Patent Publication Number: US-10787790-B2

Title: Work machine

Description:
TECHNICAL FIELD 
     The present invention relates to a work machine and particularly relates to a work machine including hydraulic actuators that drive work members and regenerating energy from the hydraulic actuators. 
     BACKGROUND ART 
     There is disclosed a technique, for purposes of providing a hydraulic control system that can improve fuel economy by making effective use of potential energy stored by work members even in a work state in which acceleration is not necessary and a work machine including the hydraulic control system, for regenerating a hydraulic working fluid discharged from a bottom side of a boom cylinder on a rod side of an arm cylinder via a valve on a regeneration line and reducing a flow rate of a hydraulic pump for the arm cylinder in accordance with a flow rate of the regenerated hydraulic fluid on condition that a boom lowering operation and an arm pushing operation are performed simultaneously and a boom bottom pressure detected by one pressure sensor is higher than an arm rod pressure detected by another pressure sensor (refer to, for example, Patent Document 1). 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Patent No. 5296570 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     According to the technique of Patent Document 1 described above, it is possible to achieve improvement of fuel economy since the potential energy of the work members can be made effective use of. However, the technique has the following problem. Since a magnitude relationship between the boom bottom pressure and the arm rod pressure detected by the pressure sensors is the condition for opening a regeneration valve, occurrence of an abnormality (including, for example, breaking of a signal line) only to the pressure sensors makes it impossible to exercise regeneration control. Owing to this, it has been desired to provide a work machine capable of exercising regeneration control even when an abnormality occurs only to the pressure sensors. 
     The present invention has been achieved on the basis of these respects and an object of the present invention is to provide a work machine that can exercise regeneration control and realize energy saving even when an abnormality occurs to pressure sensors for hydraulic actuators. 
     Means for Solving the Problem 
     To solve the problem, the present invention adopts, for example, a configuration according to claims. The present application includes a plurality of means for solving the problem. As an example of the means, there is provided a work machine including: a first hydraulic actuator; a second hydraulic actuator; a first operation device that commands an operation of the first hydraulic actuator; a second operation device that commands an operation of the second hydraulic actuator; a hydraulic pump that supplies a hydraulic fluid to the second hydraulic actuator; a regeneration circuit that regenerates a return hydraulic fluid from the first hydraulic actuator between the second hydraulic actuator and the hydraulic pump; a discharge circuit that discharges the return hydraulic fluid from the first hydraulic actuator to a tank; a regeneration amount regulation device that regulates a proportion of a flow rate of the return hydraulic fluid flowing to the regeneration circuit and a flow rate of the return hydraulic fluid flowing to the discharge circuit; and a controller that controls the regeneration amount regulation device. The work machine includes: a first operation amount sensor that detects an operation amount of the first operation device; and a first hydraulic actuator speed computing unit that computes a speed of the first hydraulic actuator. The controller controls the regeneration amount regulation device on the basis of the operation amount of the first operation device detected by the first operation amount sensor and the speed of the first hydraulic actuator computed by the first hydraulic actuator speed computing unit. 
     Effect of the Invention 
     According to the present invention, it is possible to exercise regeneration control and realize energy saving even when an abnormality occurs to pressure sensors for hydraulic actuators. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view showing a hydraulic excavator that is a first embodiment of a work machine according to the present invention. 
         FIG. 2  is a schematic diagram showing an example of a hydraulic system that configures the first embodiment of the work machine according to the present invention. 
         FIG. 3  is a control block diagram of a controller that configures the first embodiment of the work machine according to the present invention. 
         FIG. 4  is a control block diagram of a controller that configures a second embodiment of the work machine according to the present invention. 
         FIG. 5  is a control block diagram of a controller that configures a third embodiment of the work machine according to the present invention. 
         FIG. 6  is a control block diagram of a controller that configures a fourth embodiment of the work machine according to the present invention. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described hereinafter with reference to the drawings while a hydraulic excavator as a work machine is taken by way of example. It is noted that the present invention is applicable to all types of hydraulic work machines including hybrid excavators and an applicable range of the present invention is not limited to hydraulic excavators. 
     First Embodiment 
       FIG. 1  is a side view showing a hydraulic excavator that is a first embodiment of a work machine according to the present invention. 
     In  FIG. 1 , the hydraulic excavator includes a track structure  10 , a swing structure  20  swingably provided on the track structure  10 , and an excavator mechanism  30  attached to the swing structure  20 . 
