2015 International Conference on Fluid Power and Mechatronics
Research on the Performance of Hydraulic Excavator with Pump and Valve Combined Separate Meter In and Meter Out Circuits Lei Ge1, Zhixin Dong, Weinan Huang, Long Quan*2, Jing Yang3, Wenyong Li Taiyuan University of Technology Key Lab of Advanced Transducers and Intelligent Control System of Ministry of Education Taiyuan, China
[email protected],
[email protected],
[email protected]
actually only one parameter of the cylinder such as flow or pressure can be controlled. Generally, for a cylinder working in the negative load condition such as the boom cylinder, in order to improve the control performance the enough back pressure should be established in return oil cavity. The controllability of this method is poor and the energy consumption is huge especially under the boom-down motion, the swing motorbrake motion and the arm under over-running condition [13].The independent metering method was proposed to increase efficiency and performance which is low and bad in the throttling control system used mechanically connected orifices valves [4-5]. A new energy recovery configuration including five or six independent proportional valves and an accumulator was proposed in [6-7], the simulation results have shown that the proposed configuration follows a given velocity trajectory with lower energy consumption than three other valves configurations.
Abstract—Conventional hydraulic actuator is controlled by mechanically connected orifices valve. The controllability of this method is poor and the energy consumption is huge especially under the over-running condition. So a novel system configuration of the hydraulic excavator is presented to improve the problem mentioned above, in which boom cylinder, stick cylinder and swing motor are controlled with separate meter in and meter out technology, bucket cylinder and travel motors are controlled with conventional valves. Firstly, the paper provides a comprehensive review on the development of the separate meter in and meter out technology. Then the principles of load sensing system and SMISMO system applied on the excavator are illustrated though two diagram to show the difference of the two systems. And then a virtual prototype based on the real physical structures is established, which consists of the hydraulic excavator mechanical structure with multi-body dynamics and electro-hydraulic system. The model is verified by the statics and dynamics experiments. Then the dynamic, static performances as well as the energy consumption characteristics of the boom, arm and swing actuators are investigated under the condition of load sensing hydraulic system and the proposed system using the virtual prototype. The control strategy of the actuators is formulated according to their load condition and operation characteristics also based on the detailed analysis. After that, the physical prototype based on the proposed configuration system is established and its performance is tested. The experimental results show that the accuracy of the virtual prototype is validated; the proposed configuration system can significantly decreases the pressure losses through the valve and improve the energy efficiency of the machine; the pressure shocks within hydraulic actuators is decreased as well, thus the stationarity of the whole machine is improved accordingly.
Shenouda A did some research focusing on energy saving about an actuator that is controlled by the four valve independent metering configuration to move beam like members of mobile hydraulic equipment such as tractor loader backhoes, excavators, and telehandlers [8]. Flexibility is increased by removing the mechanical coupling between the meter-in and meter-out orifices in directional valves and also an individual metering system can decrease energy consumption by about 20% [9]. In order to verify the effect on energy reduction of the independent metering configuration applied to a excavator, a simulation compared power consumption of conventional main control valve and independent metering valve was carried out in [10]. A grading control method based on velocity observing and parameters estimating on line in acceleration, deceleration and brake process of high inertia loads based on the independent metering strategy is put forward to meet their demand on velocity accuracy, rapidness and smoothness in [11]. An innovative electro-hydraulic servo system that a differential cylinder is controlled closed loop with two speed variable pumps and the control strategy that control the inlet and outlet of cylinder separately was put forward, the further control strategy about
Keywords—flow matching; separate meter in and meter out; pressure and flow combined control; pump and valve hybrid control
I.
INTRODUCTION
The mobile hydraulic machinery typically works under high energy consumption condition and the velocity of the actuator was controlled by the operator by directly controlling the spool position of a 3-position, 6-way directional valve. The flow into and out of the actuator is controlled simultaneous,
978-1-4799-8770-2/15/$31.00 ©2015 IEEE
37
August 5-7, 2015 Harbin, China
multi-actuator using pump and valve composite flow matched technology was proposed [12-13].
system solutions are being realized by the hardware in the loop computer control system ds1103.
