Twin tandem wheel bearing introduced
09 July 2007
The Schaeffler Group has developed an energy efficient four-row, angular contact ball bearing, which replaces conventional tapered roller wheel bearings. This results in reduced fuel consumption and emissions on trucks, SUVs and light vans, but could potentially be developed for use in other heavy engineering applications.
By replacing ‘line’ contact associated with conventional tapered roller wheel bearings with a new design concept based on ‘point’ contact using ball bearings, automotive component and bearings manufacturer The Schaeffler Group has developed the ‘twin tandem’ wheel bearing unit, which reduces friction by around 50% over conventional tapered roller wheel bearings. The result is an approximate 1.5% reduction in fuel consumption on trucks, light vans and SUVs.
At the Hanover Fair exhibition in April, the new twin tandem wheel bearing was unveiled to the public for the first time. Visitors to Schaeffler’s stand were invited to see a demonstration of the twin tandem in operation and its reduced friction characteristics.
The demonstration comprised a complete wheel assembly, with a conventional tapered roller wheel bearing on one end of the axle and the new twin tandem unit on the other. When the power was cut off, the conventional tapered roller wheel bearing continued to rotate for around six to seven revolutions. However, visitors were amazed to see the twin tandem unit continue to rotate freely for between 48 to 50 revolutions – proving its reduced friction properties.
The twin tandem design concept is based on replacing the rows of tapered roller bearings with two rows of ball bearings in each case. A double-row tapered roller bearing therefore becomes a four-row ball bearing. Replacing the line contact of the tapered rollers with the point contact of the balls eliminates rib friction and reduces overall friction by 50%.
The twin tandem bearing also has a lower operating temperature compared to conventional tapered roller units, therefore improving the service life of the lubricants. Cornering stiffness is also increased.
The twin tandem was developed initially for trucks, light vans and SUVs, where the 1.5% reduction in fuel consumption and emissions will have the greatest benefit. However, Schaeffler will continue to develop the twin tandem for the passenger car market too.
Similar energy efficient design concepts are currently under development with customers in other manufacturing sectors, including heavy industries, such as steelmaking, machine tools, paper and wind energy.
Schaeffler has also considered interchangeability of the new twin tandem with conventional tapered units. The twin tandem is designed to cater for the use of sensors (such as ABS sensors) and installation in the wheel carrier is identical for conventional tapered roller wheel bearings.
Assuming a vehicle emits 300g/km of CO² over a distance travelled of 15,000km per year, the reduction in CO² emissions resulting from the twin tandem unit will be 67.5kg per year per vehicle. Fuel consumption is also reduced by 1.5%, giving a reduction of 40 litres per year for an average light truck travelling 15,000km per year.
The twin tandem demonstrates that even relatively minor design improvements can make a significant contribution towards reducing total fuel consumption and CO² emissions on vehicles. The previous savings of 40 litres per year per vehicle and 67.5kg per year of CO² emissions may appear a small contribution. However, in terms of the total market potential for the unit, each year around seven million vans, SUVs and light trucks are produced worldwide, whose axle loads make them suitable candidates for the twin tandem bearings. Based on the assumptions above, potential savings could amount to around 280 million litres of fuel per year, or approximately 0.5 million tonnes of CO² emissions.
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