Research on Characteristics of Three-Chamber Hydraulic Cylinder Driving Loader Boom

Abstract

When the loader boom is lifted and lowered, the hydraulic pump operates at high peak power levels. In this process, the hydraulic valve port dissipates the gravitational potential energy of the boom. Consequently, the dissipated energy is converted into thermal energy, resulting in elevated hydraulic oil temperature and reduced energy efficiency. This paper proposes a gravitational potential energy recovery system based on three-chamber cylinder and a hydraulic accumulator. The system utilizes the hydraulic accumulator to balance the weight of the loading boom and achieve energy recovery for the boom. The co-simulation model of wheel loader based on the three-chamber cylinder was built in SimulationX, then the energy consumption was analyzed under two kinds of typical operating modes. The simulation results illustrate that when the initial pressures of accumulators are 6 and 8 MPa with heavy-load and without load, the system has the highest energy utilization rate. By establishing a loader prototype and investigating the operating characteristics and energy efficiency of the boom driven by a two-chamber cylinder and a three-chamber cylinder, the experimental results illustrate that the new system operates smoothly, reducing energy consumption by 39.24% and peak power by 27.41%.

1 Introduction

The loader is one of the most widely used construction machinery. In this working process, the boom lifts and falls frequently. When the boom is lifted, the hydraulic pump drives the high-pressure oil flow to the rodless cavity of the hydraulic cylinder to raise the work-equipment. When the boom is fallen, the gravitational potential energy of the working device is converted into thermal energy in the form of throttling loss, resulting in the increase of the oil temperature and the reduction of the working efficiency of the system.

To reclaim and utilize the stored potential energy during lifting and falling of the working equipment of construction machinery, many researches have been carried out on excavators, forklifts [1,2,3,4,5]. The existing potential energy recovery methods can be categorized into electrical recovery and hydraulic recovery based on the energy storage forms. In the electrical recovery method, the electrical energy storage components are mainly ultra-capacitors and batteries. Anderaen set up a test prototype of forklift truck, using the secondary component hydraulic motor—generator recovery when the lifting mechanism is lowered. The potential energy is transformed into electric energy and subsequently reserved in the battery, and the energy recovery efficiency is obtained by about 40% [6]. Wang and Lin used a similar method to recover the potential energy of the excavator boom. By adding an accumulator in the potential energy recovery loop, the potential energy recovery rate was increased up to 41% and the peak power of the generator was decreased.

If batteries or super-capacitor are used to recover potential energy, the overall recovery efficiency will be reduced due to many more energy conversion links and the complex transfer path of energy recovery. In addition, although the battery has a high energy density, its power density is very low, only about 30–100 W/kg, which cannot meet the demand of instantaneous high power of construction machinery. As an alternative method, the power density of hydraulic accumulator can reach up to 50–1000 W/kg. As a result, the use of hydraulic energy recovery mode can better fulfill the high-power demands of construction machinery across various operating conditions. Ge utilized an asymmetric pump having three ports and an accumulator to regenerate the potential energy directly. The potential energy recovery rate was 82.7% [7]. Ranjan transformed the potential energy of the boom into the stored pressure energy within the accumulator. The pressure oil in the accumulator and the main pump were driven together as the boom was lifted. The proportional flow valve, the accumulator and the model prediction controller were used to realize the position control of the boom cylinder. The efficiency of the system was increased by 10% [8]. Hippalgaonkar introduced the high-pressure oil into the accumulator to convert the gravitational potential energy into energy in the form of hydraulic power when the boom falls. The recovered energy can be used to drive the cooling system or other auxiliary devices. The fuel consumption of the system is decreased by 27% [9]. Zhao adopted the method of energy regeneration, introduced the recovered high-pressure oil from the accumulator into the inlet of the hydraulic pump, and then used the boom potential energy, which reduced the energy consumption of the system by 14.8%.

The advantage of hydraulic energy recovery can be integrated easily into the hydraulic system. However, nearly all conventional potential energy recovery methods possess a multitude of energy conversion links, resulting in a lengthy chain for energy transfer, and the recovered hydraulic energy is not easy to be reused. Xia established a prototype of hydraulic excavator by using the method based on self-weight liquid–gas balance of the three-chamber hydraulic cylinder, and realized about 48.5% of energy consumption reduction.

