Hydraulic system for construction machine

Abstract

One aspect of the present disclosure provides a hydraulic system for a construction machine, comprising: a traveling straight spool, comprising: first and second hydraulic pumps; first and second traveling motors operable by hydraulic fluid discharged from the first and second hydraulic pumps; a front work device operable by hydraulic fluid discharged from the first and second hydraulic pumps; a first section wherein, during traveling single operation, hydraulic fluid discharged from the first hydraulic pump is supplied to the first traveling motor, and hydraulic fluid discharged from the second hydraulic pump is supplied to the second traveling motor; and a second section wherein, during traveling combined operation, hydraulic fluid discharged from the first hydraulic pump is supplied to the first and second traveling motors, and hydraulic fluid discharged from the second hydraulic pump is supplied to the front work device; and a control unit which controls the supply flow rate of the first and second hydraulic pumps to change gradually in accordance with a section change rate during section change of the traveling straight spool.

Description

TECHNICAL FIELD

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

[0002] In general, an excavator is a type of construction machinery capable of performing various operations at construction sites and the like, including excavation work for digging earth, loading work for transporting soil, trenching work for foundation construction, crushing work for building demolition, leveling work for site preparation, and grading work for surface smoothing.

[0003] Such construction machinery may be capable of operating a traveling device independently by means of a hydraulic system (travel-only operation), or of operating the traveling device and a front working implement in combination (combined travel-work operation).

[0004] Conventionally, in construction machinery such as excavators, the term "front working implement" typically refers to components such as the boom, arm, bucket, swing device, and optional attachments, "travel-only operation" means traveling using the travel device alone, and "combined travel-work operation" refers to performing travel by the travel device while simultaneously operating the front working implement, thereby executing travel and front working implement operations concurrently.

[0005] Such an excavator is equipped with at least two hydraulic pumps, wherein during combined travel-work operation, the first pump supplies working fluid to two traveling motors, and the second pump supplies working fluid to the front working implement, and a travel shock may occur due to a change in the initial travel system transitioning from a traveling-only operation to the combined travel-work operation.SUMMARY

[0006] According to a first aspect of the present disclosure, a hydraulic system for construction machinery is provided, comprising: a first and second hydraulic pump; first and second traveling motors operable by working fluid discharged from the first and second hydraulic pumps; a front working implement operable by working fluid discharged from the first and second hydraulic pumps; a travel straight spool valve including a first section, in which during travel-only operation, working fluid discharged from the first hydraulic pump is supplied to the first traveling motor and working fluid discharged from the second hydraulic pump is supplied to the second traveling motor, and a second section, in which during combined travel-work operation, working fluid discharged from the first hydraulic pump is supplied to the first and second traveling motors, and working fluid discharged from the second hydraulic pump is supplied to the front working implement; and a control unit configured to control the supply flow rates of the first and second hydraulic pumps to be gradually changed according to a section switching rate when switching between the sections of the travel straight spool valve. A first aspect of the present disclosure may provide construction machinery capable of reducing travel shock when switching from travel-only operation to combined travel-work operation. A technical advantage is that, because the flow rates of the first hydraulic pump and the second hydraulic pump are gradually changed according to the section switching rate, travel shock can be reduced during the section switching process of the travel straight spool valve.

[0007] In some examples, the construction machine may further include a first traveling spool and a second traveling spool configured to respectively control the flow rates of working fluid supplied to the first and second traveling motors, and a working implement spool comprising a first working implement spool group and a second working implement spool group configured to control the flow rate of working fluid supplied to the front working implement.

[0008] In some examples, the second section may include a first port having one side connected to the first hydraulic pump and the other side connected to the second traveling spool, and a second port having one side connected to the second hydraulic pump and the other side connected to the first working implement spool group.

[0009] In some examples, a check valve and an orifice may be disposed between the second working implement spool group connected to the second hydraulic pump and the second traveling spool.

[0010] In some examples, the control unit may include a switching flow rate calculation unit configured to calculate the flow rates of working fluid supplied from the first hydraulic pump and the second hydraulic pump according to the section switching rate of the travel straight spool valve.

[0011] In some examples, when the section switching rate of the travel straight spool valve is referred to as ratio, the switching flow rate calculation unit may calculate the flow rate Q P1 of the first hydraulic pump as Q P1 = Q TL + GainA × Q TR × ratio + Q P1Att × (1 - ratio) and may calculate the flow rate Q P2 of the second hydraulic pump as Q P2 = Q P1Att × (ratio) + Q TR × (1 - ratio) + Q P2 Att . Here, Q TL may be the flow rate of the first traveling motor; Gain A may be a correction value for compensating the flow of working fluid passing through the orifice, Q TR may be the flow rate of the second traveling motor; Q P1Att may be the flow rate of the first working implement spool group, and Q P2Att may be the flow rate of the second working implement spool group.

[0012] According to a second aspect of the present disclosure, there is provided a hydraulic system for construction machinery, the system comprising: a first hydraulic pump and a second hydraulic pump; a first traveling motor and a second traveling motor, each operable by working fluid discharged from the first and second hydraulic pumps, respectively; a front working implement operable by working fluid discharged from the first and second hydraulic pumps; a travel straight spool valve including a first section configured such that, during travel-only operation, working fluid discharged from the first hydraulic pump is supplied to the first traveling motor and working fluid discharged from the second hydraulic pump is supplied to the second traveling motor, and a second section configured such that, during combined travel-work operation, working fluid discharged from the first hydraulic pump is supplied to both the first and second traveling motors and working fluid discharged from the second hydraulic pump is supplied to the front working implement; and a control unit configured to limit the maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during the travel-only operation to be less than or equal to the maximum supply flow rate of working fluid discharged from the first hydraulic pump during the combined travel-work operation. A second aspect of the present disclosure may provide construction machinery capable of reducing travel shock when switching from travel-only operation to combined travel-work operation. A technical advantage is that, since the maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during travel-only operation is limited to be equal to or less than the maximum supply flow rate of working fluid discharged from the first hydraulic pump during combined travel-work operation, travel shock is prevented from occurring even when switching from travel-only operation to combined travel-work operation.

[0013] In some examples, the control unit may include a mode setting unit configured to set one or more modes among a travel mode prioritizing straight-travel performance, a work mode prioritizing work performance, and a neutral mode in which straight-travel performance and work performance are evenly balanced.

[0014] In some examples, the control unit may include a maximum flow rate setting unit configured to limit the maximum supply flow rate of working fluid discharged from the first hydraulic pump and the second hydraulic pump according to the mode set by the mode setting unit.

[0015] In some examples, the maximum flow rate setting unit may limit the maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during travel-only operation to the maximum supply flow rate of working fluid discharged from the first hydraulic pump during combined travel-work operation in the neutral mode.

[0016] In some examples, the maximum flow rate setting unit may set the maximum supply flow rate of working fluid discharged from the first hydraulic pump to a maximum value during combined travel-work operation in the travel mode, and limit the maximum supply flow rate of working fluid discharged from the second hydraulic pump to be less than the maximum supply flow rate of working fluid discharged from the first hydraulic pump.

[0017] In some examples, the travel mode may comprise a plurality of modes, and the maximum supply flow rate of working fluid discharged from the second hydraulic pump may be limited to different values for each mode of the travel mode.

[0018] In some examples, the maximum flow rate setting unit may set the maximum supply flow rate of working fluid discharged from the second hydraulic pump to a maximum value during combined travel-work operation in the work mode, and limit the maximum supply flow rate of working fluid discharged from the first hydraulic pump to be less than the maximum supply flow rate of working fluid discharged from the second hydraulic pump.

[0019] In some examples, the work mode may comprise a plurality of modes, and the maximum supply flow rate of working fluid discharged from the first hydraulic pump may be limited to different values for each mode of the work mode.

[0020] According to a third aspect of the present disclosure, a hydraulic system for construction machinery is provided, comprising: a first and second hydraulic pump; first and second traveling motors operable by working fluid discharged from the first and second hydraulic pumps; a front working implement operable by working fluid discharged from the first and second hydraulic pumps; a travel straight spool valve including a first section, in which during travel-only operation, working fluid discharged from the first hydraulic pump is supplied to the first traveling motor and working fluid discharged from the second hydraulic pump is supplied to the second traveling motor, and a second section, in which during combined travel-work operation, working fluid discharged from the first hydraulic pump is supplied to the first and second traveling motors and working fluid discharged from the second hydraulic pump is supplied to the front working implement; and a control unit, wherein the control unit includes a mode setting unit configured to set one or more modes selected from a travel mode prioritizing straight travel performance, a work mode prioritizing work performance, and a neutral mode in which straight travel performance and work performance are set equally; and a maximum flow rate setting unit configured to limit the maximum supply flow rate of the working fluid discharged from the first and second hydraulic pumps during travel-only operation to be equal to or less than the maximum supply flow rate of the working fluid discharged from the first hydraulic pump during the combined travel-work operation when the travel mode or work mode is selected, and to set the maximum supply flow rate of the working fluid discharged from the first and second hydraulic pumps to the maximum when the neutral mode is selected. The third embodiment of the present disclosure may provide construction machinery capable of reducing travel shock when switching from travel-only operation to combined travel-work operation. The technical advantage is that, in the neutral mode, straight travel performance can be maximized. Additionally, a technical advantage is that, in the travel mode or work mode, since the maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during travel-only operation is limited to be equal to or less than the maximum supply flow rate of working fluid discharged from the first hydraulic pump during combined travel-work operation, travel shock does not occur even when switching from travel-only operation to combined travel-work operation.

[0021] The above and subsequent embodiments disclosed herein, the appended claims, and / or examples may be appropriately combined as would be apparent to those skilled in the art.

