Patent Grant
9476180
The present invention relates to a hydraulic excavator.
As to conventional hydraulic excavators, Japanese Patent Laying-Open No. 7-207697 (PTD 1) discloses such a configuration that an electromagnetic switching valve including an oil passage position with a throttle is provided in a conduit connected to a boom-lowering pilot port of a pilot switching valve for a boom, and a pressure sensor is provided on the boom-lowering pilot port side, and a pressure signal detected by the pressure sensor is inputted to a controller.
PTD 1: Japanese Patent Laying-Open No. 7-207697
In recent years, in work vehicles, introduction of information-oriented construction has been rapidly promoted. The information-oriented construction is a system aimed at realizing highly-efficient and highly-accurate construction by detecting a position of a work implement using the information and communication technology (ICT) and automatically controlling the work implement based on the detected position of the work implement in the construction stage of a construction project.
In the case of automatically controlling the work implement in a land leveling work with a hydraulic excavator, control for raising a boom automatically and forcibly is executed when it is expected that a cutting edge of a bucket will become lower than a design surface, in order to avoid deeper excavation than the design surface.
On the other hand, the cutting edge of the bucket follows the arc-shaped path, and thus, the cutting edge of the bucket may move away from the design surface if a boom-lowering operation is not performed during a scrape-off work for forming a flat surface. Therefore, it is preferable that an operator operating the hydraulic excavator continues to perform an operation for inclining a control lever toward the boom-lowering side during the scrape-off work.
When the operator continues to perform the operation for inclining the control lever toward the boom-lowering side as described above, minute vibrations (chattering) occur in the control lever, which brings a sense of discomfort to the operator gripping the control lever.
The present invention has been made in view of the aforementioned problem and an object thereof is to provide a hydraulic excavator in which occurrence of minute vibrations in a control lever can be suppressed.
The inventor of the present invention has earnestly studied a reason why minute vibrations occur in the control lever during the boom-lowering operation. As a result, the inventor of the present invention has found that, when a pilot pressure outputted by a pilot pressure control valve in accordance with an amount of operation of the control lever fluctuates abruptly, a spool and a retainer constituting the pilot pressure control valve collide with each other repeatedly, and as a result, minute vibrations occur in the control lever. Based on this, the inventor of the present invention has obtained the findings that the occurrence of minute vibrations in the control lever can be suppressed if the fluctuations in pilot pressure can be suppressed, and has completed the present invention.
Specifically, a hydraulic excavator according to one aspect of the present invention includes: a boom; a pilot switching valve for the boom; a boom-raising pilot conduit; a boom-lowering pilot conduit; a boom-raising proportional solenoid valve; a boom-lowering proportional solenoid valve; a control lever; a pressure sensor; and a controller. The pilot switching valve for the boom has a boom-raising pilot port and a boom-lowering pilot port, and controls operation of the boom. The boom-raising pilot conduit is connected to the boom-raising pilot port. The boom-lowering pilot conduit is connected to the boom-lowering pilot port. The boom-raising proportional solenoid valve is provided in the boom-raising pilot conduit. The boom-lowering proportional solenoid valve is provided in the boom-lowering pilot conduit. The control lever is operated by an operator. The pressure sensor detects a pressure generated in the boom-lowering pilot conduit between the control lever and the boom-lowering proportional solenoid valve. The controller controls an opening degree of the boom-lowering proportional solenoid valve based on the pressure detected by the pressure sensor. The controller also controls an opening degree of the boom-raising proportional solenoid valve. An amount of increase in current per unit time when the controller outputs, to the boom-lowering proportional solenoid valve, an instruction signal for instructing an increase in opening degree is smaller than an amount of increase in current per unit time when the controller outputs, to the boom-raising proportional solenoid valve, an instruction signal for instructing an increase in opening degree.
In the hydraulic excavator according to one aspect of the present invention, fluctuations in amount of the hydraulic oil present between the control lever and the boom-lowering proportional solenoid valve can be suppressed when control for automatically raising the boom is executed, and thus, fluctuations in pressure of the hydraulic oil can be suppressed. Therefore, the occurrence of minute vibrations in the control lever can be suppressed.
In the hydraulic excavator, the amount of increase in current per unit time when the controller outputs, to the boom-lowering proportional solenoid valve, the instruction signal for instructing an increase in opening degree is smaller than an amount of decrease in current per unit time when the controller outputs, to the boom-lowering proportional solenoid valve, an instruction signal for instructing a decrease in opening degree. Thus, the boom-lowering operation can be immediately stopped when the boom-lowering operation becomes unnecessary.
The hydraulic excavator further includes a bucket having a cutting edge. The controller controls the boom to prevent a position of the cutting edge from becoming lower than construction design data. The boom-raising proportional solenoid valve is a forcible boom-raising proportional solenoid valve for forcibly raising the boom when it is expected that the position of the cutting edge will become lower than the construction design data. Thus, the land leveling work can be performed in accordance with the construction design data, and therefore, the quality and efficiency of the land leveling work with the hydraulic excavator can be enhanced.
A hydraulic excavator according to another aspect of the present invention includes: a boom; a pilot switching valve for the boom; a boom-raising pilot conduit; a boom-lowering pilot conduit; a boom-raising proportional solenoid valve; a boom-lowering proportional solenoid valve; a control lever; a first pressure sensor; a second pressure sensor; and a controller. The pilot switching valve for the boom has a boom-raising pilot port and a boom-lowering pilot port, and controls operation of the boom. The boom-raising pilot conduit is connected to the boom-raising pilot port. The boom-lowering pilot conduit is connected to the boom-lowering pilot port. The boom-raising proportional solenoid valve is provided in the boom-raising pilot conduit. The boom-lowering proportional solenoid valve is provided in the boom-lowering pilot conduit. The control lever is operated by an operator. The first pressure sensor detects a pressure generated in the boom-lowering pilot conduit between the control lever and the boom-lowering proportional solenoid valve. The second pressure sensor detects a pressure generated in the boom-raising pilot conduit between the control lever and the boom-raising proportional solenoid valve. The controller controls an opening degree of the boom-lowering proportional solenoid valve based on the pressure detected by the first pressure sensor. The controller also controls an opening degree of the boom-raising proportional solenoid valve based on the pressure detected by the second pressure sensor. An amount of increase in current per unit time when the controller outputs, to the boom-lowering proportional solenoid valve, an instruction signal for instructing an increase in opening degree is smaller than an amount of increase in current per unit time when the controller outputs, to the boom-raising proportional solenoid valve, an instruction signal for instructing an increase in opening degree.
