Technology, Xi an , China

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1 Applied Mechanics and Materials Vol. 251 (2013) pp Online available since 2012/Dec/13 at (2013) Trans Tech Publications, Switzerland doi: / Modeling and Simulation of Hydraulic System of the working device of the Wheel Loader Based on Power Bond Graph ZHENG Jian-xiao 1,a, DUAN Zhi-shan 2,b, Guo Bao-liang 3, c 1, 2, 3 School of Mechanical and Electrical Engineering, Xi an University of Architecture and Technology, Xi an , China a zjx @163.com, b duanzhishan1950@sina.com, c gbl93@163.com Keywords: Power Bond Graph, Dynamic Equation, Simulation Model, M Function File, Simulation Abstract. Based on the working principle of the hydraulic system for the working device of ZL60 wheel loader, the power bond graph of its hydraulic system is established by using the power bond graph method under the different working conditions. The power dynamic equations of the system is written out according to the established power bond graph and the simulation model has been established under the bucket backward operating condition on the basis of the power dynamic equations of the system. This simulation will be carried out by setting the simulation parameters of the hydraulic system, applying the Simulation software and compiling the M function file. Through these studies, the performance curve of the hydraulic system can be obtained. Introduction The hydraulic system of working device is an important part of the wheel loader. It plays an important role during the operation. Its performance determines the load capacity and efficiency of the wheel loader. During the operating process, the collaborative action with frequent change includes these actions, such as lifting boom, turning the bucket, the whole steering and the variable transmission. The load of the system changes in a dynamic state. Therefore, only according to the traditional static process to design the hydraulic system, the requirements of the machine can t be met. Using the bond graph method for the hydraulic system dynamic simulation is from the power perspective to diagrammatize the flow of the hydraulic system of power and related information, which leads to the dynamic equation of working device. Then, the block diagram which is included in MATLAB and Simulation model can be directly used to set the model and carry out the simulation. Comparing with the traditional method, this method has some advantages of more intuitive, convenient and flexible. So, the dynamic simulation for the hydraulic system of working device is of great importance for improving the machine performance and reliability. Besides, it is conducive to design a better hydraulic system and improve the product s development. Composition and Working Principle of Hydraulic System of Working Device of Wheel Loader The hydraulic system of the loader consists of power source, working pump, multi-directional valves and control actuators etc. The diesel engine is the power source for the system. It is used to drive the pump to convert the mechanical energy into hydraulic energy. The multi-directional valve consists of the bucket cylinder valve, the boom cylinder valve and lines etc. It is used to transfer power and control. Above all, it is a key part of the hydraulic system. The executive body is composed by two boom cylinders and two bucket cylinders, which can complete a variety work of the loader. It is directly connected to the load. Bucket cylinder valve is a three six-way spool valve, which controls the bucket forward, backward and fixed in position. When the bucket cylinder valve is in the left position or right position, the boom cylinder valve will be blocked. It does not work at this time. When it is in the medium, the boom cylinder valve will work usually. Boom cylinder is a four six-way valve to control the boom up, down, fixed and floating. The floating of the boom allows the device to float freely with the situation on the ground, when loader accumulates in the ground operation. When loader is in minerals operations, it can make the shovel blade avoid the large ore. At the same time, it improves operational efficiency. Relief valve works as a safety valve in this system. When the system All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, (ID: , Pennsylvania State University, University Park, USA-10/03/15,07:58:37)

2 222 New Trends in Mechanical Engineering and Materials pressure exceeds the maximum working pressure that is set, the relief valve opens, and oil flow back into the fuel tank, protecting the system from damage. Buffer filling oil loop consists of relief valve and check valve. It is installed in the way of the oil loop of the bucket cylinder. It can protect the bucket cylinder against damage. Modeling and Procedures of Hydraulic Systems Based on Bond Graph Bond graph is an icon of the system power flow expression. It is also a graphical representation, which can express the dynamic modeling and analysis of a unified system for handle multiple areas of energy. It can reflect the load effect and power flow between components, such as the flow of power, distribution, collection and energy conversion etc. Above all, It is a dual signal flow diagram that expressed by a set of symbols. Using of the causal relationship between variables, we can write out the dynamic equations directly from the bond graph of each function of the system components, and then to build simulation model and simulation using MATLAB software. This method is an effective tool to model for dynamic simulation in engineering, which has been widely used in dynamic simulation of hydraulic system analysis and research. Drawing the Bond Graph of the Implement Hydraulic System Power The bond graph for the working device under the condition of the bucket backward. In the condition of the bucket backward, the valve of the bucket cylinder is in the left position. The valve of the boom cylinder blocks. The boom does not work and at a fixed position. At this time, the piston rod of the bucket cylinder moves to the right and turns backward. Analysis by the condition, the hydraulic system consists of these hydraulic components, such as a working pump, relief valve, three position four way valves, double hydraulic cylinder and so on. We should consider the effect of the work capacity of the pump fluid, friction, internal leaks and inertia. As a liquid resistance, relief valve is connected to the node 0 of the working pump by a key, taking these elements into account, such as the liquid capacity of rod-less effect, friction. Based on these factors and the bond graph model of the hydraulic components, using the method of the power bond graph to connect the bond graph elements and change its causal scheme, then to draw the total bond graph of the hydraulic system. It is shown in Fig.1. Fig.1 The total bond graph of the hydraulic system when bucket backward The bond graph for the hydraulic system under the condition of the bucket forward. In the condition of bucket forward, the bucket cylinder is in the right position. At the same time, the working arm cylinder does not work and piston rod moves to the left. At this moment, the bucket moves forward and the loader uninstall. It makes the bucket quickly scroll down by gravity and hit the homeopathic limit blocks, so that the bucket clears up. When the loader discharges, the valve is in the right position. At this time, the pressure oil flow into the forward capacity of the bucket cylinder, so it makes the bucket turn round. When the gravity center of the bucket beyond the low hinge point of the

