Abstract:
A pressure control valve is provided, which can variably control the set pressure of a relief valve in accordance with pilot signal pressure that is controlled in an operator&#39;s seat and so on when the set pressure of the relief valve required in a replaced working device is changed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority from Korean Patent Application No. 10-2008-0016910, filed on Feb. 25, 2008 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 valve that can variably control a set pressure of relief valves by pilot signal pressure supplied from an outside. 
     More particularly, the present invention relates to a pressure control valve that can variably control the set pressure of a relief valve in accordance with pilot signal pressure controlled in an operator&#39;s seat and so on when the set pressure of the relief valve required in a working device (e.g. an option device) is changed. 
     2. Description of the Prior Art 
     In general, a pressure control valve is used within a set pressure of a hydraulic circuit. In the case of replacing a working device in accordance with working conditions, the set pressure of the relief valve is reset in accordance with the replaced working device. 
     In the case of controlling the set pressure of the relief valve, it is required for an operator to set the pressure of the relief valve as an operator directly confirms a pressure gauge, and this causes the operator inconvenience. In consideration of such inconvenience in use, a device, which enables an operator to control the set pressure of the relief valve by controlling pilot signal pressure on the outside of a cab or in the operator&#39;s seat, has been used. 
     As illustrated in  FIG. 1 , a conventional pressure control valve includes a first plug  1  having an inlet port  1   a  into which high-pressure hydraulic fluid from a hydraulic pump P flows and a tank path  1   b  communicating with a hydraulic tank T; a poppet  2  slidably coupled within the first plug  1  to open/close a flow path between the inlet port  1   a  and the tank path  1   b ; a poppet spring  21  elastically supporting the path between the inlet port  1   a  and the tank path  1   b  in a closed state by pressing the poppet  2 ; a guide  20  supporting the poppet spring  21 ; a pilot poppet  19  draining the hydraulic fluid in a pressure chamber c of the first plug  1  to the hydraulic tank T by opening a flow path of a valve sheet  3  when high pressure that exceeds a preset pressure is generated in the pressure chamber c; a pilot poppet spring  18  elastically supporting the path of the valve sheet  3  in a closed state by pressing the pilot poppet  19 ; a piston  17  supporting one end of the pilot poppet spring  18 , and slidably moving within a screw plug  11  to control the set pressure of a relief valve when pilot signal pressure is supplied; a spring elastically supporting the piston  17 ; a sleeve on which a pilot port  7   a  for supplying the pilot signal pressure to the piston  17  is formed; a fastening nut  10  and a second plug  12  fixed to an outer surface and an inner surface of the screw plug  11 , respectively, to prevent a pressure change after the set pressure of the relief valve is set. 
     Hereinafter, the operation of the conventional pressure control valve will be described with reference to the accompanying drawings. 
     A) In the case where the set pressure is used (i.e. the pilot signal pressure is not supplied from an outside): 
     Hydraulic fluid discharged from the hydraulic pump P flows into the pressure chamber c of the first plug through the inlet port  1   a  and an orifice in the poppet  2  in order. At this time, due to a difference in sectional area between hydraulic pressure parts of the poppet  1 , the poppet  2  is pressed in right direction as shown in the drawing to keep the flow path between the inlet port  1   a  and the tank path  1   b  in a closed state. 
     If the pressure of the hydraulic fluid supplied to the pressure chamber c reaches the set pressure of the pilot poppet spring  18 , the pilot poppet  19  moves in left direction as shown in the drawing to open the flow path of the valve sheet  3 . Accordingly, the hydraulic fluid in the pressure chamber c is returned to the hydraulic tank T through a path  5 . 
     Simultaneously, due to the opening of the pilot poppet  19 , the pressure of the hydraulic fluid in the pressure chamber c is instantaneously lowered. Accordingly, the poppet  2  moves in left direction as shown in the drawing, and the hydraulic fluid is supplied from the inlet port la to the hydraulic tank T through the tank path  1   b . At this time, the set pressure is determined in accordance with the elastic force of the pilot poppet spring  18  set by the control of the screw plug  11 . 
