EP2094915A1 - Hydraulic system for improving flatting workability in an excavator - Google Patents

Hydraulic system for improving flatting workability in an excavator

Info

Publication number
EP2094915A1
EP2094915A1 EP07851716A EP07851716A EP2094915A1 EP 2094915 A1 EP2094915 A1 EP 2094915A1 EP 07851716 A EP07851716 A EP 07851716A EP 07851716 A EP07851716 A EP 07851716A EP 2094915 A1 EP2094915 A1 EP 2094915A1
Authority
EP
European Patent Office
Prior art keywords
boom
control valve
switched
pilot line
directional control
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP07851716A
Other languages
German (de)
French (fr)
Other versions
EP2094915A4 (en
EP2094915B1 (en
Inventor
Yong-Chae Kim
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
HD Hyundai Infracore Co Ltd
Original Assignee
Doosan Infracore Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Doosan Infracore Co Ltd filed Critical Doosan Infracore Co Ltd
Publication of EP2094915A1 publication Critical patent/EP2094915A1/en
Publication of EP2094915A4 publication Critical patent/EP2094915A4/en
Application granted granted Critical
Publication of EP2094915B1 publication Critical patent/EP2094915B1/en
Not-in-force legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F3/00—Dredgers; Soil-shifting machines
    • E02F3/04—Dredgers; Soil-shifting machines mechanically-driven
    • E02F3/28—Dredgers; Soil-shifting machines mechanically-driven with digging tools mounted on a dipper- or bucket-arm, i.e. there is either one arm or a pair of arms, e.g. dippers, buckets
    • E02F3/36—Component parts
    • E02F3/42—Drives for dippers, buckets, dipper-arms or bucket-arms
    • E02F3/43—Control of dipper or bucket position; Control of sequence of drive operations
    • E02F3/435—Control of dipper or bucket position; Control of sequence of drive operations for dipper-arms, backhoes or the like
    • E02F3/437—Control of dipper or bucket position; Control of sequence of drive operations for dipper-arms, backhoes or the like providing automatic sequences of movements, e.g. linear excavation, keeping dipper angle constant
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/14—Booms only for booms with cable suspension arrangements; Cable suspensions
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2203—Arrangements for controlling the attitude of actuators, e.g. speed, floating function
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2221—Control of flow rate; Load sensing arrangements
    • E02F9/2239—Control of flow rate; Load sensing arrangements using two or more pumps with cross-assistance
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2264—Arrangements or adaptations of elements for hydraulic drives
    • E02F9/2267—Valves or distributors
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2278—Hydraulic circuits
    • E02F9/2285—Pilot-operated systems
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2278—Hydraulic circuits
    • E02F9/2292—Systems with two or more pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B13/00—Details of servomotor systems ; Valves for servomotor systems
    • F15B13/02—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors
    • F15B13/021—Valves for interconnecting the fluid chambers of an actuator
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B13/00—Details of servomotor systems ; Valves for servomotor systems
    • F15B13/02—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors
    • F15B13/04—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor
    • F15B13/0401—Valve members; Fluid interconnections therefor
    • F15B2013/0413—Valve members; Fluid interconnections therefor with four or more positions
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/305—Directional control characterised by the type of valves
    • F15B2211/3056—Assemblies of multiple valves
    • F15B2211/3059—Assemblies of multiple valves having multiple valves for multiple output members
    • F15B2211/30595—Assemblies of multiple valves having multiple valves for multiple output members with additional valves between the groups of valves for multiple output members
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/31—Directional control characterised by the positions of the valve element
    • F15B2211/3122—Special positions other than the pump port being connected to working ports or the working ports being connected to the return line
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/31—Directional control characterised by the positions of the valve element
    • F15B2211/3122—Special positions other than the pump port being connected to working ports or the working ports being connected to the return line
    • F15B2211/3133—Regenerative position connecting the working ports or connecting the working ports to the pump, e.g. for high-speed approach stroke
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/32—Directional control characterised by the type of actuation
    • F15B2211/321—Directional control characterised by the type of actuation mechanically
    • F15B2211/324—Directional control characterised by the type of actuation mechanically manually, e.g. by using a lever or pedal
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/32—Directional control characterised by the type of actuation
    • F15B2211/327—Directional control characterised by the type of actuation electrically or electronically
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/32—Directional control characterised by the type of actuation
    • F15B2211/329—Directional control characterised by the type of actuation actuated by fluid pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/355—Pilot pressure control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/635—Circuits providing pilot pressure to pilot pressure-controlled fluid circuit elements
    • F15B2211/6355—Circuits providing pilot pressure to pilot pressure-controlled fluid circuit elements having valve means

