Hydraulic control system in working machine

Abstract

To reduce cost in performing back pressure reduction control when a hammer or the like is mounted as a work tool.SOLUTION: A hydraulic control system is provided with: an unloading oil passage 12 which is formed so as to branch off of a second actuator oil passage 7 serving as an oil discharge passage in the case that a work tool 1 is a single-acting actuator, and leads to an oil tank 4; and a pilot check valve 14 which opens the unloading oil passage 12 when a signal pressure is supplied, wherein a signal pressure output region X2 and a signal pressure non-output region X1 are provided at an operating position of a control valve 5 that performs oil supply and discharge control with respect to the work tool 1, the control valve 5 is positioned in the signal output region X2 when the work tool 1 is the single-acting actuator and requires back pressure reduction control, and the control valve is positioned in the signal pressure non-output region X1 when the work tool 1 does not require the back pressure reduction control.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the technical field of hydraulic control systems for work machines such as hydraulic excavators. [Background technology]

[0002] In general, among working machines such as hydraulic excavators, there are some that are configured to be able to selectively attach a plurality of work tools. For example, in a hydraulic excavator, instead of a bucket that is generally used as a work tool, various work tools such as a hydraulically operated breaker, crusher, grapple, etc. can be detachably attached. When providing a hydraulic circuit for a work tool hydraulic actuator that drives such a work tool in a hydraulic circuit of a work machine, it is required that the circuit be shared by a plurality of work tool hydraulic actuators to save space and reduce costs, while it is also required that the circuit be capable of accommodating the operating pressure and unique control required for each individual work tool hydraulic actuator. In view of this, a conventional technique has been known in which an electromagnetic relief valve is connected to a first and second actuator oil passage that connects a work tool hydraulic actuator and a control valve (a valve that controls the supply and discharge of oil to the work tool hydraulic actuator), and the relief pressure of the electromagnetic relief valve is changed according to the type of work tool, so that the pressure of the first and second actuator oil passages can correspond to the operating pressure of each work tool hydraulic actuator. In this case, a technique is known in which first and second relief oil passages (first and second bypass oil passages) are provided from the first and second actuator oil passages (first and second pipes) to an oil tank, respectively, and an electromagnetic relief valve is provided in each of these first and second relief oil passages (see, for example, Patent Document 1), or a technique is known in which a shuttle valve is provided to select the high-pressure side of the first and second actuator oil passages, and a shared electromagnetic relief valve is provided in a relief oil passage from the outlet side of the shuttle valve to the oil tank (see, for example, FIG. 2 of Patent Document 2). Meanwhile, hydraulic actuators for work tools can be divided into those in which the oil supply direction to the work tool is unidirectional (single-acting actuators) and those in which the oil supply direction is bidirectional (double-acting actuators). Furthermore, among single-acting actuators, for example, hammers (breakers) used to break concrete, rocks, etc., high back pressure can weaken the driving force and reduce impact performance, so some require a circuit that performs special control to reduce back pressure. For this reason, in the device of Patent Document 1, when the hydraulic actuator for a work tool is a single-acting actuator that requires a reduction in back pressure, the relief pressure of the electromagnetic relief valve connected to the second actuator oil passage, which is the outflow passage of the first and second actuator oil passages, is reduced to a predetermined value, thereby reducing the back pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-53814 A [Patent Document 2] JP 2023-64458 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, as in Patent Document 1, when performing backpressure reduction control of a hammer or the like using electromagnetic relief valves provided to make the pressures of the first and second actuator oil passages correspond to the operating pressures of the hydraulic actuators for the individual work tools, the electromagnetic relief valves must have an unloading function that can instantly reduce the relief pressure to about the tank pressure, but electromagnetic relief valves with such an unloading function are expensive and hinder cost reduction. Also, as in Patent Document 2, in a case where a shared electromagnetic relief valve is connected to the first and second actuator oil passages, the operating pressure of the hydraulic actuators for the work tools cannot be secured if the relief pressure of the shared electromagnetic relief valve is reduced, so the shared electromagnetic relief valve cannot be used for backpressure reduction control, and therefore electromagnetic relief valves must be provided individually in the first and second actuator oil passages, and one of the electromagnetic relief valves must have an unloading function, which causes an increase in costs, and this is the problem to be solved by the present invention. [Means for solving the problem]