     B) In the case where the set pressure is changed (i.e. the pilot signal pressure is supplied from an outside): 
     The pilot signal pressure from an outside is supplied to the piston  17  through a pilot port  7   a  of the sleeve  7  and a path  11   a  formed in the screw plug  11 , and thus the piston  17  moves in upper left direction as shown in the drawing (in this case, the spring  14  is compressed). 
     Accordingly, since the elastic force of the pilot poppet spring  18  is reduced, the set pressure value generated in the hydraulic pump P is reduced, and the set pressure of the relief valve is varied. 
     In the case where a pipe (not illustrated) for supplying the pilot signal pressure from an outside is jointly connected to a single pilot port  7   a , it is interfered with components around the relief valve, and thus it is impossible to jointly connect the pipe to the pilot port  7   a.    
     Also, in the case where a drain hole  15  formed in the screw plug  11  is exposed to an outside and a foreign substance or rainwater flows in through the drain hole  15  after an external coating work, the hydraulic driving surface of the spring  14  or the piston  17  is corroded to shorten the life span of the corresponding component. 
     Also, frictional resistance is generated by O-rings  9  and  16  mounted to seal a gap between mutual contact surfaces of the piston  17  and the screw plug  11 , and an O-ring  13  mounted to seal a gap between mutual contact surfaces of the piston  17  and the second plug  12 . 
     Accordingly, as illustrated in  FIG. 2 , a hysteresis occurs, whereby the set pressure of the relief valve against the pilot signal pressure supplied from an outside cannot be accurately controlled. 
     Also, the hydraulic fluid fed from the hydraulic pump P and waiting in the pressure chamber c may leak to the hydraulic tank side T due to a difference between the inner diameter of the first plug  1  and the outer diameter of the poppet  2 . 
     At this time, if load is generated on the inlet port side  1   a  of the first plug  1 , a safety accident, such as falling of a working device (e.g. boom or the like), may occur. 
     In addition, in the case of setting the minimum pressure of the relief valve, the range of the minimum pressure is enlarged due to tolerance of components constituting the relief valve, and thus it becomes impossible to form the pressure desired by the user (e.g., in the case where the minimum pressure of the relief valve is 100 kg/cm 2 , the actual pressure may be set to 110 kg/cm 2 . 
     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. 
     An embodiment of the present invention relates to a pressure control valve, in which, in the case of jointly connecting a pipe for supplying pilot signal pressure from an outside to a pilot port, the connection work can be done without being interfered by components around a relief valve. 
     An embodiment of the present invention relates to a pressure control valve, in which a drain port is separately formed to prevent corresponding components from being corroded due to a foreign substance or rainwater flowing from an outside into the valve. 
     An embodiment of the present invention relates to a pressure control valve, which can reduce the manufacturing cost since the use of a sealing part (e.g. O-ring) for sealing a gap between contact surfaces of a piston is not required, and can solve the problem that the set pressure of a relief valve against the pilot pressure cannot be accurately controlled due to the frictional resistance caused by sealing mounting. 
     An embodiment of the present invention relates to a pressure control valve, which can prevent the hydraulic fluid fed from the hydraulic pump and waiting in the pressure chamber from leaking to the hydraulic tank side, and thus can prevent the falling of a working device when load is generated on an inlet port side of a relief valve. 
     An embodiment of the present invention relates to a pressure control valve, which can keep the reduction of an elastic force of a pilot poppet spring within a preset range, and thus can control the minimum pressure of a hydraulic pump against the pilot signal pressure to be constant. 
     In order to accomplish these objects, there is provided a pressure control valve, according to an embodiment of the present invention, which includes a sleeve having an inlet port into which hydraulic fluid from a hydraulic pump flows and a tank path communicating with a hydraulic tank; a poppet slidably coupled within the sleeve to open/close a flow path between the inlet port and the tank path; a poppet spring elastically supporting the path between the inlet port and the tank path in a closed state by pressing the poppet; a valve sheet installed to face the poppet so that a set pressure is formed in a pressure chamber of the sleeve; a pilot poppet draining the hydraulic fluid in the pressure chamber to the hydraulic tank by opening a flow path of the valve sheet when high pressure that exceeds the set pressure is generated in the pressure chamber; a pilot poppet spring elastically supporting the path of the valve sheet in a closed state by pressing the pilot poppet; a plug coupled to the sleeve, and having a pilot port formed therein to receive a supply of the pilot signal pressure from an outside; a main piston slidably coupled within a guide coupled to the plug to variably control the set pressure in the pressure chamber in accordance with the pilot signal pressure being supplied through a pilot port; and a control plug movably coupled to the guide to control a set pressure of a spring supporting the main piston. 
