The Effect of Slip Torque on Gearbox Design of ITM 8200 Series Tractor

Transcription

1 The Effect of Slip Torque on Gearbox Design of ITM 8200 Series Tractor Mohaad Reza KAMANDAR, Majid DOWLATI 2, 2 Faculty eber of Mechanic of Agric. Machinery Dept., Agric. College of Jiroft, Shahid Bahonar University, Keran, Iran. E-ail: Mr_kaandar@yahoo.co Abstract: In recent years, ITM 399 series tractor has been anufactured in Iran Tractor Manufacturing Copany, which can be suitable for sall fars operations. For big fars operations, for iniizing energy consuption, decreasing the tie losses and increasing the work efficiency, a heavy duty tractor of ITM 8200 series was started to design in the sae Copany. The gearbox design for this tractor with the engine power of 54 horse power and axiu engine torque of 69 Newton eter is studied in this research. A gearbox equipped with dynashift syste was used in ITM 8200 power transission syste. The dynashift syste produces four cases with 8 speeds that produced by ain gearbox, which altogether produces 32 forward speeds and 32 reverse speeds for this new tractor. To design the gearbox, with recoended speeds, gearbox ratios and gears ratios was calculated. Then by using the engine torque and slip torque on tractor power transission syste, the exerted loads on gears were calculated. After this, by using of Aerican Gear Manufacturing Association (AGMA) ethod and coputer prograing design (C prograing), the gears have been designed. Finally in ANSYS software analyzed the gears have been designed by slip torque or engine torque. The results of research show that: A. The gears can endure loading and can transfer the power requireent of new tractor. B. The design safety factor of gears who designed by slip torque effect, has been obtained by ANSYS software approxiately equals with safety factor of AGMA ethodology. C. For tractor gearbox design, it would be necessary to include slip torque, which using it will decrease the gear width and gearbox volue. D. Slip is a liiting condition for far tractors and slip torque value on gears is less than engine torque value. E. In tractor gearbox design, by consider to tractor slip speed it would be necessary selected of tractor gears and should be designed. Key words: Design, slip torque, gearbox, tractor, engine torque INTRODUCTION For achieving echanization goals, odern tractors play an iportant role that have been in existence for ore than a century (Liljedal et al, 975). Evaluation of the tractor has accopanied changes in sizes and technology of fars and has progressed fro it s as a substitute for anial power to the present units designed for ultiple uses. Traction power, power take off (P.T.O), ounted tools, and hydraulic reote control unites and steering, all serve to extend the usefulness and efficiency of the odern tractor (Price and Derek, 975).To solve the different probles of far operations developed the heavy duty agricultural tractors that today s the power and work efficiency of these tractors is high. In recent years, far tractors are developed in world wide that heavy duty tractors production is one result of this progression. By considering to this point, which latest tractor anufactured in Iran is ITM 399, can be suitable for sall and ediu fars of Iran. For big fars operations and need less to odern tractors iportation, designing of ITM 8200 that is a heavy duty tractor with the power of 54 horse power, was started in Iran Tractor Manufacturing Copany (ITM CO) and the design of the gearbox corresponding to this new tractor is studied in this research. Power Train Syste and Gearbox Design The working at rated speed is the best quality perforance of engine, which the engine provides optiu power, but faring operations as plowing, cultivation and transportation will require the different values of torque and speed. For exaple, the plowing operation requires the high torque and low speed or, the transportation requires the low torque and high Speed, which the tractor ay be provided these values. For counication between the optiu speed and 30

2 torque of engine, and requireents of agricultural operations, is used the power transission syste. Figure shows basic transission function in a flow diagra (Browing, 985). By considering to this diagra, the engine power divides between auxiliary drives, transission pup drives, engine coupling and disconnect eans of P.T.O shaft that the operator can be select each of this routes. The operator selects transission speed ratio by anipulation of gear shift and clutch controls. The engine and transission function as a te, to soe extent, strength of one can offset a shortcoing of the other. Davis developed the speed requireents for vehicles, which tractor speed requireents are shown in figure 2 (Browing, 985). A uxiliary D rives Trans ission Pu p D rives Pow er Input Engine Coupling Disconnect Means Independent or Continuous Driven P.T.O Speed Change M eans Trans ission Driven P.T.O Propulsion Outputs Ground Driven P.T.O Disconnect M eans Speed Change Means Power Take Off Shaft Operator Input Figure. Flow diagra of transission function (Browing, 985) By consider to this figure the speeds about 2 k/h are used in creeper operations, this operation have little iportance in ost of world regions, but in uch of the developing regions, usage of rotary tillers akes this an iportant speed range. Generally the speeds under 5 k/h and above are used in P.T.O or precision control (as precision cultivation) operations. In this speed range the output of tractor power transission syste is generally low due to liited draft and or high power flow through the power take-off (P.T.O) train. The high tractive operation speeds are iportant in world wide agricultural. Many tractors operate alost totally 90 percent in this speed range. Transitted power level in this speed range can be high, particularly in tillage operations, which can average 80 to 90 percent of axiu. Hence, for transission life calculations will be used field speeds. This range of speed uses for transport speeds in road that tractors are frequently used 30 to 40 percent of the tie in transport. Rated reverse speeds are typically faster up to 4 k/h (Browing, 985). When agricultural tractor operating in the higher field working speeds in good tractive conditions, the transitted power of transission syste is liited by the tractive capability of the drive wheels. Transission coponents used only under liited traction conditions ay reflect econoics in gear, bearing and or shaft designs, and not possible in speeds that norally transit full engine power. By considering the subjects have been presented, tractors with a stepped transission are liited in its speed and pull characteristics to those obtainable, as shown in figure 3 (Browing, 985). 3

