Patent Publication Number: US-2023133546-A1

Title: Working control device in working vehicle

Description:
TECHNICAL FIELD 
     The present invention relates to a working control device in a working vehicle, and more particularly to a working control device in a working vehicle comprising a hydraulic actuator. 
     TECHNICAL BACKGROUND 
     In recent years, as global warming countermeasures, an action to reduce a discharge amount of carbon dioxide using an electric motor instead of an internal combustion engine has been adopted. Even in a working vehicle such as a hydraulic shovel (excavator), a working vehicle using electric motor driving has been developed, and has been gradually introduced into the market. Under such a situation, there is a problem that an operational duration time period, which is determined depending on a battery capacity, of the electric motor is shorter than that of the internal combustion engine, and power required to drive the electric motor is required to be made as small as possible. 
     For example, Japanese Patent Publication No. 5096417 owned by the same applicant of the present application discloses a hydraulic shovel comprising two electric motors and configured to make respective hydraulic cylinders (boom cylinders, etc.) of a traveling motor and a shovel device work using hydraulic oil from a hydraulic pump to be driven by the first electric motor and make a turning motor and a blade cylinder work using hydraulic oil from a hydraulic pump to be driven by the second electric motor while generating a pilot pressure. In the hydraulic shovel, energy consumption in the two electric motors can be suppressed because a rotational speed (the number of revolutions per unit time) of the second electric motor (the electric motor for turning or the like) can be kept low during only the respective workings of the traveling motor and the shovel device and a rotational speed of the first electric motor (the electric motor for traveling or the like) can be kept low during only the respective workings of the turning motor and the blade cylinder. 
     A working control device used for the conventional hydraulic shovel controls a discharge flow rate from the hydraulic pump by feedback control to determine the discharge flow rate from the hydraulic pump based on a difference between a hydraulic pressure on the side of the hydraulic pump and a hydraulic pressure on the side of a hydraulic actuator. Thus, the working control device tends to be relatively low in control responsiveness. Therefore, in the control of the discharge flow rate, there is a problem that a control delay occurs so that hunting easily occurs in a situation where a differential pressure rapidly changes and responsiveness easily deteriorates in a situation where the differential pressure only slightly changes. In view of the foregoing, Japanese Laid-Open Patent Publication No. 2020-169708(A) discloses a hydraulic shovel using a working control device capable of controlling a discharge flow rate from a hydraulic pump while preventing hunting and a deterioration in responsiveness in control of the discharge flow rate, although owned by the same applicant of the present application. 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     Oil amount control to deliver oil from the hydraulic pump depending on an operation amount of an operation device is performed to prevent responsiveness from deteriorating in the working control device disclosed in Japanese Laid-Open Patent Publication No. 2020-169708(A). However, the working control device is configured to be able to perform feedback control to control the discharge flow rate from the hydraulic pump based on a difference between a hydraulic pressure on the side of the hydraulic pump and a hydraulic pressure on the side of a hydraulic actuator in the hydraulic shovel when proposed. That is, a hydraulic control valve using a load sensing restriction function for generating the above-described differential pressure is used. Accordingly, the above-described hydraulic pressure difference occurs by a load sensing restrictor. Thus, there is a problem that a discharge hydraulic pressure on the side of the hydraulic pump increases to correspond to the hydraulic pressure difference and required driving power of the hydraulic pump increases so that required power of the electric motor that drives the hydraulic pump increases. 
     The present invention has been made in view of the problem, and is directed to providing a working control device in a working vehicle configured to be able to appropriately perform discharge oil amount control of a hydraulic pump depending on an operation amount of an operation device while abolishing a load sensing restriction function and to be able to suppress a required energy for hydraulic pump driving. 
     Means to Solve the Problems 
     To attain the above-described object, a working control device according to a first aspect of the present invention comprises, in a working vehicle (e.g., a hydraulic shovel  1  in the embodiment) with a hydraulic working device (e.g., a crawler mechanism  15 , an upper turning body  20 , a shovel device  30  in the embodiment), a hydraulic actuator (e.g., traveling motors  16 L and  16 R, a swing cylinder  34 , a boom cylinder  36 , an arm cylinder  37 , a bucket cylinder  38 , a blade cylinder  19 ) for driving the hydraulic working device, an operation device (e.g., an operation device  160 ) that is operated by a worker (an operator) to drive the hydraulic working device upon making the hydraulic actuator work, a hydraulic oil supply source (e.g., a first hydraulic pump P 1  and a first electric motor M 1  in the embodiment) that delivers hydraulic oil required to drive the hydraulic actuator, and a delivery oil amount control device (e.g., a controller  150  that performs rotation control of the first electric motor M 1 ) that controls an amount of oil to be delivered from the hydraulic oil supply source in response to an operation of the operation device, in which the delivery oil amount control device is configured to perform a supplying oil amount control to deliver from the hydraulic oil supply source a required amount of oil for the hydraulic actuator to have a working speed corresponding to an operation of the operation device. 
     The working control device having the above-described configuration preferably further comprise a hydraulic oil supply control device that is provided in a flow path leading to the hydraulic actuator from the hydraulic oil supply source and controls an area of the flow path in response to an operation of the operation device, in which the hydraulic oil supply control device performs a control of setting the flow path area in response to an operation of the operation device so as to pass a required oil amount without limitation but to limit supply of hydraulic oil exceeding the required oil amount. 
     Further, in the working control device having the above-described configuration, the hydraulic oil supply control device preferably comprises a hydraulic oil supply control valve provided in an oil path leading to the hydraulic actuator from the hydraulic oil supply source. 
