Patent Publication Number: US-6907815-B2

Title: Control apparatus of hydraulic valve for holding load

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a control apparatus of a hydraulic valve for holding load capable of precluding momentary drop of load drop in a hydraulic actuator such as a boom cylinder, etc. for thereby effectively preventing drop of load, and in particular to a control apparatus of a hydraulic valve for holding load in which a drain line of a holding valve adapted to preclude momentary drop of load in a hydraulic actuator is substituted with a path formed in the interior of a directional control valve, so that a pipe line of a drain side functioning as a hydraulic hose and exposed to the outside is not needed in the present invention. 
   2. Description of the Background Art 
   As shown in  FIGS. 1 and 2 , a control apparatus of a hydraulic valve for holding load in a conventional art includes a hydraulic pump  19  and a pilot pump  2  connected to an engine (not shown), a hydraulic actuator (not shown) connected to the hydraulic pump  19  like a boom cylinder, etc., a directional control valve  35  disposed in a flow path between the hydraulic pump  19  and the actuator and controlling a start, stop and direction change of the actuator by a spool  14  that is switched when pilot pressure is applied, a remote control valve (RCV)  1  adapted to supply pilot pressure to the directional control valve  35 , a poppet  9  disposed in a flow path between the directional control valve  35  and the actuator and adapted to preclude momentary drop of load in the actuator, and a holding valve  20  connected to a side of a downstream of the poppet  9  and adapted to release upheld load of the actuator by a sub-spool  7  that is switched when pilot pressure is applied. 
   In the drawings, reference characters A and B represent a flow path connected to the actuator, respectively. 
   In the case that the spool  14  installed in the directional control valve  35  is at a neutral position (as shown in FIG.  1 ), a high pressure hydraulic fluid from the hydraulic actuator sequentially flows to a back chamber  10  through a port  12  formed in a holding valve block  18  and a through hole  11  formed in the poppet  9 . The flow of the hydraulic fluid is blocked by the sub-spool  7 , which is installed in the holding valve  20 , and maintains a neutral position. 
   The poppet  9  is downwardly pressurized due to a difference in a cross section area of the poppet  9  as shown in  FIG. 2 , so that the hydraulic fluid from the actuator is prevented from being drained into a hydraulic tank, whereby load of an actuator is temporarily prevented from being dropped for thus implementing a holding function. 
   In the case that it is intended to release holding load function of the actuator, the remote control valve  1  is operated in the direction “b”, so that pilot pressure Pb discharged from the pilot pump  2  is introduced into the port of a spool cap  5  engaged in a left end of the directional control valve  35  through the pilot line  4 , whereby the inner spool  14  is switched in the right direction shown in FIG.  2 . 
   At the same time, the pilot signal pressure Pb flows through a pilot line  6  divided from the pilot line  4  and enables the sub-spool  7  installed in the holding valve  20  to be switched in the left direction shown in FIG.  2 . 
   At this time, hydraulic fluid of high pressure in the back chamber  10  of the holding valve block  18  is drained to the hydraulic tank  3  through the drain line  8 . 
   As the pressure of the hydraulic fluid of the back chamber  10  is dropped to the pressure of the hydraulic tank, a high load pressure from the actuator enables the poppet  9  to be upwardly moved as shown in FIG.  2  and is fed back to the hydraulic tank through a notch  15  of the spool  14 , of which the position is switched, and a return line  16 . The load holding function of the hydraulic actuator is released, and the actuator slowly moves downward. 
   In the control apparatus of a hydraulic valve for holding load in the conventional art, the pilot line  6  adapted to supply pilot pressure to the holding valve  20  for switching the sub-spool  7  and the drain line adapted to drain the hydraulic fluid of the back chamber  120  to the hydraulic tank  3  when the sub-spool  7  is switched are exposed to the outside with the shape of hydraulic hoses and are longitudinally connected. 
