Hydraulic system for hydraulic shovel and boom control valve

Abstract

To provide a hydraulic system for a hydraulic shovel capable of preventing a vehicle body from floating with a simple configuration.SOLUTION: A hydraulic system 1A for a hydraulic shovel includes an arm control valve device 5 and a boom control valve device 4. The boom control valve device 4 is connected with a boom cylinder 11 by a head-side line 61 and a rod-side line 62, and the head-side line 61 is connected with a tank by a makeup line 66 in which a check valve 67 is provided. The boom control valve device 4 is switched among a neutral state, a driven state and a discharge limited state, permits supply of a hydraulic oil from a hydraulic pump 2 to the boom cylinder 11 and discharge of the hydraulic oil from the boom cylinder 11 to the tank in the driven state, and inhibits the supply of the hydraulic oil from the hydraulic pump 2 to the boom cylinder 11 in the discharge limited state, while the device functions as a throttle with respect to the discharge of the hydraulic oil from the boom cylinder 11 to the tank.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a hydraulic system for a hydraulic excavator and a boom control valve for a boom cylinder of a hydraulic excavator. [Background technology]

[0002] When a hydraulic excavator excavates soil, the excavation reaction force can cause the vehicle body to lift up. In this case, the operator performs a boom-up operation to prevent the vehicle body from lifting up.

[0003] In recent years, hydraulic systems capable of preventing the body of a hydraulic excavator from lifting up have been proposed. For example, Patent Document 1 discloses a hydraulic system that prevents the body from lifting up by controlling the opening of a boom regeneration valve.

[0004] Specifically, in the hydraulic system of Patent Document 1, the boom cylinder is connected to the boom control valve by a head-side line and a rod-side line, and the head-side line and the rod-side line are connected by a regeneration line. The regeneration valve is provided on the regeneration line.

[0005] The regeneration valve opens when the pressure in the rod-side chamber of the boom cylinder reaches a target pressure when the arm retraction operation is performed alone, and the opening of the regeneration valve is controlled so that the pressure in the rod-side chamber of the boom cylinder is maintained at the target pressure. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6953216 Summary of the Invention [Problem to be solved by the invention]

[0007] The hydraulic system of Patent Document 1 employs a complex configuration for controlling the opening of a boom regeneration valve in order to prevent the body of the hydraulic excavator from floating up.

[0008] Therefore, an object of the present disclosure is to provide a hydraulic system for a hydraulic excavator that can prevent the vehicle body from floating up with a simple configuration, and to provide a boom control valve that is suitable for the hydraulic system. [Means for solving the problem]

[0009] From one aspect, the present disclosure provides a hydraulic system including at least one hydraulic pump, an arm cylinder, an arm control valve device interposed between the at least one hydraulic pump and the arm cylinder, a boom cylinder, a boom control valve device interposed between the at least one hydraulic pump and the boom cylinder and connected to the boom cylinder by a head side line and a rod side line, and a make-up line connecting the head side line to a tank and provided with a check valve that allows a flow from the tank to the head side line but prohibits a flow from the head side line to the tank, The boom control valve device provides a hydraulic system for a hydraulic excavator that can be switched between a neutral state that prohibits the supply of hydraulic oil from the at least one hydraulic pump to the boom cylinder and the discharge of hydraulic oil from the boom cylinder to the tank, a drive state that allows the supply of hydraulic oil from the at least one hydraulic pump to the boom cylinder and the discharge of hydraulic oil from the boom cylinder to the tank, and a discharge restriction state that prohibits the supply of hydraulic oil from the at least one hydraulic pump to the boom cylinder while functioning as a throttle for the discharge of hydraulic oil from the boom cylinder to the tank.

[0010] From another aspect, the present disclosure provides a boom control valve for a boom cylinder of a hydraulic excavator, the boom control valve including a pump port, a tank port, a head port, and a rod port, and switchable between a neutral position in which the pump port, the tank port, the head port, and the rod port are blocked, a drive position in which the head port is communicated with the pump port and the rod port is communicated with the tank port, and a discharge limiting position in which the head port is communicated with the pump port or the pump port and the head port are blocked and the rod port is communicated with the tank port at an opening degree of 1% to 30% of a maximum opening degree. [Effects of the Invention]

[0011] According to the present disclosure, there are provided a hydraulic system for a hydraulic excavator that can prevent the vehicle body from floating up with a simple configuration, and a boom control valve that is suitable for the hydraulic system. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of a hydraulic system of a hydraulic excavator according to a first embodiment. FIG. [Figure 2] FIG. 1 is a side view of a hydraulic excavator. [Figure 3] FIG. 4 is a schematic configuration diagram of a hydraulic system of a hydraulic excavator according to a modified example of the first embodiment. [Figure 4] FIG. 4 is a schematic configuration diagram of a hydraulic system of a hydraulic excavator according to another modified example of the first embodiment. [Figure 5] FIG. 10 is a schematic configuration diagram of a hydraulic system of a hydraulic excavator according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] First Embodiment FIG. 1 shows a hydraulic system 1A for a hydraulic excavator according to a first embodiment, and FIG. 2 shows a hydraulic excavator 9 equipped with the hydraulic system 1A.

