Energy-saving hydraulic system of excavator and control method of energy-saving hydraulic system

Abstract

The invention discloses an energy-saving hydraulic system of an excavator and a control method of the energy-saving hydraulic system, and belongs to the technical field of engineering machinery. The defects that in the prior art, traditional movable arm potential energy recovery is low in potential energy recovery efficiency and high in design cost are overcome. The main body structure comprises a main pump and a main control valve, wherein the main control valve comprises a bucket working valve, a movable arm converging valve, a movable arm working valve, a rotary working valve, a bucket rod working valve B and a bucket rod working valve A; when the movable arm descends, the movable arm flow collecting valve works at the left position, the movable arm working valve works at the right position, right pump hydraulic oil of the main pump enters a channel b of the movable arm working valve through a port P and then enters a small cavity of the movable arm oil cylinder, and part of hydraulic oil of a large cavity of the movable arm oil cylinder enters the channel b again through a channel a of the movable arm working valve and finally enters the small cavity of the movable arm oil cylinder. Large-cavity flow regeneration of the movable arm oil cylinder is realized; and the other part of hydraulic oil in the large cavity of the boom cylinder returns to the oil tank through the channel c. The invention is mainly applied to engineering machinery such as excavators.

Description

Technical Field

[0001] The present invention belongs to the technical field of engineering machinery, and in particular, relates to an energy-saving hydraulic system for an excavator and a control method thereof. Background Art

[0002] When the boom of the excavator is lowering, oil enters the small chamber of the boom cylinder and returns oil to the large chamber. Due to the deadweight of the boom, the potential energy of the boom's descent is often wasted. For the potential energy of the boom's descent, one method is to convert the potential energy of the boom's descent into electrical energy and store it in energy storage batteries during the boom's descent, or another method is to convert the potential energy of the boom's descent into hydraulic energy and store it in an accumulator.

[0003] For example, the existing boom recovery system Figure 5 As shown, part of the potential energy generated by the boom lowering is stored in the battery, and part of it drives the motor to rotate, providing torque for the rotation of the main pump, reducing the power of the engine. The specific principle is: when the boom is lowered, the boom potential energy is recovered: the engine E rotates, driving the main pump to rotate, and the hydraulic oil passes through the boom main valve and enters the small chamber of the boom cylinder. At this time, the solenoid valve is energized and works in the right position. The hydraulic oil in the large chamber of the boom cylinder enters the recovery motor, driving the recovery motor to rotate, driving the generator to rotate, and after being processed by the rectifier / inverter, part of the electrical energy is stored in the battery, while the other part of the electrical energy drives the motor to rotate. The motor and the main pump are coaxial, and the motor provides torque for the rotation of the main pump.

[0004] This process collects the potential energy of the boom's descent and converts it into electrical energy, which is eventually transferred to the main pump, thereby reducing the engine power and the fuel consumption of the entire machine. However, the above solution has the following shortcomings:

[0005] 1. The existing excavator boom potential energy recovery technology generates potential energy when the boom is lowered, and then the potential energy is converted into hydraulic energy through the recovery motor, and then converted into electrical energy through the generator, and finally drives the motor to rotate. The energy is transmitted through multiple layers, and the potential energy recovery efficiency is very low, and the fuel consumption efficiency of the engine is not significantly reduced;

[0006] 2. With the energy recovery technology of the existing technology, the potential energy of the boom's descent cannot be directly utilized, and it is necessary to recover components such as motors, engines, electric machines, and batteries. The entire energy recovery system not only has a high design cost, but also a complex system with a high failure rate and high maintenance cost. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide an energy-saving hydraulic system for an excavator and a control method thereof.

[0008] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0009] An energy-saving hydraulic system for an excavator includes a main pump, the oil outlet of the main pump is respectively connected to a boom cylinder, a bucket cylinder, a dipper rod cylinder and a slewing motor through a main control valve, and the main control valve includes a bucket working valve connected to the bucket cylinder.

[0010] The boom confluence valve and boom working valve connected to the boom cylinder,

[0011] The rotary working valve connected to the rotary motor,

[0012] And a boom working valve B and a boom working valve A connected to the boom cylinder;

[0013] When the boom is lowered, the boom combining valve works in the left position and the boom working valve works in the right position. The hydraulic oil from the right pump of the main pump enters the channel b of the boom working valve through the P port, and then enters the small chamber of the boom cylinder. A part of the hydraulic oil in the large chamber of the boom cylinder re-enters the channel b through the channel a of the boom working valve, and finally enters the small chamber of the boom cylinder, thereby realizing the regeneration of the large chamber flow of the boom cylinder; another part of the hydraulic oil in the large chamber of the boom cylinder returns to the oil tank through the channel c.

[0014] Preferably, a proportional valve B is provided between the large chamber of the boom cylinder and the X chamber of the rotary motor, a proportional valve C is provided between the large chamber of the boom cylinder and the Y chamber of the rotary motor, a proportional valve D is provided between the large chamber of the boom cylinder and the large chamber of the bucket cylinder, and a proportional valve E is provided between the large chamber of the boom cylinder and the large chamber of the arm cylinder.

[0015] Preferably, a pressure sensor A for detecting the pressure of the large chamber of the boom cylinder is provided at the large chamber of the boom cylinder, a pressure sensor B for detecting the pressure of the X chamber of the swing motor is provided at the X chamber of the swing motor, a pressure sensor C for detecting the pressure of the Y chamber of the swing motor is provided at the Y chamber of the swing motor, a pressure sensor D for detecting the pressure of the large chamber of the bucket cylinder is provided at the large chamber of the bucket cylinder, and a pressure sensor E for detecting the pressure of the large chamber of the arm cylinder is provided at the large chamber of the dipper cylinder.

[0016] Preferably, a comparator B is arranged between the pressure sensor A and the pressure sensor B, a comparator C is arranged between the pressure sensor A and the pressure sensor C, a comparator D is arranged between the pressure sensor A and the pressure sensor D, and a comparator E is arranged between the pressure sensor A and the pressure sensor E.

[0017] Preferably, the electromagnetic signal end of the proportional valve B, the electromagnetic signal end of the proportional valve C, the electromagnetic signal end of the proportional valve D, the electromagnetic signal end of the proportional valve E, the comparator B, the comparator C, the comparator D and the comparator E are all electrically connected to the controller.

