Hydraulic circuits for excavators and other work machines

Abstract

To provide a technique that can suppress hunting (vibration) of electromagnetic relief valves in a hydraulic circuit of work machines such as shovels.SOLUTION: A shovel 100 according to an embodiment of the present disclosure includes: a hydraulic oil tank T for storing hydraulic oil; a main pump 14 for sucking hydraulic oil from the hydraulic oil tank T; a hydraulic actuator driven by hydraulic oil discharged from the main pump 14; a return oil passage 70 for returning hydraulic oil discharged from the hydraulic actuator to the hydraulic oil tank T; electromagnetic relief valves 82, 92 capable of discharging, to the hydraulic oil tank T, hydraulic oil at predetermined locations in an oil passage from the main pump 14 to the hydraulic oil tank T; and return oil passages 80, 90 different from the return oil passage 70, connecting the electromagnetic relief valves 82, 92 and the hydraulic oil tank T.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a shovel, etc. [Background technology]

[0002] For example, in work machines such as excavators, an electromagnetic relief valve may be adopted that can discharge hydraulic oil at a predetermined location in an oil passage from a hydraulic pump to a hydraulic oil tank and can change the relief pressure (see Patent Document 1).

[0003] In Patent Document 1, an electromagnetic relief valve is provided for pressure control of a hydraulic actuator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-141705 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Document 1, the return oil passage for returning hydraulic oil from the electromagnetic relief valve to the hydraulic oil tank and the return oil passage for returning hydraulic oil discharged from the hydraulic actuator to the hydraulic oil tank are merged into a common oil passage and connected to the hydraulic oil tank. Therefore, depending on the load state of the hydraulic actuator, the pressure fluctuation and its frequency in the return oil passage for returning the hydraulic oil discharged from the hydraulic actuator to the hydraulic oil tank may become relatively large. As a result, the pressure fluctuation and its frequency acting on the secondary side of the electromagnetic relief valve through the common oil passage may become relatively large, and hunting (vibration) may occur in the electromagnetic relief valve due to the operation of the electromagnetic relief valve to respond to the pressure fluctuation and its frequency.

[0006] In view of the above-mentioned problems, an object of the present invention is to provide a technique capable of suppressing hunting (vibration) of an electromagnetic relief valve in a hydraulic circuit of a work machine such as an excavator. [Means for solving the problem]

[0007] In order to achieve the above object, in one embodiment of the present disclosure, A hydraulic oil tank for storing hydraulic oil; a hydraulic pump that draws hydraulic oil from the hydraulic oil tank; a hydraulic actuator driven by hydraulic oil discharged from the hydraulic pump; a first return oil passage that returns hydraulic oil discharged from the hydraulic actuator to the hydraulic oil tank; an electromagnetic relief valve capable of discharging hydraulic oil at a predetermined location in an oil passage from the hydraulic pump to the hydraulic oil tank, into the hydraulic oil tank; a second return oil passage different from the first return oil passage, the second return oil passage connecting the electromagnetic relief valve and the hydraulic oil tank; 、 The second return oil passage is capable of discharging the hydraulic oil flowing in from the electromagnetic relief valve to the hydraulic oil tank without merging with the hydraulic oil in the first return oil passage. R, Shovel provided.

[0008] In another embodiment of the present disclosure, a supply oil passage that supplies hydraulic oil discharged from the hydraulic pump to the hydraulic actuator; A first return oil passage that returns hydraulic oil discharged from the hydraulic actuator to a hydraulic oil tank; an electromagnetic relief valve capable of discharging hydraulic oil at a predetermined location in an oil passage from the hydraulic pump to the hydraulic oil tank, into the hydraulic oil tank; a second return oil passage different from the first return oil passage, the second return oil passage connecting the electromagnetic relief valve and the hydraulic oil tank; 、 The second return oil passage is capable of discharging the hydraulic oil flowing in from the electromagnetic relief valve to the hydraulic oil tank without merging with the hydraulic oil in the first return oil passage. R, A hydraulic circuit for a work machine is provided. Effect of the Invention

[0009] According to the above-described embodiment, hunting (vibration) of the electromagnetic relief valve in the hydraulic circuit of a work machine such as an excavator can be suppressed. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an external view showing an example of a shovel. [Diagram 2] FIG. 2 is a block diagram showing an example of a configuration of a shovel. [Diagram 3] FIG. 2 is a block diagram showing an example of a configuration of a shovel. [Figure 4] FIG. 1 is a diagram showing a first example of a hydraulic circuit for returning hydraulic oil to a hydraulic oil tank in an excavator. [Diagram 5] FIG. 1 is a diagram showing a first example of a hydraulic circuit for returning hydraulic oil to a hydraulic oil tank in an excavator. [Figure 6] FIG. 1 is a diagram showing a hydraulic circuit for returning hydraulic oil to a hydraulic oil tank in a shovel according to a comparative example. [Figure 7] FIG. 11 is a diagram showing a second example of a hydraulic circuit for returning hydraulic oil to a hydraulic oil tank in a shovel. [Figure 8] FIG. 13 is a diagram showing a third example of a hydraulic circuit for returning hydraulic oil to a hydraulic oil tank in an excavator. [Figure 9] FIG. 13 is a diagram showing a fourth example of a hydraulic circuit for returning hydraulic oil to a hydraulic oil tank in a shovel. [Figure 10] FIG. 13 is a diagram showing a fifth example of a hydraulic circuit for returning hydraulic oil to a hydraulic oil tank in a shovel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment will be described with reference to the drawings.

[0012] [Outline of the excavator] First, an overview of a shovel 100 according to this embodiment will be described with reference to FIG.

[0013] FIG. 1 is a schematic diagram showing an example of a shovel 100 according to this embodiment.

[0014] As shown in Fig. 1, an excavator 100 according to this embodiment includes a lower traveling body 1, an upper rotating body 3 mounted on the lower traveling body 1 so as to be rotatable via a rotating mechanism 2, an attachment AT for performing various tasks, and a cabin 10. Hereinafter, the front of the shovel 100 (upper rotating body 3) corresponds to the direction in which the attachment for the upper rotating body 3 extends when the shovel 100 is viewed in a plan view (top view) from directly above along the rotation axis of the upper rotating body 3. In addition, the left and right sides of the shovel 100 (upper rotating body 3) correspond to the left and right sides, respectively, as viewed from an operator seated in a driver's seat in the cabin 10.

[0015] It should be noted that when the excavator 100 is remotely operated or operates in a fully automated manner, the cabin 10 may be omitted.

[0016] The lower traveling body 1 includes, for example, a pair of left and right crawlers 1C. The lower traveling body 1 causes the excavator 100 to travel by hydraulically driving each of the crawlers 1C by a left traveling hydraulic motor 1ML and a right traveling hydraulic motor 1MR (see FIGS. 2 and 3).

[0017] The upper rotating body 3 rotates relative to the lower traveling body 1 as a result of the rotating mechanism 2 being hydraulically driven by the rotating hydraulic motor 2A.

[0018] The attachment AT (an example of a working device) includes a boom 4 , an arm 5 , and a bucket 6 .

[0019] A boom 4 is attached to the front center of the upper rotating body 3 so as to be able to tilt up and down, an arm 5 is attached to the tip of the boom 4 so as to be able to rotate up and down, and a bucket 6 is attached to the tip of the arm 5 so as to be able to rotate up and down.

[0020] The bucket 6 is an example of an end attachment. The bucket 6 is used, for example, for excavation work. In addition, instead of the bucket 6, another end attachment may be attached to the tip of the arm 5 depending on the work content, etc. The other end attachment may be, for example, another type of bucket, such as a large bucket, a slope bucket, or a dredging bucket. The other end attachment may be a type of end attachment other than a bucket, such as an agitator, a breaker, or a grapple.

[0021] The boom 4, the arm 5, and the bucket 6 are hydraulically driven by a boom cylinder 7, an arm cylinder 8, and a bucket cylinder 9, which serve as hydraulic actuators, respectively.

[0022] The cabin 10 is a cockpit where an operator sits, and is mounted on the front left side of the upper rotating body 3.

[0023] The shovel 100 is equipped with, for example, a communication device 60, and can communicate with an external device via a predetermined communication line. This allows the shovel 100 to transmit (upload) various types of information to the external device and receive various types of signals (for example, information signals and control signals) from the external device.

[0024] The predetermined communication line includes, for example, a wide area network (WAN). The wide area network may include, for example, a mobile communication network with a base station as a terminal. The wide area network may also include, for example, a satellite communication network using a communication satellite above the shovel 100. The wide area network may also include, for example, the Internet network. The predetermined communication line may also include, for example, a local area network (LAN) of a facility in which the management device 200 is installed. The local network may be a wireless line, a wired line, or a line including both. The predetermined communication line may also include, for example, a short-distance communication line based on a predetermined wireless communication method such as WiFi or Bluetooth (registered trademark).

[0025] In response to the operation of an operator in the cabin 10, the shovel 100 operates actuators (e.g., hydraulic actuators) to drive operating elements (hereinafter referred to as "driven elements") such as the lower running body 1, upper rotating body 3, boom 4, arm 5, and bucket 6.

[0026] Further, instead of or in addition to being configured to be operable by an operator in the cabin 10, the shovel 100 may be configured to be remotely operable from outside the shovel 100. When the shovel 100 is remotely operated, the inside of the cabin 10 may be unmanned. In the following description, it is assumed that the operation of the operator includes at least one of the operation of the operating device 26 by the operator in the cabin 10 and the remote operation by an external operator.

[0027] The remote operation includes, for example, a mode in which the shovel 100 is operated by an input from a user (operator) regarding the actuator of the shovel 100 performed by a predetermined external device. In this case, the shovel 100 may transmit, for example, image information (hereinafter, "surrounding image") of the surroundings of the shovel 100 based on the output of the imaging device S6 described later to the external device, and the image information may be displayed on a display device (hereinafter, "display device for remote operation") provided in the external device. In addition, various information images (information screens) displayed on the output device 50 in the cabin 10 of the shovel 100 may also be displayed on the display device for remote operation of the external device. This allows the operator of the external device to remotely operate the shovel 100 while checking the display contents, such as the surrounding image showing the state of the surroundings of the shovel 100 and various information images displayed on the display device for remote operation. Then, the shovel 100 may operate the actuators in response to a remote operation signal indicating the contents of the remote operation received from the external device, and drive the driven elements such as the lower traveling body 1, the upper rotating body 3, the boom 4, the arm 5, and the bucket 6.

