Hydraulic system for construction machine

Abstract

A hydraulic system (1A) for a construction machine according to one embodiment of the present invention comprises a slewing control valve device (3) that controls the supply of hydraulic oil from a hydraulic pump (2) to a slewing motor (4) and the discharge of the hydraulic oil from the slewing motor (4) to a tank. When slewing of a slewing body is to be stopped, the slewing control valve device (3) prohibits the discharge of the hydraulic oil from the slewing motor (4) to the tank to reduce the slewing speed of a slewing body, and thereafter allows the discharge of the hydraulic oil from the slewing motor (4) to the tank but prohibits the supply of the hydraulic oil from the hydraulic pump (2) to the slewing motor (4).

Description

Hydraulic systems for construction machinery

[0001] The present disclosure relates to hydraulic systems for construction machines.

[0002] Construction machinery such as hydraulic excavators and hydraulic cranes are equipped with a hydraulic system that includes a swing motor that rotates a swing body. Generally, the supply of hydraulic oil from the hydraulic pump to the swing motor and the discharge of hydraulic oil from the swing motor to a tank are controlled by a swing control valve.

[0003] The swing control valve is connected to the swing motor by a pair of supply and discharge lines and is switchable between a neutral position where the pair of supply and discharge lines are blocked and an actuated position where one of the pair of supply and discharge lines is connected to the pump line and the other is connected to the tank line.

[0004] Each of the pair of supply and discharge lines is connected to the tank by a relief line equipped with a relief valve. When the rotation of the rotating body is stopped, the rotation control valve is switched from the drive position to the neutral position, and the braking action of the discharge-side relief valve reduces the rotation speed of the rotating body.

[0005] If the rotation control valve is maintained in the neutral position when the rotation of the rotating body is stopped, when the rotation speed of the rotating body becomes zero, the pressure in the supply / discharge line on the discharge side, which becomes confined, may become higher than the pressure in the discharge line on the supply side, causing the rotating body to reverse.

[0006] In order to prevent such reversal of the rotating body, a reversal prevention valve is used in general hydraulic systems. In contrast, Patent Document 1 proposes a hydraulic system in which, when stopping the rotation of the rotating body, the swing control valve is switched from the drive position to the neutral position, and when the swing speed of the rotating body has decreased to a certain extent, the swing control valve is switched from the neutral position to the drive position. This makes it possible to prevent reversal of the rotating body without using a reversal prevention valve.

[0007] Patent No. 6901875

[0008] In the hydraulic system of Patent Document 1 described above, when the swing control valve is switched from the neutral position to the drive position to prevent the swing body from reversing, not only the meter-out passage but also the meter-in passage is opened. When a swing operation is performed alone, opening the meter-in passage when stopping the swing does not pose any particular problem because the discharge pressure of the hydraulic pump becomes low when the swing is stopped. However, when a swing operation is performed simultaneously with another operation, opening the meter-in passage when stopping the swing may cause high-pressure hydraulic oil to be supplied to the swing motor, making it difficult to prevent reversal.

[0009] Therefore, an object of the present disclosure is to provide a hydraulic system for a construction machine that can stop the rotation of a rotating body while preventing it from reversing even when a rotation operation is performed simultaneously with another operation.

[0010] The present disclosure provides a hydraulic system for construction machinery comprising: a swing motor for swinging a swing body; a swing control valve device connected to the swing motor by a pair of supply and discharge lines, which controls the supply of hydraulic oil from a hydraulic pump to the swing motor and the discharge of hydraulic oil from the swing motor to a tank; a pair of relief lines each provided with a relief valve, which connect the pair of supply and discharge lines to the tank; and a pair of make-up lines each provided with a check valve, which connect the pair of supply and discharge lines to the tank, wherein, when stopping the swing of the swing body, the swing control valve device prohibits the discharge of hydraulic oil from the swing motor to the tank and reduces the swing speed of the swing body, after which it allows the discharge of hydraulic oil from the swing motor to the tank, while prohibiting the supply of hydraulic oil from the hydraulic pump to the swing motor.

[0011] According to the present disclosure, a hydraulic system for a construction machine is provided that can stop the rotation of a rotating body while preventing it from turning over even when a rotation operation is performed simultaneously with another operation.