Definitions

  • the present invention relates to a hydraulic system for an excavator, which is improved so as to easily perform flatting work on a plain or inclined ground and, more particularly, to a hydraulic system for an excavator, which enables an unskilled operator of the excavator to perform flatting work on a plain or inclined ground.
  • the flatting work of a plain or inclined ground is carried out as a part of compacting work after the ground is leveled.
  • a bucket of the excavator is pulled, while pressing the ground in the state in which a flat part of the bucket is in contact with the ground, thereby pressing and simultaneously flattening the ground, similarly ironing clothes with iron.
  • the flatting work is carried out by combined operation of a boom, an arm and a bucket with pressing the ground and simultaneously pulling the arm in the state in which the flat part of the bucket is in contact with the ground, which is essential work for making a flatly pressed surface in the plain or inclined ground
  • the force pressing the ground must be uniform to some extent.
  • the pressing work causes a problem with uniformity in flatness of the ground.
  • the force pressing the ground is determined by mechanical force applied to the bucket through the combined operation of the boom, the arm and the bucket. However, it is not easy to properly apply the mechanical force to the ground. This can be realized only by skilled operation of a joystick of the excavator. Further, in addition to the application of the uniform force, the flat part of the bucket must be continuously in contact with the ground.
  • the boom, the arm and the bucket of the excavator are operated by the joystick.
  • the typical joystick of the excavator is provided with a swing lever for swinging a body of the excavator and an arm lever for dump/crowd operation of the arm, which are installed on one side within driver's reach, and a lever for up/down operation of the boom and a lever for dump/crowd operation of the bucket, which are installed on the other side within driver's reach.
  • the results of the work are dependent on how properly the joystick is operated.
  • an object of the present invention is to provide a hydraulic system for an excavator, which enables even an unskilled operator, who is short of skill or technique of the operation of equipment, to easily perform flatting work on a plain or inclined ground.
  • the present invention provides a hydraulic system for an excavator having a boom, arm and bucket, which is structurally improved so as to easily perform flatting work on a plain or inclined ground.
  • a hydraulic system for an excavator which comprises: a pump; a boom cylinder, which drives a boom so as to be lifted and lowered using hydraulic operating fluid supplied from the pump; and a boom control valve 22, which controls flow of the hydraulic operating fluid supplied from the pump to the boom cylinder and controls operation of the boom cylinder, wherein the boom control valve 22 can be switched to one of a first position for maintaining neutrality of the boom, a second position for lifting the boom, a third position for lowering the boom, and a fourth position for allowing the boom to be freely lifted and lowered by self- weight or external force, and the boom control valve 22 blocks the hydraulic operating fluid supplied from the pump to the boom cylinder and allows head-side and rod-side chambers of the boom cylinder to communicate with each other at the fourth position thereof.
  • the hydraulic system further comprises a stopper 11, which restricts the boom control valve 22 from being switched to the fourth position so as to allow the boom control valve 22 to be switched only to one of the first, second and third positions.
  • the fourth position of the boom control valve 22 is located at one outermost port of the boom control valve, and the stopper 11 is connected to the other outermost port of the boom control valve 22 and supplies a predetermined hydraulic pressure to the other outermost port so as to restrict the boom control valve from being switched to the fourth position.
  • the hydraulic system further comprises a gear pump 9; a pilot line Pi2 connecting the stopper 11 and the gear pump 9; and a first directional control valve 8, which is installed on the pilot line Pi2 and is switched between a first position where the pilot line Pi2 communicates with the gear pump 9 and a second position where the pilot line Pi2 communicates with a tank.
  • the hydraulic system of the present invention further comprises a directional control switch 20 for switching the first directional control valve 8.
  • the directional control switch 20 is selectively switched to one of: a first position (excavating work position or Mode 1) where the first directional control valve 8 is switched to the first position, where the stopper 11 communicates with the gear pump 9 through the pilot line Pi2, and where the stopper 11 is functionally activated to restrict the boom control valve 22 from being switched to the fourth position; and a second position (flatting work position or Mode 2) where the first directional control valve 8 is switched to the second position, where the pilot line Pi2 communicates with the tank T, and where the stopper 11 is functionally inactivated to allow the boom control valve 22 to be switched to the fourth position.
  • the first position of the directional control switch corresponds to a position that is indicated by Mode 1 in FIGS. 3 and 4, which is for the excavating work. Further, the second position of the directional control switch corresponds to a position that is indicated by Mode 2 in FIGS. 3 and 4, which is for the flatting work.
  • the boom control valve 22 in order to allow the ordinary excavating work to be carried out even if the directional control switch 20 is switched so as to select the flatting work position, the boom control valve 22 is switched up to the fourth position only when the boom-up side port Pi thereof has pressure equal to or greater than a preset reference pressure, and is switched only to one of the first, second and third positions when the pressure of the boom-up side port is less than the reference pressure.
  • the reference pressure is set to pressure occurring at the boom-up side port when an operator operates an operating lever beyond a predetermined displacement or angle in a direction where the boom is lifted.
  • a hydraulic system for an excavator which is structurally improved so as to easily perform flatting work, can be applied to a two-pump hydraulic system having two pumps.
  • a hydraulic system for improving flatting workability in an excavator which comprises: first and second pumps Pl and P2; a boom cylinder, which drives a boom so as to be lifted and lowered using hydraulic operating fluid supplied from the first and second pumps; and first and second boom control valves 2 and 3, which controls flow of the hydraulic operating fluid supplied from the first and second pumps to the boom cylinder and controls operation of the boom cylinder, wherein the first and second boom control valves 2 and 3 includes boom-up side ports hydraulically connected to a boom-up pilot line Pi, the hydraulic operating fluids passing through the first and second boom control valves 2 and 3 are joined and supplied to the boom cylinder when the boom is lifted, and the first boom control valve 2 can be switched to one of a first position for maintaining neutrality of the boom, a second position for lifting the boom, a third position for lowering the boom, and a fourth position for allowing the boom to be freely lifted and lowered by self-weight or external force by blocking the hydraulic operating fluid supplied from the pumps to the boom cylinder and
  • the hydraulic system further comprises a stopper 11, which restricts the first boom control valve 2 from being switched to the fourth position so as to allow the first boom control valve 2 to be switched only to one of the first, second and third positions.
  • the hydraulic system further comprises a first directional control valve 8 for controlling the stopper.
  • the hydraulic system of the present invention further comprises means for interrupting the connection of the boom-up pilot line Pi and the second boom control valve 3.
  • One example of the interrupting means includes a second directional control valve 10, which can be switched between a first position where the boom-up pilot line Pi is connected with the second boom control valve 3 and a second position where the boom-up pilot line Pi is disconnected from the second boom control valve 3.
  • the hydraulic system according to an example of the present invention further comprises a directional control switch 20 for switching the first directional control valve 8 and the second directional control valve 10.
