Parameter matching of hydraulic balancing circuit based on AMESim

HE Ningning， ZHANG Ping， ZHANG Sen， SUN Tianyu

(School of Mechanical and Electrical Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China)

Abstract： In order to improve the stability of the hydraulic balancing circuit, taking a certain type of vehicular radar flip device as the research object, the influence of different wind load, counterbalance valve parameters and hydraulic pump flow pulsation on the system flip process are simulated and analyzed. Through the force analysis of the flipping device, the total load curve of the flip cylinder is obtained by using MATLAB simulation. The simulation model of balancing circuit and plane flip device are built by AMESim software, and the reasonable parameter matching relationship is obtained by specific simulation analysis. The simulation results show that when the wind load is to the left and decreases, the system runs more stably. When wind load works in the right direction, the load on the piston rod of the hydraulic cylinder decreases but the jitter amplitude increases. At the same time, the stability of the balancing circuit can be effectively improved by properly reducing the damping diameter of the counterbalance valve, setting the pilot ratio to 4∶1 and using the hydraulic pump with small pulsation. The optimized parameter matching relationship can not only meet the requirements of typical system conditions and responses, but also improve the performance of the circuit.

Key words： balancing circuit； parameter matching； AMESim； counterbalance valve； simulation

0 Introduction

The balancing circuit is one of the most commonly used circuits in hydraulic systems. It is used in engineering, construction, metallurgy and other mechanical fields, especially under negative load conditions to balance load gravity to achieve stable system operation. The matching performance of the circuit has a great influence on the system[1]. If the matching is unreasonable, the system will experience jitter, motion stall, excessive control pressure and inaccurate positioning, which will bring adverse effects on equipment operation safety, system energy consumption, boom and frame deformation, etc[2]. Many scholars have conducted relevant studies on the steady-state characteristics of the balancing circuit from different angles and with different methods[3-4]. The dynamic characteristics of the hydraulic counterbalance valve are studied with the method of parameter optimization[5]. AMESim is used to analyze the influence of the counterbalance valve on the jitter phenomenon of the crane lifting system[6]. The dynamic characteristics of threaded cartridge valve are simulated and analyzed through AMESim software[7-8]. The influence of counterbalance valve spring stiffness, orifice structure parameters and motor inlet and outlet controlled cavity volume on the stability of hydraulic motor circuit is studied[9]. At present, most of the research focuses on the performance of the counterbalance valve and the impact of the counterbalance valve parameters on the circuit[10-12]. However, there is no systematic research on the influence of the load change and the parameter change of other circuit components on the system performance. A certain type of vehicular radar flip system is taken as an example. The system model is established by using AMESim software, and the influences of wind load, counterbalance valve parameters and hydraulic pump pulsation on the stability of the circuit are analyzed. The parameter matching of the circuit is studied to improve the stability of the balancing circuit.

1 Working condition analysis of hydraulic system and working principle of balancing circuit

1.1 Working condition analysis of hydraulic system

The schematic diagram of a certain type of vehicular radar flip device is shown in Fig.1, which is composed of a flip cylinder, a mechanical arm and a radar antenna. The flipping angle of the mechanical arm is controlled by the extension of the hydraulic cylinder piston rod. The angle between the mechanical arm and the horizontal plane is 30°, and it rotates clockwise to 110° to reach the working position. After the work is completed, the flip cylinder is controlled to rotate to the initial position. In the flipping process, the load on the piston rod of the hydraulic cylinder changes constantly with the change of the angle of the mechanical arm. When the flip exceeds 90° and turning motion to the initial position, there is a negative load condition. If no technical measures are taken, the mechanical arm will drop at an excessive velocity. Therefore, two-way counterbalance valve should be set in the circuit. In addition, wind load is an important part of the system load, the change of overturning moment caused by high wind load will affect the circuit control accuracy and stability. In this paper, it is set that the wind load is positive to the right and negative to the left.

1—Flip hydraulic cylinder； 2—Mechanical arm； 3—Radar antenna

According to the wind load direction, the system is divided into three working conditions, and the stress situation is shown in Fig.2.