[0018] A control method for an excavator energy-saving hydraulic system adopts the excavator energy-saving hydraulic system as described above, including the following two methods: a control method when the boom is lowered plus a compound action and a control method when the boom is lowered plus more than one compound action (three or more compound actions).

[0019] Preferably, the control method for the boom lowering plus a compound action is:

[0020] Pressure sensor A detects the pressure Pa of the large chamber of the boom cylinder in real time, pressure sensor B detects the pressure Pb of the X chamber of the rotary motor in real time, pressure sensor C detects the pressure Pc of the Y chamber of the rotary motor in real time, pressure sensor D detects the pressure Pd of the large chamber of the bucket cylinder in real time, and pressure sensor E detects the pressure Pe of the large chamber of the arm cylinder in real time. The pressures of the two chambers are compared by a comparator, and the detection results are transmitted to the controller;

[0021] When Pa>Pb, proportional valve B is energized, the X chamber of the swing motor is connected with the large chamber of the boom cylinder, and the hydraulic oil enters the X chamber of the swing motor from the large chamber of the boom cylinder;

[0022] When Pa>Pc, proportional valve C is energized, the Y chamber of the swing motor is connected with the large chamber of the boom cylinder, and the hydraulic oil enters the Y chamber of the swing motor from the large chamber of the boom cylinder;

[0023] When Pa>Pd, proportional valve D is energized, the large chamber of the bucket cylinder is connected with the large chamber of the boom cylinder, and the hydraulic oil enters the large chamber of the bucket cylinder from the large chamber of the boom cylinder;

[0024] When Pa>Pe, the proportional valve E is energized, the large chamber of the arm cylinder is connected to the large chamber of the boom cylinder, and the hydraulic oil enters the large chamber of the arm cylinder from the large chamber of the boom cylinder.

[0025] Preferably, the control method for the boom lowering plus a compound action is:

[0026] Pressure sensor A detects the pressure Pa of the large chamber of the boom cylinder in real time, pressure sensor B detects the pressure Pb of the X chamber of the rotary motor in real time, pressure sensor C detects the pressure Pc of the Y chamber of the rotary motor in real time, pressure sensor D detects the pressure Pd of the large chamber of the bucket cylinder in real time, and pressure sensor E detects the pressure Pe of the large chamber of the arm cylinder in real time. The pressures of the two chambers are compared by a comparator, and the detection results are transmitted to the controller;

[0027] The pressure difference between the large chamber of the boom cylinder and other working chambers is △P. It is defined that △Pb=Pa-Pb, △Pc=Pa-Pc, △Pd=Pa-Pd, and △Pe=Pa-Pe. The size of △P is set as the basis for opening and closing the solenoid valve, and determines the flow rate of the hydraulic oil of the large chamber of the boom to other working chambers, so as to achieve the adjustable regeneration amount of the large chamber of the boom to other working chambers.

[0028] When △Pb is greater than Pb1, proportional valve B is energized, the X chamber of the swing motor is connected to the large chamber of the boom cylinder, and the hydraulic oil enters the X chamber of the swing motor from the large chamber of the boom cylinder;

[0029] When △Pc is greater than Pc1, proportional valve C is energized, the Y chamber of the swing motor is connected to the large chamber of the boom cylinder, and the hydraulic oil enters the Y chamber of the swing motor from the large chamber of the boom cylinder;

[0030] When △Pd is greater than Pd1, proportional valve D is energized, the large chamber of the bucket cylinder is connected to the large chamber of the boom cylinder, and the hydraulic oil enters the large chamber of the bucket cylinder from the large chamber of the boom cylinder;

[0031] When △Pe is greater than Pe1, proportional valve E is energized, the large chamber of the arm cylinder is connected with the large chamber of the boom cylinder, and the hydraulic oil enters the large chamber of the arm cylinder from the large chamber of the boom cylinder;

[0032] Among them, Pb1 is the pressure difference actually detected between the large cavity of the boom cylinder and the X cavity of the rotary motor, Pc1 is the pressure difference actually detected between the large cavity of the boom cylinder and the Y cavity of the rotary motor, Pd1 is the pressure difference actually detected between the large cavity of the boom cylinder and the large cavity of the bucket cylinder, and Pe1 is the pressure difference actually detected between the large cavity of the boom cylinder and the large cavity of the arm cylinder.

[0033] Preferably, the control method for the boom lowering when there is more than one compound action (three or more compound actions) is:

[0034] Pressure sensor A detects the pressure Pa of the large chamber of the boom cylinder in real time, pressure sensor B detects the pressure Pb of the X chamber of the rotary motor in real time, pressure sensor C detects the pressure Pc of the Y chamber of the rotary motor in real time, pressure sensor D detects the pressure Pd of the large chamber of the bucket cylinder in real time, and pressure sensor E detects the pressure Pe of the large chamber of the arm cylinder in real time. The pressures of the three chambers are compared by a comparator, and the detection results are transmitted to the controller;

[0035] When any of Pa>Pe (or Pd)>Pb or Pa>Pe>Pd>Pb or Pa>Pd>Pe>Pb occurs, proportional valve B is energized, the X chamber of the swing motor is connected with the large chamber of the boom cylinder, and the hydraulic oil enters the X chamber of the swing motor from the large chamber of the boom cylinder;

[0036] When any of Pa>Pe (or Pd)>Pc or Pa>Pe>Pd>Pc or Pa>Pd>Pe>Pc occurs, proportional valve C is energized, the Y chamber of the swing motor is connected with the large chamber of the boom cylinder, and the hydraulic oil enters the Y chamber of the swing motor from the large chamber of the boom cylinder;

[0037] When any of Pa>Pe (or Pb or Pc)>Pd or when Pa>Pe>Pb (or Pc)>Pd or when Pa>Pb (or Pc)>Pe>Pd occurs, proportional valve D is energized, the large chamber of the bucket cylinder is connected with the large chamber of the boom cylinder, and the hydraulic oil enters the large chamber of the bucket cylinder from the large chamber of the boom cylinder;

[0038] When Pa>Pb (or Pc or Pd)>Pe or when Pa>Pb (or Pc)>Pd>Pe or when Pa>Pd>Pb (or Pc)>Pe, any one of the following occurs, proportional valve E is energized, the large chamber of the arm cylinder is connected to the large chamber of the boom cylinder, and the hydraulic oil enters the large chamber of the arm cylinder from the large chamber of the boom cylinder.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. During the composite action of the present invention, when the boom is lowered, a part of the hydraulic oil in the large chamber of the boom cylinder enters the small chamber to achieve flow regeneration of the boom cylinder, and the other part of the hydraulic oil enters other working chambers (the large chamber of the bucket cylinder, the large chamber of the arm cylinder, the left rotary chamber of the rotary motor or the right rotary chamber of the rotary motor) according to the pressure of the composite action, so as to achieve regeneration of other working chambers by the large chamber of the boom, and recover and reuse the potential energy of the boom lowering at a deeper level, thereby reducing the displacement of the main pump to the maximum extent, and finally reducing the fuel consumption of the engine;

[0041] 2. The present invention can effectively reuse the potential energy of the boom's descent without recycling high-cost parts such as motors, generators and batteries. The potential energy of the boom's descent can be directly used in other working chambers of the hydraulic system, with a short energy transfer path and high efficiency.

[0042] 3. The invention mentions that the boom lowering potential energy recovery method can realize the direct utilization of potential energy, that is, the hydraulic oil in the boom large chamber is regenerated to other working chambers, which is separated from the energy storage part required by the traditional boom potential energy recovery technology, simplifies the hydraulic system, reduces the cost, and improves the stability of the hydraulic system;

[0043] 4. Although the present invention mentions several regeneration modes of the boom large chamber to other working chambers, such as the boom large chamber to the left rotation regeneration, the boom large chamber to the right rotation regeneration, the boom large chamber to the bucket large chamber regeneration, and the boom large chamber to the arm large chamber regeneration, in actual application, the regeneration function can be selected according to the common working conditions of the excavator, and customized hydraulic system improvements can be made according to the working conditions;

[0044] 5. The pressure difference between the large chamber of the boom and other working chambers is △P. △P can be set according to different working conditions to determine the opening and closing states of the proportional valve, thereby realizing the adjustable flow regeneration of the large chamber of the boom cylinder to the large chamber of the bucket cylinder. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a hydraulic system diagram of the present invention;

[0046] Figure 2 This is a working principle diagram of the boom working valve in the present invention;

[0047] Figure 3 It is a flow chart of the principle of regeneration of other actions by the movable arm large cavity during two compound actions in the present invention;

[0048] Figure 4 It is a flow chart of the principle of regeneration of other actions by the movable arm large cavity in the case of more than three compound actions in the present invention;

[0049] Figure 5 This is a schematic diagram of the existing boom recovery system.

[0050] In the figure: 1. engine; 2. main pump; 3. pressure sensor B; 4. proportional valve B; 5. pressure sensor C; 6. proportional valve C; 7. comparator B; 8. comparator C; 9. pressure sensor A; 10. boom cylinder; 11. comparator D; 12. pressure sensor D; 13. proportional valve D; 14. comparator E; 15. bucket cylinder; 16. pressure sensor E; 17. proportional valve E; 18. arm cylinder; 19. controller; 20. main control valve; 21. swing motor; 22. fuel tank; 201. bucket working valve; 202. arm working valve B; 203. arm working valve A; 204. boom confluence valve; 205. swing working valve; 206. boom working valve. DETAILED DESCRIPTION

[0051] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0052] Embodiment 1:

[0053] like Figure 1 As shown, an energy-saving hydraulic system for an excavator includes a main pump 2, the oil outlet of the main pump 2 is respectively connected to the boom cylinder 10, the bucket cylinder 15, the arm cylinder 18 and the swing motor 21 through a main control valve 20, and the main control valve 20 includes a bucket working valve 201 connected to the bucket cylinder 15.

[0054] The boom confluence valve 204 and the boom working valve 206 connected to the boom cylinder 10,

[0055] The rotary working valve 205 connected to the rotary motor 21,

[0056] and a boom working valve B202 and a boom working valve A203 connected to the boom cylinder 18;

[0057] When the boom is lowered, the boom combining valve 204 works in the left position and the boom working valve 206 works in the right position, and the hydraulic oil of the right pump of the main pump 2 enters the channel b of the boom working valve 206 through the P port, and then enters the small chamber of the boom cylinder 10, while a part of the hydraulic oil in the large chamber of the boom cylinder 10 re-enters the channel b through the channel a of the boom working valve 206, and finally enters the small chamber of the boom cylinder 10, thereby realizing the regeneration of the large chamber flow of the boom cylinder 10; another part of the hydraulic oil in the large chamber of the boom cylinder 10 returns to the oil tank 22 through the channel c.

[0058] The present invention can effectively reuse the potential energy of the boom's descent without recycling high-cost parts such as motors, generators and batteries. The potential energy of the boom's descent can be directly used in other working chambers in the hydraulic system. When the boom is lowered, a part of the hydraulic oil in the large chamber of the boom cylinder 10 enters the small chamber, thereby realizing flow regeneration of the boom cylinder 10, and the other part of the hydraulic oil enters other working chambers (such as the large chamber of the bucket cylinder 15, the large chamber of the arm cylinder 18, the left rotary chamber of the slewing motor 21 or the right rotary chamber of the slewing motor 21) according to the pressure of the compound action, thereby realizing the regeneration of the boom's large chamber to other working chambers, thereby reducing the displacement of the main pump 2 and ultimately achieving the effect of reducing the fuel consumption of the engine 1.

[0059] Embodiment 2:

[0060] An energy-saving hydraulic system for an excavator, which is different from Example 1 in that a proportional valve B4 is arranged between the large chamber of the boom cylinder 10 and the X chamber of the rotary motor 21, a proportional valve C6 is arranged between the large chamber of the boom cylinder 10 and the Y chamber of the rotary motor 21, a proportional valve D13 is arranged between the large chamber of the boom cylinder 10 and the large chamber of the bucket cylinder 15, and a proportional valve E17 is arranged between the large chamber of the boom cylinder 10 and the large chamber of the arm cylinder 18.

[0061] Furthermore, a pressure sensor A9 for detecting the pressure in the large chamber of the boom cylinder 10 is provided at the large chamber of the boom cylinder 10, a pressure sensor B3 for detecting the pressure in the X chamber of the swing motor 21 is provided at the X chamber of the swing motor 21, a pressure sensor C5 for detecting the pressure in the Y chamber of the swing motor 21 is provided at the Y chamber of the swing motor 21, a pressure sensor D12 for detecting the pressure in the large chamber of the bucket cylinder 15 is provided at the large chamber of the bucket cylinder 15, and a pressure sensor E16 for detecting the pressure in the large chamber of the arm cylinder 18 is provided at the large chamber of the boom cylinder 18.

[0062] Furthermore, a comparator B7 is provided between the pressure sensor A9 and the pressure sensor B3, a comparator C8 is provided between the pressure sensor A9 and the pressure sensor C5, a comparator D11 is provided between the pressure sensor A9 and the pressure sensor D12, and a comparator E14 is provided between the pressure sensor A9 and the pressure sensor E16.

[0063] Further, the electromagnetic signal end of the proportional valve B4 , the electromagnetic signal end of the proportional valve C6 , the electromagnetic signal end of the proportional valve D13 , the electromagnetic signal end of the proportional valve E17 , the comparator B7 , the comparator C8 , the comparator D11 and the comparator E14 are all electrically connected to the controller 19 .

[0064] Embodiment 3:

[0065] A control method for an excavator energy-saving hydraulic system, using the excavator energy-saving hydraulic system as described in the above-mentioned embodiment 2, includes the following two methods: a control method when the boom is lowered plus a compound action and a control method when the boom is lowered plus more than one compound action (three or more compound actions).

[0066] Embodiment 4:

[0067] like Figure 3 As shown, a control method for an energy-saving hydraulic system of an excavator, the control method when the boom is lowered and a compound action is performed is:

[0068] The pressure sensor A9 detects the pressure Pa of the large chamber of the boom cylinder 10 in real time, the pressure sensor B3 detects the pressure Pb of the X chamber of the swing motor 21 in real time, the pressure sensor C5 detects the pressure Pc of the Y chamber of the swing motor 21 in real time, the pressure sensor D12 detects the pressure Pd of the large chamber of the bucket cylinder 15 in real time, and the pressure sensor E16 detects the pressure Pe of the large chamber of the arm cylinder 18 in real time. The pressures of the two chambers are compared by a comparator, and the detection result is transmitted to the controller 19;

[0069] When Pa>Pb, the proportional valve B4 is energized, the X chamber of the swing motor 21 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the X chamber of the swing motor 21 from the large chamber of the boom cylinder 10;

[0070] When Pa>Pc, the proportional valve C6 is energized, the Y chamber of the swing motor 21 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the Y chamber of the swing motor 21 from the large chamber of the boom cylinder 10;

[0071] When Pa>Pd, the proportional valve D13 is energized, the large chamber of the bucket cylinder 15 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the large chamber of the bucket cylinder 15 from the large chamber of the boom cylinder 10;

[0072] When Pa>Pe, the proportional valve E17 is energized, the large chamber of the arm cylinder 18 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the large chamber of the arm cylinder 18 from the large chamber of the boom cylinder 10.

[0073] Embodiment 5:

[0074] A control method for an energy-saving hydraulic system of an excavator, wherein the control method when the boom is lowered and a compound action is performed is as follows:

[0075] The pressure sensor A9 detects the pressure Pa of the large chamber of the boom cylinder 10 in real time, the pressure sensor B3 detects the pressure Pb of the X chamber of the swing motor 21 in real time, the pressure sensor C5 detects the pressure Pc of the Y chamber of the swing motor 21 in real time, the pressure sensor D12 detects the pressure Pd of the large chamber of the bucket cylinder 15 in real time, and the pressure sensor E16 detects the pressure Pe of the large chamber of the arm cylinder 18 in real time. The pressures of the two chambers are compared by a comparator, and the detection result is transmitted to the controller 19;

[0076] The pressure difference between the large chamber 10 of the boom cylinder and other working chambers is △P. It is defined that △Pb=Pa-Pb, △Pc=Pa-Pc, △Pd=Pa-Pd, and △Pe=Pa-Pe. The size of △P is set as the basis for opening and closing the solenoid valve, and determines the flow rate of the hydraulic oil of the large chamber of the boom to other working chambers, so as to achieve the adjustable regeneration amount of the large chamber of the boom to other working chambers.

[0077] When △Pb is greater than Pb1, the proportional valve B4 is energized, the X chamber of the swing motor 21 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the X chamber of the swing motor 21 from the large chamber of the boom cylinder 10;

[0078] When △Pc is greater than Pc1, the proportional valve C6 is energized, the Y chamber of the swing motor 21 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the Y chamber of the swing motor 21 from the large chamber of the boom cylinder 10;

[0079] When △Pd is greater than Pd1, proportional valve D13 is energized, the large chamber of bucket cylinder 15 is connected with the large chamber of boom cylinder 10, and hydraulic oil enters the large chamber of bucket cylinder 15 from the large chamber of boom cylinder 10;

[0080] When △Pe is greater than Pe1, proportional valve E17 is energized, the large chamber of the arm cylinder 18 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the large chamber of the arm cylinder 18 from the large chamber of the boom cylinder 10;

[0081] Among them, Pb1 is the pressure difference value actually detected between the large cavity of the boom cylinder 10 and the X cavity of the rotary motor 21, Pc1 is the pressure difference value actually detected between the large cavity of the boom cylinder 10 and the Y cavity of the rotary motor 21, Pd1 is the pressure difference value actually detected between the large cavity of the boom cylinder 10 and the large cavity of the bucket cylinder 15, and Pe1 is the pressure difference value actually detected between the large cavity of the boom cylinder 10 and the large cavity of the arm cylinder 18.

[0082] Embodiment 6:

[0083] A control method for an energy-saving hydraulic system of an excavator, wherein the control method when the boom descends and increases more than one compound action (three or more compound actions) is:

[0084] The pressure sensor A9 detects the pressure Pa of the large chamber of the boom cylinder 10 in real time, the pressure sensor B3 detects the pressure Pb of the X chamber of the swing motor 21 in real time, the pressure sensor C5 detects the pressure Pc of the Y chamber of the swing motor 21 in real time, the pressure sensor D12 detects the pressure Pd of the large chamber of the bucket cylinder 15 in real time, and the pressure sensor E16 detects the pressure Pe of the large chamber of the arm cylinder 18 in real time. The pressures of the three or four chambers are compared by a comparator, and the detection results are transmitted to the controller 19;

[0085] If three compound actions occur, when Pa>Pe (or Pd)>Pb, the proportional valve B4 is energized, the X chamber of the swing motor 21 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the X chamber of the swing motor 21 from the large chamber of the boom cylinder 10;

[0086] When Pa>Pe (or Pd)>Pc, the proportional valve C6 is energized, the Y chamber of the swing motor 21 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the Y chamber of the swing motor 21 from the large chamber of the boom cylinder 10;

[0087] When Pa>Pe (or Pb or Pc)>Pd, the proportional valve D13 is energized, the large chamber of the bucket cylinder 15 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the large chamber of the bucket cylinder 15 from the large chamber of the boom cylinder 10;

[0088] When Pa>Pb (or Pc or Pd)>Pe, the proportional valve E17 is energized, the large chamber of the boom cylinder 18 is connected to the large chamber of the arm cylinder 10, and the hydraulic oil enters the large chamber of the boom cylinder 18 from the large chamber of the boom cylinder 10.

[0089] If four compound actions occur, when Pa>Pe>Pd>Pb or Pa>Pd>Pe>Pb, proportional valve B4 is energized, and other actions are the same as above;

[0090] When Pa>Pe>Pd>Pc or Pa>Pd>Pe>Pc, proportional valve C6 is energized, and other actions are the same as above;

[0091] When Pa>Pe>Pb (or Pc)>Pd or Pa>Pb (or Pc)>Pe>Pd, proportional valve D13 is energized, and other actions are the same as above;

[0092] When Pa>Pb (or Pc)>Pd>Pe or Pa>Pd>Pb (or Pc)>Pe, proportional valve E17 is energized and other actions are the same as above.

[0093] The working principle of the present invention is:

[0094] 1. The working principle of the main oil circuit is as follows: the engine 1 rotates, driving the main pump 2 to rotate, providing hydraulic oil for the hydraulic system of the whole machine:

[0095] 11) When the boom is rising, the boom confluence valve 204 works in the right position, and the boom working valve 206 works in the left position. The hydraulic oil of the left pump of the main pump 2 enters the boom confluence valve 204 through the P1 port, and the hydraulic oil of the right pump of the main pump 2 enters the boom working valve 206 through the P2 port, and after merging, they enter the large chamber of the boom cylinder 10, thereby driving the boom to rise; when the boom is descending, such as Figure 2 As shown, the boom combining valve 204 works in the left position, and the boom working valve 206 works in the right position. The hydraulic oil of the right pump of the main pump 2 enters the channel b of the boom working valve 206 through the P port, and enters the small chamber of the boom cylinder 10, while a part of the hydraulic oil of the large chamber of the boom cylinder 10 re-enters the channel b through the channel a of the boom working valve 206 and enters the small chamber of the boom cylinder 10, thereby realizing the regeneration of the large chamber flow of the boom cylinder 10; the other part of the hydraulic oil returns to the oil tank 22 through the channel c.

[0096] 12) When the rotary motor 21 of the main oil circuit is in motion, the hydraulic oil of the left pump of the main pump 2 enters the rotary working valve 205 through the P1 port, and then enters the X / Y cavity of the rotary motor 21 to realize the rotation of the rotary motor 21.

[0097] 13) When the bucket moves, the hydraulic oil of the right pump of the main pump 2 enters the bucket working valve 201 through the P2 port, and then enters the large / small chamber of the bucket cylinder 15 to realize the inward and outward swing of the bucket.

[0098] 14) When the boom is retracted, the boom working valve A203 works in the left position, and the boom working valve B202 works in the right position. The hydraulic oil of the left pump of the main pump 2 enters the boom working valve A203 through the P1 port, and the hydraulic oil of the right pump of the main pump 2 enters the boom working valve B202 through the P2 port. After the hydraulic oils are combined, they enter the large chamber of the boom cylinder 18 to achieve the boom retraction; when the boom is swung outward, the boom working valve A203 works in the right position, and the boom working valve B202 works in the left position. The hydraulic oil of the left pump of the main pump 2 enters the boom working valve A203 through the P1 port, and the hydraulic oil of the right pump of the main pump 2 enters the boom working valve B202 through the P2 port. After the hydraulic oils are combined, they enter the small chamber of the boom cylinder 18 to achieve the boom swing.

[0099] 2. The working principle of the regeneration oil circuit is:

[0100] 21), the X chamber of the slewing motor 21 and the large chamber of the boom cylinder 10 are connected together through a proportional valve B4, the Y chamber of the slewing motor 21 and the large chamber of the boom cylinder 10 are connected together through a proportional valve C6, the large chamber of the bucket cylinder 15 and the large chamber of the boom cylinder 10 are connected together through a proportional valve D13, and the large chamber of the arm cylinder 18 and the large chamber of the boom cylinder 10 are connected together through a proportional valve E17.

[0101] 22) The pressure sensor detects the pressure of each working chamber in real time: the pressure sensor A9 detects the pressure of the large chamber of the boom cylinder 10, the pressure sensor B3 detects the pressure of the X chamber of the swing motor 21, the pressure sensor C5 detects the pressure of the Y chamber of the swing motor 21, the pressure sensor D12 detects the pressure of the large chamber of the bucket cylinder 15, and the pressure sensor E16 detects the pressure of the large chamber of the arm cylinder 18.

[0102] 23) The comparator compares the pressures detected by the two pressure sensors and transmits the information to the controller 19: the function of the comparator B7 is to compare the pressure Pb of the X chamber of the rotary motor 21 with the pressure Pa of the large chamber of the boom cylinder 10; the function of the comparator C8 is to compare the pressure Pc of the Y chamber of the rotary motor 21 with the pressure Pa of the large chamber of the boom cylinder 10; the function of the comparator D11 is to compare the pressure Pd of the large chamber of the bucket cylinder 15 with the pressure Pa of the large chamber of the boom cylinder 10; the function of the comparator E14 is to compare the pressure Pe of the large chamber of the arm cylinder 18 with the pressure Pa of the large chamber of the boom cylinder 10; and each comparator transmits the result to the controller 19.

[0103] 3. The controller 19 determines the energization of the electromagnets of each proportional valve, thereby controlling the opening and closing of the proportional valves and realizing the connection between each working chamber and the large chamber of the boom:

[0104] 31) When there is only one composite action (two composite actions) of the boom lowering, the principle flow of the boom large cavity regenerating other actions Figure 3 As shown: when Pa>Pb exists, the proportional valve B4 is energized, the X chamber of the slewing motor 21 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the X chamber of the slewing motor 21 from the large chamber of the boom cylinder 10; when Pa>Pc exists, the proportional valve C6 is energized, the Y chamber of the slewing motor 21 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the Y chamber of the slewing motor 21 from the large chamber of the boom cylinder 10; when Pa>Pd exists, the proportional valve D13 is energized, the large chamber of the bucket cylinder 15 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the large chamber of the bucket cylinder 15 from the large chamber of the boom cylinder 10; when Pa>Pe exists, the proportional valve E17 is energized, the large chamber of the arm cylinder 18 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the large chamber of the arm cylinder 18 from the large chamber of the boom cylinder 10.

[0105] 32) When there is a composite action of more than one boom lowering (three or more composite actions), only the solenoid valve corresponding to the working chamber with the lowest pressure is energized, and the hydraulic oil in the large chamber of the boom only flows to the pressure chamber with the lowest pressure. For example, when the boom is lowered + the arm is swung outward + the bucket is retracted, each pressure sensor detects the pressure of each working chamber. If Pa>Pe>Pd exists, only the proportional valve D13 is energized, and the large chamber of the bucket cylinder 15 is connected with the large chamber of the boom cylinder 10, and the hydraulic oil enters the large chamber of the bucket cylinder 15 from the large chamber of the boom cylinder 10. This setting is to prevent the hydraulic oil in the large chamber of the boom corresponding to the proportional valve E17 from flowing to the large chamber of the bucket cylinder 15 corresponding to the proportional valve D13, thereby affecting the action of the boom.

[0106] The pressure difference between the large chamber of the boom and other working chambers is △P. If △Pb=Pa-Pb, △Pc=Pa-Pc, △Pd=Pa-Pd, △Pe=Pa-Pe, the size of △P can be set as the basis for opening and closing the solenoid valve, determining the flow rate of the hydraulic oil from the large chamber of the boom to other working chambers, so as to realize the adjustable regeneration amount of the large chamber of the boom to other working chambers.

[0107] Specifically, the fifth situation mentioned above is analyzed in detail. Since there are multiple compound action combinations in the actual operation process of the excavator, when the compound action includes the boom lowering action, the potential energy of the boom lowering is often not well reused. When the present invention realizes the compound action, the large chamber of the boom regenerates other working chambers, thereby reducing the displacement output of the main pump 2 and achieving the purpose of energy saving.

[0108] 1) The present invention is analyzed in detail below by taking two compound actions: boom lowering + bucket retraction as an example:

[0109] The engine 1 rotates, driving the right pump of the main pump 2 to rotate, and the hydraulic oil enters the main control valve 20 through the P2 port, the boom is lowered and the bucket is retracted. At this time, the boom working valve 206 works in the right position, and the bucket working valve 201 works in the right position. The hydraulic oil enters the small chamber of the boom cylinder 10 through the boom working valve 206, and at the same time, the hydraulic oil enters the large chamber of the bucket cylinder 15 through the bucket working valve 201. The whole machine performs the action of boom lowering + bucket retracting; at this time, the pressure sensor A9 detects the pressure Pa of the large chamber of the boom cylinder 10 in real time, and the pressure sensor D12 detects the pressure Pa of the large chamber of the bucket cylinder 15 The pressure of the cavity is Pd, and the comparator D11 compares the pressures of the two cavities and transmits the detection result to the controller 19. When it is detected that Pa>Pd exists, the pressure of the large cavity of the boom cylinder 10 is greater than the pressure of the large cavity of the bucket cylinder 15. The controller 19 energizes the electromagnet of the proportional valve D13, and the proportional valve D13 is opened. The large cavity of the boom cylinder 10 and the large cavity of the bucket cylinder 15 are connected. A part of the hydraulic oil in the large cavity of the boom cylinder 10 is regenerated to the small cavity of the boom cylinder 10 through the channel a, and the other part is regenerated to the large cavity of the bucket cylinder through the proportional valve D13. This process can also be defined as △P=Pa-Pd. When △P is greater than a certain value, the opening of the proportional valve D13 is controlled to realize the adjustable flow regeneration of the large cavity of the boom cylinder 10 to the large cavity of the bucket cylinder 15; the whole process can fully recover and utilize the energy of the boom descent, thereby reducing the displacement of the main pump 2 and realizing energy saving of the whole machine compound action.

[0110] 2) The following is a detailed analysis of the present invention by taking three compound actions: boom lowering + bucket retracting + rotation as an example:

[0111] The engine 1 rotates, driving the left and right pumps of the main pump 2 to rotate, and the hydraulic oil enters the main control valve 20 through the P2 port, the boom is lowered and the bucket is retracted. At this time, the boom working valve 206 works in the right position, and the bucket working valve 201 works in the right position. The hydraulic oil enters the small chamber of the boom cylinder 10 through the boom working valve 206, and at the same time, the hydraulic oil enters the large chamber of the bucket cylinder 15 through the bucket working valve 201. The whole machine performs the action of boom lowering + bucket retraction. The hydraulic oil enters the main control valve 20 through the P1 port again. At this time, the swing working valve 205 works in the left position, and the hydraulic oil enters the Y chamber of the swing motor 21 through the swing working valve 205, driving the swing motor 21. Rotate, the whole machine performs a rotary action at the same time; at this time, the pressure sensor A9 detects the pressure Pa of the large cavity of the boom cylinder 10 in real time, the pressure sensor D12 detects the pressure Pd of the large cavity of the bucket cylinder 15, and the pressure sensor C5 detects the pressure Pc of the Y cavity of the rotary motor 21. The comparator D11 compares the pressures of the large cavity of the boom cylinder 10 and the large cavity of the bucket cylinder 15, and transmits the detection result to the controller 19. The comparator C8 compares the pressures of the large cavity of the boom cylinder 10 and the Y cavity of the rotary motor 21, and transmits the detection result to the controller 19. The controller 19 further compares the sizes of Pc and Pd. There are the following two situations;

[0112] When it is detected that Pa>Pd>Pc exists, at this time, the pressure of the large chamber of the boom cylinder 10 is greater than the pressure of the large chamber of the bucket cylinder 15, which is greater than the pressure of the Y chamber of the swing motor 21, and the controller 19 energizes the electromagnet of the proportional valve C6. At this time, the proportional valve C6 is opened, and the large chamber of the boom cylinder 10 is connected to the Y chamber of the swing motor 21. A part of the hydraulic oil in the large chamber of the boom cylinder 10 is regenerated to the small chamber of the boom cylinder 10 through the channel a on the boom working valve 206, and the other part is regenerated to the Y chamber of the swing motor 21 through the proportional valve C6;

[0113] When it is detected that Pa>Pc>Pd exists, at this time, the pressure of the large chamber of the boom cylinder 10 is greater than the pressure of the Y chamber of the rotary motor 21, which is greater than the pressure of the large chamber of the bucket cylinder 15, and the controller 19 energizes the electromagnet of the proportional valve D13. At this time, the proportional valve D13 opens, and the large chamber of the boom cylinder 10 and the large chamber of the bucket cylinder 15 are connected. Part of the hydraulic oil in the large chamber of the boom cylinder 10 is regenerated to the small chamber of the boom cylinder 10 through the channel a on the boom working valve 206, and the other part is regenerated to the large chamber of the bucket cylinder 15 through the proportional valve D13.

[0114] This process can also define the minimum value of Pc and Pd as Pmin, and define △P'=Pa-Pmin. When △P' is greater than a certain value, it controls the opening of the proportional valve to achieve adjustable flow regeneration of the large chamber of the boom cylinder 10 to other working chambers. The whole process can fully recover and utilize the energy of the boom lowering, thereby reducing the displacement of the main pump 2 and achieving energy saving of the whole machine compound action. Among them, Pmin is the minimum value of other chambers except the large chamber of the boom, that is, Pmin=(Pb, Pc, Pd, Pe). In fact, the △P mentioned in the essence of the boom lowering + a compound action (two compound actions) can be set to make the flow regenerated from the large chamber of the boom to other working chambers adjustable, such as Figure 4 The principles of the flowchart shown are the same.

Claims

1. An energy-saving hydraulic system for an excavator, comprising a main pump (2), wherein the oil outlet of the main pump (2) is respectively connected to a boom cylinder (10), a bucket cylinder (15), an arm cylinder (18) and a slewing motor (21) through a main control valve (20), and characterized in that: The main control valve (20) comprises a bucket working valve (201) connected to the bucket cylinder (15). A boom confluence valve (204) and a boom working valve (206) connected to the boom oil cylinder (10), A rotary working valve (205) connected to the rotary motor (21), and a boom working valve B (202) and a boom working valve A (203) connected to the boom oil cylinder (18); When the boom is lowered, the boom confluence valve (204) works in the left position and the boom working valve (206) works in the right position. The hydraulic oil of the right pump of the main pump (2) enters the channel b of the boom working valve (206) through the P port and then enters the small chamber of the boom cylinder (10). A part of the hydraulic oil of the large chamber of the boom cylinder (10) re-enters the channel b through the channel a of the boom working valve (206) and finally enters the small chamber of the boom cylinder (10), thereby realizing the regeneration of the large chamber flow of the boom cylinder (10); another part of the hydraulic oil of the large chamber of the boom cylinder (10) returns to the oil tank (22) through the channel c.

2. The energy-saving hydraulic system for excavators according to claim 1, characterized in that: A proportional valve B (4) is provided between the large chamber of the boom cylinder (10) and the X chamber of the rotary motor (21), a proportional valve C (6) is provided between the large chamber of the boom cylinder (10) and the Y chamber of the rotary motor (21), a proportional valve D (13) is provided between the large chamber of the boom cylinder (10) and the large chamber of the bucket cylinder (15), and a proportional valve E (17) is provided between the large chamber of the boom cylinder (10) and the large chamber of the arm cylinder (18).

3. The energy-saving hydraulic system for excavators according to claim 2, characterized in that: A pressure sensor A (9) for detecting the pressure of the large chamber of the boom cylinder (10) is arranged at the large chamber of the boom cylinder (10); a pressure sensor B (3) for detecting the pressure of the X chamber of the swing motor (21) is arranged at the X chamber of the swing motor (21); a pressure sensor C (5) for detecting the pressure of the Y chamber of the swing motor (21) is arranged at the Y chamber of the swing motor (21); a pressure sensor D (12) for detecting the pressure of the large chamber of the bucket cylinder (15) is arranged at the large chamber of the bucket cylinder (15); and a pressure sensor E (16) for detecting the pressure of the large chamber of the arm cylinder (18) is arranged at the large chamber of the boom cylinder (18).

4. The energy-saving hydraulic system for excavators according to claim 3 is characterized in that: A comparator B (7) is provided between the pressure sensor A (9) and the pressure sensor B (3), a comparator C (8) is provided between the pressure sensor A (9) and the pressure sensor C (5), a comparator D (11) is provided between the pressure sensor A (9) and the pressure sensor D (12), and a comparator E (14) is provided between the pressure sensor A (9) and the pressure sensor E (16).

5. The energy-saving hydraulic system for excavators according to claim 4, characterized in that: The electromagnetic signal end of the proportional valve B (4), the electromagnetic signal end of the proportional valve C (6), the electromagnetic signal end of the proportional valve D (13), the electromagnetic signal end of the proportional valve E (17), the comparator B (7), the comparator C (8), the comparator D (11) and the comparator E (14) are all electrically connected to the controller (19).

6. A control method for an energy-saving hydraulic system of an excavator, characterized in that: The energy-saving hydraulic system for excavators as described in claim 5 includes the following two methods: a control method when the boom is lowered plus a compound action and a control method when the boom is lowered plus more than one compound action (three or more compound actions).

