Patent Publication Number: US-8113233-B2

Title: Hydraulic circuit of option device for excavator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority from Korean Patent Application No. 10-2006-82265, filed on Aug. 29, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hydraulic circuit of an option device for an excavator which can operate an option device such as a breaker, a hammer, a shear, and so forth, mounted on an excavator. 
     More particularly, the present invention relates to a hydraulic circuit of an option device for an excavator, which can constantly supply hydraulic fluid fed from a hydraulic pump to the option device irrespective of the size of load occurring when the option device operates, and can control respective flow rates required for various kinds of option devices. 
     2. Description of the Prior Art 
     As illustrated in  FIGS. 1 and 2 , a conventional hydraulic circuit of an option device for an excavator includes variable displacement hydraulic pump  26 ; an option device  24  (e.g., a breaker and so on) connected to the hydraulic pump  26 ; a first spool  15  installed in a flow path between the hydraulic pump  26  and the option device  24  and shifted to control hydraulic fluid being supplied to the option device  24  through an option port  22  in response to a pilot signal pressure Pi applied thereto; a poppet  14  installed in a flow path between the hydraulic pump  26  and the first spool  15  to control hydraulic fluid fed from the hydraulic pump  26  to the option device  24  when the first spool  15  is shifted; a piston  13  elastically supported in a back pressure chamber  17  of the poppet  14 ; and a second spool  3  shifted to control hydraulic fluid fed from the hydraulic pump  26  to the back pressure chamber  17  of the poppet  14  through a flow path  23  connected to the back pressure chamber  17 , in response to a difference between a pressure of an inlet part of the first spool and a sum of a pressure of an outlet part of the first spool  15  and an elastic force of a valve spring  5 . 
     The conventional hydraulic circuit of an option device for an excavator further includes a first orifice  13   a  formed in the piston  13  and controlling hydraulic fluid fed from the hydraulic pump  26  to the back pressure chamber  17  of the poppet  14  when the second spool  3  is shifted; a second orifice  30  formed in a flow path  23  between the second spool  3  and a back pressure chamber  29  of the piston  13 , and controlling hydraulic fluid fed from the hydraulic pump  26  to the back pressure chamber  29  when the second spool  3  is shifted; and a third orifice  31  installed in a flow path  16  having an inlet part connected to a flow path between the first spool  15  and the poppet  14  and an outlet part connected to the second spool  3 , and controlling hydraulic fluid which is fed from the hydraulic pump  26  to shift the second spool  3 . 
     In the drawing, reference numeral  19  denotes a pilot flow path connected to a supply line  20  of the hydraulic pump  26  to receive a signal pressure for shifting the second spool  3 . 
     Hereinafter, the operation of the conventional hydraulic circuit of an option device will be described. 
     As shown in  FIGS. 1 and 2 , the hydraulic fluid fed from the hydraulic pump  26  is supplied to the supply line  20  and the pilot flow path  19 . The hydraulic fluid fed to the supply line  20  pushes the poppet  14  upward as shown in the drawing. 
     The hydraulic fluid fed to the back pressure chamber  17  of the poppet  14  is supplied to a chamber  21  through an orifice  14   a  of the poppet  14 , and thus the poppet  14  is moved upward to be in contact with the piston  13  (in this case, the elastic member  12  is compressed). Accordingly, the hydraulic fluid on the supply line  20  is supplied to the chamber  21 . 
     When the pilot signal pressure Pi is applied to a left port of the first spool  15 , the first spool  15  is shifted in the right direction. The hydraulic fluid fed to the chamber  21  is supplied to the option device  24  through the option port  22  to drive the option device  24 . 
     In this case, when the chamber  21  and the option port  22  are connected together by the shifting of the first spool  15  and the hydraulic fluid is supplied to the option device  24 , a loss in pressure occurs between a pressure before the hydraulic fluid passes through the second spool  3  and a pressure after the hydraulic fluid passes through the second spool  3 . 
     As illustrated in  FIG. 1 , the pressure, which is increased due to the shifting of the first spool  15 , is supplied to a left end of the second spool  3  along the flow path  16  connected to the chamber  21 . When the hydraulic fluid is supplied to the second spool  3  after passing through the third orifice  31  formed at an end part of the flow path  16 , the second spool  3  is shifted in the right direction as shown in the drawing ( FIG. 2  illustrates the second spool  3  that is shifted in the left direction). In this case, if it is assumed that the cross-sectional area of a diaphragm of the second spool is A1, a force that shifts the second spool  3  in the right direction is (A1×P1). 
     The pressure in the option port  22  is applied to a right end of the second spool  3  after passing through the pilot flow path  18 . Accordingly, the second spool  3  is shifted in the left direction as shown in the drawing ( FIG. 2  illustrates the second spool  3  that is shifted in the right direction). In this case, if it is assumed that the cross-sectional area of the diaphragm of the second spool is A2, a force that shifts the second spool  3  in the left direction is (A2×P2)+F1 (which corresponds to the elastic force of the valve spring  5 ). 
     That is, the condition that the second spool  3  is kept in its initial state (which corresponds to the state as illustrated in the drawing) is given as (A1×P1)&lt;((A2×P2)+F1), and the condition that the second spool  3  is shifted in the right direction is given as (A1×P1)&gt;((A2×P2)+F1). 
     In the case of shifting the second spool  3  in the right direction as shown in  FIG. 1 , the hydraulic fluid is supplied to a left end of the second spool  3  through the flow path  16 , and the second spool  3  is shifted in the right direction. The hydraulic fluid fed to the pilot flow path  19  is supplied to the back pressure chamber  29  of the piston  13  after passing through the second spool  3 , and a through flow path  23  in order, and thus the piston is moved downward as shown in the drawing. Simultaneously, the poppet  14  elastically installed by the elastic member  12  is moved downward. 
     The flow path between the supply line  20  and the chamber  21  is blocked by the poppet  14 . AS the pressure in the flow path  16  is reduced, the second spool  3  is moved in the left direction as shown in  FIG. 1 . This corresponds to the state given as (A1×P1)&lt;((A2×P2)+F1). 
     When the second spool  3  is shifted in the left direction as shown in the drawing, the supply of the pressure in the pilot flow path  19  to the through flow path  23  is intercepted. As the poppet  14  is moved upward as shown in the drawing, the hydraulic fluid fed from the hydraulic pump  26  is supplied to the second spool  3  via the chamber  21  and the flow path  16 . This corresponds to the state given as (A1×P1)&gt;((A2×P2)+F1). Accordingly, the second spool  3  is shifted in the right direction as shown in the drawing. 
     As illustrated in  FIGS. 4A and 4B , a loss in pressure occurring between the signal pressures for shifting the second spool  3  becomes constant due to the repeated shifting of the second spool  3 . 
     That is, it is known that the flow rate Q of the hydraulic fluid being supplied to the option device  24  is Q=(Cd×A×ΔP). Here, Q denotes the flow rate, Cd denotes a flow rate coefficient, A denotes an opening area of a spool (A=constant), and ΔP denotes a loss in pressure between P1 and P2 (ΔP=constant). 
     As described above, in the conventional hydraulic control valve structure of an option device, the hydraulic fluid fed from the hydraulic pump  26  can be constantly supplied to the option device  24  irrespective of the size of a load occurring in the option device  24 . 
     By contrast, as shown in  FIG. 3 , the flow rate of the hydraulic fluid being supplied to the option device is overshot (indicated as “a” in the drawing) in an initial control period of the option device, and then is stabilized with the lapse of a predetermined time. This may cause an abnormal operation of the option device in the initial operation period of the option device to lower the stability of the option device. 
     In addition, option devices have different specifications depending on their manufacturers. Although the flow rate and pressure required for the option devices may differ, the flow rate of the hydraulic fluid being supplied to various kinds of option devices is not controlled, but the same flow rate is always applied thereto. 
     Accordingly, even an operator having wide experience in operation cannot efficiently manipulate the option devices to lower the workability. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art while advantages achieved by the prior art are maintained intact. 
     One object of the present invention is to provide a hydraulic circuit of an option device for an excavator, which can constantly supply hydraulic fluid to the option device, irrespective of the size of a load occurring in the option device, to improve the manipulation, and can control respective flow rates required for various kinds of option devices. 
     In an embodiment of the present invention, the hydraulic circuit can prevent the flow rate from being overshot in an initial control period of the option device, and thus the stability of the option device can be secured. 
     In order to accomplish these objects, there is provided a hydraulic circuit of an option device for an excavator, according to one aspect of the present invention, which includes a variable hydraulic pump; an option device connected to the hydraulic pump; a first spool installed in a flow path between the hydraulic pump and the option device and shifted to control hydraulic fluid fed from the hydraulic pump to the option device; a poppet installed to open/close a flow path between the hydraulic pump and the first spool and controlling hydraulic fluid fed from the hydraulic pump to the option device when the first spool is shifted, and a piston elastically supported in a back pressure chamber of the poppet; an option spool installed in a flow path between the first spool and the option device and shifted to control hydraulic fluid fed to the option device via the first spool; a second spool shifted to control hydraulic fluid fed from the hydraulic pump to the back pressure chamber of the poppet via a through flow path connected to the back pressure chamber of the poppet, in response to a difference between a pressure of an inlet part of the first spool and a sum of a pressure of an outlet part of the first spool and an elastic force of a valve spring; and a control means installed inside the poppet and controlling hydraulic fluid passing through an orifice of the poppet when the piston and the poppet are pressed by the hydraulic fluid fed from the hydraulic pump, through the shifting of the second spool; wherein in an initial control period of the option device, the flow rate of the hydraulic fluid fed from the back chamber of the poppet to the option device through the shifting of the second poppet is prevented from being increased over a predetermined flow rate set by the control means. 
     The control means may include a shim placed in an inlet part of the orifice of the poppet and having a through hole formed in the center thereof to be connected to the orifice of the poppet, and a check valve installed inside the orifice of the poppet and having an orifice formed in the center thereof. 
     The hydraulic circuit of an option device for an excavator may further include a first orifice formed in the piston and controlling the hydraulic fluid fed from the hydraulic pump to the back pressure chamber of the poppet when the second spool is shifted; a second orifice formed in a flow path between the second spool and the back pressure chamber of the piston and controlling the hydraulic fluid fed from the hydraulic pump to the back pressure chamber of the piston when the second spool is shifted; and a third orifice installed in a flow path having an inlet part connected to a flow path between the first spool and the poppet and an outlet part connected to the second spool, and controlling the hydraulic fluid fed from the hydraulic pump to shift the second spool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a sectional view of a conventional hydraulic circuit of an option device for an excavator; 
         FIG. 2  is a hydraulic circuit diagram of a conventional option device for an excavator; 
         FIG. 3  is a graph showing the control flow rate that is overshot in an initial control period of the conventional option device for an excavator; 
         FIGS. 4A and 4B  are graphs showing the flow rate change against pressure in the hydraulic circuit of an option device for an excavator; 
         FIG. 5  is a sectional view of main parts extracted from a hydraulic circuit of an option device for an excavator according to an embodiment of the present invention; 
         FIG. 6  is a sectional view of a flow rate control valve in a hydraulic circuit of an option device for an excavator according to an embodiment of the present invention; and 
         FIG. 7  is a hydraulic circuit diagram of an option device for an excavator according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described 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 thus the present invention is not limited thereto. 
     As shown in  FIGS. 5 to 7 , a hydraulic circuit of an option device for an excavator according to an embodiment of the present invention includes a variable hydraulic pump  26 ; an option device  24  (e.g., a hammer, a shear, a breaker, and so forth) connected to the hydraulic pump  26 ; a first spool  15  installed in a flow path between the hydraulic pump  26  and the option device  24  and shifted to control hydraulic fluid being supplied from the hydraulic pump  26  to the option device  24  in response to a pilot signal pressure Pi applied thereto; a poppet  14  installed to open/close a flow path  20  between the hydraulic pump  26  and the first spool  15  and controlling hydraulic fluid fed from the hydraulic pump  26  to the option device  24  when the first spool  15  is shifted, and a piston  13  elastically supported by an elastic member  12  (e.g., a compression coil spring) in a back pressure chamber  17  of the poppet  14 ; an option spool  25  installed in a flow path  22  between the first spool  15  and the option device  24  and shifted to control hydraulic fluid fed to the option device  24  via the first spool  15  in response to pilot signal pressures  5   pa   4  and  5   pb   4 ; a second spool  3  shifted to control hydraulic fluid fed from the hydraulic pump  26  to the back pressure chamber  17  of the poppet  14  via a through flow path  23  connected to the back pressure chamber  17  of the poppet  14 , in response to a difference between a pressure of an inlet part of the first spool  15  and a sum of a pressure of an outlet part of the first spool  15  and an elastic force of a valve spring  5 ; and a control means installed inside the poppet  14  and controlling hydraulic fluid passing through an orifice  14   a  of the poppet  14  when the piston  13  and the poppet  14  are pressed by the hydraulic fluid fed from the hydraulic pump  26 , through the shifting of the second spool  3 . 
     The control means includes a shim  14   c  placed on an inlet part of the orifice  14   a  of the poppet and having a through hole  14 - 3  formed in the center thereof to be connected to the orifice  14   a  of the poppet  14 , and a check valve  14   b  installed inside the orifice  14   a  of the poppet  14  and having an orifice  14 - 2  formed in the center thereof. 
     The hydraulic circuit of an option device for an excavator according to an embodiment of the present invention further includes a first orifice  13   a  formed in the piston  13  and controlling the hydraulic fluid fed from the hydraulic pump  26  to the back pressure chamber  17  of the poppet  14  when the second spool  3  is shifted; a second orifice  30  formed in a flow path  23  between the second spool  3  and a back pressure chamber  29  of the piston  13  and controlling the hydraulic fluid fed from the hydraulic pump  26  to the back pressure chamber  29  of the piston  13  when the second spool  3  is shifted; and a third orifice  31  installed in a flow path  16  having an inlet part connected to a flow path between the first spool  15  and the poppet  14  and an outlet part connected to the second spool  3 , and controlling the hydraulic fluid fed from the hydraulic pump  26  to shift the second spool  3 . 
     In the whole description of the present invention, the same drawing reference numerals as illustrated in  FIG. 1  are used for the same elements across various figures, and the detailed description thereof will be omitted. 
     Hereinafter, the operation of the hydraulic circuit of an option device for an excavator according to an embodiment of the present invention will be described with reference to the accompanying drawings. 
     As shown in  FIG. 7 , the hydraulic fluid fed from the hydraulic pump  26  is supplied to the supply line  20  and the pilot flow path  19 . The hydraulic fluid fed to the supply line  20  pushes the poppet  14  upward as shown in the drawing. Simultaneously, the hydraulic fluid pushes the check valve  14   b  installed inside the orifice  14   a  of the poppet  14  upward, and moves the check valve up to the position of the shim  14   c.    
     In this case, the hydraulic fluid fed to the back pressure chamber  17  of the poppet  14  is supplied to a chamber  21  through an orifice  14 - 2  of the check valve  14   b  installed inside the poppet  14 . Accordingly, the poppet  14  is moved upward to be in contact with the piston  13  (in this case, the elastic member  12  is compressed). 
     Accordingly, the hydraulic fluid on the supply line  20  is supplied to the chamber  21 . At this time, the hydraulic fluid moved to the chamber  21  is intercepted by the first spool  15  that is kept in a neutral state, and thus is not supplied to the option device  24 . 
     When the pilot signal pressure  5   pa   4  is applied to the option spool  25 , its inner spool is shifted in the left direction as shown in  FIG. 7 . Accordingly, the hydraulic fluid fed from the hydraulic pump  26  to the flow path  20 - 1  is intercepted by the shifted option spool  25 , and the hydraulic fluid fed from the hydraulic pump  26  to the flow path  22  is supplied to the option device  24  via a flow path  5 A 4 . 
     As shown in  FIG. 6 , in the case where the pilot signal pressure Pi is applied to the left port of the first spool  15 , the first spool  15  is shifted in the right direction (while in  FIG. 7 , the first spool  15  is shifted in the left direction). The hydraulic fluid fed into the chamber  21  is supplied to the option device  24  via the option port  22 , and thus the option device is driven. 
     That is, when the first spool  15  is shifted by the pilot signal pressure Pi, the cross-sectional area of a variable notch part  27  formed on the first spool  15  is varied depending on the movement of the first spool  15 . Accordingly, the flow rate of the hydraulic fluid fed to the option device  24  through the first spool  15  can be controlled. 
     As shown in  FIG. 6 , when the hydraulic fluid fed from the hydraulic pump  26  is supplied to the option spool  25  via the first spool  15 , a loss in pressure occurs between the chamber  21  and the option port  22  by the variable notch part  27  formed on the periphery of the first spool  15 . In this case, if the flow rate of the hydraulic fluid fed from the chamber  21  to the option port  22  through the shifting of the first spool  15  is increased, the pressure loss is also increased. 
     At this time, the hydraulic fluid having the pressure that is increased through the shifting of the first spool  15  is supplied to the left end of the second spool  3  after passing through the third orifice  31  of the flow path  16  connected to the chamber  21 . Accordingly, the second spool  3  is shifted in the right direction as shown in the drawing (while in  FIG. 7 , the second spool  3  is shifted in the left direction). 
     In this case, if it is assumed that the cross-sectional area of a diaphragm of the second spool is A1, a force that shifts the second spool  3  in the right direction is (A1×P1). 