[0014] The hydraulic excavator 9 includes a traveling body 91 and a rotating body 92 that is rotatably supported on the traveling body 91. A cabin 93 including a driver's seat is provided on the rotating body 92, and a boom 94 is connected to the rotating body 92. An arm 95 is connected to the tip of the boom 94, and a bucket 96 is connected to the tip of the arm 95.

[0015] The hydraulic system 1A includes, as hydraulic actuators, a boom cylinder 11, an arm cylinder 12, and a bucket cylinder 13 shown in Fig. 2, as well as a swing motor and a pair of left and right travel motors. The boom cylinder 11 raises and lowers a boom 94, the arm cylinder 12 swings an arm 95, and the bucket cylinder 13 swings a bucket 96.

[0016] As shown in FIG. 1 , the hydraulic system 1A also includes at least one hydraulic pump 2 that supplies hydraulic oil to the hydraulic actuator. In this embodiment, the hydraulic system 1A includes a first hydraulic pump 2A and a second hydraulic pump 2B. Therefore, the technical concept of the present disclosure can be applied to the hydraulic system 1A that includes the first hydraulic pump 2A and the second hydraulic pump 2B. This also applies to the second embodiment described below. However, the hydraulic system 1A may include only one hydraulic pump 2.

[0017] 1, to simplify the drawing, hydraulic actuators other than the boom cylinder 11 and the arm cylinder 12 are omitted. In the following, explanations of the configurations for hydraulic actuators other than the boom cylinder 11 and the arm cylinder 12 will be omitted unless otherwise noted.

[0018] Furthermore, the hydraulic system 1A includes a boom control valve device 4 interposed between the first hydraulic pump 2A and the second hydraulic pump 2B and the boom cylinder 11, and an arm control valve device 5 interposed between the first hydraulic pump 2A and the second hydraulic pump 2B and the arm cylinder 12. The hydraulic system 1A also includes a boom operation device 81 that receives boom-raising operations and boom-lowering operations from the operator, an arm operation device 82 that receives arm-pulling operations and arm-pushing operations from the operator, and a control device 8.

[0019] Each of the first hydraulic pump 2A and the second hydraulic pump 2B is a variable displacement pump whose tilt angle is changeable. For example, each of the first hydraulic pump 2A and the second hydraulic pump 2B is an axial piston pump such as a swash plate pump or a bent axis pump. The tilt angle of the first hydraulic pump 2A is changed by a regulator 21, and the tilt angle of the second hydraulic pump 2B is changed by a regulator 22.

[0020] In this embodiment, the regulators 21 and 22 are controlled by the control device 8. For example, if the first hydraulic pump 2A is a swash plate pump, the regulator 21 may electrically change the hydraulic pressure acting on a servo piston connected to the swash plate of the first hydraulic pump 2A, or may be an electric actuator connected to the swash plate of the first hydraulic pump 2A. Similarly, if the second hydraulic pump 2B is a swash plate pump, the regulator 22 may electrically change the hydraulic pressure acting on a servo piston connected to the swash plate of the second hydraulic pump 2B, or may be an electric actuator connected to the swash plate of the second hydraulic pump 2B.

[0021] However, the regulators 21 and 22 do not necessarily need to be controlled by the control device 8, and may be operated by the pressure of the hydraulic oil. For example, the regulators 21 and 22 may be of a negative control type or a load sensing type.

[0022] In this embodiment, hydraulic oil is supplied from both the first hydraulic pump 2A and the second hydraulic pump 2B to each of the boom cylinder 11 and the arm cylinder 12. Hydraulic oil is supplied to the other hydraulic actuators from either the first hydraulic pump 2A or the second hydraulic pump 2B.

[0023] A pump line 31 extends from the first hydraulic pump 2A. The pump line 31 includes a common path 32 on the upstream side and a plurality of branch paths 33 branching off from the common path 32 for each hydraulic actuator that the first hydraulic pump 2A is to serve. Similarly, a pump line 35 extends from the second hydraulic pump 2B. The pump line 35 includes a common path 36 on the upstream side and a plurality of branch paths 37 branching off from the common path 36 for each hydraulic actuator that the second hydraulic pump 2B is to serve.

[0024] In the following, the arm control valve device 5 will be described first, and then the boom control valve device 4 will be described.

[0025] The arm control valve device 5 is switched between a neutral state and a driving state. In the neutral state, the arm control valve device 5 prohibits the supply of hydraulic oil from the first hydraulic pump 2A and the second hydraulic pump 2B to the arm cylinder 12 and the discharge of hydraulic oil from the arm cylinder 12 to the tank. In the driving state, the arm control valve device 5 permits the supply of hydraulic oil from the first hydraulic pump 2A and the second hydraulic pump 2B to the arm cylinder 12 and the discharge of hydraulic oil from the arm cylinder 12 to the tank.

[0026] Specifically, the arm control valve device 5 includes a main first arm control valve 5A interposed between the second hydraulic pump 2B and the boom cylinder 11, and a secondary second arm control valve 5B interposed between the first hydraulic pump 2A and the boom cylinder 11.

[0027] The first arm control valve 5A is connected to the head side chamber and rod side chamber of the arm cylinder 12 by a head side line 71 and a rod side line 72, respectively, is connected to the second hydraulic pump 2B by a pump line 35, and is connected to the tank by a tank line 38. The second arm control valve 5B is connected to the head side line 71 by a head side auxiliary line 73, is connected to the rod side line 72 by a rod side auxiliary line 74, is connected to the first hydraulic pump 2A by a pump line 31, and is connected to the tank by a tank line 34.

