Patent Publication Number: US-10329737-B2

Title: Hybrid construction machine

Description:
TECHNICAL FIELD 
     The present invention relates to a hybrid construction machine on which an engine and a motor-generator are mounted. 
     BACKGROUND ART 
     In general, there is known a hybrid construction machine provided with a motor-generator that is jointed mechanically to an engine and a hydraulic pump, and an electricity storage device such as a lithium ion battery or a capacitor (for example, refer to Patent Document 1 and Patent Document 2). In this hybrid construction machine, the motor-generator plays a role of charging electric power generated by a driving force of the engine to the electricity storage device or assisting the engine by a powering operation using electric power of the electricity storage device. Many hybrid construction machines are provided with an electric motor separated from the motor-generator, and the electric motor acts for or assists in an operation of a hydraulic actuator. For example, at the time of performing a revolving movement by the electric motor, the electric motor performs or assists in the revolving movement of an upper revolving structure by electric power supply to the electric motor, and braking energy at a revolving stop is regenerated to perform a charge of the electricity storage device. 
     In this hydraulic construction machine, it is possible to enhance a reduction effect of a fuel consumption by increasing the output of the motor-generator or revolving electric motor. However, when the output of the motor-generator or the like is made large, there are some cases where sufficient electric power cannot be supplied due to the limitations of a discharge capability, a capacity, a temperature and the like of the electricity storage device. In this case, continuation of the electric power supply from the electricity storage device leads to hard use, accelerating degradation of the electricity storage device. 
     There is known the configuration made in consideration of the above problems. For example, Patent Document 1 discloses the configuration that a movement speed of a vehicle is lowered in response to a reduction of an electricity storage rate (SOC: state of charge) for preventing the degradation acceleration of the electricity storage device, preventing the hard use of the electricity storage device. 
     In addition, there are generally a plurality of parameters indicative of degradation of the electricity storage device, but it is difficult to simultaneously monitor the plurality of parameters. Therefore, Patent Document 2 discloses the configuration in which a plurality of parameters in regard to temperatures are mainly converted into given common scales a representative value of which is displayed on a monitor. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Patent No. 3941951 
     Patent Document 2: Japanese Patent No. 5271300 
     SUMMARY OF THE INVENTION 
     In the hybrid construction machine described in Patent Document 1, the movement speed of the vehicle is lowered in response to the reduction of the electricity storage rate for preventing the hard use of the electricity storage device. At this time, it is necessary to make an announcement that the movement speed is in a reduced state to an operator. In a case of making no announcement, there is a possibility that the operator determines that the reduction in the movement speed is made due to a failure, and besides, there is a possibility that strange operation feelings occur in the operator. Accordingly, it is necessary to display a state of the electricity storage device on, for example, a monitor. However, as described in Patent Document 2, only performing the monitoring display of the state of the electricity storage device cannot make a relation between the electricity storage device and the movement speed apparent. Therefore, there is a possibility that the operator cannot fully understand whether or not the movement speed is lowered at this point. In addition thereto, at the continuation of the present work, there is a problem that the operator cannot fully understand a future movement state such as a reduction in speeds, either. 
     The present invention is made in view of the aforementioned problems in the conventional technology, and an object of the present invention is to provide a hybrid construction machine that enables an operator to easily understand a relation between a state of an electricity storage device and a low speed mode. 
     For solving the above problems, a hybrid construction machine according to the present invention comprises an engine; a motor-generator that is connected mechanically to the engine; an electricity storage device that is connected electrically to the motor-generator; a hydraulic pump that is driven by torque of the engine and/or the motor-generator; a plurality of hydraulic actuators that are driven by pressurized oil from the hydraulic pump; a controller that controls output of the electricity storage device; and a monitor device that is connected to the controller, characterized in that: the controller includes: an electricity storage device state detecting section that detects a plurality of state-amounts indicative of a state of the electricity storage device; a low speed mode executing section that, when any one of the plurality of state-amounts detected by the electricity storage device state detecting section surpasses a given threshold, executes a low speed mode for reducing a movement speed of the hydraulic actuator in accordance with the surpassing degree; and a speed reduction degree calculating section that calculates a speed reduction degree of a speed of the hydraulic actuator in the low speed mode; wherein the monitor device includes a speed reduction degree displaying part that displays the speed reduction degree of the speed of the hydraulic actuator. 
     According to the present invention, an operator can easily understand a relation between the state of the electricity storage device and the low speed mode by a visual contact with the monitor device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view showing a hybrid hydraulic excavator according to an embodiment of the present invention. 
         FIG. 2  is a block diagram showing a hydraulic system and an electric system that are applied to the hybrid hydraulic excavator in  FIG. 1 . 
         FIG. 3  is a block diagram showing a hybrid control unit and a monitor device in  FIG. 2 . 
         FIG. 4  is a block diagram showing an output command calculating section in  FIG. 3 . 
         FIG. 5  is a block diagram showing a battery discharge limit value calculating section in  FIG. 4 . 
         FIG. 6  is an explanatory diagram showing a table for finding a first battery discharge power limit value from a battery electricity storage rate. 
         FIG. 7  is an explanatory diagram showing a table for finding a second battery discharge power limit value from a current square integrating rate. 
         FIG. 8  is a block diagram showing a total output upper limit value calculating section in  FIG. 4 . 
         FIG. 9  is an explanatory diagram showing a monitor display amount calculating section in  FIG. 3 . 
         FIG. 10  is a block diagram showing a maximum speed reduction rate calculating section in  FIG. 9 . 
         FIG. 11  is a block diagram showing a common scale conversion minimum value calculating section in  FIG. 9 . 
         FIG. 12  is a block diagram showing a low speed mode arrival predicting time calculating section in  FIG. 9 . 
         FIG. 13  is a block diagram showing a predicting maximum speed reduction rate calculating section in  FIG. 9 . 
         FIG. 14  is a perspective view showing an essential part showing the inside of a cab in  FIG. 1 . 
         FIG. 15  is an explanatory diagram showing an example of a display screen displayed on the monitor device. 
         FIG. 16  is an explanatory diagram showing a speed reduction degree displaying part, a common scale displaying part, a low speed mode arrival time displaying part, and a speed reduction degree predicting value displaying part in the monitor device. 
         FIG. 17  is an explanatory diagram showing a state of the electricity storage device and a display content of the monitor device in a state before use start of the electricity storage device. 
         FIG. 18  is an explanatory diagram showing a state of the electricity storage device and a display content of the monitor device in a case where a battery electricity storage rate reduces in a range of a normal mode. 
         FIG. 19  is an explanatory diagram showing a state of the electricity storage device and a display content of the monitor device in a case where a current square integrating rate increases in a range of the normal mode. 
         FIG. 20  is an explanatory diagram showing a state of the electricity storage device and a display content of the monitor device in a case where a battery electricity storage rate reduces in a range of a low speed mode. 
         FIG. 21  is an explanatory diagram showing a state of the electricity storage device and a display content of the monitor device in a case where a current square integrating rate increases in a range of the low speed mode. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, a hybrid hydraulic excavator as an example of a hybrid construction machine according to an embodiment in the present invention will be explained with reference to the accompanying drawings. 
       FIG. 1  to  FIG. 21  show an embodiment of the present invention. A hybrid hydraulic excavator  1  (hereinafter, referred to as “hydraulic excavator  1 ”) is provided with an engine  21  and a motor-generator  27 , which will be described later. The hydraulic excavator  1  includes an automotive lower traveling structure  2  of a crawler type, a revolving device  3  that is provided on the lower traveling structure  2 , an upper revolving structure  4  that is mounted through the revolving device  3  on the lower traveling structure  2  to be capable of revolving thereon, and a working mechanism  12  of an articulated structure that is provided in the front side of the upper revolving structure  4  and performs an excavating operation of earth and sand, and the like. At this time, the lower traveling structure  2  and the upper revolving structure  4  configure a vehicle body of the hydraulic excavator  1 . 
     The upper revolving structure  4  is provided with a housing cover  6  that is provided on a revolving frame  5  to accommodate therein the engine  21  and the like, and a cab  7  for an operator getting in. As shown in  FIG. 14 , an operator&#39;s seat  8  on which an operator sits is provided in the cab  7 , and a traveling operation device  9  that is composed of operating levers, operating pedals and the like, a revolving operation device  10  that is composed of an operating lever and the like, and a working operation device  11  that is composed of operating levers and the like are provided in the periphery of the operator&#39;s seat  8 . 
     The traveling operation device  9  is arranged, for example, in front of the operator&#39;s seat  8 . The revolving operation device  10  corresponds to, for example, an operating section of the operating lever in a front-rear direction arranged in the left side to the operator&#39;s seat  8 . In addition, the working operation device  11  corresponds to an operating (arm operating) section of the operating lever in a left-right direction arranged in the left side to the operator&#39;s seat  8 , and an operating (boom operating) section of the operating lever in a front-rear direction and an operating (bucket operating) section of the operating lever in a left-right direction arranged in the right side to the operator&#39;s seat  8 . It should be noted that a relation of an operating direction of the operating lever to a revolving movement or a working movement is not limited to the aforementioned relation, but may be optionally set in accordance with a specification of the hydraulic excavator  1  or the like. 
     Here, the operation devices  9  to  11  are respectively provided with operating amount sensors  9 A to  11 A that detect their operating amounts (lever operating amount OA). The operating amount sensors  9 A to  11 A configure a vehicle body operating-state detecting device that detects an operating state of the vehicle body, such as a traveling operation of the lower traveling structure  2 , a revolving operation of the upper revolving structure  4  or a lifting/tilting operation (excavating operation) of the working mechanism  12 . Further, an engine control dial  38  and a monitor device  39  which will be described later are provided in the cab  7 . 
     As shown in  FIG. 1 , the working mechanism  12  is configured of, for example, a boom  12 A, an arm  12 B and a bucket  12 C, and a boom cylinder  12 D, an arm cylinder  12 E and a bucket cylinder  12 F for driving them. The boom  12 A, the arm  12 B and the bucket  12 C are pinned to each other. The working mechanism  12  is attached to the revolving frame  5 , and extends or contracts the cylinders  12 D to  12 F to perform a lifting/tilting movement. 
     Here, the hydraulic excavator  1  is provided thereon with an electric system that controls the motor-generator  27  and the like, and a hydraulic system that controls movements of the working mechanism  12  and the like. Further, the hydraulic excavator  1  is provided with the monitor device  39  that displays a state of an electricity storage device  31 . Hereinafter, an explanation will be made of the system configuration in the hydraulic excavator  1  with reference to  FIG. 2  to  FIG. 16 . 
