Patent ID: 12258734

DESCRIPTION OF THE EMBODIMENTS

An embodiment of the present invention will be described below with reference to the drawings. In the present embodiment, a crawler type hydraulic shovel (excavator) will be described as an example of a working vehicle comprising a working control device according to the present invention. First, an entire configuration of the hydraulic shovel1will be described principally with reference toFIG.1.

The hydraulic shovel1is configured to include a lower traveling unit10being capable of traveling, an upper turning body20provided to be horizontally turnable on the top of the lower traveling unit10, and a shovel device30provided on the front of the upper turning body20, as illustrated inFIG.1. The lower traveling unit10, the upper turning body20, and the shovel device30are driven by a hydraulic actuator.

The lower traveling unit10comprises a pair of left and right crawler mechanisms15each including a drive wheel, a plurality of driven wheels, and a crawler belt13laid around the wheels, respectively, on both left and right sides of a traveling unit frame11. The left and right crawler mechanisms15respectively include left and right traveling motors16L and16R (hydraulic actuators) that drive the drive wheels to rotate. The lower traveling unit10can travel in any direction and at any speed by controlling a rotational direction and a rotational speed of the left and right traveling motors16L and16R. A blade18is provided to be vertically swingable on the front of the traveling unit frame11. The blade18is vertically swingable by making a blade cylinder19(a hydraulic actuator) provided astride between itself and the traveling unit frame11work to extend and contract.

A turning mechanism is provided in the center of the top of the traveling unit frame11. The turning mechanism includes an inner ring fixed to the traveling unit frame11, an outer ring fixed to the upper turning body20, a turning motor26(a hydraulic actuator, seeFIG.2) provided in the upper turning body20, and pipes and a swivel joint for supplying hydraulic oil from a hydraulic pump provided in the upper turning body20to the left and right traveling motors16L and16R and the blade cylinder19provided in the lower traveling unit10. The upper turning body20is attached to be horizontally turnable to the traveling unit frame11via the turning mechanism and is turnable in left and right directions with respect to the lower traveling unit10by making the turning motor26work to normally or reversely rotate.

A main-body-side bracket22protruding forward is provided in the front of the upper turning body20. The shovel device30comprises a boom bracket39attached to be swingable in left and right directions with a vertical axis as the center to the main-body-side bracket22, a boom31attached to be vertically swingable (raising/lowering movable) via a first swing pin35ato the boom bracket39, an arm32attached to be vertically swingable (bending/extending movable) via a second swing pin35bto a distal end of the boom31, and a link mechanism33provided at a distal end of the arm32. The shovel device30further comprises a swing cylinder34(a hydraulic actuator) provided astride between the upper turning body20and the boom bracket39, a boom cylinder36(a hydraulic actuator) provided astride between the boom bracket39and the boom31, an arm cylinder37(a hydraulic actuator) provided astride between the boom31and the arm32, and a bucket cylinder38(a hydraulic actuator) provided astride between the arm32and the link mechanism33.

The boom bracket39is swingable in left and right directions with respect to the upper turning body20(the main-body-side bracket22) by making the swing cylinder34work to extend and contract. The boom31is swingable in up and down directions (raising/lowering movable) with respect to the main-body-side bracket22(the upper turning body20) by making the boom cylinder36work to extend and contract. The arm32is swingable in up and down directions (bending/extending movable) with respect to the boom31by making the arm cylinder37work to extend and contract.

Various types of attachments as hydraulic working devices such as a bucket, a breaker, a crusher, a cutter, and an auger device can be vertically swingably attached to the distal end of the arm32and the link mechanism33. The attachment attached to the distal end of the arm32is vertically swingable with respect to the arm32via the link mechanism33by making the bucket cylinder38work to extend and contract. First to third attachment connection ports41to43to which a hydraulic hose for supplying hydraulic oil to the hydraulic actuators in the attachment can be connected are disposed on both left and right side surfaces of the arm32. The shovel device30configured such that the bucket is attached to the distal end of the arm32and the link mechanism33and is made to swingably work by the bucket cylinder38will be described below as an example.

The upper turning body20comprises a turning frame21the front of which is provided with the main-body-side bracket22and an operator cabin23provided on the turning frame21. The operator cabin23is formed in a substantially rectangular shape and forms an operation chamber in which an operator (worker) can get and the left side of which is provided with a cabin door24being laterally opened and closed. Inside the operator cabin23, there are provided an operator seat on which the operator sits facing forward, a display device that displays various types of vehicle information in the hydraulic shovel1, and various types of operation switches to be operated by the operator. Inside the operator cabin23, there is provided an operation device160(seeFIG.2) that is operated by the operator to make the hydraulic actuators work. The operation device160includes, as its operation sections when operated by the operator, left and right traveling operation levers or traveling operation pedals (none are illustrated) with which the lower traveling unit10is operated to travel, left and right work operation levers161and162(seeFIG.2) with which the upper turning body20and the shovel device30are operated to work, and a blade operation lever (not illustrated) with which the blade18is operated to work.

