Hydraulic system for construction machine

Abstract

One aspect of the present disclosure provides a hydraulic system for a construction machine, the system comprising: first and second hydraulic pumps; first and second traveling motors; first and second traveling spools; a front working device; a straight traveling spool including a first section in which a working fluid discharged from the first hydraulic pump is supplied to the first traveling motor and a working fluid discharged from the second hydraulic pump is supplied to the second traveling motor, and a second section in which the working fluid discharged from the first hydraulic pump is supplied to the first and second traveling motors and the working fluid discharged from the second hydraulic pump is supplied to the front working device; a working device spool controlling the flow rate of the working fluid supplied to the front working device and including a first working device spool group connected to the straight traveling spool and a second working device spool group connected to the second hydraulic pump; a blocking valve disposed on a hydraulic supplement line between the second working device spool group and the second traveling spool to open and close the hydraulic supplement line; and a control device which switches the straight traveling spool to the second section when a predetermined mode is set and controls the blocking valve to be closed to limit the supply of a working fluid through the hydraulic supplement line.

Description

Hydraulic systems for construction machinery

[0001] The present disclosure relates generally to construction machinery. In certain aspects, the present disclosure relates to a hydraulic system for construction machinery. The present disclosure may be applied to large vehicles, such as trucks, buses, and construction equipment. While the present disclosure may be described with respect to specific vehicles, the present disclosure is not limited to any particular vehicle.

[0002] In general, an excavator is a type of construction machine that performs various tasks such as digging the ground at construction sites, loading work to transport soil, excavation work to create foundations, demolition work to dismantle buildings, grading work to prepare the ground, and leveling work to level the ground.

[0003] These construction machines can have the driving device operate independently (driving-only operation) or the driving device and front working device can operate in combination (driving-combined operation) by the hydraulic system.

[0004] Typically, in construction machinery such as excavators, the term 'front working device' refers to devices such as a boom, arm, bucket, slewing device, and optional devices, 'driving-only operation' refers to driving by the driving device, and 'driving combined operation' refers to an operation in which the front working device is operated while driving, thereby simultaneously performing driving by the driving device and front work by the front working device.

[0005] Figure 1 is a hydraulic circuit diagram showing a hydraulic system of a conventional construction machine.

[0006] As shown in Fig. 1, during the driving-only operation, the operating fluid of the first hydraulic pump (P1) is supplied to the first driving motor (TL), and the operating fluid of the second hydraulic pump (P2) is supplied to the second driving motor (TR). Then, when the driving combined operation is performed, since the driving straight spool (TR-ST) is switched, only the operating fluid of the first hydraulic pump (P1) is supplied to the driving motors (TL, TR), so the supply of operating fluid is reduced by approximately half, causing an impact due to the reduction in speed.

[0007] Accordingly, a check valve (C) and an orifice (O) were conventionally installed on the hydraulic line of the second hydraulic pump (P2) to bypass the operating oil supplied to the front working device or to supplement the insufficient flow rate when the second driving motor (TR) is operated, thereby alleviating some of the shock. However, there is a limitation that when the load of the front working device is large, the amount of flow supplemented to the second driving motor (TR) decreases, so shock still occurs, and in addition, the operating oil supplied to the front working device also decreases, so the speed of the front working device also slows down.

[0008] According to a first aspect of the present disclosure, there is provided a driving straight spool comprising first and second hydraulic pumps, first and second travel motors operable by operating fluids discharged from the first and second hydraulic pumps, first and second travel spools for controlling the flow rates of operating fluids supplied to the first and second travel motors, respectively, a front working device operable by operating fluids discharged from the first and second hydraulic pumps, a first section in which operating fluid discharged from the first hydraulic pump is supplied to the first travel motor and operating fluid discharged from the second hydraulic pump is supplied to the second travel motor, and a second section in which operating fluid discharged from the first hydraulic pump is supplied to the first and second travel motors and operating fluid discharged from the second hydraulic pump is supplied to the front working device, a first working device spool group connected to the travel straight spool and connected to the second hydraulic pump. A hydraulic system for a construction machine is provided, comprising: a work device spool including a second work device spool group; a shut-off valve arranged on a hydraulic replenishment line to open and close the hydraulic replenishment line; and a control device that controls, when a predetermined mode is set, to switch the driving straight spool to the second section and close the shut-off valve to limit the supply of operating fluid through the hydraulic replenishment line. The technical advantage is that in creep mode, the first hydraulic pump (101) and the second hydraulic pump (102) operate independently, so that no shock occurs even when switching from a driving-only operation to a driving-combined operation, and further, since the hydraulic replenishment line (70) is closed by the shut-off valve (80), the working performance of the front work device (400) does not deteriorate.