[0028] Each of the first arm control valve 5A and the second arm control valve 5B is driven by an electric signal. Specifically, each of the first arm control valve 5A and the second arm control valve 5B is a spool valve including a spool and a drive unit that receives a command current to drive the spool. A command current is supplied to the drive unit from a control device 8. Note that in FIG. 1, some signal lines are not shown to simplify the drawing. For example, the drive unit may include a pair of electromagnetic proportional valves that output secondary pressures that act on the spool in opposite directions, or may be a linear motion mechanism that is connected to the spool and includes an electric motor, a ball screw, or the like.

[0029] The first arm control valve 5A has a pump port 51 to which the pump line 35 is connected, a tank port 52 to which the tank line 38 is connected, a head port 53 to which the head side line 71 is connected, and a rod port 54 to which the rod side line 72 is connected. The first arm control valve 5A is switchable between a neutral position 5b and a first drive position 5a for pulling the arm and a second drive position 5c for pushing the arm, which are located on either side of the neutral position 5b. In other words, the spool of the first arm control valve 5A can move in both directions from a state in which the first arm control valve 5A is located in the neutral position 5b.

[0030] When the first arm control valve 5A is located in the neutral position 5b, it blocks the pump port 51, the tank port 52, the head port 53, and the rod port 54. When the first arm control valve 5A is located in the first drive position 5a, it connects the head port 53 to the pump port 51 and the rod port 54 to the tank port 52. When the first arm control valve 5A is located in the second drive position 5c, it connects the rod port 54 to the pump port 51 and the head port 53 to the tank port 52.

[0031] The second-arm control valve 5B has a pump port 55 to which the pump line 31 is connected, a tank port 56 to which the tank line 34 is connected, a head port 57 to which the head-side auxiliary line 73 is connected, and a rod port 58 to which the rod-side auxiliary line 74 is connected. The second-arm control valve 5B is switchable between a neutral position 5e and a first drive position 5d for pulling the arm and a second drive position 5f for pushing the arm, which are located on either side of the neutral position 5e. In other words, the spool of the second-arm control valve 5B is movable in both directions from a state in which the second-arm control valve 5B is located in the neutral position 5e.

[0032] When the second arm control valve 5B is in the neutral position 5e, it blocks the pump port 55, the tank port 56, the head port 57, and the rod port 58. When the second arm control valve 5B is in the first drive position 5d, it connects the head port 57 to the pump port 55 and the rod port 58 to the tank port 56. When the second arm control valve 5B is in the second drive position 5f, it connects the rod port 58 to the pump port 55 and the head port 57 to the tank port 56.

[0033] The neutral state of the arm control valve device 5 described above is a state in which the first arm control valve 5A is located at the neutral position 5b and the second arm control valve 5B is located at the neutral position 5e. The drive states of the arm control valve device 5 are a state in which the first arm control valve 5A is located at the first drive position 5a and the second arm control valve 5B is located at the first drive position 5d, or a state in which the first arm control valve 5A is located at the second drive position 5c and the second arm control valve 5B is located at the second drive position 5f.

[0034] The boom control valve device 4 is switchable between a neutral state, a drive state, and a discharge restriction state. In the neutral state, the boom control valve device 4 prohibits the supply of hydraulic oil from the first hydraulic pump 2A and the second hydraulic pump 2B to the boom cylinder 11 and the discharge of hydraulic oil from the boom cylinder 11 to the tank. In the drive state, the boom control valve device 4 permits the supply of hydraulic oil from the first hydraulic pump 2A and the second hydraulic pump 2B to the boom cylinder 11 and the discharge of hydraulic oil from the boom cylinder 11 to the tank. In the discharge restriction state, the boom control valve device 4 prohibits the supply of hydraulic oil from the first hydraulic pump 2A and the second hydraulic pump 2B to the boom cylinder 11, while functioning as a throttle for the discharge of hydraulic oil from the boom cylinder 11 to the tank.

[0035] Specifically, the boom control valve device 4 includes a primary first boom control valve 4A interposed between the first hydraulic pump 2A and the boom cylinder 11, a secondary second boom control valve 4B interposed between the second hydraulic pump 2B and the boom cylinder 11, and a meter-in cut valve 4C for the first boom control valve 4A. In this embodiment, the second boom control valve 4B is a two-port, two-position valve that operates only when the boom is raised. However, the second boom control valve 4B may also be a four-port, three-position valve that operates when the boom is raised and when the boom is lowered.

[0036] The first boom control valve 4A is connected to the head side chamber and rod side chamber of the boom cylinder 11 by a head side line 61 and a rod side line 62, respectively, is connected to the first hydraulic pump 2A by a pump line 31, and is connected to the tank by a tank line 34. The second boom control valve 4B is connected to the head side line 61 by a head side auxiliary line 63, and is connected to the second hydraulic pump 2B by a pump line 35. The meter-in cut valve 4C is provided in a branch path 33 of the pump line 31 for the boom cylinder 11.