     In a preferred embodiment of the present invention, the pressure control valve further includes a connection member rotatably coupled to an outer side of the plug, and having a path formed therein to communicate with the pilot port. 
     The pressure control valve according to a preferred embodiment of the present invention may further include a first stopper slidably installed in the guide to face the pilot poppet and to prevent the set pressure of the pilot poppet spring from being lowered below a predetermined value. 
     The pressure control valve according to a preferred embodiment of the present invention may further include a stepped portion formed on an inner side of the guide to limit the movement of the first stopper within a predetermined section when the set pressure of the pilot poppet spring is lowered. 
     The pressure control valve according to a preferred embodiment of the present invention may further include a second stopper installed between the main piston and the control plug to limit the movement of the main piston within a predetermined section when the pilot signal pressure is applied to variably control the set pressure of the pressure chamber. 
     The pressure control valve according to a preferred embodiment of the present invention may further include a sealing part mounted on an outer side of the poppet to seal a gap between mutual contact surfaces of the sleeve and the poppet, so that the hydraulic fluid in the pressure chamber is prevented from leaking to the hydraulic tank through the gap. 
     A drain port is formed in the control plug to feed the hydraulic fluid in the pressure chamber back to the hydraulic tank when the main piston moves in accordance with a supply of the pilot signal pressure thereto. 
    
    
     
       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 pressure control valve; 
         FIG. 2  is a graph explaining the control of the set pressure of the pressure control valve in accordance with the pilot signal pressure; 
         FIG. 3  is a sectional view of a pressure control valve according to an embodiment of the present invention; 
         FIG. 4  is a view illustrating the first use state of a pressure control valve according to an embodiment of the present invention; and 
         FIG. 5  is a view illustrating the second use state of a pressure control valve 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. 3 to 5 , a pressure control valve according to an embodiment of the present invention includes a sleeve  50  having an inlet port  50   a  into which high-pressure hydraulic fluid from a hydraulic pump P flows, and a tank path  50   b  communicating with a hydraulic tank T; a poppet  51  slidably coupled within the sleeve  50  to open/close a flow path between the inlet port  50   a  and the tank path  50   b ; a piston  54  elastically supported by a spring  52  to slidably move within the poppet  51 , and becoming in contact with the pilot poppet  53  when it moves by an initial pressure of the hydraulic pump P; a poppet spring  55  elastically supporting the path between the inlet port  50   a  and the tank path  50   b  in a closed state by pressing the poppet  51 ; a valve sheet  56  installed within the sleeve  50  to face the poppet  51  so that a set pressure is formed in a pressure chamber c of the sleeve  50 ; a pilot poppet  53  draining the hydraulic fluid in the pressure chamber c to the hydraulic tank T via through-holes  59   a  and  50   c  by opening a flow path of the valve sheet  56  when high pressure that exceeds the set pressure is generated in the pressure chamber c; a pilot poppet spring  57  elastically supporting the path of the valve sheet  56  in a closed state by pressing the pilot poppet  53 ; a plug  59  coupled to the sleeve  50 , and having a pilot port  58  formed therein to receive a supply of the pilot signal pressure from an outside; a guide  61  movably screw-engaged with the plug  59 , and having a through-hole  60  formed thereon to receive a supply of the pilot signal pressure through the pilot port  58 ; a main piston  62  slidably coupled within the guide  61  to variably control the set pressure in the pressure chamber c in accordance with the pilot signal pressure being supplied through a pilot port  58  and a through-hole  60 ; a control plug  65  movably coupled to an outer end of the guide  61  to control the set pressure of a spring  63  elastically supporting the main piston  62 ; and a fastening part  64  (e.g. nut) fixed to the guide  61  and a fastening part  66  (e.g. nut) fixed to the control plug  65  so as to prevent the pressure change after the set pressure of the relief valve is set. 
