Construction machine

A construction machine that precisely enables derivation of the operation characteristics of hydraulic actuators in a high-velocity area with less calibration operation is provided. A controller (10) has a calibration mode in which the controller (10) derives operation characteristics (α(xs)) representing a relation among a spool position (xs) of a meter-in valve (8a1), an operation velocity (Va) of a hydraulic actuator (4a), and a differential pressure (ΔP) across the meter-in valve (8a1), and is configured to, in a case where the spool position (xs) of the meter-in valve (8a1) has changed in a direction to increase the opening area of the meter-in valve (8a1) in the calibration mode, output a command signal to increase the opening area of a bleed-off valve (8b1) to a bleed-off solenoid proportional pressure-reducing valve (8b2) as a command signal to reduce the differential pressure (ΔP).

TECHNICAL FIELD

The present invention relates to a construction machine such as a hydraulic excavator.

BACKGROUND ART

In recent years, along with efforts being made to support information-oriented construction, there are construction machines such as hydraulic excavators having the machine control functionality of controlling the position and posture of a work mechanism such as a boom, an arm or a bucket such that the work mechanism moves along a target construction surface. As a known representative example of those construction machines, there has been known a construction machine that limits the operation of a work mechanism such that the bucket tip does not move ahead further when the bucket tip gets close to a target construction surface.

Engineering works construction management standards specify standard values of tolerated precision about target construction surfaces in the height direction. In a case where the precision of a finished form of a construction surface exceeds a tolerated value, it becomes necessary to redo the construction, and thereby the work efficiency deteriorates. Accordingly, the machine control functionality is demanded to have control precision that is necessary for satisfying the tolerated precision of finished forms.

In order to control the position and posture of a work mechanism precisely, it is necessary to accurately know the operation characteristics of hydraulic actuators. The operation characteristics of actuators are affected by the installation positions of pressure sensors, and computation errors of relations of opening areas relative to spool positions (opening characteristics). Accordingly, for more accurate derivation of the operation characteristics, the operation characteristics are desirably derived from measurement data that is obtained when hydraulic excavators are actually caused to operate.

As techniques to derive the operation characteristics of hydraulic actuators, Patent Document 1 discloses a construction machine control system, a construction machine and a construction machine control method that enable derivation of the operation characteristics of hydraulic cylinders. A hydraulic excavator control system illustrated in Patent Document 1 has a deriving section that derives the operation characteristics of actuators. The deriving section acquires measurement data by actually causing the hydraulic excavator to operate, and derives the operation characteristics of the actuators on the basis of the measurement data.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

The “deriving section” in Patent Document 1 performs direct mapping of relations between the spool positions of meter-in valves and actuator velocities as operation characteristics. Because of this, when measurement data in a high-velocity area of the actuator velocities is to be acquired, the actuators are required to be actually moved at high velocities. Mapping is performed by using velocities at the steady state as true values, but in a case where the actuators are moved at high velocities, high accelerations occur more easily, and the influence of the inertia due to link motion and the viscous resistance of a hydraulic fluid become dominant. Accordingly, it becomes difficult to accurately map velocities at the steady state relative to the spool positions of the meter-in valves. In addition, actual hydraulic excavators have movable ranges. Accordingly, it is difficult to acquire data in a high-velocity area by calibration operation performed only once, and it is necessary to suspend calibration to correct the posture of a hydraulic excavator.

One of possible solutions to the problems described above is to gradually accelerate an actuator by setting the acceleration of the spool to be low at the time of calibration operation. However, if the spool is accelerated for a long time, the limit of the movable range of the actuator is exceeded. Accordingly, there is a limit of the minimum value of the acceleration, and it is difficult to eliminate the influence of the inertia of the actuator and the viscous resistance of the hydraulic fluid in a high-velocity area.

The present invention has been made in view of the problems described above, and an object of the present invention is to provide a construction machine that allows precise derivation of the operation characteristics of hydraulic actuators in a high-velocity area with less calibration operation.

Means for Solving the Problem

In order to achieve the object described above, the present invention provides a construction machine including: a prime mover; a tank that stores a hydraulic operating fluid; a hydraulic pump that is driven by the prime mover, and delivers, as a hydraulic fluid, the hydraulic operating fluid sucked in from the tank; a hydraulic actuator that is driven by the hydraulic fluid delivered from the hydraulic pump; a meter-in valve that adjusts a flow rate of the hydraulic fluid supplied from the hydraulic pump to the hydraulic actuator; a meter-in spool position adjusting device that adjusts a spool position of the meter-in valve; and a controller that outputs a command signal to the meter-in spool position adjusting device. The construction machine includes: a velocity sensor for sensing an operation velocity of the hydraulic actuator; a meter-in spool position sensor that senses the spool position of the meter-in valve; a pressure sensor that senses a differential pressure across the meter-in valve; and a pressure adjusting device that adjusts the differential pressure across the meter-in valve. The controller has a calibration mode in which the controller derives operation characteristics that represent a relation among the spool position of the meter-in valve, the operation velocity of the hydraulic actuator, and the differential pressure across the meter-in valve, and is configured to, in a case where the spool position of the meter-in valve has changed in a direction to increase an opening area of the meter-in valve in the calibration mode, output a command signal to reduce the differential pressure across the meter-in valve to the pressure adjusting device such that increase in the flow rate of the hydraulic fluid to be flown into the meter-in valve is suppressed.