3 Applied Mechanics and Materials Vol bucket, the gravity of the bucket makes the bucket speed up to turn round. But its speed is limited by the oil pumping speed. Since the one-way valve in the buffer fill valve to shovel up the oil into the forward capacity of the bucket cylinder, so that the bucket quickly turns and hits the limit block to achieve the bucket discharge. From the above analysis we can see that when the bucket turns forward, the total hydraulic system includes these working components, such as a working pump, relief valve, three four-way slide valve, double hydraulic cylinder, etc. In addition, with the connection to the rod-less chamber, the one-way fill valve in the buffer fill oil back on the road is also working, so the bond graph of the hydraulic system is on the basis of the bond graph of the bucket backward, and then adding a 1result point to connect the fluid resistance of the one-way fill valve. And its bond graph is shown in Fig.2. Fig.2 The total bond graph of the hydraulic system when bucket forward Dynamic simulation of the hydraulic system The Simulation in MATLAB software is a software package for modeling, simulation and analysis. It also can be used for calculating the hydraulic system, modeling and dynamic simulation. So, after the dynamic equation by the bond graph is listed, a corresponding simulation program should be built. M function file is to solve the calculation of the model in the Matlab software. Specific parameters are calculated by the hydraulic system design specifications and parameters of hydraulic components. The Simulation for hydraulic system of working device. The simulation model for each functional element in the hydraulic system should be built. Then, according to the circuit characteristics and different working conditions of the hydraulic system of the working device, the simulation model of these modules will be combined. Thus, the simulation model of the whole hydraulic system gradually is built. Through detail analysis of the hydraulic system of the loader, the system bond graph model and mathematical model under different conditions can be obtained. Taking the condition of the bucket backward as an example, the dynamic simulation of the loader hydraulic system will be completed. According to the specific parameter value of the hydraulic system to do initialization and assignment values, an M function file for simulation calculation in MATKAB-Simulation software can be established. The total model of the hydraulic cylinder and hydraulic system is shown in Fig.3and Fig.4. After building the simulation model of hydraulic system, we can run the M function file of the parameters. Setting and modifying the specific design parameters and parameters of hydraulic components through Simulation model, and then run the simulation. In the simulation, you can real-time monitor the created modules. Turning the simulation result into data files, you can always call and output. By this means, it can provide zero-crossing detection and error control. And its relative error can be controlled in After running the simulation, we can type the command plot in the MATLAB command window, and then you can obtain the simulation images. In the condition of bucket backward, the bucket has shoveled the material. The bucket mouth moves from the upright position to a horizontal position. At this point, the reaction torque on the bucket from windrow is the resistance torque for bucket turning. At the first moment of the bucket fully into the windrow, the bucket has a maximum value of static resistance torque, and the shovel is zero. Thereafter, the static

4 224 New Trends in Mechanical Engineering and Materials resistance torque for bucket turning changes in the hyperbolic properties with bucket turning angle until the bucket cutting edge leaving the slope line of the windrow. After simulation, the piston pump output pressure and its angular velocity increases to a constant value. Rod-less cylinder cavity pressure increases, the rod pressure increases and the output power of the hydraulic cylinder increases. The symbol of the curve stands for the direction and the absolute determines it to increase or decrease. Because the limit of considering all the deficiencies of the parameters setting and the influencing factors for each hydraulic component, the simulation results can be a curve or a straight line. Some parts of simulation results are shown in Fig.5 and Fig.6. Fig.3 Simulation model of the cylinder for the condition of the bucket backward Fig.4 Simulation model of the cylinder for the condition of the bucket forward

5 Applied Mechanics and Materials Vol 换向换换向向向向 Qsp(m3/s) t(s) Fig.5 The simulation of flow cavity for the directional valve oil-in Qzp(m3/s) t(s) Fig.6 The simulation of flow cavity for the directional valve oil-back Conclusion For the object of ZL60 wheel loader, the hydraulic system of the working device has been deeply analyzed. So the power bond graph of the working device will be used to build the model for total Simulation bond graph and the corresponding power state equation in the condition of the bucket backward. And these researches also have been done, such as digital simulation of hydraulic system by Simulation, M function file procedures will be programmed to calculate the simulation result by inputting the parameter data. The result shows that the effect is perfect. And it can provide the theoretical basis for designing hydraulic system of wheel loader. Acknowledgements This work was financially supported by the natural science foundation of Shaanxi province (2012JM7015). References [1] Yang Zhanmin, Wang Zhiming, Zhang Chunqiu etc. The wheel loader. Beijing: Chemical Industry Press, [2] FENG Jing, TAO Ran, MA Shenggang. Application of Power Bond Graph-State Equations in Dynamic Capability Analysis of New Type Relief Valve. Machine Tool & Hydraulics, 2009, 37(8): [3] WANG Xin, SONG Xiaoguang, XUE Lin. The Application of Power Bond Graph Based on Matlab/Simulink in Hydraulic Dynamic Simulation System. Machine Tool & Hydraulics, 2007, 35(6): [4] Yang Guoping,Liu Zhong. Modern engineering mechanical hydraulic pressure and hydraulic practical technology. Beijing: China Communications Press, 2003.

6 New Trends in Mechanical Engineering and Materials / Modeling and Simulation of Hydraulic System of the Working Device of the Wheel Loader Based on Power Bond Graph /