Abstract:
Disclosed are a system for driving a boom of a hybrid excavator, and a method for controlling same. The disclosed system comprises: an electric motor operating by means of a motor or generator; a capacitor for storing electricity generated by the electric motor; a hydraulic pump motor driven by the electric motor to supply working oil to a boom; a boom control valve having a closed circuit for selectively connecting/disconnecting a discharge line and an inlet line of the hydraulic pump motor to/from a head or a load of the boom; a main pump driven by a driving source arranged separately from the motor so as to supply working oil to a bucket, driving motor, or arm; a boom-assisting valve, which connects a discharge line of the main pump to the discharge line of the hydraulic pump motor, such that working oil discharged from the main pump and the hydraulic pump motor can be combined; and a control unit for controlling the electric motor, the hydraulic pump motor, and the boom control valve. The system of the present disclosure minimizes the loss of energy during excavation, which is the main use of an excavator, while using the electric motor, ensures the operating performance of the boom, and recovers regenerative energy from the boom.

Description:
[0001]    This Application is a Section 371 National Stage Application of International Application No. PCT/KR2010/009236, filed Dec. 23, 2010 and published, not in English, as WO2011/078586 on Jun. 30, 2011. 
     
    
     BACKGROUND 
       [0002]    The present disclosure is contrived to solve the problems in the related art and an object of the present disclosure is to provide a system for driving a boom of a hybrid excavator that minimize energy loss, ensures operability of a boom, and restores recoverable energy of the boom while excavating that is the main use of the excavator, even with a use of an electric motor, and a method of controlling the system. 
         [0003]    The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. 
       SUMMARY 
       [0004]    A system for driving a boom in a hybrid excavator according to the present disclosure includes: an electric motor that operates as a motor or an electricity generator; a capacitor that stores electricity generated by the electric motor; a hydraulic pump motor that is driven by the electric motor and supplies working fluid to a boom; a boom control valve that constitutes a closed circuit selectively connecting/disconnecting a discharge line and an intake line of the hydraulic pump motor to/from a head or a rod of the boom; a main pump that is driven by a driving source disposed separately from the electric motor and supplies the working fluid to a bucket, a traveling motor, or an arm; a boom-assistant valve that allows the working fluid discharged from the main pump and the hydraulic pump motor to meet each other by connecting the discharge line of the main pump to the discharge line of the hydraulic pump motor; and a control unit that controls the electric motor, the hydraulic pump motor, and the boom control valve. 
         [0005]    The first control valve is selectively switched when the boom is lifted, and is disconnected when the boom is descended, and the second control valve is disconnected when the boom is lifted, and is selectively switched when the boom is descended. 
         [0006]    Further, the first control valve may be connected and allow the flow rate flowing into the hydraulic pump motor from the boom cylinder to flow into the tank, when the flow rate flowing into the hydraulic pump motor from the boom cylinder exceeds the available capacity of the hydraulic pump motor or the capacity of the electric motor when the boom is descended. 