When there is no wind load during the flipping process, as shown in Fig.2(a), the torque balance equation is

L3Fcosαsinβ+L3Fsinαcosβ-W(L2+L3)cosβ=0.

(1)

When the wind load direction is to the right during the flipping process, as shown in Fig.2(b), the torque balance equation is

L3Fcosαsinβ+L3Fsinαcosβ-W(L2+L3)cosβ+

F1(L1+L2+L3)sinβ=0.

(2)

(a) No wind load

When the wind load direction is to the left during the flipping process, as shown in Fig.2(c), the torque balance equation is

L3Fcosαsinβ+L3Fsinαcosβ-W(L2+L3)cosβ-

F1(L1+L2+L3)sinβ=0,

(3)

whereFrepresents the force on the piston rod of the hydraulic cylinder;F1represents wind load;L1represents the distance from the top of the mechanical arm to the center of gravity, the size is 1 000 mm;L2represents the distance from the center of gravity to the hinge point of the flip hydraulic cylinder and the mechanical arm, the size is 1 382 mm;L3represents the distance from the hinge point of the flip hydraulic cylinder and the mechanical arm to the bottom end of the mechanical arm, the size is 618 mm;αrepresents the initial angle between the flip hydraulic cylinder and the horizontal plane;βrepresents the angle between the mechanical arm and the horizontal plane, the value range is 30°to 110°;Wrepresents the total gravity of the system, the size is 40 kN. The relationship betweenαandβis

(4)

The load on the piston rod of the cylinder is simulated by MATLAB, and the load curve is shown in Fig.3. It can be seen from the simulation curve that the load on the piston rod of the cylinder under the three working conditions gradually decreases with the increase of the turning angle of the manipulator. The maximum positive load is 203 868 N, and the maximum negative load is 88 885 N.

Fig.3 Variation of load curves

1.2 Working principle of balancing circuit

The schematic diagram of a certain type of vehicular radar hydraulic system is shown in Fig.4[13-14]. The balancing circuit consists of hydraulic cylinder, counterbalance valves,Ytype reversing valve, relief valve and hydraulic pump. The counterbalance valve structure is shown in Fig.5, which is mainly composed of main valve core, check valve core, pressure adjusting spring and other components. The counterbalance valve 1 is on the side without rod cavity of hydraulic cylinder, and the counterbalance valve 2 is on the side with rod cavity of hydraulic cylinder. The working principle of the balancing circuit is as follows.

In the process of flipping to the specified position, the counterbalance valve 1 is equivalent to a check valve, and the counterbalance valve 2 is equivalent to a sequence valve. A part of the oil enters portathrough the right position of the reversing valve, overcomes the spring force of the check valve core, enters the rodless cavity of the hydraulic cylinder, and pushes the piston to move. A part of the oil acts on the main valve core of the counterbalance valve 2 through the pilot portc. The main valve core of counterbalance valve 2 opens under the combined action of pilot oil pressure, rod chamber oil pressure and main valve core spring force, and returns to the tank from portd. In the process of turning to the initial position, the functions of counterbalance valve 1 and counterbalance valve 2 are opposite to the flipping process. The oil enters portdthrough the left position of the reversing valve, portbis the pilot port, and returns to the tank from porta. When the reversing valve is placed in the neutral position, it can be used in conjunction with the counterbalance valve to keep the hydraulic cylinder at any position, which has a good pressure-keeping effect.

1—Hydraulic pump； 2—Relief valve； 3—Reversing valve； 4—Counterbalance valve； 5—Hydraulic cylinder

1—Pressure regulating screw； 2—Pressure adjusting nut； 3—Pressure adjusting spring； 4—Main valve core； 5—Check valve core； 6—Reset spring

2 Balancing circuit simulation model

According to the hydraulic system principle of a certain type of vehicular radar flip device, the counterbalance valve and axial plunger pump model are built by using the HCD (Hydraulic component design) library of AMESim software, and the plane mechanism library is used to build the system flip device model. The internal gear pump and other hydraulic components are selected from the standard hydraulic library model to build the system. The built system simulation model is shown in Fig.6, and the plunger pump model is shown in Fig.7. Set the parameters of the model according to the actual parameters of the circuit. The cylinder diameter is 140 mm, the piston rod diameter of the hydraulic cylinder is 100 mm, and the cylinder stroke is 794 mm.

