Effect of Transmission Type on Wheel Slip under Overload – Presented on the Example of the AGT 835 T Tractors

During their occasional work on small forest holdings, forest owners often use tractors that are, as a rule, not intended for professional forest purposes. Due to their small size, these tractors are appropriate for cultivating smaller agricultural areas and, with additional forestry equipment, also for forestry operations. This paper analyses their performance at the capacity limits, since this type of use is possible but very limited due to their low technical characteristics. Here, a comparison is made between two AGT 835 T tractors produced in Slovenia, with the same basic characteristics but different types of the engine power transmission to the forest ground (comparison between a machine with a standard mechanical transmission system and a machine with a newer version of a hydro-mechanical transmission system). The analysis focuses on the wheel slip – this time only in the last meters of skidding when the slip reaches its peak and the tractors stop because of excessively demanding working conditions. Both tractors were used for skidding timber in the same working conditions – the same skid trail and the same load size. On the steepest section with a 27% longitudinal incline and under the load of 1 m, both tractors stopped due to excessively demanding working conditions. However, there was a fundamental difference between the two machines in the final section of skidding. The mechanical transmission system enabled rotation of tractor wheels, which led to a multi-fold increase in slip values (remarkable 80% in the last metre of movement). Contrary to that, the system with hydro-mechanical power transmission resulted in a substantially lower wheel slip (no more than 31%). In the latter case the tractor stopped due to excessively demanding working conditions but the hydro-mechanical steering system reduced the wheel slip. It is important to know that the selected transmission system can significantly influence the efficiency of transmitting power to the ground surface – with a smaller slip, which is also important for the forest ground and the environment

Merjenje mejnih sposobnosti pri spravilu lesa navzgor z gozdarskim traktorjem WOODY 110

The paper deals with the test results of uphill skidding of wood with a WOODY 110 cable skidder. The aim of the study was to find the limits of uphill skidding in relation to load size, log orientation and the slope. The trial was prepared on a test track of concave shape in the forest and with pre-designed loads of different sizes. The loads were skidded uphill once withbutt-end and then with top-end forward, until the tractor stopped because of the slope. The results show that butt-end forward skidding is more efficient. The difference between maximum loads at specific maximum slopes is almost constant (0.53 t). Proper load formation (butt-end forward if possible)is more important when skidding on steeper slopes.V članku obravnavamo spravilo lesa navzgor s traktorjem zgibnikom WOODY 110. Cilj študije je bil iskanje mej spravila lesa navzgor v odvisnosti od velikosti kosa lesa, orientacije bremena in naklona terena. Poskus smo pripravili v gozdu na testni vlaki konkavne oblike in z vnaprej pripravljenimibremeni. Bremena smo vlačili enkrat z debelim, enkrat s tankim koncem naprej, dokler se traktor ni zaustavil zaradi prevelikega naklona. Rezultati so pokazali, da je spravilo z debelim koncem naprej učinkovitejše. Razlika med maksimalnimi bremeni pri nekem naklonu je bila skoraj konstantna (0,53 t). Pravilno oblikovanje bremena (debeli konec naprej) je pomembnejše, kadar spravljamo les navzgor na večjih naklonih terena

Dinamika tehničnih parametrov traktorja WOODY 110 v območju zaustavljanja zaradi preobremenitve pri vlačenju lesa navzgor