7. The control method of the energy-saving hydraulic system of an excavator according to claim 6, characterized in that: The control method when the boom is lowered and a compound action is performed is: The pressure sensor A (9) detects the pressure Pa of the large chamber of the boom cylinder (10) in real time, the pressure sensor B (3) detects the pressure Pb of the X chamber of the rotary motor (21) in real time, the pressure sensor C (5) detects the pressure Pc of the Y chamber of the rotary motor (21) in real time, the pressure sensor D (12) detects the pressure Pd of the large chamber of the bucket cylinder (15) in real time, and the pressure sensor E (16) detects the pressure Pe of the large chamber of the arm cylinder (18) in real time. The pressures of the two chambers are compared by a comparator, and the detection result is transmitted to the controller (19); When Pa>Pb, the proportional valve B (4) is energized, the X chamber of the swing motor (21) is connected to the large chamber of the boom cylinder (10), and the hydraulic oil enters the X chamber of the swing motor (21) from the large chamber of the boom cylinder (10); When Pa>Pc, the proportional valve C (6) is energized, the Y chamber of the swing motor (21) is connected to the large chamber of the boom cylinder (10), and the hydraulic oil enters the Y chamber of the swing motor (21) from the large chamber of the boom cylinder (10); When Pa>Pd, the proportional valve D (13) is energized, the large chamber of the bucket cylinder (15) is connected to the large chamber of the boom cylinder (10), and the hydraulic oil enters the large chamber of the bucket cylinder (15) from the large chamber of the boom cylinder (10); When Pa>Pe, the proportional valve E (17) is energized, the large chamber of the arm cylinder (18) is connected to the large chamber of the boom cylinder (10), and the hydraulic oil enters the large chamber of the arm cylinder (18) from the large chamber of the boom cylinder (10).

8. The control method of the energy-saving hydraulic system of an excavator according to claim 6, characterized in that: The control method when the boom is lowered and a compound action is performed is: The pressure sensor A (9) detects the pressure Pa of the large chamber of the boom cylinder (10) in real time, the pressure sensor B (3) detects the pressure Pb of the X chamber of the rotary motor (21) in real time, the pressure sensor C (5) detects the pressure Pc of the Y chamber of the rotary motor (21) in real time, the pressure sensor D (12) detects the pressure Pd of the large chamber of the bucket cylinder (15) in real time, and the pressure sensor E (16) detects the pressure Pe of the large chamber of the arm cylinder (18) in real time. The pressures of the two chambers are compared by a comparator, and the detection result is transmitted to the controller (19); The pressure difference between the large chamber of the boom oil cylinder (10) and the other working chambers is ΔP, and ΔPb=Pa-Pb, ΔPc=Pa-Pc, ΔPd=Pa-Pd, and ΔPe=Pa-Pe are defined. The size of ΔP is set as the basis for opening and closing the solenoid valve, and determines the flow rate of the hydraulic oil of the large chamber of the boom to the other working chambers, so as to achieve the adjustable regeneration amount of the large chamber of the boom to the other working chambers; When ΔPb is greater than Pb1, the proportional valve B (4) is energized, the X chamber of the swing motor (21) is connected to the large chamber of the boom cylinder (10), and the hydraulic oil enters the X chamber of the swing motor (21) from the large chamber of the boom cylinder (10); When ΔPc is greater than Pc1, the proportional valve C (6) is energized, the Y chamber of the swing motor (21) is connected to the large chamber of the boom cylinder (10), and the hydraulic oil enters the Y chamber of the swing motor (21) from the large chamber of the boom cylinder (10); When ΔPd is greater than Pd1, the proportional valve D (13) is energized, the large chamber of the bucket cylinder (15) is connected to the large chamber of the boom cylinder (10), and the hydraulic oil enters the large chamber of the bucket cylinder (15) from the large chamber of the boom cylinder (10); When ΔPe is greater than Pe1, the proportional valve E (17) is energized, the large chamber of the arm cylinder (18) is connected to the large chamber of the boom cylinder (10), and the hydraulic oil enters the large chamber of the arm cylinder (18) from the large chamber of the boom cylinder (10); Among them, Pb1 is the pressure difference value actually detected between the large cavity of the boom cylinder (10) and the X cavity of the rotary motor (21), Pc1 is the pressure difference value actually detected between the large cavity of the boom cylinder (10) and the Y cavity of the rotary motor (21), Pd1 is the pressure difference value actually detected between the large cavity of the boom cylinder (10) and the large cavity of the bucket cylinder (15), and Pe1 is the pressure difference value actually detected between the large cavity of the boom cylinder (10) and the large cavity of the arm cylinder (18).

9. The control method of the energy-saving hydraulic system of an excavator according to claim 6, characterized in that: The control method when the boom lowering is greater than one compound action (three or more compound actions) is: The pressure sensor A (9) detects the pressure Pa of the large chamber of the boom cylinder (10) in real time, the pressure sensor B (3) detects the pressure Pb of the X chamber of the rotary motor (21) in real time, the pressure sensor C (5) detects the pressure Pc of the Y chamber of the rotary motor (21) in real time, the pressure sensor D (12) detects the pressure Pd of the large chamber of the bucket cylinder (15) in real time, and the pressure sensor E (16) detects the pressure Pe of the large chamber of the arm cylinder (18) in real time. The pressures of the three chambers are compared by a comparator, and the detection results are transmitted to a controller (19); When any of Pa>Pe (or Pd)>Pb or Pa>Pe>Pd>Pb or Pa>Pd>Pe>Pb occurs, the proportional valve B (4) is energized, the X chamber of the swing motor (21) is connected to the large chamber of the boom cylinder (10), and the hydraulic oil enters the X chamber of the swing motor (21) from the large chamber of the boom cylinder (10); When any of Pa>Pe (or Pd)>Pc or Pa>Pe>Pd>Pc or Pa>Pd>Pe>Pc occurs, the proportional valve C (6) is energized, the Y chamber of the swing motor (21) is connected to the large chamber of the boom cylinder (10), and the hydraulic oil enters the Y chamber of the swing motor (21) from the large chamber of the boom cylinder (10); When any of Pa>Pe (or Pb or Pc)>Pd or when Pa>Pe>Pb (or Pc)>Pd or when Pa>Pb (or Pc)>Pe>Pd occurs, the proportional valve D (13) is energized, the large chamber of the bucket cylinder (15) is connected with the large chamber of the boom cylinder (10), and the hydraulic oil enters the large chamber of the bucket cylinder (15) from the large chamber of the boom cylinder (10); When Pa>Pb (or Pc or Pd)>Pe or when Pa>Pb (or Pc)>Pd>Pe or when Pa>Pd>Pb (or Pc)>Pe When any of these occurs, proportional valve E (17) is energized, and the large chamber of the arm cylinder (18) is connected to the large chamber of the boom cylinder (10). The hydraulic oil enters the large chamber of the boom cylinder (18) from the large chamber of the boom cylinder (10).

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