Speed ​​and ground preparation impact traction and fuel consumption.

The agricultural tractor is the main source of power used to perform various operations necessary in the production process of many commercially grown crops. A thorough understanding of the tractor's performance capabilities allows manufacturers to develop more efficient products, so that farmers can better utilize the operational characteristics of this machine.

To maximize the use of energy generated by the engine and transmitted to the drawbar, studies are needed on various load conditions on the drawbar, especially regarding its traction development. These tests aim to obtain information about the performance of the wheels related to the characteristics of their interaction with the ground.

Average drawbar yield values ​​for a mechanized unit can vary depending on several factors inherent to the machine, such as tractor make and model, power, and the engine's power-to-weight ratio. However, factors such as travel speed and soil preparation type also contribute significantly to higher or lower drawbar yield.

In a study conducted by the Integrated Center for Mechanization and Agricultural Projects (Nimpa) aimed at evaluating the performance of the tractor-seeder drawbar as a function of soil preparation and gear ratio, it was possible to verify the behavior of force and power at the drawbar.

Thus, a Tatu Marchesan brand seed drill/fertilizer applicator, model SDA³, continuous flow, 15 rows, with a maximum capacity of 595L and 570L in the seed and fertilizer hoppers, respectively, was used, where 50% of this volume was utilized. A 4x2 TDA (Front-Wheel Drive) tractor of 88,26kW (120hp) with front-wheel drive engaged was used to power the seed drill/fertilizer applicator.

The tractor-seeder unit was evaluated with three gear settings: L3T, L3C, and L4C, corresponding to speeds of 4,56 km/h, 5,71 km/h, and 7,63 km/h, respectively, and two types of soil preparation (plow + harrow and scarifier). For soil preparation, a fixed-disc plow was used, along with a Marchesan brand light trailed harrow, model GN, Off-Set, and a Marchesan brand scarifier, model AST/Matic 450, configured with five tines and a narrow tip with a clod-breaking roller.

The parameters evaluated were speed in km/h, average drawbar pull in kN, average drawbar pull in kW, and fuel consumption in L/h. The travel speed was determined by time, measured using a digital stopwatch, which was started and stopped according to the passage of the tractor's front wheels laterally to the stakes that delimited the length of the plots.

The values ​​of the force on the drawbar were obtained using an HBM brand load cell, model U 10M, with a sensitivity of 135kW. The HBM Quantum XMX804A data acquisition system, capable of monitoring and recording information at a frequency of 19.200Hz, was used to collect the load cell data. The power on the drawbar was calculated indirectly as a function of the traction force and the travel speed.

For the acquisition of fuel consumption data, an electronic system with pulse counters was used to obtain readings from the oval "Flowmate" brand flowmeters, model Oval M-III and LSF 41, with an accuracy of 0,01 ml, installed in series at the inlet and return of the injection pump, thus obtaining the volume of fuel consumed by the tractor.

The fact that the traction force is greater at higher speeds is associated with the direct relationship between force and speed; that is, the increase in force is directly proportional to the increase in speed. Figure 1 shows the increase in force on the drawbar with the increase in speed from 4,56 km/h to 5,71 km/h in the two types of soil preparation (plow + harrow and scarifier).

Regarding the drawbar power (Figure 2), higher values ​​were observed in the scarified soil (19,68 kW) and lower values ​​in the soil prepared using a plow and harrow (17,89 kW), a result that may be associated with the more consolidated soil condition, prepared using a plow and harrow.

For the different gear ratios, it was observed that the power demand at the drawbar increased with each gear ratio, reaching 25,44 kW for gear L4C (7,63 km/h), an increase of more than 50% when compared to gear L3T (4,56 km/h), since power is a product of traction force and speed, with the increase in force or speed being a coherent factor for the increase in required power.

Another very important point to consider regarding drawbar strength and power is fuel consumption. Figure 3 shows a significant increase in fuel consumption in L/h with the increased drawbar strength and power demand under both soil preparation conditions (plow + harrow and scarifier).

Final considerations

The type of soil preparation directly affects the performance of the drawbar, requiring greater force and power in less consolidated soil conditions. Increased speed results in greater availability of force and power at the drawbar. Increased fuel consumption is directly proportional to the increased demand for force and power at the drawbar.

*Per Marcelo Queiroz Amorim, Carlos Alessandro Chioderoli, Leonardo de Almeida Monteiro, Daniel Albiero, Elivânia Maria Sousa Nascimento e Danilo Roberto Loureiro, from UFC