     The track structure  10  is configured with a pair of crawlers  11   a  and  11   b  and a pair of crawler frames  12   a  and  12   b  (only one side of each pair is shown in  FIG. 1 ), a pair of track hydraulic motors  13   a  and  13   b  and speed reduction mechanisms of the track hydraulic motors  13   a  and  13   b  that control the crawlers  11   a  and  11   b  independently, and the like. 
     The swing structure  20  is configured with a swing frame  21 , an engine  22  provided on the swing frame  21  and serving as a prime mover, a swing hydraulic motor  27 , a speed reduction mechanism  26  reducing a speed of rotation of the swing hydraulic motor  27 , and the like. A driving force of the swing hydraulic motor  27  is transmitted via the speed reduction mechanism  26 , and the swing structure  20  (swing frame  21 ) is driven to swing with respect to the track structure  10  by the driving force. 
     Furthermore, the excavator mechanism (front implement)  30  is mounted in the swing structure  20 . The excavator mechanism  30  is configured with a boom  31 , a boom cylinder  32  for driving the boom  31 , an arm  33  rotatably and pivotally supported by a neighborhood of a tip end portion of the boom  31 , an arm cylinder  34  for driving the arm  33 , a bucket  35  rotatably and pivotally supported by a tip end of the arm  33 , a bucket cylinder  36  for driving the bucket  35 , and the like. 
     Moreover, a hydraulic system  40  for driving hydraulic actuators such as the track hydraulic motors  13   a  and  13   b , the boom cylinder  32 , the arm cylinder  34 , and the bucket cylinder  36  is mounted on the swing frame  21  of the swing structure  20 . 
     Further, a boom angle sensor  48  that detects an angle of the boom  31  is provided in a base end portion of the boom  31  supported by the swing structure  20 . An arm angle sensor  49  that detects an angle of the arm  33  with respect to the boom  31  is provided in the tip end portion of the boom  31  by which one end side of the arm  33  is rotatably supported. Angle signals detected by these angle sensors  48  and  49  are input to a controller  100  to be described later. 
       FIG. 2  is a schematic diagram showing an example of a hydraulic system that configures the first embodiment of the work machine according to the present invention. 
     In  FIG. 2 , the hydraulic system  40  includes a first hydraulic pump  41   a  and a second hydraulic pump  41   b , the boom cylinder  32  (first hydraulic actuator) to which a hydraulic fluid is supplied from the first hydraulic pump  41   a  and which drives the boom  31  (refer to  FIG. 1 ) of the hydraulic excavator, the arm cylinder  34  (second hydraulic actuator) to which a hydraulic fluid is supplied from the second hydraulic pump  41   b  and which drives the arm  33  (refer to  FIG. 1 ) of the hydraulic excavator, a boom spool  43  that controls a flow (a flow rate and a direction) of the hydraulic fluid supplied from the first hydraulic pump  41   a  to the boom cylinder  32 , an arm spool  44  that controls a flow (a flow rate and a direction) of the hydraulic fluid supplied from the second hydraulic pump  41   b  to the arm cylinder  34 , a boom operation device  51  (first operation device) that outputs an operation command for the boom  31  and changes over the boom spool  43 , and an arm operation device  52  (second operation device) that outputs an operation command for the arm  33  and changes over the arm spool  44 . While the first hydraulic pump  41   a  and the second hydraulic pump  41   b  are also connected to spools that are not shown so that the hydraulic fluids are supplied to other actuators that are not shown, circuit parts for these elements are omitted. 
     The first hydraulic pump  41   a  and the second hydraulic pump  41   b  are variable displacement hydraulic pumps that are driven to rotate by the engine  22  and deliver the hydraulic working fluids each proportional to a product between a revolution speed and a capacity and include regulators  42   a  and  42   b  serving as pump flow rate regulation devices, respectively. The regulators  42   a  and  42   b  are driven by control signals from the controller  100  (to be described later), thereby controlling tilting angles (capacities) of the hydraulic pumps  41   a  and  41   b  and controlling delivery flow rates thereof. The first hydraulic pump  41   a  and the second hydraulic pump  41   b  are connected to the boom spool  43  and the arm spool  44  via hydraulic fluid supply pipes  14  and  15 , and the hydraulic fluids delivered by the hydraulic pumps  41   a  and  41   b  are supplied to the boom spool  43  and the arm spool  44 . 
