Construction machine

Abstract

A hydraulic shovel (1) comprises a closed circuit pump (29), a hydraulic actuator (16), a hydraulic oil tank (61), an air vent pipe (71), a first circuit switching valve (72), a second circuit switching valve (73), and a charge relief valve (70). The air vent pipe (71) is connected to the hydraulic oil tank (61) via the charge relief valve (70). The first circuit switching valve (72), the second circuit switching valve (73), and the charge relief valve (70) are attached to one manifold block (38) in which the air vent pipe (71) is formed. The first circuit switching valve (72) and the second circuit switching valve (73) are disposed below the charge relief valve (70).

Description

Construction machinery

[0001] The present disclosure relates to a construction machine such as a hydraulic excavator.

[0002] Generally, construction machines such as hydraulic excavators and wheel loaders have hydraulic circuits for driving hydraulic actuators. The hydraulic circuits are composed of various hydraulic devices such as hydraulic actuators, hydraulic pumps, and control valves, as well as pipelines (pipes). After manufacturing and assembly, or after maintenance work such as periodic replacement of hydraulic devices, the hydraulic circuits are filled with hydraulic oil. At this time, air (hereinafter referred to as air) may remain in some of the hydraulic devices and pipelines.

[0003] The effects of air remaining in the pipelines can include, for example, noise being generated when a hydraulic pump sucks in air along with the hydraulic oil and then discharges it. Furthermore, air in the hydraulic oil can reduce the responsiveness of hydraulic equipment. For this reason, it is necessary to bleed the air from the hydraulic circuit after assembling hydraulic equipment and pipelines, or after maintenance work, before starting normal operation.

[0004] Patent Document 1 describes a construction machine that allows for the bleeding of air from a closed hydraulic circuit. The construction machine in Patent Document 1 includes a closed circuit, a hydraulic oil tank, a charge pump, a charge flow path, a first check valve, a second check valve, a first circuit switching valve, a second circuit switching valve, and an air bleeding flow path.

[0005] According to the construction machine of Patent Document 1, a charge pump draws hydraulic oil with little air mixed in from a hydraulic oil tank, and this hydraulic oil flows from the charge passage through the first and second check valves into the closed circuit. As a result, the hydraulic oil containing air in the closed circuit is pushed by the hydraulic oil that flows into the closed circuit from the charge pump through the first and second check valves, and is discharged to the hydraulic oil tank through the first and second circuit switch valves and the air vent passage. This allows the closed circuit to be quickly filled with hydraulic oil that is free of air.

[0006] Japanese Patent Application Laid-Open No. 2021-050805

[0007] Patent Document 1 discloses a circuit for bleeding air. However, Patent Document 1 does not describe how to arrange the switching valves (first circuit switching valve, second circuit switching valve) and air bleeding flow path that make up the circuit for bleeding air. To bleed air, it is desirable for the hydraulic oil containing air to flow from downstream to upstream toward the hydraulic oil tank. Therefore, if the first circuit switching valve and the second circuit switching valve are not positioned appropriately, the air in the closed circuit may not be completely bled, and air may remain in the closed circuit. Furthermore, if air remains in the closed circuit, the closed circuit pump, which is a hydraulic device in the closed circuit, may be damaged by air entrapment. This may also result in noise or a decrease in responsiveness.

[0008] An object of the present invention is to provide a construction machine that can suppress the residual air in the closed circuit and improve the air bleeding performance, for example.

[0009] The present invention preferably relates to a hydraulic system including a closed circuit pump, a hydraulic actuator, a first flow path connecting one input / output port of the closed circuit pump and one input / output port of the hydraulic actuator, a second flow path connecting the other input / output port of the closed circuit pump and the other input / output port of the hydraulic actuator, a closed circuit switching valve switchable between a flow position that allows flow through the first flow path and the second flow path and a blocking position that blocks flow through the first flow path and the second flow path, a hydraulic oil tank, a charge pump that discharges hydraulic oil sucked from the hydraulic oil tank, a first pump-side flow path between the closed circuit pump and the closed circuit switching valve in the first flow path, and a second flow path between the closed circuit pump and the closed circuit switching valve in the second flow path. In a construction machine equipped with a charge flow path connecting a second pump side flow path and a discharge port of the charge pump, an air vent flow path connected to the hydraulic oil tank, a first circuit switching valve capable of switching between opening and closing the first pump side flow path and the air vent flow path, and a second circuit switching valve capable of switching between opening and closing the second pump side flow path and the air vent flow path, the air vent flow path is connected to the hydraulic oil tank via a charge relief valve, and the first circuit switching valve, the second circuit switching valve, and the charge relief valve are attached to a single manifold block in which the air vent flow path is formed, and the first circuit switching valve and the second circuit switching valve are arranged below the charge relief valve.

[0010] According to the present invention, it is possible to suppress the air remaining in the closed circuit, and to improve the air removal performance.

[0011] 8 is a right side view showing a hydraulic excavator according to an embodiment. FIG. 9 is a plan view showing an upper rotating body of the hydraulic excavator, with buildings and the like omitted. FIG. 10 is a rear view showing the closed circuit control valve device, the open circuit control valve device, the hydraulic oil tank, etc., as viewed from the A-A direction in FIG. 2. FIG. 11 is a right side view showing the closed circuit control valve device. FIG. 12 is a plan view showing the closed circuit control valve device. FIG. 13 is a rear view showing the closed circuit control valve device. FIG. 14 is a cross-sectional view showing the closed circuit control valve device, with some oil passages omitted. FIG. 15 is a hydraulic circuit diagram of the hydraulic excavator. FIG. 16 is a hydraulic circuit diagram showing, in a simplified form, circuits related to the first closed circuit system and the first open circuit system in FIG.

[0012] Hereinafter, a hydraulic excavator (more specifically, a large hydraulic excavator) will be taken as an example of a construction machine according to an embodiment and will be described in detail with reference to FIGS. 1 to 9. FIG.

[0013] 1, a hydraulic excavator 1, which is a representative example of construction machinery, is used for excavating earth and sand, etc. The hydraulic excavator 1 includes a self-propelled crawler-type undercarriage 2, an upper rotating body 5 that is rotatably mounted on the undercarriage 2 and forms a vehicle body together with the undercarriage 2, and a working device 12 that is mounted on the front side of the upper rotating body 5. The hydraulic excavator 1 performs excavation work of earth and sand, etc., using the working device 12.

[0014] The undercarriage 2 includes a track frame 2A, drive wheels 2B provided on both the left and right sides of the track frame 2A, idler wheels 2C provided on both the left and right sides of the track frame 2A on the opposite sides in the longitudinal direction to the drive wheels 2B, and crawler tracks 2D (only the right side of each is shown) wound around the drive wheels 2B and the idler wheels 2C. The left drive wheel is rotationally driven by a left hydraulic travel motor 3 (see FIG. 8). The right drive wheel 2B is rotationally driven by a right hydraulic travel motor 4 (see FIG. 8). The hydraulic travel motors 3 and 4 constitute hydraulic actuators.

[0015] The upper rotating body 5 is rotatably mounted on the lower traveling body 2 via a rotating device 6 (see FIG. 1 ). The rotating device 6 includes a hydraulic swing motor 7 (see FIG. 8 ) as a hydraulic actuator, a reduction mechanism, and a swing bearing (none of which are shown). The rotating device 6 (hydraulic swing motor 7) drives the upper rotating body 5 to rotate relative to the lower traveling body 2.

[0016] As shown in Figures 1 and 2, the upper rotating body 5 is equipped with a rotating frame 8 as a vehicle body frame that serves as a support structure and has a working device 12 mounted on the front side thereof, a cab 9 that is mounted on the front left side of the rotating frame 8 and forms an operator's cabin therein, a building 22 that is located behind the cab 9 and houses an engine 19, closed circuit pumps 29, 29, open circuit pumps 35, 35, etc. that are mounted on the rotating frame 8, and a counterweight 10 that is attached to the rear of the rotating frame 8 and balances the weight of the working device 12.

