Abstract:
The present invention relates to a holding valve that is used for a hydraulic circuit for controlling a working device actuator of construction equipment, and to a holding valve for construction equipment in which a double nut and a sleeve are removed such that an assembling efficiency is improved and the cost is reduced, and further, the abnormal assembling of a piston can be prevented.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a holding valve for a construction machine. More particularly, the present invention relates to a holding valve, which is used in a hydraulic circuit for controlling an actuator for a work apparatus of a construction machine. 
       BACKGROUND OF THE INVENTION 
       [0002]    In general, a construction machine such as an excavator or a loader can easily perform an excavating and loading work, and the like. Such a construction machine employs a holding valve that is used in an actuator-controlling hydraulic circuit in order to perform a function of a valve for both preventing a naturally descending motion caused by a leakage of a hydraulic fluid in a neutral position of the work apparatus such as an arm and controlling the flow rate of the hydraulic fluid during the drive of the work apparatus 
         [0003]    A conventional holding valve is shown in  FIGS. 1 and 2 . The holding valve  1  is mounted between an actuator (not shown) for a work apparatus such as a boom or arm cylinder and a direction control valve C. 
         [0004]    The detailed structure of the holding valve  1  will be described hereinafter. 
         [0005]    The holding valve  1  includes a valve block  2 , a sleeve  3  mounted in the valve block  2 , a spool  4  coupled to the inside of the sleeve  3  so as to be slidably moved in the sleeve  3 , a spool guide  5  fitted around the outer circumference of an upper end of the spool  4 , a spring  6  fitted around the outer circumference of the spool  4  in such a manner as to be located between the spool guide  5  and the sleeve  3  and configured to elastically support the spool  4 , a double nut  7  configured to prevent the escape of the spool guide  5  from the spool  4 , a piston  8  mounted above the spool and elastically supported by a spring  8   a , a holding poppet  9  mounted below the spool and including a back pressure chamber  9   a  filled with a hydraulic fluid to form a hydraulic pressure P 1  therein, and a cover  10  configured to cover the piston  8 . 
         [0006]    The operation of the holding valve  1  will be described hereinafter. 
         [0007]    First, in the case where a holding function is performed, the spool  4  is seated on the sleeve  3  and a force acting due to the internal pressure P 1  of the holding poppet  9  is always maintained to be larger than a force acting contrarily to the force acting due to the internal pressure P 1  at a part C 1  connected to a boom or arm cylinder, so that a leakage of the hydraulic fluid from C 1  to C 2  is suppressed, thereby preventing a free fall of the boom or arm cylinder. 
         [0008]    In the case where the holding function is released, when the piston  8  exerts a force to the spool  4  in response to a pilot signal pressure P 1  applied to a pilot signal pressure port  11  from the outside and the spool  4  is slidably moved downwardly on the drawing sheet, the hydraulic fluid filled in the internal back pressure chamber  9   a  of the holding poppet  9  is drained to a return flow path C 2  of the direction control valve C through a check valve  12  via a flow path  13   
         [0009]    Eventually, the flow rate of the hydraulic fluid in the holding poppet  9  is decreased to cause the internal pressure P 1  of the back pressure chamber  9   a  to be lowered, so that a force acting due to the pressure P 1  is smaller than a force acting contrarily to the force acting due to the pressure P 1  at C 1 . Thus, the holding poppet  9  is moved upwardly on the drawing sheet to cause the hydraulic fluid of C 1  to be flown to C 2  to operate the boom or arm cylinder in the holding state. 
         [0010]    However, the conventional holding valve  1  entails a problem in that the spool  4  is coupled to the outer circumference of the sleeve  5  by means of the double nut  7 , thereby degrading assemblability and structural stability. 
         [0011]    In addition, the cover  10  of the conventional holding valve  1  is fastened to the valve block  1  by means of bolts (not shown) in a state in which the piston  8  is covered by the cover  10 . In this process, since there occurs a phenomenon that the piston  7  is projected outwardly due to an elastic force of the spring  8   a , the piston  7  may be assembled abnormally, thereby having an adverse effect on operability of the holding valve. 
         [0012]    A non-explained reference numeral  15  denotes a spring for elastically supporting the holding poppet  9  and a non-explained reference numeral  14  denotes a drain flow path for preventing the generation of the back pressure. 
       DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problems 
       [0013]    Accordingly, the present invention was made to solve the aforementioned problem occurring in the prior art, and it is an object of the present invention to provide a holding valve for a construction machine, which can eliminate the necessity of the double nut and the sleeve, thereby improving assemblability and reducing the manufacturing cost. 
         [0014]    Another object of the present invention is to provide a holding valve for a construction machine, which can prevent abnormal assembly of the piston. 
       Technical Solution 
       [0015]    To accomplish the above object, in accordance with an embodiment of the present invention, there is provided a holding valve for a construction machine including: a valve block mounted between an actuator for a work apparatus and a direction control valve, the valve block including a space portion formed at an upper portion thereof, a vertical hole formed under the space portion, and a plurality of drain flow paths; a spool assembly including a spool slidably coupled to the vertical hole of the valve block, a spool guide fitted around the outer circumference of an upper end of the spool, and a ring member interposed between the outer circumference of the upper end of the spool and the inner circumference of the spool guide so as to securely fix the spool and the spool guide with respect to each other; an elastic member fitted around the outer circumference of the spool guide in such a manner as to be seated at a lower end thereof on a face adjacent to the vertical hole of the valve block and supported at an upper end thereof by the spool guide; a piston mounted in the space portion of the valve block in such a manner as to be located above the spool to allow a pilot pressure chamber to be formed in the space portion, so that the piston is moved slidably downwardly when a pilot signal pressure is applied from the outside; and a holding poppet mounted at the direction control valve in such a manner as to be located below the spool, the holding poppet including a back pressure chamber filled with a hydraulic fluid. 
         [0016]    In accordance with a preferable embodiment, the spool may have a groove formed on the outer circumference of the upper end thereof so that the ring member is partially fitted into the groove when viewed from a cross section of the ring member. 
         [0017]    In accordance with another preferable embodiment, the holding valve may further include a plug fittingly coupled to the space portion of the valve block and configured to prevent the upward movement of the piston, the plug including a pilot signal pressure port formed at a top thereof. In this case, the plug may be screw-coupled to the space portion  120  of the valve block. 
         [0018]    In accordance with still another preferable embodiment, an O-ring may be interposed between the plug and the valve block to hermetically seal the space portion of the valve block. 
       Advantageous Effect 
       [0019]    The holding valve for a construction machine in accordance with an embodiment of the present invention as constructed above has the following advantages. 
         [0020]    The vertical hole is formed in the valve block to allow the spool to be slidably coupled to the hole, so that a conventionally used sleeve can be removed, thereby making a structure of the holding valve simple and reducing the manufacturing cost. 
         [0021]    In addition, since the spool and the spool guide are securely fixed in position by means of the ring member interposed therebetween, assemblability is relatively further improved as compared to the case where a double nut is applied to the holding valve. 
         [0022]    Further, the plug is fittingly coupled to the space portion of the valve block so that an abnormal assembly of the piston can be prevented unlike a conventional holding valve to which a cover is applied. 
     
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
         [0023]    The above objects, other features and advantages of the present invention will become more apparent by describing the preferred embodiments thereof with reference to the accompanying drawings, in which: 
           [0024]      FIG. 1  is a schematic perspective view showing a conventional holding valve for a construction machine in accordance with the prior art; 
           [0025]      FIG. 2  is a schematic cross-sectional view showing a state in which the holding vale shown in  FIG. 1  is mounted on a direction control valve; 
           [0026]      FIG. 3  is a schematic cross-sectional view showing a state in which a holding vale for a construction machine in accordance with an embodiment of the present invention is mounted on a direction control valve; and 
           [0027]      FIG. 4  is an enlarged view showing a main element of the holding valve for a construction machine shown in  FIG. 3 . 
       
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
       [0028]    Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The matters defined in the description, such as the detailed construction and elements, are nothing but specific details provided to assist those of ordinary skill in the art in a comprehensive understanding of the invention, and the present invention is not limited to the embodiments disclosed hereinafter. 
         [0029]    Hereinafter, a holding valve for a construction machine in accordance with an embodiment of the present invention will be described with reference to  FIGS. 3 and 4 . 
         [0030]    As shown in  FIGS. 3 and 4 , the holding valve  1  for a construction machine includes a valve block  100 , a spool assembly  200 , an elastic member  300 , a piston  400 , and a holding poppet  500 . The most distinct aim of the holding valve  1  for a construction machine is to improve assemblability and reduce the manufacturing cost. In addition, the holding valve  1  may include a plug  600 . 