[0009] Optionally, in some examples, the first driving spool and the first work device spool group may be connected by a first bypass line, and a first bypass cut valve may be arranged on the first bypass line downstream of the first work device spool group to open and close the first bypass line, and the second driving spool and the second work device spool group may be connected by a second bypass line, and a second bypass cut valve may be arranged on the second bypass line downstream of the second work device spool group to open and close the second bypass line.

[0010] Optionally, in some examples, the control device may control the first and second bypass cut valves to close the first and second bypass lines when, in the predetermined mode, the first and second driving motors are operating and the front working device is not operating.

[0011] Optionally, in some examples, the predetermined mode may be comprised of multiple stages, and the control device may limit the maximum flow rate of the first hydraulic pump differently for each stage.

[0012] Optionally, in some examples, the maximum flow rate of the first hydraulic pump may increase as the mode step increases.

[0013] Optionally, in some examples, the maximum flow rate of the first hydraulic pump in the highest stage mode may be set to the maximum value that can be supplied by the first hydraulic pump.

[0014] Optionally, in some examples, a check valve may further be disposed on the hydraulic replenishment line.

[0015] Optionally, in some examples, an orifice may be located downstream of the check valve in the hydraulic replenishment line.

[0016] The above-described aspects, appended claims, and / or examples disclosed herein above and hereinafter may be suitably combined with one another as will be apparent to one of ordinary skill in the art.

[0017] Additional features and advantages are set forth in the following description, claims, and drawings, and in part will be readily apparent to those skilled in the art from the foregoing or may be recognized by practicing the teachings herein.

[0018] With reference to the accompanying drawings, a more detailed description of embodiments of the present disclosure, cited as examples, follows below.

[0019] Figure 1 is a hydraulic circuit diagram showing a hydraulic system of a conventional construction machine.

[0020] Figures 2 and 3 are hydraulic circuit diagrams showing a hydraulic system of a construction machine according to one embodiment.

[0021] Figure 4 is a block diagram of a control device according to one embodiment.

[0022] Figure 5 is a drawing showing the maximum flow rate of the first hydraulic pump at each stage of creep mode.

[0023] The aspects described below represent information necessary to enable a person skilled in the art to practice the present disclosure.

[0024] Figures 2 and 3 are hydraulic circuit diagrams showing a hydraulic system of a construction machine according to one embodiment.

[0025] Referring to FIGS. 2 and 3, a hydraulic system (1) of a construction machine according to one embodiment of the present invention is a system that controls hydraulic pressure so that the driving device of the construction machine can operate independently to drive, or the driving device and the front work device can operate in combination to perform driving and front work simultaneously, and comprises a first hydraulic pump (101), a second hydraulic pump (102), a first driving motor (201) operable by operating fluid discharged from the first hydraulic pump (101), a second driving motor (202) operable by operating fluid discharged from the first hydraulic pump (101) or the second hydraulic pump (102), first and second driving spools (301, 302) for controlling the flow rate of operating fluid supplied to the first and second driving motors (201, 202) according to the displacement amount of a spool provided therein, and operating fluid discharged from the first hydraulic pump (101) or the second hydraulic pump (102). It may include a possible front working device (400), a working device spool (500) for controlling the flow of working fluid supplied to the front working device (400), a driving straight spool (600) and a control device (700) arranged between the first and second hydraulic pumps (101, 102) and the first and second driving motors (201, 202) and the front working device (400) to control the flow direction of working fluid supplied from the first and second hydraulic pumps (101, 102) to the first and second driving motors (201, 202) and the front working device (400).

[0026] Construction machinery may include excavators, wheel loaders, forklifts, and the like. The following description will focus on the case where the construction machinery is an excavator. However, it should be understood that the driving control system according to the exemplary embodiments is not limited to controlling excavators.

[0027] A construction machine may include a lower drive body, an upper drive body that is swivelably mounted on the lower drive body, and a driver's cab and a front working device (400) installed on the upper drive body. For example, the excavator may be a crawler type excavator. The lower drive body may include a right track and a left track. The first and second drive motors (201, 202) may rotate the right track and the left track, respectively.

