Abstract:
A pressure control valve for heavy equipment. The pressure control valve can smoothly operate a working device having a high load pressure by limiting a supply of hydraulic fluid to a working device having a low load pressure in the case of simultaneously operating a plurality of working devices in a hydraulic circuit in which a plurality of control valves (e.g., a boom control valve and a bucket control valve) are connected in parallel to a single hydraulic pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority from Korean Patent Application No. 10-2006-0094810, filed on Sep. 28, 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 pressure control device for heavy equipment which can distribute and supply hydraulic fluid fed from a hydraulic pump to a plurality of working devices having different load pressures, such as a boom and a bucket, in the case of simultaneously operating the working devices having different operating pressures using a single hydraulic pump. 
     More particularly, the present invention relates to a pressure control valve for heavy equipment which can smoothly operate a working device having a high load pressure by limiting a supply of hydraulic fluid to a working device having a low load pressure in the case of simultaneously operating a plurality of working devices in a hydraulic circuit in which a plurality of control valves (e.g., a boom control valve and a bucket control valve) are connected in parallel to a single hydraulic pump. 
     2. Description of the Prior Art 
     Generally, in the case of simultaneously operating a plurality of working devices (e.g., a boom and a bucket) in a hydraulic circuit in which a plurality of control valves for the working devices are connected in parallel to a single hydraulic pump, the flow rate of hydraulic fluid being supplied from the hydraulic pump to the bucket having a low load pressure becomes lower than the flow rate of hydraulic fluid being supplied to the boom having a relatively high load pressure. Since this makes it impossible to operate the boom smoothly, the flow rate of the hydraulic fluid being supplied to the bucket is compulsorily adjusted. 
     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 pressure control device for heavy equipment that can smoothly operate a plurality of working devices having different operating pressures in the case of simultaneously operating the working devices connected in parallel to a single hydraulic pump. 
     In order to accomplish the object, there is provided a pressure control device for heavy equipment, according to one aspect of the present invention, which includes a valve body having an input port, an output port, and a drain port, formed thereon; a spool, slidably installed in the valve body, for being shifted to connect the input port to the output port in response to a pressure obtained by adding an elastic force of a valve spring to a pressure being applied from the input port to a diaphragm of a first piston that is elastically supported in a first back chamber, and being shifted to disconnect the input port from the output port in response to a pressure being applied from the output port to a diaphragm of a second piston installed in a second back chamber; and a signal pressure port for applying a signal pressure to a diaphragm of the spool located in a third back chamber formed in the valve body, disconnecting the input port from the output port by shifting the spool in response to the pressure in the second back chamber and the signal pressure, and returning the pressure in the output port to the drain port; wherein the spool is shifted, corresponding to the signal pressure applied from an outside to the third back chamber, to control the operating pressure being applied from the input port to the output port. 
     The pressure control device for heavy equipment according to one aspect of the present invention may further includes a first land part, formed on a periphery of the spool, for connecting the input port to the output port; a first passage, formed through the spool, for connecting the first land part to the first back chamber and supplying the hydraulic fluid fed from the input port to the first back chamber; a second land part, formed on the periphery of the spool, for connecting to the drain port; and a second passage for supplying the hydraulic fluid fed from the input port to the second back chamber, and connecting the output port to the drain port when the spool is shifted. 
     In another aspect of the present invention, there is provided a pressure control device for heavy equipment, according to one aspect of the present invention, which includes a valve body having an input port, an output port, and a drain port, formed thereon; a spool, slidably installed in the valve body, for being shifted to connect the input port to the output port in response to a pressure obtained by adding an elastic force of a valve spring to a pressure being applied from the input port to a diaphragm of a first piston that is elastically supported in a first back chamber, and being shifted to disconnect the input port from the output port in response to a pressure being applied from the output port to a diaphragm located on an outer surface of the spool; and a signal pressure port for applying a signal pressure to a diaphragm of the spool located in a third back chamber formed on the valve body, disconnecting the input port from the output port by shifting the spool in response to a pressure acting upon the diaphragm located on the outer surface of the spool and the signal pressure, and returning the pressure in the output port to the drain port; wherein the spool is shifted, corresponding to the signal pressure applied from an outside to the third back chamber, to control the operating pressure being applied from the input port to the output port. 
    
    
     
       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 pressure control device for heavy equipment according to an embodiment of the present invention; 
         FIG. 2  is a hydraulic circuit diagram of the control device illustrated in  FIG. 1 ; 
         FIG. 3  is a view explaining the characteristic of a pressure control valve in the control device illustrated in  FIG. 1 ; 
         FIG. 4  is a sectional view of a pressure control device for heavy equipment according to another embodiment of the present invention; and 
         FIG. 5  is a sectional view of a pressure control device shown in  FIG. 1 , when the spool is shifted by the signal pressure. 
     
    
    
     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. 1 to 3 , a pressure control device for heavy equipment according to an embodiment of the present invention includes a valve body  5  having an input port  1 , an output port  2 , and a drain port  3 , formed thereon; a spool  13 , slidably installed in the valve body  5 , for being shifted to connect the input port  1  to the output port  2  in response to a pressure obtained by adding an elastic force of a valve spring  9  to a pressure P 1  being applied from the input port  1  to a fluid pressure receiving portion D 1  of a first piston  7  that is elastically supported in a first back chamber  6 , and being shifted to disconnect the input port  1  from the output port  2  in response to a pressure P 2  being applied from the output port  2  to a fluid pressure receiving portion D 2  of a second piston  11  installed in a second back chamber  10 ; and a signal pressure port  4  for applying a signal pressure P 3  to a fluid pressure receiving portion D 3  of the spool  13  located in a third back chamber  14  formed on the valve body  5 , disconnecting the input port  1  from the output port  2  by shifting the spool  13  in response to the pressure P 2  in the second back chamber  10  and the signal pressure P 3 , and returning the pressure P 2  in the output port  2  to the drain port  3 . The spool  13  is shifted, corresponding to the signal pressure P 3  applied from an outside to the third back chamber  14 , to control the operating pressure being applied from the input port  1  to the output port  2 . 
     The pressure control device for heavy equipment according to one aspect of the present invention may further includes a first ring-shaped annular notch  15 , formed on a periphery of the spool  13 , for connecting the input port  1  to the output port  2 ; a first passage  16 , formed through the spool  13 , for connecting the first annular notch  15  to the first back chamber  6  and supplying the hydraulic fluid fed from the input port  1  to the first back chamber  6 , a second ring-shaped annular notch  17 , formed on the periphery of the spool  13 , for connecting to the drain port  3  when the spool  13  is shifted, corresponding to the signal pressure P 3  applied to the third back chamber  14 ; and a second passage  18  for supplying the hydraulic fluid fed from the input port  1  to the second back chamber  10 , and connecting the output port  2  to the drain port  3  when the spool  13  is shifted, corresponding to the signal pressure P 3  applied to the third back chamber  14 . 
     Hereinafter, the operation of the pressure control device for heavy equipment according to an embodiment of the present invention will be described with reference to the accompanying drawings. 
     As shown in  FIGS. 1 to 5 , when the pressure P 1  fed to the input port  1  passes through the output port  2 , the spool  13  is shifted corresponding to the signal pressure P 3  being applied from an outside to the spool  13  through the signal pressure port  4 , so that the pressure P 2  passing through the output port  2  can be controlled. 
     Specifically, the pressure P 1  fed through the input port  1  is applied to the first back chamber  6  through the first annular notch  15  and the first passage  16 . 
     In this case, the equilibrium relationship among a force which is applied to the first back chamber  6  of the spool  13  and presses the fluid pressure receiving portion D 1  of the first piston  7 , an elastic force Fs of the valve spring  9 , a force which is applied to the second back chamber  10  of the spool  13  after passing through the input port  1  and presses the fluid pressure receiving portion D 2  of the second piston  11 , and a signal pressure P 3  which is applied to the third back chamber  14  through the signal pressure port  4  and presses the fluid pressure receiving portion (i.e., the fluid pressure receiving portion D 3  of the spool  13 —the fluid pressure receiving portion D 2  of the second piston  11 ) is given by the following equation.
 
( P 1 ×D 1)+ Fs =( P 2 ×D 2)+ P 3( D 3 −D 2)
 
     Accordingly, the pressure P 2  in the output port  2  can be constantly controlled as the signal pressure P 3  being applied to the signal pressure port  4 , with respect to the pressure P 1  of the input port  1 . 
     In this case, if the signal pressure P 3  is not applied from the outside to the signal pressure port  4 , the pressure obtained by adding the elastic force of the valve spring  9  to the pressure P 1  being applied to the first back chamber  6  is higher than the pressure P 2  being applied to the second back chamber  10 . Accordingly, the spool  13  is kept pressed to the extent of “L 1 ” in the right direction as shown in the drawing by the pressures P 1  and P 2  that are applied to the first and second back chambers  6  and  10 , respectively, and thus the pressure P 1  in the input port  1  becomes equal to the pressure P 2  in the output port  2 . 
     On the other hand, if the pressure P 1  in the input port  1  is kept constant and the signal pressure P 3  being applied to the third back chamber  14  is increased, the pressure P 1  in the input port  1  is kept equal to the pressure P 2  in the output port  2  until the increased signal pressure P 3  reaches an equilibrium point in the above-described force equilibrium relationship. 
     If the signal pressure P 3  is further increased over the equilibrium point and the spool  13  is moved to the extent of “L 1 ” in the left direction as shown in the drawing, the pressure P 1  in the input port  1  and the pressure P 2  in the output port  2  are intercepted from each other. 
     Then, if the spool  13  is further moved to the extent of “L 2 ” in the left direction as shown in the  FIG. 5 , the output port  2  is connected to the drain port  3  via the second annular notch  17 , and thus the pressure P 2  of the output port  2  is discharged to the drain port  3 . 
     Accordingly, the pressure P 2  in the output port  2  is reduced, and the spool  13  is moved in the right direction as shown in the  FIG. 1 . Thus, the pressure P 1  in the input port  1  and the pressure P 2  in the output port  2  are repeatedly intercepted from and connected to each other to keep the pressures in equilibrium. 
     As shown in  FIG. 3 , as the signal pressure P 3  being applied to the third back chamber  14  is increased, the pressure P 2  being applied from the input port to the output port  2  is reduced. 
     On the other hand, if the pressure P 1  in the input port  1  is increased or decreased in a state that the signal pressure P 3  being applied to the third back chamber  14  is kept constant, the pressure P 1  in the input port P 1  is kept a reduced pressure P 2  by the signal pressure P 3  being applied to the spool  13 . In this state, if the pressure P 1  is further increased, the spool  13  is moved in the right direction as shown in the drawing. 
     Consequently, the pressure P 1  in the input port  1  and the pressure P 2  in the output port  2  are repeatedly intercepted from and connected to each other to keep the pressures in equilibrium. 
     As shown in  FIG. 3 , if the pressure P 1  in the input port  1  is increased or decreased in a state that the signal pressure P 3  being applied to the third back chamber  14  is kept constant, the pressure P 2  in the output port  2  is increased or decreased. 
     As shown in  FIG. 4 , a pressure control device for heavy equipment according to another embodiment of the present invention includes a valve body  5  having an input port  1 , an output port  2 , and a drain port  3 , formed thereon; a spool  13   a , slidably installed in the valve body  5 , for being shifted to connect the input port  1  to the output port  2  in response to a pressure obtained by adding an elastic force of a valve spring  9  to a pressure being applied from the input port  1  to a diaphragm  8  of a first piston  7  that is elastically supported by the valve spring  9  in a first back chamber  6 , and being shifted to disconnect the input port  1  from the output port  2  in response to a pressure being applied from the output port  2  to a diaphragm  20  located on an outer surface of the spool; and a signal pressure port  4  for applying a signal pressure to a diaphragm  19   a  of the spool  13   a  located in a third back chamber  14  formed on the valve body  5 , disconnecting the input port  1  from the output port  2  by shifting the spool  13   a  in response to a pressure acting upon the diaphragm  20  located on the outer surface of the spool  13   a  and a signal pressure P 3 , and returning the pressure in the output port  2  to the drain port  3 . 
     The spool  13   a  is shifted, corresponding to the signal pressure P 3  applied from an outside to the third back chamber  14  through the signal pressure port  4 , to control the operating pressure being applied from the input port  1  to the output port  2 . 
     In this case, the construction including the first piston  7  elastically supported in the first back chamber  6 , the valve body  5  having the input port  1 , the output port  2 , and the drain port  3 , and the third back chamber  14  to which the signal pressure P 3  fed from the outside is applied through the signal pressure port  4 , is substantially equal to that according to an embodiment of the present invention, the detailed description thereof will be omitted. Also, in the whole description of the present invention, the same drawing numerals are used for the same elements across various figures. 
     As described above, the pressure control device for heavy equipment according to the embodiments of the present invention has the following advantages. 
     In the case of simultaneously operating a plurality of working devices connected in parallel to a single hydraulic pump, it is possible to smoothly operate the working devices having different operating pressures, and thus the operation of the equipment is improved with the working efficiency thereof heightened. 
     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.