[0005] The present invention has been made in view of the above-mentioned circumstances and with the objective of solving these problems. The invention of claim 1 relates to a hydraulic control system for a work machine comprising: a hydraulic actuator for a work tool that is selectively attached to a work machine and driven by pressure oil supplied from a hydraulic pump; a control valve that operates based on the operation of a work tool operating implement to control the supply and discharge of oil to and from the hydraulic actuator for the work tool; a control device that controls the operation of the control valve; and first and second actuator oil passages that connect the control valve and the hydraulic actuator for the work tool, wherein the hydraulic actuator for the work tool comprises a single-acting actuator that uses the first actuator oil passage as an oil inflow passage and the second actuator oil passage as an oil outflow passage, and a control device that uses the first and second actuator oil passages as oil inflow passages and oil outflow passages. and a double-acting actuator used in a work machine, wherein the hydraulic control system is provided with an unloaded oil passage branched off from the second actuator oil passage to an oil tank, and a pilot check valve which closes the unloaded oil passage when no signal pressure is supplied and opens the unloaded oil passage when signal pressure is supplied, and the control valve has an operating position which has a signal output region where signal pressure is output to the pilot check valve and a signal non-output region where no signal pressure is output, while the control device positions the control valve in the signal output region when the work tool hydraulic actuator is a single-acting actuator and requires backpressure reduction control, and positions the control valve in the signal non-output region when the work tool hydraulic actuator does not require backpressure reduction control. The invention of claim 2 is a hydraulic control system for a work machine, characterized in that, in claim 1, the control of the oil supply from the control valve to the single-acting actuator can be selectively performed between constant flow control, which supplies a constant flow rate to the single-acting actuator, and variable flow control, which increases or decreases the flow rate supplied to the single-acting actuator depending on the amount of operation of a work tool operating device, and the control device positions the control valve in a signal output region when performing constant flow control of the single-acting actuator, and positions it in a signal non-output region when performing variable flow control. Effect of the Invention

[0006] According to the invention of claim 1, back pressure reduction control can be performed using a pilot check valve that opens the unloading oil passage when signal pressure is supplied from the control valve, thereby contributing to cost reduction. By adopting the invention of claim 2, even if the hydraulic actuator for the work tool is a single-acting actuator, the speed of the work tool can be controlled by using variable flow control in an area where the amount of operation of the work tool operating device is small, while in an area where the amount of operation is large, that is, an area where the flow rate is high and back pressure is likely to occur, the unloading oil passage can be opened to use constant flow control, thereby enabling control to reduce back pressure. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a hydraulic circuit diagram for a hydraulic actuator for a work tool. [Diagram 2] 5A and 5B are diagrams illustrating the relationship between the operating amount of the operating tool and the control signal value in each mode. [Diagram 3] 11 is a diagram showing the relationship between the spool movement stroke and the opening area of ​​the supply oil passage, the discharge oil passage, and the signal oil passage in the non-signal output region and the signal output region of the first operating position. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a hydraulic circuit diagram relating to a hydraulic actuator for a work tool in a hydraulic control system provided in a hydraulic excavator (not shown) which is an example of the work machine of the present invention. In FIG. 1, reference numeral 1 denotes the hydraulic actuator for the work tool; 2 denotes a hydraulic pump which serves as a hydraulic supply source for hydraulic actuator 1 for the work tool; 3 denotes a pump line to which discharge oil from hydraulic pump 2 is supplied; 4 denotes an oil tank; 5 denotes a control valve, described below, which controls the supply and discharge of oil to and from hydraulic actuator 1 for the work tool; and 6 and 7 denote first and second actuator oil passages which connect a pair of inlet and outlet ports 1a, 1b provided in hydraulic actuator 1 for the work tool to control valve 5.

[0009] The work tool hydraulic actuator 1 is a hydraulic actuator provided on a work tool to drive a work tool selectively attached to a hydraulic excavator with pressure oil supplied from a hydraulic pump 2. For example, when a hammer (breaker) is attached as the work tool, it is a hammer hydraulic actuator, and when a grapple is attached, it is a grapple hydraulic actuator for opening and closing the claws of the grapple. The work tool hydraulic actuator 1 includes a single-acting actuator (e.g., a hydraulic actuator for a hammer, harvester, mulcher, etc.) 1S in which the first actuator oil passage 6 is used as an oil inflow passage and the second actuator oil passage 7 is used as an oil outflow passage, that is, the oil supply direction to the work tool hydraulic actuator 1 is one-way, and a double-acting actuator 1D (e.g., a hydraulic actuator for a grapple, etc.) in which both the first and second actuator oil passages 6, 7 are used as an oil inflow passage and an oil outflow passage, that is, the oil supply direction to the work tool hydraulic actuator 1 is two-way, reciprocating. In the following description, the work tool hydraulic actuator 1 may also be simply referred to as the work tool 1. Furthermore, when it is necessary to distinguish between single-acting and double-acting, the work tool 1 will be referred to as a single-acting actuator 1S or a double-acting actuator 1D, and when there is no need to distinguish between them, it will be referred to as the work tool 1. In FIG. 1, a hydraulic cylinder which is a double-acting actuator is shown as the work tool 1.