[0017] Here, a driver's seat (not shown) for an operator is provided inside the cab 9. Furthermore, operation devices 11 (see FIG. 8 ) for operating the hydraulic excavator 1 are provided in front of, to the left, and to the right of the driver's seat. As an example of a combination of an operation target and a lever operation, the operation device 11 is configured to include a left operation lever 11A, a right operation lever 11B, and left and right travel lever / pedals 11C and 11D. The left operation lever 11A operates, for example, the swing hydraulic motor 7 and the arm cylinder 17. The right operation lever 11B operates, for example, the boom cylinder 16 and the bucket cylinder 18. The left and right travel lever / pedals 11C and 11D operate, for example, the left travel hydraulic motor 3 and the right travel hydraulic motor 4.

[0018] The operation device 11 is connected to the controller 75 via a signal line or the like. By operating the operation device 11, the operator can rotate the upper rotating body 5, turn the working device 12, and travel the lower traveling body 2. For example, by operating the left operation lever 11A, the operator can extend or retract the arm cylinder 17 and rotate the arm 14. In addition, by operating the right operation lever 11B, the operator can extend or retract the boom cylinder 16 and rotate the boom 13.

[0019] 1 , the working device 12 includes a boom 13 rotatably attached to the front side of the revolving frame 8, an arm 14 rotatably attached to the tip of the boom 13, and a bucket 15 rotatably attached to the tip of the arm 14. The boom 13, arm 14, and bucket 15 are driven by a boom cylinder 16, an arm cylinder 17, and a bucket cylinder 18, each of which is a hydraulic cylinder. The boom cylinder 16 rotates the boom 13 relative to the revolving frame 8, the arm cylinder 17 rotates the arm 14 relative to the boom 13, and the bucket cylinder 18 rotates the bucket 15 relative to the arm 14.

[0020] The boom cylinder 16, arm cylinder 17, and bucket cylinder 18, which serve as hydraulic actuators, extend and retract based on hydraulic oil (pressurized oil) from closed circuit pumps 29, 29 and open circuit pumps 35, 35, thereby changing the posture of the work implement 12. That is, during excavation work for earth and sand, for example, the boom cylinder 16, arm cylinder 17, and bucket cylinder 18 extend and retract based on operation of the left operation lever 11A and the right operation lever 11B, thereby rotating the boom 13, arm 14, and bucket 15. This allows earth and sand to be excavated by the bucket 15.

[0021] The boom cylinder 16, arm cylinder 17, and bucket cylinder 18 are configured as single-rod hydraulic cylinders that extend and retract based on the supply and discharge of hydraulic oil. That is, the boom cylinder 16, arm cylinder 17, and bucket cylinder 18 are configured from a tube, a piston that is slidably inserted into the tube and divides the inside of the tube into a bottom-side oil chamber and a rod-side oil chamber, and a rod whose base end is attached to the piston and whose tip end protrudes outside the tube.

[0022] As shown in FIG. 2 , an engine 19 serving as a prime mover is mounted on the revolving frame 8, positioned in front of the counterweight 10. The engine 19 is, for example, a diesel engine. One engine 19 is mounted horizontally on the rear side of the revolving frame 8, extending in the left-right direction. As shown in FIGS. 1 and 2 , to the right of the engine 19, for example, a plurality of closed-circuit pumps 29, 29, open-circuit pumps 35, 35, a charge pump 62 (see FIGS. 8 and 9 ), etc. are attached via a power transmission device 20. The power transmission device 20 has a plurality of gear mechanisms that transmit the rotation of the output shaft of the engine 19, and each gear mechanism is connected to the plurality of closed-circuit pumps 29, 29, the open-circuit pumps 35, 35, the charge pump 62, etc. In addition, a heat exchanger 21 including a radiator, an oil cooler, a condenser, etc. is disposed on the left side of the engine 19.

[0023] The prime mover may be a hybrid prime mover that combines a diesel engine and an electric motor, or a prime mover that is an electric motor alone. Alternatively, the prime mover may be provided in a longitudinally mounted state extending in the fore-and-aft direction of the upper rotating body 5. Two prime movers may also be arranged side by side in the left-right direction.

[0024] The building 22 is provided on the swivel frame 8 so as to cover the equipment including the engine 19, the closed circuit pumps 29, 29, the open circuit pumps 35, 35, and the heat exchanger 21. The building 22 is configured to include a left side panel (not shown), a right side panel 23, and a top panel 24. The building 22 is formed, for example, by attaching iron plates or the like to a framework made of multiple steel members.

[0025] Next, the configurations of the closed circuit systems 25, 26, 27, and 28 and the open circuit systems 31, 32, 33, and 34 mounted on the hydraulic excavator 1 will be described with reference to Fig. 8. Note that the configuration of the hydraulic circuit diagram shown in Fig. 8 is described in detail in, for example, Japanese Patent Application Laid-Open No. 2016-118281, and therefore the following description will focus on the configuration related to the embodiment.

[0026] 8, the hydraulic system (hydraulic drive unit 51) of the hydraulic excavator 1 includes four closed circuit pumps 29, 29 and four hydraulic actuators 16, 17, 18, 7 (i.e., the boom cylinder 16, the arm cylinder 17, the bucket cylinder 18 and the swing hydraulic motor 7). The hydraulic system (hydraulic drive unit 51) of the hydraulic excavator 1 also includes four open circuit pumps 35, 35 and two hydraulic actuators 3, 4 (i.e., the left traveling hydraulic motor 3 and the right traveling hydraulic motor 4).

[0027] The hydraulic system (hydraulic drive device 51) of the hydraulic excavator 1 is configured so that the four closed circuit pumps 29, 29 and the four hydraulic actuators 16, 17, 18, 7 can be connected in a closed circuit by a closed circuit control valve device 37 (see FIGS. 2 to 7). The controller 75 controls the closed circuit control valve device 37 in accordance with the operation status and work status, that is, by controlling the control valves (closed circuit switching valves 39A to 39D, 40A to 40D, 41A to 41D, 42A to 42D) of the closed circuit control valve device 37, thereby switching the connection relationship between each of the hydraulic actuators 16, 17, 18, 7 and each of the closed circuit pumps 29, 29.

[0028] Here, in the embodiment, an example will be described in which four closed circuit systems 25, 26, 27, 28 are configured by connecting each closed circuit pump 29, 29 one-to-one with each hydraulic actuator 16, 17, 18, 7. That is, the closed circuit configured by the leftmost closed circuit pump 29 in Fig. 8 and the boom cylinder 16 is referred to as the first closed circuit system 25. The closed circuit configured by the second closed circuit pump 29 from the left in Fig. 8 and the arm cylinder 17 is referred to as the second closed circuit system 26. The closed circuit configured by the third closed circuit pump 29 from the left in Fig. 8 and the bucket cylinder 18 is referred to as the third closed circuit system 27. The closed circuit configured by the fourth closed circuit pump 29 from the left in Fig. 8 and the swing hydraulic motor 7 is referred to as the fourth closed circuit system 28.

[0029] 8 , the first closed circuit system 25 includes a closed circuit pump 29 driven by the engine 19 and a plurality of closed circuit lines 30, 30 connecting the closed circuit pump 29 and the boom cylinder 16. The first closed circuit system 25 also includes a closed circuit switching valve 39A, which is a control valve of a closed circuit control valve device 37, provided midway through the plurality of closed circuit lines 30, 30. The closed circuit lines 30, 30 branch off midway and are also connected to the arm cylinder 17, the bucket cylinder 18, and the swing hydraulic motor 7 via other closed circuit switching valves 39B, 39C, 39D, which are control valves of the closed circuit control valve device 37.