[0028] The first and second hydraulic pumps (101, 102) can be connected to an engine (not shown) via a power transmission device. Power from the engine can be transmitted to the first and second hydraulic pumps (101, 102).

[0029] The operating fluid discharged from the first and second hydraulic pumps (101, 102) is supplied to the first and second driving motors (201, 202) through the first and second driving spools (301, 302), respectively.

[0030] In detail, the first hydraulic pump (101) and the first driving spool (301) are connected through the first hydraulic line (10), and the first driving motor (201) is operable by the operating fluid discharged from the first hydraulic pump (101). The second hydraulic line (20) branching from the first hydraulic line (10) is connected to the driving straight spool (600).

[0031] In addition, the second hydraulic pump (102) is connected to the driving straight spool (600) through the third hydraulic line (30), and the driving straight spool (600) and the second driving spool (302) are connected through the fourth hydraulic line (40). The second driving motor (202) is operable by operating fluid discharged from at least one of the first hydraulic pump (101) and the second hydraulic pump (102) according to the switching of the driving straight spool (600).

[0032] Meanwhile, the first driving spool (301) and the second driving spool (302) can be switched to various states depending on the input pilot signal pressure.

[0033] In addition, the operating fluid discharged from the first and second hydraulic pumps (101, 102) can be supplied to the front working device (400) through the working device spool (500).

[0034] The front working device (400) may include a boom, an arm, and a bucket. A boom cylinder may be installed between the boom and the upper swivel body to control the movement of the boom. An arm cylinder may be installed between the boom and the arm to control the movement of the arm. In addition, a bucket cylinder may be installed between the arm and the bucket to control the movement of the bucket. As the boom cylinder, the arm cylinder, and the bucket cylinder extend or contract, the boom, the arm, and the bucket can implement various movements, and the front working device (400) can perform various tasks.

[0035] The front working device (400) may include a first working device group (410) and a second working device group (420).

[0036] The first working device group (410) may include a rock cylinder (411) and a swing motor (412). The second working device group (420) may include a boom cylinder (421a, 421b) and a bucket cylinder (422).

[0037] The work device spool (500) can control the flow of operating oil supplied to the front work device (400). The work device spool (500) maintains the flow of operating oil blocked during the driving-only operation, and switches to allow the operating oil to flow when the driving-only operation is changed to the driving-combined operation.

[0038] For example, the work device spool (500) may include a first work device spool group (510) connected to the sixth hydraulic line (60) and a second work device spool group (520) connected to the fifth hydraulic line (50).

[0039] For example, the work device spool (500) may include a first female control valve (511) and a second female control valve (521) for controlling the female cylinder (411).

[0040] For example, the work device spool (500) may include a swing motor control valve (513) for controlling the swing motor (412).

[0041] For example, the work device spool (500) may include a first boom control valve (512) and a second boom control valve (522) for controlling the boom cylinders (421a, 421b).

[0042] For example, the work device spool (500) may include a bucket control valve (523) for controlling the bucket cylinder (422).

[0043] In detail, the first working device spool group (510) can be connected to the driving straight spool (600) via the sixth hydraulic line (60), and the second working device spool group (520) can be connected to the second hydraulic pump (102) via the fifth hydraulic line (50) branched from the third hydraulic line (30).

[0044] Meanwhile, the respective control valves of the first driving spool (301) and the first working device spool group (510) are connected by the first bypass hydraulic line (91). The respective control valves of the second driving spool (302) and the second working device spool group (512) are connected by the second bypass hydraulic line (92).

[0045] A first bypass cut valve (91a) for opening and closing the first bypass line (91) may be arranged on the first bypass line (91), and a second bypass cut valve (92a) for opening and closing the second bypass line (92) may be arranged on the second bypass line (92).

[0046] In detail, the first bypass cut valve (91a) is disposed on the first bypass line (91) downstream from the first work device spool group (510), and the second bypass cut valve (92a) is disposed on the second bypass line (92) downstream from the second work device spool group (520).

[0047] The spools of the first and second bypass cut valves (91a, 92a) can be switched by an electronic proportional pressure reducing valve (not shown) controlled by a control device (700).

[0048] The oil tank (93) recovers the operating oil discharged from the hydraulic pump (101, 102) and moved along the first and second bypass lines (91, 92).