The article deals with uphill wood skidding with WOODY 110 skidder and the changes taking place in technical parameters: slip, torque, tractive forces, and weight distribution of a loaded tractor in the last three meters of skidding, which is defined as a range of stopping due to overload. The test was performed on a concave skid trail, where tractor loaded with 8 meter long fir logs stopped at the 32% incline. It stopped somewhat later when skidding with butt-end forward in comparison to skidding with top-end forward. The loadweight with butt-end forward was 31.69 kN, whereas with top-end forward itweighed 33.53 kN. The measured speeds showed minute changes until the last meter, but decreased swiftly after stopping. Regarding some technical parameters, there were almost no changes at the end of stopping, two exceptions being the slip, which increased in the range of stopping, and the forward torque, which decreased in this range. The results showed that the hydrostatic transmission was efficient, considering that in a relatively well-controlled slip (the slip values increase only in the last three meters, which approximately equals the half of tractor\u27s length) there was less grounddamage.Članek obravnava vlačenje lesa z zgibnim traktorjem WOODY 110 navzgor, in sicer spremembe tehničnih parametrov: zdrsa, navora, vlečne sile in razporeditve teže traktorja z bremenom v zadnjih treh metrih vlačenja, ki smo ga imenovali območje ustavljanja zaradi preobremenitve. Poskus je potekal na konkavni vlaki, kjer se je traktor, ki je bil obremenjen s štirimi osemmetrskimi jelovimi hlodi, zaustavil pri naklonu 32 %, ko je vlačil les z debelim koncem naprej, in nekaj prej, ko je vlačil les s tankim koncem naprej.Breme je pri vlačenju z debelim koncem naprej tehtalo 31,69 kN, pri tankem koncu naprej pa 33,53 kN. Merjene hitrosti so skoraj do zadnjega metra pokazale majhne spremembe, nato pa so ob zaustavitvi hitro upadle. Pri nekaterih tehničnih parametrih prav tako skoraj do konca zaustavitve ne prihaja do bistvenih sprememb. Izjema je zdrs, ki v območju ustavljanja naraste, in navor spredaj, ki v tem območju upade. Rezultati kažejo, da je hidrostatski prenos učinkovit, saj z razmeroma dobro kontroliranim zdrsom (vrednosti zdrsa narastejo šele v zadnjih treh metrih, kar je enako približno polovici dolžine traktorja) prispevajo k manjšim poškodbam tal

Ugotavljanje maksimalnih bremen pri spravilu lesa s traktorji navzgor

The results of measuring maximum loads on different slopes when skidding uphill with WOO DY 110 cable skidder and adapted 4WD agricultural tractor AGT 835 are described in the article. Both tractors are very different and were chosen for the purpose of finding the limits of uphill skidding. Besides the slope, the pre-designated loads of different sizes and log orientation (butt-end or top-end forward) have been main variables. The trial was conducted on two concave shaped test skid trails in the forest. On the lower altitudes, the skid trails had small inclination, which slowly increased to 42% on the track where WOODY 110 was tested, and 27% where AGT 835 was measured. First the loads were skidded uphill with butt-end and then with top-end forward. The purpose was to choose too heavy loads, as we wished to stop tractors due to overload, but on different slopes. The proper load formation (butt-end forward if possible) in uphill skidding is most important on steeper skid trails. The dependency between maximum load and slope is linear. The calculated theoretical maximum load on horizontal surface enables us to make similar assessment for any other tractor weighing between 2 and 7 tons. For this purpose, John Deere 6220 and LIMB 80 LUXS adapted agricultural tractors for forest use were chosen and compared. The ratio between the tractor load on different slopes and tractor weight was calculated for all four tractors included in our comparison. Apart from the weight, tractor\u27s engine torque (power) has the decisive influence on the load size. Maximum loads on different slope categories were calculated according to different engine powers.Članek obravnava rezultate meritev spravila navzgor z gozdarskim traktorjem WOODY 110 in prilagojenim kmetijskim traktorjem s pogonom na štiri kolesa AGT 835 z mehanskim in hidrostatsko-mehanskim pogonom. Namen analize je bilo ugotavljanje maksimalnih bremen. Oba traktorja sta zelo različna in sta bila izbrana zato, da bi ocenili zmogljivosti traktorjev pri spravilu lesa navzgor. Poleg naklona vlake so bile spremenljivke še vnaprej določene velikosti bremen in njihove orientacije (z debelim oz. tanjšim koncem naprej). Meritve so bile opravljene v gozdu na dveh testnih vlakah konkavne oblike. Vlake so imele v spodnjem delu majhen naklon, ki se je pri vlaki za WOODY 110 povzpel na 42 % in na 27 % na vlaki, kjer je bil merjen AGT 835. Bremena so bila vlečena navzgor z debelim in v drugem poskusu s tankim koncem pri traktorju. Namen je bil izbrati pretežka bremena za takšne naklone, da bi se traktor zaradi preobremenitve zaustavil pri nekem naklonu vlake. Pokazalo se je, da je pri spravilu navzgor pravilno oblikovanje bremena (če je mogoče, z debelim koncem naprej) najpomembnejše na zelo strmih vlakah. Odvisnost največjega bremena in naklona vlake je linearna. Izračunano teoretično, največje breme na horizontalni podlagi omogoča oceno za katerikoli traktor, ki tehta med 2 in 7 tonami. V ta namen smo izbrali za spravilo lesa prilagojena kmetijska traktorja John Deere 6220 in LIMB 80 LUXS. Za vse štiri traktorje smo izračunali razmerje med največjim bremenom in težo traktorja. Na velikost največjega bremena poleg teže traktorja odločilno vpliva navor (in moč) motorja, zato je za različne kategorije terena izračunana odvisnost med največjim bremenom in močjo motorja