In the hydraulic excavator according to another aspect of the present invention, fluctuations in amount of the hydraulic oil present between the control lever and the boom-lowering proportional solenoid valve can be suppressed when control for moving the boom upwardly and downwardly in accordance with the operation of the control lever is executed, and thus, fluctuations in pressure of the hydraulic oil can be suppressed. Therefore, the occurrence of minute vibrations in the control lever can be suppressed.
The hydraulic excavator further includes a bucket having a cutting edge. The controller controls the boom to prevent a position of the cutting edge from becoming lower than construction design data. Thus, the land leveling work can be performed in accordance with the construction design data, and therefore, the quality and efficiency of the land leveling work with the hydraulic excavator can be enhanced.
In the hydraulic excavator, the controller transmits and receives information to and from the outside by satellite communication. Thus, the information-oriented construction based on the information transmitted and received to and from the outside becomes possible, and the highly-efficient and highly-accurate land leveling work with the hydraulic excavator can be realized.
As described above, according to the present invention, fluctuations in hydraulic pressure outputted in accordance with the amount of operation of the control lever can be suppressed, and thus, the occurrence of minute vibrations in the control lever can be suppressed.
An embodiment of the present invention will be described hereinafter with reference to the drawings.
First, a configuration of a hydraulic excavator to which an idea of the present invention is applicable will be described.
Undercarriage 2 has a pair of left and right crawler belts. It is configured to allow hydraulic excavator 1 to be self-propelled by rotation of the pair of crawler belts. Upper revolving unit 3 is disposed to be pivotable with respect to undercarriage 2.
Upper revolving unit 3 includes a cab 4 that is a space for an operator to operate hydraulic excavator 1. Cab 4 is included in the work vehicle main body. On the backward side B, upper revolving unit 3 includes an engine compartment that houses an engine, and a counter weight. In the present embodiment, the frontward side (front side) of the operator when seated in cab 4 will be referred to as frontward side F of upper revolving unit 3, and the side opposite to frontward side F, i.e., the backward side of the operator will be referred to as backward side B of upper revolving unit 3. The left side of the operator when seated will be referred to as left side L of upper revolving unit 3, and the right side of the operator when seated will be referred to as right side R of upper revolving unit 3. In the following description, it is assumed that the frontward-backward and left-right directions of upper revolving unit 3 match the frontward-backward and left-right directions of hydraulic excavator 1.
Work implement 5 that performs works such as soil excavation is pivotably supported by upper revolving unit 3 so as to be operable in the upward-downward direction. Work implement 5 has a boom 6 attached to a substantially central portion on frontward side F of upper revolving unit 3 so as to be operable in the upward-downward direction, an arm 7 attached to a tip of boom 6 so as to be operable in the backward-frontward direction, and a bucket 8 attached to a tip of arm 7 so as to be operable in the backward-frontward direction. Bucket 8 has a cutting edge 8a at a tip thereof. Boom 6, arm 7 and bucket 8 are configured to be driven by a boom cylinder 9, an arm cylinder 10 and a bucket cylinder 11 that are hydraulic cylinders, respectively.
Cab 4 is arranged on frontward side F and on left side L of upper revolving unit 3. With respect to cab 4, work implement 5 is provided on right side R that is one side portion side of cab 4. It should be noted that the arrangement of cab 4 and work implement 5 is not limited to the example shown in
A space surrounded by each pillar and the floor and roof portions of cab 4 forms an interior space of cab 4. Operator's seat 24 is housed in the interior space of cab 4 and is arranged at a substantially center of the floor portion of cab 4. A side surface on left side L of cab 4 is provided with a door for the operator to get in or out of cab 4.
A front window is arranged on frontward side F with respect to operator's seat 24. The front window is made of a transparent material and the operator seated on operator's seat 24 can view the outside of cab 4 through the front window. For example, as shown in
A monitor device 26 is disposed on frontward side F inside cab 4. Monitor device 26 is arranged at a corner on the frontward right side inside cab 4, and is supported by a support extending from the floor portion of cab 4. Monitor device 26 is arranged on the operator's seat 24 side with respect to the front pillar. Monitor device 26 is arranged in front of the front pillar when viewed from the operator seated on operator's seat 24.
For multipurpose use, monitor device 26 includes a planar display surface 26d having various monitor functions, a switch unit 27 having a plurality of switches to which many functions are assigned, and a sound generator 28 that expresses by sound the contents displayed on display surface 26d. This display surface 26d is configured by a graphic indicator such as a liquid crystal indicator and an organic EL indicator. Although switch unit 27 includes a plurality of key switches, the present invention is not limited thereto. Switch unit 27 may include touch panel-type touch switches.
Travel control levers (left and right travel control levers) 22a and 22b for the left and right crawler belts are provided on frontward side F of operator's seat 24. Left and right travel control levers 22a and 22b form a travel control unit 22 for controlling undercarriage 2.
A first control lever 44 for the operator on cab 4 to control driving of boom 6 and bucket 8 of work implement 5 is provided on right side R of operator's seat 24. A switch panel 29 having various switches and the like mounted thereon is also provided on right side R of operator's seat 24. A second control lever 45 for the operator to control driving of arm 7 of work implement 5 and revolving of upper revolving unit 3 is provided on left side L of operator's seat 24.
A monitor 21 is arranged above monitor device 26. Monitor 21 has a planar display surface 21d. Comparing display surface 26d of monitor device 26 and display surface 21d of monitor 21 shown in
Monitor 21 is attached to the front pillar on right side R, which is the side close to work implement 5, of the pair of front pillars. Monitor 21 is arranged in front of the front pillar in the line of sight of the operator seated on operator's seat 24 toward the frontward right direction. By attaching monitor 21 to the front pillar on right side R in hydraulic excavator 1 including work implement 5 on right side R of cab 4, the operator can view both work implement 5 and monitor 21 with a small amount of line-of-sight movement.