[0030] The second closed circuit system 26 includes a closed circuit pump 29 driven by the engine 19 and a plurality of closed circuit lines 30, 30 connecting the closed circuit pump 29 and the arm cylinder 17. The second closed circuit system 26 also includes a closed circuit switching valve 40B, which is a control valve of a closed circuit control valve device 37, provided midway through the plurality of closed circuit lines 30, 30. The closed circuit lines 30, 30 branch off midway and are also connected to the boom cylinder 16, the bucket cylinder 18, and the swing hydraulic motor 7 via other closed circuit switching valves 40A, 40C, 40D, which are control valves of the closed circuit control valve device 37.

[0031] The third closed circuit system 27 includes a closed circuit pump 29 driven by the engine 19 and a plurality of closed circuit lines 30, 30 connecting the closed circuit pump 29 and the bucket cylinder 18. The third closed circuit system 27 also includes a closed circuit switching valve 41C, which is a control valve of a closed circuit control valve device 37, provided midway through the plurality of closed circuit lines 30, 30. The closed circuit lines 30, 30 branch off midway and are also connected to the boom cylinder 16, the arm cylinder 17, and the swing hydraulic motor 7 via other closed circuit switching valves 41A, 41B, 41D, which are control valves of the closed circuit control valve device 37.

[0032] The fourth closed circuit system 28 includes a closed circuit pump 29 driven by the engine 19, and a plurality of closed circuit lines 30, 30 connecting the closed circuit pump 29 and the swing hydraulic motor 7. The fourth closed circuit system 28 also includes a closed circuit switching valve 42D, which is a control valve of the closed circuit control valve device 37, provided midway through the plurality of closed circuit lines 30, 30. The closed circuit lines 30, 30 branch off midway and are also connected to the boom cylinder 16, the arm cylinder 17, and the bucket cylinder 18 via other closed circuit switching valves 42A, 42B, 42C, which are control valves of the closed circuit control valve device 37.

[0033] As shown in FIGS. 1 and 2 , multiple (e.g., four) closed circuit pumps 29, 29 that make up the closed circuit system 25, 26, 27, 28 are attached to the right side of the engine 19 (power transmission device 20). The four closed circuit pumps 29, 29 are, for example, variable displacement swash plate hydraulic pumps, bent-axis hydraulic pumps, radial piston hydraulic pumps, etc. To avoid overcomplicating the drawing, FIG. 2 only shows two pump-side pipes 54, 55 connecting the closed circuit pumps 29, 29 to the closed circuit control valve device 37. Also, FIG. 2 only shows two actuator-side pipes 56, 57 connecting the closed circuit control valve device 37 to the hydraulic actuators 16, 17, 18, 7. In this case, the actuator-side pipes 56, 57 are indicated by two-dot chain lines in FIG. 2 .

[0034] The closed circuit control valve device 37 is configured to include closed circuit switching valves 39A to 39D, 40A to 40D, 41A to 41D, and 42A to 42D. The closed circuit switching valves 39A to 39D, 40A to 40D, 41A to 41D, and 42A to 42D are configured, for example, as 4-port 2-position solenoid switching valves and are connected to the controller 75 via signal lines. The closed circuit control valve device 37 (i.e., the closed circuit switching valves 39A to 39D, 40A to 40D, 41A to 41D, and 42A to 42D) are provided midway through the closed circuit lines 30, 30 of the closed circuit systems 25, 26, 27, and 28.

[0035] In this embodiment, it is possible to arbitrarily switch which closed circuit pumps 29 are connected to which hydraulic actuators 16, 17, 18, 7. That is, the closed circuit pumps 29 and the pump-side lines 54, 55 (see FIGS. 2, 3, and 9) connected to the closed circuit pumps 29 can be selectively connected to various hydraulic actuators 16, 17, 18, 7 depending on the state of the closed circuit control valve device 37, i.e., the switching states of the closed circuit switching valves 39A to 39D, 40A to 40D, 41A to 41D, and 42A to 42D. In this case, connections can be made depending on the operating status of the operation device 11, such as connecting all of the closed circuit pumps 29 to the boom cylinder 16 when only the boom cylinder 16 is driven.

[0036] Next, the open circuit systems 31, 32, 33, and 34 will be described. As shown in Fig. 8 , the hydraulic system (hydraulic drive device 51) of this embodiment includes four open circuit systems 31, 32, 33, and 34, namely, a first open circuit system 31, a second open circuit system 32, a third open circuit system 33, and a fourth open circuit system 34. The open circuit systems 31, 32, 33, and 34 are hydraulic systems for compensating for a shortage of hydraulic oil in the first closed circuit system 25, the second closed circuit system 26, and the third closed circuit system 27. The open circuit systems 31, 32, 33, and 34 are hydraulic systems for supplying hydraulic oil (pressurized oil) to the traveling hydraulic motors 3 and 4.

[0037] That is, the hydraulic system (hydraulic drive device 51) of the hydraulic excavator 1 is configured so that the four open circuit pumps 35, 35 can be connected to the closed circuit systems 25, 26, 27 or the traveling hydraulic motors 3, 4 by an open circuit control valve device 45 ( FIGS. 2 and 3 ). The controller 75 switches the connection relationship between the open circuit pumps 35, 35 and the closed circuit systems 25, 26, 27 or the traveling hydraulic motors 3, 4 by controlling the open circuit control valve device 45, that is, by controlling the control valves (open circuit switching valves 47, 47) of the open circuit control valve device 45.

[0038] 8 , the first open circuit system 31 includes an open circuit pump 35 driven by the engine 19 and an open circuit line 36 connecting the open circuit pump 35 to the closed circuit line 30 of the first closed circuit system 25. The first open circuit system 31 also includes an open circuit switching valve 47, which is a control valve of the open circuit control valve device 45, provided midway along the open circuit line 36. The open circuit line 36 branches midway and is connected to the second closed circuit system 26, the third closed circuit system 27, and the traveling hydraulic motors 3 and 4 via other open circuit switching valves 47, 47, which are control valves of the open circuit control valve device 45. Note that the second open circuit system 32, the third open circuit system 33, and the fourth open circuit system 34 have substantially the same configuration as the first open circuit system 31, and therefore are denoted by the same reference numerals as the first open circuit system 31, and description thereof will be omitted.

[0039] As shown in FIGS. 1 and 2 , multiple (e.g., four) open circuit pumps 35, 35 that make up the open circuit systems 31, 32, 33, and 34 are attached to the right side of the engine 19 (power transmission device 20). The four open circuit pumps 35, 35 are, for example, variable displacement swash plate hydraulic pumps, bent-axis hydraulic pumps, radial piston hydraulic pumps, etc. To avoid overcomplicating the drawing, FIG. 2 only shows two pump-side pipes 36A, 36A connecting the open circuit pumps 35, 35 to the open circuit control valve device 45. Also, FIG. 2 only shows two actuator-side pipes 36B, 36B connecting the open circuit control valve device 45 to the closed circuit systems 25, 26, and 27 and the hydraulic actuators 3 and 4. In this case, the pump-side pipes 36A, 36A are indicated by dashed lines, and the actuator-side pipes 36B, 36B are indicated by chain lines.

[0040] The open circuit control valve device 45 includes open circuit switching valves 47, 47. The open circuit switching valves 47, 47 are, for example, two-port, two-position solenoid switching valves and are connected to the controller 75 via signal lines. The open circuit control valve device 45 (i.e., the open circuit switching valves 47, 47) are provided in the open circuit lines 36 of the open circuit systems 31, 32, 33, and 34. The controller 75 controls the open circuit control valve device 45, i.e., the control valves (open circuit switching valves 47, 47) of the open circuit control valve device 45, depending on the status of the closed circuit systems 25, 26, and 27 and the open circuit systems 31, 32, 33, and 34, thereby compensating for a shortage of hydraulic oil in the closed circuit systems 25, 26, and 27. In addition, the controller 75 controls the control valves (open circuit switching valves 47 , 47 ) of the open circuit control valve device 45 to supply hydraulic oil (pressure oil) to the traveling hydraulic motors 3 , 4 .