         [0007]    A method of controlling a system for driving a boom of a hybrid excavator according to the present disclosure includes: detecting the amount of operation of a boom joystick; determining lifting or descending of a boom due to operation of the boom joystick; opening a first control valve when the boom is lifted; comparing the driving power of the boom according to the amount of operation of the boom joystick with the maximum suppliable power of an electric motor when the boom is lifted and comparing the consumed flow rate of a boom cylinder with the maximum flow rate of a hydraulic pump motor when the driving power of the boom is smaller than the maximum suppliable power of the electric motor; disconnecting the boom-assistant valve, when the consumed flow rate of the boom cylinder is smaller than the maximum flow rate of the hydraulic pump motor; connecting the boom-assistant valve, when the driving power of the boom is larger than the maximum suppliable power of the electric motor; opening the second control valve when the boom is descended, comparing the recovery flow rate of the boom cylinder with the available flow rate of the hydraulic pump motor, when the recovery power of the boom is larger the maximum recoverable power of the electric motor by comparing the recovery power of the boom with the maximum recoverable power of the electric motor; disconnecting the first control valve, when the recovery flow rate of the boom cylinder is smaller than the available flow rate of the hydraulic pump motor; connecting the first control valve, when the recovery flow rate of the boom cylinder is larger than the available flow rate of the hydraulic pump motor; and connecting the first control valve, when the recovery power of the boom is larger than the maximum recoverable power of the electric motor. 
         [0008]    According to the system for driving a boom in a hybrid excavator and a control method thereof of the present disclosure, it is possible to minimize energy loss, ensure operational performance of a boom and recover recoverable energy of the boom, while excavating that is the main use of the excavator, even with a use of an electric motor. 
         [0009]    That is, it is possible to improve fuel efficiency by removing a loss generated in a hydraulic system in a low-flow rate fine operation by driving the boom, using the electric motor and the boom hydraulic pump motor when the boom is lifted. 
         [0010]    Further, the flow rate required for the initial fine operation section when the boom operates alone is supplied from the electric motor and the boom hydraulic pump motor, and the part exceeding the part corresponding to the maximum suppliable flow rate of the boom and power can be supplied by using the existing hydraulic system with the main pump. 
         [0011]    Further, it is possible to ensure operation performance of the boom equivalent to the existing excavator while using small-capacity electric motor and pump motor, and recover the energy of the boom, and when high power and a large flow rate are suddenly required, it is possible to ensure the performance equivalent to the existing excavator by assisting power and flow rate by using the existing hydraulic system. 
         [0012]    Further, when there is suddenly large recovery energy, the part exceeding the capacity is bypassed, and it is possible to supply most energy required to drive the boom from only the capacities of the hydraulic pump and the electric motor of about the maximum suppliable flow rate of the boom and the maximum power of the engine, and it is possible to recover most of the recoverable energy of the boom. 
         [0013]    Further, it is possible to remove a loss in the existing hydraulic system and simplify the structure of the main control valve, by separating the boom from the existing hydraulic system. 
         [0014]    Further, it is possible to improve operational performance of the arm and the bucket by making two main pumps in charge of the arm and the bucket. 
         [0015]    This summary and the abstract are provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. The summary and the abstract are not intended to identify key features or essential features of the claimed subject matter, nor are they intended to be used as an aid in determining the scope of the claimed subject matter. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a configuration diagram of a system for driving a boom of a hybrid excavator according to an exemplary embodiment of the present disclosure. 
           [0017]      FIG. 2  is a configuration diagram showing a lifting state of the boom of  FIG. 1 . 
           [0018]      FIG. 3  is a configuration diagram showing a descending state of the boom of  FIG. 1 . 
           [0019]      FIG. 4  is a flowchart of a method of controlling a system for driving a boom of a hybrid excavator according to an exemplary embodiment of the present disclosure. 
           [0000]    
         
           
                 
                 
               
             
                 
                     
                 
               
               
                 
                   100: Boom 
                   105: Boom cylinder 
                 
                 
                   106: Head 
                   107: Rod 
                 
                 
                   110: Electric motor 
                   115: Capacitor 
                 
                 
                   116: Electricity storage 
                 
                 
                   120: Hydraulic pump motor 
                 
                 
                   121: Discharge line 
                   122: Intake line 
                 
                 
                   125: Boom control valve 
                 
                 
                   126: Normal-directional connecting portion 
                 
                 
                   127: Cross-connecting portion 
                 
                 
                   128: Disconnecting portion 
                 
                 
                   129: Check valve 
                   140: Main pump 
                 
                 
                   141: Engine 
                   144: Boom-assistant valve 
                 
                 
                   145: Boom-assistant line 
                 
                 
                   151: First control valve 
                 
                 
                   152: Second control valve 
                 
                 
                   160: Control unit 
                 
                 
                   170: Tilting angle control device 
                 
                 
                     
                 
               
            
           
         
       
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Hereinafter, preferable embodiments of a system for driving a boom of a hybrid excavator according to the present disclosure and a method of controlling the system will be described with reference to the accompanying drawings. The thicknesses of lines or sizes of components illustrated in the drawings may be exaggerated for the clarity and convenience of the following description. Further, the terminologies described below are terminologies determined in consideration of the functions in the present disclosure and may be construed in different ways by the intention of users and operators or a custom. 
         [0021]      FIG. 1  is a configuration diagram of a system for driving a boom of a hybrid excavator according to an exemplary embodiment of the present disclosure,  FIG. 2  is a configuration diagram showing a lifting state of the boom of  FIG. 1 ,  FIG. 3  is a configuration diagram showing a descending state of the boom of  FIG. 1 , and  FIG. 4  is a flowchart of a method of controlling a system for driving a boom of a hybrid excavator according to an exemplary embodiment of the present disclosure. 
         [0022]    Referring to  FIG. 1 , a system for driving a boom of a hybrid excavator according to an exemplary embodiment of the present disclosure includes an electric motor  110  that is operated as a motor or an electricity generator, a capacitor  115  that stores electricity generated by the electric motor  110 , a hydraulic pump motor  120  that is driven by the electric motor  110  and supplies working fluid to a boom  110 , and a boom control valve  125  that selectively connects/disconnects a discharge line  121  and an intake line  122  of the hydraulic pump motor  120  to/from a head  106  or a rod  107  of the boom  100 . The capacitor of the present exemplary embodiment can be supplied with most power by the operation of a motor/electricity generator (not shown) connected to an engine. 
         [0023]    The boom control valve  125  is connected to a main pump  140  by a boom-assistant line  145  through which working fluid is supplied. Two main pumps  140  are provided and supply the working fluid to a bucket, a traveling motor, or an arm by being driven by an engine  141 . 
         [0024]    The hydraulic pump motor  120  is connected with the discharge line  121  through which the working fluid is discharged and the intake line  122  through which the working fluid flows inside. The discharge line  121  and the intake line  122  are connected to the head  106  or the rod  107  of a boom cylinder  105  by the boom control valve  125 . That is, the hydraulic circuit contact point of the discharge line  121  and the intake line  122  is connected or disconnected by the boom control valve  125 . 
         [0025]    The boom control valve  125  has a normal-directional connecting portion  126  for lifting the boom  100  by connecting the discharge line  121  with the intake line  122  in a normal direction, a cross-connecting portion  127  that connects the discharge line  121  with the intake line  122  in the opposite direction, and a disconnecting portion  128  that cuts the connection between the discharge line  121  and the intake line  122 . The boom control valve  125  is operated by an electronic proportional control valve or a separate pilot hydraulic line and changes the connection state between the discharge line  121  and the intake line  122 . 
         [0026]    A check valve  129  is disposed in the discharge line  121  of the hydraulic pump motor  120  to prevent a backward flow and the boom-assistant line  145  is connected close to the check valve  129  from the hydraulic pump motor  120 . A first control valve  151  for connection with a tank is connected between the hydraulic pump motor  120  and the discharge line  121  of the boom control line  125 . A second control valve  152  for connection with the tank is connected between the connection portion of the boom-assistant line  145  and the hydraulic pump motor  120 . The operations of the electric motor  110 , the hydraulic pump motor  120 , the boom control valve  125 , the first control valve  151 , and the second control valve  152  are controlled by a control unit  160 . 
         [0027]    Referring to  FIG. 2 , when a signal for lifting the boom  100  is input to the control unit  160  from a boom joystick  161 , the electric motor  110  is operated as a motor by the control unit  160  and drives the hydraulic pump motor  120  as a pump. Further, the outlet of the hydraulic pump motor  120  is connected to the head  106  of the boom  100  through the discharge line  121  and the rod  107  of the boom  100  is connected to the inlet of the hydraulic pump motor  120  through the intake line  122  of the hydraulic pump motor  120 , by switching the boom control valve  125 . In this process, the boom  100  starts to be lifted by the flow rate discharged from the hydraulic pump motor  120  and the speed of the boom  100  is controlled by control of the revolution speed of the electric motor  110  and tilting angle control performed by a tilting angle control device  170 . 
         [0028]    A closed circuit is implemented between the hydraulic pump motor  120  and the boom cylinder  105  and the flow rate supplied to the hydraulic pump motor  120  from the boom cylinder  105  is smaller than the flow rate supplied to the boom cylinder  105  from the hydraulic pump motor  120  by a cylinder area difference. The deficit of the flow rate is supplied from the tank by connecting the first control valve  151 . 
         [0029]    Further, the control unit  160  calculates the power of the electric motor  110  from the torque and rotation speed of the electric motor  110  and monitors the flow rate of the hydraulic pump motor  120  from the tilting angle and the rotation speed outputted from the tilting angle control device  170 . 
         [0030]    Meanwhile, when the control signal of the boom joystick  161  increases over the flow rate supplied from the hydraulic pump motor  120  or the capacity of the electric motor  110 , the control unit  160  supplies the flow rate of the main pump  140  to the boom cylinder  105  by controlling the boom-assistant valve  144 . The control unit  160  controls opening/closing of the boom-assistant valve  144  such that the boom cylinder  105  can follow the signal of the boom joystick  161 . The boom-assistant valve  144  is switched to the right by the control unit  160  when being disconnected, and the boom-assistant line  145  is connected to the main pump  140  driven by the engine  141 . 
         [0031]    Referring to  FIG. 3 , when a signal for descending the boom  100  is inputted to the control unit  160  from the boom joystick  161 , the hydraulic pump motor  120  is operated by the flow rate returning from the boom cylinder  105  by the control unit  160 , the electric motor  110  is operated as an electricity generator by the driving force of the hydraulic pump motor  120 , and the generated power is stored in an electricity storage  116  equipped with the capacitor  115 . 
         [0032]    As the boom  100  is descended, the boom control valve  125  is switched and the head  106  of the boom  100  is connected to the inlet of the hydraulic pump motor  120  by the intake line  122 , and the rod  107  of the boom  100  is connected to the outlet of the hydraulic pump motor  120  by the discharge line  121 . The descending speed of the boom  100  is controlled by controlling the rotation speed of the hydraulic pump motor  120  by controlling the tilting angle through the tilting angle control device  170 , and the amount of electricity generated by the electric motor  110  is also controlled. 
         [0033]    Further, a closed circuit is implemented between the hydraulic pump motor  120  and the cylinder and the flow rate supplied to the hydraulic pump motor  120  from the boom cylinder  105  is larger than the flow rate supplied to the boom cylinder  105  from the hydraulic pump motor  120  by an area difference of the boom cylinder  105  due to whether there is the rod  107 . The excessive flow rate supplied from the hydraulic pump motor  120  to the boom cylinder  105  is discharged to the tank, as the second control valve  152  connected to the discharge line  121  is connected by a signal of the control unit  160 . 
         [0034]    Further, when a flow rate over the available flow rate of the hydraulic pump motor  120  or the capacity of the electric motor  110  is discharged from the boom cylinder  105  and supplied to the hydraulic pump motor  120 , the control unit  160  can discharge an excessive flow rate over the capacities of the hydraulic pump motor  120  and the electric motor  110  to the tank by connecting the first control valve  151 . The first control valve  151  discharges the excessive flow rate of the working fluid flowing to the hydraulic pump motor  120  through the intake line  122  from the boom cylinder  105  to the tank. 
         [0035]    Referring to  FIGS. 2 and 3 , the first control valve  151  can supply insufficient working fluid to the boom cylinder  105  by connecting the tank when the boom  100  is lifted, and on the contrary, it is disconnected except for when an excessive flow rate is generated to the hydraulic pump motor  120  from the boom cylinder  105 , when the boom  100  is descended. 
         [0036]    Further, the second control valve  152  that has been disconnected when the boom  100  is lifted discharges the flow rate excessively supplied to the boom cylinder  105  from the hydraulic pump motor  120  to the tank by being connected when the boom  100  is descended, The second control valve  152  can be controlled when being open as the boom is descended, as described above, but it may be additionally controlled, as described below. 
         [0037]    That is, the second control valve  152  may be controlled to be opened only when the flow rate supplied through the hydraulic pump motor  120  is larger than the flow rate necessary for the boom head  106 , while keeping closed when the boom  100  is descended. 
         [0038]    Further, when the hydraulic pump motor  120  supplies an unnecessarily excessive flow rate due to various problems, the flow rate circulating is drained to prevent a safety accident and damage to the system, in which it is more preferable that the first control valve  151  operates with the second control valve  152  to be opened such that the working fluid is drained. 
         [0039]    Further, the boom-assistant valve  144  is connected by the control unit  160  such that the flow rate of the main pump  140  is supplied to the boom cylinder  105 , when the control signal of the boom joystick  161  increases over the flow rate supplied from the hydraulic pump motor  120  or the capacity of the electric motor  110 . 
         [0040]    Referring to  FIGS. 2 to 4 , a method of controlling a system for driving a boom of a hybrid excavator according to an exemplary embodiment of the present disclosure includes (a) detecting the amount of operation of the boom joystick  161 , (b) determining lifting or descending of the boom  100  due to the operation of the boom joystick  161 , (c) opening the first control valve  151  when the boom  100  is lifted, (d) comparing the driving power of the boom  100  according to the amount of operation of the boom joystick  161  with the maximum suppliable power of the electric motor  110  when the boom  100  is lifted, and (e) comparing the consumed flow rate of the boom cylinder  105  with the maximum flow rate of the hydraulic pump motor  120  when the driving power of the boom  100  is smaller than the maximum suppliable power of the electric motor  110 . 
         [0041]    When the consumed flow rate of the boom cylinder  105  is smaller than the maximum flow rate of the hydraulic pump motor  120 , (f) disconnecting the boom-assistant valve  144  is performed. Further, when the driving power of the boom  100  is larger than the maximum suppliable power of the electric motor  110 , (g) supplying insufficient working fluid by connecting the main pump  140  by opening to the boom-assistant valve  144  is included. 
         [0042]    Meanwhile, when the boom  100  is descended, (h) opening the second control valve  152  and (i) comparing the recovery power of the boom  100  with the maximum recoverable power of the electric motor  110  is included. Further, when the recovery power of the boom  100  is smaller the maximum recoverable power of the electric motor  110 , (j) comparing the recovery flow rate of the boom cylinder  105  with the available flow rate of the hydraulic pump motor  120  is included. When the recovery flow rate of the boom cylinder  105  is smaller than the available flow rate of the hydraulic pump motor  120 , (k) disconnecting the first control valve  151  is included. On the contrary, when the recovery flow rate of the boom cylinder  105  is larger than the available flow rate of the hydraulic pump motor  120 , (l) discharging the excessive flow rate to the tank by connecting the first control valve  151  is included. Further, when the recovery power of the boom  100  is larger than the maximum recoverable power of the electric motor  110 , (m) discharging the excessive flow rate to the tank by connecting the first control valve  151  is included. 
         [0043]    As described above, the system for driving a boom of a hybrid excavator according to an exemplary embodiment of the present disclosure and a method of controlling the system can improve fuel efficiency by removing a loss generated in a hydraulic system in a low-flow rate fine operation by driving the boom  100  by using the electric motor  110  and the hydraulic pump motor  120  when the boom  100  is lifted. 
         [0044]    Further, the flow rate required for the initial fine operation section when the boom  100  operates alone is supplied from the electric motor  110  and the hydraulic pump motor  120 , and the part exceeding the part corresponding to the maximum suppliable flow rate of the boom  100  can be supplied by using the existing hydraulic system with the main pump  140 . 
         [0045]    Further, it is possible to ensure operation performance of the boom  100  equivalent to the existing excavator even while using the small-capacity electric motor  110  and pump motor, and recover the energy of the boom  100 . Further, the hybrid driving system using the electric motor  110  and the hydraulic pump motor  120  can perform most energy supply and energy recovery in excavating. 
         [0046]    Further, when high power and large flow rate are suddenly required, it is possible to ensure the performance equivalent to the existing excavator by assisting power and flow rate by using the existing hydraulic system. Further, when there is a suddenly large recovery energy, the part exceeding the capacity is bypassed, and it is possible to supply most energy required to drive the boom  100  from only the capacities of the hydraulic pump and the electric motor  110  of about the maximum suppliable flow rate of the boom  100  and the maximum power of the engine  141 , and it is possible to recover most of the recoverable energy of the boom  100 . 
         [0047]    The present disclosure may be applied to a system for driving a hybrid excavator in construction equipment. 
         [0048]    Although the present disclosure has been described with reference to exemplary and preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosure.