【正文】 s of the MultiBody library. The input signals, ., the reference signals of the driver of the excavator, are given by tables, specifying the diameter of the metering orifice, . the reference value for the flow rate. From the mechanical part of the excavator only the ponents are shown in Figure 12 that are directly coupled with hydraulic elements, such as line force elements to which the hydraulic cylinders are attached. 8. Model of LS Control For this study the following approach is chosen: Model the mechanics of the excavator, the cylinders and to a certain extent the pump and metering valves in detail because only the parameters of the ponents will be changed, the general structure is fixed. This means that the diameter of the bucket cylinder may be changed but there will be exactly one cylinder working as shown in Figure 1. That is different for the rest of the hydraulic system. In this paper a Load Sensing system, or LS system for short, using one pump is shown but there are other concepts that have to be evaluated during an initial design phase. For instance the use of two pumps, or a separate pump for the swing. The hydraulic control system can be set up using meshed control loops. As there is (almost) no way to implement phase shifting behavior in purely hydraulic control systems the following generic LS system uses only proportional controllers. A detailed model based on actual ponents would be much bigger and is usually not available at the begin of an initial design phase. It could be built with the ponents from the hydraulics library but would require a considerable amount of time that is usually not available at the beginning of a project. In Tables 1 and 2, the implementation of the LS control in form of equations is shown. Usually, it is remended for Modelica models to either use graphical model deposition or to define the model by equations, but not to mix both descrip tion forms on the same model level. For the LS system this is different because it has 17 input signals and 5 output signals. One might built one block with 17 inputs and 5 outputs and connect them to the hydraulic circuit. However, in this case it seems more understandable to provide the equations directly on the same level as the hydraulic circuit above and access the input and output signals directly. For example, ”” used in table 2 is the measured pressure at port_A of the metering orifice metOri1. The calculated values of the LS controller, ., the pump flow rate “[1] = ...” is the signal at the filled blue rectangle of the “pump” ponent, see Figure 12). The strong point of Modelica is that a seamless integration of the 3dimensional mechanical library, the hydraulics library and the non standard, and therefore in no library available, model of the control system is easily done. The library ponents can be graphically connected in the object diagram and the text based model can access all needed variables. 9. Some Simulation Results The plete model was built using the Modelica modeling and simulation environment Dymola (Dymola 2020), translated, piled and simulated for 5 s. The simulation time was 17 s using the DASSL integrator with a relative tolerance of 106 on a GHz notebook, ., about times slower as realtime. The animation feature in Dymola makes it possible to view the movements in an almost realistic way which helps to explain the results also to nonexperts, see Figure 9. Figure 13 gives the reference signals for the three cylinders and the swing, the pump flow rate and pressure. From t = s until s and from t = s until s the pump delivers the maximum flow rate. From t = s until s the maximum allowed pressure is reached. Figure 14 gives the position of the boom and the bucket cylinders and the swing angle. It can be seen that there is no significant change in the piston movement if another movement starts or ends. The control 畢業(yè)設(shè)計（論文）報告紙 共 頁 第 5 頁 ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 裝 ┊ ┊ ┊ ┊ ┊ 訂 ┊ ┊ ┊ ┊ ┊ 線 ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ system reduces the couplings between the consumers which are very severe for simple throttling control. Figure 15 shows the operation of the bucket cylinder. The top figure shows the reference trajectory, i. e. the opening of the directional valve. The middle figure shows the conductance of the pensators. With the exception of two spikes it is open from t = 0 s until t = 1 s. This means that in that interval the pump pressure is manded by that bucket cylinder. After t = 1 s the boom cylinder requires a considerably higher pressure and the bucket pensator therefore increases the resistance (smaller conductance). The bottom figure shows that the flow rate control works fine. Even though there is a severe disturbance (high pump pressure after t = 1 s due to the boom) the manded flow rate is fed with a small error to the bucket cylinder. 10. Conclusion For the evaluation of different hydraulic circuits a dynamic model of an excavator was built. It consists of a detailed model of the 3 dimensional mechanics of the carriage, including boom, arm and bucket and the standard hydraulic ponents like pump or cylinder. The control system was not modeled on a ponent basis but the system was described by a set of nonlinear equations. The system was modeled using the Modelica MultiBody library, the hydraulics library Hylib and a set of application specific equations. With the tool Dymol