Research on the System of Boom Potential Recovery in Hydraulic Excavator

Xiaojian Zhang, Shaojun Liu, Zhonghua Huang, Lingping Chen

School of Mechanical and Electrical Engineering, Key Laboratory of Modern Complex Equipment Design and Extreme Manufacturing

Central South University Changsha, China

E-mail: zxj851205@163.com

Abstract—The failure of energy recovery with descending of regular hydraulic excavator's boom causes heat release problem, disfunction, and accelerated wear. According to this issue, this paper proposes a hydraulic excavator boom potential recovery system based on accumulator-hydraulic motor-generator. The accumulator of the system stores potential energy from construction of boom hydraulic cylinder through energy recovery. Then the generator generates electricity by driving the hydraulic motor using the energy saved in the accumulator. Hydraulic excavator boom potential recovery is accomplished. System model is built using AMESim software; a simulation research about the Hydraulic excavator boom potential recovery system is studied. Both the theoretical analysis and simulation research show that the system is able to save energy by improving the efficiency of hydraulic excavator boom potential recovery.

Keywords- hydraulic excavator； boom potential； energy recovery；accumulator；hydraulic motor

I. INTRODUCTION Hydraulic excavators work under poor condition and

consume huge amount of fuel, so the research of saving energy will bring a huge economic benefit. Based on the current hydraulic excavators energy saving procedures, improving the equipment working conditions, hydraulic system structure and power matching of engine-hydraulic pump have the energy saving potential of hydraulic excavator[1]. The inefficiency of hydraulic system is one of the main reasons of hydraulic excavator’s huge energy consuming, so coordinate with hybrid dynamic drive system, the study of hydraulic motor energy recovery has good energy saving prospect [2].

During the hydraulic excavator's working, boom, dipper and bucket swing up and down frequently as well as the rotary body turning motion. The snub braking release huge energy because of the huge inertia of components. That energy wasted on the valve will cause the system heat release problem and reduce the using life of the components [3][4]. In order to reduce energy consumption and improve the life of components, energy recovery becomes one of the efficient measures [5]. Currently, even though our country has developed some research on hydraulic potential energy recovery, the recovery is not suitable for hydraulic excavator

energy recovery [6][7]. Thus, it is necessary to research on hydraulic excavator energy recovery system.

This paper proposes a hydraulic excavator boom potential recovery system based on accumulator-hydraulic motor-generator. System model is built using AMESim software; a simulation research about the hydraulic excavator boom potential recovery system is studied.

II. BOOM POTENTIAL RECOVERY SYSTEM

A. System Conceptual Design Hybrid hydraulic excavators are equipped with storage

battery and generator. Theoretically, the potential energy produced by the descending of the hydraulic excavator's boom is able to transfer to electricity then be saved in storage battery. The electricity will drive the driving engine at the appropriate time[8]. The existing hybrid hydraulic excavator boom potential recovery method is adopted on boom hydraulic cylinder oil gallery connected the hydraulic motor and generator. Transfer and recovery the boom potential into electricity through the driving of generator by hydraulic motor[9]. The time of energy recovery during the descending of hydraulic excavator's boom is less than 2 seconds and the hydraulic fluid faces high pressure fluctuation, as a result, the generator works in a low efficiency area and has low recovery efficiency[10][11]. This paper proposes a hydraulic excavator boom potential recovery system, in order to improve the recovery efficiency of hydraulic excavator boom potential.

This system is composed by accumulator, hydraulic motor and generator etc. The structure is shown in figure 1. This system accomplishes hydraulic excavator boom potential recovery by: The accumulator of the system stores potential energy from construction of boom hydraulic cylinder through energy recovery. Then the generator generates electricity by driving the hydraulic motor using the energy saved in the accumulator. Hydraulic excavator boom potential recovery is accomplished.

2010 International Conference on Digital Manufacturing & Automation

978-0-7695-4286-7/10 $26.00 © 2010 IEEE

DOI 10.1109/ICDMA.2010.269

304

2010 International Conference on Digital Manufacturing & Automation

978-0-7695-4286-7/10 $26.00 © 2010 IEEE

DOI 10.1109/ICDMA.2010.269

303

Figure 1. Hydraulic excavator boom potential recovery system

1 controller. 2 accumulator. 3 hydraulic cylinder. 4 two-position two-port electromagnetic valve. 5 tow-position two-port electromagnetic valve. 6 two-position two-port proportional valve. 7 two-position two-port electromagnetic valve. 8 oil tank. 9 generator. 10 hydraulic motor.

11 inverter. 12 storage battery.

The system accomplishes the high efficient recovery of hydraulic excavator boom potential, the theory is using accumulator to change the working time of the hydraulic oil used for power generation, provide buffer to the potential recovery. Besides, using proportioner’s throttle to reduce the pressure fluctuations of hydraulic oil during generating electricity, the working speed adjustment of generator is achieved. Thus the generator’s working efficiency is improved. At the end improves the efficiency of energy recovery.

B. Operating Principle analysis The operating principle analysis of hydraulic excavator

boom potential recovery system is shown as below: When the piston rod of the hydraulic cylinder 3 draws

back, if energy recovery is not needed, then turn on the two-position two-port electromagnetic valves 4, 7, turn off two-position two-port electromagnetic valve 5 and two-position two-port proportional valve 6, the hydraulic oil in the oil tank 8 flows into rod end chamber of hydraulic cylinder 3 through two-position two-port electromagnetic valve 4. The oil in the non-rod end chamber of hydraulic cylinder 3 flows into oil tank through two-position two-port electromagnetic valve 7. If energy recovery is needed, turn off two-position two-port electromagnetic valve 7 and two-position two-port proportional valve 6, then turn on two-position two-port electromagnetic valves 4,5, the hydraulic oil in the oil tank 8 flows into rod end chamber of hydraulic cylinder 3 through two-position two-port electromagnetic valve 4, the oil in the non-rod end chamber of hydraulic cylinder 3 flows into accumulator 2. If energy recovery is needed, controller 1 will turn off tow-position two-port electromagnetic valves 5,7 and connect two-position two-port electromagnetic valve 4

and two-position two-port proportional valve 6. Oil in the accumulator 2 will flow into hydraulic motor 10, drives generator 9 to generate electricity, the electricity is stored into storage battery 12 through inverter 11.

Accumulator 2 transfers the potential energy produced by the draw back of hydraulic cylinder 3 into pressure energy, and then through the controlling of controller 2, drives the generator 9 to generate electricity by using the oil in accumulator 2. Because of the effect of energy saving of accumulator 2, the problem of energy recovery only working in the draw back of hydraulic cylinder 3 is avoided. The time of energy recovery is enriched.

Using controller 1 adjust two-position two-port proportional valve 6, maintain the constant of pressure differential caused by the oil flowing through generator 9. Accomplish that generator 9 generates electricity stably and regulate the rotate speed of generator 9 insure that generator 9 works efficiently.

III. BOOM POTENTIAL RECOVERY SYSTEM SIMULATION MODEL

A. Selection of Simulation Software Simulating the complicated hydraulic system of the

excavator qualitatively and quantitatively, the traditional differential and difference equations could not simulate the system dynamic change accurately. Currently, most of researchers use Simulink module of MATLAB software to simulate the excavator’s hydraulic system. Because Simulink module dose not provide specialized components library for hydraulic system simulation, the researchers have to write their own program and built mathematic model of hydraulic components. This brings a challenge to engineers [12].

AMESim (Advanced Modeling Environment for Performing Simulation of Engineering Systems) is a graphical development environment released by IMAGINE corporation in 1995. The software is used to analysis the modeling, simulating and dynamic study of hydraulic/ mechanism system. Researchers could use the model libraries of AMESim to design system, so the final goal of modeling simulation is accomplished. The software also provide the connection for software MATLAB, ADAMS etc, could combine these software together to accomplish the simulation conveniently [13][14]. This paper utilizes AMESim software to do the research on hydraulic excavator boom potential recovery simulation.

B. Building System Simulation Model The simulation of the hydraulic system model utilizing

AMESim needs 4 steps [15]: 1) Sketch. Choose the existing graphics modules from

different application libraries to build system model. 2) Submodels. Choose mathematical model for each

graphics modules (set the suitable hypothesis for model ) 3) Parameters. Set up the parameters for each graphics

modules. 4) Simulation. Accomplish the simulation and analysis

the simulation results.

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In order to research the recovery efficiency of energy recovery system, the system model is built in AMESim,

show as figure 2:

Figure 2. Boom potential recovery system simulation model

C. Setting of Simulation Parameters Set parameters for each graphics module in submodels

and parameters according to existing design. 1) The density of hydraulic oil is 850kg/m3. The air

content of hydraulic oil (volume) is 0.1%. 2) The nominal rotate speed of the volume adjustable

hydraulic pump is 1500r/min. The displacement of hydraulic motor is 30ml/r.

3) The length of stroke of hydraulic cylinder is 885mm, the diameter of piston is 115mm, and the diameter of piston rod is 65mm.

4) The volume of accumulator is 25L; the gas precharge pressure is 15 bar.

5) The rated flow of electromagnetic directional valve is 60L/min.

6) The internal diameter of oil pipe is 25mm.

IV. SIMULATION OF BOOM POTENTIAL RECOVERY SYSTEM

A. Simulation analysis of boom cylinder piston moving The moving of boom cylinder piston and velocity is

showed in figure 3 and 4. Pressure oil flows into non-rod end chamber of cylinder and pushes piston rod to move in a certain speed and moves up the load. During the first stage of descending, oil flows into accumulator, the piston retracted slowly. The oil flow into oil tank directly during the second stage, the piston retracted quickly. As the curves of the figures show, the boom potential recovery system simulates the working condition of hydraulic excavator’s boom correctly.

Figure 3. Boom cylinder piston moving curve

Figure 4. Boom cylinder piston velocity curve

B. Analysis of recovery hydraulic motor Figure 5 is the rotate speed curve of recovery hydraulic

motor. The system starts to recover the energy at 10s. The rotate speed of hydraulic motor raise to approximately 750r/min. Because the system uses accumulator, the electricity generating time of hydraulic oil is changed, so gives buffering to potential recovery, maintains the rotate speed of motor at 750r/min, and insures the generator driven by hydraulic motor working efficiently. Electricity generating efficiency is improved as wall as the whole efficiency of system energy recovery system.

Figure 5. Rotate speed of recovery hydraulic motor

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V. CONCLUSIONS According to the analysis of hydraulic excavator working

condition, this paper proposes a hydraulic excavator boom potential recovery system based on accumulator-hydraulic mentor-generator. The accumulator of the system stores potential energy from construction of boom hydraulic cylinder through energy recovery. Then the generator generates electricity by driving the hydraulic motor using the energy saved in the accumulator. Hydraulic excavator boom potential recovery is accomplished.

System model is built using AMESim software; a simulation research about the hydraulic excavator boom potential recovery system is studied. Both the theoretical analysis and simulation research show that the energy saving function of accumulator matches the motor rotate speed and generator. Thus the generator’s working efficiency is improved. The system is able to save energy by improving the efficiency of hydraulic excavator boom potential energy recovery.

REFERENCES [1] Song Liu，Bin Yao．Energy-saving control of single-rod hydraulic

cylinders with mable valves and improved working mode selection[C]．49th National Conference on Fluid Power, Mar l9—21，Las Vegas，Nevada，USA：2002：81-91．

[2] Margolis D. Energy regenerative actuator for motion control with application to fluid power systems [J] ．Journal of Dynamic System, Measurement and Control，2005，127 (1) ：33-40．

[3] DAI Xin, ZHANG Chang-ning，HANG Xin-cheng. Energy recovery system simulation and research of hybrid hydraulic excavator[J]. Journal of Beijing Technology and Business University(Natural Science Edition)， 2010，28(1)：43-47.

[4] PEI Lei，GUAN Cheng，QIU Qingying. Research of Boom Energy Recovery System in Hybrid Excavator[J]. Machine tool and hydraulics，2009，37(3)：64-67.

[5] Bing Xu， Jian Yang，Huayong Yang．Comparison of energy-saving on the speed control of the VVVF hydraulic elevator with and without the pressure accumulator [J]. Mechatronics，2005，15(10)：1159—1174．

[6] HOU Bo. Design of Energy Recovery System for Hydraulic Elevator[J]. Chinese Hydraulics and Pneumatics，2006， (3)：65-67.

[7] RUAN Xueyun，HOU Bo，LI Qiong. Analysis of the Hydraulic System for Recycling the Potential Energy of the Elevator[J]. Chinese Hydraulics and Pneumatics，2009，(4)：28-31.

[8] Lin Xiao，Guan Cheng，Pei Lei，Pan Shuangxia. Research on the System of Arm Potential Energy Recovery in Hybrid Hydraulic Excavators[J]. Transactions of the chinese society for agricultural machinery，2009，40(4)：96-101.

[9] Xu Bing ， Lin Jianjie ， Yang Huayong. The Energy Recovery Technology in Hydraulic Elevators.

[10] Wang Qingfeng ， Zhang Yanting ， Xiao Qing． Evaluation for energy saving effect and simulation research on energy saving of hydraulic system in hybrid construction machinery [J]．Chinese Journal of Mechanical Engineering，2005，41(12)：135-140.

[11] Jiang Fengnian，Duan Jingyun，Zhu Xiaoyi．A new hydraulic lift system with energy recycling function [J] ．Hydraulic Pneumatics and Seals，2005 (1) ：36-37．

[12] ZHAO Guangjun，LV Jiangang，SONG Bin，LIUYun. Model and simulation analysis on tracked vehicle hydraulic accumulator regenerative braking system[J]. Journal of Mechanical and Electrical Engineering，2010，27(3)：45-48.

[13] GUO Yong，ZHANG Desheng，JI Qian. Study on hydraulic circuit simulation based on AMESim for boom of excavator [J]. Hydrodynamics and Hydrostatics，2007，12：96-98.

[14] ZHU Wenjie，ZHAI Yao，ZHANG Xiang. Model for Parallel Hybrid Electrical Vehicle System with Regenerative Braking System in AMEsim[J]. Tractor and FarmTransporter，2008，35(2)：22-23.

[15] WANG Tao， TAO Wei. Motion Simulation and the Optimization of Control Parameters of Hydraulic Excavator Based on AMEsim Software[J]. Machine Tool and Hydraulics，2009，37(7)：180-182.

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