Information can be transmitted and received between controller 20 and an external monitoring station 96. In the present embodiment, controller 20 and monitoring station 96 communicate with each other by satellite communication. A communication terminal 91 having a satellite communication antenna 92 is connected to controller 20. As shown in
An example of applying the information-oriented construction system to hydraulic excavator 1 according to the present embodiment will be described. Construction design data created by a three-dimensional CAD (Computer Aided Design) is prestored in controller 20. Monitor 21 updates and displays the externally-received current position of hydraulic excavator 1 on the screen in real time, such that the operator can constantly check the work state of hydraulic excavator 1.
Controller 20 compares the construction design data with the position and posture of work implement 5 in real time, and drives a hydraulic circuit based on the result of comparison, thereby controlling work implement 5. More specifically, controller 20 compares the position for construction based on the construction design data (design surface) with the position of bucket 8, and executes control to prevent cutting edge 8a of bucket 8 from being located lower than the design surface to prevent deeper excavation than the design surface. As a result, the construction efficiency and the construction accuracy can be enhanced, and high-quality construction can be easily performed.
Main operation valve 34 has a pilot switching valve for the arm 36, a pilot switching valve for the boom 37, a pilot switching valve for left travel 38, a pilot switching valve for right travel 39, and a pilot switching valve for the bucket 40. Pilot switching valve for the arm 36 controls supply and discharge of the hydraulic oil to and from arm cylinder 10. Pilot switching valve for the boom 37 controls supply and discharge of the hydraulic oil to and from boom cylinder 9. Pilot switching valve for left travel 38 controls supply and discharge of the hydraulic oil to and from left travel motor 17. Pilot switching valve for right travel 39 controls supply and discharge of the hydraulic oil to and from right travel motor 16. Pilot switching valve for the bucket 40 controls supply and discharge of the hydraulic oil to and from bucket cylinder 11.
Each of pilot switching valve for the arm 36, pilot switching valve for the boom 37, pilot switching valve for left travel 38, pilot switching valve for right travel 39, and pilot switching valve for the bucket 40 has a pair of pilot ports p1 and p2. The hydraulic oil having a prescribed pilot pressure is supplied to each of pilot ports p1 and p2, and thereby, each of pilot switching valves 36 to 40 is controlled.
The pilot pressures applied to pilot switching valve for the arm 36, pilot switching valve for the boom 37 and pilot switching valve for the bucket 40 are controlled by operating a first control lever device 41 and a second control lever device 42. The pilot pressures applied to pilot switching valve for left travel 38 and pilot switching valve for right travel 39 are controlled by operating left and right travel control levers 22a and 22b shown in
First control lever device 41 has first control lever 44 operated by the operator, a first pilot pressure control valve 41A, a second pilot pressure control valve 41B, a third pilot pressure control valve 41C, and a fourth pilot pressure control valve 41D. First pilot pressure control valve 41A, second pilot pressure control valve 41B, third pilot pressure control valve 41C, and fourth pilot pressure control valve 41D are provided to correspond to the four directions, i.e., the frontward-backward and left-right directions, of first control lever 44.
Second control lever device 42 has second control lever 45 operated by the operator, a fifth pilot pressure control valve 42A, a sixth pilot pressure control valve 42B, a seventh pilot pressure control valve 42C, and an eighth pilot pressure control valve 42D. Fifth pilot pressure control valve 42A, sixth pilot pressure control valve 42B, seventh pilot pressure control valve 42C, and eighth pilot pressure control valve 42D are provided to correspond to the four directions, i.e., the frontward-backward and left-right directions of second control lever 45.
Pilot pressure control valves 41A to 41D and 42A to 42D for controlling driving of hydraulic cylinders 9, 10 and 11 for work implement 5 as well as a swing motor are connected to first control lever 44 and second control lever 45, respectively. Pilot pressure control valves for controlling driving of right and left travel motors 16 and 17 are connected to left and right travel control levers 22a and 22b, respectively.
First pilot pressure control valve 41A has a first pump port X1, a first tank port Y1 and a first supply/discharge port Z1. First pump port X1 is connected to a pump flow path 51. First tank port Y1 is connected to a tank flow path 52. Pump flow path 51 and tank flow path 52 are connected to tank 35 that stores the hydraulic oil. A third hydraulic pump 50 is provided in pump flow path 51. Third hydraulic pump 50 is different from first hydraulic pump 31 and second hydraulic pump 32 described above. However, instead of third hydraulic pump 50, first hydraulic pump 31 or second hydraulic pump 32 may be used. First supply/discharge port Z1 is connected to a first pilot conduit 53.
In accordance with the operation of first control lever 44, first pilot pressure control valve 41A is switched between an output state and a discharge state. In the output state, first pilot pressure control valve 41A causes first pump port X1 and first supply/discharge port Z1 to communicate with each other, and outputs the hydraulic oil having a pressure corresponding to an amount of operation of first control lever 44 from first supply/discharge port Z1 to first pilot conduit 53. In the discharge state, first pilot pressure control valve 41A causes first tank port Y1 and first supply/discharge port Z1 to communicate with each other.
Second pilot pressure control valve 41B has a second pump port X2, a second tank port Y2 and a second supply/discharge port Z2. Second pump port X2 is connected to pump flow path 51. Second tank port Y2 is connected to tank flow path 52. Second supply/discharge port Z2 is connected to a second pilot conduit 54.
In accordance with the operation of first control lever 44, second pilot pressure control valve 41B is switched between an output state and a discharge state. In the output state, second pilot pressure control valve 41B causes second pump port X2 and second supply/discharge port Z2 to communicate with each other, and outputs the hydraulic oil having a pressure corresponding to an amount of operation of first control lever 44 from second supply/discharge port Z2 to second pilot conduit 54. In the discharge state, second pilot pressure control valve 41B causes second tank port Y2 and second supply/discharge port Z2 to communicate with each other.
