Hydraulic system for work equipment, and work equipment

Abstract

To stabilize supply of hydraulic oil to a first hydraulic device irrespective of operation of a second hydraulic device.SOLUTION: A hydraulic system of a work machine includes: a first hydraulic pump; a first hydraulic device; a hydraulic oil tank; a first discharge oil passage for making hydraulic oil discharged from the first hydraulic device flow to the hydraulic oil tank; a second hydraulic pump connected to the hydraulic oil tank via a suction oil passage and sucking hydraulic oil from the hydraulic oil tank via the suction oil passage; a second hydraulic device in which a deviation between a flow quantity of hydraulic oil supplied from the second hydraulic pump and a flow quantity of discharged hydraulic oil fluctuates according to operation; a second discharge oil passage connected to a suction port of the first hydraulic pump and making hydraulic oil discharged from a hydraulic cylinder flow to the first hydraulic pump; a connection oil passage branched from the second discharge oil passage and connected to a suction oil passage between the hydraulic oil tank and the second hydraulic pump; and a replenishing part connected to the second discharge oil passage and replenishing the second discharge oil passage with hydraulic oil.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a hydraulic system for a work machine such as a skid steer loader or a compact track loader, and to the work machine. [Background technology]

[0002] BACKGROUND ART A hydraulic system for a work machine is known from the prior art, as disclosed in Patent Document 1. The hydraulic system of a work machine disclosed in Patent Document 1 includes a first hydraulic pump, a first hydraulic device (travel hydraulic device) operated by hydraulic oil discharged by the first hydraulic pump, oil passages (first discharge oil passage, third discharge oil passage, and sixth discharge oil passage) that flow the hydraulic oil discharged from the hydraulic device to a discharge section, a second hydraulic pump connected to the discharge section and that discharges the hydraulic oil from the discharge section, a second hydraulic device (work hydraulic device) that operates by hydraulic oil discharged by the second hydraulic pump, and in which the deviation between the flow rate of hydraulic oil supplied from the second hydraulic pump and the flow rate of the discharged hydraulic oil fluctuates depending on the operation, and oil passages (seventh discharge oil passage and eighth discharge oil passage) that are connected to the discharge section and that flow the hydraulic oil discharged from the second hydraulic device to the discharge section. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-96474 Summary of the Invention [Problem to be solved by the invention]

[0004] In the hydraulic system of the work machine of Patent Document 1, hydraulic oil is discharged from the traveling hydraulic equipment to the discharge section via the seventh discharge oil line and the eighth discharge oil line, and hydraulic oil is discharged from the working hydraulic equipment to the discharge section via the first discharge oil line, the third discharge oil line, and the sixth discharge oil line. However, when the discharge part that discharges the hydraulic oil discharged from the traveling hydraulic equipment is a hydraulic oil tank and the discharge part that discharges the hydraulic oil discharged from the working hydraulic equipment is the suction port of the first hydraulic pump, if the flow rate of the hydraulic oil discharged by the second hydraulic equipment fluctuates depending on the operation, for example, like a hydraulic cylinder, and the flow rate of the discharged hydraulic oil becomes less than the flow rate of the hydraulic oil supplied, negative pressure may occur in the oil passage connected to the suction port of the first hydraulic pump.

[0005] The present invention has been made to solve the problems of the conventional technology, and aims to provide a hydraulic system for a work machine and a work machine that can stabilize the supply of hydraulic oil to a first hydraulic device regardless of the operation of a second hydraulic device. [Means for solving the problem]

[0006] A hydraulic system for a work machine according to one aspect of the present invention includes a first hydraulic pump, a first hydraulic device operated by hydraulic oil discharged by the first hydraulic pump, a hydraulic oil tank that stores hydraulic oil, a first discharge oil line that allows hydraulic oil discharged from the first hydraulic device to flow to the hydraulic oil tank, a second hydraulic pump connected to the hydraulic oil tank via an intake oil line and that draws hydraulic oil from the hydraulic oil tank via the intake oil line, a second hydraulic device operated by hydraulic oil discharged by the second hydraulic pump, where the difference between the flow rate of hydraulic oil supplied from the second hydraulic pump and the flow rate of hydraulic oil discharged from the second hydraulic pump varies depending on the second hydraulic device's operation, and an intake port of the first hydraulic pump. and the second hydraulic device directly without going through the hydraulic oil tank. connection death a second oil discharge passage for allowing hydraulic oil discharged from the second hydraulic device to flow to the first hydraulic pump; One end Branching from the second oil discharge passage, The other end The hydraulic oil supply system includes a connecting oil passage connected to the intake oil passage, and a refill unit connected to the second discharge oil passage and refilling the second discharge oil passage with hydraulic oil.

[0007] The second hydraulic device may be a hydraulic cylinder, and may include a cylinder tube, a piston provided inside the cylinder tube, and a rod attached to the piston. The refill section may be a bypass oil passage that connects the second discharge oil passage and the hydraulic oil tank. In addition, the intake oil passage may have one end connected to the second hydraulic pump and the other end connected to an oil filter provided inside the hydraulic oil tank, and the bypass oil passage may be a separate oil passage from the connection oil passage, with one end connected to the second discharge oil passage and the other end connected to the intake oil passage. The bypass oil passage may have an inner diameter larger than the inner diameter of the connecting oil passage and the inner diameter of the second discharge oil passage.

[0008] The replenishing section may be an accumulator that stores hydraulic oil under pressure and supplies the stored hydraulic oil to the second discharge oil passage. The replenishing unit may be a reserve tank that stores hydraulic oil separately from the hydraulic oil tank and supplies the stored hydraulic oil to the second discharge oil passage. The reserve tank may be provided with a breather that connects the inside and outside of the reserve tank. Furthermore, an oil cooler that cools the hydraulic oil may be provided in the second oil discharge passage.

[0009] In addition, the hydraulic system of the work machine may include a prime mover, and the first hydraulic device may include a travel pump operated by the power of the prime mover, a travel motor that can be rotated by hydraulic oil discharged by the travel pump, a circulation oil passage connecting the travel pump and the travel motor, and a charge oil passage that supplies the hydraulic oil discharged by the first hydraulic pump to the circulation oil passage. The work machine also includes a body, a traveling device that is provided on the body and driven by the first hydraulic device to impart propulsive force to the body, and a work device that is provided on the body and driven by the second hydraulic device. [Effects of the Invention]

[0010] According to the hydraulic system for the work machine and the work machine described above, the supply of hydraulic oil to the first hydraulic device can be stabilized regardless of the operation of the second hydraulic device. [Brief explanation of the drawings]

[0011] [Figure 1]2 is a diagram showing a hydraulic circuit of a traveling system in the hydraulic system of the work machine in the first embodiment. FIG. [Figure 2] 2 is a diagram showing a hydraulic circuit of a work system in the hydraulic system of the work machine in the first embodiment. FIG. [Figure 3] FIG. 4 is a diagram illustrating the flow of hydraulic oil in the first embodiment when the amount of return oil discharged to the second hydraulic device is greater than the flow rate of hydraulic oil sucked by the first hydraulic pump. [Figure 4] FIG. 4 is a diagram illustrating the flow of hydraulic oil in the first embodiment when the amount of return oil discharged from the second hydraulic device is less than the flow rate of hydraulic oil sucked by the first hydraulic pump. [Figure 5] FIG. 6 is a diagram showing a hydraulic circuit of a traveling system in a hydraulic system of a work machine in a second embodiment. [Figure 6] FIG. 4 is a diagram showing a hydraulic circuit of a working system in a hydraulic system of a work machine in a second embodiment. [Figure 7] FIG. 10 is a diagram showing a hydraulic circuit of a working system in a hydraulic system of a work machine according to a third embodiment. [Figure 8] 1 is a side view showing a skid steer loader as an example of a work machine. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [First embodiment] Fig. 8 shows a side view of a work machine 1 according to the present invention. Fig. 8 shows a skid steer loader as an example of the work machine 1. However, the work machine 1 according to the present invention is not limited to a skid steer loader, and may be, for example, another type of loader work machine, such as a compact track loader. Furthermore, the work machine 1 may be a work machine other than a loader work machine.

[0013] As shown in Fig. 8, the work machine 1 comprises a machine body 2, a cabin 3, a work device 4, and a traveling device 5. In the embodiment of the present invention, the direction in which a driver seated in the driver's seat 8 of the work machine 1 faces (the left side in Fig. 8) is referred to as the forward direction, and the opposite direction (the right side in Fig. 8) is referred to as the rearward direction. The left side of the driver (the front side in Fig. 8) is referred to as the left side, and the right side of the driver (the back side in Fig. 8) is referred to as the right side. The horizontal direction, which is perpendicular to the front-to-rear direction, is referred to as the machine body width direction.

[0014] The cabin 3 is mounted on the machine body 2. A driver's seat 8 is provided in the cabin 3. The work device 4 is attached to the machine body 2. A prime mover 6 is mounted at the rear of the machine body. The traveling device 5 is provided on the outside of the machine body 2. The traveling device 5 includes a first traveling device 5L provided on the left side of the machine body 2 and a second traveling device 5R provided on the right side of the machine body 2. The working device 4 will be described in detail below with reference to Figure 8. The working device 4 has a boom 10, a working implement 11, a lift link 12, a control link 13, a boom cylinder 14, and a bucket cylinder 15.

[0015] The booms 10 are mounted on the left and right sides of the cabin 3 so as to be able to swing up and down. The work implement 11 is, for example, a bucket, and is mounted on a first end (front end) 10a of the boom 10 so as to be able to swing up and down. A lift link 12 and a control link 13 support a second end (rear end) 10b, which is the end opposite the first end 10a of the boom 10, so as to be able to swing up and down. The boom cylinder 14 extends and retracts to raise and lower the boom 10. The bucket cylinder 15 extends and retracts to swing the work implement 11.

[0016] The first ends (front ends) 10a of the left boom 10 and the right boom 10 are connected to each other by an irregularly shaped connecting pipe (not shown). The second ends (rear ends) 10b of the left boom 10 and the right boom 10 are connected to each other by a circular connecting pipe. The lift link 12, the control link 13, and the boom cylinder 14 are provided on the left and right sides of the machine body 2 corresponding to the left and right booms 10, respectively.

[0017] The lift link 12 is provided vertically behind the second end 10b of the boom 10. A first end (upper end) 12a of the lift link 12 is pivoted rotatably about a horizontal axis via a pivot shaft 16 near the rear of the second end 10b of the boom 10. Furthermore, a second end (lower end) 12b, which is the end opposite to the first end 12a of the lift link 12, is pivoted rotatably about a horizontal axis via a pivot shaft 17 near the rear of the machine body 2.

[0018] A first end (upper end) 14a of the boom cylinder 14 is pivoted rotatably about a horizontal axis via a pivot shaft 18. The pivot shaft 18 is provided near the front of the second end 10b of the boom 10. A second end (lower end) 14b, which is the end opposite to the first end 14a of the boom cylinder 14, is pivoted rotatably about a horizontal axis via a pivot shaft 19. The pivot shaft 19 is provided below the rear of the machine body 2.

[0019] The control link 13 is provided in front of the lift link 12. A first end (front end) 13a of this control link 13 is pivoted rotatably about a horizontal axis via a pivot shaft 20. The pivot shaft 20 is provided on the aircraft body 2 in front of the lift link 12. A second end (rear end) 13b of the control link 13, which is the end opposite to the first end 13a, is pivoted rotatably about a horizontal axis via a pivot shaft 21. The pivot shaft 21 is provided on the boom 10 in front of and above the pivot shaft 17.

[0020] Therefore, the second end 10b of the boom 10 is supported by the lift link 12 and the control link 13, and swings up and down around the pivot shaft 16 by extending and retracting the boom cylinder 14. This causes the first end 10a of the boom 10 to rise and fall. Additionally, the control link 13 swings up and down around the pivot shaft 20 in conjunction with the up and down swing of the boom 10. The lift link 12 swings back and forth around the pivot shaft 17 in conjunction with the up and down swing of the control link 13.

[0021] 8, a bucket is attached to the first end 10a of the boom 10 as the work implement 11, but another work implement 11 can be attached to the first end 10a of the boom 10 instead of a bucket. Examples of another work implement 11 that can be attached to the first end 10a of the boom 10 include attachments (spare attachments) such as a hydraulic crusher, hydraulic breaker, angle broom, earth auger, pallet fork, sweeper, mower, and snow blower. The spare attachment has a hydraulic device such as a hydraulic motor and hydraulic cylinder C, and is operated by supplied hydraulic oil.

[0022] A connecting member 25 is provided at a first end 10a of the left boom 10. The connecting member 25 is a member that connects a first pipe (not shown) connected to a spare attachment and a second pipe (not shown) such as a pipe provided on the boom 10. The bucket cylinders 15 are each disposed on the first end 10a side of the boom 10. The first end (upper end) 15a of the bucket cylinder 15 is pivotally supported rotatably about a horizontal axis via a pivot shaft 22. The pivot shaft 22 is provided near the rear side of the first end 10a of the boom 10. A second end (lower end) 15b of the bucket cylinder 15, which is the end opposite to the first end 15a, is pivoted so as to be rotatable about a horizontal axis via a pivot shaft 23. The pivot shaft 23 is provided on the upper side of the rear of the working implement 11. As a result, the bucket cylinder 15 extends and retracts, thereby swinging the working implement 11.

[0023] In the following description, the bucket cylinder 15, the boom cylinder 14, and the hydraulic device of the auxiliary attachment may be referred to as a hydraulic actuator AC. In this embodiment, the left traveling device 5 (first traveling device 5L) and the right traveling device 5 (second traveling device 5R) are wheel-type traveling devices 5 having front and rear wheels. Note that the traveling devices 5 are not limited to the wheel-type traveling device shown in FIG. 8, and may be crawler-type or semi-crawler-type traveling devices 5.

[0024] The prime mover 6 is an internal combustion engine (engine) such as a diesel engine or a gasoline engine, an electric motor, etc. In this embodiment, the prime mover 6 is a diesel engine, but is not limited to this. The following describes the hydraulic system of the work machine 1. Fig. 1 shows a hydraulic circuit for a traveling system in the hydraulic system of the work machine 1 in the first embodiment. Fig. 2 shows a hydraulic circuit for a working system in the hydraulic system of the work machine 1 in the first embodiment.

[0025] As shown in FIGS. 1 and 2, the work machine 1 includes a first hydraulic pump P1, a second hydraulic pump P2, and a hydraulic oil tank T. The first hydraulic pump P1 is operated by power from a prime mover 6 and discharges hydraulic oil. The first hydraulic pump P1 is configured as a fixed-displacement gear pump. In particular, the first hydraulic pump P1 supplies hydraulic oil used to control the traveling system and working system of the work machine 1. Of the hydraulic oil discharged from the first hydraulic pump P1, the hydraulic oil used for control is sometimes referred to as pilot oil, and the pressure of the pilot oil is sometimes referred to as pilot pressure. Specifically, a first discharge oil passage 40 is connected to a discharge port (first port) P1a of the first hydraulic pump P1. The first discharge oil passage 40 is an oil passage through which the hydraulic oil discharged from the first hydraulic pump P1 flows. A second discharge oil passage 72, which will be described later, is connected to a suction port (second port) P1b of the first hydraulic pump P1.

[0026] The second hydraulic pump P2 is operated by the power of the prime mover 6 and discharges hydraulic oil. The second hydraulic pump P2 is configured as a fixed displacement gear pump. In particular, the second hydraulic pump P2 supplies hydraulic oil to a hydraulic system of the working system, which will be described later. Specifically, a second discharge oil passage 45 is connected to a discharge port (third port) P2a of the second hydraulic pump P2. The second discharge oil passage 45 is an oil passage through which the hydraulic oil discharged by the second hydraulic pump P2 flows. In addition, a suction oil passage 35 that supplies hydraulic oil to the second hydraulic pump P2 is connected to a suction port (fourth port) P2b of the second hydraulic pump P2. The suction oil passage 35 connects the fourth port P2b of the second hydraulic pump P2 to the hydraulic oil tank T. In other words, the second hydraulic pump P2 draws hydraulic oil from the hydraulic oil tank T via the suction oil passage 35. More specifically, an oil filter (suction filter) is provided inside the hydraulic oil tank T, and the intake oil passage 35 is connected to the suction filter .

[0027] As in this embodiment, the second port P1b of the first hydraulic pump P1 is not connected to the hydraulic oil tank T but to the second discharge oil passage 72, and the fourth port P2b of the second hydraulic pump P2 is connected to the hydraulic oil tank T via the suction oil passage 35, thereby reducing the overall amount of hydraulic oil flowing through the hydraulic system of the work machine. This allows the size of the hydraulic oil tank T to be reduced. The flow rate of hydraulic oil discharged per predetermined time from the second hydraulic pump P2 is equal to or greater than the flow rate of hydraulic oil discharged per predetermined time from the first hydraulic pump P1. In this embodiment, the flow rate of hydraulic oil discharged per predetermined time from the second hydraulic pump P2 is greater than the flow rate of hydraulic oil discharged per predetermined time from the first hydraulic pump P1.

[0028] The hydraulic oil tank T is a tank that stores hydraulic oil. That is, an intake oil passage 35 connected to the hydraulic oil tank T allows the hydraulic oil that the second hydraulic pump P2 draws from the hydraulic oil tank T to flow. The hydraulic oil tank T is provided with a breather (air breather) 30 that connects the inside and outside of the hydraulic oil tank T. Next, the hydraulic system of the traveling system will be described using Figure 1. The hydraulic system of the traveling system of the work machine 1 is a system that operates the traveling device 5. The hydraulic system of the work machine 1 is equipped with a first hydraulic device S. The first hydraulic device S is operated by hydraulic oil discharged from a first hydraulic pump P1. In addition, the first hydraulic device S is a device that drives the traveling device 5, and is equipped with a traveling pump 50, a traveling motor 51, a circulation oil passage 52, and a charge oil passage 53.

[0029] The travel pump 50 is a pump that is operated by the power of the prime mover 6. In this embodiment, the travel pump 50 includes a first travel pump 50L and a second travel pump 50R. Specifically, the travel pump 50 is a swash plate-type variable displacement axial pump that is operated by the power of the prime mover 6. The travel pump 50 has a forward pressure receiving portion 50a and a reverse pressure receiving portion 50b to which a pilot pressure acts. The angle of the swash plate of the travel pump 50 is changed according to the pilot pressure acting on the forward pressure receiving portion 50a and the reverse pressure receiving portion 50b. By changing the angle of the swash plate, the travel pump 50 can change the discharge amount (output) and discharge direction of the hydraulic oil supplied from the first discharge oil passage 40 via the charge oil passage 53.

[0030] The travel motor 51 is a motor that is operated by hydraulic oil discharged from the travel pump 50 and transmits power to the drive shaft of the travel device 5. Therefore, the travel device 5 is driven by the first hydraulic device S (travel motor 51) to provide propulsive force to the machine body 2. In this embodiment, the travel motor 51 includes a first travel motor 51L and a second travel motor 51R. The first travel motor 51L is a motor that transmits power to the drive shaft of the travel device 5 (first travel device 5L) provided on the left side of the machine body 2. The second travel motor 51R is a motor that transmits power to the drive shaft of the travel device 5 (second travel device 5R) provided on the right side of the machine body 2.

[0031] The circulation oil passage 52 is an oil passage that connects the travel pump 50 and the travel motor 51. In this embodiment, the circulation oil passage 52 includes a first circulation oil passage 52a and a second circulation oil passage 52b. The first circulation oil passage 52a connects the first travel motor 51L and the first travel pump 50L. Therefore, the first travel pump 50L can supply hydraulic oil to the first travel motor 51L via the first circulation oil passage 52a. This allows the first travel motor 51L to change its rotational speed (number of revolutions) based on the flow rate of hydraulic oil supplied from the first travel pump 50L.

[0032] The second circulation oil passage 52b connects the second travel motor 51R and the second travel pump 50R. Therefore, the second travel pump 50R can supply hydraulic oil to the second travel motor 51R via the second circulation oil passage 52b. This allows the second travel motor 51R to change its rotational speed (number of revolutions) based on the flow rate of hydraulic oil supplied from the second travel pump 50R.

[0033] The charge oil passage 53 is an oil passage that supplies hydraulic oil discharged by the first hydraulic pump P1 to the circulation oil passage 52. The charge oil passage 53 is connected to the first supply oil passage 40a branching from the first discharge oil passage 40, and supplies hydraulic oil flowing from the first supply oil passage 40a to the circulation oil passage 52. The charge oil passage 53 has an oil passage provided with a check valve in its middle and an oil passage provided with a relief valve in its middle. The check valve allows hydraulic oil to flow from the first hydraulic pump P1 to the circulation oil passage 52 and prevents hydraulic oil from flowing from the circulation oil passage 52 to the first hydraulic pump P1. The oil passage provided with the relief valve is connected to an oil passage so as to bypass the check valve. In this embodiment, the charge oil passage 53 includes a first charge oil passage 53a and a second charge oil passage 53b. The first charge oil passage 53a supplies the hydraulic oil discharged by the first hydraulic pump P1 to the first circulation oil passage 52a. The second charge oil passage 53b supplies the hydraulic oil discharged by the first hydraulic pump P1 to the second circulation oil passage 52b.

[0034] As shown in FIG. 1 , the hydraulic system of the work machine 1 includes a first oil discharge passage 71. The first oil discharge passage 71 is an oil passage that flows hydraulic oil discharged from a first hydraulic device S to a hydraulic oil tank T. In this embodiment, the first oil discharge passage 71 includes a first oil passage 71a and a second oil passage 71b. The first oil passage 71a is an oil passage that connects a drain port of the travel pump 50 to the hydraulic oil tank T. In this embodiment, the travel pump 50 discharges hydraulic oil flowing through the circulation oil passage 52 from the drain port both when the supply of hydraulic oil to the travel motor 51 is stopped and when hydraulic oil is being supplied to the travel motor 51. Therefore, the first oil passage 71a can flow hydraulic oil discharged from the travel pump 50 to the hydraulic oil tank T both when the travel motor 51 is not driven and when the travel motor 51 is driven.

[0035] Additionally, the second oil passage 71b is an oil passage that connects the drain port of the travel motor 51 and the hydraulic oil tank T. In this embodiment, when hydraulic oil is supplied from the travel pump 50, the travel motor 51 discharges the hydraulic oil flowing through the circulation oil passage 52 from the drain port, and when the supply of hydraulic oil from the travel pump 50 is stopped, the travel motor 51 does not discharge the hydraulic oil flowing through the circulation oil passage 52. Therefore, when the travel motor 51 is driven, the second oil passage 71b allows the hydraulic oil discharged from the travel motor 51 to flow to the hydraulic oil tank T.

[0036] As a result, when the travel motor 51 is not driven, the hydraulic oil supplied from the charge oil passage 53 to the circulation oil passage 52 (i.e., the hydraulic oil discharged by the first hydraulic pump P1 to the first hydraulic device S) is discharged from the first oil passage 71a to the hydraulic oil tank T. On the other hand, when the travel motor 51 is driven, the hydraulic oil supplied from the charge oil passage 53 to the circulation oil passage 52 is discharged from the first oil passage 71a and the second oil passage 71b to the hydraulic oil tank T.

[0037] As described above, the first discharge oil passage 71 can discharge the hydraulic oil discharged from the first hydraulic device S to the hydraulic oil tank T. In other words, the first discharge oil passage 71 can discharge the hydraulic oil supplied to the first hydraulic device S to the hydraulic oil tank T. When the travel motor 51 is driving, the flow rate of the hydraulic oil discharged from the first oil passage 71a to the hydraulic oil tank T and the flow rate of the hydraulic oil discharged from the second oil passage 71b to the hydraulic oil tank T vary depending on the rotation speed of the travel motor 51, in other words, the flow rate of the hydraulic oil supplied from the travel pump 50 to the travel motor 51.

[0038] In the above example, the first discharge oil passage 71 includes the first oil passage 71a and the second oil passage 71b. However, if the hydraulic system of the work machine 1 has a first hydraulic device S, separate from the travel pump 50 and the travel motor 51, to which the hydraulic oil discharged by the first hydraulic pump P1 is supplied, the hydraulic system may include an oil passage connected to the first hydraulic device S, separate from the first oil passage 71a and the second oil passage 71b. The following provides a detailed description of operations related to the traveling of the work machine 1, that is, operations (traveling operations) of the traveling device 5. As shown in FIG.

[0039] The first operating device 54 is a device that operates the travel pumps 50 (first travel pump 50L, second travel pump 50R). The first operating device 54 can change the angle of the swash plate (swash plate angle) of the travel pump 50 by changing the pilot pressure acting on the forward pressure receiving portion 50a and the reverse pressure receiving portion 50b. The first operating device 54 includes a first operating member (travel lever) 55 and a plurality of first operating valves (travel operating valves) 56.

[0040] The first operating member 55 is an operating lever that swings left and right (aircraft body width direction) or front and rear. The multiple first operating members 55 are supported by a first operating valve 56. The first operating member 55 can be operated forward (in the direction of arrow A1 in FIG. 1) and backward (in the direction of arrow A2 in FIG. 1) from the neutral position N as a reference, and can also be operated left (in the direction of arrow A3 in FIG. 1) and right (in the direction of arrow A4 in FIG. 1) from the neutral position N. In other words, the first operating member 55 can swing in at least four directions from the neutral position N as a reference.

[0041] The multiple first operating valves 56 are valves that are actuated by operation of the first operating member 55. Specifically, the multiple first operating valves 56 are connected to a second supply oil passage 40b that branches off from the first discharge oil passage 40, and are capable of changing the pressure (pilot pressure) of the pilot oil, which is the hydraulic oil supplied from the first discharge oil passage 40. The multiple first operating valves 56 are operated by a common first operating member 55, i.e., a single operating lever. As shown in FIG. 1 , the multiple first operating valves 56 are connected to the travel pump 50 by a travel oil passage 42. The travel oil passage 42 is an oil passage that connects the multiple first operating valves 56 to the forward pressure receiving portion 50a and the reverse pressure receiving portion 50b of the travel pump 50.

[0042] Therefore, when the first operating member 55 is operated, the multiple first operating valves 56 change the pressure (pilot pressure) of the pilot oil, which is the hydraulic oil supplied from the first discharge oil passage 40, and the travel oil passage 42 acts on the forward pressure receiving section 50a and reverse pressure receiving section 50b of the travel pump 50, thereby operating the travel pump 50 (first travel pump 50L, second travel pump 50R).

[0043] Next, the hydraulic system of the work system will be described using Figure 2. The hydraulic system of the work system of the work implement 1 is a system that operates the work implement 4. The hydraulic system of the work implement 1 includes a second hydraulic device C that operates using hydraulic oil discharged from the second hydraulic pump P2, and a plurality of control valves 60. The second hydraulic device C is a second hydraulic device that operates using hydraulic oil discharged from the second hydraulic pump P2, and the deviation between the flow rate of hydraulic oil supplied from the second hydraulic pump P2 and the flow rate of hydraulic oil discharged varies in accordance with this operation. More specifically, the second hydraulic device C is a hydraulic actuator AC that drives the work implement 4, and is a hydraulic cylinder C. In this embodiment, the second hydraulic device C also includes a boom cylinder 14 and a bucket cylinder 15.

[0044] Specifically, the hydraulic cylinder C includes a cylinder tube (cylinder) c1, a piston c2 provided inside the cylinder tube c1, and a rod c3 attached to the piston c2. The piston c2 is provided inside the cylinder tube c1 so as to be slidable in the axial direction. The piston c2 divides the interior of the cylinder tube c1 into a first oil chamber c1a and a second oil chamber c1b. The first oil chamber c1a is an oil chamber at the base end of the cylinder tube c1 (the portion opposite the rod c3). The second oil chamber c1b is an oil chamber at the tip end of the cylinder tube c1 (the portion where the rod c3 is located). The base end of the cylinder tube c1 is provided with a first supply / discharge port that is a port for supplying / discharging hydraulic oil and communicates with the first oil chamber c1a. The tip end of the cylinder tube c1 is provided with a second supply / discharge port that is a port for supplying / discharging hydraulic oil and communicates with the second oil chamber c1b.

[0045] The hydraulic cylinder C may be any hydraulic actuator AC that has a cylinder tube c1, a piston c2, and a rod c3 and that expands and contracts with hydraulic oil, and is not limited to the boom cylinder 14 and the bucket cylinder 15. For example, the hydraulic cylinder C of the hydraulic system of the work implement 1 may be a hydraulic cylinder C of an auxiliary attachment of the work implement 1.

[0046] The control valves 60 are valves capable of controlling the hydraulic actuators AC. Specifically, the control valves 60 are connected to the second discharge oil passage 45 and can switch the discharge amount (output) and discharge direction of the hydraulic oil supplied from the second discharge oil passage 45 in response to the pilot pressure. In this way, the control valves 60 control the hydraulic actuators AC. In this embodiment, the control valves 60 are pilot-operated direct-acting spool-type three-position switching valves. The control valves 60 have pressure-receiving portions 60A and 60B and can be switched to a third position (neutral position) 60c, a first position 60a different from the third position 60c, and a second position 60b different from the third position 60c and the first position 60a in response to the pilot pressure acting on the pressure-receiving portions 60A and 60B. In this way, the control valves 60 can switch the discharge amount (output) and discharge direction of the hydraulic oil supplied from the second discharge oil passage 45. The plurality of control valves 60 may be any valve capable of switching the discharge amount (output) of the hydraulic oil supplied from the second discharge oil passage 45 and the discharge direction of the hydraulic oil, and may be, for example, an electromagnetic three-position switching valve.

[0047] The first control valve 61 is a valve that controls the hydraulic cylinder C (boom cylinder 14) that controls the boom 10. The second control valve 62 is a valve that controls the hydraulic cylinder C (bucket cylinder 15) that controls the work implement 11. The third control valve 63 is a valve that controls the hydraulic device of the auxiliary attachment. The multiple control valves 60 are connected to the hydraulic actuator AC by supply / discharge oil passages 64. Specifically, the first control valve 61 is connected to the boom cylinder 14 by a first supply / discharge oil passage 64a. The second control valve 62 is connected to the bucket cylinder 15 by a second supply / discharge oil passage 64b. The third control valve 63 is connected to the spare attachment by a third supply / discharge oil passage 64c. Below, the connections between the first supply / discharge oil passage 64a, the first control valve 61, and the boom cylinder 14 (hydraulic cylinder C) will be described in detail, and a detailed description of the second supply / discharge oil passage 64b and the third supply / discharge oil passage 64c will be omitted.

[0048] One end of the first supply / discharge oil passage 64a is connected to the supply / discharge port of the first control valve 61, and the other end opposite the one end is connected to the first supply / discharge port of the hydraulic cylinder C. Specifically, the first supply / discharge oil passage 64a has a first oil passage 64a1 connecting the supply / discharge port of the first control valve 61 to the first supply / discharge port of the hydraulic cylinder C, and a second oil passage 64a2 connecting the supply / discharge port of the first control valve 61 to the second supply / discharge port of the hydraulic cylinder C. In other words, the first oil passage 64a1 supplies hydraulic oil to the first oil chamber c1a of the hydraulic cylinder C and allows hydraulic oil discharged from the first oil chamber c1a to flow through it. On the other hand, the second oil passage 64a2 supplies hydraulic oil to the second oil chamber c1b of the hydraulic cylinder C and allows hydraulic oil discharged from the second oil chamber c1b to flow through it.

[0049] Therefore, when the first control valve 61 is switched from the third position 60c to the first position 60a, it supplies hydraulic oil to the first oil passage 64a1, stops supplying hydraulic oil to the second oil passage 64a2, and supplies hydraulic oil to the first oil chamber c1a via the first oil passage 64a1 and the first supply / discharge port. As a result, the hydraulic oil supplied to the first oil chamber c1a from the first supply / discharge port acts on the piston c2, causing the piston c2 to slide toward its tip. Therefore, the rod c3 moves together with the piston c2, thereby extending the hydraulic cylinder C. Furthermore, as the piston c2 moves, hydraulic oil in the second oil chamber c1b is discharged via the second supply / discharge port and the second oil passage 64a2.

[0050] On the other hand, when the first control valve 61 is switched from the third position 60c to the second position 60b, it supplies hydraulic oil to the second oil passage 64a2, stops supplying hydraulic oil to the first oil passage 64a1, and supplies hydraulic oil to the second oil chamber c1b via the second oil passage 64a2 and the second supply / discharge port. As a result, the hydraulic oil supplied to the second oil chamber c1b from the second supply / discharge port acts on the piston c2, causing the piston c2 to slide toward the base end. Therefore, the rod c3 moves together with the piston c2, causing the hydraulic cylinder C to contract. Furthermore, as the piston c2 moves, the hydraulic oil in the first oil chamber c1a is discharged via the first supply / discharge port and the first oil passage 64a1. In the following description, one of the second oil supply / discharge passages 64b will be referred to as a first oil passage 64b1, and the other will be referred to as a second oil passage 64b2. Also, one of the third oil supply / discharge passages 64c will be referred to as a first oil passage 64c1, and the other will be referred to as a second oil passage 64c2.