[0041] In this case, it is possible to arbitrarily switch which open circuit systems 31, 32, 33, 34 (open circuit pumps 35, 35) are connected to which closed circuit systems 25, 26, 27 or travel hydraulic motors 3, 4. That is, each open circuit pump 35, 35 and the pump-side pipes 36A, 36A connected to the open circuit pump 35, 35 (see FIGS. 2, 3 and 9) can be selectively connected to each closed circuit system 25, 26, 27 or travel hydraulic motor 3, 4 depending on the state of the open circuit control valve device 45, i.e., the switching state of open circuit switching valves 47, 47 which are control valves of the open circuit control valve device 45.

[0042] Next, the air bleeding configuration of the closed circuit systems 25, 26, 27, and 28 will be described with reference to Fig. 9. The hydraulic circuit diagram in Fig. 9 corresponds to the first closed circuit system 25 and the first open circuit system 31 in Fig. 8. In this case, the hydraulic circuit diagram in Fig. 9 shows the circuits of the first closed circuit system 25 and the first open circuit system 31 in a simplified form. For this reason, some of the hydraulic devices (relief valves, check valves, switching valves, etc.) and oil lines (pipes connected to the other systems 26, 27, 28, 32, 33, and 34, etc.) in the first closed circuit system 25 in Fig. 8 are omitted in the hydraulic circuit diagram in Fig. 9.

[0043] The hydraulic circuit diagram in Fig. 9 also shows hydraulic equipment (a first circuit switching valve 72, a second circuit switching valve 73) and oil passages (an air bleed pipe 71) that are omitted from the hydraulic circuit diagram in Fig. 8. The air bleed configurations of the second closed circuit system 26, the third closed circuit system 27, and the fourth closed circuit system 28 are substantially the same as the air bleed configuration of the first closed circuit system 25, except for the hydraulic actuators 16, 17, 18, and 7, and therefore will not be described again. The charge pump 62 and the charge relief valve 70 shown in Fig. 9 are the same charge pump 62 and charge relief valve 70 used in the four closed circuit systems 25, 26, 27, and 28 as shown in Fig. 8.

[0044] 9 , a hydraulic drive unit 51 including a first closed circuit system 25 and a first open circuit system 31 drives a boom cylinder 16, which is a hydraulic actuator, in a closed circuit. The hydraulic drive unit 51 includes a closed circuit pump 29, a hydraulic actuator 16, closed circuit lines 30, 30, and a closed circuit switching valve 39A. The closed circuit lines 30, 30 include a first line 52 serving as a first flow path (first oil line) and a second line 53 serving as a second flow path (second oil line). The first line 52 connects one input / output port 29A of the closed circuit pump 29 to one input / output port 16A of the hydraulic actuator 16. The second line 53 connects the other input / output port 29B of the closed circuit pump 29 to the other input / output port 16B of the hydraulic actuator 16.

[0045] The closed circuit switching valve 39A is provided midway through the first line 52 and the second line 53. The closed circuit switching valve 39A is switchable between a flow position that allows the flow of hydraulic oil through the first line 52 and the second line 53 and a block position that blocks the flow of hydraulic oil through the first line 52 and the second line 53. That is, when in the flow position, the closed circuit switching valve 39A allows the flow of hydraulic oil through the first line 52 and the second line 53. This allows the flow of hydraulic oil between the closed circuit pump 29 and the hydraulic actuator 16. On the other hand, when in the block position, the closed circuit switching valve 39A blocks the flow of hydraulic oil through the first line 52 and the second line 53. This blocks the flow of hydraulic oil between the closed circuit pump 29 and the hydraulic actuator 16.

[0046] Here, a section of the first conduit 52 between one input / output port 29A of the closed circuit pump 29 and the closed circuit switching valve 39A is referred to as a first pump-side conduit 54 serving as a first pump-side flow path (first pump-side oil path). A section of the first conduit 52 between the closed circuit switching valve 39A and one input / output port 16A of the hydraulic actuator 16 is referred to as a first actuator-side conduit 56 serving as a first actuator-side flow path (first actuator-side oil path). A section of the second conduit 53 between the other input / output port 29B of the closed circuit pump 29 and the closed circuit switching valve 39A is referred to as a second pump-side conduit 55 serving as a second pump-side flow path (second pump-side oil path). A section of the second conduit 53 between the closed circuit switching valve 39A and the other input / output port 16B of the hydraulic actuator 16 is referred to as a second actuator-side conduit 57 serving as a second actuator-side flow path (second actuator-side oil path).

[0047] As shown in FIG. 9 , two ports of the closed circuit pump 29, i.e., two input / output ports 29A and 29B, are connected to the boom cylinder 16 via a first pipe 52 and a second pipe 53, which form a closed circuit. That is, the input / output ports 29A and 29B of the closed circuit pump 29 are connected to pump-side pipes 54 and 55, respectively, and are connected to the boom cylinder 16 via the closed circuit switching valve 39A and actuator-side pipes 56 and 57. This connects the closed circuit pump 29 and the boom cylinder 16 in a closed circuit configuration. The closed circuit switching valve 39A has a flow-through position, which places the pump-side pipes 54 and 55 and the actuator-side pipes 56 and 57 in a flow-through state, and a shut-off position, which places the pump-side pipes 54 and 55 and the actuator-side pipes 56 and 57 in a shut-off state. The closed circuit switching valve 39A is switched based on an opening / closing control command value received from the controller 75.

[0048] 8 and 9, the hydraulic drive system 51 includes a hydraulic oil tank 61, a charge pump 62, a charge line 63, a return line 66, and a charge relief valve 70. The hydraulic drive system 51 also includes a first check valve 64 and a second check valve 65. The hydraulic oil tank 61 stores hydraulic oil. The hydraulic oil tank 61 is connected to the suction side of the charge pump 62 and the suction side of the open circuit pumps 35, 35. As shown in FIG. 9, the hydraulic oil tank 61 is connected to the suction port 62A of the charge pump 62 via a suction line 68. The charge pump 62 discharges hydraulic oil drawn from the hydraulic oil tank 61 to the charge line 63. The charge pump 62 is configured, for example, as a fixed displacement swash plate hydraulic pump, a bent axis hydraulic pump, a radial piston hydraulic pump, or the like. The charge pump 62 has a suction port 62A that draws hydraulic oil from the hydraulic oil tank 61 and a discharge port 62B that discharges the drawn hydraulic oil into the charge line 63.

[0049] The charge line 63 connects the discharge port 62B of the charge pump 62 to the closed circuit lines 30, 30 (the first line 52 and the second line 53). Specifically, as shown in FIG. 9 , the charge line 63 has a discharge line 63A, a pump-side charge line 63B, and an actuator-side charge line 63C. The discharge line 63A extends from the discharge port 62B of the charge pump 62. The pump-side charge line 63B connects the discharge line 63A to the first line 52 (the first pump-side line 54) and the second line 53 (the second pump-side line 55). The actuator-side charge line 63C connects the discharge line 63A to the first line 52 (the first actuator-side line 56) and the second line 53 (the second actuator-side line 57).

[0050] The charge line 63 is connected to the hydraulic oil tank 61 via a return line 66. In Figure 9, the return line 66 branches off from the actuator-side charge line 63C. That is, the upstream side of the return line 66 is connected to the actuator-side charge line 63C. As will be described later, the upstream side of the return line 66 is connected to the downstream side of an air vent line 71, which will be described later. The downstream side of the return line 66 is connected to the hydraulic oil tank 61. A charge relief valve 70, which will be described later, is provided in the return line 66.