According to the thus-configured present invention, since the relation between the spool position of the meter-in valve and the actuator velocity is mapped indirectly by using the differential pressure across the meter-in valve, it becomes possible to perform the mapping of the operation characteristics without actually moving the actuator at a high velocity. Additionally, by adjusting the differential pressure across the meter-in valve at the time of calibration operation of deriving the operation characteristics of the hydraulic actuator, and keeping the actual velocity of the hydraulic actuator low such that the limit of the movable range of the actuator is not exceeded, the influence of the inertia of the hydraulic actuator and the viscous resistance of the hydraulic fluid that can be causes of errors of the mapping of the operation characteristics is mitigated. Thereby, it becomes possible to improve the precision of operation characteristics of hydraulic actuators in a high-velocity area with less calibration operation.

Advantages of the Invention

According to the present invention, it becomes possible, in a construction machine such as a hydraulic excavator, to improve the precision of operation characteristics of hydraulic actuators in a high-velocity area with less calibration operation.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, as an example of a construction machine according to embodiments of the present invention, a hydraulic excavator is explained with reference to the drawings. Note that equivalent members are given the same reference characters in the drawings, and overlapping explanations are omitted as appropriate.

First Embodiment

FIG. 1is a figure schematically illustrating the external appearance of a hydraulic excavator according to a first embodiment of the present implementation.

InFIG. 1, a hydraulic excavator100includes: an articulated front device (front work implement)1including a plurality of driven members (a boom4, an arm5and a bucket (work instrument)6) that are individually vertically pivoted, and are coupled with each other; and an upper swing structure2and a lower track structure3which configure a machine body. The upper swing structure2is swingably provided relative to the lower track structure3. In addition, the base end of the boom4of the front device1is vertically pivotably supported at a front section of the upper swing structure2, one end of the arm5is vertically pivotably supported at an end section (tip) of the boom4different from its base end, and the bucket6is vertically pivotably supported at the other end of the arm5. The boom4, the arm5, the bucket6, the upper swing structure2and the lower track structure3are driven by a boom cylinder4a, an arm cylinder5a, a bucket cylinder6a, a swing motor2a, and left and right travel motors3a(only one travel motor is illustrated), respectively, which are hydraulic actuators. The boom cylinder4a, the arm cylinder5a, and the bucket cylinder6ahave built-in cylinder position sensors mentioned below that can measure their cylinder positions. By performing numerical differentiation of the measured cylinder positions, cylinder velocities are computed. That is, the cylinder position sensors configure a velocity sensor for sensing the operation velocities of the hydraulic actuators.

The boom4, the arm5and the bucket6operate on a single plane (hereinafter, an operation plane). The operation plane is a plane orthogonal to the pivot axes of the boom4, the arm5and the bucket6, and can be set such that it passes through the widthwise centers of the boom4, the arm5and the bucket6.

An operation lever device (operation device)9athat outputs operation signals for operating the hydraulic actuators2a,4a,5aand6ais provided in a cab9in which an operator gets. The operation lever device9aincludes an operation lever that can be inclined forward and backward, and leftward and rightward, and a sensor that electrically senses an operation signal corresponding to an inclination amount (lever operation amount) of the operation lever. The operation lever device9aoutputs the lever operation amount sensed by the sensor to a controller10which is a controller (illustrated inFIG. 2) via an electric wiring. In addition, a man-machine interface9bis installed in the cab9. The man-machine interface9bdisplays an operation instruction and a target surface sent from an operation state display control section10bmentioned below (illustrated inFIG. 2), and gives an instruction about an operation mode to a hydraulic system control section10cmentioned below (illustrated inFIG. 2).

The operation control of the boom cylinder4a, the arm cylinder5a, the bucket cylinder6a, the swing motor2aand the left and right travel motors3ais performed by controlling, with a control valve8, the direction and flow rate of a hydraulic operating fluid supplied from a hydraulic pump7driven by an engine40to each of the hydraulic actuators2ato6a. The control of the control valve8is performed by drive signals (pilot pressures) output from a pilot pump70mentioned below via a solenoid proportional valve. By controlling the solenoid proportional valve with the controller10based on the operation signals from the operation lever device9a, the operation of each of the hydraulic actuators2ato6ais controlled.

