Hydraulic system

Abstract

To enable silting of a solenoid valve to be prevented, without increasing the installation space thereof.SOLUTION: A solenoid valve 14 for driving warming-up circuit is configured in the following manner: an electromagnetic actuator 22 is switchable among a neutral position (IV), a first position (VI), and a second position (V); in the neutral position (IV) and the first position (VI) of a pilot spool 27, a tank port 25C communicates with an output port 25B, while the output port 25B is shut off from a primary pressure port 25A; and in the second position (V), the output port 25B communicates with the primary pressure port 25A, while the tank port 25C is shut off from the output port 25B. A control device 30, when outputting no control signal for switching the pilot spool 27 to the second position (V), to the electromagnetic actuator 22, outputs a control signal for alternately moving the pilot spool 27 between the neutral position (IV) and the first position (VI), to the electromagnetic actuator 22.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a hydraulic system provided in a hydraulic circuit of a construction machine and including a solenoid valve and a control device. [Background technology]

[0002] Construction machinery such as hydraulic excavators is comprised of a self-propelled vehicle body and a working device attached to the vehicle body. The vehicle body of the construction machinery is also equipped with various devices, including a prime mover for generating pressurized oil as a power source, a hydraulic pump, a solenoid valve for controlling the flow of the pressurized oil, and a control device for controlling the prime mover, hydraulic pump, solenoid valve, etc.

[0003] Construction machinery is equipped with many solenoid valves for various control purposes. Some of these solenoid valves are only used under certain conditions and are therefore shut down for long periods of time. For example, construction machinery used in cold climates may be provided with a warm-up circuit for warming the hydraulic oil in the hydraulic circuit to prevent delays in the operation of hydraulic equipment due to an increase in the viscosity of the hydraulic oil. The solenoid valve for driving this warm-up circuit is shut down for long periods of time outside of winter.

[0004] In this way, if the solenoid valve is left in a stopped state for a long period of time, foreign matter mixed in the pressure oil may accumulate between the spool and the housing that make up the solenoid valve, causing silting, which causes the spool to stick.

[0005] Therefore, some construction machinery is equipped with a control device that, when the ignition key is turned from the OFF position to the ON position while the engine is stopped and it is determined that the power is turned ON, periodically outputs a drive current to a solenoid valve that is at risk of silting, thereby driving the solenoid valve (Patent Document 1).This prevents silting by periodically driving only the solenoid valve in question, without affecting other controlled equipment or solenoid valves in other sections.

[0006] In addition, other construction machinery has two solenoid valves connected in series and alternately supplied with drive current, which alternately opens the valves without overlapping, thereby preventing silting without affecting the controlled equipment or solenoid valves in other sections (Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-145178 [Patent Document 2] Jikko No. 62-1430 Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, construction machinery includes ultra-large hydraulic excavators used in open-cut mines and the like. When these ultra-large hydraulic excavators are operated automatically in mines and the like, once operation starts, they will continue to work for long periods of time. In this work environment, the frequency of situations where the engine is stopped and the ignition key is turned from OFF to ON to turn the power ON occurs less frequently. Therefore, the control method according to the invention of Patent Document 1 does not provide an opportunity to periodically output a drive current, which results in the problem of silting occurring in the solenoid valve.

[0009] Furthermore, the invention of Patent Document 2 can perform silting prevention processing regardless of the condition in which the ignition key is turned from the OFF position to the ON position and the power is turned ON. However, the invention of Patent Document 2 has the problem that it requires an expanded installation space because it uses two solenoid valves, which becomes an obstacle to miniaturization of construction machinery.

[0010] An object of one embodiment of the present invention is to provide a hydraulic system that can prevent silting of a solenoid valve without increasing the installation space. [Means for solving the problem]

[0011] One embodiment of the present invention is a hydraulic system including a solenoid valve and a control device that outputs a control signal to control the solenoid valve, wherein the solenoid valve includes a housing having a first port, a second port, and a spool slide hole that communicates with the first port and the second port, a spool that is inserted into the spool slide hole so as to be movable in the axial direction, and a solenoid that moves the spool in the axial direction by a control signal output from the control device, wherein the solenoid moves the spool between a neutral position, a first position that is moved axially from the neutral position, and a second position that is moved axially from the neutral position. when the spool is switched between the neutral position and the first position, the first port and the second port are blocked, and when the spool is switched to the second position, the first port and the second port are connected, and when the control device does not output a control signal to the solenoid to switch the spool to the second position, the control device outputs a control signal to the solenoid to move the spool alternately between the neutral position and the first position.