[0049] When the bypass cut valve (91a, 92a) is switched to the closed state, the operating fluid discharged from the hydraulic pump (101, 102) is prevented from moving along the bypass line (91, 92) and returning to the oil tank (93). When the bypass cut valve (91a, 92a) is switched to the open state, the operating fluid discharged from the hydraulic pump (101, 102) can return to the oil tank (93).

[0050] The driving straight spool (600) may be a two-stage control spool consisting of a first section (610) and a second section (620). The driving straight spool (600) may be switched by an electronic proportional pressure reducing valve (not shown) controlled by a control device (700).

[0051] The first section (610) is generally a section that controls the flow of operating fluid during driving-only operation, and may be composed of a first port (611) and a second port (612).

[0052] Referring to FIG. 2, when driving alone, the first port (611) of the first section (610) is connected to the first hydraulic pump (101) on one side by the second hydraulic line (20) and to the first work device spool group (510) on the other side by the sixth hydraulic line (60), and the second port (612) of the first section (610) is connected to the second hydraulic pump (102) on one side by the third hydraulic line (30) and to the second driving spool (302) on the other side by the fourth hydraulic line (40).

[0053] Since the work device spool (500) is maintained in a blocked state during the driving-only operation, the operating fluid of the first hydraulic pump (101) is not supplied to the front work device (400) but is supplied to the first driving motor (201) to drive the first driving motor (201).

[0054] The operating fluid of the second hydraulic pump (102) is supplied to the second driving motor (202) via the second port (612) to drive the second driving motor (202).

[0055] Accordingly, when the construction machine is driven independently, the operating fluid of the first hydraulic pump (101) is supplied to the first driving motor (201), and the operating fluid of the second hydraulic pump (102) is supplied to the second driving motor (202), so that the construction machine can drive forward or backward.

[0056] The second section (620) is a section that generally controls the flow of operating oil during a driving complex operation, and may be composed of a first port (621) and a second port (622).

[0057] The first port (621) may be a port for supplying operating fluid to the second driving motor (202), and allows half of the operating fluid of the first hydraulic pump (101) to flow to the second driving motor (202) during the driving composite operation. At this time, the remaining half of the operating fluid of the first hydraulic pump (101) is supplied to the first driving motor (201).

[0058] The second port (622) may be a port for supplying operating fluid to the front working device (400), and allows all of the operating fluid of the second hydraulic pump (102) to flow to the front working device (400) during the driving composite working operation.

[0059] Referring to FIG. 3, during the driving composite operation, the first port (621) of the second section (620) is connected to the first hydraulic pump (101) on one side by the second hydraulic line (20) and to the second driving spool (302) on the other side by the fourth hydraulic line (40), and the second port (622) of the second section (620) is connected to the second hydraulic pump (102) on one side by the third hydraulic line (30) and to the first working device spool group (510) on the other side by the sixth hydraulic line (60).

[0060] During the driving combined operation, the operating fluid of the first hydraulic pump (101) not only drives the first driving motor (201) via the first driving spool (301), but also drives the second driving motor (202) via the first port (621) and the second driving spool (302). That is, the operating fluid of the first hydraulic pump (101) is distributed and supplied to the first and second driving motors (201, 202) during the driving combined operation.

[0061] During the driving composite operation, the operating fluid of the second hydraulic pump (102) passes through the second port (622) and the first work device spool group (510) or passes through the fifth hydraulic line (50) and the second work device spool (520) to drive the first work device group (410) and the second work device group (420).

[0062] Meanwhile, as the section of the driving straight valve (600) is switched from the first section (610) to the second section (620) during the driving composite operation, the operating fluid of the first hydraulic pump (101) flows to the driving motor (201, 202), and the operating fluid of the second hydraulic pump (102) suddenly flows toward the front working device (400) or the working device spool (500), which may cause a driving shock.

[0063] Accordingly, a hydraulic supplement line (70) may be connected between the fourth hydraulic line (40) and the fifth hydraulic line (50), and a check valve (71) and an orifice (72) may be provided on the hydraulic supplement line (70).

[0064] The check valve (71) and orifice (72) allow a portion of the operating fluid discharged from the second hydraulic pump (102) to flow to the second driving motor (202) through the second port (622) during the driving combined operation, and prevent the operating fluid discharged from the first hydraulic pump (101) and flowing into the first port (621) from flowing to the fifth hydraulic line (50).

