Evaluation of Turnability of Tracked Vehicle

Transcription

1 JARQ 3, ) Evaluation of Turnability of Tracked Veicle Nobutaka ITO Department of Bioproduction and Macinery, Faculty of Bioresources, Mie University Tsu, Mie, 514 Japan) Abstract Rice combine arvester is one of te typical agricultural macines developed in te process of rice production in Japan. Recently 5 kinds of turning metods ave been introduced in wic 3 of tem ave already been applied to commercial macines wile te oter 2 are subjected to experimentation for future commercialization. In tis paper, te turning metods were evaluated from different viewpoints in terms of smoot turning wit less energy and less disturbance of te top soil in paddy fields wit empasis placed on 1) energy conservation, 2) safety and 3) automation. Discipline: Agricultural macinery Additional key words: rice cultivation, top soil disturbance, operation efficiency, arvesting operation, turning metod Introduction Various types of tracked veicles are used not only in agriculture and forestry but also in te field of construction macinery and military operations because of teir outstanding mobility and maneuverability especially in roug terrain. Current trend of tracked veicle is caracterized by te use of rubber track equipment wic is environment-friendly. Tis condition is important for practical applications in agricultural macines suc as rice combine arvester and construction veicles like bulldozers and excavators. Turning metods tat are currently used can be classified into 5 systems: I) Pivot turn system In tis system, te veicle turns wit one track being operated wile te oter is not operated and/ or braked. Bot tracks are in full contact wit te ground surface no control of contact area of tracks) 7 >. 2) Pivot turn system wit control Basically tis system is te same as te pivot turn system, except tat te contact lengt wit te ground surface of te braked track is sortened to reduce te turning motion resisting moment >. 3) Spin turn Since bot tracks are operated in opposite directions during te turning motion, sortening of te turning radius and completion of te turning motion can be acieved quickly and smootly. As a consequence owever, more power is consumed 1 >. 4) Soft turn Tis system as been recently applied to commercial macines. Bot tracks are operated in te same direction but te speed is different. As a result, te turning radius is larger, but top soil disturbance is reduced wen te veicle is turning 1 >. 5) Turntable metod In tis system, turning takes place by using a turntable and not by te running gear. Operator's safety can be secured in addition to smoot turning motion. Typical application of tis system can be seen in excavators, one of te construction macines 3 5 >. Among te turning systems listed above, systems 1), 3) and 4) ave already been applied to commercial macines. Te oter 2 systems 2) and 5) were proposed by te autor, but tey are not practically applied yet. In tis paper, te evaluation of te 2 turning systems wic te autor proposed was discussed in terms of practical use in agriculture and comparison wit pivot turn system as standard basis. Pivot turn system As stated earlier, te contact lengt of te braked track is sortened to reduce te turning motion resisting moment, as sown in te following equation

2 25 JARQ 34) 1996 Tuming direction <Pb Fig. 2. Relationsip between te work requirement and te turning angle for pivot turn sys1em witout control Fig. J. Conventional pivot turn system wi1ou1 co111rol Turning direction for braked track Fig. I). Mo = _!_ µ.p1bl 2, P1 = 4 w 2bL... I) L I Mo = - µ. WL... 2) 8 were L: ground contact lengt of braked track m)' b : ground contact widt of braked track m), W: load acting on bot tracks N), µ. : coefficient of friction between te track and ground surface, /J-o: coefficient of rolling resistance of te track, R: turning radius m). Assuming tat F1 is te driving force of te operated track and F1' is te frictional resistance for te tracks, te rolling resistance of te operated track, Qi, can be expressed as: w Q, = - /J-... 3) 2 For a braked track, te rolling resistance Q2 =, since it is not moving. Considering te momenta! balance at point, F1 - Q1) = 2Mo, ten, te driving force required for turning can be expressed as: µwl W Fi = ---+ µ ) Te work required for turning, E J) can be expressed \ operated './t I..,,./ Fig y ~ B ',,.,,, Pivo1 rnrn system wi1 control of co111act lengt of track by using te turning angle ip rad) as follows: Eo = FJR</> = --+ µ.. - Rip... 5) µ. WL W) Fig. 2 sows te relationsip between te work required for turning EoJ) and te turning angle <borad). It can be concluded tat te work required for turning increased proportionally wit te increase of te turning angle of te track. Pivot turn system wit control Fig. 3 sows a scematic representation of a pivot turn system wit control of te contact lengt from L to L, for braked track in turning motion. Turning motion resisting moment under tis condition becomes