Note that the operation lever device9amay be a hydraulic pilot operation lever device different from the one described above, and may be configured to supply, as drive signals to the control valve8, pilot pressures according to operation directions and operation amounts of the operation lever operated by an operator, and drive each of the hydraulic actuators2ato6a.

FIG. 2is a figure schematically illustrating part of the processing functionality of the controller mounted on the hydraulic excavator100.

InFIG. 2, the controller10has various functionalities for controlling the operation of the hydraulic excavator100, and has a target operation calculating section10a, the operation state display control section10b, and the hydraulic system control section10c.

On the basis of design data11such as a three-dimensional construction drawing stored in advance by a construction manager in a storage device which is not illustrated or the like, a target construction surface computed according to the design data11, and an input through the operation lever device9aoperated by an operator, the target operation calculating section10acalculates target operation of the machine body, and gives the hydraulic system control section10cmentioned below a command about target positions of hydraulic actuators according to the target operation of the machine body.

The operation state display control section10bcontrols display of the man-machine interface9bprovided in the cab9and the like. On the basis of the target construction surface, and postural information about the front device1and a bucket target velocity which are calculated at the hydraulic system control section10cmentioned below, the operation state display control section10bcalculates an instruction content about operation assistance for the operator, and displays the instruction content on the man-machine interface9bin the cab9or gives a sound notification about the instruction content.

That is, the operation state display control section10bperforms part of the functionality as a machine guidance system that assists operation performed by the operator by displaying, on the man-machine interface9b, the posture of the front device1having driven members such as the boom4, the arm5and the bucket6, and the tip position, angle, velocity and the like of the bucket6, for example.

The hydraulic system control section10ccontrols the hydraulic system of the hydraulic excavator100including the hydraulic pump7, the control valve8, the hydraulic actuators2ato6aand the like. On the basis of target operation of each actuator calculated at the target operation calculating section10a, and a measurement value of each sensor attached to the hydraulic system of the hydraulic excavator100mentioned below, the hydraulic system control section10ccalculates a control command to realize the target operation, and controls the hydraulic system of the hydraulic excavator100. That is, the hydraulic system control section10cperforms part of the functionality as a machine control system that performs control of limiting the operation of the front device1such that portions other than the back surface of the bucket6do not contact the target surface, for example.

FIG. 3is a figure schematically illustrating the hydraulic system mounted on the hydraulic excavator100. Note that only portions related to the operation of the boom4are illustrated inFIG. 3. The other portions related to the operation of the hydraulic actuators are similar to those for the boom4, and thus explanations thereof are omitted.

InFIG. 3, a hydraulic system200includes: the control valve8that drives each of the hydraulic actuators2ato6a; the hydraulic pump7that supplies a hydraulic fluid to the control valve8; the pilot pump70that supplies pilot pressure to hydraulic equipment; and the engine40for driving the hydraulic pump7. The hydraulic system200operates according to control commands given from the controller10.

A bleed-off section8bof the control valve8is configured independently of a boom section8amentioned below. The bleed-off section8bis connected with a supply hydraulic line31, and is supplied with the hydraulic fluid from the hydraulic pump7. The supply hydraulic line31branches into a supply hydraulic line32and a supply hydraulic line33. The supply hydraulic line33is connected to a discharge hydraulic line34via a bleed-off valve8b1, and the discharge hydraulic line34is connected to a tank12. The bleed-off valve8b1is driven by a bleed-off solenoid proportional pressure-reducing valve8b2operating on the basis of a control input which is a command given from the controller10, establishes communication between the supply hydraulic line31and the discharge hydraulic line34, and bleeds off the hydraulic fluid from the hydraulic pump7. On the other hand, the supply hydraulic line32is connected to the boom section8a, and supplies the hydraulic fluid from the hydraulic pump7to the boom section8a.

In the boom section8a, the supply hydraulic line32is connected to the boom cylinder4avia a directional control valve8a1. The directional control valve8a1functions as a valve (meter-in valve) through which one of a bottom-side oil chamber4a1and a rod-side oil chamber4a2of the boom cylinder4acommunicates with a hydraulic line communicating with the hydraulic pump7, and as a valve (meter-out valve) through which the other one of the bottom-side oil chamber4a1and the rod-side oil chamber4a2of the boom cylinder4acommunicates with a hydraulic line communicating with the tank12. The meter-in valve8a1is driven by a directional-control-valve solenoid proportional pressure-reducing valve8a2operating based on a control input which is a command given from the controller10, and controls the flow rate of the hydraulic fluid from the hydraulic pump7. By driving a solenoid proportional pressure reducing valve8a2a, the hydraulic fluid is flown from the bottom-side oil chamber4a1to the rod-side oil chamber4a2. On the other hand, by driving a solenoid proportional pressure reducing valve8a2b, the hydraulic fluid is flown from the rod-side oil chamber4a2to the bottom-side oil chamber4a1. As the spool position of the meter-in valve8a1moves in the positive direction, the opening area of the meter-in valve8a1increases, and the flow rate of the hydraulic fluid to be flown therethrough increases. A cylinder position sensor4a4is attached to the boom cylinder4a, and a sensor signal is transmitted to the controller10.

