Hydraulic system of construction machine

Abstract

The present disclosure relates to a hydraulic system of a construction machine. The hydraulic system of the construction machine includes: an electronic proportional pressure reducing valve configured to control a flow rate, to which a maximum pressure is input as a control current value, and which is set to a minimum flow rate; a gear pump configured to provide pilot operation oil to the EPPRV; a shuttle valve configured to compare a pressure of first pilot operation oil passing through the EPPRV and a pressure of a flow rate control signal, and output second pilot operation oil having the greater pressure; a hydraulic pump of which a swash plate angle is controlled by the second pilot operation oil; and a pump control device configured to control a pressure of the EPPRV to be decreased from a maximum pressure by a predetermined inclination when the flow rate control signal is generated.

Claims

1. A hydraulic system of a construction machine, comprising: an electronic proportional pressure reducing valve (EPPRV) configured to control a flow rate, to which a maximum pressure is input as a control current value, and which is set to a minimum flow rate; a gear pump configured to provide pilot operation oil to the EPPRV; a shuttle valve configured to compare a pressure of first pilot operation oil passing through the EPPRV and a pressure of a flow rate control signal, and output second pilot operation oil having the greater pressure; a hydraulic pump of which a swash plate angle is controlled by the second pilot operation oil; and a pump control device configured to control the pressure of first pilot operation oil to be decreased from a maximum pressure by a predetermined inclination when the flow rate control signal is generated.

2. The hydraulic system of claim 1, wherein a plurality of pressures of the flow rate control signal is input by first and second flow rate control signal lines, the shuttle valve includes a first shuttle valve configured to compare a first pressure of the first flow rate control signal line and the first pilot operation oil pressure and output the greater pressure as third pilot operation oil, and a second shuttle valve configured to compare a second pressure of the second flow rate control signal line and the first pilot operation oil pressure, and output the greater pressure as fourth pilot operation oil and the hydraulic pump includes a first hydraulic pump of which a swash plate angle is controlled by the third pilot operation oil, and a second hydraulic pump of which a swash plate angle is controlled by the fourth pilot operation oil.

3. The hydraulic system of claim 1, wherein when the flow rate control signal is not generated, the pump control device controls the maximum pressure to be input as the control current value, and setting of the minimum flow rate to be returned.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram for describing a hydraulic system for a construction machine.

(2) FIG. 2 is a diagram for describing a control of a mechanical hydraulic pump in the hydraulic system of the construction machine.

(3) FIG. 3 is a diagram for describing a change in a flow rate in a constant horse power control in the hydraulic system of the construction machine in the related art.

(4) FIG. 4 is a diagram for describing a change in a pump discharged flow rate, a change in an rpm of an engine, and a change in an output of the engine by an operation of a joystick in the hydraulic system of the construction machine in the related art.

(5) FIG. 5 is a diagram for describing a hydraulic system of a construction machine according to an exemplary embodiment of the present disclosure.

(6) FIG. 6 is a diagram for describing a change in a flow rate by a flow rate control and a power shift control in the hydraulic system of the construction machine according to the exemplary embodiment of the present disclosure.

(7) FIG. 7 is a diagram for describing a change in a pump discharged flow rate by an operation of a joystick in the hydraulic system of the construction machine according to the exemplary embodiment of the present disclosure.

(8) FIG. 8 is a diagram for describing a change in pump input horse power by an operation of the joystick in the hydraulic system of the construction machine according to the exemplary embodiment of the present disclosure.

(9) FIG. 9 is a diagram for describing a change in a pump regulator control pressure of a discharged hydraulic pressure by an operation of the joystick in the hydraulic system of the construction machine according to the exemplary embodiment of the present disclosure.

(10) FIG. 10 is a diagram for describing a change in an rpm of the engine and a change in an output of the engine by an operation of the joystick in the hydraulic system of the construction machine according to the exemplary embodiment of the present disclosure.

(11) TABLE-US-00001 Description of Main Reference Numerals of Drawings 10: Hydraulic pump 11, 12: First and second hydraulic 20: Main control valve (MCV) pumps 40, 40a: Pump regulator 30: Actuator 60: Electronic proportional 50: Pump control device pressure reducing valve (EPPR) 70: Gear pump 80: Shuttle valve 81, 82: First and second shuttle 100: Engine valves 104: Engine control unit (ECU) 102: Engine rpm controller L1~L5: First to fifth hydraulic lines 106: Engine governor s1~s2: First and second signal lines pi: Flow rate control signal line pi-1, pi-2: First and second flow rate control signal lines r: Swash plate r1, r2: First, second swash plate

DETAILED DESCRIPTION

(12) Advantages and characteristics of the present disclosure, and a method of achieving the advantages and characteristics will be clear with reference to an exemplary embodiment described in detail together with the accompanying drawings.

