DESIGNING FRAMEWORK OF A SEGMENTED RUBBER TRACKED VEHICLE FOR SEPANG PEAT TERRAIN IN MALAYSIA

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1 DESIGNING FRAMEWORK OF A SEGMENTED RUBBER TRACKED VEHICLE FOR SEPANG PEAT TERRAIN IN MALAYSIA ATAUR RAHMAN, AZMI YAHAYA, MOHD. ZOHADIE, DESA AHMAD AND WAN ISHAK Faculty of Engineering, Univeity Putra Malaysia, 43400, Serdang, Selangor, Malaysia Abstract: The focus of this aer is to resent the designing framework of an off-road secial segmented rubber tracked vehicle that may be required to run on low bearing caacity eat terrain. To comlete this study: tly, mechanical roerties of the eat terrain were t determined by using different tye of aaratus. Direct shear test was erformed using a Wykeham Farrance 540 shear box aaratus to determine the internal friction angle, cohesiveness and shear deformation modulus of the eat samle. Load-sinkage test was erformed using a secially made bearing caacity aaratus to determine the stiffness values of surface mat and underlying eat. Secondly, substantiate the validity of the mathematical model and nally design aramete of the secial segmented rubber tracked vehicle were otimized by simulation. Keywords: Tracked vehicle, eat terrain, tractive erformance. 1. INTRODUCTION In Malaysia, new requirements for greater mobility over a wide range of eat terrain, and growing demands for environmental rotection and collection-transortation goods by vehicles on unreared eat terrain constitute a signicant art of the overall transortation activities. This has led to the necessity of develoing segmented rubber tracked vehicle and establishing mathematical models for the vehicle-eat terrain systems, that will enable design enginee, as well as use, to evaluate a wide range of otions for the selection of an otimum conguration for a given mission and environment. Various organizations in Malaysia are introduced different tye of machines for erforming several tasks on eat land. The machines suitabilities were justied based on the mechanical roerties [] of Seang eat land. It was found that the engine ower of all the machines are quite reasonable based on their carrying caacity. However, the tractive erformances is severely affected due to the higher ground ressure distribution. Corresonding author 1

2 . MATERIALS AND METHODS The feasibility of the land locomotion of the tracked vehicle oerating on the weak eat terrain is discussed from the eective of the terramechanics. Figure 1 shows the rocesses for designing a segmented tracked vehicle. This aer resents the discussion until the design arameter otimization technique. Segmented Track Vehicle Oerating Terrain- Peat Mechanical Proerties of Peat Design Paramete Selection and otimization Algorithm Validity Develoed Algorithm Basic Design Paramete Identication Hydraulic Power Estimation Engine Power Requirement Auto CAD Design Construction Field Test Fig. 1: Flow chart for the rocesses of designing a segmented tracked vehicle..1 Mechanical Proerties of Peat Terrain To roerly identify the mechanical roerties of eat from a vehicle mobility viewoint, measurement has been taken under loading conditions similar to those exerted by a vehicle on the eat terrain. Field tests were carried out at Seang eat area, located about 45 km from Kuala Lumur Malaysia for determining the mechanical roerties of eat terrain including moisture content, bulk density, cohesiveness, internal friction angle, shear deformation modulus, vane shearing strength, surface mat stiffness, and underlying stiffness of eat. The mechanical roerties of Seang eat terrain including the terrain moisture content, bulk density d, eat surface mat stiffness m m, underlying stiffness of eat k, cohesiveness c, internal frictional angle, and shear deformation modulus K w that are found from an earlier work [] are given in Table 1.

3 Table 1. Peat terrain aramete. Paramete Un-drained Drained Mean value SD Mean value SD, (%) d, (kn/m 3 ) c, kn/m ) , (degree) Kw, (cm) m m,(kn/m 3 ) k, (kn/m 3 ) Notication: SD-Standard deviation, Source [].. Mathematical Model Consider a rigid link segmented rubber track vehicle of weight W, track size including track ground contact length L, width B, itch T, and grouser height H, radius of the front idler R, rear srocket R, and road-wheel R w, and height of center of gravity (C.G) h cg, which is traveing under traction on a eat terrain at a constant seed of v t and alied a driving torque Q at the rear srocket by the hydraulic motor as in Fig. 10. If the ressure distribution in the track-terrain interface is assumed to be non-uniform by locating vehicle C.G rearward of the track mid oint, the vehicle will travee on the secied terrain by making an angle ti. Consequently, the track entry and exit angles at the front idler and rear srocket, the reaction ressure at the front idler P, main straight art Po, and rear srocket P, and the sinkage of the front idler z, main straight art z m, and rear srocket z and tangential force reveal different values due to the different amount of sliage at each of the grouser ositions of the rigid link tracks at the bottom track elements of the front idler i, main straight arts i m, and rear srocket i as shown in Fig.. Fig. : Force acting on the track system of the vehicle during traveing on eat terrain with a sliage of 10%. 3