1—Hydraulic pump； 2—Reversing valve； 3—Control signal； 4—Counterbalance valve； 5—Hydraulic cylinder； 6—Load application module

Fig.7 Plunger pump model

3 Dynamic performance simulation of balancing circuit

The dynamic characteristics of the circuit are achieved by simulation. The simulation time is 130 s, including flipping stage, stay stage and turning motion stage. Specific simulation and analysis of the influence of wind load changes, counterbalance valve parameters and hydraulic pump flow pulsation on the performance of the balancing circuit.

3.1 Impact of wind load on the balancing circuit

3.1.1 Influence of wind load size on the balancing circuit

Set three working conditions, the wind load is to the left (that is in the windward state) and the size is 20 kN, 10 kN and no wind load. It can be seen from Figs.8 and 9 that the size of the wind load has a significant impact on the stability of the system. In the process of flipping, with the continuous decrease of wind load on the system, the load on the piston rod of the hydraulic cylinder decreases, the displacement of the main valve core of the counterbalance valve 2 decreases, and the velocity fluctuation of the hydraulic cylinder piston rod becomes smaller and smaller. It can be seen that the system is more stable when the wind load is reduced.

Fig.8 Displacement curves of counterbalance valve 2 main valve core

Fig.9 Velocity curves of hydraulic cylinder piston rod

3.1.2 Influence of wind load direction on balancing circuit

There are three working conditions: wind load to the left is 5 kN, no wind load and wind load to the right is 5 kN. During the flipping process, with the change of the angle of the mechanical arm, the load on the piston rod of the hydraulic cylinder also changes, and the load on the piston rod decreases when the wind load changes from left to right. It can be seen from Fig.10 that with the change of wind load from left to right, the displacement of the main valve core of the counterbalance valve 2 decreases. It can be seen from Fig.11 that when the wind load is to the left and decreases, the load on the piston rod of the hydraulic cylinder decreases and the speed jitter amplitude decreases. However, when the wind load is to the right and increases, the load on the piston rod of the hydraulic cylinder decreases and the speed jitter amplitude increases. It shows the direction of the wind load has a great influence on the balancing circuit.

Fig.10 Displacement curves of counterbalance valve 2 main valve core

Fig.11 Velocity curves of hydraulic cylinder piston rod

3.2 Influence of counterbalance valve parameters on the balancing circuit

3.2.1 Control influence of port damping diameter

The diameter of the damping hole of the control oil port is 1 mm, 0.5 mm and 0.2 mm, respectively, and the influence of different orifice diameters on the stability of the circuit is studied. It can be seen from the simulation curves of Figs.12 and 13 that as the damping diameter of the control port decreases, both the displacement of the main valve core of the counterbalance valve 2 during the flipping process and the overshoot of the movement velocity of the hydraulic cylinder piston rod in the turning process increase. The time for the main valve core to reach the stable opening degree is shortened, and the velocity of the hydraulic cylinder piston rod is faster to reach the stable state, but too small diameter will lead to the delay of the system and the increase of the velocity jitter of the hydraulic cylinder piston rod. Therefore, appropriately reducing the control port damping diameter can effectively improve the stability of the counterbalance valve, so the damping diameter of control port is 0.5 mm.