[0012] FIG. 3 is a schematic diagram of a hydraulic system for a construction machine according to a first embodiment. FIG. 4 is a side view of a hydraulic excavator, which is an example of a construction machine. FIG. 3A to FIG. 3D are graphs showing a swing stop in the first embodiment, with FIG. 3A showing the change over time in the swing operation amount, FIG. 3B showing the change over time in the swing speed, FIG. 3C showing the change over time in the anti-reverse opening command, and FIG. 3D showing the change over time in the meter-out opening area. FIG. 4 is an image diagram of a characteristics map defining the correspondence between the meter-out opening area and the moment of inertia and the swing acceleration. FIG. 5 is a schematic diagram of a hydraulic system for a construction machine according to a second embodiment. FIG. 6A is a graph showing the relationship between the spool stroke and the meter-in opening area and the meter-out opening area in the second embodiment, and FIG. 6B is a graph showing the relationship between the spool stroke and the meter-in opening area and the meter-out opening area in a modified example of the second embodiment. FIG. 5 is a schematic diagram of a hydraulic system for a construction machine according to a third embodiment.

[0013] <First embodiment> Fig. 1 shows a hydraulic system 1A for a construction machine according to a first embodiment, and Fig. 2 shows a construction machine 9 equipped with the hydraulic system 1A. The construction machine 9 shown in Fig. 2 is a hydraulic excavator, but the construction machine 9 may be another type of construction machine, such as a hydraulic crane.

[0014] The construction machine 9 shown in Figure 2 is self-propelled and includes a running body 91 and a rotating body 92 that is rotatably supported on the running body 91. A cabin 93 including a driver's seat is provided on the rotating body 92, and a boom 94 is connected to it. An arm 95 is connected to the tip of the boom 94, and a bucket 96 is connected to the tip of the arm 95. However, the construction machine 9 does not have to be self-propelled.

[0015] The hydraulic system 1A includes, as hydraulic actuators, a boom cylinder 41, an arm cylinder 42, and a bucket cylinder 43 shown in Fig. 2, as well as the swing motor 4 shown in Fig. 1 and a pair of left and right travel motors (not shown). The swing motor 4 rotates the swing body 92. The hydraulic system 1A also includes a hydraulic pump 2 that supplies hydraulic fluid to these hydraulic actuators, as shown in Fig. 1.

[0016] 1, for the sake of simplicity, hydraulic actuators other than the swing motor 4 are omitted. In the following, explanations of the configurations for hydraulic actuators other than the swing motor 4 will be omitted unless otherwise noted.

[0017] The hydraulic system 1A includes a swing control valve device 3 that controls the supply of hydraulic fluid from the hydraulic pump 2 to the swing motor 4 and the discharge of hydraulic fluid from the swing motor 4 to a tank, a swing operation device 6 that includes an operating lever that receives swing operations from the operator, and a processing circuit 7.

[0018] The hydraulic pump 2 is a variable displacement pump whose tilt angle is changeable. For example, the hydraulic pump 2 is an axial piston pump such as a swash plate pump or a bent axis pump. The tilt angle of the hydraulic pump 2 is changed by a regulator 21.

[0019] In this embodiment, the regulator 21 is controlled by the processing circuit 7. For example, if the hydraulic pump 2 is a swash plate pump, the regulator 21 may be a device that electrically changes the hydraulic pressure acting on a servo piston connected to the swash plate of the hydraulic pump 2, or may be an electric actuator connected to the swash plate of the hydraulic pump 2.

[0020] However, the regulator 21 does not necessarily need to be controlled by the processing circuit 7, and may be operated by the pressure of the hydraulic oil. For example, the regulator 21 may be of a negative control type or a load sensing type.

[0021] A supply line 11 extends from the hydraulic pump 2, and pump lines 12 branch off from the supply line 11 for each hydraulic actuator. An unloading line 15 branches off from the supply line 11, and an unloading valve 16 is provided in the unloading line 15. The unloading valve 16 is controlled by the processing circuit 7. Note that in FIG. 1, some signal lines are not shown to simplify the drawing. Furthermore, a relief line branches off from the supply line 11, and a relief valve is provided in the relief line to maintain the discharge pressure of the hydraulic pump 2 at or below an upper limit pressure.

[0022] The swing control valve device 3 described above is interposed between the hydraulic pump 2 and the swing motor 4. Specifically, the swing control valve device 3 is connected to the swing motor 4 by a pair of supply and discharge lines 51, 52, is connected to the hydraulic pump 2 via the pump line 12 and the supply line 11, and is connected to the tank by the tank line 14.

[0023] In this embodiment, the swing control valve device 3 includes a pair of mutually independent control valves 3A and 3B. The control valves 3A and 3B do not need to be physically separated from each other, and spools (described later) of the control valves 3A and 3B may be slidably held in a common housing.

