Work machine

Abstract

A work machine is provided with: a boom; a boom cylinder having a cylinder bottom chamber and a cylinder head chamber; a boom pump having a suction port and a discharge port; a hydraulic oil tank; a boom operating valve having a pump port connected to the discharge port via a pump flow path, a cylinder bottom port connected to the cylinder bottom chamber via a cylinder bottom flow path, a cylinder head port connected to the cylinder head chamber via a cylinder head flow path, a tank port connected to the hydraulic tank via a tank flow path, and a regeneration port connected to the suction port via a regeneration flow path; a reservoir connected to the regeneration flow path via a reservoir flow path; an accumulator switching valve for adjusting the flow rate of the hydraulic oil in the accumulator flow path; and a controller that controls the boom operation valve and the accumulator switching valve such that the hydraulic oil discharged from the cylinder bottom chamber is distributed to the suction port and the accumulator during the lowering operation of the boom.

Description

Technical Field

[0001] The present invention relates to a working machine. Background Art

[0002] In the technical field related to working machines, a hydraulic drive system for a construction machine as disclosed in Patent Document 1 is known.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2019-052702 Summary of the Invention

[0004] In Patent Document 1, when the boom is lowered, hydraulic oil discharged from the boom cylinder is supplied to the accumulator via the regeneration valve, the first pump, and the accumulator switching valve. In Patent Document 1, the hydraulic oil used to accumulate pressure in the accumulator passes through the first pump, so the accumulator may not be able to accumulate pressure efficiently.

[0005] An object of the present disclosure is to efficiently accumulate pressure in an accumulator using hydraulic oil discharged from a boom cylinder when a boom is lowered.

[0006] According to the present disclosure, a working machine is provided, which comprises: a boom; a boom cylinder having a cylinder bottom chamber and a cylinder head chamber; a boom pump having a suction port and a discharge port; a hydraulic oil tank; a boom operating valve having: a pump interface connected to the discharge port via a pump flow path, a cylinder bottom interface connected to the cylinder bottom chamber via a cylinder bottom flow path, a cylinder head interface connected to the cylinder head chamber via a cylinder head flow path, a tank interface connected to the hydraulic oil tank via a tank flow path, and a regeneration interface connected to the suction port via a regeneration flow path; a reservoir connected to the regeneration flow path via a reservoir flow path; a reservoir switching valve for adjusting the flow rate of hydraulic oil in the reservoir flow path; and a controller, which controls the boom operating valve and the reservoir switching valve during the lowering action of the boom so that the hydraulic oil discharged from the cylinder bottom chamber is distributed to the suction port and the reservoir, respectively.

[0007] According to the present disclosure, the hydraulic oil discharged from the boom cylinder when the boom is lowered can be used to efficiently store pressure in the accumulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a perspective view showing a working machine according to the embodiment.

[0009] Figure 2 It is a diagram showing a hydraulic system of a working machine according to an embodiment.

[0010] Figure 3 This is a diagram showing a hydraulic system when the boom is raised by hydraulic oil discharged from the boom pump according to the embodiment.

[0011] Figure 4This is a diagram showing a hydraulic system when the boom is lowered according to the embodiment.

[0012] Figure 5 It is a diagram schematically showing a boom cylinder according to the embodiment.

[0013] Figure 6 This is a diagram showing an example of data related to the embodiment.

[0014] Figure 7 This is a diagram showing a hydraulic system when the boom is raised by hydraulic oil released from the reservoir according to the embodiment. DETAILED DESCRIPTION

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings, but the present disclosure is not limited to the embodiments. The constituent elements of the embodiments described below can be combined as appropriate. In addition, there are also cases where some constituent elements are not used.

[0016] Operating machinery

[0017] Figure 1 This is a perspective view of a work machine 1 according to an embodiment. The work machine 1 is operating at a work site. In the embodiment, the work machine 1 is a hydraulic excavator. In the following description, the work machine 1 may be referred to as the hydraulic excavator 1. The hydraulic excavator 1 includes a traveling body 2, a swing body 3, a work machine 4, a work machine cylinder 5, and a controller 6.

[0018] The walking body 2 travels while supporting the revolving body 3. The walking body 2 has a pair of crawler tracks 2A. The crawler tracks 2A rotate based on the travel motor. The walking body 2 travels based on the rotation of the crawler tracks 2A. The revolving body 3 is supported by the walking body 2. The revolving body 3 is provided with a cab. The working machine 4 is mounted on the revolving body 3. The working machine 4 includes: a boom 41, an arm 42, and a bucket 43. The working machine cylinder 5 is used to move the working machine 4. The working machine cylinder 5 is a hydraulic cylinder. The working machine cylinder 5 includes: a boom cylinder 51, an arm cylinder 52, and a bucket cylinder 53. The controller 6 includes a computer system. The controller 6 is used to control the hydraulic excavator 1.

[0019] hydraulic system

[0020] Figure 2 This diagram shows a hydraulic system 10 of a hydraulic excavator 1 according to an embodiment. The hydraulic system 10 includes an engine 15, a main hydraulic pump 11, a main valve 21, an arm cylinder 52, a bucket cylinder 53, a travel motor 7, a travel motor 8, a swing motor 9, a boom pump 12, a boom cylinder 51, a boom operating valve 22, a reservoir 14, a reservoir switching valve 23, a hydraulic oil tank 16, an operating lever 17, and a controller 6.

