Abstract:
Disclosed is a hydraulic system for a construction machine, which makes it possible to adjust the geometric position of a working device comprising a boom and an arm by means of a single manipulation lever, thereby enabling a leveling/flattening process to be conveniently performed. The hydraulic system includes: a working mode selection switch for selecting a leveling/flattening process; a boom driving switch valve for controlling the driving of a boom cylinder in response to a control signal from a first manipulation lever; an arm driving switch valve for controlling the driving of an arm cylinder in response to a control signal from a second manipulation lever; a shuttle valve including input parts that connect to both an electronic proportional control valve and to the first manipulation lever, respectively, and an output part connecting to the boom driving switch valve; and an electronic controller.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a hydraulic system for construction equipment, which is configured to perform a leveling work using an excavator. More particularly, the present invention relates to such a hydraulic system which is configured to conveniently perform a leveling work by simultaneously manipulating work apparatuses such as a boom and an arm using a single manipulation lever (RCV). 
       BACKGROUND OF THE INVENTION 
       [0002]    A conventional hydraulic system for construction equipment as shown in  FIG. 1  includes:
       first and second variable displacement hydraulic pumps (hereinafter, referred to as “first and second hydraulic pumps”)  1  and  2 ;   a boom cylinder  3  connected to the first hydraulic pump  1 ;   first and second manipulation levers  4  and  7  (for example, hydraulic joysticks are used) configured to generate control signals in proportion to an operator&#39;s manipulation amounts, respectively;   a boom-driving switching valve  5  installed in a flow path between the first hydraulic pump  1  and the boom cylinder  3  and configured to control a start, a stop, and a direction change of the boom cylinder  3  when a spool is shifted in response to the control signal generated from the first manipulation lever  4 ;   an arm cylinder  6  connected to the second hydraulic pump  2 ;   an arm-driving switching valve  8  installed in a flow path between the second hydraulic pump  2  and the arm cylinder  6  and configured to control a start, a stop, and a direction change of the arm cylinder  6  when a spool is shifted in response to the control signal generated from the second manipulation lever  7 ; and   an electronic controller (V-ECU)  9  configured to detect the control signals (referring to secondary signal pressures) that are generated in accordance with the manipulation of the first and second manipulation levers  4  and  7 , and control the discharge flow rates of the first and second hydraulic pump  1  and  2  based on the detected control signals, respectively.       
 
         [0010]    Thus, when an operator manipulates the first and second manipulation levers  4  and  7  simultaneously to shift the spools of the boom-driving switching valve  5  and the arm-driving switching valve  8 , the boom cylinder  3  and the arm cylinder  6  are driven by hydraulic fluids supplied thereto from the first and second hydraulic pumps  1  and  2 , respectively, to perform a leveling work. 
         [0011]    The conventional hydraulic system for construction equipment entails a problem in that since the operator must manipulate the first and second manipulation levers  4  and  7  properly in a geometrical manner to distribute the hydraulic fluids supplied to the boom cylinder  3  and the arm cylinder  6 , which makes it difficult to control the geometrical position of the work apparatuses such as the boom and the arm, leading to an increase in the time spent to perform a leveling work through the simultaneous manipulation of the first and second manipulation levers  4  and  7 , and thus causing a deterioration of the work efficiency. 
       DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problems 
       [0012]    Accordingly, the present invention was made to solve the aforementioned problem occurring in the prior art, and it is an object of the present invention to provide a hydraulic system for construction equipment, in which the geometrical position of work apparatuses (referring to a boom and an arm) is controlled by manipulation of a single manipulation lever to conveniently perform a leveling work, thereby shortening the work time and thus improving the work efficiency of construction equipment. 
       Technical Solution 
       [0013]    To accomplish the above object, in accordance with an embodiment of the present invention, there is provided a hydraulic system for construction equipment. 
         [0014]    The hydraulic system for construction equipment includes:
       first and second variable displacement hydraulic pumps;   first and second manipulation levers configured to generate control signals in proportion to an operator&#39;s manipulation amounts, respectively;   a working mode selection switch configured to select a leveling work;   a boom cylinder connected to the first hydraulic pump;   a boom-driving switching valve installed in a flow path between the first hydraulic pump and the boom cylinder and shifted in response to the control signal generated from the first manipulation lever to control a start, a stop, and a direction change of the boom cylinder;   an arm cylinder connected to the second hydraulic pump;   an arm-driving switching valve installed in a flow path between the second hydraulic pump and the arm cylinder and shifted in response to the control signal generated from the second manipulation lever to control a start, a stop, and a direction change of the arm cylinder;   an electrical proportional pressure control valve configured to generate a secondary control signal indicative of a signal pressure in proportional to an electric control signal applied thereto from the outside;   a shuttle valve connected at input portions thereof to the electrical proportional pressure control valve and the first manipulation lever, respectively, and connected at an output portion thereof to the boom-driving switching valve; and   an electronic controller configured to detect and calculate a control signal that is generated from the second manipulation lever in accordance with the manipulation of the second manipulation lever, control the discharge flow rate of the second hydraulic pump based on the calculated control signal value, and control the discharge flow rate of the first hydraulic pump by shifting the boom-driving switching valve through the shuttle valve using the secondary control signal that is generated from the electrical proportional pressure control valve in proportional to the calculated control signal value, in the case where a control signal in accordance with selection of the leveling work is applied to the electronic controller from the working mode selection switch.       
 
         [0025]    In the hydraulic system for construction equipment, the arm-driving switching valve and the boom-driving switching valve may be shifted by an electric joystick connected to the electronic controller. 
         [0026]    In the hydraulic system for construction equipment, the arm-driving switching valve and the boom-driving switching valve may be shifted by the electrical proportional pressure control valve that generates the secondary control signal in proportion to the electric control signal outputted from the electric joystick connected to the electronic controller. 
       Advantageous Effect 
       [0027]    The hydraulic system according to the embodiment of the present invention as constructed above has the following advantage. 
         [0028]    The geometrical position of work apparatuses such as a boom and an arm is controlled by manipulation of one manipulation lever to conveniently perform a leveling work using an excavator, thereby shortening the work time and thus improving the work efficiency of construction equipment. 
     
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
         [0029]    The above objects, other features and advantages of the present invention will become more apparent by describing the preferred embodiments thereof with reference to the accompanying drawings, in which: 
           [0030]      FIG. 1  is a schematic block diagram showing a hydraulic system for construction equipment in accordance with the prior art; and 
           [0031]      FIG. 2  is a schematic block diagram showing a hydraulic system for construction equipment in accordance with an embodiment of the present invention; 
       
    
    
     EXPLANATION ON REFERENCE NUMERALS OF MAIN ELEMENTS IN THE DRAWINGS 
       [0000]    
       
           11 : first variable displacement hydraulic pump 
           12 : second variable displacement hydraulic pump 
           13 : boom cylinder 
           14 : first manipulation lever 
           15 : boom-driving switching valve 
           16 : arm cylinder 
           17 : second manipulation lever 
           18 : arm-driving switching valve 
           19 : electronic controller (V-ECU) 
           20 : working mode selection switch 
           21 : hydraulic pump 
           22 : electrical proportional pressure control valve 
           23 : shuttle valve 
       