[0051] As shown in Fig. 2, the hydraulic system of the work machine 1 includes a second discharge oil passage 72. The second discharge oil passage 72 is connected to the second port P1a of the first hydraulic pump P1, and is an oil passage through which hydraulic oil discharged from a second hydraulic device (hydraulic cylinder) C flows to the first hydraulic pump P1. The second discharge oil passage 72 includes a third oil passage 72a, a fourth oil passage 72b, and a fifth oil passage 72c. The third oil passage 72a is connected to the supply / discharge oil passage 64, and is an oil passage through which hydraulic oil discharged from the hydraulic cylinder C flows. One end of the third oil passage 72a branches and is connected to a first oil passage 64a1 and a second oil passage 64a2 of the supply / discharge oil passage 64, respectively. A relief valve is provided at one end of the third oil passage 72a.

[0052] The fourth oil passage 72b is connected to the third oil passage 72a and serves as an oil passage through which the hydraulic oil flowing through the third oil passage 72a flows. Specifically, one end of the fourth oil passage 72b is connected to the other end of the third oil passage 72a, and hydraulic oil discharged from the first oil passage 64a1 and the second oil passage 64a2 of the first to third oil supply / discharge passages 64a to 64c can flow via the third oil passage 72a. In this embodiment, a sixth oil passage 72d, which passes hydraulic oil discharged from the second hydraulic pump P2 when the third control valve 63 is in the third position 60c, joins one end of the fourth oil passage 72b. An oil cooler 73 and an oil filter (return filter) 74 are provided midway through the fourth oil passage 72b.

[0053] The fifth oil passage 72c connects the fourth oil passage 72b and the first hydraulic pump P1 and supplies the hydraulic oil flowing through the fourth oil passage 72b to the first hydraulic pump P1. Specifically, the other end of the fourth oil passage 72b is connected to one end of the fifth oil passage 72c, and the hydraulic oil discharged from the first oil passages 64a1, 64b1, 64c1 and the second oil passages 64a2, 64b2, 64c2 of the first to third oil supply / discharge passages 64a to 64c can flow through the third oil passage 72a and the fourth oil passage 72b. According to the above configuration, by supplying the hydraulic oil cooled by the oil cooler 73 to the first hydraulic pump P1, the cooled hydraulic oil can be preferentially supplied to the first hydraulic device S. That is, in this embodiment, it is possible to cool the hydraulic oil flowing through the circulation oil passage 52, where the oil temperature is likely to rise.

[0054] The hydraulic system of the work machine 1 also includes a connecting oil passage 36. The connecting oil passage 36 branches off from the second discharge oil passage 72 and is connected to the suction oil passage 35. The connecting oil passage 36 branches off from the middle of the fifth oil passage 72c and merges with the suction oil passage 35. The connecting oil passage 36 is also connected to a portion of the suction oil passage 35 that is closer to the second hydraulic pump P2. The following provides a detailed description of the operation related to the work of the work machine 1, that is, the operation (work operation) of the work device 4. As shown in FIG.

[0055] The second operating device 67 is a device that operates the hydraulic actuators AC of the work system, such as the boom cylinder 14 and the bucket cylinder 15, among the hydraulic actuators AC. In other words, the second operating device 67 can switch the discharge amount (output) of hydraulic oil supplied to the boom cylinder 14, the bucket cylinder 15, etc., and the discharge direction of the hydraulic oil by changing the pilot pressure acting on the pressure-receiving portions 60A, 60B of the plurality of control valves 60. The second operating device 67 includes a second operating member (work lever) 68, a plurality of second operating valves (work operating valves) 69, a plurality of proportional valves 65, and a backup operating member 101.

[0056] The second operating member 68 is an operating lever that swings left and right (aircraft body width direction) or front and rear. The second operating member 68 is supported by a plurality of second operating valves 69. The second operating member 68 can be operated forward (in the direction of arrow A1 in FIG. 2) and backward (in the direction of arrow A2 in FIG. 2) from the neutral position N as a reference, and can also be operated left (in the direction of arrow A3 in FIG. 2) and right (in the direction of arrow A4 in FIG. 2) from the neutral position N. In other words, the second operating member 68 can swing in at least four directions from the neutral position N as a reference.

[0057] The plurality of second operating valves 69 are valves that are actuated by operation of a second operating member 68. Specifically, the plurality of second operating valves 69 are connected to a third supply oil passage 40c branching from the first discharge oil passage 40, and are capable of changing the pressure (pilot pressure) of pilot oil, which is hydraulic oil supplied from the first discharge oil passage 40. The plurality of second operating valves 69 are operated by a common second operating member 68, i.e., a single operating lever. As shown in FIG. 2 , the plurality of second operating valves 69 are connected to the plurality of control valves 60 by a working oil passage 46. The working oil passage 46 is an oil passage that connects the plurality of second operating valves 69 and the plurality of control valves 60.

[0058] Therefore, when the second operating member 68 is operated, the multiple second operating valves 69 change the pressure (pilot pressure) of the pilot oil, which is the hydraulic oil supplied from the first discharge oil passage 40, and the working oil passage 46 acts on the pressure-receiving portions 60A, 60B of the first control valve 61 and the pressure-receiving portions 60A, 60B of the second control valve 62, thereby operating the first control valve 61 and the second control valve 62.

[0059] The plurality of proportional valves 65 are valves that operate the third control valve 63. Specifically, the proportional valves 65 are solenoid valves whose opening degree can be changed by excitation. The proportional valves 65 are connected to a fourth supply oil passage 40d branching from the first discharge oil passage 40, and can change the pressure (pilot pressure) of the pilot oil, which is the hydraulic oil supplied from the first discharge oil passage 40. In this embodiment, the plurality of proportional valves 65 are a first proportional valve 65A and a second proportional valve 65B. The proportional valve 65 is connected to the pressure receiving portions 60A, 60B of the third control valve 63 by a control oil passage 66. The control oil passage 66 is an oil passage that allows pilot oil supplied from the multiple proportional valves 65 (first proportional valve 65A and second proportional valve 65B) to flow to the pressure receiving portions 60A, 60B of the third control valve 63.

[0060] The auxiliary operation member 101 is a switch for operating an auxiliary attachment. The auxiliary operation member 101 is operated by an operator or the like, and inputs the operation signal to the control device 100. The control device 100 is provided in the work machine 1, and is a device that is configured from electric and electronic circuits, programs stored in a CPU, an MPU, etc. The control device 100 controls the switching of the auxiliary operation member 101. Based on the operation, a control signal (for example, voltage, current, etc.) is output to the plurality of proportional valves 65 to operate (open / close) the proportional valves 65. The auxiliary operating member 101 is configured, for example, by a seesaw switch that can be swung freely, a slide switch that can be slid freely, or a push switch that can be pressed freely.

[0061] Therefore, when the auxiliary operating member 101 is operated, the multiple proportional valves 65 change the pressure (pilot pressure) of the pilot oil, which is the hydraulic oil supplied from the first discharge oil passage 40, and the connecting oil passage 36 acts on the pressure-receiving portions 60A, 60B of the third control valve 63, thereby operating the third control valve 63.

[0062] The flow of hydraulic oil will be described below with reference to Figures 3 and 4, with reference to the first hydraulic pump P1. Figure 3 shows the flow of hydraulic oil in the first embodiment when the amount of return oil discharged from the second hydraulic device C is greater than the flow rate of hydraulic oil sucked into the first hydraulic pump P1. Figure 4 shows the flow of hydraulic oil in the first embodiment when the amount of return oil discharged from the second hydraulic device C is less than the flow rate of hydraulic oil sucked into the first hydraulic pump P1. As shown in Figures 3 and 4, the first hydraulic pump P1 sucks hydraulic oil from the second discharge oil passage 72. When the first hydraulic pump P1 discharges hydraulic oil, the hydraulic oil is supplied to the first hydraulic device S via the first discharge oil passage 40 and the first supply oil passage 40a. The hydraulic oil supplied to the first hydraulic device S is discharged to the hydraulic oil tank T via the first discharge oil passage 71. Specifically, when the travel motor 51 is not driven, the hydraulic oil supplied from the charge oil passage 53 to the circulation oil passage 52 (i.e., the hydraulic oil supplied by the first hydraulic pump P1 to the first hydraulic device S) is discharged from the first oil passage 71a to the hydraulic oil tank T. On the other hand, when the travel motor 51 is driven, the hydraulic oil supplied from the charge oil passage 53 to the circulation oil passage 52 is discharged from the first oil passage 71a and the second oil passage 71b to the hydraulic oil tank T.

[0063] The second hydraulic pump P2 also draws hydraulic oil from the hydraulic oil tank T via the intake oil passage 35. When the second hydraulic pump P2 discharges hydraulic oil, the hydraulic oil is supplied to the plurality of control valves 60 via the second discharge oil passage 45. The hydraulic oil supplied to the plurality of control valves 60 passes through the plurality of control valves 60 and flows to the second discharge oil passage 72. Here, when considering a cross section (cross section perpendicular to the rod c3) of the rod c3 and piston c2 in the hydraulic cylinder C, the cross-sectional area of ​​the piston c2 is larger than the cross-sectional area of ​​the rod c3. In other words, the cross-sectional area of ​​the oil chamber (second oil chamber c1b) where the rod c3 is located in the cylinder tube c1 differs from the cross-sectional area of ​​the oil chamber (first oil chamber c1a) on the opposite side due to the rod c3. Therefore, when the hydraulic cylinder C extends, the flow rate of hydraulic oil discharged from the second supply / discharge port is less than the flow rate of hydraulic oil supplied to the first supply / discharge port. On the other hand, when the hydraulic cylinder C retracts, the flow rate of hydraulic oil discharged from the first supply / discharge port is greater than the flow rate of hydraulic oil supplied to the second supply / discharge port.

[0064] In particular, when the hydraulic cylinder C reaches the stroke end or starts to extend, the flow rate of hydraulic oil discharged from the second oil chamber c1b to the second oil supply / discharge port is less than the flow rate of hydraulic oil supplied from the first oil supply / discharge port to the first oil chamber c1a. In other words, when the hydraulic cylinder C extends, the amount of hydraulic oil discharged to the second oil discharge passage 72 (the amount of return oil) is less. For this reason, if the discharge flow rate per predetermined time of the first hydraulic pump P1 is "F1," the discharge flow rate per predetermined time of the second hydraulic pump P2 is "F2," and the flow rate of hydraulic oil flowing through the second discharge oil passage 72 per predetermined time is "F3," when the hydraulic cylinder C is not contracted or driven, the flow rate F3 of hydraulic oil flowing through the second discharge oil passage 72 per predetermined time will be equal to or greater than the discharge flow rate F2 per predetermined time of the second hydraulic pump P2 (F3≧F2). Here, the discharge flow rate F2 of hydraulic oil per predetermined time of the second hydraulic pump P2 is equal to or greater than the discharge flow rate F1 of hydraulic oil per predetermined time of the first hydraulic pump P1 (F2≧F1), and therefore the flow rate F3 of hydraulic oil flowing through the second discharge oil passage 72 per predetermined time will be equal to or greater than the discharge flow rate F1 per predetermined time of the first hydraulic pump P1 (F3≧F1). Therefore, as shown in FIG. 3, of the hydraulic oil flowing through the second discharge oil passage 72, the remaining hydraulic oil sucked by the first hydraulic pump P1 is sucked by the second hydraulic pump P2 via the connecting oil passage 36.

[0065] On one hand, when the hydraulic cylinder C extends and the flow rate F3 of the hydraulic oil flowing through the second discharge oil passage 72 per predetermined time becomes less than the discharge flow rate F2 of the second hydraulic pump P2 per predetermined time (F3 < F2). For this reason, the flow rate F3 of the hydraulic oil flowing through the second discharge oil passage 72 per predetermined time becomes less than the discharge flow rate F1 of the first hydraulic pump P1 per predetermined time (F3 < F1), and a negative pressure is generated in the second discharge oil passage 72. Therefore, in the present embodiment, the hydraulic system of the work machine 1 includes a replenishment portion 75 to suppress the second discharge oil passage 72 from sucking hydraulic oil from the suction oil passage 35 through the connection oil passage 36 due to the negative pressure generated in the second discharge oil passage 72. When the flow rate F3 of the hydraulic oil flowing through the second discharge oil passage 72 per predetermined time is less than the discharge flow rate F2 of the second hydraulic pump P2 per predetermined time (F3 < F2). For this reason, the flow rate F3 of the hydraulic oil flowing through the second discharge oil passage 72 per predetermined time becomes less than the discharge flow rate F1 of the first hydraulic pump P1 per predetermined time (F3 < F1), and a negative pressure is generated in the second discharge oil passage 72. Therefore, in the present embodiment, the hydraulic system of the work machine 1 includes a replenishment portion 75 to suppress the second discharge oil passage 72 from sucking hydraulic oil from the suction oil passage 35 through the connection oil passage 36 due to the negative pressure generated in the second discharge oil passage 72.

[0066] When the second discharge oil passage 72 sucks hydraulic oil from the suction oil passage 35 through the connection oil passage 36, the flow of the hydraulic oil in the connection oil passage 36 suddenly switches from the direction from the second discharge oil passage 72 to the suction oil passage 35 to the direction from the suction oil passage 35 to the second discharge oil passage 72 (transitions from the state of FIG. 3 to the state of FIG. 4). That is, at the timing when the flow of the hydraulic oil in the connection oil passage 36 switches (changes), the hydraulic oil sucked by the first hydraulic pump P1 becomes insufficient, and a negative pressure surge occurs in the second discharge oil passage 72. In such a case, the first hydraulic pump P1 cannot stably discharge the hydraulic oil.

[0067] The replenishing unit 75 is connected to the second discharge oil passage 72 and replenishes hydraulic oil to the second discharge oil passage 72. In the present embodiment, the replenishing unit 75 is a bypass oil passage 76 that connects the second discharge oil passage 72 and the hydraulic oil tank T. The bypass oil passage 76 branches off from a midpoint of the fifth oil passage 72c and merges with a midpoint of the suction oil passage 35. One end of the bypass oil passage 76 is connected to the fifth oil passage 72c, and the other end of the bypass oil passage 76 is connected to the suction oil passage 35. Preferably, the other end of the bypass oil passage 76 is connected to the suction oil passage 35 so as to be connected in parallel to the tubing 35a of the suction oil passage 35 that is connected to the second hydraulic pump P2. In other words, the other end of the bypass oil passage 76 is preferably connected to the oil passage 35b between the tubing 35a and the suction filter 34 of the suction oil passage 35. Therefore, the bypass oil passage 76 indirectly connects the second discharge oil passage 72 and the hydraulic oil tank T, separately from the connecting oil passage 36 .

[0068] In the present embodiment, one end of the bypass oil passage 76 is connected to the fifth oil passage 72c, but the bypass oil passage 76 may be connected to at least a portion of the second discharge oil passage 72 downstream of the junction where the hydraulic oil flowing through the supply / discharge oil passage 64 joins. In other words, one end of the bypass oil passage 76 may be connected to the fourth oil passage 72b, and its position may be upstream or downstream of the oil cooler 73 and the return filter 74, or may be a portion between the oil cooler 73 and the return filter 74.

[0069] In addition, in this embodiment, the other end of the bypass oil passage 76 is connected to the intake oil passage 35, but the bypass oil passage 76 only needs to be able to connect the second discharge oil passage 72 to the hydraulic oil tank T, and may also be directly connected to the hydraulic oil tank T. 4, even if the hydraulic cylinder C is extended and negative pressure is generated in the second discharge oil passage 72, the bypass oil passage 76 replenishes hydraulic oil to the second discharge oil passage 72, and the first hydraulic pump P1 draws hydraulic oil from the connection oil passage 36, thereby preventing changes in the flow of hydraulic oil in the connection oil passage 36. In other words, the pressure of the hydraulic oil flowing through the second discharge oil passage 72 satisfies the allowable negative pressure value of the first hydraulic pump P1, and the first hydraulic pump P1 can stably discharge hydraulic oil.

[0070] Regarding the relationship between the inner diameter of the bypass oil passage 76 and the inner diameters of the other oil passages, the inner diameter of the bypass oil passage 76 is larger than the inner diameter of the connecting oil passage 36 and the inner diameter of the second discharge oil passage 72. Furthermore, the inner diameter of the connecting oil passage 36 is smaller than the inner diameter of the second discharge oil passage 72. In other words, if the inner diameter of the bypass oil passage 76 is "p1," the inner diameter of the connecting oil passage 36 is "p2," and the inner diameter of the second discharge oil passage 72 is "p3," the relationship among the inner diameters of the bypass oil passage 76, the connecting oil passage 36, and the second discharge oil passage 72 is "p1>p3>p2." Furthermore, in this embodiment, the inner diameter of the bypass oil passage 76 is the same as the inner diameter of the pipe member 35a of the suction oil passage 35. Therefore, pressure loss in the bypass oil passage 76 can be suppressed, and the pressure of the hydraulic oil flowing through the second discharge oil passage 72 can more reliably satisfy the allowable negative pressure value of the first hydraulic pump P1. This makes it possible to avoid a shortage of hydraulic oil drawn into the first hydraulic pump P1, and to suppress an increase in the flow rate of the hydraulic oil in the second discharge oil passage 72 and an increase in the negative pressure in the second discharge oil passage 72. This allows the first hydraulic pump P1 to stably discharge the hydraulic oil.

[0071] The hydraulic system of the work machine 1 described above includes a first hydraulic pump P1, a first hydraulic device S that operates with hydraulic oil discharged by the first hydraulic pump P1, a hydraulic oil tank T that stores hydraulic oil, a first discharge oil passage 71 that flows hydraulic oil discharged from the first hydraulic device S to the hydraulic oil tank T, a second hydraulic pump P2 that is connected to the hydraulic oil tank T via an intake oil passage 35 and that draws hydraulic oil from the hydraulic oil tank T via the intake oil passage 35, and a second hydraulic pump P2 that operates with the hydraulic oil discharged by the second hydraulic pump P2 and that operates the second hydraulic device C, in which the deviation between the flow rate of hydraulic oil supplied from the second hydraulic pump P2 and the flow rate of hydraulic oil discharged varies depending on the operation of the second hydraulic pump P2; a second discharge oil passage 72, connected to the suction port P1b of the first hydraulic pump P1, for allowing the hydraulic oil discharged from the second hydraulic device C to flow to the first hydraulic pump P1; a connection oil passage 36, branched from the second discharge oil passage 72 and connected to the suction oil passage 35; and a refill unit 75, connected to the second discharge oil passage 72, for refilling the second discharge oil passage 72 with hydraulic oil.

[0072] According to the above configuration, even if negative pressure occurs in the second discharge oil passage 72 when the flow rate of the hydraulic oil discharged from the second hydraulic device C becomes smaller than the flow rate of the hydraulic oil supplied to the second hydraulic device C, the hydraulic oil can be replenished to the second discharge oil passage 72, and therefore it is possible to prevent the first hydraulic pump P1 from drawing hydraulic oil from the connecting oil passage 36. In other words, it is possible to prevent changes in the flow of hydraulic oil in the connecting oil passage 36, and it is possible for the pressure of the hydraulic oil flowing through the second discharge oil passage 72 to satisfy the allowable negative pressure value of the first hydraulic pump P1. The second hydraulic device C is a hydraulic cylinder, and includes a cylinder tube c1, a piston c2 provided inside the cylinder tube c1, and a rod c3 attached to the piston c2.

[0073] According to the above configuration, the cross-sectional area of ​​the oil chamber (second oil chamber c1b) in which the rod c3 in the cylinder tube c1 is located and the oil chamber (first oil chamber c1a) on the opposite side differ depending on the rod c3. As a result, when the hydraulic cylinder C reaches its stroke end or starts to extend, the flow rate of hydraulic oil discharged during extension of the hydraulic cylinder C becomes smaller than the flow rate of hydraulic oil supplied, which may cause negative pressure in the second discharge oil passage 72. However, by replenishing the second discharge oil passage 72 with hydraulic oil, it is possible to prevent the first hydraulic pump P1 from drawing in hydraulic oil via the connecting oil passage 36. In other words, it is possible to prevent changes in the flow of hydraulic oil in the connecting oil passage 36, and the pressure of the hydraulic oil flowing through the second discharge oil passage 72 can satisfy the allowable negative pressure value of the first hydraulic pump P1. The refilling section 75 is a bypass oil passage 76 that connects the second discharge oil passage 72 and the hydraulic oil tank T.

[0074] According to the above configuration, by providing the bypass oil passage 76, hydraulic oil can be replenished to the second discharge oil passage 72 relatively easily and reliably, and the pressure of the hydraulic oil flowing through the second discharge oil passage 72 can satisfy the allowable negative pressure value of the first hydraulic pump P1. The inner diameter of the bypass oil passage 76 is larger than the inner diameter of the connecting oil passage 36 and the inner diameter of the second discharge oil passage 72 . According to the above configuration, it is possible to suppress pressure loss in the bypass oil passage 76, more reliably avoid a shortage of hydraulic oil drawn into the first hydraulic pump P1, and suppress an increase in the flow rate of the hydraulic oil in the second discharge oil passage 72 and an increase in negative pressure in the second discharge oil passage 72. Therefore, the pressure of the hydraulic oil flowing through the second discharge oil passage 72 can satisfy the allowable negative pressure value of the first hydraulic pump P1.

[0075] Further, the second oil discharge passage 72 is provided with an oil cooler 73 that cools the hydraulic oil. According to the above configuration, by supplying the hydraulic oil cooled by the oil cooler 73 to the first hydraulic pump P1, the cooled hydraulic oil can be preferentially supplied to the first hydraulic device S. Therefore, even if the hydraulic oil in the first hydraulic device S becomes relatively hot, the first hydraulic device S can be operated favorably by supplying cooled hydraulic oil.

[0076] The hydraulic system of the work machine 1 includes a prime mover 6, and the first hydraulic device S includes a travel pump 50 that is operated by the power of the prime mover 6, a travel motor 51 that can be rotated by hydraulic oil discharged from the travel pump 50, a circulation oil passage 52 that connects the travel pump 50 and the travel motor 51, and a second hydraulic device S. and a charge oil passage 53 that supplies the hydraulic oil discharged by the hydraulic pump P1 to the circulation oil passage 52.

[0077] According to the above configuration, hydraulic oil can be replenished to the second discharge oil passage 72, so that the travel motor 51 can be driven stably even when the flow rate of hydraulic oil discharged when the hydraulic cylinder C is extended becomes less than the flow rate of hydraulic oil supplied. The work machine 1 also includes a hydraulic system for the work machine 1, a machine body 2, a traveling device 5 provided on the machine body 2 and driven by a first hydraulic device S to provide propulsion force to the machine body 2, and a work device 4 provided on the machine body 2 and driven by a second hydraulic device C.

[0078] According to the above configuration, when the working device 4 is being driven, that is, even if the second hydraulic device C is operating and negative pressure is generated in the second discharge oil passage 72, the first hydraulic pump P1 can be prevented from drawing hydraulic oil from the connecting oil passage 36. In other words, changes in the flow of hydraulic oil in the connecting oil passage 36 can be prevented, and the pressure of the hydraulic oil flowing through the second discharge oil passage 72 can satisfy the allowable negative pressure value of the first hydraulic pump P1. Therefore, regardless of whether the working device 4 is being driven, hydraulic oil can be stably supplied to the first hydraulic pump P1, and the traveling device 4 can be stably driven.

[0079] [Second embodiment] FIG. 5 shows a hydraulic circuit of the travel system in the hydraulic system of the work machine 1 in the second embodiment. FIG. 6 is a diagram showing a hydraulic circuit of the work system in the hydraulic system of the work machine 1 in the second embodiment. In the second embodiment, a configuration different from the above-described embodiment will be described. As shown in FIGS. 5 and 6, in the second embodiment, the replenishing unit 75 is an accumulator 77. Note that in the second embodiment, an example is described in which the hydraulic system of the work machine 1 includes an accumulator 77 instead of the bypass oil passage 76 as the replenishing unit 75. However, the hydraulic system of the work machine 1 may also include the bypass oil passage 76 and the accumulator 77 as the replenishing unit 75. The accumulator 77 is connected to the second discharge oil passage 72, accumulates hydraulic oil under pressure, and supplies the accumulated hydraulic oil to the second discharge oil passage 72. Therefore, the accumulator 77 is a pressure accumulator that absorbs pressure fluctuations in the second oil chamber c1b of the hydraulic cylinder C.

[0080] The accumulator 77 is connected to a portion of the fifth oil passage 72c that is upstream of the connection portion 36a to which the connecting oil passage 36 is connected. In the present embodiment, the accumulator 77 is connected to the fifth oil passage 72c, but the accumulator 77 may be connected to at least a portion of the second discharge oil passage 72 that is downstream of the junction where the hydraulic oil flowing through the supply / discharge oil passage 64 joins. In other words, the accumulator 77 may be connected to the fourth oil passage 72b, and its position may be upstream or downstream of the oil cooler 73 and the return filter 74, or may be a portion between the oil cooler 73 and the return filter 74.

[0081] As a result, when the hydraulic cylinder C is extended and negative pressure is generated in the second discharge oil passage 72, the accumulator 77 replenishes hydraulic oil to the second discharge oil passage 72, and can prevent the first hydraulic pump P1 from drawing hydraulic oil from the connecting oil passage 36. In other words, it is possible to prevent a shortage of hydraulic oil drawn into the second hydraulic pump P2, and the second hydraulic pump P2 can stably discharge hydraulic oil. The above-mentioned replenishing section 75 is an accumulator 77 that stores hydraulic oil under pressure and supplies the stored hydraulic oil to the second discharge oil passage 72. According to the above configuration, by providing the accumulator 77, hydraulic oil can be replenished to the second discharge oil passage 72 relatively easily and reliably, and the pressure of the hydraulic oil flowing through the second discharge oil passage 72 can satisfy the allowable negative pressure value of the first hydraulic pump P1.

[0082] [Third embodiment] FIG. 7 is a diagram showing a hydraulic circuit of the work system in the hydraulic system of the work machine 1 in the third embodiment. In the third embodiment, a configuration different from the above-described embodiments will be described. As shown in FIG. 7, in the third embodiment, the replenishing section 75 is a reserve tank 78. Note that in the third embodiment, an example will be described in which the hydraulic system of the work machine 1 is provided with a reserve tank 78 as the replenishing section 75 instead of the bypass oil passage 76 and the accumulator 77. The hydraulic system may include, as the replenishing unit 75, a reserve tank 78 and at least one of a bypass oil passage 76 and an accumulator 77.

[0083] The reserve tank 78 stores hydraulic oil separately from the hydraulic oil tank T, and supplies the stored hydraulic oil to the second discharge oil passage 72. The reserve tank 78 is connected to the second discharge oil passage 72. The reserve tank 78 is also provided with a breather 79 that connects the inside of the reserve tank 78 to the outside. The reserve tank 78 is connected to a portion of the fifth oil passage 72c that is upstream of the connection portion 36a to which the connecting oil passage 36 is connected. In the present embodiment, the reserve tank 78 is connected to the fifth oil passage 72c, but the reserve tank 78 may be connected to at least a portion of the second discharge oil passage 72 that is downstream of the junction where the hydraulic oil flowing through the supply / discharge oil passage 64 joins. In other words, the reserve tank 78 may be connected to the fourth oil passage 72b, and its position may be upstream or downstream of the oil cooler 73 and the return filter 74, or may be a portion between the oil cooler 73 and the return filter 74.

[0084] As a result, when the hydraulic cylinder C is extended and negative pressure is generated in the second discharge oil passage 72, the reserve tank 78 replenishes hydraulic oil to the second discharge oil passage 72, and can prevent the first hydraulic pump P1 from drawing hydraulic oil from the connecting oil passage 36. In other words, it is possible to prevent a shortage of hydraulic oil drawn into the second hydraulic pump P2, and the second hydraulic pump P2 can stably discharge hydraulic oil. The above-mentioned replenishing section 75 is a reserve tank 78 that stores hydraulic oil separately from the hydraulic oil tank T and supplies the stored hydraulic oil to the second discharge oil passage 72.

[0085] According to the above configuration, by providing a spare tank 78, hydraulic oil can be replenished to the second discharge oil passage 72 relatively easily and reliably, and the pressure of the hydraulic oil flowing through the second discharge oil passage 72 can satisfy the allowable negative pressure value of the first hydraulic pump P1. The reserve tank 78 is also provided with a breather 79 that connects the inside and outside of the reserve tank 78 . According to the above configuration, even if negative pressure occurs in the second discharge oil passage 72, hydraulic oil can be more reliably replenished from the reserve tank 78 to the second discharge oil passage 72, so that hydraulic oil can be replenished to the second discharge oil passage 72 and the pressure of the hydraulic oil flowing through the second discharge oil passage 72 can satisfy the allowable negative pressure value of the first hydraulic pump P1.

[0086] Although the present invention has been described above, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0087] 1 Work equipment 2 aircraft 3 Cabins 4 Work equipment 5 Running gear 6. Prime Mover 35 Suction oil path 36 Connecting oil passage 50 Travel pump 51 Travel motor 52 Circulating oil path 53 Charging oil passage 71 1st discharge oil path 72 2nd discharge oil path 75 Replenishment Department 76 Bypass oil passage 77 Accumulator 78 Spare Tank 79 Breather C. Second hydraulic equipment (hydraulic cylinder) c1 Cylinder tube (cylindrical body) c2 piston c3 rod P1 First hydraulic pump P1b Intake port (second port) P2 Second hydraulic pump S First hydraulic equipment T Hydraulic oil tank

Claims

1. a first hydraulic pump; a first hydraulic device that operates using hydraulic oil discharged from the first hydraulic pump; a hydraulic oil tank for storing hydraulic oil; a first oil discharge passage through which hydraulic oil discharged from the first hydraulic device flows to the hydraulic oil tank; a second hydraulic pump connected to the hydraulic oil tank via an intake oil passage and configured to draw hydraulic oil from the hydraulic oil tank via the intake oil passage; a second hydraulic device that is operated by the hydraulic oil discharged from the second hydraulic pump, and in which a deviation between a flow rate of the hydraulic oil supplied from the second hydraulic pump and a flow rate of the hydraulic oil discharged from the second hydraulic pump fluctuates in response to the operation of the second hydraulic device; a second discharge oil passage that directly connects the suction port of the first hydraulic pump and the second hydraulic device without passing through the hydraulic oil tank, and that allows hydraulic oil discharged from the second hydraulic device to flow to the first hydraulic pump; a connecting oil passage having one end branched from the second discharge oil passage and the other end connected to the intake oil passage; a replenishing unit connected to the second discharge oil passage and replenishing hydraulic oil to the second discharge oil passage; A hydraulic system of a work implement comprising:

2. the second hydraulic device is a hydraulic cylinder, A cylinder tube; a piston provided inside the cylinder tube; a rod attached to the piston; 2. The hydraulic system of claim 1, further comprising:

3. 3. The hydraulic system for a work machine according to claim 1, wherein the refill section is a bypass oil passage that connects the second discharge oil passage and the hydraulic oil tank.

4. The intake oil passage has one end connected to the second hydraulic pump and the other end connected to an oil filter provided inside the hydraulic oil tank, 4. A hydraulic system for a work machine as described in claim 3, wherein the bypass oil passage is a separate oil passage from the connecting oil passage, and has one end connected to the second discharge oil passage and the other end connected to the suction oil passage.

5. 5. The hydraulic system for a work machine according to claim 3, wherein an inner diameter of the bypass oil passage is larger than an inner diameter of the connecting oil passage and an inner diameter of the second discharge oil passage.

6. 3. The hydraulic system for a work machine according to claim 1, wherein the replenishing unit is an accumulator that stores hydraulic oil under pressure and supplies the stored hydraulic oil to the second discharge oil passage.

7. 3. The hydraulic system for a work machine according to claim 1, wherein the refill unit is a reserve tank that stores hydraulic oil separately from the hydraulic oil tank and supplies the stored hydraulic oil to the second discharge oil passage.

8. 8. The hydraulic system for a work machine according to claim 7, wherein the reserve tank is provided with a breather that connects the inside and outside of the reserve tank.

9. 9. The hydraulic system for a work machine according to claim 1, wherein an oil cooler for cooling hydraulic oil is provided in the second oil discharge passage.

10. Equipped with a prime mover, The first hydraulic device is a travel pump operated by the power of the prime mover; a travel motor that can be rotated by the hydraulic oil discharged by the travel pump; a circulation oil passage connecting the travel pump and the travel motor; a charge oil passage that supplies hydraulic oil discharged by the first hydraulic pump to the circulation oil passage; The hydraulic system for a work machine according to any one of claims 1 to 9, comprising:

11. A hydraulic system for a work machine according to any one of claims 1 to 10; The aircraft and a traveling device that is provided on the machine body and is driven by the first hydraulic device to impart a propulsive force to the machine body; a working device provided on the machine body and driven by the second hydraulic device; A work machine equipped with the above.

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