In the boom section8a, a pressure sensor8a3(hereinafter, a meter-in valve upstream pressure sensor) is installed before the meter-in valve8a1, a pressure sensor8a4(hereinafter, a meter-in valve downstream pressure sensor) is installed after the meter-in valve8a1, and a meter-in spool position sensor8a5is installed at the meter-in valve8a1. In the pressure sensors8a4,8a4afunctions as a meter-in valve downstream pressure sensor in a case where the bottom-side oil chamber4a1communicates with the hydraulic pump7, and8a4bfunctions as a meter-in valve downstream pressure sensor in a case where the rod-side oil chamber4a2communicates with the hydraulic pump7. Each sensor is connected to the controller10, and a sensor signal is transmitted to the controller10.

The controller10receives inputs of a lever operation signal from the operation lever device9acorresponding to boom-operation, a calibration mode start signal and a calibration actuator selection signal from the man-machine interface9bmentioned below, and sensor signals of the cylinder position sensor built in the boom cylinder4a, and the meter-in valve upstream pressure sensor8a3, the meter-in valve downstream pressure sensor8a4and the meter-in spool position sensor8a5installed in the boom section8a. On the basis of these signals, the directional-control-valve solenoid proportional pressure-reducing valve8a2and the bleed-off solenoid proportional pressure-reducing valve8b2are driven.

Here, the controller10has a normal mode for driving actuators such as the boom cylinder4a, and a calibration mode for deriving the operation characteristics of the actuators such as the boom cylinder4a. The man-machine interface9bincludes a switch (e.g. a manually operated push type switch) that outputs an instruction to switch the operation mode from the normal mode to the calibration mode, and an electric signal for giving an instruction to switch actuators to be calibrated.

FIG. 4is a functional block diagram representing details of the hydraulic system control section10c. Note that only functionalities related to the calibration operation are illustrated inFIG. 4. Explanations of other functionalities are omitted because they are not related to the present invention directly.

InFIG. 4, the hydraulic system control section10chas an operation characteristics calculating section10c1, an operation characteristics storage section10c2, a calibration command calculating section10c3, and a control command output section10c4.

On the basis of an actuator velocity Vacomputed by performing numerical differentiation of an actuator position xaacquired from the cylinder position sensor4a4, a meter-in spool position xsacquired from the meter-in spool position sensor8a5, a meter-in valve upstream pressure Pinacquired from the meter-in valve upstream pressure sensor8a3, and a meter-in valve downstream pressure Poutacquired from the meter-in valve downstream pressure sensor8a4, the operation characteristics calculating section10c1calculates a relation between the meter-in spool position xsand the actuator velocity Va. Here, the actuator velocity Vamay be measured directly by using an Inertial Measurement Unit (IMU) or the like, without performing numerical differentiation of the actuator position xa.

The relation between the meter-in spool position xsand the actuator velocity Vacan be expressed by Formula (1) by using the meter-in valve upstream pressure Pinand the meter-in valve downstream pressure Pout.
[Equation 1]
Va=α(xs)√{square root over (Pin−Pout)}  (1)

Here, α(xs) is a monotonically increasing function of xs, and is a function reflecting the relation between the meter-in spool position xsand the opening area of the meter-in valve8a1(opening characteristics), and the influence of the pressure loss due to the misalignment of the installation positions of the pressure sensors8a3and8a4. In this document, a map of α(xs) in relation to xsis defined as the operation characteristics of the actuator. The calculated operation characteristics α(xs) are sent to the operation characteristics storage section10c2mentioned below.

FIG. 5is one example of an operation characteristics map derived by the operation characteristics calculating section10c1.

α(xs) is the operation characteristics derived by the operation characteristics calculating section10c1, and computed according to Formula (2) obtained by transposition of Formula (1).

The operation characteristics calculating section10c1derives the operation characteristics map illustrated inFIG. 5by mapping the operation characteristics α(xs) in relation to the meter-in spool position xs.

Returning toFIG. 4, the operation characteristics storage section10c2has the functionality of storing the operation characteristics α(xs) sent from the operation characteristics calculating section10c1. Every time the calibration operation is completed once and the operation characteristics α(xs) derived by the operation characteristics calculating section10c1are sent to the operation characteristics calculating section10c1, the operation characteristics α(xs) having been stored in the operation characteristics calculating section10c1are updated.