[0010] 1, reference numeral 8 denotes a pressure reducing valve for generating pilot primary pressure connected to the pump line 3, and the pressure reducing valve 8 reduces the discharge pressure of the hydraulic pump 2 to a set pressure that is preset as the pilot primary pressure, and supplies the pressure to a pilot primary side oil passage 9. The pilot primary side oil passage 9 is connected to the input sides of first and second solenoid proportional valves 10 and 11, which will be described later, and is used as a pilot hydraulic pressure source, and is also connected to a signal pressure input port 5e of the control valve 5, and is used as a signal pressure supply source.

[0011] 1, reference numeral 12 denotes an unloaded oil passage branched off from a second actuator oil passage (an oil passage that serves as an oil outflow passage from the single-acting actuator 1S when the work tool 1 is a single-acting actuator 1S) 7 and leading to the oil tank 4, and a pilot check valve 14 having a pilot port 14a is disposed in the unloaded oil passage 12. The pilot check valve 14 is configured to close the unloaded oil passage 12 when no signal pressure is supplied to the pilot port 14a from a signal line 15, which will be described later, and to open the unloaded oil passage 12 when signal pressure is supplied.

[0012] The signal line 15 is an oil passage for supplying the signal pressure output from the signal pressure output port 5g of the control valve 5 to the pilot port 14a of the pilot check valve 14, and a drain oil passage 17 for flowing the pressure oil of the signal line 15 to the oil tank 4 via an orifice 16 is branched from the signal line 15. When the signal pressure is output from the signal pressure output port 5g of the control valve 5, the signal pressure is supplied to the pilot port 14a of the pilot check valve 14 via the signal line 15, while when the signal pressure is not output from the signal pressure output port 5g of the control valve 5, the signal pressure of the signal line 15 flows to the oil tank 4 via the drain oil passage 17, so that the signal pressure is not supplied to the pilot port 14a of the pilot check valve 14. In this embodiment, the drain oil passage 17 is provided outside the control valve 5, but a drain oil passage for flowing the signal pressure to the oil tank 4 may be provided inside the control valve 5.

[0013] On the other hand, the control valve 5 is a pilot operated spool valve which switches the supply / discharge direction for the work tool 1 and controls the oil supply / discharge flow rate, and is provided with first and second pilot ports 5a, 5b which are connected to first and second solenoid proportional valves 10, 11, respectively, which output pilot pressure based on a control signal output from a controller 18, a pump port 5c which is connected to the hydraulic pump 2 via a pump line 3, a tank port 5d which is connected to the oil tank 4 via a tank line 19, a signal pressure input port 5e which is connected to the pilot primary side oil passage 9, a sensor port 5f which is connected to a pressure sensor 20 for detecting the operating pressure of the work tool 1, a signal pressure output port 5g which is connected to the signal line 15, a first actuator port 5h which is connected to a first actuator oil passage 6, and a second actuator port 5i which is connected to a second actuator oil passage 7. When no pilot pressure is input to the first and second pilot ports 5a, 5b, the control valve 5 closes the first and second actuator ports 5i, 5h so as not to control the supply and discharge of the work tool 1, and also closes the signal pressure input port 5e and the signal pressure output port 5g so as to be in a neutral position N where no signal pressure is output to the signal line 15. However, when pilot pressure is input to the first pilot port 5a, the control valve 5 switches to a signal non-output region X1 or a signal output region X2 of a first operating position X described later, and when pilot pressure is input to the second pilot port 5b, the control valve 5 switches to a second operating position Y.

[0014] As described above, the first and second solenoid proportional valves 10, 11 output pilot pressures to the first and second pilot ports 5a, 5b of the control valve 5 based on the control signal from the controller 18, and in this case, the controller 18 outputs a control signal to the first and second solenoid proportional valves 10, 11 based on the mode set by the mode setting means 30 and the operation of the work tool operating device 31. The first and second solenoid proportional valves 10, 11 then output pilot pressures corresponding to the control signal value input from the controller 18. The controller 18 constitutes the control device of the present invention.

[0015] The mode setting means 30 is a means for setting a control mode for the work tool 1 by an operator operating, for example, a monitor device or a mode setting dial arranged near the driver's seat. In this embodiment, the mode selection means 30 can selectively set one of the control modes, "one-way constant flow mode", "one-way variable flow mode" and "bidirectional mode". The "one-way constant flow mode" is a mode selected when the work tool 1 is a single-acting actuator 1S, and a constant flow rate is supplied to the single-acting actuator 1S, i.e., the actuator is driven at a constant speed, and back pressure reduction control is required, and is selected when the work tool 1 is, for example, a hammer or a harvester. The "one-way variable flow mode" is a mode selected when the work tool 1 is a single-acting actuator 1S, and a flow rate according to the operation amount of the work tool operating tool 31 is supplied to the single-acting actuator 1S, and is selected when the work tool 1 is, for example, a mulcher or a hammer, and the actuator is driven at a speed according to the operation amount of the operating tool. Incidentally, even in the "one-way variable flow rate mode", when the work tool operating device 31 is operated by a set operation amount C or more, which will be described later, a constant flow rate is supplied to the single-acting actuator 1S and back pressure reduction control is performed. Furthermore, the "bi-directional mode" is a mode selected when the work tool 1 is a double-acting actuator 1D, and is selected when the work tool 1 is, for example, a grapple. In this embodiment, the work tool operating device 31 is a sliding thumbwheel switch provided on the grip portion of a joystick-type operating lever located on the left and right side of the driver's seat, and is operated by sliding it left and right with a thumb or the like from the neutral position. When the work tool 1 is a single-acting actuator 1S, it is set to be operated in either the left or right direction from the neutral position, and when it is a double-acting actuator 1D, it is set to be operated in both the left and right directions.

[0016] Then, the controller 18 outputs a control signal to the first and second electromagnetic proportional valves 10, 11 based on the mode set by the mode setting means 30 and the operation of the work tool operating device 31 as described above. Here, Fig. 2 shows the relationship between the operating device operation amount in each mode and the control signal value output to the first and second electromagnetic proportional valves 10, 11. When the work tool operating device 31 is operated in one direction beyond the dead band in a state where the "one-way constant flow mode" is set, the controller 18 outputs a 100% control signal value (maximum signal value output from the controller 18 to the first electromagnetic proportional valve 10) to the first electromagnetic proportional valve 10 regardless of the operating device operation amount (in this embodiment, the sliding amount of the thumb wheel switch). As a result, the first electromagnetic proportional valve 10 outputs 100% pilot pressure (maximum pilot pressure output from the first electromagnetic proportional valve 10) to the first pilot port 5a of the control valve 5. When the work tool operating device 31 is operated in the other direction while the “unidirectional constant flow rate mode” is set, no control signal is output from the controller 18 to the first and second solenoid proportional valves 10, 11.

[0017] Furthermore, when the "one-way variable flow mode" is set and the work tool operating device 31 is operated in one direction beyond the dead band, the controller 18 outputs to the first solenoid proportional valve 10 a control signal value that increases as the operating device operating amount increases and reaches 100% at the predetermined operating amount A when the operating amount of the work tool operating device 31 is less than a predetermined operating amount A (when the maximum operating amount of the work tool operating device 31 is 100%, the predetermined operating amount is, for example, 50% of the operating amount), and outputs a 100% control signal value to the first solenoid proportional valve 10 when the operating device operating amount is equal to or greater than the predetermined operating amount A. As a result, the first solenoid proportional valve 10 outputs a pilot pressure that increases as the operating device operating amount increases to the first pilot port 5a of the control valve 5 when the operating device operating amount is less than the predetermined operating amount A, and outputs 100% pilot pressure to the first pilot port 5a when the operating device operating amount is equal to or greater than the predetermined operating amount A. When the work tool operating device 31 is operated in the other direction while the "one-way variable flow mode" is set, no control signal is output from the controller 18 to the first and second solenoid proportional valves 10, 11, just as in the "one-way constant flow mode".

[0018] On the other hand, when the "bidirectional mode" is set and the work tool operating device 31 is operated in one direction beyond the dead band, the controller 18 outputs a control signal value that increases as the operating device operation amount increases to the first solenoid proportional valve 10, and when the work tool operating device 31 is operated in the other direction beyond the dead band, the controller 18 outputs a control signal value that increases as the operating device operation amount increases to the second solenoid proportional valve 11. In this case, as shown in Fig. 2, when the operating device operation amount reaches 100%, the control signal value output from the controller 18 to the first and second solenoid proportional valves 10, 11 is controlled to a preset set signal value B that is less than 100% (for example, a control signal value of 80%). As a result, when the "bidirectional mode" is set, a control signal is output from the controller 18 to the first or second solenoid proportional valve 10, 11 in accordance with the operating direction of the work tool operating device 31, and the first and second solenoid proportional valves 10, 11 output pilot pressures that increase in accordance with an increase in the operating device operation amount to the first and second pilot ports 5a, 5b of the control valve 5, respectively, and the maximum value of the output pilot pressure is controlled to be a preset set pilot pressure P (output pilot pressures from the first and second solenoid proportional valves 10, 11 when the control signal value from the controller 18 is the set signal value B) that is less than 100%.

[0019] The control valve 5 has a spool that moves axially to one side or the other with a movement stroke according to the magnitude of the pilot pressure input to the first and second pilot ports 5a, 5b, thereby opening an oil passage connecting the aforementioned ports 5a to 5i to control the work tool 1. When pilot pressure is input to the first pilot port 5a, the control valve 5 is located in a signal non-output region X1 of the first operating position X if the pilot pressure is less than the aforementioned set pilot pressure P (the control signal value from the controller 18 is less than the aforementioned set signal value B), and is located in a signal output region X2 of the first operating position X if the pilot pressure is equal to or greater than the set pilot pressure P. On the other hand, when pilot pressure is input to the second pilot port 5b, the control valve 5 is located in the second operating position Y. As a result, when the work tool operating device 31 is operated, the control valve 5 is located in the signal output region X2 in the "one-way constant flow mode" and in the "one-way variable flow mode" when the input pilot pressure to the first pilot port 5a is less than the set pilot pressure P and is located in the signal output region X1 when it is equal to or greater than the set pilot pressure P, whereas in the "both-way mode" when the control valve 5 is operated in one direction, the control valve 5 is located in the signal output region X1 and in the second operating position Y when it is operated in the other direction (see FIG. 2). Here, in FIG. 2, C is a set operation amount that is set as the operation amount of the work tool operating device 31 when the input pilot pressure to the first pilot port 5a becomes the set pilot pressure P (the control signal value from the controller 18 becomes the set signal value B) in the "one-way variable flow mode".

[0020] The control valve 5 in the signal non-output region X1 is configured to open the supply oil passage from the pump port 5c to the first actuator port 5h, the discharge oil passage from the second actuator port 5i to the tank port 5d, and the working pressure detection oil passage branched from the supply oil passage to the sensor port 5f, and close the signal pressure input port 5e and the signal pressure output port 5g (see FIG. 1). In this case, the opening areas of the supply oil passage and the discharge oil passage in the signal non-output region X1 are set to increase with an increase in the moving stroke of the spool (an increase in the pilot pressure input to the first pilot port 5a), as shown in FIG. 3. FIG. 3 is a diagram showing the relationship between the spool moving stroke and the opening areas of the supply oil passage, the discharge oil passage, and the signal oil passage described later when the control valve 5 is located in the signal non-output region X1 and the signal output region X2 of the first operating position X. In FIG. 3, S is the moving stroke of the spool when the pilot pressure input to the first pilot port 5a is the set pilot pressure P. As described above, the control valve 5 is located in the signal non-output region X1 when the "one-way variable flow mode" is set and the input pilot pressure to the first pilot port 5a is less than the set pilot pressure P (the operating tool operation amount is less than the set operating amount C), or when the "bi-directional mode" is set and the control valve 5 is operated in one direction. In the state where the control valve 5 is located in the signal non-output region X1, the supply oil passage from the pump port 5c to the first actuator port 5h is opened, so that pressurized oil is supplied from the hydraulic pump 2 to one of the inlet / outlet ports 1a of the work tool 1 via the first actuator oil passage 6 as an oil inflow passage, while the discharge oil passage from the second actuator port 5i to the tank port 5d is opened, so that oil is discharged from the other inlet / outlet port 1b to the oil tank 4 via the second actuator oil passage 7 as an oil outflow passage. In this case, the opening areas of the supply oil passage and the discharge oil passage are set to increase with an increase in the movement stroke of the spool, so that the higher the pilot pressure input to the first pilot port 5a (the higher the amount of operation of the operating tool), the higher the supply flow rate and the discharge flow rate, and the faster the operating speed of the work tool 1 becomes, that is, a variable flow rate control is performed in which the supply flow rate to the work tool 1 is increased or decreased according to the amount of operation of the operating tool. Also, in a state in which the signal non-output region X1 is located, the signal pressure input port 5e and the signal pressure output port 5g are closed, so that no signal pressure is supplied to the pilot port 14a of the pilot check valve 14, and thus the unload oil passage 12 is in a closed state, and all of the oil discharged from the work tool 1 is controlled to flow to the oil tank 4 via the discharge oil passage of the control valve 5, and therefore backpressure reduction control for reducing the backpressure of the work tool 1 by opening the unload oil passage 12 is not performed. In other words, when the control valve 5 is in the "one-way variable flow mode" and the input pilot pressure to the first pilot port 5a is less than the set pilot pressure P, or when the control valve 5 is operated in one direction and the "bi-directional mode" is set, the control valve 5 is located in the non-signal output region X1. When the control valve 5 is in the signal non-output region X1, variable flow control is performed in which the supply flow rate to the work tool 1 is increased or decreased depending on the amount of operation of the operating tool, and backpressure reduction control in which the unloaded oil passage 12 is opened is not performed.

[0021] On the other hand, the control valve 5 in the signal output region X2 is configured to open a supply oil passage from the pump port 5c to the first actuator port 5h, a discharge oil passage from the second actuator port 5i to the tank port 5d, a working pressure detection oil passage branched from the supply oil passage to the sensor port 5f, and a signal oil passage from the signal pressure input port 5e to the signal pressure output port 5g (see FIG. 1). In this case, the opening areas of the supply oil passage and the discharge oil passage are set to be maximum opening areas (see FIG. 3). As described above, the control valve 5 is located in the signal output region X2 when the "one-way constant flow mode" is set, or when the "one-way variable flow mode" is set and the input pilot pressure to the first pilot port 5a is equal to or greater than the set pilot pressure P (the operating tool operation amount is equal to or greater than the set operation amount C), and in the state where it is located in the signal output region X2, the supply oil passage from the pump port 5c to the first actuator port 5h is opened, so that the first actuator oil passage 6 serves as an oil inflow passage and the pressure oil is supplied from the hydraulic pump 2 to one of the inflow / outflow ports 1a of the work tool 1, while the discharge oil passage from the second actuator port 5i to the tank port 5d is opened, so that the second actuator oil passage 7 serves as an oil outflow passage and the oil is discharged from the other of the inflow / outflow ports 1b to the oil tank 4. In this case, the opening areas of the supply oil passage and the discharge oil passage are set to be maximum, so that a constant flow control is performed in which a constant maximum flow rate is supplied to the work tool 1. Furthermore, in a state where the work tool is located in signal output region X2, a signal oil passage from signal pressure input port 5e to signal pressure output port 5g is opened, and signal pressure is supplied to pilot port 14a of pilot check valve 14 via signal line 15, thereby opening unload oil passage 12. Then, opening of unload oil passage 12 causes oil in second actuator oil passage 7, which serves as an oil outflow passage from the work tool 1, to flow via unload oil passage 12 to the oil tank 4, thereby performing backpressure reduction control that can reduce the backpressure applied to the work tool 1. In other words, when the "one-way constant flow mode" is set, or when the "one-way variable flow mode" is set and the input pilot pressure to first pilot port 5a is equal to or higher than the set pilot pressure P, the control valve 5 is located in the signal output region X2. When the control valve 5 is located in the signal output region X2, constant flow control is performed in which a constant flow rate is supplied to the work tool 1, and backpressure reduction control is performed in which oil discharged from the work tool 1 flows into the oil tank 4 via the unloaded oil passage 12.

[0022] Furthermore, the control valve 5 in the second operating position Y is configured to open the supply oil passage from the pump port 5c to the second actuator port 5i, the discharge oil passage from the first actuator port 5h to the tank port 5d, and the operating pressure detection oil passage branched from the supply oil passage to the sensor port 5f, while closing the signal pressure input port 5e and the signal pressure output port 5g (see FIG. 1). In this case, the opening areas of the supply oil passage and the discharge oil passage in the second operating position Y are set to increase with an increase in the spool movement stroke (an increase in the pilot pressure input to the first pilot port 5a), similar to the case of the signal non-output region X1 described above. As described above, when the control valve 5 is operated in the other direction while the "bidirectional mode" is set, the control valve 5 is located at the second operating position Y. In the state where the control valve 5 is located at the second operating position Y, the supply oil passage from the pump port 5c to the second actuator port 5i is opened, and the second actuator oil passage 7 is used as an oil inflow passage to supply pressure oil from the hydraulic pump 2 to the other inflow / outflow port 1b of the work tool 1, while the discharge oil passage from the first actuator port 5h to the tank port 5d is opened, and the first actuator oil passage 6 is used as an oil outflow passage to discharge oil from one inflow / outflow port 1a to the oil tank 4. In this case, as in the case of the signal non-output region X1 described above, variable flow control is performed in which the supply flow rate to the work tool 1 is increased or decreased according to the operating amount of the operating tool. In addition, since the signal pressure input port 5e and the signal pressure output port 5g are closed, the unload oil passage 12 is closed as in the case of the signal non-output region X1 described above, and the back pressure reduction control is not performed. The second operating position Y is included in the signal non-output region of the present invention.

[0023] Here, the tank line 19 connected to the tank port 5d of the control valve 5 is connected to the oil tank 4 via a cooling oil passage 21 that passes through the oil cooler 13 or a non-cooling oil passage 22 that does not pass through the oil cooler 13, and spring-loaded check valves 21a, 22a are provided in the cooling oil passage 21 and the non-cooling oil passage 22, respectively. On the other hand, the unloading oil passage 12 is connected to the cooling oil passage 21 downstream of the spring-loaded check valve 21a and upstream of the oil cooler 13, so that the pressure of the unloading oil passage 12 can be made lower than that of the tank line 19.

[0024] 1, reference numeral 23 denotes a shuttle valve which selects the higher pressure side of the first and second actuator oil passages 6, 7, 24 denotes a relief oil passage which runs from the outlet side of the shuttle valve 23 to the oil tank 4 via the tank line 19, and 25 denotes an electromagnetic relief valve disposed in the relief oil passage 24, and the set relief pressure of the electromagnetic relief valve 25 can be changed in accordance with the type of work tool 1, etc., based on a control signal from the controller 18. By changing the set relief pressure of the electromagnetic relief valve 25, the pressure of the higher pressure side of the first and second actuator oil passages 6, 7, i.e., the first or second actuator oil passage 6, 7 which serves as the oil supply passage to the work tool 1, can be controlled to an operating pressure corresponding to each work tool 1, and in this case, the electromagnetic relief valve 25 is shared for limiting the pressure of both the first and second actuator oil passages 6, 7, thereby reducing the number of electromagnetic relief valves.

[0025] Furthermore, in FIG. 1, reference numeral 26 denotes a make-up oil passage which connects the first and second actuator oil passages 6, 7 to the tank line 19 via a pair of check valves 27. The make-up oil passage 26 enables oil to be supplied from the tank line 19 to the first and second actuator oil passages 6, 7 when negative pressure is applied to the first and second actuator oil passages 6, 7. Furthermore, in FIG. 1, reference numeral 28 denotes a main relief valve that limits the maximum pressure of the pump line 3, and 29 denotes a pump pressure sensor that detects the pressure of the pump line 3 (the discharge pressure of the hydraulic pump 2).

[0026] In the present embodiment configured as described above, the hydraulic control system for the hydraulic excavator is provided with a work tool (hydraulic actuator for a work tool) 1 that is selectively attached to the hydraulic excavator and driven by pressure oil supply from a hydraulic pump 2, a control valve 5 that operates based on the operation of a work tool operating device 31 to control the supply and discharge of oil to and from the work tool 1, a controller 18 that controls the operation of the control valve 5, and first and second actuator oil passages 6, 7 that connect the control valve 5 and the work tool 1, and the first actuator oil passage 6 is used as an oil inlet passage for the work tool 1, and the second actuator oil passage 7 is used as an oil outlet passage for the work tool 1. A single-acting actuator 1S is fitted which uses the first and second actuator oil passages 6, 7 as an oil outflow passage, and a double-acting actuator 1D which uses the first and second actuator oil passages 6, 7 as oil inflow and outflow passages. These actuators are further provided with an unloaded oil passage 12 which branches off from the second actuator oil passage 7 and leads to the oil tank 4, and a pilot check valve 14 which closes the unloaded oil passage 12 when no signal pressure is supplied and opens the unloaded oil passage 12 when signal pressure is supplied, and the operating position of the control valve 5 is provided with a signal output region X2 which outputs signal pressure to the pilot check valve 14 and a signal non-output region X1 which does not output signal pressure. The controller 18 positions the control valve 5 in the signal output region X2 when the work tool 1 requires back pressure reduction control with the single-acting actuator 1S (in this embodiment, when the "one-way constant flow mode" is set, or when the "one-way variable flow mode" is set and the operation amount of the work tool operating device 31 is equal to or greater than the set operation amount C), and positions the control valve 5 in the signal non-output region X1 when the work tool 1 does not require back pressure reduction control (in this embodiment, when the "one-way variable flow mode" is set and the operation amount of the work tool operating device 31 is less than the set operation amount C, or when the "bi-directional mode" is set).

[0027] Thus, when the work tool 1 is a single-acting actuator 1S and back pressure reduction control is required, the control valve 5 is located in the signal output region X2, and the control valve 5 in the signal output region X2 outputs a signal pressure to the pilot check valve 14, and when the signal pressure is supplied to the pilot check valve 14, the pilot check valve 14 opens the unloaded oil passage 12 which is branched off from the second actuator oil passage 7 which serves as an oil discharge passage when the work tool 1 is the single-acting actuator 1S and leads to the oil tank 4, thereby allowing the oil discharged from the work tool 1 to flow to the oil tank 4 with its back pressure sufficiently reduced. In this way, in this embodiment, back pressure reduction control can be performed using the pilot check valve 14 which opens the unloaded oil passage 12 with the signal pressure from the control valve 5, and the pilot check valve 14 is less expensive than an electromagnetic relief valve having an unloading function, thereby contributing to cost reduction. Furthermore, this back pressure reduction control does not use a relief valve for limiting the maximum pressure in the first and second actuator oil passages 6, 7 in order to supply an operating pressure corresponding to each work tool 1. Therefore, even in a relief circuit provided with the electromagnetic relief valve 25 shared by the first and second actuator oil passages 6, 7 as in this embodiment, back pressure reduction control can be performed without any modification of the relief circuit.

[0028] Furthermore, in this device, the control of the oil supply from the control valve 5 to the single-acting actuator 1S can be selectively performed between constant flow control, in which a constant flow rate is supplied to the single-acting actuator 1S (in this embodiment, when the "one-way constant flow mode" is set, or when the "one-way variable flow mode" is set and the operation amount of the work tool operation device 31 is equal to or greater than the set operation amount C), and variable flow control, in which the supply flow rate to the single-acting actuator 1S is increased or decreased in accordance with the operation amount of the work tool operation device 31 (in this embodiment, when the "one-way variable flow mode" is set and the operation amount of the work tool operation device 31 is less than the set operation amount C), and the controller 18 positions the control valve 5 in the signal output region X2 when performing constant flow control of the single-acting actuator 1S, and positions it in the signal non-output region X1 when performing variable flow control. As a result, when constant flow control of the single-acting actuator 1S is performed, signal pressure is output from the control valve 5 to the pilot check valve 14 to open the unloading oil passage 12, thereby performing backpressure reduction control, whereas in variable flow control of the single-acting actuator 1S, signal pressure is not output from the control valve 5 to the pilot check valve 14, so the unloading oil passage 12 is closed. Thus, even with the single-acting actuator 1S, by configuring it to perform variable flow control in the region where the operation amount of the work tool operating device 31 is small (in this embodiment, when it is less than the set operation amount C), it is possible to control the speed of the work tool 1 by means of the variable flow control.

[0029] Of course, the present invention is not limited to the above embodiment, and for example, in the above embodiment, a mode setting means for setting a plurality of control modes and a work tool operating device that can be used in common to each control mode are provided, but a configuration without a mode setting means can be achieved by providing a work tool operating device for each mode. For example, an ON / OFF switch can be provided as an operating device for use in the "unidirectional constant flow mode", a thumb wheel switch can be provided as an operating device for use in the "unidirectional variable flow mode", and an operating pedal can be provided as an operating device for use in the "bidirectional mode", and the controller 18 can identify the mode based on input signals from each operating device, thereby making the mode setting means unnecessary. In the present embodiment, a work tool operating device common to each control mode is provided, thereby reducing the number of work tool operating devices. [Industrial Applicability]

[0030] The present invention can be utilized when an actuator for a work tool that requires back pressure reduction control, such as a breaker, is mounted on a work machine such as a hydraulic excavator. [Explanation of symbols]

[0031] 1 Hydraulic actuator for work tools 2 Hydraulic pump 4 Oil tank 5. Control valve 6 First actuator oil passage 7 Second actuator oil passage 12 Unloading oil passage 14 Pilot check valve 18 Controller 31 Work tool operating equipment X1 signal non-output area X2 signal output area

Claims

1. A hydraulic control system for a work machine comprising: a work tool hydraulic actuator that is selectively attached to the work machine and driven by pressure oil supplied from a hydraulic pump; a control valve that operates based on operation of a work tool operating implement to control oil supply and discharge to the work tool hydraulic actuator; a control device that controls operation of the control valve; and first and second actuator oil lines that connect the control valve and the work tool hydraulic actuator, The hydraulic actuator for a work tool includes either a single-acting actuator using a first actuator oil passage as an oil inlet passage and a second actuator oil passage as an oil outlet passage, or a double-acting actuator using the first and second actuator oil passages as an oil inlet passage and an oil outlet passage, The hydraulic control system includes: an unloading oil passage branched off from the second actuator oil passage and leading to an oil tank; and a pilot check valve that closes the unloading oil passage when no signal pressure is supplied and opens the unloading oil passage when the signal pressure is supplied; The control valve has an operating position including a signal output region where a signal pressure is output to the pilot check valve and a signal non-output region where no signal pressure is output, a control device for controlling a hydraulic actuator for a work machine, the control device being configured to position the control valve in a signal output region when the hydraulic actuator for the work tool is a single-acting actuator and requires back pressure reduction control, and to position the control valve in a signal non-output region when the hydraulic actuator for the work tool does not require back pressure reduction control.

2. 2. A hydraulic control system for a work machine as claimed in claim 1, characterized in that control of oil supply from the control valve to the single acting actuator can be selectively performed between constant flow control, in which a constant flow rate is supplied to the single acting actuator, and variable flow control, in which the flow rate supplied to the single acting actuator is increased or decreased in accordance with the amount of operation of a work tool operating implement, and the control device positions the control valve in a signal output region when performing constant flow control of the single acting actuator, and positions the control valve in a signal non-output region when performing variable flow control.

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