3 Figure 2. The diagra of tractors speed requireents (Browing, 985). Pay attention to respective gears in figure 3, the engine governor and torque characteristics describe a liiting perforance envelope, which greater power or speed ay not be obtained. The cobined envelope under all gears and the traction pull liit is the tractor perforance envelope (Browing, 985). MARIAL and METHOD The new gearbox includes a four speed synchroesh section which these altogether with the four ratios ade available on the input, by eans of the dynahsift unit, offers 32 forward speeds and 32 reverse speeds which the ain gearbox offers 8 forward and 8 reverse speeds. This syste contains Dynashift syste, Main gearbox, Differential and final drive, which can fill requireents of heavy duty tractors and uses in world wide for heavy duty tractors. For gearbox design, the Iran Tractor Manufacturing Copany recoended a speed range for this tractor, the below inforation about engine and Power transission syste of ITM 8200 series tractor. (Technical Archive of ITM Co). Figure 3. The liiting drawbar pull in stepped transission (Browing, 985) Drawbar pull (axiu value): 55.5 KN Maxiu torque: 69 N. Differential ratio: Final drive ratio: 4.5 Maxiu forward speed: 40.2 k/h Miniu forward speed: 2.6 k/h Front tyre: 20.8R-38 Rear tyre: 6.9R-28 Rear dynaic radius: 855 Front dynaic radius: 670 Front ass: 930 kg Rear ass: 4680 kg Wheel base 2.83 Length 5.38 Engine type: Perkins (006.60TWG) Engine rated speed: 2200 rev/in Engine power in rated speed: 54 hp Torque Types in Gearbox Design The first consideration in gearbox design, is deterining the type of torque to be iposed on the gearbox, it is necessary to device a ethod for analyzing the character of the load, which will be iposed on the gears of gearbox. Type of torque is 32

4 used for tractor gearbox design, includes engine torque and slip torque. For ost vehicles, the governor torque on power transission syste is based on axiu theoretical engine torque value, which can be developed by the vehicle engine and delivered to the wheels. The axiu engine torque on vehicles differential ay be deterined as follows. (Thoas, 990). K o.. T. C. G TPMG () T PMG : The engine torque on vehicle differential K o : Overload factor for shock loads T E : Maxiu torque output of engine T : Transission ratio in lowest gear G : Bevel or hypoid drive gear ratio : Nuber of driving axels C : Autoatic transission converter In this research the engine torque on tractor gearbox will be deterined as follows (Kaandar, 2004). Ko.. T TPMG (2) T : Maxiu dynashift ratio T PMG : The engine torque on the gearbox The slip torque is a liiting condition for far tractors. Wheel slip torque varies due to a change in loaded weight on driving axle, road surface condition and coefficient of friction between wheels and road. The slip torque on differential pinion is (Thoas, 990). K N. W. FS. rr. G TWSG (3). A T WSG : Maxiu wheel slip torque on gearbox W: Loaded weight on driving axle F S : Coefficient of friction between tires and road (for far tractor: F S 0.6) D: Tire rolling radius G : Bevel or hypoid gear ratio A : Final drive ratio K N : Convert unit factor The slip torque on gearbox or differential pinion is (Kaandar, 2004). K N. W. FS. rr TWSG (4). A. G The loaded weight on driving axels is: (Koarizade, 997). W ( x ) x2 + P. y W (5) x T WSGB : Maxiu slip torque on gearbox W: Loaded weight on driving axle r D : Tire rolling radius P: Drawbar pull of tractor y: Height of drawbar x : Wheelbase of tractor x 2 : Distance between rear axle and gravity center The Engine Torque and Slip Torque Calculations The equation has been presented by Kaandar for slip torque on tractor differential pinion is different to Thoas equation and pointes Thoas equation is false. Thus in this research is used of equation has been presented by Kaandar and gears of gearbox are designed The slip torque on differential pinion and gearbox: Fs. rd. WD TWSG. A. G (6) N The slip torque on final drive of tractor: Fs. rd. WD TWSf. A (7) N The slip torque on tractor wheels: Fs. rd. WD TWSW (8) N. The engine torque on differential pinion and gearbox: K o.. T TPMG N (9) D N. The engine torque on final drive of tractor: Ko.. T. C TPMf (0) N. The engine torque on tractor wheels: Ko.. T. C. G TPMW () 8958 N. The suary results of deterination have been presented in table. 33

5 Table.The coparing between slip torque and engine torque on power train of ITM 8200 series Power Train Engine Torque (N.) Slip torque (N.) The pinion of differential The Final drive The wheel of tractor The Transfer Load on Gears and Gearbox Design Analysis and design of helical gears to resist bending failure of tooth and pitting failure of tooth surface in gearbox design is iportant and failure by bending will accrue when the tooth bending stress equals or exceeds either the yield strength. The bending endurance strength and surface failure occurs when the contact stress equals or exceeds the surface endurance strength. The Aerican Gear Manufacturers Association (AGMA) has been responsible authority for the knowledge disseination of gearing design and analysis in world wide that the gear design ethods of this organization will be used for designing the gears of gearbox (Litvin et al, 2003). After slip torque and engine torque calculations, the slip speed is calculated that slip K speed is: V By consider to this speed are h selected the gears corresponding to slip speed, finally the gears designed. For exaple the results of one gear design of gearbox have been presented in table 2. CONCLUSION and DISCUSSION In this research for design evaluation and controlling, has used ANSYS software (Moaveni, 999). At beginning, one gear is selected for analysis and analyzed under real conditions of gearbox and transfer load. The axiu bending stress value has been resulted by ANSYS software is: 504 Mpa (figure 4) and axiu bending strength has been calculated by AGMA ethodology is: 543 Mpa. By consider to this point, the below results have been obtained: a. The gears can endure loading and transfer the requireent power of ITM 8200 tractor. b. The design safety factor has been obtained by ANSYS software equals with AGMA ethodology safety factor. (S f.2). c. The axiu stress value has been obtained by ANSYS, approxiately equals with the strength of gear aterial, thus will be resulted that the designing of gear is reliable and careful. Table 2. The result of one gear of gearbox designing Gear properties PSI syste SI syste The diaeteral pitch of gear and pinion in 77.8 The pitch diaeter of gear in 84.9 Teeth nuber of gear Teeth width of gear in 39. The bending safety factor of gear The upper ri thickness of gear in 9.79 The lower ri thickness of gear in 8.6 The transfer load lb N The addendu of gear in 3.9 The dedendu of gear in 4.89 The bending strength of gear Kpsi 60 Mpa The pitting resistance of gear Kpsi Mpa 34

6 d. For tractor gearbox design, it would be necessary to include slip torque which, using it will decrease the gear width and volue of gearbox. Thoas, J.990. Design and anufacture of spiral bevel and hypoid gears for heavy-duty drive axles. SAE paper no www. Massy Ferguson. Co Figure 4. The result of linear solution (Kaandar, 2004) REFERENCES Borgan, D. E., E. Hainline, M. E. Long. Fundaentals of achine operation. John deere services training. Browing, E. P Design of agricultural tractor transission eleents. Distinguished series of ASAE. Technical Archive of Iran Tractor Manufacturing Copany. Chen,Y. C., C. B. Tsay Stress analysis of a helical gear set with localized bearing contact. Finite eleent in analysis and design Kaandar M. R The gearbox design for heavy duty tractors of ITM 8200 series. Thesis. Univ. Uria. Iran Koarizade. M. H.997. Mechanic of tractors and agricultural achine. Univ. Uria. Iran. Liljedani, J.B., P. K. Turnquist, D.W.Sit, M. Hoki. Tractors and their power units. ASAE Textbook. Litvin,F., A. Fuentes, I. G. Carvendali, K. Kawasaki, R. F. Handschun Modified involute helical gears coputerized design, siulation of eshing and stress analysis. Coput. Methods Appl. Mech. Engrg Moaveni, S Finite eleent analysis theory and application with ANSYS. Prentic-Hill, inc. Price, D. S., Derek, 975. Gears fro the Greeks, science history publications. 35