Construction machine

Abstract

To easily perform work by an attachment such as a breaker performing work by being pressed against a processing object in a short time, when the attachment is mounted on a work machine.SOLUTION: A construction machine has a variable relief valve provided on a second oil passage for connecting a first direction control valve to a rod side chamber of a boom cylinder, when a down mode is selected, performs control so as to maintain a pressure of pressure oil of the rod side chamber of the boom cylinder to a predetermined pressure, thereby drives a boom by the boom cylinder, and can press an attachment which is a tip work tool of the work machine to a processing object with constant force.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a construction machine, and more particularly to a construction machine that can easily perform work by pressing an attachment (front attachment) of the work machine against an object to be treated with a constant force. [Background technology]

[0002] A hydraulic excavator, a typical example of construction machinery, is usually equipped with a bucket as a front attachment on the work machine, and the bucket is used for excavation work, leveling work, and the like.

[0003] When performing ground leveling work using such a hydraulic excavator, the float mode (float function) is selected to connect the head side chamber and rod side chamber of the boom cylinder, and excess hydraulic oil is returned to the tank, allowing the bucket to move along the undulating shape of the ground while the weight of the work equipment facilitates ground leveling work. A construction machine with such a float function is described, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-2092 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the construction machine described in Patent Document 1 has the following problems.

[0006] When performing demolition work using a hydraulic breaker attached to a work machine, selecting float mode causes the boom to automatically lower under the machine's own weight, allowing the tip of the breaker to come into contact with the object to be demolished (concrete, etc.).

[0007] However, when float mode is selected, the head side chamber and rod side chamber of the boom cylinder are connected and excess hydraulic oil is returned to the tank. Therefore, if float mode is selected with a breaker attached, the tip of the breaker cannot be pressed sufficiently against the object to be demolished, and the object cannot be properly destroyed.

[0008] On the other hand, if the float mode is deselected, the pushing force from the boom cylinder can be applied to the tip of the breaker, but the operator must operate the boom control device to press the tip of the breaker against the object to be demolished with just the right amount of force.In this case, precise boom lowering operations are required, which requires skilled techniques.

[0009] The object of the present invention is to provide a construction machine that, when an attachment such as a breaker that performs work by pressing it against an object to be treated is attached to the work machine, can easily perform the operation of pressing the attachment against the object to be treated. [Means for solving the problem]

[0010] The present invention includes a plurality of means for solving the above problems, examples of which are as follows.

[0011] That is, in order to solve the above-mentioned problems, the construction machine of the present invention comprises a vehicle body, a work implement which is attached to the vehicle body and has a boom which is movable up and down relative to the vehicle body at its base end and has a tip end work implement at its tip end, a boom cylinder which moves the boom up and down, a first hydraulic pump which supplies and discharges pressurized oil to the boom cylinder, a first directional control valve which controls the flow of pressurized oil discharged from the first hydraulic pump based on an operation signal generated by an operation device, a first oil passage which connects the first directional control valve with a bottom side chamber of the boom cylinder, and a second oil passage which connects the first directional control valve with a rod side chamber of the boom cylinder, and the construction machine further comprises a mode selection device which selects, as an operation mode of the front work implement, a normal work mode or a down mode in which work is performed by pressing an attachment attached to the front work implement as the tip end work implement against an object to be processed, and a variable relief valve connected to the second oil passage, and when the down mode is selected by the mode selection device, the variable relief valve is controlled to maintain the pressure of the pressurized oil in the rod side chamber of the boom cylinder at a predetermined pressure.

[0012] According to the present invention configured in this manner, when down mode is selected, the variable relief valve controls the pressure of the pressurized oil in the rod-side chamber of the boom cylinder so that it does not exceed a predetermined pressure, thereby enabling the boom cylinder to drive the boom and press the attachment against the object to be treated with a constant force. Therefore, if the work machine is equipped with an attachment that performs work by pressing it against the object to be treated, such as a breaker, selecting down mode allows the attachment to be pressed with a constant force to perform the work, so that the attachment can be placed on the ground with just the right pressing force, allowing work with the attachment to be performed easily and in a short amount of time. [Effects of the Invention]

[0013] According to the present invention, when an attachment such as a breaker that performs work by pressing it against an object to be treated is attached to a work machine, work using the attachment can be performed easily in a short time. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing a hydraulic excavator, which is a construction machine equipped with a hydraulic drive system according to the present invention. [Figure 2] 1 is a diagram showing a hydraulic drive system according to a first embodiment of the present invention. [Figure 3] 10A to 10C are diagrams showing screen transitions of a mode selection device displayed on a monitor. [Figure 4] 10 is a flow chart showing the mode setting function of the monitor mode selection device. [Figure 5] 10 is a flowchart showing details of a down mode control function. [Figure 6] 10 is a flowchart showing details of a float mode control function. [Figure 7] FIG. 1 is a side view of a hydraulic excavator in which the vehicle body (a collective term for the upper rotating body and the lower traveling body) of the work machine is in a jacked-up state. [Figure 8] 7 is a flowchart showing the logic for determining whether the vehicle body is in a jacked-up state, which is performed in step S240 of FIG. 5 and step S340 of FIG. 6. [Figure 9] FIG. 4 is a diagram showing a hydraulic drive system according to a second embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing a hydraulic drive system according to a third embodiment of the present invention. [Figure 11] FIG. 10 is a diagram illustrating a system configuration related to a controller of a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] First Embodiment ~Construction machinery~ FIG. 1 is a diagram showing a hydraulic excavator, which is a construction machine equipped with a hydraulic drive system according to the present invention.

[0017] 1, the hydraulic excavator is equipped with an upper rotating body 300 and a lower traveling body 301 that constitute the vehicle body. The hydraulic excavator also has a work implement 302 that performs work such as excavating earth and sand and leveling ground. The work implement 302 is equipped with a boom 306, an arm 307, and a bucket 308. The upper rotating body 300 is driven by a swing motor 305 and swings on the lower traveling body 301. A swing post 303 that swings horizontally by extension and contraction of a swing cylinder 303-1 is attached to the upper rotating body 300, and the work implement 302 is attached to the swing post 303 so as to be rotatable up and down.

[0018] The work machine 302 also has a boom cylinder 309 that drives the boom 306, an arm cylinder 310 that drives the arm 307, and a bucket cylinder 311 that drives the bucket 308, and the boom 306, arm 307, and bucket 308 rotate up and down relative to the swing post 303, boom 306, and arm 307 by extending and retracting the boom cylinder 309, arm cylinder 310, and bucket cylinder 311, respectively.

[0019] A blade 304 that moves up and down by extension and contraction of a blade cylinder 312 is attached to the front of the lower traveling body 301. The lower traveling body 301 travels by driving a right crawler 315 and a left crawler 316 with a right traveling motor 313 and a left traveling motor 314.

[0020] Bucket 308 is the tip work implement of work machine 302 that is attached as an attachment for standard work, and by driving boom cylinder 309, the boom of work machine 302 moves up and down, and work is performed using the tip work implement of work machine 302. In this way, work machine 302 is attached to upper rotating body 300 (vehicle body), and has boom 306 at the base end that can move up and down relative to upper rotating body 300 (vehicle body), and has tip work implement (bucket 308) at the tip end. In addition to bucket 308, work machine 302 can also be equipped with specific attachments other than buckets as tip work implements to perform work.

[0021] The upper rotating body 300 is equipped with a cabin 317, and the driver's compartment within the cabin 317 is equipped with various operating devices (for example, the operating device 10 described below) such as a driver's seat, left and right operating lever devices for front and rotation, and left and right operating lever / pedal devices for traveling, as well as a monitor 40 (described below).

[0022] ~Hydraulic System~ FIG. 2 is a diagram showing a hydraulic drive system according to a first embodiment of the present invention.

