ENGINEERING FOR RURAL DEVELOPMENT Jelgava, SIMULATION OF PRESSURE OSCILLATION IN HYDRAULIC HITCH-SYSTEM

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1 SIMULATION OF PRESSURE OSCILLATION IN HYDRAULIC HITCH-SYSTEM Janis Laceklis-Bertmanis, Edgars Repsa, Eriks Kronbergs Latvia University o Agriculture janis.laceklis@llu.lv, edgars.repsa@llu.lv, eriks.kronbergs@llu.lv Abstract. The paper presents simulation results o tractor movement with attached disc harrow over rough surace. Working Model sotware is used or simulation. Hitch-system cylinder is replaced as coupler with spring and damper characteristic in model. Dynamic orce on coupler is obtained as simulation result and depending on it hydraulic pressure in hitch-system cylinder had been calculated. Simulation results are evaluated on basis o experimental investigations. Key words: tractor hitch system, pressure oscillation simulation. Introduction During tractor movement, with attached to hitch-system working equipment (plough, harrow), over rough road suraces oscillation o machine take place. These oscillations are a reason o pressure pulsations in hydraulic hitch-system. Pressure pulse reduction in tractor hitch-system is important or increasing o system components lietime. Pressure oscillations damping in the tractor hydraulic hitch-system can reduce overall system oscillations and improve the driving control. Modern tractor linkage system is itted with oscillation damper, with reduces the hydraulic hitch-system pressure oscillations. Simulations o tractor hydraulic system oscillation enable determination o hydraulic system stiness and damping parameters or minimizing amplitude o pressure pulsations. Working Model sotware let to create dynamic model or tractor vertical oscillations and simulate movement with dierent speed and road roughness values. Materials and methods For evolution o Working Model simulation results preliminary experiments on tractor movement over artiicial roughness test road had been carried out. Using the Working Model sotware [1] is necessary to determinate the hydraulic system pressure in tractor (Class Ares 557 ATX) hydraulic hitch-system hydro cylinder depending on the attached equipment weight, road roughness and tractor speed. In Working Model sotware dynamic model the same parameters o tractor and attached equipment [-5] weight, road roughness and movement speed as in experimental investigation had been used. Oil volume stiness or tractor hydraulic system was calculated [6]. Simulation model (see Figure 1) is used in the side-view. The parameters o hydraulic cylinder and tyres are entered two times larger in simulation model. Sinusoid unction is used or the road roughness description in model [7]: where a roughness amplitude, m; ω orced oscillation requency, s -1 ; t time, s. y = a sin( ω t), (1) Road roughness amplitude is constant value a = 0.05 m. Frequency orced oscillation o is dependent on tractor driving speed and road roughness step (). Road roughness step s = m is equal with the step o experimental road. where v tractor drive speed, m s -1 ; s road roughness step, m. v π ω =, () s 144

2 Fig. 1. Tractor model in Working Model sotware: 1 tractor Class Ares 557 ATX, tractor ront tyres (13.6R8), 3 ront weight, 4 ront actuator, 5 ront tyres (characterization by spring and damper), 6 road roughness, 7 ront tyres control units, 8 tractor rear tyres (16.9R38), 9 rear actuator, 10 rear tyres (characterization by spring and damper), 11 hydraulic cylinder (characterization by spring and damper), 1 rear tyres control units, 13 tractor hitch-system, 14 soil cultivator implements, 15 hitch-system control units Tractor wheelbase is l t =.564 m. As the tractor wheelbase does not coincide with road roughness step, the time delay t between roughness impact on ront wheels and rear wheels: l t =, (3) v where t time delay, s; l step dierence between tractor wheelbase and road roughness, m. l is calculated: l = l s. (4) Function o road roughness surace in Working Model program is assured with actuators 4 and 9 (see Figure 1). Actuator unctions o the ront and rear wheels are given in program by equation (5), where y 1 is the unction o ront wheel oscillations, but y is or back wheels. y y 1 t = b + i ( a sin( ω ( t + t)) < 0,0,( a sin( ω ( t + t)))) = b + i ( a sin( ω t) < 0,0,( a sin( ω t))) where b initial length o actuator, m. I the unction y = a sin(ω t) < 0, then the unction value is 0, but i a sin(ω t) > 0, then the unction value is y = a sin(ω t). Road roughness simulation is showed in Figure. (5) 145

3 Fig.. Road roughness: t oscillation time delay, s road roughness step, a road roughness amplitude Road surace and tractor movement descriptive values are used in simulation and given in Table 1. Table 1 The input parameter o simulation Angular requency ω, s Velocity v, m s -1 Oscillation time delay t, s In the model hitch-system hydraulic cylinder 11 (Figure 1) is created and described with spring and damper characteristic. The spring and damper are characterized by stiness and damping coeicients. Tractor hitch-system hydraulic cylinder parameters are changed with control button 1 (Figure 1). Approximate spring stiness coeicient can be calculated rom ormula (6). where c spring stiness coeicient, N m -1 ; F orce, N; x displacement, m. F c =, (6) x The orce F value is obtained rom experiment results (F = N). Displacement x is equal to the hitch-system hydraulic cylinder displacement at pressure pulse. It can be calculated [6] rom volume change V in hydraulic cylinder rom equation: where E liquid modulus o elasticity, N m - ; V volume change in the size o the pressure changes, m 3 ; V 0 initial volume o liquid at atmospheric pressure, m 3 ; p pressure change, N m -. 1 V =, (7) E p V Values o pressure changes is determinated rom experimental tests p = N m -. Oil modulus o elasticity E = N m -. Initial luid volume in hydraulic hitch-system cylinder at atmospheric pressure is calculated: 0 d h V0 = π, (8) 4 146