     
       PREFERRED EMBODIMENTS OF THE INVENTION 
       [0045]    Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The matters defined in the description, such as the detailed construction and elements, are nothing but specific details provided to assist those of ordinary skill in the art in a comprehensive understanding of the invention, and the present invention is not limited to the embodiments disclosed hereinafter. 
         [0046]    As shown in  FIG. 2 , the hydraulic system for construction equipment according to an embodiment of the present invention includes:
       first and second variable displacement hydraulic pumps (hereinafter, referred to as “first and second hydraulic pumps”)  11  and  12 ;   first and second manipulation levers (for example, hydraulic joysticks are used)  14  and  17  configured to generate control signals in proportion to an operator&#39;s manipulation amounts, respectively;   a working mode selection switch  20  configured to select a leveling work;   a boom cylinder  13  connected to the first hydraulic pump  11 ;   a boom-driving switching valve  15  installed in a flow path between the first hydraulic pump  11  and the boom cylinder  13  and shifted in response to the control signal generated from the first manipulation lever  14  to control a start, a stop, and a direction change of the boom cylinder  13 ;   an arm cylinder  16  connected to the second hydraulic pump  12 ;   an arm-driving switching valve  18  installed in a flow path between the second hydraulic pump  12  and the arm cylinder  16  and shifted in response to the control signal generated from the second manipulation lever  17  to control a start, a stop, and a direction change of the arm cylinder  16 ;   an electrical proportional pressure control valve  22  configured to generate a secondary control signal (referring to signal pressure) in proportional to an electric control signal applied thereto from the outside;   a shuttle valve  23  connected at input portions thereof to the electrical proportional pressure control valve  22  and the first manipulation lever  14 , respectively, and connected at an output portion thereof to the boom-driving switching valve  15 ; and   an electronic controller (V-ECU)  19  configured to detect and calculate a control signal that is generated from the second manipulation lever in accordance with the manipulation of the second manipulation lever  17 , control the discharge flow rate of the second hydraulic pump  12  based on the calculated control signal value, and control the discharge flow rate of the first hydraulic pump  1  by shifting the boom-driving switching valve through the shuttle valve using the secondary control signal that is generated from the electrical proportional pressure control valve  22  in proportional to the calculated control signal value, in the case where a control signal in accordance with selection of the leveling work is applied to the electronic controller from the working mode selection switch  20 .       
 