Fig.12 Displacement curves of counterbalance valve 2 main valve core in flipping stage

Fig.13 Velocity curves of piston rod of hydraulic cylinder in turning motion stage

3.2.2 Influence of size of pilot ratio

By setting the size of the counterbalance valve oil cavity and the spring cavity, the pilot ratio of the counterbalance valve is set to 5∶1, 4∶1 and 3∶1, respectively. The movement velocity of hydraulic cylinder piston rod and the displacement curve of counterbalance valve 2 main valve core under different pilot ratio are obtained by simulation. It can be seen from Figs.14 and 15 that when the pilot ratio is 4∶1, the running speed of the piston rod of the hydraulic cylinder is relatively stable. The number of jitter and overshoot of the main valve core are reduced at the same time, and the time to reach the stable opening is also shortened, so the pilot ratio is set to 4∶1 can effectively improve circuitstability.

Fig.14 Velocity curves of hydraulic cylinder piston rod

Fig.15 Displacement curves of counterbalance valve 2 main valve core

3.3 Influence of hydraulic pump pulsation on balancing circuit

The internal gear pump and axial plunger pump are used in the simulation circuit. The outlet flow curves of the hydraulic pump and the displacement curves of the main valve core of the counterbalance valve 2 are obtained as shown in Figs.16 and 17.

Fig.16 Flow curves of pump outlet

Fig.17 Displacement curves of counterbalance valve 2 main valve core

According to the simulation results, it can be concluded that the flow pulsation of the gear pump is higher than that of the axial plunger pump. When the flow pulsation of the hydraulic pump decreases in the initial flipping process, the overshoot of the main valve core of the counterbalance valve 2 changes little, and the time for the main valve core to reach the stable opening degree is reduced from 2.1 s to 1.3 s. Smaller flow pulsation can make the circuit reach stable state faster.

3.4 System dynamic performance analysis

Reasonable parameter matching is carried out according to the simulation results.Under different working conditions, the load variation curves of the hydraulic cylinder piston rod during the flipping stage is shown in Fig.18, which is basically consistent with the theoretical load curve shown in Fig.3. It can be seen from Figs.19 and 20 that the hydraulic cylinder piston rod moves at a constant velocity in the process of flipping, stays working after flipping to a certain angle, and finally turns back to the initial state smoothly.

Fig.18 Force curves of piston rod of hydraulic cylinder

Fig.19 Displacement curve of hydraulic cylinder piston rod

The displacement of the counterbalance valve during the flipping stage is shown in Figs.21 and 22. The check valve core of counterbalance valve 1 is open, and the main valve core is closed. The check valve core of balancing valve 2 is closed, and the main valve core is open. As the load decreases, the valve core displacement decreases gradually, and the turning motion stage is reversed. After the parameters are matched, the hydraulic cylinder piston rod velocity oscillation decreases, the main valve core opens normally, and the system runs stably and has good performance.

Fig.20 Velocity curves of hydraulic cylinder piston rod

Fig.21 Displacement curves of check valve core

Fig.22 Displacement curves of counterbalance valve main valve core

4 Conclusions

1) The simulation model of the balancing circuit and the plane flip mechanism is built by AMESim software, and the force curves of the piston rod of the hydraulic cylinder under different working conditions are simulated and analyzed for a certain type of vehicle radar flip device. The results are basically consistent with the load curve of the hydraulic cylinder piston rod under different wind loads obtained by MATLAB simulation.

2) Through the simulation analysis, it is found that the magnitude and direction of wind load have great influence on the circuit. When the wind load direction is to the left and the size is different, the load on the piston rod of the hydraulic cylinder decreases with the decrease of the wind load, and the hydraulic cylinder runs more smoothly. When the wind load direction is different, the comparison of the wind load to the right and the no wind load conditions shows that the load on the piston rod of the hydraulic cylinder decreases, but the vibration amplitude of the hydraulic cylinder increases, and the circuit stability becomes worse. The system can operate stably under a certain range of wind load.

3) It can improve the movement stability of the hydraulic cylinder piston rod by appropriately reducing the diameter of the orifice of the control port of the counterbalance valve and setting the pilot ratio to 4∶1. At the same time, the oil pulsation output by the hydraulic pump is directly related to the stability of the circuit. A pump with a smaller pulsation can shorten the time for the system to reach a stable state. After reasonable parameter matching, the system performance is improved.