     A working control device according to a second aspect of the present invention comprises, in a working vehicle with a hydraulic working device that performs a plurality of workings, a plurality of hydraulic actuators for making the hydraulic working device perform the plurality of workings, an operation device enabling a plurality of operations to be performed by a worker (operator) to make the plurality of hydraulic actuators selectively or compositely work to drive the hydraulic working device, a hydraulic oil supply source that delivers hydraulic oil required to drive the plurality of hydraulic actuators, a delivery oil amount control device that controls an amount of oil to be delivered from the hydraulic oil supply source in response to operations of the operation device, and a plurality of hydraulic oil supply control devices that are respectively provided in a plurality of flow paths leading to the plurality of hydraulic actuators from the hydraulic oil supply source and each control an area of the flow path in response to the corresponding operation of the operation device, in which the delivery oil amount control device performs a supplying oil amount control to deliver from the hydraulic oil supply source an amount of oil corresponding to a total amount of oil amounts respectively required to make the plurality of hydraulic actuators work at speeds corresponding to operations of the operation device, and the plurality of hydraulic oil supply control devices each control the area of the flow path in response to the corresponding operation of the operation device and control the flow path area in response to operations of the operation device so as to pass a required oil amount for the hydraulic actuator to have a working speed corresponding to the corresponding operation of the operation device without limitation but to limit supply of hydraulic oil exceeding the required oil amount. 
     In the working control device having the above-described configuration, a pressure compensation valve is provided in each of the plurality of hydraulic oil supply control devices, and the pressure compensation valve limits, when control to make the plurality of hydraulic actuators compositely work upon compositely operating the operation device has been performed, an amount of supply oil to the hydraulic actuator having a lower hydraulic oil pressure among the plurality of hydraulic actuators and keeps a supply oil amount balance. 
     In the working control device having the above-described configuration, the hydraulic oil supply control device preferably comprises a plurality of hydraulic oil supply control valves respectively provided in a plurality of oil paths leading to the plurality of hydraulic actuators from the hydraulic oil supply source. 
     In the working control device having the above-described configuration, the hydraulic oil supply control device preferably comprises a hydraulic pump to be driven by an electric motor, and the delivery oil amount control device preferably controls the number of revolutions of the electric motor. In this case, the hydraulic pump is preferably a fixed displacement type hydraulic pump. The hydraulic pump may be a variable displacement type hydraulic pump. 
     In the working control device having the above-described configuration, the hydraulic oil supply source may comprise a variable displacement type hydraulic pump to be driven by an engine, and the delivery oil amount control device may perform variable displacement control of the hydraulic pump. 
     Advantageous Effects of the Invention 
     With the working control device in the working vehicle according to the first aspect of the present invention, the delivery oil amount control device performs the supplying oil amount control to control an amount of oil to be delivered from the hydraulic oil supply source in response to an operation of the operation device and deliver from the hydraulic oil supply source an amount of oil required for the hydraulic actuator to have the working speed corresponding to an operation of the operation device. Therefore, a load sensing restrictor can be abolished. A delivery oil amount control of the hydraulic pump can be appropriately performed depending on an operation amount of the operation device, and a required energy for hydraulic pump driving can be kept minimum required. 
     With the working control device in the working vehicle according to the second aspect of the present invention, the delivery oil amount control device performs the supplying oil amount control to deliver from the hydraulic oil supply source the amount of oil corresponding to the total oil amount of the oil amounts respectively required to make the plurality of hydraulic actuators work at the speeds corresponding to the operations of the operation device, and the plurality of hydraulic oil supply control devices each control the flow path area in response to the corresponding operations of the operation device and perform control to set the flow path area in response to the operations of the operation device to pass hydraulic oil in the required oil amount for the hydraulic actuator to have the working speed corresponding to the operations of the operation device without limitation but to limit supply of hydraulic oil exceeding the required oil amount. Therefore, a load sensing restrictor can be abolished, delivery oil amount control of the hydraulic pump can be appropriately performed depending on an operation amount of the operation device, and required energy for hydraulic pump driving can be kept to a necessary minimum. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention. 
         FIG.  1    is a perspective view of a hydraulic shovel comprising a working control device according to the present invention; 
         FIG.  2    is a hydraulic circuit diagram illustrating the working control device according to the present invention; 
         FIG.  3    is a hydraulic circuit diagram illustrating a working control device in a portion that performs working control of a boom cylinder and a bucket cylinder as a specific example of the working control device according to the present invention; 
         FIG.  4    is a hydraulic circuit diagram illustrating a state where a boom control valve has worked in the hydraulic circuit diagram of  FIG.  3   ; 
         FIG.  5    is a hydraulic circuit diagram illustrating a state where both the boom control valve and a bucket control valve have worked in the hydraulic circuit diagram of  FIG.  3   ; 
         FIG.  6    is a graph illustrating a relationship between a spool stroke (ST 1 ) and a valve opening area (A 1 ) in the boom control valve; 
         FIG.  7    is a graph illustrating a relationship between a spool stroke (ST 2 ) and a valve opening area (A 2 ) in the bucket control valve; and 
         FIG.  8    is a graph illustrating a relationship between the spool stroke (ST 1 , ST 2 ) and a valve opening area (A 1 , A 2 ) in a composite working of the boom control valve and the bucket control valve. 
     
    
    
     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 shovel  1  will be described principally with reference to  FIG.  1   . 
     The hydraulic shovel  1  is configured to include a lower traveling unit  10  being capable of traveling, an upper turning body  20  provided to be horizontally turnable on the top of the lower traveling unit  10 , and a shovel device  30  provided on the front of the upper turning body  20 , as illustrated in  FIG.  1   . The lower traveling unit  10 , the upper turning body  20 , and the shovel device  30  are driven by a hydraulic actuator. 
     The lower traveling unit  10  comprises a pair of left and right crawler mechanisms  15  each including a drive wheel, a plurality of driven wheels, and a crawler belt  13  laid around the wheels, respectively, on both left and right sides of a traveling unit frame  11 . The left and right crawler mechanisms  15  respectively include left and right traveling motors  16 L and  16 R (hydraulic actuators) that drive the drive wheels to rotate. The lower traveling unit  10  can travel in any direction and at any speed by controlling a rotational direction and a rotational speed of the left and right traveling motors  16 L and  16 R. A blade  18  is provided to be vertically swingable on the front of the traveling unit frame  11 . The blade  18  is vertically swingable by making a blade cylinder  19  (a hydraulic actuator) provided astride between itself and the traveling unit frame  11  work to extend and contract. 
