机械专业外文翻译－挖掘机的机械学和液压学-液压系统(编辑修改稿)

机械专业外文翻译－挖掘机的机械学和液压学-液压系统(编辑修改稿)内容摘要：

t visualized by a red cylinder directed along the axis of rotation of the joint. The default animation (with only a few minor adaptations) of the excavator is shown if Figure 8. The light blue spheres characterize the center of mass of bodies. The line force elements that visualize the hydraulic cylinders are defined by two cylinders (yellow and grey color) that are moving in each other. As can be seen, the default animation is useful to get, without extra work from the user side, a rough picture of the model that allows to check the most important properties visually, ., whether the center of masses or attachment points are at the expected places. For every ponent the default animation can be switched off via a Boolean flag. Removing appropriate default animations, such as the “centerof mass spheres”, and adding some ponents that have pure visual information (all visXXX ponents in the schematic of Figure 6) gives quickly a nicer animation, as is demonstrated in Figure 9. Also CAD data could be utilized for the animation, but this was not available for the examination of this excavator. 6. The Hydraulics Library HyLib The (mercial) Modelica library HyLib (Beater 2020, HyLib 2020) is used to model the pump, metering orifice, load pensator and cylinder of the hydraulic circuit. All these ponents are standard ponents for hydraulic circuits and can be obtained from many manufacturers. Models of all of them are contained in HyLib. These mathematical models include both standard textbook models (e. g. Dransfield 1981, Merrit 1967, Viersma 1980) and the most advanced published models that take the behavior of real ponents into account (Schulz 1979, Will 1968). An example is the general pump model where the output flow is reduced if pressure at the inlet port falls below atmospheric pressure. Numerical properties were also considered when selecting a model (Beater 1999). One point worth mentioning is the fact that all models can be viewed at source code level and are documented by approx. 100 references from easily available literature. After opening the library, the main window is displayed (Figure 10). A double click on the “pumps” icon opens the selection for all ponents that are needed to originate or end an oil flow (Figure 11). For the problem at hand, a hydraulic flow source with internal leakage and externally manded flow rate is used. Similarly the needed models for the valves, cylinders and other ponents are chosen. All ponents are modeled hierarchically. Starting with a definition of a connector – a port were the oil enters or leaves the ponent – a template for ponents with two ports is written. This can be inherited for ideal models, ., a laminar resistance or a pressure relief valve. While it usually makes sense to use textual input for these basic models most of the main library models were programmed graphically, ., posed from basic library models using the graphical user interface. Figure12 gives an example of graphical programming. All mentioned ponents were chosen from the library and then graphically connected. 毕业设计（论文）报告纸 共 页 第 4 页 ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 装 ┊ ┊ ┊ ┊ ┊ 订 ┊ ┊ ┊ ┊ ┊ 线 ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 7. Library Components in Hydraulics Circuit The position diagram in Figure 12 shows the graphically posed hydraulics part of the excavator model. The sub models are chosen from the appropriate libraries, connected and the parameters input. Note that the cylinders and the motor from HyLib can be simply connected to the also shown ponents 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。