[0065] That is, a check valve (71) and an orifice (72) are installed on the hydraulic replenishment line (70) to bypass the operating oil that is rapidly supplied to the front working device (400) or the working device spool (500) during the driving combined operation, or to supplement the insufficient flow rate when the second driving motor (202) is operated.

[0066] A shut-off valve (80) may be provided upstream of a check valve (71) on a hydraulic replenishment line (70). The spool of the shut-off valve (80) may be switched by an electronic proportional pressure reducing valve (not shown) controlled by a control device (700). When the shut-off valve (80) is closed, the hydraulic replenishment line (70) is closed, thereby stopping the supply of operating fluid through the hydraulic replenishment line (70).

[0067] Figure 4 is a block diagram of a control device according to one embodiment.

[0068] Referring to FIG. 4, a control device (700) according to one embodiment of the present invention may include a data receiving unit (710), a mode setting unit (720), a maximum flow limiting unit (730), a storage unit (740), and an output unit (750).

[0069] The data receiving unit (710) can receive an operator's operation signal from the operating unit. The data receiving unit (710) can receive the amount of driving pedal operation as the operator's driving operation signal from the driving pedal (not shown).

[0070] Here, the operating unit may include a driving pedal or driving lever for operating the first and second driving motors and a joystick for operating the working device.

[0071] When an operator operates the driving pedal and joystick, an operation signal corresponding to the operation (i.e., a driving motor operation signal and a work device operation signal) may be generated. The driving pedal and joystick may include a sensor that measures the driving pedal operation amount and the work device operation amount (or angle). The driving pedal and joystick may output a signal, such as a voltage signal or a current signal, corresponding to the measured operation amount.

[0072] The data receiving unit (710) can receive the joystick operation amount as a front working device operation signal for the boom, arm, bucket, and swing from the joystick. For example, the data receiving unit (710) can receive the boom joystick operation amount as an operation signal for the boom cylinder.

[0073] The creep mode of the construction machine can be set through the mode setting unit (720). The operator can turn the creep mode on and off through the mode switch or display provided in the driver's cabin.

[0074] Below, the creep mode is described in detail with reference to FIGS. 2 to 4.

[0075] As described above, when switching from a driving-only operation to a driving-combined operation, the driving straight spool (600) switches from the first section (610) to the second section (620), and as the first hydraulic pump (101) supplies operating oil to the two driving motors (201, 202), a driving shock occurs.

[0076] Specifically, assuming that the maximum flow rate that can be supplied by each of the first hydraulic pump (101) and the second hydraulic pump (102) is P, for example, a total flow rate of up to 2P can be supplied to the first driving motor (201) and the second driving motor (202) during driving-only operation.

[0077] However, during the driving combined operation, the operating fluid of the first hydraulic pump (101) is distributed and supplied to the first and second driving motors (201, 202). When the maximum flow rate that can be supplied from the first hydraulic pump (101) is P, half (P / 2) of the operating fluid of the first hydraulic pump (101) flows to the second driving motor (202), and the remaining half (P / 2) of the operating fluid of the first hydraulic pump (101) is supplied to the first driving motor (201). That is, when the driving straight spool (600) is located in the second section (620), the first driving motor (201) and the second driving motor (202) can be supplied with a total maximum flow rate of P.

[0078] Accordingly, when the front working device (400) is operated during the driving-only operation and the driving straight spool (600) is switched to the second section (620), the flow rate of the operating oil supplied to the first driving motor (201) and the second driving motor (202) is rapidly reduced from the maximum 2P to P, so that a driving shock occurs.

[0079] In general, a check valve (71) and an orifice (72) are installed on the hydraulic replenishment line (70) to bypass the working fluid supplied to the front working device (400) or to supplement the insufficient flow rate during operation of the second driving motor (202) to alleviate some of the shock. However, if the load of the front working device (400) is large, the amount of fluid supplemented to the second driving motor (202) decreases, so that the shock still occurs, and in addition, as the working fluid is supplemented to the second driving motor (202), the working fluid supplied to the front working device (400) decreases, so that the speed of the front working device (400) slows down, which is a limitation.

[0080] Accordingly, in the present invention, when operating in creep mode, the blocking valve (80) is closed while the driving straight spool (600) is switched to the second section (620).

[0081] In detail, when the creep mode is set, the driving straight spool (600) is fixed to the second section (620) as shown in FIG. 3. That is, when the creep mode is set, the driving straight spool (600) is positioned in the second section (620) regardless of the driving-only operation or the driving-combined operation. In addition, since the shut-off valve (80) is closed and the hydraulic replenishment line (70) is closed, the supply of operating oil through the hydraulic replenishment line (70) is stopped.