     A turning mechanism is provided in the center of the top of the traveling unit frame  11 . The turning mechanism includes an inner ring fixed to the traveling unit frame  11 , an outer ring fixed to the upper turning body  20 , a turning motor  26  (a hydraulic actuator, see  FIG.  2   ) provided in the upper turning body  20 , and pipes and a swivel joint for supplying hydraulic oil from a hydraulic pump provided in the upper turning body  20  to the left and right traveling motors  16 L and  16 R and the blade cylinder  19  provided in the lower traveling unit  10 . The upper turning body  20  is attached to be horizontally turnable to the traveling unit frame  11  via the turning mechanism and is turnable in left and right directions with respect to the lower traveling unit  10  by making the turning motor  26  work to normally or reversely rotate. 
     A main-body-side bracket  22  protruding forward is provided in the front of the upper turning body  20 . The shovel device  30  comprises a boom bracket  39  attached to be swingable in left and right directions with a vertical axis as the center to the main-body-side bracket  22 , a boom  31  attached to be vertically swingable (raising/lowering movable) via a first swing pin  35   a  to the boom bracket  39 , an arm  32  attached to be vertically swingable (bending/extending movable) via a second swing pin  35   b  to a distal end of the boom  31 , and a link mechanism  33  provided at a distal end of the arm  32 . The shovel device  30  further comprises a swing cylinder  34  (a hydraulic actuator) provided astride between the upper turning body  20  and the boom bracket  39 , a boom cylinder  36  (a hydraulic actuator) provided astride between the boom bracket  39  and the boom  31 , an arm cylinder  37  (a hydraulic actuator) provided astride between the boom  31  and the arm  32 , and a bucket cylinder  38  (a hydraulic actuator) provided astride between the arm  32  and the link mechanism  33 . 
     The boom bracket  39  is swingable in left and right directions with respect to the upper turning body  20  (the main-body-side bracket  22 ) by making the swing cylinder  34  work to extend and contract. The boom  31  is swingable in up and down directions (raising/lowering movable) with respect to the main-body-side bracket  22  (the upper turning body  20 ) by making the boom cylinder  36  work to extend and contract. The arm  32  is swingable in up and down directions (bending/extending movable) with respect to the boom  31  by making the arm cylinder  37  work 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 arm  32  and the link mechanism  33 . The attachment attached to the distal end of the arm  32  is vertically swingable with respect to the arm  32  via the link mechanism  33  by making the bucket cylinder  38  work to extend and contract. First to third attachment connection ports  41  to  43  to 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 arm  32 . The shovel device  30  configured such that the bucket is attached to the distal end of the arm  32  and the link mechanism  33  and is made to swingably work by the bucket cylinder  38  will be described below as an example. 
     The upper turning body  20  comprises a turning frame  21  the front of which is provided with the main-body-side bracket  22  and an operator cabin  23  provided on the turning frame  21 . The operator cabin  23  is 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 door  24  being laterally opened and closed. Inside the operator cabin  23 , 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 shovel  1 , and various types of operation switches to be operated by the operator. Inside the operator cabin  23 , there is provided an operation device  160  (see  FIG.  2   ) that is operated by the operator to make the hydraulic actuators work. The operation device  160  includes, 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 unit  10  is operated to travel, left and right work operation levers  161  and  162  (see  FIG.  2   ) with which the upper turning body  20  and the shovel device  30  are operated to work, and a blade operation lever (not illustrated) with which the blade  18  is operated to work. 
     In the hydraulic shovel  1 , the operator gets in the operator cabin  23  and 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 mechanisms  15  (the traveling motors  16 L and  16 R) depending on respective operation directions and operation amounts of the left and right traveling operation levers to travel the hydraulic shovel  1 . The left and right work operation levers  161  and  162  are operated to be inclined back and forth and right and left, thereby making it possible to drive the upper turning body  20  and the shovel device  30  depending on the operation directions and the operation amounts of the left and right traveling operation levers to perform work such as excavation. 
     A horn device  28  is provided in the front of the turning frame  21 . When a horn switch in the operator cabin  23  is operated to be pressed, a warning tone to call attention can be generated from the horn device  28  to the periphery of the hydraulic shovel  1 . At the back of the turning frame body  20 , a mounting chamber, in which a main part of a working control device  100  described below is mounted, is provided at a position behind the operator cabin  23 . A counter weight  29  in a curved surface shape is provided to form a rear wall of the mounting chamber. 
     The working control device  100  comprises a hydraulic oil tank T, a fixed displacement type first hydraulic pump P 1  that discharges hydraulic oil for making the left and right traveling motors  16 L and  16 R, the hydraulic actuator for making the shovel device  30  work, and the like work, a fixed displacement type turning hydraulic pump P 2  that discharges hydraulic oil for making the turning motor  26  work, a control valve unit  110  that controls a supply direction and a flow rate of hydraulic oil in supplying the hydraulic oil discharged from the first hydraulic pump P 1  to the left and right traveling motors  16 L and  16 R, the hydraulic actuator for making the shovel device  30 , and the like, work, a turning control valve  121  that controls a supply direction of hydraulic oil to be discharged from the turning hydraulic pump P 2  and supplied to the turning motor  26 , and a pilot pressure supply valve unit  130  that supplies a pilot pressure for respectively controlling workings of the control valve unit  110  and the turning control valve  121 , as illustrated in  FIG.  2   . 
     The control valve unit  110  comprises 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 motors  16 L and  16 R, the boom cylinder  36 , the arm cylinder  37 , the bucket cylinder  38 , the swing cylinder  34 , the blade cylinder  19 , and the first to third attachment connection ports  41  to  43 . Examples of the control valves include left and right traveling control valves  111  and  112 , a boom control valve  113 , an arm control valve  114 , a bucket control valve  115 , a swing control valve  116 , a blade control valve  117 , and an attachment control valve  118 . In each of the control valves  111  to  118 , a spool incorporated therein is moved by a pilot pressure to be supplied from the pilot pressure supply valve unit  130 . 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 valve  121 , a spool incorporated therein is moved by a pilot pressure to be supplied from the pilot pressure supply valve unit  130 , like in the control valves  111  to  118 . In the turning control valve  121 , only supply/discharge and a supply direction of hydraulic oil to be supplied to the turning motor  26  are controlled to switch by movement of the spool. Flow rate control of the hydraulic oil to be supplied to the turning motor  26  (i.e., turning speed control of the upper turning body  20 ) is performed by rotation control of a second electric motor M 2 . 
     The pilot pressure supply valve unit  130  is provided in a branch oil path L 2  branching from a pump oil path L 1  leading to the control valve unit  110  from a discharge port of the first hydraulic pump P 1 . The branch oil path L 2  is provided with a check valve  135  for keeping a hydraulic pressure required for the pilot pressure supply valve unit  130  to generate a pilot pressure. The pilot pressure supply valve unit  130  generates pilot pressures respectively corresponding to operation directions and operation amounts of a traveling operation lever (traveling operation pedal), the work operation levers  161  and  162 , and the blade operation lever provided in the operator cabin  23  using hydraulic oil to be discharged from the first hydraulic pump P 1 , and respectively supplies the pilot pressures to the corresponding control valves. The pilot pressure supply valve unit  130  includes a plurality of electromagnetic proportion type pilot pressure supply valves for respectively supplying the pilot pressures to the corresponding control valves. 
     The working control device  100  further comprises a first electric motor M 1  that drives the first hydraulic pump P 1 , the second electric motor M 2  that drives the turning hydraulic pump P 2 , a battery  105  (a storage battery) rechargeable from an external power supply or the like, an inverter  106  that converts DC power from the battery  105  into AC power to change a frequency and the magnitude of a voltage, a first pressure sensor S 1  that detects a pressure of hydraulic oil (a pump pressure) to be discharged from the first hydraulic pump P 1 , a controller  150  that performs various types of control (described in detail below), and the above-mentioned operation device  160 . 
     The first and turning hydraulic pumps P 1  and P 2  are 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 M 1  and M 2 . That is, discharge oil amounts of the first and turning hydraulic pumps P 1  and P 2  can be respectively controlled by controlling the rotational speeds of the first and second electric motors M 1  and M 2 . A variable displacement type hydraulic pump may be used as the pumps. 
     Then, a control content by the controller  150  will be described. As described above, the operator who gets in the operator cabin  23  operates the working operation levers  161  and  162  constituting the operation device  160  to incline the working operation levers back and forth and left and right, thereby making it possible to drive the upper turning body  20  and the shovel device  30  depending 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 levers  161  and  162  will be described below with reference to  FIG.  3    in addition to  FIG.  2   .  FIG.  3    is a hydraulic circuit diagram for describing a control content when the controller  150  performs working control of the boom cylinder  36  and the bucket cylinder  38 .  FIG.  3    illustrates components required to describe working control of the boom cylinder  36  and the bucket cylinder  38  from the control device illustrated in  FIG.  2    in an extracted manner. 
     The working operation levers  161  and  162  are each a joystick type operation lever, and respectively output, when a boom working lever operation (e.g., an operation for inclining the working operation lever  161  back and forth) and a bucket working lever operation (e.g., an operation for inclining the working operation lever  162  right and left) are performed, operation output signals respectively corresponding to the operations are outputted to the controller  150 . Specifically, an operation output signal for making the boom cylinder  36  work is outputted when the boom working lever operation is performed, and the operation output signal for making the bucket cylinder  38  work 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 controller  150 , and the number of driving revolutions of the first electric motor M 1  is controlled via the inverter  106 . Further, the controller  150  that has received the operation output signals also performs working control of the pilot pressure supply valve unit  130 . As a result, working control of the boom control valve  113  and the bucket control valve  115  is performed upon receipt of supply of the pilot pressure by the pilot pressure supply valve unit  130  so that the boom cylinder  36  and the bucket cylinder  38  are controlled to work. The control will be described in detail below with reference to  FIG.  3    to  FIG.  5   . 
     First, the working control device illustrated in a hydraulic circuit diagram of  FIG.  3    will be described. In the working control device illustrated in  FIG.  3   , the controller  150  performs rotation driving control of the first electric motor M 1  via the inverter  106 , as illustrated in  FIG.  2   . When the rotation driving control is thus performed by the first electric motor M 1 , hydraulic oil in the tank T is discharged into the pump oil path L 1  by the first hydraulic pump P 1 . The pump oil path L 1  branches into a first branch pump oil path L 11  and a second branch pump oil path L 12  and is connected thereto, and the second branch pump oil path L 12  is connected to an unload valve  60  to be made to work upon receiving a hydraulic pressure in a feedback oil path L 20 . Accordingly, respective hydraulic pressures in the pump oil path L 1  and the first and second branch pump oil paths L 11  and L 12  are set depending on the hydraulic pressure in the feedback oil path L 20  by the unload valve  60 . The hydraulic pressure in the feedback oil path L 20  will be described below. Oil to be discharged from the unload valve  60  flows out to a tank oil path LT, and returns to the tank T through the tank oil path LT. 
     A boom first oil path L 31  is provided to be connected to the first branch pump oil path L 11 . The boom first oil path L 31  is connected to the boom control valve  113 . The boom control valve  113  is a three-position switching valve including six ports to which six lines (a boom first oil path L 31  to a boom sixth oil path L 36 ) are respectively connected. The boom second oil path L 32  is connected to an inlet port of a boom pressure compensation valve  70 , the boom third oil path L 33  is connected to an outlet port of the boom pressure compensation valve  70 , the boom fourth oil path L 34  is connected to a bottom-side oil chamber of the boom cylinder  36 , the boom fifth oil path L 35  is connected to a rod-side oil chamber of the boom cylinder  36 , and the boom sixth oil path L 36  is connected to the tank oil path LT. The boom second oil path L 32  is connected to the feedback oil path L 20  via a boom pilot oil path L 37  including a check valve  73 . The check valve  73  is closed when the hydraulic pressure in the feedback oil path L 20  is higher than a hydraulic pressure in the boom second oil path L 32 , and is opened when a reverse pressure relationship holds. A check valve  74  is provided in the boom third oil path L 33 , to prevent backflow. 
     The boom control valve  113  has pilot ports  113   a  and  113   b  respectively provided at both its ends (upper and lower ends in  FIG.  3   ), and pilot pressure supply oil paths L 41  and L 42  are respectively connected to the pilot ports  113   a  and  113   b.  A boom pilot hydraulic pressure is supplied in response to a boom working lever operation to the pilot pressure supply oil paths L 41  and L 42  from the pilot pressure supply valve unit  130  so that the boom control valve  113  is controlled to work.  FIG.  3    illustrates 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 L 41  and L 42 , and the boom control valve  113  is positioned at a neutral position. In this state, all the six ports to which the six lines (the boom first oil path L 31  to the boom sixth oil path L 36 ) are respectively connected each enter a closed state. 
     Then, a case where a pilot pressure is supplied to the pilot port  113   a  from the pilot pressure supply valve unit  130  via the pilot pressure supply oil path L 41  by the boom working lever operation being performed will be described. When the pilot pressure is supplied to the pilot port  113   a,  the boom control valve  113  is moved downward in  FIG.  3   . This state is illustrated in  FIG.  4    and  FIG.  5   , where the boom first oil path L 31  communicates with the boom second oil path L 32 . 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 valve  113 , the spool moves upon receiving the pilot pressure, and an opening area A 1  of the boom control valve  113  (an area in which the boom first oil path L 31  and the boom second oil path L 32  communicate with each other) changes depending on a spool movement amount (spool stroke). 
     The opening area A 1  is set, as indicated by a solid line in  FIG.  6   , with respect to a spool stroke ST 1 . The spool stroke ST 1  changes 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 in  FIG.  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 valve  113  in 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 valve  113  is configured not using a load sensing restriction function by increasing the opening area. That is, the opening area A 1  illustrated in  FIG.  6    is set to such an area as to allow passage of discharge oil from the first pump P 1  the 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 A 1  need 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 in  FIG.  6    is 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 cylinder  36  and the bucket cylinder  38 ). 
     Further, with the boom control valve  113  moved downward, the boom third oil path L 33  communicates with the boom fourth oil path L 34 , and the boom fifth oil path L 35  communicates with the boom sixth oil path L 36 . 
     On the other hand, when a pilot pressure is supplied to the pilot port  113   b  from the pilot pressure supply valve unit  130  via the pilot pressure supply oil path L 42  by the boom working lever operation in an opposite direction to that described above being performed, the boom control valve  113  is moved upward in  FIG.  3   . As a result, the boom first oil path L 31  communicates with the boom second oil path L 32 , the boom third oil path L 33  communicates with the boom fifth oil path L 35 , and the boom fourth oil path L 34  communicates with the boom sixth oil path L 36 . 
     The boom pressure compensation valve  70  is a two-position switching valve, and receives a hydraulic pressure in the feedback oil path L 20  on the side of its upper end and receives a hydraulic pressure in the boom second oil path L 32  on the side of its lower end. The boom pressure compensation valve  70  includes a spring that urges the boom pressure compensation valve  70  upward. Accordingly, when the hydraulic pressure in the feedback oil path L 20  is smaller than a force obtained by adding a spring urging force to the hydraulic pressure in the boom second oil path L 32 , there occurs a state where the boom pressure compensation valve  70  moves upward as illustrated, to make the boom second oil path L 32  and the boom third oil path L 33  communicate with each other as they are. When the hydraulic pressure in the feedback oil path L 20  is larger than a force obtained by adding the spring urging force to the hydraulic pressure in the boom second oil path L 32 , the boom pressure compensation valve  70  moves downward, and the boom second oil path L 32  and the boom third oil path L 33  communicate with each other with the oil paths restricted by a boom pressure compensation restrictor  71 . 
     Further, a bucket first oil path L 51  is provided to be connected to the first branch pump oil path L 11 . The bucket first oil path L 51  is connected to the bucket control valve  115 . The bucket control valve  115  is a three-position switching valve including six ports to which six lines (a bucket first oil path L 51  to a bucket sixth oil path L 56 ) are respectively connected. The bucket second oil path L 52  is connected to an inlet port of a bucket pressure compensation valve  80 , the bucket third oil path L 53  is connected to an outlet port of the bucket pressure compensation valve  80 , the bucket fourth oil path L 54  is connected to a bottom-side oil chamber of the bucket cylinder  38 , the bucket fifth oil path L 55  is connected to a rod-side oil chamber of the bucket cylinder  38 , and the bucket sixth oil path L 56  is connected to the tank oil path LT. The bucket second oil path L 52  is connected to the feedback oil path L 20  via a bucket pilot oil path L 57  including a check valve  83 . The check valve  83  is closed when the hydraulic pressure in the feedback oil path L 20  is higher than a hydraulic pressure in the bucket second oil path L 52 , and is opened when a reverse pressure relationship holds. A check valve  84  is provided in the bucket third oil path L 53 , to prevent backflow. 
     The bucket control valve  115  has pilot ports  115   a  and  115   b  respectively provided at both its ends (upper and lower ends in  FIG.  3   ), and pilot pressure supply oil paths L 45  and L 46  are respectively connected to the pilot ports  115   a  and  115   b.  A bucket pilot hydraulic pressure is supplied in response to a bucket working lever operation to the pilot pressure supply oil paths L 45  and L 46  from the pilot pressure supply valve unit  130  so that a working of the bucket control valve  115  is controlled to work.  FIG.  3    illustrates 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 L 45  and L 46 , and the bucket control valve  115  is positioned at a neutral position. In this state, all the six ports to which the six lines (the bucket first oil path L 51  to the bucket sixth oil path L 56 ) are respectively connected each enter a closed state. 