In the hydraulic shovel1, the operator gets in the operator cabin23and operates the left and right traveling operation levers (or traveling operation pedals) to be inclined back and forth, thereby making it possible to drive the left and right crawler mechanisms15(the traveling motors16L and16R) depending on respective operation directions and operation amounts of the left and right traveling operation levers to travel the hydraulic shovel1. The left and right work operation levers161and162are operated to be inclined back and forth and right and left, thereby making it possible to drive the upper turning body20and the shovel device30depending on the operation directions and the operation amounts of the left and right traveling operation levers to perform work such as excavation.

A horn device28is provided in the front of the turning frame21. When a horn switch in the operator cabin23is operated to be pressed, a warning tone to call attention can be generated from the horn device28to the periphery of the hydraulic shovel1. At the back of the turning frame body20, a mounting chamber, in which a main part of a working control device100described below is mounted, is provided at a position behind the operator cabin23. A counter weight29in a curved surface shape is provided to form a rear wall of the mounting chamber.

The working control device100comprises a hydraulic oil tank T, a fixed displacement type first hydraulic pump P1that discharges hydraulic oil for making the left and right traveling motors16L and16R, the hydraulic actuator for making the shovel device30work, and the like work, a fixed displacement type turning hydraulic pump P2that discharges hydraulic oil for making the turning motor26work, a control valve unit110that controls a supply direction and a flow rate of hydraulic oil in supplying the hydraulic oil discharged from the first hydraulic pump P1to the left and right traveling motors16L and16R, the hydraulic actuator for making the shovel device30, and the like, work, a turning control valve121that controls a supply direction of hydraulic oil to be discharged from the turning hydraulic pump P2and supplied to the turning motor26, and a pilot pressure supply valve unit130that supplies a pilot pressure for respectively controlling workings of the control valve unit110and the turning control valve121, as illustrated inFIG.2.

The control valve unit110comprises control valves that control supply/discharge, supply directions, and flow rates of hydraulic oil to be supplied to each of the left and right traveling motors16L and16R, the boom cylinder36, the arm cylinder37, the bucket cylinder38, the swing cylinder34, the blade cylinder19, and the first to third attachment connection ports41to43. Examples of the control valves include left and right traveling control valves111and112, a boom control valve113, an arm control valve114, a bucket control valve115, a swing control valve116, a blade control valve117, and an attachment control valve118. In each of the control valves111to118, a spool incorporated therein is moved by a pilot pressure to be supplied from the pilot pressure supply valve unit130. The movement of the spool makes it possible to control supply/discharge, a supply direction, and a flow rate of hydraulic oil to be supplied to each of the hydraulic actuators.

In the turning control valve121, a spool incorporated therein is moved by a pilot pressure to be supplied from the pilot pressure supply valve unit130, like in the control valves111to118. In the turning control valve121, only supply/discharge and a supply direction of hydraulic oil to be supplied to the turning motor26are controlled to switch by movement of the spool. Flow rate control of the hydraulic oil to be supplied to the turning motor26(i.e., turning speed control of the upper turning body20) is performed by rotation control of a second electric motor M2.

The pilot pressure supply valve unit130is provided in a branch oil path L2branching from a pump oil path L1leading to the control valve unit110from a discharge port of the first hydraulic pump P1. The branch oil path L2is provided with a check valve135for keeping a hydraulic pressure required for the pilot pressure supply valve unit130to generate a pilot pressure. The pilot pressure supply valve unit130generates pilot pressures respectively corresponding to operation directions and operation amounts of a traveling operation lever (traveling operation pedal), the work operation levers161and162, and the blade operation lever provided in the operator cabin23using hydraulic oil to be discharged from the first hydraulic pump P1, and respectively supplies the pilot pressures to the corresponding control valves. The pilot pressure supply valve unit130includes a plurality of electromagnetic proportion type pilot pressure supply valves for respectively supplying the pilot pressures to the corresponding control valves.

The working control device100further comprises a first electric motor M1that drives the first hydraulic pump P1, the second electric motor M2that drives the turning hydraulic pump P2, a battery105(a storage battery) rechargeable from an external power supply or the like, an inverter106that converts DC power from the battery105into AC power to change a frequency and the magnitude of a voltage, a first pressure sensor S1that detects a pressure of hydraulic oil (a pump pressure) to be discharged from the first hydraulic pump P1, a controller150that performs various types of control (described in detail below), and the above-mentioned operation device160.

The first and turning hydraulic pumps P1and P2are each a fixed displacement type hydraulic pump and respectively discharge hydraulic oils having flow rates corresponding to rotational speeds of the first and second electric motors M1and M2. That is, discharge oil amounts of the first and turning hydraulic pumps P1and P2can be respectively controlled by controlling the rotational speeds of the first and second electric motors M1and M2. As shown inFIGS.2-5, a variable displacement type hydraulic pump may be used as the pumps.