To solve the problem of large energy loss during the loader boom lifting and falling process, this paper proposes an energy recovery system based on the three-chamber hydraulic cylinder driving the loader boom. A good energy-saving effect had been achieved on excavators, however excavators have different external load characteristics from loaders, and the excavator's ratio of the external load to the weight is much smaller than the loader’s. As a result, the balance position of the hydraulic and gas balance system of the excavator is basically unchanged when the bucket is lifted with full load and is fallen without load, while the balance position of the loader changes greatly. Therefore, it is necessary to study the dynamic and energy consumption characteristics of the liquid–gas balance energy recovery and reuse system of the three-chamber cylinder of the loader under different load conditions. When the initial working pressure of the accumulator is different, the energy recovery efficiency of the system is also different. The energy recovery efficiency of the liquid–gas balance system can be optimized through experiments. The supreme merit of this method is that it does not require to change the original boom structure and the original hydraulic system. The three-chamber cylinder is used to substitute the traditional single lever hydraulic cylinder, which can directly transform the hydraulic energy and potential energy, and it has high recycling efficiency.

In this paper, the mechanical-hydraulic joint simulation model of the three-chamber hydraulic cylinder driving the loader boom is firstly established. The initial pressure of the accumulator is set as 6 MPa and 8 MPa respectively when the loader is under heavy and no-load conditions. A test prototype of a loader with the three-chamber hydraulic cylinder driving the boom is entrenched. The operating characteristics and energy efficiency characteristics of the system are analyzed and compared by the experimental analysis when the two-chamber hydraulic cylinder and the three-chamber hydraulic cylinder are used to drive the boom.

The key contribution of this paper is to propose a method of potential energy of loader boom recovery and reuse based on the three-chamber hydraulic cylinder. In the proposed method, the potential energy recovery chamber in the three-chamber hydraulic cylinder is connected with the accumulator, and the gravitational potential energy is directly recovered and utilized. The loader is the construction machinery for shovel excavation and the piston stroke of the boom cylinder is basically the same in each working cycle. Therefore, the initial pressure of the accumulator is optimized to obtain higher energy efficiency.

The following is the compositional structure of the remainder of the paper. In Sect. 2, the working principle of the three-chamber cylinder driving loader boom hydraulic system with gravitational potential energy recovery is analyzed. In Sect. 3, the co-simulation model is established and the energy consumption is analyzed. In Sect. 4, A prototype of loader is established, Experimental studies were conducted to investigate the operational characteristics and energy efficiency of the boom driven by a two-chamber cylinder and a three-chamber cylinder. Finally, Sect. 5 offers some Summary recommendations about this study.

2 System Working Principle

The hydraulic circuit principle of the three-chamber hydraulic cylinder driving the boom is shown in Fig. 1. The signal test system is also shown in Fig. 1. Chamber C of the three-chamber hydraulic cylinder is composed of hollow piston rod and fixed plunger on the cylinder body, the original chamber without piston-rod and chamber with piston-rod are chambers A and B separately. Chambers A and B are joined with the original hydraulic circuit, which realize the oil inlet and outflow of chambers A and B of the three-cavity hydraulic cylinder. Chamber C is directly connected with the hydraulic accumulator, which realized the direct the recuperation and utilization of the potential energy stored in the boom.

Fig. 1

Boom driving system based on three-chamber cylinder

In order to further explain the change of dynamic characteristics in the working process of the new system and the operation of the boom by replacing the two-chamber hydraulic cylinder with the three-chamber hydraulic cylinder, the transfer function of the valve-control three-chamber hydraulic cylinder is established. The influence of initial pressure, hydraulic frequency and damping ratio of accumulator on operating characteristics of the boom are analyzed by the transfer function.

Flow continuity equation of a chamber of the three-chamber cylinder is:

$$\frac{{V}_{A}}{{\beta }_{e}}\frac{d{p}_{A}}{dt}={q}_{A}-{A}_{A}\frac{d{x}_{P}}{dt}-{c}_{ep}{p}_{A}$$

(1)

where V_A is the volume of chamber A of three-chamber hydraulic cylinder (including valve and connecting pipe), β_e is the effective bulk elastic modulus of hydraulic oil (including hydraulic oil, mechanical flexibility of connecting pipes and cylinder blocks), p_A is the pressure in chamber A, q_A is the flow of chamber A, A_A is the area of chamber A, x_p is the piston displacement of the three-chamber hydraulic cylinder, c_ep is the external leakage coefficient of hydraulic cylinder.