(13) Throughout the specification, the same reference numeral denotes the same constituent element, and the same reference numeral is assigned to the same constituent element as that of the related art, and thus a repeated description will be omitted.

(14) In the meantime, the terms used in the description below are defined considering the functions of the present disclosure, and may vary depending on the intention or usual practice of a manufacturer, so that the definitions thereof should be made based on the entire contents of the present specification.

(15) Hereinafter, a hydraulic system of a construction machine according to an exemplary embodiment of the present disclosure will be described with reference to FIG. 5.

(16) FIG. 5 is a diagram for describing a hydraulic system of a construction machine according to an exemplary embodiment of the present disclosure.

(17) A hydraulic pump 10 includes a first hydraulic pump 11 and a second hydraulic pump 12. The first and second hydraulic pumps 11 and 12 become first and second swash plates r1 and r2, respectively.

(18) A plurality of spools is provided inside a main control valve 20. More particularly, the main control valve 20 includes a first spool group handled by the first hydraulic pump 11, and a second spool group handled by the second hydraulic pump 12.

(19) The first spool group includes an arm 1 spool, a boom 2 spool, a swing spool, an option spool, and a right travel motor (Travel R) spool.

(20) The second spool group includes an arm 2 spool, a boom 1 spool, a bucket spool, and a left travel motor (Travel L) spool.

(21) Further, two joysticks may be provided, and pilot pressures for operating a specific spool among the plurality of spools is formed by operating the joysticks in a left-right direction and a front-rear direction, respectively. Each of the pilot pressures is provided to the main control valve 20 through first and second flow rate control signal lines pi-1 and pi-2.

(22) In the meantime, a gear pump 70 is provided at one side of the first and second hydraulic pumps 11 and 12. A first hydraulic line L1 is provided so that pilot operation oil discharged from the gear pump 70 passes through an electronic proportional pressure reducing valve 60 to be connected to a first shuttle valve 81. One side of the first shuttle valve 81 is connected to the first flow rate control signal pi-1 to receive a first pressure.

(23) The first shuttle valve 81 selects a larger pressure between a first pilot operation oil pressure of the first hydraulic line L1 and the first pressure of the first flow rate control signal, and provides the selected pressure to a pump regulator 40 through a second hydraulic line L2. The pump regulator 40 controls a swash plate angle of the first hydraulic pump 11. Similarly, the second shuttle valve 82 selects a larger pressure between a first pilot operation oil pressure of the first and fourth hydraulic lines L1 and L4 and a second pressure of the second flow rate control signal, and provides the selected pressure to a pump regulator 40a through a fifth hydraulic line L5. The pump regulator 40a controls a swash plate angle of the second hydraulic pump 12.

(24) Further, the pilot operation oil discharged from the gear pump 70 passes through the electronic proportional pressure reducing valve 60 to become first pilot operation oil, and the fourth hydraulic line L4 is connected to the second shuttle valve 82. One side of the second shuttle valve 82 is connected to the second flow rate control signal line pi-2 to receive a second pressure. In the meantime, the first hydraulic line L1 and the fourth hydraulic line L4 are provided to be connected so that the pilot operation oil bilaterally flows.

(25) The second shuttle valve 82 selects a larger pressure between the first pilot operation oil pressure of the fourth hydraulic line L4 and the second pressure of the second flow rate control signal line pi-2, and makes the selected pressure pass through the second hydraulic line L2 and control the swash plate of the second hydraulic pump 12.

(26) That is, the pilot operation oil discharged from the gear pump 70 is provided to the first and second shuttle valves 81 and 82 in an opened state of the electronic proportional pressure reducing valve 60 to control the swash plate angles of the first and second hydraulic pumps 11 and 10.

(27) In the meantime, the electronic proportional pressure reducing valve (EPPRV) 60 for the flow rate control is set so that a maximum pressure is input to the EPPRV 60 as a control current value, and a flow rate is set to a minimum flow rate to be maintained.

(28) Further, in the hydraulic system according to the exemplary embodiment of the present disclosure, there is no input from the joystick in an idle state, in which an operation device of the construction machine does not move, so that a maximum pressure is input as a pressure of a foot relief valve.

(29) The EPPRV 60 is used for controlling an optional flow rate in a general situation, and in a case where an optional operation is not performed, the flow rate control signal is not generated, so that the EPPRV 60 may return to an initial state to be used for controlling an operation flow rate. That is, the EPPRV 60 described in the present disclosure may be used when the flow rate control for the first and second hydraulic pumps 11 and 12 is performed by operating the joystick.