     The pressure control valve according to an embodiment of the present invention further includes a connection member  68  rotatably coupled to an outer side of the plug  59 , and having a path  67  formed therein to communicate with the pilot port  58 . 
     The pressure control valve according to an embodiment of the present invention further includes a first stopper  69  slidably installed in the guide  61  to face the pilot poppet  53  and to prevent the set pressure of the pilot poppet spring  57  from being lowered below a predetermined value. 
     The pressure control valve according to an embodiment of the present invention further includes a stepped portion  70  formed on an inner side of the guide  61  to limit the movement of the first stopper  69  within a predetermined section Y when the set pressure of the pilot poppet spring  57  is lowered. 
     The pressure control valve according to an embodiment of the present invention further includes a second stopper  71  installed between the main piston  62  and the control plug  65  to limit the movement of the main piston  62  within a predetermined section X when the pilot signal pressure is applied through the connection member  68  to variably control the set pressure of the pressure chamber c. 
     The pressure control valve according to an embodiment of the present invention further includes a sealing part  72  (e.g. a backup ring and an O-ring) mounted on an outer side of the poppet  51  to seal a gap between mutual contact surfaces of the sleeve  50  and the poppet  51 , so that the hydraulic fluid in the pressure chamber c is prevented from leaking to the hydraulic tank T. 
     A drain port  73  is formed in the control plug  65  to feed the hydraulic fluid in a back pressure chamber d back to the hydraulic tank T when the main piston  62  moves in accordance with a supply of the pilot signal pressure thereto through the connection member  68 . 
     Hereinafter, the operation of the pressure control valve according to an embodiment of the present invention will be described with reference to the accompanying drawings. 
     A) In the case where the set pressure is used (i.e. the pilot signal pressure is not supplied from an outside): 
     Hydraulic fluid discharged from the hydraulic pump P flows into the pressure chamber c of the sleeve  50  through the inlet port  50   a  and an orifice in the poppet  51 . At this time, due to a difference in sectional area between hydraulic pressure parts of the poppet  51 , the poppet  51  is pressed in left direction as shown in the drawing to keep the flow path between the inlet port  50   a  and the tank path  50   b  in a closed state (See  FIG. 3 ). 
     If the pressure of the hydraulic fluid supplied to the pressure chamber c reaches the set pressure of the pilot poppet spring  57 , the pilot poppet  53  moves in right direction as shown in the drawing to open the flow path of the valve sheet  56 . Accordingly, the hydraulic fluid in the pressure chamber c is returned to the hydraulic tank T through a through-hole  50   c  of the sleeve  50 . 
     Simultaneously, due to the opening of the pilot poppet  53 , the pressure of the hydraulic fluid in the pressure chamber c is instantaneously lowered. Accordingly, the poppet  51  moves in right direction as shown in the drawing, and the hydraulic fluid is supplied from the inlet port  50   a  to the hydraulic tank T through the tank path  501   b . At this time, the set pressure is determined in accordance with the elastic force of the pilot poppet spring  57  set by the control of the guide  61  (See  FIGS. 4 and 5 ). 
     B) In the case where the set pressure is changed (i.e. the pilot signal pressure is supplied from an outside): 
     As illustrated in  FIG. 5 , the pilot signal pressure from an outside is supplied to the main piston  62  through the path of the connection member  68 , a pilot port  58  of the plug  59  and a through-hole  60  of the guide  61  in order. At this time, due to the difference in section area between hydraulic pressure parts of the main piston  62 , the main piston  62  moves in right direction as shown in the drawing (at this time, the spring  63  is compressed). 
     That is, since the spring  63  is compressed due to the movement of the main piston  62 , and the elastic force of the pilot poppet spring  57  is reduced simultaneously, the set pressure value generated in the hydraulic pump P is reduced, and the set pressure of the relief valve is varied. 