         [0031]    The valve block  100  is mounted between an actuator for a work apparatus (not shown) such as a boom or arm cylinder and a direction control valve C. The valve block  100  includes a space portion  120  formed at an upper portion thereof so that the spool assembly  200 , the elastic member  300 , and the piston  400  are accommodated in the space portion  120 . In addition, the valve block  100  includes a vertical hole  110  formed under the space portion  120 . The vertical hole  110  of the valve block  100  is provided to enable the spool assembly  200  to be slidably moved vertically along the hole  110 . Also, the valve block  100  includes a plurality of drain flow paths  130  and  140 . A first drain flow path  130  of the valve block  100  is provided to drain a hydraulic fluid when a holding function is released, and a second drain flow path  140  is provided to prevent a back pressure of the piston  400  from being generated. 
         [0032]    The spool assembly  200  functions to hold a high load in the valve block  100 , and includes a spool  210 , a spool guide  220 , and a ring member  230  as shown in  FIGS. 3 and 4 . 
         [0033]    The spool  210  is slidably coupled to the vertical hole  110  of the valve block  100 . In this case, the diameters of the vertical hole  110  of the valve block  100  and the spool  210  are formed to correspond to each other, so that the necessity of a sleeve used to couple a spool to a valve block in a conventional holding vale is eliminated, thereby making a structure of the holding valve simple and reducing the manufacturing cost. 
         [0034]    In addition, it is required that a lower end of the spool  210  should be formed extendably to prevent the spool  210  from being passing through the vertical hole  110  of the valve block  100 . Further, the lower end of the spool  210  seal the vertical hole  110  of the valve block  100  in a state in which the spool  210  is not downwardly moved by means of the elastic member  300 , which will be described later. Resultantly, a back pressure chamber  510  of the holding poppet  500  is closed so that the pressure of a hydraulic fluid contained in the back pressure chamber  510  is held in the back pressure chamber  510 . 
         [0035]    The spool guide  220  is fixedly fitted around the outer circumference of the upper end of the spool  210 . The spool guide  220  includes a protruding part (not designated by a reference numeral) formed protrudingly along the outer circumference of the upper end thereof. The protruding part of the spool guide  220  is provided to support the elastic member  300  that gives an elastic force to the spool assembly  200 . 
         [0036]    The ring member  230  is interposed between the outer circumference of the upper end of the spool  210  and the inner circumference of the spool guide  220  so as to securely fix the spool guide  220  and the spool  210  with respect to each other. That is, the spool  210  and the spool guide  220  are securely fixed using the ring member  230  to improve assemblability unlike a conventional holding valve in which the spool guide  220  is fixed to the spool  210  using the double nut. 
         [0037]    In this case, preferably, the spool  210  has a groove (not designated by a reference numeral) formed on the outer circumference of the upper end thereof so that the ring member  230  can be partially fitted into the groove when viewed from a cross section of the ring member as shown in  FIG. 4 . For example, when the inner diameter of the outer circumference of the upper end of the spool guide  220  is formed to be larger than the outer diameter of the outer circumference of the upper end of the spool  210  and the groove of the spool  210  is formed such that the ring member  230  is fitted by about the half into the groove when viewed from a cross section of the ring member, the remaining half portion of the ring member  230 , which is protruded outwardly from the spool  210  is brought into close contact with the inner circumferential surface of the upper end of the spool guide  220  so that the spool guide  220  and the spool  210  are securely fixed with respect to each other. In this case, the ring member  230  is fixedly fitted into the groove of the spool  210 , and thus the spool  210  is prevented from being moved upwardly or downwardly relative to the spool guide  220  so that the spool guide  220  and the spool  210  can be firmly fixed with respect to each other. The reason for this is that the groove of the spool  210  serves as a sort of retaining step. 
         [0038]    A C-ring or retainer may be used as the ring member  230 . 
         [0039]    The elastic member  300  is provided to give an elastic member. The elastic member  300  is fitted around the outer circumference of the spool guide  220 . In this case, the elastic member  300  is seated at a lower end thereof on a face adjacent to the vertical hole  110  of the valve block  100  and supported at an upper end thereof by the spool guide  220 . 
         [0040]    In this case, as described above, the protruding part is preferably formed at the upper end of the spool guide  220  in order to support the elastic member  300  without any escape. Thus, the upper end of the elastic member  300  is supported by the underside of the protruding part of the spool guide  220 . 
         [0041]    Members made of various elastic materials can be used as the elastic member  300 , and a compression spring is the most suitable for the elastic member  300 . 
         [0042]    The piston  400  is mounted in the space portion  120  of the valve block  100  in such a manner as to be located above the spool  210 , and a pilot pressure chamber is formed in the space portion  120  of the valve block  100 . The piston  400  is moved slidably downwardly and provides a force for enabling the spool assembly  200  to be slidably moved downwardly when a pilot signal pressure is applied from the outside to release a high load. Meanwhile, a spring  410  is separately mounted on the underside of the piston  400  so as to provide an elastic force. 
         [0043]    The holding poppet  500  serves to temporarily limit a high load by which the actuator for a work apparatus descends. The holding poppet  500  is mounted at the direction control valve C in such a manner as to be located below the spool  210 , and includes a back pressure chamber  510  filled with a hydraulic fluid. 
         [0044]    The plug  600  as a substitute for a conventional cover is provided to prevent abnormal assembly of the piston  400 . The plug  600  is fittingly coupled to an upper portion of the space portion  120  of the valve block  100  so as to prevent the upward movement of the piston  400 . The plug  600  includes a pilot signal pressure port  610  formed at a top thereof so that a pilot signal pressure is applied to the piston  400  from the outside through the pilot signal pressure port. In this case, the plug  600  is fittingly coupled to the space portion  120  of the valve  100 , and may be screw-coupled to the space portion  120  to achieve a more secure coupling between the plug  600  and the valve block  100 . 
         [0045]    Meanwhile, in the case where the plug  600  is coupled to the space portion  120  of the valve block  100 , an O-ring  620  is preferably interposed between the plug  600  and the valve block  100  so as to hermetically seal the space portion  120 . 
         [0046]    For reference, in  FIG. 3 , a non-explained reference numeral  520  denotes a spring mounted in the holding poppet  500  to give an elastic force to the holding poppet  500 , and a reference numeral  530  denotes an orifice for pressure communication between the back pressure chamber  510  of the holding poppet  500  and the actuator for a work apparatus. 
         [0047]    The operation principle of the holding valve for construction machine in accordance with an embodiment of the present invention will be described hereinafter. 
         [0048]    The holding valve  1  performs a holding function to prevent a free fall of an actuator of the construction, for example, a boom or arm cylinder. As shown in  FIG. 3 , a pressure P 1  of the back pressure chamber  510  of the holding poppet  500  is identical to a pressure of the actuator C 1  for work apparatus through the orifice  530 , but a hydraulic pressure area of the back pressure chamber  510  is larger than that of the actuator for a work apparatus, leading to a further increase in pressure. For this reason, the holding poppet  500 , i.e., a hydraulic tank-side flow path C 2  for a hydraulic fluid returned from the actuator for a work apparatus is held in a closed state by a seat part of the holding poppet  500 , so that the work apparatus such as the boom or the arm can maintain a holding state without any free fall. 
         [0049]    On the other hand, when a pilot signal pressure Pi is applied to the piston  400  to operate the work apparatus such as the boom or the arm, the piston  400  is moved downwardly or descends, so that the spool  210  is slidably moved downwardly on the vertical hole  110  of the valve block  100  to cause the hydraulic fluid filled in the back pressure chamber  510  of the holding poppet  500  to be supplied to the hydraulic tank-side flow path C 2  through the check valve  700  via the first drain flow path  130  and the drain flow path C 3  of the direction control valve C. 
         [0050]    Accordingly, the holding poppet  500  is moved upwardly or ascends due to a force acting by the pressure C 1  of the actuator for a work apparatus, i.e., the outside of the holding poppet  500  along with a drop of the internal pressure P 1  of the holding poppet  500 . Resultantly, the hydraulic fluid of the boom or arm cylinder flows to C 2  from C 1  to cause the boom or arm cylinder to be operated. 
       INDUSTRIAL APPLICABILITY 
       [0051]    As described above, the holding valve for a construction machine in accordance with the present invention the spool can be coupled to the hole of the valve block without a separate sleeve, and the spool guide can securely fixed to the spool by means of the ring member, but not the double nut, thereby making a structure of the holding valve simple, improving assemblability, and reducing the manufacturing cost.