Justification of Power/Weight Ratio of a Wheel Tractor on the Basis of Data of Control Dynamometer Test of the Aggregate
The purpose of the study was to determine the compliance of the traction-speed performance of the tractor, included into the composition of a machine-tractor unit (MTU), to the requirements of aggregation, taking into account the random nature of changes in the external operating factors. The work was carried out on the example of MTU Fendt 936 Vario + AVA-12.6 “Agropitatel” in the Leninsk-Kuznetsky district of the Kemerovo region in 2017. The method of control dynamometer test established probabilistic characteristic of traction resistance of an agricultural machine, its dependence on the speed at primary tillage and intra-soil application of liquid fertilizers. The tests were conducted on medium-humic podzolized chernozem soil against a stubble background at the depth of tillage and plant fertilizing of 21 cm and the average rut of 1100 m. The modified values of traction resistance of the MTU (to the speed of 5 km/h) were 5.04 kN/m and 6.14 kN/m for tillage and fertilizing operations, respectively. The coefficients of proportionality were 0.034 s2/m2 and 0.030 s2/m2, and the variation coefficients were 2.1% and 3.5% (p was less than 0.05), respectively. Tractor Fendt 936 Vario did not meet the requirements for working speed and propulsion skidding while operating at average specific traction resistance M(k0) within the range of 4.38-6.56 kN/m. The calculated average value of the required nominal rated power of the engine of the aggregate power unit (APU) was 349.8 kW (476 h.p.), so the required operational weight for the unit to perform the loosening operation was 221.3 kN with the need for additional loading up to 251.8 kN for the work of MTU in the mode of plant-feeder. The APU with the calculated parameters will have a power/weight ratio of 1.39-1.58 kW/kN and will provide an increase in traction efficiency by 4.7-13.6% in comparison with the Fendt 936 Vario tractor; it will cause an increase in the average working traction on the hook by 8.1-8.2%, implemented without violating the established requirements. As a result, the average operating speeds of the MTU will increase by 20.2-27.5% and its net hourly productivity will grow by 22.8-27.3%.