     The boom spool  43  and the arm spool  44  are connected to bottom-side hydraulic chambers  32   a  and  34   a  or rod-side hydraulic chambers  32   b  and  34   b  of the boom cylinder  32  and the arm cylinder  34  via bottom-side lines  17  and  19  or rod-side lines  16  and  18 , respectively. The hydraulic fluids delivered by the hydraulic pumps  41   a  and  41   b  are supplied, in response to the switching positions of the respective spools  43  and  44 , from the spools  43  and  44  to the bottom-side hydraulic chambers  32   a  and  34   a  or the rod-side hydraulic chambers  32   b  and  34   b  of the boom cylinder  32  and the arm cylinder  34  via the bottom-side lines  17  and  19  or the rod-side lines  16  and  18 . At least part of the hydraulic fluid discharged from the boom cylinder  32  is recirculated from the boom spool  43  to a tank via a line. All of the hydraulic fluid discharged from the arm cylinder  34  is recirculated from the arm spool  44  to the tank via a line. 
     The boom operation device  51  and the arm operation device  52  have operation levers  51   a  and  52   a  and pilot valves that are not shown, respectively. The pilot valves are connected to operation sections  43   a  and  43   b  of the boom spool  43  and operation sections  44   a  and  44   b  of the arm spool  44  via pilot lines  53  and  54  and pilot lines  55  and  56 . 
     When the boom operation lever  51   a  is operated in a boom raising direction (rightward in  FIG. 2 ), the pilot valve generates an operation pilot pressure in response to an operation amount of the boom operation lever  51   a . This operation pilot pressure is transmitted to the operation section  43   b  of the boom spool  43  via the pilot line  54 , and a position of the boom spool  43  is changed over to a position in the boom raising direction (to a left-hand position in  FIG. 2 ). When the boom operation lever  51   a  is operated in a boom lowering direction (leftward in  FIG. 2 ), the pilot valve generates an operation pilot pressure in response to an operation amount of the boom operation lever  51   a . This operation pilot pressure is transmitted to the operation section  43   a  of the boom spool  43  via the pilot line  53 , and the position of the boom spool  43  is changed over to a position in the boom lowering direction (to a right-hand position in  FIG. 2 ). 
     When the arm operation lever  52   a  is operated in an arm crowding direction (rightward in  FIG. 2 ), the pilot valve generates an operation pilot pressure in response to an operation amount of the arm operation lever  52   a . This operation pilot pressure is transmitted to the operation section  44   b  of the arm spool  44  via the pilot line  55 , and a position of the arm spool  44  is changed over to a position in the arm crowding direction (to a left-hand position in  FIG. 2 ). When the arm operation lever  52   a  is operated in an arm dumping direction (leftward in  FIG. 2 ), the pilot valve generates an operation pilot pressure in response to an operation amount of the arm operation lever  52   a . This operation pilot pressure is transmitted to the operation section  44   a  of the arm spool  44  via the pilot line  56 , and the position of the arm spool  44  is changed over to a position in the arm dumping direction (to a right-hand position in  FIG. 2 ). 
     The hydraulic system  40  according to the present embodiment includes, in addition to the constituent elements described above, a two-position, three-port regeneration control valve  45  that serves as a regeneration flow rate regulation device, that is disposed in the bottom-side line  17  of the boom cylinder  32 , and that can distribute the flow rate of the hydraulic fluid discharged from the bottom-side hydraulic chamber  32   a  of the boom cylinder  32  to a boom spool  43 -side (tank side) and a hydraulic fluid supply line  15 -side of the arm cylinder  34  (regeneration line side); a regeneration line  47  that has one end connected to one outlet port of the regeneration control valve  45  and the other end connected to the hydraulic fluid supply line  15 ; a discharge line  46  that has one end connected to the other outlet port of the regeneration control valve  45  and the other end connected to a port of the boom spool  43 ; pressure sensors  23 ,  24 ,  28 , and  29 ; and the controller  100 . 
     The regeneration control valve  45  is a solenoid proportional valve including an electromagnetic solenoid section  45   a  that is directly controlled by electric power from the controller  100 . The regeneration control valve  45  regulates a discharge flow rate of the hydraulic working fluid flowing from the bottom-side hydraulic chamber  32   a  of the boom cylinder  32  to the tank side (boom spool  43 -side) and a regeneration flow rate of the hydraulic working fluid flowing from the bottom-side hydraulic chamber  32   a  of the boom cylinder  32  to an arm spool  44 -side via the regeneration line  47  by controlling a stroke. 