Flow continuity equation of chamber B of the three-chamber cylinder is:

$$\frac{{V}_{B}}{{\beta }_{e}}\frac{d{p}_{B}}{dt}={A}_{B}\frac{d{x}_{P}}{dt}-{c}_{ep}{p}_{B}-{q}_{B}$$

(2)

where V_B is the volume of chamber B (including valve and connecting pipe), p_B is the pressure in chamber B, A_B is the area of chamber B, q_B is the flow of chamber B.

Flow continuity equation of chamber C of the three-chamber cylinder is:

$$\frac{{V}_{C}}{{\beta }_{e}}\frac{d{p}_{C}}{dt}={A}_{C}\frac{d{x}_{P}}{dt}-{q}_{C}-{c}_{ep}{p}_{C}$$

(3)

where V_C is the volume of chamber C (including valve and connecting pipe), p_C is the pressure in chamber C, A_C is the area of chamber C, and q_c is the flow from accumulator to chamber C.

Chamber C of the three-chamber hydraulic cylinder is directly connected to the accumulator through pipelines, ignoring the pressure loss, thus the pressure in chamber C is equivalent to the oil pressure in the accumulator. Due to the use of bladder accumulator, the relationship between pressure and gas volume in the accumulator satisfies the gas state equation, as shown in the formula (4). Since the accumulator acts as an auxiliary oil source to release energy rapidly, This is commonly recognized as an adiabatic process., so for $n=1.4$.

$${p}_{0}{V}_{0}^{n}={p}_{c}{{V}_{c}}^{{\prime}n}=Const$$

(4)

where ${p}_{0}$ is the accumulator initial state pressure, ${V}_{0}$ is the volume of gas at the initial state of the accumulator, ${V}_{c}^{\prime}$ is the volume of gas in the accumulator when the pressure being p_C, where${V}_{c}^{\prime}={V}_{0}-\Delta V$, $\Delta V$ is the oil volume released by chamber C during operation.

The equation of force balance for this hydraulic cylinder is,

$${A}_{A}{p}_{A}+{A}_{C}{p}_{C}={m}_{t}\frac{{d}^{2}{x}_{p}}{d{t}^{2}}+{B}_{p}\frac{d{x}_{p}}{dt}+{F}_{L}$$

(5)

where m_t is the total effect of the three-chamber hydraulic cylinder piston mass and the mass converted to the piston, B_p is the viscous damping coefficient, F_L is the external load acting on the piston.

By applying Laplace transform to the Eqs. (1)–(5), we can get:

$${Q}_{L}={K}_{q}{X}_{v}-{K}_{C}{P}_{L}$$

(6)

$${Q}_{L}={A}_{P}s{X}_{P}+{C}_{tp}{P}_{L}+\frac{{V}_{t}}{4{\beta }_{e}}s{P}_{L}$$

(7)

$${A}_{A}{P}_{A}+{A}_{C}{P}_{C}={m}_{t}{s}^{2}{X}_{P}+{B}_{P}s{X}_{P}+{F}_{L}$$

(8)

where V_t is the total compression volume.

The velocity transfer function of three-chamber cylinder is obtained by:

$${X}_{P}=\frac{{P}_{0}{A}_{C}+\frac{{A}_{A}{K}_{q}{X}_{v}}{{C}_{tp}+\frac{{V}_{t}}{4{\beta }_{e}}s+{K}_{c}}-{F}_{L}}{({m}_{t}+m){s}^{2}+2{B}_{P}s+\frac{{A}_{A}^{2}s}{{K}_{c}+{C}_{tp}+\frac{{V}_{t}}{4{\beta }_{e}}s}}$$

(9)

Natural frequency of hydraulic system and damping ratio are:

$${w}_{n}=\sqrt{\frac{1}{({m}_{t}+m)\frac{{v}_{t}}{4{\beta }_{e}}}}$$

(10)

and

$${\zeta }_{n}=\frac{{K}_{ce}({m}_{t}+m)+\frac{{B}_{P}{V}_{t}}{2{\beta }_{e}}}{2\sqrt{({m}_{t}+m)\frac{{V}_{t}}{4{\beta }_{e}}}}$$

(11)

where m is the mass of the oil in the accumulator, and ${K}_{ce}$ is the total flow-pressure coefficient.

Increasing the initial pressure p₀ of the accumulator can improve the response speed of the boom. Reducing the oil mass m (i.e., reducing the accumulator volume V₀) in the accumulator can improve the natural frequency of the system and make the system respond quickly, where it reduces the damping ratio and weakens the stability of the system. Therefore, on the basis of comprehensive consideration of the dynamic response speed, stability and energy consumption of the system, the volume of the accumulator should be reduced as much as possible. Therefore, the accumulator volume is preliminarily determined to be 4 L. The initial pressure of the accumulator is determined according to the following simulation study.

3 Simulation Study

Firstly, the 3D model of the loader's working device was established in Pro/E software. Meanwhile, The hydraulic system model of the whole machine was established by using simulation and analysis software SimulationX. SimulationX is a universal CAE tool for modeling, simulation and analysis in a multidisciplinary field. It has a powerful library of standard components and provides a high-effective method of co-simulation between mechanical devices, hydraulic system and control system.

The 3D model was imported into the simulation software SimulationX, in which the 3D model and the simulation model were connected through the three-chamber hydraulic cylinder model to establish the mechanic-hydraulic co-simulation model of the three-chamber hydraulic cylinder driving the boom. The co-simulation model is shown in Fig. 2.

Fig. 2

Co-simulation model

According to the load characteristics and reserved installation space of the boom hydraulic cylinder, the geometrical parameters of the three-chamber hydraulic cylinder are selected, as shown in Table 1. In Table 1. D_a is the diameter of chamber A, D_b is the diameter of chamber B, Dc is the plunger diameter of chamber C, and L represents the stroke of three-chamber hydraulic cylinder. In the simulation model, three plunger hydraulic cylinders are used to replace the three-chamber hydraulic cylinder, and other hydraulic components are introduced directly from the component library of software SimulationX.

Table 1 The main parameters of the three-chamber cylinder

The lifting and falling process of the loaded boom is simulated under no-load and heavy-load conditions separately. The power and energy simulation curves of the accumulator within a single period of lifting and falling process of the boom under different initial pressures of the accumulator are shown in Fig. 3. The simulation result of the hydraulic pump output power is shown in Fig. 4. The power P_s and energy E_s stored in the accumulator are calculated by Eqs. (12) and (13) respectively, and the output power P_p and energy E_p of the hydraulic pump are calculated by Eqs. (14) and (15) separately.

$${P}_{s}={p}_{c}{A}_{c}v$$

(12)

$${E}_{s}=\int {p}_{C}{A}_{C}vdt$$

(13)

$${P}_{p}={p}_{p}{q}_{p}$$

(14)

$${E}_{p}=\int {p}_{p}{q}_{p}dt$$

(15)

where ${p}_{p}$ represents the output pressure of the hydraulic pump. ${q}_{p}$ represents the output flow of hydraulic pump.

Fig. 3

Simulation result of power and energy of the accumulator

Fig. 4

Simulation result of power and energy of the pump outlet

The energy consumption characteristics of the system are shown in Table 2 for the initial working pressures of the accumulator at 4, 6, and 8 MPa. Based on the data in Table 2, it is observed that the hydraulic pump has the minimum peak power and energy consumption under a no-load condition when the initial working pressure of the accumulator is 6 MPa. Additionally, the hydraulic pump exhibits the minimum peak power and energy consumption under a heavy-load condition when the initial pressure of the accumulator is 8 MPa. Therefore, based on these results, the following experiments were conducted: no-load and heavy-load tests were carried out at the initial working pressure of the accumulator of 6 MPa and 8 MPa, respectively.

Table 2 Simulation results of energy consumption characteristics under different pressures in the accumulator

4 Experimental Study

XG916 II loader test prototype photos is shown in Fig. 5. The test principle is shown in Fig. 1. Atos pressure sensor is used to test the pressure in each chamber of the hydraulic cylinder. The wire-drawing displacement sensor tests the displacement of the hydraulic cylinder. In the meanwhile, the output power of hydraulic pump also needs to be tested. Considering the throttling loss caused by the flow sensor, the real-time rotation speed of diesel crankshaft is measured by photoelectric sensor. The diesel engine drives the hydraulic pump through the splitter box (the transmission ratio is 1:1), and the real-time rotation speed of the hydraulic pump shaft can be obtained. The hydraulic pump is a gear fixed displacement pump, whose nominal displacement is 50 ml/r, rated pressure is 16 MPa, and rated speed is 2000 r/min. Volumetric efficiency of the hydraulic pump is approximately 92%. When the loader boom is lifted, if the outlet pressure of the hydraulic pump does not reach 16 MPa (i.e., the set value of the overflow valve), all the output oil of the hydraulic pump is supplied to the mobile arm hydraulic cylinder.