[0023] In Figure 2, in this embodiment, a hydraulic breaker 320 is attached as an attachment (tip work tool) to the work machine 302, and the hydraulic circuit portion of this embodiment (hereinafter referred to as the hydraulic system) includes a first hydraulic pump 1-1 that supplies pressurized oil to the boom cylinder 309 and the breaker 320, and a control valve block 3 to which the pressurized oil discharged from the first hydraulic pump 1-1 is guided, and the hydraulic actuator (hereinafter sometimes referred to as the attachment actuator) 320-1 of the boom cylinder 309 and the attachment (breaker) 320 is connected to the first hydraulic pump 1-1 via the control valve block 3.

[0024] The control valve block 3 distributes the pressurized oil discharged from the first hydraulic pump 1-1 to the boom cylinder 309 and the attachment actuator 320-1 to operate the boom 306 and the attachment 320, and is equipped with a first directional control valve 3-1 that controls the flow of pressurized oil discharged from the first hydraulic pump 1-1 based on an operation signal generated by the oil operation device 10 (described later) and supplies the pressurized oil to the boom cylinder 309, and a second directional control valve 3-2 that guides the pressurized oil discharged from the first hydraulic pump 1-1 and supplies the pressurized oil to the actuator 320-1 of the attachment 320.

[0025] Although not shown in Figure 2, the control valve block 3 further includes directional control valves for driving the swing motor 305, the travel motors 313, 314, the swing cylinder 303-1, and the blade cylinder 312, and for operating the upper swing body 300, the lower travel body 301, the swing post 303, and the blade 304.

[0026] The first and second directional control valves 3-1 and 3-2 are also called changeover valves, flow control valves, directional control valves, etc., and the first directional control valve 3-1 can be switched between a neutral position shown in the figure, a boom-raising stroke position on the right side of the figure, and a boom-lowering stroke position on the left side of the figure. The boom-raising and boom-lowering stroke positions each change as the spool stroke increases, and by increasing the opening area of ​​the meter-in (supply side) and meter-out (discharge side) of the first directional control valve 3-1, the drive speed of the boom cylinder 309 is increased.

[0027] Hereinafter, the "boom-raising stroke position" and the "boom-lowering stroke position" will be referred to as the "boom-raising direction position" and the "boom-lowering direction position", respectively.

[0028] The hydraulic system of this embodiment also includes an operating device 10 that generates an operating signal for switching the first directional control valve 3-1 by operating an operating lever 10-1, and the first directional control valve 3-1 can be switched from a central neutral position to a boom-up position on the right side of the figure and a boom-down position on the left side of the figure by this operating signal. Although not shown, similar operating devices are also provided for the second directional control valve 3-2 and other directional control valves not shown, and they can be switched by their operating signals.

[0029] In this embodiment, the operating device 10 is a hydraulic pilot type operating device that includes pressure reducing valves 10-2 and 10-3 and generates pilot operating pressure based on the oil discharged from the pilot pump 2 as an operating signal.

[0030] The pilot operating pressure generated by the pressure reducing valve 10-2 is led to the pressure receiving portion 3-11 of the first directional control valve 3-1 via a pilot oil line 10-4, switching the first directional control valve 3-1 to the boom-up direction position on the right side in the figure. The pilot operating pressure generated by the pressure reducing valve 10-3 is led to the pressure receiving portion 3-12 of the first directional control valve 3-1 via a pilot oil line 10-5, switching the first directional control valve 3-1 to the boom-down direction position on the left side in the figure.

[0031] The boom cylinder 309 has two cylinder chambers: a rod-side chamber 309-2 and a bottom-side chamber 309-1. The bottom-side chamber 309-1 is connected to the first direction control valve 3-1 via a first oil passage 4-1, and the rod-side chamber 309-2 is connected to the first direction control valve 3-1 via a second oil passage 4-2. That is, the hydraulic system of this embodiment includes the first oil passage 4-1 that connects the first direction control valve 3-1 and the bottom-side chamber 309-1 of the boom cylinder 309, and the second oil passage 4-2 that connects the first direction control valve 3-1 and the rod-side chamber 309-2 of the boom cylinder 309.

[0032] In addition, the hydraulic system of this embodiment is equipped with a variable relief valve 21 connected to the second oil passage 4-2, and when the down mode is selected by the mode selection device 41 (see Figure 3) of the monitor 40, the variable relief valve 21 is controlled to maintain the pressure of the pressurized oil in the rod side chamber 309-2 of the boom cylinder 309 at a predetermined pressure.

[0033] In this specification, down mode refers to a work mode in which an attachment attached to the work machine 302 as a tip work tool is pressed against the object to be processed, and tip work tools used in down mode include a breaker and a sweeper with a brush function.

[0034] When the down mode is selected, the action of the variable relief valve 21 as described above presses the breaker attachment 320 against the object to be treated with a constant force, so that the attachment 320 touches the ground with just the right amount of pressing force, allowing work with the attachment 320 to be carried out easily and in a short time.

[0035] The relief pressure of the variable relief valve 21 is set to a predetermined maximum relief pressure when the normal operation mode is selected by the mode selection device 41 (see Figure 3) of the monitor 40, and is set to a predetermined relief pressure lower than the maximum relief pressure when the down mode is selected.

[0036] The maximum relief pressure can be set to, for example, the same value as the relief pressure of an overload relief valve that is normally installed in the actuator oil passage of a hydraulic system to prevent overload of the hydraulic actuator. In this case, the overload relief valve in the second oil passage 4-2 can be omitted, and the adjustable relief valve 21 can also serve as the overload relief valve.

[0037] The relief pressure of the variable relief valve 21 used in the down mode can be changed to a desired value by a relief pressure input device 42 of the monitor 40 (described later, see FIG. 3).

[0038] The variable relief valve 21 is an electromagnetic variable relief valve having a relief valve body 21-1 and a solenoid 21-2, and the set pressure (relief pressure) of the variable relief valve 21 can be changed by changing the voltage applied to the solenoid 21-2.

[0039] The hydraulic system of this embodiment also includes a solenoid pressure reducing valve 26 arranged in the pilot oil passage 10-5 between the operating device 10 and the first directional control valve 3-1. When the normal mode is selected, the solenoid pressure reducing valve 26 is in a first position, on the lower side in the figure, where the pilot operating pressure generated by the operating device 10 is introduced directly to the first directional control valve 3-1, and when the down mode is selected, the solenoid pressure reducing valve 26 switches to a position intermediate between the first position and a second position where the transmission of the pilot operating pressure to the first directional control valve 3-1 is blocked. In this intermediate position, the solenoid pressure reducing valve 26 generates a pilot control pressure that switches the first directional control valve 3-1 to an intermediate opening position in the boom lowering direction based on the pilot operating pressure generated by the operating device 10, and the pilot control pressure is introduced to the first directional control valve 3-1. In this way, by moving the electromagnetic pressure reducing valve 26 to the intermediate position and switching the first directional control valve 3-1 to the intermediate opening position in the boom lowering direction and opening it slightly, a controlled flow rate of pressurized oil is supplied to the rod side chamber 309-2 of the boom cylinder 309, and it is possible to supply only the flow rate necessary to press the attachment 320 against the object to be treated with a constant force, regardless of the input amount of the operating lever 10-1 of the operating device 10. Note that an electromagnetic proportional pressure reducing valve may be used as the electromagnetic pressure reducing valve 26.