Zdrs koles pri vlačenju lesa s prilagojenim kmetijskim traktorjem AGT 835 T

The paper presents a wheelslip measurement method for small farm tractors (AGT835 T) adapted for skidding, with mechanical and hydrostatic mechanical transmissions. The research focused on uphill skidding, as slip values measured in uphill skidding are higher than in downhill skidding. A comparisonwas made of the performance of tractors carrying equal load but equipped with mechanical and hydrostatic transmission systems. The hydrostaticdrive causes higher negative load values in downhill skidding, and slightly higher slippage. As for hydrostatic tractors, wheelslip is higher in uphill skidding than in downhill skidding. The increase in the sloping of the terrain causes wheelslip to rise progressively. When a tractor travels uphill,slip is linked to a loss of energy. Wheelslip measurements are therefore important for determining the optimum conditions for individual tractor types.Predstavljena je metoda merjenja zdrsa na majhnih prilagojenih kmetijskih traktorjih - AGT 835 T - za spravilo lesa z mehansko in hidrostatsko-mehansko transmisijo. Poudarek je na spravilu lesa navzgor, kjer je bil ugotovljen tudivečji zdrs kot pri vožnji navzdol. Narejena je primerjava med mehansko in hidrostatsko transmisijo traktorja pri enaki obremenitvi. Hidrostatski pogon povzroča večje negativne obremenitve pri spravilu navzdol, in tudi nekaj večjizdrs. Pri spravilu navzgor je zdrs pri hidrostatski izvedbi znatno manjši. Naklon terena z večanjem progresivno vpliva na večanje zdrsa. Zdrs privožnji traktorjev navzgor pomeni izgubo energije, zato je meritev zdrsa pomembna za določanje optimalnih razmer posameznih tipov traktorjev

Krojenje iglavcev z glavo za izdelavo Woody 60 na žičnem žerjavu Syncrofalke 3T v predalpskih razmerah

The paper investigates mechanized bucking of conifers with a processor mounted on a cable crane system in the mountain conditions of the Alpine foothills. It analyses the measurement accuracy of various log types and explains its effect on the market price of these products. In the studied area, trees were felled by chain saw and the full-tree method was used to skid the felled trees to the cable yarder site using the Syncrofalke cable crane with a mounted Woody H 60 processor head. Further wood processing operations were carried out at the yarder site. Length measurement accuracy was illustrated through the frequency distribution and the modus of various lengths. The share of logs within a 5 cm interval - modus - (the best five) was 54.3%. The difference between the nominal log length and the minimum required length resulted in a loss of 4.38% of the total log value. Further more, it was established that the first quarter of the stem actually contained 64% of the total stem value. This means that the first cross-cut was responsible for nearly 50% of the total loss and the second crosscut pushed the figure to 80%. The present research only considered the losses incurred either by positive or negative cross-cut allowance or by insufficiently accurate length measurement of a certain log type.V članku obravnavamo strojno krojenje iglavcev s procesorjem na žičnici na objektu v predalpskem hribovju. Predstavljamo natančnost izmere posameznih sortimentov in njen vpliv na njihovo tržno vrednost. Posamezna drevesa so podrli z motorno žago in jih nato z žičnim žerjavom s stolpom Syncrofalke, na katerem je bil montiran procesor Woody H 60, z drevesno metodo spravili do stojišča žičnega žerjava. Na stojišču žičnice so opravili dodelavo. Natančnost merjenja dolžin smo ponazorili s pomočjo njihove frekvenčne porazdelitve in modusa. Izračun deleža sortimentov znotraj 5 cm širokega intervala, v sredini katerega je bil modus porazdelitve (the best five), je znašal 54,3 %. Zaradi razlike med dejansko dolžino hloda in minimalno zahtevano dolžino smo ugotovili izgubo v višini 4,38 % od vrednosti sortimentov. Ugotovili smo, da je v prvi četrtini debla 64 % njegove celotne vrednosti. Tako smo že ob prvem prerezu dosegli skoraj 50 % skupne izgube, pri drugem prerezu pa že več kot 80 %. To so zgolj izgube, ki so nastale zaradi prevelike ali premajhne nadmere pri določenem sortimentu, torej zaradi premalo natančne izmere dolžin posameznih sortimentov

