Tire pressure and wheel load are both easily managed parameters which play a significant role in tillage operations for limiting slip which involves energy loss. To a great extent, this aspect affects the fuel consumption and the time required for soil tillage. The study was focused on the tire pressure and extra weight variation effect on fuel consumption and work productivity for soil tillage at normal tractor wheels slippage (7-15%). The experimental research unit composed of an 82.3 kW 4WD tractor and a reversible 4-bodies plough is presented. Tests were carried out on a stubble loam, where slip of tractor driving wheels was  15%, tractor front ballast mass was varied in the range from 0 to 520 kg and inflation pressure in the tires from 240 kPa to 100 kPa. Dependences of tractor performance indicators on ballast mass and tires inflation pressure are presented. When tractor tire slip varies in the range from 7 to 15 percent (which is normal slip in the soil), reducing the tires inflation pressure decreases the driving wheel slip and fuel consumption, while increases work productivity. Increasing the additional mass of the tractor (adding ballast weights) decreases the driving wheel slip, increases work productivity, but also increases fuel consumption and soil compaction.

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Tractors are the main machines in agricultural production processes. Agricultural tractors commonly employ a four-wheel drive transmission. To reach maximum efficiency in production works, tractors are loaded by as high thrust as possible. The consequence of it, quite often, is that the slippage of driving wheels grows to the limit that is not allowed. To reduce the slippage, various ways are pointed out in terramechanics. One way is to increase the tractor's weight by adding ballast. The other way is to increase the contact area between tires and the supporting surface. The slippage can be also reduced with traction control and other relevant systems. These methods, which help to reduce slippage, also affect tire deformation. When proportion of tires deformation is not the same as proportion of their sizes, the consequence is change of the lead of front wheels. In this paper analysis is presented, how the lead of front wheels affects the work of MFWD tractor in different conditions. Test results are presented for a MFWD tractor, how the lead of front wheels varies depending on deformation ratios between front and rear tires. For a MFWD tractor, values of deformation ratio between front and rear tires were determined, which ensured effective and which produced unreasonable values of lead of front wheels.

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Abstract. Tractor load influences engine work parameters having an influence on the working economy and productivity of the complete tractor aggregate. The operational economy and productivity of the tractor is mostly evident when its engine power is utilized at least at 80% and engine speed is as low as possible. The paper analyses the engine parameters of tractor Massey Ferguson MF 8480 during the operational period of road construction works. Control tests on the parameters of the engine load of the tractor engine in combination with the employed milling equipment WS 2500 produced by the company 'Wirtgen' were performed. The study was carried out using engine load tables and graphs collected and stored in the so called ECU Load Profile integrated in Electronic Engine Control Units. Theoretical analysis was made and an equation presented to establish the relation between engine power, engine speed and the quantities of cyclic fuel consumption. The study results present the distribution graphs of work time and fuel consumption at different engine speed during the operational period. The paper also indicates engine load and fuel consumption graphs of the tractor in combination with milling equipment. The article has also disclosed that the analysis of engine speed and load modes using information obtained from tractor-integrated digital microprocessors reveals the operation quality of the tractor.

The wheel slippage of agricultural tractors is a critical parameter for fuel consumption and field performance. Optimally it should be in the range of 8-12 % and should not exceed 15 %. Therefore, during assembling agricultural units, it is not enough to consider the traction characteristics, but also the recommended value of the slippage must be followed. Of the available solutions to decrease the tractor driving wheel slippage is to decrease the air pressure in the tires and increase the additional mass (ballast weight) of the tractor, avoid tilling soil that is too wet or too dry and choose the right implement, tillage speed and depth. The wheels' slippage could be reduced with a traction control and other relevant tractor systems. Agricultural/field applications require tractors with 4WD or 2WD driving systems. Engaging the four-wheel drive, when using the tractor for tillage operations, also can decrease the wheel slippage. In any case, the fuel consumption must be taken into consideration. For the theoretical calculation of the optimal tractor wheel slippage it is important to know the attraction factor dependence on the size of the traction force and the vertical load on the tires and the tire pressure indicators as well. However, literature analysis shows that known tractor wheel slippage determination mathematical modules do not take into consideration the tire inflation pressure. The goal of this study is to investigate the tire air pressure influence on the driving wheel slippage, tractive force and the traction coefficient for 4WD and 2WD driving systems of the tractor. With help of mathematical equations the traction force and wheel slippage coefficient dependencies on the air pressure in tractor tires are calculated. As well, according to the research result data, the wheel slippage forecasting methodology based on the numerical evaluation of the tire inflation pressure for 4WD and 2WD driving systems of the tractor is provided.