  • the two-pump hydraulic system can be also designed so that, in order to allow the ordinary excavating work to be carried out even if the directional control switch 20 is switched so as to select the flatting work position, when the directional control switch 20 is switched to a first position, the first boom control valve 2 is switched up to the fourth position only when the boom-up side port Pi thereof has pressure equal to or greater than a preset reference pressure, and is switched only to one of the first, second and third positions when the pressure of the boom-up side port is less than the reference pressure.
  • FIG. 1 is a schematic view illustrating configuration of a boom control valve 22 and its peripheral attachments in a known excavator
  • FIG. 2 is a schematic view illustrating configuration of a boom control valve 22 and its peripheral attachments in an excavator according to an embodiment of the present invention
  • FIG. 3 is a hydraulic circuit diagram illustrating a two- pump hydraulic system having two pumps, which improves flatting workability, according to an example of the present invention
  • FIG. 4 schematically illustrates the first boom control valve 1 and its peripheral attachments in the hydraulic circuit diagram of FIG. 3;
  • FIG. 5 is a hydraulic circuit diagram illustrating a joystick that is an operating device of the excavator
  • FIG. 6 is a graph showing hydraulic characteristics of a pilot valve
  • FIG. 7 illustrates the state in which an excavator carries out flatting work on a plain ground
  • FIG. 8 illustrates the state in which an excavator carries out flatting work on an inclined ground.
  • stopper 20 directional control switch
  • FIG. 1 is a schematic view illustrating configuration of a boom control valve 22 and its peripheral attachments in an ordinary excavator having a boom, an arm and a bucket.
  • a boom control valve 22 can be switched to one of three positions: one for lifting a boom 24, one for maintaining neutrality of the boom 24, and one for lowering the boom 24, when viewed from the left side.
  • FIG. 2 is a schematic view illustrating configuration of a boom control valve 22 and its peripheral attachments in an excavator according to an embodiment of the present invention.
  • the boom control valve 22 has a first position for maintaining neutrality of a boom 24, a second position for lifting the boom 24, a third position for lowering the boom 24, and a fourth position for allowing the boom 24 to be lifted and lowered by self-weight or external force.
  • the boom control valve 22 can be switched to one of the four positions.
  • the boom control valve 22 can be operated by a boom-up pilot signal Pi and a boom down pilot signal, which are generated by manipulation of a joystick of an excavator operator (see FIG. 5) .
  • the operator does not require to carry out boom-up or boom-down operation.
  • the flatting work can be done by operating only the bucket and arm in the state in which the boom control valve is fixed to a preset position, i.e. the fourth position.
  • the boom control valve is fixed to the fourth position, the arm is stretched to the maximum extent, and thereby the bucket is located at a place remotest from a body of the excavator, as illustrated in FIGS. 7 and 8.
  • a flat outer surface of the bucket is controlled to be parallel to the ground.
  • an arm controlling joystick is controlled toward a crowd side, so that the flatting work is naturally carried out while the arm is pulled.
  • the bucket must be controlled such that the flat outer surface thereof is parallel to the ground. In this case, since the flat outer surface of the bucket has only to be minutely controlled while performing simple operation of pulling the arm (arm crowd operation) , the flatting work can be easily carried out.
  • the hydraulic system comprises a stopper 11, which controls the boom control valve 22 to prevent from being arbitrarily switched to the fourth position.
  • the boom control valve 22 is further provided with the stopper 11 on one side thereof which restricts the boom control valve 22 from being switched to the fourth position so as to allow the boom control valve 22 to be switched only to one of the first, second and third positions.
  • the boom control valve 22 has the fourth position adjacent to a boom-up side port thereof, that is, one outermost port thereof, and the stopper 11 is connected to another outermost port, that is, a boom-down side port. The application of a predetermined hydraulic pressure to the stopper restricts the boom control valve 22 from being switched to the fourth position.
  • the hydraulic system of the present invention can further comprise a first directional control valve 8 for controlling the stopper.
  • the hydraulic system further comprises a gear pump 9, and a pilot line Pi2 connecting the stopper 11 and the gear pump 9.
  • the first directional control valve can be installed on the pilot line Pi2.
  • the hydraulic system of the present invention can further comprise a directional control switch 20.
  • a work mode is determined by the directional control switch.
  • the boom control valve 22 can be adapted to be switched to the fourth position. In the other cases, the boom control valve 22 can be adapted to be not switched to the fourth position.
  • the directional control switch 20 can be selectively switched to one of a first position (Mode 1) and a second position (Mode 2) by manipulation of an operator.
  • the directional control switch is provided in a knob shape at a predetermined position within a cab (not shown) , and is electrically connected with the solenoid-type first directional control valve 8 as described below as well as a second directional control valve 10 in the next embodiment, which will be described below.
  • the first position of the directional control switch 20 refers to a position where the first directional control valve 8 is switched to the first position so as to allow the stopper 11 to communicate with the gear pump 9 through the pilot line Pi2.
  • the second position of the directional control switch 20 refers to a position where the first directional control valve 8 is switched to the second position so as to allow the pilot line Pi2 to communicate with a tank T.
  • the stopper 11 releases its function, so that the boom control valve 22 can be switched to the fourth position.
  • the first position of the directional control switch 20 corresponds to a position that is indicated by Mode 1 in FIGS. 3 and 4, which is for the excavating work.
  • the second position of the directional control switch 20 corresponds to a position that is indicated by Mode 2 in FIGS. 3 and 4, which is for the flatting work.
  • the directional control switch 20 may be adapted to carry out the ordinary excavating work.
  • a boom-up side hydraulic line Pi of the boom control valve 22 has pressure equal to and greater than a preset reference pressure, for instance 26k, the boom control valve 22 can be adapted to be switched to the fourth position.
  • a first boom control valve is adapted to be switched only to one of the first, second and third positions so as to be able to carry out the ordinary excavating work.
  • the pressure occurring when the operator pulls the operation lever of the joystick at a displacement of 10 mm in the direction where the boom is lifted can be set to become the preset reference pressure of the hydraulic line.
  • the first boom control valve can be adapted to be switched only to one of the first, second and third positions.
  • the first boom control valve can be adapted to be switched to one of the first through fourth positions.
  • FIG. 3 is a hydraulic circuit diagram illustrating a two-pump hydraulic system having two pumps according to an example of the present invention.
  • FIG. 4 schematically illustrates the first boom control valve 1 and its peripheral attachments in the hydraulic circuit diagram of FIG. 3.
  • FIG. 5 is a hydraulic circuit diagram illustrating a joystick that is an operating device of the excavator.
  • the hydraulic system illustrated in FIG. 3 comprises first and second pumps Pl and P2, a control valve section 21, an arm crowd pilot line Pac, a boom-up pilot line Pi, a first directional control valve 8, and a second directional control valve 10.
  • control valve section 21 includes first and second boom control valves 2 and 3, first and second arm control valves 4 and 5, and other valves such as a straight traveling control valve, a left/right turning control valve, an option control valve and a swing control valve.
  • first and second boom control valves 2 and 3 first and second arm control valves 4 and 5, and other valves such as a straight traveling control valve, a left/right turning control valve, an option control valve and a swing control valve.
  • other valves such as a straight traveling control valve, a left/right turning control valve, an option control valve and a swing control valve.
  • the first boom control valve 2 and the second arm control valve 5 communicate with the first pump Pl through a center parallel line Ps.
  • the second boom control valve 3 and the first arm control valve 4 communicate with the second pump P2 through another center parallel line Ps.