3 N. Ito: Evaluarion of Tuma/Ji/it)! for Tracked Veicle M1 = - µwl,.... 6) 8 For te driving force F1, it is expressed as sown below: µwl + Lr) F 1 = + µ ) 88 2 Te work required for turning in tis system E,J) can be derived by using te turning angle of track cf>, rad). E, = +--,cf>, ) W µl + L,) fto )wr 1 W were L,: controlled ground contact lengt of track m), R,: turning radius of pivot turn wit control m). In te above equation, te second term on te rigtand side, W)/2, indicates te work required for lifting te braked track up 1 te eigt,, were te time for tis controlled motion was relatively sort and te eigt, was very small compared to te contact lengt. Fig. 4 sows te relationsip between te work required for turning, E,J) and te turning angle of track cf>, rad). It is obvious tat in tis system, a braked track is controlled 1 sorten te ground contact lengt and reduce te turning motion resisting moment. Terefore te work, W)/2, is required as soon as te lllrning motion starts. However once te turning motion proceeds, te work required increases wit a comparatively lower rate tan in te pivot turn system previously described. Comparison between pivot turn system and pivot turn system wit control It was already demonstrated based on te equations presented earlier tat te sortening of te ground contact lengt must be witin a limited range sufficient to support te load acting on te braked track to be more effective in reducing te turning motion resisting moment and to improve te turnability of te tracked veicle. Actual mecanism for practical application was also proposed troug te prototype veicle used in te experiment Fig. 4). Pivot turn system wit control can be recommended for reducing te turning motion resisting moment. However te additional controlling unit wic must be installed will also increase te macine price. Terefore a comparison of te cost/performance of te macines sould be made for evaluation. Fig. 5 sows a grap of te relationsip between te work required for turning and te turning angle for bot pivot turn system and te system wit control. Improvement of turnability can be acieved by te following metods: I) by sortening te lengt OQ = W/2) in E-cf> grap as muc as possible or 2) by lowering te slope OP in E-</> grap as muc as possible. For metod 1), eiter W or or bot W and must be reduced for actual use. For metod 2), controlled ground contact lengt of track sould be minimized as muc as possible, wic can be mecanically determined using te value of eigt,. In Fig. 5, point P is te intersection point of 2 lines of te work graps of te 2 turning systems pivot turn and tat wit control). Te turning angle cf>b corresponding to te point P indicates te boundary turning angle to determine wic turn system sould Pivot tum ---;,,-<I> t wit control ---</> </>b Fig. 4. Rela1ionsip between work requirement and turning angle for pivot turn system wit control Fig. 5. Comparison of te work between pivot turn system wit control and te one witout control