(30) Particularly, when an optional operation (ex. a breaker/shear) is performed, a flow rate control signal Pi of the hydraulic pump, which is not used for the optional operation, is high (for example, a negative control), so that the discharged flow rate is minimum and thus the optional operation may be performed.

(31) Further, when an operation other than the optional operation is performed, a pressure corresponding to pressures of the flow rate control signals Pi, pi-1, and pi-2 is set as the current of the EPPRV 60 in an idle state, so that when the actuator 30 is operated, an inclination of the EPPRV 60 may be appropriately adjusted in accordance with the sharply decreased pressures of the flow rate control signals Pi, pi-1, and pi-2 to prevent a rotation speed of the engine from being decreased.

(32) Hereinafter, an operation of the hydraulic system of the construction machine according to the present disclosure will be described with reference to FIGS. 6 to 10.

(33) FIG. 6 is a diagram for describing a change in a flow rate by a flow rate control and a power shift control in the hydraulic system of the construction machine according to the exemplary embodiment of the present disclosure.

(34) As illustrated in FIG. 6, in a Comparative Example, an excessive flow rate is discharged by a response delay of the pump regulators 40 and 40a before the pump flow rate reaches the stabilization by the constant horse power control.

(35) That is, in the Comparative Example of the related art, the flow rate is sharply increased (q1.fwdarw.q2) from a time point (Pi start point), at which the joystick is operated, to a time point (Pi end point), at which the operation of the joystick is ended, by the flow rate control. Then, the power shift control reacts with a time difference due to the response delay to decrease the flow rate to a flow rate q3 so that the belatedly increased pump load is maintained at an end point of the pump load pressure (Pd end point).

(36) As described above, in the Comparative Example of the related art, the excessive flow rate discharge generated when the joystick is sharply operated may not be controlled, and further, the horse power consumed by the pump is increased according to the excessive flow rate increase, so that the load of the engine is increased, and thus the pump power shift control is performed by the control of the target rpm to decrease the flow rate of the pump, thereby causing deterioration in equipment performance.

(37) However, the hydraulic system according to the present disclosure may promptly increase the load of the pump by promptly operating the pump regulators 40 and 40a with the pilot operation oil flowing from the gear pump 70, and thus the power shift control prevents the flow rate from being excessively discharged at the initial stage, thereby smoothly implementing an increase tendency of the flow rate.

(38) Particularly, when the joystick is operated, the pressure of the flow control signal is sharply increased from the time point (Pi start point), at which the joystick is operated, to the time point (Pi end point) at which the operation of the joystick is ended, and the hydraulic system according to the present disclosure decreases the pressure from the maximum pressure by a predetermined inclination by using the EPPRV 60 for the flow rate control, thereby controlling the discharged flow rate to be smoothly increased.

(39) Accordingly, the hydraulic system according to the present disclosure may adjust a rate of the pump horse power increase by the excessive discharged flow rate, and may be minimally influenced by the pump power shift control according to the load of the engine, which is the problem in the hydraulic system in the related art, thereby preventing equipment performance from deteriorating and being advantageous to operate the equipment.

(40) Further, the excessive discharged flow rate of the first and second hydraulic pumps 11 and 12 is controlled, so that an equipment impact is decreased, and the discharged flow rate is smoothly increased, thereby improving general controllability when a joystick is operated.

(41) A change in a pump discharged flow rate will be described with reference to FIG. 7. FIG. 7 is a diagram for describing a change in a pump discharged flow rate by an operation of the joystick in the hydraulic system of the construction machine according to the exemplary embodiment of the present disclosure.

(42) As illustrated in FIG. 7, in the Comparative Example, when the joystick is suddenly operated, the flow rate is sharply increased just after a time point t1, at which the joystick is operated, so that a delta flow rate Qp is excessively discharged, and the flow rate is stabilized from a stabilization time point t2 after a predetermined time elapses.

(43) However, in the hydraulic system according to the present disclosure, even though the joystick is suddenly operated, the pressure may be decreased from the maximum pressure by the predetermined inclination by the EPPRV 60 as described above, thereby controlling the discharged flow rate to be smoothly increased.

(44) Hereinafter, a change in pump input horse power will be described with reference to FIG. 8. FIG. 8 is a diagram for describing a change in pump input horse power by an operation of the joystick in the hydraulic system of the construction machine according to the exemplary embodiment of the present disclosure.

(45) As illustrated in FIG. 8, in the Comparative Example, when the joystick is suddenly operated, pump input horse power is sharply increased just after the time point t1, at which the joystick is operated, to form a peak, and then the pump input horse power is decreased, so that the pump input horse power is stabilized from a stabilization time point t2 after a predetermined time elapses.