[0037] Each of the first boom control valve 4A and the second boom control valve 4B is driven by an electric signal. Specifically, each of the first boom control valve 4A and the second boom control valve 4B is a spool valve including a spool and a drive unit that receives a command current to drive the spool. A command current is supplied to the drive unit from the control device 8. For example, the drive unit may include a pair of electromagnetic proportional valves that output secondary pressures that act on the spool in opposite directions, or may be a linear motion mechanism that is connected to the spool and includes an electric motor, a ball screw, or the like.

[0038] The first boom control valve 4A has a pump port 41 to which the pump line 31 is connected, a tank port 42 to which the tank line 34 is connected, a head port 43 to which the head side line 61 is connected, and a rod port 44 to which the rod side line 62 is connected. The first boom control valve 4A is switchable between a neutral position 4c, a first drive position 4a for boom-raising and a second drive position 4d for boom-lowering which are located on either side of the neutral position 4c, and a discharge limiting position 4b which is located between the neutral position 4c and the first drive position 4a. In other words, the spool of the first boom control valve 4A can move in both directions from a state in which the first boom control valve 4A is located in the neutral position 4c.

[0039] When the first boom control valve 4A is located in the neutral position 4c, it blocks the pump port 41, the tank port 42, the head port 43, and the rod port 44. When the first boom control valve 4A is located in the first drive position 4a, it connects the head port 43 to the pump port 41 and connects the rod port 44 to the tank port 42. When the first boom control valve 4A is located in the second drive position 4d, it connects the rod port 44 to the pump port 41 and connects the head port 43 to the tank port 42.

[0040] When the first boom control valve 4A is located at the discharge limiting position 4b, it communicates the head port 43 with the pump port 41 and communicates the rod port 44 with the tank port 42 at an opening degree of 1% to 30% of the maximum opening degree. The opening degree at the discharge limiting position 4b is a fixed value according to the required excavation depth and is determined, for example, by experiment. Alternatively, a pressure gauge may be provided in the rod-side line 62, and the opening degree between the rod port 44 and the tank port 42 at the discharge limiting position 4b may be controlled so that the pressure in the rod-side chamber of the boom cylinder 11 detected by the pressure gauge becomes a predetermined value.

[0041] The second boom control valve 4B has a pump port 45a to which the pump line 35 is connected and a head port 45b to which the head-side auxiliary line 63 is connected. The second boom control valve 4B is switchable between a neutral position 4f and an actuated position 4e. In other words, the spool of the second boom control valve 4B is movable in one direction from a state in which the second boom control valve 4B is located in the neutral position 4f.

[0042] When the second boom control valve 4B is in the neutral position 4f, it blocks the pump port 45a and the head port 45b. When the second boom control valve 4B is in the drive position 4e, it connects the pump port 45a to the head port 45b.

[0043] The meter-in cut valve 4C is, for example, a poppet valve that is driven by an electric signal. A command current is sent to the meter-in cut valve 4C from the control device 8. The meter-in cut valve 4C opens and closes the branch path 33 for the boom cylinder 11 in the pump line 31 in response to the command current sent thereto.

[0044] The neutral state of the boom control valve device 4 described above is a state in which the first boom control valve 4A is located in the neutral position 4c and the second boom control valve 4B is located in the neutral position 4f. In the neutral state, the meter-in cut valve 4C may open or close the pump line 31. The drive state of the boom control valve device 4 is a state in which the first boom control valve 4A is located in the first drive position 4a and the second boom control valve 4B is located in the drive position 4e, or a state in which the first boom control valve 4A is located in the second drive position 4d and the second boom control valve 4B is located in the neutral position 4f, and the meter-in cut valve 4C opens the pump line 31. The discharge restriction state of the boom control valve device 4 is a state in which the first boom control valve 4A is located in the discharge restriction position 4b and the second boom control valve 4B is located in the neutral position 4f, and the meter-in cut valve 4C closes the pump line 31.

[0045] A head side line 61 between the boom cylinder 11 and the first boom control valve 3A is connected to a tank by a relief line 64. A relief valve 65 is provided in the relief line 64. Furthermore, the head side line 61 is connected to the tank by a make-up line 66. A check valve 67 is provided in the make-up line 66, which allows a flow from the tank to the head side line 61 but prohibits a flow from the head side line 61 to the tank.

[0046] The arm operating device 82 described above outputs arm operating signals corresponding to the operation amount, which is the tilt angle of the operating lever, and the tilt direction, i.e., an arm pull operation signal and an arm push operation signal. Similarly, the boom operating device 81 described above outputs boom operating signals corresponding to the operation amount, which is the tilt angle of the operating lever, and the tilt direction, i.e., a boom-raising operation signal and a boom-lowering operation signal. In this embodiment, the arm operating device 82 and the boom operating device 81 are each an electric joystick that outputs an electric signal as an operation signal. The arm operating signal output from the arm operating device 82 and the boom operating signal output from the boom operating device 81 are input to the control device 8.

[0047] Furthermore, the control device 8 is electrically connected to a selector 83 provided in the cabin 93. The selector 83 accepts a selection from the pilot to turn on or off the lift-off prevention function.

[0048] With respect to the controller 8, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, application-specific integrated circuits (ASICs), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor.

[0049] The control device 8 controls the regulators 21, 22 so that the discharge flow rates of the first hydraulic pump 2A and the second hydraulic pump 2B increase as the operation amount of the arm operation device 82 or the operation amount of the boom operation device 81 increases.

