Construction machine

Abstract

The present invention comprises an additional control valve that connects a tank-side oil passage to each of a bottom-side oil passage via which the bottom side of a hydraulic cylinder for driving a work device is connected to a main control valve and a rod-side oil passage via which the rod side of the hydraulic cylinder is connected to the main control valve. The additional control valve is provided with: a variable relief valve that is provided between the rod-side oil passage and the tank-side oil passage, the variable relief valve performing control so that the pressure of the rod-side oil passage is equal to or less than a predetermined target pressure; and a check valve that allows only the flow of pressure oil from the tank-side oil passage to the bottom-side oil passage. When switched to a float mode in which work carried out using the dead weight of the work device is performed, the additional control valve cuts off a meter-in control valve of the main control valve, sets the target pressure of the variable relief valve to the minimum value of a predetermined pressure range, and discharges the pressure oil in the rod-side oil passage to a pressure oil tank. This makes it possible to improve operability during float work while suppressing any worsening of control performance and pressure loss.

Description

Construction machinery

[0001] The present invention relates to a construction machine.

[0002] In construction machinery such as hydraulic excavators that have an articulated front working mechanism, it is known to perform work by connecting the bottom-side oil chamber and rod-side oil chamber of a boom cylinder that raises and lowers the boom to a hydraulic oil tank, thereby allowing the front working mechanism to float.

[0003] For example, Patent Document 1 describes a system in which the position of a boom directional control valve during boom lowering is controlled between two regions, a first region and a second region, and in floating-state descent control, the supply of pressurized oil from the pump to the rod-side oil chamber is cut off while descent control is performed in the first region in response to the weight of the front working implement. Furthermore, during normal operation, boom lowering control in the air is performed in the first region, and boom lowering control after the bucket touches down is performed in the second region where the pump and rod oil chamber are connected, thereby ensuring a pressing force against the ground after touchdown. In other words, during normal operation, the directional control valve control during floating operation and boom lowering in the air is the same, so there is no sense of incongruity in operation depending on the operation mode, resulting in excellent operability.

[0004] Japanese Patent Application Laid-Open No. 2021-179079

[0005] However, when two different regions are incorporated into a single directional control valve, as in the above-described conventional technology, the spool stroke of the directional control valve must also be changed rapidly to change the opening more rapidly in response to changes in pilot pressure. Such a rapid change in the spool stroke increases the sensitivity of the opening change to the pilot pressure, potentially worsening the opening controllability. Furthermore, the spool stroke of the directional control valve is limited, making it difficult to increase the maximum opening. This reduces the maximum opening of the supply oil passage, potentially resulting in excessive pressure loss.

[0006] The present invention has been made in consideration of the above, and aims to provide a construction machine that can improve operability during floating operations while suppressing deterioration of control performance and pressure loss.

[0007] The present application includes a plurality of means for solving the above-mentioned problems, and one example thereof includes a machine body, a working device swingably attached to the machine body, a variable displacement hydraulic pump driven by a prime mover mounted on the machine body, a hydraulic cylinder that drives the working device with pressure oil discharged by the hydraulic pump, a main control valve that is provided between the hydraulic pump and the hydraulic cylinder and controls the flow rate and direction of pressure oil supplied from the hydraulic pump to the hydraulic cylinder, additional control valves that are provided in oil passages that respectively connect a bottom-side oil passage that connects the main control valve with a bottom side of the hydraulic cylinder, a rod-side oil passage that connects the main control valve with a rod side of the hydraulic cylinder, and a tank-side oil passage that returns pressure oil to a pressure oil tank, an operating device that outputs operation signals to operate the main control valve and the additional control valve, and a controller that controls the main control valve and the additional control valve based on the operation signals output from the operating device. the main control valve comprises at least one meter-in control valve that controls the flow rate of pressurized oil supplied from the hydraulic pump to the rod chamber of the hydraulic cylinder via the rod-side oil passage, and at least one meter-out control valve that controls the flow rate of pressurized oil returning from the bottom chamber of the hydraulic cylinder to the pressurized oil tank via the bottom-side oil passage and the tank-side oil passage; the additional control valve is provided between the rod-side oil passage and the tank-side oil passage, and comprises a variable relief valve that controls the pressure of the rod-side oil passage to be equal to or lower than a predetermined target pressure, and a check valve that allows only the flow of pressurized oil from the tank-side oil passage to the bottom-side oil passage; and when a work mode switching device that switches the work mode of the working device switches to a float mode in which the working device works by its own weight, the controller shuts off the meter-in control valve of the main control valve, sets the target pressure of the variable relief valve to a minimum value of a predetermined pressure range, and discharges the pressurized oil in the rod-side oil passage to the pressurized oil tank.

[0008] According to the present invention, it is possible to improve operability during floating operation while suppressing deterioration of control performance and pressure loss.

[0009] FIG. 1 is a side view schematically showing the overall configuration of a hydraulic excavator, which is an example of a work machine. FIG. 1 is a diagram showing a hydraulic circuit system of a hydraulic excavator according to a first embodiment, extracted together with related components. FIG. 1 is a diagram showing a configuration of a control system for controlling the operation of the entire hydraulic excavator including the hydraulic circuit system according to the first embodiment. FIG. 1 is a flowchart showing the content of control processing for an operate check valve constituting a boom assist valve. FIG. 1 is a flowchart showing the content of control processing for a variable relief valve constituting a boom assist valve. FIG. 2 is a flowchart showing the content of limit value setting processing for an operating pilot pressure related to a boom lowering operation of a first directional control valve for a boom cylinder. FIG. 3 is a flowchart showing the content of limit value setting processing for an operating pilot pressure related to a boom lowering operation of a second directional control valve for a boom cylinder. FIG. 4 is a diagram showing a calculation function unit that calculates a target value (target pilot pressure) of an operating pilot pressure for boom raising and boom lowering operations. FIG. 5 is a diagram showing a calculation function unit that calculates a target current value of a control current output to an electromagnetic proportional valve of a solenoid valve unit for a directional control valve related to a boom cylinder. FIG. 6 is a diagram showing an operation example 1. FIG. 7 is a diagram showing an operation example 2. FIG. 8 is a diagram showing an operation example 3. 1 is a diagram showing an outline of the configuration of a control system for controlling the operation of the entire hydraulic excavator including the hydraulic circuit system according to a second embodiment. 2 is a flowchart showing the content of control processing for a flow control valve connected to a first directional control valve for a boom cylinder and a bypass cut valve connected to a discharge oil passage of a first pump. 3 is a diagram showing a calculation function unit that calculates a target current value of a control current output to an electromagnetic proportional valve of a solenoid valve unit for a directional control valve associated with a boom cylinder.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, a hydraulic excavator will be described as an example of a work machine, but the present invention is not limited to this and can be applied to other work machines, for example, that have a work implement that is provided so as to be able to swing up and down.

[0011] First Embodiment A first embodiment of the present invention will be described with reference to FIGS.

[0012] FIG. 1 is a side view showing a schematic overall configuration of a hydraulic excavator, which is an example of a work machine according to this embodiment.

[0013] As shown in Fig. 1, the hydraulic excavator 100 includes a lower traveling structure 1, an upper rotating structure 2 that is rotatably mounted on the upper part of the lower traveling structure 1, and a front working mechanism 3 that is vertically swingable mounted in front of the upper rotating structure 2. The lower traveling structure 1 and the upper rotating structure 2 form the machine body, which is the basic configuration of the hydraulic excavator 100.

[0014] The undercarriage 1 is generally composed of a pair of left and right track frames 10, a pair of tracks 11 (crawlers) respectively wound around the pair of track frames 10, and traveling devices 12 which drive the pair of tracks 11. The traveling devices 12 are composed of a hydraulic traveling motor, a reduction mechanism, sprockets, etc. (not shown). Note that in Fig. 1, only one of the pair of left and right components of the undercarriage 1 is shown and referenced, and the other component is not shown.