   In the conventional art, as the hydraulic hoses are exposed to the outside, the fabrication cost is increased. The length of the hydraulic hoses of the drain line  8  is increased, so that a backpressure is formed in the drain line. Therefore, the response time is decreased during the operation of the remote control valve  1 , so that it is difficult to control the equipment. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a control apparatus of a hydraulic valve for holding load in which a drain line of a holding valve is substituted with a path formed in the interior of a directional control valve, so that a hydraulic hose exposed to the outside is not needed for thereby decreasing a fabrication cost. 
   It is another object of the present invention to provide a control apparatus for a hydraulic valve for holding load capable of decreasing the length of a hydraulic hose of a drain line of a holding valve and preventing the response time from being delayed due to the back pressure in drain line, thus enhancing the control performance of an equipment. 
   To achieve the above objects, there is provided a control apparatus of a hydraulic valve for holding load, comprising a hydraulic pump connected to an engine, an actuator connected to the hydraulic pump, a directional control valve disposed between the hydraulic pump and the actuator and switchable by pilot pressure from a remote control valve and adapted to control a start, stop and direction change of the actuator, a poppet disposed between the directional control valve and the actuator and adapted to preclude momentary drop of load in the actuator, a holding valve block connected to a downstream side of the poppet and having a sub-spool switchable by pilot pressure applied thereto and adapted to release upheld load of the actuator, and a drain line adapted to allow hydraulic fluid returned during a switching operation of the sub-spool to flow in a pilot line of the side of a drain corresponding to the opposite side of a pilot line adapted to pressurize the spool of the directional control valve. 
   To achieve the above objects, there is provided a control apparatus of a hydraulic valve for holding load, comprising a hydraulic pump connected to an engine, an actuator connected to the hydraulic pump, a directional control valve disposed between the hydraulic pump and the actuator and switchable by pilot pressure from a remote control valve and adapted to control a start, stop and direction change of the actuator, a poppet disposed between the directional control valve and the actuator and adapted to preclude momentary drop of load in the actuator, a holding valve block connected to a downstream side of the poppet and having a sub-spool switchable by pilot pressure applied thereto and adapted to release upheld load of the actuator, and a drain line formed in the interiors of the holding valve block and the directional control valve and adapted to allow hydraulic fluid returned during a switching operation of the sub-spool to flow in a pilot line of the side of a drain corresponding to the opposite side of a pilot line adapted to pressurize the spool of the directional control valve. 
   There is further provided a piston installed in an opposite side of a valve spring of the sub-spool and movable by pilot pressure for thereby switching the sub-spool. 
   The drain line includes a first drain line communicating with a back chamber formed between the piston and the sub-spool and formed in the interior of the holding valve block, a second drain line having one end connected to the first drain line and formed in the interior of the directional control valve, and a third drain line communicating with the other end of the second drain line and communicating with the pilot line of the side of the drain corresponding to the opposite side of the pilot line adapted to pressurize the spool of the directional control valve. 
   The drain line includes a first drain line communicating, with the back chamber between the piston and the sub-spool and formed in the interior of the holding valve block, and a fourth drain line having one end communicating with the first drain line, and the other end communicating with the pilot line of the side of the drain corresponding to the opposite side of the pilot line adapted to pressurize the spool of the directional control valve. 
   There is further provided a first poppet opened during a switching operation of the sub-spool as the piston is moved and formed integrally with the sub-spool for thereby supplying hydraulic fluid of a back chamber to a return line of the actuator, and a second poppet openably and closably installed between the sub-spool and the return line of the actuator and operating in cooperation with the first poppet. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become better understood with reference to the accompanying drawings which are given only by way of illustration and thus are not limitative of the present invention, wherein; 
       FIG. 1  is a view illustrating a hydraulic circuit of a control apparatus of a hydraulic valve for holding load in a conventional art; 
       FIG. 2  is a cross sectional view illustrating a control apparatus of a hydraulic valve for holding load in a conventional art; 
       FIG. 3  is a view illustrating a hydraulic circuit of a control apparatus of a hydraulic valve for holding load according to the present invention; 
       FIG. 4  is a cross sectional view illustrating a control apparatus of a hydraulic valve for holding load according to the present invention; and 
       FIG. 5  is a cross sectional view illustrating another embodiment of a control apparatus of a hydraulic valve for holding load according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The preferred embodiments of the present invention will be described with reference to the accompanying drawings. 