     When the regeneration control valve  45  controls the hydraulic working fluid to flow from the boom cylinder bottom-side hydraulic chamber  32   a  to the arm spool  44  and the flow rate of the hydraulic working fluid delivered by the second hydraulic pump  41   b  is reduced in accordance with a flow rate of the hydraulic working fluid from the boom cylinder bottom-side hydraulic chamber  32   a , it is possible to reduce power of the engine  22  that drives the hydraulic pumps  41   a  and  41   b  and, therefore, reduce fuel consumption without changing an operating speed of the arm  33 . In addition, when the regeneration control valve  45  controls the hydraulic working fluid to flow from the boom cylinder bottom-side hydraulic chamber  32   a  to the arm spool  44  but the flow rate of the hydraulic working fluid delivered by the second hydraulic pump  41   b  is not reduced, it is possible to increase the operating speed of the arm  33 . 
     The pressure sensor  23  is provided in the rod-side line  16  for the boom cylinder  32 , and the pressure sensor  24  is provided in the bottom-side line  17  for the boom cylinder  32 . The pressure sensor  28  is provided in the rod-side line  18  for the arm cylinder  34 , and the pressure sensor  29  is provided in the bottom-side line  19  for the arm cylinder  34 . 
     A pressure sensor  53   a  is provided in the pilot line  53  and detects the operation pilot pressure in the boom lowering direction generated by the boom operation device  51 , and a pressure sensor  54   a  is provided in the pilot line  54  and detects the operation pilot pressure in the boom raising direction generated by the boom operation device  51 . In addition, a pressure sensor  55   a  is provided in the pilot line  55  for the arm operation device  52  and detects the operation pilot pressure in the arm crowding direction generated by the arm operation device  52 , and a pressure sensor  56   a  is provided in the pilot line  56  for the arm operation device  52  and detects the operation pilot pressure in the arm dumping direction generated by the arm operation device  52 . 
     The controller  100  receives detection signals input from the pressure sensors  23 ,  24 ,  28 ,  29 ,  53   a ,  54   a ,  55   a , and  56   a , performs predetermined computation on the basis of those signals, and outputs control commands to the regeneration control valve  45  that is the solenoid proportional valve and the regulators  42   a  and  42   b . In the present embodiment, a case in which the pressure sensors  23 ,  24 ,  28 , and  29  for the hydraulic actuators fail is assumed and the controller that does not use input signals from these pressure sensors for the hydraulic actuators will be described. The boom angle signal detected by the boom angle sensor  48  and the arm angle signal detected by the arm angle sensor are input to the controller  100  in place of the signals from these pressure sensors. 
     A control method according to the present embodiment will next be described with reference to  FIG. 3 .  FIG. 3  is a control block diagram of the controller that configures the first embodiment of the work machine according to the present invention. In  FIG. 3 , constituent elements denoted by the same reference characters as those shown in  FIGS. 1 and 2  are the same as those shown in  FIGS. 1 and 2 ; detailed description thereof will be, therefore, omitted. 
     As shown in  FIG. 3 , control according to the present embodiment is configured with the controller  100 , the pressure sensor  53   a  that serves as a boom lowering operation amount detection unit, a boom lowering speed computing unit  111 , and the regeneration control valve  45  that serves as a regeneration amount regulation device, and internal computation of the controller  100  is configured with a regeneration amount regulation device command value computing section  130 . 
     The boom lowering operation amount detection unit is configured with, for example, the pressure sensor  53   a  that detects the operation pilot pressure in the boom lowering direction generated by the boom operation device  51 . A signal of a boom lowering amount detected by the pressure sensor  53   a  is output to the regeneration amount regulation device command value computing section  130  of the controller  100 . 
     The boom lowering speed computing unit  111  is configured with, for example, the boom angle sensor  48  that detects the angle of the boom  31  with respect to the swing structure  20 , and another controller that computes an angular speed by performing differential computation on the boom angle signal detected by the boom angle sensor  48  and that outputs a signal of the calculated angular speed to the regeneration amount regulation device command value computing section  130  of the controller  100  as a boom lowering speed signal. This controller referred to as another controller is provided separately from the controller  100 . 
     It is noted that the controller  100  may execute computation of the angular speed; in that case, a value detected by the boom angle sensor  48  is directly input to the controller  100 . Furthermore, a displacement sensor (boom stroke sensor) that detects a displacement of the boom cylinder  32  may be used in place of the boom angle sensor  48 . In this case, the controller computes the boom lowering speed by differentiating the detected displacement signal similarly to the boom angle sensor  48 . Moreover, if the angle sensor or the cylinder displacement sensor used in the boom lowering speed computing unit  111  is commonly used as that used in a stability calculation or a computer aided construction during crane work, it is possible to achieve cost saving. 