[0040] As described above, the hydraulic system of this embodiment is equipped with the second directional control valve 3-2 to which pressure oil discharged from the first hydraulic pump 1-1 is guided, and also with the electromagnetic pressure reducing valve 26. When the down mode is selected and the operation signal is a signal instructing the boom lowering direction, the electromagnetic differential pressure valve 26 switches the first directional control valve 3-1 to an intermediate opening position in the boom lowering direction. As a result, the first directional control valve 3-1 is not fully opened, and the remaining pressure oil discharged from the first hydraulic pump 1-1 but not supplied to the first directional control valve 3-1 is supplied to the second directional control valve 3-2, thereby ensuring the flow rate of pressure oil supplied to the attachment 320. As a result, the relief pressure set in the variable relief valve 21 presses the breaker 320 against the workpiece with a constant force regardless of the input amount of the operation lever 10-1, while also supplying the breaker 320 with the necessary flow rate, allowing for efficient work.

[0041] The hydraulic system of this embodiment further includes a solenoid valve block 50. The solenoid valve block 50 includes a first solenoid valve 50-1 connected to the oil passage between the first oil line 4-1 and the tank and equipped with a check valve in the closed position, and a second solenoid valve 50-2 connected to the oil passage between the second oil line 4-2 and the tank and equipped with a check valve in the closed position. The first solenoid valve 50-1 and the second solenoid valve 50-2 are in the closed position when the normal operation mode or the down mode is selected, and are switched to the open position when the float mode is selected. As a result, in the float mode, the boom cylinder 309 is in a free state where it can operate passively, allowing the boom 306 to move up and down in accordance with the undulating shape of the ground. Therefore, when a bucket 308 is attached to the work implement 302 as an attachment, the bucket 308 can follow the undulating shape of the ground, facilitating plowing work.

[0042] In addition, in the hydraulic system of this embodiment, the first oil passage 4-1 is equipped with a holding valve 25 that prevents the pressurized oil from flowing out of the bottom side chamber 309-1 of the boom cylinder 309 and causing the boom 306 to fall if the hose of the first oil passage 4-1 is unintentionally broken.

[0043] The holding valve 25 has a valve body 25-1 that can be switched between a fall prevention position on the right side of the figure where the check valve functions and an open position on the left side of the figure, and a pressure receiving portion 25-2 to which the pilot operating pressure of the operating device 10 is guided.

[0044] When the operating device 10 is not being operated, the valve body 25-1 is in the fall prevention position on the right side of the figure, and the check valve prevents the outflow of pressurized oil from the bottom side chamber 309-1 of the boom cylinder 309, thereby maintaining the boom 306 in a stopped position.

[0045] When the operating device 10 is operated in the boom-raising direction, pressurized oil sent from the first hydraulic pump 1-1 via the first directional control valve 3-1 is supplied to the bottom side chamber 309-1 of the boom cylinder 309, allowing the boom 306 to be raised.

[0046] Furthermore, if the hose of the first oil passage 4-1 between the first directional control valve 3-1 and the holding valve 25 breaks during the boom-raising operation, the check valve in the valve body 25-1 blocks the outflow of pressurized oil from the bottom-side chamber 309-1 of the boom cylinder 309, preventing the boom 306 from falling.

[0047] When the operating device 10 is operated in the boom-lowering direction, the pilot operating pressure in the boom-lowering direction is guided to the pressure-receiving portion 25-2 of the holding valve 25 to move the valve body 25-1 to the open position, and the pressurized oil in the bottom-side chamber 309-1 of the boom cylinder 309 is discharged to the tank via the first directional control valve 3-1, allowing the boom 306 to be lowered.

[0048] Furthermore, even if the hose of the first oil passage 4-1 breaks during operation in the boom-up direction as described above and the check valve of the valve body 25-1 blocks the outflow of pressurized oil from the bottom-side chamber 309-1 of the boom cylinder 309, the operating device 10 can be operated in the boom-down direction to open the valve body 25-1, thereby discharging the pressurized oil in the bottom-side chamber 309-1 of the boom cylinder 309 into the tank and lowering the boom 306.

[0049] Variable relief valve 21 is equipped with a bypass circuit in which makeup check valve 21-3 is arranged, and rod side chamber 309-2 of boom cylinder 309 can draw hydraulic oil from the tank via the bypass circuit. First oil passage 4-1 is connected to the tank via makeup check valve 29, and bottom side chamber 309-1 of boom cylinder 309 can also draw hydraulic oil from the tank via makeup check valve 29.

[0050] Additionally, a bottom-side pressure sensor 20-1 is attached to the first oil passage 4-1, and can detect the pressure in a bottom-side chamber 309-1 of the boom cylinder 309. Similarly, a rod-side pressure sensor 20-2 is attached to the second oil passage 4-2, and can detect the pressure in a rod-side chamber 309-2 of the boom cylinder 309.

[0051] Furthermore, a pressure sensor 28 is attached to the pilot oil passage 10-5 on the boom lowering side of the operation device 10, and can detect the operating pilot pressure for boom lowering.

[0052] In FIG. 1, a gate lock lever (not shown) that is raised and lowered by the operator to open and close the passage is installed at the entrance to the driver's cab inside the cabin 317 of the hydraulic excavator, and a gate lock sensor 31 that detects when the gate lock lever is lowered and the passage is blocked is installed at the base end of the gate lock lever.

[0053] The gate lock sensor 31 is, for example, a switch that outputs an ON signal when the gate lock lever is lowered and the passage is blocked, and stops outputting the ON signal when the gate lock lever is raised and the passage is opened.

[0054] A gate lock valve 55 is also disposed in the pilot line between the pilot pump 2 and the operating device 10. When the gate lock sensor 31 detects that the gate lock lever is lowered and the passage is closed, the gate lock sensor 31 turns its output signal ON, and this ON signal is sent to the controller 30 (described later). The controller 30 outputs a drive signal to the gate lock valve 55 based on the ON signal. This drive signal switches the gate lock valve 55 to the right-hand position in the figure, enabling the operating device 10 to generate pilot operating pressure. When the gate lock lever is raised and the passage is opened, the gate lock sensor 31 stops outputting the ON signal and turns its output signal OFF, and the controller 30 also stops outputting the drive signal to the gate lock valve 55. As a result, the gate lock valve 55 switches to the right-hand position in the figure, cutting off communication between the pilot pump 2 and the operating device 10 and disabling operation by the operating device 10.

[0055] A boom assist switch 27 is also installed in the driver's compartment of cabin 317, for example, in a console box to the right of the driver's seat. When down mode or float mode is selected by mode selection device 41 of monitor 40, boom assist switch 27 is a switch that confirms that there is no problem with the selection of down mode or float mode, and after confirming that there is no problem with the selection of down mode or float mode, the operator operates boom assist switch 27 to the ON position and outputs an ON signal. When it is desired to temporarily disable boom assist and return to normal work mode or when changing operators, the operator operates boom assist switch 27 to the OFF position and turns off the output signal.

[0056] ~Monitor and Controller~ In addition to the hydraulic system described above, the hydraulic drive system of this embodiment further includes a monitor 40 equipped with a mode selection device 41 (see FIG. 3) that selects a normal work mode or a down mode as the operating mode of the work machine 302, and a relief pressure input device 42 (see FIG. 3) that can input a relief pressure for the adjustable relief valve 21 when the down mode is selected, and a controller 30. The controller 30 is connected to the monitor 40, and when the normal work mode is selected by the mode selection device 41 of the monitor 40, the controller 30 sets a predetermined maximum relief pressure for the adjustable relief valve 21, and when the down mode is selected, the controller 30 sets a predetermined relief pressure that is lower than the maximum relief pressure for the adjustable relief valve 21. By providing the mode selection device 41 in the monitor 40 in this way and configuring the mode selection device 41 to set the relief pressure for the adjustable relief valve 21 when the down mode is selected, it is possible to realize a configuration in which the attachment 320 is pressed against the object to be processed with a constant force when the down mode is selected.

[0057] The monitor 40 can display a screen (a screen 160 described later) that functions as a mode selection device 41 through an operator's operation input. This allows the operator to easily select the down mode or the float mode using the screen 160 of the monitor 40.

[0058] Furthermore, when the down mode is selected and the monitor 40 functions as a relief pressure input device 42 that can input the relief pressure of the adjustable relief valve 21, the monitor 40 can display a screen (screen 180 described below) for inputting the relief pressure of the adjustable relief valve 21. This allows the operator to easily set the pressing force of the attachment 320 against the ground in the down mode to a desired value using the screen 180 of the monitor 40, and place the attachment 320 on the ground with just the right pressing force.

[0059] Furthermore, the mode selection device 41 of the monitor 40 can select a float mode in addition to the normal work mode and down mode as the operating mode of the work implement 302. When the mode selection device 41 does not select the float mode, the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2 are in the closed position, and when the mode selection device 41 selects the float mode, the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2 are switched to the open position, setting the boom cylinder 309 in a free state in which it can operate passively. As described above, this enables the boom 306 to move up and down in accordance with the undulating shape of the ground, and when a bucket 308 is attached to the work implement 302 as an attachment, the bucket 308 can perform work by following the undulating shape of the ground.

[0060] The function of the mode selection device 41 of the monitor 40 will be described in detail below with reference to the drawings.

[0061] ~Monitor screen transitions and mode settings~ FIG. 3 shows screen transitions of the mode selection device 41 displayed on the monitor 40. As shown in FIG.

[0062] In Figure 3, screen 160 is a menu screen for selecting the mode selection device 41 of the monitor 40, screen 170 is a boom assist setting screen of the mode selection device 41, and screen 180 is a boom assist setting screen for setting the boom lowering force (pushing force) of the down mode of the mode selection device 41.

[0063] The menu screen 160 includes a "Boom Assist" item, and when the operator moves the cursor onto the "Boom Assist" item by key operation and presses the execute key, "Boom Assist" is selected. At this time, the screen of the monitor 40 transitions to a boom assist setting screen 170. Next, when the operator moves the cursor onto the "Down Mode" item on the boom assist setting screen 170 and presses the execute key, and then moves the cursor onto the "Enable" item and presses the execute key, "Down Mode" is selected. At this time, the screen of the monitor 40 transitions to a boom assist setting screen 180. The boom assist setting screen 180 displays that "Boom Assist" is enabled and that "Down Mode" is enabled, and also displays an additional item for "Down Mode Pressure Setting." Then, when the operator moves the cursor onto the "Down Mode Pressure Setting" item and presses the execute key, the relief pressure of the adjustable relief valve 21 ("5 MPa" in the illustrated example) is selected.

[0064] Furthermore, on the boom assist setting screen 170, if the cursor is moved onto the "Float mode" item and the execute key is pressed, and then the cursor is moved onto the "Enable" item and the execute key is pressed, "Float mode" is selected. In this case, too, the screen of the monitor 40 transitions to the boom assist setting screen 180 (however, the "Down mode pressure setting" item is not additionally displayed), and the boom assist setting screen 180 displays that "Boom assist" is enabled and "Float mode" is enabled.

[0065] FIG. 4 is a flow chart showing the mode setting function of the mode selection device 41 of the monitor 40.

[0066] In Fig. 4, the mode selection device 41 of the monitor 40 determines whether the selected work mode is the normal work mode, the down mode, or the float mode based on the information selected on the menu screen 160 of Fig. 3 (step S110). If "boom assist" is not selected on the menu screen 160 of Fig. 3, if "boom assist" is selected on the menu screen 160 of Fig. 3 and "down mode" or "float mode" is not selected on the boom assist setting screen 170 of Fig. 3, or if a cancel key (not shown) that ends the "down mode" or "float mode" is pressed after "down mode" or "float mode" is selected on the boom assist setting screen 170 of Fig. 3, the mode transitions to the normal work mode (step S120). In the normal work mode, conventional hydraulic excavator work can be performed.

[0067] When "Boom Assist" is selected on the menu screen 160 in FIG. 3 and "Down Mode" is selected on the boom assist setting screen 170 in FIG. 3, the system transitions to "Down Mode" and transmits a down mode command signal to the controller 30 (step S130).

[0068] Furthermore, if the relief pressure of the variable relief valve 21 ("5 MPa" in the illustrated example) is selected on the boom assist setting screen 180 in Figure 3, the screen transitions to "Down mode pressure setting", a relief pressure command signal is sent to the controller 30 (step S150), and the selected relief pressure is set.

[0069] When "Boom Assist" is selected on the menu screen 160 in FIG. 3 and "Float Mode" is selected on the boom assist setting screen 170 in FIG. 3, the system transitions to "Float Mode" and transmits a float mode command signal to the controller 30 (step S140).

[0070] ~Controller processing functions~ <Down mode> The controller 30 receives detection signals from the bottom side pressure sensor 20-1 and the rod side pressure sensor 20-2, and the controller 30 receives an operation signal indicating the boom lowering direction. At this time, it is determined whether the work implement 302 is in a jacked-up state based on the detection values ​​of the bottom side pressure sensor 20-1 and the rod side pressure sensor 20-2, and if it is determined that the work implement 302 is not in a jacked-up state, it sets the variable relief valve 21 to a relief pressure lower than the maximum relief pressure set in the normal work mode, and if it is determined that the work implement 302 is in a jacked-up state, it sets the variable relief valve 21 to the maximum relief pressure.

[0071] The control function of the down mode will be described in detail with reference to FIG.

[0072] FIG. 5 is a flowchart showing the details of the down mode control function.

[0073] In step S130 of the flowchart in FIG. 4, when a down mode command signal is sent from the mode selection device 41 of the monitor 40 to the controller 30, in FIG. 5, the controller 30 determines whether the output signal of the gate lock sensor 31, which detects the raising and lowering of the gate lock lever, is ON or not (step S210), and if the output signal of the gate lock sensor 31 is ON, it further determines whether the output signal of the boom assist switch 27 is ON or not, and if the output signal of the gate lock sensor 31 is OFF or the output signal of the boom assist switch 27 is OFF, the control ends.

[0074] In step S210, if the output signal of the gate lock sensor 31 is ON, and in step S220, if the output signal of the boom assist switch 27 is ON, then it is determined based on the detection signal of the pressure sensor 28 whether or not an operating pilot pressure for boom lowering is being input (step S230), and if an operating pilot pressure for boom lowering is being input (when the operation signal indicates the boom lowering direction), it is further determined based on the detection values ​​of the bottom side pressure sensor 20-1 and the rod side pressure sensor 20-2 whether or not the work implement 302 is in a jacked-up state (step S240).

[0075] When the controller 30 determines that the work implement 302 is in a jack-up state, the controller 30 ends the control.

[0076] In addition, when the controller 30 determines that the work implement 302 is not in a jacked-up state, it outputs a corresponding electrical signal (voltage signal) to the solenoid 21-2 of the variable relief valve 21 based on the relief pressure command signal transmitted from the mode selection device 41 of the monitor 40, thereby setting the relief pressure of the variable relief valve 21 to the value selected on the boom assist setting screen 180 ("5 MPa" in the illustrated example) (step S250).

[0077] Furthermore, the controller 30 outputs a command signal (electrical signal) to the solenoid 26-1 of the electromagnetic pressure reducing valve 26 to move the electromagnetic pressure reducing valve 26 to the intermediate position, and switches the first directional control valve 3-1 to the intermediate opening position in the boom lowering direction to open slightly.

[0078] In this way, when the controller 30 determines that the work implement 302 is not in a jacked-up state while the operation signal indicates a boom-down direction, it sets the relief pressure of the variable relief valve 21 to the value selected on the boom assist setting screen 180 ("5 MPa" in the illustrated example), thereby enabling work in down mode.

[0079] Furthermore, the controller 30 disables the control when it determines that the work implement 302 is in a jacked-up state, so that if the down mode is selected while the vehicle body is being jacked up, the jacked-up vehicle body part can be prevented from falling.

[0080] Furthermore, the controller 30 outputs a command signal (electrical signal) to the solenoid 26-1 of the electromagnetic pressure reducing valve 26 to move the electromagnetic pressure reducing valve 26 to the intermediate position and switches the first directional control valve 3-1 to the intermediate opening position in the boom lowering direction to open it slightly, thereby supplying pressure oil at a controlled flow rate to the rod side chamber 309-2 of the boom cylinder 309. This makes it possible to supply only the flow rate necessary to press the attachment 320 against the object to be treated with a constant force, regardless of the input amount of the operating lever 10-1 of the operating device 10.

[0081] Furthermore, the first direction control valve 3-1 is not fully opened, and the remaining pressure oil that is discharged from the first hydraulic pump 1-1 and not supplied to the first direction control valve 3-1 is supplied to the second direction control valve 3-2, thereby ensuring the flow rate of pressure oil to be supplied to the attachment 320. As a result, the relief pressure set in the variable relief valve 21 presses the breaker 320 against the object to be treated with a constant force regardless of the input amount of the operation lever 10-1, while also supplying the breaker 320 with the necessary flow rate, allowing work to be performed efficiently.

[0082] <Float mode> When the operation signal is a signal instructing the boom lowering direction, the controller 30 determines whether the work implement 302 is in a jacked-up state based on the detection values ​​of the bottom side pressure sensor 20-1 and the rod side pressure sensor 20-2, and if it determines that the work implement 302 is not in a jacked-up state, it switches the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2 to the open position, enabling work in float mode, and if it determines that the work implement 302 is in a jacked-up state, it disables the control and holds the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2 in the closed position.

[0083] The details of the control function of the float mode will be explained using FIG.

[0084] FIG. 6 is a flow chart showing the details of the float mode control function.

[0085] In step S140 of the flowchart in FIG. 4, when a float mode command signal is sent from the mode selection device 41 of the monitor 40 to the controller 30, in FIG. 6, the controller 30 first determines whether the output signal of the gate lock sensor 31, which detects the raising and lowering of the gate lock lever, is ON or not (step S310), and if the output signal of the gate lock sensor 31 is ON, it further determines whether the output signal of the boom assist switch 27 is ON or not, and if the output signal of the gate lock sensor 31 is OFF or the output signal of the boom assist switch 27 is OFF, the control ends.

[0086] In step S210, if the output signal of the gate lock sensor 31 is ON, and in step S320, if the output signal of the boom assist switch 27 is ON, then it is determined based on the detection signal of the pressure sensor 28 whether or not an operating pilot pressure for boom lowering is being input (step S330), and if an operating pilot pressure for boom lowering is being input (when the operation signal indicates the boom lowering direction), it is further determined based on the detection values ​​of the bottom side pressure sensor 20-1 and the rod side pressure sensor 20-2 whether or not the work implement 302 is in a jacked-up state (step S340).

[0087] When the controller 30 determines that the work implement 302 is in a jack-up state, the controller 30 ends the control.

[0088] Furthermore, when the controller 30 determines that the work implement 302 is not in a jack-up state, the controller 30 switches the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2 to the open position by transmitting corresponding drive signals (electrical signals) to the solenoids of the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2 based on the open signals for the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2 transmitted from the mode selection device 41 of the monitor 40. Furthermore, the controller 30 switches the solenoid pressure reducing valve 26 to the second position to hold the first directional control valve 3-1 in the neutral position.

[0089] In this way, when the operation signal indicates the boom lowering direction and the controller 30 determines that the work implement 302 is not in a jacked-up state, it switches the first electromagnetic on-off valve 50-1 and the second electromagnetic on-off valve 50-2 to the open position, thereby enabling operation in float mode.

[0090] Furthermore, the controller 30 disables control when it determines that the work implement 302 is in a jacked-up state, so that if the float mode is selected while the vehicle body is being jacked up, the jacked-up vehicle body part can be prevented from falling.

[0091] <Jack-up judgement of the controller> FIG. 7 is a side view of the hydraulic excavator showing an example of a state in which the vehicle body (a collective term for the upper revolving body 300 and the lower traveling body 301) of the hydraulic excavator is jacked up.

[0092] The jacked-up state of the vehicle body refers to a state in which, for example, as shown in Fig. 7, the work implement 302 is lowered with the bucket 308 on the ground, and then the boom cylinder 309 is retracted as indicated by arrow S, thereby lifting part of the vehicle body off the ground. In the illustrated example, the upper rotating body 300 is rotated approximately 90 degrees relative to the lower traveling body 301, and after the work implement 302 is lowered in that position and the bucket 308 is brought into contact with the ground, the boom cylinder 309 is retracted to brace the work implement 302 against the ground, thereby lifting the left crawler 316 off the ground.

[0093] While the vehicle body is being jacked up, a downward external force acts on the work machine 302 due to the weight of the hydraulic excavator body, and an opposite upward force acts on the piston inside the boom cylinder 309 that supports it. For this reason, during jacking up, high pressure acts on the rod side chamber 309-2 of the boom cylinder 309, while the pressure in the bottom side chamber 309-1 of the boom cylinder 309 becomes low, close to the tank pressure.

[0094] When the down mode or float mode is selected while the vehicle body is being jacked up, if the judgment process of step S240 in FIG. 5 or step S340 in FIG. 6 is not performed and a jack-up judgment is not made, the process will transition from the process of step S230 in FIG. 5 or step S330 in FIG. 6 to the process of step S250 in FIG. 5 or step S350 in FIG. 6, and the control of step S250 in FIG. 5 or step S350 in FIG. 6 will be initiated, causing the lifted vehicle body part to suddenly fall.

[0095] In other words, if the down mode is selected while the vehicle body is being jacked up, the relief pressure of the variable relief valve 21 is set to a value lower than the maximum relief pressure selected on the boom assist setting screen 180 ("5 MPa" in the illustrated example), causing pressurized oil to flow out of the rod side chamber 309-2 of the boom cylinder 309 via the variable relief valve 21, and the rod side chamber 309-2 of the boom cylinder 309 will no longer be able to support the downward force of the vehicle body part on the left crawler 316 side.

[0096] Furthermore, if the float mode is selected while the vehicle body is being jacked up, the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2 are switched to the open position, and pressurized oil flows out from the rod side chamber 309-2 of the boom cylinder 309 through the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2, and similarly, the rod side chamber 309-2 of the boom cylinder 309 becomes unable to support the downward force of the vehicle body portion on the left crawler 316 side.

[0097] Therefore, it is necessary to check whether the vehicle body is in a jacked-up state before starting the down mode control or float control.

[0098] In the present invention, the controller 30 determines that the work implement 302 is not in a jacked-up state when the pressure in the rod-side chamber 309-2 of the boom cylinder 309 detected by the bottom-side pressure sensor 20-1 is equal to or lower than a preset first threshold value and the pressure in the bottom-side chamber 309-1 detected by the rod-side pressure sensor 20-2 is higher than a preset second threshold value. Furthermore, the controller 30 determines that the work implement 302 is in a jacked-up state when the pressure in the rod-side chamber 309-2 of the boom cylinder 309 detected by the bottom-side pressure sensor 20-1 is higher than the preset first threshold value and the pressure in the bottom-side chamber 309-1 detected by the rod-side pressure sensor 20-2 is lower than the preset second threshold value.

[0099] In this embodiment, the pressure in both the rod side chamber 309-2 and the bottom side chamber 309-1 of the boom cylinder 309 is detected to determine whether the work implement 302 is in a jacked-up state. However, as a simpler method, only the rod side pressure sensor 20-2 may be provided, and only the rod side chamber 309-2 of the boom cylinder 309 may be detected, and when the pressure in the rod side chamber 309-2 of the boom cylinder 309 is higher than a preset first threshold value, it may be determined that the work implement 302 is in a jacked-up state.

[0100] FIG. 8 is a flowchart showing the logic for determining whether the vehicle body is jacked up, which is performed in step S240 of FIG. 5 and step S340 of FIG.

[0101] In FIG. 8, the controller 30 reads the pressure on the rod chamber side of the boom cylinder 309 from the detection value of the bottom side pressure sensor 20-1, and determines whether the pressure is equal to or lower than a first threshold value that is normally set to the pressure in the rod side chamber 309-2 when jacking up the vehicle body (step S410).If the pressure on the rod chamber side of the boom cylinder 309 is higher than the first threshold value, it determines that the vehicle body may be in a jacked-up state and terminates control.

[0102] Furthermore, if the pressure on the rod chamber side of the boom cylinder 309 is below the first threshold, the controller 30 further reads the pressure in the bottom side chamber 309-1 of the boom cylinder 309 from the detection value of the rod side pressure sensor 20-2, and determines whether the pressure is above a second threshold which is normally set as the pressure on the bottom chamber side when the vehicle body is jacked up (step S420).If the pressure in the bottom side chamber 309-1 of the boom cylinder 309 is lower than the second threshold, it determines that the vehicle body may be in a jacked-up state, and terminates control.

[0103] On the other hand, if the pressure in the rod chamber side of the boom cylinder 309 is equal to or less than the first threshold value and the pressure in the bottom side chamber 309-1 of the boom cylinder 309 is equal to or greater than the second threshold value, it is determined that the vehicle body is not likely to be in a jacked-up state, and the controller 30 proceeds to step S250 in FIG. 5 or step S350 in FIG. 6.

[0104] In this way, by comparing the pressure in both the rod side chamber and the bottom side chamber of the boom cylinder 309 with the respective threshold values ​​and making a judgment, it is possible to accurately determine whether the vehicle body is in a jacked-up state.

[0105] ~Effects~ According to this embodiment, the following effects can be obtained.

[0106] 1. When the work machine 302 is equipped with an attachment 320 such as a breaker or a sweeper with a brush function that performs work by pressing it against the object to be treated, selecting the down mode allows the attachment 320 to be pressed with a constant force to perform work, so that the attachment 320 can be grounded against the object to be treated with just the right pressing force, and work using the attachment 320 can be performed easily and in a short time.

[0107] 2. When the down mode is selected, the electromagnetic pressure reducing valve 26 is moved to the intermediate position and the first directional control valve 3-1 is switched to the intermediate opening position in the boom lowering direction and opened slightly, so that only the flow rate necessary to press the attachment 320 against the object to be treated with a constant force can be supplied regardless of the input amount of the operating lever 10-1 of the operating device 10.

[0108] 3. The second directional control valve 3-2 to which pressure oil discharged from the first hydraulic pump 1-1 is guided is provided, and an electromagnetic pressure reducing valve 26 is also provided, and when the down mode is selected, the electromagnetic pressure reducing valve 26 is moved to the intermediate position and the first directional control valve 3-1 is switched to the intermediate opening position in the boom lowering direction and opened slightly, so that the remaining pressure oil discharged from the first hydraulic pump 1-1 that has not been supplied to the first directional control valve 3-1 is supplied to the second directional control valve 3-2, thereby ensuring the flow rate of pressure oil supplied to the attachment 320. As a result, the relief pressure set in the variable relief valve 21 presses the breaker 320 against the object to be treated with a constant force regardless of the input amount of the operation lever 10-1, while also supplying the breaker 320 with the necessary flow rate, allowing for efficient work.

[0109] 4. By providing a mode selection device 41 on the monitor 40 and configuring it so that the relief pressure of the variable relief valve 21 is set when the down mode is selected using the mode selection device 41, it is possible to realize a configuration in which the attachment 320 is pressed against the object to be treated with a constant force when the down mode is selected.

[0110] 5. The monitor 40 can display the menu screen 160, which functions as the mode selection device 41, through the operator's input, so that the operator can easily select the down mode or the float mode using the menu screen 160 on the monitor 40.

[0111] 6. When the down mode is selected, the monitor 40 can display the boom assist setting screen 180 for changing the relief pressure of the variable relief valve 21. Therefore, the operator can use the boom assist setting screen 180 on the monitor 40 to easily set the pressing force of the attachment 320 against the ground in the down mode to a desired value, and can land the attachment 320 on the ground with just the right pressing force.

[0112] 7. When float mode is not selected, the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2 are in the closed position, and when float mode is selected, the first solenoid on-off valve 50-1 and the second solenoid on-off valve 50-2 are switched to the open position, and the boom cylinder 309 is set to a free state in which it can operate passively. Therefore, in float mode, the boom 306 can move up and down in accordance with the undulating shape of the ground, and when a bucket 308 is attached to the work implement 302 as an attachment, the bucket 308 can be made to follow the undulating shape of the ground, making plowing work easy.

[0113] 8. The controller 30 disables control when it determines that the work implement 302 is in a jacked-up state, so that if the down mode or float mode is selected while the vehicle body is being jacked up, the jacked-up vehicle body part can be prevented from falling.

[0114] Second Embodiment FIG. 9 is a diagram showing a hydraulic drive system according to a second embodiment of the present invention.

[0115] In Figure 9, the hydraulic drive system of this embodiment further includes a second hydraulic pump 1-2 in addition to the first hydraulic pump 1-1, and the pressurized oil discharged from the second hydraulic pump 1-2 is guided to the second directional control valve 3-2 of the main control valve block 3 and supplied to the actuator 320-1 of the attachment 320.

[0116] In addition, the hydraulic drive system of this embodiment is provided with a first connecting oil passage 5-1 that guides the pressurized oil discharged from the first hydraulic pump 1-1 and passed through the first direction control valve 3-1 to the second direction control valve 3-2 when the first direction control valve 3-1 is in the neutral position.

[0117] Furthermore, the hydraulic drive system of this embodiment is provided with a second connecting oil passage 5-2 that guides the pressurized oil discharged from the first hydraulic pump 1-1 to the second directional control valve 3-2, and, similar to the first embodiment, is provided with an electromagnetic pressure reducing valve 26 that is arranged in a pilot oil passage 10-5 between the operating device 10 and the first directional control valve 3-1 and switches the first directional control valve 3-1 to an intermediate opening position in the boom lowering direction when the down mode is selected and the operating signal from the operating device 10 is a signal instructing the boom lowering direction.

[0118] As described above, when the down mode is selected and the operation signal indicates the boom lowering direction, the electromagnetic pressure reducing valve 26 switches the first direction control valve 3-1 to the intermediate opening position in the boom lowering direction, so that the first direction control valve 3-1 is not fully opened and a portion of the pressure oil discharged from the first hydraulic pump 1-1 can be supplied to the attachment 320 via the second direction control valve 3-2.

[0119] The maximum required flow rate of the actuator 320-1 of the attachment 320 varies depending on the size and type of the attachment, and depending on the attachment, the flow rate of one pump may not be sufficient.

[0120] In the present embodiment, when the first direction control valve 3-1 for the boom is not in use, the pressurized oil that has passed through the center bypass oil passage of the first direction control valve 3-1 is made to merge with the second direction control valve 3-2 for the attachment via the first connecting oil passage 5-1, thereby allowing the discharge flow rates of the two hydraulic pumps 1-1, 1-2 to flow to the actuator 320-1 side of the attachment 320, and making it possible to supply pressurized oil that corresponds to the required flow rate.

[0121] Furthermore, even when the first direction control valve 3-1 is used to lower the boom in down mode, the opening of the first direction control valve 3-1 for the boom is adjusted (without being fully open) by the electromagnetic pressure reducing valve 26, and the discharge oil of the first hydraulic pump 1-1 that was not supplied to the first direction control valve 3-1 is supplied via the second connecting oil passage 5-2, so that a flow rate of pressurized oil corresponding to the required flow rate can be supplied to the actuator 320-1 of the attachment 320 via the second direction control valve 3-2.

[0122] <Third embodiment> Fig. 10 is a diagram showing a hydraulic drive system according to a third embodiment of the present invention, and Fig. 11 is a diagram showing a system configuration related to a controller of this embodiment.

[0123] In the hydraulic drive system of this embodiment, the operating device is an electric operating device 10X that generates an electric operating signal (electric signal) as shown in FIG. 11, and the electric operating signal is sent from the operating device 10X to a controller 30X, and an electric command signal is sent from the controller 30X to a control valve block 3X.

[0124] The control valve block 3X is equipped with electromagnetic proportional pressure reducing valves 6-1, 6-2, 6-3, and 6-4 including a first electromagnetic proportional pressure reducing valve 6-1 that generates a boom-up pilot control pressure for the first directional control valve 3-1 and a second electromagnetic proportional pressure reducing valve 6-2 that generates a boom-lowering pilot control pressure for the first directional control valve 3-1, and when the normal mode is selected, the controller 30X generates an electric command signal based on an electric operation signal and outputs the command signal to the corresponding electromagnetic proportional pressure reducing valves, for example, the first electromagnetic proportional pressure reducing valve 6-1 and the second electromagnetic proportional pressure reducing valve 6-2, thereby switching the first directional control valve 3-1, and when the down mode is selected, the controller 30X generates a command signal not based on an electric operation signal and outputs the command signal to the second electromagnetic proportional pressure reducing valve 6-2, thereby switching the first directional control valve 3-1 to the intermediate opening position in the boom-lowering direction.

[0125] In addition, the holding valve 25 (see Figure 2) has been replaced with a holding valve 25A equipped with a solenoid 25-2A, and when the boom is lowered, an electrical command signal is sent from the controller 30X to the solenoid 25-2A, causing the holding valve 25A to switch from the fall prevention position on the right side of the figure to the open position on the left side of the figure.

[0126] Next, the system configuration related to the controller 30X and the processing functions of the controller 30X will be described in detail.

[0127] In FIG. 11, the electric operating device 10X has an electric operating device 10A for the boom, an electric operating device 10B for the arm, an electric operating device 10C for the bucket, an electric operating device 10D for the rotating body, an electric operating device 10E for the right crawler of the traveling body, an electric operating device 10F for the right crawler of the traveling body, an electric operating device 10G for the swing, an electric operating device 10H for the blade, and an electric operating device 10I for the actuator, and generates electric operating signals in accordance with the amount of operation of each operating lever / pedal, and the generated operating signals are sent to the controller 30X via a communication network 60 established within the hydraulic excavator.

[0128] Controller 30X receives operation signals from electric operating device 10X, performs predetermined arithmetic processing to generate command signals for the electromagnetic proportional pressure reducing valves, and outputs the command signals to, for example, electromagnetic proportional pressure reducing valves 6-1, 6-2, 6-3, and 6-4. As a result, pilot control pressures generated by electromagnetic proportional pressure reducing valves 6-1, 6-2, 6-3, and 6-4 are sent to pressure receiving portions 3-11 and 3-12 of first directional control valve 3-1 and pressure receiving portions 3-21 and 3-22 of second directional control valve 3-2, causing first directional control valve 3-1 and second directional control valve 3-2 to switch, and pressure oil discharged from first hydraulic pump 1-1 is supplied to boom cylinder 309 and attachment actuator 320-1 via first directional control valve 3-1 and second directional control valve 3-2. The same applies to the other electromagnetic proportional pressure reducing valves.

[0129] In addition to the above-mentioned electrical operation signals, the controller 30X also receives detection signals from the bottom side pressure sensor 20-1 and the rod side pressure sensor 20-2, an output signal from the boom assist switch 27, an output signal from the gate lock sensor 31, and a down mode command signal or a float mode command signal from the monitor 40 (mode selection device 41) via the communication network 60, and the controller 30X performs the following calculation processing.

[0130] 1. Only when the output signal of the gate lock sensor 31 is ON, the controller 30X generates a command signal for the electromagnetic proportional pressure reducing valve based on the electric operation signal of the electric operation device 10X, and outputs the command signal to, for example, the electromagnetic proportional pressure reducing valves 6-1, 6-2, 6-3, and 6-4. The same applies to the other electromagnetic proportional pressure reducing valves.

[0131] 2. When the electric boom operating device 10A is operated in the boom-lowering direction, the controller 30X generates a command signal for the holding valve 25A and outputs the command signal to the solenoid 25-2A of the holding valve 25A. This moves the valve element 25-1 to the open position, and the pressure oil in the bottom-side chamber 309-1 of the boom cylinder 309 is discharged to the tank via the first directional control valve 3-1, enabling the boom 306 to be lowered.

[0132] 5 based on the output signal of the gate lock sensor 31 and the output signal of the boom assist switch 27, and when both output signals are ON, the controller 30X makes the determination in step S230 of the flowchart in Fig. 5 based on the electrical operation signal of the electric operation device 10A for the boom. Then, when an operation signal for lowering the boom is input, the controller 30X makes the determination in step S240, i.e., the determinations in steps S410 and S420 of Fig. 7, based on the detection values ​​of the bottom side pressure sensor 20-1 and the rod side pressure sensor 20-2, and when the work implement 302 is not in a jack-up state, performs processing on the adjustable relief valve 21 in step S250 of the flowchart in Fig. 5. That is, based on the relief pressure command signal transmitted from the mode selection device 41 of the monitor 40, the controller 30X sets the relief pressure of the variable relief valve 21 to the value selected on the boom assist setting screen 180 ("5 MPa" in the illustrated example).

[0133] 3-2. Furthermore, when the work implement 302 is not in a jack-up state, the controller 30X performs processing on the second electromagnetic proportional pressure reducing valve 6-2 for boom lowering relative to the first directional control valve 3-1 similar to the processing performed on the electromagnetic pressure reducing valve 26 in step S250 of the flowchart in FIG. 5. That is, the controller 30X outputs a command signal (electrical signal) to the solenoid of the second electromagnetic proportional pressure reducing valve 6-2 to move the second electromagnetic proportional pressure reducing valve 6-2 to an intermediate position, thereby switching the first directional control valve 3-1 to an intermediate opening position in the boom lowering direction and slightly opening it, and supplying pressure oil from the first hydraulic pump 1-1 to the rod side chamber 309-2 of the boom cylinder 309 while controlling the flow rate. At this time, by not fully opening the first directional control valve 3-1, the remaining discharge oil from the first hydraulic pump 1-1 is supplied to the second directional control valve 3-2, and a flow rate for the breaker 320 is ensured.

[0134] 4. When a float mode command signal is sent from the monitor 40 (mode selection device 41), the controller 30X makes the determinations in steps S310 and S320 of the flowchart in Fig. 6 based on the output signal of the gate lock sensor 31 and the output signal of the boom assist switch 27, and when both output signals are ON, makes the determination in step S330 of the flowchart in Fig. 6 based on the electrical operation signal of the electric operating device 10A for the boom. Then, when an operation signal for lowering the boom is input, makes the determination in step S340, i.e., the determinations in steps S410 and S420 of Fig. 7, based on the detection values ​​of the bottom side pressure sensor 20-1 and the rod side pressure sensor 20-2, and when the work implement 302 is not in a jacked-up state, performs processing for the first solenoid on-off valves 50-1 and 50-2 in step S350 of the flowchart in Fig. 6. That is, the controller 30X switches the first electromagnetic on-off valve 50-1 and the second electromagnetic on-off valve 50-2 to the open position, enabling the boom to move up and down according to the undulating shape of the ground. Also, by switching the second electromagnetic proportional pressure reducing valve 6-2 to the second position and holding the first directional control valve 3-1 in the neutral position, the supply of pressure oil from the first hydraulic pump 1-1 is cut off.

[0135] According to this embodiment, in a hydraulic drive system in which the operating device is constituted by an electric operating device 10X, when an attachment that performs work by pressing it against the object to be processed, such as a breaker or a sweeper with a brush function, is attached, the attachment 320 can be grounded to the ground with just the right pressing force, and work using the attachment 320 can be performed easily in a short time, thereby achieving the same effects as in the first embodiment. [Explanation of symbols]

[0136] 1-1: First hydraulic pump 1-2: Second hydraulic pump 3,3X: Control valve 3-1: First directional control valve 3-2: Second directional control valve 4-1: No. 1 oil road 4-2: 2nd oil road 6-1, 6-2, 6-3, 6-4 Solenoid proportional pressure reducing valve 10: Operating device (hydraulic pilot type operating device) 10X: Operating device (electric operating device) 20-1: Bottom pressure sensor 20-2: Rod side pressure sensor 21: Variable relief valve 25: Holding valve 26: Electromagnetic proportional pressure reducing valve 27: Boom assist switch 28: Pressure sensor 30, 30X: Controller 40: Monitor 41: Mode selection device 42: Relief pressure input device 50-1: First solenoid valve 50-2: Second solenoid valve 302: Work equipment 306: Boom 308: Bucket 309: Boom cylinder 309-1: Bottom Concubine 309-2: Rod's concubine 320: Attachment 320-1: Attachment actuator

Claims

1. The car body and, A work machine attached to the vehicle body, having a boom at its base end that can move up and down relative to the vehicle body, and having a work tool at its tip end, A boom cylinder that moves the boom up and down, A first hydraulic pump that supplies pressurized oil to the boom cylinder, A first directional control valve controls the flow of pressurized oil discharged from the first hydraulic pump based on an operating signal generated by an operating device, A first oil passage connecting the first directional control valve and the bottom side chamber of the boom cylinder, In a construction machine comprising a first directional control valve and a second oil passage connecting the rod side chamber of the boom cylinder, A mode selection device for selecting the operating mode of the work machine, which is either a normal work mode or a down mode in which the attachment mounted on the work machine as the tip work tool is pressed against the object to be processed. The system includes a variable relief valve connected to the second oil passage, The construction machine is characterized in that the variable relief valve is controlled to maintain the pressure of the pressurized oil in the rod side chamber of the boom cylinder at a predetermined pressure when the down mode is selected by the mode selection device.

2. In the construction machine described in claim 1, The aforementioned operating device is a hydraulic pilot-type operating device that generates pilot operating pressure as the operating signal, The system further comprises an electromagnetic pressure reducing valve positioned between the operating device and the first directional control valve, The electromagnetic pressure reducing valve is in a first position when the normal operation mode is selected, which directs the pilot operating pressure directly to the first directional control valve. When the down mode is selected, it switches to an intermediate position between the first position and a second position which blocks the transmission of the pilot operating pressure to the first directional control valve. In this intermediate position, it generates a pilot control pressure that switches the first directional control valve to an intermediate opening position in the boom lowering direction based on the pilot operating pressure.

3. In the construction machine described in claim 1, A second directional control valve receives pressurized oil discharged from the first hydraulic pump and supplies the pressurized oil to the actuator of the attachment, A construction machine further comprising an electromagnetic pressure reducing valve that switches the first directional control valve to an intermediate opening position in the boom lowering direction when the down mode is selected and the operation signal is a signal indicating the boom lowering direction.

4. In the construction machine described in claim 1, The system includes a controller that controls the variable relief valve, The controller is characterized in that, when the normal work mode is selected by the mode selection device, it sets a predetermined maximum relief pressure in the variable relief valve, and when the down mode is selected, it sets a predetermined relief pressure lower than the maximum relief pressure in the variable relief valve.

5. In the construction machine described in claim 1, A construction machine characterized by comprising a relief pressure input device capable of inputting the relief pressure of the variable relief valve when the down mode is selected.

6. In the construction machine described in claim 1, A rod-side pressure sensor for detecting the pressure in the rod-side chamber of the boom cylinder, The system further comprises a controller to which the detection signal from the rod-side pressure sensor is input, The aforementioned controller, When the down mode is selected and the operation signal is a signal indicating the boom lowering direction, it is determined whether the work machine is in a jacked-up state based on the detected value of the rod-side pressure sensor. When it is determined that the work machine is not in a jacked-up state, the variable relief valve is set to a relief pressure lower than the maximum relief pressure set in the normal work mode. A construction machine characterized in that, when it is determined that the work machine is in a jacked-up state, the maximum relief pressure is set in the variable relief valve.

7. In the construction machine described in claim 1, The system further comprises a first electromagnetic valve connected to the oil passage between the first oil passage and the tank, and equipped with a check valve in the closed position, and a second electromagnetic valve connected to the oil passage between the second oil passage and the tank, and equipped with a check valve in the closed position. The mode selection device can further select a float mode as the operating mode of the work machine. A construction machine characterized in that the first electromagnetic valve and the second electromagnetic valve are in the closed position when the mode selection device selects the normal operation mode or the down mode, and are switched to the open position when the mode selection device selects the float mode.

8. In the construction machine described in claim 7, A rod-side pressure sensor for detecting the pressure in the rod-side chamber of the boom cylinder, The system further comprises a controller that receives the detection signal from the rod-side pressure sensor, The aforementioned controller, When the float mode is selected and the operation signal is a signal indicating the boom lowering direction, it is determined whether or not the work machine is in a jacked-up state based on the detected value of the rod-side pressure sensor. When it is determined that the work machine is not in a jacked-up state, the first electromagnetic valve and the second electromagnetic valve are switched to the open position. A construction machine characterized in that, when it is determined that the work machine is in a jacked-up state, the first electromagnetic valve and the second electromagnetic valve are held in the closed position.

9. In the construction machine according to claim 6 or 8, The controller is characterized in that it determines that the work machine is in a jacked-up state when the pressure in the rod-side chamber of the boom cylinder, detected by the rod-side pressure sensor, is higher than a preset first threshold.

10. In the construction machine described in claim 1, The second hydraulic pump, A second directional control valve receives pressurized oil discharged from the second hydraulic pump and supplies the pressurized oil to the actuator of the attachment, A construction machine further comprising a first connecting oil passage that, when the first directional control valve is in the neutral position, guides pressurized oil discharged from the first hydraulic pump and passing through the first directional control valve to the second directional control valve.

11. In the construction machine according to claim 10, A second connecting oil passage that guides the pressurized oil discharged from the first hydraulic pump to the second directional control valve, A construction machine further comprising an electromagnetic pressure reducing valve that switches the first directional control valve to an intermediate opening position in the boom lowering direction when the down mode is selected and the operation signal is a signal indicating the boom lowering direction.

12. In the construction machine described in claim 1, The aforementioned operating device is an electrically operated operating device that generates an electrical operating signal. A first electromagnetic proportional pressure reducing valve generates a pilot control pressure for raising the boom relative to the first directional control valve, A second electromagnetic proportional pressure reducing valve generates a pilot control pressure for lowering the boom relative to the first directional control valve, A construction machine further comprising a controller that, when the normal operation mode is selected, generates an electrical command signal based on the electrical operation signal and outputs the command signal to the corresponding electromagnetic proportional pressure reducing valves of the first and second electromagnetic proportional pressure reducing valves, thereby switching the first directional control valve; and when the down mode is selected, generates a command signal that is not based on the electrical operation signal and outputs the command signal to the second electromagnetic proportional pressure reducing valve, thereby switching the first directional control valve to the intermediate opening position in the boom lowering direction.

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