Introduction

2. Introduction Fluid power systems, in which working pressure (pressure in pump output) is kept proportional to load, are called hydraulic load-sensing systems. Such systems are mainly used with the purpose to save energy. Hydraulic load-sensing systems are automatically regulating systems with a number of components and several feedbacks. Feedbacks make the system very sensitive and unstable for performance and simulation. A very precise parameter setting, especially for resistances of hydraulic valve spools and for spring characteristics, is required to make the system function. Steady state conditions and dynamic behavior of the hydraulic load-sensing system are simulated.

5. Object-oriented modelling based on multi-pole models with oriented causality is used for fluid power systems.

6. Composing the model

7. Simulation steps First, the hydraulic motor, hydraulic pump, electric motor and fluid parameters must be chosen. Second, initial approximate values of pressures, pressure differences for pump control, maximum displacements of the valves, parameters of springs, geometry of valves working slots, etc. must be set up. �� Third, all the models of components must be tested separately. For this purpose, for every component the simulation problem must be composed, approximate input signals must be chosen and finally, action of the component must be simulated. Fourth, the separately tested component models must be connected into more complicated subsystems and finally into whole system and tested in behavior.� Fifth, components models must be revised and parameters values of the system must be adjusted as a result of solving simulation tasks.

8. Meter-out throttle edge for hydraulic motor

9. Clutch with inertia

10. Hydraulic motor subsystem

11. Simulation of steady state conditions

12. Simulation of dynamics Simulation characteristics Initial displacement of the directional valve 0.0045 m. Initial load moment of the drive mechanism 65 Nm. Step change (during 0.01 s) is applied to: - the initial load moment - the initial displacement of the directional valve. Time step 5 �s. Simulated time 0.5 s (results are calculated for 100 000 points).

13. Initial displacement of the directional valve 0.0045 m Load moment of the drive mechanism 65 Nm Step change 0.001 m (during 0.01 s) applied to the initial displacement Time step is 5 �s Simulated time is 0.5 s (results have been calculated for 100 000 points). Simulation time 17.1 s

15. Size and complexity The package for modelling and simulation of the load-sensing system contains: - 42 classes, including 27 component classes; - more than 1000 variables; - 17 variables that have to be iterated during the computations; - 73 links between system components. The automatically constructed Java code for solving the simulation task of the dynamics of the load-sensing system contains 4124 lines and involves 5 algorithms for solving subtasks.

16. 3D simulation 3D simulation of steady state conditions Calculated 1000 x 1000 points Calculation time 119 s