     Then, a case where a pilot pressure is supplied to the pilot port  115   a  from the pilot pressure supply valve unit  130  via the pilot pressure supply oil path L 45  by the bucket working lever operation being performed will be described. When the pilot pressure is supplied to the pilot port  115   a  from the pilot pressure supply valve unit  130  via the pilot pressure supply oil path L 45 , the bucket control valve  115  is moved downward as shown in  FIG.  3    (see  FIG.  5   ). As a result, the bucket first oil path L 51  communicates with the bucket second oil path L 52 . 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 valve  115 , a spool moves upon receiving the pilot pressure, and an opening area A 2  of the bucket control valve  115  (an area in which the bucket first oil path L 51  and the bucket second oil path L 52  communicate with each other) changes depending on a spool movement amount (spool stroke). 
     The opening area A 2  is set, as indicated by a solid line in  FIG.  7   , with respect to a spool stroke ST 2 . The spool stroke ST 2  changes 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 in  FIG.  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 valve  115  in 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 A 2  illustrated in  FIG.  7    is set to such an area as to allow passage of discharge oil from the first pump P 1  the 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 A 2  need 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 in  FIG.  8    is 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 cylinder  36  and the bucket cylinder  38 ). 
     Further, with the bucket control valve  115  moved downward, the bucket third oil path L 53  communicates with the bucket fourth oil path L 54 , and the bucket fifth oil path L 55  communicates with the bucket sixth oil path L 56 . 
     On the other hand, when a pilot pressure is supplied to the pilot port  115   b  from the pilot pressure supply valve unit  130  via the pilot pressure supply oil path L 46  by the bucket working lever operation in an opposite direction to that described above being performed, the bucket control valve  115  is moved upward in  FIG.  3   . As a result, the bucket first oil path L 51  communicates with the bucket second oil path L 52 , the bucket third oil path L 53  communicates with the bucket fifth oil path L 55 , and the bucket fourth oil path L 54  communicates with the bucket sixth oil path L 56 . 
     The bucket pressure compensation valve  80  is a two-position switching valve, and receives a hydraulic pressure in the feedback oil path L 20  on the side of its upper end and receives a hydraulic pressure in the bucket second oil path L 52  on the side of its lower end. The bucket pressure compensation valve  80  includes a spring that urges the bucket pressure compensation valve  80  upward. Accordingly, when the hydraulic pressure in the feedback oil path L 20  is smaller than a force obtained by adding a spring urging force to the hydraulic pressure in the bucket second oil path L 52 , there occurs a state where the bucket pressure compensation valve  80  moves upward as illustrated, to make the bucket second oil path L 52  and the bucket third oil path L 53  communicate with each other as they are. When the hydraulic pressure in the feedback oil path L 20  is larger than a force obtained by adding the spring urging force to the hydraulic pressure in the bucket second oil path L 52 , the bucket pressure compensation valve  80  moves downward, and the bucket second oil path L 52  and the bucket third oil path L 53  communicate with each other with the oil paths restricted via a bucket pressure compensation restrictor  81 . 
     The working of the working control device  100  configured as described above will be described below. When the operator performs the boom working lever operation, the operation device  160  feeds signals respectively representing its operation direction and operation amount to the controller  150 . The controller  150  performs rotation driving control of the first electric motor M 1  via the inverter  106  based on such operation information, and controls a discharge amount from the first hydraulic pump P 1 . As the rotation driving control, the controller  150  sets a discharge amount of the first hydraulic pump P 1  required for the actuator (e.g., the boom cylinder  36 , the bucket cylinder  38 ) to have a working speed corresponding to a lever operation amount and performs the rotation driving control of the first electric motor M 1  to obtain the set pump discharge amount. The first hydraulic pump P 1  may comprise a variable displacement type pump, and discharge amount control of the first hydraulic pump P 1  may be performed for the actuator (e.g., the boom cylinder  36 , the bucket cylinder  38 ) to have a working speed corresponding to the lever operation amount. The controller  150  also performs working control of the pilot pressure supply valve unit  130  in parallel with the control. 
     The control by the controller  150  is also performed with a lever operation not performed. With the lever operation not performed by the operator, both the boom control valve  113  and the bucket control valve  115  are each in a neutral state, and are as illustrated in  FIG.  3   . In the neutral state, all the six ports to be respectively connected to the six lines (the boom first oil path L 31  to the boom sixth oil path L 36 ) each enter a closed state in the boom control valve  113 , and all the six ports to be respectively connected to the six lines (the bucket first oil path L 51  to the bucket sixth oil path L 56 ) each similarly enter a closed state in the bucket control valve  115 . As a result, pressures in the boom second oil path L 32  and the bucket second oil path L 52  are respectively low pressures, and a pressure in the feedback oil path L 20  to be connected to the oil paths, respectively, via the boom and bucket pilot oil paths L 37  and L 57  is also a low pressure. Accordingly, a hydraulic pressure in the pump oil path L 1  (and the first and second branch pump oil paths L 11  and L 12 ) is also set to a low pressure by the unload valve  60  to be operated upon receiving a hydraulic pressure in the feedback oil path L 20 . In this state, a discharge oil amount from the first hydraulic pump P 1  is not required or may be a necessary minimum, and the controller  150  performs control to stop the first electric motor M 1  or control to drive the first electric motor M 1  to rotate in a minimum number of revolutions. As a result, power consumption required to drive the first electric motor M 1  can be minimized. 
     Then, the working in a case where the operator operates the work operation levers  161  and  162  to 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 to  FIG.  4   . 
     In this case, rotation driving control of the first electric motor M 1  by the controller  150  is first performed. When the operator performs the boom working lever operation, the controller  150  sets a discharge amount of the first hydraulic pump P 1  required for the actuator (e.g., the boom cylinder  36 ) to have a working speed corresponding to a lever operation amount and performs the rotation driving control of the first electric motor M 1  to obtain the set pump discharge amount. Further, in parallel therewith, working control of the pilot pressure supply valve unit  130  is also performed. The controller  150  controls a working of the pilot pressure supply valve unit  130 , to supply a pilot pressure to the pilot port  113   a  from the pilot pressure supply valve unit  130  via the pilot pressure supply oil path L 41 , for example. Consequently, the boom control valve  113  is moved downward, to enter a state illustrated in  FIG.  4   . When a boom working lever operation opposite thereto has been performed, a pilot pressure is supplied to the pilot port  113   b,  and the boom control valve  113  is moved upward. The bucket working lever operation has not been performed. Thus, the bucket control valve  115  is at a neutral position as illustrated, and the six ports are closed. 
     In the state illustrated in  FIG.  4   , the boom control valve  113  makes the boom first oil path L 31  communicate with the boom second oil path L 32 , makes the boom third oil path L 33  communicate with the boom fourth oil path L 34 , and makes the boom fifth oil path L 35  communicate with the boom sixth oil path L 36 . In this state, the boom second oil path L 32  and the feedback oil path L 20  communicate with each other via the boom pilot oil path L 37 , and a hydraulic pressure in the boom second oil path L 32  and a hydraulic pressure in the feedback oil path L 20  are equal to each other. Accordingly, the boom pressure compensation valve  70  is moved upward with a spring urging force, and the boom second oil path L 32  and the boom third oil path L 33  communicate with each other as they are. 
     As a result, although discharge oil in the first hydraulic pump P 1  flows from the boom first oil path L 31  to the boom second oil path L 32 , a communication opening area A 1  between the oil paths is set to change depending on the magnitude of a pilot pressure, and is indicated by a solid line in  FIG.  6   . Accordingly, a flow rate of the discharge oil flowing through the boom second oil path L 32  is a flow rate corresponding to the opening area indicated by the solid line in  FIG.  6   . The opening area A 1  indicated by the solid line in  FIG.  6    is set to such an area as to allow passage of discharge oil from the first pump P 1  the 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 P 1  is not limited, to flow from the boom first oil path L 31  to the boom second oil path L 32  as it is. As a result, a differential pressure that has been required in conventional feedback control need not be produced in the boom control valve  113 , 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 L 32  is fed to the boom fourth oil path L 34  through the boom control valve  113  after passing through the check valve  74  from the boom third oil path L 33  through the boom pressure compensation valve  70 , and is supplied to the bottom-side oil chamber of the boom cylinder  36 . As a result, the boom cylinder  36  works to extend. Thus, the hydraulic oil is discharged from the boom fifth oil path L 35  from the rod-side oil chamber of the boom cylinder  36 , to flow to the tank oil path LT from the boom sixth oil path L 36  after passing through the boom control valve  113  and returns to the tank T. 
     A hydraulic pressure in the boom second oil path L 32  (the hydraulic pressure is equal to a hydraulic pressure in the bottom-side oil chamber of the boom cylinder  36 ) is transmitted to the feedback oil path L 20  via the check valve  73 , to act on the unload valve  60 . Accordingly, the unload valve  60  sets respective hydraulic pressures in the pump oil path L 1  and the first and second branch pump oil paths L 11  and L 12  to correspond to a hydraulic pressure in the feedback oil path L 20  (i.e., a hydraulic pressure in the bottom-side oil chamber of the boom cylinder  36 ). 
     Then, a case where the operator has operated the work operation levers  161  and  162  and has simultaneously performed the boom working lever operation and the bucket working lever operation (has performed a composite operation) will be described with reference to  FIG.  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 M 1  by the controller  150  is performed. The controller  150  finds an oil amount required for the boom cylinder  36  to have a working speed corresponding to the boom working lever operation and an oil amount required for the bucket cylinder  38  to have a working speed corresponding to the bucket working lever operation. The controller  150  sets an oil amount obtained by summing both the oil amounts as a discharge amount of the first hydraulic pump P 1 , and performs the rotation driving control of the first electric motor M 1  to obtain the set pump discharge amount. 
     Further, in parallel therewith, working control of the pilot pressure supply valve unit  130  is also performed. For example, a pilot pressure is supplied to the pilot port  113   a  from the pilot pressure supply valve unit  130  via the pilot pressure supply oil path L 41 , and the boom control valve  113  is moved downward. Further, simultaneously therewith, in the bucket control valve  115 , a pilot pressure is supplied to the pilot port  115   a  from the pilot pressure supply valve unit  130  via the pilot pressure supply oil path L 45 , and the bucket control valve  115  is moved downward. As a result, both the valves  113  and  115  each enter a state illustrated in  FIG.  5   . 
     A working of the boom cylinder  36  by the boom control valve  113  at this time, excluding a working of the boom pressure compensation valve  70 , is as described above with reference to  FIG.  4   . Thus, description of the working is omitted, and a working of the bucket cylinder by the bucket control valve  115  will be described. The working of the boom pressure compensation valve  70 , together with a working of the bucket pressure compensation valve  80 , will be described below. 
     When the bucket control valve  115  enters the state illustrated in  FIG.  5   , the bucket first oil path L 51  communicates with the bucket second oil path L 52 , the bucket third oil path L 53  communicates with the bucket fourth oil path L 54 , and the bucket fifth oil path L 55  communicates with the bucket sixth oil path L 56 . As a result, although discharge oil in the first hydraulic pump P 1  flows from the bucket first oil path L 51  to the bucket second oil path L 52 , a communication opening area A 2  between the oil paths is set to change depending on the magnitude of a pilot pressure, and is indicated by a solid line in  FIG.  7   . 
