana addresses this problem by exhausting the air bags in the tag axle suspension when the differential lock is engaged, temporarily shifting all the weight to the driven axle at low speed. This provides the same traction as a tandem axle, Wenstrup says.
The second objection says that used single drive vehicles with tag axles sell for less than traditional tandem drive tractors. To meet this objection, Spicer proposes to use its R21BS reconfigurable tag axle, which is basically a trailing tandem axle housing without a gear set. At resale time, the seller can order a conversion kit from Dana and convert the tag axle to a live drive axle. In the event that the vehicle was equipped for maximum fuel economy, Eaton Corporation may possibly offer a conversion kit to change transmission calibrations from fuel economy settings to high performance settings for the automated transmission.
Dana has applied for a patent on the single drive and tag axle combination that it calls the Dana Spicer Super 40 D40-170. The axle combination is aimed at the premium owner-operator market and other weight critical users, Wenstrup says. The price of the gear set and driveline kit to convert the axle combination to tandem drive is projected to be less than the increased market value of a tandem drive tractor compared to a single drive tractor with the same weight capacity.
