TEKA. COMMISSION OF MOTOIZATION AN ENEGETICS IN AGICULTUE 2013, Vol. 13, No. 1, 3 8 Evaluation o changes in traction properties o tyres on selected arming suraces Włodzimierz Białczyk, Marek Brennensthul, Anna Cudzik, Jarosław Czarnecki Institute o Agricultural Engineering, Wroclaw University o Environmental and Lie Sciences ul. Chełmońskiego 37/41, 51-630 Wrocław, e-mail: marek.brennensthul@up.wroc.pl eceived January 5.2013; accepted March 14.2013 Summary. The paper presents the results o tests on two tractor tyres with dierent designs and external dimensions; these tyres were tested on arming suraces with various properties. The tests were carried out using a stand operating with a arm tractor. Changes in traction properties were evaluated; values o orces were analysed, and the balance o power on the tested wheels was established. It was demonstrated that the two tyres reacted in dierent ways to the change o surace. Key words: ing resistance, power balance INTOUCTION Farm tractors are the main sources o pulling energy in arming. Currently, a substantial group includes multi-purpose tractors with lower pulling classes, one superior eature o these vehicles is variety o application. Such tractors can tation work, quite oten they are also used in other special purpose tasks. The consequence o arm tractor versatility is the act that they are used on dierentiated suraces with various properties. The manner o utilisation is connected with dierent conditions o interaction between the vehicle wheels and the surace. On more deormable suraces, a bigger immersion o the wheel will occur, as a result o which traction orce will be transerred by shearing o the top layer o the surace. On the other hand, on less deormable suraces, where immersion o the wheel is limited, the phenomenon o riction will prevail during transer o traction orce [15, 22, 25]. It should be mentioned that or economic reasons multi-purpose arm tractors are usually equipped with one set o tyres tyres are not replaced when the type o surace changes. It is reasonable to ask the question: what type o tyres will be optimal or the multi-purpose arm tractor? In the literature, studies discussing compatibility o arm vehicle tyres with suraces o various properties can be ound. It was proven that on suraces with lower strength, greater amounts o wheel rolling resistance and slip occurred, and as a consequence greater losses power on the outlet and intake o the wheel/surace system, but does not show with what phenomena losses in it seems reasonable to carry out power balancing which will describe in detail what proportion o power is used in the orm o pulling orce and how much power is lost to rolling resistance and wheel slip [24]. Until now, this issue It is reasonable to examine it with respect to various tyres on dierent suraces. The causes presented in the introduction led to the undertaking o tests the objectives o which were to: determine and compare the values o traction orce, o wheels provided with dierent tyres, analyse changes o tractive properties as a result o changes o surace type, determine the power o wheels provided with the tested tyres on dierent suraces based on the completed energy balance. Two tyres were accepted or testing diering both in internal design and external dimensions. One common ea- producer o both tyres. The basic parameters o the tested tyres are presented in Table 1.