[0051] 9 , pump-side charge line 63B includes a first connecting line 63B1 connected to first pump-side line 54 and a second connecting line 63B2 connected to second pump-side line 55. First connecting line 63B1 is provided with a first check valve 64. As a result, charge pump 62 is connected to first line 52 (first pump-side line 54) via discharge line 63A, first connecting line 63B1 of pump-side charge line 63B, and first check valve 64. Second connecting line 63B2 is provided with a second check valve 65. As a result, charge pump 62 is connected to second line 53 (second pump-side line 55) via discharge line 63A, second connecting line 63B2 of pump-side charge line 63B, and second check valve 65.

[0052] In this way, charge line 63 (more specifically, discharge line 63A and pump-side charge line 63B) serving as a charge flow path (charge oil path) connects "first pump-side line 54 and second pump-side line 55" and "discharge port 62B of charge pump 62." First check valve 64 permits hydraulic oil to flow from charge line 63 (discharge line 63A and pump-side charge line 63B) to first pump-side line 54, and prohibits (blocks) hydraulic oil from first pump-side line 54 to charge line 63 (discharge line 63A and pump-side charge line 63B). The second check valve 65 allows the flow of hydraulic oil from the charge line 63 (discharge line 63A and pump side charge line 63B) to the second pump side line 55, and prohibits (blocks) the flow of hydraulic oil from the second pump side line 55 to the charge line 63 (discharge line 63A and pump side charge line 63B).

[0053] Charge pump 62 is driven by power received from engine 19 via power transmission 20. Charge pump 62 draws hydraulic oil from hydraulic oil tank 61 via suction line 68 and discharges it to discharge line 63A. Discharge line 63A is connected to pump-side charge line 63B. As a result, charge pump 62 is connected to first pump-side line 54 via first check valve 64 and to second pump-side line 55 via second check valve 65.

[0054] The discharge line 63A is also connected to an actuator-side charge line 63C. A flushing valve 69 is provided in the actuator-side charge line 63C. A return line 66 is also connected to the actuator-side charge line 63C. The return line 66 connects the actuator-side charge line 63C and the hydraulic oil tank 61. A charge relief valve 70 is provided in the return line 66. That is, the return line 66, which branches off from the actuator-side charge line 63C, is connected to the hydraulic oil tank 61 via the charge relief valve 70.

[0055] Charge pump 62, discharge line 63A, pump-side charge line 63B, check valves 64, 65, and charge relief valve 70 constitute a charge circuit that replenishes hydraulic oil to closed circuit lines 30, 30 (first line 52, second line 53). When the pressure in closed circuit lines 30, 30 (first line 52, second line 53) drops below the set pressure of charge relief valve 70, the charge circuit supplies hydraulic oil discharged from charge pump 62 to closed circuit lines 30, 30 (first line 52, second line 53) via check valves 64, 65.

[0056] This maintains the minimum pressure in the closed circuit lines 30, 30 (first line 52, second line 53) at a pressure equal to the set pressure of the charge relief valve 70. In other words, when the pressure in the closed circuit lines 30, 30 (first line 52, second line 53) drops below the pressure in the charge line 63, hydraulic oil from the charge pump 62 is supplied to the closed circuit lines 30, 30 via the check valves 64, 65, thereby suppressing cavitation in these closed circuit lines 30, 30 (first line 52, second line 53).

[0057] The charge relief valve 70 is provided between the charge line 63 and the hydraulic oil tank 61. More specifically, the charge relief valve 70 is provided in the return line 66 that connects the charge line 63 and the hydraulic oil tank 61. The charge relief valve 70 is configured as a variable set pressure relief valve, for example, an electromagnetic proportional relief valve, and is connected to the controller 75 via a signal line. The charge relief valve 70 is controlled by commands from the controller 75, and variably adjusts the pressure in the charge line 63 (charge pressure).

[0058] The flushing valve 69 is provided in the actuator-side charge line 63C. As a result, the actuator-side charge line 63C is connected to the closed circuit lines 30, 30 (first line 52, second line 53) via the flushing valve 69. The flushing valve 69 switches so that the line (first line 52 or second line 53) with the lower pressure out of the closed circuit lines 30, 30 (first line 52, second line 53) is connected to the actuator-side charge line 63C.

[0059] As shown in FIG. 9 , the hydraulic drive unit 51 includes an air vent line 71, a first circuit switching valve 72, and a second circuit switching valve 73. The air vent line 71, the first circuit switching valve 72, and the second circuit switching valve 73 are omitted from FIG. 8 . The air vent line 71, which serves as an air vent flow path (air vent oil line), is connected to the hydraulic oil tank 61. That is, the air vent line 71 connects the first line 52 (first pump-side line 54) and the second line 53 (second pump-side line 55) to the return line 66. As a result, the first line 52 (first pump-side line 54) and the second line 53 (second pump-side line 55) are connected to the hydraulic oil tank 61 via the air vent line 71 and the return line 66. The air vent line 71 is also connected to the hydraulic oil tank 61 via a charge relief valve 70. The first circuit switching valve 72 can switch between allowing and blocking the flow of hydraulic oil between the first pump side conduit 54 and the air vent conduit 71. That is, when the first circuit switching valve 72 is in the open position, it allows the flow of hydraulic oil from the first pump side conduit 54 to the air vent conduit 71. On the other hand, when the first circuit switching valve 72 is in the closed position, it prevents the flow of hydraulic oil from the first pump side conduit 54 to the air vent conduit 71.

[0060] On the other hand, the second circuit switching valve 73 can switch between allowing and blocking the flow of hydraulic oil between the second pump side conduit 55 and the air vent conduit 71. That is, when the second circuit switching valve 73 is in the open position, it allows the flow of hydraulic oil from the second pump side conduit 55 to the air vent conduit 71. Conversely, when the second circuit switching valve 73 is in the closed position, it blocks the flow of hydraulic oil from the second pump side conduit 55 to the air vent conduit 71. The first circuit switching valve 72 and the second circuit switching valve 73 are, for example, configured as two-port two-position solenoid switching valves, and are connected to a controller 75 via signal lines. The first circuit switching valve 72 and the second circuit switching valve 73 are switched between an open position and a closed position by the controller 75.

[0061] As shown in Figure 9, the pump-side lines 54, 55 of the closed circuit lines 30, 30 (first line 52 and second line 53) that make up the closed circuit are connected to an air vent line 71 and a return line 66 via circuit selector valves 72, 73. The circuit selector valves 72, 73 automatically switch between flowing and blocking hydraulic oil between the pump-side lines 54, 55 and the air vent line 71 and the return line 66. The air vent line 71 and the return line 66 are connected to the hydraulic oil tank 61 via a filter 74. The filter 74 traps foreign matter that has become mixed in the hydraulic oil, thereby preventing damage to the hydraulic actuator, the sliding parts of each valve, and the like.

[0062] Next, the air bleeding operation of the hydraulic drive system 51 will be described with reference to Figure 9. Air bleeding from the hydraulic drive system 51 can be performed, for example, while the engine 19 is waiting at low idle. At this time, the circuit switching valves 72, 73 are controlled to open automatically in response to a command from the controller 75, and air bleeding from the closed circuit is performed automatically.

[0063] That is, after the engine 19 starts, the charge pump 62 and the closed circuit pump 29 are driven via the power transmission device 20. The closed circuit pump 29 is controlled so that its discharge flow rate is zero in a standby state. For example, if the closed circuit pump 29 is a swash plate-type hydraulic pump, it is in a neutral state with its swash plate at an angle of 90° (a state in which the pistons do not reciprocate even when the pump's rotary shaft is rotated; in other words, a state in which the pistons cannot reciprocate even when oil is fed, and the pump's rotary shaft cannot be rotated). The charge pump 62 draws hydraulic oil from the hydraulic oil tank 61 through a suction line 68 and discharges the hydraulic oil to a charge line 63. The hydraulic oil discharged from charge pump 62 is discharged into hydraulic oil tank 61 via pump-side charge line 63B of charge line 63, check valves 64, 65, pump-side lines 54, 55 of closed circuit lines 30, 30 (first line 52 and second line 53), circuit switching valves 72, 73, air vent line 71, return line 66, charge relief valve 70, and filter 74. When hydraulic oil is discharged from closed circuit pump 29 at this time, air inside closed circuit pump 29 can also be efficiently discharged.

