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Aleksandras Kirka Lithuanian University of Agriculture Research in ...

Aleksandras Kirka Lithuanian University of Agriculture Research in ...

ENGINEERING FOR RURAL

ENGINEERING FOR RURAL DEVELOPMENT Jelgava, 26.-27.05.2011. determining the workbench stopping characteristic A DR =f(h), i.e., determining the variation dependence of the cross area A DR of the throttle on the process of the hydraulic cylinder plunger h. The scheme of the device turn system is presented in Fig. 1. Fig. 1. Kinematical scheme of workbench turn mechanism: 1 – hydraulic cylinder; 2 – coulisse; 3 – speed regulation system The hydraulic system of the workbench gear is presented in Fig. 2. The hydraulic cylinder controlled by mass kinetic energy is equal to [5]: where m – mass in motion; v – speed of movement. 2 mν W K = , (1) 2 The kinetic energy change is converted into thermal energy and is equal to: where ∆P DR – power throttling losses. The power throttling losses are calculated in the following way: Since ∆P DR = p DR·Q DR , that where p DR – pressure before throttle; Q DR – oil flow through throttle. The pressure before the throttle is equal to: ∆ W = ∆P ⋅t , (2) p K DR ∆WK ∆ PDR = . (3) t DR p ∆WK ⋅ QDR = , (4) t DR ∆WK = , (5) Q ⋅t DR Since Q DR = A⋅ν , that where A – plunger area. F ST ∆PDR = , (6) ν 154

ENGINEERING FOR RURAL DEVELOPMENT Jelgava, 26.-27.05.2011. Because Q DR 2 = µ ⋅ ADR ⋅ pDR [3], that ρ A DR FST ⋅ h = . (7) 2 3 µ ⋅t ⋅ pDR ρ The experimental research was performed using the above-described device with constructional changes introduced into its hydraulic cylinder, i.e., the sizes of throttles and their arrangement were modified according to the theoretically determined throttle characteristic A DR = f(h). Fig. 2. Hydraulic system of workbench gear: 1 – pump; 2 – distributor; 3 – hydraulic accumulator; 4 - hydraulic cylinder; 5 – regulated throttle Research results In order to reduce the duration of the workbench turn, the pressure in the hydraulic system had to be increased from 60 bar to 70 bar. When the pressure is increased, the speed of the hydraulic cylinder plunger also increases; however, a more complicated problem arises, namely smooth stopping of the workbench. Since the workbench is hydraulically stopped, i.e., creating a counter-pressure to the plunger movement using throttles, the danger of very high pressure emerges. Moreover, when the speed of the workbench turn grows, dynamic loads of mechanical elements of the turn gear also increase; therefore, due to this danger, a modest pressure increase (up to 70 bar) was selected in the hydraulic system. The results, obtained during the experimental research, are given in Fig 3. The 155

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