[0024] The supply and discharge lines 51 and 52 are connected to the control valves 3A and 3B, respectively. Furthermore, the pump line 12 for the swing motor 4 includes a common line on the upstream side and a pair of branch lines on the downstream side, which are connected to the control valves 3A and 3B, respectively. The common line is provided with a check valve 13. Furthermore, the tank line 14 includes a pair of branch lines on the upstream side and a common line on the downstream side, which are connected to the control valves 3A and 3B, respectively.

[0025] Each of the supply and discharge lines 51 and 52 is connected to a tank by a relief line 53. Each of the relief lines 53 is provided with a relief valve 54. Each of the supply and discharge lines 51 and 52 is also connected to a tank by a makeup line 55. Each makeup line 55 is provided with a check valve 56 that allows flow toward the supply and discharge line 51 or 52 but prohibits flow in the opposite direction.

[0026] One control valve, 3A, can be switched between a neutral position 3b, which is the center position in Fig. 1, a supply position 3c, which is the right-hand position in Fig. 1, and a discharge position 3a, which is the left-hand position in Fig. 1. In the neutral position 3b, the control valve 3A blocks the branch path of the pump line 12, the branch path of the tank line 14, and the supply / discharge line 51. In the supply position 3c, the control valve 3A blocks the branch path of the tank line 14 while communicating the supply / discharge line 51 with the branch path of the pump line 12. In the discharge position 3a, the control valve 3A blocks the branch path of the pump line 12 while communicating the supply / discharge line 51 with the branch path of the tank line 14.

[0027] The other control valve 3B can be switched between a neutral position 3e, which is the center position in Fig. 1, a supply position 3d, which is the left side position in Fig. 1, and a discharge position 3f, which is the right side position in Fig. 1. In the neutral position 3e, the control valve 3B blocks the branch path of the pump line 12, the branch path of the tank line 14, and the supply / discharge line 52. In the supply position 3d, the control valve 3B blocks the branch path of the tank line 14 while communicating the supply / discharge line 52 with the branch path of the pump line 12. In the discharge position 3f, the control valve 3B blocks the branch path of the pump line 12 while communicating the supply / discharge line 52 with the branch path of the tank line 14.

[0028] The control valves 3A, 3B are driven by electric signals. Specifically, each of the control valves 3A, 3B includes a spool and a drive unit that receives a command current to drive the spool. The command current is supplied to the drive unit from the processing circuit 7. For example, the drive unit may include a pair of electromagnetic proportional valves that output secondary pressures that act on the spool in opposite directions, or may be a linear motion mechanism that is connected to the spool and includes an electric motor, a ball screw, or the like.

[0029] In control valve 3A or 3B, as the command current supplied to the drive unit increases, the spool stroke increases, and the meter-in opening area, which is the opening area of ​​the meter-in passage at supply position 3c or 3d, or the meter-out opening area, which is the opening area of ​​the meter-out passage at discharge position 3a or 3f, increases. Note that in this disclosure, the "neutral position" of a control valve includes not only a case where the spool stroke is zero, but also a case where the opening areas of the meter-in passage and the meter-out passage are maintained at zero regardless of the spool stroke.

[0030] The swing operation device 6 outputs swing operation signals corresponding to the swing operation amount, which is the tilt angle of the operation lever, and the tilt direction, i.e., left swing operation signal and right swing operation signal. In this embodiment, the swing operation device 6 is an electric joystick that outputs an electric signal as the swing operation signal. The swing operation signal output from the swing operation device 6 is input to the processing circuit 7. Note that if the construction machine 9 is an unmanned machine, the swing operation device 6 may be omitted, and the processing circuit 7 may generate the swing operation signal itself based on an image captured by a camera, etc.

[0031] With respect to processing circuitry 7, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, application-specific integrated circuits (ASICs), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor.

[0032] The processing circuit 7 controls the regulator 21 so that the discharge flow rate of the hydraulic pump 2 increases as the amount of swing operation increases, and also controls the unloading valve 16 so that the opening degree of the unloading valve 16 decreases as the amount of swing operation increases.

[0033] Furthermore, when a left-swing operation signal is output from the swing operation device 6, the processing circuit 7 switches the control valve 3A to the supply position 3c and the control valve 3B to the discharge position 3f, and increases the command current supplied to the drive units of the control valves 3A and 3B as the swing operation amount increases. Conversely, when a right-swing operation signal is output from the swing operation device 6, the processing circuit 7 switches the control valve 3B to the supply position 3d and the control valve 3A to the discharge position 3a, and increases the command current supplied to the drive units of the control valves 3A and 3B as the swing operation amount increases.