[0082] In this case, the operating fluid of the first hydraulic pump (101) is supplied to the driving motors (201, 202). In addition, the operating fluid of the second hydraulic pump (102) is not supplied to the second driving motor (202), but is supplied only to the front working device (400) or the working device spool (500).

[0083] That is, in creep mode, the first hydraulic pump (101) and the second hydraulic pump (102) operate independently, so that no shock occurs even when switching from a driving-only operation to a driving-combined operation, and furthermore, since the hydraulic replenishment line (70) is closed by the blocking valve (80), the working performance of the front working device (400) does not deteriorate.

[0084] Meanwhile, the respective control valves of the first driving spool (301) and the first working device spool group (510) are connected by the first bypass hydraulic line (91), and the respective control valves of the second driving spool (302) and the second working device spool group (512) are connected by the second bypass hydraulic line (92).

[0085] Therefore, in the creep mode, the first and second driving motors (201, 202) operate and in the driving-only operation in which the front working device (400) does not operate, if the bypass cut valve (91a, 92a) is positioned in the open state, the operating oil discharged from the hydraulic pump (101, 102) returns to the oil tank (93), so the driving performance may be reduced.

[0086] Accordingly, when driving alone in creep mode, the control device (700) switches the bypass cut valve (91a, 92a) to a closed state to block the operating oil discharged from the hydraulic pump (101, 102) from moving along the bypass line (91, 92) and returning to the oil tank (93).

[0087] Preferably, the creep mode can consist of multiple stages. For example, the creep mode can consist of stages 1 through 5. The operator can set the stages of the creep mode through a mode switch or display provided in the operator's cab.

[0088] Figure 5 is a drawing showing the maximum flow rate of the first hydraulic pump at each stage of creep mode.

[0089] The maximum flow limiting unit (730) can limit the maximum flow rate supplied from the first hydraulic pump (101) according to the stage of the creep mode set in the mode setting unit (720). The maximum flow limiting unit (730) can limit the maximum flow rate of the first hydraulic pump (101) differently according to the stage of the set creep mode.

[0090] For example, referring to FIG. 5, the maximum flow rate of the first hydraulic pump (101) may be set to increase from the first stage (L1) to the fifth stage (L5). Preferably, the maximum flow rate of the first hydraulic pump (101) in the fifth stage (L5) may be set to the maximum value that can be supplied by the first hydraulic pump (101). For example, assuming that the maximum flow rate that can be supplied by the first hydraulic pump (101) is P1, the maximum flow rate of the first hydraulic pump (101) in the fifth stage (L5) may be P1.

[0091] That is, the creep mode can further improve straight-line driving performance as it progresses from stage 1 (L1) to stage 5 (L5).

[0092] In this way, the maximum flow limiting unit (730) of the present invention can provide a difference in driving performance through a relative difference in the maximum flow rate of the first hydraulic pump (101).

[0093] In the storage unit (740), a restriction map including information on the maximum flow rate for each stage of the creep mode of the maximum flow rate restriction unit (730) as shown in FIG. 5 can be stored.

[0094] The output unit (750) can operate the first and second driving motors (201, 202) and the front working unit (400) by controlling the first and second driving spools (301, 302) and the working unit spools (500) in response to the operating signals received from the data receiving unit (710).

[0095] In detail, the output unit (750) can receive an operation signal proportional to the amount of operation of the operator from the operation unit, generate a control signal corresponding to the received amount of operation, for example, a current, and apply the control signal to the electronic proportional pressure reducing valve. The electronic proportional pressure reducing valves can move the spools of the first and second driving spools (301, 302) and the working device spool (500) according to the amount of the applied pilot signal pressure by supplying a pilot signal pressure proportional to the amount of the applied current to the spools of the first and second driving spools (301, 302) and the working device spool (500), respectively.

[0096] The output unit (750) can output a control signal to the driving straight spool (600) to switch the section of the driving straight spool (600) to the first section (610) or the second section (620) in response to the operation signal received from the data receiving unit (710).

[0097] The output section (750) receives whether the creep mode is operating from the mode setting section (720), and when an operating signal for the creep mode is input, a control signal can be output to the driving straight spool (600) to switch the section of the driving straight spool (600) to the second section (620).

[0098] When an operating signal of creep mode is input, the output unit (750) can output a control signal to the blocking valve (80) so that the hydraulic replenishment line (70) is blocked.

[0099] The output unit (750) can output a control signal to the bypass cut valve (91a, 92a) to block the operating fluid discharged from the hydraulic pump (101, 102) during the driving-only operation in creep mode from moving along the bypass line (91, 92) and returning to the oil tank (93).

[0100] When an operating signal of the creep mode is input, the output unit (750) receives the maximum flow rate value calculated from the maximum flow rate limit unit (730) and can adjust the flow rate of the first hydraulic pump (101) so that the flow rates of the first hydraulic pump (101) and the second hydraulic pump (102) are lower than or equal to the calculated maximum flow rate value.

[0101] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly dictates otherwise. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. It will also be understood that the terms “comprises,” “comprising,” “includes,” and / or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0102] While terms such as "first" and "second" may be used herein to describe various components, it is to be understood that these components are not limited by these terms. These terms are used solely to distinguish one component from another. For example, a first component could be referred to as a "second component," and similarly, a second component could be referred to as a "first component," without departing from the scope of the present disclosure.

[0103] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe one element's relationship to another, as illustrated in the drawings. It will be understood that these terms, and those discussed above, are intended to encompass different orientations of the device in addition to the orientations depicted in the drawings. When an element is referred to as being "connected" or "coupled" to another element, it will be understood that it may be directly connected or coupled to the other element, or that intervening elements may be present. Conversely, when an element is referred to as being "directly connected" or "directly coupled" to another element, no intervening elements are present.

[0104] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Furthermore, it is to be understood that terms used herein should be interpreted to have a meaning consistent with their meaning within the context of this specification and related technologies, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

Claims

1. 1st and 2nd hydraulic pumps; First and second driving motors operable by operating fluid discharged from the first and second hydraulic pumps; First and second driving spools for controlling the flow rate of operating oil supplied to the first and second driving motors, respectively; A front working device operable by operating fluid discharged from the first and second hydraulic pumps; A travel straight spool including a first section in which the operating fluid discharged from the first hydraulic pump is supplied to the first travel motor and the operating fluid discharged from the second hydraulic pump is supplied to the second travel motor, and a second section in which the operating fluid discharged from the first hydraulic pump is supplied to the first and second travel motors and the operating fluid discharged from the second hydraulic pump is supplied to the front working device; A work device spool that controls the flow rate of operating oil supplied to the front work device and includes a first work device spool group connected to the driving straight spool and a second work device spool group connected to the second hydraulic pump; A shut-off valve disposed on the hydraulic replenishment line between the second work device spool group and the second driving spool to open and close the hydraulic replenishment line; and A hydraulic system for a construction machine, comprising: a control device that controls the driving straight spool to be switched to the second section when a predetermined mode is set and the shut-off valve to be closed to limit the supply of operating oil through the hydraulic replenishment line; 2. In paragraph 1, The first driving spool and the first working device spool group are connected to a first bypass line, and a first bypass cut valve for opening and closing the first bypass line is arranged on the first bypass line downstream of the first working device spool group. A hydraulic system for a construction machine, wherein the second driving spool and the second working device spool group are connected to a second bypass line, and a second bypass cut valve for opening and closing the second bypass line is arranged on the second bypass line downstream of the second working device spool group.

3. In paragraph 2, The above control device, A hydraulic system of a construction machine, wherein, in the above-described mode, the first and second driving motors operate and, when the front working device does not operate, the first and second bypass cut valves are controlled to close the first and second bypass lines.

4. In paragraph 1, The above-mentioned predetermined mode consists of multiple stages, The above control device, A hydraulic system for construction machinery, wherein the maximum flow rate of the first hydraulic pump is differently limited for each stage.

5. In paragraph 4, A hydraulic system for construction machinery, wherein the maximum flow rate of the first hydraulic pump increases as the mode stage increases.

6. In paragraph 5, A hydraulic system of a construction machine, wherein the maximum flow rate of the first hydraulic pump in the highest stage mode is set to the maximum value that can be supplied by the first hydraulic pump.

7. In paragraph 1, A hydraulic system for a construction machine, further comprising a check valve disposed on the hydraulic replenishment line.

8. In paragraph 7, A hydraulic system for construction machinery, wherein an orifice is arranged downstream of the check valve of the hydraulic replenishment line.

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