4 Ta b l e 1. Parameters o tyres accepted or testing Tyre esign diameter [mm] Width [mm] eight o tread protrusions [mm] [kg] pressure 11.224 radial 285 1215 diagonal 785 25 11.224 was characterized by greater external diameter and height o tread protrusions, but lesser width. uring testing, one level o static vertical load o wheels was used - dictated by the act that it is typical or the multi-purpose nature o the arm tractor operation. Following acceptance o the concept, the tests were perormed on two suraces with dierent properties. The one ground orest road. The conditions o both suraces were characterized on the basis o conducted measurements o moisture, compactness and shearing stresses. The results o these measurements are presented in table 2; the values o compactness and shearing stresses were established using mean values calculated or the measurement depth o Ta b l e 2. Parameters o the tested suraces Parameter Surace moisture [%] compactness shearing stresses [kpa] Stubble 7 Tests o tractive properties were conducted using a specialist stand suitable or operation with a arm tractor, class Fig. 1. Scheme o the stand or testing tractive properties (description in the text) (2). rive or the tested wheel mounted on the shat (8) was obtained rom the power take-o o the tractor (1) through - was located between the ront and rear parts o the rame. ment o the actual distance, a potentiometric sensor placed near the additional wheel (11) was used, and the theoretical distance was determined using a sensor (12) placed near transmitted to an electronic registering unit operating with a portable computer. Testing o traction properties consisted in transmitting drive to the tested wheel and setting the stand and the tractor in motion together. uring driving, data measured part o the measurement, the stand was braked using the as a result a ull range o slipping or the tested wheel was obtained. wheels and values o traction orce, pulling orce and trac- s 100 1, st [1] M O PT, r [2] P P P T P r 100 M O, [4] where:, s actual distance o the wheel [m], st theoretical distance o the wheel [m], PT traction orce [N], MO wheel torque [Nm], r dynamic radius o the wheel [m], P rolling resistance [N], P pulling orce [N],
. 5 The value o dynamic radius (r) was determined based on the measured value o the distance covered by the wheel during ten ull rotations. Power balancing o wheels equipped with the tested tyres was carried out based on values determined according N N N, [5] k N N P v N P v, [7] N T PT r vt r v v T r T, [8] where: Nk power supplied to the wheel (total) [W], N pulling, N power lost to overcome rolling resistance [W], power lost to slipping [W], v actual velocity (ratio o actual distance to measurement time) [ms -1 ], vt theoretical velocity (ratio o theoretical distance to measurement time) [ms -1 ]. Figure 2 presents the courses o traction orce as a unction o slipping o wheels equipped with the tested tyres, on both types o surace. traction orce [N]. 11.224 stubble 11.224 ground road 5 15 25 Fig. 2. Courses o traction orce o the tested tyres on both tested suraces as a unction o wheel slip tion orce within the entire slip range considered concerned tyre 11.224 on the stubble. The greatest growth o this The value o traction orce or tyre 11.224 on the road and the road; in this case, the lowest growth o traction orce with low slip values was also recorded. To some extent, the courses obtained relates to results presented in the literature. It was shown that traction orce increases at the highest rate the values o the traction orce o tyres with dierent diameters is associated with more deormable suraces, which is Since traction orce is the sum o pulling orce and rolling resistance, it is reasonable to present the proportions o these components. The summary o mean values o these pulling orce, rolling resistance [N] 1475 Fig. 3. Summary o mean values o pulling orce and rolling resistance or the tested tyres on both suraces with slips within orce P is traction orce PT) The analysis o the above summary allows us to conclude that both tyres on various suraces were characterized by similar values o pulling orce (relative dierence did not exceed 5%). owever, dierences in the values o rolling resistance were larger. On both suraces, higher values o this parameter were obtained by tyre 11.214, or this tyre also a higher change in rolling resistance as a result o changing the surace type was observed. Tyre 11.224 had smaller width so it should be assumed that the higher rolling resistance is the eect o its greater immersion in the surace. In all cases, values o rolling resistance were higher than values o pulling orce this situation was connected to the method o conducting the measurement; the resistance o motion o the entire stand consisted o rolling resistance o the tested wheel and rolling resistance o the tractor wheels within which the stand was operating. The results presented correspond with the results o other researchers; it was proven that higher values o traction orce (that is the sum o pulling orce and rolling resistance) were also highlighted that on less resistant suraces, the values o results o the completed tests. with traction orce, it was presented as a unction o slip the courses are presented in Figure 4. While analysing the above courses, it can be observed highest values and growths o the analysed parameter appear - 1441 stubble ground road stubble ground road 11.224 P P
tractive eiciency [%]. 11.224 stubble 11.224 ground road 5 15 25 Fig. 4. tested suraces as a unction o wheel slip ciency concerned tyre 11.224 on the stubble, and the lowest on the stubble were caused by higher deormability o this surace, and as a consequence higher rolling resistance. In ad- this tyre on the stubble was higher. The character o changes presented in the literature; it was proven that the highest occurred were higher than in the obtained test results [17, 18]. It was also demonstrated that tyres with larger external - scribe accurately the type o energy losses that dominate in the wheel/surace system. ence it is reasonable to perorm energy balancing which will show what part o the power supplied to the wheel is used in the orm o pulling orce and what parts o power are lost to rolling resistance and wheel slip. Figure 5 illustrates courses o power as a unction o slip on the stubble. cluded that the character o changes in individual powers as a unction o slip was similar or both wheels, however the values o these powers made the dierence. igher values o power were achieved by the wheel with tyre 11.224. increases in pulling power, power lost to rolling resistance pulling power and power lost to rolling resistance showed small changes and lack o growth. In both cases, power lost to slip was showed growth proportional to slip, and or the noticed ater exceeding 15% slip. slip on the ground road. ter o courses is slightly dierent than in the case described a. Nk N N b. Nk N N 5 15 25 5 15 25 Fig. 5. a. Nk N N b. Nk N N 5 15 25 5 15 25 Fig. 6.