[0022] Additional features and advantages are described in the following description, claims, and drawings, and will be recognized in part as being readily apparent to those skilled in the art or through the practice of the disclosures set forth herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] With reference to the accompanying drawings, a more detailed description of the embodiments of the present disclosure, cited herein by way of example, will follow. FIGS. 1 and 2 are hydraulic circuit diagrams showing a hydraulic system of construction machinery according to one embodiment. FIG. 3 is a block diagram of a control unit according to one embodiment. FIG. 4 is a diagram illustrating the section shift rate according to the pilot pressure of the travel straight spool valve. FIGS. 5 and 6 are diagrams illustrating the maximum flow rates of the first hydraulic pump and the second hydraulic pump for each mode. DETAILED DESCRIPTION

[0024] The embodiments described below provide the information necessary for a person skilled in the art to carry out the present disclosure.

[0025] FIGS. 1 and 2 are hydraulic circuit diagrams showing a hydraulic system of construction machinery according to one embodiment.

[0026] With reference to FIGS. 1 and 2, the hydraulic system 1 of construction machinery according to an embodiment of the present invention is a system for controlling hydraulic pressure to allow either a travel unit of the construction machinery to operate independently (hereinafter referred to as "travel-only operation") to enable travel, or to allow both the travel unit and a front working implement to operate in combination (hereinafter referred to as "combined travel-work operation") to simultaneously perform travel and front work, and may include a first hydraulic pump 101, a second hydraulic pump 102, a first traveling motor 201 operable by working fluid discharged from the first hydraulic pump 101, a second traveling motor 202 operable by working fluid discharged from the first hydraulic pump 101 or the second hydraulic pump 102, first and second traveling spools 301 and 302 configured to control, according to the displacement of spools provided therein, the flow rate of working fluid supplied respectively to the first and second traveling motors 201 and 202, a front working implement 400 operable by working fluid discharged from the first hydraulic pump 101 or the second hydraulic pump 102, a working implement spool 500 configured to control the flow of working fluid supplied to the front working implement 400, a travel straight spool valve 600 disposed between the first and second hydraulic pumps 101 and 102 and the first and second traveling motors 201 and 202 and the front working implement 400 to control the flow direction of working fluid supplied from the first and second hydraulic pumps 101 and 102 to the first and second traveling motors 201 and 202 and the front working implement 400, and a control unit 700.

[0027] The construction machinery may include an excavator, a wheel loader, a forklift, and the like. Hereinafter, the construction machinery will be described with respect to the case where the construction machinery is an excavator. However, it will be understood that the travel control system according to the exemplary embodiments is not limited to controlling excavators.

[0028] The construction machinery may include a lower traveling body, an upper revolving body mounted on the lower traveling body to be rotatable, and a cab and a front working implement 400 installed on the upper revolving body. For example, the excavator may be a crawler type excavator. The lower traveling body may include a right track and a left track. The first and second traveling motors 201 and 202 may respectively rotate the right track and the left track.

[0029] The first and second hydraulic pumps 101 and 102 may be connected to the engine (not shown) through a power transmission device. Power from the engine may be transmitted to the first and second hydraulic pumps 101 and 102.

[0030] The working fluid discharged from the first and second hydraulic pumps 101 and 102 is respectively supplied to the first and second traveling motors 201 and 202 through the first and second traveling spools 301 and 302.

[0031] Specifically, the first hydraulic pump 101 and the first traveling spool 301 are connected via the first hydraulic line 10, and the first traveling motor 201 is operable by the working fluid discharged from the first hydraulic pump 101. The second hydraulic line 20 branching from the first hydraulic line 10 is connected to the travel straight spool valve 600.

[0032] In addition, the second hydraulic pump 102 is connected to the travel straight spool valve 600 via a third hydraulic line 30, and the travel straight spool valve 600 and the second traveling spool 302 are connected via a fourth hydraulic line 40. The second traveling motor 202 is operable by working fluid discharged from one or both of the first hydraulic pump 101 and the second hydraulic pump 102, depending on the switching of the travel straight spool valve 600.

[0033] Meanwhile, the first traveling spool 301 and the second traveling spool 302 are not limited to the illustrated state and may be switchable to various states according to the input pilot signal pressure.

[0034] In addition, the working fluid discharged from the first and second hydraulic pumps 101 and 102 may be supplied to the front working implement 400 through the working implement spool 500.

[0035] The above front working implement 400 may include a boom, an arm, and a bucket. A boom cylinder for controlling the movement of the boom may be installed between the boom and the upper revolving body. An arm cylinder for controlling the movement of the arm may be installed between the boom and the arm. And a bucket cylinder for controlling the movement of the bucket may be installed between the arm and the bucket. As the boom cylinder, the arm cylinder, and the bucket cylinder extend or contract, the boom, the arm, and the bucket may perform various movements, and the front working implement 400 may carry out a variety of tasks.

[0036] The front working implement 400 may include a first working implement group 410 and a second working implement group 420.

[0037] The first working implement group 410 may include an arm cylinder 411 and a swing motor 412. The second working implement group 420 may include boom cylinders 421a and 421b, and a bucket cylinder 422.

[0038] The working implement spool 500 can control the flow of working fluid supplied to the front working implement 400. The working implement spool 500 maintains a blocked state of working fluid flow during travel-only operation and switches to allow working fluid flow when changing from travel-only operation to combined travel-work operation.

[0039] For example, the working implement spool 500 may include a first working implement spool group 510 and a second working implement spool group 520 for controlling the first working implement group 410 and the second working implement group 420, respectively.

[0040] For example, the working implement spool 500 may include a first arm control valve 511 and a second arm control valve 521 for controlling the arm cylinder 411.

[0041] For example, the working implement spool 500 may include a swing motor control valve 513 for controlling the swing motor 412.

[0042] For example, the working implement spool 500 may include a first boom control valve 512 and a second boom control valve 522 for controlling the boom cylinders 421a and 421b.

[0043] For example, the working implement spool 500 may include a bucket control valve 523 for controlling the bucket cylinder 422.

[0044] Specifically, the first working implement spool group 510 may be connected to the travel straight spool valve 600 via a sixth hydraulic line 60, and the second working implement spool group 520 may be connected to the second hydraulic pump 102 via a fifth hydraulic line 50 branched from the third hydraulic line 30.

[0045] The travel straight spool valve 600 may be configured so that, upon switching from travel-only operation to combined travel-work operation, the working fluid from the first hydraulic pump 101 is distributed and supplied to the first and second traveling motors 201 and 202, and the working fluid from the second hydraulic pump 102 is supplied to the front working implement 400.

[0046] Such a travel straight spool valve 600 may be a two-stage control spool consisting of a first section 610 and a second section 620. The travel straight spool valve 600 can be switched by an electronically controlled proportional pressure-reducing valve (not shown) controlled by the control unit 700.

[0047] The first section 610 is a section that controls the flow of working fluid during travel-only operation and may comprise a first port 611 and a second port 612.

[0048] With reference to FIG. 1, during travel-only operation, the first port 611 of the first section 610 is connected on one side to the first hydraulic pump 101 via the second hydraulic line 20, and on the other side to the first working implement spool group 510 via the sixth line 60, while the second port 612 of the first section 610 is connected on one side to the second hydraulic pump 102 via the third hydraulic line 30, and on the other side connected to the second traveling spool 302 via the fourth line 40.

[0049] During travel-only operation, the working fluid from the first hydraulic pump 101 is not supplied to the front working implement 400 because the working implement spool 500 remains in a closed state, and is supplied to the first traveling motor 201 because the first traveling spool 301 remains open, thereby driving the first traveling motor 201.

[0050] The working fluid from the second hydraulic pump 102 is supplied to the second traveling motor 202 via the second port 612, thereby driving the second traveling motor 202.

[0051] Accordingly, during travel-only operation, the working fluid from the first hydraulic pump 101 is supplied to the first traveling motor 201, and the working fluid from the second hydraulic pump 102 is supplied to the second traveling motor 202, enabling the construction machinery to perform forward or reverse travel.

[0052] The second section 620 may be a section that controls the flow of working fluid during combined travel-work operation and may include a first port 621 and a second port 622.

[0053] The first port 621 may be a port that supplies working fluid to the second traveling motor 202 and allows half of the working fluid from the first hydraulic pump 101 to flow to the second traveling motor 202 during combined travel-work operation. At this time, the remaining half of the working fluid from the first hydraulic pump 101 is supplied to the first traveling motor 201.

[0054] The second port 622 may be a port that supplies working fluid to the front working implement 400, allowing all of the working fluid from the second hydraulic pump 102 to flow to the front working implement 400 during combined travel-work operation.

[0055] In addition, a seventh hydraulic line 70 may be connected between the fourth hydraulic line 40 and the fifth hydraulic line 50, and a check valve 80 and an orifice 81 may be provided on the seventh hydraulic line 70.

[0056] The check valve 80 and orifice 81 allow a portion of the working fluid discharged from the second hydraulic pump 102 during combined travel-work operation to flow to the second traveling motor 202 through the second port 622 and prevent the working fluid discharged from the first hydraulic pump 101 and flowing into the first port 621 from flowing into the fifth hydraulic line 50.

[0057] Specifically, during the combined travel-work operation, as the section of the travel straight valve 600 switches from the first section 610 to the second section 620, the working fluid from the first hydraulic pump 101 flows to the traveling motors 201 and 202, and the working fluid from the second hydraulic pump 102 suddenly flows toward the front working implement 400 or the working implement spool 500, which may cause travel shock. Accordingly, on the seventh hydraulic line 70, a check valve 80 and an orifice 81 are installed to bypass rapidly supplied working fluid to the front working implement 400 or the working implement spool 500 during combined travel-work operation, or to supplement insufficient flow rate during operation of the second traveling motor 202.

[0058] With reference to FIG. 2, during the combined travel-work operation, the first port 621 of the second section 620 is connected on one side to the first hydraulic pump 101 via the second hydraulic line 20, and connected on the other side to the second traveling spool 302 via the fourth hydraulic line 40, while the second port 622 of the second section 620 is connected on one side to the second hydraulic pump 102 via the third hydraulic line 30, and connected on the other side to the first working implement spool group 510 via the sixth hydraulic line 60. In addition, a check valve 80 and an orifice 81 are provided between the fourth hydraulic line 40 and the fifth hydraulic line 50.

[0059] During the combined travel-work operation, the working fluid discharged from the first hydraulic pump 101 not only drives the first traveling motor 201 via the first traveling spool 301, but also drives the second traveling motor 202 via the first port 621 and the second traveling spool 302. That is, the working fluid discharged from the first hydraulic pump 101 is distributed and supplied to the first and second traveling motors 201 and 202 during the combined travel-work operation.

[0060] During the combined travel-work operation, the working fluid discharged from the second hydraulic pump 102 is supplied to drive the first working implement group 410 and the second working implement group 420, either via the second port 622 and the first working implement spool group 510, or via the fifth hydraulic line 50 and the second work implement spool group 520.

[0061] That is, during the transition from travel-only operation, in which the working fluid from the first hydraulic pump 101 is supplied to the first traveling motor 201 and the working fluid from the second hydraulic pump 102 is supplied to the second traveling motor 202, to combined travel-work operation, travel shock may occur as the first hydraulic pump 101 begins supplying working fluid to both traveling motors 201 and 202.

[0062] FIG. 3 is a block diagram of a control unit according to one embodiment.

[0063] With reference to FIG. 3, the control unit 700 according to an embodiment of the present invention may include a data receiving unit 710, a switching flow rate calculation unit 720, a mode setting unit 730, a maximum flow rate setting unit 740, a storage unit 750, and an output unit 760.

[0064] The data receiving unit 710 may receive an operation signal from an operator via an operation unit. The data receiving unit 710 may receive a travel operation signal from the travel pedal (not shown), specifically the operation amount of the travel pedal, from the operator.

[0065] Herein, the operation unit may include a travel pedal or travel lever for operating the first and second traveling motors 201 and 202, and a joystick for operating the work device.

[0066] When the operator manipulates the travel pedal and joystick, an operation signal corresponding to the manipulation (that is, a traveling motor operation signal and a work device operation signal) may be generated. The travel pedal and joystick may include sensors configured to measure the travel pedal operation amount and the work device operation amount (or angle). The travel pedal and joystick may output signals, such as voltage signals or current signals, corresponding to the measured operation amounts.

[0067] The data receiving unit 710 may receive, from the joystick, the joystick operation amounts as work device operation signals for the boom, arm, bucket, and swing. For example, the data receiving unit 710 may receive the boom joystick operation amount as an operation signal for the boom cylinder.

[0068] FIG. 4 is a diagram illustrating the section shift rate according to the pilot pressure of the travel straight spool valve.

[0069] With reference to FIG. 4, the travel straight spool valve 600 begins to switch the section when the magnitude of the applied pilot pressure exceeds a first preset pressure, and the section is fully switched when the pilot pressure reaches a second preset pressure. For example, as referenced in FIG. 4, when the first preset pressure is A or lower, the section switching ratio (ratio) may be 0%, and when the second preset pressure is B or higher, the section switching ratio may be 100%.

[0070] At this time, when the pilot pressure applied to the travel straight spool valve 600 is between the first preset pressure and the second preset pressure, the first section 610 and the second section 620 of the travel straight spool valve 600 are each partially opened, so that the first hydraulic pump 101 and the second hydraulic pump 102 supply working fluid to the first traveling motor 201, the second traveling motor 202, and the front working implement 400, respectively.

[0071] At this time, the switching flow rate calculation unit 720 may gradually adjust the flow rates of the working fluid supplied from the first hydraulic pump 101 and the second hydraulic pump 102 according to the section switching rate of the travel straight spool valve 600.

[0072] Specifically, when the section switching rate or spool displacement of the travel straight spool valve 600 according to the pilot pressure is denoted as ratio, the flow rate Q P1 discharged from the first hydraulic pump 101 can be calculated as Q P1 = Q TL + Gain A × Q TR × ratio + Q P1Att × (1 - ratio). Here, Q TL is the flow rate supplied to the first traveling motor 201, Gain A is a correction value to compensate for the flow entering from the second hydraulic pump 102 side to the first hydraulic pump 101 side through the orifice 81, Q TR is the flow rate supplied to the second traveling motor 202, and Q P1Att is the flow rate supplied to the first work device spool group 510.

[0073] In addition, the flow rate Q P2 discharged from the second hydraulic pump 102 can be calculated as Q P2 = Q P1Att × (ratio) + Q TR × (1 - ratio) + Q P2 Att . Here, Q P1Att is the flow rate supplied to the first work device spool group 510, Q TR is the flow rate supplied to the second traveling motor 202, and Q P2Att is the flow rate supplied to the second work device spool group 520.

[0074] According to the above equations, when the ratio is 0, the flow rate of the first hydraulic pump 101 can be calculated as Q P1 = Q TL + Q P1 Att , and the flow rate of the second hydraulic pump 102 can be calculated as Q P2 = Q TR + Q P2 Att . That is, when the ratio is 0, it corresponds to the case where the travel straight spool valve 600 is in the first section 610.

[0075] Additionally, when the ratio is 1, the flow rate Q P1 = Q TL + GainA × Q TR of the first hydraulic pump 101 and the flow rates Q P2 = Q P1 Att + Q P2Att of the second hydraulic pump 102 can be calculated accordingly. That is, when the ratio is 1, it corresponds to the case where the travel straight spool valve 600 is in the second section 620.

[0076] As described above, by gradually varying the flow rates of the first hydraulic pump 101 and the second hydraulic pump 102 according to the section switching ratio (ratio), it is possible to reduce the shock that may occur due to the section switching of the travel straight spool valve 600.

[0077] Via the mode setting unit 730, the operator may select a travel mode, a work mode, or a neutral mode of the construction machinery. When the travel mode is selected, straight travel performance is prioritized; when the work mode is selected, work performance is prioritized over travel performance; and when the neutral mode is selected, both straight travel performance and work performance are set to be balanced.

[0078] Specifically, the travel mode and the work mode may each be configured with a plurality of modes. For example, the travel mode may consist of a first travel mode to a fourth travel mode, wherein the straight travel performance may be progressively enhanced from the first travel mode to the fourth travel mode.

[0079] Additionally, the work mode may consist of a first work mode to a fourth work mode, wherein the work performance may be progressively enhanced from the first work mode to the fourth work mode. However, the number of travel modes and work modes is not limited thereto, and various numbers of modes may be applied.

[0080] Preferably, the operator can set the mode through a mode switch or a display provided in the cab.

[0081] FIGS. 5 and 6 are diagrams illustrating the maximum flow rates of the first hydraulic pump and the second hydraulic pump for each mode.

[0082] The maximum flow rate setting unit 740 may limit the maximum flow rates of the working fluid supplied from the first hydraulic pump 101 and the second hydraulic pump 102 based on a preset restriction map stored in the storage unit 750, according to the mode set by the mode setting unit 730.

[0083] Hereinafter, the maximum flow rates of the first hydraulic pump 101 and the second hydraulic pump 102 are each assumed as P. However, this is not limited thereto, and the maximum flow rates of the first hydraulic pump 101 and the second hydraulic pump 102 may differ from each other.

[0084] During travel-only operation, the working fluid from the first hydraulic pump 101 is supplied to the first traveling motor 201, and the working fluid from the second hydraulic pump 102 is supplied to the second traveling motor 202. That is, the maximum supply flow rate of the working fluid discharged from the first hydraulic pump 101 and the second hydraulic pump 102 is 2P. That is, the first traveling motor 201 and the second traveling motor 202 can be supplied with a combined maximum flow rate of 2P.

[0085] However, during the combined travel-work operation, the working fluid from the first hydraulic pump 101 is distributed and supplied to the first and second traveling motors 201 and 202. That is, when the maximum supply flow rate of the working fluid discharged from first hydraulic pump 101 is P, half of the working fluid (P / 2) from first hydraulic pump 101 flows to second traveling motor 202, and the remaining half of the working fluid (P / 2) from first hydraulic pump 101 is supplied to first traveling motor 201. That is, the first traveling motor 201 and the second traveling motor 202 can be supplied with a combined maximum flow rate of P.

[0086] Accordingly, when the boom cylinder is operated during travel-only operation and the travel straight spool valve 600 is switched to perform the combined travel-work operation, the flow rate of the working fluid supplied to the first traveling motor 201 and the second traveling motor 202 abruptly decreases from a maximum of 2P to P, thereby causing travel shock.

[0087] To prevent this, as illustrated in FIG. 5(a), the maximum flow rate setting unit 740 of the present invention limits the maximum flow rates of the first hydraulic pump 101 and the second hydraulic pump 102 to the maximum flow rate of the first hydraulic pump 101 during the combined travel-work operation, that is, to P or less, even during travel-only operation in all modes. In this case, even when switching from travel-only operation to combined travel-work operation, the flow rate of the working fluid supplied to the first traveling motor 201 and the second traveling motor 202 is set to a maximum of P or less, thereby preventing the occurrence of travel shock.

[0088] However, this is not limited thereto, and as shown in FIG. 6(a), the maximum flow rate setting unit 740 may set the maximum supply flow rate of the working fluid discharged from the first hydraulic pump 101 and the second hydraulic pump 102 to 2P during travel-only operation in the neutral mode (N). In this case, the operator can maximize straight travel performance by selecting the neutral mode (N) in the mode setting unit 730.

[0089] In addition, the maximum flow rate setting unit 740 of the present invention is characterized in that, during the combined travel-work operation, it prioritizes either the travel performance or the work performance based on the relative difference in the maximum supply flow rates of the first hydraulic pump 101 and the second hydraulic pump 102.

[0090] For example, with reference to FIG. 5(b), during the combined travel-work operation in the first travel mode TR1 through the fourth travel mode TR4, the maximum flow rate TR of the first hydraulic pump 101 supplied to the first traveling motor 201 and the second traveling motor 202 may be set to P. Additionally, the maximum flow rate TR of the first hydraulic pump 101 may be gradually decreased up to Q from the first work mode BU1 to the fourth work mode BU4. Preferably, Q may be set to half or less of P.

[0091] During the combined travel-work operation, in the first work mode BU1 through the fourth work mode BU4, the maximum flow rate BU of the second hydraulic pump 102 supplied to the front working implement 400, for example, the boom cylinder, may be set to P. In addition, the maximum flow rate BU of the second hydraulic pump 102 may be gradually decreased to Q as it moves from the first travel mode TR1 to the fourth travel mode TR4. Preferably, Q may be set to half or less of P.

[0092] That is, during combined travel-work operation in the travel mode, the maximum flow rate BU of the second hydraulic pump 102 may be set smaller than the maximum flow rate TR of the first hydraulic pump 101, and the difference may be configured to increase progressively from the first travel mode TR1 to the fourth travel mode TR4.

[0093] Additionally, during combined travel-work operation in the work mode, the maximum flow rate TR of the first hydraulic pump 101 may be set smaller than the maximum flow rate BU of the second hydraulic pump 102, and the difference may be configured to increase progressively from the first work mode BU1 to the fourth work mode BU4.

[0094] That is, during combined travel-work operation, the travel performance or work performance can be improved by adjusting the relative difference between the maximum flow rates of the first hydraulic pump 101 and the second hydraulic pump 102.

[0095] In addition, with reference to FIG. 5(a) and FIG. 5(b), to prevent travel shock caused by switching from travel-only operation to combined travel-work operation, the maximum flow rates TR of the first hydraulic pump 101 and the second hydraulic pump 102 during travel-only operation may be set to be the same as the maximum flow rate TR of the first hydraulic pump 101 during combined travel and work operation.

[0096] Although the hydraulic system of the construction machinery has been described with respect to the case where a boom-up operation is performed during travel-only operation, it is to be understood that the invention is not limited thereto and may be applied substantially in the same manner to cases such as arm or bucket operations.

[0097] The storage unit 750 may store the flow rate calculation formula for the first hydraulic pump 101, the flow rate calculation formula for the second hydraulic pump 102, and the Gain A value.

[0098] The storage unit 750 may store a limitation map including information on the maximum flow rates for each mode of the maximum flow rate setting unit 740. Preferably, the storage unit 750 stores a plurality of limitation maps having different maximum flow rates for each mode, as illustrated in FIGS. 5 or 6, allowing the user to select a desired limitation map.

[0099] The output unit 760 can operate the first and second traveling motors 201 and 202 and the front working implement 400 by controlling the first and second traveling spools 301 and 302 and the working implement spool 500 in response to the operation signals received from the data receiving unit 710.

[0100] Specifically, the output unit 760 receives operation signals proportional to the operator's manipulated quantities from the operation unit, and generates control signals corresponding to the received manipulated quantities, such as current, which can be applied to the electronic proportional pressure relief valve. The electronic proportional pressure relief valves supply pilot signal pressures proportional to the applied current intensity to the spools of the first and second traveling spools 301, 302 and the working implement spool 500, respectively, thereby moving the spools of the first and second traveling spools 301, 302 and the working implement spool 500 according to the intensity of the applied pilot signal pressure.

[0101] The output unit 760 may output a control signal to the travel straight spool valve 600 so as to switch the section of the travel straight spool valve 600 to the first section 610 or the second section 620 in response to the operation signal received from the data receiving unit 710.

[0102] The output unit 760 receives the value calculated by the switching flow rate calculation unit 720 and adjusts the flow rates of the first hydraulic pump 101 and the second hydraulic pump 102 correspondingly.

[0103] The output unit 760 may receive a maximum value calculated by the maximum flow rate setting unit 740, and may control the flowrates of the first hydraulic pump 101 and the second hydraulic pump 102 such that the flowrates of the first hydraulic pump 101 and the second hydraulic pump 102 do not exceed the calculated maximum value.

[0104] The terminology used herein is employed solely to describe specific embodiments and is not intended to limit the present disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. As used herein, the term "and / or" encompasses any and all possible combinations of one or more of the associated listed items. As used herein, the terms "comprises," "comprising," "includes," and / or "including" specify the presence of the stated functions, integers, steps, operations, elements, and / or components, but are understood not to exclude the presence or addition of one or more other functions, integers, steps, operations, elements, components, and / or groups thereof.

[0105] Although 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 element from another. For example, without departing from the scope of the present disclosure, the first component may be referred to as the second component, and similarly, the second component may be referred to as the first component.

[0106] Relative terms such as "below," "above," "upper side," "lower side," "horizontal," and "vertical" may be used herein to describe the relationship between one element and another as illustrated in the drawings. It should be understood that these terms, along with the terms discussed above, are intended to include different directions of the apparatus in addition to the directions illustrated in the drawings. When an element is described as being "connected" or "coupled" to another element, it is to be understood that the element may be directly connected or coupled to the other element, or may be connected or coupled via one or more intervening elements. In contrast, when an element is described as "directly connected" or "directly coupled" to another element, no intervening element exists therebetween.

[0107] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those of ordinary skill in the art to which the present disclosure pertains. Additionally, the terms used herein are to be interpreted as having meanings consistent with their meanings in the context of this specification and the related art, and unless explicitly defined herein, are not to be construed in an idealized or overly formal manner.

Examples

Embodiment Construction

[0024]The embodiments described below provide the information necessary for a person skilled in the art to carry out the present disclosure.

[0025]FIGS. 1 and 2 are hydraulic circuit diagrams showing a hydraulic system of construction machinery according to one embodiment.

[0026]With reference to FIGS. 1 and 2, the hydraulic system 1 of construction machinery according to an embodiment of the present invention is a system for controlling hydraulic pressure to allow either a travel unit of the construction machinery to operate independently (hereinafter referred to as "travel-only operation") to enable travel, or to allow both the travel unit and a front working implement to operate in combination (hereinafter referred to as "combined travel-work operation") to simultaneously perform travel and front work, and may include a first hydraulic pump 101, a second hydraulic pump 102, a first traveling motor 201 operable by working fluid discharged from the first hydraulic pump 101, a second ...

TECHNICAL FIELD

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

[0002] In general, an excavator is a type of construction machinery capable of performing various operations at construction sites and the like, including excavation work for digging earth, loading work for transporting soil, trenching work for foundation construction, crushing work for building demolition, leveling work for site preparation, and grading work for surface smoothing.

[0003] Such construction machinery may be capable of operating a traveling device independently by means of a hydraulic system (travel-only operation), or of operating the traveling device and a front working implement in combination (combined travel-work operation).

[0004] Conventionally, in construction machinery such as excavators, the term "front working implement" typically refers to components such as the boom, arm, bucket, swing device, and optional attachments, "travel-only operation" means traveling using the travel device alone, and "combined travel-work operation" refers to performing travel by the travel device while simultaneously operating the front working implement, thereby executing travel and front working implement operations concurrently.

[0005] Such an excavator is equipped with at least two hydraulic pumps, wherein during combined travel-work operation, the first pump supplies working fluid to two traveling motors, and the second pump supplies working fluid to the front working implement, and a travel shock may occur due to a change in the initial travel system transitioning from a traveling-only operation to the combined travel-work operation.SUMMARY

[0006] According to a first aspect of the present disclosure, a hydraulic system for construction machinery is provided, comprising: a first and second hydraulic pump; first and second traveling motors operable by working fluid discharged from the first and second hydraulic pumps; a front working implement operable by working fluid discharged from the first and second hydraulic pumps; a travel straight spool valve including a first section, in which during travel-only operation, working fluid discharged from the first hydraulic pump is supplied to the first traveling motor and working fluid discharged from the second hydraulic pump is supplied to the second traveling motor, and a second section, in which during combined travel-work operation, working fluid discharged from the first hydraulic pump is supplied to the first and second traveling motors, and working fluid discharged from the second hydraulic pump is supplied to the front working implement; and a control unit configured to control the supply flow rates of the first and second hydraulic pumps to be gradually changed according to a section switching rate when switching between the sections of the travel straight spool valve. A first aspect of the present disclosure may provide construction machinery capable of reducing travel shock when switching from travel-only operation to combined travel-work operation. A technical advantage is that, because the flow rates of the first hydraulic pump and the second hydraulic pump are gradually changed according to the section switching rate, travel shock can be reduced during the section switching process of the travel straight spool valve.

[0007] In some examples, the construction machine may further include a first traveling spool and a second traveling spool configured to respectively control the flow rates of working fluid supplied to the first and second traveling motors, and a working implement spool comprising a first working implement spool group and a second working implement spool group configured to control the flow rate of working fluid supplied to the front working implement.

[0008] In some examples, the second section may include a first port having one side connected to the first hydraulic pump and the other side connected to the second traveling spool, and a second port having one side connected to the second hydraulic pump and the other side connected to the first working implement spool group.

[0009] In some examples, a check valve and an orifice may be disposed between the second working implement spool group connected to the second hydraulic pump and the second traveling spool.

[0010] In some examples, the control unit may include a switching flow rate calculation unit configured to calculate the flow rates of working fluid supplied from the first hydraulic pump and the second hydraulic pump according to the section switching rate of the travel straight spool valve.

[0011] In some examples, when the section switching rate of the travel straight spool valve is referred to as ratio, the switching flow rate calculation unit may calculate the flow rate Q P1 of the first hydraulic pump as Q P1 = Q TL + GainA × Q TR × ratio + Q P1Att × (1 - ratio) and may calculate the flow rate Q P2 of the second hydraulic pump as Q P2 = Q P1Att × (ratio) + Q TR × (1 - ratio) + Q P2 Att . Here, Q TL may be the flow rate of the first traveling motor; Gain A may be a correction value for compensating the flow of working fluid passing through the orifice, Q TR may be the flow rate of the second traveling motor; Q P1Att may be the flow rate of the first working implement spool group, and Q P2Att may be the flow rate of the second working implement spool group.

[0012] According to a second aspect of the present disclosure, there is provided a hydraulic system for construction machinery, the system comprising: a first hydraulic pump and a second hydraulic pump; a first traveling motor and a second traveling motor, each operable by working fluid discharged from the first and second hydraulic pumps, respectively; a front working implement operable by working fluid discharged from the first and second hydraulic pumps; a travel straight spool valve including a first section configured such that, during travel-only operation, working fluid discharged from the first hydraulic pump is supplied to the first traveling motor and working fluid discharged from the second hydraulic pump is supplied to the second traveling motor, and a second section configured such that, during combined travel-work operation, working fluid discharged from the first hydraulic pump is supplied to both the first and second traveling motors and working fluid discharged from the second hydraulic pump is supplied to the front working implement; and a control unit configured to limit the maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during the travel-only operation to be less than or equal to the maximum supply flow rate of working fluid discharged from the first hydraulic pump during the combined travel-work operation. A second aspect of the present disclosure may provide construction machinery capable of reducing travel shock when switching from travel-only operation to combined travel-work operation. A technical advantage is that, since the maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during travel-only operation is limited to be equal to or less than the maximum supply flow rate of working fluid discharged from the first hydraulic pump during combined travel-work operation, travel shock is prevented from occurring even when switching from travel-only operation to combined travel-work operation.

[0013] In some examples, the control unit may include a mode setting unit configured to set one or more modes among a travel mode prioritizing straight-travel performance, a work mode prioritizing work performance, and a neutral mode in which straight-travel performance and work performance are evenly balanced.

[0014] In some examples, the control unit may include a maximum flow rate setting unit configured to limit the maximum supply flow rate of working fluid discharged from the first hydraulic pump and the second hydraulic pump according to the mode set by the mode setting unit.

[0015] In some examples, the maximum flow rate setting unit may limit the maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during travel-only operation to the maximum supply flow rate of working fluid discharged from the first hydraulic pump during combined travel-work operation in the neutral mode.

[0016] In some examples, the maximum flow rate setting unit may set the maximum supply flow rate of working fluid discharged from the first hydraulic pump to a maximum value during combined travel-work operation in the travel mode, and limit the maximum supply flow rate of working fluid discharged from the second hydraulic pump to be less than the maximum supply flow rate of working fluid discharged from the first hydraulic pump.

[0017] In some examples, the travel mode may comprise a plurality of modes, and the maximum supply flow rate of working fluid discharged from the second hydraulic pump may be limited to different values for each mode of the travel mode.

[0018] In some examples, the maximum flow rate setting unit may set the maximum supply flow rate of working fluid discharged from the second hydraulic pump to a maximum value during combined travel-work operation in the work mode, and limit the maximum supply flow rate of working fluid discharged from the first hydraulic pump to be less than the maximum supply flow rate of working fluid discharged from the second hydraulic pump.

[0019] In some examples, the work mode may comprise a plurality of modes, and the maximum supply flow rate of working fluid discharged from the first hydraulic pump may be limited to different values for each mode of the work mode.

[0020] According to a third aspect of the present disclosure, a hydraulic system for construction machinery is provided, comprising: a first and second hydraulic pump; first and second traveling motors operable by working fluid discharged from the first and second hydraulic pumps; a front working implement operable by working fluid discharged from the first and second hydraulic pumps; a travel straight spool valve including a first section, in which during travel-only operation, working fluid discharged from the first hydraulic pump is supplied to the first traveling motor and working fluid discharged from the second hydraulic pump is supplied to the second traveling motor, and a second section, in which during combined travel-work operation, working fluid discharged from the first hydraulic pump is supplied to the first and second traveling motors and working fluid discharged from the second hydraulic pump is supplied to the front working implement; and a control unit, wherein the control unit includes a mode setting unit configured to set one or more modes selected from a travel mode prioritizing straight travel performance, a work mode prioritizing work performance, and a neutral mode in which straight travel performance and work performance are set equally; and a maximum flow rate setting unit configured to limit the maximum supply flow rate of the working fluid discharged from the first and second hydraulic pumps during travel-only operation to be equal to or less than the maximum supply flow rate of the working fluid discharged from the first hydraulic pump during the combined travel-work operation when the travel mode or work mode is selected, and to set the maximum supply flow rate of the working fluid discharged from the first and second hydraulic pumps to the maximum when the neutral mode is selected. The third embodiment of the present disclosure may provide construction machinery capable of reducing travel shock when switching from travel-only operation to combined travel-work operation. The technical advantage is that, in the neutral mode, straight travel performance can be maximized. Additionally, a technical advantage is that, in the travel mode or work mode, since the maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during travel-only operation is limited to be equal to or less than the maximum supply flow rate of working fluid discharged from the first hydraulic pump during combined travel-work operation, travel shock does not occur even when switching from travel-only operation to combined travel-work operation.

[0021] The above and subsequent embodiments disclosed herein, the appended claims, and / or examples may be appropriately combined as would be apparent to those skilled in the art.

[0022] Additional features and advantages are described in the following description, claims, and drawings, and will be recognized in part as being readily apparent to those skilled in the art or through the practice of the disclosures set forth herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] With reference to the accompanying drawings, a more detailed description of the embodiments of the present disclosure, cited herein by way of example, will follow. FIGS. 1 and 2 are hydraulic circuit diagrams showing a hydraulic system of construction machinery according to one embodiment. FIG. 3 is a block diagram of a control unit according to one embodiment. FIG. 4 is a diagram illustrating the section shift rate according to the pilot pressure of the travel straight spool valve. FIGS. 5 and 6 are diagrams illustrating the maximum flow rates of the first hydraulic pump and the second hydraulic pump for each mode. DETAILED DESCRIPTION

[0024] The embodiments described below provide the information necessary for a person skilled in the art to carry out the present disclosure.

[0025] FIGS. 1 and 2 are hydraulic circuit diagrams showing a hydraulic system of construction machinery according to one embodiment.

[0026] With reference to FIGS. 1 and 2, the hydraulic system 1 of construction machinery according to an embodiment of the present invention is a system for controlling hydraulic pressure to allow either a travel unit of the construction machinery to operate independently (hereinafter referred to as "travel-only operation") to enable travel, or to allow both the travel unit and a front working implement to operate in combination (hereinafter referred to as "combined travel-work operation") to simultaneously perform travel and front work, and may include a first hydraulic pump 101, a second hydraulic pump 102, a first traveling motor 201 operable by working fluid discharged from the first hydraulic pump 101, a second traveling motor 202 operable by working fluid discharged from the first hydraulic pump 101 or the second hydraulic pump 102, first and second traveling spools 301 and 302 configured to control, according to the displacement of spools provided therein, the flow rate of working fluid supplied respectively to the first and second traveling motors 201 and 202, a front working implement 400 operable by working fluid discharged from the first hydraulic pump 101 or the second hydraulic pump 102, a working implement spool 500 configured to control the flow of working fluid supplied to the front working implement 400, a travel straight spool valve 600 disposed between the first and second hydraulic pumps 101 and 102 and the first and second traveling motors 201 and 202 and the front working implement 400 to control the flow direction of working fluid supplied from the first and second hydraulic pumps 101 and 102 to the first and second traveling motors 201 and 202 and the front working implement 400, and a control unit 700.

[0027] The construction machinery may include an excavator, a wheel loader, a forklift, and the like. Hereinafter, the construction machinery will be described with respect to the case where the construction machinery is an excavator. However, it will be understood that the travel control system according to the exemplary embodiments is not limited to controlling excavators.

[0028] The construction machinery may include a lower traveling body, an upper revolving body mounted on the lower traveling body to be rotatable, and a cab and a front working implement 400 installed on the upper revolving body. For example, the excavator may be a crawler type excavator. The lower traveling body may include a right track and a left track. The first and second traveling motors 201 and 202 may respectively rotate the right track and the left track.

[0029] The first and second hydraulic pumps 101 and 102 may be connected to the engine (not shown) through a power transmission device. Power from the engine may be transmitted to the first and second hydraulic pumps 101 and 102.

[0030] The working fluid discharged from the first and second hydraulic pumps 101 and 102 is respectively supplied to the first and second traveling motors 201 and 202 through the first and second traveling spools 301 and 302.

[0031] Specifically, the first hydraulic pump 101 and the first traveling spool 301 are connected via the first hydraulic line 10, and the first traveling motor 201 is operable by the working fluid discharged from the first hydraulic pump 101. The second hydraulic line 20 branching from the first hydraulic line 10 is connected to the travel straight spool valve 600.

[0032] In addition, the second hydraulic pump 102 is connected to the travel straight spool valve 600 via a third hydraulic line 30, and the travel straight spool valve 600 and the second traveling spool 302 are connected via a fourth hydraulic line 40. The second traveling motor 202 is operable by working fluid discharged from one or both of the first hydraulic pump 101 and the second hydraulic pump 102, depending on the switching of the travel straight spool valve 600.