According to the literature about independent metering strategy of domestic and overseas, it is validated that it increases energy efficient and performance compared to the traditional directional valves. However the research about independent metering method mainly focused on a typical hydraulic actuator rather than a multi-actuator system and also there is little literature concerning about the pressure and flow matched using pump and valve composite strategy. Therefore, our goal is to development a overall prototype using the pump and valve combined separate meter in and meter out method. And then the performance of the prototype is compared with a same load-sensing excavator under identical condition in this paper. II.
STRUCTURE AND PAREMETERS OF THE HYDRAULIC SYSYTEM
The hydraulic system with directional valves is widely used on the hydraulic excavator which include load-sensing circuit, positive control circuit and negative control circuit. A 6-ton hydraulic excavator with flow-saturated resistant system ( LUDV system for short) is the object for this research.
Fig. 1. Configuration of the excavator with LUDV
A. LUDV System The configuration of the LUDV system is shown in Fig.1. It can be seen that the hydraulic system consists of a load-sensing variable pump, a sandwich plate designed control block with pressure compensator, shuttle valves and actuators such as boom, arm, bucket and swing. LUDV control valves operate with a pressure compensator built into the valve downstream of the throttle section. In some block, the compensator plays as the shuttle valve also. The system works as below: the shuttle valves detected the highest load pressure then applied it to all the compensator and feed back to the LS pump via the LS line, the compensator is always being acted upon by the highest load pressure and the pressure after the throttle section to adjust the pressure drop across the spool as a same level in a dynamical process, the pump change the flow to match the pressure drop set by a spring in pump controller. Even if the flow demand is above the pump limited, the flow distribution ratio is still as the set value defined by the displacement of the spool.
Fig. 2. Configuration of the excavator with SMISMO
B. Flow Matched Separate Meter In and Meter Out System The system in which boom cylinder, stick cylinder and swing motor with separate meter in and meter out technology ( SMISMO system for short) using two proportional valves, bucket cylinder and travel motors controlled with conventional valves, proposed in this paper, is shown in Fig.2. An electrohydraulic axial piston variable displacement pump which the pressure and flow are continuously tunable is used in this system. There are additional instruments such as displacement sensor in every actuator, pressure sensor beside the pump and the actuator, the flow sensor and rotating speed sensor on the engine which are employed to detect the corresponding variables and some of them are used for feedback control. The circuit control concepts of the SMISMO
III.
MULTI-BODY MODEL OF THE EXCAVATOR
In order to have a knowledge about the performance of new proposed system applied on the excavator, a prototype which consists of the hydraulic excavator mechanical structure with multi-body dynamics and electro-hydraulic system based on the real physical structures established in SimulationX, is shown in Fig.3. The moment of inertia and mass of the mechanical are taken into account and also the force acts on the bucket can be transmitted to other actuators in real time. So the model of the hydraulic system and the model of the mechanism influence each other just as the real physical structure.
38
IV.
CONTROL SYSTEM DESIGN
As shown in Fig.7, an overall experimental platform is established to study the SMISMO system for hydraulic excavator. The dSPACE controller takes in the inputs of joystick and the measured quantities such as the pressures, displacements, flow and speed of the engine. And then the controller analysis the demand automatically and output the voltages signals directly applied to the pump and the valves according to the set strategy. Pi
Fi, vi, M, w
6WLFN YDOYHV
ȈQ, Pmax
Qi SMISMO valves
xi
Fig. 3. Multi-body model of the excavator in SimulationX
Pi
Joystick
Pcontrol Qcontrol
6ZLQJYDOYHV
Controller
vset
The complete prototype of the excavator was verified by static and dynamic experiments as depicted in Fig.4-6. Firstly, the pressure results of every actuator when the excavator keeps motionless at a set state is shown in Fig.4. And then the boom and stick experimental results were chosen to show the dynamic performance, as shown in Figs.5-6. According to the figure, it is evident that there is a good relation between the simulation and the experiment results.