Then, a control content by the controller150will be described. As described above, the operator who gets in the operator cabin23operates the working operation levers161and162constituting the operation device160to incline the working operation levers back and forth and left and right, thereby making it possible to drive the upper turning body20and the shovel device30depending on the operation directions and the operation amounts of the working operation levers to perform work such as excavation. Control to perform a boom working lever operation and a bucket working lever operation, respectively, in the working operation levers161and162will be described below with reference toFIG.3in addition toFIG.2.FIG.3is a hydraulic circuit diagram for describing a control content when the controller150performs working control of the boom cylinder36and the bucket cylinder38.FIG.3illustrates components required to describe working control of the boom cylinder36and the bucket cylinder38from the control device illustrated inFIG.2in an extracted manner.

The working operation levers161and162are each a joystick type operation lever, and respectively output, when a boom working lever operation (e.g., an operation for inclining the working operation lever161back and forth) and a bucket working lever operation (e.g., an operation for inclining the working operation lever162right and left) are performed, operation output signals respectively corresponding to the operations are outputted to the controller150. Specifically, an operation output signal for making the boom cylinder36work is outputted when the boom working lever operation is performed, and the operation output signal for making the bucket cylinder38work is outputted when the bucket working lever operation is performed. Each of the lever operations is configured to be responsive to its operation amount (operation stroke) to output such an operation output signal that the larger the operation amount is, the higher a signal level (e.g., a voltage value and a current value) is.

The operation output signals to be thus respectively outputted in response to the boom and bucket working lever operations are fed to the controller150, and the number of driving revolutions of the first electric motor M1is controlled via the inverter106. Further, the controller150that has received the operation output signals also performs working control of the pilot pressure supply valve unit130. As a result, working control of the boom control valve113and the bucket control valve115is performed upon receipt of supply of the pilot pressure by the pilot pressure supply valve unit130so that the boom cylinder36and the bucket cylinder38are controlled to work. The control will be described in detail below with reference toFIG.3toFIG.5.

First, the working control device illustrated in a hydraulic circuit diagram ofFIG.3will be described. In the working control device illustrated inFIG.3, the controller150performs rotation driving control of the first electric motor M1via the inverter106, as illustrated inFIG.2. When the rotation driving control is thus performed by the first electric motor M1, hydraulic oil in the tank T is discharged into the pump oil path L1by the first hydraulic pump P1. The pump oil path L1branches into a first branch pump oil path L11and a second branch pump oil path L12and is connected thereto, and the second branch pump oil path L12is connected to an unload valve60to be made to work upon receiving a hydraulic pressure in a feedback oil path L20. Accordingly, respective hydraulic pressures in the pump oil path L1and the first and second branch pump oil paths L11and L12are set depending on the hydraulic pressure in the feedback oil path L20by the unload valve60. The hydraulic pressure in the feedback oil path L20will be described below. Oil to be discharged from the unload valve60flows out to a tank oil path LT, and returns to the tank T through the tank oil path LT.

A boom first oil path L31is provided to be connected to the first branch pump oil path L11. The boom first oil path L31is connected to the boom control valve113. The boom control valve113is a three-position switching valve including six ports to which six lines (a boom first oil path L31to a boom sixth oil path L36) are respectively connected. The boom second oil path L32is connected to an inlet port of a boom pressure compensation valve70, the boom third oil path L33is connected to an outlet port of the boom pressure compensation valve70, the boom fourth oil path L34is connected to a bottom-side oil chamber of the boom cylinder36, the boom fifth oil path L35is connected to a rod-side oil chamber of the boom cylinder36, and the boom sixth oil path L36is connected to the tank oil path LT. The boom second oil path L32is connected to the feedback oil path L20via a boom pilot oil path L37including a check valve73. The check valve73is closed when the hydraulic pressure in the feedback oil path L20is higher than a hydraulic pressure in the boom second oil path L32, and is opened when a reverse pressure relationship holds. A check valve74is provided in the boom third oil path L33, to prevent backflow.

The boom control valve113has pilot ports113aand113brespectively provided at both its ends (upper and lower ends inFIG.3), and pilot pressure supply oil paths L41and L42are respectively connected to the pilot ports113aand113b.A boom pilot hydraulic pressure is supplied in response to a boom working lever operation to the pilot pressure supply oil paths L41and L42from the pilot pressure supply valve unit130so that the boom control valve113is controlled to work.FIG.3illustrates a state where the boom working lever operation is not performed, a boom working lever is at a neutral position, a pilot pressure is not supplied to the pilot pressure supply oil paths L41and L42, and the boom control valve113is positioned at a neutral position. In this state, all the six ports to which the six lines (the boom first oil path L31to the boom sixth oil path L36) are respectively connected each enter a closed state.