[0033] Meanwhile, the first traveling spool 301 and the second traveling spool 302 are not limited to the illustrated state and may be switchable to various states according to the input pilot signal pressure.

[0034] In addition, the working fluid discharged from the first and second hydraulic pumps 101 and 102 may be supplied to the front working implement 400 through the working implement spool 500.

[0035] The above front working implement 400 may include a boom, an arm, and a bucket. A boom cylinder for controlling the movement of the boom may be installed between the boom and the upper revolving body. An arm cylinder for controlling the movement of the arm may be installed between the boom and the arm. And a bucket cylinder for controlling the movement of the bucket may be installed between the arm and the bucket. As the boom cylinder, the arm cylinder, and the bucket cylinder extend or contract, the boom, the arm, and the bucket may perform various movements, and the front working implement 400 may carry out a variety of tasks.

[0036] The front working implement 400 may include a first working implement group 410 and a second working implement group 420.

[0037] The first working implement group 410 may include an arm cylinder 411 and a swing motor 412. The second working implement group 420 may include boom cylinders 421a and 421b, and a bucket cylinder 422.

[0038] The working implement spool 500 can control the flow of working fluid supplied to the front working implement 400. The working implement spool 500 maintains a blocked state of working fluid flow during travel-only operation and switches to allow working fluid flow when changing from travel-only operation to combined travel-work operation.

[0039] For example, the working implement spool 500 may include a first working implement spool group 510 and a second working implement spool group 520 for controlling the first working implement group 410 and the second working implement group 420, respectively.

[0040] For example, the working implement spool 500 may include a first arm control valve 511 and a second arm control valve 521 for controlling the arm cylinder 411.

[0041] For example, the working implement spool 500 may include a swing motor control valve 513 for controlling the swing motor 412.

[0042] For example, the working implement spool 500 may include a first boom control valve 512 and a second boom control valve 522 for controlling the boom cylinders 421a and 421b.

[0043] For example, the working implement spool 500 may include a bucket control valve 523 for controlling the bucket cylinder 422.

[0044] Specifically, the first working implement spool group 510 may be connected to the travel straight spool valve 600 via a sixth hydraulic line 60, and the second working implement spool group 520 may be connected to the second hydraulic pump 102 via a fifth hydraulic line 50 branched from the third hydraulic line 30.

[0045] The travel straight spool valve 600 may be configured so that, upon switching from travel-only operation to combined travel-work operation, the working fluid from the first hydraulic pump 101 is distributed and supplied to the first and second traveling motors 201 and 202, and the working fluid from the second hydraulic pump 102 is supplied to the front working implement 400.

[0046] Such a travel straight spool valve 600 may be a two-stage control spool consisting of a first section 610 and a second section 620. The travel straight spool valve 600 can be switched by an electronically controlled proportional pressure-reducing valve (not shown) controlled by the control unit 700.

[0047] The first section 610 is a section that controls the flow of working fluid during travel-only operation and may comprise a first port 611 and a second port 612.

[0048] With reference to FIG. 1, during travel-only operation, the first port 611 of the first section 610 is connected on one side to the first hydraulic pump 101 via the second hydraulic line 20, and on the other side to the first working implement spool group 510 via the sixth line 60, while the second port 612 of the first section 610 is connected on one side to the second hydraulic pump 102 via the third hydraulic line 30, and on the other side connected to the second traveling spool 302 via the fourth line 40.

[0049] During travel-only operation, the working fluid from the first hydraulic pump 101 is not supplied to the front working implement 400 because the working implement spool 500 remains in a closed state, and is supplied to the first traveling motor 201 because the first traveling spool 301 remains open, thereby driving the first traveling motor 201.

[0050] The working fluid from the second hydraulic pump 102 is supplied to the second traveling motor 202 via the second port 612, thereby driving the second traveling motor 202.

[0051] Accordingly, during travel-only operation, the working fluid from the first hydraulic pump 101 is supplied to the first traveling motor 201, and the working fluid from the second hydraulic pump 102 is supplied to the second traveling motor 202, enabling the construction machinery to perform forward or reverse travel.

[0052] The second section 620 may be a section that controls the flow of working fluid during combined travel-work operation and may include a first port 621 and a second port 622.

[0053] The first port 621 may be a port that supplies working fluid to the second traveling motor 202 and allows half of the working fluid from the first hydraulic pump 101 to flow to the second traveling motor 202 during combined travel-work operation. At this time, the remaining half of the working fluid from the first hydraulic pump 101 is supplied to the first traveling motor 201.

[0054] The second port 622 may be a port that supplies working fluid to the front working implement 400, allowing all of the working fluid from the second hydraulic pump 102 to flow to the front working implement 400 during combined travel-work operation.

[0055] In addition, a seventh hydraulic line 70 may be connected between the fourth hydraulic line 40 and the fifth hydraulic line 50, and a check valve 80 and an orifice 81 may be provided on the seventh hydraulic line 70.

[0056] The check valve 80 and orifice 81 allow a portion of the working fluid discharged from the second hydraulic pump 102 during combined travel-work operation to flow to the second traveling motor 202 through the second port 622 and prevent the working fluid discharged from the first hydraulic pump 101 and flowing into the first port 621 from flowing into the fifth hydraulic line 50.

[0057] Specifically, during the combined travel-work operation, as the section of the travel straight valve 600 switches from the first section 610 to the second section 620, the working fluid from the first hydraulic pump 101 flows to the traveling motors 201 and 202, and the working fluid from the second hydraulic pump 102 suddenly flows toward the front working implement 400 or the working implement spool 500, which may cause travel shock. Accordingly, on the seventh hydraulic line 70, a check valve 80 and an orifice 81 are installed to bypass rapidly supplied working fluid to the front working implement 400 or the working implement spool 500 during combined travel-work operation, or to supplement insufficient flow rate during operation of the second traveling motor 202.

[0058] With reference to FIG. 2, during the combined travel-work operation, the first port 621 of the second section 620 is connected on one side to the first hydraulic pump 101 via the second hydraulic line 20, and connected on the other side to the second traveling spool 302 via the fourth hydraulic line 40, while the second port 622 of the second section 620 is connected on one side to the second hydraulic pump 102 via the third hydraulic line 30, and connected on the other side to the first working implement spool group 510 via the sixth hydraulic line 60. In addition, a check valve 80 and an orifice 81 are provided between the fourth hydraulic line 40 and the fifth hydraulic line 50.

[0059] During the combined travel-work operation, the working fluid discharged from the first hydraulic pump 101 not only drives the first traveling motor 201 via the first traveling spool 301, but also drives the second traveling motor 202 via the first port 621 and the second traveling spool 302. That is, the working fluid discharged from the first hydraulic pump 101 is distributed and supplied to the first and second traveling motors 201 and 202 during the combined travel-work operation.

[0060] During the combined travel-work operation, the working fluid discharged from the second hydraulic pump 102 is supplied to drive the first working implement group 410 and the second working implement group 420, either via the second port 622 and the first working implement spool group 510, or via the fifth hydraulic line 50 and the second work implement spool group 520.

[0061] That is, during the transition from travel-only operation, in which the working fluid from the first hydraulic pump 101 is supplied to the first traveling motor 201 and the working fluid from the second hydraulic pump 102 is supplied to the second traveling motor 202, to combined travel-work operation, travel shock may occur as the first hydraulic pump 101 begins supplying working fluid to both traveling motors 201 and 202.

[0062] FIG. 3 is a block diagram of a control unit according to one embodiment.

[0063] With reference to FIG. 3, the control unit 700 according to an embodiment of the present invention may include a data receiving unit 710, a switching flow rate calculation unit 720, a mode setting unit 730, a maximum flow rate setting unit 740, a storage unit 750, and an output unit 760.

[0064] The data receiving unit 710 may receive an operation signal from an operator via an operation unit. The data receiving unit 710 may receive a travel operation signal from the travel pedal (not shown), specifically the operation amount of the travel pedal, from the operator.

[0065] Herein, the operation unit may include a travel pedal or travel lever for operating the first and second traveling motors 201 and 202, and a joystick for operating the work device.

[0066] When the operator manipulates the travel pedal and joystick, an operation signal corresponding to the manipulation (that is, a traveling motor operation signal and a work device operation signal) may be generated. The travel pedal and joystick may include sensors configured to measure the travel pedal operation amount and the work device operation amount (or angle). The travel pedal and joystick may output signals, such as voltage signals or current signals, corresponding to the measured operation amounts.

[0067] The data receiving unit 710 may receive, from the joystick, the joystick operation amounts as work device operation signals for the boom, arm, bucket, and swing. For example, the data receiving unit 710 may receive the boom joystick operation amount as an operation signal for the boom cylinder.

[0068] FIG. 4 is a diagram illustrating the section shift rate according to the pilot pressure of the travel straight spool valve.

[0069] With reference to FIG. 4, the travel straight spool valve 600 begins to switch the section when the magnitude of the applied pilot pressure exceeds a first preset pressure, and the section is fully switched when the pilot pressure reaches a second preset pressure. For example, as referenced in FIG. 4, when the first preset pressure is A or lower, the section switching ratio (ratio) may be 0%, and when the second preset pressure is B or higher, the section switching ratio may be 100%.

[0070] At this time, when the pilot pressure applied to the travel straight spool valve 600 is between the first preset pressure and the second preset pressure, the first section 610 and the second section 620 of the travel straight spool valve 600 are each partially opened, so that the first hydraulic pump 101 and the second hydraulic pump 102 supply working fluid to the first traveling motor 201, the second traveling motor 202, and the front working implement 400, respectively.

[0071] At this time, the switching flow rate calculation unit 720 may gradually adjust the flow rates of the working fluid supplied from the first hydraulic pump 101 and the second hydraulic pump 102 according to the section switching rate of the travel straight spool valve 600.

[0072] Specifically, when the section switching rate or spool displacement of the travel straight spool valve 600 according to the pilot pressure is denoted as ratio, the flow rate Q P1 discharged from the first hydraulic pump 101 can be calculated as Q P1 = Q TL + Gain A × Q TR × ratio + Q P1Att × (1 - ratio). Here, Q TL is the flow rate supplied to the first traveling motor 201, Gain A is a correction value to compensate for the flow entering from the second hydraulic pump 102 side to the first hydraulic pump 101 side through the orifice 81, Q TR is the flow rate supplied to the second traveling motor 202, and Q P1Att is the flow rate supplied to the first work device spool group 510.

[0073] In addition, the flow rate Q P2 discharged from the second hydraulic pump 102 can be calculated as Q P2 = Q P1Att × (ratio) + Q TR × (1 - ratio) + Q P2 Att . Here, Q P1Att is the flow rate supplied to the first work device spool group 510, Q TR is the flow rate supplied to the second traveling motor 202, and Q P2Att is the flow rate supplied to the second work device spool group 520.

[0074] According to the above equations, when the ratio is 0, the flow rate of the first hydraulic pump 101 can be calculated as Q P1 = Q TL + Q P1 Att , and the flow rate of the second hydraulic pump 102 can be calculated as Q P2 = Q TR + Q P2 Att . That is, when the ratio is 0, it corresponds to the case where the travel straight spool valve 600 is in the first section 610.

[0075] Additionally, when the ratio is 1, the flow rate Q P1 = Q TL + GainA × Q TR of the first hydraulic pump 101 and the flow rates Q P2 = Q P1 Att + Q P2Att of the second hydraulic pump 102 can be calculated accordingly. That is, when the ratio is 1, it corresponds to the case where the travel straight spool valve 600 is in the second section 620.

[0076] As described above, by gradually varying the flow rates of the first hydraulic pump 101 and the second hydraulic pump 102 according to the section switching ratio (ratio), it is possible to reduce the shock that may occur due to the section switching of the travel straight spool valve 600.

[0077] Via the mode setting unit 730, the operator may select a travel mode, a work mode, or a neutral mode of the construction machinery. When the travel mode is selected, straight travel performance is prioritized; when the work mode is selected, work performance is prioritized over travel performance; and when the neutral mode is selected, both straight travel performance and work performance are set to be balanced.

[0078] Specifically, the travel mode and the work mode may each be configured with a plurality of modes. For example, the travel mode may consist of a first travel mode to a fourth travel mode, wherein the straight travel performance may be progressively enhanced from the first travel mode to the fourth travel mode.

[0079] Additionally, the work mode may consist of a first work mode to a fourth work mode, wherein the work performance may be progressively enhanced from the first work mode to the fourth work mode. However, the number of travel modes and work modes is not limited thereto, and various numbers of modes may be applied.

[0080] Preferably, the operator can set the mode through a mode switch or a display provided in the cab.

[0081] FIGS. 5 and 6 are diagrams illustrating the maximum flow rates of the first hydraulic pump and the second hydraulic pump for each mode.

[0082] The maximum flow rate setting unit 740 may limit the maximum flow rates of the working fluid supplied from the first hydraulic pump 101 and the second hydraulic pump 102 based on a preset restriction map stored in the storage unit 750, according to the mode set by the mode setting unit 730.

[0083] Hereinafter, the maximum flow rates of the first hydraulic pump 101 and the second hydraulic pump 102 are each assumed as P. However, this is not limited thereto, and the maximum flow rates of the first hydraulic pump 101 and the second hydraulic pump 102 may differ from each other.

[0084] During travel-only operation, the working fluid from the first hydraulic pump 101 is supplied to the first traveling motor 201, and the working fluid from the second hydraulic pump 102 is supplied to the second traveling motor 202. That is, the maximum supply flow rate of the working fluid discharged from the first hydraulic pump 101 and the second hydraulic pump 102 is 2P. That is, the first traveling motor 201 and the second traveling motor 202 can be supplied with a combined maximum flow rate of 2P.

[0085] However, during the combined travel-work operation, the working fluid from the first hydraulic pump 101 is distributed and supplied to the first and second traveling motors 201 and 202. That is, when the maximum supply flow rate of the working fluid discharged from first hydraulic pump 101 is P, half of the working fluid (P / 2) from first hydraulic pump 101 flows to second traveling motor 202, and the remaining half of the working fluid (P / 2) from first hydraulic pump 101 is supplied to first traveling motor 201. That is, the first traveling motor 201 and the second traveling motor 202 can be supplied with a combined maximum flow rate of P.

[0086] Accordingly, when the boom cylinder is operated during travel-only operation and the travel straight spool valve 600 is switched to perform the combined travel-work operation, the flow rate of the working fluid supplied to the first traveling motor 201 and the second traveling motor 202 abruptly decreases from a maximum of 2P to P, thereby causing travel shock.

[0087] To prevent this, as illustrated in FIG. 5(a), the maximum flow rate setting unit 740 of the present invention limits the maximum flow rates of the first hydraulic pump 101 and the second hydraulic pump 102 to the maximum flow rate of the first hydraulic pump 101 during the combined travel-work operation, that is, to P or less, even during travel-only operation in all modes. In this case, even when switching from travel-only operation to combined travel-work operation, the flow rate of the working fluid supplied to the first traveling motor 201 and the second traveling motor 202 is set to a maximum of P or less, thereby preventing the occurrence of travel shock.

[0088] However, this is not limited thereto, and as shown in FIG. 6(a), the maximum flow rate setting unit 740 may set the maximum supply flow rate of the working fluid discharged from the first hydraulic pump 101 and the second hydraulic pump 102 to 2P during travel-only operation in the neutral mode (N). In this case, the operator can maximize straight travel performance by selecting the neutral mode (N) in the mode setting unit 730.

[0089] In addition, the maximum flow rate setting unit 740 of the present invention is characterized in that, during the combined travel-work operation, it prioritizes either the travel performance or the work performance based on the relative difference in the maximum supply flow rates of the first hydraulic pump 101 and the second hydraulic pump 102.

[0090] For example, with reference to FIG. 5(b), during the combined travel-work operation in the first travel mode TR1 through the fourth travel mode TR4, the maximum flow rate TR of the first hydraulic pump 101 supplied to the first traveling motor 201 and the second traveling motor 202 may be set to P. Additionally, the maximum flow rate TR of the first hydraulic pump 101 may be gradually decreased up to Q from the first work mode BU1 to the fourth work mode BU4. Preferably, Q may be set to half or less of P.

[0091] During the combined travel-work operation, in the first work mode BU1 through the fourth work mode BU4, the maximum flow rate BU of the second hydraulic pump 102 supplied to the front working implement 400, for example, the boom cylinder, may be set to P. In addition, the maximum flow rate BU of the second hydraulic pump 102 may be gradually decreased to Q as it moves from the first travel mode TR1 to the fourth travel mode TR4. Preferably, Q may be set to half or less of P.

[0092] That is, during combined travel-work operation in the travel mode, the maximum flow rate BU of the second hydraulic pump 102 may be set smaller than the maximum flow rate TR of the first hydraulic pump 101, and the difference may be configured to increase progressively from the first travel mode TR1 to the fourth travel mode TR4.

[0093] Additionally, during combined travel-work operation in the work mode, the maximum flow rate TR of the first hydraulic pump 101 may be set smaller than the maximum flow rate BU of the second hydraulic pump 102, and the difference may be configured to increase progressively from the first work mode BU1 to the fourth work mode BU4.

[0094] That is, during combined travel-work operation, the travel performance or work performance can be improved by adjusting the relative difference between the maximum flow rates of the first hydraulic pump 101 and the second hydraulic pump 102.

[0095] In addition, with reference to FIG. 5(a) and FIG. 5(b), to prevent travel shock caused by switching from travel-only operation to combined travel-work operation, the maximum flow rates TR of the first hydraulic pump 101 and the second hydraulic pump 102 during travel-only operation may be set to be the same as the maximum flow rate TR of the first hydraulic pump 101 during combined travel and work operation.

[0096] Although the hydraulic system of the construction machinery has been described with respect to the case where a boom-up operation is performed during travel-only operation, it is to be understood that the invention is not limited thereto and may be applied substantially in the same manner to cases such as arm or bucket operations.

[0097] The storage unit 750 may store the flow rate calculation formula for the first hydraulic pump 101, the flow rate calculation formula for the second hydraulic pump 102, and the Gain A value.

[0098] The storage unit 750 may store a limitation map including information on the maximum flow rates for each mode of the maximum flow rate setting unit 740. Preferably, the storage unit 750 stores a plurality of limitation maps having different maximum flow rates for each mode, as illustrated in FIGS. 5 or 6, allowing the user to select a desired limitation map.

[0099] The output unit 760 can operate the first and second traveling motors 201 and 202 and the front working implement 400 by controlling the first and second traveling spools 301 and 302 and the working implement spool 500 in response to the operation signals received from the data receiving unit 710.

[0100] Specifically, the output unit 760 receives operation signals proportional to the operator's manipulated quantities from the operation unit, and generates control signals corresponding to the received manipulated quantities, such as current, which can be applied to the electronic proportional pressure relief valve. The electronic proportional pressure relief valves supply pilot signal pressures proportional to the applied current intensity to the spools of the first and second traveling spools 301, 302 and the working implement spool 500, respectively, thereby moving the spools of the first and second traveling spools 301, 302 and the working implement spool 500 according to the intensity of the applied pilot signal pressure.

[0101] The output unit 760 may output a control signal to the travel straight spool valve 600 so as to switch the section of the travel straight spool valve 600 to the first section 610 or the second section 620 in response to the operation signal received from the data receiving unit 710.

[0102] The output unit 760 receives the value calculated by the switching flow rate calculation unit 720 and adjusts the flow rates of the first hydraulic pump 101 and the second hydraulic pump 102 correspondingly.

[0103] The output unit 760 may receive a maximum value calculated by the maximum flow rate setting unit 740, and may control the flowrates of the first hydraulic pump 101 and the second hydraulic pump 102 such that the flowrates of the first hydraulic pump 101 and the second hydraulic pump 102 do not exceed the calculated maximum value.

[0104] The terminology used herein is employed solely to describe specific embodiments and is not intended to limit the present disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. As used herein, the term "and / or" encompasses any and all possible combinations of one or more of the associated listed items. As used herein, the terms "comprises," "comprising," "includes," and / or "including" specify the presence of the stated functions, integers, steps, operations, elements, and / or components, but are understood not to exclude the presence or addition of one or more other functions, integers, steps, operations, elements, components, and / or groups thereof.

[0105] Although 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 element from another. For example, without departing from the scope of the present disclosure, the first component may be referred to as the second component, and similarly, the second component may be referred to as the first component.

[0106] Relative terms such as "below," "above," "upper side," "lower side," "horizontal," and "vertical" may be used herein to describe the relationship between one element and another as illustrated in the drawings. It should be understood that these terms, along with the terms discussed above, are intended to include different directions of the apparatus in addition to the directions illustrated in the drawings. When an element is described as being "connected" or "coupled" to another element, it is to be understood that the element may be directly connected or coupled to the other element, or may be connected or coupled via one or more intervening elements. In contrast, when an element is described as "directly connected" or "directly coupled" to another element, no intervening element exists therebetween.

[0107] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those of ordinary skill in the art to which the present disclosure pertains. Additionally, the terms used herein are to be interpreted as having meanings consistent with their meanings in the context of this specification and the related art, and unless explicitly defined herein, are not to be construed in an idealized or overly formal manner.

Examples

Embodiment Construction

[0024]The embodiments described below provide the information necessary for a person skilled in the art to carry out the present disclosure.

[0025]FIGS. 1 and 2 are hydraulic circuit diagrams showing a hydraulic system of construction machinery according to one embodiment.

[0026]With reference to FIGS. 1 and 2, the hydraulic system 1 of construction machinery according to an embodiment of the present invention is a system for controlling hydraulic pressure to allow either a travel unit of the construction machinery to operate independently (hereinafter referred to as "travel-only operation") to enable travel, or to allow both the travel unit and a front working implement to operate in combination (hereinafter referred to as "combined travel-work operation") to simultaneously perform travel and front work, and may include a first hydraulic pump 101, a second hydraulic pump 102, a first traveling motor 201 operable by working fluid discharged from the first hydraulic pump 101, a second ...

Claims

1. A hydraulic system for construction machinery, the system comprising a first and a second hydraulic pump; a first and a second traveling motor, each configured to be driven by working fluid discharged from the respective first and second hydraulic pumps; a front working implement configured to be driven by working fluid discharged from the first and second hydraulic pumps; a travel straight spool valve including a first section, in which, during travel-only operation, working fluid discharged from the first hydraulic pump is supplied to the first traveling motor and working fluid discharged from the second hydraulic pump is supplied to the second traveling motor, and a second section, in which, during combined travel-work operation, working fluid discharged from the first hydraulic pump is supplied to both the first and second travel motors and working fluid discharged from the second hydraulic pump is supplied to the front working implement; and a control unit configured to gradually change the supply flow rates of the first and second hydraulic pumps according to a section switching rate when switching between the sections of the travel straight spool valve.

2. The hydraulic system for construction machinery according to claim 1, further comprising: a first and a second traveling spool configured to respectively control flow rates of working fluid supplied to a first and a second traveling motor; and a working implement spool comprising a first working implement spool group and a second working implement spool group, the working implement spool being configured to control a flow rate of working fluid supplied to a front working implement.

3. The hydraulic system for construction machinery according to claim 2, wherein the second section comprises: a first port having one side connected to the first hydraulic pump and the other side connected to the second traveling spool; and a second port having one side connected to the second hydraulic pump and the other side connected to the first working implement spool group.

4. The hydraulic system for construction machinery according to claim 3, wherein a check valve and an orifice are disposed between the second working implement spool group connected to the second hydraulic pump, and the second traveling spool.

5. The hydraulic system for construction machinery according to claim 4, wherein the control unit comprises a switching flow rate calculation unit configured to calculate flow rates of working fluid supplied from the first hydraulic pump and the second hydraulic pump based on a section switching ratio of a travel straight spool valve.

6. The hydraulic system for construction machinery according to claim 5, wherein the switching flow rate calculation unit is configured to calculate a flow rate of the first hydraulic pump QP1, based on a section switching ratio of the travel straight spool valve, as: Q P 1 = Q TL + Gain A × Q TR × ratio × Q P 1 Att × 1 − ratio , and to calculate a flow rate of the second hydraulic pump QP2 as: Q P 2 = Q P 1 Att × ratio + Q TR × 1 − ratio + Q P 2 Att , wherein QTL is a flow rate of the first traveling motor, Gain A is a correction factor for the flow rate of working fluid passing through the orifice, QTR is a flow rate of the second travel motor, QP1Att is a flow rate of the first working implement spool group, and QP2Att is a flow rate of the second working implement spool group.

7. A hydraulic system for construction machinery, comprising: a first and a second hydraulic pump; a first and a second traveling motor operable by working fluid discharged from the first and second hydraulic pumps, respectively; a front working implement operable by working fluid discharged from the first and second hydraulic pumps; a travel straight spool valve comprising: a first section configured to supply working fluid discharged from the first hydraulic pump to the first travel motor and working fluid discharged from the second hydraulic pump to the second travel motor during a travel-only operation; and a second section configured to supply working fluid discharged from the first hydraulic pump to the first and second travel motors and supply working fluid discharged from the second hydraulic pump to the front working implement during a combined travel-work operation; and a control unit configured to limit a maximum supply flow rate of the working fluid discharged from the first and second hydraulic pumps during the travel-only operation to be equal to or less than a maximum supply flow rate of the working fluid discharged from the first hydraulic pump during the combined travel-work operation.

8. The hydraulic system for construction machinery according to claim 7, wherein the control unit comprises a mode setting unit configured to set one or more modes selected from: a travel mode prioritizing straight travel performance; a work mode prioritizing work performance; and a neutral mode in which straight travel performance and work performance are equally balanced.

9. The hydraulic system for construction machinery according to claim 8, wherein the control unit comprises a maximum flow rate setting unit configured to limit a maximum supply flow rate of working fluid discharged from the first hydraulic pump and the second hydraulic pump based on the mode set by the mode setting unit.

10. The hydraulic system for construction machinery according to claim 9, wherein the maximum flow rate setting unit limits, in the neutral mode, a maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during travel-only operation to the maximum supply flow rate of working fluid discharged from the first hydraulic pump during combined travel-work operation.

11. The hydraulic system for construction machinery according to claim 9, wherein the maximum flow rate setting unit, in the travel mode during combined travel-work operation, sets the maximum supply flow rate of working fluid discharged from the first hydraulic pump to a maximum level and limits the maximum supply flow rate of working fluid discharged from the second hydraulic pump to be less than the maximum supply flow rate of working fluid discharged from the first hydraulic pump.

12. The hydraulic system for construction machinery according to claim 11, wherein the travel mode includes a plurality of sub-modes, and the maximum flow rate setting unit limits the maximum supply flow rate of working fluid discharged from the second hydraulic pump to different values for each of the sub-modes of the travel mode.

13. The hydraulic system for construction machinery according to claim 9, wherein, in the work mode during combined travel-work operation, the maximum flow rate setting unit sets the maximum supply flow rate of working fluid discharged from the second hydraulic pump to a maximum level and limits the maximum supply flow rate of working fluid discharged from the first hydraulic pump to be less than the maximum supply flow rate of working fluid discharged from the second hydraulic pump.

14. The hydraulic system for construction machinery according to claim 13, wherein the work mode includes a plurality of sub-modes, and the maximum flow rate setting unit limits the maximum supply flow rate of working fluid discharged from the first hydraulic pump to different values for each of the sub-modes of the work mode.

15. A hydraulic system for construction machinery, comprising: a first and a second hydraulic pump; a first and a second traveling motor operable by working fluid discharged from the first and second hydraulic pumps, respectively; a front working implement operable by working fluid discharged from the first and second hydraulic pumps; a travel straight spool valve including a first section configured to supply working fluid discharged from the first hydraulic pump to the first travel motor and working fluid discharged from the second hydraulic pump to the second travel motor during a travel-only operation; and a second section configured to supply working fluid discharged from the first hydraulic pump to both the first and second travel motors, and to supply working fluid discharged from the second hydraulic pump to the front work device during a combined travel-work operation; and a control unit, the control unit including: a mode setting unit configured to set one or more modes selected from among a travel mode prioritizing straight travel performance, a work mode prioritizing work performance, and a neutral mode in which straight travel performance and work performance are equally prioritized; and a maximum flow rate setting unit configured to, when either the travel mode or the work mode is set by the mode setting unit, limit a maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during travel-only operation to be equal to or less than a maximum supply flow rate of working fluid discharged from the first hydraulic pump during combined travel-work operation, and to, when the neutral mode is set by the mode setting unit, set the maximum supply flow rate of working fluid discharged from the first and second hydraulic pumps during travel-only operation to a maximum level.

Images