Y. Stoyanov1, G. Tihanov2

1Technical University of Sofia, Branch Plovdiv, Department of Transport and Aircraft Equipment and Technologies, 25 Tsanko Diustabanov str.,4000 Plovdiv, Bulgaria
2Department of Agricultural Engineering, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria

(Manuscript received 22 March 2025; accepted for publication 24 July 2025)

Abstract. The objective of this article is to examine the hydrostatic four-wheel drive system of self-propelled grain harvesters. The selection of hydraulic pumps is carried out in accordance with the operational parameters of the harvester’s internal combustion engine, ensuring the generation of the required hydraulic fluid flow rate and pressure to meet the demands of the hydraulic motors. The configuration, involving hydraulic pumps with relatively low flow rates and hydraulic motors with comparatively high flow rates, contributes to the efficient and stable performance of the system. Under these operating conditions, overloads are not observed. The pumps driven by the internal combustion engine are typically of variable displacement or variable geometry, while the motors used for driving the running wheels are of fixed geometry or fixed displacement. The selection of pumps and motors is based on the portion of engine power allocated for driving the running gear.