   As shown in  FIGS. 3 through 5 , the present invention includes a hydraulic pump  19  and a pilot pump  32  connected to an engine (not shown) respectively, an actuator (not shown) connected to the hydraulic pump  19 , a directional control valve  35  disposed in a flow path between the hydraulic pump  19  and the actuator and adapted to control start, stop and direction change of the actuator as an internal spool  50  is switched in accordance with pilot pressure applied from a remote control valve (RCV)  31 , a poppet  44  disposed in a flow path between the directional control valve  35  and the actuator and adapted to preclude momentary drop of load in the actuator, and a holding valve block  37  connected to a downstream side of the poppet  44  and having a sub-spool  39  switched in accordance with pilot pressure applied from the pilot pump  32  and adapted to release upheld load of the actuator. The above construction is the same as the conventional art. Therefore, the details of the construction and operation will be omitted. 
   As shown in  FIGS. 3 and 4 , the control apparatus of a hydraulic valve for holding load according to the present invention includes a piston  38  installed in an opposite side of a valve spring  39   a  of the sub-spool  39  and pressurized in accordance with pilot pressure for thereby switching the sub-spool  39 , and a drain line AA adapted to allow hydraulic fluid, which is returned during the switching operation of the sub-spool  39  based on pressurizing operation of the piston  38 , to flow into the pilot line  55  of the side of the drain corresponding to the opposite side of the pilot line  34  adapted to pressurize the spool  50  of the directional control valve  35 . 
   There is further provided a first poppet  40  integrally formed in the sub-spool  39  in such a manner that the first poppet  40  is opened during the switching operation of the sub-spool  39  based on the movement of the piston  38  in order to allow hydraulic fluid of the back chamber  46  to be supplied to a return line  47 , and a second poppet  42  openably and closably installed in a flow path between the sub-spool  39  and the return line  47  of the actuator and operating in cooperation with the first poppet  40 . 
   As shown in  FIG. 4 , the drain line AA includes a first drain line  52  provided in the interior of the holding valve block  37  for thereby communicating with the back chamber  51  formed between the piston  38  and the sub-spool  39 , a second drain line  53  having one end communicating with the first drain line  52  and being formed in the interior of the directional control valve  35 , and a third drain line  54  communicating with the other end of the second drain line  53  and the pilot line  55  of the side of the drain corresponding to the opposite side of the pilot line  34  adapted to pressurize the spool  50  of the directional control valve  35 . 
   The operation of the control apparatus of a hydraulic valve for holding load according to the present invention will be described with reference to the accompanying drawings. 
   As shown in  FIGS. 3 and 4 , in order to release load holding function capable of precluding momentary drop of load in hydraulic actuator such as a boom cylinder, etc., the remote control valve  31  is operated in the direction “b”, and the pilot signal pressure Pb discharged from the pilot pump  32  is introduced into the left side end of the directional control valve  35  through the pilot line  34 , so that the internal spool  50  is switched in the right direction as shown in FIG.  4 . 
   At the same time, the pilot signal pressure Pb is applied through the pilot line  36  divided from the pilot line  34  and pressurizes the piston  38  provided in the holding valve block  37  in the downward direction as shown in FIG.  4 . The sub-spool  39  moves downwardly in cooperation with the movement of the piston  38 . 
   At this time, the high pressure oil from the hydraulic actuator (not shown) is flown into the through hole  45  of the poppet  44  provided in the directional control valve  35  and is held by the back chamber  46 . The first poppet  40  seated integrally with the sub-spool  39  is downwardly moved as shown in FIG.  4  and is opened, so that the hydraulic fluid held in the back chamber  46  is introduced into the return line  47  through the return line  41 , the second poppet  42  and the flow path  43 , sequentially. 