Then, a case where a pilot pressure is supplied to the pilot port113afrom the pilot pressure supply valve unit130via the pilot pressure supply oil path L41by the boom working lever operation being performed will be described. When the pilot pressure is supplied to the pilot port113a,the boom control valve113is moved downward inFIG.3. This state is illustrated inFIG.4andFIG.5, where the boom first oil path L31communicates with the boom second oil path L32. A communication opening at this time is set to change depending on the magnitude of the pilot pressure (i.e., the magnitude of an operation amount of the boom working lever operation). That is, in the boom control valve113, the spool moves upon receiving the pilot pressure, and an opening area A1of the boom control valve113(an area in which the boom first oil path L31and the boom second oil path L32communicate with each other) changes depending on a spool movement amount (spool stroke).

The opening area A1is set, as indicated by a solid line inFIG.6, with respect to a spool stroke ST1. The spool stroke ST1changes depending on the magnitude of the pilot pressure (i.e., the magnitude of the operation amount of the boom working lever operation). A relationship set in a conventional boom control valve is indicated by a broken line inFIG.6. Thus, in a conventional technique, the conventional boom control valve is made to have a load sensing restriction function by decreasing an opening area with respect to a spool stroke so that a predetermined differential pressure occurs in a portion where the opening area has been decreased. However, the boom control valve113in the present embodiment is controlled to have a pump discharge amount corresponding to the magnitude of the operation amount of the boom working lever operation, as described below, whereby a differential pressure need not be produced in this portion. Therefore, the conventional boom control valve113is configured not using a load sensing restriction function by increasing the opening area. That is, the opening area A1illustrated inFIG.6is set to such an area as to allow passage of discharge oil from the first pump P1the discharge amount of which is to be controlled to correspond to the magnitude of the operation amount of the boom working lever operation as it is but to limit a flow rate exceeding the discharge oil amount. In this meaning, the boom control valve may have an oil path switching function, and the opening area A1need not be variably set. However, when a plurality of valve workings are performed (e.g., when the boom and bucket working lever operations are simultaneously performed), setting as illustrated inFIG.6is performed such that oil having a desired flow rate corresponding to each of lever operation amounts can be supplied to the corresponding actuator (the boom cylinder36and the bucket cylinder38).

Further, with the boom control valve113moved downward, the boom third oil path L33communicates with the boom fourth oil path L34, and the boom fifth oil path L35communicates with the boom sixth oil path L36.

On the other hand, when a pilot pressure is supplied to the pilot port113bfrom the pilot pressure supply valve unit130via the pilot pressure supply oil path L42by the boom working lever operation in an opposite direction to that described above being performed, the boom control valve113is moved upward inFIG.3. As a result, the boom first oil path L31communicates with the boom second oil path L32, the boom third oil path L33communicates with the boom fifth oil path L35, and the boom fourth oil path L34communicates with the boom sixth oil path L36.

The boom pressure compensation valve70is a two-position switching valve, and receives a hydraulic pressure in the feedback oil path L20on the side of its upper end and receives a hydraulic pressure in the boom second oil path L32on the side of its lower end. The boom pressure compensation valve70includes a spring that urges the boom pressure compensation valve70upward. Accordingly, when the hydraulic pressure in the feedback oil path L20is smaller than a force obtained by adding a spring urging force to the hydraulic pressure in the boom second oil path L32, there occurs a state where the boom pressure compensation valve70moves upward as illustrated, to make the boom second oil path L32and the boom third oil path L33communicate with each other as they are. When the hydraulic pressure in the feedback oil path L20is larger than a force obtained by adding the spring urging force to the hydraulic pressure in the boom second oil path L32, the boom pressure compensation valve70moves downward, and the boom second oil path L32and the boom third oil path L33communicate with each other with the oil paths restricted by a boom pressure compensation restrictor71.

Further, a bucket first oil path L51is provided to be connected to the first branch pump oil path L11. The bucket first oil path L51is connected to the bucket control valve115. The bucket control valve115is a three-position switching valve including six ports to which six lines (a bucket first oil path L51to a bucket sixth oil path L56) are respectively connected. The bucket second oil path L52is connected to an inlet port of a bucket pressure compensation valve80, the bucket third oil path L53is connected to an outlet port of the bucket pressure compensation valve80, the bucket fourth oil path L54is connected to a bottom-side oil chamber of the bucket cylinder38, the bucket fifth oil path L55is connected to a rod-side oil chamber of the bucket cylinder38, and the bucket sixth oil path L56is connected to the tank oil path LT. The bucket second oil path L52is connected to the feedback oil path L20via a bucket pilot oil path L57including a check valve83. The check valve83is closed when the hydraulic pressure in the feedback oil path L20is higher than a hydraulic pressure in the bucket second oil path L52, and is opened when a reverse pressure relationship holds. A check valve84is provided in the bucket third oil path L53, to prevent backflow.

The bucket control valve115has pilot ports115aand115brespectively provided at both its ends (upper and lower ends inFIG.3), and pilot pressure supply oil paths L45and L46are respectively connected to the pilot ports115aand115b.A bucket pilot hydraulic pressure is supplied in response to a bucket working lever operation to the pilot pressure supply oil paths L45and L46from the pilot pressure supply valve unit130so that a working of the bucket control valve115is controlled to work.FIG.3illustrates a state where the bucket working lever operation is not performed, a bucket working lever is at a neutral position, a pilot pressure is not supplied to the pilot pressure supply oil paths L45and L46, and the bucket control valve115is positioned at a neutral position. In this state, all the six ports to which the six lines (the bucket first oil path L51to the bucket sixth oil path L56) are respectively connected each enter a closed state.