[0064] After the hydraulic drive unit 51 is assembled or the closed circuit pump 29 is replaced during regular maintenance, air is trapped in the closed circuit (pump-side lines 54, 55). A maintenance worker then removes the air. At this time, the charge pump 62 draws hydraulic oil with little air mixed in from the hydraulic oil tank 61 and discharges this hydraulic oil into the charge line 63. The hydraulic oil with little air mixed in flows into the pump-side lines 54, 55 and the closed circuit pump 29 via the pump-side charge line 63B of the charge line 63 and the check valves 64, 65.

[0065] On the other hand, the hydraulic oil containing air is pushed by the hydraulic oil from the charge pump 62 and discharged from the closed circuit pump 29 and pump-side lines 54, 55 to the hydraulic oil tank 61 via the circuit switching valves 72, 73, the air vent line 71, the return line 66, the charge relief valve 70, and the filter 74. As a result, the pump-side lines 54, 55 connected to the closed circuit pump 29 are quickly filled with hydraulic oil that is not mixed with air. As a result, during normal operation, even when the closed circuit pump 29 draws in and discharges hydraulic oil, noise caused by air, reduced responsiveness, and the like can be suppressed.

[0066] The aforementioned Patent Document 1 discloses a circuit for bleeding air. However, Patent Document 1 does not describe how to arrange the switching valves (first circuit switching valve, second circuit switching valve) and air bleeding flow path that make up the circuit for bleeding air. To bleed air, it is desirable for the hydraulic oil containing air to flow from downstream to upstream toward the hydraulic oil tank. Therefore, if the first circuit switching valve and the second circuit switching valve are not positioned appropriately, the air in the closed circuit may not be completely bled, resulting in residual air remaining in the closed circuit. Therefore, in this embodiment, the first circuit switching valve 72 and the second circuit switching valve 73 are arranged below the charge relief valve 70 to prevent residual air in the closed circuit, i.e., to improve air bleeding performance. This point will be explained in detail below.

[0067] As shown in FIG. 2 , the hydraulic excavator 1 is equipped with a closed circuit control valve device 37 and an open circuit control valve device 45. The closed circuit control valve device 37 is provided between the closed circuit pumps 29, 29 and the hydraulic actuators 16, 17, 18, 7. The open circuit control valve device 45 is provided between the open circuit pumps 35, 35 and the closed circuit systems 25, 26, 27 and the traveling hydraulic motors 3, 4. In this embodiment, the closed circuit control valve device 37 and the open circuit control valve device 45 are installed horizontally, extending in the left-right direction. Therefore, the front and rear surfaces of the manifold block 38 of the closed circuit control valve device 37 and the manifold block 46 of the open circuit control valve device 45 serve as mounting surfaces for the various valves 39A to 39D, 40A to 40D, 41A to 41D, 42A to 42D, 47, 69, 72 (72A to 72D), and 73 (73A to 73D). When the control valve device is installed in a vertical position extending in the front-to-rear direction, the left and right surfaces of the manifold block become the mounting surfaces for the various valves.

[0068] The closed circuit control valve device 37 is provided on the revolving frame 8, located in front of the engine 19. The closed circuit control valve device 37 is installed horizontally extending in the left-right direction and toward the left of the revolving frame 8. As shown in Figures 2 to 6, the closed circuit control valve device 37 includes a manifold block 38, closed circuit switching valves 39A to 39D, 40A to 40D, 41A to 41D, and 42A to 42D, a flushing valve 69, circuit switching valves 72A to 72D and 73A to 73D, a charge relief valve 70, and a filter 43.

[0069] 3 and 6 correspond to the first circuit switching valve 72 in Fig. 9, and the circuit switching valves 73A to 73D in Fig. 3 and 6 correspond to the second circuit switching valve 73 in Fig. 9. In this case, the circuit switching valves 72A and 73A in Fig. 3 and 6 are the first circuit switching valve 72A and the second circuit switching valve 73A of the first closed circuit system 25. The circuit switching valves 72B and 73B in Fig. 3 and 6 are the first circuit switching valve 72B and the second circuit switching valve 73B of the second closed circuit system 26. The circuit switching valves 72C and 73C in Fig. 3 and 6 are the first circuit switching valve 72C and the second circuit switching valve 73C of the third closed circuit system 27. 3 and 6 are the first circuit switching valve 72D and the second circuit switching valve 73D of the fourth closed circuit system 28. The filter 43 provided on the upper surface of the manifold block 38 corresponds to the filter 43 provided midway along the closed circuit lines 30, 30, and is omitted from the hydraulic circuit diagram in Fig. 9. In other words, the filter 43 on the upper surface of the manifold block 38 is a different filter from the filter 74 in Fig. 9.

[0070] The manifold block 38 is the base of the closed circuit control valve device 37. The manifold block 38 is attached to the swivel frame 8. The manifold block 38 is a structure in which oil passages are formed inside, and the above-mentioned multiple valves are attached to it. At the same time, the manifold block 38 is connected to the pipes (pump-side pipes 54, 55) from the closed circuit pumps 29, 29 and the pipes (actuator-side pipes 56, 57) from the hydraulic actuators 16, 17, 18, 7. In other words, the manifold block 38 is a structure in which oil passages are formed inside, which guide the pressure oil supplied from the closed circuit pumps 29, 29 to the multiple valves and output the pressure oil controlled by the multiple valves to the hydraulic actuators 16, 17, 18, 7.

[0071] The manifold block 38 is formed as a rectangular parallelepiped block (block-shaped structure) that is flat in the front-rear direction and extends in the left-right and up-down directions. Therefore, the width direction of the manifold block 38 is the left-right direction. A lower portion 38A of the manifold block 38 is detachably attached to the revolving frame 8 using bolts (not shown). A filter 43 and a charge relief valve 70 are attached to an upper surface 38B of the manifold block 38.

[0072] The manifold block 38 has two surfaces facing each other in the front-rear direction, i.e., a front surface and a rear surface. One of the surfaces, the rear surface, serves as a first mounting surface 38C. As shown in FIGS. 3 to 6 , closed circuit switching valves 39A-39D and 40A-40D are mounted on the first mounting surface 38C. Flushing valves 69 and 69 are also mounted on the first mounting surface 38C. Circuit switching valves 72A-72D and 73A-73D (circuit switching valves 72A and 73A of the first closed circuit system 25, circuit switching valves 72B and 73B of the second closed circuit system 26, circuit switching valves 72C and 73C of the third closed circuit system 27, and circuit switching valves 72D and 73D of the fourth closed circuit system 28) are also mounted on the first mounting surface 38C. For this purpose, the first mounting surface 38C has connection openings for circulating hydraulic oil between the valves. Each valve is attached to the first mounting surface 38C using bolts or the like so as to communicate with a connection opening formed in the first mounting surface 38C.

[0073] Meanwhile, the manifold block 38 has a front and a rear surface facing each other in the front-to-rear direction, and the other of these surfaces, the front surface, serves as a second mounting surface 38D. The closed circuit switching valves 41A to 41D and 42A to 42D are mounted to the second mounting surface 38D. For this purpose, the second mounting surface 38D also has connection openings for circulating hydraulic oil between the valves. Each valve is mounted to the second mounting surface 38D using bolts or the like so as to communicate with the connection openings formed in the second mounting surface 38D.