[0012] Moreover, one embodiment of the present invention is a device including a solenoid valve and a control device that outputs a control signal to control the solenoid valve, wherein the solenoid valve includes a housing provided with a first port, a second port, a third port, and a spool slide hole communicating with the first port, the second port, and the third port; In a hydraulic system including a spool inserted into the spool slide hole so as to be axially movably, and a solenoid that moves the spool axially in response to a control signal output from the control device, the solenoid of the solenoid valve can switch the spool to three positions: a neutral position, a first position moved axially from the neutral position, and a second position moved axially from the neutral position to the opposite side of the first position; when the spool is switched between the neutral position and the first position, the first port and the second port are connected to each other and the second port and the third port are blocked; and when the spool is switched to the second position, the second port and the third port are connected to each other and the first port and the second port are blocked; and when the control device does not output a control signal to the solenoid that switches the spool to the second position, it outputs a control signal to the solenoid that moves the spool alternately between the neutral position and the first position. [Effects of the Invention]

[0013] According to one embodiment of the present invention, silting of the solenoid valve can be prevented and reliability can be improved without increasing the installation space. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a hydraulic circuit diagram of a hydraulic system according to a first embodiment of the present invention. [Figure 2] 2 is a cross-sectional view showing a warm-up circuit driving solenoid valve in FIG. 1. [Figure 3] 4 is a flowchart showing a control process of a warm-up circuit driving electromagnetic valve executed by a control device. [Figure 4] FIG. 4 is a characteristic diagram showing an output signal of the control device when silting of the solenoid valve for driving the warm-up circuit is prevented. [Figure 5] 4 is a characteristic diagram showing an output signal of the control device when the solenoid valve for driving the warm-up circuit is driven for warm-up; FIG. [Figure 6] FIG. 4 is a cross-sectional view showing a warm-up circuit driving solenoid valve according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a hydraulic circuit diagram of a hydraulic system including a warm-up circuit driving solenoid valve according to a modified example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Below, a hydraulic system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings, taking as an example a case where the hydraulic system is applied to a solenoid valve for driving a warm-up circuit of a solenoid valve unit with a warm-up circuit that is mounted on a hydraulic excavator that is larger than a standard machine (medium-sized machine) as a construction machine.

[0016] 1 to 5 show a first embodiment of the present invention. In Fig. 1, a hydraulic system 1 includes a warm-up circuit driving solenoid valve 14, a control device 30, etc., which will be described later. A hydraulic pump 2 constitutes a main hydraulic power source together with a hydraulic oil tank 3. The hydraulic pump 2 is driven to rotate by a prime mover (not shown), such as an engine, an electric motor, or a combination of these, and discharges hydraulic oil drawn from the hydraulic oil tank 3 as high-pressure oil.

[0017] A working hydraulic cylinder 4 is shown as a representative example of a hydraulic actuator. The hydraulic cylinder 4 constitutes, for example, a boom cylinder, an arm cylinder, a bucket cylinder (none of which are shown) or the like provided in the working device of a hydraulic excavator. The hydraulic cylinder 4 is composed of a tube 4A, a piston 4B, a rod 4C, etc.

[0018] The hydraulic cylinder 4 has a tube 4A that is divided into two cylinder oil chambers 4D and 4E by a piston 4B. The base end of a rod 4C is attached to the piston 4B. The tip end of the rod 4C protrudes outside the tube 4A. The hydraulic cylinder 4 extends and retracts the rod 4C using pressurized oil that is supplied to and discharged from the hydraulic pump 2 to the cylinder oil chambers 4D and 4E in the tube 4A. Note that the hydraulic actuator is not limited to the hydraulic cylinder 4 and may be, for example, a hydraulic motor for swinging or traveling of a hydraulic excavator.

[0019] The directional control valve 5 controls the extension and retraction of the hydraulic cylinder 4. The directional control valve 5 is provided between the hydraulic pump 2 and the hydraulic cylinder 4. The directional control valve 5 is configured, for example, as a 6-port 3-position hydraulic pilot type directional control valve. Hydraulic pilot sections 5A, 5B are provided on both the left and right sides of the directional control valve 5. The hydraulic pilot sections 5A, 5B of the directional control valve 5 are connected to electromagnetic proportional pressure reducing valves 13A, 13B (described later) via pilot pressure lines 6A, 6B.

[0020] The directional control valve 5 is switched from the neutral position (I) to either the switching position (II) or the switching position (III) by supplying pilot pressure from the electromagnetic proportional pressure reducing valves 13A, 13B to the hydraulic pilot sections 5A, 5B.

[0021] As a result, pressure oil from the hydraulic pump 2 is supplied to and discharged from the cylinder oil chambers 4D, 4E of the hydraulic cylinder 4 via the pair of main lines 7A, 7B, and the rod 4C of the hydraulic cylinder 4 is extended and retracted from the tube 4A. At this time, the flow rate of pressure oil supplied to and discharged from the cylinder oil chambers 4D, 4E of the hydraulic cylinder 4 is variably controlled in response to the displacement amount of the directional control valve 5 (i.e., an operation signal based on the tilt operation amount of the operating lever 11A, which will be described later).

[0022] The pilot pump 8 constitutes a pilot hydraulic pressure source (pilot pressure source) together with the hydraulic oil tank 3. The pilot pump 8 is rotationally driven together with the main hydraulic pump 2 by, for example, a prime mover.

[0023] A low-pressure relief valve 9 is provided on the discharge side of the pilot pump 8 between the pilot pump 8 and the hydraulic oil tank 3. This low-pressure relief valve 9 keeps the discharge pressure of the pilot pump 8 below a predetermined relief set pressure.

[0024] The pilot pressure generated by the pilot pump 8 is supplied via a primary pressure line 17, which will be described later, to pump ports 19A, 19B of the electromagnetic proportional pressure reducing valves 13A, 13B and to a warm-up circuit 15 on the primary pressure line side of the warm-up circuit driving solenoid valve 14.

[0025] The high-pressure relief valve 10 is provided between the discharge side of the hydraulic pump 2 and the hydraulic oil tank 3. This high-pressure relief valve 10 keeps the discharge pressure of the hydraulic pump 2 below a predetermined relief set pressure to prevent excessive pressure from occurring in the hydraulic pump 2. The relief set pressure of the high-pressure relief valve 10 is set to a pressure that is sufficiently higher than the relief set pressure of the low-pressure relief valve 9.

[0026] The operating lever device 11 is an electric operating device configured as an electric lever device that remotely controls the movement of the hydraulic cylinder 4. The operating lever device 11 is provided in a cab (not shown) that forms the driver's compartment of the hydraulic excavator, and has an operating lever 11A that is manually tilted by the operator. The operating lever device 11 outputs operating signals corresponding to the operating direction and amount of operation of the operating lever 11A to the electromagnetic proportional pressure reducing valves 13A, 13B via the control device 30.

[0027] The solenoid valve unit 12 is composed of electromagnetic proportional pressure reducing valves 13A, 13B and a warm-up circuit driving solenoid valve 14. The electromagnetic proportional pressure reducing valves 13A, 13B supply pilot pressure proportional to the current controlled by the control device 30 to pilot pressure lines 6A, 6B in response to an operation signal from the operating lever device 11. The pilot pressure at this time is supplied to hydraulic pilot sections 5A, 5B, whereby the directional control valve 5 is switched from the neutral position (I) to either the switching position (II) or the switching position (III).

[0028] The hydraulic cylinder 4 extends and retracts the rod 4C by supplying and discharging pressurized oil from the hydraulic pump 2 to and from the cylinder oil chambers 4D and 4E via a pair of main lines 7A and 7B. In this way, the hydraulic cylinder 4 is remotely controlled to extend and retract via the electromagnetic proportional pressure reducing valves 13A and 13B and the directional control valve 5 in response to an operation signal from the operating lever device 11.

[0029] The solenoid valve 14 for driving the warm-up circuit is switched from a neutral position (IV) to either a first position (VI) or a second position (V) in accordance with a first position drive current IB and a second position drive current IA (see FIGS. 4 and 5) controlled by the control device 30. In the neutral position (IV) and the first position (VI), the primary pressure line side warm-up circuit 15 and the drain line side warm-up circuit 16 are not in communication with each other, and pressure oil is blocked. In addition, in the neutral position (IV) and the first position (VI), the drain port 20C and the drain line side warm-up circuit 16 are in communication with each other, thereby releasing pressure from the lines.

[0030] In the second position (V), the primary pressure line warm-up circuit 15 and the drain line warm-up circuit 16 are connected to each other, so that pressure oil flows from the primary pressure line 17 to the drain line 18 via the warm-up circuit driving solenoid valve 14. This causes high-temperature pressure oil to circulate within the solenoid valve unit 12 and warm it up. The detailed configuration of this warm-up circuit driving solenoid valve 14 will be described later.

[0031] The base end of the primary pressure line 17 is connected to the discharge side of the pilot pump 8, and the tip end is connected to the pump ports 19A, 19B of the electromagnetic proportional pressure reducing valves 13A, 13B and the primary pressure line side warm-up circuit 15 of the warm-up circuit driving solenoid valve 14, respectively.

[0032] As a result, the pilot pressure discharged from the pilot pump 8 is supplied to the pump ports 19A, 19B as the primary pressure for the electromagnetic proportional pressure reducing valves 13A, 13B. Furthermore, the hydraulic oil discharged from the pilot pump 8 is supplied to the primary pressure line side warm-up circuit 15 to warm up the solenoid valve unit 12. The drain line 18 constantly connects the drain ports 20A, 20B of the electromagnetic proportional pressure reducing valves 13A, 13B and the drain line side warm-up circuit 16 of the warm-up circuit drive solenoid valve 14 to the hydraulic oil tank 3, respectively.

[0033] The oil temperature sensor 21 is connected to the drain line 18. The oil temperature sensor 21 outputs a voltage signal to the control device 30 according to the temperature of the hydraulic oil in the drain line 18.

[0034] Next, the specific configuration of the warm-up circuit driving solenoid valve 14 will be described in detail with reference to FIG.

[0035] The warm-up circuit driving solenoid valve 14 includes, for example, an electromagnetic actuator 22 (described later) configured by an electromagnetic proportional solenoid, and an electromagnetically operated communication valve 23 that is switched via a connecting rod 22C by the electromagnetic actuator 22. The electromagnetic actuator 22 includes an actuator case 22A that forms an outer shell, a connector portion 22B that is provided in the actuator case 22A and connected to a control device 30 (see FIG. 1) via a signal line or the like, a solenoid (not shown) that is provided within the actuator case 22A and displaces in the axial direction (directions of arrows A and B in FIG. 2) when power is supplied, and a connecting rod 22C that connects the solenoid to a pilot spool 27 (described later).

[0036] A first position drive current IB and a second position drive current IA (see FIGS. 4 and 5) are input to the electromagnetic actuator 22 via the connector 22B from the control device 30. When the first position drive current IB exceeds a threshold IB_ON, the actuator case 22A drives the connecting rod 22C to contract in the direction of arrow B in FIG. 2. On the other hand, when the second position drive current IA exceeds a threshold IA_ON, the actuator case 22A drives the connecting rod 22C to extend in the direction of arrow A.

[0037] This allows the electromagnetic actuator 22 to switch the pilot spool 27 between three positions: a neutral position (IV), a first position (VI) moved from the neutral position (IV) to one side in the axial direction, and a second position (V) moved from the neutral position (IV) to the other side opposite the first position (VI) in the axial direction.

[0038] The communication valve 23 of the warm-up circuit driving solenoid valve 14 is fitted into the solenoid valve cartridge insertion hole 24A of the block 24 forming the outer shell, and is configured to include a cylindrical housing 25 arranged coaxially with the connecting rod 22C of the electromagnetic actuator 22, and a cylindrical pilot spool 27 movably inserted into a spool sliding hole 26 formed on the inner side of the housing 25.

[0039] The housing 25 of the communication valve 23 is attached such that the outer periphery on one axial side is screwed with the opening on the other side of the actuator case 22A of the electromagnetic actuator 22. As a result, the warm-up circuit driving solenoid valve 14 has a cartridge structure in which the electromagnetic actuator 22, the housing 25 of the communication valve 23, the pilot spool 27, and the neutral springs 28A and 28B are pre-assembled.

[0040] In this state, the housing 25, together with the pilot spool 27 and neutral springs 28A and 28B, is attached so as to be pushed from one axial side to the other into the solenoid valve cartridge insertion hole 24A of the block 24. In other words, the actuator case 22A of the electromagnetic actuator 22 is attached to the block 24 so as to close the solenoid valve cartridge insertion hole 24A of the block 24 and the spring accommodating hole portion 26A of the spool sliding hole 26 from one axial side.

[0041] The housing 25 is provided with a radial primary pressure port 25A, an output port 25B, and a tank port 25C that are spaced apart from one another in the axial direction and communicate with the inside of the spool sliding hole 26. In the housing 25, the primary pressure port 25A is the third port, the output port 25B is the second port, and the tank port 25C is the first port.

[0042] A primary pressure port 25A located toward one axial end of the housing 25 is constantly connected to the primary pressure line warm-up circuit 15 of the block 24. An output port 25B located in the middle in the axial direction is constantly connected to the drain line warm-up circuit 16. A tank port 25C located toward the other axial end of the housing 25 is constantly connected to the drain port 20C. The primary pressure port 25A, output port 25B, and tank port 25C are mutually sealed by O-rings or the like on the outer periphery of the housing 25.

[0043] The spool sliding hole 26 is formed on the inner peripheral side of the housing 25. The spool sliding hole 26 is configured to include a spring accommodating hole portion 26A located on one axial side (open end side) and sliding hole portions 26B to 26E formed with a smaller diameter than the spring accommodating hole portion 26A. The spring accommodating hole portion 26A is formed as an expanded diameter hole with an inner diameter larger than that of the sliding hole portion 26B, which is located closest to the one axial side among the sliding hole portions 26B to 26E. An end portion (one axial end portion) of the spring accommodating hole portion 26A is an open end that communicates (opens) with the other side opening of the actuator case 22A on one side of the block 24.

[0044] Spool slide hole 26 is a stepped circular hole formed on the inner circumferential side of housing 25, and has a plurality of slide hole portions 26B, 26C, 26D, and 26E into which pilot spool 27 is slidably inserted. These slide hole portions 26B to 26E are formed to have the same inner diameter.

[0045] A pilot spool 27 serving as a spool is inserted into a spool slide hole 26 of the housing 25 so as to be movable in the axial direction. In this state, a boss portion 27A, which is a closed end on one axial side of the pilot spool 27, is fastened to a connecting rod 22C of the electromagnetic actuator 22. As the connecting rod 22C extends from the actuator case 22A in the direction of arrow A in FIG. 2 or contracts in the direction of arrow B, the pilot spool 27 is pushed and pulled in the axial direction within the spool slide hole 26, moving (sliding displacement) from the neutral position.

[0046] Furthermore, a flange-shaped spring receiver 27J is fitted around the periphery of boss 27A of pilot spool 27. This spring receiver 27J is biased to one side by neutral spring 28A and to the other side by neutral spring 28B. That is, when pilot spool 27 is not forced to move by connecting rod 22C, it is located in a neutral position (IV) where the biasing forces of neutral springs 28A and 28B are equal.

[0047] On the other hand, four lands 27B, 27C, 27D, and 27E are provided axially spaced apart from one another on the outer periphery of pilot spool 27, and each of lands 27B to 27E has the same outer diameter. Intermediate lands 27C and 27D, located between land 27B on one side and land 27E on the other side, are formed as annular flanges.

[0048] Furthermore, when the pilot spool 27 is inserted into the housing 25 (spool sliding hole 26), the land 27B on one side is arranged to slide and displace in the axial direction within the sliding hole portion 26B, and the land 27E on the other side is arranged to slide and displace in the sliding hole portion 26E.

[0049] Of the intermediate lands 27C and 27D, the intermediate land 27C closer to one side is disposed so as to slide and displace within the sliding hole portion 26C, while the intermediate land 27D closer to the other side is disposed at a position that allows the output port 25B to communicate with the sliding hole portion 26D.

[0050] When the intermediate land 27C moves from the sliding hole portion 26C to the position of the output port 25B, the sliding hole portion 26C (primary pressure line side warm-up circuit 15) is connected to the drain line side warm-up circuit 16 via the output port 25B. At this time, the intermediate land 27D is inserted into the sliding hole portion 26D. That is, the output port 25B (drain line side warm-up circuit 16) is blocked from communication with the drain port 20C (sliding hole portion 26D).

[0051] In this way, the intermediate land 27C closer to one side is a land provided on the pilot spool 27 to establish communication between and disconnect the primary pressure line side warm-up circuit 15 and the drain line side warm-up circuit 16. On the other hand, the intermediate land 27D closer to the other side is a land provided on the pilot spool 27 to establish communication between and disconnect the drain line side warm-up circuit 16 and the drain port 20C.

[0052] When the pilot spool 27 is in the neutral position (IV) or the first position (VI), the intermediate land 27C on one side is inserted into the sliding hole portion 26C of the spool sliding hole 26, blocking communication between the primary pressure port 25A and the output port 25B (between the primary pressure line side warm-up circuit 15 and the drain line side warm-up circuit 16).

[0053] However, when the pilot spool 27 moves to the second position on the other side in the axial direction (the direction of arrow A in Figure 2) and the intermediate land 27C is positioned from the sliding hole portion 26C to the position of the output port 25B, communication is established between the primary pressure port 25A and the output port 25B (between the primary pressure line side warm-up circuit 15 and the drain line side warm-up circuit 16).

[0054] As a result, the hydraulic oil supplied from the primary pressure line 17 shown in Figure 1 to the primary pressure line side warm-up circuit 15 flows from the primary pressure port 25A through the space between the housing 25 and the pilot spool 27, and then flows from the output port 25B to the hydraulic oil tank 3 via the drain line side warm-up circuit 16 and the drain line 18.

[0055] Pilot spool 27 also has a bottomed axial hole 27F that extends axially from the other end face toward boss portion 27A. Shaft hole 27F is constantly in communication with oil chamber 29. Pilot spool 27 also has oil passages 27G and 27H that extend radially from axial hole 27F and penetrate outward. Oil passage 27G on one side constantly connects axial hole 27F to spring accommodating hole 26A of spool sliding hole 26, and oil passage 27H on the other side constantly connects axial hole 27F to tank port 25C.

[0056] Low-pressure hydraulic oil is guided from drain port 20C through oil passage 27H, shaft hole 27F, and oil passage 27G to spring accommodating hole 26A of spool sliding hole 26 provided in housing 25. This low-pressure hydraulic oil is guided from the outer periphery of boss 27A along the periphery of connecting rod 22C into actuator case 22A of electromagnetic actuator 22. This keeps the interior of actuator case 22A lubricated for the hydraulic oil and cools the solenoid, etc.

[0057] Oil chamber 29 is located at the other end of pilot spool 27, and is formed as a circular space surrounded by the inner wall surface (slide hole portion 26E) of housing 25 and block 24. Oil chamber 29 is constantly in communication with axial hole 27F of pilot spool 27. Therefore, when pilot spool 27 moves axially toward the other side (the direction of arrow A in FIG. 2) within housing 25 (spool slide hole 26), the hydraulic oil in oil chamber 29 is discharged into axial hole 27F.

[0058] The control device 30 is electrically connected to the operating lever device 11, the electromagnetic proportional pressure reducing valves 13A, 13B, the oil temperature sensor 21, etc. The control device 30 controls the value of the current flowing through the electromagnetic proportional pressure reducing valves 13A, 13B by pulse width modulating the voltage applied to the electromagnetic proportional pressure reducing valves 13A, 13B. The control device 30 also controls the voltage applied to the warm-up circuit driving solenoid valve 14 based on a signal from the oil temperature sensor 21, thereby controlling the first position drive current IB and the second position drive current IA flowing through the warm-up circuit driving solenoid valve 14.

[0059] Next, the control by the control device 30 when finally preventing silting of the warm-up circuit driving solenoid valve 14 and driving the warm-up circuit will be described with reference to FIGS.

[0060] 3 is a flowchart illustrating the operation related to the control logic of the control device 30 when preventing silting of the warm-up circuit driving solenoid valve 14 and driving the warm-up circuit. In the flowchart of FIG. 3, steps are represented by "S," and for example, step 1 is represented as "S1."

[0061] First, in step 1, an output voltage Vθ, which varies depending on the temperature of the hydraulic oil in the solenoid valve unit 12 (drain oil passage 18), is obtained from the oil temperature sensor 21. In the following step 2, the hydraulic oil temperature ΘD is calculated based on the output voltage Vθ obtained from the oil temperature sensor 21. In step 3, it is determined whether the hydraulic oil temperature ΘD is equal to or higher than a threshold value Θ0. In this case, the threshold value Θ0 is the lowest hydraulic oil temperature that does not interfere with the operation of the solenoid valve unit 12.

[0062] If the answer to step 3 is YES, the hydraulic oil temperature ΘD is equal to or greater than the threshold value Θ0, so the process moves to step 4, where a silting prevention signal (described later) is output. On the other hand, if the answer to step 3 is NO, the hydraulic oil temperature ΘD has not reached the threshold value Θ0, so the process moves to step 5, where a warm-up circuit drive signal (described later) is output.

[0063] The silting prevention signal shown in Figure 4 is composed of a first position drive current IB and a second position drive current IA. The first position drive current IB of the silting prevention signal is a control signal consisting of a square wave that alternates between a current value of 0 and a current value exceeding the threshold value IB_ON, and its cycle is set to several seconds to several minutes. On the other hand, the second position drive current IA of the silting prevention signal is always a current value of 0.

[0064] On the other hand, the warm-up circuit drive signal shown in Figure 5 is composed of a first position drive current IB and a second position drive current IA, just like the silting prevention signal. The first position drive current IB of the warm-up circuit drive signal is always 0. On the other hand, the second position drive current IA of the warm-up circuit drive signal is always a current value that exceeds the threshold value IA_ON.

[0065] The above control processing is written as a program in the control device 30, and the processing shown in FIG.

[0066] Next, the operation of the hydraulic system 1 when the warm-up circuit driving solenoid valve 14 is driven by the control device 30 will be described with reference to FIGS.

[0067] When the temperature ΘD of the hydraulic oil in the solenoid valve unit 12 is lower than the threshold value Θ0, the control device 30 outputs a warm-up circuit drive signal shown in Fig. 5 to the warm-up circuit drive solenoid valve 14 based on the output voltage Vθ from the oil temperature sensor 21. At this time, the warm-up circuit drive solenoid valve 14 is switched from the neutral position (IV) to the second position (V), thereby connecting the primary pressure line side warm-up circuit 15 and the drain line side warm-up circuit 16, and hydraulic oil flows from the primary pressure line 17 to the drain line 18. As a result, high-temperature pressure oil circulates within the solenoid valve unit 12, thereby warming up the solenoid valve unit 12.

[0068] On the other hand, when the temperature ΘD of the hydraulic oil in the solenoid valve unit 12 is equal to or higher than the threshold value Θ0, the control device 30 outputs a silting prevention signal shown in Fig. 4 to the warm-up circuit driving solenoid valve 14 based on the output voltage Vθ from the oil temperature sensor 21. At this time, the warm-up circuit driving solenoid valve 14 is alternately switched between the neutral position (IV) and the first position (VI) as a silting prevention process.

[0069] In this case, the primary pressure line side warm-up circuit 15 and the drain line side warm-up circuit 16 do not communicate with each other, and the pilot spool 27 of the warm-up circuit drive solenoid valve 14 is driven at a constant frequency in accordance with the square wave. That is, in the silting prevention operation, hydraulic oil does not flow from the primary pressure line 17 to the drain line 18, and the pilot spool 27 is driven at a constant frequency, so silting of the warm-up circuit drive solenoid valve 14 can be prevented without affecting the solenoid valves of other sections, including the electromagnetic proportional pressure reducing valves 13A and 13B.

[0070] Thus, according to this embodiment, the warm-up circuit driving solenoid valve 14 is capable of switching the pilot spool 27 by the electromagnetic actuator 22 between three positions: a neutral position (IV), a first position (VI) in which the pilot spool 27 is moved from the neutral position (IV) to one side in the axial direction, and a second position (V) in which the pilot spool 27 is moved from the neutral position (IV) to the other side opposite to the first position (VI) in the axial direction. When the pilot spool 27 is switched between the neutral position (IV) and the first position (VI), the tank port 25C as the first port and the output port 25B as the second port are connected to each other, and the output port 25C is connected to the tank port 25C. When the control device 30 does not output a control signal to the electromagnetic actuator 22 to switch the pilot spool 27 to the second position (V), it outputs a control signal to the electromagnetic actuator 22 to move the pilot spool 27 alternately between the neutral position (IV) and the first position (VI).

[0071] As a result, even in cases where work is performed continuously for long periods of time, such as with an ultra-large hydraulic excavator, the pilot spool 27 can be driven at a constant frequency, so that silting of the warm-up circuit drive solenoid valve 14, which operates extremely infrequently, can be prevented without affecting the solenoid valves of other sections, thereby improving reliability. In addition, because only a solenoid valve that can be switched to three positions is used, the number of parts can be reduced, which saves installation space and allows the hydraulic system 1 to be made more compact.

[0072] Next, Fig. 6 shows a second embodiment of the present invention. This embodiment is characterized in that the first port is a primary pressure port, the second port is an output port, and the third port is a tank port. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted. In the second embodiment, the switching position of the spool is the second position when moved from the neutral position to one side in the axial direction, and the first position when moved from the neutral position to the other side, which is the axial opposite side of the second position.

[0073] In FIG. 6, a solenoid valve 31 according to the second embodiment includes a communication valve 32, which includes a housing 33 and a pilot spool 34, which will be described later.

[0074] The housing 33 according to the second embodiment includes a primary pressure port 33A, an output port 33B, and a tank port 33C, similar to the housing 25 according to the first embodiment. However, the housing 33 according to the second embodiment differs from the housing 25 according to the first embodiment in that the primary pressure port 33A is the first port, the output port 33B is the second port, and the tank port 33C is the third port.

[0075] A pilot spool 34 as a spool according to the second embodiment includes a boss portion 34A, lands 34B and 34C, a shaft hole 34D, oil passages 34E and 34F, and a spring receiving portion 34G.

[0076] In the second embodiment configured in this manner, when the pilot spool 34 is in the neutral position or in the second position moved in the direction of arrow B, the primary pressure port 33A and the output port 33B are connected, and the output port 33B and the tank port 33C are blocked by the land 34C.

[0077] On the other hand, when the pilot spool 27 is moved in the direction of arrow A to a first position, the primary pressure port 33A and the output port 33B are blocked by the land 34B, and the output port 33B and the tank port 33C are connected to each other.

[0078] Thus, the second embodiment configured as described above can also achieve the same effects as the first embodiment. In particular, in the second embodiment, by outputting a signal similar to the silting prevention signal shown in Fig. 4 of the first embodiment to the electromagnetic actuator 22, when a control signal for switching the pilot spool 27 to the second position is not output to the electromagnetic actuator 22, the pilot spool 34 can be moved between the neutral position and the first position while the primary pressure port 33A and the output port 33B are in communication with each other. This makes it possible to perform silting prevention processing for the solenoid valve 31.

[0079] In the first embodiment, the warm-up circuit driving solenoid valve 14 is provided with three ports: a tank port 25C as a first port, an output port 25B as a second port, and a primary pressure port 25A as a third port. However, the present invention is not limited to this, and may be configured, for example, as a hydraulic system 41 according to a modified example shown in FIG. 7.

[0080] That is, the warm-up circuit driving solenoid valve 42 of the hydraulic system 41 has two ports: a primary pressure port 42A as a first port and an output port 42B as a second port. The warm-up circuit driving solenoid valve 42 is configured to block the primary pressure port 42A (primary pressure line side warm-up circuit 15) from the output port 42B (drain line side warm-up circuit 16) when the spool is switched between the neutral position (IV) and the first position (VI), and to connect the primary pressure port 42A (primary pressure line side warm-up circuit 15) to the output port 42B (drain line side warm-up circuit 16) when the spool is switched to the second position (V).

[0081] Furthermore, when the control device 43 does not output a control signal to the electromagnetic actuator 44 as a solenoid to switch the spool of the warm-up circuit driving solenoid valve 42 to the second position (V), the control device 43 outputs a control signal to the electromagnetic actuator 44 to move the spool alternately between the neutral position (IV) and the first position (VI). This makes it possible to perform a process to prevent silting of the warm-up circuit driving solenoid valve 42.

[0082] In addition, in the first embodiment and the modified example, the solenoid valves have been described as examples of the warm-up circuit driving solenoid valves 14, 42. However, the present invention is not limited to this, and can be applied to other solenoid valves that are used less frequently, such as spare solenoid valves used for additional operations of attachments of a work device.

[0083] Furthermore, in each embodiment, the hydraulic systems 1, 41 have been described as being applied to a hydraulic excavator as a construction machine, but the present invention is not limited to this and may be configured to be applied to other construction machines such as a dump truck, a wheel loader, a hydraulic crane, etc. [Explanation of symbols]

[0084] 1,41 Hydraulic system 14,42 Warm-up circuit drive solenoid valve (solenoid valve) 22,44 Electromagnetic actuator (solenoid) 25,33 Housing 25A Primary pressure port (3rd port) 25B Output port (second port) 25C Tank port (1st port) 26 Spool sliding hole 27,34 Pilot spool (spool) 30,43 Control device 31 Solenoid valve 33A Primary pressure port (1st port) 33B Output port (second port) 33C Tank port (3rd port) 42A Primary pressure port (1st port) 42B Output port (second port)

Claims

1. a control device that outputs a control signal to control the solenoid valve; The solenoid valve is a housing provided with a first port, a second port, and a spool slide hole communicating with the first port and the second port; a spool inserted into the spool slide hole so as to be axially movable; a solenoid that moves the spool in the axial direction in response to a control signal output from the control device; In a hydraulic system comprising: The solenoid valve is The solenoid can switch the spool between three positions: a neutral position, a first position moved axially from the neutral position, and a second position moved axially opposite to the first position from the neutral position, When the spool is switched between the neutral position and the first position, the first port and the second port are blocked, When the spool is switched to the second position, the first port and the second port are communicated with each other, When the control device does not output a control signal to the solenoid that switches the spool to the second position, the control device outputs a control signal to the solenoid that moves the spool alternately between the neutral position and the first position.

2. a control device that outputs a control signal to control the solenoid valve; The solenoid valve is a housing provided with a first port, a second port, a third port, and a spool slide hole communicating with the first port, the second port, and the third port; a spool inserted into the spool slide hole so as to be axially movable; a solenoid that moves the spool in the axial direction in response to a control signal output from the control device; In a hydraulic system comprising: The solenoid valve is The solenoid can switch the spool between three positions: a neutral position, a first position moved axially from the neutral position, and a second position moved axially opposite to the first position from the neutral position, When the spool is switched between the neutral position and the first position, the first port and the second port are communicated with each other, and the second port and the third port are blocked from each other; When the spool is switched to the second position, the second port and the third port are communicated with each other, and the first port and the second port are blocked from each other, When the control device does not output a control signal to the solenoid that switches the spool to the second position, the control device outputs a control signal to the solenoid that moves the spool alternately between the neutral position and the first position.

3. 3. The hydraulic system according to claim 2, 1. A hydraulic system comprising: a first port configured to be a tank port; a second port configured to be an output port; and a third port configured to be a primary pressure port.

4. 3. The hydraulic system according to claim 2, 1. A hydraulic system comprising: a first port configured to be a primary pressure port; a second port configured to be an output port; and a third port configured to be a tank port.

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