  • Hydraulic operating fluid passing through the second boom control valve 3 joins that passing through the first boom control valve 2 via a predetermined path A8', and then is supplied to a boom cylinder.
  • the boom-up side ports of the first and second boom control valves 2 and 3 are hydraulically connected to each other through the boom-up pilot line Pi. Further, it can be found that the boom-up side ports of the first and second boom control valves 2 and 3 are hydraulically connected to each other such that the hydraulic operating fluids passing through the first and second boom control valves 2 and 3 can be joined when the boom is lifted.
  • the first boom control valve 2 has a first position for maintaining neutrality of the boom, a second position for lifting the boom, a third position for lowering the boom, and a fourth position for allowing the boom 24 to be freely lifted and lowered by self-weight or external force.
  • the first boom control valve 2 can be switched to one of the four positions.
  • a neutral position is a position where inlet and outlet of the boom cylinder are closed.
  • the hydraulic system comprises a stopper 11, which restricts the first boom control valve 2 from being switched to the fourth position so as to allow the first boom control valve 2 to be switched only to one of the first, second and third positions. More specifically, the first boom control valve 2 has the fourth position adjacent to one outermost port thereof, and the stopper 11 is connected to the other outermost port. The application of a predetermined hydraulic pressure to the other port of the first boom control valve restricts the first boom control valve from being switched to the fourth position. In FIG. 3, the stopper 11 is installed on the boom-down side port of the first boom control valve 2.
  • the hydraulic system illustrated in FIGS. 3 and 4 can further comprise a gear pump 9, a pilot line Pi2 connecting the stopper 11 and the gear pump 9, and a first directional control valve 8, which is installed on the pilot line Pi2 and is switched between a first position where the pilot line Pi2 communicates with the gear pump 9 and a second position where the pilot line Pi2 communicates with a tank.
  • the stopper functions to prevent the first boom control valve from being switched to the fourth position when the first directional control valve 8 is switched to the first position, the communicating position.
  • the first boom control valve 2 can be switched to the fourth position.
  • the hydraulic operating fluid can be supplied to the boom cylinder through the second boom control valve 3.
  • the hydraulic system can employ a method of blocking the boom-up pilot line Pi applied to the second boom control valve 3 during the flatting work.
  • the two-pump hydraulic system can further comprise means for interrupting the connection of the boom-up pilot line Pi and the second boom control valve 3.
  • This interrupting means includes the second directional control valve 10.
  • the second directional control valve 10 can be adapted to be switched between a first position where the boom-up pilot line Pi is connected with the second boom control valve 3 and a second position where the boom-up pilot line Pi is disconnected from the second boom control valve 3.
  • the hydraulic system can further comprise a directional control switch 20, which switches the first directional control valve 8 and the second directional control valve 10.
  • the directional control switch 20 can be adapted to be selectively switched to one of: a first position where it switches the first directional control valve 8 to the first position and causes the stopper 11 to communicate with the gear pump 9 through the pilot line Pi2 such that the stopper 11 is functionally activated to restrict the first boom control valve 2 from being switched to the fourth position, and where it switches the second directional control valve 10 to the first position and causes the second boom control valve 3 to communicate with the boom-up pilot line Pi such that the first boom control valve 2 and the second boom control valve 3 can be switched in the diction where the boom is lifted; and a second position where it switches the first directional control valve 8 to the second position and causes the pilot line Pi2 to communicate with the tank T so that the stopper 11 is functionally inactivated to allow the first boom control valve 2 to be switched up to the fourth position, and where it switches the second directional
  • the first boom control valve 2 is connected with the boom-up pilot line Pi on the left side thereof, and is provided with the stopper 11 on the right side thereof.
  • the stopper 11 can communicate with the first directional control valve 8 at the first position of the first directional control valve 8, and thus can be supplied with the hydraulic operating fluid from the gear pump 9.
  • the pressure oil discharged from the first pump Pl flows through the center parallel line Ps, and the hydraulic operating fluid is supplied to the boom cylinder in response to the switching of the first boom control valve 2. Meanwhile, although the directional control switch 20 is operated so as to select the flatting work position, the excavator can be adapted to perform the ordinary excavating work.
  • the boom control valve 22 can be adapted to be switched to the fourth position.
  • the first boom control valve is adapted to be switched only to one of the first, second and third positions so as to be able to carry out the ordinary excavating work.
  • the first boom control valve can be adapted to be switched only to one of the first, second and third positions, but when the displacement is more than 10 mm, the first boom control valve can be adapted to be switched to one of the first through fourth positions.
  • This method of operating the boom-up joystick in order to switch the first boom control valve 2 to the fourth position can be changed to the case in which the boom 24 is operated in a lowering direction. In this case, the boom 24 will be operated in a manner such that it is lowered by its self-weight while being lowered.
  • the first directional control valve 8 When the operator switches the directional control switch 20 to the second position, which corresponds to the flatting work mode, for the purpose of the flatting work, the first directional control valve 8 is switched to the second position, and the pilot line Pi2 communicates with the tank T. As a result, the stopper 11 is functionally inactivated, and thus the first boom control valve 2 can be switched up to the fourth position. Further, the second directional control valve 10 is switched to the second position, thereby allowing the boom-up pilot line Pi of the second boom control valve 3 to communicate with the tank T, so that the second boom control valve 3 is not switched. At this time, when the first boom control valve 2 is switched to the fourth position, the inlet and outlet ports of the boom cylinder 23 communicate with each other.
  • the front including the boom is lowered by its self- weight, and the flat surface of the bucket comes into contact with the ground, so that pressing action occurs. Subsequently, when the arm is pulled in a crowd direction, the self-weight of the front is applied to the ground, so that the flatting work is realized as in FIGS. 7 and 8.
  • the hydraulic characteristics of the boom control valves 2 and 3 can be divided into two stages, as illustrated in FIG. 6, such that the operation thereof can be changed.
  • the first boom control valve 2 can be switched to one of the first, second and third positions under the conditions: pilot pressure of 20k and stroke of 10 mm or less, such that the ordinary excavating work permitting boom-up/-down operation is carried out. Only when the pilot pressure exceeds 20k, the first boom control valve 2 is adapted to be switched to the fourth position.
  • the second directional control valve 10 When the operator switches the directional control switch 20 to the first position for the purpose of the excavating work, the second directional control valve 10 is switched to the first position. Thereby, the boom-up pilot lines Pi of the first and second boom control valves 2 and 3 communicate to allow the first and second boom control valves 2 and 3 to be switched in the direction where the boom is lifted. Simultaneously, the first directional control valve 8 is switched to the first position, so that the stopper 11 of the boom-down side port of the first boom control valve 2 communicates with the gear pump 9 through the pilot line Pi2. Thereby, the function of the stopper 11 is restored, so that the first boom control valve 2 is prevented from being switched to the fourth position.
  • the first and second boom control valves 2 and 3 are operated within a range from the first position and the third position for the purpose of the excavating work, that is, the boom-up, boom-down and boom stop, so that the ordinary excavating work is performed together with the other front attachments.