     The pressure in the option port  22  is applied to the right end of the second spool  3  after passing through the pilot flow path  18 . Accordingly, the second spool  3  is shifted in the left direction as shown in  FIG. 6  (while, in  FIG. 7 , the second spool  3  is shifted in the right direction). In this case, if it is assumed that the cross-sectional area of the diaphragm of the second spool  3  is A2, a force that shifts the second spool  3  in the left direction is (A2×P2)+F1 (which corresponds to the elastic force of the valve spring  5 ). 
     The condition that the second spool  3  is kept in its initial state, i.e., in its non-shifted state, (which corresponds to the state as shown in  FIG. 6 ) is given as (A1×P1)&lt;((A2×P2)+F1). 
     By contrast, the condition that the second spool  3  is shifted in the right direction as shown in  FIG. 6  is given as (A1×P1)&gt;((A2×P2)+F1). 
     In the case of shifting the second spool  3  in the right direction as shown in  FIG. 6 , the hydraulic fluid fed to the pilot flow path  19  connected to the supply line  20  is supplied to the back pressure chamber  29  of the piston  13  after passing through the second spool  3  and a through flow path  23  in order. Accordingly, the piston  13  is moved downward as shown in the drawing. Simultaneously, the poppet  14  elastically supported by the elastic member  12  is moved downward. 
     At this time, if the second spool  3  is shifted and the piston  13  is pressed by the hydraulic fluid fed from the hydraulic pump  26 , the flow rate of the hydraulic fluid passing through the orifice  14   a  of the poppet  14  can be reduced by the shim  14   c  and the check valve  14   b  installed in the poppet  14 . 
     That is, the hydraulic fluid fed from the back pressure chamber  17  passes in order through a through hole  14 - 3  formed on the shim  14   c  placed in the inlet part of the orifice  14   a  of the poppet  14  and an orifice  14 - 2  formed on the check valve  14   b  installed inside the orifice  14   a  of the poppet  14 . 
     Accordingly, at an initial operation of the option device  24 , the time when the hydraulic fluid fed from the back pressure chamber  17  passes through the orifice  14   a  of the poppet  14  and the flow rate of the hydraulic fluid passing through the orifice  14   a  can be reduced. 
     By the movement of the poppet  14 , the flow path between the supply line  20  and the chamber  21  is blocked. AS the pressure in the flow path  16  is reduced, the second spool  3  is moved in the left direction as shown in  FIG. 6 . This corresponds to the condition given as (A1×P1)&lt;((A2×P2)+F1). 
     When the second spool  3  is shifted in the left direction as shown in the drawing, the supply of the pressure in the pilot flow path  19  to the through flow path  23  is intercepted. Accordingly, as the poppet  14  is moved upward as shown in the drawing, the hydraulic fluid fed from the hydraulic pump  26  is supplied to the left end of the second spool  3  via the supply line  20 , the chamber  21  and the flow path  16 . 
     This is, the condition that the second spool  3  is shifted in the right direction as shown in the drawing is given as (A1×P1)&gt;((A2×P2)+F1). Accordingly, the second spool  3  is shifted in the right direction as shown in the drawing. 
     Accordingly, as the repeated shifting of the second spool  3  is performed, the loss in pressure occurring between the chamber  21  and the option port  22  becomes constant. 
     As illustrated in  FIGS. 4A and 4B , it is known that the flow rate Q of the hydraulic fluid being supplied to the option device  24  is Q=(Cd×A×ΔP). Here, Q denotes the flow rate, Cd denotes a flow rate coefficient, A denotes an opening area of a spool (A=constant), and ΔP denotes a loss in pressure between P1 and P2 (ΔP=constant). 
     As described above, when an excavator having option devices mounted thereon operates, the hydraulic fluid fed from the hydraulic pump  26  can be constantly supplied to the option device  24 , irrespective of the size of a load occurring in the option device  24 . Also, the flow rates required for various kinds of option devices can be respectively controlled. In addition, the flow rate of the hydraulic fluid being supplied to the option device  24  in an initial control period of the option device can be prevented from being overshot over the predetermined flow rate. 
     From the foregoing, it will be apparent that the hydraulic circuit of an option device for an excavator according to an embodiment of the present invention has the following advantages. 
     The hydraulic circuit can constantly supply the hydraulic fluid to the option device, irrespective of the size of a load of the option device, and thus the operation speed of the option device is kept constant to improve the manipulation. Also, the hydraulic circuit can respectively control the flow rates required for various kinds of option devices. 
     The hydraulic circuit can prevent the flow rate from being overshot in an initial control period of the option device, and thus the stability of the option device can be secured. 
     Although preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.