[0050] Furthermore, when an arm retraction operation signal is output from the arm operating device 82, the control device 8 switches the first arm control valve 5A to the first drive position 5a and the second arm control valve 5B to the first drive position 5d, and the greater the amount of operation of the arm operating device 82, the greater the command current supplied to the drive sections of the first arm control valve 5A and the second arm control valve 5B, thereby increasing the opening degree.

[0051] Conversely, when an arm pushing operation signal is output from the arm operating device 82, the control device 8 switches the first arm control valve 5A to the second drive position 5c and the second arm control valve 5B to the second drive position 5f, and the greater the amount of operation of the arm operating device 82, the greater the command current supplied to the drive parts of the first arm control valve 5A and the second arm control valve 5B, thereby increasing the opening degree.

[0052] When a boom-raising operation signal is output from the boom operation device 81, the control device 8 switches the first boom control valve 4A to the first drive position 4a and the second boom control valve 4B to the drive position 4e, and the greater the amount of operation of the boom operation device 81, the greater the command current supplied to the drive sections of the first boom control valve 4A and the second boom control valve 4B, thereby increasing the opening degree.

[0053] Conversely, when a boom lowering operation signal is output from the boom operation device 81, the control device 8 switches the first boom control valve 4A to the second drive position 4d while maintaining the second boom control valve 4B in the neutral position 4f, and increases the command current supplied to the drive section of the first boom control valve 4A to increase the opening degree as the amount of operation of the boom operation device 81 increases.

[0054] With regard to the meter-in cut valve 4C, whether a boom-raising operation signal is output from the boom operating device 81 or a boom-lowering operation signal is output, the control device 8 maintains the meter-in cut valve 4C in an open position in which the meter-in cut valve 4C opens the pump line 31.

[0055] The above-described control of the arm control valve device 5 and the boom control valve device 4 is performed when the selector 83 receives a selection to turn the lift-up prevention function off. On the other hand, when the selector 83 receives a selection to turn the lift-up prevention function on, the control device 8 switches the first boom control valve 4A to the discharge limiting position 4b while maintaining the second boom control valve 4B in the neutral position 4f, and switches the meter-in cut valve 4C to the closed position where the meter-in cut valve 4C closes the pump line 31. In other words, the boom control valve device 4 is switched to the discharge limiting state.

[0056] When the arm retraction operation is performed with the boom control valve device 4 switched to the discharge restriction state, if the pressure in the rod side chamber of the boom cylinder 11 is low, the throttling action of the boom control valve device 4, more precisely, the throttling action of the first boom control valve 4A, prevents the boom cylinder 11 from extending. On the other hand, if the pressure in the rod side chamber of the boom cylinder 11 increases, hydraulic oil passes through the boom control valve device 4, which functions as a throttle, and is discharged from the rod side chamber of the boom cylinder 11 to the tank, and hydraulic oil is supplied to the head side chamber of the boom cylinder 11 through the makeup line 66 and the head side line 61, causing the boom cylinder 11 to passively extend. Therefore, excavation can be performed to an appropriate excavation depth according to the throttling action of the boom control valve device 4, while preventing the vehicle body from lifting up.

[0057] As described above, the hydraulic system 1A of the present embodiment can prevent the vehicle body from floating up with a simple configuration in which the boom control valve device 4 can be switched to the discharge restriction state. Moreover, when the boom cylinder 11 is extended, no hydraulic oil is supplied from the first hydraulic pump 2A and the second hydraulic pump 2B to the boom cylinder 11, so the amount of hydraulic oil supplied to the arm cylinder 12 is not reduced and the arm retraction speed is not reduced.

[0058] Furthermore, for an existing hydraulic system that includes a meter-in cut valve 4C but does not have a lift-up prevention function, the lift-up prevention function can be added simply by changing the first boom control valve 4A, for example, by replacing the spool of the first boom control valve 4A.

[0059] In addition, in this embodiment, a selector 83 is provided, so that the operator of the hydraulic excavator 9 can select whether the lift-up prevention function is on or off.

[0060] Furthermore, the first boom control valve 4A that can be switched to the discharge limiting position 4b is suitable for the hydraulic system 1A.

[0061] <Modification> 3, the first boom control valve 4A may be switched among a neutral position 4c, a first drive position 4a, a second drive position 4d, and a regeneration position 4g between the first drive position 4a and the neutral position 4c. In the regeneration position 4g, the first boom control valve 4A connects the pump port 41 to the head port 43 and blocks the tank line 34. Furthermore, in the regeneration position 4g, the first boom control valve 4A connects the rod port 44 to the head port 43 and functions as a throttle for the supply of hydraulic oil from the rod port 44 to the head port 43, i.e., for regeneration.

[0062] Furthermore, as in another modified hydraulic system 1C shown in Fig. 4, the first boom control valve 4A may block the pump port 41 and the head port 43 when in the discharge limiting position 4b. In this case, the meter-in cut valve 4C that was necessary in the first embodiment is not necessary. Note that, in the hydraulic system 1C shown in Fig. 4 as well, a pressure gauge may be provided in the rod-side line 62, and the opening between the rod port 44 and the tank port 42 of the first boom control valve 4A when in the discharge limiting position 4b may be controlled so that the pressure in the rod-side chamber of the boom cylinder 11 detected by the pressure gauge becomes a predetermined value.