Possibilities of Using Small Tractors for Forestry Operations on Private Property

The difficulty of working conditions and the scope of forestry operations dictate the selection of suitable tractors. In areas with the prevailing private, small and fragmented forest property structure, the small machines may also be applied. Due to their technical characteristics, their scope of operation is often somewhat limited. Nevertheless, these machines can represent a reasonable choice for less demanding working conditions. They may be used for thinning operations or for assembling small loads, mostly in the downhill skidding operations. In regard to the uphill skidding, they may only be applied where the working conditions so allow. The test included AGT 835, a small agricultural tractor, featuring basic forestry upgrades. The test determined its usability and suitability for working operations according to three factors: tractive force, load size and longitudinal skidding incline. The spatial analysis was conducted in regard to the suitability of forests, where the AGT 835 tractor could be used. The share of forest is shown where the tractor could be successfully applied in accordance with its limitations. The study encompassed only private forests, namely the forest areas featuring terrain slope and stand conditions that allow the use of small tractors in the first place. The analysis showed a relatively frequent possibility of using small tractors, which are suitable on a smallscale forest property and which are generally considered as less suitable for forest operations

Limiting forces and load masses during timber winching

Stabilnost traktora osim uzdužnog i poprečnog kuta stabilnosti podrazumijeva i sigurnost sidrenja traktora pri privitlavanju drva. Privitlavanje predstavlja vuču drvnih sortimenta po tlu od mjesta izrade u sječini do šumskog vozila za privlačenje drva opremljenog sa šumskim vitlom. Kod određenog graničnog tovara i nagiba terena dolazi do narušavanja uzdužne stabilnosti šumskog vozila s vitlom. Pri tome je faktor prijanjanja skidera i traktora sa podlogom važan pokazatelj mogućnosti sigurnog i pravilnog privitlavanja drva.Na osnovi općeg izraza za faktor prijanjaja skidera na ravnom terenu određen je faktor prijanjanja pri privitlavanju drva na nagibu te prikazan dinamički model opterećenja šumskog vozila pri privitlavanju drva.U rezultatima su prikazane granične horizontalne komponente sile u užetu i granične mase tovara u slučaju privitlavanja drva skiderom Ecotrac 120 V. Prema dobivenim vrijednostima graničnih horizontalnih komponenti sila u užetu može se zaključiti da je upravo stabilnost vozila definirana pomakom vozila u nazad granični uvjet privitlavanja drva. Prikazani model privitlavanja drva na nagibu prikazuje temeljni princip za određivanje graničnih tovara i nagiba terena, a koji se može lako prilagoditi ostalim uvjetima privitlavanja drva pri različitim položajima vozila i pravcima privitlavanja drva s obzirom na stvarne eksploatacijske uvjete.The stability of a forest vehicle apart from the longitudinal and transversal stability angle implies the safety of tractor anchoring during timber winching. Timber winching is a dragging of timber assortmens on the ground from the stump to a forest vehicle equipped with the forest winch. At a certain limiting load and slope of the terrain, disturbance of the longitudinal stability of the forest vehicle with the winch is occured. In this case, the adhesion factor of skidder and tractor on the ground is an important indicator of the possibility of safe and proper timber winching.The adhesion factor of the skidder during timber winching on the slope is detremined on the basis of the general expression of the adhesion factor on the skidder on the flat ground. Also, determined the dynamic model of the loading of the forest vehicle is presented during timber winching on the slope.The results show the horizontal components of forces in the rope and the limiting masses of the loads during timber winching by skidder Ecotrac 120 V. According to the obtained values of the horizontal components of forces in the rope, it can be concluded that the stability of the vehicle, defined by the displacement of the vehicle backwards is the limitation of the timber winching.The presented model of timber winching on the slope shows the basic principle for determining the limiting load masses and slope of the terrain, which can applied to all types of forest vehicles equipped with winch as well as easily be adapted to other conditions of timber winching at different positions of the vehicle and the direction of timber winching