[0034] The processing circuit 7 is electrically connected to a speed detector 83 that detects the rotation speed ω of the rotating unit 92. The speed detector 83 is, for example, a gyro sensor provided on the rotating unit 92. However, the speed detector 83 may also be, for example, an encoder or resolver attached to the rotation motor 4.

[0035] The processing circuit 7 is also electrically connected to a pair of pressure gauges 81, 82 provided in the supply and discharge lines 51, 52, respectively. One of the pressure gauges 81, 82 detects the inflow pressure Pi of the swing motor 4, and the other of the pressure gauges 81, 82 detects the outflow pressure Po of the swing motor 4.

[0036] When stopping the rotation of the rotating body 92, the processing circuit 7 prohibits the discharge of hydraulic oil from the swing motor 4 to the tank and reduces the swing speed of the swing body 92, and then controls the swing control valve device 3 so as to permit the discharge of hydraulic oil from the swing motor 4 to the tank, while prohibiting the supply of hydraulic oil from the hydraulic pump 2 to the swing motor 4. The processing circuit 7 also determines the meter-out opening area A when permitting the discharge of hydraulic oil from the swing motor 4 to the tank, based on the swing speed ω detected by the speed detector 83 and the inflow pressure Pi and outflow pressure Po detected by the pressure gauges 81, 82.

[0037] Below, as an example, we will explain the case where the rotating body 92 rotates to the left, in other words, the case where the control valve 3A and the supply / discharge line 51 are on the supply side and the control valve 3B and the supply / discharge line 52 are on the discharge side.However, when the rotating body 92 rotates to the right, the control valve 3A and the supply / discharge line 51 and the control valve 3B and the supply / discharge line 52 simply switch places, so we will omit the explanation.

[0038] As shown in Fig. 3A, the processing circuit 7 simultaneously switches the control valve 3A from the supply position 3c to the neutral position 3b and switches the control valve 3B from the discharge position 3f to the neutral position 3e as shown in Fig. 3D. This causes the braking action of the discharge-side relief valve 54 to reduce the swing speed ω of the swing body 92. The processing circuit 7 subsequently maintains the control valve 3A in the neutral position 3b.

[0039] On the other hand, with regard to the control valve 3B, when the swing speed ω detected by the speed detector 83 falls below the first threshold value α as shown in Fig. 3B, the processing circuit 7 switches the control valve 3B from the neutral position 3e to the discharge position 3f as shown in Fig. 3D. This causes the outflow pressure of the swing motor 4 to decrease to zero.

[0040] Thereafter, when the rotation speed ω of the rotating unit 92 detected by the speed detector 83 falls below a second threshold value β that is smaller than the first threshold value α, the processing circuit 7 switches the control valve 3B from the discharge position 3f to the neutral position 3e. This causes the rotating unit 92 to completely stop. In this manner, the control valve 3B is switched from the discharge position 3f to the neutral position 3e, the discharge position 3f, and then back to the neutral position 3e.

[0041] The first threshold value α and the second threshold value β may be predetermined fixed values, or may be calculated each time by multiplying the turning speed ω before the turning stops by a coefficient. For example, if the first threshold value α and the second threshold value β are fixed values, the first threshold value α is 5 to 20% of the maximum speed, and the second threshold value β is 1 to 10% of the maximum speed.

[0042] The processing circuit 7 generates an anti-reverse opening command for the meter-out opening area A when the control valve 3B is switched back to the discharge position 3f, as shown in Figure 3C, that is, when the swing control valve device 3 allows the discharge of hydraulic oil from the swing motor 4 to the tank when the swing of the swing body 92 is stopped.

[0043] First, the processing circuit 7 calculates the moment of inertia I of the swing body 92 based on the inflow pressure Pi and outflow pressure Po detected by the pair of pressure gauges 81, 82, and the swing speed ω detected by the speed detector 83. More specifically, the processing circuit 7 calculates the moment of inertia I using the following equation (1): I=η·qm·ΔP / (2πa) (1) where η: mechanical efficiency of the swing motor 4, qm: volume of the swing motor 4, ΔP: pressure difference between the inflow pressure Pi and the outflow pressure Po, and a: swing acceleration, a=dω / dt

[0044] The processing circuit 7 stores in advance a characteristic map that defines the correspondence between the meter-out opening area A, the moment of inertia I, and the swing acceleration a, as shown in Fig. 4. After calculating the moment of inertia I, the processing circuit 7 determines the meter-out opening area A using the characteristic map, and outputs a command current corresponding to the determined meter-out opening area A to the drive section of the control valve 3B as a reversal prevention opening command. In other words, the processing circuit 7 controls the swing control valve device 3 so that the meter-out opening area A becomes an opening area corresponding to the moment of inertia I. For example, in the characteristic map, the meter-out opening area A may decrease as the moment of inertia I increases.