[0063] Second Embodiment 5 shows a hydraulic system 1D for a hydraulic excavator according to a second embodiment. In this embodiment, the same components as those in the first embodiment are given the same reference numerals, and redundant explanations will be omitted.

[0064] In this embodiment, as in the first embodiment, the boom control valve device 4 is switched between a neutral state, a drive state, and a discharge limit state. In the neutral state, the boom control valve device 4 prohibits the supply of hydraulic oil from the first hydraulic pump 2A and the second hydraulic pump 2B to the boom cylinder 11 and the discharge of hydraulic oil from the boom cylinder 11 to the tank. In the drive state, the boom control valve device 4 permits the supply of hydraulic oil from the first hydraulic pump 2A and the second hydraulic pump 2B to the boom cylinder 11 and the discharge of hydraulic oil from the boom cylinder 11 to the tank. In the discharge limit state, the boom control valve device 4 prohibits the supply of hydraulic oil from the first hydraulic pump 2A and the second hydraulic pump 2B to the boom cylinder 11, while functioning as a throttle for the discharge of hydraulic oil from the boom cylinder 11 to the tank.

[0065] In this embodiment, the first boom control valve 4A is switched between a neutral position 4c, a first drive position 4a, and a second drive position 4d, and a meter-in cut valve 4C is not employed. Also, in this embodiment, the second boom control valve 4B is switched between a neutral position 4j, a first drive position 4h, a discharge limiting position 4i, and a second drive position 4k. That is, in this embodiment, the spool of the second boom control valve 4B is movable in both directions from a state in which the second boom control valve 4B is positioned in the neutral position 4j, and the discharge limiting position 4i is located between the first drive position 4h and the neutral position 4j.

[0066] In this embodiment, the second boom control valve 4B is connected to the head side line 61 by a head side auxiliary line 68 and is also connected to the rod side line 62 by a rod side auxiliary line 69.

[0067] Specifically, the second boom control valve 4B has a pump port 46 to which the pump line 35 is connected, a tank port 47 to which the tank line 38 is connected, a head port 48 to which the head side auxiliary line 68 is connected, and a rod port 49 to which the rod side auxiliary line 69 is connected.

[0068] When the second boom control valve 4B is located in the neutral position 4j, it blocks the pump port 46, the tank port 47, the head port 48, and the rod port 49. When the second boom control valve 4B is located in the first drive position 4h, it connects the head port 48 to the pump port 46 and connects the rod port 49 to the tank port 47. When the second boom control valve 4B is located in the second drive position 4k, it connects the rod port 49 to the pump port 46 and connects the head port 48 to the tank port 47.

[0069] When the second boom control valve 4B is positioned at the discharge limiting position 4i, it blocks the pump port 46 and the head port 48, and communicates the rod port 49 with the tank port 47 at an opening degree of 1% to 30% of the maximum opening degree. The opening degree at the discharge limiting position 4i is a fixed value according to the required excavation depth and is determined, for example, by experiment. Alternatively, a pressure gauge may be provided in the rod-side line 62, and the opening degree between the rod port 49 and the tank port 47 at the discharge limiting position 4i may be controlled so that the pressure in the rod-side chamber of the boom cylinder 11 detected by the pressure gauge becomes a predetermined value.

[0070] The neutral state of the boom control valve device 4 described above is a state in which the first boom control valve 4A is located in the neutral position 4c and the second boom control valve 4B is located in the neutral position 4j. The drive state of the boom control valve device 4 is a state in which the first boom control valve 4A is located in the first drive position 4a and the second boom control valve 4B is located in the first drive position 4h, or a state in which the first boom control valve 4A is located in the second drive position 4d and the second boom control valve 4B is located in the second drive position 4k. The discharge restriction state of the boom control valve device 4 is a state in which the first boom control valve 4A is located in the neutral position 4c and the second boom control valve 4B is located in the discharge restriction position 4i.

[0071] In this embodiment, as in the first embodiment, when the selector 83 receives a selection to turn on the lift-up prevention function, the control device 8 switches the second boom control valve 4B to the discharge limiting position 4i while maintaining the first boom control valve 4A in the neutral position 4c. In other words, the boom control valve device 4 is switched to the discharge limiting state. Therefore, the same effects as in the first embodiment can be obtained.

[0072] <Other embodiments> The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present disclosure.

[0073] For example, when there is only one hydraulic pump 2, the boom control valve device 4 may include only the first boom control valve 4A shown in FIG.

[0074] <Summary> As a first aspect, the present disclosure provides, from one aspect, a hydraulic system comprising: at least one hydraulic pump; an arm cylinder; an arm control valve device interposed between the at least one hydraulic pump and the arm cylinder; a boom cylinder; a boom control valve device interposed between the at least one hydraulic pump and the boom cylinder and connected to the boom cylinder by a head side line and a rod side line; and a makeup line connecting the head side line to a tank, the makeup line being provided with a check valve that allows a flow from the tank to the head side line but prohibits a flow from the head side line to the tank. and a hydraulic system for a hydraulic excavator, wherein the boom control valve device is switchable between a neutral state that prohibits the supply of hydraulic oil from the at least one hydraulic pump to the boom cylinder and the discharge of hydraulic oil from the boom cylinder to the tank, a drive state that allows the supply of hydraulic oil from the at least one hydraulic pump to the boom cylinder and the discharge of hydraulic oil from the boom cylinder to the tank, and a discharge restriction state that prohibits the supply of hydraulic oil from the at least one hydraulic pump to the boom cylinder while functioning as a throttle on the discharge of hydraulic oil from the boom cylinder to the tank.

[0075] According to the above configuration, when an arm retraction operation is performed with the boom control valve device switched to the discharge limiting state, if the pressure in the rod-side chamber of the boom cylinder is low, the throttling action of the boom control valve device prevents the boom cylinder from extending. On the other hand, if the pressure in the rod-side chamber of the boom cylinder increases, hydraulic oil is discharged from the rod-side chamber of the boom cylinder to the tank through the boom control valve device, which functions as a throttle, and hydraulic oil is supplied to the head-side chamber of the boom cylinder through the makeup line and the head-side line, passively extending the boom cylinder. Therefore, while preventing the vehicle body from lifting up, it is possible to excavate at an appropriate excavation depth according to the throttling action of the boom control valve device. In this way, with a simple configuration in which the boom control valve device can be switched to the discharge limiting state, vehicle body lifting up can be prevented. Moreover, because hydraulic oil is not supplied from the hydraulic pump to the boom cylinder when the boom cylinder is extended, the amount of hydraulic oil supplied to the arm cylinder is not reduced, and the arm retraction speed is not reduced.

[0076] As a second aspect, in the first aspect, the boom control valve device includes a boom control valve having a head port to which the head side line is connected, a rod port to which the rod side line is connected, a pump port to which a pump line is connected, and a tank port to which a tank line is connected, and a meter-in cut valve provided in the pump line, and in the neutral state, the boom control valve is located at a neutral position that blocks the pump port, the tank port, the head port, and the rod port, and in the driven state, the boom control valve connects the head port to the pump port. the boom control valve may be in a first drive position where it communicates with the head port and communicates the rod port with the tank port, or in a second drive position where it communicates with the pump port and communicates the head port with the tank port, and the meter-in cut valve opens the pump line, and in the discharge restriction state, the boom control valve may be in a discharge restriction position where it communicates with the head port and communicates the rod port with the tank port at an opening of 1% to 30% of a maximum opening, and the meter-in cut valve closes the pump line. According to this configuration, an existing hydraulic system that includes a meter-in cut valve but does not have a lift-up prevention function can be provided with a lift-up prevention function simply by changing the boom control valve.

[0077] As a third aspect, in the second aspect, the at least one hydraulic pump may include a first hydraulic pump and a second hydraulic pump, the boom control valve may be a first boom control valve interposed between the first hydraulic pump and the boom cylinder, and the boom control valve device may include a second boom control valve interposed between the second hydraulic pump and the boom cylinder. With this configuration, the technical concept of the present disclosure can be applied to a hydraulic system including a first hydraulic pump and a second hydraulic pump.

[0078] As a fourth aspect, in the first aspect, the at least one hydraulic pump may include a first hydraulic pump and a second hydraulic pump, and the boom control valve device may include a first boom control valve interposed between the first hydraulic pump and the boom cylinder and a second boom control valve interposed between the second hydraulic pump and the boom cylinder, the second boom control valve having a head port to which a head side auxiliary line is connected, a rod port to which a rod side auxiliary line is connected, a pump port to which a pump line is connected, and a tank port to which a tank line is connected, and in the neutral state, the second boom control valve is located at a neutral position that blocks the pump port, the tank port, the head port, and the rod port, and in the drive state, the second boom control valve is located at a drive position that communicates the head port with the pump port and communicates the rod port with the tank port, and in the discharge limiting state, the second boom control valve is located at a discharge limiting position that blocks the pump port and the head port and communicates the rod port with the tank port at an opening degree of 1% to 30% of a maximum opening degree. According to this configuration, the technical concept of the present disclosure can be applied to a hydraulic system including the first hydraulic pump and the second hydraulic pump.

[0079] As a fifth aspect, in any of the first to fourth aspects, the hydraulic system may further include a selector that accepts a selection between on and off of an uplift prevention function, and the boom control valve device may be switched to the discharge limiting state when the selector accepts a selection of on for the uplift prevention function. With this configuration, the operator of the hydraulic excavator can select between on and off of the uplift prevention function.

[0080] In a sixth aspect, the present disclosure, from another aspect, provides a boom control valve for a boom cylinder of a hydraulic excavator, the boom control valve including a pump port, a tank port, a head port, and a rod port, and is switchable between a neutral position in which the pump port, the tank port, the head port, and the rod port are blocked, a drive position in which the head port is communicated with the pump port and the rod port is communicated with the tank port, and a discharge limiting position in which the head port is communicated with the pump port or the pump port and the head port are blocked and the rod port is communicated with the tank port at an opening degree of 1% to 30% of a maximum opening degree.

[0081] According to the above configuration, a boom control valve suitable for the hydraulic system is provided.

[0082] As a seventh aspect, in the sixth aspect, for example, the boom control valve may be a spool valve including a spool that is movable in one direction or both directions from a state in which the boom control valve is positioned at the neutral position, and the discharge restriction position may be between the drive position and the neutral position.

[0083] As an eighth aspect, in the sixth or seventh aspect, for example, the drive position may be a first drive position, and the boom control valve may be switched among the neutral position, the first drive position, the discharge restriction position, and a second drive position that connects the rod port with the pump port and connects the head port with the tank port. [Explanation of symbols]

[0084] 1A, 1B, 1C, 1D Hydraulic System 11 Boom cylinder 12 Arm cylinder 2 hydraulic pumps 2A First hydraulic pump 2B Second hydraulic pump 31,35 Pump line 34,38 Tank Line 4. Boom control valve device 4A First boom control valve 4B Second boom control valve 4C Meter-in cut valve 41 Pump port 42 Tank port 43 Head Port 44 Rod Port 46 Pump port 47 Tank port 48 Head Port 49 Rod Port 5-arm control valve device 61 Head side line 62 Rod side line 63 Head side auxiliary line 64 Relief Line 65 Relief valve 66 Makeup Line 67 Check valve 68 Head side auxiliary line 69 Rod side auxiliary line 83 Selector 9. Hydraulic excavator 94 Boom 95 Arm

Claims

1. at least one hydraulic pump; An arm cylinder; an arm control valve device interposed between the at least one hydraulic pump and the arm cylinder; A boom cylinder; a boom control valve device interposed between the at least one hydraulic pump and the boom cylinder and connected to the boom cylinder by a head side line and a rod side line; a make-up line that connects the head side line to a tank and is provided with a check valve that allows a flow from the tank to the head side line but prohibits a flow from the head side line to the tank, a hydraulic system for a hydraulic excavator, wherein the boom control valve device is switchable between a neutral state in which the supply of hydraulic oil from the at least one hydraulic pump to the boom cylinder and the discharge of hydraulic oil from the boom cylinder to the tank are prohibited; a drive state in which the supply of hydraulic oil from the at least one hydraulic pump to the boom cylinder and the discharge of hydraulic oil from the boom cylinder to the tank are permitted; and a discharge restriction state in which the supply of hydraulic oil from the at least one hydraulic pump to the boom cylinder is prohibited while functioning as a throttle on the discharge of hydraulic oil from the boom cylinder to the tank.

2. the boom control valve device includes a boom control valve having a head port to which the head side line is connected, a rod port to which the rod side line is connected, a pump port to which a pump line is connected, and a tank port to which a tank line is connected, and a meter-in cut valve provided in the pump line, In the neutral state, the boom control valve is located at a neutral position blocking the pump port, the tank port, the head port, and the rod port, In the driving state, the boom control valve is located at a first driving position where the head port is communicated with the pump port and the rod port is communicated with the tank port, or at a second driving position where the rod port is communicated with the pump port and the head port is communicated with the tank port, and the meter-in cut valve opens the pump line, 2. The hydraulic system for a hydraulic excavator according to claim 1, wherein, in the discharge restriction state, the boom control valve is located at a discharge restriction position that communicates the head port with the pump port and communicates the rod port with the tank port at an opening degree of 1% to 30% of a maximum opening degree, and the meter-in cut valve closes the pump line.

3. the at least one hydraulic pump includes a first hydraulic pump and a second hydraulic pump; the boom control valve is a first boom control valve interposed between the first hydraulic pump and the boom cylinder, 3. The hydraulic system for a hydraulic excavator according to claim 2, wherein the boom control valve device includes a second boom control valve interposed between the second hydraulic pump and the boom cylinder.

4. the at least one hydraulic pump includes a first hydraulic pump and a second hydraulic pump; the boom control valve device includes a first boom control valve interposed between the first hydraulic pump and the boom cylinder, and a second boom control valve interposed between the second hydraulic pump and the boom cylinder, the second boom control valve has a head port to which a head side auxiliary line is connected, a rod port to which a rod side auxiliary line is connected, a pump port to which a pump line is connected, and a tank port to which a tank line is connected, In the neutral state, the second boom control valve is located at a neutral position blocking the pump port, the tank port, the head port, and the rod port, In the driving state, the second boom control valve is located at a driving position that connects the head port with the pump port and connects the rod port with the tank port, 2. The hydraulic system for a hydraulic excavator according to claim 1, wherein, in the discharge restriction state, the second boom control valve is positioned at a discharge restriction position that blocks the pump port and the head port and communicates the rod port with the tank port at an opening degree that is 1% to 30% of a maximum opening degree.

5. Further provided is a selector for receiving a selection of whether the lift-up prevention function is on or off, 5. The hydraulic system for a hydraulic excavator according to claim 1, wherein the boom control valve device is switched to the discharge restriction state when the selector receives a selection of turning on an anti-lift function.

6. A boom control valve for a boom cylinder of a hydraulic excavator, It has a pump port, a tank port, a head port and a rod port. a neutral position in which the pump port, the tank port, the head port, and the rod port are blocked; a drive position in which the head port is connected to the pump port and the rod port is connected to the tank port; and a discharge restriction position in which the head port is connected to the pump port or the pump port and the head port are blocked and the rod port is connected to the tank port at an opening of 1% to 30% of a maximum opening.

7. the boom control valve is a spool valve including a spool that is movable in one direction or both directions from a state in which the boom control valve is positioned at the neutral position, The boom control valve of claim 6 , wherein the discharge limiting position is between the drive position and the neutral position.

8. the drive position is a first drive position, 8. The boom control valve according to claim 6 or 7, wherein the boom control valve is switchable among the neutral position, the first drive position, the discharge restriction position, and a second drive position that connects the rod port with the pump port and connects the head port with the tank port.

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