First pilot pressure control valve 41A and second pilot pressure control valve 41B form a pair and correspond to the operation directions of first control lever 44 that are opposite to each other. For example, first pilot pressure control valve 41A corresponds to the operation for inclining first control lever 44 toward the frontward direction, and second pilot pressure control valve 41B corresponds to the operation for inclining first control lever 44 toward the backward direction. Either first pilot pressure control valve 41A or second pilot pressure control valve 41B is selected in accordance with the operation of first control lever 44. That is, when first pilot pressure control valve 41A is in the output state, second pilot pressure control valve 41B is in the discharge state. When first pilot pressure control valve 41A is in the discharge state, second pilot pressure control valve 41B is in the output state.
First pilot pressure control valve 41A controls supply and discharge of the hydraulic oil to and from second pilot port p2 of pilot switching valve for the boom 37. Second pilot pressure control valve 41B controls supply and discharge of the hydraulic oil to and from first pilot port p1 of pilot switching valve for the boom 37. In accordance with the operation of first control lever 44, supply and discharge of the hydraulic oil to and from boom cylinder 9 are controlled, and extension and contraction of boom cylinder 9 are controlled. As a result, the operation for raising or lowering boom 6 is controlled in accordance with the operation of first control lever 44.
First pilot port p1 of pilot switching valve for the boom 37 has a function as a boom-raising pilot port supplied with the hydraulic oil at the time of the operation for raising boom 6. Second pilot port p2 of pilot switching valve for the boom 37 has a function as a boom-lowering pilot port supplied with the hydraulic oil at the time of the operation for lowering boom 6.
The pressure (pilot pressure) of the hydraulic oil supplied to first pilot conduit 53 via first pilot pressure control valve 41A is detected by a hydraulic pressure sensor 63. Hydraulic pressure sensor 63 outputs, to controller 20, a pressure signal P3 that is an electric detection signal corresponding to the detected pilot pressure of the hydraulic oil. In addition, the pressure (pilot pressure) of the hydraulic oil supplied to second pilot conduit 54 via second pilot pressure control valve 41B is detected by a hydraulic pressure sensor 64. Hydraulic pressure sensor 64 outputs, to controller 20, a pressure signal P4 that is an electric detection signal corresponding to the detected pilot pressure of the hydraulic oil.
A relay block 70 is provided in a hydraulic pressure path connecting first and second control lever devices 41 and 42 and main operation valve 34. Relay block 70 is configured to include a plurality of proportional solenoid valves 73 to 79. Proportional solenoid valve 73 is provided in first pilot conduit 53. Hydraulic pressure sensor 63 is provided between first pilot pressure control valve 41A and proportional solenoid valve 73 in first pilot conduit 53. Proportional solenoid valve 74 is provided in second pilot conduit 54. Hydraulic pressure sensor 64 is provided between second pilot pressure control valve 41B and proportional solenoid valve 74 in second pilot conduit 54. Proportional solenoid valves 73 and 74 are provided to control the operation for moving boom 6 upwardly and downwardly in accordance with the operation of first control lever 44.
Based on the pilot pressure of first pilot conduit 53 detected by hydraulic pressure sensor 63, controller 20 controls proportional solenoid valve 73. That is, hydraulic pressure sensor 63 has a function as a first pressure sensor for detecting the hydraulic pressure generated in first pilot conduit 53 between first pilot pressure control valve 41A and proportional solenoid valve 73 in accordance with the operation of first control lever 44. In accordance with the hydraulic pressure detected by hydraulic pressure sensor 63, controller 20 outputs an instruction signal G3 to proportional solenoid valve 73 and adjusts the opening degree thereof, thereby changing a flow rate of the hydraulic oil flowing through first pilot conduit 53, and controlling the hydraulic pressure transmitted to second pilot port p2 of pilot switching valve for the boom 37.
Based on the hydraulic pressure detected by hydraulic pressure sensor 63, controller 20 controls the opening degree of proportional solenoid valve 73 and outputs, to proportional solenoid valve 73, an instruction signal for instructing boom-lowering. In accordance with the degree of the hydraulic pressure transmitted to second pilot port p2, the speed of boom 6 when lowered is adjusted.
In addition, based on the pilot pressure of second pilot conduit 54 detected by hydraulic pressure sensor 64, controller 20 controls proportional solenoid valve 74. That is, hydraulic pressure sensor 64 has a function as a second pressure sensor for detecting the hydraulic pressure generated in second pilot conduit 54 between second pilot pressure control valve 41B and proportional solenoid valve 74 in accordance with the operation of first control lever 44. In accordance with the hydraulic pressure detected by hydraulic pressure sensor 64, controller 20 outputs an instruction signal G4 to proportional solenoid valve 74 and adjusts the opening degree thereof, thereby changing a flow rate of the hydraulic oil flowing through second pilot conduit 54, and controlling the hydraulic pressure transmitted to first pilot port p1 of pilot switching valve for the boom 37.
Based on the hydraulic pressure detected by hydraulic pressure sensor 64, controller 20 controls the opening degree of proportional solenoid valve 74 and outputs, to proportional solenoid valve 74, an instruction signal for instructing boom-raising. In accordance with the degree of the hydraulic pressure transmitted to first pilot port p1, the speed of boom 6 when raised is adjusted.
A shuttle valve 80 is provided in second pilot conduit 54. Shuttle valve 80 has two entrance ports and one exit port. The exit port of shuttle valve 80 is connected to first pilot port p1 of pilot switching valve for the boom 37 via second pilot conduit 54. One entrance port of shuttle valve 80 is connected to second pilot pressure control valve 41B via second pilot conduit 54. The other entrance port of shuttle valve 80 is connected to a pump flow path 55.
Pump flow path 55 branches off from pump flow path 51. One end of pump flow path 55 is connected to pump flow path 51 and the other end of pump flow path 55 is connected to shuttle valve 80. The hydraulic oil transported by third hydraulic pump 50 flows to first control lever device 41 and second control lever device 42 via pump flow path 51, and also flows to shuttle valve 80 via pump flow paths 51 and 55.
Shuttle valve 80 is a shuttle valve of higher pressure priority type. Shuttle valve 80 compares the hydraulic pressure in second pilot conduit 54 connected to one entrance port and the hydraulic pressure in pump flow path 55 connected to the other entrance port, and selects the higher pressure. Shuttle valve 80 causes a higher pressure-side flow path of second pilot conduit 54 and pump flow path 55 to communicate with the exit port, and supplies the hydraulic oil flowing through this higher pressure-side flow path to first pilot port p1 of pilot switching valve for the boom 37.