4 where d hydraulic cylinder diameter, m; h hydraulic cylinder stroke, m. From tractor Class Ares hydraulic hitch-system cylinder determinate sizes d = 0.075m and h = 0.3m. Displacement x is calculate rom ormula (9). 4 V x =. (9) π d The approximate stiness coeicient can be calculated ater the displacement x determination according ormula (6). Input constant parameters are given in Table. Table Parameters o simulation Road roughness step s, m Road roughness amplitude Tyre stiness coeicient c, N m -1 Tyre damping coeicient b, N s m -1 Hitch-system parameters a, m Front Rear Front Rear Stiness coeicient, N m -1 Damping coeicient, N s m Tractor tyre parameters are dependent on tire pressure. Decreasing tire pressure rom 1. to 0.8 bar, maximum average values o pressure in hydraulic hitch-system during oscillations are decreased. Force is measured when tractor model hydraulic hitch-system hydraulic cylinder oscillation is simulated with Working Model sotware. Corresponding pressure is calculated: Fu p =, (10) A where p pressure, Pa; F u hydraulic hitch-system hydro cylinder orce, N; A area o hydraulic cylinder, m. With constant spring stiness coeicient, reducing the damping coeicient, the orce o hydraulic hitch-system hydro cylinder decreases. Changing the damping coeicient values rom N s m -1 pressure values similar to experimental values are obtained. Working Model tractor simulation model checking on the basis o experimental investigations let improve it coincidence with real machine aggregate. Results and discussion Changing the tractor hydraulic hitch-system (stiness and damping) parameters and speeds rom 3-14 km h -1 there are obtained the dierent pressure values in linkage cylinder. The experimentally obtained hydraulic hitch-system pressure values and the Working Model program simulation pressure values are shown in Figure 3. The maximum pressure oscillation amplitude is observed at the speed 7.8 km h -1, and reaches 188 bar in experiments, but at the same speed reaches 18 bar in simulation results. The dierences between simulation and experimental investigation results vary with in -10 %. These dierences are caused with some inconsistency or stiness o tyres in simulation model and can be eliminated. Thereore Working Model simulation or tractor hydraulic hitch-system can be recommended or investigation o possibility to reduce amplitude o pressure pulsations by changing parameters o hydraulic system. 147

5 Fig. 3. Pressure in tractor hydraulic hitch-system o hydraulic cylinder Conclusions 1. Working Model sotware lets to create dynamic model or tractor vertical oscillations and simulate movement with dierent speed and road roughness values.. Working Model tractor simulation model checking on the basis o experimental investigations let improve it coincidence with real machine aggregate. 3. The maximum pressure oscillation amplitude is observed at the speed 7.8 km h -1, and reaches 188 bar in experiments, but at the same speed reaches 18 bar in simulation results. 4. The dierences between simulation and experimental investigation results vary within -10 %. 5. Working Model simulation or tractor hydraulic hitch-system can be recommended or investigation o possibility to reduce amplitude o pressure pulsations by changing parameters o hydraulic system. Acknowledgement Paper becomes written by inancial support o European Structural Fund Support or Realization o Doctoral Studies in Latvia University o Agriculture - realized by Project Department o Latvia University o Agriculture (contract no. 009/0180/1DP/ /09/IPIA/VIAA/017). Reerences 1. MSC. Sotware Corporation. Working Model D sotware, User s Manual, Laceklis-Bertmanis J., Pirs V., Jesko Z. Investigation o Pressure Oscillation in Hydraulic Hitch-System. Proceedings o the 16th International Scientiic Conerence Research or Rural Development. Jelgava: LUA, 010. (Article in press). 3. LEMKEN GmbH & Co.KG. Technical Data Compact Disc Harrow Heliodor, 010. [online] [ ]. Available at: &dbc=d41c7cade7 64dc9bb388a a9. 4. LEMKEN GmbH & Co.KG. Technical Data Rubber rings Rullers, 010. [online] [ ]. Available at: 5. Company Claas KGaA mbh, Harsewinkel. Claas Areas 5543 Handbook, Башта Т.М. Объемнные насосы и гидравличесткие двигатели гидросистем (Volume Pumps and Hydraulic Motors o Hydraulic System). Москва: Машиностроение, p. 7. Яценко Н.Н., Прутчиков О.К. Плавность хода грузовых автомобилей (The Release Motion o Trucks). Москва: Машиностроение, p. 148