Monitoring the Quality and Quantity of Beechwood from Tree to Sawmill Product

The analysis evaluates the potential and methods of the respective assessment of beech trees, beech logs and sawn timber. The objective of the study was to assess the impact of the quality of the incoming raw material (tree) on the quality and quantity of products – obtained at the sawmill. The study presents a model that indicates the relations between the assessment of the quality of a standing beech tree and the quality of the sawmill products obtained from its wood. In addition, relations between individual quality classes of sawlogs, pulpwood, energy wood and sawn timber are shown. Standing trees were assessed in three sites according to the national 5-grade quality scale, assortments produced from selected trees pursuant to the EN 1316-1 standard, and sawn timber produced from assortments according to the rules of the European Organisation of the Sawmill Industry (EOS). In total, 87.04 m3 of timber was harvested. In higher quality trees (quality 1 and 2), the shares of sawlogs were between 53% and 72% of gross tree volume, but in the poorest quality trees, the shares were only between 23% and 36%. What remained was pulp and energy wood. In trees of excellent quality (quality 1), sawlogs of the highest quality prevailed (A and B quality grade), while sawlogs of C and B quality prevailed in trees of lower quality. Covered knots and heart defects were typically the decisive criteria for classifying sawlogs quality in all three sites. A total of 30,786 m3 of unedged timber was sawn from the sawlogs, which comprised 35% of the total gross quantity of trees on average. Nine percent of the sawn timber was classified into the A–EOS class (top quality), 27% into the B–EOS class and 47% into the C–EOS class. Seventeen percent of the timber was only suitable for post-processing. The crucial criteria for classifying sawn timber were as follows: dead and rotten knots, heart, curvature and cracks. Above-average sawlogs (A and B quality grade) was mainly obtained from trees of better quality. Relations between the quality of trees, sawlogs and sawn timber indicated the suitability of classifying standing trees and sawlogs, since it was possible to produce sawn timber of higher quality from quality trees or logs. The model presents a rare attempt to establish and monitor quality and quantity from standing tree to end product

Links between beech tree quality and assortments made of them

V raziskavi smo obravnavali stoječe drevo, oceno njegove kakovosti in kakovost iz njega izdelanih sortimentov. Pri tem smo kritično obravnavali različna merila, ki so aktualna v praksi - petstopenjsko lestvico ocenjevanja kakovosti stoječih dreves, ki je v rabi na stalnih vzorčnih ploskvah, in aktualne standarde za ocenjevanje kakovosti izdelanih sortimentov. Na podlagi majhnega analiziranega vzorca ocenjenih in nato posekanih dreves smo ugotavljali povezave med kakovostjo dreves in sortimentov ter podobnosti in razlike, ki nastajajo, če pri presoji kakovosti sortimentov uporabljamo različna merila. Izpostavljamo problematiko različnih standardov, ki so trenutno veljavni pri nas ali pa jih pogosto uporabljamo v praksi.In our research we dealt with the standing tree, estimation of the standing tree, evaluation of its quality and evaluation of quality of assortments made of it. Thereby we critically discussed diverse criteria, currently used in the practice - the five-grade scale for standing tree evaluation, used on permanent sampling plots, and current standards for evaluating the quality of the produced assortments. On the basis of a small analyzed sample of the evaluated and afterwards felled trees we were determining links between quality of trees and assortments as well as similarities and differences occurring when we use different standards for estimation of assortments. We highlight the issues of diverse standards, which are currently valid or most frequently used in practice in Slovenia