A proportional solenoid valve 75 included in relay block 70 is provided in pump flow path 55. Proportional solenoid valve 75 is a valve for forcible boom-raising intervention. Proportional solenoid valve 75 receives an instruction signal G5 outputted from controller 20, and adjusts the opening degree thereof. Regardless of the operation of first control lever device 41 by the operator, controller 20 outputs instruction signal G5 to proportional solenoid valve 75 and adjusts the opening degree thereof, thereby changing a flow rate of the hydraulic oil flowing through pump flow path 55, and controlling the hydraulic pressure transmitted to first pilot port p1 of pilot switching valve for the boom 37. By adjustment of the opening degree of proportional solenoid valve 75, controller 20 controls the operation for forcibly raising boom 6.
Third pilot pressure control valve 41C and fourth pilot pressure control valve 41D have configurations similar to those of first pilot pressure control valve 41A and second pilot pressure control valve 41B described above. Similarly to first pilot pressure control valve 41A and second pilot pressure control valve 41B, third pilot pressure control valve 41C and fourth pilot pressure control valve 41D form a pair, and either third pilot pressure control valve 41C or fourth pilot pressure control valve 41D is selected in accordance with the operation of first control lever 44. For example, third pilot pressure control valve 41C corresponds to the operation for inclining first control lever 44 toward the left direction, and fourth pilot pressure control valve 41D corresponds to the operation for inclining first control lever 44 toward the right direction.
Third pilot pressure control valve 41C is connected to pump flow path 51, tank flow path 52 and a third pilot conduit 56. Third pilot pressure control valve 41C controls supply and discharge of the hydraulic oil to and from second pilot port p2 of pilot switching valve for the bucket 40. Fourth pilot pressure control valve 41D is connected to pump flow path 51, tank flow path 52 and a fourth pilot conduit 57. Fourth pilot pressure control valve 41D controls supply and discharge of the hydraulic oil to and from first pilot port p1 of pilot switching valve for the bucket 40. In accordance with the operation of first control lever 44, supply and discharge of the hydraulic oil to and from bucket cylinder 11 are controlled, and extension and contraction of bucket cylinder 11 are controlled. As a result, the operation of bucket 8 toward the excavation direction or the open direction is controlled in accordance with the operation of first control lever 44.
The pressure (pilot pressure) of the hydraulic oil supplied to third pilot conduit 56 via third pilot pressure control valve 41C is detected by a hydraulic pressure sensor 66. Hydraulic pressure sensor 66 outputs, to controller 20, a pressure signal P6 corresponding to the detected pilot pressure of the hydraulic oil. A proportional solenoid valve 76 is provided in third pilot conduit 56 connecting third pilot pressure control valve 41C and second pilot port p2 of pilot switching valve for the bucket 40. In accordance with the hydraulic pressure detected by hydraulic pressure sensor 66, controller 20 outputs an instruction signal G6 to proportional solenoid valve 76, and controls the hydraulic pressure transmitted to second pilot port p2 of pilot switching valve for the bucket 40. In accordance with the degree of the hydraulic pressure transmitted to second pilot port p2, the speed of bucket 8 when moved toward the excavation direction is adjusted.
The pressure (pilot pressure) of the hydraulic oil supplied to fourth pilot conduit 57 via fourth pilot pressure control valve 41D is detected by a hydraulic pressure sensor 67. Hydraulic pressure sensor 67 outputs, to controller 20, a pressure signal P7 corresponding to the detected pilot pressure of the hydraulic oil. A proportional solenoid valve 77 is provided in fourth pilot conduit 57 connecting fourth pilot pressure control valve 41D and first pilot port p1 of pilot switching valve for the bucket 40. In accordance with the hydraulic pressure detected by hydraulic pressure sensor 67, controller 20 outputs an instruction signal G7 to proportional solenoid valve 77, and controls the hydraulic pressure transmitted to first pilot port p1 of pilot switching valve for the bucket 40. In accordance with the degree of the hydraulic pressure transmitted to first pilot port p1, the speed of bucket 8 when moved toward the open direction is adjusted.
Fifth pilot pressure control valve 42A, sixth pilot pressure control valve 42B, seventh pilot pressure control valve 42C, and eighth pilot pressure control valve 42D have configurations similar to those of first pilot pressure control valve 41A, second pilot pressure control valve 41B, third pilot pressure control valve 41C, and fourth pilot pressure control valve 41D described above. Fifth pilot pressure control valve 42A and sixth pilot pressure control valve 42B form a pair, and either fifth pilot pressure control valve 42A or sixth pilot pressure control valve 42B is selected in accordance with the operation of second control lever 45. Seventh pilot pressure control valve 42C and eighth pilot pressure control valve 42D form a pair, and either seventh pilot pressure control valve 42C or eighth pilot pressure control valve 42D is selected in accordance with the operation of second control lever 45.
For example, fifth pilot pressure control valve 42A corresponds to the operation for inclining second control lever 45 toward the frontward direction, and sixth pilot pressure control valve 42B corresponds to the operation for inclining second control lever 45 toward the backward direction. Seventh pilot pressure control valve 42C corresponds to the operation for inclining second control lever 45 toward the left direction, and eighth pilot pressure control valve 42D corresponds to the operation for inclining second control lever 45 toward the right direction.
Fifth pilot pressure control valve 42A is connected to pump flow path 51, tank flow path 52 and a fifth pilot conduit 60. Sixth pilot pressure control valve 42B is connected to pump flow path 51, tank flow path 52 and a sixth pilot conduit 61. A not-shown electric motor for revolving upper revolving unit 3 is controlled based on the pressure of the hydraulic oil supplied to fifth pilot conduit 60 via fifth pilot pressure control valve 42A and the pressure of the hydraulic oil supplied to sixth pilot conduit 61 via sixth pilot pressure control valve 42B. Rotational driving of this electric motor when the hydraulic oil is supplied to fifth pilot conduit 60 is opposite to rotational driving of the electric motor when the hydraulic oil is supplied to sixth pilot conduit 61. In accordance with the direction of operation and the amount of operation of second control lever 45, the revolving direction and the revolving speed of upper revolving unit 3 are controlled.