4 252 JARQ 34) 1996 be applied. In conclusion, a) t e pivot turn system can be recommended wen te veicle is turned or steered in te range were te turning angle is less tan </>b, owever b) te pivot turn system wit control of te contact lengt sould be used wen te veicle needs to turn or to be steered over a range were te turning angle exceeds <Pb Te value for te boundary turning angle <l>b can be determined by te measurement during te field test for practical application. Te equation for estimating te value of te turning angle <l>b can be derived as follows: Let 2 equations 5) and 8) be equal: Eo = E 1. Ten, µl µo) W<J,oR = µl + L,) +..E.Q..) WR,</>,+ _I W' In te above equation, c/>o = <J,, = <l>b, <Pb = L LR - L+L, R,)+µo R - R,) ) Te boundary turning angle <Jib can be expressed as te function of L, L,, R, R,. B,, µ, µ. ): <l>b = fl, L,, R, R,, B,, µ., µ ). Considering te non-dimensional values sown below and substituting tem in te above equation, c/>b can be rewritten as: <l>b = _ µ_ LRI - I + Ki K2) + P.o RI - K2) ) If R = R,. ten K2 = I. Rearranging equation 1) tf,t, = ) _L LR I - I + Kt ) 2B 2 Calculation for practical application Te estimation of te value for <l>b using te following data taken from te actual commercial macine combine arvester) is sown ere: =5 mm, µ=.7, L = l,4 mm, K1 =.3, B = 9 mm, R = 1,1 mm, L, = 312 mm assuming tat L,/ L = I /3). Determination of lifting eigt, Wit te lifting action of track, te load acting on te track is concentrated on te central part and te contact pressure beneat te track increases as sown below. w w w P = - = Pi = ) A bl bl, T e contact pressure of t e track in relation to te sinkage is sown using te equation p = kz"... 13) were k and n: constants for soil specified. It can be rewritten by combining te above equations as: z = [ /:i, ] ) Considering tis equation, te lifting eigt of track, sould be larger tan te track sinkage, z. Terefore te following condition sould be satisfied for determining te degree of eigt, : < z. Using te data sown above and assuming tat te controlled contact lengt of te track is L, = 312 mm, te contact lengt of te track is sortened to 1/3 from its original lengt. Using te above data and substituting tem into equation 11 ), te following can be obtained consequently: cf>b =.16 rad) = 9.17 degree). Results and discussion It was estimated from te calculation tat te value of <Pb was approximately 9. However tis value may cange depending on te soil conditions, since it can increase wit an increase of te value of te frictional coefficient at te interaction between te soil and te track. Table I sows te values of tf>b obtained for various kinds of ground surface, in wic te veicle was operated for testing. It appears tat te value of te boundary angle, <l>b can be canged depending on te surface condition of te ground, wic is likely to affect t e coefficient of friction beween te track and te ground surface. Normally since te frictional coefficient

5 N. fro: Eva/11ario11 of Tumability for Tracked Veicle 253 Table 1. Value of ef>o for various kinds of ground sur face Kind of ground surface Concre1e Hard sandy soil almos1 equal 1 1e level for te introduction of te combine arvester for arves1ing af1er drainage) Hard grassland Value of </>b ) for a concrete surface is iger, te value of ef>b for a concrete surface is smaller tan te oters. Conclusions In tis paper a pivot turn system wit control of te contact lengt of track was evaluated and compared wit te conventional pivot turn witout any control system of track's contact lengt. Te boundary turning angle t/>b) was used as one of te measures to determine te range in wic te controlled pivot turn system sould be applied using te example of calculation for te rice combine arvester and te experimental results of te test veicle constructed specifically for tis purpose on various kinds of ground surface. Te results can be practically applied to te automatic guidance control of te combine arvester wen it travels along te rice plant row during arvesting operation under a certain steering angle. In tis case te boundary turning angle can be used for te steering control regardless of weter te pivot turn system is activated. Only wen te value of te actual steering angle exceeds te value of te boundary turning angle t/>b, sould te pivot turn system wit control be activated. On te oter and, te average steering angle can be calculated based on statistical analysis to determine ow muc te rice plant row fluctuates in an actual paddy field. Based on te results of tjs survey, a decision can be made for te equipmem of te pivot turn system wit control. In addition, te concept of controlled pivot turn system is suitable for larger scale macines like bulldozers, to drastically reduce te turning motion resisting moment. References I) Hirata, K., Saiwai, N. & Yamagata, H. 1993) : New turning metod for rice combine arvester - Developmem of spin turn and soft turn-. Kubota Tec. Rep., 26, ) Ito, N. 1983) : Study on te tracked veicle under turning motion. Bull. Fae. Agric., Mie Univ. 67, ) Ito, N. 199) : Te development of te turntable combine arvesier for improving turnabilily and operation efficiency. J. Terrameca11ics, 27 3), ) Ito, N. et al. 1985): Practical metod for reducing turning motion resistance. Terramecanics, S, ) Ito, N. & Utsuno, A. 1988): Application of turntable function to agricultural macinery and its evaluation. J. Jpn. Soc. Agric. Mac., 56), ) Ito, N. & Wang, X. 1988): Effect of te distance between tracks and te pivoti ng location on te turnability of te tracked veicle. J. Jpn. Soc. Agric. Mac., 55), ) Kitano, M. & Watanabe, IC 1983) : Study on te improvement of turnability for tracked veicle. Terramecanics, 3, Received for publication, January 8, 1996)