     The opening area A 2  indicated by the solid line in  FIG.  7    is set to such an area as to allow passage of discharge oil from the first pump P 1  the 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 cylinder  36  to have a working speed corresponding to the boom working lever operation and an oil amount required for the bucket cylinder  38  to have a working speed corresponding to the bucket working lever operation is supplied from the first hydraulic pump P 1 . At this time, the opening area A 2  indicated by the solid line in  FIG.  7    is set to make an amount of oil required for the bucket cylinder  38  to 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 A 1  between the boom first oil path L 31  and the boom second oil path L 32  in the boom control valve  113  is set to make an amount of oil required for the boom cylinder  36  to 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 A 1  and A 2  of the boom control valve  113  and the bucket control valve  115  as illustrated in  FIG.  6    and  FIG.  7    is 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 L 52  is fed to the bucket fourth oil path L 54  through the bucket control valve  115  after passing through the check valve  84  from the bucket third oil path L 53  through the bucket pressure compensation valve  80 , and is supplied to the bottom-side oil chamber of the bucket cylinder  38 . As a result, the bucket cylinder  38  works to extend. Accordingly, the hydraulic oil is discharged from the bucket fifth oil path L 55  from the rod-side oil chamber of the bucket cylinder  38 , to flow to the tank oil path LT from the bucket sixth oil path L 56  after passing through the bucket control valve  115  and return to the tank. 
     Respective workings of the boom pressure compensation valve  70  and the bucket pressure compensation valve  80  will be described. Both the boom pressure compensation valve  70  and the bucket pressure compensation valve  80  are controlled to work upon receiving a hydraulic pressure in the feedback oil path L 20  on the side of its upper end and receiving respective hydraulic pressures in the boom second oil path L 32  and the bucket second oil path L 52  on the side of its lower end. Respective working loads of the boom cylinder  36  and the bucket cylinder  38  vary 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 cylinder  36  is large, a load of the bucket cylinder  38  is small, and hydraulic pressures in the boom first oil path L 31  to the boom fourth oil path L 34  are respectively higher than hydraulic pressures in the bucket first oil path L 51  to the bucket fourth oil path L 54  will be considered as an example. 
     The hydraulic pressure in the boom second oil path L 32  is transmitted to the feedback oil path L 20  via the boom pilot oil path L 37 , and the hydraulic pressure in the bucket second oil path L 52  is transmitted to the feedback oil path L 20  via the bucket pilot oil path L 57 . At this time, the check valves  73  and  83  are respectively provided in both the pilot oil paths L 37  and L 57 . Thus, although the hydraulic pressure in the boom second oil path L 32  on the high-pressure side is transmitted to the feedback oil path L 20 , the hydraulic pressure in the bucket second oil path L 52  on the low-pressure side is not transmitted thereto upon being blocked by the check valve  83 . As a result, the boom pressure compensation valve  70  is moved upward to make the boom second oil path L 32  and the boom third oil path L 33  communicate with each other as they are. On the other hand, the bucket pressure compensation valve  80  is moved downward to constitute an oil path passing through the bucket pressure compensation restrictor  81  because the hydraulic pressure in the feedback oil path L 20  is higher than the hydraulic pressure in the bucket second oil path L 52 . 
     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 valve  70  is not limited while remaining opened on the side on which respective load pressures in the boom cylinder  36  and the bucket cylinder  38  that 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 valve  80  is limited by the bucket pressure compensation restrictor  81  on 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 cylinders  36  and  38  from the first hydraulic pump P 1  as 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 restrictor  81 , to prevent this problem. This makes it possible to set a flow ratio of the boom cylinder  36  and the bucket cylinder  38 . For example, a working of the bucket cylinder  38  can be given priority to if the bucket pressure compensation restrictor  81  is widened, and a working of the boom cylinder  36  can be given priority to if the bucket pressure compensation restrictor  81  is narrowed. The same applies to the boom pressure compensation restrictor  71 . The working of the boom cylinder  36  can be given priority to if the boom pressure compensation restrictor  71  is widened, and the working of the bucket cylinder  38  can be given priority to if the boom pressure compensation restrictor  71  is 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 cylinder  36  work at a speed corresponding to the lever operation is supplied to the boom cylinder  36  upon controlling a flow rate by the boom control valve  113 , and hydraulic oil in an oil amount required to make the bucket cylinder  38  work at a speed corresponding to the lever operation is simultaneously supplied to the bucket cylinder  38  upon controlling a flow rate by the bucket control valve  115 . A relationship between the spool stroke ST 1  and the valve opening area A 1  in the boom control valve  113  and a relationship between the spool stroke ST 2  and the valve opening area A 2  in the bucket control valve  115  at this time are illustrated in  FIG.  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 valves  111  to  118  are controlled by the pilot pressure to be supplied from the pilot pressure supply valve unit  130 , it may be configured such that the control valves  111  to  118  each comprise an electromagnetic proportion type control valve and the respective openings of the control valves  111  to  118  are electromagnetically controlled. The openings of the control valves  111  to  118  may be controlled using a driving device such as an electric motor. 
     Although the first hydraulic pump P 1  and the turning hydraulic pump P 2  each comprise a fixed displacement type hydraulic pump in the above-described embodiment, the hydraulic pumps P 1  and P 2  may be each a variable displacement type hydraulic pump. The hydraulic pump P 1  and the turning hydraulic pump P 2  may 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 controller  150 , 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 
     
         
           1  hydraulic shovel 
           10  lower traveling unit 
           16 L,  16 R traveling motor 
           20  upper turning body 
           26  turning motor 
           30  shovel device 
           36  boom cylinder 
           37  arm cylinder 
           38  bucket cylinder 
           100  working control device 
           110  control valve unit 
           113  boom control valve 
           115  bucket control valve 
           130  pilot pressure supply valve unit 
           150  controller 
           160  operation device 
         M 1  first electric motor 
         M 2  second electric motor 
         P 1  first hydraulic pump 
         P 2  turning hydraulic pump