[0045] As described above, in this embodiment, when stopping the rotation of the rotating body 92, the rotation control valve device 3 prohibits and then permits the discharge of hydraulic oil from the rotation motor 4 to the tank, thereby preventing the rotating body 92 from reversing. Meanwhile, since the rotation control valve device 3 prohibits the supply of hydraulic oil from the hydraulic pump 2 to the rotation motor 4 when stopping the rotation of the rotating body 92, hydraulic oil is supplied to the supply-side supply / discharge line 51 or 52 through the makeup line 55. Therefore, even when a rotation operation is performed simultaneously with another operation, the rotation of the rotating body 92 can be stopped while preventing reversal.

[0046] In addition, in this embodiment, the swing control valve device 3 includes a pair of control valves 3A, 3B that are independent of each other, so that the meter-in opening area and the meter-out opening area can be controlled independently.

[0047] Furthermore, in this embodiment, the swing control valve device 3 is controlled so that the meter-out opening area A when the control valve 3A or 3B is switched back to the discharge position 3a or 3f becomes an opening area corresponding to the moment of inertia I of the swing body 92, thereby achieving good swing stopping performance regardless of the working posture of the construction machine 9 or the inclination of the ground.

[0048] <Second embodiment> Fig. 5 shows a hydraulic system 1B for a construction machine according to a second embodiment. In this embodiment and a third embodiment described later, the same components as those in the first embodiment are given the same reference numerals, and redundant explanations will be omitted.

[0049] In this embodiment, the swing control valve device 3 includes a control valve 3C to which supply and discharge lines 51, 52, a pump line 12, and a tank line 14 are connected. Similar to the control valves 3A and 3B of the first embodiment, the control valve 3C includes a spool and a drive unit that receives a command current to drive the spool. A command current is sent to the drive unit from a processing circuit 7. For example, the drive unit may include a pair of electromagnetic proportional valves that output secondary pressures that act on the spool in opposite directions, or may be a linear motion mechanism that is connected to the spool and includes an electric motor, a ball screw, or the like.

[0050] Although the opening areas of the meter-in and meter-out passages of the control valve 3C increase as the stroke of the spool increases, the meter-out passage is configured to open before the meter-in passage, as shown in Fig. 6A. In Fig. 6A, the meter-out opening area first increases and then decreases as the stroke of the spool increases, and then increases together with the meter-in opening area. However, the meter-out opening area may also increase continuously, as shown in Fig. 6B.

[0051] Specifically, the control valve 3C can be switched between a neutral position 3i, which is the center position in Figure 5, a first discharge permission position 3h, which is the position immediately to the left of the center position in Figure 5, a first drive position 3g, which is the position further to the left in Figure 5, a second discharge permission position 3j, which is the position immediately to the right of the center position in Figure 5, and a second drive position 3k, which is the position further to the right in Figure 5.

[0052] In the neutral position 3i, the control valve 3C blocks the pump line 12, the tank line 14, and the supply / discharge lines 51 and 52. In the first discharge permission position 3h, the control valve 3C connects the supply / discharge line 52 to the tank line 14 while blocking the pump line 12 and the supply / discharge line 51. In the first drive position 3g, the control valve 3C connects the supply / discharge lines 51 and 52 to the pump line 12 and the tank line 14, respectively. In the second discharge permission position 3j, the control valve 3C connects the supply / discharge line 51 to the tank line 14 while blocking the pump line 12 and the supply / discharge line 52. In the second drive position 3k, the control valve 3C connects the supply / discharge lines 52 and 51 to the pump line 12 and the tank line 14, respectively.

[0053] When stopping the rotation of the swing unit 92, the processing circuit 7, as in the first embodiment, prohibits the discharge of hydraulic oil from the swing motor 4 to the tank and reduces the swing speed of the swing unit 92, and then controls the swing control valve device 3 to permit the discharge of hydraulic oil from the swing motor 4 to the tank, while prohibiting the supply of hydraulic oil from the hydraulic pump 2 to the swing motor 4. The processing circuit 7 also determines the meter-out opening area A when permitting the discharge of hydraulic oil from the swing motor 4 to the tank, based on the swing speed ω detected by the speed detector 83 and the inflow pressure Pi and outflow pressure Po detected by the pressure gauges 81, 82. The method of determining the meter-out opening area A is the same as in the first embodiment, and therefore will not be described again.