(46) However, in the hydraulic system according to the present disclosure, even though the joystick is suddenly operated, the pressure may be decreased from the maximum pressure by the predetermined inclination by the EPPRV 60 as described above, thereby controlling the pump input horse power to be smoothly increased by a predetermined inclination.

(47) Hereinafter, a change in a discharged hydraulic pressure will be described with reference to FIG. 9. FIG. 9 is a diagram for describing a change in a pump regulator control pressure of a discharged hydraulic pressure by an operation of the joystick in the hydraulic system of the construction machine according to the exemplary embodiment of the present disclosure.

(48) As illustrated in FIG. 9, a pump regulator control pressure is a pressure applied to the first and fifth hydraulic lines L2 and L5, and a pressure for substantially controlling the first and second swash plates r1 and r2 of the first and second hydraulic pumps.

(49) As illustrated in FIG. 9, in the Comparative Example, when the joystick is suddenly operated, the pump regulator control pressure is sharply decreased just after the time point t1 at which the joystick is operated. Then, the pump regulator control pressure is stabilized from the stabilization time point t2 after a predetermined time elapses.

(50) However, in the hydraulic system according to the present disclosure, even though the joystick is suddenly operated, the pressure may be decreased from the maximum pressure by the predetermined inclination by the EPPRV 60 as described above, thereby controlling the pump input horse power to be smoothly decreased at a predetermined inclination.

(51) Hereinafter, a change in a characteristic of the engine will be described with reference to FIG. 10. FIG. 10 is a diagram for describing a change in an rpm of the engine and a change in an output of the engine by an operation of the joystick in the hydraulic system of the construction machine according to the exemplary embodiment of the present disclosure.

(52) As illustrated in FIG. 10, when the demanded flow rate is increased, or the high horse power is demanded, the rpm of the engine is increased. However, in order to increase the rpm of the engine to the target rpm of the engine to implement a desired output of the engine, a predetermined time is required.

(53) That is, an engine governing section is essentially required to increase the rpm of the engine, and a time, at which the turbo charger normally performs a function, is included in the engine governing section. When the turbo charger does not normally perform the normal function, a high rpm of the engine may not be expected.

(54) The Comparative Example represents a change trend of the rpm of the engine in the hydraulic system in the related art, and the load of the pump is sharply increased just after the joystick is suddenly operated, so that the rpm of the engine is sharply decreased at a large level (see the delta rpm of the Comparative Example).

(55) When the rpm of the engine reaches the desired target rpm after the time of the engine governing section elapses, the rpm is gradually stabilized.

(56) However, in the hydraulic system according to the exemplary embodiment of the present disclosure, the load of the pump applied to the pump is gradually increased, so that even though the rpm of the engine is decreased, the rpm of the engine is decreased at a relatively small level in comparison with that of the Comparative Example (see the delta rpm of the Example).

(57) That is, the pump power shift control according to the load of the engine is minimally applied, so that it is possible to prevent equipment performance from deteriorating, which is advantageous to operate equipment of the construction machine.

(58) Further, the rpm of the engine reaches the desired target rpm while the time of the engine governing section elapses after the rpm of the engine is decreased, and the decrease level of the rpm of the engine is small, so that the rpm of the engine may more promptly reach the desired target rpm to be stabilized.

(59) In the hydraulic system of the construction machine adopting the mechanical hydraulic pump according to the present disclosure, which is configured as described above, it is possible to control the flow rate discharged from the hydraulic pump to be smoothly increased by controlling the hydraulic pump so as to decrease a pressure from a maximum pressure by a predetermined inclination by the electronic proportional pressure reducing valve even though a demanded flow rate is sharply increased, thereby preventing a hydraulic impact.

(60) Further, in the hydraulic system of the construction machine adopting the mechanical hydraulic pump according to the present disclosure, it is possible to prevent a load of the engine from being sharply increased by smoothly increasing pump input horse power, thereby preventing an rpm of the engine from being sharply decreased, and improving fuel efficiency.

(61) The exemplary embodiments of the present disclosure have been described with reference to the accompanying drawings, but those skilled in the art will understand that the present disclosure may be implemented in another specific form without changing the technical spirit or an essential feature thereof.

(62) Accordingly, it will be understood that the aforementioned exemplary embodiments are described for illustration in all aspects and are not limited, and it will be construed that the scope of the present disclosure of the detailed description is represented by the claims to be described below, and all of the changes or modified forms induced from the meaning and the scope of the claims, and an equivalent concept thereof are included in the scope of the present disclosure.

(63) The hydraulic system of the construction machine according to the present disclosure may be used for decreasing fuel consumption when a joystick is suddenly operated and improving manipulability in the hydraulic system adopting a mechanical hydraulic pump.

(64) Although the present disclosure has been described with reference to exemplary and preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosure.