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2009-12-18 | 000-002-136 DE-EN
SCHAEFFLER KG, LANDSHUT/HERZOGENAURACH

High reliability and maximum performance under all operating conditions

Energy-Efficient Gearboxes in Tractors and Graders

Tractors and graders operate with high drive power and at high speeds. Reduced fuel consumption and environmental friendliness are crucial requirements for these machines, in addition to absolute operational reliability under all conceivable loads and speeds. Many modern tractors offer more than 100 kW drive power and some can even achieve road speeds of up to 80 km/h. Graders mostly operate under full load at speeds of up to 40 km/h. The high power required for such applications is transmitted by the gearbox and the differential. Increasing the efficiency in the drive train therefore holds great fuel saving potential. In order to meet these performance requirements, Schaeffler Group Industrial has developed new bearing designs for maximum energy efficiency.

Friction-reduced bearings
Rolling bearings and energy efficiency – these terms can be used almost synonymously. After all, rolling bearings are used in order to save energy. Wherever mechanical work is done and things are in motion, rolling bearings ensure reduced friction and thus increased efficiency. So the rolling bearing as a universal and very frequently used machine component is and will remain one of the keys to lower energy consumption. The continuous improvement of simulation methods and calculation tools today is the central prerequisite for being able to develop even better bearings – bearings that are tailored even more precisely to customer requirements and render even higher energy efficiency. It is not only the selection of the most suitable bearing type that plays a key role in this context. The internal design of a rolling bearing, for instance the cage design, also has a major impact on its performance capacity and on friction. Another approach involves the use of friction-reducing, wear-resistant materials as well as corresponding coatings, and the achievement of further surface quality improvements in the functional areas during volume production.

Friction-reduced tapered roller bearings
Friction-reduced tapered roller bearings are optimized in terms of bearing geometry, surface structure and materials as well as dimensional and running accuracy. This has resulted in up to 20-percent increase in dynamic load ratings and approximately 70 percent increase in basic rating life. For specific applications it is possible to select smaller bearings, which leads to a further reduction in friction. The use of premium materials and special heat treatments offering higher resistance to solid particles plays an important role in this context. In addition, a well-adjusted logarithmic profile was developed for the raceways and roller surfaces which compensates for stress peaks during high loading and possible misalignment. Thanks to the optimized surfaces and contact geometry, an elastohydrodynamic lubricant film will build up even at very low speeds. This permits high loading of the bearings immediately during start-up and reduce the frictional torque by up to 75 percent compared to conventional products.

Friction-optimized tandem angular contact ball bearings
The tandem angular contact ball bearings developed by INA and FAG experts prevent the loss of preload and also reduce friction losses. Thus they increase the efficiency of the gearbox and enable significant fuel savings to be achieved. Angular contact ball bearings can support axial and radial loads, just like tapered roller bearings. But due to their point contact they invariably produce less friction and unlike tapered roller bearings they have no roller/rib sliding contact that would adversely influence friction. Their point contact is easier to lubricate than the line contact of tapered roller bearings. This means that angular contact ball bearings run with lower friction than tapered roller bearings of the same size. The use of double-row angular contact ball bearings ensures that the required load carrying capacity can be achieved and at the same time the frictional torque is lower than that of single-row angular contact ball bearings offering the same load carrying capacity. Another advantage of angular contact ball bearings is the preservation of preload, resulting in consistently high rigidity.

Friction-optimized tandem ball roller bearings
The innovation “ball roller bearing” is based on an ingenious idea and a novel rolling element in combination with new assembly methods. All areas of the conventional rolling element “ball” that are not under load are removed. This means that 15 percent of the ball diameter is cut off on both sides of the ball. The result is the so-called ball roller, a ball that is flattened on both sides, being 30 percent narrower than a true ball. This saves valuable space. Moreover, the particularly “slim” shape of the ball roller, as well as specially developed assembly methods, allow an increase in the number of rolling elements so that a filling capacity of up to approx. 90 percent can be achieved. More rolling elements in the same space result in clearly higher load ratings and correspondingly longer service life. This also opens up new downsizing opportunities for products and assemblies. The two-cage design enables the optimal adjustment of the two raceways independently of each other to perfectly match the application. This ensures maximum load support with minimum bearing size and even lower friction.