[0054] In the following, as an example, we will explain the case where the rotating body 92 rotates to the left, but when the rotating body 92 rotates to the right, the supply and discharge lines 51 and 52 are swapped, and the first drive position 3g and the first discharge permitted position 3h are swapped with the second drive position 3k and the second discharge permitted position 3j, so we will not explain this case again.

[0055] At the same time that the left swing operation amount is set to zero as shown in Fig. 3A, the processing circuit 7 switches the control valve 3C from the first drive position 3g to the neutral position 3i via the first discharge permission position 3h as shown in Fig. 3D. As a result, the swing speed ω of the swing body 92 is reduced by the braking action of the discharge-side relief valve 54.

[0056] 3B, when the swing speed ω detected by the speed detector 83 falls below the first threshold value α, the processing circuit 7 switches the control valve 3C from the neutral position 3i to the first discharge permission position 3h, thereby reducing the outflow pressure of the swing motor 4 to zero.

[0057] Thereafter, when the rotation speed ω of the rotating unit 92 detected by the speed detector 83 falls below the second threshold value β, the processing circuit 7 switches the control valve 3C from the first discharge permission position 3h to the neutral position 3i, as shown in Figure 3D. This causes the rotating unit 92 to completely stop. In this way, the control valve 3C is switched from the first drive position 3g to the neutral position 3i, the first discharge permission position 3h, and the neutral position 3e in this order.

[0058] In this embodiment, as in the first embodiment, even when a swing operation is performed simultaneously with another operation, it is possible to stop the swing of the swing body 92 while preventing reversal. Furthermore, in this embodiment, the swing control valve device 3 includes a control valve 3C in which the meter-out passage opens before the meter-in passage, so that the swing control valve device 3 can be configured with a single control valve 3C.

[0059] 7 shows a hydraulic system 1C for a construction machine according to a third embodiment. In this embodiment, the swing control valve device 3 includes a control valve 3D to which supply and discharge lines 51, 52, a pump line 12, and a tank line 14 are connected, and a priority valve 3E that opens and closes the pump line 12. The priority valve 3E is controlled by a processing circuit 7.

[0060] Like the control valves 3A and 3B of the first embodiment, the control valve 3D includes a spool and a drive unit that receives a command current to drive the spool. A command current is supplied to the drive unit from the processing circuit 7. For example, the drive unit may include a pair of electromagnetic proportional valves that output secondary pressures that act on the spool in opposite directions, or may be a linear motion mechanism that is connected to the spool and includes an electric motor, a ball screw, or the like.

[0061] The control valve 3D is switchable among a neutral position 3m, which is the center position in Fig. 7, a first drive position 3l, which is the left position in Fig. 7, and a second drive position 3n, which is the right position in Fig. 7. In the neutral position 3m, the control valve 3D blocks the pump line 12, the tank line 14, and the supply and discharge lines 51 and 52. In the first drive position 3l, the control valve 3D connects the supply and discharge lines 51 and 52 to the pump line 12 and the tank line 14, respectively. In the second drive position 3n, the control valve 3D connects the supply and discharge lines 52 and 51 to the pump line 12 and the tank line 14, respectively.

[0062] When stopping the rotation of the swing unit 92, the processing circuit 7, as in the first embodiment, prohibits the discharge of hydraulic oil from the swing motor 4 to the tank and reduces the swing speed of the swing unit 92, and then controls the swing control valve device 3 to permit the discharge of hydraulic oil from the swing motor 4 to the tank, while prohibiting the supply of hydraulic oil from the hydraulic pump 2 to the swing motor 4. The processing circuit 7 also determines the meter-out opening area A when permitting the discharge of hydraulic oil from the swing motor 4 to the tank, based on the swing speed ω detected by the speed detector 83 and the inflow pressure Pi and outflow pressure Po detected by the pressure gauges 81, 82. The method of determining the meter-out opening area A is the same as in the first embodiment, and therefore will not be described again.

[0063] In the following, as an example, we will explain the case where the rotating body 92 rotates to the left, but when the rotating body 92 rotates to the right, the supply and discharge lines 51 and 52 are simply swapped, and the first drive position 3l and the second drive position 3n are simply swapped, so we will not explain this case again.