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Abstract

Disclosed is a hydraulic system for an excavator, which is structurally improved so as to easily perform flatting work on a plain or inclined ground. A boom control valve has a fourth position on one side thereof such that a boom cylinder can be freely lifted and lowered by blocking a channel through which hydraulic operating fluid is supplied from a pump and by allowing hydraulic operating fluid inlet and outlet ports of the boom cylinder system to communicate with each other.

Description

HYDRAULIC SYSTEM FOR IMPROVING FLATTING WORKABILITY IN AN
EXCAVATOR
[Technical Field]
The present invention relates to a hydraulic system for an excavator, which is improved so as to easily perform flatting work on a plain or inclined ground and, more particularly, to a hydraulic system for an excavator, which enables an unskilled operator of the excavator to perform flatting work on a plain or inclined ground. [Background Art]
Among the works using an excavator, the flatting work of a plain or inclined ground is completely dependent on experience and skill of an operator of the excavator, and is known to be difficult by a beginner who is not skilled in the operation of equipment .
The flatting work of a plain or inclined ground, sometimes called ironing, is carried out as a part of compacting work after the ground is leveled. In the flatting work, a bucket of the excavator is pulled, while pressing the ground in the state in which a flat part of the bucket is in contact with the ground, thereby pressing and simultaneously flattening the ground, similarly ironing clothes with iron.
The flatting work is carried out by combined operation of a boom, an arm and a bucket with pressing the ground and simultaneously pulling the arm in the state in which the flat part of the bucket is in contact with the ground, which is essential work for making a flatly pressed surface in the plain or inclined ground At this time, the force pressing the ground must be uniform to some extent. Meanwhile, if the ground is pressed with excessive or non-uniform force, the pressing work causes a problem with uniformity in flatness of the ground. The force pressing the ground is determined by mechanical force applied to the bucket through the combined operation of the boom, the arm and the bucket. However, it is not easy to properly apply the mechanical force to the ground. This can be realized only by skilled operation of a joystick of the excavator. Further, in addition to the application of the uniform force, the flat part of the bucket must be continuously in contact with the ground.
In general, the boom, the arm and the bucket of the excavator are operated by the joystick. As illustrated in FIG. 5, the typical joystick of the excavator is provided with a swing lever for swinging a body of the excavator and an arm lever for dump/crowd operation of the arm, which are installed on one side within driver's reach, and a lever for up/down operation of the boom and a lever for dump/crowd operation of the bucket, which are installed on the other side within driver's reach. In this excavator, the results of the work are dependent on how properly the joystick is operated.
However, in the conventional excavator, it is not easy to operate the joystick to carry out the flatting work properly. The up/down operation of the boom, the dump/crowd operation of the arm, and the dump/crowd operation of the bucket should be properly balanced by the control of the joystick to operate the boom, arm and bucket. As such, unskilled operators have a great difficulty in controlling the joystick taking into consider of the operations of all the three parts.
[Disclosure] [Technical Problem]
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a hydraulic system for an excavator, which enables even an unskilled operator, who is short of skill or technique of the operation of equipment, to easily perform flatting work on a plain or inclined ground. [Technical Solution]
In order to achieve the above object, the present invention provides a hydraulic system for an excavator having a boom, arm and bucket, which is structurally improved so as to easily perform flatting work on a plain or inclined ground.
According to an embodiment of the present invention, there is provided a hydraulic system for an excavator, which comprises: a pump; a boom cylinder, which drives a boom so as to be lifted and lowered using hydraulic operating fluid supplied from the pump; and a boom control valve 22, which controls flow of the hydraulic operating fluid supplied from the pump to the boom cylinder and controls operation of the boom cylinder, wherein the boom control valve 22 can be switched to one of a first position for maintaining neutrality of the boom, a second position for lifting the boom, a third position for lowering the boom, and a fourth position for allowing the boom to be freely lifted and lowered by self- weight or external force, and the boom control valve 22 blocks the hydraulic operating fluid supplied from the pump to the boom cylinder and allows head-side and rod-side chambers of the boom cylinder to communicate with each other at the fourth position thereof.
According to an example of the present invention, the hydraulic system further comprises a stopper 11, which restricts the boom control valve 22 from being switched to the fourth position so as to allow the boom control valve 22 to be switched only to one of the first, second and third positions.
According to an example of the present invention, the fourth position of the boom control valve 22 is located at one outermost port of the boom control valve, and the stopper 11 is connected to the other outermost port of the boom control valve 22 and supplies a predetermined hydraulic pressure to the other outermost port so as to restrict the boom control valve from being switched to the fourth position. According to another example of the present invention, the hydraulic system further comprises a gear pump 9; a pilot line Pi2 connecting the stopper 11 and the gear pump 9; and a first directional control valve 8, which is installed on the pilot line Pi2 and is switched between a first position where the pilot line Pi2 communicates with the gear pump 9 and a second position where the pilot line Pi2 communicates with a tank.
Further, the hydraulic system of the present invention further comprises a directional control switch 20 for switching the first directional control valve 8. According to an example of the present invention, the directional control switch 20 is selectively switched to one of: a first position (excavating work position or Mode 1) where the first directional control valve 8 is switched to the first position, where the stopper 11 communicates with the gear pump 9 through the pilot line Pi2, and where the stopper 11 is functionally activated to restrict the boom control valve 22 from being switched to the fourth position; and a second position (flatting work position or Mode 2) where the first directional control valve 8 is switched to the second position, where the pilot line Pi2 communicates with the tank T, and where the stopper 11 is functionally inactivated to allow the boom control valve 22 to be switched to the fourth position.
The first position of the directional control switch corresponds to a position that is indicated by Mode 1 in FIGS. 3 and 4, which is for the excavating work. Further, the second position of the directional control switch corresponds to a position that is indicated by Mode 2 in FIGS. 3 and 4, which is for the flatting work.
Meanwhile, according to another example of the present invention, in order to allow the ordinary excavating work to be carried out even if the directional control switch 20 is switched so as to select the flatting work position, the boom control valve 22 is switched up to the fourth position only when the boom-up side port Pi thereof has pressure equal to or greater than a preset reference pressure, and is switched only to one of the first, second and third positions when the pressure of the boom-up side port is less than the reference pressure. Thereby, the boom-up/-down operation required for the excavating work can be controlled. In this case, the reference pressure is set to pressure occurring at the boom-up side port when an operator operates an operating lever beyond a predetermined displacement or angle in a direction where the boom is lifted. According to another aspect of the present invention, a hydraulic system for an excavator, which is structurally improved so as to easily perform flatting work, can be applied to a two-pump hydraulic system having two pumps.
In detail, there is provide a hydraulic system for improving flatting workability in an excavator, which comprises: first and second pumps Pl and P2; a boom cylinder, which drives a boom so as to be lifted and lowered using hydraulic operating fluid supplied from the first and second pumps; and first and second boom control valves 2 and 3, which controls flow of the hydraulic operating fluid supplied from the first and second pumps to the boom cylinder and controls operation of the boom cylinder, wherein the first and second boom control valves 2 and 3 includes boom-up side ports hydraulically connected to a boom-up pilot line Pi, the hydraulic operating fluids passing through the first and second boom control valves 2 and 3 are joined and supplied to the boom cylinder when the boom is lifted, and the first boom control valve 2 can be switched to one of a first position for maintaining neutrality of the boom, a second position for lifting the boom, a third position for lowering the boom, and a fourth position for allowing the boom to be freely lifted and lowered by self-weight or external force by blocking the hydraulic operating fluid supplied from the pumps to the boom cylinder and by allowing head-side and rod-side chambers of the boom cylinder to communicate with each other.
According to an example of the present invention, the hydraulic system further comprises a stopper 11, which restricts the first boom control valve 2 from being switched to the fourth position so as to allow the first boom control valve 2 to be switched only to one of the first, second and third positions. According to another example of the present invention, the hydraulic system further comprises a first directional control valve 8 for controlling the stopper.
E'urther, the hydraulic system of the present invention further comprises means for interrupting the connection of the boom-up pilot line Pi and the second boom control valve 3. One example of the interrupting means includes a second directional control valve 10, which can be switched between a first position where the boom-up pilot line Pi is connected with the second boom control valve 3 and a second position where the boom-up pilot line Pi is disconnected from the second boom control valve 3.
Further, the hydraulic system according to an example of the present invention further comprises a directional control switch 20 for switching the first directional control valve 8 and the second directional control valve 10.
Meanwhile, the two-pump hydraulic system can be also designed so that, in order to allow the ordinary excavating work to be carried out even if the directional control switch 20 is switched so as to select the flatting work position, when the directional control switch 20 is switched to a first position, the first boom control valve 2 is switched up to the fourth position only when the boom-up side port Pi thereof has pressure equal to or greater than a preset reference pressure, and is switched only to one of the first, second and third positions when the pressure of the boom-up side port is less than the reference pressure. [Advantageous Effects]
With use of the excavator having the hydraulic system according to the present invention, even an unskilled operator, who is short of skill or technique of the operation of equipment, can naturally perform the flatting work on the plain or inclined ground with ease. [Description of Drawings]