   In the case that the pilot pressure applied to the directional control valve  35  through the pilot line  34  exceeds a certain level, the spool  50  is moved in the right direction as shown in  FIG. 4 , so that the return line  47  comes to communicate with the hydraulic tank  49  by a notch portion  48  formed in one side of the outer surface of the spool  50 , whereby the pressure of the hydraulic fluid of the back chamber  46  is dropped to the pressure level of the hydraulic tank. 
   Therefore, the poppet  44  is upwardly moved by the pressure difference as shown in FIG.  4 . The hydraulic fluid, which is returned from the actuator, is fed into the hydraulic tank  49 , and load holding function of the hydraulic actuator is released, so that the actuator is gradually operated in the downward direction. 
   At this time, the hydraulic fluid of the back chamber  51  formed between the piston  38  and the sub-spool  39  flows through the drain line AA ( 52 ,  53 ,  54 ) formed in the interior of the holding valve block  37  and the directional control valve  35 . When the hydraulic fluid passes through the spool cap  56  provided in the right end of the directional control valve  35 , the hydraulic fluid is drained to the hydraulic tank  33  through the pilot line  55  of the side of the drain corresponding to the opposite side of the pilot line  34  adapted to pressure the spool  50  of the directional control valve  35 . 
   The drain line of the holding valve adapted to preclude spontaneous drop of load in the hydraulic actuator is combined with the pilot line  55  of the side of the drain of the directional control valve  35  through the passage type drain lines  52 ,  53  and  54  formed in the interiors of the holding valve block  37  and the directional control valve  35 . Therefore, it is not needed to use externally exposed hydraulic hoses. The fabrication cost and the length of the drain line are decreased. It is possible to prevent the response time from being decreased during the operation of the remote control valve  31 . 
   As shown in  FIG. 5 , in the control apparatus of a hydraulic valve for holding load according to another embodiment of the present invention, the drain line AA includes a first drain line  52  communicating with the back chamber  51  formed between the piston  38  and the sub-spool  39  and formed in the interior of the holding valve block  37 , and a fourth drain line  71  having one end communicating with the first drain line  52  through a drain port  70  and the other end communicating with the drain line  73  that communicates with a spool cap  56  of the directional control valve  35 , and the pilot line  55  of the side of the drain corresponding to the opposite side of the pilot line  34  adapted to pressurize the spool  50  of the directional control valve  35 . 
   The constructions except for the above-described constructions are the same as the construction of the earlier one embodiment of the present invention. Therefore, the descriptions of the same constructions will be omitted. The reference numerals for the same constructions will be given the same reference numerals. 
   Therefore, the first drain line  52  formed in the interior of the holding valve block  37  and the drain line  73  communicating with the spool cap  56  of the directional control valve  35  communicate each other through the fourth drain line  71  provided between the first drain line  52  and the drain line  73 , so that the hydraulic fluid returned during the switching operation of the sub-spool  39  is allowed to flow into the pilot line  55  of the side of the drain of the directional control valve  35  for thereby draining the hydraulic fluid into the hydraulic tank  33 . 
   Therefore, in the present invention, the drain line of the holding valve is extended to the outside of the directional control valve  35 . Therefore, the length of the hydraulic hose is decreased, so that it is possible to prevent back pressure from being formed in the drain line. 
   The control apparatus of the hydraulic valve for holding load according to the present invention has the following advantages. 
   The drain line of the holding valve adapted to preclude momentary drop of load in the hydraulic actuator is connected to the pilot line of the side of the drain corresponding to the opposite side of the pilot line of the pressurizing side of the directional control valve through the internal path of the directional control valve, so that it is not needed to use the hydraulic hose exposed to the outside for thereby decreasing the fabrication cost. 
   In addition, the length of the hydraulic hose of the drain line of the holding valve is decreased, so that it is possible to prevent the response time from being decreased due to the back pressure formed in the drain line, for thereby enhancing the performance of an expensive heavy equipment. 
   As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described examples are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.