[0064] At the same time that the left swing operation amount is set to zero as shown in Fig. 3A, the processing circuit 7 closes the pump line 12 with the priority valve 3E and switches the control valve 3D from the first drive position 3l to the neutral position 3m as shown in Fig. 3D. As a result, the swing speed ω of the swing body 92 is reduced by the braking action of the discharge-side relief valve 54.

[0065] As shown in Fig. 3B, when the swing speed ω detected by the speed detector 83 falls below the first threshold value α, the processing circuit 7 switches the control valve 3D from the neutral position 3m to the first drive position 3l as shown in Fig. 3D. This causes the outflow pressure of the swing motor 4 to decrease to zero.

[0066] Thereafter, when the rotation speed ω of the rotating unit 92 detected by the speed detector 83 falls below the second threshold value β, the processing circuit 7 switches the control valve 3D from the first drive position 3l to the neutral position 3m. This causes the rotating unit 92 to completely stop. In this manner, the control valve 3D is switched from the first drive position 3l to the neutral position 3m, the first drive position 3l, and back to the neutral position 3m in this order.

[0067] In this embodiment, as in the first embodiment, even when a swing operation is performed simultaneously with another operation, it is possible to stop the swing of the swing body 92 while preventing reversal. Furthermore, in this embodiment, since the swing control valve device 3 includes the control valve 3D and the priority valve 3E, a normal control valve in which the meter-out passage opens simultaneously with the meter-in passage can be used as the control valve 3D of the swing control valve device 3.

[0068] Other Embodiments The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present disclosure.

[0069] For example, in the first to third embodiments, the timing at which the swing control valve device 3 again allows the discharge of hydraulic oil from the swing motor 4 to the tank may be when the outflow pressure of the swing motor 4 falls below the threshold value γ instead of when the swing speed ω falls below the first threshold value α.

[0070] Furthermore, in a hydraulic system using three hydraulic pumps, when one hydraulic pump is dedicated to the swing motor 4, the swing control valve device 3 may be a normal control valve in which the meter-out passage opens simultaneously with the meter-in passage. In this case, if the meter-out opening area A when the swing control valve device 3 again permits the discharge of hydraulic oil from the swing motor 4 to the tank is controlled to be an opening area corresponding to the moment of inertia I of the swing body 92, good swing stopping performance can be obtained regardless of the working posture of the construction machine 9 or the inclination of the ground.

[0071] In addition, in the second and third embodiments, the unloading line 15 may be omitted, and instead the supply line 11 may double as a center bypass line that passes through the control valve 3C or 3D for the swing motor 4 and the control valves for other hydraulic actuators.

[0072] <Summary> In a first aspect, the present disclosure provides a hydraulic system for construction machinery, comprising: a swing motor for swinging a swing body; a swing control valve device connected to the swing motor by a pair of supply and discharge lines, the swing control valve device controlling the supply of hydraulic oil from a hydraulic pump to the swing motor and the discharge of hydraulic oil from the swing motor to a tank; a pair of relief lines each provided with a relief valve, connecting the pair of supply and discharge lines to the tank; and a pair of make-up lines each provided with a check valve, connecting the pair of supply and discharge lines to the tank, wherein, when stopping the swing of the swing body, the swing control valve device prohibits the discharge of hydraulic oil from the swing motor to the tank and reduces the swing speed of the swing body, after which it allows the discharge of hydraulic oil from the swing motor to the tank, while prohibiting the supply of hydraulic oil from the hydraulic pump to the swing motor.

[0073] According to the above configuration, when stopping the rotation of the rotating body, the rotation control valve device prohibits and then permits the discharge of hydraulic oil from the rotation motor to the tank, thereby preventing the rotating body from tipping over. Meanwhile, since the rotation control valve device prohibits the supply of hydraulic oil from the hydraulic pump to the rotation motor when stopping the rotation of the rotating body, hydraulic oil is supplied to the supply-side supply / discharge line through the makeup line. Therefore, even when a rotation operation is performed simultaneously with another operation, the rotation of the rotating body can be stopped while preventing tipping over.

[0074] As a second aspect, in the first aspect, the swing control valve device may include a pair of control valves independent of each other and connected to the pair of supply and discharge lines, each control valve being switchable between a neutral position that blocks the supply and discharge lines, a supply position that connects the supply and discharge lines to a pump line, and a discharge position that connects the supply and discharge lines to a tank line, and when the swing of the swing body is stopped, the discharge-side control valve is switched from the discharge position to the neutral position, the discharge position, and again to the neutral position in that order, and the supply-side control valve is switched from the supply position to the neutral position and then maintained in the neutral position. With this configuration, the meter-in opening area and the meter-out opening area can be controlled independently.

[0075] As a third aspect, in the first aspect, the swing control valve device may include a control valve in which a meter-out passage opens earlier than a meter-in passage, and the control valve is switchable between a neutral position in which the pair of supply and discharge lines are blocked, a discharge permitting position in which one of the pair of supply and discharge lines is blocked while the other is connected to a tank line, and a drive position in which the pair of supply and discharge lines are connected to a pump line and a tank line, respectively, and when the swing of the swing body is stopped, the control valve is switched from the drive position to the neutral position, the discharge permitting position, and the neutral position in this order. According to this configuration, the swing control valve device can be configured with a single control valve.

[0076] As a fourth aspect, in the first aspect, the swing control valve device may include a control valve to which the pair of supply and discharge lines, the pump line, and the tank line are connected, and a priority valve for opening and closing the pump line, and the priority valve may close the pump line when the swing of the swing body is stopped. According to this configuration, a normal control valve can be used as the control valve of the swing control valve device.

[0077] As a fifth aspect, in any of the first to fourth aspects, the hydraulic system may further include a speed detector that detects the swing speed of the swing body, a pair of pressure gauges that detect the inflow and outflow pressures of the swing motor, and a processing circuit that calculates the moment of inertia of the swing body based on the inflow and outflow pressures detected by the pair of pressure gauges and the swing speed detected by the speed detector, and controls the swing control valve device so that the meter-out opening area when the swing control valve device allows the discharge of hydraulic oil from the swing motor to the tank when stopping the swing of the swing body is an opening area corresponding to the moment of inertia. With this configuration, good swing stopping performance can be obtained regardless of the working posture of the construction machine or the inclination of the ground.

Claims

1. A hydraulic system for construction machinery comprising: a swing motor for swinging a swing body; a swing control valve device connected to the swing motor by a pair of supply and discharge lines, which controls the supply of hydraulic oil from a hydraulic pump to the swing motor and the discharge of hydraulic oil from the swing motor to a tank; a pair of relief lines each equipped with a relief valve, which connect the pair of supply and discharge lines to the tank; and a pair of make-up lines each equipped with a check valve, which connect the pair of supply and discharge lines to the tank, wherein, when stopping the swing of the swing body, the swing control valve device prohibits the discharge of hydraulic oil from the swing motor to the tank and allows the discharge of hydraulic oil from the swing motor to the tank after reducing the swing speed of the swing body, while prohibiting the supply of hydraulic oil from the hydraulic pump to the swing motor.

2. A hydraulic system for a construction machine as described in claim 1, wherein the swing control valve device includes a pair of mutually independent control valves respectively connected to the pair of supply and discharge lines, and each control valve is switchable between a neutral position that blocks the supply and discharge line, a supply position that connects the supply and discharge line to a pump line, and a discharge position that connects the supply and discharge line to a tank line, and when the swing body stops swinging, the discharge-side control valve is switched from the discharge position to the neutral position, the discharge position, and then the neutral position, and the supply-side control valve is switched from the supply position to the neutral position and then maintained in the neutral position.

3. A hydraulic system for a construction machine as described in claim 1, wherein the swing control valve device includes a control valve in which the meter-out passage opens before the meter-in passage, and the control valve is switched between a neutral position in which the pair of supply and discharge lines are blocked, a discharge permitting position in which one of the pair of supply and discharge lines is blocked while the other is connected to a tank line, and a drive position in which the pair of supply and discharge lines are connected to a pump line and a tank line, respectively, when the swing body stops swinging, the control valve is switched from the drive position to the neutral position, the discharge permitting position and then to the neutral position in that order.

4. A hydraulic system for a construction machine as described in claim 1, wherein the swing control valve device includes a control valve to which the pair of supply and discharge lines, the pump line, and the tank line are connected, and a priority valve that opens and closes the pump line, and when the swing body stops swinging, the priority valve closes the pump line.

5. A hydraulic system for a construction machine as described in any one of claims 1 to 4, further comprising: a speed detector that detects the rotation speed of the rotating body; a pair of pressure gauges that detect the inflow and outflow pressures of the rotation motor; and a processing circuit that calculates the moment of inertia of the rotating body based on the inflow and outflow pressures detected by the pair of pressure gauges and the rotation speed detected by the speed detector, and controls the rotation control valve device so that the meter-out opening area when the rotation control valve device allows the discharge of hydraulic oil from the rotation motor to the tank when stopping the rotation of the rotating body becomes an opening area corresponding to the moment of inertia.

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