[0021] The engine 15 is a power source of the hydraulic excavator 1. The engine 15 is connected (directly coupled) to each of the main hydraulic pump 11 and the boom pump 12. The engine 15 drives each of the main hydraulic pump 11 and the boom pump 12.

[0022] The main hydraulic pump 11 discharges hydraulic oil for operating the arm cylinder 52, bucket cylinder 53, travel motor 7, travel motor 8, and slewing motor 9. The main hydraulic pump 11 is connected to the boom pump 12 (directly connected). In the embodiment, two main hydraulic pumps 11 are provided. The main hydraulic pump 11 includes a main hydraulic pump 111 and a main hydraulic pump 112. The main hydraulic pump 111 and the main hydraulic pump 112 are both variable capacity hydraulic pumps whose pump capacity changes according to the swash plate angle. The suction port of the main hydraulic pump 11 is connected to the hydraulic oil tank 16. The discharge port of the main hydraulic pump 11 is connected to the main valve 21. The main hydraulic pump 11 sucks hydraulic oil from the hydraulic oil tank 16 from the discharge port and discharges it to the main valve 21 from the discharge port. In addition, the main hydraulic pump 11 can also be any plural number of one or more than three.

[0023] The main valve 21 controls the flow rate and direction of the hydraulic oil supplied from the main hydraulic pump 11 to the arm cylinder 52. The main valve 21 controls the flow rate and direction of the hydraulic oil supplied from the main hydraulic pump 11 to the bucket cylinder 53. The main valve 21 controls the flow rate and direction of the hydraulic oil supplied from the main hydraulic pump 11 to the travel motor 7. The main valve 21 controls the flow rate and direction of the hydraulic oil supplied from the main hydraulic pump 11 to the travel motor 8. The main valve 21 controls the flow rate and direction of the hydraulic oil supplied from the main hydraulic pump 11 to the swing motor 9.

[0024] The arm cylinder 52, bucket cylinder 53, travel motor 7, travel motor 8, and swing motor 9 are main hydraulic actuators that are different from the boom cylinder 51. The arm cylinder 52 is a hydraulic cylinder used to cause the arm 42 to perform digging and bucket tipping actions. The bucket cylinder 53 is a hydraulic cylinder used to cause the bucket 43 to perform digging and bucket tipping actions. The travel motor 7 is a hydraulic motor used to rotate the left crawler track 2A. The travel motor 8 is a hydraulic motor used to rotate the right crawler track 2A. The swing motor 9 is a hydraulic motor used to rotate the rotating body 3.

[0025] The boom pump 12 is a hydraulic pump for discharging the hydraulic oil used to actuate the boom cylinder 51. The boom pump 12 discharges the hydraulic oil supplied to the boom cylinder 51. The boom pump 12 is a variable capacity hydraulic pump whose pump capacity changes according to the swash plate angle. The boom pump 12 has a suction port 12A and a discharge port 12B. The boom pump 12 discharges the hydraulic oil sucked in from the suction port 12A from the discharge port 12B. The suction port 12A of the boom pump 12 is not connected to the hydraulic oil tank 16. The boom pump 12 does not directly suck in the hydraulic oil from the hydraulic oil tank 16. The hydraulic oil discharged from the discharge port 12B of the boom pump 12 is supplied to the boom cylinder 51 via the boom operating valve 22. The boom pump 12 is a hydraulic pump / motor. The boom pump 12 can function as a hydraulic motor.

[0026] The boom cylinder 51 is a hydraulic cylinder used to raise and lower the boom 41. The boom cylinder 51 extends to raise the boom 41. The boom cylinder 51 retracts when the boom 41 is lowered. The boom cylinder 51 includes a cylinder bottom chamber 51A and a cylinder head chamber 51B. The boom cylinder 51 extends by supplying hydraulic oil to the cylinder bottom chamber 51A and discharging the hydraulic oil from the cylinder head chamber 51B. The boom cylinder 51 retracts by supplying hydraulic oil to the cylinder head chamber 51B and discharging the hydraulic oil from the cylinder bottom chamber 51A.

[0027] The boom operating valve 22 controls the flow rate and flow direction of the hydraulic oil supplied from the boom pump 12 to the boom cylinder 51. When the boom 41 is raised, the boom operating valve 22 supplies the hydraulic oil discharged from the discharge port 12B of the boom pump 12 to the cylinder bottom chamber 51A. When the boom 41 is lowered, at least a portion of the hydraulic oil discharged from the cylinder bottom chamber 51A is returned to the suction port 12A of the boom pump 12 via the boom operating valve 22. However, when the pressure of the hydraulic oil discharged from the cylinder bottom chamber 51A is lower than the set storage pressure of the reservoir 14 due to the action of the first one-way valve 24 described later, the hydraulic oil discharged from the cylinder bottom chamber 51A is discharged to the hydraulic oil tank 16.

