The A1VO axial piston variable displacement pump designed by Rexroth especially for the segment of small tractors reduces diesel fuel consumption by around 10,000 liters over the entire useful life of 6,000 operating hours. The new variable displacement pump reduces the cost differential compared with constant displacement pumps so greatly that it enables for the first time an economical switch from the traditional open-center design to a load-sensing system. This approach summons hydraulic power as it is needed. Simulations based on a 90 hp diesel engine actually used in the marketplace verify fuel savings of between ten and 15 percent per operating hour in mixed usage.
In larger tractors load-sensing systems as a consumption- and thereby emissions-reducing technology have already proven themselves. But for the very price-sensitive segment of small tractors this technology has until now been unaffordable. Rexroth has therefore tailored the design of the new A1VO variable displacement pump to the needs of this market segment – for example by relocating all the connections to the port plate and significantly reducing the number of different models. This simplifies manufacturing, which helps the small-tractor segment achieve a commensurate price/performance ratio.
To make the switch easier for tractor manufacturers, the A1VO has similar dimensions and performance data to the otherwise generally used constant displacement pumps. With a suction volume of 35 cm3 it is designed for speeds up to 3,000 rpm. The variable displacement pump achieves a working pressure of 250 bar and a peak pressure of up to 315 bar and moves up to 105 l/min. The efficiency is nearly 90 percent. Service life is comparable to the A10VO and A10VNO version used on the large tractors.
In comprehensive simulations using OEM engine map data of a commercially available 90-hp-diesel Rexroth calculated consumption savings of between ten and 15.9 percent per operating hour. The results also took into account varying load cycles: from pure travel mode with zero hydraulic output to partial-load operation and full-load operation of the working hydraulics.
The new pump achieved the greatest savings in diesel fuel consumption in partial load operation such as holding the plow during transport or working with the front loader. Projected on to the usual life expectancy of 6,000 hours and assuming a typical load cycle distribution, an overall savings of around 10,000 liters of diesel fuel can be expected.