Fig. 5

The test bench

The output power of hydraulic pump in energy consumption analysis can be calculated by the following equation:

$${P}_{0}=\frac{pVn{\tau }_{c}}{60}$$

(16)

where P₀ is the output power of the hydraulic pump in the test, p is the output pressure of the hydraulic pump in the test, τ_c is the volumetric efficiency, V is the displacement of the pump, and n is the rotating speed of the pump.

The original hydraulic cylinder of the loader boom is a single-rod piston hydraulic cylinder, of which the area of rod-less chamber is 6362 mm² and the area of rod chamber is 4398 mm². The size of the three-chamber hydraulic cylinder is determined by the installation space and simulation results. The area of chamber A is 4938 mm², the area of chamber B is 1944 mm², and the area of chamber C is 1964 mm². Thus, the area of chamber B and that of chamber C is approximately equal. The volume of the hydraulic accumulator is 4 L, and the initial pressure of the hydraulic accumulator is determined by the optimization of simulation results.

Two-chamber hydraulic cylinders and three-chamber hydraulic cylinders are used to drive the loader boom under no-load and heavy-load conditions.

4.1 No-Load Operation Characteristics

4.1.1 Two-Chamber Hydraulic Cylinder Driving the Boom

The displacement and velocity of the hydraulic cylinder are shown in Fig. 6 during the three working cycles when the two-chamber hydraulic cylinder is used to drive the loader boom.

Fig. 6

Displacement and speed characteristics of the two-chamber hydraulic cylinder

The dynamic working process and energy consumption characteristics of the boom are analyzed in detail for one working cycle. The falling-lifting cycle of the boom is selected from 10 to 28 s in Fig. 6, the pressure curve of each chamber when the two-chamber hydraulic cylinder drives the boom in this cycle are shown in Fig. 7. When the boom starts to fall, the pressure in chambers A and B fluctuates obviously because of the impact of high-pressure oil on the rod-less chamber when the hydraulic valve core moves. The piston rod of the hydraulic cylinder is retracted by the gravity of the boom itself in the steady descending stage, so the pressure of the rod chamber (chamber B) keeps low, while the pressure of the rodless chamber (chamber A) decreases from 2.1 MPa to about 1.5 MPa to balance the gravity of the arm. At the end of the boom falling, the contact between the bucket and ground results in the impact of external load on the system, and the pressure of chamber A fluctuates sharply. When the boom lifts, the pressure of chamber A fluctuates obviously at the moment of starting, which causes the velocity fluctuation of the hydraulic cylinder. After that, the pressure of chamber A rises to about 2.5 MPa to drive the boom lifting.

Fig. 7

Pressure curve of two-chamber hydraulic cylinder

The output power and energy curve of the hydraulic pump are shown in Fig. 8 when the two-chamber hydraulic cylinder drives the boom under no-load condition. The power and energy of the hydraulic pump are calculated by Eq. (16) according to the pressure data collected by the pressure sensor and the crankshaft speed of the diesel engine collected by the speed sensor. At the initial stage of the boom falling, the output power of the hydraulic pump was instantly increased to drive the boom to accelerate falling, and then remained at about 0.51 kW. The peak power of the hydraulic pump in this stage was 4.10 kW, and the total output energy of the hydraulic pump was 4.47 kJ.

Fig. 8

Power and energy of pump outlet of two-chamber hydraulic cylinder

4.1.2 Three-Chamber Hydraulic Cylinder Driving the Boom

The displacement and velocity curves of the hydraulic cylinder is shown in Fig. 9 when the three-chamber hydraulic cylinder is used to drive the boom without load. In the new system, the accumulator is joined with chamber C, so the system damping increases. When comparing three-chamber hydraulic cylinders to two-chamber hydraulic cylinders, it can be observed that the former experiences less peak velocity oscillation, and thus the operation is relatively stable.