         [0057]    In drawings, a non-explained reference numeral  21  denotes a fixed displacement hydraulic pump that discharges a pilot signal pressure, which is in turn supplied to the boom-driving switching valve  15  and the arm-driving switching valve  18 , to shift the boom-driving switching valve  15  and the arm-driving switching valve  18  when the first and second manipulation levers  14  and  17  are manipulated. 
         [0058]    The use example of the hydraulic system for construction equipment according to an embodiment of the present invention will be described hereinafter in detail with reference to the accompanying drawings. 
         [0059]    As shown in  FIG. 2 , a spool of the boom-driving switching valve  15  is shifted in response to a control signal that is generated from the first manipulation lever in accordance with the manipulation of the first manipulation lever  14 , so that the boom cylinder  13  can be driven by a hydraulic fluid supplied thereto from the first hydraulic pump  11 . In this case, the hydraulic fluid returning from the boom cylinder  13  is moved to a hydraulic tank T via the boom-driving switching valve  15 . 
         [0060]    In addition, a spool of the arm-driving switching valve  18  is shifted in response to a control signal that is generated from the second manipulation lever in accordance with the manipulation of the first manipulation lever  17 , so that the arm cylinder  16  can be driven by a hydraulic fluid supplied thereto from the second hydraulic pump  12 . In this case, the hydraulic fluid returning from the arm cylinder  16  is moved to the hydraulic tank T via the arm-driving switching valve  18 . 
         [0061]    In the meantime, the spools of the arm-driving switching valve  18  and the boom-driving switching valve  15  are shifted simultaneously by manipulation of the second manipulation lever  17 , so that the discharge flow rates of the first and second hydraulic pumps  11  and  12  can be controlled to conveniently perform the leveling work using the work apparatuses such as the boom and arm. 
         [0062]    That is, when an operator manipulates the working mode selection switch  20 , a control signal from the working mode selection switch  20  is applied to the electronic controller  19  to perform the leveling work using an excavator. At this time, the electronic controller  19  recognizes that the work mode is converted to a leveling work mode. 
         [0063]    The spool of the arm-driving switching valve  18  is shifted in response to the control signal generated from the second manipulation lever  17  in accordance with the manipulation of the second manipulation lever  17  to cause the hydraulic fluid from the second hydraulic pump  12  to be supplied to the arm cylinder  16 . In this case, the electronic controller  19  detects and calculates the control signal from generated from the second manipulation lever  17  in accordance with the manipulation of the second manipulation lever  17 . The electronic controller  19  controls the discharge flow rate of the hydraulic fluid, which is to be supplied to the arm cylinder  16  from the second hydraulic pump  12  based on the calculated control signal value. At the same time, the electrical proportional pressure control valve  22  generates a secondary control signal in proportional to an electric control signal applied thereto from the electronic controller  19  based on the calculated control signal 
         [0064]    Meanwhile, the electronic controller  19  controls the discharge flow rate of the hydraulic fluid, which is to be supplied to the boom cylinder  13  from the first hydraulic pump  11  by controlling the shift of a spool of the boom-driving switching valve  15  through the shuttle valve  23  using the secondary control signal generated from the electrical proportional pressure control valve  22 . 
         [0065]    Thus, the spool of the arm-driving switching valve  18  is shifted in response to the control signal generated from the second manipulation lever  17  in accordance with the manipulation of the second manipulation lever  17  so that the flow rate of the hydraulic fluid supplied to the arm cylinder  16  from the second hydraulic pump  12  can be controlled. At this time, the electronic controller  19  detects and calculates the control signal from generated from the second manipulation lever  17  in accordance with the manipulation of the second manipulation lever  17 , and generates an electric control signal in response to the calculated control signal value for application to the electrical proportional pressure control valve  22 . 
         [0066]    The spool of the boom-driving switching valve  15  is shifted in response to a secondary control signal generated from the electrical proportional pressure control valve  22  in proportional to the electric control signal applied to the electrical proportional pressure control valve  22  so that the flow rate of the hydraulic fluid supplied to the boom cylinder  13  from the first hydraulic pump  11  can be controlled. 
         [0067]    As such, the spools of the arm-driving switching valve  18  and the boom-driving switching valve  15  are shifted simultaneously by manipulation of a single second manipulation lever  17 , so that the arm cylinder  16  and the boom cylinder  13  can be driven to conveniently perform the leveling work. 
         [0068]    Meanwhile, although not shown in the drawing, the arm cylinder may be connected to the first hydraulic pump  11  and the boom cylinder is connected to the second hydraulic pump  12  to cause a boom-driving switching valve (i.e., control valve denoted by reference numeral  18 ) to be shifted by manipulation of the second manipulation lever  17  so that the flow rate of the hydraulic fluid supplied to the boom cylinder from the second hydraulic pump  12  can be controlled. At the same time, the electronic controller  19  detects and calculates a control signal from generated from the second manipulation lever  17  in accordance with the manipulation of the second manipulation lever  17 , and the electrical proportional pressure control valve  22  generates a secondary control signal in proportional to an electric control signal applied thereto from the electronic controller  19  in response to the calculated control signal outputted from the electronic controller  19 . An arm-driving switching valve (i.e., control valve denoted by reference numeral  15 ) to be shifted in response to the secondary control signal generated from the electrical proportional pressure control valve  22  through the operation of the shuttle valve  23  so that the flow rate of the hydraulic fluid supplied to the arm cylinder from the first hydraulic pump  11  can be controlled. 
         [0069]    Although not shown in the drawing, it is of course to be noted that the arm-driving switching valve  18  and the boom-driving switching valve  15  may be shifted by electric joysticks connected to the electronic controller  19 . 
         [0070]    Also, although not shown in the drawing, it is of course to be noted that the arm-driving switching valve  18  and the boom-driving switching valve  15  may be shifted by the electrical proportional pressure control valve  22  that generates the secondary control signal in proportion to the electric control signal outputted from the electric joysticks connected to the electronic controller  19 . 
       INDUSTRIAL APPLICABILITY 
       [0071]    According to the hydraulic system for construction equipment of the present invention as constructed above, in the case where the leveling work is performed using an excavator, the arm-driving switching valve is shifted by manipulation of an arm manipulation lever to drive an work apparatus such as an arm, and simultaneously the boom-driving switching valve is shifted, so that a leveling work is conveniently performed, thereby shortening the work time and thus improving the work efficiency of construction equipment.