[0028] Further, the remote operation may include, for example, a mode in which the shovel 100 is operated by an external voice input or gesture input to the shovel 100 by a person (e.g., a worker) around the shovel 100. Specifically, the shovel 100 recognizes voices uttered by surrounding workers or gestures made by the workers through a voice input device (e.g., a microphone) or an imaging device mounted on the shovel 100 (the shovel's own machine). Then, the shovel 100 may operate actuators according to the contents of the recognized voices or gestures, and drive driven elements such as the lower traveling body 1, the upper rotating body 3, the boom 4, the arm 5, and the bucket 6.

[0029] The shovel 100 may automatically operate the actuators regardless of the contents of the operation by the operator. This allows the shovel 100 to realize a function of automatically operating at least some of the driven elements such as the lower traveling body 1, the upper rotating body 3, the boom 4, the arm 5, and the bucket 6, i.e., a so-called "automatic driving function" or "machine control (MC) function."

[0030] The automatic operation function may include a function of automatically operating a driven element (actuator) other than the driven element (actuator) to be operated in response to an operator's operation of the operating device 26 or remote operation, i.e., a so-called "semi-automatic operation function" or "operation support type MC function". The automatic operation function may also include a function of automatically operating at least a part of a plurality of driven elements (hydraulic actuators) on the premise that there is no operation or remote operation of the operating device 26 by the operator, i.e., a so-called "fully automatic operation function" or "fully automatic type MC function". In the excavator 100, when the fully automatic operation function is enabled, the inside of the cabin 10 may be unmanned. The semi-automatic operation function, the fully automatic operation function, etc. may also include a mode in which the operation content of the driven element (actuator) to be the target of automatic operation is automatically determined according to a rule defined in advance. In addition, the semi-automatic driving function and the fully automatic driving function may include a mode in which the shovel 100 autonomously makes various decisions and autonomously determines the operation content of the driven element (hydraulic actuator) that is the target of the automatic driving based on the results of those decisions (so-called "autonomous driving function").

[0031] [Excavator configuration] Next, the configuration of the shovel will be described with reference to Figs.

[0032] 2 and 3 are block diagrams showing an example and another example of the configuration of the shovel 100 according to this embodiment. In Fig. 2 and Fig. 3, a path through which mechanical power is transmitted is indicated by a double line, a path through which high-pressure hydraulic oil for driving a hydraulic actuator flows is indicated by a solid line, a path through which pilot pressure is transmitted is indicated by a dashed line, and a path through which an electric signal is transmitted is indicated by a dotted line.

[0033] The shovel 100 includes various components, such as a hydraulic drive system for hydraulically driving the driven elements, an operation system for operating the driven elements, a user interface system for exchanging information with the user, a communication system for communicating with the outside world, and a control system for various controls.

[0034] <<Hydraulic drive system>> 2 and 3, the hydraulic drive system of the excavator 100 according to this embodiment includes hydraulic actuators that hydraulically drive each of the driven elements, such as the lower traveling body 1 (left and right crawlers 1C), upper rotating body 3, boom 4, arm 5, and bucket 6, as described above. The hydraulic actuators include traveling hydraulic motors 1ML, 1MR, swing hydraulic motor 2A, boom cylinder 7, arm cylinder 8, and bucket cylinder 9. The hydraulic drive system of the excavator 100 according to this embodiment also includes an engine 11, a regulator 13, a main pump 14, and a control valve 17.

[0035] The engine 11 is a prime mover and a main power source in the hydraulic drive system. The engine 11 is, for example, a diesel engine that uses light oil as fuel. The engine 11 is mounted, for example, on the rear of the upper rotating body 3. The engine 11 rotates at a constant speed at a preset target speed under direct or indirect control by a controller 30 (described later), and drives the main pump 14 and the pilot pump 15.

[0036] The regulator 13 controls (adjusts) the discharge amount of the main pump 14 under the control of the controller 30. For example, the regulator 13 adjusts the angle of the swash plate of the main pump 14 (hereinafter, the “tilt angle”) in response to a control command from the controller 30.

[0037] The main pump 14 (an example of a hydraulic pump) supplies hydraulic oil to the control valve 17 through a high-pressure hydraulic line. The main pump 14 is mounted, for example, on the rear of the upper rotating body 3, similar to the engine 11. As described above, the main pump 14 is driven by the engine 11. The main pump 14 is, for example, a variable displacement hydraulic pump, and as described above, under the control of the controller 30, the tilt angle of the swash plate is adjusted by the regulator 13 to adjust the stroke length of the piston, thereby controlling the discharge flow rate (discharge pressure).

[0038] There may be one main pump 14, or, as described below, there may be a plurality of main pumps 14. For example, the main pump 14 includes two main pumps 14A and 14B (see FIGS. 5 and 7 to 10).

[0039] The control valve 17 is a hydraulic control device that controls the hydraulic actuators in response to the contents of the operator's operation on the operating device 26 or the remote operation, or in response to an operation command related to an automatic operation function output from the controller 30. The control valve 17 is mounted, for example, in the center of the upper rotating body 3. As described above, the control valve 17 is connected to the main pump 14 via a high-pressure hydraulic line, and selectively supplies the hydraulic oil supplied from the main pump 14 to each hydraulic actuator in response to the operator's operation or an operation command output from the controller 30. Specifically, the control valve 17 includes a plurality of control valves (also referred to as "directional control valves") 17A to 17G that control the flow rate and flow direction of the hydraulic oil supplied from the main pump 14 to each hydraulic actuator. Hereinafter, the control valves 17A to 17G may be collectively referred to as "control valve 17X," or any one of the control valves 17A to 17G may be individually referred to as "control valve 17X."

[0040] The control valve 17A is configured to be able to supply hydraulic oil to the traveling hydraulic motor 1ML, and to discharge the hydraulic oil from the traveling hydraulic motor 1ML and return it to the hydraulic oil tank T. This allows the control valve 17B to drive the traveling hydraulic motor 1ML by pilot pressure supplied from the operating device 26 or the hydraulic control valve 31.

[0041] The control valve 17B is configured to be able to supply hydraulic oil to the traveling hydraulic motor 1MR, and to discharge the hydraulic oil from the traveling hydraulic motor 1MR and return it to the hydraulic oil tank T. This allows the control valve 17B to drive the traveling hydraulic motor 1MR by pilot pressure supplied from the operating device 26 or the hydraulic control valve 31.

[0042] The control valve 17C is configured to be able to supply hydraulic oil to the swing hydraulic motor 2A, and to discharge the hydraulic oil from the swing hydraulic motor 2A and return it to the hydraulic oil tank T. This allows the control valve 17C to drive the swing hydraulic motor 2A by pilot pressure supplied from the operating device 26 or the hydraulic control valve 31.

[0043] The control valve 17D is configured to be able to supply hydraulic oil to the boom cylinder 7, and to discharge the hydraulic oil from the boom cylinder 7 and return it to the hydraulic oil tank T. In this way, the control valve 17D can drive the boom cylinder 7 in response to the pilot pressure supplied from the operating device 26 or the hydraulic control valve 31. Also, a plurality of control valves 17D may be provided.

[0044] The control valve 17E is configured to be able to supply hydraulic oil to the arm cylinder 8, and to discharge the hydraulic oil from the arm cylinder 8 and return it to the hydraulic oil tank T. This allows the control valve 17E to drive the arm cylinder 8 by pilot pressure supplied from the operation device 26 or the hydraulic control valve 31. Also, a plurality of control valves 17E may be provided.

[0045] The control valve 17F is configured to be able to supply hydraulic oil to the bucket cylinder 9, and to discharge the hydraulic oil from the bucket cylinder 9 and return it to the hydraulic oil tank T. In this way, the control valve 17F can drive the bucket cylinder 9 in response to the pilot pressure supplied from the operating device 26 or the hydraulic control valve 31.

[0046] The control valve 17G supplies hydraulic oil to a hydraulic actuator HA (see FIGS. 8 to 10) built into the auxiliary attachment OP (see FIGS. 8 to 10).

[0047] The spare attachment OP includes, for example, a crusher, a grappler, a breaker, etc. that can be attached to the tip of the arm 5 instead of the bucket 6 as an end attachment. The spare attachment OP also includes, for example, a tiltrotator, a quick coupling, etc. that are interposed between the arm 5 and the end attachment.

[0048] Specifically, when the spare attachment OP is a single-acting type, the control valve 17G supplies hydraulic oil to the spare attachment OP (hydraulic actuator HA), and the hydraulic oil inside the hydraulic actuator HA returns to the hydraulic oil tank T, bypassing the control valve 17G, via the switching valve VC (see Figures 8 to 10).

[0049] In addition, when the auxiliary attachment OP is a double-acting type, the control valve 17G is configured to supply hydraulic oil to the auxiliary attachment OP (hydraulic actuator HA) and to discharge the hydraulic oil from the auxiliary attachment OP (hydraulic actuator HA) and return it to the hydraulic oil tank T.

[0050] The control valve 17X is, for example, a spool valve having two ports to which pilot pressure is supplied. The control valve 17X has a built-in spool that is movable in the axial direction, and the spool is biased toward the opposite end by spring members provided at both ends of the spool so as to balance the spool at a predetermined neutral position.

[0051] When hydraulic oil is supplied to one port of the control valve 17X, the pressure (pilot pressure) acts on one axial end of the spool, and the spool moves axially to the other end with respect to the neutral position. As a result, as the spool moves, the control valve 17X connects a path that supplies hydraulic oil to one of the two hydraulic oil supply and discharge ports of the hydraulic actuator and discharges hydraulic oil from the other, thereby driving the hydraulic actuator in one direction.

[0052] On the other hand, when hydraulic oil is supplied to the other port of the control valve 17X, the pressure (pilot pressure) acts on the other axial end of the spool, and the spool moves axially toward one end with respect to the neutral position. As a result, as the spool moves, the control valve 17X opens a path that supplies hydraulic oil to the other of the two hydraulic oil supply and discharge ports of the hydraulic actuator and discharges hydraulic oil from one of them, thereby driving the hydraulic actuator in the other direction.

[0053] <<Operation system>> 2 and 3, the operating system of the shovel 100 according to this embodiment includes a pilot pump 15, an operating device 26, and a hydraulic control valve 31. Furthermore, as shown in Fig. 2, the operating system of the shovel 100 according to this embodiment includes a shuttle valve 32 and a hydraulic control valve 33 when the operating device 26 is of a hydraulic pilot type.

[0054] The pilot pump 15 supplies pilot pressure to various hydraulic devices via a pilot line 25. The pilot pump 15 is mounted on the rear of the upper rotating body 3, for example, similar to the engine 11. The pilot pump 15 is, for example, a fixed displacement hydraulic pump, and is driven by the engine 11 as described above.

[0055] The pilot pump 15 may be omitted. In this case, the relatively high pressure hydraulic oil discharged from the main pump 14 is reduced in pressure by a predetermined pressure reducing valve, and the resulting relatively low pressure hydraulic oil is supplied to various hydraulic devices as pilot pressure.

[0056] The operation device 26 is provided near the cockpit of the cabin 10, and is used by the operator to operate various driven elements (lower traveling body 1, upper rotating body 3, boom 4, arm 5, bucket 6, etc.). In other words, the operation device 26 is used by the operator to operate hydraulic actuators (i.e., traveling hydraulic motors 1ML, 1MR, swing hydraulic motor 2A, boom cylinder 7, arm cylinder 8, bucket cylinder 9, etc.) that drive the respective driven elements. The operation device 26 includes, for example, lever devices that operate each of the boom 4 (boom cylinder 7), arm 5 (arm cylinder 8), bucket 6 (bucket cylinder 9), and upper rotating body 3 (swing hydraulic motor 2A). The operation device 26 also includes, for example, pedal devices or lever devices that operate each of the left and right crawlers (traveling hydraulic motors 1ML, 1MR) of the lower traveling body 1.

[0057] For example, as shown in FIG. 2, the operating device 26 is of a hydraulic pilot type. Specifically, the operating device 26 uses hydraulic oil supplied from the pilot pump 15 through a pilot line 25 and a pilot line 25A branched therefrom, and outputs a pilot pressure corresponding to the operation content to a secondary pilot line 27A. The pilot line 27A is connected to one inlet port of a shuttle valve 32, and is connected to the control valve 17 through a pilot line 27 connected to an outlet port of the shuttle valve 32. Thus, pilot pressure corresponding to the operation content related to various driven elements (hydraulic actuators) in the operating device 26 can be input to the control valve 17 through the shuttle valve 32. Therefore, the control valve 17 can drive each hydraulic actuator according to the operation content of the operating device 26 by an operator or the like.

[0058] 3, the operating device 26 is of an electrical type. Specifically, the operating device 26 outputs an electric signal (hereinafter, "operation signal") corresponding to the operation content, and the operation signal is input to the controller 30. The controller 30 then outputs a control command corresponding to the operation signal, that is, a control signal corresponding to the operation content for the operating device 26, to the hydraulic control valve 31. As a result, a pilot pressure corresponding to the operation content of the operating device 26 is input from the hydraulic control valve 31 to the control valve 17, and the control valve 17 can drive each hydraulic actuator according to the operation content of the operating device 26.

[0059] Furthermore, the control valve 17X (directional control valve) that drives each hydraulic actuator built into the control valve 17 may be of an electromagnetic solenoid type. In this case, an operation signal output from an operating device 26 may be input directly to the control valve 17, i.e., the electromagnetic solenoid type control valve 17X.

[0060] The hydraulic control valve 31 is provided for each driven element (hydraulic actuator) to be operated by the operating device 26. That is, the hydraulic control valve 31 is provided for each of the left crawler (traveling hydraulic motor 1ML), the right crawler (traveling hydraulic motor 1MR), the upper swing body 3 (swing hydraulic motor 2A), the boom 4 (boom cylinder 7), the arm 5 (arm cylinder 8), and the bucket 6 (bucket cylinder 9). The hydraulic control valve 31 may be provided, for example, in the pilot line 25B between the pilot pump 15 and the control valve 17, and configured to be changeable in its flow path area (i.e., a cross-sectional area through which the hydraulic oil can flow). This allows the hydraulic control valve 31 to output a predetermined pilot pressure to the secondary pilot line 27B by using the hydraulic oil of the pilot pump 15 supplied through the pilot line 25B. Therefore, as shown in FIG. 2, the hydraulic control valve 31 can indirectly apply a predetermined pilot pressure corresponding to a control signal from the controller 30 to the control valve 17 through the shuttle valve 32 between the pilot line 27B and the pilot line 27. 3, the hydraulic control valve 31 can directly apply a predetermined pilot pressure corresponding to a control signal from the controller 30 to the control valve 17 through the pilot line 27B and the pilot line 27. Therefore, the controller 30 can supply a pilot pressure corresponding to the operation of the electric operating device 26 from the hydraulic control valve 31 to the control valve 17, thereby realizing the operation of the excavator 100 based on the operation of the operator.

[0061] Furthermore, the controller 30 may, for example, control the hydraulic control valve 31 to realize an automatic driving function. Specifically, the controller 30 outputs a control signal corresponding to an operation command related to the automatic driving function to the hydraulic control valve 31, regardless of whether the operating device 26 is operated or not. As a result, the controller 30 causes the hydraulic control valve 31 to supply a pilot pressure corresponding to the operation command related to the automatic driving function to the control valve 17, thereby realizing the operation of the excavator 100 based on the automatic driving function.

[0062] Furthermore, the controller 30 may, for example, control the hydraulic control valve 31 to realize remote operation of the shovel 100. Specifically, the controller 30 outputs a control signal corresponding to the content of remote operation specified by a remote operation signal received from the management device 200 to the hydraulic control valve 31 via the communication device 60. As a result, the controller 30 can supply a pilot pressure corresponding to the content of the remote operation from the hydraulic control valve 31 to the control valve 17, thereby realizing the operation of the shovel 100 based on the remote operation by the operator.

[0063] As shown in FIG. 2, the shuttle valve 32 has two inlet ports and one outlet port, and outputs hydraulic oil having a higher pilot pressure of the pilot pressures input to the two inlet ports to the outlet port. The shuttle valve 32 is provided for each driven element (hydraulic actuator) to be operated by the operation device 26. That is, the shuttle valve 32 is provided for each of the left crawler (travel hydraulic motor 1ML), the right crawler (travel hydraulic motor 1MR), the upper rotating body 3 (swing hydraulic motor 2A), the boom 4 (boom cylinder 7), the arm 5 (arm cylinder 8), and the bucket 6 (bucket cylinder 9). One of the two inlet ports of the shuttle valve 32 is connected to a pilot line 27A on the secondary side of the operation device 26 (specifically, the above-mentioned lever device or pedal device included in the operation device 26), and the other is connected to a pilot line 27B on the secondary side of the hydraulic control valve 31. The outlet port of the shuttle valve 32 is connected to the pilot port of the corresponding control valve of the control valve 17 through the pilot line 27. The corresponding control valve is a control valve that drives a hydraulic actuator that is the object of operation of the above-mentioned lever device or pedal device connected to one inlet port of the shuttle valve 32. Therefore, each of these shuttle valves 32 can apply the higher of the pilot pressure of the pilot line 27A on the secondary side of the operating device 26 and the pilot pressure of the pilot line 27B on the secondary side of the hydraulic control valve 31 to the pilot port of the corresponding control valve. In other words, the controller 30 can control the corresponding control valve regardless of the operation of the operating device 26 by the operator by outputting a pilot pressure higher than the pilot pressure on the secondary side of the operating device 26 from the hydraulic control valve 31. Therefore, the controller 30 can control the operation of the driven elements (the lower traveling body 1, the upper rotating body 3, and the attachment AT) regardless of the operating state of the operating device 26 by the operator, thereby realizing an automatic driving function.

[0064] As shown in FIG. 2, the hydraulic control valve 33 is provided in the pilot line 27A that connects the operating device 26 and the shuttle valve 32. The hydraulic control valve 33 is configured to be able to change its flow path area, for example. The hydraulic control valve 33 operates in response to a control signal input from the controller 30. As a result, the controller 30 can forcibly reduce the pilot pressure output from the operating device 26 when the operating device 26 is operated by the operator. Therefore, even when the operating device 26 is being operated, the controller 30 can forcibly suppress or stop the operation of the hydraulic actuator corresponding to the operation of the operating device 26. In addition, the controller 30 can reduce the pilot pressure output from the operating device 26 to be lower than the pilot pressure output from the hydraulic control valve 31, for example, even when the operating device 26 is being operated. Therefore, the controller 30 can reliably apply a desired pilot pressure to the pilot port of the control valve in the control valve 17, for example, regardless of the operation content of the operating device 26, by controlling the hydraulic control valve 31 and the hydraulic control valve 33. Therefore, the controller 30 can more appropriately realize the automatic operation function and remote control function of the shovel 100 by controlling the hydraulic control valve 33 in addition to the hydraulic control valve 31, for example.

[0065] <<User interface system>> As shown in FIGS. 2 and 3, the user interface system of the shovel 100 according to this embodiment includes an operation device 26, an output device 50, and an input device 52.

[0066] The output device 50 outputs various types of information to a user (operator) of the excavator 100 inside the cabin 10.

[0067] For example, the output device 50 includes indoor lighting devices and display devices that are provided in a place that is easily visible to an operator seated in the cabin 10 and output various information in a visual manner. The lighting devices are, for example, warning lights, etc. The display devices are, for example, liquid crystal displays and organic EL (Electroluminescence) displays.

[0068] Furthermore, for example, the output device 50 includes a sound output device that outputs various information by an auditory method, such as a buzzer or a speaker.

[0069] Also, for example, the output device 50 includes a device that outputs various information in a tactile manner, such as by vibration of the cockpit.

[0070] The input device 52 is provided within a range close to an operator seated inside the cabin 10 and receives various inputs from the operator. Signals corresponding to the received inputs are taken into the controller 30.

[0071] For example, the input device 52 is an operation input device that accepts operation input. The operation input device may include a touch panel mounted on the display device, a touch pad installed around the display device, a button switch, a lever, a toggle, a knob switch provided on the operation device 26 (lever device), and the like.

[0072] Furthermore, for example, the input device 52 may be a voice input device that accepts voice input from an operator. The voice input device includes, for example, a microphone.

[0073] Furthermore, for example, the input device 52 may be a gesture input device that accepts a gesture input by an operator. The gesture input device includes, for example, an imaging device (an interior camera) installed in the cabin 10.

[0074] <<Communications>> As shown in FIGS. 2 and 3, the communication system of the shovel 100 according to this embodiment includes a communication device 60.

[0075] The communication device 60 connects to a predetermined communication line and communicates with a device (e.g., the management device 200) provided separately from the shovel 100. The device provided separately from the shovel 100 may include a device outside the shovel 100, as well as a portable terminal device brought into the cabin 10 by the user of the shovel 100. The communication device 60 may be, for example, 4G (4 th Generation) and 5G (5 th The communication device 60 may include a mobile communication module conforming to a standard such as IEEE 802.11 Generation. The communication device 60 may also include a satellite communication module. The communication device 60 may also include a WiFi communication module, a Bluetooth (registered trademark) communication module, or the like.

[0076] <<Control system>> 2 and 3, the control system of the shovel 100 according to this embodiment includes a controller 30. The control system of the shovel 100 according to this embodiment also includes a boom angle sensor S1, an arm angle sensor S2, a bucket angle sensor S3, a machine body attitude sensor S4, a swing angle sensor S5, and an imaging device S6. As shown in FIG. 2, the control system of the shovel 100 according to this embodiment also includes an operating pressure sensor 29 when the operating device 26 is of a hydraulic pilot type.

[0077] The controller 30 performs various controls related to the shovel 100. The functions of the controller 30 may be realized by any hardware or any combination of hardware and software. For example, the controller 30 is configured mainly with a computer including a central processing unit (CPU), a memory device such as a random access memory (RAM), a non-volatile auxiliary storage device such as a read only memory (ROM), and various interface devices for input and output. The controller 30 realizes various functions by, for example, loading a program installed in the auxiliary storage device into the memory device and executing the program on the CPU.

[0078] The controller 30 performs control related to the operation of a hydraulic actuator (driven element) of the shovel 100, for example, with a hydraulic control valve 31 as a control object.

[0079] Specifically, the controller 30 may control the operation of a hydraulic actuator (driven element) of the shovel 100 based on the operation of the operating device 26, with the hydraulic control valve 31 as the control target.

[0080] Furthermore, the controller 30 may perform control related to remote operation of a hydraulic actuator (driven element) of the shovel 100, with the hydraulic control valve 31 as a control target. That is, the operation of the hydraulic actuator (driven element) of the shovel 100 may include remote operation of the hydraulic actuator from outside the shovel 100.

[0081] Furthermore, the controller 30 may control the automatic operation function of the shovel 100 by controlling the hydraulic control valve 31. That is, the operation of the hydraulic actuator of the shovel 100 may include an operation command for the hydraulic actuator of the shovel 100 that is output based on the automatic operation function.

[0082] Furthermore, the controller 30 performs control related to, for example, the electromagnetic relief valves 82, 92 described below. Specifically, when the pressure of the hydraulic oil on the primary side of the electromagnetic relief valves 82, 92 reaches or exceeds a predetermined relief pressure (set value), the controller 30 may output a control command to the electromagnetic relief valves 82, 92 to discharge the hydraulic oil on the primary side to the secondary side (hydraulic oil tank). Furthermore, the controller 30 may set a new relief pressure for the electromagnetic relief valves 82, 92 from a user (operator) received via the input device 52, or change the setting of an already set relief pressure.

[0083] Note that some of the functions of the controller 30 may be realized by another controller (control device). That is, the functions of the controller 30 may be realized in a distributed manner by a plurality of controllers.

[0084] 2, the operating pressure sensor 29 detects the pilot pressure on the secondary side (pilot line 27A) of the hydraulic pilot type operating device 26, i.e., the pilot pressure corresponding to the operating state of each driven element (hydraulic actuator) in the operating device 26. A detection signal of the pilot pressure by the operating pressure sensor 29, which corresponds to the operating state of the lower traveling body 1, upper rotating body 3, boom 4, arm 5, bucket 6, etc. in the operating device 26, is input to the controller 30.

[0085] The boom angle sensor S1 acquires detection information related to the attitude angle of the boom 4 (hereinafter referred to as "boom angle") with respect to a predetermined reference (for example, a horizontal plane or a state at either end of the movable angle range of the boom 4, etc.). The boom angle sensor S1 may include, for example, a rotary encoder, an acceleration sensor, an angular velocity sensor, a six-axis sensor, an IMU (Inertial Measurement Unit), etc. The boom angle sensor S1 may also include a cylinder sensor capable of detecting the extension / retraction position of the boom cylinder 7.

[0086] The arm angle sensor S2 acquires detection information related to the attitude angle of the arm 5 (hereinafter referred to as "arm angle") with respect to a predetermined reference (for example, a straight line connecting the connection points at both ends of the boom 4 or a state at either end of the movable angle range of the arm 5). The arm angle sensor S2 may include, for example, a rotary encoder, an acceleration sensor, an angular velocity sensor, a six-axis sensor, an IMU, etc. The arm angle sensor S2 may also include a cylinder sensor capable of detecting the extension / retraction position of the arm cylinder 8.

[0087] The bucket angle sensor S3 acquires detection information related to the attitude angle of the bucket 6 (hereinafter referred to as "bucket angle") with respect to a predetermined reference (for example, a straight line connecting the connection points at both ends of the arm 5 or a state at either end of the movable angle range of the bucket 6). The bucket angle sensor S3 may include, for example, a rotary encoder, an acceleration sensor, an angular velocity sensor, a six-axis sensor, an IMU, etc. The bucket angle sensor S3 may also include a cylinder sensor capable of detecting the extension / retraction position of the bucket cylinder 9.

[0088] The vehicle attitude sensor S4 acquires detection information regarding the attitude state of the vehicle including the lower running body 1 and the upper rotating body 3. The attitude state of the vehicle includes the inclination state of the vehicle. The inclination state of the vehicle includes, for example, a tilt state in the front-rear direction corresponding to the attitude state around the left-right axis of the upper rotating body 3, and a tilt state in the left-right direction corresponding to the attitude state around the front-rear axis of the upper rotating body 3. The attitude state of the vehicle also includes a rotation state of the upper rotating body 3 corresponding to the attitude state around the rotation axis of the upper rotating body 3. The vehicle attitude sensor S4 is mounted on the upper rotating body 3, for example, and acquires (outputs) detection data regarding the attitude angles of the front-rear axis, left-right axis, and rotation axis of the upper rotating body 3 (hereinafter, "front-rear tilt angle" and "left-right tilt angle"). As a result, the vehicle attitude sensor S4 can acquire detection information regarding the orientation of the upper rotating body 3 with respect to the ground (rotation attitude around the rotation axis). The orientation of the upper rotating body 3 means, for example, the direction in which the attachment AT extends when viewed from above, that is, the forward direction as viewed from the upper rotating body 3. The aircraft attitude sensor S4 may include, for example, an acceleration sensor (inclination sensor), an angular velocity sensor, a six-axis sensor, an IMU, etc.

[0089] The information on the orientation of the upper rotating body 3 with respect to the ground may be acquired from another device instead of or in addition to the aircraft attitude sensor S4. For example, a geomagnetic sensor (first acquisition device) may be mounted on the upper rotating body 3. In this case, the controller 30 can acquire information on the orientation of the upper rotating body 3 with respect to the ground from the geomagnetic sensor. Also, for example, the controller 30 may determine the orientation of the upper rotating body 3 with respect to the ground by determining the direction of the captured surrounding objects (particularly, fixed objects such as utility poles and trees) based on the output (captured image) of the imaging device S6. In other words, the information on the orientation of the upper rotating body 3 with respect to the ground may be acquired from the imaging device S6.

[0090] The swing angle sensor S5 acquires detection information on the relative swing angle of the upper swing body 3 with respect to the lower running body 1 as a reference. As a result, the swing angle sensor S5 acquires detection information on the swing angle of the upper swing body 3 with respect to a predetermined reference (for example, a state in which the forward direction of the lower running body 1 and the front of the upper swing body 3 coincide with each other). The swing angle sensor S5 includes, for example, a potentiometer, a rotary encoder, a resolver, etc.

[0091] The information on the orientation of the upper rotating body 3 with respect to the lower running body 1 as a reference may be acquired from another device instead of or in addition to the rotation angle sensor S5. For example, a geomagnetic sensor may be mounted on each of the lower running body 1 and the upper rotating body 3. In this case, the controller 30 can acquire information on the orientation of the upper rotating body 3 with respect to the lower running body 1 as a reference based on the output of the geomagnetic sensor of the lower running body 1 and the output of the geomagnetic sensor of the upper rotating body 3. Also, for example, the controller 30 may use the output (captured image) of the imaging device S6 to determine the orientation of the upper rotating body 3 with respect to the lower running body 1 as a reference from the position where the lower running body 1 is captured in the imaging device. In other words, the information on the orientation of the upper rotating body 3 with respect to the lower running body 1 as a reference may be acquired from the imaging device S6. Also, instead of or in addition to the information on the orientation of the upper rotating body 3 with respect to the ground and the lower running body 1 as a reference, information on the orientation of the lower running body 1 with respect to the ground may be acquired. The orientation of the lower running structure 1 means, for example, a direction along the front-rear axis of the lower running structure 1, that is, a direction along the longitudinal axis of the crawler 1C. For example, the lower running structure 1 may be equipped with an IMU, a geomagnetic sensor, or the like.

[0092] In addition, for example, the shovel 100 may further be equipped with a positioning device capable of measuring the absolute position of the shovel 100 itself. The positioning device is, for example, a Global Navigation Satellite System (GNSS) sensor. This can improve the estimation accuracy of the attitude state of the shovel 100.

[0093] The imaging device S6 captures and outputs the captured image of the periphery of the shovel 100. The captured image output from the imaging device S6 is input to the controller 30.

[0094] The imaging device S6 includes, for example, a monocular camera, a stereo camera, a depth camera, etc. Furthermore, the imaging device S6 may acquire three-dimensional data (for example, point cloud data or surface data) representing the positions and shapes of objects around the shovel 100 within a predetermined imaging range (angle of view) based on the captured image.

[0095] Furthermore, instead of or in addition to the imaging device S6, a distance sensor such as a LIDAR (Light Detecting and Ranging), a millimeter wave radar, an ultrasonic sensor, an infrared sensor, or a distance image sensor may be mounted on the shovel 100. The distance sensor may acquire three-dimensional data (e.g., point cloud data) that indicates the positions and shapes of objects around the shovel 100 within a predetermined detection range.

[0096] As shown in FIG. 1, the imaging device S6 is attached to, for example, the front end of the upper surface of the cabin 10, and acquires an image of the front of the upper rotating body 3 including the working range of the end attachment (bucket 6). This allows the controller 30 to recognize the situation in front of the shovel 100 based on the output of the imaging device S6. The controller 30 can also recognize the position of the shovel 100 and the rotation state of the upper rotating body 3 based on the positions and changes in appearance of objects around the shovel 100 recognized from the output (captured image) of the imaging device S6. The imaging range of the imaging device S6 includes the boom 4, the arm 5, and the end attachment (bucket 6), that is, the attachment. This allows the controller 30 to recognize the attitude state of the attachment (for example, at least one attitude angle of the boom 4, the arm 5, and the bucket 6) based on the output of the imaging device S6. Therefore, when the shovel 100 is remotely operated, the controller 30 transmits the surrounding image based on the imaging device S6 and information on the recognition result to the management device 200, etc., and can provide an external operator with information on the shovel 100 (own machine) and its surrounding conditions. Also, when the shovel 100 operates with a fully automatic driving function, a control device (for example, the controller 30) related to the fully automatic driving function can output an operation command related to the hydraulic actuator while grasping the surrounding conditions of the shovel 100 and the attitude state of the own machine. Also, when the shovel 100 operates with a fully automatic driving function, the controller 30 transmits the surrounding image based on the imaging device S6 and information on the recognition result to the management device 200, etc., and can provide a user (monitor) who monitors the work from the outside with information on the shovel 100 (own machine) and its surrounding conditions.

[0097] Furthermore, the imaging device S6 may be further configured to be capable of acquiring an image relating to at least one of the left, right, and rear of the upper rotating body 3. Specifically, the imaging device S6 may include at least one of a camera capable of imaging the left, right, and rear of the upper rotating body 3, in addition to a camera capable of imaging the front of the upper rotating body 3. This allows the controller 30 to recognize the situation not only in front of the shovel 100 (upper rotating body 3) but also to the left, right, and rear of the shovel 100 (upper rotating body 3).

[0098] [First example of hydraulic circuit] Next, a first example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T in the excavator 100 will be described with reference to Figs.

[0099] 4 and 5 are diagrams showing a first example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T in the excavator 100. Specifically, Fig. 4 is a diagram showing a first example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T, which is applied to a hydraulic system in which one main pump 14 supplies hydraulic oil to all hydraulic actuators, and Fig. 5 is a diagram showing a first example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T, which is applied to a hydraulic system in which two main pumps 14A, 14B supply hydraulic oil to all hydraulic actuators.

[0100] 4 and 5, the spool positions of the control valves 17D and 17F in the neutral state are depicted. Also, in Fig. 4 and 5, of the control valves 17A to 17G included in the control valve 17, the control valves 17A to 17C, 17E, and 17G are omitted from the illustration.

[0101] As shown in FIG. 4, one main pump 14 supplies hydraulic oil to the control valves 17A to 17G through a center bypass oil passage OC1 and a parallel oil passage OC2 (both of which are examples of supply oil passages).

[0102] The center bypass oil passage OC1 passes through the control valves 17A to 17G in series, and reaches the hydraulic oil tank T. This enables the main pump 14 to circulate the hydraulic oil through the center bypass oil passage OC1.

[0103] The parallel oil passage OC2 branches off upstream of the control valves 17A-17G arranged in series with the center bypass oil passage OC1, and is connected in parallel to a plurality of downstream control valves excluding the most upstream control valve among the control valves 17A-17G. As a result, even if the flow path area of ​​the center bypass oil passage OC1 is restricted or the center bypass oil passage OC1 is blocked by a relatively upstream control valve, hydraulic oil is supplied to the downstream control valve through the parallel oil passage OC2.

[0104] 5, the main pump 14A supplies hydraulic oil to some of the control valves 17A to 17G through a center bypass oil passage OC11 and a parallel oil passage OC12 (both of which are examples of supply oil passages). The main pump 14B supplies hydraulic oil to the remaining control valves 17A to 17G through a center bypass oil passage OC21 and a parallel oil passage OC22 (both of which are examples of supply oil passages).

[0105] For example, the main pump 14A supplies hydraulic oil to the control valve 17D, and the main pump 14B supplies hydraulic oil to the control valve 17F.

[0106] The center bypass oil passage OC11 passes through some of the control valves 17A to 17G in series, and merges with the center bypass oil passage OC21 to reach the hydraulic oil tank T.

[0107] The parallel oil passage OC12 branches off upstream of the control valves arranged in series with the center bypass oil passage OC11, and is connected in parallel to the downstream control valves except for the most upstream control valve among those control valves. As a result, even if the flow path area of ​​the center bypass oil passage OC11 is restricted or the center bypass oil passage OC11 is blocked by a relatively upstream control valve, hydraulic oil is supplied to the downstream control valve through the parallel oil passage OC12.

[0108] The center bypass oil passage OC21 passes through the remaining control valves among the control valves 17A to 17G in series, merges with the center bypass oil passage OC11, and leads to the hydraulic oil tank T.

[0109] The parallel oil passage OC22 branches off upstream of the control valves arranged in series with the center bypass oil passage OC21, and is connected in parallel to the downstream control valves except for the most upstream control valve among those control valves. As a result, even if the flow area of ​​the center bypass oil passage OC21 is restricted or the center bypass oil passage OC21 is blocked by a relatively upstream control valve, hydraulic oil is supplied to the downstream control valve through the parallel oil passage OC22.

[0110] As shown in FIGS. 4 and 5, the control valves 17A to 17G supply the hydraulic oil supplied from the main pump 14 to the hydraulic actuators, and discharge the hydraulic oil from the insides (oil chambers) of the hydraulic actuators to the hydraulic oil tank T, as described above.

[0111] For example, when the boom 4 is operated in the up direction, the spool of the control valve 17D moves to the right in the figure and supplies hydraulic oil to the bottom-side oil chamber of the boom cylinder 7 through oil passage 17DB. Then, the control valve 17D discharges the hydraulic oil in the rod-side oil chamber of the boom cylinder 7 toward the hydraulic oil tank T through oil passage 17DA. On the other hand, when the boom 4 is operated in the down direction, the control valve 17D moves the spool to the left in the figure and supplies hydraulic oil to the rod-side oil chamber of the boom cylinder 7 through oil passage 17DA. Then, the control valve 17D discharges the hydraulic oil in the bottom-side oil chamber of the boom cylinder 7 toward the hydraulic oil tank T through oil passage 17DB.

[0112] Furthermore, for example, when the control valve 17F is operated in the closing direction of the bucket 6, the spool moves to the right in the drawing, supplies hydraulic oil to the bottom side oil chamber of the bucket cylinder 9, and discharges the hydraulic oil in the rod side oil chamber of the bucket cylinder 9 toward the hydraulic oil tank T. On the other hand, when the control valve 17F is operated in the opening direction of the bucket 6, the spool moves to the left in the drawing, supplies hydraulic oil to the rod side oil chamber of the bucket cylinder 9, and discharges the hydraulic oil in the bottom side oil chamber of the bucket cylinder 9 toward the hydraulic oil tank T.

[0113] The control valves 17A to 17G are each connected to a return oil passage for returning hydraulic oil toward a hydraulic oil tank T, and return hydraulic oil discharged from the hydraulic actuator to the hydraulic oil tank T through the return oil passage. Then, each return oil passage finally merges into a return oil passage 70 (an example of a first return oil passage), and the hydraulic oil discharged from the hydraulic actuator is returned to the hydraulic oil tank T through the return oil passage 70.

[0114] For example, the control valves 17D and 17F are connected to return oil passages 70D and 70F, respectively, and the return oil passages 70D and 70F merge into the return oil passage 70.

[0115] A back pressure check valve 72 is provided in the return oil passage 70 .

[0116] The back pressure check valve 72 is a check valve with a spring for preventing the backflow of hydraulic oil from the hydraulic oil tank T to the upstream side. When the pressure of the hydraulic oil on the upstream side is equal to or higher than a predetermined standard, the back pressure check valve 72 allows the hydraulic oil on the upstream side to flow toward the hydraulic oil tank T by the action of the spring. This makes it possible to maintain the back pressure of the return oil passage from the control valves 17A to 17G in a relatively high state (a state equal to or higher than the predetermined standard). This makes it possible to suppress a situation in which the operation of the control valves 17A to 17G is affected by fluctuations in the back pressure of the return oil passage.

[0117] A return oil passage 80 is connected to oil passage 17DB that connects the bottom side oil chamber of boom cylinder 7 and control valve 17D.

[0118] The return oil passage 80 (an example of a second return oil passage) returns the hydraulic oil in the bottom side oil chamber of the boom cylinder 7 to the hydraulic oil tank T, bypassing the control valve 17D.

[0119] The return oil passage 80 is provided with an electromagnetic relief valve 82 and a back pressure check valve 84 .

[0120] When the pressure of the hydraulic oil on the upstream side of the return oil passage 80, i.e., in the oil passage 17DB, reaches or exceeds a predetermined relief pressure, the electromagnetic relief valve 82 causes the hydraulic oil to flow downstream and returns the hydraulic oil to the hydraulic oil tank T through the return oil passage 80. The electromagnetic relief valve 82 operates according to a control command (control current) input from the controller 30.

[0121] For example, due to the operation of the attachment AT or the like, a forward tipping moment that exceeds the moment that suppresses tipping of the excavator 100 due to its own weight may occur. In this case, the pressure of the hydraulic oil in the bottom-side oil chamber of the boom cylinder 7 becomes relatively high, so the electromagnetic relief valve 82 can discharge the hydraulic oil in the bottom-side oil chamber of the boom cylinder 7 to the hydraulic oil tank T and reduce the pressure of the hydraulic oil in the bottom-side oil chamber of the boom cylinder 7. Therefore, the boom cylinder 7 functions as a cushion against the forward tipping moment of the excavator 100, suppressing the occurrence of lifting of the rear of the excavator 100 and an increase in the lifting that has occurred, thereby suppressing the excavator 100 from tipping forward.

[0122] The back pressure check valve 84 is disposed downstream of the electromagnetic relief valve 82 in the return oil passage 80. The back pressure check valve 84 is a spring-loaded check valve capable of preventing backflow of hydraulic oil from the hydraulic oil tank T to the upstream side. When the pressure of the hydraulic oil on the upstream side, i.e., on the electromagnetic relief valve 82 side, is equal to or higher than a predetermined standard, the back pressure check valve 84 allows the hydraulic oil on the upstream side to flow toward the hydraulic oil tank T by the action of the spring. This makes it possible to maintain the back pressure of the electromagnetic relief valve 82 in a relatively high state (a state equal to or higher than a predetermined standard). Therefore, the operation of the electromagnetic relief valve 82 to respond to the back pressure fluctuations in the return oil passage 80 makes it possible to suppress a situation in which hunting (vibration) occurs in the electromagnetic relief valve 82.

[0123] Incidentally, the electromagnetic relief valve 82 may be provided to discharge the hydraulic oil in the rod-side oil chamber of the boom cylinder 7 to the hydraulic oil tank T. In this case, the return oil passage 80 is connected to the oil passage 17DA. Also, two electromagnetic relief valves 82 may be provided corresponding to the rod-side oil chamber and the bottom-side oil chamber of the boom cylinder 7, respectively. The same may be true for the case of a second example described below.

[0124] For example, due to the operation of the attachment AT or the like, a backward tipping moment that exceeds the moment that suppresses tipping of the excavator 100 due to its own weight may occur. In this case, the pressure of the hydraulic oil in the rod-side oil chamber of the boom cylinder 7 becomes relatively high, so the electromagnetic relief valve 82 can discharge the hydraulic oil in the rod-side oil chamber of the boom cylinder 7 to the hydraulic oil tank T and reduce the pressure of the hydraulic oil in the bottom-side oil chamber of the boom cylinder 7. Therefore, the boom cylinder 7 functions as a cushion against the backward tipping moment of the excavator 100, suppressing the occurrence of lifting of the front of the excavator 100 and an increase in the lifting that has occurred, thereby suppressing the excavator 100 from tipping backward.

[0125] [Operation of the first example of hydraulic circuit] Next, with reference to FIG. 6, the operation of the first example of the hydraulic circuit (FIGS. 4 and 5) for returning the hydraulic oil to the hydraulic oil tank T will be described.

[0126] Fig. 6 is a diagram showing a hydraulic circuit for returning hydraulic oil in a shovel according to a comparative example to a hydraulic oil tank T. In Fig. 6, the same components as those in the above-mentioned first example (Fig. 5) are given the same reference numerals, and components unique to the shovel according to the comparative example are given unique reference numerals.

[0127] As shown in FIG. 6, the shovel according to the comparative example differs from the above-described first example (FIG. 5) in that the return oil passage 80 is replaced with a return oil passage 80c.

[0128] The return oil passage 80c branches off from the oil passage 17DB and merges with the return oil passage 70. An electromagnetic relief valve 82 is provided in the return oil passage 80c.

[0129] In the comparative example, the return oil passage 80 merges with the return oil passage 70 together with the return oil passages of the control valves 17A to 17F, so that the return oil passage 80 communicates with the return oil passages of the control valves 17A to 17F, and the back pressure of the electromagnetic relief valve 82 is affected by the return oil passages of the control valves 17A to 17F. Therefore, depending on the load state of the hydraulic actuators controlled by the control valves 17A to 17F, the back pressure of the electromagnetic relief valve 82 may fluctuate relatively greatly or fluctuate relatively frequently. As a result, the electromagnetic relief valve 82 may cause hunting (vibration) by performing an operation to respond to the relatively large or relatively frequent back pressure fluctuations under the control of the controller 30.

[0130] In contrast to this, in the above-mentioned first example, the return oil passage 70 that returns the hydraulic oil of the control valves 17A to 17G to the hydraulic oil tank is separated from the return oil passage 80 in which the electromagnetic relief valve 82 is disposed. Therefore, it is possible to suppress back pressure fluctuations in the electromagnetic relief valve 82 and to suppress hunting (vibration) of the electromagnetic relief valve 82.

[0131] As described above, in the first example, the excavator 100 includes the return oil passage 70, the electromagnetic relief valve 82, and the return oil passage 80 that is different from the return oil passage 70. Specifically, the return oil passage 70 returns the hydraulic oil discharged from the hydraulic actuator to the hydraulic oil tank. The electromagnetic relief valve 82 is configured to be able to discharge the hydraulic oil at a predetermined location in the oil passage from the main pump 14 to the hydraulic oil tank T to the hydraulic oil tank T. The return oil passage 80 connects the electromagnetic relief valve 82 and the hydraulic oil tank T.

[0132] More specifically, in the above-described first example, the return oil passage 80 is provided separately from the return oil passage 70 where the return oil passages of all the hydraulic actuators join together.

[0133] As a result, as described above, the shovel 100 can separate the return oil path 70 for the hydraulic oil discharged from the hydraulic actuator from the return oil path 80 for the hydraulic oil from the electromagnetic relief valve 82, thereby suppressing hunting (vibration) of the electromagnetic relief valve 82.

[0134] Incidentally, the return oil passage 80 may be configured to merge with the return oil passages of some of the hydraulic actuators to return the hydraulic oil to the hydraulic oil tank T. In this case, the return oil passages of some of the hydraulic actuators with relatively small load fluctuations among all the hydraulic actuators may merge with the return oil passage 80 between the electromagnetic relief valve 82 and the back pressure check valve 84. The same may be true for the second to fifth examples described below.

[0135] In the first example described above, the excavator 100 is provided with a back pressure check valve 84 provided in the return oil passage 80 downstream of the electromagnetic relief valve 82.

[0136] This enables the shovel 100 to further suppress back pressure fluctuations in the electromagnetic relief valve 82.

[0137] In the first example described above, the electromagnetic relief valve 82 is provided so as to be able to discharge hydraulic oil in the oil chamber of the boom cylinder 7 that drives the boom 4 with hydraulic oil supplied from the main pump 14, to the hydraulic oil tank.

[0138] As a result, the electromagnetic relief valve 82 allows the boom cylinder 7 to function as a cushion against the front or rear of the shovel 100 being lifted up due to the tipping moment acting on the shovel 100, thereby preventing the shovel 100 from tipping over.

[0139] The electromagnetic relief valve 82 may be provided so as to be able to discharge hydraulic oil in the oil chamber of the arm cylinder 8, which drives the arm 5, with hydraulic oil supplied from the main pump 14, to the hydraulic oil tank T. This allows the arm cylinder 8 to function as a cushion against the lifting of the front or rear of the shovel 100 due to the overturning moment acting on the shovel 100, by the action of the electromagnetic relief valve 82, thereby preventing the shovel 100 from overturning. The same may be true for the case of a second example described below.

[0140] [Second example of hydraulic circuit] Next, a second example of a hydraulic circuit for returning the hydraulic oil to the hydraulic oil tank T in the excavator 100 will be described with reference to FIG.

[0141] Fig. 7 is a diagram showing a second example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T in the excavator 100. Specifically, Fig. 7 is a diagram showing a second example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T, which is applied to a hydraulic system in which two main pumps 14A, 14B supply hydraulic oil to all hydraulic actuators. The following description will focus on the parts that differ from the above-mentioned first example.

[0142] As in the first example described above, the hydraulic circuit for returning the hydraulic oil to the hydraulic oil tank of this example may be applied to a hydraulic system in which one main pump 14 supplies hydraulic oil to all hydraulic actuators (see FIG. 4).

[0143] As shown in FIG. 7, the excavator 100 of this embodiment is provided with make-up oil passages 86, 88, unlike the first embodiment described above.

[0144] The make-up oil passage 86 connects the oil passage 17DA and the hydraulic oil tank T. A check valve 87 is provided in the make-up oil passage 86.

[0145] The check valve 87 allows hydraulic oil to flow from the hydraulic oil tank T to the oil passage 17DA, i.e., to the rod side oil chamber of the boom cylinder 7, but does not allow (prohibit) flow in the opposite direction. As a result, the make-up oil passage 86 can suck up the hydraulic oil from the hydraulic oil tank T to the rod side oil chamber of the boom cylinder 7 while preventing the hydraulic oil from flowing out of the rod side oil chamber of the boom cylinder 7 into the hydraulic oil tank T. Therefore, when cavitation occurs in the rod side oil chamber of the boom cylinder 7 and negative pressure is generated, for example, the excavator 100 can suck up the hydraulic oil through the make-up oil passage 86 and suppress cavitation.

[0146] The make-up oil passage 88 connects between the oil passage 17DB (an example of a connecting oil passage) and the hydraulic oil tank T. A check valve 89 is provided in the make-up oil passage 88.

[0147] The check valve 89 allows hydraulic oil to flow from the hydraulic oil tank T to the oil passage 17DB, i.e., the bottom-side oil chamber of the boom cylinder 7, but does not allow (prohibit) flow in the opposite direction. As a result, the make-up oil passage 88 can suck up hydraulic oil from the hydraulic oil tank T to the bottom-side oil chamber of the boom cylinder 7 while preventing the hydraulic oil from flowing out of the bottom-side oil chamber of the boom cylinder 7 into the hydraulic oil tank. Therefore, when cavitation occurs in the bottom-side oil chamber of the boom cylinder 7 and negative pressure is generated, for example, the excavator 100 can suck up the hydraulic oil through the make-up oil passage 88 and suppress cavitation.

[0148] Thus, in this example, the excavator 100 is provided with a make-up oil passage 88 that is provided separately from the return oil passage 80 in which the back pressure check valve 84 is provided, and that connects between the control valve 17D and the boom cylinder 7, and the hydraulic oil tank T.

[0149] This allows the shovel 100 to suck up the hydraulic oil into the bottom-side oil chamber of the boom cylinder 7 through the makeup oil passage 88. Therefore, the shovel 100 can suppress cavitation in the bottom-side oil chamber of the boom cylinder 7, as described above.

[0150] [Third example of hydraulic circuit] Next, a third example of a hydraulic circuit for returning the hydraulic oil to the hydraulic oil tank T in the excavator 100 will be described with reference to FIG.

[0151] Fig. 8 is a diagram showing a third example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T in the excavator 100. Specifically, Fig. 8 is a diagram showing a third example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T, which is applied to a hydraulic system in which two main pumps 14A, 14B supply hydraulic oil to all actuators. The following description will focus on the parts that differ from the above-mentioned first example and the like.

[0152] As in the first example described above, the hydraulic circuit for returning the hydraulic oil to the hydraulic oil tank of this example may be applied to a hydraulic system in which one main pump 14 supplies hydraulic oil to all hydraulic actuators (see FIG. 4).

[0153] As shown in FIG. 8, the control valves 17A to 17G supply the hydraulic oil supplied from the main pump 14 to the hydraulic actuators, as described above, and discharge the hydraulic oil inside the hydraulic actuators to the hydraulic oil tank.

[0154] For example, when the hydraulic actuator HA (in this example, a hydraulic cylinder) of a double-acting auxiliary attachment OP is operated in the extension direction, the spool of the control valve 17G moves to the right in the figure, and supplies hydraulic oil to the bottom-side oil chamber of the hydraulic cylinder through oil passage 17GB (an example of an auxiliary oil passage). Then, the control valve 17G discharges hydraulic oil in the rod-side oil chamber of the hydraulic cylinder toward the hydraulic oil tank T through oil passage 17GA (an example of an auxiliary oil passage). On the other hand, when the hydraulic cylinder is operated in the contraction direction, the spool of the control valve 17G moves to the left in the figure, and supplies hydraulic oil to the rod-side oil chamber of the hydraulic cylinder through oil passage 17GA, and discharges hydraulic oil in the bottom-side oil chamber of the hydraulic cylinder toward the hydraulic oil tank T through oil passage 17GB.

[0155] Gate valves VA and VB are provided in oil passages 17GA and 17GB extending from control valve 17G, respectively. With this, when a spare attachment is not used and a spare attachment OP is not connected to the ends of oil passages 17GA and 17GB, the gate valves VA and VB are closed to prevent hydraulic oil from control valve 17G from leaking out of oil passages 17GA and 17GB to the outside.

[0156] A switching valve VC is provided in the oil passage 17GB at a position closer to the control valve 17G than the gate valve VB.

[0157] The switching valve VC switches between a state in which the gate valve VB side, i.e., the oil passage 17GB on the hydraulic actuator HA side is connected to the control valve 17G and a state in which the oil passage 17GB is connected to the hydraulic oil tank T through a return oil passage 90 described later, in response to a control command (control current) from the controller 30. Specifically, the switching valve VC switches between a state in which the inlet port connected to the oil passage 17GB on the hydraulic actuator HA side is connected to either a first outlet port connected to the oil passage 17GB on the control valve 17G side or a second outlet port connected to the return oil passage 90. When the auxiliary attachment OP (hydraulic actuator HA) is a double-acting type, the switching valve VC maintains, under the control of the controller 30, a state in which the oil passage 17GB on the hydraulic actuator HA side is connected to the control valve 17G, i.e., a state in which the inlet port is connected to the first outlet port. On the other hand, when the spare attachment OP is single acting, the switching valve VC maintains a state in which the oil passage 17GB on the hydraulic actuator HA side is connected to the hydraulic oil tank T through the return oil passage 90, in other words, a state in which the inlet port is connected to the second outlet port, under the control of the controller 30. As a result, the switching valve VC can supply and discharge hydraulic oil to the spare attachment OP using the common oil passages 17GA, 17GB, whether the spare attachment OP is single acting or double acting.

[0158] A return oil passage 90A is connected to the oil passage 17GA at a position closer to the control valve 17G than the gate valve VA, and a return oil passage 90B is connected to the oil passage 17GB at a position between the gate valve VA and the switching valve VC.

[0159] The return oil passages 90A, 90B merge into a return oil passage 90 (an example of a second return oil passage), and the return oil passage 90 is connected to a hydraulic oil tank T.

[0160] A check valve 91A is provided in the return oil passage 90A.

[0161] The check valve 91A allows hydraulic oil to flow from the oil passage 17GA toward the return oil passage 90 (hydraulic oil tank T) and does not allow (prohibit) the flow in the opposite direction. This prevents hydraulic oil from flowing from the return oil passage 90 (hydraulic oil tank T) side into the oil passage 17GA through the return oil passage 90A.

[0162] Similarly, a check valve 91B is provided in the return oil passage 90B.

[0163] The check valve 91B allows hydraulic oil to flow from the oil passage 17GB toward the return oil passage 90 (hydraulic oil tank T) and does not allow (prohibit) the flow in the opposite direction. This enables the check valve 91B to prevent hydraulic oil from flowing into the oil passage 17GB from the return oil passage 90 (hydraulic oil tank T) side through the return oil passage 90B.

[0164] An electromagnetic relief valve 92 is provided in the return oil passage 90 .

[0165] When the pressure of the hydraulic oil on the upstream side of the return oil passage 90, i.e., in the oil passage 17GA or the oil passage 17GB, reaches or exceeds a predetermined relief pressure, the electromagnetic relief valve 92 causes the hydraulic oil to flow downstream and returns the hydraulic oil to the hydraulic oil tank T through the return oil passage 90. The electromagnetic relief valve 92 operates according to a control command (control current) input from the controller 30. This is because an allowable upper limit value for the pressure of the hydraulic oil supplied to the auxiliary attachment OP is predetermined depending on the type of the attachment.

[0166] A second outlet port of the switching valve VC is connected to the downstream (hydraulic oil tank T) side of the electromagnetic relief valve 92 in the return oil passage 90. As a result, when the spare attachment OP is a single-acting type, the switching valve VC can return the hydraulic oil flowing out from the hydraulic actuator HA to the hydraulic oil tank T through the return oil passage 90, regardless of the operation of the electromagnetic relief valve 92.

[0167] Further, a back pressure check valve 94 is provided on the downstream (hydraulic oil tank) side of the electromagnetic relief valve 92 in the return oil passage 90 and downstream of the connection point with the second outlet port of the switching valve VC.

[0168] The back pressure check valve 94 is a check valve with a spring that can prevent backflow of hydraulic oil from the hydraulic oil tank T to the upstream (electromagnetic relief valve 92) side. When the pressure of the hydraulic oil on the upstream side, i.e., on the electromagnetic relief valve 92 side, is equal to or higher than a predetermined standard, the back pressure check valve 94 allows the hydraulic oil on the upstream side to flow toward the hydraulic oil tank T by the action of the spring. This makes it possible to maintain the back pressure of the electromagnetic relief valve 92 in a relatively high state (a state equal to or higher than a predetermined standard). Therefore, it is possible to suppress a situation in which hunting (vibration) occurs in the electromagnetic relief valve 92 due to the operation of the electromagnetic relief valve 92 to respond to fluctuations in the back pressure in the return oil passage 90.

[0169] Thus, in this example, the excavator 100 includes the return oil passage 70, the electromagnetic relief valve 92, and the return oil passage 90 which is different from the return oil passage 70. Specifically, the return oil passage 70 returns the hydraulic oil discharged from the hydraulic actuator to the hydraulic oil tank. Also, the electromagnetic relief valve 92 is configured to be able to discharge the hydraulic oil at a predetermined location in the oil passage from the main pump 14 to the hydraulic oil tank T to the hydraulic oil tank T. And the return oil passage 80 connects the electromagnetic relief valve 82 and the hydraulic oil tank T.

[0170] More specifically, in the above-described first example, the return oil passage 80 is provided separately from the return oil passage 70 where the return oil passages of all the hydraulic actuators join together.

[0171] As a result, the shovel 100, as in the first example etc. described above, can separate the return oil path 70 of the hydraulic oil discharged from the hydraulic actuator from the return oil path 80 of the hydraulic oil from the electromagnetic relief valve 92, thereby suppressing hunting (vibration) of the electromagnetic relief valve 92.

[0172] In addition, in this example, the shovel 100 is equipped with a back pressure check valve 94 provided in the return oil passage 90 downstream of the electromagnetic relief valve 92.

[0173] This enables the shovel 100 to further suppress back pressure fluctuations in the electromagnetic relief valve 92.

[0174] In this example, the electromagnetic relief valve 92 is provided so as to be able to discharge, to the hydraulic oil tank T, the hydraulic oil in the oil passages 17GA, 17GB, which are for supplying and discharging the hydraulic oil of the main pump 14 to and from the auxiliary attachment OP.

[0175] As a result, the shovel 100 can, by the action of the electromagnetic relief valve 92, suppress the pressure of the hydraulic oil supplied to the auxiliary attachment OP (hydraulic actuator HA) to a predetermined level or lower that is determined for each type of auxiliary attachment OP.

[0176] [Fourth example of hydraulic circuit] Next, a fourth example of a hydraulic circuit for returning the hydraulic oil to the hydraulic oil tank T in the excavator 100 will be described with reference to FIG.

[0177] Fig. 9 is a diagram showing a fourth example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T in the excavator 100. Specifically, Fig. 9 is a diagram showing a fourth example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T, which is applied to a hydraulic system in which two main pumps 14A, 14B supply hydraulic oil to all hydraulic actuators. The following description will focus on the parts that differ from the above-mentioned third example.

[0178] As in the first example described above, the hydraulic circuit for returning the hydraulic oil to the hydraulic oil tank of this example may be applied to a hydraulic system in which one main pump 14 supplies hydraulic oil to all hydraulic actuators (see FIG. 4).

[0179] As shown in FIG. 9, the excavator 100 of this embodiment is provided with make-up oil passages 96, 98, unlike the third embodiment described above.

[0180] The make-up oil passage 96 connects between the oil passage 17GA (an example of a connecting oil passage) and the hydraulic oil tank T. A check valve 97 is provided in the make-up oil passage 96.

[0181] The check valve 97 allows hydraulic oil to flow from the hydraulic oil tank T to the oil passage 17GA, i.e., to the rod side oil chamber of the hydraulic actuator HA (hydraulic cylinder), but does not allow (prohibit) flow in the opposite direction. As a result, the make-up oil passage 96 can suck up hydraulic oil from the hydraulic oil tank T to the rod side oil chamber of the hydraulic cylinder while preventing the hydraulic oil from flowing out of the rod side oil chamber of the hydraulic cylinder into the hydraulic oil tank T. Therefore, when cavitation occurs in the rod side oil chamber of the hydraulic cylinder and negative pressure is generated, for example, the excavator 100 can suck up the hydraulic oil through the make-up oil passage 96 and suppress cavitation.

[0182] The make-up oil passage 98 connects between the oil passage 17GB (an example of a connecting oil passage) and the hydraulic oil tank T. A check valve 99 is provided in the make-up oil passage 98.

[0183] The check valve 99 allows hydraulic oil to flow from the hydraulic oil tank T to the oil passage 17DB, i.e., to the bottom-side oil chamber of the hydraulic actuator HA (hydraulic cylinder), but does not allow (prohibit) flow in the opposite direction. This allows the make-up oil passage 98 to suck up hydraulic oil from the hydraulic oil tank T to the bottom-side oil chamber of the hydraulic cylinder while preventing the hydraulic oil from flowing out of the bottom-side oil chamber of the hydraulic cylinder into the hydraulic oil tank. Therefore, when cavitation occurs in the bottom-side oil chamber of the hydraulic cylinder and negative pressure is generated, for example, the excavator 100 can suck up the hydraulic oil through the make-up oil passage 98 and suppress cavitation.

[0184] Thus, in this example, the excavator 100 is provided with make-up oil passages 96, 98 which are provided separately from the return oil passage 90 in which the back pressure check valve 94 is provided and which connect the control valve 17G and the hydraulic actuator HA (hydraulic cylinder) and between the control valve 17G and the hydraulic oil tank T.

[0185] This allows the shovel 100 to suck up the hydraulic oil into the oil chamber of the hydraulic actuator HA (hydraulic cylinder) through the makeup oil passages 96, 98. Therefore, the shovel 100 can suppress cavitation of the hydraulic actuator HA (hydraulic cylinder).

[0186] [Fifth example of hydraulic circuit] Next, a fifth example of a hydraulic circuit for returning the hydraulic oil to the hydraulic oil tank T in the excavator 100 will be described with reference to FIG.

[0187] Fig. 10 is a diagram showing a fifth example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T in the excavator 100. Specifically, Fig. 10 is a diagram showing the fifth example of a hydraulic circuit for returning hydraulic oil to the hydraulic oil tank T, which is applied to a hydraulic system in which two main pumps 14A, 14B supply hydraulic oil to all actuators. The following description will focus on the parts that differ from the above-mentioned fourth example.

[0188] As in the first example described above, the hydraulic circuit for returning the hydraulic oil to the hydraulic oil tank of this example may be applied to a hydraulic system in which one main pump 14 supplies hydraulic oil to all hydraulic actuators (see FIG. 4).

[0189] As shown in FIG. 10, this embodiment differs from the above-described fourth embodiment in that the back pressure check valve 94 is replaced with a throttle 95, and the arrangement of make-up oil passages 96, 98 is different.

[0190] The throttle 95 is provided on the downstream (hydraulic oil tank) side of the electromagnetic relief valve 92 in the return oil passage 90 and downstream of the connection point with the second outlet port of the switching valve VC. The throttle 95 is, for example, an orifice. This makes it possible to maintain the back pressure of the electromagnetic relief valve 92 in a relatively high state (a state equal to or higher than a predetermined standard). Therefore, it is possible to suppress a situation in which hunting (vibration) occurs in the electromagnetic relief valve 92 due to the operation of the electromagnetic relief valve 92 to respond to the back pressure fluctuation in the return oil passage 90. Furthermore, unlike the back pressure check valve 94, the throttle 95 can allow the flow of hydraulic oil from the hydraulic oil tank T to the upstream (oil passages 17GA, 17GB) side in the return oil passage 90.

[0191] The make-up oil passage 96 connects the return oil passage 90 on the downstream side (hydraulic oil tank T) of the electromagnetic relief valve 92 to the upstream side of the electromagnetic relief valve 92, i.e., the oil passage 17GA, so as to bypass the electromagnetic relief valve 92. The make-up oil passage 96 is provided with a check valve 97, as in the case of the above-mentioned fourth example. As a result, the make-up oil passage 96 can suck up hydraulic oil from the hydraulic oil tank T through the return oil passage 90 and supply it to the oil passage 17GA, bypassing the electromagnetic relief valve 92, while preventing hydraulic oil from flowing out from the oil passage 17GA to the return oil passage 90 in a manner that bypasses the electromagnetic relief valve 92. Therefore, the excavator 100 can suck up hydraulic oil through the make-up oil passage 96 and suppress cavitation, for example, when cavitation occurs in the rod-side oil chamber of the hydraulic cylinder, generating negative pressure.

[0192] The make-up oil passage 98 bypasses the electromagnetic relief valve 92. HelloThe make-up oil passage 98 connects the return oil passage 90 on the downstream side (hydraulic oil tank T) of the electromagnetic relief valve 92 to the upstream side of the electromagnetic relief valve 92, i.e., the oil passage 17GB. As in the case of the above-mentioned fourth example, the make-up oil passage 98 is provided with a check valve 99. As a result, the make-up oil passage 98 can suck up hydraulic oil from the hydraulic oil tank T through the return oil passage 90 and supply it to the oil passage 17GB, bypassing the electromagnetic relief valve 92, while preventing hydraulic oil from flowing out from the oil passage 17GB to the return oil passage 90 in a manner that bypasses the electromagnetic relief valve 92. Therefore, the excavator 100 can suck up hydraulic oil through the make-up oil passage 98 and suppress cavitation, for example, when cavitation occurs in the bottom-side oil chamber of the hydraulic cylinder, generating negative pressure.

[0193] Thus, in this example, the shovel 100 is provided with a throttle 95 provided in the return oil passage 90 downstream of the electromagnetic relief valve 82.

[0194] This enables the shovel 100 to further suppress back pressure fluctuations in the electromagnetic relief valve 82.

[0195] Moreover, in this example, the excavator 100 is provided with makeup oil passages 96, 98 and check valves 97, 99. Specifically, the makeup oil passages 96, 98 each connect between the return oil passage 90, in which the throttle 95 is provided, and the oil passages 17GA, 17GB, which connect the control valve 17G and the hydraulic actuator HA, so as to bypass the electromagnetic relief valve 92. The check valves 97, 99 are each provided in the makeup oil passages 96, 98, and allow the flow of hydraulic oil from the return oil passage 90 to the oil passages 17GA, 17GB on the primary side (upstream side) of the electromagnetic relief valve 92.

[0196] As a result, the shovel 100 can suck up the hydraulic oil into the oil chamber of the hydraulic actuator HA (hydraulic cylinder) through the makeup oil passages 96, 98, bypassing the electromagnetic relief valve 92, while utilizing the return oil passage 90. Therefore, the shovel 100 can suppress cavitation of the hydraulic actuator HA (hydraulic cylinder) while configuring the makeup oil passages 96, 98 to be relatively short.

[0197] As in the present example, in the above-mentioned second example (FIG. 7), the back pressure check valve 84 may be replaced with a throttle, and the make-up oil passage 88 may connect the downstream side (hydraulic oil tank T) of the electromagnetic relief valve 82 to the upstream side, i.e., the oil passage 17DB, so as to bypass the electromagnetic relief valve 82.

[0198] [Transformation / Change] Although the embodiments have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist described in the claims.

[0199] Also, for example, in the above-described embodiment and the like, the main pump 14 and the pilot pump 15 may be driven by another prime mover (for example, an electric motor) instead of or in addition to the engine 11. That is, the shovel 100 may be a hybrid shovel, an electric shovel, or the like in which the main pump 14 and the pilot pump 15 are driven by an electric motor.

[0200] Also, for example, in the above-described embodiment and the like, the shovel 100 may be configured such that some of the driven elements, such as the lower traveling body 1, the upper rotating body 3, the boom 4, the arm 5, and the bucket 6, are electrically driven. In other words, the shovel 100 may be a hybrid shovel, an electric shovel, or the like, in which some of the driven elements are driven by an electric actuator. [Explanation of symbols]

[0201] 1 Undercarriage 1C Crawler 1ML, 1MR Travel hydraulic motor (hydraulic actuator) 2A Swing Hydraulic Motor (Hydraulic Actuator) 3. Upper rotating body 4. Boom 5 Arm 6 Bucket (end attachment) 7 Boom cylinder (hydraulic actuator) 8 Arm cylinder (hydraulic actuator) 9 Bucket cylinder (hydraulic actuator) 10 Cabin 11 Engine 13 Regulator 14 Main pump (hydraulic pump) 15 Pilot pump 17 Control valve 17A~17G Control valve 17DA,17DB Oil line (connection oil line) 17FA,17FB Oil road 17GA, 17GB Oil passage (spare oil passage, connecting oil passage) 25 Pilot Line 26 Operating device 30 Controller 50 Output Device 52 Input Devices 70 Return oil passage (first return oil passage) 72 Back pressure check valve 80 Return oil passage (second return oil passage) 82 Solenoid relief valve 84 Back pressure check valve (spring loaded check valve) 86 Make-up Oil Road 87 Check valve 88 Make-up Oil Road 89 Check valve 90 Return oil passage (second return oil passage) 92 Solenoid relief valve 94 Back pressure check valve (spring loaded check valve) 95 aperture 96 Makeup Oil Road 97 Check valve 98 Makeup Oil Road 99 Check valve 100 Shovel (working machine) AT Attachment HA Hydraulic Actuator OC1, OC11, OC21 Center bypass oil passage (oil supply passage) OC2, OC12, OC22 Parallel oil passage (oil supply passage) OP Spare Attachment T Hydraulic Oil Tank

Claims

1. A hydraulic oil tank for storing hydraulic oil; a hydraulic pump that draws hydraulic oil from the hydraulic oil tank; a hydraulic actuator driven by hydraulic oil discharged from the hydraulic pump; a first return oil passage for returning hydraulic oil discharged from the hydraulic actuator to the hydraulic oil tank; an electromagnetic relief valve capable of discharging hydraulic oil at a predetermined location in an oil passage from the hydraulic pump to the hydraulic oil tank, into the hydraulic oil tank; a second return oil passage different from the first return oil passage, the second return oil passage connecting the electromagnetic relief valve and the hydraulic oil tank; The second return oil passage is capable of discharging the hydraulic oil flowing in from the electromagnetic relief valve to the hydraulic oil tank without merging with the hydraulic oil in the first return oil passage. Shovel.

2. The hydraulic actuator is provided in a plurality of positions. The second return oil passage is provided separately from the first return oil passages of all the hydraulic actuators. The shovel according to claim 1.

3. a throttle provided in the second return oil passage, or a spring-loaded check valve provided in the second return oil passage and allowing a flow of hydraulic oil from the electromagnetic relief valve toward the hydraulic oil tank; The shovel according to claim 1 or 2.

4. a control valve that allows hydraulic oil supplied from the hydraulic pump to flow into the hydraulic actuator and that discharges hydraulic oil from the hydraulic actuator and returns the hydraulic oil to the hydraulic oil tank; the spring-loaded check valve provided in the second return oil passage; a make-up oil passage provided separately from the second return oil passage and connecting a connection oil passage between the control valve as the predetermined location and the hydraulic actuator and the hydraulic oil tank; The shovel according to claim 3.

5. a control valve that allows hydraulic oil supplied from the hydraulic pump to flow into the hydraulic actuator and that discharges hydraulic oil from the hydraulic actuator and returns the hydraulic oil to the hydraulic oil tank; The throttle provided in the second return oil passage; a make-up oil passage that connects the second return oil passage and a connecting oil passage between the control valve as the predetermined location and the hydraulic actuator so as to bypass the electromagnetic relief valve; a check valve provided in the make-up oil passage and allowing a flow of hydraulic oil from the second return oil passage to a primary oil passage of the electromagnetic relief valve; The shovel according to claim 3.

6. A lower running body; An upper rotating body rotatably mounted on the lower traveling body; A working device mounted on the upper rotating body and including a boom, an arm, and an end attachment; the electromagnetic relief valve is provided so as to be able to discharge hydraulic oil from an oil chamber of a boom cylinder that drives the boom with hydraulic oil supplied from the hydraulic pump, or an arm cylinder that drives the arm with hydraulic oil supplied from the hydraulic pump, to the hydraulic oil tank; A shovel according to any one of claims 1 to 5.

7. A spare oil passage is provided for supplying and discharging hydraulic oil from the hydraulic pump to a spare attachment, The electromagnetic relief valve is provided so as to be able to discharge the hydraulic oil in the reserve oil passage to the hydraulic oil tank. A shovel according to any one of claims 1 to 5.

8. a supply oil passage that supplies hydraulic oil discharged from the hydraulic pump to the hydraulic actuator; a first return oil passage for returning hydraulic oil discharged from the hydraulic actuator to a hydraulic oil tank; an electromagnetic relief valve capable of discharging hydraulic oil at a predetermined location in an oil passage from the hydraulic pump to the hydraulic oil tank, into the hydraulic oil tank; a second return oil passage different from the first return oil passage, the second return oil passage connecting the electromagnetic relief valve and the hydraulic oil tank; The second return oil passage is capable of discharging the hydraulic oil flowing in from the electromagnetic relief valve to the hydraulic oil tank without merging with the hydraulic oil in the first return oil passage. Hydraulic circuits for work machines.

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