Fig. 9

Displacement and speed characteristics of three-chamber hydraulic cylinder

The pressure of each chamber when the three-chamber hydraulic cylinder drives the boom in a working cycle without load is shown in Fig. 10. Chamber C is joined with the accumulator, and the working pressure of the accumulator is 6Mpa when the boom is at the initial position. When the piston rod of the hydraulic cylinder extends to the maximum displacement, the oil volume of the accumulator is the smallest, and the minimum pressure is about 2.8 MPa. During the descent of the boom, the oil in chamber C enters the accumulator under the action of the gravity of the boom. The accumulator pressure rises with the increase of the oil volume and rises to 6 MPa at the end of the descent. During this process, The potential energy of the boom is transformed into hydraulic energy and reserved in the accumulator. Since the pressure offered by the accumulator in the descending stage of the boom can basically balance the weight of the boom, The pressure in chamber A is relatively low. The pressure in chamber B fluctuates obviously when the boom begins to drop, and increases with the increase of the pressure in the chamber C. During the boom lifting process, the accumulator releases high-pressure oil into chamber C, and the pressure in chamber A is very low. With the extension of piston rod, the volume of chamber C increases, the oil volume in the accumulator decreases, and the pressure decreases gradually. Therefore, the pressure in chamber A rises gradually to drive the boom lifting, while the pressure in chamber B remains low.

Fig. 10

Pressure curve of three-chamber hydraulic cylinder

The output power and energy curve of the hydraulic pump when the three-chamber hydraulic cylinder drives the boom without load are shown in Fig. 11. The power and energy curves of accumulator charging and discharging are shown in Fig. 12. In the boom falling stage, as the accumulator recovers potential energy, chambers A and B maintain low pressure, so the hydraulic pump needs to output energy to drive the boom falling, and the peak output power of this stage is 2.25 kW, and the output energy is 6.82 kJ. In the boom lifting stage, the self-weight of the boom is balanced by the accumulator oil hydraulic pressure at the initial position, so the pressure of chamber A is low. As its area is small, so the flow rate is small, and the output power of hydraulic pump is not large. With the decrease of hydraulic oil pressure in the accumulator, the pressure of chamber A of hydraulic cylinder increases, and the output power of hydraulic pump increases gradually. In this stage, the peak output power of hydraulic pump is 1.43 kW and the output energy is 4.41 kJ. The total output energy of the hydraulic pump is 12.46 kJ when the boom is lowered and lifted in one cycle under no-load condition.

Fig. 11

Power and energy of pump outlet of three-chamber hydraulic cylinder

Fig. 12

Power and energy characteristics of accumulator

4.2 Comparison of No-Load Energy Consumption Characteristics

The energy consumption of the new system and the original system in a lifting cycle is shown in Table 3. In the boom falling stage, the output energy of the hydraulic pump in the original system is 4.47 kJ. Due to an accumulator is used in the new system, more output energy is needed to drive the boom falling, and the hydraulic pump outputs 6.82 kJ. When lifting the boom, the energy output of the hydraulic pump in the new system is 4.41 kJ, while that of the original system is 8.55 kJ, and the energy output of the accumulator is 0.68 kJ. In a complete work cycle of the boom, the peak power output of the hydraulic pump decreased from 3.63 to 1.43 kW, reducing by 60.61%. The energy output of the hydraulic pump decreased from 16.55 to 12.46 kJ, reducing the energy consumption by 24.71%.

Table 3 Comparison of energy consumption under no-load condition

4.3 Heavy-Load Performance

4.3.1 Conventional Hydraulic Cylinder Driving Boom

The velocity, the displacement and the pressure of the two-chamber hydraulic cylinder under heavy load are shown in Figs. 13 and 14. As can be seen from Fig. 13, when the throttle angle of the diesel engine remains unchanged, compared with the no-load condition, in the heavy-load condition the speed of the boom decreases slightly when it rises, but becomes faster when it falls, and the operation process is relatively stable. It can be seen from Fig. 14 that under different working conditions, the pressure of chamber B does not change much, while the pressure of chamber A increases obviously under heavy load.

Fig. 13

Displacement and speed characteristics of two-chamber hydraulic cylinder under heavy load condition

Fig. 14

Pressure curve of two-chamber hydraulic cylinder

The output power and energy of the hydraulic pump under heavy load condition are shown in Fig. 15. When the boom is lifted and fallen, the output power of the hydraulic pump fluctuates instantly. In the boom falling stage, the peak value of hydraulic pump is 2.77 kW and the output energy is 1.87 kJ. In the boom lifting stage, the peak value of the hydraulic pump is 3.72 kW and the output energy is 13.31 kJ. The total output energy of the hydraulic pump is 21.56 kJ under heavy load condition within a cycle of boom fall-lift.

Fig. 15

Power and energy of pump outlet under heavy load

4.3.2 Three-Chamber Hydraulic Cylinder Driving the Boom

The displacement, the velocity and the pressure of the three-chamber hydraulic cylinder under heavy load are shown respectively in Fig. 16 and Fig. 17. During the boom lifting stage, the pressure of chamber A increases as the pressure of chamber C decreases gradually, and the output power of the hydraulic pump also increases. At the initial stage of boom falling, the pressure of chamber B raises briefly and then maintains at a low pressure. During the movement of the boom, the pressure of each chamber of the hydraulic cylinder fluctuates slightly.

Fig. 16

Displacement and speed characteristics of

Fig. 17

Pressure curve of three-chamber hydraulic cylinder

Figure 18 shows the output power and energy of the hydraulic pump under heavy load condition are shown in Fig. 18. The power and energy curves of accumulator charging and discharging liquid are shown in Fig. 19. When the boom is falling, the peak power of the hydraulic pump is 0.51 kW and the output energy is 1.89 kJ. When the boom is lifted, the peak power of the hydraulic pump is 3.72 kW and the output energy is 12.31 kJ. The total output energy in one cycle of the hydraulic pump is 13.10 kJ under heavy load condition within one cycle of the boom fall-lift.

Fig. 18

Power and energy of pump outlet

Fig. 19

Power and energy characteristics of accumulator

4.4 Comparison of Energy Consumption Characteristics Under Heavy Load Conditions

Table 4 shows the energy consumption of the new system and the original system within a cycle of boom fall-lift. The peak output power of the hydraulic pump decreased from 3.72 to 2.70 kW, i.e., a decrease of 27.41% is obtained. The output energy of hydraulic pump decreased from 21.56 to 13.10 kJ, and the energy consumption is decreased by 39.23%.

Table 4 Energy consumption under heavy-load condition

5 Conclusion

This paper proposes a potential energy recovery system based on three-chamber hydraulic cylinder driving loader boom to recover and reuse the potential energy of gravity. Chamber C is directly connected to accumulator. As the boom is fallen the gravitational potential energy is transformed into hydraulic energy and reserved in the accumulator; as the boom is lifted, the stored energy is released into chamber C and lift the boom auxiliary. Through theoretical analysis and experimental research, the following conclusions are obtained.

The three-chamber hydraulic cylinder is adopted to replace the two-chamber hydraulic cylinder in the original system to drive the loader boom lifting. The three-chamber hydraulic cylinder and the accumulator constitute a liquid–gas energy storage system that can balance the weight of the boom. Through this, the potential energy of the boom can be recovered and reused directly, and the energy consumption and the installed power can be significantly reduced. The output energy of the hydraulic pump is 39.24% less than the former system in one working cycle, the peak power output of the hydraulic pump was reduced by 27.41% compared with the original system in the boom lifting stage. With the benefits of the proposed method, this study made the following contributions. First, the running speed of the system slightly fluctuates to decrease the peak value because the access of the accumulator provides damping for the new system. The required flow rate is reduced at the same speed condition, which further reduces the throttling loss because the area of the working oil chamber is reduced. Second, the Hydraulic-Gas balancing energy recovery system has the characteristics of the reduced number of energy conversion links and shorter energy transfer chains, the system exhibits high efficiency in energy utilization.

In the proposed system, Due to the mechanical connection between the inlet and outlet orifices, a valve control system with a single degree of freedom is used to control chamber A and chamber B in the three-chamber hydraulic cylinder with poor controllability, so that the pressure and the flow of chambers A and B cannot be controlled in the mean time, The throttle is applied simultaneously to both the inlet and outlet of the valve, so the pressure loss is large.

In view of the above limitations, in order to minimize the throttling losses in the system, The next step of the research work involves implementing and testing the use of pumps, valves, synergistic control, and the flow matching method in the hydraulic excavator system to achieve precise control of throttle points for fluid intake and outflow on the basis of the three-chamber hydraulic cylinder, and to realize the independent adjustment of the pressure and flow of chamber A and chamber B in the three-chamber hydraulic cylinder.