7 were lower than on the stubble. The highest increases in total power, pulling power and power lost to rolling resist- rolling resistance were maintained at a similar level, when slip was higher, higher values related to power lost to rolling resistance. Power lost to slip or both wheels showed growth proportional to the growth o slip, a slightly higher growth rate was recorded or the wheel with tyre 11.224. The character o changes in power as a unction o slip is similar to other test results. It was proven that the greatest increase in pulling power, power lost to rolling resistance and total power occurred at low slips, ater which the courses was stabilized, the character o changes in power lost to slip In order to determine dierences between values o individual powers, mean values o these calculated or slip within this summary, higher values o total power occurred or the wheel with tyre 11.224. For both wheels, higher demand or total power appeared on the stubble, and or the wheel with tyre 11.224 the dierence in the values o power on the two suraces was higher than or the other wheel. This situation is probably connected with a dierent degree o deormability or the two tested suraces and as a consequence dierent can be the act that the greatest dierences concerned only power lost to wheel rolling resistance. Since the values o total power presented above diered, comparison o the two wheels on the tested suraces required presentation o the shares o individual powers in total power. Such summary is illustrated in Figure 8. proportions o shares o power or the two tyres were dierent; there was also dissimilarity with respect to various suraces. The highest shares o pulling or both wheels occurred on the ground road, and the lowest share o this power occurred or the wheel with tyre 11.224 on the stubble. In this case, the highest share o power lost to rolling resistance was also observed. Furthermore, it can be observed that shares o individual powers as a result o change o surace type. ierent proportions o power shares on individual suraces are probably connected with the dierent degrees o deormability o these suraces and dierent values o wheels to the change o surace type can be the result o was characterized by greater width, hence its immersion eect could be smaller than or tyre 11.224. Similar values regarding shares o power lost to slipping or both wheels can be caused by a similar design o tread. The obtained results were processed using statistical analysis. Since the requirement regarding applicability o - accepting the hypothesis that the given actor lacks an essential el, this hypothesis will be rejected (the actor has an essential pulling orce and power lost to slipping was ound. The obtained results enabled ormulation o the ollowing conclusions: 1. The tyres reacted to the change o surace in dierent ways; larger dierences in traction properties on dierent suraces were present or tyre 11.224. on the ground road which was the result o the lesser tendency o this surace to deorm, and as a consequence lower rolling resistance. 52 115 127 stubble ground road stubble ground road N N share o power [%]. 15 14 57 41 stubble ground road stubble ground road N N 11.224 11.224 Fig. 7. Summary o mean power values calculated or slip within Fig. 8. Summary o shares o pulling power and lost power in total power Ta b l e 2. esults o statistical analysis (p probability level) Factor P P P T N k N N N Surace type Tyre design
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