[0074] Furthermore, the manifold block 38 has a plurality of oil passages therein that connect the connection openings and also connect other connection openings to the upper surface 38B (filter 43) as appropriate. As shown in FIG. 7 (described later), the plurality of oil passages can be formed, for example, by drilling holes in the manifold block 38, which is a block body, and then closing the openings as necessary. The oil passages shown in FIG. 7 , i.e., the air vent pipe 71 for bleeding air and the return pipe 66 (first internal pipe 81, second internal pipe 82, third internal pipe 83), will be described later.

[0075] As shown in FIGS. 2 and 3 , the open circuit control valve device 45 is mounted on the revolving frame 8 and located in front of the engine 19. Specifically, the open circuit control valve device 45 is installed horizontally extending in the left-right direction and toward the right of the revolving frame 8 (to the right of the closed circuit control valve device 37). Like the closed circuit control valve device 37, the open circuit control valve device 45 includes a manifold block 46, open circuit switching valves 47, 47, and a filter 48. Note that the open circuit switching valve 47 is not shown in FIG. 3 . The filter 48 mounted on the upper surface of the manifold block 46 corresponds to the filter 48 mounted midway through the open circuit lines 36, 36, and is not shown in the hydraulic circuit diagram of FIG. 9 . In other words, the filter 48 mounted on the upper surface of the manifold block 46 is a different filter from the filter 74 in FIG. 9 .

[0076] Like the manifold block 38 of the closed circuit control valve device 37, the manifold block 46 of the open circuit control valve device 45 is formed as a rectangular parallelepiped block (block-shaped structure) that is flat in the front-rear direction and extends in the left-right and up-down directions. The manifold block 46 has an upper surface 46A, a first mounting surface 46B, and a second mounting surface 46C. The lower portion of the manifold block 46 is detachably attached to the revolving frame 8 using bolts (not shown). A filter 48 is attached to the upper surface 46A of the manifold block 46.

[0077] The manifold block 46 has a first mounting surface 46B on the rear side and a second mounting surface 46C on the front side which serve as mounting surfaces for the open circuit switching valve 47. The first mounting surface 46B and the second mounting surface 46C are provided with connection openings for circulating hydraulic oil between the first mounting surface 46B and the second mounting surface 46C and the open circuit switching valve 47. The manifold block 46 also has a plurality of oil passages that communicate between the connection openings and appropriately communicate between the connection openings and the upper surface 46A.

[0078] The hydraulic oil tank 61, which stores hydraulic oil to be supplied to the open circuit pumps 35, 35, the charge pump 62, etc., is provided on the swivel frame 8. The controller 75 is connected via signal lines to the operation device 11, the closed circuit control valve device 37 (closed circuit switching valves 39A to 39D, 40A to 40D, 41A to 41D, 42A to 42D, flushing valve 69, circuit switching valves 72A to 72D, 73A to 73D, charge relief valve 70), and the open circuit control valve device 45 (open circuit switching valves 47, 47). The controller 75 switches each valve of the closed circuit control valve device 37 and the open circuit control valve device 45 based on a signal from the operation device 11.

[0079] In this embodiment, the manifold block 38 of the closed circuit control valve device 37 has the first circuit switching valves 72A to 72D and the second circuit switching valves 73A to 73D attached to a first mounting surface 38C that is a side surface of the manifold block 38. In contrast, the charge relief valve 70 is attached to an upper surface 38B of the manifold block 38. As a result, the first circuit switching valves 72A to 72D and the second circuit switching valves 73A to 73D are located below the charge relief valve 70.

[0080] That is, the first circuit switching valves 72A to 72D, the second circuit switching valves 73A to 73D, and the charge relief valve 70 are attached to a single manifold block 38 having an air bleed pipe 71 formed therein. In this case, the first circuit switching valves 72A to 72D and the second circuit switching valves 73A to 73D are disposed below the charge relief valve 70. For this reason, when air is bled, the hydraulic oil containing air that has passed through the first circuit switching valves 72A to 72D and the second circuit switching valves 73A to 73D flows from the bottom to the top toward the charge relief valve 70. This allows the air to escape to the charge relief valve 70 side without accumulating below.

[0081] Fig. 7 is a cross-sectional view of the manifold block 38. Fig. 7 illustrates the first circuit switching valve 72A, the second circuit switching valve 73A, and the pipes 54, 55, 66, and 71 associated with the closed circuit pump 29 of the first closed circuit system 25. That is, Fig. 7 omits the circuit switching valves 72B and 73B associated with the closed circuit pump 29 of the second closed circuit system 26, the circuit switching valves 72C and 73C associated with the closed circuit pump 29 of the third closed circuit system 27, the circuit switching valves 72D and 73D associated with the closed circuit pump 29 of the fourth closed circuit system 28, and the pipes 54, 55, 66, and 71 associated therewith.

[0082] As shown in FIG. 7 , the manifold block 38 is formed with a pair of first internal conduits 81, 81 corresponding to the pump-side conduits 54, 55, and a second internal conduit 82 and a third internal conduit 83 corresponding to the air vent conduit 71 and the return conduit 66. The first internal conduits 81, 81, serving as first internal flow paths (first internal oil paths), extend vertically within the manifold block 38. The second internal conduit 82, serving as a second internal flow path (second internal oil path), is located below the manifold block 38 and extends laterally (left-right, horizontally). The third internal conduit 83, serving as a third internal flow path (third internal oil path), extends vertically within the manifold block 38. One end (lower end) of the third internal conduit 83 is connected to the second internal conduit 82, and the other end (upper end) is open to the top surface 38B of the manifold block 38.

[0083] The first circuit switching valve 72A and the second circuit switching valve 73A are mounted between the lower ends of the first internal conduits 81, 81 and the second internal conduit 82. The charge relief valve 70 is mounted on the upper surface 38B of the manifold block 38 at a position corresponding to the opening of the upper end (other end) of the third internal conduit 83. As shown in FIG. 3 , the charge relief valve 70 is connected to the hydraulic oil tank 61 by a hose 84. The hose 84 corresponds to the return conduit 66. The hose connection port 70A provided on the charge relief valve 70, i.e., the hose connection port 70A to which one end (left end) of the hose 84 is connected, is located below the hose connection port 61A provided on the hydraulic oil tank 61, i.e., the hose connection port 61A to which the other end (right end) of the hose 84 is connected.

[0084] When bleeding air, the hydraulic oil containing air that has passed through the third internal conduit 83 (return conduit 66) and the charge relief valve 70 returns to the hydraulic oil tank 61 via the hose 84. At this time, the hose connection port 70A to the charge relief valve 70 is positioned lower than the hose connection port 61A to the hydraulic oil tank 61. Therefore, when bleeding air is performed, the hydraulic oil containing air does not remain in the charge relief valve 70 but instead flows through the hose 84 to the hydraulic oil tank 61.

[0085] The hydraulic excavator 1 according to the embodiment has the above-described configuration, and its operation will now be described.

[0086] The operator in the cab 9 starts the engine 19. When the engine 19 starts, the closed circuit pump 29 and the open circuit pump 35 are driven by the engine 19. In this state, the undercarriage 2 can be moved forward or backward by operating the left and right travel levers / pedals 11C, 11D. Meanwhile, the upper rotating body 5 can be rotated and the working device 12 can be turned by operating the left operating lever 11A and right operating lever 11B for work. This enables the hydraulic excavator 1 to perform excavation work for earth and sand, etc.

[0087] Furthermore, when the closed circuit pump 29 is replaced for periodic maintenance or the like, air is bled from the closed circuit (pump-side conduits 54, 55). At this time, as shown in FIG. 7 , the hydraulic oil containing air in the pump-side conduits 54, 55 passes through the first internal conduits 81, 81 of the manifold block 38, passes through the circuit switching valves 72A, 73A, passes through the second internal conduit 82 that becomes the air bleed conduit 71, and flows upward through the third internal conduit 83 that becomes the return conduit 66. The hydraulic oil then passes through the third internal conduit 83 and the charge relief valve 70, passes further upward through the hose 84 (see FIG. 3 ) that becomes the return conduit 66, and returns to the hydraulic oil tank 61.