FTG. 1 is a schematic view illustrating configuration of a boom control valve 22 and its peripheral attachments in a known excavator; FIG. 2 is a schematic view illustrating configuration of a boom control valve 22 and its peripheral attachments in an excavator according to an embodiment of the present invention; FIG. 3 is a hydraulic circuit diagram illustrating a two- pump hydraulic system having two pumps, which improves flatting workability, according to an example of the present invention;
FIG. 4 schematically illustrates the first boom control valve 1 and its peripheral attachments in the hydraulic circuit diagram of FIG. 3;
FIG. 5 is a hydraulic circuit diagram illustrating a joystick that is an operating device of the excavator;
FIG. 6 is a graph showing hydraulic characteristics of a pilot valve;
FIG. 7 illustrates the state in which an excavator carries out flatting work on a plain ground; and
FIG. 8 illustrates the state in which an excavator carries out flatting work on an inclined ground. <Description of Symbols of the Main Parts in the Drawings>
2 : first boom control valve
3 : second boom control valve
4 : first arm control valve
5 : second arm control valve 6: bucket control valve
8: first directional control valve
9: gear pump
10: second directional control valve
11: stopper 20: directional control switch
21: control valve section
22: boom control valve 23: boom cylinder 24: boom
[Mode for Invention]
Reference will now be made in greater detail to an exemplary embodiment of the invention, an example of which is illustrated in the accompanying drawings.
Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. First, FIG. 1 is a schematic view illustrating configuration of a boom control valve 22 and its peripheral attachments in an ordinary excavator having a boom, an arm and a bucket. As can be seen from FIG. 1, such a boom control valve can be switched to one of three positions: one for lifting a boom 24, one for maintaining neutrality of the boom 24, and one for lowering the boom 24, when viewed from the left side.
FIG. 2 is a schematic view illustrating configuration of a boom control valve 22 and its peripheral attachments in an excavator according to an embodiment of the present invention. As can be seen from FIG. 2, the boom control valve 22 has a first position for maintaining neutrality of a boom 24, a second position for lifting the boom 24, a third position for lowering the boom 24, and a fourth position for allowing the boom 24 to be lifted and lowered by self-weight or external force. The boom control valve 22 can be switched to one of the four positions. According to the present invention, the boom control valve 22 can be operated by a boom-up pilot signal Pi and a boom down pilot signal, which are generated by manipulation of a joystick of an excavator operator (see FIG. 5) . When the boom control valve 22 is switched to the fourth position, a channel, through which hydraulic operating fluid is supplied from a pump to a boom cylinder, is blocked. At this time, since a head-side hydraulic operating fluid chamber and a rod-side hydraulic operating fluid chamber communicate with each other to form a closed loop, the boom cylinder can be not only freely lowered by self-weight, but also freely lift by external force (a geographical problem) . In this state, flatting work can be carried out by force resulting from the self-weight of the boom. In this case, since the force applied to the ground by the self-weight of the boom may be said to be relatively constant, it is not necessary to separately control the force for lowering the boom during the flatting work. Thus, the operator does not require to carry out boom-up or boom-down operation. As a result, the flatting work can be done by operating only the bucket and arm in the state in which the boom control valve is fixed to a preset position, i.e. the fourth position.
More specifically, after the boom control valve is fixed to the fourth position, the arm is stretched to the maximum extent, and thereby the bucket is located at a place remotest from a body of the excavator, as illustrated in FIGS. 7 and 8. At this time, a flat outer surface of the bucket is controlled to be parallel to the ground. Then, in order to pull the arm, an arm controlling joystick is controlled toward a crowd side, so that the flatting work is naturally carried out while the arm is pulled. At this time, the bucket must be controlled such that the flat outer surface thereof is parallel to the ground. In this case, since the flat outer surface of the bucket has only to be minutely controlled while performing simple operation of pulling the arm (arm crowd operation) , the flatting work can be easily carried out. Meanwhile, if the boom control valve 22 is switched to the fourth position in spite of out carrying out the flatting work, the boom abruptly makes free motion during another work, and thus is lowered. This abrupt lowering of the boom causes an accident. In order to prevent this accident, it is necessary to prevent the boom control valve 22 from being switched to the fourth position while the excavator carries out the work, such as the excavating work, other than the flatting work.
To this end, according to an example of the present invention, the hydraulic system comprises a stopper 11, which controls the boom control valve 22 to prevent from being arbitrarily switched to the fourth position.
It can be apparent from FIG. 2 that the boom control valve 22 is further provided with the stopper 11 on one side thereof which restricts the boom control valve 22 from being switched to the fourth position so as to allow the boom control valve 22 to be switched only to one of the first, second and third positions. According to an example of the present invention which has the configuration as in FIG. 2, the boom control valve 22 has the fourth position adjacent to a boom-up side port thereof, that is, one outermost port thereof, and the stopper 11 is connected to another outermost port, that is, a boom-down side port. The application of a predetermined hydraulic pressure to the stopper restricts the boom control valve 22 from being switched to the fourth position.
B'urther, referring to FIG. 2, the hydraulic system of the present invention can further comprise a first directional control valve 8 for controlling the stopper. To control, the stopper using the first directional control valve 8, the hydraulic system further comprises a gear pump 9, and a pilot line Pi2 connecting the stopper 11 and the gear pump 9. The first directional control valve can be installed on the pilot line Pi2.
Further, the hydraulic system of the present invention can further comprise a directional control switch 20. A work mode is determined by the directional control switch. In the case of the flatting work, the boom control valve 22 can be adapted to be switched to the fourth position. In the other cases, the boom control valve 22 can be adapted to be not switched to the fourth position.
In detail, according to an example of the present invention, the directional control switch 20 can be selectively switched to one of a first position (Mode 1) and a second position (Mode 2) by manipulation of an operator. In this embodiment, the directional control switch is provided in a knob shape at a predetermined position within a cab (not shown) , and is electrically connected with the solenoid-type first directional control valve 8 as described below as well as a second directional control valve 10 in the next embodiment, which will be described below. Here, the first position of the directional control switch 20 refers to a position where the first directional control valve 8 is switched to the first position so as to allow the stopper 11 to communicate with the gear pump 9 through the pilot line Pi2. With this configuration, the stopper 11 is operated, so that the boom control valve 22 can be prevented from being switched to the fourth position. The second position of the directional control switch 20 refers to a position where the first directional control valve 8 is switched to the second position so as to allow the pilot line Pi2 to communicate with a tank T. Thus, the stopper 11 releases its function, so that the boom control valve 22 can be switched to the fourth position.
Here, the first position of the directional control switch 20 corresponds to a position that is indicated by Mode 1 in FIGS. 3 and 4, which is for the excavating work. Further, the second position of the directional control switch 20 corresponds to a position that is indicated by Mode 2 in FIGS. 3 and 4, which is for the flatting work. Meanwhile, even if the directional control switch 20 is manipulated so as to select the flatting work, it may be adapted to carry out the ordinary excavating work. As illustrated in FIG. 6, only when a boom-up side hydraulic line Pi of the boom control valve 22 has pressure equal to and greater than a preset reference pressure, for instance 26k, the boom control valve 22 can be adapted to be switched to the fourth position. Thereby, in the case in which the joystick is controlled such that the pressure of the boom- up side hydraulic line is less than the reference pressure, a first boom control valve is adapted to be switched only to one of the first, second and third positions so as to be able to carry out the ordinary excavating work. According to the configuration of FIG. 6, the pressure occurring when the operator pulls the operation lever of the joystick at a displacement of 10 mm in the direction where the boom is lifted can be set to become the preset reference pressure of the hydraulic line. In the case in which the operator pulls the operation lever of the joystick at a displacement of 10 mm or less in the direction where the boom is lifted, the first boom control valve can be adapted to be switched only to one of the first, second and third positions. In contrast, in the case in which the operator pulls the operation lever of the joystick at a displacement of 10 mm or more in the direction where the boom is lifted, the first boom control valve can be adapted to be switched to one of the first through fourth positions.
Meanwhile, FIG. 3 is a hydraulic circuit diagram illustrating a two-pump hydraulic system having two pumps according to an example of the present invention. FIG. 4 schematically illustrates the first boom control valve 1 and its peripheral attachments in the hydraulic circuit diagram of FIG. 3. Further, FIG. 5 is a hydraulic circuit diagram illustrating a joystick that is an operating device of the excavator. The hydraulic system illustrated in FIG. 3 comprises first and second pumps Pl and P2, a control valve section 21, an arm crowd pilot line Pac, a boom-up pilot line Pi, a first directional control valve 8, and a second directional control valve 10. First, the control valve section 21 includes first and second boom control valves 2 and 3, first and second arm control valves 4 and 5, and other valves such as a straight traveling control valve, a left/right turning control valve, an option control valve and a swing control valve. Here, the detailed description associated with functions of the straight traveling control valve, the left/right turning control valve, the option control valve and the swing control valve will be omitted, and so their numbering will be omitted.
In FIG. 3, the first boom control valve 2 and the second arm control valve 5 communicate with the first pump Pl through a center parallel line Ps. The second boom control valve 3 and the first arm control valve 4 communicate with the second pump P2 through another center parallel line Ps. Hydraulic operating fluid passing through the second boom control valve 3 joins that passing through the first boom control valve 2 via a predetermined path A8', and then is supplied to a boom cylinder. Further, the boom-up side ports of the first and second boom control valves 2 and 3 are hydraulically connected to each other through the boom-up pilot line Pi. Further, it can be found that the boom-up side ports of the first and second boom control valves 2 and 3 are hydraulically connected to each other such that the hydraulic operating fluids passing through the first and second boom control valves 2 and 3 can be joined when the boom is lifted.
