Bearings promote more energy-efficient hydraulics
26 October 2010
The use of low friction rolling element bearings in a new range of axial piston pumps and motors has seen a significant lift in their operating efficiencies, shaving around 6% off the energy consumption of a wheeled loader with a typical hydraulic drive system comprising one pump and two motors
Sauer-Danfoss’ new H1 Series axial piston pumps and motors are achieving significant energy savings for end users. For example, by utilising one H1 hydraulic pump and two H1 hydraulic motors, a wheeled loader with a nominal drive power of 140kW can save around 9kW. This has been attributed in no small part to the use of low friction, optimised rolling bearings from Schaeffler, which have had a positive impact on the H1’s performance, not just in terms of power reduction, but also installation space and weight reduction across the range.
For example, a new option for the H1 axial piston pump in swashplate configuration is a new swashplate cradle bearing. Here, compact, low friction cylindrical roller bearings were used to support the drive shaft. Compared with the previous version, installation space and weight were substantially reduced and efficiency was increased by around 2%.
H1 axial piston motors in swashplate configuration utilise Schaeffler’s low friction, optimised X-life (premium quality) tapered roller bearings, and have the benefit of a new steel sealing ring that achieves significantly improved sealing performance. These developments have seen a reduction in the length and weight of the motor and power losses trimmed by approximately 2% compared with the previous model.
Schaeffler’s new X-life (premium quality) cylindrical roller bearings with optimised rib contact have made a further contribution to these design improvements. The special curvature of the roller end faces improves the contact geometry between these and the bearing ribs, minimising contact pressures and enabling the formation of a load carrying lubricant film. The rollers now slide on the lubricant film under axial load, so the bearings can operate with a much higher ratio of axial to radial load (60% instead of the more conventional 40%). Moreover, frictional torque is as much as 50% lower, depending on the magnitude of the axial load, ensuring lower operating temperatures, higher efficiency and reduced energy consumption.
Optimised rib contact is also critical for Schaeffler’s X-life tapered roller bearings, specially under axial load, when frictional torque can increase markedly. These bearings have subsequently been improved and, as a result, they now yield up to 20% higher basic dynamic load ratings increasing their basic rated life span by around 70%. At the same time, improved dimensional accuracy, combined with improved surfaces, have reduced frictional torque by up to 75% compared with conventional bearings. The contact geometry of the inner ring rib and the roller end face were also redesigned in order to reduce friction, thus reducing stress on the lubricant and extending maintenance intervals.
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