[0088] In this way, the hydraulic oil containing air flows upward after passing through the circuit switching valves 72A, 73A. Therefore, the air contained in the hydraulic oil flows upward. This prevents air from flowing back into the closed circuit (pump-side pipes 54, 55) from the circuit switching valves 72A, 73A, and prevents air from remaining in the closed circuit (pump-side pipes 54, 55). This prevents noise and reduced responsiveness of hydraulic equipment caused by air in the hydraulic oil.

[0089] 7, the hydraulic oil containing air that has passed through the circuit switching valves 72A, 73A can be joined together in the second internal pipeline 82 and the third internal pipeline 83. Moreover, as shown in FIG. 3, because the hose connection port 70A of the charge relief valve 70 is located lower than the hose connection port 61A of the hydraulic oil tank 61, the hydraulic oil containing air is released into the hydraulic oil tank 61 without the air remaining in the charge relief valve 70.

[0090] As described above, according to the embodiment, the air vent pipe 71 is connected to the hydraulic oil tank 61 via the charge relief valve 70. Furthermore, the first circuit switching valves 72 (72A to 72D), the second circuit switching valves 73 (73A to 73D), and the charge relief valve 70 are attached to one manifold block 38 in which the air vent pipe 71 is formed. In addition, the first circuit switching valves 72 (72A to 72D) and the second circuit switching valves 73 (73A to 73D) are disposed below the charge relief valve 70.

[0091] Therefore, when air is bled, the hydraulic oil containing air flows from the first pump-side conduit 54 and the second pump-side conduit 55 of the closed circuit through the first circuit switching valve 72 (72A to 72D) and the second circuit switching valve 73 (73A to 73D) and then flows from the first circuit switching valve 72 (72A to 72D) and the second circuit switching valve 73 (73A to 73D) from bottom to top toward the charge relief valve 70. This prevents air from accumulating at the bottom and escapes upward, preventing backflow of air toward the first pump-side conduit 54 and the second pump-side conduit 55. As a result, air remaining in the closed circuit can be reduced, improving air bleeding performance. This prevents damage to the closed circuit pump 29 due to air entrapment, noise generation, and reduced responsiveness.

[0092] 7 , the first circuit switching valves 72 (72A to 72D) and the second circuit switching valves 73 (73A to 73D) are attached between the lower end side of the first internal pipe 81 and the second internal pipe 82 of the manifold block 38. The charge relief valve 70 is attached to the upper surface 38B of the manifold block 38 at a position corresponding to the opening at the other end (upper end side) of the third internal pipe 83. Therefore, the hydraulic oil containing air that has passed through the first circuit switching valves 72 (72A to 72D) and the second circuit switching valves 73 (73A to 73D) joins together at the second internal pipe 82 and flows from the bottom to the top of the third internal pipe 83.

[0093] This eliminates the need to provide separate conduits (flow paths, oil passages) for passing hydraulic oil containing air between the first circuit switching valves 72 (72A to 72D) and the second circuit switching valves 73 (73A to 73D). That is, only one conduit (flow path, oil passage) for passing hydraulic oil containing air is required, namely, the second internal conduit 82 and the third internal conduit 83. This allows the manifold block 38 to be made smaller, and the processing costs for the manifold block 38 to be reduced.

[0094] 3, the hose connection port 70A of the charge relief valve 70 is located lower than the hose connection port 61A of the hydraulic oil tank 61. Therefore, hydraulic oil containing air does not remain in the charge relief valve 70 and is released into the hydraulic oil tank 61 via the hose 84. This also improves air bleeding performance.

[0095] In the embodiment, an example has been described in which the closed circuit control valve device 37 and the open circuit control valve device 45 are arranged side by side in the left-right direction on the revolving frame 8. However, the present invention is not limited to this. For example, a configuration may be adopted in which one common manifold block is provided and various valves of the closed circuit control valve device and various valves of the open circuit control valve device are attached to this common manifold block. Also, a configuration in which three or more control valve devices are provided may be adopted.

[0096] In the embodiment, a large hydraulic excavator has been described as an example of the hydraulic excavator 1. However, the hydraulic excavator is not limited to this, and may be a small, medium, or other hydraulic excavator other than a large hydraulic excavator.

[0097] In the embodiment, the hydraulic excavator 1 equipped with a backhoe-type working implement 12 has been described as an example of a construction machine. However, the present invention is not limited to this and can be widely applied to other construction machines, such as a hydraulic excavator equipped with a loading shovel-type working implement.

[0098] DESCRIPTION OF SYMBOLS 1 Hydraulic excavator (construction machine) 3, 4 Travel hydraulic motor (hydraulic actuator) 7 Swing hydraulic motor (hydraulic actuator) 16 Boom cylinder (hydraulic actuator) 16A, 16B Input / output port 17 Arm cylinder (hydraulic actuator) 18 Bucket cylinder (hydraulic actuator) 29 Closed circuit pump 29A, 29B Input / output port 30 Closed circuit pipeline (first oil passage, second oil passage) 38 Manifold block 38B Top surface 39A to 39D, 40A to 40D, 41A to 41D, 42A to 42D Closed circuit switching valve 52 First pipeline (first oil passage) 53 Second pipeline (second oil passage) 54 First pump side pipeline (first pump side flow path) 55 Second pump side pipeline (second pump side flow path) 61 Hydraulic oil tank 61A Hose connection port 62 Charge pump 62B Discharge port 63 Charge line (charge flow path) 64 First check valve 65 Second check valve 70 Charge relief valve 70A Hose connection port 71 Air vent line (air vent flow path) 72 First circuit switching valve 73 Second circuit switching valve 81 First internal line (first internal flow path) 82 Second internal line (second internal flow path) 83 Third internal line (third internal flow path) 84 Hose

Claims

1. A closed circuit pump; a hydraulic actuator; a first flow path connecting one input / output port of the closed circuit pump and one input / output port of the hydraulic actuator; a second flow path connecting the other input / output port of the closed circuit pump and the other input / output port of the hydraulic actuator; a closed circuit switching valve switchable between a flow position that allows flow between the first flow path and the second flow path and a blocking position that blocks flow between the first flow path and the second flow path; a hydraulic oil tank; a charge pump that discharges hydraulic oil sucked from the hydraulic oil tank; a charge flow path connecting a first pump side flow path of the first flow path that is between the closed circuit pump and the closed circuit switching valve and a second pump side flow path of the second flow path that is between the closed circuit pump and the closed circuit switching valve, and a discharge port of the charge pump; an air vent flow path connected to the hydraulic oil tank; and a first circuit switching valve switchable between flow and blocking between the first pump side flow path and the air vent flow path. a second circuit switching valve capable of switching between communication and cut-off between the second pump-side flow path and the air vent flow path, wherein the air vent flow path is connected to the hydraulic oil tank via a charge relief valve, the first circuit switching valve, the second circuit switching valve, and the charge relief valve are attached to a single manifold block in which the air vent flow path is formed, and the first circuit switching valve and the second circuit switching valve are arranged below the charge relief valve.

2. A construction machine as described in claim 1, characterized in that the manifold block is formed with: a first internal flow path extending in the vertical direction; a second internal flow path located below the manifold block and extending horizontally; and a third internal flow path extending in the vertical direction, one end of which is connected to the second internal flow path and the other end of which opens on the top surface of the manifold block; the first circuit switching valve and the second circuit switching valve are attached between the lower end of the first internal flow path and the second internal flow path; and the charge relief valve is attached on the top surface of the manifold block at a position corresponding to the opening on the other end side of the third internal flow path.

3. A construction machine as described in claim 1, characterized in that the charge relief valve and the hydraulic oil tank are connected by a hose, and the hose connection port on the charge relief valve to which one end of the hose is connected is located lower than the hose connection port on the hydraulic oil tank to which the other end of the hose is connected.

Images