[0028] The boom operating valve 22 has a pump interface 22A, a cylinder head interface 22B, a cylinder bottom interface 22C, a tank interface 22D, and a regeneration interface 22E. The pump interface 22A is connected to the discharge port 12B of the boom pump 12 via the pump flow path 31. The cylinder head interface 22B is connected to the cylinder head chamber 51B of the boom cylinder 51 via the cylinder head flow path 32. The cylinder bottom interface 22C is connected to the cylinder bottom chamber 51A of the boom cylinder 51 via the cylinder bottom flow path 33. The tank interface 22D is connected to the hydraulic oil tank 16 via the tank flow path 34. The regeneration interface 22E is connected to the suction port 12A of the boom pump 12 via the regeneration flow path 35.

[0029] The boom operating valve 22 is movable among a raised position R, a neutral position N, and a lowered position D. The boom operating valve 22 moves based on a control command from the controller 6. When the boom 41 is raised, the boom operating valve 22 is located in the raised position R. When the boom 41 is lowered, the boom operating valve 22 is located in the lowered position D. When the boom 41 is stopped, the boom operating valve 22 is located in the neutral position N. Figure 2 The boom operating valve 22 is shown in a state where it is located at the neutral position N.

[0030] The reservoir 14 is connected to the regeneration flow path 35 via the reservoir flow path 36. When the boom 41 is lowered, at least a portion of the hydraulic oil discharged from the cylinder bottom chamber 51A is supplied to the reservoir 14 via the reservoir flow path 36. The reservoir 14 is pressurized based on the hydraulic oil supplied from the cylinder bottom chamber 51A. However, if the pressure of the hydraulic oil discharged from the cylinder bottom chamber 51A is lower than the set storage pressure of the reservoir 14 due to the action of the first check valve 24 described later, the hydraulic oil discharged from the cylinder bottom chamber 51A is discharged to the hydraulic oil tank 16, and the reservoir 14 is not pressurized.

[0031] The reservoir flow path 36 is connected to the connection portion 61 of the regeneration flow path 35 between the regeneration port 22E and the suction port 12A. A first check valve 24 is disposed in the regeneration flow path 35 between the regeneration port 22E and the connection portion 61. The first check valve 24 allows the flow of hydraulic oil from the regeneration port 22E to the connection portion 61, while preventing the flow of hydraulic oil from the connection portion 61 to the regeneration port 22E.

[0032] The reservoir switching valve 23 is used to adjust the flow rate of the hydraulic oil in the reservoir flow path 36. The reservoir switching valve 23 is arranged in the reservoir flow path 36. By adjusting the opening area of ​​the reservoir switching valve 23, the flow rate of the hydraulic oil in the reservoir flow path 36 is adjusted.

[0033] The reservoir switching valve 23 can be moved to a fully open position A or a fully closed position B. The reservoir switching valve 23 moves in response to a control command from the controller 6. The controller 6 can adjust the opening area of ​​the reservoir switching valve 23. By configuring the reservoir switching valve 23 in the fully open position A, the opening area of ​​the reservoir switching valve 23 becomes 100%, allowing hydraulic oil to flow through the reservoir flow path 36. By configuring the reservoir switching valve 23 in the fully closed position B, the opening area of ​​the reservoir switching valve 23 becomes 0%, preventing hydraulic oil from flowing through the reservoir flow path 36. Figure 2 The state where the reservoir switching valve 23 is arranged in the fully closed position B is shown.

[0034] To operate the boom operating valve 22, the operating lever 17 is operated. The operating lever 17 is located in the cab of the hydraulic excavator 1. The operating lever 17 is operated by an operator riding in the cab of the hydraulic excavator 1. The operating lever 17 is tilted. The operating signal generated by operating the operating lever 17 is transmitted to the controller 6.

[0035] The controller 6 controls the flow rate and direction of the hydraulic oil supplied to the boom cylinder 51 via the boom operating valve 22 based on an operating signal from the operating lever 17. The controller 6 adjusts the flow rate of the hydraulic oil supplied to the boom cylinder 51 based on the lever angle, which represents the operating angle of the operating lever 17. A greater lever angle increases the flow rate of the hydraulic oil supplied to the boom cylinder 51, thereby increasing the speed at which the boom cylinder 51 can be extended or retracted. A smaller lever angle decreases the flow rate of the hydraulic oil supplied to the boom cylinder 51, thereby decreasing the speed at which the boom cylinder 51 can be extended or retracted.

[0036] In the embodiment, the boom pump 12 is directly connected to the booster pump 13. The suction port of the booster pump 13 is connected to the hydraulic oil tank 16. The discharge port of the booster pump 13 is connected to the connection portion 62 of the regeneration flow path 35 via the boost flow path 37. The connection portion 62 is provided in the regeneration flow path 35 between the connection portion 61 and the suction port 12A.

[0037] Connecting portion 63 of boost flow path 37 is connected to safety flow path 38. Safety valve 26 is disposed in safety flow path 38. Booster pump 13 is connected in parallel with safety valve 26. A second check valve 25 is disposed in boost flow path 37 between connection portion 63 and connection portion 62. Second check valve 25 allows the flow of hydraulic oil from connection portion 63 to connection portion 62, while preventing the flow of hydraulic oil from connection portion 62 to connection portion 63.