On the basis of a signal that identifies an actuator to be calibrated and is input from the man-machine interface9b, the calibration command calculating section10c3selects the actuator about which the operation characteristics α(xs) are to be derived, and calculates a meter-in spool position command xs,reffor operation calibration, and a bleed-off spool position command xb,reffor adjusting the differential pressure across the meter-in valve8a1. A predetermined waveform is used for the meter-in spool position command Xs, refirrespective of measurement results of sensors. The bleed-off spool position command xb,refis determined on the basis of the meter-in spool position command xs,ref, the meter-in valve upstream pressure Pinsent from the meter-in valve upstream pressure sensor8a3, and the meter-in valve downstream pressure Poutsent from the meter-in valve downstream pressure sensor8a4. Details of derivation of these position commands are mentioned below. These position commands are sent to the control command output section10c4mentioned below. In addition, in a case where the calibration command calculating section10c3is performing calculation, a signal indicating that calibration operation is continued (a calibration operation continuation flag signal) is sent to the operation state display control section10b.

FIG. 6is a figure illustrating one example of the command waveform of the meter-in spool position command xs,refcalculated by the calibration command calculating section10c3.

The command waveform of the meter-in spool position command xs,refis determined in advance as time series changes from a minimum stroke (0) to a full stroke xs,max. In the case explained here, a sine waveform like the one mentioned below is input as one example of the command waveform.

[Equation⁢⁢3]xs,ref=0.5⁢xs,max⁢sin⁡(πtf⁢(2⁢t-tf2))+0.5⁢xs,max(3)
Here, tfis the period of the sine waveform to give commands. The command waveform may be a triangular waveform. It is assumed that the sine waveform to give commands can repetitively give commands with different phases, and the number of times of the repetitions can be selected by an operator as desired. In a case where the operation characteristics map illustrated inFIG. 5is derived by using the least-squares method according to Formula (2), the influence of variations of measurement sensors decreases as the number of times of the repetitions of the command waveform increases, and the precision of the derivation of the operation characteristics α(xs) improves.

FIG. 7is a figure illustrating one example of a command-value computation map for the bleed-off spool position command xs,refcalculated by the calibration command calculating section10c3.

The bleed-off spool position command xb,refis determined on the basis of the meter-in spool position command xs,ref, the meter-in valve upstream pressure Pinsent from the meter-in valve upstream pressure sensor8a3, and the meter-in valve downstream pressure Poutsent from the meter-in valve downstream pressure sensor8a4. First, a target differential pressure ΔPtargetacross the meter-in valve8a1is determined on the basis of the map illustrated inFIG. 7and the meter-in spool position command xs,ref. In the map illustrated inFIG. 7, the target differential pressure ΔPtargetacross the meter-in valve8a1is mapped such that it decreases as the meter-in spool position command xs,refincreases. At this time, the maximum value ΔPmaxof the target differential pressure ΔPtargetis set to a level that is sufficient to overcome the static friction and the own weight of the actuator. Although the value of ΔPmaxdiffers depending on the operation direction of the actuator, it is preferably 5 to 10 MPa. In addition, the minimum value ΔPminof the target differential pressure ΔPtargetis set to a level that is sufficient to negate measurement variations of the installed pressure sensors8a3and8a4. Preferably, the value of ΔPminis approximately 1 MPa. On the basis of results of the mapping, the bleed-off spool position command xb,refis determined according to the following formula such that the difference between the target differential pressure ΔPtargetacross the meter-in valve and an actual differential pressure ΔP=Pin−Poutacross the meter-in valve8a1measured by the meter-in valve upstream pressure sensor8a3and the meter-in valve downstream pressure sensor8a4becomes small.
[Equation 4]
xb,ref=xb,pre+Kp(ΔPtarget−ΔP)  (4)
Here, Kpis the feedback gain, and is an optional positive constant. Xb,preis a bleed-off spool position command of the previous calculation period.

Returning toFIG. 4, on the basis of the meter-in spool position command xs,refand the bleed-off spool position command xb,refsent from the calibration command calculating section10c3, the control command output section10c4outputs current commands to the directional-control-valve solenoid proportional pressure-reducing valve8a2and the bleed-off solenoid proportional pressure-reducing valve8b2. The control command output section10c4has a map used for converting each spool position command into a current command, and current command values are determined on the basis of the map.

FIG. 8is a figure illustrating a calibration command calculation flow of the hydraulic system control section10cin the calibration mode.

First, at Step FC1, a signal that identifies an actuator to be calibrated and is sent from the man-machine interface9bis sent to the calibration command calculating section10c3, and the actuator to be calibrated is selected.

At Step FC2, the calibration command calculating section10c3acquires pressure values measured by the meter-in valve upstream pressure sensor8a3and the meter-in valve downstream pressure sensor8a4.

At Step FC3, it is decided whether or not calibration operation has been completed. If calibration operation has not been completed, the process proceeds to Step FC4, and the meter-in spool position command xs,refat the current time is determined on the basis of the target meter-in spool position command waveform illustrated inFIG. 6.

At Step FC5, on the basis of the command-value computation map for the bleed-off spool position command Xb,refillustrated inFIG. 7and the actual differential pressure ΔP across the meter-in valve8a1measured by the meter-in valve upstream pressure sensor8a3and the meter-in valve downstream pressure sensor8a4, the bleed-off spool position command xb,refis determined according to Formula (4).

At Step FC6, the commands determined at Step FC4and Step FC5are sent to the control command output section10c4, and current commands are output to the directional-control-valve solenoid proportional pressure-reducing valve8a2and the bleed-off solenoid proportional pressure-reducing valve8b2.

In this manner, in the present embodiment, the hydraulic excavator100(construction machine) including: the engine40(prime mover); the tank12that stores the hydraulic operating fluid; the hydraulic pump7that is driven by the engine40and delivers, as a hydraulic fluid, the hydraulic operating fluid sucked in from the tank12; the hydraulic actuator4adriven by the hydraulic fluid delivered from the hydraulic pump7; the meter-in valve8a1that adjusts the flow rate of the hydraulic fluid supplied from the hydraulic pump7to the hydraulic actuator4a; the directional-control-valve solenoid proportional pressure-reducing valve8a2(meter-in spool position adjusting device) that adjusts the spool position xsof the meter-in valve8a1; and the controller10that outputs the command signal to the directional-control-valve solenoid proportional pressure-reducing valve8a2according to an operation signal from the operation lever device9a(operation device) includes the cylinder position sensor4a4(velocity sensor) for sensing the operation velocity Vaof the hydraulic actuator4a, the meter-in spool position sensor8a5(meter-in spool position sensor) that senses the spool position xsof the meter-in valve8a1, the pressure sensors8a3and8a4(pressure sensors) that sense the differential pressure ΔP across the meter-in valve8a1, and the bleed-off valve8b1(pressure adjusting device) and the bleed-off solenoid proportional pressure-reducing valve8b2(pressure adjusting device) that adjust the differential pressure ΔP across the meter-in valve8a1. The controller10has the calibration mode in which the controller10derives the operation characteristics α(xs) representing the relation among the spool position xsof the meter-in valve8a1, the operation velocity Vaof the hydraulic actuator4a, and the differential pressure ΔP across the meter-in valve8a1. In the calibration mode, and in a case where the spool position xsof the meter-in valve8a1has changed in a direction to increase the opening area of the meter-in valve8a1, the controller10outputs a command signal to increase the opening area of the bleed-off valve8b1to the bleed-off solenoid proportional pressure-reducing valve8b2as a command signal to reduce the differential pressure ΔP across the meter-in valve8a1. Thereby, the flow rate of the hydraulic fluid discharged from the hydraulic pump7to the tank12increases, and the upstream pressure Pinof the meter-in valve8a1lowers to reduce the differential pressure ΔP.

According to the hydraulic excavator100according to the thus-configured present embodiment, the following effects are attained.

FIG. 9is a figure illustrating changes in the meter-in spool position command xs,ref, the differential pressure ΔP across the meter-in valve8a1, and the actuator velocity Vain the calibration mode.

For the meter-in spool position command xs,reffor one reciprocating movement given as a command for calibration operation, the bleed-off spool position command xb,refis determined according to Formula (4) on the basis of the command-value computation map for the bleed-off spool position command xb,ref, and the actual differential pressure ΔP across the meter-in valve8a1. Thereby, the differential pressure ΔP across the meter-in valve8a1like the one illustrated inFIG. 9is obtained, and increase in the actuator velocity Vais suppressed. That is, as compared with conventional techniques in which the differential pressure ΔP across the meter-in valve8a1is not adjusted during calibration operation, the meter-in spool can be operated in a state in which the actuator velocity Vais kept low in the present invention. The actuator velocity Vaat this time is adjusted, by using a target velocity Va,targetindicated by Formula (5) as a reference, as a velocity at which the limit of a movable range Laof the actuator is not exceeded in the period tfof the meter-in spool position command.

[Equation⁢⁢⁢5]Va,target=Latf(5)
As a result, the spool of the meter-in valve8a1can be caused to make one reciprocating movement in the movable range of the actuator4a, and measurement data of the entire calibration area can be acquired with the calibration operation performed once. Accordingly, the time efficiency of the operation calibration is improved. In conventional techniques, the limit of the maximum movable range of the actuator is reached at a time tendbefore the velocity of the actuator reaches the maximum velocity Va,maxof the actuator necessary for calibration. Accordingly, the calibration cannot be completed by performing the operation only once, and the calibration operation needs to be performed multiple times with different patterns of the meter-in spool position command xs,ref.

FIG. 10is a figure illustrating one example of operation characteristics derivation results in the present embodiment.

The graph inFIG. 10illustrates results of mapping the actuator velocity Varelative to the meter-in spool position xs,refin the present embodiment in comparison with supposed true values, and mapping results in a conventional technique in which the differential pressure ΔP across the meter-in valve8a1is not adjusted at the time of calibration operation. Mapping results of the present invention are obtained by assigning, in Formula (1), the operation characteristics α(xs,ref) relative to the meter-in spool position xs,refcomputed by using the operation characteristics α(xs) illustrated inFIG. 5, and the meter-in valve upstream pressure Pinand meter-in valve downstream pressure Poutrelative to the meter-in spool position Xs,ref, and computing the actuator velocity Varelative to the meter-in spool position xs,ref.

In the present invention, as can be known from the relation indicated by Formula (1), by adjusting the actual differential pressure ΔP across the meter-in valve8a1at the time of calibration operation, data for deriving the operation characteristics is measured in a state in which the actuator velocity Vais kept low. Thereby, the influence of the inertia and the viscous resistance of the hydraulic fluid that increase in proportion to the actuator velocity Vais suppressed, and calibration results that are closer to true values can be obtained in an area where the opening area of the meter-in valve8a1is large, that is, in a high-velocity area of the actuator velocity Vaas compared with conventional techniques. Accordingly, the calibration precision is improved. That is, it becomes possible to precisely derive the operation characteristics α(xs) of the hydraulic actuator in the high-velocity area with less calibration operation.

In the cases that are explained in the following embodiments, means other than the bleed-off circuit are used as pressure adjusting devices that adjust the differential pressure ΔP across the meter-in valve8a1.

Second Embodiment

A second embodiment of the present invention, mainly differences of the second embodiment from the first embodiment, is explained.

FIG. 11is a schematic diagram of the hydraulic system mounted on the hydraulic excavator100according to the present embodiment.

InFIG. 11, a hydraulic system200A in the present embodiment has a variable displacement hydraulic pump7a, and the controller10controls the flow rate of the hydraulic fluid supplied from the hydraulic pump7ato meter-in valve8a1, and thereby adjusts the upstream pressure Pinof the meter-in valve8a1.

In this manner, in the present embodiment, the hydraulic pump7ais a variable displacement hydraulic pump, and the pressure adjusting device that adjusts the differential pressure ΔP across the meter-in valve8a1is a regulator7bthat adjusts the delivery flow rate of the hydraulic pump7a. In a case where the spool position xsof the meter-in valve8a1has changed in the direction to increase the opening area of the meter-in valve8a1in the calibration mode, the controller10outputs a command signal to reduce the delivery flow rate of the hydraulic pump7ato the regulator7bas the command signal to reduce the differential pressure ΔP across the meter-in valve8a1. Thereby, the flow rate of the hydraulic fluid supplied from the hydraulic pump7ato the meter-in valve8a1decreases, and the upstream pressure Pinof the meter-in valve8a1lowers to reduce the differential pressure ΔP.

In the hydraulic excavator100thus-configured according to the present embodiment also, effects similar to those in the first embodiment are attained.

In addition, by adjusting the upstream pressure Pinof the meter-in valve8a1by the supply flow rate control of the variable displacement hydraulic pump7a, the flow rate of the hydraulic fluid to be wastefully discharged at the time of calibration operation decreases. Accordingly, the energy efficiency is improved. In addition, the upstream pressure Pinof the meter-in valve8a1can be controlled without changing the revolution speed of the engine40, and thus it becomes possible to suppress the influence on the entire operation of the hydraulic excavator100.

Third Embodiment

A third embodiment of the present invention, mainly differences of the third embodiment from the first embodiment, is explained.

FIG. 12is a schematic diagram of the hydraulic system mounted on the hydraulic excavator100according to the present embodiment.

InFIG. 12, in a hydraulic system200B in the present embodiment, the controller10is given the functionality of controlling the revolution speed of the engine40, and by controlling the revolution speed of the engine40, the flow rate of the hydraulic fluid supplied from the hydraulic pump7to the meter-in valve8a1is controlled.

In this manner, in the present embodiment, the pressure adjusting device that adjusts the differential pressure ΔP across the meter-in valve8a1is the engine40(prime mover). In a case where the spool position xsof the meter-in valve8a1has changed in the direction to increase the opening area of the meter-in valve8a1in the calibration mode, the controller10outputs a command signal to lower the revolution speed of the engine40to the engine40as the command signal to reduce the differential pressure ΔP across the meter-in valve8a1. Thereby, the flow rate of the hydraulic fluid supplied from the hydraulic pump7to the meter-in valve8a1decreases, and the upstream pressure Pinof the meter-in valve8a1lowers to reduce the differential pressure ΔP.

In the hydraulic excavator100according to the thus-configured present embodiment also, effects similar to those in the first embodiment are attained.

In addition, the upstream pressure Pinof the meter-in valve8a1can be adjusted by controlling the supply hydraulic fluid flow rate. By adjusting the upstream pressure Pinof the meter-in valve8a1by the revolution speed control of the engine40, the flow rate of the hydraulic fluid to be wastefully discharged at the time of calibration operation decreases. Accordingly, the energy efficiency is improved. In addition, it becomes possible to control the upstream pressure Pinof the meter-in valve8a1also in a case where the hydraulic pump7used is a fixed displacement hydraulic pump.

Fourth Embodiment

A fourth embodiment of the present invention, mainly differences of the fourth embodiment from the first embodiment, is explained.

FIG. 13is a schematic diagram of the hydraulic system mounted on the hydraulic excavator100according to the present embodiment.

InFIG. 13, a hydraulic system200C in the present embodiment has, in the boom section8a, a directional control valve8a6which is independent of the directional control valve8a1. Similar to the directional control valve8a1, the directional control valve8a6functions as a valve (meter-in valve) through which one of the bottom-side oil chamber4a1and the rod-side oil chamber4a2of the boom cylinder4acommunicates with the hydraulic line communicating with the hydraulic pump7, and as a valve (meter-out valve) through which the other one of the bottom-side oil chamber4a1and the rod-side oil chamber4a2of the boom cylinder4acommunicates with the hydraulic line communicating with the tank12. In a case where the directional control valve8a1is functioning as a meter-in valve, the directional control valve8a6functions as a meter-out valve, and in a case where the directional control valve8a6is functioning as a meter-in valve, the directional control valve8a1functions as a meter-out valve. In addition, in a case where the directional control valve8a1is functioning as a meter-in valve, a spool position sensor8a5afunctions as the meter-in spool position sensor8a5that measures the meter-in spool position, and in a case where the directional control valve8a6is functioning as a meter-in valve, a spool position sensor8a5bfunctions as the meter-in spool position sensor8a5that measures the meter-in spool position. The directional control valve8a6is driven by a directional-control-valve proportional solenoid pressure-reducing valve8a7being operated based on a control input given as a command from the controller10. The flow rate of the hydraulic fluid to be discharged from the boom cylinder4ato the tank12is controlled by the operation of the meter-out valve8a6or8a1, and thereby the downstream pressure Poutof the meter-in valve8a1or8a6is adjusted.

In this manner, in the present embodiment, the pressure adjusting device that adjusts the differential pressure ΔP across the meter-in valve8a1or8a6has the meter-out valve8a6or8a1provided independently of the meter-in valve8a1or8a6and adjusting the flow rate of the hydraulic fluid discharged from the hydraulic actuator4ato the tank12, and has the directional-control-valve proportional solenoid pressure-reducing valve8a7or8a2controlling the opening area of the meter-out valve8a6or8a1. In a case where the spool position xsof the meter-in valve8a1or8a6has changed in a direction to increase the opening area of the meter-in valve8a1or8a6in the calibration mode, the controller10outputs a command signal to reduce the opening area of the meter-out valve8a6or8a1to the directional-control-valve proportional solenoid pressure-reducing valve8a7or8a2as a command signal to reduce the differential pressure ΔP across the meter-in valve8a1or8a6. Thereby, the flow rate of the hydraulic fluid discharged from the hydraulic actuator4ato the tank12decreases, and the downstream pressure Poutof the meter-in valve8a1or8a6increases to lower the differential pressure ΔP.

In the hydraulic excavator100thus-configured according to the present embodiment also, effects similar to those in the first embodiment are attained.

In addition, due to the control of the meter-out valve8a6or8a1, the downstream pressure Poutof the meter-in valve8a1or8a6can be precisely adjusted, and the hydraulic actuator4ais effectively prevented from leaping due to gravity or inertia, thereby allowing the enhancement of the measurement precision of the actuator velocity Va.

Although embodiments of the present invention have been mentioned in detail thus far, the present invention is not limited to the embodiments described above, and includes various modification examples. For example, the embodiments described above are explained in detail in order to explain the present invention in an easy-to-understand manner, and embodiments of the present invention are not necessarily limited to those including all the configurations explained.

In addition, it is also possible to add some of the configurations of an embodiment to the configurations of another embodiment, it is possible to remove some of the configurations of an embodiment, or it is also possible to replace some of the configurations of an embodiment with some of the configurations of another embodiment.

DESCRIPTION OF REFERENCE CHARACTERS