     The regeneration control valve  45  that serves as the regeneration amount regulation device is driven on the basis of a command value (electric power) received in the electromagnetic solenoid section  45   a  from the controller  100  to change over a valve position. When the command value is equal to or lower than a minimum value, the regeneration control valve  45  is driven to a position at which a return hydraulic fluid from the boom cylinder bottom-side hydraulic chamber  32   a  entirely flows to the boom spool  43 . When the command value is a maximum value, the regeneration control valve  45  is driven to a position at which the return hydraulic fluid from the boom cylinder bottom-side hydraulic chamber  32   a  entirely flows to the arm spool  44 . When the command value is between the minimum value and the maximum value, the regeneration control valve  45  is driven to a position at which the return hydraulic fluid from the boom cylinder bottom-side hydraulic chamber  32   a  is distributed to the boom spool  43  and the arm spool  44 . It is noted that the regeneration control valve  45  that serves as the regeneration amount regulation device may be configured such that a hydraulic pressure is generated on the basis of the command value from the controller without using the electric power at a time of changing over the position of the regeneration control valve  45  and that the valve is changed over by the hydraulic pressure. In this case, the command value to the valve may be in a range, for example, from 0 MPa to 4 MPa. 
     First, the regeneration amount regulation device command value computing section  130  computes a boom lowering speed target value in such a manner that the boom lowering speed target value becomes higher as the input boom lowering operation amount is higher using a preset table. Next, the regeneration amount regulation device command value computing section  130  subtracts an actual boom lowering speed (a value computed by the boom lowering speed computing unit  111 ) from the computed boom lowering speed target value to calculate a deviation. Finally, the regeneration amount regulation device command value computing section  130  computes the regeneration amount regulation device command value in such a manner that the regeneration amount regulation device command value is closer to the minimum value as the deviation is larger in a positive direction, and that the regeneration amount regulation device command value is closer to the maximum value as the deviation is larger in a negative direction using a preset table, and outputs the regeneration amount regulation device command value. 
     Specifically, when the actual boom lowering speed is lower than the boom lowering speed target value, the deviation becomes large in the positive direction. In this case, the regeneration amount regulation device command value computing section  130  makes the command value closer to the minimum value. Through this computation, the regeneration control valve  45  is driven to the position at which the return hydraulic fluid from the boom cylinder bottom-side hydraulic chamber  32   a  entirely flows to the boom spool  43 . The boom lowering speed, therefore, increases to be closer to the boom lowering speed target value. Conversely, when the actual boom lowering speed is higher than the boom lowering speed target value, the deviation becomes large in the negative direction. In this case, the regeneration amount regulation device command value computing section  130  makes the command value closer to the maximum value. Through this computation, the regeneration control valve  45  is driven to the position at which the return hydraulic fluid from the boom cylinder bottom-side hydraulic chamber  32   a  entirely flows to the arm spool  44 . The boom lowering speed, therefore, decreases to be closer to the boom lowering speed target value. 
     Exercising control as described above enables a regeneration amount to be regulated in such a manner that the boom lowering speed conforms with the target speed. It is noted that control may be exercised on the basis of not the deviation but an integral value of the deviation, whereby it is possible to eliminate a stationary deviation. 
     According to the first embodiment of the work machine of the present invention described above, it is possible to exercise regeneration control and realize energy saving even when an abnormality occurs to the pressure sensors for the hydraulic actuators. 
     While the control exercised when the pressure sensors for the hydraulic actuators fail has been described in the present embodiment, the present invention is also applicable to a work machine that does not originally include these pressure sensors. 
     Second Embodiment 
     A second embodiment of the work machine according to the present invention will be described hereinafter with reference to the drawings.  FIG. 4  is a control block diagram of a controller that configures the second embodiment of the work machine according to the present invention. In  FIG. 4 , constituent elements denoted by the same reference characters as those shown in  FIGS. 1 to 3  are the same as those shown in  FIGS. 1 to 3 ; detailed description thereof will be, therefore, omitted. 
     In the second embodiment of the work machine according to the present invention, the control block diagram is additionally configured with the pressure sensors  55   a  and  56   a  that serve as an arm operation amount detection unit and the regulator  42   b  that serves as the pump flow rate regulation device, compared with the control block diagram of the first embodiment shown in  FIG. 3 . In addition, the internal computation of the controller is additionally configured with a pump flow rate reference value computing section  131  and a pump flow rate regulation device command value computing section  132 . 
     The arm operation amount detection unit is configured with, for example, the pressure sensor  55   a  that detects the operation pilot pressure in the arm crowding direction generated by the arm operation device  52 , and the pressure sensor  56   a  that detects the operation pilot pressure in the arm dumping direction. Signals of arm operation amounts detected by the pressure sensors  55   a  and  56   a  are output to the regeneration amount regulation device command value computing section  130  and the pump flow rate reference value computing section  131  of the controller  100 . 
     The regulator  42   b  that serves as the pump flow rate regulation device is driven on the basis of a command value (electric power) from the controller  100 , and controls a pump delivery flow rate by regulating the tilting angle (capacity) of the second hydraulic pump  41   b . When the command value is a minimum value, the regulator  42   b  regulates the tilting angle of the second hydraulic pump  41   b  in such a manner that the capacity thereof becomes a minimum. When the command value is a maximum value, the regulator  42   b  regulates the tilting angle of the second hydraulic pump  41   b  in such a manner that the capacity thereof becomes a maximum. When the command value is between the minimum value and the maximum value, the regulator  42   b  regulates the tilting angle of the second hydraulic pump  41   b  in such a manner that the capacity thereof becomes a value between the minimum value and the maximum value. It is noted that the regulator  42   b  that serves as the pump flow rate regulation device may be configured such that a hydraulic pressure is generated on the basis of the command value from the controller without using the electric power at a time of regulating the tilting angle of the second hydraulic pump  41   b  and that the tilting angle is changed over by the hydraulic pressure. In this case, the command value for the hydraulic pressure may be in a range, for example, from 0 MPa to 4 MPa. 
     The regeneration amount regulation device command value computing section  130  computes the regeneration amount regulation device command value from the boom lowering operation amount from the boom lowering operation amount detection unit and the boom lowering speed from the boom lowering speed computing unit  111 , and outputs the regeneration amount regulation device command value, similarly to the first embodiment. This enables the regeneration amount to be regulated in such a manner that the boom lowering speed conforms with the target speed. In the present embodiment, an arm crowding operation amount and an arm dumping operation amount are input from the arm operation amount detection unit. This is intended to make it possible to add a function of setting a command value to be output to 0 since regeneration is unnecessary when the arm crowding operation amount and the arm dumping operation amount are both 0. 
     First, the pump flow rate reference value computing section  131  computes pump flow rate reference value 1 in such a manner that the pump flow rate reference value 1 becomes higher as the input arm crowding operation amount is higher using a preset table. Likewise, the pump flow rate reference value computing section  131  computes pump flow rate reference value 2 in such a manner that the pump flow rate reference value 2 becomes higher as the input arm dumping operation amount is higher using a preset table. Finally, the pump flow rate reference value computing section  131  compares the pump flow rate reference value 1 with the pump flow rate reference value 2, and outputs a higher pump flow rate reference value to the pump flow rate regulation device command value computing section  132  as a pump flow rate reference value. 
     The pump flow rate regulation device command value computing section  132  receives the regeneration amount regulation device command value input from the regeneration amount regulation device command value computing section  130  and the pump flow rate reference value input from the pump flow rate reference value computing section  131 . First, the pump flow rate regulation device command value computing section  132  computes a pump flow rate reduction value in such a manner that the pump flow rate reduction value becomes higher as the input regeneration amount regulation device command value is higher using a preset table. Next, the pump flow rate regulation device command value computing section  132  outputs a value obtained by subtracting the pump flow rate reduction value from the input pump flow rate reference value as a pump flow rate regulation device command value. 
     Specifically, the pump flow rate reference value calculated by the pump flow rate reference value computing section  131  on the basis of the signals from the arm operation amount detection unit corresponds to a demanded flow rate of the second hydraulic pump  41   b  that is necessary for the second hydraulic actuator and necessary for the work. On the other hand, the pump flow rate regulation device command value computing section  132  computes the pump flow rate reduction value from the regeneration amount regulation device command value input from the regeneration amount regulation device command value computing section  130 . This pump flow rate reduction value corresponds to a regeneration flow rate from the first hydraulic actuator that is added to the delivery flow rate of the second hydraulic pump  41   b . The pump flow rate regulation device command value computing section  132  subtracts the regeneration flow rate from the first hydraulic actuator from the demanded flow rate of the second hydraulic pump  41   b  to compute a flow rate of the hydraulic working fluid to be delivered solely by the second hydraulic pump  41   b , and outputs the command value to the regulator  42   b.    
     Exercising such control makes it possible to reduce a flow rate of the hydraulic working fluid delivered by the second hydraulic pump  41   b  without changing the operating speed of the arm  33  and reduce fuel consumption. 
     It is noted that it is possible to increase the operating speed of the arm  33  if the pump flow rate regulation device command value computing section  132  outputs the pump flow rate reference value as the pump flow rate regulation device command value as it is without executing subtraction of the pump flow rate reduction value from the pump flow rate reference value. 
     In the present embodiment, it is possible to further improve fuel economy since the regeneration flow rate by the regeneration flow rate regulation device and the delivery flow rate of the second hydraulic pump can be controlled independently. 
     The second embodiment of the work machine according to the present invention described above can attain similar effects to those of the first embodiment described above. 
     Third Embodiment 
     A third embodiment of the work machine according to the present invention will be described hereinafter with reference to the drawings.  FIG. 5  is a control block diagram of a controller that configures the third embodiment of the work machine according to the present invention. In  FIG. 5 , constituent elements denoted by the same reference characters as those shown in  FIGS. 1 to 4  are the same as those shown in  FIGS. 1 to 4 ; detailed description thereof will be, therefore, omitted. 
     In the third embodiment of the work machine according to the present invention, the control block diagram is additionally configured with an arm speed computing unit  113 , and the internal computation of the controller differs in a computation method of the pump flow rate regulation device command value computing section  132 , compared with the control block diagram of the second embodiment shown in  FIG. 4 . Furthermore, the regeneration amount regulation device command value from the regeneration amount regulation device command value computing section  130  is not input to the pump flow rate regulation device command value computing section  132 , and an arm speed signal from the arm speed computing unit  113  and the pump flow rate reference value from the pump flow rate reference value computing section  131  are input to the pump flow rate regulation device command value computing section  132 . 
     The arm speed computing unit  113  is configured with, for example, the arm angle sensor  49  that detects the angle of the arm  33  with respect to the boom  31 , and another controller that computes an angular speed by performing differential computation on the arm angle signal detected by the arm angle sensor  49  and that outputs a signal of the calculated angular speed to the pump flow rate regulation device command value computing section  132  of the controller  100  as an arm speed signal. This controller referred to as another controller is provided separately from the controller  100 . 
     It is noted that the controller  100  may execute computation of the angular speed; in that case, a value detected by the arm angle sensor  49  is directly input to the controller  100 . Furthermore, a displacement sensor (arm stroke sensor) that detects a displacement of the arm cylinder  34  may be used in place of the arm angle sensor  49 . In this case, the controller computes the arm speed by differentiating the detected displacement signal similarly to the arm angle sensor  49 . Moreover, if the angle sensor or the cylinder displacement sensor used in the arm speed computing unit  113  is commonly used as that used in the stability calculation or the computer aided construction during crane work, it is possible to achieve cost saving. 
     First, the pump flow rate regulation device command value computing section  132  computes an arm speed target value from the arm crowding operation amount when the arm crowding operation is performed and from the arm dumping operation amount when an arm dumping operation is performed, using a preset table. Next, the pump flow rate regulation device command value computing section  132  subtracts an actual arm speed (a value computed by the arm speed computing unit  113 ) from the computed arm speed target value to calculate a deviation. Finally, the pump flow rate regulation device command value computing section  132  computes the pump flow rate reduction value in such a manner that the pump flow rate reduction value is closer to a minimum value as the deviation is larger in the positive direction, and that the pump flow rate reduction value is closer to a maximum value as the deviation is larger in the negative direction using a preset table. 
     Specifically, when the actual arm speed is lower than the arm speed target value, the deviation becomes large in the positive direction. In this case, the pump flow rate regulation device command value computing section  132  makes the pump flow rate reduction value closer to the minimum value. By doing so, the pump flow reduction value subtracted from the pump flow rate reference value calculated by the pump flow rate reference value computing section  131  becomes the minimum value, and the pump flow rate regulation device command value computing section  132 , therefore, outputs the command value to the regulator  42   b  in such a manner that the flow rate of the hydraulic working fluid to be delivered solely by the second hydraulic pump  41   b  increases. The actual arm speed thereby increases to be closer to the arm speed target value. Conversely, when the actual arm speed is higher than the arm speed target value, the deviation becomes large in the negative direction. In this case, the pump flow rate regulation device command value computing section  132  makes the pump flow rate reduction value closer to the maximum value. By doing so, the pump flow rate reduction value subtracted from the pump flow rate reference value becomes the maximum value, and the pump flow rate regulation device command value computing section  132 , therefore, outputs the command value to the regulator  42   b  in such a manner that the flow rate of the hydraulic working fluid to be delivered solely by the second hydraulic pump  41   b  decreases. The actual arm speed thereby decreases to be closer to the arm speed target value. 
     Exercising control as described above enables the hydraulic pump flow rate to be regulated in such a manner that the actual arm speed conforms with the target speed. It is noted that control may be exercised on the basis of not the deviation but the integral value of the deviation, whereby it is possible to eliminate the stationary deviation. It is thereby possible to reduce the flow rate of the hydraulic working fluid delivered by the second hydraulic pump  41   b  without changing the operating speed of the arm  33  and reduce fuel consumption. 
     The third embodiment of the work machine according to the present invention described above can attain similar effects to those of the first embodiment described above. 
     Furthermore, according to the third embodiment of the work machine of the present invention described above, it is possible to reduce the flow rate of the hydraulic working fluid delivered by the second hydraulic pump  41   b  without changing the operating speed of the arm  33  and reduce fuel consumption. 
     Fourth Embodiment 
     A fourth embodiment of the work machine according to the present invention will be described hereinafter with reference to the drawings.  FIG. 6  is a control block diagram of a controller that configures the fourth embodiment of the work machine according to the present invention. In  FIG. 6 , constituent elements denoted by the same reference characters as those shown in  FIGS. 1 to 5  are the same as those shown in  FIGS. 1 to 5 ; detailed description thereof will be, therefore, omitted. 
     In the fourth embodiment of the work machine according to the present invention, the control block diagram differs from that of the third embodiment shown in  FIG. 5  in the computation method of the pump flow rate regulation device command value computing section  132  in the internal computation of the controller  100 . Furthermore, the regeneration amount regulation device command value from the regeneration amount regulation device command value computing section  130  is input to the pump flow rate regulation device command value computing section  132 . 
     First, the pump flow rate regulation device command value computing section  132  computes the arm speed target value from the arm crowding operation amount when the arm crowding operation is performed and from the arm dumping operation amount when the arm dumping operation is performed, using the preset table. Next, the pump flow rate regulation device command value computing section  132  subtracts the actual arm speed (the value computed by the arm speed computing unit  113 ) from the computed arm speed target value to calculate the deviation. Finally, the pump flow rate regulation device command value computing section  132  computes the pump flow rate reduction value in such a manner that the pump flow rate reduction value is closer to the minimum value as the deviation is larger in the positive direction, that the pump flow rate reduction value is closer to the maximum value as the deviation is larger in the negative direction, and that the pump flow rate reduction value becomes higher as the regeneration amount regulation device command value from the regeneration amount regulation device command value computing section  130  is higher, using a preset two-dimensional table. 
     It is noted that control may be exercised on the basis of not the deviation but the integral value of the deviation, whereby it is possible to eliminate the stationary deviation. It is thereby possible to reduce the flow rate of the hydraulic working fluid delivered by the second hydraulic pump  41   b  without changing the operating speed of the arm  33  and reduce fuel consumption. 
     The fourth embodiment of the work machine according to the present invention described above can attain similar effects to those of the first embodiment described above. 
     Furthermore, according to the fourth embodiment of the work machine of the present invention described above, it is possible to reduce the flow rate of the hydraulic working fluid delivered by the second hydraulic pump  41   b  without changing the operating speed of the arm  33  and reduce fuel consumption. 
     The present invention is not limited to the first to fourth embodiments described above but encompasses various modifications. The abovementioned embodiments have been described in detail for describing the present invention so that the present invention is easy to understand. The present invention is not always limited to the embodiments having all the configurations. For example, the configuration of a certain embodiment can be partially replaced by the configuration of another embodiment or the configuration of another embodiment can be added to the configuration of the certain embodiment. Furthermore, for a part of the configuration of each embodiment, addition, deletion, and/or replacement of the other configuration can be made. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
           10 : Track structure 
           11 : Crawler 
           12 : Crawler frame 
           13 : Track hydraulic motor 
           20 : Swing structure 
           21 : Swing frame 
           22 : Engine 
           26 : Speed reduction mechanism 
           27 : Swing hydraulic motor 
           30 : Excavator mechanism 
           31 : Boom 
           32 : Boom cylinder (first hydraulic actuator) 
           33 : Arm 
           34 : Arm cylinder (second hydraulic actuator) 
           35 : bucket 
           36 : Bucket cylinder 
           40 : Hydraulic system 
           41   a : First hydraulic pump 
           41   b : Second hydraulic pump 
           42   a ,  42   b : Regulator (hydraulic pump flow rate regulation device) 
           43 : Boom spool 
           44 : Arm spool 
           44 : Regeneration amount regulation device (regeneration control valve) 
           51 : Boom operation device (first operation device) 
           52 : Arm operation device (second operation device) 
           100 : Controller 
           111 : Boom lowering speed computing unit 
           113 : Arm speed computing unit 
           130 : Regeneration amount regulation device command value computing section 
           132 : Pump flow rate regulation device command value computing section