[0038] Boom raising action based on boom pump

[0039] Figure 3 1 is a diagram showing a hydraulic system 10 in which the boom 41 is raised by the hydraulic oil discharged from the boom pump 12 according to the embodiment. Figure 3 In FIG. 5 , arrow Fa indicates the direction of flow of hydraulic oil, and arrow Fb indicates the extension and contraction direction of boom cylinder 51. Figure 3 The boom operating valve 22 shown is a portion of the boom operating valve 22 that is located at the raised position R. Figure 3 The illustrated reservoir switching valve 23 is a partially extracted view of the reservoir switching valve 23 disposed in the fully open position A.

[0040] The operating lever 17 is operated to raise the boom 41. Based on the operating signal from the operating lever 17, the controller 6 outputs a control command to the boom operating valve 22 to place the boom operating valve 22 in the raised position R. When the boom 41 is raised, the controller 6 outputs a control command to the accumulator switching valve 23 to place the accumulator switching valve 23 in the fully open position A.

[0041] The boom pump 12 is driven by the rotational force generated by the engine 15. Figure 3 As shown by the arrow Fc, the rotational force generated by the engine 15 is transmitted to the boom pump 12 via the main hydraulic pump 11. By transmitting the rotational force of the engine 15 to the boom pump 12, the boom pump 12 is driven. The boom pump 12 discharges the hydraulic oil sucked in from the suction port 12A from the discharge port 12B. The hydraulic oil discharged from the discharge port 12B is supplied to the cylinder bottom chamber 51A of the boom cylinder 51 via the pump flow path 31, the pump interface 22A of the boom operating valve 22, the cylinder bottom interface 22C of the boom operating valve 22, and the cylinder bottom flow path 33. By supplying hydraulic oil to the cylinder bottom chamber 51A, the boom cylinder 51 is extended, and the boom 41 performs an upward movement.

[0042] In the embodiment, the boom operating valve 22 includes a bifurcated portion 22F for distributing hydraulic oil from the cylinder head port 22B to the tank port 22D and the regeneration port 22E, and a throttle valve 22G disposed between the bifurcated portion 22F and the tank port 22D. A portion of the hydraulic oil discharged from the cylinder head chamber 51B is discharged to the hydraulic oil tank 16 via the cylinder head flow path 32, the cylinder head port 22B of the boom operating valve 22, the bifurcated portion 22F of the boom operating valve 22, the tank port 22D of the boom operating valve 22, and the tank flow path 34. A portion of the hydraulic oil discharged from the cylinder head chamber 51B is supplied to the suction port 12A of the boom pump 12 via the cylinder head flow path 32, the cylinder head port 22B of the boom operating valve 22, the bifurcated portion 22F of the boom operating valve 22, the regeneration port 22E of the boom operating valve 22, and the regeneration flow path 35.

[0043] The booster pump 13 is used to compensate for the hydraulic oil supplied to the suction port 12A. The booster pump 13 supplies hydraulic oil to the suction port 12A via the booster flow path 37, the connection portion 62, and a portion of the regeneration flow path 35 so that the flow rate of the hydraulic oil discharged from the discharge port 12B matches the flow rate of the hydraulic oil flowing into the suction port 12A. By discharging the hydraulic oil from the booster pump 13 so that the flow rate of the hydraulic oil discharged from the discharge port 12B matches the flow rate of the hydraulic oil flowing into the suction port 12A, negative pressure in the suction port 12A and the regeneration flow path 35 is suppressed. By suppressing negative pressure in the suction port 12A and the regeneration flow path 35, cavitation in the suction port 12A and the regeneration flow path 35 can be suppressed.

[0044] Lowering action of the boom

[0045] Figure 4 1 is a diagram showing a hydraulic system 10 when the boom 41 is lowered according to the embodiment. Figure 4 In FIG. 5 , arrow Fa indicates the direction of flow of hydraulic oil, and arrow Fb indicates the extension and contraction direction of boom cylinder 51. Figure 4 The boom operating valve 22 shown is a portion of the boom operating valve 22 that is located at the lowered position D. Figure 4 The illustrated reservoir switching valve 23 is a partially extracted view of the reservoir switching valve 23 disposed in the fully open position A.

[0046] When the boom 41 is lowered, the boom cylinder 51 contracts due to the weight of the boom 41, discharging hydraulic oil from the cylinder bottom chamber 51A. When the boom 41 is lowered, the controller 6 controls the boom operating valve 22 and the reservoir switching valve 23 so that the hydraulic oil discharged from the cylinder bottom chamber 51A is distributed to the suction port 12A of the boom pump 12 and the reservoir 14, respectively. Specifically, when the operating lever 17 is operated to lower the boom 41, the controller 6 outputs a control command to the boom operating valve 22 based on the operating signal from the operating lever 17, placing the boom operating valve 22 in the lowered position D. Furthermore, the controller 6 outputs a control command to the reservoir 14, placing the reservoir 14 in the fully open position A.

[0047] A portion of the hydraulic oil discharged from the cylinder bottom chamber 51A is supplied to the suction port 12A of the boom pump 12 via the cylinder bottom flow path 33, the cylinder bottom port 22C of the boom operating valve 22, the regeneration port 22E of the boom operating valve 22, and the regeneration flow path 35. The boom pump 12 is driven by the hydraulic oil supplied to the suction port 12A. The boom pump 12 functions as a hydraulic motor when the boom 41 is lowered. Figure 4 As shown by arrow Fd, when the boom 41 is lowered, the rotational energy of the boom pump 12 is transmitted as regenerative energy to the main hydraulic pump 11. The rotational energy of the boom pump 12 assists the rotation of the main hydraulic pump 11. The main hydraulic pump 11 is driven based on the rotational force of the engine 15 and the rotational force of the boom pump 12.

[0048] A portion of the hydraulic oil discharged from the cylinder bottom chamber 51A is supplied to the reservoir 14 via the cylinder bottom flow path 33, the cylinder bottom port 22C of the boom operating valve 22, the regeneration port 22E of the boom operating valve 22, a portion of the regeneration flow path 35, the connecting portion 61, and the reservoir flow path 36. The reservoir 14 is pressurized based on the hydraulic oil supplied from the cylinder bottom chamber 51A.

[0049] In the embodiment, the distribution ratio of the hydraulic oil discharged from the cylinder bottom chamber 51A to the suction port 12A and the accumulator 14 during the lowering operation of the boom 41 is determined based on the cross-sectional area ratio of the cylinder bottom chamber 51A and the cylinder head chamber 51B.

[0050] Figure 5 Schematically shows the boom cylinder 51 of the embodiment. Figure 5 As shown, the boom cylinder 51 includes a cylinder tube 511, a piston 512, and a piston rod 513. The piston rod 513 is located in the cylinder head chamber 51B. Because the piston rod 513 is located in the cylinder head chamber 51B, the cross-sectional area Ab of the cylinder bottom chamber 51A is smaller than the cross-sectional area Ah of the cylinder head chamber 51B. In the embodiment, the cross-sectional area Ah of the cylinder head chamber 51B is 1 / 2 of the cross-sectional area of ​​the cylinder bottom chamber 51A (Ab:Ah = 2:1).

[0051] In order to prevent the cylinder head chamber 51B from becoming negatively pressurized when the boom cylinder 51 contracts during the lowering operation of the boom 41, the controller 6 determines the distribution ratio of the hydraulic oil discharged from the cylinder bottom chamber 51A to the suction port 12A and the accumulator 14 based on the cross-sectional area ratio of the cylinder bottom chamber 51A to the cylinder head chamber 51B. In the embodiment, the cross-sectional area ratio of the cylinder bottom chamber 51A to the cylinder head chamber 51B is [Ab:Ah=2:1]. Therefore, the controller 6 distributes the hydraulic oil discharged from the cylinder bottom chamber 51A to the suction port 12A and the accumulator 14 at a distribution ratio of [1:1].

[0052] exist Figure 4 For example, when the flow rate of hydraulic oil discharged from the cylinder bottom chamber 51A is 150 L / min, the controller 6 controls the opening area of ​​the reservoir switching valve 23 and the swash plate angle of the boom pump 12 so that hydraulic oil is supplied to the suction port 12A at a flow rate of 75 L / min and to the reservoir 14 at a flow rate of 75 L / min. For example, when the reservoir switching valve 23 is positioned in the fully open position A during the boom 41 lowering operation so that the opening area is 100%, the opening area of ​​the boom operating valve 22 is adjusted in accordance with the opening area of ​​the reservoir switching valve 23. Since hydraulic oil is supplied to the suction port 12A at a flow rate of 75 L / min, hydraulic oil is supplied to the cylinder head chamber 51B from the discharge port 12B at a flow rate of 75 L / min.

[0053] When the flow rate of hydraulic oil discharged from the cylinder bottom chamber 51A is 150 L / min, the flow rate of hydraulic oil supplied to the cylinder head chamber 51B is adjusted to 75 L / min based on the cross-sectional area ratio between the cylinder bottom chamber 51A and the cylinder head chamber 51B. This prevents the cylinder head chamber 51B from developing a negative pressure. This prevents the cylinder head chamber 51B from developing a negative pressure, thereby suppressing cavitation in the cylinder head chamber 51B.

[0054] Furthermore, when the boom 41 is lowering, the controller 6 controls the swash plate angle of the boom pump 12 and the opening area of ​​the reservoir switching valve 23 based on the engine speed, which represents the rotational speed of the engine 15, and the lever angle, which represents the operating angle of the operating lever 17, so as to maintain a constant ratio between the boom pump speed, which represents the rotational speed of the boom pump 12, and the boom cylinder speed, which represents the extension and retraction speed of the boom cylinder 51. The controller 6 controls the swash plate angle of the boom pump 12 and the opening area of ​​the reservoir switching valve 23 based on the engine speed and the lever angle so that the boom cylinder 51 operates at the desired boom cylinder speed. The engine speed is consistent with the boom pump speed. The boom cylinder speed is proportional to the flow rate of the hydraulic oil discharged by the boom pump 12. The flow rate of the hydraulic oil discharged by the boom pump 12 is consistent with the product of the boom pump speed and the swash plate angle of the boom pump 12 (the volume of the boom pump 12). In the embodiment, data indicating the relationship between the engine speed, the rod angle, the swash plate angle of the boom pump 12, and the opening area of ​​the accumulator switching valve 23 for maintaining a constant ratio between the boom pump speed and the boom cylinder speed is previously determined and stored in the controller 6. Based on the engine speed, the rod angle, and the data, the controller 6 controls the swash plate angle of the boom pump 12 and the opening area of ​​the accumulator switching valve 23 so as to maintain a constant ratio between the boom pump speed and the boom cylinder speed.

[0055] Figure 6 FIG is a diagram showing an example of data related to an implementation method. Figure 6 As shown, for maintaining a constant ratio between the boom pump rotational speed and the boom cylinder speed, data indicating the relationship between the ratio of the engine rotational speed when the maximum value of the engine rotational speed is set to 100%, the ratio of the rod angle when the maximum value of the rod angle is set to 100%, the ratio of the swash plate angle when the maximum value of the swash plate angle of the boom pump 12 is set to 100%, and the ratio of the opening area of ​​the accumulator switching valve 23 when the maximum value of the opening area of ​​the accumulator switching valve 23 is set to 100% are obtained in advance and stored in the controller 6. The data can be obtained through preliminary tests or simulations.

[0056] Figure 6 This is a graph showing the relationship between the ratio of the engine speed, the ratio of the rod angle, the ratio of the swash plate angle, and the ratio of the opening area of ​​the accumulator switching valve. Figure 6 In the graph shown, the vertical axis represents the ratio of engine speed, and the horizontal axis represents the ratio of rod angle. Furthermore, within a grid, the upper value represents the ratio of swash plate angle, and the lower value represents the ratio of reservoir switching valve opening area.

[0057] The controller 6 determines the distribution ratio (flow rate) of the hydraulic oil to be distributed between the suction port 12A and the reservoir 14 based on the cross-sectional area ratio between the cylinder bottom chamber 51A and the cylinder head chamber 51B. While allowing the determined flow rate of hydraulic oil to flow into the suction port 12A, the controller 6 controls the swash plate angle of the boom pump 12 and the opening area of ​​the reservoir switching valve 23 based on the engine speed, the lever angle, and related data to maintain a constant ratio between the boom pump speed and the boom cylinder speed. For example, if the engine 15 is equipped with an engine speed sensor, the controller 6 can monitor the engine speed based on the detection data of the engine speed sensor. The controller 6 can also monitor the lever angle based on the operating signal from the operating lever 17.

[0058] As described above, the engine 15, the main hydraulic pump 11, and the boom pump 12 are connected (directly coupled). When the boom 41 is lowered, the rotational force of the engine 15 and the rotational force of the boom pump 12 are each transmitted to the main hydraulic pump 11. When the boom 41 is lowered, the swash plate angle of the boom pump 12 and the opening area of ​​the accumulator switching valve 23 are controlled to maintain a constant ratio between the boom pump rotational speed and the boom cylinder speed. This allows the engine 15, the main hydraulic pump 11, and the boom pump 12 to all be driven smoothly.

[0059] Boom raising operation with assistance from the accumulator

[0060] Figure 7 1 is a diagram showing a hydraulic system 10 in which the boom 41 is raised by hydraulic oil released from the reservoir 14 according to the embodiment. Figure 7 In FIG. 5 , arrow Fa indicates the direction of flow of hydraulic oil, and arrow Fb indicates the extension and contraction direction of boom cylinder 51. Figure 7 The boom operating valve 22 shown is a portion of the boom operating valve 22 that is located at the raised position R. Figure 7 The illustrated reservoir switching valve 23 is a partially extracted view of the reservoir switching valve 23 disposed in the fully open position A.

[0061] When the reservoir 14 is pressurized, the boom pump 12 is driven based on the rotational force generated by the engine 15 and the pressure of the hydraulic oil released from the reservoir 14. When the boom 41 is raised, the controller 6 controls the boom operating valve 22 and the reservoir switching valve 23 so that the hydraulic oil discharged from the discharge port 12B of the boom pump 12 is supplied to the cylinder bottom chamber 51A of the boom cylinder 51, and hydraulic oil is supplied from the reservoir 14 to the suction port 12A of the boom pump 12. Specifically, when the operating lever 17 is operated to raise the boom 41, the controller 6 outputs a control command to the boom operating valve 22 based on the operating signal from the operating lever 17, positioning the boom operating valve 22 in the raised position R. Furthermore, the controller 6 outputs a control command to the reservoir 14 so that the reservoir 14 is positioned in the fully open position A.

[0062] The hydraulic oil released from the reservoir 14 is supplied to the suction port 12A of the boom pump 12 via the reservoir flow path 36, the connection portion 61, and a portion of the regeneration flow path 35. The high-pressure hydraulic oil is supplied from the reservoir 14 to the suction port 12A. Figure 7 As shown by the arrow Fc, the rotational force generated by the engine 15 is transmitted to the boom pump 12 via the main hydraulic pump 11. The boom pump 12 discharges the hydraulic oil sucked in from the suction port 12A through the discharge port 12B. The hydraulic oil discharged from the discharge port 12B is supplied to the cylinder bottom chamber 51A of the boom cylinder 51 via the pump flow path 31, the pump port 22A of the boom operating valve 22, the cylinder bottom port 22C of the boom operating valve 22, and the cylinder bottom flow path 33. By supplying hydraulic oil to the cylinder bottom chamber 51A, the boom cylinder 51 extends, and the boom 41 is raised.

[0063] The hydraulic oil discharged from the cylinder head chamber 51B is discharged to the hydraulic oil tank 16 via the cylinder head flowpath 32 , the cylinder head port 22B of the boom operating valve 22 , the tank port 22D of the boom operating valve 22 , and the tank flowpath 34 .

[0064] When the hydraulic oil is released from the reservoir 14, the pressure of the regeneration flow path 35 is greater than the pressure of the hydraulic oil released from the reservoir 14. The pressure of the hydraulic oil discharged from the cylinder head chamber 51B is less than the pressure of the hydraulic oil released from the reservoir 14. Therefore, the hydraulic oil discharged from the cylinder head chamber 51B does not flow into the regeneration flow path 35 via the boom operating valve 22. For example, when the flow rate of the hydraulic oil released from the reservoir 14 is 150 L / min, the flow rate of the hydraulic oil flowing from the reservoir 14 to the suction port 12A of the boom pump 12 is 150 L / min, the flow rate of the hydraulic oil supplied from the discharge port 12B to the cylinder bottom chamber 51A is 150 L / min, and the flow rate of the hydraulic oil discharged from the cylinder head chamber 51B is 75 L / min, all the hydraulic oil discharged from the cylinder head chamber 51B is discharged to the hydraulic oil tank 16.

[0065] Effect

[0066] As described above, in the embodiment, the hydraulic excavator 1 includes: a boom 41; a boom cylinder 51 having a cylinder bottom chamber 51A and a cylinder head chamber 51B; a boom pump 12 having a suction port 12A and a discharge port 12B; a boom operating valve 22 having a pump port 22A connected to the discharge port 12B via a pump flow path 31, a cylinder bottom port 22C connected to the cylinder bottom chamber 51A via a cylinder bottom flow path 33, and a cylinder head port 22B connected to the cylinder head chamber 51B via a cylinder head flow path 32. And a regeneration interface 22E connected to the suction port 12A via the regeneration flow path 35; a reservoir 14, which is connected to the regeneration flow path 35 via the reservoir flow path 36; a reservoir switching valve 23, which is used to adjust the flow rate of hydraulic oil in the reservoir flow path 36; and a controller 6, which controls the boom operating valve 22 and the reservoir switching valve 23 during the lowering action of the boom 41, so that the hydraulic oil discharged from the cylinder bottom chamber 51A is distributed to the suction port 12A and the reservoir 14 respectively.

[0067] According to the embodiment, when the boom 41 is lowered, the hydraulic oil discharged from the boom cylinder 51 is supplied to the reservoir 14 before flowing into the suction port 12A of the boom pump 12. Since the hydraulic oil used to accumulate pressure in the reservoir 14 does not flow through the boom pump 12, the reservoir 14 can be efficiently accumulated.

[0068] Furthermore, a portion of the hydraulic oil discharged from the boom cylinder 51 is returned to the boom pump 12. Since not all of the hydraulic oil discharged from the boom cylinder 51 is returned to the boom pump 12, there is no need to unnecessarily increase the pump capacity of the boom pump 12. Consequently, an increase in the size of the boom pump 12 can be suppressed.

[0069] When the boom 41 is raised, the controller 6 controls the boom operating valve 22 and the reservoir switching valve 23 so that hydraulic oil discharged from the discharge port 12B is supplied to the cylinder bottom chamber 51A and hydraulic oil is supplied from the reservoir 14 to the suction port 12A. The hydraulic oil stored in the reservoir 14 assists the driving of the boom pump 12 during the boom 41's raising operation. Furthermore, the reservoir 14 is connected to the suction port 12A via the reservoir flow path 36 and the regeneration flow path 35. Therefore, even when the pressure applied to the suction port 12A by the reservoir 14 is not excessive, the reservoir 14 can assist the driving of the boom pump 12. Furthermore, because the torque generated by the engine 15 and the pressure of the hydraulic oil released from the reservoir 14 are both input to the boom pump 12 during the boom 41's raising operation, the boom pump 12 can be driven even when the torque of the engine 15 is low, thereby reducing the engine 15's fuel consumption.

[0070] The ratio of the cross-sectional areas of the cylinder bottom chamber 51A and the cylinder head chamber 51B determines the distribution ratio of the hydraulic oil discharged from the cylinder bottom chamber 51A to the suction port 12A and the accumulator 14 during the lowering operation of the boom 41. This prevents the cylinder head chamber 51B from developing a negative pressure during the lowering operation of the boom 41. This prevents the cylinder bottom chamber 51A from developing a negative pressure, thereby suppressing cavitation in the cylinder bottom chamber 51A.

[0071] When the boom 41 is lowered, the rotational energy of the boom pump 12 is transmitted to the main hydraulic pump 11. Thus, the rotational energy of the boom pump 12 generated during the lowering operation of the boom 41 is effectively utilized as regenerative energy.

[0072] When the boom 41 is lowered, the controller 6 determines the flow rate of hydraulic oil flowing into the suction port 12A based on the cross-sectional area ratio of the cylinder bottom chamber 51A to the cylinder head chamber 51B. Then, based on the determined flow rate, the engine speed, and the rod angle, the controller 6 controls the swash plate angle of the boom pump 12 and the opening area of ​​the accumulator switching valve 23 to maintain a constant ratio between the rotational speed of the boom pump 12 and the boom cylinder speed, which represents the extension and retraction speed of the boom cylinder 51. Since the ratio between the rotational speed of the boom pump 12 and the boom cylinder speed is constant during the boom 41 lowering operation, the engine 15, the main hydraulic pump 11, and the boom pump 12 can all be driven smoothly.

[0073] Explanation of symbols

[0074] 1…Hydraulic excavator (working machine); 2…Traveling body; 2A…Crawler tracks; 3…Swinging body; 4…Working machine; 5…Working machine cylinder; 6…Controller; 7…Travel motor (main hydraulic actuator); 8…Travel motor (main hydraulic actuator); 9…Swing motor (main hydraulic actuator); 10…Hydraulic system; 11…Main hydraulic pump; 12…Boom pump; 12A…Suction port; 12B…Discharge port; 13…Booster pump; 14…Reservoir; 15…Engine; 16…Hydraulic oil tank; 17…Operating lever; 21…Main valve; 22…Boom operating valve; 22A…Pump port; 22B…Cylinder head port; 22C…Cylinder bottom port; 22D…Tank port; 22E…Regeneration port; 22F…Bifurcation; 22G…Throttle valve; 23…Reservoir switching valve; 2 4…1st check valve; 25…2nd check valve; 26…safety valve; 31…pump flow path; 32…cylinder head flow path; 33…cylinder bottom flow path; 34…tank flow path; 35…regeneration flow path; 36…reservoir flow path; 37…boost flow path; 38…safety flow path; 41…boom; 42…arm; 43…bucket; 51…boom cylinder; 51A…cylinder bottom chamber; 51B…cylinder head chamber; 52…arm cylinder (main hydraulic actuator); 53…bucket cylinder (main hydraulic actuator); 61…connecting part; 62…connecting part; 63…connecting part; 111…main hydraulic pump; 112…main hydraulic pump; 511…cylinder barrel; 512…piston; 513…piston rod; A…fully open position; B…fully closed position; D…lowered position; N…neutral position; R…raised position.

Claims

1. A working machine, characterized in that: have: boom; The boom cylinder 51 has a cylinder bottom chamber and a cylinder head chamber; a boom pump 12 having a suction port and a discharge port; Hydraulic oil tank; a boom operating valve having: a pump port connected to the discharge port via a pump flow path, a cylinder bottom port connected to the cylinder bottom chamber via a cylinder bottom flow path, a cylinder head port connected to the cylinder head chamber via a cylinder head flow path, a tank port connected to the hydraulic oil tank via a tank flow path, and a regeneration port connected to the suction port via a regeneration flow path; a liquid reservoir connected to the regeneration flow path via a liquid reservoir flow path; a reservoir switching valve for adjusting the flow rate of the hydraulic oil in the reservoir flow path; as well as A controller controls the boom operating valve and the accumulator switching valve during a lowering operation of the boom so that the hydraulic oil discharged from the cylinder bottom chamber is distributed to the suction port and the accumulator, respectively.

2. The working machine according to claim 1, characterized in that: During the boom raising operation, the controller controls the boom operating valve and the accumulator switching valve so that the hydraulic oil discharged from the discharge port is supplied to the cylinder bottom chamber and the hydraulic oil is supplied from the accumulator to the suction port.

3. The working machine according to claim 1, characterized in that: A distribution ratio of the hydraulic oil discharged from the cylinder bottom chamber to the suction port and the accumulator during the lowering operation of the boom is determined according to a cross-sectional area ratio between the cylinder bottom chamber and the cylinder head chamber.

4. The working machine according to claim 1, wherein: have: main hydraulic actuator; and A main hydraulic pump connected to the boom pump discharges hydraulic oil for actuating the main hydraulic actuator. During the boom lowering operation, the rotational energy of the boom pump is transmitted to the main hydraulic pump.

5. The working machine according to claim 4, characterized in that: The boom pump is a variable capacity hydraulic pump whose pump capacity changes according to the swash plate angle. The working machine includes: an engine for driving the main hydraulic pump and the boom pump respectively; as well as an operating lever, which is operated to actuate the boom operating valve; During the lowering action of the boom, the controller controls the swash plate angle of the boom pump and the opening area of ​​the reservoir switching valve according to the engine speed representing the rotational speed of the engine and the lever angle representing the operating angle of the operating lever, so as to keep the ratio of the rotational speed of the boom pump to the extension and retraction speed of the boom cylinder constant.

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