Then, a case where a pilot pressure is supplied to the pilot port115afrom the pilot pressure supply valve unit130via the pilot pressure supply oil path L45by the bucket working lever operation being performed will be described. When the pilot pressure is supplied to the pilot port115afrom the pilot pressure supply valve unit130via the pilot pressure supply oil path L45, the bucket control valve115is moved downward as shown inFIG.3(seeFIG.5). As a result, the bucket first oil path L51communicates with the bucket second oil path L52. A communication opening at this time is set to change depending on the magnitude of the pilot pressure (i.e., the magnitude of an operation amount of the bucket working lever operation). That is, in the bucket control valve115, a spool moves upon receiving the pilot pressure, and an opening area A2of the bucket control valve115(an area in which the bucket first oil path L51and the bucket second oil path L52communicate with each other) changes depending on a spool movement amount (spool stroke).

The opening area A2is set, as indicated by a solid line inFIG.7, with respect to a spool stroke ST2. The spool stroke ST2changes depending on the magnitude of the pilot pressure (i.e., the magnitude of the operation amount of the bucket working lever operation). A relationship set in a conventional bucket control valve is indicated by a broken line inFIG.7. Thus, in a conventional technique, the conventional bucket control valve is made to have a load sensing restriction function by decreasing an opening area with respect to a spool stroke so that a predetermined differential pressure occurs in a portion where the opening area has been decreased. However, the bucket control valve115in the present embodiment is controlled to have a pump discharge amount corresponding to the magnitude of the operation amount of the bucket working lever operation, as described below, whereby a differential pressure need not be produced in this portion. Therefore, the bucket control valve is configured not using a load sensing restriction function by increasing the opening area. That is, the opening area A2illustrated inFIG.7is set to such an area as to allow passage of discharge oil from the first pump P1the discharge amount of which is to be controlled to correspond to the magnitude of the operation amount of the bucket working lever operation as it is but to limit a flow rate exceeding the discharge oil amount. In this meaning, the bucket control valve may have an oil path switching function, and the opening area A2need not be variably set. However, when a plurality of valve workings are performed (e.g., when the boom and bucket working lever operations are simultaneously performed), setting as illustrated inFIG.8is performed such that oil having a desired flow rate corresponding to each of lever operation amounts can be supplied to the corresponding actuator (the boom cylinder36and the bucket cylinder38).

Further, with the bucket control valve115moved downward, the bucket third oil path L53communicates with the bucket fourth oil path L54, and the bucket fifth oil path L55communicates with the bucket sixth oil path L56.

On the other hand, when a pilot pressure is supplied to the pilot port115bfrom the pilot pressure supply valve unit130via the pilot pressure supply oil path L46by the bucket working lever operation in an opposite direction to that described above being performed, the bucket control valve115is moved upward inFIG.3. As a result, the bucket first oil path L51communicates with the bucket second oil path L52, the bucket third oil path L53communicates with the bucket fifth oil path L55, and the bucket fourth oil path L54communicates with the bucket sixth oil path L56.

The bucket pressure compensation valve80is a two-position switching valve, and receives a hydraulic pressure in the feedback oil path L20on the side of its upper end and receives a hydraulic pressure in the bucket second oil path L52on the side of its lower end. The bucket pressure compensation valve80includes a spring that urges the bucket pressure compensation valve80upward. Accordingly, when the hydraulic pressure in the feedback oil path L20is smaller than a force obtained by adding a spring urging force to the hydraulic pressure in the bucket second oil path L52, there occurs a state where the bucket pressure compensation valve80moves upward as illustrated, to make the bucket second oil path L52and the bucket third oil path L53communicate with each other as they are. When the hydraulic pressure in the feedback oil path L20is larger than a force obtained by adding the spring urging force to the hydraulic pressure in the bucket second oil path L52, the bucket pressure compensation valve80moves downward, and the bucket second oil path L52and the bucket third oil path L53communicate with each other with the oil paths restricted via a bucket pressure compensation restrictor81.

The working of the working control device100configured as described above will be described below. When the operator performs the boom working lever operation, the operation device160feeds signals respectively representing its operation direction and operation amount to the controller150. The controller150performs rotation driving control of the first electric motor M1via the inverter106based on such operation information, and controls a discharge amount from the first hydraulic pump P1. As the rotation driving control, the controller150sets a discharge amount of the first hydraulic pump P1required for the actuator (e.g., the boom cylinder36, the bucket cylinder38) to have a working speed corresponding to a lever operation amount and performs the rotation driving control of the first electric motor M1to obtain the set pump discharge amount. The first hydraulic pump P1may comprise a variable displacement type pump, and discharge amount control of the first hydraulic pump P1may be performed for the actuator (e.g., the boom cylinder36, the bucket cylinder38) to have a working speed corresponding to the lever operation amount. The controller150also performs working control of the pilot pressure supply valve unit130in parallel with the control.

The control by the controller150is also performed with a lever operation not performed. With the lever operation not performed by the operator, both the boom control valve113and the bucket control valve115are each in a neutral state, and are as illustrated inFIG.3. In the neutral state, all the six ports to be respectively connected to the six lines (the boom first oil path L31to the boom sixth oil path L36) each enter a closed state in the boom control valve113, and all the six ports to be respectively connected to the six lines (the bucket first oil path L51to the bucket sixth oil path L56) each similarly enter a closed state in the bucket control valve115. As a result, pressures in the boom second oil path L32and the bucket second oil path L52are respectively low pressures, and a pressure in the feedback oil path L20to be connected to the oil paths, respectively, via the boom and bucket pilot oil paths L37and L57is also a low pressure. Accordingly, a hydraulic pressure in the pump oil path L1(and the first and second branch pump oil paths L11and L12) is also set to a low pressure by the unload valve60to be operated upon receiving a hydraulic pressure in the feedback oil path L20. In this state, a discharge oil amount from the first hydraulic pump P1is not required or may be a necessary minimum, and the controller150performs control to stop the first electric motor M1or control to drive the first electric motor M1to rotate in a minimum number of revolutions. As a result, power consumption required to drive the first electric motor M1can be minimized.

Then, the working in a case where the operator operates the work operation levers161and162to perform the boom working lever operation and the bucket working lever operation will be described below. First, a case where only the boom working lever operation (a single operation) has been performed will be described with reference toFIG.4.

In this case, rotation driving control of the first electric motor M1by the controller150is first performed. When the operator performs the boom working lever operation, the controller150sets a discharge amount of the first hydraulic pump P1required for the actuator (e.g., the boom cylinder36) to have a working speed corresponding to a lever operation amount and performs the rotation driving control of the first electric motor M1to obtain the set pump discharge amount. Further, in parallel therewith, working control of the pilot pressure supply valve unit130is also performed. The controller150controls a working of the pilot pressure supply valve unit130, to supply a pilot pressure to the pilot port113afrom the pilot pressure supply valve unit130via the pilot pressure supply oil path L41, for example. Consequently, the boom control valve113is moved downward, to enter a state illustrated inFIG.4. When a boom working lever operation opposite thereto has been performed, a pilot pressure is supplied to the pilot port113b,and the boom control valve113is moved upward. The bucket working lever operation has not been performed. Thus, the bucket control valve115is at a neutral position as illustrated, and the six ports are closed.

In the state illustrated inFIG.4, the boom control valve113makes the boom first oil path L31communicate with the boom second oil path L32, makes the boom third oil path L33communicate with the boom fourth oil path L34, and makes the boom fifth oil path L35communicate with the boom sixth oil path L36. In this state, the boom second oil path L32and the feedback oil path L20communicate with each other via the boom pilot oil path L37, and a hydraulic pressure in the boom second oil path L32and a hydraulic pressure in the feedback oil path L20are equal to each other. Accordingly, the boom pressure compensation valve70is moved upward with a spring urging force, and the boom second oil path L32and the boom third oil path L33communicate with each other as they are.

As a result, although discharge oil in the first hydraulic pump P1flows from the boom first oil path L31to the boom second oil path L32, a communication opening area A1between the oil paths is set to change depending on the magnitude of a pilot pressure, and is indicated by a solid line inFIG.6. Accordingly, a flow rate of the discharge oil flowing through the boom second oil path L32is a flow rate corresponding to the opening area indicated by the solid line inFIG.6. The opening area A1indicated by the solid line inFIG.6is set to such an area as to allow passage of discharge oil from the first pump P1the discharge amount of which is to be controlled to correspond to the magnitude of an operation amount of the boom working lever operation as it is, as described above. Accordingly, the discharge oil from the first hydraulic pump P1is not limited, to flow from the boom first oil path L31to the boom second oil path L32as it is. As a result, a differential pressure that has been required in conventional feedback control need not be produced in the boom control valve113, a pump discharge pressure can be reduced to correspond to the differential pressure, and pump driving power can be more reduced than in the conventional technique.

Hydraulic oil that has thus flowed through the boom second oil path L32is fed to the boom fourth oil path L34through the boom control valve113after passing through the check valve74from the boom third oil path L33through the boom pressure compensation valve70, and is supplied to the bottom-side oil chamber of the boom cylinder36. As a result, the boom cylinder36works to extend. Thus, the hydraulic oil is discharged from the boom fifth oil path L35from the rod-side oil chamber of the boom cylinder36, to flow to the tank oil path LT from the boom sixth oil path L36after passing through the boom control valve113and returns to the tank T.

A hydraulic pressure in the boom second oil path L32(the hydraulic pressure is equal to a hydraulic pressure in the bottom-side oil chamber of the boom cylinder36) is transmitted to the feedback oil path L20via the check valve73, to act on the unload valve60. Accordingly, the unload valve60sets respective hydraulic pressures in the pump oil path L1and the first and second branch pump oil paths L11and L12to correspond to a hydraulic pressure in the feedback oil path L20(i.e., a hydraulic pressure in the bottom-side oil chamber of the boom cylinder36).

Then, a case where the operator has operated the work operation levers161and162and has simultaneously performed the boom working lever operation and the bucket working lever operation (has performed a composite operation) will be described with reference toFIG.5.

When the composite operation for simultaneously performing the boom working lever operation and the bucket working lever operation is performed, the rotation driving control of the first electric motor M1by the controller150is performed. The controller150finds an oil amount required for the boom cylinder36to have a working speed corresponding to the boom working lever operation and an oil amount required for the bucket cylinder38to have a working speed corresponding to the bucket working lever operation. The controller150sets an oil amount obtained by summing both the oil amounts as a discharge amount of the first hydraulic pump P1, and performs the rotation driving control of the first electric motor M1to obtain the set pump discharge amount.

Further, in parallel therewith, working control of the pilot pressure supply valve unit130is also performed. For example, a pilot pressure is supplied to the pilot port113afrom the pilot pressure supply valve unit130via the pilot pressure supply oil path L41, and the boom control valve113is moved downward. Further, simultaneously therewith, in the bucket control valve115, a pilot pressure is supplied to the pilot port115afrom the pilot pressure supply valve unit130via the pilot pressure supply oil path L45, and the bucket control valve115is moved downward. As a result, both the valves113and115each enter a state illustrated inFIG.5.

A working of the boom cylinder36by the boom control valve113at this time, excluding a working of the boom pressure compensation valve70, is as described above with reference toFIG.4. Thus, description of the working is omitted, and a working of the bucket cylinder by the bucket control valve115will be described. The working of the boom pressure compensation valve70, together with a working of the bucket pressure compensation valve80, will be described below.

When the bucket control valve115enters the state illustrated inFIG.5, the bucket first oil path L51communicates with the bucket second oil path L52, the bucket third oil path L53communicates with the bucket fourth oil path L54, and the bucket fifth oil path L55communicates with the bucket sixth oil path L56. As a result, although discharge oil in the first hydraulic pump P1flows from the bucket first oil path L51to the bucket second oil path L52, a communication opening area A2between the oil paths is set to change depending on the magnitude of a pilot pressure, and is indicated by a solid line inFIG.7.

The opening area A2indicated by the solid line inFIG.7is set to such an area as to allow passage of discharge oil from the first pump P1the discharge amount of which is to be controlled to correspond to the magnitude of an operation amount of the bucket working lever operation as it is. The boom working lever operation and the bucket working lever operation are simultaneously performed, and a total oil amount of an oil amount required for the boom cylinder36to have a working speed corresponding to the boom working lever operation and an oil amount required for the bucket cylinder38to have a working speed corresponding to the bucket working lever operation is supplied from the first hydraulic pump P1. At this time, the opening area A2indicated by the solid line inFIG.7is set to make an amount of oil required for the bucket cylinder38to have a working speed corresponding to the bucket working lever operation flow without limitation but to limit a flow rate exceeding the oil amount. On the other hand, the communication opening area A1between the boom first oil path L31and the boom second oil path L32in the boom control valve113is set to make an amount of oil required for the boom cylinder36to have a working speed corresponding to the boom working lever operation flow without limitation but to limit a flow rate exceeding the oil amount. Control to respectively set the opening areas A1and A2of the boom control valve113and the bucket control valve115as illustrated inFIG.6andFIG.7is thus performed, to perform control to respectively supply required flow rates corresponding to the boom working lever operation and the bucket working lever operation in a balanced manner.

Hydraulic oil that has thus flowed through the bucket second oil path L52is fed to the bucket fourth oil path L54through the bucket control valve115after passing through the check valve84from the bucket third oil path L53through the bucket pressure compensation valve80, and is supplied to the bottom-side oil chamber of the bucket cylinder38. As a result, the bucket cylinder38works to extend. Accordingly, the hydraulic oil is discharged from the bucket fifth oil path L55from the rod-side oil chamber of the bucket cylinder38, to flow to the tank oil path LT from the bucket sixth oil path L56after passing through the bucket control valve115and return to the tank.

Respective workings of the boom pressure compensation valve70and the bucket pressure compensation valve80will be described. Both the boom pressure compensation valve70and the bucket pressure compensation valve80are controlled to work upon receiving a hydraulic pressure in the feedback oil path L20on the side of its upper end and receiving respective hydraulic pressures in the boom second oil path L32and the bucket second oil path L52on the side of its lower end. Respective working loads of the boom cylinder36and the bucket cylinder38vary depending on a work content, and a hydraulic pressure corresponding to the working load is generated in each of the oil paths. A case where a load of the boom cylinder36is large, a load of the bucket cylinder38is small, and hydraulic pressures in the boom first oil path L31to the boom fourth oil path L34are respectively higher than hydraulic pressures in the bucket first oil path L51to the bucket fourth oil path L54will be considered as an example.

The hydraulic pressure in the boom second oil path L32is transmitted to the feedback oil path L20via the boom pilot oil path L37, and the hydraulic pressure in the bucket second oil path L52is transmitted to the feedback oil path L20via the bucket pilot oil path L57. At this time, the check valves73and83are respectively provided in both the pilot oil paths L37and L57. Thus, although the hydraulic pressure in the boom second oil path L32on the high-pressure side is transmitted to the feedback oil path L20, the hydraulic pressure in the bucket second oil path L52on the low-pressure side is not transmitted thereto upon being blocked by the check valve83. As a result, the boom pressure compensation valve70is moved upward to make the boom second oil path L32and the boom third oil path L33communicate with each other as they are. On the other hand, the bucket pressure compensation valve80is moved downward to constitute an oil path passing through the bucket pressure compensation restrictor81because the hydraulic pressure in the feedback oil path L20is higher than the hydraulic pressure in the bucket second oil path L52.

When the composite operation of the boom working lever operation and the bucket working lever operation is thus performed, an oil path of the boom pressure compensation valve70is not limited while remaining opened on the side on which respective load pressures in the boom cylinder36and the bucket cylinder38that work in response to the operation increase, e.g., on the boom cylinder side in the above-described case. However, an oil path of the bucket pressure compensation valve80is limited by the bucket pressure compensation restrictor81on the side on which the load pressures decrease, e.g., on the bucket cylinder side. In the device, hydraulic oil is supplied to both the cylinders36and38from the first hydraulic pump P1as the same hydraulic oil supply source. Accordingly, there is a problem that a large amount of hydraulic oil flows to the cylinder having the lower load so that a supplied oil amount of the cylinder having the higher load decreases. Therefore, a flow rate of the cylinder having the lower load is limited by the pressure compensation restrictor81, to prevent this problem. This makes it possible to set a flow ratio of the boom cylinder36and the bucket cylinder38. For example, a working of the bucket cylinder38can be given priority to if the bucket pressure compensation restrictor81is widened, and a working of the boom cylinder36can be given priority to if the bucket pressure compensation restrictor81is narrowed. The same applies to the boom pressure compensation restrictor71. The working of the boom cylinder36can be given priority to if the boom pressure compensation restrictor71is widened, and the working of the bucket cylinder38can be given priority to if the boom pressure compensation restrictor71is narrowed.

As can be seen from the foregoing description, when the composite operation is performed, hydraulic oil in an oil amount required to make the boom cylinder36work at a speed corresponding to the lever operation is supplied to the boom cylinder36upon controlling a flow rate by the boom control valve113, and hydraulic oil in an oil amount required to make the bucket cylinder38work at a speed corresponding to the lever operation is simultaneously supplied to the bucket cylinder38upon controlling a flow rate by the bucket control valve115. A relationship between the spool stroke ST1and the valve opening area A1in the boom control valve113and a relationship between the spool stroke ST2and the valve opening area A2in the bucket control valve115at this time are illustrated inFIG.8.

Although the embodiment of the present invention has been described above, the scope of the present invention is not limited to the above-described embodiment. For example, although the above embodiment is configured such that the respective openings of the control valves111to118are controlled by the pilot pressure to be supplied from the pilot pressure supply valve unit130, it may be configured such that the control valves111to118each comprise an electromagnetic proportion type control valve and the respective openings of the control valves111to118are electromagnetically controlled. The openings of the control valves111to118may be controlled using a driving device such as an electric motor.

Although the first hydraulic pump P1and the turning hydraulic pump P2each comprise a fixed displacement type hydraulic pump in the above-described embodiment, the hydraulic pumps P1and P2may be each a variable displacement type hydraulic pump. The hydraulic pump P1and the turning hydraulic pump P2may each comprise a variable displacement type hydraulic pump to be driven by an engine to perform variable displacement control.

Setting of respective working characteristics of hydraulic actuators corresponding to an operation of an operation lever may be changeable for each of the hydraulic actuators. For example, to change setting of a correspondence between an operation amount of the operation lever and a working speed (supply oil amount) of the corresponding hydraulic actuator, setting of a ratio of a required discharge flow rate and an operation amount may be changeable. The setting can be changed via a portable computer (loaded with a program for changing the setting) to be electrically connected to the controller150, for example.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

RELATED APPLICATIONS

This invention claims the benefit of Japanese Patent Application No. 2021-178942 which is hereby incorporated by reference.

EXPLANATION ABOUT NUMERALS AND CHARACTERS

1hydraulic shovel10lower traveling unit16L,16R traveling motor20upper turning body26turning motor30shovel device36boom cylinder37arm cylinder38bucket cylinder100working control device110control valve unit113boom control valve115bucket control valve130pilot pressure supply valve unit150controller160operation deviceM1first electric motorM2second electric motorP1first hydraulic pumpP2turning hydraulic pump