Pump Ppump Qpump
Simulink ControlDesk
dSPACE
%RRP 9DOYHV
3XPS
Fig. 7. The Structure of the SMISMO System
A. Power Management Control The excavator may work under a huge power demand condition that may be beyond the maximum power output of the engine which may cause the halt of the engine. A PID maximum constant power controller is designed to limit the control power in this paper. The maximum constant power is belong to the speed of the engine. B. The Boom Up and Down Control As we know, the boom of the excavator works under a negative load usually, an extension of the boom cylinder to a working position generates amount of potential energy and then for a retraction of the cylinder, the pressure flow from the large chamber is transitioned to the tank though a back pressure valve. A new control circuit for the boom cylinder was designed as follows.
Fig. 4. The Static Results Compared
the system operating in the boom cylinder extension is that the joystick output the signals belongs to the operator controls to the dSPACE and then the controller control the pump and the valves as the set strategy. The valves of the boom is set fully open and the flow into the large chamber and the pressure are controlled directly by the pump belongs to the signals output by the joystick in this proceed to decrease the power loss. However, when the boom cylinder retracts, the regeneration method was applied. In this proceed, the pump works at a very low flow output condition and the valves of the boom connected to the tank, the valve of the small chamber was set fully open and the speed of the cylinder was controlled by changing the opening ratio of the large chamber valve.
Fig. 5. The Dynamic Results of the Boom Compared
C. The Stick Extend and Retract Control The stick is a four quadrant operation actuator, in order to take advantage of the gravity potential energy, the strategy should change when the stick works under different quadrant condition. There is a switching point when the stick is vertical with the horizontal plan, it works under the over-running load before the point and after under the negative load model. No matter under what model the stick works, the flow inlet valve
Fig. 6. The Dynamic Results of the Stick Compared
39
was set fully open to decrease the pressure drop. Working in the over-running load, the pump fill the oil needed in the inlet chamber at a low pressure level and the return oil cavity was controlled based on the pressure in it and the speed set. Working in the negative load model, the strategy is just like the strategy of the boom extension. The pressure of the return oil cavity was selected as the switch reason in the controller.
the regeneration method is applied. So it is proper to control the boom by the new system and the control strategy.
D. The Swing Control As a high inertia system, the pressure of the swing motor in acceleration proceed will be the spillway pressure, so the control pressure of the pump was set lower than the spillway pressure and the two valves were fully opening. In the brake process, the filling oil cavity was connected to the tank and the back pressure cavity was connected to the tank also though a small throttling orifice to prevent the backswing from shocking.
Fig. 9. Results of Boom with LUDV System
E. Multi-actuator Compound Action The control pressure of the pump was set to meet the maximum load and the control flow signal was calculated to match the operator settings. The filling valve of the maximum load actuator are fully opening and the filling valves of the last actuators are controlled with the pressure compensation method. So every actuator works under SMISMO method and the throttling loss was less in this way. V.
TEST RESULTS
In this research, the test was based on a 6-ton hydraulic excavator applying LUDV and the new SMISMO system, as shown in Fig.8. The working performance of the single actuator such as the boom, stick and swing is tested to analysis and compare the features of the systems. And then the energy of the pump output was calculated about the boom test and the stick test. Test with LUDV
Fig. 10. Results of Boom with SMISMO System
The stick test is taken to show that if the system switches automatically between models. Fig.11 and 12 demonstrate that the switch strategy of the stick control model is effective and the speed of the cylinder around the switch point changed a little. And also the throttle losses in the stick system is minimized based on the control method.
Test with SMISMO
Fig.13 and 14 illustrates the pressure of the swing motor and the pump. It can be seen that in the brake proceed there is underdamping oscillogram in the swing cavity of the LUDV system while the pressure curve of the SMISMO system is slide. Fig. 8. The Test Proceed
The Fig.9-14 present the experimental results of the outlet pressure of the pump, the pressures of the actuator chambers and the displacement of the actuators at highest actuator velocity. By referring to the results in Fig.9-10, the pressure pulsations of the pump when the boom starts to move reduced from 6.9MPa to 1.7MPa and also the pressure of the LUDV system shocks as a underdamping oscillogram while the pressure of the SMISMO system has only a fluctuation. The boom control performance under the SMISMO is good and the pressure of the piston rod chamber is more than 0.4 MPa when
Fig. 11. Results of Stick with LUDV System
40
VI.
CONCLUSION
The control performance of the hydraulic excavator with the SMISMO system and the energy-saving control strategy is studied in this paper. The characteristics of the control system are analyzed by experiment. The control strategy of the actuators is designed by modeling and experiments. The experimental results show that the proposed control scheme can significantly decreases the pressure losses through the valve and improve the energy efficiency of the machine, just as the energy consumption of the boom and arm system fell 15% and 5.6% compared to the load sensing system; the pressure shocks within hydraulic actuators is decreased as well, for example the pressure pulsations of the pump when the boom starts to move reduced from 6.9MPa to 1.7MPa and also the backswing shocks when the swing is braking is eliminated, thus the stationarity of the whole machine is improved accordingly.
Fig. 12. Results of Stick with SMISMO System
REFERENCES [1]
[2]
[3] Fig. 13. Results of Swing with LUDV System [4]
[5] [6]
[7]
[8] Fig. 14. Results of Swing with SMISMO System
[9]
The energy outputs of the pump based on the experimental results are summarized in TABLE ǿ. From the data of the table, the proposed configuration system can significantly decreases the pressure losses through the valve and improve the energy efficiency of the machine, just as the energy consumption of the boom and arm system fell 15% and 5.6% compared to the load sensing system. TABLE I.
[10]
[11]
[12]
COMPARISON OF OUTPUT ENERGY OF THE PUMP
8
Boom (kJ)
Stick (kJ)
With LUDV
37.6
10.8
With SMISMO
32.4
10.2
[13]
41
Zimmerman, Joshua D., et al. "Energy Consumption of an LS Excavator Hydraulic System." ASME 2007 International Mechanical Engineering Congress and Exposition American Society of Mechanical Engineers, 2007:117-126. Yang, Jing, Q. Long, and Y. Yang. "Excavator Energy-saving Efficiency Based on Diesel Engine Cylinder Deactivation Technology." Chinese Journal of Mechanical Engineering 25.5(2012):897-904. ZHANG Yanting. "Simulation and experimental research on energy regeneration with hydraulic motor for hybrid drive excavator." Chinese Journal of Mechanical Engineering 43(2007):224-228. Backé, W. "Design systematics and performance of cartridge valve controls." International conference on fluid power, tampere, finland. Vol. 3. 1987. Andersson, Bo. "Hydraulic valve means." U.S. Patent No. 4,662,601. 5 May 1987. Yao, Bin, and Chris DeBoer. "Energy-saving adaptive robust motion control of single-rod hydraulic cylinders with programmable valves." American Control Conference, 2002. Proceedings of the 2002. Vol. 6. IEEE, 2002. Yao, Bin, and Song Liu. "Energy-saving control of hydraulic systems with novel programmable valves." Intelligent Control and Automation, 2002. Proceedings of the 4th World Congress on. Vol. 4. IEEE, 2002. Shenouda, Amir. "Quasi-static hydraulic control systems and energy savings potential using independent metering four-valve assembly configuration." (2006). Eriksson, Björn. "Mobile Fluid Power Systems Design: with a Focus on Energy Efficiency." (2010). Choi, Kyujeong, et al. "Energy-saving in excavators with application of independent metering valve." Journal of Mechanical Science and Technology 29.1 (2015): 387-395. Wang Qingfeng, et al. "Research on Electro hydraulic Meter in and Meter out Independent Regulation System." China Mechanical Engineering (1999). Quan, Long, and Z. Lian. "Improving the Efficiency of Pump Controlled Differential Cylinder System with Inlet and Outlet Separately controlled principle." Chinese Journal of Mechanical Engineering 41.3 (2005): 123-127. QUAN Long, FENG Kewen, Chen Qing. "Independent control electrohydraulic system of oil inlet and outlet with pump valve composite flux matched." China. Patent No. 101109398A. January 2008.