Seventh pilot pressure control valve 42C is connected to pump flow path 51, tank flow path 52 and a seventh pilot conduit 58. Seventh pilot pressure control valve 42C controls supply and discharge of the hydraulic oil to and from first pilot port p1 of pilot switching valve for the arm 36. Eighth pilot pressure control valve 42D is connected to pump flow path 51, tank flow path 52 and an eighth pilot conduit 59. Eighth pilot pressure control valve 42D controls supply and discharge of the hydraulic oil to and from second pilot port p2 of pilot switching valve for the arm 36. In accordance with the operation of second control lever 45, supply and discharge of the hydraulic oil to and from arm cylinder 10 are controlled, and extension and contraction of arm cylinder 10 are controlled. As a result, the operation for relatively rotating arm 7 with respect to boom 6 is controlled in accordance with the operation of second control lever 45.
The pressure (pilot pressure) of the hydraulic oil supplied to seventh pilot conduit 58 via seventh pilot pressure control valve 42C is detected by a hydraulic pressure sensor 68. Hydraulic pressure sensor 68 outputs, to controller 20, a pressure signal P8 corresponding to the detected pilot pressure of the hydraulic oil. A proportional solenoid valve 78 is provided in seventh pilot conduit 58 connecting seventh pilot pressure control valve 42C and first pilot port p1 of pilot switching valve for the arm 36. In accordance with the hydraulic pressure detected by hydraulic pressure sensor 68, controller 20 outputs an instruction signal G8 to proportional solenoid valve 78, and controls the hydraulic pressure transmitted to first pilot port p1 of pilot switching valve for the arm 36. In accordance with the degree of the hydraulic pressure transmitted to first pilot port p1, the speed of arm 7 when moved toward the direction of extending arm 7, i.e., toward the direction in which arm 7 moves away from upper revolving unit 3, is adjusted.
The pressure (pilot pressure) of the hydraulic oil supplied to eighth pilot conduit 59 via eighth pilot pressure control valve 42D is detected by a hydraulic pressure sensor 69. Hydraulic pressure sensor 69 outputs, to controller 20, a pressure signal P9 corresponding to the detected pilot pressure of the hydraulic oil. A proportional solenoid valve 79 is provided in eighth pilot conduit 59 connecting eighth pilot pressure control valve 42D and second pilot port p2 of pilot switching valve for the arm 36. In accordance with the hydraulic pressure detected by hydraulic pressure sensor 69, controller 20 outputs an instruction signal G9 to proportional solenoid valve 79, and controls the hydraulic pressure transmitted to second pilot port p2 of pilot switching valve for the arm 36. In accordance with the degree of the hydraulic pressure transmitted to second pilot port p2, the speed of arm 7 when moved toward the direction of bending arm 7, i.e., toward the direction in which arm 7 comes closer to upper revolving unit 3, is adjusted.
The setting of a correspondence relationship between the operation directions of first and second control levers 44 and 45 and the operation of work implement 5 and the revolving operation of upper revolving unit 3 may be switchable to desired patterns. For example, first pilot pressure control valve 41A and second pilot pressure control valve 41B may correspond to the operations for inclining first control lever 44 toward the frontward and backward directions, respectively, or may correspond to the operations for inclining first control lever 44 toward the left and right directions, respectively.
A hollow and closed-end cylindrical cylinder portion 82 is formed in a valve main body 81, and a piston 83 is arranged inside cylinder portion 82. Piston 83 is provided to be capable of reciprocating along the axial direction of cylinder portion 82. Piston 83 has a stepped portion 83a, and a diameter of piston 83 changes at stepped portion 83a. Piston 83 has an upper end 83b at an end on the side where the diameter gets smaller at stepped portion 83a (on the upper side in
At upper end 83b, piston 83 is in contact with first control lever 44. Upper end 83b has a spherical outer surface, which allows piston 83 to smoothly move along the axial direction of cylinder portion 82 in line with the operation of first control lever 44. Lower end 83c of piston 83 faces a bottom surface 82b of cylinder portion 82.
Piston 83 is formed to be hollow. A plate-like retainer 84 is provided on an inner wall of stepped portion 83a of piston 83. Retainer 84 has, at a central portion thereof, a through hole passing through retainer 84 in the thickness direction. A spool 85 is arranged to pass through the through hole of retainer 84. Spool 85 is arranged in a hollow space defined by piston 83. Retainer 84 is provided to be capable of reciprocating along the axial direction of cylinder portion 82 in line with the operation of piston 83. Spool 85 is also provided to be capable of reciprocating along the axial direction of cylinder portion 82.
Spool 85 has a tip large-diameter portion 85a that is an end on the upper end 83b side of piston 83, a small-diameter portion 85b having a smaller diameter than that of tip large-diameter portion 85a, and an intermediate large-diameter portion 85c having a larger diameter than that of small-diameter portion 85b. As compared with the through hole formed in retainer 84, tip large-diameter portion 85a and intermediate large-diameter portion 85c are provided to have larger diameters than that of the through hole, and small-diameter portion 85b is provided to have a smaller diameter than that of the through hole. Small-diameter portion 85b can be inserted into the through hole of retainer 84, whereas tip large-diameter portion 85a and intermediate large-diameter portion 85c cannot be inserted into the through hole of retainer 84.
The length of small-diameter portion 85b is larger than the thickness of retainer 84. Therefore, within the range of the length of small-diameter portion 85b, spool 85 is provided to be capable of relatively reciprocating along the axial direction of cylinder portion 82 with respect to retainer 84. Tip large-diameter portion 85a and intermediate large-diameter portion 85c restrict the relative upward and downward movement of spool 85 with respect to retainer 84. Within the range from a position where retainer 84 is in contact with tip large-diameter portion 85a to a position where retainer 84 is in contact with intermediate large-diameter portion 85c, spool 85 is relatively movable with respect to retainer 84.
A main spring 86 is provided between retainer 84 and bottom surface 82b of cylinder portion 82. Main spring 86 pushes up piston 83 in the upward direction in
Main spring 86 generates reactive force in the direction in which lower end 83c of piston 83 comes closer to bottom surface 82b of cylinder portion 82 (in the downward direction in the figure), the reactive force being proportional to an amount of relative movement of piston 83 with respect to cylinder portion 82. Spring 87 generates reactive force in the direction in which intermediate large-diameter portion 85c of spool 85 comes closer to retainer 84, the reactive force being proportional to an amount of relative movement of spool 85 with respect to retainer 84.
Retainer 84 relatively moves with respect to spool 85 in the direction in which retainer 84 moves away from tip large-diameter portion 85a of spool 85 and comes closer to intermediate large-diameter portion 85c. While retainer 84 is moving along small-diameter portion 85b of spool 85, retainer 84 does not apply stress to spool 85 and spool 85 is maintained in the original position shown in
Due to this movement of spool 85, the hydraulic oil having a prescribed pilot pressure is supplied from first pilot pressure control valve 41A to first pilot conduit 53. As a result, the pilot pressure is supplied to pilot port p2 of pilot switching valve for the boom 37 via first pilot conduit 53 and the operation of boom 6 in the direction of lowering boom 6 is controlled. A flow rate of the hydraulic oil supplied to boom cylinder 9 is determined by the operation for inclining first control lever 44 by the operator. As the inclination angle of first control lever 44 becomes larger, the flow rate of the hydraulic oil becomes larger and the moving speed of the spool of pilot switching valve for the boom 37 also becomes larger.
The land leveling work with hydraulic excavator 1 having the aforementioned configuration will be described below.
Cutting edge 8a of bucket 8 moves to follow the arc-shaped path. Therefore, when design surface S is a flat surface, cutting edge 8a of bucket 8 may move away from the design surface if the operation for lowering boom 6 is not performed. Therefore, the operator operating work implement 5 operates second control lever 45 to perform the excavation operation by arm 7, and also continues to perform the operation for inclining first control lever 44 toward the first pilot pressure control valve 41A side to perform the operation for lowering boom 6.
In the case where cutting edge 8a of bucket 8 moves to be lower than design surface S and excavates the ground excessively when work implement 5 is operated in accordance with the aforementioned operator's operation, an instruction for forcibly raising boom 6 is outputted from controller 20. When it is expected that cutting edge 8a of bucket 8 will move to be lower than design surface S, controller 20 executes control for automatically raising boom 6 to prevent cutting edge 8a of bucket 8 from becoming lower than design surface S. At this time, controller 20 outputs instruction signal G3 for decreasing the opening degree of proportional solenoid valve 73 and instruction signal G5 for increasing the opening degree of proportional solenoid valve 75. As a result, proportional solenoid valve 73 that has been in the open state enters the fully-closed state, and proportional solenoid valve 75 that has been in the fully-closed state enters the open state.
When proportional solenoid valve 75 is opened, the discharge pressure on the exit side of third hydraulic pump 50 is applied to shuttle valve 80 via pump flow path 55. Shuttle valve 80 of higher pressure priority type operates to cause pump flow path 55 and first pilot port p1 of pilot switching valve for the boom 37 to communicate with each other. As a result, the high-pressure hydraulic oil is supplied to first pilot port p1 of pilot switching valve for the boom 37, and thus, the operation for raising boom 6 is performed.
In the case where cutting edge 8a of bucket 8 moves away from the ground when the operation for raising boom 6 is continued, forcible raising of boom 6 is stopped and an instruction for lowering boom 6 is outputted from controller 20 in accordance with the lowering operation of first control lever 44. At this time, controller 20 outputs instruction signal G3 for increasing the opening degree of proportional solenoid valve 73 and instruction signal G5 for decreasing the opening degree of proportional solenoid valve 75. As a result, proportional solenoid valve 73 that has been in the fully-closed state enters the open state, and proportional solenoid valve 75 that has been in the open state enters the fully-closed state.
When proportional solenoid valve 73 is opened, the hydraulic oil having a prescribed pilot pressure is supplied to second pilot port p2 of pilot switching valve for the boom 37 via first pilot conduit 53, and thus, the operation for lowering boom 6 is performed.
Pump flow path 55 has a function as a boom-raising pilot conduit connected to first pilot port p1 of pilot switching valve for the boom 37 via shuttle valve 80. First pilot conduit 53 has a function as a boom-lowering pilot conduit connected to second pilot port p2 of pilot switching valve for the boom 37. Proportional solenoid valve 75 provided in pump flow path 55 has a function as a boom-raising proportional solenoid valve. Proportional solenoid valve 73 provided in first pilot conduit 53 has a function as a boom-lowering proportional solenoid valve.
Both second pilot conduit 54 and pump flow path 55 have a function as a boom-raising pilot conduit. More specifically, second pilot conduit 54 functions as a normal boom-raising pilot conduit, and pump flow path 55 functions as a forcible boom-raising pilot conduit. In addition, both proportional solenoid valve 74 and proportional solenoid valve 75 have a function as a boom-raising proportional solenoid valve. More specifically, proportional solenoid valve 74 can be expressed as a normal boom-raising proportional solenoid valve, and proportional solenoid valve 75 can be expressed as a forcible boom-raising proportional solenoid valve.
Hydraulic pressure sensor 63 detects the hydraulic pressure generated in first pilot conduit 53 between first pilot pressure control valve 41A and proportional solenoid valve 73 in accordance with the operation of first control lever 44. Based on the hydraulic pressure detected by hydraulic pressure sensor 63, controller 20 outputs instruction signal G3 to proportional solenoid valve 73 and controls the opening degree of proportional solenoid valve 73. Controller 20 outputs instruction signal G5 to proportional solenoid valve 75 and controls the opening degree of proportional solenoid valve 75.
When the current position of cutting edge 8a of bucket 8 is compared with design surface S and cutting edge 8a is located at a position higher than design surface S, control for lowering boom 6 is executed. When it becomes highly likely that cutting edge 8a erodes design surface S, control for raising boom 6 is executed. Therefore, when the current position of cutting edge 8a of bucket 8 fluctuates with respect to design surface S, the setting of the opening degrees of proportional solenoid valve 73 and proportional solenoid valve 75 also changes frequently.