In the two-pump hydraulic system as in FIG. 3, the first boom control valve 2 has a first position for maintaining neutrality of the boom, a second position for lifting the boom, a third position for lowering the boom, and a fourth position for allowing the boom 24 to be freely lifted and lowered by self-weight or external force. The first boom control valve 2 can be switched to one of the four positions.
Here, when the first boom control valve 2 is switched to the fourth position, the excavator has a flatting work mode. For reference, a neutral position is a position where inlet and outlet of the boom cylinder are closed. It can be apparent from FIG. 3 that the hydraulic system comprises a stopper 11, which restricts the first boom control valve 2 from being switched to the fourth position so as to allow the first boom control valve 2 to be switched only to one of the first, second and third positions. More specifically, the first boom control valve 2 has the fourth position adjacent to one outermost port thereof, and the stopper 11 is connected to the other outermost port. The application of a predetermined hydraulic pressure to the other port of the first boom control valve restricts the first boom control valve from being switched to the fourth position. In FIG. 3, the stopper 11 is installed on the boom-down side port of the first boom control valve 2.
In conjunction with the control of the stopper 11, the hydraulic system illustrated in FIGS. 3 and 4 can further comprise a gear pump 9, a pilot line Pi2 connecting the stopper 11 and the gear pump 9, and a first directional control valve 8, which is installed on the pilot line Pi2 and is switched between a first position where the pilot line Pi2 communicates with the gear pump 9 and a second position where the pilot line Pi2 communicates with a tank.
The stopper functions to prevent the first boom control valve from being switched to the fourth position when the first directional control valve 8 is switched to the first position, the communicating position.
Meanwhile, in the case in which the function of the stopper 11 is released by the switching of the first directional control valve 8, the first boom control valve 2 can be switched to the fourth position.
Meanwhile, in the case of the two-pump hydraulic system, in spite of the flatting work where the first boom control valve 2 is switched to the fourth position, the hydraulic operating fluid can be supplied to the boom cylinder through the second boom control valve 3. Particularly, when the hydraulic operating fluid is supplied to the boom cylinder in the direction where the second boom control valve 3 lifts the boom, the flatting work based on the self-weight is not properly performed, and the boom may make irregular motion, which is dangerous. In order to prevent this danger, it is necessary to fix the second boom control valve 3 so as not to be switched while the flatting work is being performed. To this end, a control signal sent to the second boom control valve 3 can be interrupted. According to an example of the present invention, the hydraulic system can employ a method of blocking the boom-up pilot line Pi applied to the second boom control valve 3 during the flatting work.
To this end, the two-pump hydraulic system can further comprise means for interrupting the connection of the boom-up pilot line Pi and the second boom control valve 3. One example of this interrupting means includes the second directional control valve 10. The second directional control valve 10 can be adapted to be switched between a first position where the boom-up pilot line Pi is connected with the second boom control valve 3 and a second position where the boom-up pilot line Pi is disconnected from the second boom control valve 3.
According to an example of the present invention, the hydraulic system can further comprise a directional control switch 20, which switches the first directional control valve 8 and the second directional control valve 10. More specifically, the directional control switch 20 can be adapted to be selectively switched to one of: a first position where it switches the first directional control valve 8 to the first position and causes the stopper 11 to communicate with the gear pump 9 through the pilot line Pi2 such that the stopper 11 is functionally activated to restrict the first boom control valve 2 from being switched to the fourth position, and where it switches the second directional control valve 10 to the first position and causes the second boom control valve 3 to communicate with the boom-up pilot line Pi such that the first boom control valve 2 and the second boom control valve 3 can be switched in the diction where the boom is lifted; and a second position where it switches the first directional control valve 8 to the second position and causes the pilot line Pi2 to communicate with the tank T so that the stopper 11 is functionally inactivated to allow the first boom control valve 2 to be switched up to the fourth position, and where it switches the second directional control valve 10 to the second position, causes the boom-up pilot line Pi to communicate with the tank T, and prevents the second boom control valve 3 from communicating with the boom-up pilot line Pi so that the second boom control valve 3 cannot be switched. According to an example of the present invention, the directional control switch 20 can be hydraulically and electrically connected with the first and second directional control valves 8 and 10.
In FIG. 4, the connection of the first boom control valve 2 of the present invention is illustrated in detail. The first boom control valve 2 is connected with the boom-up pilot line Pi on the left side thereof, and is provided with the stopper 11 on the right side thereof. The stopper 11 can communicate with the first directional control valve 8 at the first position of the first directional control valve 8, and thus can be supplied with the hydraulic operating fluid from the gear pump 9.
The pressure oil discharged from the first pump Pl flows through the center parallel line Ps, and the hydraulic operating fluid is supplied to the boom cylinder in response to the switching of the first boom control valve 2. Meanwhile, although the directional control switch 20 is operated so as to select the flatting work position, the excavator can be adapted to perform the ordinary excavating work.
In other words, as illustrated in FIG. 6, only when a boom-up side hydraulic line Pi of the boom control valve 22 has pressure equal to and greater than a preset reference pressure, for instance 26k, the boom control valve 22 can be adapted to be switched to the fourth position. Thereby, in the case in which the joystick is controlled such that the pressure of the boom-up side hydraulic line is less than the reference pressure, the first boom control valve is adapted to be switched only to one of the first, second and third positions so as to be able to carry out the ordinary excavating work. For example, with the configuration of FIG. β, on the basis of the operator pulling the operation lever of the joystick at a displacement of 10 mm in the direction where the boom is lifted, when the displacement is less than 10 mm, the first boom control valve can be adapted to be switched only to one of the first, second and third positions, but when the displacement is more than 10 mm, the first boom control valve can be adapted to be switched to one of the first through fourth positions. This method of operating the boom-up joystick in order to switch the first boom control valve 2 to the fourth position can be changed to the case in which the boom 24 is operated in a lowering direction. In this case, the boom 24 will be operated in a manner such that it is lowered by its self-weight while being lowered.
The flatting work and the ordinary excavating work using the excavator having the above-mentioned hydraulic system according to the present invention will be described below.
<Flatting Work> Second Position of Directional Control Switch 20
When the operator switches the directional control switch 20 to the second position, which corresponds to the flatting work mode, for the purpose of the flatting work, the first directional control valve 8 is switched to the second position, and the pilot line Pi2 communicates with the tank T. As a result, the stopper 11 is functionally inactivated, and thus the first boom control valve 2 can be switched up to the fourth position. Further, the second directional control valve 10 is switched to the second position, thereby allowing the boom-up pilot line Pi of the second boom control valve 3 to communicate with the tank T, so that the second boom control valve 3 is not switched. At this time, when the first boom control valve 2 is switched to the fourth position, the inlet and outlet ports of the boom cylinder 23 communicate with each other.
Thus, the front including the boom is lowered by its self- weight, and the flat surface of the bucket comes into contact with the ground, so that pressing action occurs. Subsequently, when the arm is pulled in a crowd direction, the self-weight of the front is applied to the ground, so that the flatting work is realized as in FIGS. 7 and 8.
Meanwhile, when it is necessary to inevitably carry out boom-up operation during the flatting work, the hydraulic characteristics of the boom control valves 2 and 3 can be divided into two stages, as illustrated in FIG. 6, such that the operation thereof can be changed. In FIG. 6, the first boom control valve 2 can be switched to one of the first, second and third positions under the conditions: pilot pressure of 20k and stroke of 10 mm or less, such that the ordinary excavating work permitting boom-up/-down operation is carried out. Only when the pilot pressure exceeds 20k, the first boom control valve 2 is adapted to be switched to the fourth position.
In other words, when the operator slightly pulls the boom- up joystick (pressure of 20k or less, and displacement of 10 mm or less) in spite of the selection of the directional control switch 20 in the flatting work mode, the first boom control valve 2 is switched within a range from the first position to the third position without being switched to the fourth position, and the second boom control valve 3 is not yet switched. In this case, the boom 24 is lifted and lowered by the hydraulic operating fluid passing through the first boom control valve 2. Meanwhile, it is not until the operator pulls the boom-up joystick at a displacement of 10 mm or more and thus the pilot pressure exceeds 20k that the first boom control valve 2 is switched to the fourth position, the floating state, and thus the boom is lowered toward the ground by its self- weight.
<Ordinary Work> First Position of Directional Control Switch 20
When the operator switches the directional control switch 20 to the first position for the purpose of the excavating work, the second directional control valve 10 is switched to the first position. Thereby, the boom-up pilot lines Pi of the first and second boom control valves 2 and 3 communicate to allow the first and second boom control valves 2 and 3 to be switched in the direction where the boom is lifted. Simultaneously, the first directional control valve 8 is switched to the first position, so that the stopper 11 of the boom-down side port of the first boom control valve 2 communicates with the gear pump 9 through the pilot line Pi2. Thereby, the function of the stopper 11 is restored, so that the first boom control valve 2 is prevented from being switched to the fourth position. Thus, when the operator operates the front attachments, the first and second boom control valves 2 and 3 are operated within a range from the first position and the third position for the purpose of the excavating work, that is, the boom-up, boom-down and boom stop, so that the ordinary excavating work is performed together with the other front attachments.
In the drawings and specification, typical exemplary embodiments of the invention have been disclosed, and although specific terms are employed, they are used in a generic and descriptive sense only and are not for the purposes of limitation, the scope of the invention being set forth in the following claims.

Claims

[CLAIMS]
[Claim l]
A hydraulic system for improving flatting workability in an excavator, comprising: a pump; a boom cylinder, which drives a boom so as to be lifted and lowered using hydraulic operating fluid supplied from the pump; and a boom control valve (22) , which controls flow of the hydraulic operating fluid supplied from the pump to the boom cylinder and controls operation of the boom cylinder, wherein the boom control valve (22) can be switched to one of a first position for maintaining neutrality of the boom, a second position for lifting the boom, a third position for lowering the boom, and a fourth position for allowing the boom to be freely lifted and lowered by self-weight or external force, and the boom control valve (22) blocks the hydraulic operating fluid supplied from the pump to the boom cylinder and allows head-side and rod-side chambers of the boom cylinder to communicate with each other at the fourth position thereof. [Claim 2]
The hydraulic system according to claim 1, further comprising a stopper (11) , which restricts the boom control valve (22) from being switched to the fourth position so as to allow the boom control valve (22) to be switched only to one of the first, second and third positions. [Claim 3]
The hydraulic system according to claim 2, wherein: the fourth position of the boom control valve (22) is located at one outermost port of the boom control valve; and the stopper (11) is connected to the other outermost port of the boom control valve (22) and supplies a predetermined hydraulic pressure to the other outermost port so as to restrict the boom control valve from being switched to the fourth position. [Claim 4]
The hydraulic system according to claim 2, further comprising: a gear pump (9) ; a pilot line (Pi2) connecting the stopper (11) and the gear pump (9) ; and a first directional control valve (8) , which is installed on the pilot line (Pi2) and is switched between a first position where the pilot line (Pi2) communicates with the gear pump (9) and a second position where the pilot line (Pi2) communicates with a tank. [Claim 5]
The hydraulic system according to claim 4, further comprising a directional control switch (20) for switching the first directional control valve (8), wherein the directional control switch (20) is selectively switched to one of: a first position where the first directional control valve (8) is switched to the first position, where the stopper (11) communicates with the gear pump (9) through the pilot line (Pi2), and where the stopper (11) is functionally activated to restrict the boom control valve (22) from being switched to the fourth position; and a second position where the first directional control valve (8) is switched to the second position, where the pilot line (Pi2) communicates with the tank (T), and where the stopper (11) is functionally inactivated to allow the boom control valve (22) to be switched to the fourth position. [Claim β]
The hydraulic system according to claim 5, wherein: when the directional control switch (20) is switched to the first position, the boom control valve (22) is switched up to the fourth position only when the boom-up side port (Pi) thereof has pressure equal to or greater than a preset reference pressure, and is switched only to one of the first, second and third positions when the pressure of the boom-up side port is less than the reference pressure; and the reference pressure is set to pressure occurring at the boom-up side port when an operator operates an operating lever beyond a predetermined displacement or angle in a direction where the boom is lifted. [Claim 7]
A hydraulic system for improving flatting workability in an excavator, comprising: first and second pumps (Pl and P2) ; a boom cylinder, which drives a boom so as to be lifted and lowered using hydraulic operating fluid supplied from the first and second pumps; and first and second boom control valves (2 and 3) , which controls flow of the hydraulic operating fluid supplied from the first and second pumps to the boom cylinder and controls operation of the boom cylinder, wherein the first and second boom control valves (2 and 3) includes boom-up side ports hydraulically connected to a boom- up pilot line (Pi) , the hydraulic operating fluids passing through the first and second boom control valves (2 and 3) are joined and supplied to the boom cylinder when the boom is lifted, and the first boom control valve 2 can be switched to one of a first position for maintaining neutrality of the boom, a second position for lifting the boom, a third position for lowering the boom, and a fourth position for allowing the boom to be freely lifted and lowered by self-weight or external force by blocking the hydraulic operating fluid supplied from the pumps to the; boom cylinder and by allowing head-side and rod-side chambers of the boom cylinder to communicate with each other. [Claim 8]
The hydraulic system according to claim 7, further comprising a stopper (11), which restricts the first boom control valve (2) from being switched to the fourth position so as to allow the first boom control, valve (2) to be switched only to one of the first, second and third positions. [Claim 9] The hydraulic system according to claim 8, wherein: the fourth position of the first boom control valve (2) is located at one outermost port of the boom control valve; and the stopper (11) is connected to the other outermost port of the first boom control valve (2) and supplies a predetermined hydraulic pressure to the other outermost port so as to restrict the boom control valve from being switched to the fourth position.
[Claim 10] The hydraulic system according to claim 8, further comprising: a gear pump (9); a pilot line (Pi2) connecting the stopper (11) and the gear pump (9) ; and a first directional control valve (8), which is installed on the pilot line (Pi2) and is switched between a first position where the pilot line (Pi2) communicates with the gear pump (9) and a second position where the pilot line (Pi2) communicates with a tank. [Claim 11]
The hydraulic system according to claim 10, further comprising means for interrupting the connection of the boom-up pilot line (Pi) and the second boom control valve (3) when the stopper (11) is functionally inactivated by the switching of the first directional control valve (8) . [Claim 12]
The hydraulic system according to claim 11, wherein the interrupting means includes a second directional control valve
(10) , which can be switched between a first position where the boom-up pilot line (Pi) is connected with the second boom control valve (3) and a second position where the boom-up pilot line (Pi) is disconnected from the second boom control valve (3).
[Claim 13]
The hydraulic system according to claim 12, further comprising a directional control switch (20) for switching the first directional control valve (8) and the second directional control valve (10) , wherein the directional control switch (20) is selectively switched to one of: a first position where the first directional control valve
(8) is switched to the first position, where the stopper (11) communicates with the gear pump (9) through the pilot line
(Pi2), where the stopper (11) is functionally activated to restrict the first boom control valve (2) from being switched to the fourth position, where the second directional control valve (10) is switched to the first position, where the second boom control valve (3) communicates with the boom-up pilot line
(Pi), and where the first boom control valve (2) and the second boom control valve (3) can be switched in a diction where the boom is lifted; and a second position where the first directional control valve (8) is switched to the second position, where the pilot line (Pi2) communicates with the tank (T) , where the stopper
(11) is functionally inactivated to allow the first boom control valve (2) to be switched up to the fourth position, where the second directional control valve (10) is switched to the second position, where the boom-up pilot line (Pi) communicates with the tank (T) , and where the second boom control valve (3) is prevented from communicating with the boom-up pilot line (Pi) and is not switched. [Claim 14]
The hydraulic system according to claim 13, wherein: when the directional control switch (20) is switched to the first position, the first boom control valve (2) is switched up to the fourth position only when the boom-up side port (Pi) thereof has pressure equal to or greater than a preset reference pressure, and is switched only to one of the first, second and third positions when the pressure of the boom-up side port is less than the reference pressure; and the reference pressure is set to pressure occurring at the boom-up side port when an operator operates an operating lever beyond a predetermined displacement or angle in a direction where the boom is lifted.
EP07851716.6A 2006-12-22 2007-12-21 Hydraulic system for improving flatting workability in an excavator Not-in-force EP2094915B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
KR1020060133167A KR101265342B1 (en) 2006-12-22 2006-12-22 Flat and slant improvement device of excavator
PCT/KR2007/006754 WO2008078930A1 (en) 2006-12-22 2007-12-21 Hydraulic system for improving flatting workability in an excavator

Publications (3)

Publication Number Publication Date
EP2094915A1 true EP2094915A1 (en) 2009-09-02
EP2094915A4 EP2094915A4 (en) 2014-04-02
EP2094915B1 EP2094915B1 (en) 2015-05-27

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KR (1) KR101265342B1 (en)
CN (1) CN101573498B (en)
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Also Published As

Publication number Publication date
CN101573498A (en) 2009-11-04
CN101573498B (en) 2011-06-15
WO2008078930A1 (en) 2008-07-03
EP2094915A4 (en) 2014-04-02
EP2094915B1 (en) 2015-05-27
KR20080058939A (en) 2008-06-26
KR101265342B1 (en) 2013-05-20

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