[0015] The front working mechanism 3 is an articulated working mechanism formed by connecting multiple front members (a boom 4, an arm 5, and a bucket 6 (work implement)) that each rotate vertically. The base end of the boom 4 is supported at the front of the upper rotating body 2 so as to be rotatable in the vertical direction, one end of the arm 5 is supported at an end (tip) different from the base end of the boom 4 so as to be rotatable in the vertical direction, and the bucket 6 is supported at the other end of the arm 5 so as to be rotatable in the vertical direction. The front members of the front working mechanism 3 are driven to rotate by a boom cylinder 7, an arm cylinder 8, and a bucket cylinder 9, respectively. Note that, in this embodiment, a case where a bucket 6 is attached to the tip of the front working mechanism 3 will be described as an example, but other attachments may also be attached.

[0016] The upper rotating body 2 is installed so as to be able to rotate relative to the lower traveling body 1, and is driven to rotate by a hydraulic swing motor (not shown). A hydraulic circuit system is configured on the upper rotating body 2, and includes an engine (not shown) as a prime mover, various hydraulic pumps (see FIG. 2) driven by the engine, and a control valve 13 (see FIG. 2) that controls the direction and flow rate of the pressure oil (working oil) discharged from the hydraulic pump and supplied to hydraulic actuators such as hydraulic cylinders 7, 8, and 9 and hydraulic motors.

[0017] At the front of the upper rotating body 2, next to the support section for the front working implement 3, there is disposed a cab 2a where an operator sits and operates the hydraulic excavator 100. The cab 2a is equipped with an operation device 41 (see FIG. 3 ) that allows the operator to drive the front working implement 3, operate the undercarriage 1, and operate the upper rotating body 2, as well as a display device 43 (see FIG. 3 ) that presents various types of information to the operator and allows the operator to input various settings.

[0018] The operating device 41 outputs an operating signal according to the amount of operation by the operator, and is composed of an operating lever 41a that is tilted by the operator, and an operating amount sensor 41b that detects the amount of tilt of the operating lever 41a and outputs the result as an operating signal.

[0019] The operator inputs setting information into the display device 43, such as the setting of normal mode or boom assist mode (pushing mode or float mode) as the work mode for the front working implement 3, and the setting of the pushing force adjustment value for the pushing mode of the boom assist mode. In other words, the display device 43 functions as a work mode switching device.

[0020] Fig. 2 is a diagram illustrating the hydraulic circuit system of the hydraulic excavator according to this embodiment together with the related configuration. Fig. 3 is a diagram schematically illustrating the configuration of a control system that controls the operation of the entire hydraulic excavator, including the hydraulic circuit system according to this embodiment. Note that, for ease of illustration and explanation, Fig. 2 shows only a boom cylinder and its related configuration as representatives of the multiple hydraulic actuators, and illustration and explanation of the other hydraulic actuators are omitted as appropriate.

[0021] 2 , the hydraulic circuit system includes variable displacement hydraulic pumps (first pump 20 a, second pump 20 b, third pump 20 c) driven by a prime mover, a control valve 13 (main control valve) that controls the flow rate and direction of pressure oil supplied from the hydraulic pumps 20 a, 20 b, 20 c to hydraulic actuators such as hydraulic cylinders 7, 8, 9 and hydraulic motor 12, and a boom assist valve 50 (additional control valve) that branches oil passages (bottom oil passage 71, rod oil passage 72) connecting the control valve 13 to the hydraulic actuator (here, boom cylinder 7) toward the pressure oil tank (hydraulic oil tank). The bottom oil passage 71 of the boom cylinder 7 is also provided with an operate check valve 7 a (boom holding valve) that switches the flow of pressure oil from the rod oil passage 72 to the variable relief valve 51 depending on the control pressure from the control system. The tilt angles (pump discharge flow rates) of the first pump 20a, the second pump 20b, and the third pump 20c are controlled in accordance with control currents Ip1, Ip2, and Ip3 from the control system, respectively.

[0022] The control valve 13 includes a right traveling hydraulic motor directional control valve 21 a (Travel_R), a bucket cylinder directional control valve 22 (Bucket), an arm cylinder second directional control valve 24 b (Arm2), and a boom cylinder first directional control valve 23 a (Boom1), which are connected to a discharge oil passage from the first pump 20 a (Pump1), and a left traveling hydraulic motor directional control valve 21 b (Travel_R), which is connected to a discharge oil passage from the second pump 20 b. el_L), a first directional control valve for an attachment 26a (Att. 1), a first directional control valve for an arm cylinder 24a (Arm1), and a second directional control valve for a boom cylinder 23b (Boom2), and a second directional control valve for an attachment 26b (Att. 2), a third directional control valve for a boom cylinder 23c (Boom3), and a directional control valve for a swing hydraulic motor 25 (Swing) are connected to a discharge oil line from the third pump 20c.

[0023] Each of the directional control valves 21a, 21b, 22, 23a, 23b, 23c, 24a, 24b, 25, 26a, and 26b is driven in both directions by a pair of operating pilot pressures. For example, the first boom cylinder directional control valve 23a (Boom1) is driven by operating pilot pressures PI1a and PI1b, the second boom cylinder directional control valve 23b (Boom2) is driven by operating pilot pressures PI2a and PI2b, and the third boom cylinder directional control valve 23c (Boom3) is driven by operating pilot pressures PI3a and PI3b. Similarly, the first directional control valve 24a (Arm1) for the arm cylinder is driven by operating pilot pressures PI4a and PI4b, the second directional control valve 24b (Arm2) for the arm cylinder is driven by operating pilot pressures PI5a and PI5b, the directional control valve 22 (Bucket) for the bucket cylinder is driven by operating pilot pressures PI6a and PI6b, the directional control valve 25 (Swing) for the swing hydraulic motor is driven by operating pilot pressures PI7a and PI7b, and the right traveling hydraulic The motor directional control valve 21a (Travel_R) is driven by operating pilot pressures PI8a and PI8b, the left traveling hydraulic motor directional control valve 21b (Travel_L) is driven by operating pilot pressures PI9a and PI9b, the first attachment directional control valve 26a (Att. 1) is driven by operating pilot pressures PI10a and PI10b, and the second attachment directional control valve 26b (Att. 2) is driven by operating pilot pressures PI11a and PI11b.

[0024] Here, the operation of the hydraulic circuit related to the boom cylinder 7 that drives the boom 4 will be described in detail.

[0025] The first directional control valve 23a for the boom cylinder moves to the raising side position 23a1 upon input of the operating pilot pressure PI1a (boom 1 raising operating pilot pressure), and opens the throttle openings to the discharge oil passage of the first pump 20a and the bottom oil passage 71 of the boom cylinder 7, as well as the throttle openings to the rod oil passage 72 and the tank return oil passage (tank oil passage 73).

[0026] In addition, the first directional control valve 23a for the boom cylinder moves to the lowering side position 23a2 upon input of the operating pilot pressure PI1b (boom 1 lowering operating pilot pressure), and opens the throttle openings to the discharge oil passage of the first pump 20a and the rod oil passage 72 of the boom cylinder 7, as well as the throttle openings to the bottom oil passage 71 and the tank return oil passage (tank oil passage 73).

[0027] The second directional control valve 23b for the boom cylinder moves to the raising side position 23b1 upon input of the operating pilot pressure PI2a (boom 2 raising operating pilot pressure), and opens the throttle openings to the discharge oil passage of the second pump 20b and the bottom oil passage 71 of the boom cylinder 7, as well as the throttle openings to the rod oil passage 72 and the tank return oil passage (tank oil passage 73).

[0028] In addition, the second directional control valve 23b for the boom cylinder moves to the lowering side position 23b2 upon input of the operating pilot pressure PI2b (boom 2 lowering operating pilot pressure), and opens the throttle openings to the discharge oil passage of the second pump 20b and the rod oil passage 72 of the boom cylinder 7, as well as the throttle openings to the bottom oil passage 71 and the tank return oil passage (tank oil passage 73).

[0029] The third directional control valve 23c for the boom cylinder moves to the raising side position 23c1 upon input of the operating pilot pressure PI3a (boom 3 raising operating pilot pressure), and opens the throttle openings to the discharge oil passage of the third pump 20c and the bottom oil passage 71 of the boom cylinder 7, as well as the throttle openings to the rod oil passage 72 and the tank return oil passage (tank oil passage 73).

[0030] Furthermore, boom cylinder third directional control valve 23c moves to lowering position 23c2 upon input of operating pilot pressure PI3b (boom 3 lowering operating pilot pressure), opening the throttle openings of bottom oil passage 71 and tank return oil passage (tank oil passage 73) of boom cylinder 7, and also opening the throttle openings of bottom oil passage 71 and rod oil passage 72 via hollow oil passages and check valves, thereby supplying (regenerating) pressurized oil from bottom oil passage 71 to rod oil passage 72. This oil passage connecting bottom oil passage 71 and rod oil passage 72 via hollow oil passages and check valves is referred to as an internal regeneration oil passage. Note that in lowering position 23c2, boom cylinder third directional control valve 23c does not have a circuit connecting the discharge oil passage of third pump 20c to rod oil passage 72. This boom cylinder third directional control valve 23c, or its lowering position 23c2, constitutes a regeneration control valve.

[0031] The bottom oil passage 71 and rod oil passage 72 of the boom cylinder 7 of the control valve 13 are provided with overload relief valves 28a, 28b with make-up functions, a boom bottom pressure sensor 42a that detects the pressure in the bottom oil passage 71, and a boom rod pressure sensor 42b that detects the pressure in the rod oil passage 72. The overload relief valves 28a, 28b are provided to prevent damage to the hydraulic cylinders including the boom cylinder 7 and the structures of the front working implement 3 due to overload when an external force is applied to the boom cylinder 7.

[0032] The boom assist valve 50 (additional control valve) is provided by branching the bottom oil passage 71 and rod oil passage 72, which connect the control valve 13 and the boom cylinder 7, to the pressurized oil tank (hydraulic oil tank) side, and is equipped with a variable relief valve 51, a check valve 52, an operated check valve 53, and an electromagnetic switching valve 54.

[0033] The variable relief valve 51 is provided between the rod oil passage 72 and an oil passage (tank oil passage 73) connected to the pressure oil tank, and controls the pressure in the rod oil passage 72 to be equal to or lower than a predetermined relief pressure (target pressure), and is capable of adjusting the relief pressure according to the control current I21. The upper limit of the relief pressure that can be set in the variable relief valve 51 is a pressure that is equal to or lower than that of the overload relief valves 28a, 28b, and the lower limit is approximately 0 (zero) MPa.

[0034] The check valve 52 is provided between the bottom oil passage 71 and the tank oil passage 73, and allows only the flow of pressurized oil from the tank oil passage 73 to the bottom oil passage 71, while blocking the flow of pressurized oil from the bottom oil passage 71 to the tank oil passage 73.

[0035] The operated check valve 53 is provided between the rod oil passage 72 and the adjustable relief valve 51, and switches between allowing and not allowing the flow of pressure oil from the rod oil passage 72 to the adjustable relief valve 51 using a control pressure from the electromagnetic changeover valve 54. The electromagnetic changeover valve 54 adjusts the control pressure to the operated check valve 53 in accordance with a control current I22. When the position of the electromagnetic changeover valve 54 is switched to the permissive side (upper side in FIG. 2 ) in accordance with the control current I22, a pilot pressure Pi is sent to the operated check valve 53, and the operated check valve 53 is switched to a state that allows the flow of pressure oil from the rod oil passage 72 to the adjustable relief valve 51. When the position of the electromagnetic changeover valve 54 is switched to the blocking side (lower side in FIG. 2 ) in accordance with the control current I22, a tank pressure Dr (approximately 0 (zero) MPa) is sent to the operated check valve 53, and the operated check valve 53 is switched to a state that blocks the flow of pressure oil from the rod oil passage 72 to the adjustable relief valve 51.

[0036] As shown in Figure 3, the control system is composed of a controller 40, an electromagnetic valve unit 44, an operating device 41 and a display device 43 provided in the driver's cab 2a, a boom bottom pressure sensor 42a provided in the bottom oil passage 71, and a boom rod pressure sensor 42b provided in the rod oil passage 72.

[0037] The information (setting information) input and set by the operator on the display device 43 includes information related to the work mode of the front working implement 3. The work mode settings include normal mode and boom assist mode. When boom assist mode is set, either press mode or float mode is selectively set. For the press mode of the boom assist mode, a pressing force adjustment value is set as necessary. The pressing force setting value may be a preset standard value, a value arbitrarily input by the operator, or a value selected from a plurality of candidate values ​​prepared in advance.

[0038] Based on operation signals from the operating device 41, detection signals from the sensors 42a, 42b, setting information from the display device 43, etc., the controller 40 generates control signals I1a, I1b, ..., I12, ... to be output to the solenoid valve unit 44, control currents I21, I22 to be output to the variable relief valve 51 and solenoid switching valve 54 of the boom assist valve 50, and control currents Ip1, Ip2, Ip3 to be output to the hydraulic pumps 20a, 20b, 20c.

[0039] The solenoid valve unit 44 is made up of a plurality of reference solenoid valves respectively corresponding to the directional control valves 21a, 21b, 22, 23a, 23b, 23c, 24a, 24b, 25, 26a, 26b of the control valve 13. The proportional solenoid valves of the solenoid valve unit 44 are driven by control commands generated by the controller 40 based on the operation of the operating device 41 to generate operating pilot pressures PI1a, PI1b, ..., PI12, ..., and these operating pilot pressures are used to drive and control the directional control valves of the control valve 13, thereby operating the hydraulic actuators 7, 8, 9 and the like that make up the front working mechanism 3.

[0040] FIG. 4 is a flowchart showing the control process of the operate check valve that constitutes the boom assist valve.

[0041] In FIG. 4, the controller 40 first acquires setting information from the display device 43 and determines whether the boom assist function is enabled (step S41).

[0042] If the determination result in step S41 is YES, i.e., if the boom assist function is enabled (in the boom assist mode), the boom cylinder load Fc is then obtained (step S42). The boom cylinder load Fc can be calculated using the detection value p_b of the boom bottom pressure sensor 42a, the detection value p_r of the boom rod pressure sensor 42b, the bottom-side oil passage cross-sectional area Sb of the boom cylinder 7, and the rod-side oil passage cross-sectional area Sr of the boom cylinder 7, as follows: Fc = p_b × Sb - p_r × Sr. For example, if the boom cylinder load Fc satisfies (Fc > 0), this means that a load is being applied so as to support the falling boom 4, and if it satisfies (Fc ≦ 0), this means that a load is being applied so as to impede the force attempting to lift the boom 4 (for example, when an excavation reaction force is being applied, or when the bucket 6 is on the ground and the boom 4 is being jacked up by the front working implement 3).

[0043] Next, it is determined whether or not a boom-raising operation is being performed (step S43). In the determination of step S43, it is determined that a boom-raising operation is being performed if the boom-raising operation by the operation device 41 is ON (for example, if the boom-raising operation amount is 10% or more).

[0044] If the determination result in step S43 is YES, it is then determined whether or not an operation other than the boom-raising operation is being performed (step S44). In the determination in step S44, if any of the operations (e.g., arm operation, bucket operation, etc.) other than the boom-raising operation by the operating device 41 is ON (e.g., if the absolute value of any of the operation amounts is 10% or more), it is determined that an operation other than the boom-raising operation is being performed.

[0045] If the determination result in step S44 is YES, it is then determined whether the boom cylinder load Fc is greater than the first cylinder load threshold th1 and less than the second cylinder load threshold th2 (step S45). The first cylinder load threshold th1 is a threshold for determining whether the vehicle body is in a jacked-up state (a state in which the bucket 6 is pressed against the ground and one end of the undercarriage 1 is lifted off the ground). For example, if (th1<Fc) is satisfied, this indicates that the vehicle body is in a jacked-up state. The second cylinder load threshold th2 is a threshold for determining whether the bucket 6 is in a ground contact state (a state in which almost no load is applied to the boom cylinder 7). For example, if (Fc<th2) is satisfied, this indicates that the bucket 6 is in a ground contact state.

[0046] If the determination result in step S45 is YES, the controller 40 outputs the control current I22 to the electromagnetic switching valve 54 to open the operated check valve 53 (step S46), and the process returns to step S41.

[0047] Also, if the determination result in step S41 is NO, that is, if the boom assist function is set to disabled (in the case of normal mode), the controller 40 outputs a control current I22 (for example, a sufficiently small current value or a control current of 0 (zero)) that closes the operate check valve 53 to the electromagnetic switching valve 54 (step S47), and returns to the processing of step S41.

[0048] If the determination result in step S43 is NO, i.e., if it is determined that the boom-raising operation is not being performed, it is then determined whether or not an operation other than the boom-raising operation is being performed (step S48). In the determination in step S48, if any of the operations (e.g., arm operation, bucket operation, etc.) other than the boom-raising operation by the operating device 41 is ON (e.g., if the absolute value of any of the operation amounts is 10% or more), it is determined that an operation other than the boom-raising operation is being performed.

[0049] If the determination result in step S48 is YES, it is then determined whether or not the boom cylinder load Fc is greater than the first cylinder load threshold th1 (step S49).

[0050] If the determination result in step S49 is YES, the controller 40 outputs the control current I22 to the electromagnetic switching valve 54 to open the operated check valve 53 (step S46), and the process returns to step S41.

[0051] Furthermore, if any of the judgment results in steps S44, S45, S48, and S49 is NO, the controller 40 outputs a control current I22 (for example, a sufficiently small current value or a control current of 0 (zero)) to the electromagnetic switching valve 54 to close the operate check valve 53 (step S47), and returns to the processing of step S41.

[0052] FIG. 5 is a flowchart showing the control process of the variable relief valve that constitutes the boom assist valve.

[0053] In FIG. 5, the controller 40 first acquires setting information from the display device 43 and determines whether the boom assist function is enabled (step S51).

[0054] If the determination result in step S51 is YES, that is, if the boom assist function is enabled (in the case of the boom assist mode), it is then determined whether or not the float mode has been selected in the boom assist mode (step S52).

[0055] If the determination result in step S52 is YES, that is, if the float mode is selected, the target pressure Ps_tgt of the variable relief valve 51 is then set to the minimum value Ps_min (e.g., 0.5 MPa) of a predetermined settable pressure range (step S53), a control current I21 corresponding to the set target pressure Ps_tgt is calculated, and output to the variable relief valve 51 (step S57), and the process returns to step S51.

[0056] Furthermore, if the determination result in step S51 is NO, that is, if the boom assist function is set to disabled (in the case of normal mode), the controller 40 sets the target pressure Ps_tgt of the variable relief valve 51 to the maximum value Ps_max (e.g., 20 MPa) of a predetermined settable pressure range (step S56), calculates a control current I21 according to the set target pressure Ps_tgt, outputs it to the variable relief valve 51 (step S57), and returns to the processing of step S51.

[0057] Furthermore, if the determination result in step S52 is NO, that is, if the pressing mode has been selected, then the pressing force adjustment value α (e.g., 0 to 100%) is obtained from the display device 43 (step S54), the target pressure Ps_tgt of the variable relief valve 51 is set to a value corresponding to the pressing force adjustment value α (e.g., (Ps_max-Ps_min) x α) (step S55), the control current I21 corresponding to the set target pressure Ps_tgt is calculated and output to the variable relief valve 51 (step S57), and the process returns to step S51.

[0058] 6 is a flowchart showing the process of setting a limit value for the operating pilot pressure related to the boom lowering operation of the boom cylinder first directional control valve 23 a. The limit value setting process is a process of setting an upper limit value for the operating pilot pressure PI1 b (boom 1 lowering operating pilot pressure) related to the boom lowering operation of the boom cylinder first directional control valve 23 a.

[0059] In FIG. 6, the controller 40 first acquires setting information from the display device 43 and determines whether the boom assist function is enabled (step S61).

[0060] If the determination result in step S61 is YES, that is, if the boom assist function is enabled (in the case of the boom assist mode), it is then determined whether or not the float mode has been selected in the boom assist mode (step S62).

[0061] If the determination result in step S62 is YES, that is, if the float mode is selected, the limit value PI1b_max of the operating pilot pressure PI1b related to the boom lowering operation of the first directional control valve 23a for the boom cylinder is then set to the minimum value PI_min (e.g., 0 (zero) MPa) of a predetermined settable pressure range (step S63), and the process returns to step S61.

[0062] Furthermore, if the determination result in step S61 is NO, that is, if the boom assist function is disabled (in the case of the normal mode), the controller 40 sets the limit value PI1b_max of the operating pilot pressure PI1b related to the boom lowering operation of the boom cylinder first direction control valve 23a to the maximum value PI_max of a predetermined settable pressure range (step S65), and returns to the processing of step S61. Here, the maximum value PI_max is a value (e.g., 1.5 MPa, depending on the opening characteristics of the boom cylinder first direction control valve 23a) that allows a minimum amount of pressure oil to flow from the boom cylinder first direction control valve 23a to the rod oil passage 72.

[0063] Furthermore, if the determination result in step S62 is NO, that is, if the press mode is selected, the limit value PI1b_max of the operating pilot pressure PI1b related to the boom lowering operation of the first directional control valve 23a for the boom cylinder is set to the upper limit value PI_lim of the pilot system (for example, 4 MPa) (step S64), and the process returns to step S61.

[0064] 7 is a flowchart showing the contents of a limit value setting process for the operating pilot pressure related to the boom lowering operation of the boom cylinder second directional control valve 23b. The limit value setting process is a process for setting an upper limit value for the operating pilot pressure Pi2b (boom 2 lowering operating pilot pressure) related to the boom lowering operation of the boom cylinder second directional control valve 23b.

[0065] In FIG. 7, the controller 40 first acquires setting information from the display device 43 and determines whether the boom assist function is enabled (step S71).

[0066] If the determination result in step S71 is YES, that is, if the boom assist function is enabled (in the case of boom assist mode: float mode or press mode), the limit value PI2b_max of the operating pilot pressure PI2b related to the boom lowering operation of the second directional control valve 23b for the boom cylinder is set to the minimum value PI_min (for example, 0 (zero) MPa) of a predetermined settable pressure range (step S72), and the process returns to step S61.

[0067] Also, if the judgment result in step S71 is NO, that is, if the boom assist function is set to disabled (in normal mode), the limit value PI2b_max of the operating pilot pressure PI2b related to the boom lowering operation of the second directional control valve 23b for the boom cylinder is set to the upper limit value PI_lim of the pilot system (e.g., 4 MPa) (step S73), and the processing returns to step S71.

[0068] FIG. 8 is a diagram showing a calculation function unit that calculates a target value (target pilot pressure) of the operating pilot pressure in the boom-up and boom-down operations.

[0069] As shown in FIG. 8 , the calculation function unit of the controller 40 acquires the boom operation amount (e.g., expressed as a range from −100% to 100%, with larger values ​​in the 0% to 100% range indicating a larger raising operation amount and smaller values ​​in the −100% to 0% range indicating a larger lowering operation amount). The calculation function unit converts the boom-raising operation amount to an operating pilot pressure via a predetermined table calculation unit O7a, and converts the boom-lowering operation amount to an operating pilot pressure via a predetermined table calculation unit O7c after inverting the sign via an inversion unit O7b. Then, depending on the determination result (TRUE or RALSE) of a determination unit O7d, which determines whether the value of the boom operation amount is positive, the selection units O7e and O7f output the target value of the boom-raising pilot pressure or the boom-lowering target pilot pressure. Note that the target value of the boom-raising pilot pressure or the boom-lowering target pilot pressure not selected by the selection units O7e and O7f depending on the determination result of the determination unit O7d, is output as 0 (zero).

[0070] FIG. 9 is a diagram showing a calculation function unit that calculates a target current value of a control current output to an electromagnetic proportional valve of a solenoid valve unit for a directional control valve associated with a boom cylinder.

[0071] As shown in FIG. 9, for boom-raising operation, the calculation function unit of the controller 40 converts the target value (see FIG. 8) of the boom-raising pilot pressure (operation pilot pressure) into a current value via table calculation units O8a and O8b, and outputs these to the solenoid valve unit 44 as target current values ​​I1a_tgt, I2a_tgt, and I3a_tgt of the control currents related to the boom-raising operation of the directional control valves 23a, 23b, and 23c, respectively.

[0072] Furthermore, for boom lowering operations, the calculation function unit of the controller 40 converts the detection value of the boom bottom pressure sensor 42a into a limit value for the operating pilot pressure of the directional control valves 23a, 23b via a table calculation unit O8c and outputs the result to a minimum selection unit O8d. Specifically, the limit value is calculated so that the limit value for the boom bottom pressure in the air is 0 (zero), and the limit value for the boom bottom pressure when the bucket touches the ground is the maximum pressure of the pilot system (e.g., 4 MPa). Note that the table calculation unit O8c may have a hysteresis function in the calculation table to prevent control hunting due to pressure fluctuations in the boom bottom pressure.

[0073] The minimum selection unit O8d selects the minimum value from the target value of the boom lowering pilot pressure (operation pilot pressure) and the limit value of the target pilot pressure for boom lowering calculated by the table calculation unit O8c, and outputs it to the minimum selection units O8e and O8g.

[0074] The minimum selection unit O8e selects the minimum value from the output from the minimum selection unit O8d and the limit value PI1b_max (see Figure 6) of the operating pilot pressure PI1b related to the boom lowering operation of the first directional control valve 23a for the boom cylinder, converts it into a current value via a table calculation unit O8f, and outputs it to the solenoid valve unit 44 as the target current value I1b_tgt of the control current related to the boom lowering operation of the directional control valve 23a.

[0075] Similarly, the minimum selection unit O8g selects the minimum value from the output from the minimum selection unit O8d and the limit value PI2b_max (see Figure 7) of the operating pilot pressure PI2b related to the boom lowering operation of the second directional control valve 23b for the boom cylinder, converts it into a current value via the table calculation unit O8h, and outputs it to the solenoid valve unit 44 as the target current value I2b_tgt of the control current related to the boom lowering operation of the directional control valve 23b.

[0076] In addition, the target value of the boom lowering pilot pressure (operation pilot pressure) (see Figure 9) is converted into a current value via the table calculation unit O8i and output to the solenoid valve unit 44 as the target current value I3b_tgt of the control current related to the boom lowering operation of the directional control valve 23c.

[0077] In addition, the target value (see Figure 9) of the boom lowering pilot pressure (operation pilot pressure) is converted into a control pressure target value for the boom holding valve (operate check valve 7a) via table calculation unit O8j, and further converted into a current value via table calculation unit O8k, and output to the solenoid valve unit 44 as the target current value I12_tgt of the control current for the boom holding valve.

[0078] The operation of the present embodiment configured as above will now be described.

[0079] (Operation Example 1) First, as one operation example, a case will be described in which the operation device 41 is operated to lower the boom in the air, and the lowering operation is continued after the bucket touches the ground. Figure 10 is a diagram showing the state of Operation Example 1.

[0080] When the operation device 41 is operated to lower the boom in the air, the boom bottom pressure sensor value is high, and the boom 1 lowering and boom 2 lowering operation pilot pressures are limited to near 0 (zero) (see table calculation unit O8c in FIG. 9 ). At this time, the supply of pressure oil from the first pump 20a and second pump 20b to the rod oil passage 72 of the boom cylinder 7 is cut off, and there is no circuit from the discharge oil passage of the third pump 20c to the rod oil passage 72 of the boom cylinder 7, so pressure oil from the bottom oil passage 71 is supplied to the rod oil passage 72 of the boom cylinder 7 by the internal regeneration oil passage of the directional control valve 23c. Because the pressure oil at the boom bottom, which would normally be discharged to the tank through pressure loss, is regenerated without using the pump discharge oil, the boom lowering operation can be performed in an energy-saving manner.

[0081] As the boom 4 continues to be lowered and the bucket 6 touches the ground, the boom bottom pressure decreases, and therefore the limits on the boom 1 lowering and boom 2 lowering operation pilot pressures are removed (see table calculation unit O8c in FIG. 9). When the boom assist function is disabled (normal mode), the boom 1 lowering pilot pressure limit value and the boom 2 lowering pilot pressure limit value are the maximum pilot pressures (see FIGS. 6 and 7), so the boom lowering operation pilot pressure target values ​​are output for the boom 1 lowering operation pilot pressure and the boom 2 lowering operation pilot pressure (see FIG. 8), and pressure oil is supplied from the first pump 20a and the second pump 20b to the rod oil passage 72 of the boom cylinder 7. Furthermore, at this time, that is, when the work mode is switched to the normal mode and it is determined that the front working implement 3 (more specifically, the bucket 6) has touched the ground, the first boom cylinder directional control valve 23a and the second boom cylinder directional control valve 23b are moved to their lowering positions 23a2 and 23b2, respectively, in response to the output of an operation signal from the operating device 41 (i.e., the meter-in control valve of the main control valve is opened in response to the output of an operation signal from the operating device 41: see functional parts O8c, ..., O8h, etc. in FIG. 9 ). This presses the bucket 6 against the ground, and if the lowering operation continues, the front end of the crawler of the undercarriage 1 will rise up, resulting in a jacked-up state (see FIG. 11 ). In this way, after the bucket has touched the ground, a pressing force similar to that of a conventional hydraulic excavator is realized.

[0082] In contrast to the conventional technology in which pressurized oil from the tank is supplied by using the second lowering position of the boom directional control valve, this invention uses a directional control valve with three positions: neutral position, raised position, and lowered position, so that a large stroke amount for opening change can be taken, reducing pressure loss by widening the maximum opening, and providing excellent controllability by gradual opening change.

[0083] In boom float mode, when the bucket 6 is placed on the ground, the boom 1 lowering and boom 2 lowering operation pilot pressure is limited by the limit value PI_min (see FIGS. 6 and 7), so pump discharge oil is not supplied to the boom rod oil passage even after the bucket touches the ground. As a result, the bucket pressing force is limited to approximately the weight of the front working implement.

[0084] In the boom press mode, when the bucket 6 is placed on the ground, the boom 1 lowering and boom 2 lowering operation pilot pressures are limited by the limit value PI_lim (see FIGS. 6 and 7). As a result, a small amount of oil is discharged from the first pump 20a and the second pump 20b and supplied to the rod oil passage 72 of the boom cylinder 7. In addition, in the control flow for the operate check valve 53 (see FIG. 4), the process transitions to step S49 based on the operation conditions. Furthermore, since the cylinder load Fc is not high enough to jack up the vehicle, it is higher than the first cylinder load threshold th1, and the operate check valve 53 is opened. In addition, in the control flow for the variable relief valve (see FIG. 5), since the mode is the press mode, the process transitions to steps S54 and S55, and the variable relief valve 51 is set to a pressing force according to the pressing force adjustment parameter set on the display device 43. A small amount of oil discharged from first pump 20a and second pump 20b passes through operated check valve 53 and is maintained at a constant pressure by variable relief valve 51, allowing the operator to set the force with which bucket 6 is pressed against the ground, and a stable force can be maintained regardless of the magnitude of boom lowering operation. This means that even if a breaker or the like is attached instead of bucket 6, for example, the chisel pressing force can be adjusted using a parameter to a level that does not cause jacking up. In other words, this eliminates the need for the operator to adjust the chisel pressing force by appropriately adjusting boom operation, leading to reduced operator fatigue.

[0085] (Operation Example 2) Next, as another operation example, a case will be described in which the arm is pulled in the air by the operating device 41, the boom 4 is lowered by the operating device 41, and the arm is pulled even after the bucket toe touches the ground. Figure 11 is a diagram showing the state of operation example 2.

[0086] If the arm is pulled in the air using the operating device 41, the boom is lowered using the operating device 41, and the arm continues to be pulled even after the bucket toe touches the ground, and the boom assist function is disabled (normal mode), the operate check valve 53 does not open (see FIG. 4), and the bucket toe digs into the ground or the vehicle body is jacked up until the rod pressure of the boom cylinder 7 reaches the relief pressure of the overload relief valve 28b. This allows sufficient digging force to be exerted even when working on hard ground.

[0087] On the other hand, in boom float mode, the operate check valve 53 opens (see FIG. 4), and the variable relief valve set pressure Ps_tgt becomes the minimum value Ps_min (for example, 0 MPs) (see FIG. 5), so the pressurized oil in the rod oil passage 72 of the boom cylinder 7 is discharged to the pressurized oil tank at minimum pressure. At this time, the boom cylinder 7 moves almost freely in the boom-raising direction due to the reaction force from the ground, and only a force equivalent to the weight of the front working implement 3 acts on the bucket tip. This makes it possible to perform work such as smoothing the ground without operating the boom to raise it, making it easy to perform tasks such as scooping concrete rubble on a steel plate, for example.

[0088] Furthermore, when the bucket toe is in contact with the ground and the arm is operated while the boom is lowered, the bottom oil passage 71 of the boom cylinder 7 is connected to the rod oil passage 72 via the internal regeneration oil passage of the directional control valve 23c. Therefore, when the free boom cylinder 7 moves downward due to arm operation in float mode (for example, when the arm is pushed), the pressurized oil in the bottom oil passage 71 of the boom cylinder 7 flows back to the rod oil passage 72, enabling smooth operation.

[0089] Furthermore, in the pressing mode, the variable relief valve set pressure can be changed in accordance with the operator's pressing force adjustment parameter (see FIG. 7), and when pressurized oil is discharged from the rod oil passage 72 of the boom cylinder 7 to the variable relief valve 51, the boom cylinder rod pressure can be maintained at the set pressure set by the controller 40. This makes it possible to adjust the pressing force of the bucket toe, making it possible to easily perform light excavation work such as dredging, for example.

[0090] In the above-described tracking operation, it is necessary to supply hydraulic oil to the bottom side of the boom cylinder 7, and cavitation is prevented by having the check valve 52 of the boom assist valve 50 supply hydraulic oil to the bottom oil passage 71 of the boom cylinder 7 through the tank return oil passage (tank oil passage 73). That is, because the size of the overload relief valve 28b with makeup function is limited, it is conceivable that the valve supply capacity will be insufficient if only the makeup flow rate from the overload relief valve 28b is supplied, but in the present invention, a sufficient supply of hydraulic oil can be achieved by the externally provided check valve 52.

[0091] (Operation Example 3) Next, as another operation example, a case where an operation is performed during jacking up will be described.

[0092] In float mode, if the operating device 41 is used to perform an operation such as lowering the boom or retracting the arm while the vehicle is jacked up, the operate check valve 53 does not open (see FIG. 4 ). On the other hand, once the jacked-up state is released and the bucket 6 is pressed against the ground, the operate check valve 53 opens according to the work mode. If the operate check valve 53 were opened while the vehicle was being jacked up and the set pressure of the variable relief valve was low, the pressurized oil on the rod side of the boom cylinder 7 would be suddenly discharged into the pressurized oil tank, which could cause the vehicle body to suddenly fall from the jacked-up state. In contrast, in the present invention, the jacked-up state can be maintained, allowing work to be performed safely.

[0093] (Operation Example 4) Next, an example of a case where the boom is raised in the air in the float mode will be described.

[0094] When the boom is raised using the operating device 41 and then stopped, low boom rod pressure can result in poor stopping performance. In contrast, in the present invention, when the boom is raised alone, the process transitions from step S44 to step S47 in Figure 4, and the operate check valve 53 is closed. As a result, the boom rod pressure rises to the maximum overload relief pressure, ensuring the ability to stop the boom 4.

[0095] (Operation Example 5) Next, an example will be described in which the operation device 41 is used to perform fine boom-up operation and arm-pulling operation in the air in the float mode, and the toe of the bucket touches the ground.

[0096] When the operation device 41 is used to perform fine boom-raising operations and arm-pulling operations in the air in float mode and the bucket 6 touches the ground, the processing of step S45 in Figure 4 determines that the boom cylinder load Fc is lower than the load for airborne operation, and the operate check valve 53 opens. As a result, even when the arm 5 continues to be pulled, the pressurized oil in the rod chamber of the boom cylinder 7 is discharged from the variable relief valve 51, and hydraulic oil is supplied to the bottom chamber of the boom cylinder 7 through the tank return oil line (tank oil line 73) by the check valve 52 of the boom assist valve 50, thereby achieving a float state.

[0097] (Operation Example 6) Next, an example will be described in which the operation device 41 is used to perform boom raising and arm retraction operations in the air in the float mode, and then the boom is stopped.

[0098] If the boom is raised and the arm is pulled in the air in float mode and then the boom is stopped, the boom cylinder load is equal to or greater than the second cylinder load threshold th2, so the process transitions from step S45 to step S47 in Figure 4, and the operate check valve 53 is closed. As a result, the boom rod pressure rises to the maximum overload relief pressure, ensuring the ability to stop the boom 4.

[0099] (Effects of the First Embodiment) The effects of the present embodiment configured as above will be described.

[0100] In this embodiment, the control of aerial boom lowering remains the same between normal mode and float mode, minimizing discomfort in operability. Furthermore, by using a typical three-position directional control valve, it is possible to achieve the same control performance and pressure loss as in the past. Furthermore, by providing a variable relief valve 51 and a push mode that allows for adjustable push force separately from the float mode, it is possible to reduce the workload on the operator, for example, by maintaining the chisel push force during breaker operation or performing light excavation during dredging work.

[0101] Furthermore, by using the check valve 52 in the boom assist valve 50 to perform makeup on the boom cylinder bottom-side oil passage during a tracking operation, the risk of cavitation occurring can be minimized.

[0102] Furthermore, the boom assist valve 50 of this embodiment can be easily applied to the system of a normal hydraulic excavator that has a meter-in cut function when the aerial boom is lowered. That is, a normal hydraulic excavator can be changed as needed between a hydraulic excavator that has a float mode and a push mode simply by adding or removing the boom assist valve 50 and adding or removing the controller I / O and control, facilitating option support and retrofitting as a later addition to an existing hydraulic excavator.

[0103] In this embodiment, an operated check valve 53 is provided upstream of the variable relief valve 51. If the maximum settable pressure of the variable relief valve is sufficiently high, the operated check valve 53 is not necessary. However, since it is generally difficult to manufacture a variable relief valve capable of adjusting the relief pressure up to the system upper limit pressure, there is a risk of a decrease in the overload relief pressure in the boom rod oil passage. In this case, there is a risk of a decrease in vehicle performance, such as the boom being lifted by external forces when excavating hard ground. According to this embodiment, in normal mode, closing the operated check valve 53 blocks the oil passage leading to the variable relief valve 51, preventing a decrease in the overload relief pressure. This allows the vehicle performance to be maintained as it was previously. Furthermore, because an operated check valve generally has superior leak performance compared to a relief valve, it also has the effect of minimizing the amount of boom movement due to leaks when not being operated.

[0104] Second Embodiment A second embodiment of the present invention will be described with reference to FIGS.

[0105] In this embodiment, each hydraulic actuator is driven by two hydraulic pumps, a first pump and a second pump. In this embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

[0106] Fig. 12 is a diagram illustrating the hydraulic circuit system of the hydraulic excavator according to this embodiment together with the related configuration. Fig. 13 is a diagram schematically illustrating the configuration of a control system that controls the operation of the entire hydraulic excavator including the hydraulic circuit system according to this embodiment. Note that, for ease of illustration and explanation, Fig. 12 shows only the boom cylinder and its related configuration as a representative of the multiple hydraulic actuators, and illustration and explanation of the other hydraulic actuators are omitted as appropriate.

[0107] 12 , the hydraulic circuit system includes variable displacement hydraulic pumps (first pump 20 a, second pump 20 b) driven by a prime mover, a control valve 13A (main control valve) that controls the flow rate and direction of pressure oil supplied from the hydraulic pumps 20 a, 20 b, and 20 c to hydraulic actuators such as hydraulic cylinders 7, 8, and 9 and hydraulic motor 12, and a boom assist valve 50 (additional control valve) that branches oil passages (bottom oil passage 71 and rod oil passage 72) connecting the control valve 13A to the hydraulic actuator (here, boom cylinder 7) toward the pressure oil tank (hydraulic oil tank). The bottom oil passage 71 of the boom cylinder 7 is provided with an operate check valve 7 a (boom holding valve) that switches the flow of pressure oil from the rod oil passage 72 to the variable relief valve 51 depending on the control pressure from the control system. The tilt angles (pump discharge flow rates) of the first pump 20 a and the second pump 20 b are controlled according to control currents Ip1 and Ip2 from the control system, respectively.

[0108] The control valve 13A includes a right traveling hydraulic motor directional control valve 21 a (Travel_R), a bucket cylinder directional control valve 22 (Bucket), an arm cylinder second directional control valve 24 b (Arm2), and a boom cylinder first directional control valve 23 a (Boom1), which are connected to a discharge oil passage from the first pump 20 a (Pump1), and a left traveling hydraulic motor directional control valve 21 b (Travel_L), an attachment first directional control valve 26 a (Att.1), an arm cylinder first directional control valve 24 a (Arm1), a boom cylinder second directional control valve 23 b (Boom2), and a swing hydraulic motor directional control valve 25 (Swing), which are connected to a discharge oil passage from the second pump 20 b.

[0109] A flow control valve 60 is provided between the discharge oil passage of the first pump 20a and the first directional control valve 23a (Boom1) for the boom cylinder, and is driven by an operating pilot pressure IP60. The flow control valve 60 is configured to reduce its opening as the operating pilot pressure PI60 increases.

[0110] The lowering side position 23a2 of the first directional control valve 23a for the boom cylinder (boom 1 directional control valve) is provided with a meter-in oil passage that leads from the discharge oil passage of the first pump 20a to the rod oil passage 72 of the boom cylinder 7, a meter-out oil passage that leads from the bottom oil passage 71 to the tank return oil passage (tank oil passage), and a regeneration oil passage that leads from the bottom oil passage 71 to the rod oil passage 72 through a check valve.

[0111] Similarly to the first boom cylinder direction control valve 23a, a meter-in oil passage and a meter-out oil passage are provided at the lowering side position 23b2 of the second boom cylinder direction control valve 23b (boom two-way control valve).

[0112] A bypass cut valve 61 is provided at the most downstream of the discharge oil passage of the first pump 20a and is driven by an operating pilot pressure IP61. The bypass cut valve 61 is configured to reduce its opening as the operating pilot pressure PI61 increases.

[0113] As shown in Figure 13, the control system is composed of a controller 40A, an electromagnetic valve unit 44A, an operating device 41 and a display device 43 provided in the driver's cab 2a, a boom bottom pressure sensor 42a provided in the bottom oil passage 71, and a boom rod pressure sensor 42b provided in the rod oil passage 72.

[0114] Based on operation signals from the operating device 41, detection signals from the sensors 42a, 42b, setting information from the display device 43, etc., the controller 40A generates control signals I1a, I1b, ..., I12, IP60, IP61 ... to be output to the solenoid valve unit 44A, control currents I21, I22 to be output to the variable relief valve 51 and solenoid switching valve 54 of the boom assist valve 50, and control currents Ip1, Ip2 to be output to the hydraulic pumps 20a, 20b.

[0115] The solenoid valve unit 44A is made up of a plurality of reference solenoid valves corresponding respectively to the directional control valves 21a, 21b, 22, 23a, 23b, 24a, 24b, 25, and 26a of the control valve 13A, and the proportional solenoid valves of the solenoid valve unit 44 are driven by control commands generated by the controller 40A based on the operation of the operating device 41 to generate operating pilot pressures PI1a, PI1b, ..., PI12, IP60, IP61 .... These operating pilot pressures are used to drive and control the directional control valves of the control valve 13A, thereby operating the hydraulic actuators 7, 8, 9, etc. that make up the front working mechanism 3.

[0116] FIG. 14 is a flowchart showing the control process for the flow control valve connected to the first directional control valve for the boom cylinder and the bypass cut valve connected to the discharge oil passage of the first pump.

[0117] In FIG. 14, the controller 40A first acquires setting information from the display device 43 and determines whether the boom assist function is enabled (step S141).

[0118] If the determination result in step S141 is YES, that is, if the boom assist function is enabled (in the case of the boom assist mode), it is then determined whether or not the float mode has been selected in the boom assist mode (step S142).

[0119] If the determination result in step S142 is YES, that is, if the float mode is selected, the control pressure lower limit value PI60_min of the flow control valve 60 is set to the upper limit value PI_max of the pilot system (e.g., 4 MPa), and the control pressure upper limit value PI61_max of the bypass cut valve 61 is set to PI_min (e.g., 0 (zero) MPa) (step S143), and the process returns to step S141.

[0120] Furthermore, if the determination result in step S141 is NO, that is, if the boom assist function is disabled (in the case of normal mode), the controller 40A sets the control pressure lower limit value PI60_min of the flow control valve 60 to PI_min (e.g., 0 (zero) MPa) and sets the control pressure upper limit value PI61_max of the bypass cut valve 61 to the upper limit value PI_max of the pilot system (e.g., 4 MPa) (step S145), and returns to the processing of step S141.

[0121] If the determination result in step S142 is NO, that is, if the press mode is selected, the control pressure lower limit value PI60_min of the flow control valve 60 is set to the first limit value PI_lim1, and the control pressure upper limit value PI61_max of the bypass cut valve 61 is set to the second limit value PI_lim2 (step S144), and the process returns to step S141. Here, the limit values ​​PI_lim1 and PI_lim2 are values ​​that allow a minimum amount of pressure oil to flow from the discharge oil passage of the first pump 20a to the rod oil passage 72.

[0122] FIG. 15 is a diagram showing a calculation function unit that calculates a target current value of a control current output to an electromagnetic proportional valve of a solenoid valve unit for a directional control valve associated with a boom cylinder.

[0123] As shown in FIG. 15, for boom-raising operations, the calculation function unit of the controller 40A converts the target value (see FIG. 8) of the boom-raising pilot pressure (operation pilot pressure) into a current value via table calculation units O14a and O14b, and outputs these to the solenoid valve unit 44A as target current values ​​I1a_tgt and I2a_tgt of the control currents related to the boom-raising operations of the directional control valves 23a and 23b, respectively.

[0124] Furthermore, for the boom lowering operation, the calculation function unit of the controller 40A converts the target value (see Figure 8) of the boom lowering pilot pressure (operation pilot pressure) into a current value via the table calculation unit O14c, and outputs it to the solenoid valve unit 44A as the target current value I1b_tgt of the control current related to the boom lowering operation of the directional control valve 23a.

[0125] The table calculation unit O14d converts the detection value of the boom bottom pressure sensor 42a into the control pressure of the flow control valve 60 and outputs it to the minimum selection unit O14e. Specifically, the control pressure is calculated so that the control pressure is 0 (zero) when the boom bottom pressure is low and a predetermined value when the boom bottom pressure is high. Note that the table calculation unit O14d may have a hysteresis function in its calculation table.

[0126] The minimum selection unit O14e selects the minimum value from the target value of the boom lowering pilot pressure (operation pilot pressure) and the control pressure of the flow control valve 60 calculated by the table calculation unit O14d, and outputs it to the maximum selection unit O14f.

[0127] The maximum selection unit O14f selects the maximum value from the output from the minimum selection unit O14e and the control pressure lower limit value PI60_min (see Figure 14) of the flow control valve 60, converts it into a current value via the table calculation unit O14g, and outputs it to the solenoid valve unit 44A as the target current value I60_tgt of the control pressure of the flow control valve 60.

[0128] The table calculation unit O14h also converts the detection value of the boom bottom pressure sensor 42a into a limit value for the operating pilot pressure of the directional control valve 23b and outputs it to the minimum selection unit O14i. Specifically, the limit value is calculated so that the limit value for the boom bottom pressure in the air is 0 (zero) and the limit value for the boom bottom pressure when the bucket touches the ground is the maximum pressure of the pilot system (for example, 4 MPa). Note that the table calculation unit O14i may have a hysteresis function in the calculation table to prevent control hunting due to pressure fluctuations in the boom bottom pressure.

