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2010, vol. 36, br. 1, str. 10-20
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Uticaj ekscentrične vuče na vučne karakteristike traktora točkaša
The influence of eccentric traction on the traction characteristics of wheeled tractors
Projekat: Projekat Ministarstva nauke Republike Srbije, br. 20078: Unapređenje energetskih i ekoloških efikasnosti traktora i mobilnih sistema
Keywords: wheeled tractor; power delivery efficiency; eccentric traction
Sažetak
Ekscentrična vuča nastaje kao posledica lošeg položaja priključne mašine u odnosu na traktor, kada se linija vuče traktora i linija otpora oruđa ne poklapaju, nego su međusobno paralelne. Najčešći slučaj pojave ekscentrične vuče u praksi je kod traktorskog agregata za oranje. U ovom radu ispitivan je uticaj ekscentrične vuče na vučne karakteristike traktora točkaša. Posmatran je uticaj ekscentričnosti na vučnu snagu, vučni stepen korisnosti i koeficijent neto vuče traktora. Ispitivanja su obavljena na strnjici simuliranjem stvarnih uslova koji se pojavljuju u toku rada s ekscentričnom vučom, i to paralelnim pomeranjem pravca delovanja vučne sile traktora izvan njegove podužne ose. Pravac delovanja vučne sile traktora tokom ispitivanja paralelno je pomeran izvan podužne ose udesno (e = 0) za vrednost ekscentra e = 160 mm i e = 320 mm. Utvrđeno je da je vučni stepen iskorišćenja traktora na strnjici, pri ekscentričnoj vuči e = 160 mm, manji za 13,69%, a pri e = 320 mm za 27,71% u odnosu na centričnu vuču. Optimalnim agregatiranjem traktora i priključne mašine izbegava se pojava ekscentrične vuče, postižu se uštede u radu, smanjuju gubici u vremenu, kvalitet obavljenog posla je na višem nivou, a rizici od havarija manji. Optimalno agregatiranje podrazumeva odabir i podešavanje priključnog oruđa sa traktorom kod kojeg se sila vuče i otpor vuče slažu i po intenzitetu i po pravcu.
Abstract
Agricultural tractors are basically a mobile source of energy necessary for conduction of technological operations in agriculture. Agricultural tractors should have optimal performance depending on the requirements imposed by agrotechnics and technology for the production of healthy safe food. During fuel combustion in the engine of a tractor, heat energy is released and then converted into mechanical energy. The energy is distributed to the drive mechanism of tractor through the transmission system. Tractors performing agrotechnical operations with towed machines use rather low level of fuel energy, rating from 20 to 30%, and in the conditions of high humidity and uncultivated land, this fuel use is even less than 20%. The efficiency of tractor system, while the traction force is transferred to attachment over the drawbar, is expressed with power delivery efficiency of a tractor. Power delivery efficiency shows how much available engine power is used for the tractor's drawbar. The tractors with high power delivery efficiency have good energetic efficiency. Tractor's traction efficiency is influenced by numerous factors such as: type and condition of soil, pneumatic tires construction and pressure, eccentric and transverse traction etc. The eccentric traction is defined as a factor with the highest influence on power delivery efficiency of the wheeled tractor. Eccentric traction occurs as a consequence of bad position of tractor attachment, when traction line of the tractor and resistance line of the instrument are parallel and do not coincide. The most common occurrence of eccentric traction in practice is in the tractor aggregate for plowing. Elimination of eccentric traction becomes even more significant when considering the fact that 60% of total energy necessary for a single cycle of agricultural production is spent on plowing. The occurrence of eccentric traction can be avoided by optimal tractor and attachment aggregation, which can also lead to labor saving, reducing time losses, enhancing quality of work, and reducing risk of breaking down. Optimal aggregation means choosing and setting up attachments with a tractor, where the traction force and traction resistance have equal intensity and direction. The aim of this research was to determine the influence of eccentric traction on traction characteristics of wheeled tractor for different eccentricity values. The influence of eccentricity on drawbar power, power delivery efficiency and net traction ratio of a tractor were observed in this paper. The researches were conducted on stubble by simulating real conditions, under which the work with eccentric traction was carried out, and by paralelly changing the directions of traction force of the tractor beyond its longitudinal axis. During the research, the direction of traction force was paralelly changed beyond longitudinal axis on the right (e = 0) for the eccentre value of e = 160 mm and e = 320 mm. It was determined that the power delivery efficiency on stubble at eccentric traction of e = 160 mm was lower by 13,69%, and at e = 320 mm it was lower by 27,71% in comparison to centric traction. Based on the eccentric traction influence and optimal aggregation, it was possible to maximize the potential traction characteristics of tractor and increase its energetic efficiency.
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