     The engine  21  is mounted on the revolving frame  5 . The engine  21  is configured of an internal combustion engine such as a diesel engine. As shown in  FIG. 2 , a hydraulic pump  23  and the motor-generator  27 , which will be described later, are attached mechanically to the output side of the engine  21  for serial connection. The hydraulic pump  23  and the motor-generator  27  are driven by the engine  21 . Here, an operation of the engine  21  is controlled by an engine control unit  22  (hereinafter, referred to as “ECU  22 ”). The ECU  22  controls output torque, a rotational speed (engine rotational number) and the like of the engine  21  based upon an engine output command Pe from an HCU  36 . It should be noted that the maximum output of the engine  21  is made smaller than the maximum power of the hydraulic pump  23 , for example. 
     The hydraulic pump  23  is connected mechanically to the engine  21 . The hydraulic pump  23  can be driven by the torque of the engine  21  alone. In addition, the hydraulic pump  23  can be driven by compound torque (total torque) made by adding assist torque of the motor-generator  27  to the torque of the engine  21 . The hydraulic pump  23  pressurizes operating oil reserved in a tank (not shown), which is delivered to a traveling hydraulic motor  25 , a revolving hydraulic motor  26 , the cylinders  12 D to  12 F of the working mechanism  12 , and the like as pressurized oil. 
     The hydraulic pump  23  is connected through a control valve  24  to the traveling hydraulic motor  25 , the revolving hydraulic motor  26 , and the cylinders  12 D to  12 F as hydraulic actuators. The hydraulic motors  25 ,  26  and the cylinders  12 D to  12 F are driven by the pressurized oil from the hydraulic pump. The control valve  24  supplies or discharges the pressurized oil delivered from the hydraulic pump  23  to or from the traveling hydraulic motor  25 , the revolving hydraulic motor  26 , and the cylinders  12 D to  12 F in response to operations to the traveling operation device  9 , the revolving operation device  10  and the working operation device  11 . 
     Specifically, the pressurized oil is supplied to the traveling hydraulic motor  25  from the hydraulic pump  23  in response to an operation of the traveling operation device  9 . As a result, the traveling hydraulic motor  25  drives/travels the lower traveling structure  2 . The pressurized oil is supplied to the revolving hydraulic motor  26  from the hydraulic pump  23  in response to an operation of the revolving operation device  10 . As a result, the revolving hydraulic motor  26  performs a revolving movement of the upper revolving structure  4 . The pressurized oil is supplied to the cylinders  12 D to  12 F from the hydraulic pump  23  in response to an operation of the working operation device  11 . As a result, the cylinders  12 D to  12 F lift/tilt the working mechanism  12 . 
     The motor-generator  27  is connected mechanically to the engine  21 . The motor-generator  27  is configured of, for example, a synchronous electric motor and the like. The motor-generator  27  plays two roles of power generation of performing power supply to the electricity storage device  31  and the revolving electric motor  33  by acting as an electric generator using the engine  21  as a power source, and a powering operation of assisting in driving the engine  21  and the hydraulic pump  23  by acting as a motor using electric power from the electricity storage device  31  and the revolving electric motor  33  as a power source. Accordingly, the assist torque of the motor-generator  27  is added to the torque of the engine  21  in response to the state, and the hydraulic pump  23  is driven by the engine torque and the assist torque. The movement of the working mechanism  12 , a travel of the vehicle and the like are performed by the pressurized oil delivered from the hydraulic pump  23 . 
     As shown in  FIG. 2 , the motor-generator  27  is connected to a pair of DC buses  29 A,  29 B through a first inverter  28 . The first inverter  28  is configured using a plurality of switching elements such as a transistor and an insulating gate bipolar transistor (IGBT), and ON/OFF of each of the switching elements is controlled by a motor-generator control unit  30  (hereinafter, referred to as “MGCU  30 ”). The DC buses  29 A,  29 B are paired at a positive terminal side and at a negative terminal side, and, for example, a DC voltage of approximately several hundred V is applied thereto. 
     At the power generation of the motor-generator  27 , the first inverter  28  converts AC power from the motor-generator  27  into DC power, which is supplied to the electricity storage device  31  or the revolving electric motor  33 . At the powering operation of the motor-generator  27 , the first inverter  28  converts the DC power of the DC buses  29 A,  29 B into AC power, which is supplied to the motor-generator  27 . The MGCU  30  controls ON/OFF of each of the switching elements in the first inverter  28  based upon a motor-generator powering operation output command Pmg from the HCU  36  and the like. Thereby, the MGCU  30  controls generator power at the power generation of the motor-generator  27  and driving electric power at the powering operation of the motor-generator  27 . 
     The electricity storage device  31  is connected electrically to the motor-generator  27 . The electricity storage device  31  is configured of a plurality of cells (not shown) composed of, for example, lithium ion batteries and is connected to the DC buses  29 A,  29 B. 
     The electricity storage device  31  is charged with power supplied from the motor-generator  27  at the power generation of the motor-generator  27  and supplies driving electric power toward the motor-generator  27  at the powering operation (at the assist drive) of the motor-generator  27 . In addition, the electricity storage device  31  is charged with regeneration power supplied from the revolving electric motor  33  at the regeneration of the revolving electric motor  33  and supplies driving electric power toward the revolving electric motor  33  at the powering operation of the revolving electric motor  33 . In this way, the electricity storage device  31  stores therein the power generated by the motor-generator  27 , and further, absorbs the regeneration power generated by the revolving electric motor  33  at the revolving braking of the hydraulic excavator  1  to hold the voltage of the DC buses  29 A,  29 B to be constant. 
     A charge operation or a discharge operation of the electricity storage device  31  is controlled by a battery control unit  32  (hereinafter, referred to as “BCU  32 ”). The BCU  32  configures an electricity storage device state detecting section. The BCU  32  detects, for example, a battery electricity storage rate SOC and a current square integrating rate Risc as a plurality of state-amounts of the electricity storage device  31 . Further, the BCU  32  detects charge power to the electricity storage device  31  as a battery power value Pc, and calculates a battery allowance discharge power Pbmax based upon, for example, a cell voltage or a hardware current upper limit value. The battery allowance discharge power Pbmax indicates power that can be discharged by the present electricity storage device  31 . The BCU  32  outputs the battery allowance discharge power Pbmax, the battery power value Pc, the battery electricity storage rate SOC, the current square integrating rate Risc and the like to the HCU  36 . 
     In addition, the BCU  32  controls the charge/discharge of the electricity storage device  31  such that the revolving electric motor  33  and the motor-generator  27  are driven in response to an electric/revolving output command Per and the motor-generator powering operation output command Pmg from the HCU  36 . At this time, the battery electricity storage rate SOC becomes a value corresponding to the electricity storage amount of the electricity storage device  31 . 
     It should be noted that in the present embodiment, a lithium ion battery, for example, having a voltage of 350 V, a discharge capacity of 5 Ah, an appropriate use range of the battery electricity storage rate SOC (electricity storage rate) set to, for example, 30% to 70% and an appropriate use cell temperature set to 60° C. or less is used in the electricity storage device  31 . The appropriate use range of the battery electricity storage rate SOC and the like are not limited to the above values, but are optionally set in accordance with a specification of the electricity storage device  31  or the like. 
     Here, the maximum output of the engine  21  is smaller than the maximum pump absorption power. In this case, as compared to when the engine  21  has a sufficiently large output to the maximum pump absorption power, a rate of contribution of engine assist by a powering operation of the motor-generator  27  at the vehicle body movement is larger. Therefore, the electricity storage device  31  severely repeats charge and discharge. 
     When the electricity storage device  31  generally performs excessive charge or discharge, the degradation is accelerated to lower the output. A degradation speed of the electricity storage device  31  differs depending upon the battery electricity storage rate SOC at the charging or discharging, or intensity of the charge or discharge itself. For example, in the electricity storage device  31  such as a lithium ion battery, an appropriate use range is defined to the electricity storage rate or the cell temperature by a manufacturer (for example, 30% to 70% in the electricity storage rate and 60° C. or less in the cell temperature). When the electricity storage device  31  is used over this range, the degradation speed greatly increases. 
     Likewise an appropriate use range of the electricity storage device  31  is in advance defined to the intensity of the charge or discharge as well. A current square integrating value is generally used as an index of the intensity of the charge or discharge. This is an index indicative of how much input or output of current is performed for a past constant time T traced back from the present time by integrating the square of the current for T time. At this time, in many cases the time T is set by plural times. This index is optionally set in accordance with a specification of the electricity storage device  31  or the like. Accordingly, when the electricity storage device  31  is used over an upper limit value of the current square integrating value, the degradation of the electricity storage device  31  is accelerated. Therefore, the electricity storage device  31  is used not to surpass the upper limit value of the current square integrating value as much as possible. 
     Hereinafter, a case where the time T is set to 100 seconds will be explained as one example. That is, the upper limit value of the current square integrating value for 100 seconds in the past is in advance determined. Therefore, by defining a rate of the present value and the upper limit value of the current square integrating value as the current square integrating rate Risc, the use of the electricity storage device  31  is controlled such that the current square integrating rate Risc does not surpass 100%. Accordingly, the appropriate use range of the current square integrating rate Risc is 0 to 100%. At this time, the BCU  32  is provided with, for example, a current sensor (not shown) that detects a current of the charge or discharge of the electricity storage device  31 , and calculates the current square integrating rate Risc based upon the detected current. The current square integrating rate Risc is not limited to the calculation by the BCU  32 , but, for example, the current of the electricity storage device  31  at the charging and the discharging may be detected from the BCU  32  and the current square integrating rate Risc may be calculated based upon the detected value of this current by the HCU  36 . Likewise, the battery power value Pc may be also calculated based upon the detected value of the current of the electricity storage device  31  by the HCU  36 . 
     The revolving electric motor  33  is driven by the power from the motor-generator  27  or the electricity storage device  31 . The revolving electric motor  33  is configured of, for example, a three-phase induction motor, and is provided on the revolving frame  5  together with the revolving hydraulic motor  26 . The revolving electric motor  33  drives the revolving device  3  in cooperation with the revolving hydraulic motor  26 . Therefore, the revolving device  3  is driven by compound torque of the revolving hydraulic motor  26  and the revolving electric motor  33  to drive and revolve the upper revolving structure  4 . 
     As shown in  FIG. 2 , the revolving electric motor  33  is connected to the DC buses  29 A,  29 B through a second inverter  34 . The revolving electric motor  33  plays two roles of a powering operation of being driven/rotated by receiving the power from the electricity storage device  31  or the motor-generator  27 , and regeneration of storing electricity in the electricity storage device  31  by generating power with extra torque at the revolving braking. Therefore, the power from the motor-generator  27  or the like is supplied through the DC buses  29 A,  29 B to the revolving electric motor  33  at the powering operation. Thereby, the revolving electric motor  33  generates rotational torque in response to an operation of the revolving operation device  10  to assist in a drive of the revolving hydraulic motor  26 , and drive the revolving device  3  to perform a revolving movement of the upper revolving structure  4 . 
     The second inverter  34  is, as similar to the first inverter  28 , configured using a plurality of switching elements. ON/OFF of each of the switching elements in the second inverter  34  is controlled by a revolving electric motor control unit  35  (hereinafter, referred to as “RMCU  35 ”). At the powering operation of the revolving electric motor  33 , the second inverter  34  converts the DC power of the DC buses  29 A,  29 B into AC power to be supplied to the revolving electric motor  33 . At the regeneration of the revolving electric motor  33 , the second inverter  34  converts the AC power from the revolving electric motor  33  into DC power to be supplied to the electricity storage device  31  and the like. 
     The RMCU  35  controls ON/OFF of each of the switching elements in the second inverter  34  based upon the electric/revolving output command Per from the HCU  36  and the like. Thereby, the RMCU  35  controls regeneration power at the regeneration of the revolving electric motor  33  and driving electric power at the powering operation thereof. 
     The hybrid control unit  36  (hereinafter, referred to as “HCU  36 ”) configures a controller together with the BCU  32  to control the output of the electricity storage device  31 . The HCU  36  is configured of, for example, a microcomputer, and is connected electrically to the ECU  22 , the MGCU  30 , the RMCU  35  and the BCU  32  using a CAN  37  (Controller Area Network) and the like. The HCU  36  exchanges communications with the ECU  22 , the MGCU  30 , the RMCU  35  and the BCU  32 , while controlling the engine  21 , the motor-generator  27 , the revolving electric motor  33  and the electricity storage device  31 . 
     The battery allowance discharge power Pbmax, the battery power value Pc, the battery electricity storage rate SOC, the current square integrating rate Risc, other vehicle body information V 1 , pump loads, mode information and the like are input through the CAN  37  and the like to the HCU  36 . The operating amount sensors  9 A to  11 A that detect the lever operating amount OA of the operation devices  9  to  11  are connected to the HCU  36 . As a result, the lever operating amount OA is input to the HCU  36 . Further, the engine control dial  38  is connected to the HCU  36 , and an engine target rotational speed we set by the engine control dial  38  is input to the HCU  36 . 
     The HCU  36  has a normal mode NMODE and a low speed mode LSMODE. The HCU  36  selects and executes any one of the normal mode NMODE and the low speed mode LSMODE. Here, in the low speed mode LSMODE, for example, when the output beyond the actual output of the engine  21  is needed, a movement speed of each of the revolving device  3  and the working mechanism  12  is reduced. On the other hand, in the normal mode NMODE, a reduction in the movement speed by the low speed mode LSMODE is released. 
     The engine control dial  38  is configured of a rotatable dial, and sets the target rotational speed ωe of the engine  21  in accordance with a rotational position of the dial. The engine control dial  38  is positioned in the cab  7  and is operable to be rotated by an operator, outputting a command signal in accordance with the target rotational speed ωe. 
     The monitor device  39  is connected to the HCU  36 , and displays various pieces of information in regard to the vehicle body. As shown in  FIG. 14  and  FIG. 15 , the monitor device  39  is arranged in the cab  7 , and displays, for example, a remaining amount of fuel, a water temperature of engine cooling water, a working time and an in-vehicular compartment temperature. In addition thereto, the monitor device  39  includes a speed reduction degree displaying part  39 A, a common scale displaying part  39 B, a low speed mode arrival time displaying part  39 C and a speed reduction degree predicting value displaying part  39 D. 
     As shown in  FIG. 15  and  FIG. 16 , the speed reduction degree displaying part  39 A displays a maximum speed reduction rate DRs as a speed reduction degree of the speed of the hydraulic actuator (the hydraulic motors  25 ,  26  and cylinders  12 D to  12 F) in the low speed mode LSMODE. The speed reduction degree displaying part  39 A is configured of, for example, a bar that expands/contracts in a longitudinal direction, a minimum value of the maximum speed reduction rate DRs is positioned in a lower end thereof, and a maximum value of the maximum speed reduction rate DRs is positioned in an upper end thereof. A maximum value section of the speed reduction degree displaying part  39 A is continuous to a minimum value section of the common scale displaying part  39 B. At this time, the maximum value of the maximum speed reduction rate DRs is 100%, for example, and the minimum value of the maximum speed reduction rate DRs is a maximum speed reduction rate minimum value DRsmin (for example, 70%). 
     When the HCU  36  is executing the normal mode NMODE, the maximum speed reduction rate DRs is the maximum value. Therefore, the bar of the speed reduction degree displaying part  39 A becomes in the most extended state. On the other hand, when the HCU  36  is executing the low speed mode LSMODE, the maximum speed reduction rate DRs is a value between the maximum value and the minimum value. Therefore, the bar of the speed reduction degree displaying part  39 A is contracted from the maximum extension and has a length dimension in accordance with the maximum speed reduction rate DRs. 
     The common scale displaying part  39 B displays a common scale conversion minimum value Emin. When the respective present values of a plurality of state-amounts (battery electricity storage rate SOC, current square integrating rate Risc) of the electricity storage device  31  are converted into common scale values, the common scale conversion minimum value Emin indicates a representative value composed of anyone thereof. Specifically, the common scale conversion minimum value Emin indicates a minimum value of a first conversion value Eb made by converting the battery electricity storage rate SOC into the common scale and a second conversion value Er made by converting the current square integrating rate Risc into the common scale. 
     The common scale displaying part  39 B is configured of, for example, a bar that expands/contracts in a longitudinal direction. The bar of the common scale displaying part  39 B, for distinction from the speed reduction degree displaying part  39 A, is displayed in a different color, for example. In the common scale displaying part  39 B, the minimum value of the common scale conversion minimum value Emin is positioned in a lower end thereof, and the maximum value of the common scale conversion minimum value Emin is positioned in an upper end thereof. 
     At this time, the common scale conversion minimum value Emin is a value in accordance with allowance on transfer from the normal mode NMODE to the low speed mode LSMODE. Therefore, the common scale displaying part  39 B informs that the transfer to the low speed mode LSMODE comes nearby contraction of the bar in accordance with the common scale conversion minimum value Emin. In addition, a minimum value section of the common scale displaying part  39 B is continuous to a maximum value section of the speed reduction degree displaying part  39 A. Therefore, when the common scale conversion minimum value Emin is lowered to transfer to the low speed mode LSMODE, the bar of the common scale displaying part  39 B is contracted to be switched continuously to expansion/contraction of the bar of the speed reduction degree displaying part  39 A. Therefore, an operator can continuously understand an allowance section in the normal mode NMODE and the speed reduction degree of the speed in the low speed mode LSMODE. 
     The low speed mode arrival time displaying part  39 C displays a low speed mode arrival predicting time PT until arriving in the low speed mode LSMODE. The low speed mode arrival time displaying part  39 C is positioned in the vicinity to the speed reduction degree displaying part  39 A and the common scale displaying part  39 B to display a numerical value of the low speed mode arrival predicting time PT in a given section (for example, in a minute section or in a second section). 
     The speed reduction degree predicting value displaying part  39 D displays a predicting maximum speed reduction rate PDRs as a predicting value of a speed reduction degree of a speed of each of the hydraulic actuators (the hydraulic motors  25 ,  26  and the cylinders  12 D to  12 F) at the transferring to the low speed mode LSMODE. The speed reduction degree predicting value displaying part  39 D is configured of an indicator disposed in the vicinity to the speed reduction degree displaying part  39 A. The indicator of the speed reduction degree predicting value displaying part  39 D indicates a length position (height position) of the bar of the speed reduction degree displaying part  39 A where the arrival is predicted when the present movement continues to be performed. 
     Next, an explanation will be made of a specific configuration of the HCU  36 . As shown in  FIG. 3 , the HCU  36  includes an output command calculating section  40  and a monitor display amount calculating section  50 . 
     The output command calculating section  40  configures a low speed mode executing section. The output command calculating section  40  executes the low speed mode LSMODE for, when any one of the plurality of state-amounts (the battery electricity storage rate SOC and current square integrating rate Risc) detected by the BCU  32  surpasses a given threshold (an appropriate reference value SOC 1  or appropriate reference value Risc 1 ), reducing a movement speed of each of the hydraulic actuators (the hydraulic motors  25 ,  26  and cylinders  12 D to  12 F) in accordance with the surpassing degree. 
     As shown in  FIG. 4 , the output command calculating section  40  includes a battery discharge limit value calculating section  41 , a total output upper limit value calculating section  42 , a movement output distribution calculating section  43  and a hydraulic/electric output distribution calculating section  44 . The output command calculating section  40  calculates a battery discharge power limit value Plim 0 , an engine output upper limit value Pemax, an engine output command Pe, an electric/revolving output command Per and a motor-generator powering operation output command Pmg based upon the battery allowance discharge power Pbmax, the battery electricity storage rate SOC, the current square integrating rate Risc, the engine target rotational speed ωe, the lever operating amount OA and other vehicle body information V 1 . The output command calculating section  40  outputs the battery discharge power limit value Plim 0  and the engine output upper limit value Pemax to the monitor display amount calculating section  50 , outputs the engine output command Pe to the ECU  22 , outputs the electric/revolving output command Per to the RMCU  35  and outputs the motor-generator powering operation output command Pmg to the MGCU  30 . 
     As shown in  FIG. 5 , the battery discharge limit value calculating section  41  includes a first battery discharge power limit value calculating part  41 A, a second battery discharge power limit value calculating part  41 B and a minimum value selecting part  41 C. The battery electricity storage rate SOC, the current square integrating rate Risc and the battery allowance discharge power Pbmax are input to the battery discharge limit value calculating section  41  from the BCU  32 . 
     Since the first battery discharge power limit value calculating part  41 A, for example, has a table T 1  as shown in  FIG. 6  for calculating a first battery discharge power limit value Plim 1  based upon the battery electricity storage rate SOC. The first battery discharge power limit value calculating part  41 A uses the table  1  to calculate the first battery discharge power limit value Plim 1  in accordance with the battery electricity storage rate SOC. 
     Since the second battery discharge power limit value calculating part  41 B, for example, has a table T 2  as shown in  FIG. 7  for calculating a second battery discharge power limit value Plim 2  based upon the current square integrating rate Risc. The second battery discharge power limit value calculating part  41 B uses the table  2  to calculate the second battery discharge power limit value Plim 2  in accordance with the current square integrating rate Risc. 
     At this time, maximum values P 11 , P 21  of the battery discharge power limit values Plim 1 , Plim 2  in  FIG. 6  and  FIG. 7  are set to values close to the battery allowance discharge power Pbmax typical when the electricity storage device  31  is a new product and a cell temperature is a room temperature. Therefore, the maximum value P 11  and the maximum value P 21  have the same value, for example. 
     The table T 1 , when the battery electricity storage rate SOC is lower than a minimum value SOC 2  in an appropriate use range, sets the battery discharge power limit value Plim 1  to a minimum value P 10  (for example, P 10 =0 kW), and when the battery electricity storage rate SOC is higher than an appropriate reference value SOC 1  as a threshold, sets the battery discharge power limit value Plim 1  to the maximum value P 11 . In addition, when the battery electricity storage rate SOC becomes a value between the minimum value SOC 2  and the appropriate reference value SOC 1 , the table T 1  increases the battery discharge power limit value Plim 1  with an increase in the battery electricity storage rate SOC. That is, when the battery electricity storage rate SOC is lower than the appropriate reference value SOC 1  as the threshold from a value equal to or more than the appropriate reference value SOC 1 , the table T 1  sets the battery discharge power limit value Plim 1  to a value between the minimum value P 10  and the maximum value P 11  in accordance with the reduction degree. Here, the appropriate reference value SOC 1  is set to a large value having a predetermined margin from the minimum value SOC 2 . For example, when the minimum value SOC 2  becomes 30%, the appropriate reference value SOC 1  is set to a value of approximately 35%. 
     The table T 2 , when the current square integrating rate Risc is higher than a maximum value Risc 2  in an appropriate use range, sets the battery discharge power limit value Plim 2  to a minimum value P 20  (for example, P 20 =0 kW), and when the current square integrating rate Risc is lower than an appropriate reference value Risc 1  as a threshold, the table T 2  sets the battery discharge power limit value Plim 2  to the maximum value P 21 . In addition, when the current square integrating rate Risc becomes a value between the maximum value Risc 2  and the appropriate reference value Risc 1 , the table T 2  reduces the battery discharge power limit value Plim 2  with an increase in the current square integrating rate Risc. That is, when the current square integrating rate Risc is higher than the appropriate reference value Risc 1  as the threshold from a value equal to or less than the appropriate reference value Risc 1 , the table T 2  sets the battery discharge power limit value Plim 2  to a value between the minimum value P 20  and the maximum value P 21  in accordance with the increase degree. Here, the appropriate reference value Risc 1  is set to a small value having a predetermined margin from the maximum value Risc 2 . For example, when the maximum value Risc 2  becomes 100%, the appropriate reference value Risc 1  is set to a value of approximately 90%. 
     The minimum value selecting part  41 C compares the three values of the battery discharge power limit values Plim 1 , Plim 2  calculated by the first and second battery discharge power limit value calculating parts  41 A,  41 B and the battery allowance discharge power Pbmax. The minimum value selecting part  41 C selects a minimum value of the battery discharge power limit values Plim 1 , Plim 2  and the battery allowance discharge power Pbmax to be outputted as the battery discharge power limit value Plim 0 . 
     As shown in  FIG. 8 , the total output upper limit value calculating section  42  includes a motor-generator powering operation output upper limit value calculating part  42 A, an engine output upper limit value calculating part  42 B and an adder  42 C. The battery discharge power limit value Plim 0  and the target rotational speed ωe of the engine  21  determined by a command of the engine control dial  38  and the like are input to the total output upper limit value calculating section  42 . 
     The motor-generator powering operation output upper limit value calculating part  42 A calculates a motor-generator output upper limit value Pmgmax considering hardware restrictions such as an efficiency of the motor-generator  27 . Specifically, the motor-generator powering operation output upper limit value calculating part  42 A calculates the motor-generator output upper limit value Pmgmax based upon a product of an efficiency gain at the time the motor-generator  27  performs a powering operation and the battery discharge power limit value Plim 0 . The motor-generator output upper limit value Pmgmax indicates the output when the motor-generator  27  performs the powering operation at the maximum in a range of the battery discharge power limit value Plim 0 . It should be noted that the motor-generator powering operation output upper limit value calculating part  42 A may calculate the motor-generator output upper limit value Pmgmax in consideration of a temperature of the motor-generator  27  and the like in addition to the efficiency of the motor-generator  27 . 
     The engine output upper limit value calculating part  42 B calculates an output maximum value of the engine  21  that can be outputted in the target rotational speed ωe to be outputted as the engine output upper limit value Pemax. The engine output upper limit value calculating part  42 B includes a torque map  42 B 1 , an engine output calculating part  42 B 2  and an amplifier  42 B 3 . 
     The torque map  42 B 1  preliminarily stores a relation between the rotational speed and output torque Te of the engine  21 . Therefore, the torque map  42 B 1 , when the target rotational speed ωe of the engine  21  is input thereto, calculates the output torque Te when the engine  21  rotates in the target rotational speed ωe. 
     The engine output calculating part  42 B 2  calculates a product of the target rotational speed ωe and the output torque Te of the engine  21 . The amplifier  42 B 3  amplifies the product of the target rotational speed ωe and the output torque Te with a gain in consideration of the efficiency of the engine  21  and the like. Thereby, the amplifier  42 B 3  outputs the engine output upper limit value Pemax as an output maximum value of the engine  21  when the engine  21  rotates in the target rotational speed ωe. 
     The adder  42 C calculates a total amount (Pmgmax+Pemax) of the motor-generator output upper limit value Pmgmax as a powering operation output upper limit value of the motor-generator  27  calculated in the motor-generator powering operation output upper limit value calculating part  42 A and the engine output upper limit value Pemax calculated in the engine output upper limit value calculating part  42 B. The adder  42 C outputs this total value as a total output upper limit value Ptmax. 
     The movement output distribution calculating section  43  calculates distribution of movement outputs Pox of various movements such as the traveling movement, the revolving movement and the lifting/tilting movement of the working mechanism  12  based upon the total output upper limit value Ptmax and the lever operating amount OA. The total output upper limit value Ptmax and the lever operating amount OA are input to the movement output distribution calculating section  43 . The movement output distribution calculating section  43  adjusts magnitudes and the distribution of the movement outputs Pox of the various movements such that the vehicle moves in accordance with the lever operating amount OA in a range where a sum of the movement outputs does not surpass the total output upper limit value Ptmax. The movement output distribution calculating section  43  outputs each movement output Pox adjusted in the magnitude and distribution to the hydraulic/electric output distribution calculating section  44 . 
     The battery discharge power limit value Plim 0 , the total output upper limit value Ptmax, each movement output Pox and the other vehicle body information VI are input to the hydraulic/electric output distribution calculating section  44 . The hydraulic/electric output distribution calculating section  44  calculates the respective outputs shared by the revolving electric motor  33 , the motor-generator  27  and the engine  21  such that the energy efficiency is optimal and the vehicle body movement can be performed in response to the lever operation based upon the input information. The hydraulic/electric output distribution calculating section  44  outputs the electric/revolving output command Per, the motor-generator powering operation output command Pmg and the engine output command Pe as the calculation results. 
     For example, the hydraulic/electric output distribution calculating section  44  calculates the electric/revolving output command Per as an output target value of the revolving electric motor  33  based upon the battery discharge power limit value Plim 0  and the movement output Pox of the revolving movement. Thereby, the hydraulic/electric output distribution calculating section  44  supplies as much electric power as possible to the powering operation of the revolving electric motor  33  in a range of not surpassing the battery discharge power limit value Plim 0 . 
     The movements other than the revolving movement are performed by the pressurized oil delivered from the hydraulic pump  23 . Therefore, the hydraulic/electric output distribution calculating section  44  subtracts a section of the electric/revolving output command Per from the sum of the movement outputs Pox to calculate an output target value of the hydraulic pump  23 . The hydraulic/electric output distribution calculating section  44  calculates the engine output command Pe as an output target value of the engine  21  necessary for acquiring the output target value of the hydraulic pump  23 . In addition, when the output target value of the engine  21  surpasses the output upper limit value of the engine  21 , the difference is complemented by the powering operation of the motor-generator  27 . Therefore, the hydraulic/electric output distribution calculating section  44  calculates the motor-generator powering operation output command Pmg as an output target of the motor-generator  27  based upon the difference between the output target value and the output upper limit value of the engine  21 . 
     Thereby, the output command calculating section  40  executes the normal mode NMODE when the battery electricity storage rate SOC and the current square integrating rate Risc are in a range of a given threshold, and outputs the electric/revolving output command Per, the motor-generator powering operation output command Pmg and the engine output command Pe in accordance with the lever operating amount OA. On the other hand, the output command calculating section  40  executes the low speed mode LSMODE when the battery electricity storage rate SOC is lower than a given threshold (appropriate reference value SOC 1 ) or when the current square integrating rate Risc is higher than a given threshold (appropriate reference value Risc 1 ). As a result, the output command calculating section  40  lowers the electric/revolving output command Per, the motor-generator powering operation output command Pmg and the engine output command Pe in accordance with the degree when the battery electricity storage rate SOC or the current square integrating rate Risc surpasses the given threshold to reduce the movement speeds of the hydraulic motors  25 ,  26  and the cylinders  12 D to  12 F. 
     It should be noted that the hydraulic/electric output distribution calculating section  44  may optionally adjust the electric/revolving output command Per, the motor-generator powering operation output command Pmg and the engine output command Pe based upon the total output upper limit value Ptmax and the other vehicle body information VI. At this time, the other vehicle body information VI corresponds to, for example, a vehicle speed, a cooling water temperature, a fuel remaining amount and the like. The calculation methods for the electric/revolving output command Per, the motor-generator powering operation output command Pmg and the engine output command Pe are not limited to the above-mentioned methods, but may be optionally set in accordance with a specification of a vehicle or the like in a range where the output of the entire vehicle does not surpass the total output upper limit value Ptmax. 
     The HCU  36  further calculates a revolving electric motor torque command, a motor-generator powering operation torque command and an engine rotational speed command based upon the electric/revolving output command Per, the motor-generator powering operation output command Pmg and the engine output command Pe to be outputted to the RMCU  35 , the MGCU  30 , the ECU  22  and the BCU  32 . The RMCU  35 , the MGCU  30 , the ECU  22  and the BCU  32  control the revolving electric motor  33 , the motor-generator  27 , the engine  21  and the electricity storage device  31  to realize the respective commands, realizing the vehicle body movement in accordance with requirements of an operator. 
     The monitor display amount calculating section  50  calculates the maximum speed reduction rate DRs, the maximum speed reduction rate minimum value DRsmin, the common scale conversion minimum value Emin, the low speed mode arrival predicting time PT and the predicting maximum speed reduction rate PDRs based upon the battery discharge power limit value Plim 0 , the engine output upper limit value Pemax, the battery electricity storage rate SOC, the current square integrating rate Risc and the battery power value Pc. As shown in  FIG. 9 , the monitor display amount calculating section  50  includes a maximum speed reduction rate calculating section  51 , a common scale conversion minimum value calculating section  52 , a low speed mode arrival predicting time calculating section  53  and a predicting maximum speed reduction rate calculating section  54 . 
     The maximum speed reduction rate calculating section  51  configures a speed reduction degree calculating section. The maximum speed reduction rate calculating section  51  calculates a speed reduction degree of a speed of each of the hydraulic actuators (the hydraulic motors  25 ,  26  and the cylinders  12 D to  12 F) in the low speed mode LSMODE. Specifically, the maximum speed reduction rate calculating section  51  calculates the maximum speed reduction rate DRs and the maximum speed reduction rate minimum value DRsmin based upon the battery discharge power limit value Plim 0  and the engine output upper limit value Pemax. As shown in  FIG. 10 , the maximum speed reduction rate calculating section  51  includes a motor-generator maximum powering operation output calculating part  51 A, a motor-generator powering operation output calculating part  51 B, a minimum value selecting part  51 C, a total output calculating part  51 D, a maximum total output calculating part  51 E, first and second rate calculating parts  51 F,  51 G and percentage conversion parts  51 H,  51 I. 
     The motor-generator maximum powering operation output calculating part  51 A calculates maximum output acquired by a powering operation of the motor-generator  27  in a state where the battery discharge power from the electricity storage device  31  is not restricted, as a first motor-generator maximum powering operation output Pmgmax 1 . 
     The motor-generator powering operation output calculating part  51 B is configured substantially in the same way as, for example, the motor-generator powering operation output upper limit value calculating part  42 A. Therefore, the motor-generator maximum powering operation output calculating part  51 A calculates second motor-generator maximum powering operation output Pmgmax 2  based upon, for example, a product of an efficiency gain at the time the motor-generator  27  performs a powering operation and the battery discharge power limit value Plim 0 . The second motor-generator maximum powering operation output Pmgmax 2  indicates maximum output acquired by the powering operation of the motor-generator  27  in a state where the battery discharge power from the electricity storage device  31  is restricted by the battery discharge power limit value Plim 0 . The second motor-generator maximum powering operation output Pmgmax 2  is substantially the same value as the motor-generator output upper limit value Pmgmax by the motor-generator powering operation output upper limit value calculating part  42 A. 
     The minimum value selecting part  51 C compares the first motor-generator maximum powering operation output Pmgmax 1  by the motor-generator maximum powering operation output calculating part  51 A and the second motor-generator maximum powering operation output Pmgmax 2  by the motor-generator maximum powering operation output calculating part  51 B. The minimum value selecting part  51 C selects a minimum value of the first motor-generator maximum powering operation output Pmgmax 1  and the second motor-generator maximum powering operation output Pmgmax 2  to be outputted as motor-generator maximum powering operation output Pmgmax 0 . 
     The total output calculating part  51 D is configured of an adder. The total output calculating part  51 D adds the motor-generator maximum powering operation output Pmgmax 0  and the engine output upper limit value Pemax, and outputs a total value thereof as total output Ptmax 0 . 
     The maximum total output calculating part  51 E is configured of an adder. The maximum total output calculating part  51 E adds the motor-generator maximum powering operation output Pmgmax 1  and the engine output upper limit value Pemax, and outputs a total value thereof as maximum total output Ptmax 1 . 
     The first rate calculating part  51 F divides the total output Ptmax 0  by the maximum total output Ptmax 1 , and calculates this ratio (Ptmax 0 /Ptmax 1 ). This ratio (Ptmax 0 /Ptmax 1 ) is converted into a percentage value by being multiplied by a given efficient in the percentage conversion part  51 H. As a result, the percentage conversion part  51 H outputs the maximum speed reduction rate DRs in accordance with a ratio of the total output Ptmax 0  and the maximum total output Ptmax 1 . 
     The second rate calculating part  51 G divides the engine output upper limit value Pemax by the maximum total output Ptmax 1 , and calculates this ratio (Pemax/Ptmax 1 ). This ratio (Pemax/Ptmax 1 ) is converted into a percentage value by being multiplied by a given efficient in the percentage conversion part  51 I. Here, when the low speed mode LSMODE is executed and the electric power supply from the electricity storage device  31  is stopped, various movements are to be performed by the output of the engine  21 . At this time, a maximum value of the movement output corresponds to the engine output upper limit value Pemax. Therefore, the ratio (Pemax/Ptmax 1 ) corresponds to a minimum value of the maximum speed reduction rate DRs. As a result, the percentage conversion part  51 I outputs the maximum speed reduction rate minimum value DRsmin in accordance with the ratio of the engine output upper limit value Pemax and the maximum total output Ptmax 1 . 
     The common scale conversion minimum value calculating section  52  configures a common scale representative value specifying section. The common scale conversion minimum value calculating section  52  converts a region of not transferring in the low speed mode LSMODE to each of a plurality of state-amounts (the battery electricity storage rate SOC and current square integrating rate Risc) indicative of a state of the electricity storage device  31  into a common scale, and thereby, converts the present value of each of the plurality of state-amounts into a value of the common scale to specify any one of these values as a representative value. 
     Specifically, the common scale conversion minimum value calculating section  52  calculates the common scale conversion minimum value Emin based upon the battery electricity storage rate SOC and the current square integrating rate Risc. The common scale conversion minimum value Emin, when the battery electricity storage rate SOC and the current square integrating rate Risc are converted into values of the common scale, indicates a minimum value of the two values. As shown in  FIG. 11 , the common scale conversion minimum value calculating section  52  includes an electricity storage rate conversion part  52 A, a current square integrating rate conversion part  52 B and a minimum value selecting part  52 C. 
     The electricity storage rate conversion part  52 A converts the battery electricity storage rate SOC into a first conversion value Eb of the predetermined common scale (for example, percentage). As shown in  FIG. 6 , a range where the battery discharge power is not restricted, that is, a range where the battery discharge power limit value Plim 1  is 100% (Plim 1 =P 11 ) exists in the battery electricity storage rate SOC. For example, when the battery electricity storage rate SOC has an appropriate use range of 30% to 70%, the electricity storage device  31  is controlled to reach 60% as a target value of the battery electricity storage rate SOC for causing allowance to the upper limit. In addition, the electricity storage device  31  is controlled such that the battery electricity storage rate SOC is normally 35% or more for causing allowance to the lower limit as well. 
     When the battery electricity storage rate SOC is lower than 35%, the battery discharge power limit value Plim 1  is also lowered. That is, how higher the battery electricity storage rate SOC is as compared to 35% indicates the allowance of the battery electricity storage rate SOC. Therefore, the electricity storage rate conversion part  52 A converts a range of 35% to 60% as the battery electricity storage rate SOC into a percentage value. As a result, when the battery electricity storage rate SOC is 60% as the target value, the first conversion value Eb becomes 100%, and when the battery electricity storage rate SOC is 35%, the first conversion value Eb becomes 0%. 
     The current square integrating rate conversion part  52 B converts the current square integrating rate Risc into a second conversion value Er of the predetermined common scale (for example, percentage). As shown in  FIG. 7 , a range where the battery discharge power is not restricted, that is, a range where the battery discharge power limit value Plim 2  is 100% (Plim 2 =P 21 ) exists in the current square integrating rate Risc. For example, the electricity storage device  31  is controlled such that the current square integrating rate Risc becomes in a range of 0% to 90%. When the current square integrating rate Risc increases to be higher than 90%, the battery discharge power limit value Plim 2  is lowered. That is, how lower the current square integrating rate Risc is as compared to 90% indicates the allowance of the current square integrating rate Risc. Therefore, the current square integrating rate conversion part  52 B converts a range of 0% to 90% as the current square integrating rate Risc into a percentage value. As a result, when the current square integrating rate Risc is 0%, the second conversion value Er becomes 100%, and when the current square integrating rate Risc is 90%, the second conversion value Er becomes 0%. 
     The minimum value selecting part  52 C compares the first conversion value Eb by the electricity storage rate conversion part  52 A and the second conversion value Er by the current square integrating rate conversion part  52 B. The minimum value selecting part  52 C selects a minimum value of the first conversion value Eb and the second conversion value Er to be outputted as the common scale conversion minimum value Emin. 
     The low speed mode arrival predicting time calculating section  53  configures a low speed mode arrival time predicting section. The low speed mode arrival predicting time calculating section  53  predicts the low speed mode arrival predicting time PT until arriving in the low speed mode LSMODE based upon a reducing speed or an increasing speed of each value of a plurality of state-amounts (the battery electricity storage rate SOC and current square integrating rate Risc). Specifically, the low speed mode arrival predicting time calculating section  53  calculates the low speed mode arrival predicting time PT based upon the battery electricity storage rate SOC and the current square integrating rate Risc. As shown in  FIG. 12 , the low speed mode arrival predicting time calculating section  53  includes a reducing rate calculating part  53 A of an electricity storage rate, a subtracter  53 B, a first predicting time calculating part  53 C, an increasing rate calculating part  53 D of a current square integrating rate, a subtracter  53 E, a second predicting time calculating part  53 F and a minimum value calculating part  53 G. 
     The reducing rate calculating part  53 A of the electricity storage rate calculates a reducing rate DRsoc of the electricity storage rate indicative of a reducing rate of the battery electricity storage rate SOC based upon the battery electricity storage rate SOC. Specifically, the reducing rate calculating part  53 A of the electricity storage rate measures a changing component of the battery electricity storage rate SOC for a predetermined given time, and calculates the reducing rate DRsoc of the electricity storage rate based upon a relation of this changing component and the given time. A cycle time of a loading movement as a general work is approximately 20 sec. In consideration of this point, the given time for calculating the reducing rate DRsoc of the electricity storage rate is set to, for example, approximately 30 sec with some allowance to the cycle time of the loading work. 
     The subtracter  53 B subtracts a given threshold (appropriate reference value SOC 1 ) from the battery electricity storage rate SOC. At this time, when the battery electricity storage rate SOC is lower than the appropriate reference value SOC 1 , the first battery discharge power limit value Plim 1  is lowered from 100%. Therefore, the subtracter  53 B calculates an allowance component ΔSOC of the battery electricity storage rate SOC until the battery discharge power is restricted. 
     The first predicting time calculating part  53 C calculates a first arrival predicting time PT 1  until the transfer to the low speed mode LSMODE based upon the battery electricity storage rate SOC by dividing the allowance component ΔSOC by the reducing rate DRsoc of the electricity storage rate. 
     The increasing rate calculating part  53 D of the current square integrating rate calculates an increasing rate IRrisc of the current square integrating rate indicative of an increasing rate of the current square integrating rate Risc based upon the current square integrating rate Risc. Specifically, the increasing rate calculating part  53 D of the current square integrating rate measures a changing component of the current square integrating rate Risc for a predetermined given time (for example, approximately 30 sec), and calculates the increasing rate IRrisc of the current square integrating rate based upon a relation between this changing component and the given time. 
     The subtracter  53 E subtracts a given threshold (appropriate reference value Risc 1 ) from the current square integrating rate Risc. At this time, when the current square integrating rate Risc is higher than the appropriate reference value Risc 1 , the second battery discharge power limit value Plim 2  is lowered from 100%. Therefore, the subtracter  53 E calculates an allowance component ΔRisc of the current square integrating rate Risc until the battery discharge power is restricted. 
     The second predicting time calculating part  53 F calculates a second arrival predicting time PT 2  until the transfer to the low speed mode LSMODE based upon the current square integrating rate Risc by dividing the allowance component ΔRisc by the increasing rate IRrisc of the current square integrating rate. 
     The minimum value calculating part  53 G compares the first arrival predicting time PT 1  by the first predicting time calculating part  53 C and the second arrival predicting time PT 2  by the second predicting time calculating part  53 F. The minimum value calculating part  53 G outputs a minimum value of the first arrival predicting time PT 1  and the second arrival predicting time PT 2  as the low speed mode arrival predicting time PT. 
     The predicting maximum speed reduction rate calculating section  54  configures a speed reduction degree predicting value calculating section. The predicting maximum speed reduction rate calculating section  54  calculates a predicting value of a speed reduction degree of a speed of the hydraulic actuator at the transferring to the low speed mode LSMODE when it is determined to transfer to the low speed mode LSMODE based upon an increasing/reducing speed of each value of the plurality of state-amounts of the electricity storage device  31 . Specifically, the predicting maximum speed reduction rate calculating section  54  calculates the predicting maximum speed reduction rate PDRs based upon the battery power value Pc and the engine output upper limit value Pemax. As shown in  FIG. 13 , the predicting maximum speed reduction rate calculating section  54  includes an average generating power calculating part  54 A, a first motor-generator powering operation output calculating part  54 B, a second motor-generator powering operation output calculating part  54 C, adders  54 D to  54 F, first and second rate calculating parts  54 G,  54 H, percentage conversion parts  54 I,  54 J and a minimum value selecting part  54 K. 
     The average generating power calculating part  54 A calculates electric charging power of the electricity storage device  31  for a predetermined given time based upon the battery power value Pc to output an average generating power Pca. At this time, the given time for calculating the average generating power Pca is set to, for example, approximately 30 sec corresponding to the given time at the time of calculating the reducing rate of the battery electricity storage rate SOC. 
     The first motor-generator powering operation output calculating part  54 B is configured substantially in the same way as, for example, the motor-generator maximum powering operation output calculating part  51 A. Therefore, the first motor-generator maximum powering operation output calculating part  54 B calculates maximum power acquired by the powering operation of the motor-generator  27  as a first motor-generator powering operation output Pmg 1  in a state where the battery discharge power from the electricity storage device  31  is not restricted. At this time, the first motor-generator powering operation output Pmg 1  is substantially the same value as the first motor-generator maximum powering operation output Pmgmax 1 . 
     The second motor-generator powering operation output calculating part  54 C calculates, for example, a second motor-generator powering operation output Pmg 2  in consideration of an efficiency of the motor-generator  27  to an electric power conversion value of an upper limit value of the current square integrating value. At this time, the second motor-generator powering operation output Pmg 2  is a value when the vehicle speed is lowered based upon an increase in the current square integrating rate Risc, and corresponds to the output of the motor-generator  27  at the time of driving the electricity storage device  31  by a value acquired by the electric power conversion of the upper limit value in the current square integrating value. 
     The second motor-generator powering operation output calculating part  54 C, as hereinafter described, calculates the second motor-generator powering operation output Pmg 2  based upon the battery power value Pc. First, an appropriate reference power Px corresponding to the appropriate reference value Risc 1  of the current square integrating rate Risc shown in  FIG. 7  is in advance found. This power Px is calculated by a product of the current in accordance with the appropriate reference value Risc 1  and the voltage of the electricity storage device  31 . At this time, the voltage of the electricity storage device  31  is defined as a constant value, for example. Likewise, a maximum power Py corresponding to a maximum value Risc 2  of the current square integrating rate Risc is in advance found. This power Py is calculated by a product of the current in accordance with the maximum value Risc 2  and the voltage of the electricity storage device  31 . 
     On the other hand, an effective power Pnow is calculated based upon the current value between the present time and time T 0  tracing back to the past. The effective power Pnow can be calculated based upon the battery power value Pc. It should be noted that preferably the time T 0  is, for expressing a use way of the present electricity storage device  31 , for example, a time longer than a cycle time (for example, approximately 20 sec) of a gravel loading movement and sorter than an integrated time T (for example, T=100 sec) of the current square integrating value. Therefore, the time T 0  is set to, for example, approximately 30 sec. 
     When the effective power Pnow is the appropriate reference power Px or less (Pnow≤Px), even when the present movement continues to be performed, the current square integrating rate Risc does not surpass the appropriate reference value Risc 1 . In this case, it is not necessary to restrict the battery discharge power. 
     On the other hand, when the effective power Pnow is larger than the appropriate reference power Px (Pnow&gt;Px), when the present movement continues to be performed, the current square integrating rate Risc will surpass the appropriate reference value Risc 1  in the future. In this case, since the battery discharge power is restricted based upon the current square integrating rate Risc, the current square integrating rate Risc converges into some value between the appropriate reference value Risc 1  and the maximum value Risc 2 . In a region where the effective power Pnow is larger than the appropriate reference power Px, a value into which the current square integrating rate Risc finally converges is indicated at a converging value Risc 3 , and the battery discharge power limit value Plim 2  in accordance with the converging value Risc 3  is indicated at a predicting limit value Pend. As shown in  FIG. 7 , since the current square integrating rate Risc is in proportion to the battery discharge power limit value Plim 2  in this region, a relation indicated in Formula 1 as follows is established to the predicting limit value Pend based upon a geometric similarity.
 
 P 21:( Risc 2 −Risc 1)= P end:( Risc 2 −Risc 3)  [Formula 1]
 
     When the electric power in accordance with the converging value Risc 3  becomes the predicting limit value Pend, both are in a balancing state. Therefore, when the appropriate reference value Risc 1 , the maximum value Risc 2  and the converging value Risc 3  are replaced by electric powers (the appropriate reference power Px, the maximum power Py and the predicting limit value Pend) corresponding to the respective values, the predicting limit value Pend can be expressed by Formula 2 as follows. 
     
       
         
           
             
               
                 
                   Pend 
                   = 
                   
                     
                       
                         Py 
                         ⨯ 
                         P 
                       
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                       21 
                     
                     
                       Py 
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                         21 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
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     Accordingly, when the output begins to be restricted by the current square integrating rate Risc, in a case where the movement is performed by the electric power larger than the appropriate reference power Px corresponding to the appropriate reference value Risc 1 , the output converges into a restriction state of moving in the predicting limit value Pend finally indicated in Formula 2 regardless of the magnitude. 
     Therefore, the second motor-generator powering operation output calculating part  54 C calculates the effective power Pnow based upon the battery power value Pc, and compares the effective power Pnow and the appropriate reference power Px. When the effective power Pnow is lower than the appropriate reference power Px, the second motor-generator powering operation output calculating part  54 C outputs the maximum value P 21  of the battery discharge power limit value Plim 2  as the second motor-generator powering operation output Pmg 2 . On the other hand, when the effective power Pnow is larger than the appropriate reference power Px, the second motor-generator powering operation output calculating part  54 C outputs the predicting limit value Pend acquired in Formula 2 as the second motor-generator powering operation output Pmg 2 . It should be noted that the predicting limit value Pend changes with magnitudes of the appropriate reference value Risc 1 , the maximum value Risc 2  and the maximum value P 21 . Therefore, the predicting limit value Pend is optionally set in accordance with, for example, specifications of the hydraulic excavator  1 , the electricity storage device  31  and the like. 
     The adder  54 D adds the average generating power Pca and the engine output upper limit value Pemax. The adder  54 E adds the first motor-generator powering operation output Pmg 1  and the engine output upper limit value Pemax. The adder  54 F adds the second motor-generator powering operation output Pmg 2  and the engine output upper limit value Pemax. 
     The first rate calculating part  54 G divides the additional value (Pca+Pemax) by the adder  54 D by the additional value (Pmg 1 +Pemax) by the adder  54 E, and calculates this ratio ((Pca+Pemax)/(Pmg 1 +Pemax)). This ratio ((Pca+Pemax)/(Pmg 1 +Pemax)) is converted into a percentage value by being multiplied by a given coefficient in the percentage conversion part  54 I. As a result, at the transferring to the low speed mode LSMODE based upon a reduction in the battery electricity storage rate SOC, the percentage conversion part  54 I outputs a first predicting maximum speed reduction rate PDRs 1  as a maximum speed reduction rate predicted at this time. 
     The second rate calculating part  54 H divides the additional value (Pmg 2 +Pemax) by the adder  54 F by the additional value (Pmg 1 +Pemax) by the adder  54 E, and calculates this ratio ((Pmg 2 +Pemax)/(Pmg 1 +Pemax)). This ratio ((Pmg 2 +Pemax)/(Pmg 1 +Pemax)) is converted into a percentage value by being multiplied by a given coefficient in the percentage conversion part  54 J. As a result, at the transferring to the low speed mode LSMODE based upon an increase in the current square integrating rate Risc, the percentage conversion part  54 J outputs a second predicting maximum speed reduction rate PDRs 2  as a maximum speed reduction rate predicted at this time. 
     A minimum value selecting part  54 K compares the first and second predicting maximum speed reduction rates PDRs 1 , PDRs 2 . The minimum value selecting part  54 K selects a minimum value of the first predicting maximum speed reduction rate PDRs 1  and the second predicting maximum speed reduction rate PDRs 2  to be outputted as the predicting maximum speed reduction rate PDRs. 
     The hybrid hydraulic excavator according to the present embodiment has the configuration as described above, and next, an explanation will be made of a display content of the monitor device  39  based upon a state of the electricity storage device  31  with reference to  FIG. 17  to  FIG. 21 . It should be noted that  FIG. 17  to  FIG. 21  show an example of a case where the maximum speed reduction rate minimum value DRsmin is 70%. In addition, the predicting limit value Pend is set to such a value that the second predicting maximum speed reduction rate PDRs 2  becomes 80%.  FIG. 17  to  FIG. 21  show each example of the maximum speed reduction rate DRs, the common scale conversion minimum value Emin, the low speed mode arrival predicting time PT and the predicting maximum speed reduction rate PDRs. These values may be optionally changed in accordance with the specification of the hydraulic excavator  1  and the like. 
     First, an explanation will be made of the display content in the monitor device  39  before use start of the electricity storage device  31  with reference to  FIG. 17 . At this time, the battery electricity storage rate SOC is 60% as the maximum value in a normal use range. In addition, the current square integrating rate Risc is 0% since the electricity storage device  31  is before the use start. 
     As shown in  FIG. 17 , the first conversion value Eb by the battery electricity storage rate SOC and the second conversion value Er by the current square integrating rate Risc both are 100%. That is, this is a state having the maximum allowance to the transferring from the normal mode NMODE to the low speed mode LSMODE. In addition, the maximum speed reduction rate DRs is not lowered based upon either one of the battery electricity storage rate SOC and the current square integrating rate Risc, and is 100%. Therefore, the battery discharge power from the electricity storage device  31  is not restricted, and the HCU  36  operates in the normal mode NMODE. As a result, the speed reduction degree displaying part  39 A and the common scale displaying part  39 B are displayed in a state where the bars thereof are expanded at the maximum. 
     In addition, since the electricity storage device  31  is not used, the time until the transferring to the low speed mode LSMODE is not calculated. That is, a first arrival predicting time PT 1  by the battery electricity storage rate SOC and a second arrival predicting time PT 2  by the current square integrating rate Risc both are not calculated. Therefore, the effect that the low speed mode arrival predicting time PT is not calculated and the transfer to the low speed mode LSMODE is not performed is displayed on the low speed mode arrival time displaying part  39 C. 
     Further, since the transfer to the low speed mode LSMODE is not predicted, the first predicting maximum speed reduction rate PDRs 1  by the battery electricity storage rate SOC and the second predicting maximum speed reduction rate PDRs 2  by the current square integrating rate Risc both are 100%. Therefore, an indicator of the speed reduction degree predicting value displaying part  39 D is arranged in a position of the maximum value (DRs=100%) in the bar of the speed reduction degree displaying part  39 A. 
     Next, an explanation will be made of the display content in the monitor device  39  in a case where the battery electricity storage rate SOC is lowered in a range of the normal mode NMODE with reference to  FIG. 18 . At this time, the battery electricity storage rate SOC is 47.5%, and the current square integrating rate Risc is 30%. 
     As shown in  FIG. 18 , the battery electricity storage rate SOC is an intermediate value of 35% to 60% as the appropriate use range in the normal mode NMODE. Therefore, the first conversion value Eb is 50%. On the other hand, the current square integrating rate Risc increases by 1/3 of 0% to 90% as the appropriate use range in the normal mode NMODE, and the allowance is lowered to 2/3. Therefore, the second conversion value Er is approximately 66.7%. 
     The maximum speed reduction rate DRs is not lowered based upon either one of the battery electricity storage rate SOC and the current square integrating rate Risc, and is 100%. Therefore, the battery discharge power from the electricity storage device  31  is not restricted, and the HCU  36  operates in the normal mode NMODE. As a result, the bar of the speed reduction degree displaying part  39 A is displayed in the most expanded state. On the other hand, the bar of the common scale displaying part  39 B is displayed in a state of being contracted to the half based upon the first conversion value Eb. 
     In addition, the electricity storage device  31  is in a use state. Therefore, the first arrival predicting time PT 1  is calculated as, for example, two minutes based upon the battery electricity storage rate SOC. On the other hand, the second arrival predicting time PT 2  is calculated as, for example, 10 minutes based upon the current square integrating rate Risc. At this time, the battery electricity storage rate SOC has less allowance than the current square integrating rate Risc. Therefore, the first arrival predicting time PT 1  is shorter than the second arrival predicting time PT 2 . As a result, the low speed mode arrival predicting time PT (PT=two minutes) based upon the first arrival predicting time PT 1  is displayed on the low speed mode arrival time displaying part  39 C. 
     Further, the first predicting maximum speed reduction rate PDRs 1  by the battery electricity storage rate SOC is predicted as 75%, and the second predicting maximum speed reduction rate PDRs 2  by the current square integrating rate Risc is predicted as 80%. Therefore, a value of the first predicting maximum speed reduction rate PDRs 1  is selected as the predicting maximum speed reduction rate PDRs, and an indicator of the speed reduction degree predicting value displaying part  39 D is arranged in a position (a value of 75%) of the first predicting maximum speed reduction rate PDRs 1  in the bar of the speed reduction degree displaying part  39 A. 
     Next, an explanation will be made of the display content in the monitor device  39  in a case where the current square integrating rate Risc increases in a range of the normal mode NMODE with reference to  FIG. 19 . At this time, the battery electricity storage rate SOC is 55%, and the current square integrating rate Risc is 30%. 
     As shown in  FIG. 19 , the battery electricity storage rate SOC is a value of 4/5 of 35% to 60% as the appropriate use range in the normal mode NMODE. Therefore, the first conversion value Eb is 80%. On the other hand, the current square integrating rate Risc increases by 1/3 of 0% to 90% as the appropriate use range in the normal mode NMODE, and the allowance is lowered to 2/3. Therefore, the second conversion value Er is approximately 66.7%. 
     The maximum speed reduction rate DRs is not lowered based upon either one of the battery electricity storage rate SOC and the current square integrating rate Risc, and is 100%. Therefore, the battery discharge power from the electricity storage device  31  is not restricted, and the HCU  36  operates in the normal mode NMODE. As a result, the bar of the speed reduction degree displaying part  39 A is displayed in the most expanded state. On the other hand, the bar of the common scale displaying part  39 B is displayed in a state of being contracted to 2/3 based upon the second conversion value Er. 
     In addition, the electricity storage device  31  is in a use state. Therefore, the first arrival predicting time PT 1  is calculated as, for example, 10 minutes based upon the battery electricity storage rate SOC. On the other hand, the second arrival predicting time PT 2  is calculated as, for example, three minutes based upon the current square integrating rate Risc. At this time, the current square integrating rate Risc has less allowance than the battery electricity storage rate SOC. Therefore, the second arrival predicting time PT 2  is shorter than the first arrival predicting time PT 1 . As a result, the low speed mode arrival predicting time PT (PT=three minutes) based upon the second arrival predicting time PT 2  is displayed on the low speed mode arrival time displaying part  39 C. 
     Further, the first predicting maximum speed reduction rate PDRs 1  by the battery electricity storage rate SOC is predicted as 90%, and the second predicting maximum speed reduction rate PDRs 2  by the current square integrating rate Risc is predicted as 80%. Therefore, a value of the second predicting maximum speed reduction rate PDRs 2  is selected as the predicting maximum speed reduction rate PDRs, and an indicator of the speed reduction degree predicting value displaying part  39 D is arranged in a position (a value of 80%) of the second predicting maximum speed reduction rate PDRs 2  in the bar of the speed reduction degree displaying part  39 A. 
     Next, an explanation will be made of the display content in the monitor device  39  in a case where the battery electricity storage rate SOC reduces in a range of the low speed mode LSMODE with reference to  FIG. 20 . At this time, the battery electricity storage rate SOC is 32.5%, and the current square integrating rate Risc is 30%. 
     As shown in  FIG. 20 , the battery electricity storage rate SOC is lower than 35% as the lower limit value (appropriate reference value SOC 1 ) of the appropriate use range in the normal mode NMODE. Therefore, the first conversion value Eb is 0%. On the other hand, the current square integrating rate Risc increases by 1/3 to 0% to 90% as the appropriate use range in the normal mode NMODE, and the allowance is lowered to 2/3. Therefore, the second conversion value Er is approximately 66.7%. 
     In addition, the battery electricity storage rate SOC is an intermediate value of 30% to 35% as a range in the low speed mode LSMODE. Therefore, the maximum speed reduction rate DRs by the battery electricity storage rate SOC is 85% as an intermediate value of 70% to 100%. On the other hand, since the maximum speed reduction rate DRs is a value in a range of the normal mode NMODE, the maximum speed reduction rate DRs by the current square integrating rate Risc is 100%. Therefore, the battery discharge power from the electricity storage device  31  is restricted based upon the battery electricity storage rate SOC, and the HCU  36  operates in the low speed mode LSMODE. As a result, the bar of the speed reduction degree displaying part  39 A is displayed in a state of being contracted to a position of 85% (a position of the half) based upon the maximum speed reduction rate DRs by the battery electricity storage rate SOC. On the other hand, since the mode is already transferred to the low speed mode LSMODE, the bar of the common scale displaying part  39 B is not displayed. 
     In addition, the mode is already transferred to the low speed mode LSMODE based upon a reduction of the battery electricity storage rate SOC. Therefore, the first arrival predicting time PT 1  is calculated as 0 minutes. On the other hand, the second arrival predicting time PT 2  is not calculated since the mode does not transfer to the low speed mode LSMODE based upon the current square integrating rate Risc. As a result, the low speed mode arrival predicting time PT (PT=0 minutes) based upon the first arrival predicting time PT 1  is displayed on the low speed mode arrival time displaying part  39 C. 
     Further, the first predicting maximum speed reduction rate PDRs 1  by the battery electricity storage rate SOC is predicted as 80%, and the second predicting maximum speed reduction rate PDRs 2  by the current square integrating rate Risc is predicted as 100%. Therefore, a value of the first predicting maximum speed reduction rate PDRs 1  is selected as the predicting maximum speed reduction rate PDRs, and an indicator of the speed reduction degree predicting value displaying part  39 D is arranged in a position (a value of 80%) of the first predicting maximum speed reduction rate PDRs 1  in the bar of the speed reduction degree displaying part  39 A. 
     Next, an explanation will be made of the display content in the monitor device  39  in a case where the current square integrating rate Risc increases in a range of the low speed mode LSMODE with reference to  FIG. 21 . At this time, the battery electricity storage rate SOC is 55%, and the current square integrating rate Risc is 96.7%. 
     As shown in  FIG. 21 , the battery electricity storage rate SOC is a value of 4/5 of 35% to 60% as the appropriate use range in the normal mode NMODE. Therefore, the first conversion value Eb is 80%. On the other hand, the current square integrating rate Risc increases more than 90% as the upper limit value (appropriate reference value Risc 1 ) of the appropriate use range in the normal mode NMODE. Therefore, the second conversion value Er is 0%. 
     In addition, the battery electricity storage rate SOC is a value in a range in the normal mode NMODE. Therefore, the maximum speed reduction rate DRs by the battery electricity storage rate SOC is 100%. On the other hand, the maximum speed reduction rate DRs is a value of 2/3 of 90% to 100% as a range of the low speed mode LSMODE. Therefore, the maximum speed reduction rate DRs by the current square integrating rate Risc is 80% as a value that has increased by 1/3 in a range (70% to 100%) in the low speed mode LSMODE, that is, as a value that has increased by 10% from the maximum speed reduction rate minimum value DRsmin. Therefore, the battery discharge power from the electricity storage device  31  is restricted based upon the current square integrating rate Risc, and the HCU  36  operates in the low speed mode LSMODE. As a result, the bar of the speed reduction degree displaying part  39 A is displayed in a state of being contracted to a position of 80% based upon the maximum speed reduction rate DRs by the current square integrating rate Risc. On the other hand, since the mode is already transferred to the low speed mode LSMODE, the bar of the common scale displaying part  39 B is not displayed. 