[0129] The minimum selection unit O14i selects the minimum value from the target value of the boom lowering pilot pressure (operation pilot pressure) and the limit value of the target pilot pressure for boom lowering calculated by the table calculation unit O14h, and outputs it to the minimum selection units O14j and O14l.

[0130] The minimum selection unit O14j selects the minimum value from the output from the minimum selection unit O14i and the limit value PI2b_max (see Figure 7) of the operating pilot pressure PI2b related to the boom lowering operation of the second directional control valve 23b for the boom cylinder, converts it into a current value via the table calculation unit O14k, and outputs it to the solenoid valve unit 44A as the target current value I2b_tgt of the control current related to the boom lowering operation of the directional control valve 23b.

[0131] The minimum selection unit O14l selects the minimum value from the output from the minimum selection unit O14i and the control pressure upper limit value PI61_max (see Figure 14) of the bypass cut valve 61, converts it into a current value via the table calculation unit O14m, and outputs it to the solenoid valve unit 44A as the target current value I61_tgt of the control pressure of the bypass cut valve 61.

[0132] In addition, the target value of the boom lowering pilot pressure (operating pilot pressure) (see Figure 8) is converted into a control pressure target value for the boom holding valve (operate check valve 7a) via table calculation unit O14n, and further converted into a current value via table calculation unit O14o, and output to solenoid valve unit 44A as target current value I12_tgt for the control current related to the boom holding valve.

[0133] The other configurations are the same as those of the first embodiment.

[0134] The present embodiment configured as above can also achieve the same effects as the first embodiment.

[0135] Furthermore, for example, compared to the first embodiment, a hydraulic excavator, which is a construction machine, can be driven with a smaller number of hydraulic pumps (main pumps), which is advantageous in terms of mountability and cost.

[0136] <Others> The present invention is not limited to the above-described embodiments, and includes various modifications within the scope of the gist thereof. Furthermore, for example, the present invention is not limited to those having all of the configurations described in the above-described embodiments, and includes those in which some of the configurations are omitted. Furthermore, it is possible to add or replace some of the configurations according to one embodiment with the configurations according to another embodiment.

[0137] For example, in the present embodiment, a hydraulic excavator 100 equipped with a front working mechanism 3 is shown as an example of a construction machine, and an example has been described in which the boom cylinder 7 that drives the boom 4 is controlled in accordance with the work mode. However, the present invention is not limited to this, and for example, a configuration may be adopted in which a blade is provided on the undercarriage 1 as a working mechanism, and a hydraulic actuator (hydraulic cylinder) that drives the blade is controlled in accordance with the work mode.

[0138] Furthermore, the components of the control device, as well as the functions and execution processes of the components, may be partially or entirely implemented by hardware (e.g., by designing logic for executing each function using an integrated circuit). The components of the control device may also be implemented as a program (software) that is read and executed by an arithmetic processing unit (e.g., a CPU) to implement the functions of the control device. Information related to the program may be stored in, for example, a semiconductor memory (flash memory, SSD, etc.), a magnetic storage device (hard disk drive, etc.), or a recording medium (magnetic disk, optical disk, etc.).

[0139] DESCRIPTION OF SYMBOLS 1...undercarriage, 2...upper revolving body, 2a...operator cab, 3...front working device, 4...boom, 5...arm, 6...bucket, 7...boom cylinder, 7a...operate check valve, 8...arm cylinder, 9...bucket cylinder, 10...track frame, 11...crawler track, 12...traveling device, 13, 13A...control valve, 20a...first pump, 20b...second pump, 20c...third pump, 21a...direction control valve for right traveling hydraulic motor, 21b...direction control valve for left traveling hydraulic motor, 22...direction control valve for bucket cylinder, 23a...first direction control valve for boom cylinder, 23b...second direction control valve for boom cylinder, 23c...third direction control valve for boom cylinder, 24a...first direction control valve for arm cylinder, 24b...arm Second directional control valve for cylinder, 25...directional control valve for swing hydraulic motor, 26a...first directional control valve for attachment, 26b...second directional control valve for attachment, 28a...overload relief valve, 28b...overload relief valve, 40, 40A...controller, 41...operation device, 41a...operation lever, 41b...operation amount sensor, 42a...boom bottom pressure sensor, 42b...boom rod pressure sensor, 43...display device, 44, 44A...solenoid valve unit, 50...boom assist valve, 51...adjustable relief valve, 52...check valve, 53...operated check valve, 54...solenoid switching valve, 60...flow rate control valve, 61...bypass cut valve, 71...bottom oil passage, 72...rod oil passage, 73...tank oil passage, 100...hydraulic excavator

Claims

a variable displacement hydraulic pump driven by a prime mover mounted on the machine body; a hydraulic cylinder that drives the working device with pressure oil discharged by the hydraulic pump; a main control valve that is provided between the hydraulic pump and the hydraulic cylinder and controls the flow rate and direction of pressure oil supplied from the hydraulic pump to the hydraulic cylinder; additional control valves that are provided in oil passages that respectively connect a bottom-side oil passage that connects the main control valve to the bottom side of the hydraulic cylinder, a rod-side oil passage that connects the main control valve to the rod side of the hydraulic cylinder, and a tank-side oil passage that returns pressure oil to a pressure oil tank; an operating device that outputs operation signals to operate the main control valve and the additional control valve; a controller that controls the main control valve and the additional control valve based on the operation signals output from the operating device; and the main control valve is at least one meter-in control valve that controls the flow rate of pressure oil supplied from the hydraulic pump to the rod chamber of the hydraulic cylinder via the rod-side oil passage. at least one meter-out control valve that controls the flow rate of pressurized oil returning from a bottom chamber of the hydraulic cylinder to the pressurized oil tank via the bottom-side oil line and the tank-side oil line, wherein the additional control valve comprises: a variable relief valve that is provided between the rod-side oil line and the tank-side oil line and that controls the pressure of the rod-side oil line to be equal to or lower than a predetermined target pressure; and a check valve that allows only the flow of pressurized oil from the tank-side oil line to the bottom-side oil line, wherein when a work mode switching device that switches the work mode of the work device switches to a float mode in which work is performed by the work device's own weight, the controller shuts off the meter-in control valve of the main control valve and sets the target pressure of the variable relief valve to a minimum value of a predetermined pressure range, and discharges the pressurized oil in the rod-side oil line to the pressurized oil tank.

2. A construction machine according to claim 1, wherein the controller, when the work mode switching device is switched to a pushing mode in which the work device is pressed against an object to perform work, determines whether the work device is grounded or not, and when it determines that the work device is not grounded, closes the meter-in control valve of the main control valve, when the work mode switching device is switched to a normal mode and it determines that the work device is grounded, opens the meter-in control valve of the main control valve in response to the output of an operation signal from the operating device, and when the work mode switching device is switched to a pushing mode and it determines that the work device is grounded, reduces the opening of the meter-in control valve of the main control valve compared to the opening in the normal mode.

3. A construction machine according to claim 1, wherein the working device attached to the machine body in a swingable manner is a multi-joint front working device in which a boom, an arm, and a working implement are rotatably connected to one another, and the hydraulic cylinder that drives the working device is a boom hydraulic cylinder that drives the boom.

4. A construction machine according to claim 1, further comprising an operate check valve provided between the rod-side oil passage and the variable relief valve, which switches whether or not pressurized oil is allowed to flow from the rod-side oil passage to the variable relief valve, and when the controller and the work mode switching device have switched to float mode and it is determined that the work device is grounded, the operate check valve is closed to cut off the flow of pressurized oil from the rod-side oil passage to the variable relief valve.

5. A construction machine according to claim 1, wherein the main control valve is provided with at least one regeneration control valve that controls the flow rate of pressurized oil flowing from the bottom-side oil passage to the rod-side oil passage; and when a work mode switching device that switches the work mode of the work implement switches to a float mode in which the work implement works under its own weight, the controller shuts off the meter-in control valve of the main control valve and sets the target pressure of the variable relief valve to the minimum value of a predetermined pressure range, thereby connecting the rod chamber of the hydraulic cylinder to the pressurized oil tank; and the regeneration control valve is switched to allow the flow of pressurized oil from the bottom-side oil passage to the rod-side oil passage based on an operation signal output from the operation device.

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