     On the other hand, the connection member  68  supplying the pilot signal pressure from the outside is rotatably coupled to the outer side of the plug  59  (i.e., 360° rotatable in Y-axis direction), and thus in the case where a pipe (not illustrated) for supplying the pilot signal pressure is jointly connected to the pilot port  58 , it is not interfered with components around the relief valve, and thus it is possible to continue the connection work. 
     Also, since the use of O-rings for sealing the gap between the contact surfaces of the main piston  62  is not required, the frictional resistance occurring due to the O-ring mounting is prevented, and thus the set pressure of the relief valve against the pilot pressure can be accurately controlled. 
     Also, by the sealing part  72  mounted on the outer side of the poppet  51  to seal the gap of the contact surfaces of the poppet  51  and the sleeve  50 , the hydraulic fluid waiting in the pressure chamber c is prevented from leaking to the hydraulic tank side T through the gap. Accordingly, even in the case where load is generated on the inlet part side  50   a  of the relief valve, the falling of a working device can be prevented. 
     Also, since the drain port  73  for feeding the hydraulic fluid in the back pressure chamber d back to the hydraulic tank T is separately formed in the control plug  65 , the permeation of a foreign substance or moisture such as rainwater and so on through the drain port  73  can be prevented. Accordingly, the corrosion of the hydraulic driving surfaces of the main piston  62  or the spring  63  can be prevented. 
     Also, after the initial pressure setting (corresponding to the state as illustrated in  FIG. 4 ), the pilot signal pressure is applied from the outside through the connection member  68 , and the main piston  62  moves in right direction as shown in the drawing (i.e. as shown in  FIG. 4 , the main piston moves in X-axis direction within the range “X”). At this time, the hydraulic fluid in the back pressure chamber d is returned to to the embodiments of the present invention has the following advantages. 
     In the case of jointly connecting a pipe for supplying the pilot signal pressure from an outside to the pilot port, the connection work can be easily done without being interfered by components around the relief valve, and thus the workability can be improved. 
     Also, the drain port is separately formed to prevent the components from being corroded due to a foreign substance or rainwater flowing from an outside into the valve, and thus the shortening of the life span of the corresponding components can be prevented. 
     Also, the use of O-rings for sealing the gap between the contact surfaces of the piston is unnecessary, and thus the manufacturing cost of the valve is reduced. Also, the problem that the set pressure of the relief valve against the pilot pressure cannot be accurately controlled due to the frictional resistance occurring during the mounting of the O-rings can be solved, and thus the reliability of the valve can be improved. 
     Also, the hydraulic fluid fed from the hydraulic pump and waiting in the pressure chamber is prevented from leaking to the hydraulic tank side, and thus the falling of a working device can be prevented even when load is generated on an inlet port side of a relief valve. 
     Also, after the initial pressure of the relief value is the hydraulic tank T through the through-hole  71   a  of the second stopper  71  and the drain port  73 . 
     When the main piston  62  moves, the first stopper  69  also moves in right direction as shown in the drawing. Accordingly, the set pressure of the pilot poppet spring  57  is reduced. 
     At this time, the first stopper  69  slidably moves in X-axis direction within the range “Y” (See  FIG. 4 ). That is, the moving distance of the first stopper is limited by the stepped portion  70  formed on the inner side of the guide  61  (as illustrated in  FIG. 4 , the first stopper moves as much as “Y” at maximum). 
     Accordingly, the minimum pressure of the hydraulic pump P, which is decreased as the pilot signal pressure being supplied to the main piston  62  is increased, can be accurately controlled. That is, since the minimum pressure of the hydraulic pump P against the pilot signal pressure can be accurately controlled, the low-pressure forming range of the relief valve can be kept constant. 
     As illustrated in  FIG. 2 , in accordance with the control of the pilot signal pressure, the set pressure of the relief valve desired by the user can be variably controlled. That is, the set pressures A, B, and C of the relief valve can be respectively controlled to correspond to the pilot signals P 1 , P 2 , and P 3 , respectively. 
     As described above, the pressure control valve according set, the minimum value of the hydraulic pump against the pilot signal pressure can be controlled constantly by keeping the elastic force reduction range of the pilot poppet spring with a predetermined value, and thus a low-pressure setting required by the user becomes possible. 
     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.