     In addition, since the mode does not transfer to the low speed mode LSMODE based upon the battery electricity storage rate SOC, the first arrival predicting time PT 1  is not calculated. On the other hand, the mode is already transferred to the low speed mode LSMODE based upon an increase of the current square integrating rate Risc. Therefore, the second arrival predicting time PT 2  is calculated as 0 minutes. As a result, the low speed mode arrival predicting time PT (PT=0 minutes) based upon the second arrival predicting time PT 2  is displayed on the low speed mode arrival time displaying part  39 C. 
     Further, the first predicting maximum speed reduction rate PDRs 1  by the battery electricity storage rate SOC is predicted as 100%, and the second predicting maximum speed reduction rate PDRs 2  by the current square integrating rate Risc is predicted as 80%. Therefore, a value of the second predicting maximum speed reduction rate PDRs 2  is selected as the predicting maximum speed reduction rate PDRs, and an indicator of the speed reduction degree predicting value displaying part  39 D is arranged in a position (a value of 80%) of the second predicting maximum speed reduction rate PDRs 2  in the bar of the speed reduction degree displaying part  39 A. 
     Thus, according to the present embodiment, the monitor device  39  is provided with the speed reduction degree displaying part  39 A. Therefore, the maximum speed reduction rate DRs can be displayed as the speed reduction degree of the speed of the hydraulic actuator (the hydraulic motors  25 ,  26  and the cylinders  12 D to  12 F) on the speed reduction degree displaying part  39 A. As a result, at the transferring to the low speed mode LSMODE, the speed reduction degree of the speed can be displayed on the monitor device  39 . Accordingly, an operator makes visual contact with the monitor device  39 , making it possible to easily understand whether or not the movement speed is lowered by the transferring to the low speed mode LSMODE and the degree of the speed reduction when the movement speed is lowered. That is, the operator makes visual contact with the monitor device  39 , making it possible to instantly and intuitively understand the present situation of the hydraulic excavator  1 . As a result, for example, the operator can be encouraged to make the determination of the continuation or cease of the work, to perform an efficient work in accordance with the state of the electricity storage device  31 . 
     In addition, the HCU  36  is further provided with the common scale conversion minimum value calculating section  52  (the common scale representative value specifying section) that converts into a common scale a region of not transferring in the low speed mode LSMODE to each of a plurality of state-amounts (the battery electricity storage rate SOC and the current square integrating rate Risc) indicative of a state of the electricity storage device  31 , and thereby, converts the present value of each of the plurality of state-amounts into a value of the common scale to specify any one of these values as a representative value. In addition thereto, the monitor device  39  is further provided with the common scale displaying part  39 B that displays the common scale conversion minimum value Emin as the representative value. Therefore, an operator makes visual contact with the common scale displaying part  39 B in the monitor device  39 , thus making it possible to understand with how much allowance the present hydraulic excavator  1  operates to the low speed mode LSMODE to perform the work in accordance with the state of the present vehicle body. 
     The HCU  36  is further provided with the low speed mode arrival predicting time calculating section  53  (the low speed mode arrival time predicting section) that predicts the low speed mode arrival predicting time PT until arriving in the low speed mode LSMODE based upon a reducing speed or an increasing speed of each value of the plurality of state-amounts (the battery electricity storage rate SOC and the current square integrating rate Risc). In addition thereto, the monitor device  39  is further provided with the low speed mode arrival time displaying part  39 C that displays the low speed mode arrival predicting time PT. As a result, an operator in visual contact with the low speed mode arrival time displaying part  39 C in the monitor device  39 , can understand the remaining time until arriving in the low speed mode LSMODE when the present work continues to be performed. Accordingly, for example, since the work stops before transferring to the low speed mode LSMODE to suppress the transfer to the low speed mode LSMODE, the stress due to a reduction in the movement speed can be reduced. 
     The HCU  36  is further provided with the predicting maximum speed reduction rate calculating section  54  (the speed reduction degree predicting value calculating section) that calculates the predicting maximum speed reduction rate PDRs as the predicting value of the speed reduction degree of the speed of the hydraulic actuator at the transferring to the low speed mode LSMODE when it is determined to transfer to the low speed mode LSMODE based upon the reducing speed or the increasing speed of each value of the plurality of state-amounts (the battery electricity storage rate SOC and the current square integrating rate Risc). In addition thereto, the monitor device  39  is further provided with the speed reduction degree predicting value displaying part  39 D that displays the predicting maximum speed reduction rate PDRs. As a result, an operator in visual contact with the speed reduction degree predicting value displaying part  39 D of the monitor device  39 , can understand a magnitude of the present work load. 
     In addition, the plurality of state-amounts of the electricity storage device  31  to be input to the HCU  36  include the battery electricity storage rate SOC of the electricity storage device  31  and the current square integrating rate Risc (current square integrating value) of the electricity storage device  31 . Therefore, the output command calculating section  40  (low speed mode executing section) of the HCU  36  executes the low speed mode LSMODE when the battery electricity storage rate SOC and the current square integrating rate Risc of the electricity storage device  31  surpass a given threshold, extending a lifetime of the electricity storage device  31 . 
     The maximum output of the engine  21  is made smaller than the maximum power of the hydraulic pump  23 . Therefore, in the normal mode NMODE, when the hydraulic pump  23  is driven by the maximum power, the powering operation of the motor-generator  27  can assist in the engine  21  to drive the hydraulic pump  23 . In addition, in the low speed mode LSMODE, for example, the output by the powering operation of the motor-generator  27  is reduced, making it possible to drive the hydraulic pump  23 . Further, since the maximum output of the engine  21  is made smaller than the maximum power of the hydraulic pump  23 , it is possible to use the engine  21  that is small-sized and can reduce a fuel consumption. 
     It should be noted that  FIG. 15  to  FIG. 21  show as an example a case where the maximum speed reduction rate DRs, the common scale conversion minimum value Emin, the low speed mode arrival predicting time PT and the predicting maximum speed reduction rate PDRs which are calculated by the HCU  36  are displayed on the monitor device  39  by the expansion/contraction of the bar, the position of the indicator or the like. However, the present invention is not limited to this embodiment, but may be changed as needed in the scope not departing from the subject of the present invention. 
     The above embodiment explains as an example a case where the current square integrating value or the current square integrating rate Risc is used as the charge/discharge intensity index of the electricity storage device  31 , but the charge/discharge intensity index is not limited thereto. When the finding of the threshold for accelerating the degradation of the electricity storage device is only acquired, any factor for being able to relatively compare a magnitude of the charge/discharge amount may be used as the charge/discharge intensity index. Therefore, for example, a current effective value or an electric power effective value of a past constant time may be used for the charge/discharge intensity index. 
     In the above embodiment, the HCU  36  is provided with two kinds of modes composed of the normal mode NMODE and the low speed mode LSMODE. However, the present invention is not limited thereto, but, for example, by adding a heavy load mode in which the battery discharge power limit value Plim 0  of the electricity storage device  31  is temporarily released in response to heavy loads to the normal mode NMODE and the low speed mode LSMODE, the HCU  36  may be configured to be provided with three kinds of modes or four kinds or more of modes. 
     In the above embodiment, the HCU  36  is configured to transfer from the normal mode NMODE to the low speed mode LSMODE based upon the battery electricity storage rate SOC and the current square integrating rate Risc. However, the present invention is not limited thereto, but the HCU  36  may be configured to transfer from the normal mode NMODE to the low speed mode LSMODE in response to the cell temperature of the electricity storage device  31 , the temperature of the motor-generator  27 , the temperature of the revolving electric motor  33  and the like. Further, the mode transfer may be manually switched by the mode selection switch or the like other than the automatic transfer by the HCU  36 . 
     In the above embodiment, the maximum output of the engine  21  is made smaller than the maximum power of the hydraulic pump  23 , but the maximum output of the engine  21  is optionally set in accordance with a specification of the hydraulic excavator  1  or the like. Therefore, the maximum output of the engine  21  may be approximately the same as the maximum power of the hydraulic pump  23 , or may be smaller than the maximum power of the hydraulic pump  23 . 
     In the above embodiment, an example of using the lithium ion battery in the electricity storage device  31  is explained, but a secondary battery (for example, a nickel cadmium battery or nickel hydrogen battery) or a capacitor that can supply required electric power may be adopted. In addition, a step-up and -down device such as a DC-DC converter may be provided between the electricity storage device and the DC bus. 
     In the above embodiment, an example of using the hybrid hydraulic excavator  1  of a crawler type as the hybrid construction machine is explained. However, the present invention is not limited thereto, but the present invention may be applied to a hybrid construction machine that is only provided with a motor-generator jointed to an engine and a hydraulic pump, and an electricity storage device, and may be applied to various types of construction machines such as a wheel type hybrid hydraulic excavator, a hybrid wheel loader or a hybrid lift truck. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               1 : Hybrid-type hydraulic excavator (Hybrid construction machine) 
               2 : Lower traveling structure 
               4 : Upper revolving structure 
               12 : Working mechanism 
               12 D: Boom cylinder (Hydraulic actuator) 
               12 E: Arm cylinder (Hydraulic actuator) 
               12 F: Bucket cylinder (Hydraulic actuator) 
               21 : Engine 
               23 : Hydraulic pump 
               25 : Traveling hydraulic motor (Hydraulic actuator) 
               26 : Revolving hydraulic motor (Hydraulic actuator) 
               27 : Motor-generator 
               31 : Electricity storage device 
               32 : Battery control unit (Electricity storage device state detecting section) 
               33 : Revolving electric motor 
               36 : Hybrid control unit (Controller) 
               39 : Monitor device 
               39 A: Speed reduction degree displaying part 
               39 B: Common scale displaying part 
               39 C: Low speed mode arrival time displaying part 
               39 D: Speed reduction degree predicting value displaying part 
               40 : Output command calculating section (Low speed mode executing section) 
               50 : Monitor display amount calculating section 
               51 : Maximum speed reduction rate calculating section (Speed reduction degree calculating section) 
               52 : Common scale conversion minimum value calculating section (Common scale representative value specifying section) 
               53 : Low speed mode arrival predicting time calculating section (Low speed mode arrival time predicting section) 
               54 : Predicting maximum speed reduction rate calculating section (Speed reduction degree predicting value calculating section)