4 The following assumtions were made in order for the equation used in the mathematical modelling to be valided: i. Vehicle theoretical seed was considered to be 10 km/hr on zero sloe terrain ii. iii. iv. based on various off-road oerations ASAE D497.3 NOV96, ASAE standard (1996). Vehicle total weight was considered to be 19.6 kn with ayload of 9.81kN based on the in-eld maximum fresh bunches collection racticed. Vehicle s track critical sinkage was considered to be 0.1m based on exerimental data on Seang Peat terrain []. Aerodynamic resistance was neglected, due to the low oerating seed. v. Vehicle s belly drag was considered to be zero since the vehicle hull was not in contact with the terrain. vi. Vehicle seed fluctuation was considered to be.75% based on Wong [7]. vii. Road-wheel sacing was considered to be 0.45m to ensure good drawbar erformance based on Wong [7]...1 Sliage Sliage is one of the functional aramete for the vehicle traction mechanism. It reveals different value at the bottom track art of front idler, main straight art, and rear srocket if the vehicle travees on unreared eat terrain with non-uniform ground ressure distribution. Therefore, it is imortant to comute the sliage of the front idler, track main straight art, and rear srocket searately to determine the vehicle erformance over the eat terrain. For the sliage of the ground contact track of front idler, the relationshi between the front idler sliage i, the entry angle of the track at front idler, the track trim angle ti, the sliage ratio i and front idler radius R can be modeled by the following equation [5]. i R isin 1 ti sin (1) ti L where, the sli ratio, i v v t a, track trim angle, ti arcsin vt entry angle arccos cos z R and L ti R z z L, and track. For the sliage of the ground contact track of rear srocket, the relationshi between the sliage of rear srocket i and front idler i, rear srocket radius R, the track entry ti 4

5 angle,, the track trim angle ti, and exit angle can be modeled by the following equation of Ataur et al.[5] : i L R isin i i 1 ti sinti L L () where, track exit angle front idler, z k D 4m m z arcsin z arccos L R z z h k D 4 m h m D h m m R, sinkage of the, sinkage of the rear srocket, k D h k D h D h 4 4 m m m m m m z, hydraulic diameter of the terrain due to front 4BL b idler, Dh, rear srocket, 4BLb Dh and L R ti. L B L B b.. Tractive Effort The tractive effort is denveloed not only on the ground contact art of the track but also on the side arts of the ground contact track grouser and on arts of front idler and rear srocket. The initial track tension 1% of the total vehicle weight is assumed to be constant in every oint of the track system in order to avoid the track deflection aarently between consecutive road-wheels..3 Ground Contact Part of the Track The traction mechanics of the track bottom art of the front idler, road-wheels, and rear srocket are different due to its different angle of entry and exit. It is also different due to the different sinkage of the track front idler, main straight art, and rear srocket when the vehicle travees on the unreared eat terrain with non-uniform ground ressure distribution. Therefore, it is imortant to comute the traction of the individual comonents bottom track segment, searately. For the tractive effort develoed at the track ground contact length of the front idler, the relationshi between the tractive effort F b develoed at the ground contact track, track ground contact length L, track width B, terrain cohesiveness c, normal stress, shear stress, shear deformation modulus Kw, and sliage ratio of the track-terrain interfaces i can be modeled by the following equation of Ataur et al.[5]: 1 e K K F b BL b c 1 i L b i L b b w w b tan 1 ex (3) i K L w 5

6 with L b R ti The tractive effort of the track main straight art and rear srocket ground contact track was comuted by Eq. (3)..4 Side of the Ground Contact Track Wong [7] suggested that the traction mechanics of the track at the side of the grouser is highly signicant on the develoment of vehicle traction if the vehicle sinkage is more than the grouser height. In this study, it was assumed that the sinkage of the vehicle was more than the grouser height of the vehicles track. For the tractive effort develoed at the side of the ground contact length of the front idler track, the relationshi between the tractive effort Fs develoed at the side of the track ground contact art, track grouser height H, track ground contact length L, terrain cohesiveness c, normal stress, shear stress, shear deformation modulus K w, and sliage i of the vehicle track-terrain interfaces can be modeled by the following equation of Ataur et al. [5]: 1 e K w K w i L F s 4HL b c tan cos 1 ex 1 i L b i L b K with arctan cot b (4) H B The tractive effort at the side of the track main straight art and rear srocket ground contact track was comuted using Eq. (4)..5 Motion Resistance When the same vehicle as shown in Fig., travees on the eat terrain with nonuniform ressure distribution, the vehicle individual comonents such as front idler, main straight art, and rear srocket reveal different values of motion resistances due to the different sinkages. Therefore, it is imortant to comute the motion resistance of the individual comonent for undetanding the vehicle erformance. For the motion resistance of the vehicle due to terrain comaction R c, the ground contact length L, track width B, sinkage of the vehicle z, stiffness of eat surface mat mm and underlying eat k can be modeled by equation of Ataur et al. [5]: w L k z 4 3 Lm k z mm z L 3Dh L Rc B L k z 4 3 m mz L 3Dh m 4 3D hm m 3 mzm (5) 6

7 where D h 4 BL, L B D hm 4BL m, and L B m D h 4 BL L B For the motion resistance of the vehicle due to bull dozing effect, the relationshi between the motion resistance of the vehicle due to bull dozing effect Rb, the bulk density of the terrain d, the internal frictional angle, track width B, and terrain cohesiveness c can be modeled by the following general equation of Wong [7]: R B z tan 45 cz tan 45 (6) b d The total external motion resistance of the rubber track vehicle R tm, can be comuted as the sum of the individual motion resistance comonents by: Retm R c Rmsc Rc Rb Rmsb Rb (7).6 Srocket Torque When torque is alied at the srocket, it starts driving the track and the vehicle starts moving. A frictional torque aea in the bearings of moving elements of the track system, resisting the vehicle motion. The forces aear at the track interface due to the terrain comaction and vehicle bulldozing effect, resisting the vehicle motion. Therefore, the vehicle needs to develo sufcient tractive effort after develoing shear stress at the track-terrain interface in order to move forward and overcoming all of the motion resistance. The tension in each track segment does not affect the torque of the vehicle motion since it was assumed to be constant due to the geometrical arrangement of the road-wheel and initial tension equals to 1% of the total weight of the vehicle. For the torque of the srocket, the relationshi between the torque of the srocket Q, vehicle total tractive effort F tt, total motion resistance R tm, srocket radius R, track grouser height H, vehicle total weight W, and vehicle normal reaction force Fn and track ground contact length L can be modeled by using the following equation: Q R H W h cg R sin ti LF n W 0.5 ecos ti D (8) where F n W F tt sin cos ti ti.7 Vehicle Steerability The force system assumed to be acting on a tracked vehicle in general lanar motion is shown in Fig. 3 and Fig. 4. In these gures, Fot and Fit are the thrusts on the outer and inner tracks. R lnot and R lnit are the longitudinal forces exerted by the terrain to er unit length of the outer and inner track, fr and l are the coefcients of the longitudinal and 7

8 lateral motion resistance, resectively, B stc is the vehicle tracks tread, F cent is the centrifugal force and is the sli angle. Fig. 3: Force acting on the track during turning at 6 km/hr. Fig. 4. Force acting on the track during turning at 10 km/hr. During a turn, centrifugal force aea at the mass centre of the vehicle. When the vehicle turns at a traveling seed of 6 km/hr with locating C.G at the middle of the track system, the sli angle of the vehicle is assumed to be zero due to negligible effect of centrifugal forces. The lateral motion resistance assumed to be equally distributed around the C.G of the vehicle and reresented by equal triangles F1 to F4 as shown in Fig. 3. When the vehicle turns at a traveling seed of 10km/hr with locating C.G at 0.0 m rearward from the middle oint of the track system, the sli angle of the track system is considered signicant higher value and signicantly affect the vehicle stability and 8

9 steerability. Therefore, the lateral force distributions on the track system to be congruent are reresented by the triangles F1 to F4 as shown in Fig. 4. The vehicle must have rotated about an instantaneous center oint O located at a distance of D ahead of the vehicle C.G for the dynamic equilibrium. This force is generated by a shift to the oint O ahead of C.G and the vehicle will be oriented by an sli angle, which can be comuted as arctan L, the yaw velocity of the vehicle can be comuted as 4gl ot it R,where, R is the radius of the srocket. The vehicle follows the R dashed trajectory, turning to the right around the instantaneous centre oint O with turning radius R..8 Dynamic Load on the Tracks From the sliage equations of the outer and the inner track it can be identied that when the loading condition of the vehicle changes, as the vehicle is accelerating, the sliages of the vehicle track changes. Therefore, in order to adjust the vehicle sliage on given terrain it is necessary to estimate the roer loading condition for getting the high steerability of the vehicle The centrifugal force of the vehicle that will develo during turning at seed of 10km/hr can be comuted as Fcent W R cos g, which causes lateral load transfer. The weight transfer from the inner track to the outer track is mainly due to the centrifugal force. If the centrifugal force is taken into consideration the dynamic loads of the outside and inside track will be different. For the dynamic load of the vehicle outer and inner track, the relationshi between the dynamic load of outside and inside track W ot and W it, yaw movement of the vehicle, turning radius R, sli angle and acceleration due to gravity g, can be modeled using the following equations of Ataur et al.[3]: W W ot it W hcgw R cos (9) B g stc W hcgw R cos (10) B g stc where D arctan R Drawbar ull The drawbar ower is referred to as the otential roductivity of the vehicle, that is, the rate at which roductive work may be done. It is comuted using the following equation: P D V (11) d a with D F tt R tm 9

10 Tractive efciency Tractive efciency is used to characterize the efciency of the track vehicle in transforming the engine ower to the ower available at the drawbar. It is dened by the following equation: P d d (1) Pe 3. MATHEMATICAL MODEL VALIDATION The drawbar ull and the tractive efciency of light eat rototye Kubota Carrier RC0P track vehicle having track width of 0.43 m, track ground contact length of 1.85 m, total weight of 645 kg including ayload 1000 kg and three neumatic road-wheels on each track, oerating on a eat terrain were redicted through simulation. Basic aramete of the reference vehicle that used in the study are shown in Table. Table. Basic aramete of Kubota Carrier RC0P track vehicle. Paramete Symbol Values Vehicle aramete Machine weight, kn W 1645 Max. loading caacity, kn W l 1000 Rated ower, kw@rm P 8.@300 Track aramete Ground contact length, m L 1.85 Width, m B 0.43 Grouser height, m H 0.05 Machine aramete Length, m L t.98 Width, m B t 1.76 Height, m Ht 1.45 Ground clearance, m G c 0.7 Source: Ooi [6] Table 3 shows that the regression model is highly signicant at a signicance level of P r0.01. In the regression model, t values of for i and 7.84 for i are higher than t* 16 (0.01)=.69. Hence, the null hyothesis is rejected. This imlies that the sliage of the vehicle has signicant effect on the drawbar ull of the vehicle. A standard error value of 0.03 for i and for i are concluded that both of the redicted and measured drawbar ull is retty tightly bunched together. The variability of the redicted and measured drawbar ulls of the vehicle has the less variability around the best tted regression line, i 0.005( i ) where, D is the drawbar ull of the D vehicle in kn and i is the sliage of the vehicle in ercentage. Therefore, based on the 10

11 vehicle estimated standard error of 0.03 and the R-square values of 0.967, it can be concluded that the redicted and the measured drawbar ull are strongly correlated. Table 3: Regression analysis on the drawbar ull of Kubota Carrier RC0P track vehicle. Source df SS F value P value R square Model Error C total Estimated Parameter Intercet i i Coefcient T for H0: Parameter= Standard Error P r T Table 4 shows that the sliage of the vehicle signicantly (Pr 0.01) affects the vehicle drawbar ull. While, the non-signicant value of treatments (redicted and measured drawbar ull) indicates that there is no signicant difference between the treatments. Therefore, the close agreement between the redicted and measured drawbar ull of the vehicle substantiates the validity of the simulation model. Table 4: ANOVA on the drawbar ull of Kubota Carrier RC0P track vehicle Sliage Treatment Error Total Table 5 shows that the regression model is highly signicant at signicance level of Pr0.01. In the regression model, t values of.91 for i and for i are higher than t* 35(0.01) =.67. Hence, the null hyothesis is rejected. This imlies that the sliage of the vehicle has signicant effect on the tractive efciency of the vehicle. The standard error values of 0.3 for i and for i concluded that both of the redicted and measured drawbar ull are retty tightly bunched together. The variability of the redicted and measured drawbar ulls of the vehicle have less variability around the best tted regression line, T ( i) i where, T is the tractive efciency of the vehicle in ercentage and i is the sliage of the vehicle in ercentage. Therefore, based on the standard error estimated values of the vehicle of 0.3 and the R-square value of 0.79, it can be concluded that the redicted and the measured drawbar ulls are strongly correlated. 11

12 Table 5: Regression analysis on the tractive efciency of Kubota Carrier RC0P track vehicle. Source df SS F value P Model Error C total Estimate Coefcien T for H0: Standar P rt Intercet Table 6 shows that the sliage of the vehicle signicantly (P r 0.01) affects the tractive efciency of the vehicle. The non-signicant value of treatments (redicted and measured tractive efciency) indicates that there is no signicant difference between the treatments on the model. Therefore, the closed agreement between the redicted and measured tractive efciency of the vehicle substantiates the validity of the simulation model. Table 6: ANOVA on the tractive efciency of Kubota Carrier RC0P track vehicle. Source df SS F value P value Sliage Treatment Error 18.8 Total VEHICLE DESIGN PARAMETERS OPTIMIZATION Tractive erformance of the rigid link segmented rubber tracked vehicle has been comuted with the comuter simulation method based on the new mathematical model for undrained eat terrain. It aeared that the engine size and tractive erformance of the vehicle on eat terrain vary with: the variation of vehicle weight, track size including track ground contact length, width, itch and grouser height track entry and exit angle, idler diameter and location, srocket diameter and location, road-wheel diameter, sacing and geometrical arrangement, and location of center of gravity. Therefore, for the selection and otimization design aramete of the vehicle track size, idler diameter and location, srocket diameter and location, number of road-wheel, road-wheel diameter, sacing and geometrical arrangement, ratio of the road wheel sacing to track itch, ratio of the srocket diameter to track itch, and the location of the center of gravity are taken into account. The otimization design aramete of the vehicle have been erformed by using the Microsoft Excel software with erforming calculations, analyzing information and managing lists in sreadsheets. 1

13 4.1 Track Width and Ground Contact Length The length of the track in contact with the ground and the level of ressure within the ground are the most imortant facto that influenced tracked vehicle tractive erformance. To evaluate the effects of track system conguration on the vehicle ground ressure distribution and surface mat stiffness, it is imortant to study track ground contact length and width. Figures 5(a) and 5(b) show that the vehicle ground ressure distribution decreases with increasing vehicle track ground contact length and width. The vehicles under consideration are traveing on a zero sloe terrain with a travel seed of 10 km/hr. From the eld exeriment on Seang, it was found that the bearing caacity for the undrained eat terrain was 17 kn/m. It aea that if a ground contact ressure of the 19.6 kn vehicle, with a moderate ayload of 5.89 kn, is limited to kn/m by designing a track with ground contact area of 30x000 mm then the sinkage and external motion resistance of the vehicle will be low and tractive effort will be high, yielding a desired travel seed of 10 km/hr and vehicle roductivity. Ground contact ressure,kn/m Track w idth,m Ground contact ressure, kn/m Track Ground contact length,m 11.77kN vehicle 17.65kN vehicle kN vehicle 1.5kN vehicle 17.65kN vehicle Fig. 5: Variation of ground ressure distribution with (a) variation of track width at constant track ground contact length of 00 cm and (b) variation of track ground contact length at constant track width of 30 cm. Figures. 6 (a) and 6(b) show that the sinkage of the vehicle decreases with increasing track width and track ground contact length. If the track size of the vehicles is limited to 300 x 000 mm, then the sinkage of the kn, kn, and 1.5 kn vehicles will be 61, 81.8, and 110 mm, resectively. From the eld exeriment, it was found that the surface mat thickness of the Seang eat terrain was 100 mm, which will suort the maximum load of the vehicle during static and dynamic as well. Therefore, if the vehicle sinkage is more than 100 mm the vehicle will sink rather than travee. If the vehicle total weight is considered to 19.6 kn and the track ground contact area to 300x000 mm, the vehicle will travee on the eat terrain with sinkage of 90 mm or 10 % less than the Seang eat terrain surface mat thickness and exit ground ressure of 16 kn/m or 6 % less than the wot condition Seang eat terrain bearing caacity. Based on the 19.6 kn vehicle sinkage and ground contact ressure, it may be conclude that the vehicle will not 13

14 in risk to travee on eat terrain if the vehicle used the track ground contact area of 300x000 mm. Sinkage,m Track width,m 11.77kN vehicle 17.65kN vehicle 1.5kN vehicle Sinkage,cm Track Ground Contact Length,cm Vehicle weight, 11.77kN Vehicle weight,17.65kn Vehicle weight, 1.5kN Fig. 6: Variation of vehicle sinkage with (a) variation of track width at constant track ground contact length of 00 cm and (b) variation of track ground contact length at constant track width of 30 cm. Therefore, the best choice is to select a vehicle track ground contact area of 300x000 mm for the vehicle to roduce an effective tractive erformance. The conclusion is further suorted by the relation between the track size and motion resistance with keeing otion either track width or track ground contact length could increase to adjust the track ground contact area for getting the desired vehicle ground contact ressure. Figures 7(a) and 7(b) show that the motion resistance coefcient of the vehicle increases with increasing track width and decreases with increasing track ground contact length. Figure 7(a) shows that the motion resistance coefcient increased 18.1 % for kn vehicle, % for kn vehicle and 4.1 % for 1.58 kn vehicle with increasing the track width from 0. to 0.4m when the track ground contact length considered to kee in constant at.0m. Whereas, Fig. 7(b) shows that the vehicle motion resistance coefcient of the vehicle decreased 1.09 % for kn vehicle, 4.07% for kn vehicle and 4.5 % for 1.58 kn vehicle with increasing the track ground contact length from 1.3 to.m when the track width considered to kee in constant at 0.3m. From the justication of vehicle motion resistance coefcient based on vehicle track width and track ground contact length, it could be noted that the vehicle track ground contact length should be considered to increase instead of increase the track width in order to get the vehicle lower ground contact ressure of 16 kn/m on Seang eat terrain. Therefore, it was found that for a given overall dimension of 300x000 mm track system, the maximum motion resistance coefcient of the 19.6 kn vehicle is 5.4 %, which could be good enough for a track vehicle on soft terrain [7]. 14

15 0 Motion resistance coefcient,% Track width,m 11.77kN vehicle 17.65kN vehicle 1.5kN vehicle Motion resistance coefcient,% Track ground contact length,m 11.77kN vehicle 17.65kN vehicle 1.5kN vehicle Fig. 7: Effect of track size on vehicle tractive erformance (a) track width and (b) track ground contact Based on Figs. 8(a) and 8(b), it could be ointed out that if the 19.6 kn vehicle track size is considered to be 300x000 mm, the vehicle ground ressure exit on track-terrain interfaces is 16 kn/m with sinkage of 90mm and motion resistance coefcient of 5.4%. Therefore, the 19.6 kn vehicle track system overall dimension can be otimized by selecting track width of 300 mm and ground contact length of 000 mm. Track entry angle,degree Track entry Idler angle, diameter,m degree Sinkage,m Fig. 8: Relationshi between track entry angle, sinkage and idler diameter. 4. Track Grouser Size To fully utilize the shear strength of the eat surface mat for generating tractive effort, the use of grouser on tracks would be required. From the eld exeriment on Seang, it was found that the shear strength of the eat surface mat is considerably higher than that of the underlying eat deosit and that there is well dened shear-off oint beyond which the resistance to shearing is signicantly reduced. This would, however, considerably Sinkage,m 15

16 increase the risk of tearing off the surface mat unless the sli of the track is roerly controlled. Thus, the use of aggressive grouser on vehicles for use in organic terrain does not aear to be desirable from traction as well as environmental viewoints. The surface mat thickness of Seang eat terrain was found to be about 0.1m. In order to fully utilize the shear strength of the surface mat and to increase the trafc ability of the terrain the grouser height of the track is considered to be 0.06 m. 4.3 Srocket Location and Size The location of drive srocket has a noticeable effect on the vehicle tractive erformance. Wong et al. [6] (1986) reorted that in forward motion, the to run of the track is subjected to higher tension when the srocket is located at the front than when the srocket is located at the rear. Thus, with a front srocket drive, a larger roortion of the track is subjected to higher tension and the overall elongation and internal losses of the track will be higher than with a rear srocket drive. With higher elongation, more track length is available for deflection and the track segments between road-wheels take fewer loads and the vibration of the track increase, which will cause the fluctuation of the track. Consequently, the sinkage and motion resistance will be higher and the mobility of the vehicle will be affected severely on the unreared eat terrain. Therefore, the srocket could be considered to locate at the rear art of the track system conguration in order to distribute the vehicle normal ressure to the track-terrain interfaces uniformly. The center oint of the srocket is considered the (0,0) coordinate system of the vehicle. Generally, it could be mentioned that the srocket is the most imortant comonent of the vehicle track system, which roels the vehicle with sufcient torque, control the vehicle seed fluctuation and maintain the vehicle tractive erformance. Therefore, the size of the srocket can be determined from the relationshi between the relationshi between the srocket torque, vehicle seed fluctuation, and vehicle turning radius. From the simulation result, it was found that the ratio of the srocket diameter to track itch have signicant effect on the vehicle tractive erformance. Therefore, the ratio of the srocket itch diameter to track itch should be a value which will stand to meet the eld requirement. Further suort to otimize the srocket size of the vehicle track system, the following equation on vehicle seed fluctuation can be considered. For the relation of vehicle seed fluctuation and the ratio of the vehicle srocket itch diameter to tract itch the following mathematical model of Wong [7]can be used: D r s T (13) where is the seed fluctuation in ercentage, track itch in roortion. D T is the srocket itch diameter to Using D T equals to 4.00, the comuted value of is 3.17%. According to Wong [7], the industrial and agricultural track vehicle seed fluctuation should be in the range of 3.7 to.75%. Since the seed fluctuation of the vehicle was found of 3.17%, the ratio of 16

17 the vehicle srocket itch diameter to track itch can be otimized at Consequently, the srocket itch diameter was otimized at 400mm by using the track itch of 100mm. 4.4 Idler location and size Idler is located at.0 m front of the track system. It was earlier reorted that the surface mat thickness of Seang eat terrain in the ranged of 100 to 50 mm which is considered the suorting latform of the vehicle. It could be noted that if the sinkage of any vehicle on the Seang eat terrain is more than 100mm will cause the vehicle to bog down. Furthermore, from the simulation it was found that the track entry angle was signicantly affect the vehicle front idler size and tractive erformance. Therefore, from the relationshi between the vehicle sinkage, track entry angle and idler diameter, the idler diameter can be identied. Figure 8 shows that the vehicle track entry angle at front idler and sinkage decreases with increasing vehicle front idler diameter. If the vehicle critical sinkage of the vehicle is considered to 100 mm, the corresonding front idler diameter and track entry angle were found 400 mm and 78, resectively. This conclusion can be further suorted from the relationshi between the track entry angle, sliage and vehicle tractive erformance. Figure 9 shows that the relationshi between the vehicle track entry angle, sliage, and tractive efciency. At track entry angle 78, the vehicle sliage and tractive efciency were found 18% and 70.5%, resectively, which was found at srocket itch diameter of 400mm. Therefore, the front idler diameter 400mm can be otimized at 400mm for getting the tractive efciency of the vehicle 70.5% and high roductivity. Tractive efciency,% Track Entry Angle,degree Sliage, % Tractive efciency,% Sliage,% Fig. 9: Track entry angle, tractive erformance and sliage. 4.5 Roadwheel diameter, Track itch, and Number of Roadwheel Wong [7] reorted that the ratio of road wheel sacing to track itch is a signicant arameter that affects the tractive erformance of tracked vehicle, articularly on soft terrain. The decrease in the track motion resistance coefcient with the increase of the number of road wheels was rimarily due to the reduction in the eak ressures and 17

18 sinkage under the road wheels. The longer track itch would lead to an imrovement in tractive erformance over soft terrain. But, it may cause a wider fluctuation in vehicle seed and higher associated vibration. Consequently, a roer comromise between tractive erformance and smoothness of oeration must be struck. Road-wheel diameter can be redicted based on the following equation: S r D1 D G (14) where, Sr is the road-wheel sacing in mm, D1 is the t road-wheel diameter in mm, D is the second road-wheel diameter in mm and G is the ga between consecutive roadwheel is assumed to be 5mm for avoiding the track deflection between the consecutive road-wheel. In the track system all the road-wheel dimension (D 1 = D =------= D 7) are considered as equal size. If the roadwheel sacing equals to 5mm, the ga between two consecutive road-wheel on the track system equals to 5 mm, the comuted value of roadwheel diameter equals to 0 mm. Figure 10 shows that the vehicle drawbar ull increases with increasing the ratio roadwheel sacing to track itch and tractive efciency increases with increasing the ratio of road-wheel sacing to track itch until.1 and then decreases with further increasing of the ratio of road-wheel sacing to track itch. If the ratio of road-wheel sacing to track itch is considered to be.5, the tractive efciency of the vehicle is found 70.5%. Whereas, the tractive efciency of the vehicle is found 70.5% for the otimum srocket itch diameter of 400 mm and idler diamete of 400 mm. Therefore, the ratio of roadwheel sacing to track itch should be.5 if the otimum srocket itch diameter and idler diamete each is limited to 400 mm. By using S r/t equals to.5 and S r equals to 5mm, the comuted value of T equals to 100 mm. The number of road-wheels can be comuted based on Fig. by the following equation [5]: n r L ( D D ) D r s r G where, L is the total ground contact length in mm, D is the outside diameter of the srocket in mm, D and D r are the diameter of the front idler and road-wheel in mm and n r is the number of road-wheel. The outside diameter of the srocket (i.e, D D H ) is considered to 460mm based on the grouser height. By using L equals to 00 mm, D equals to 460 mm, D equals to 400 mm, Dr equals to 0 mm, G equals to 5mm, the comuted value of n r is 7. Therefore, total number of roadwheel seven with diameter of 0 mm on the 19.6 kn vehicle track system would signicantly reduce vehicle vibration during traveing on the unreared eat terrain by making zero deflection of the track between two consecutive road-wheel. (15) 18

19 4.6 Center of Gravity Location Center of gravity of a tracked vehicle is a most imortant design arameter for getting the high tractive erformance. Figure 10 shows that the tractive efciency of the vehicle increases steely with increasing the sliage of the vehicle until a certain value and then start to decrease with increasing the sliage of the vehicle. The vehicle under consideration with total weight 19.6 kn including ayload of 5.89 kn is traveing on a zero sloe terrain with traveling seed of 10 km/hr. Figure 11 shows the maximum tractive efciency of 79.8% at 11% sliage for the vehicle with center of gravity located at 300 mm rearward from the mid-oint of the track ground contact length and 70.5% at 1% sliage for the vehicle with center of gravity located at the mid-oint of the track ground contact length. Tractive efciency,% Ratio of roadw heel sacing to track itch Tractive efciency,% Drawbar ull,kn Drawbar ull,kn Fig. 10: Relationshi between tractive efciency, drawbar ull and the ratio of the road-wheel sacing to track itch 75 Tractive efciency,% Sliage, % Center of gravity at midoint of track Center of gravity at 0.m rearward track middle Fig. 11: Relationshi between tractive efciency and sliage. 19

20 From the comarison of the vehicle based on the location of center of gravity, it is found that the tractive efciency of the vehicle with center of gravity is located at 00 mm rearward from the mid oint of the track ground contact length is 13.% higher than the tractive efciency of the vehicle with the center of gravity is located at the mid-oint of the track ground contact length. The variation of tractive efciency is found between the vehicle with the locations of center of gravity due to the difference of external motion resistance. It could be ointed out that the vehicle with location of center of gravity at 00mm rearward from the mid oint of the track ground contact length reveals lower sinkage at the frontal art of the track ground contact art causes the lower external motion resistance and the vehicle consume lower engine ower for develoing effective tractive effort in order to travee the vehicle easily on the low bearing caacity eat terrain. Whereas, the vehicle with location of center of gravity at the midoint of the track ground contact length reveals the equal sinkage to all over the ground contact art causes the higher external motion resistance and vehicle consume maximum engine ower for develoing the required tractive effort in order to travee the vehicle on the low bearing caacity eat terrain. Therefore, the vehicle center of gravity location of 300mm rearward from the mid-oint of the track ground contact length could be otimized the center of gravity location for the vehicle. The basic design aramete of the vehicle found from the simulation study are shown in Table 7 Table 7. Basic design aramete of the secial segmented rubber tracked vehicle Vehicle Paramete Total weight including 9.81kN ayload, kn W 19.6 Vehicle traveling seed, km/hr v t 10 Center of gravity, x coordinate, m x cg Centre of gravity, y coordinate,m y cg 0.45 Srocket itch diameter, m D 0.40 Idler diameter, m D 0.40 Idler center, x coordinate, m x c -.0 Idler center, y coordinate, m y c 0 Number of road-wheels (each side) n 7 Road-wheel diameter, m Dr 0. Road-wheel sacing, m Sr 0.5 Number of suorting rolle (each side) ns 3 Suorting rolle diameter, m Ds 0.0 Track Paramete Track total length (each side), m L c 5.90 Track itch, m T 0.10 Track width, m B 0.30 Track ground contact length, m L.00 Road-wheel sacing to track itch S r/t.5 Vehicle seed fluctuation, ercentage 3.17 Grouser height, m H 0.06 Note: Coordinates origin is at the center of the srocket. Positive x and y coordinates are to the rear and to, resectively. 0

21 5. CONCLUSION The following conclusions were made based on the analysis of this aer: Based on the results of mechanical roerties of eat in the area studied, the mean values for moisture content of %, bulk density of 1.53 kn/m 3, cohesiveness of 1.36kN/m 3, internal friction angle of 6., shear deformation modulus of 11. mm, surface mat stiffness of 13.6 kn/m 3, and underlying eat stiffness of kn/m 3. Based on the results of detailed study on vehicle aramete, an otimized track system conguration for the 19.6 kn vehicle has seven roadwheels with diameter of 0.4 m, a track itch of 0.1m, a ratio of the initial track tension to vehicle weight of 1 %, a location of center of gravity at 30cm rearward of the mid-oint of the track ground contact length ensure the vehicle to develo the maximum tractive efciency of 74 % during traveing at 10km/hr on the secied eat terrain. Based on the simulation study, it was found that the track itch, number of road wheels, and location of centre of gravity have noticeable effects on the tractive erformance of the vehicle. The maximum tractive efciency of the vehicle is in the range of 74 to 7 % and 50 to 48% with the sli range of 9 to1 % when the vehicle traveled at 10km/hr without ayload and with ayload, resectively. Furthermore, the tractive efciency of the vehicle with center of gravity located at 300mm rearward of the mid-oint of track ground contact length are 10% higher than the vehicle center of gravity located at the mid-oint of track ground contact length. ACKNOWLEDGEMENT This research roject is classied under RM7 IRPA Project No The autho are very grateful to the Ministry of Science, Technology and the Environment of Malaysia for granting the nancial assistance. REFERENCES [1] ASAE, Agricultural Enginee Yearbook of Standards, American Society of Agricultural Enginee, Michigan,1996. [] R. Ataur, Y. Azmi, M. Zohadie, A. Desa, W. Ishak, and A. Kheiralla, Mechanical Proerties in Relation to Vehicle Mobility of Seang Peat Terrain in Malaysia, Journal of Terramechanics, 41(1), 4-45, 004. [3] R. Ataur, Y. Azmi, M. Zohadie, D. Ahmad, and W. Ishak, Simulated Steerability Of A Segmented Rubber Tracked Vehicle During Turning On Seang Peat Terrain in Malaysia, Int. J. of Heavy Vehicle Systems (IJHVS), Indecience Publisher, UK: Vol.1, No., , 005a. [4] R. Ataur, Y. Azmi, M. Zohadie, D. Ahmad, and W. Ishak Design and Develoment of a Segmented Rubber Tracked Vehicle for Seang Peat Terrain in Malaysia, Int. J. of Heavy Vehicle Systems (IJHVS), Indecience Publisher, UK: Vol.1 No.3, 005b 1

22 [5] Ataur, R., Azmi, Y., Zohadie, M. Ishak, W and Ahmad, D. Design Paramete Otimization Simulation of a Segmented Rubber Tracked Vehicle for Seang Peat in Malaysia, American Journal of Alied Science, Science Publications, New York, USA: Vol.(3), , 005c. [6] H.S. Ooi Performance of Modied Kubota Carrier RC0P and Porter P6-11 on eat soil, MARDI Reort no.110, [7] J.Y. Wong Otimization of design aramete of rigid-link track systems using an advanced comuter aided method, Proc. Instn. Mech. Eng, 08(D), , 1998.