A value of the boom-lowering EPC current shown in the lower graph in
When the PPC pressure decreases, spool 85 and retainer 84 of first pilot pressure control valve 41A (refer to
Hydraulic excavator 1 according to the present embodiment has been made to solve this problem.
All of the horizontal axes of the four graphs in
The lowest graph and the second lowest graph among the four graphs in
The amount of increase in current per unit time will now be described.
That is, the amount of increase in current per unit time is calculated in accordance with the following equation:
(amount of increase in current per unit time)=(i2−i1)/(t2−t1).
Referring to the lowest graph among the four graphs in
The amount of decrease in current per unit time will now be described.
That is, the amount of decrease in current per unit time is calculated in accordance with the following equation:
(amount of decrease in current per unit time)=(i3−i4)/(t4−t3).
Next, the function and effect of the present embodiment will be described.
According to the present embodiment, as shown in
By relatively reducing a rate of increase in current when proportional solenoid valve 73 is opened and reducing the valve opening speed of proportional solenoid valve 73, abrupt flow of the hydraulic oil to the pilot switching valve for the boom 37 side via proportional solenoid valve 73 can be suppressed. Therefore, sharp decrease in amount of the hydraulic oil present in first pilot conduit 53 between first pilot pressure control valve 41A that constitutes first control lever device 41 and proportional solenoid valve 73 can be suppressed. As a result, fluctuations in pressure of the hydraulic oil between first pilot pressure control valve 41A and proportional solenoid valve 73 can be suppressed, and thus, the frequency of increase and decrease in PPC pressure is low as shown in the uppermost graph in
In the upper graph in
Therefore, in hydraulic excavator 1 according to the present embodiment, occurrence of minute vibrations in first control lever 44 can be suppressed, and thus, occurrence of the problem of bringing a sense of discomfort to the operator can be avoided.
If the rate of increase in current when the opening degree of proportional solenoid valve 73 is increased is reduced excessively, the responsiveness to the operator's operation decreases. That is, it takes time from when the operator performs the operation for inclining first control lever 44 to when boom 6 operates, and the operator may feel that the operation of boom 6 is slow and may feel stress. Therefore, it is desirable to reduce the rate of increase in current when the opening degree of proportional solenoid valve 73 is increased, so as not to affect the responsiveness of the operation of work implement 5 at the time of manual operation. For example, the rate of increase in current when the opening degree of proportional solenoid valve 73 is increased may be set to fall within 1/100 times or more and ½ times or less of a rate of increase in current when the opening degree of proportional solenoid valve 75 is increased.
In addition, as shown in
As described above, by reducing the rate of increase in current when proportional solenoid valve 73 is opened, fluctuations in PPC pressure can be suppressed and occurrence of minute vibrations in first control lever 44 can be suppressed. On the other hand, by relatively increasing a rate of decrease in current when proportional solenoid valve 73 is closed as compared with the rate of increase in current when proportional solenoid valve 73 is opened, the valve closing speed of proportional solenoid valve 73 becomes relatively high.
The case of closing proportional solenoid valve 73 during automatic control corresponds to the case in which the instruction for lowering boom 6 to prevent cutting edge 8a of bucket 8 from moving away from the ground is no longer necessary. In this case, it is desirable to shorten the time to continue the operation for lowering boom 6 and immediately stop the operation for lowering boom 6. By relatively increasing the valve closing speed of proportional solenoid valve 73, the operation for lowering boom 6 can be stopped immediately, and thus, occurrence of the problem of excessive excavation with respect to design surface S can be avoided more reliably. Therefore, the efficiency and quality during the work for leveling the ground with hydraulic excavator 1 can be enhanced.
In the aforementioned embodiment, description has been given that the rate of increase in current when proportional solenoid valve 73 is opened is compared with the rate of increase in current when the opening degree of proportional solenoid valve 75 is increased, and thereby, the rate of increase in current when proportional solenoid valve 73 is opened is reduced. However, a target for comparison with the rate of increase in current when proportional solenoid valve 73 is opened is not limited to the rate of increase in current when the opening degree of proportional solenoid valve 75 is increased. The target for comparison may be a rate of increase in current when other proportional solenoid valves 74 and 76 to 79 are opened.
Specifically, description has been given that the second lowest graph among the four graphs in
Therefore, the amount of increase in current per unit time when controller 20 outputs, to proportional solenoid valve 73, the instruction signal for instructing an increase in opening degree of proportional solenoid valve 73 is smaller than the amount of increase in current per unit time when controller 20 outputs, to proportional solenoid valve 74, the instruction signal for instructing an increase in opening degree of proportional solenoid valve 74. Comparing the time that elapses before the current value outputted to each of proportional solenoid valves 73 and 74 increases from zero and reaches the same value when the current value increases, it takes a longer time in proportional solenoid valve 73.
An amount of change per unit time in current outputted to other proportional solenoid valves 76 to 79 by controller 20 is also the same as the amount of change in current per unit time shown in the second lowest graph in
As described above, by relatively reducing the amount of increase in current per unit time for the instruction signal outputted to boom-lowering proportional solenoid valve 73, occurrence of minute vibrations in first control lever 44 can be suppressed.
It should be understood that the embodiment disclosed herein is illustrative and not limitative in any respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
1 hydraulic excavator; 2 undercarriage; 3 upper revolving unit; 4 cab; 5 work implement; 6 boom; 7 arm; 8 bucket; 8a cutting edge; 9 boom cylinder; 20 controller; 34 main operation valve; 35 tank; 37 pilot switching valve for the boom; 41 first control lever device; 41A to 41D, 42A to 42D pilot pressure control valve; 42 second control lever device; 44 first control lever; 45 second control lever; 50 third hydraulic pump; 51, 55 pump flow path; 52 tank flow path; 53, 54, 56 to 61 pilot conduit; 63, 64, 66 to 69 hydraulic pressure sensor; 70 relay block; 73 to 79 proportional solenoid valve; 80 shuttle valve; 81 valve main body; 82 cylinder portion; 83 piston; 84 retainer; 85 spool; 86 main spring; 87 spring; G3 to G9 instruction signal; P3, P4, P6 to P9 pressure signal; S design surface; p1 first pilot port; p2 second pilot port.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/082825 | 12/6/2013 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2014/192190 | 12/4/2014 | WO | A |
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