Abstract:
A method for controlling a safety feature for a hydraulic machine is provided. The method includes detecting when at least control valve for a controller of an implement for the hydraulic machine is stuck in a position. An exhaust valve for the hydraulic control system is then moved to a closed position to prevent movement of the implement of the hydraulic machine.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a hydraulic control system, and more particularly, to a control valve safety feature for the hydraulic control system 
       BACKGROUND OF THE INVENTION 
       [0002]    Hydraulic systems for heavy equipment, such as excavators, backhoes, bulldozers, front end loaders, earthmovers, etc., typically use hydraulic controls to manipulate implements of the equipment. For example, hydraulic controls are used to manipulate the load basket for front end loaders. The hydraulic control system includes multiple control valves to provide for manipulation of each sub-system of the implement separately. Additionally, each sub-system may include multiple control valves to thereby control the movement of the implement. Therefore, the hydraulic control system typically includes multiple control valves for controlling multiple features of each implement. 
       SUMMARY OF THE INVENTION 
       [0003]    A method for controlling a hydraulic control system is provided. The method includes detecting a condition in which at least one control valve for a controller of an implement for the hydraulic fluid control system is stuck in an open position. An exhaust valve for the fluid control system is then moved to a closed position. 
         [0004]    A method for controlling a safety feature for a hydraulic machine is provided. The method includes detecting when at least one control valve of a first rod controller, a first head controller, a second rod controller, or a second head controller of a fluid control system for the hydraulic machine is stuck in a position. An exhaust valve for the fluid control system is then moved to a closed position to prevent movement of a sub-assembly of the hydraulic machine. 
         [0005]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a general perspective illustration of an embodiment of construction equipment utilizing a hydraulic control system; 
           [0007]      FIG. 2  is a schematic illustration of a piston and cylinder for the construction equipment of  FIG. 1 ; 
           [0008]      FIG. 3  is a schematic illustration of a first embodiment of a hydraulic control system for the construction equipment of  FIG. 1 ; and 
           [0009]      FIG. 4  is an enlarged schematic illustration of a portion of the first embodiment of the hydraulic control system of  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0010]    Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  illustrates a piece of construction equipment  10 , such as but not limited to, an excavator, a backhoe, a bulldozer, an earth mover, etc. The construction equipment  10  includes at least one implement  12 . In the embodiment shown the construction equipment  10  is a front end loader and the implement  12  is a lift basket. The equipment  10  includes a hydraulic control system  14  for manipulating the implement  12 . The implement  12  may include multiple sub-assemblies requiring independent control to manipulate the implement  12 . In the embodiment shown, the multiple sub-assemblies for the equipment  10  include a first piston assembly  16  for tilting the implement  12  and a second piston assembly  18  for lifting the implement  12 . In the embodiment shown the sub-assemblies are utilized for lifting and tilting the implement  12 . However, other sub-assemblies for different purposes in manipulating the implement  12  may be utilized depending on the type of equipment  10  that the hydraulic control system  14  is utilized with. 
         [0011]    Referring to  FIGS. 1 and 2 , the first piston assembly  16  includes a first piston  20  and cylinder  22 . The first piston  20  and the first cylinder  22  define a first rod chamber  24  and a first head chamber  26 . Likewise, the second piston assembly  18  includes a second piston  28  and a second cylinder  30 . The second piston  28  and the second cylinder  30  define a second rod chamber  32  and a second head chamber  34 . The hydraulic control system  14  individually controls fluid flow to the first rod chamber  24 , first head chamber  26 , second rod chamber  32  and the second head chamber  34 . 
         [0012]    Referring to  FIGS. 2 and 3 , an embodiment of the hydraulic control system  14  is explained. The hydraulic control system  14  includes a first rod controller  36  to control the flow of fluid with respect to the first rod chamber  24 . A first head controller  38  controls the flow of fluid with respect to the first head chamber  26 . A second rod controller  40  controls the flow of fluid with respect to the second rod chamber  32 . Finally, a second head controller  42  controls the flow of fluid with respect to the second head chamber  34 . 
         [0013]    The first rod controller  36 , first head controller  38 , second rod controller  40  and the second head controller  42  are arranged in parallel with one another. Operation of the first rod controller  36  and the first head controller  38  may be coordinated with one another due to the corresponding positions of the controllers on opposing ends of the first piston assembly  16 . Likewise, operation of the second rod controller  40  and the second head controller  42  may be coordinated with one another due to the corresponding positions of the controllers on opposing ends of the second piston assembly  18 . 
         [0014]    A variable displacement supply pump  46  moves the fluid from a supply tank  45  to the first rod controller  36 , first head controller  38 , second rod controller  40 , and second head controller  42 . The supply pump  46  and the flow of fluid to the first rod controller  36 , first head controller  38 , second rod controller  40 , and the second head controller  42  are controlled by a main supply valve  56 . A tank controller  44  controls the flow of return fluid from the first rod controller  36 , first head controller  38 , second rod controller  40  and the second head controller  42  through a hydraulic return line  47  back to the supply tank  45 . 
         [0015]    The tank controller  44  includes an electrically controlled tank pilot valve  68 , a hydraulically controlled middle-stage pilot valve  54  and a hydraulically controller tank poppet valve  66 . The tank pilot valve  68  adjusts the tank middle-stage pilot valve  54  which in turn adjusts the tank poppet valve  66  to control the return of fluid to the supply tank  45  from the first rod controller  36 , first head controller  38 , second rod controller  40 , and the second head controller  42 . Together the tank pilot valve  68  and the tank middle-stage pilot valve  54  provide a two-stage control of return fluid to the tank  45 . 
         [0016]    Referring to  FIG. 4 , an enlarged view of a portion of the hydraulic control system  16  shown. Operation of the hydraulic control system  16  is explained with respect to the first rod controller  36  although the first head controller  38 , second rod controller  40  and the second head controller  42  operate in a similar manner. 
         [0017]    The first rod controller  36  includes a middle-stage pilot valve  48  a main stage poppet valves  60  and  62  which control the flow of fluid into and out of the first rod chamber  24 . The middle-stage pilot valve  48  is a variable valve which is hydraulically controlled by a pilot valve  58 . The pilot valve  58  controls the position of the middle-stage pilot valve  48  to adjust the fluid flow into the first rod chamber  24 . The pilot valve  58  is electrically controlled by the first rod controller  36 . Together the pilot valve  58  and the middle-stage pilot valve  48  provide a two-stage control of fluid flow for the first rod chamber  24 . 
         [0018]    During operation of the hydraulic control system  14  the first rod controller  36  may detect that the pilot valve  58 , the middle-stage pilot valve  48  or the main stage poppet valves  60  and  62  are stuck. For example, the first rod controller  36  may detect the open position of the pilot valve  58 , the middle-stage pilot valve  48 , the main stage poppet valve  60 , or the main stage poppet valve  62  through a valve position sensor  64 . Other means and sensors for detecting an open position for the pilot valve  58 , the middle-stage pilot valve  48 , the main stage poppet valve  60 , or the main stage poppet valve  62  may also be utilized. 
         [0019]    If the pilot valve  58 , the middle-stage pilot valve  48 , the main stage poppet valve  60 , or the main stage poppet valve  62  is stuck in position then the flow of fluid into and out of the first rod chamber  24  can not be controlled. While the first head controller  38  may still be operational, the position of the first piston assembly  16  (shown in  FIGS. 1 and 2 ) can no longer be controlled. When the pilot valve  58 , the middle-stage pilot valve  48 , the main stage poppet valve  60 , or the main stage poppet valve  62  for the first rod controller  36  cannot be adjusted the flow of fluid into or out of the first rod chamber  24  cannot be adjusted. This may create undesirable fluid flow between the first rod chamber  24  and the hydraulic return line  47  which may result in undesirable movement of the implement  12 . The tank controller  44  is used to close the tank poppet valve  66  to ensure that any undesirable movement of the implement  12  does not occur. Closing the tank poppet valve  66  prevents the flow of fluid back to the tank  45 . Therefore, flow of fluid from the hydraulic return line  47  to the tank  45  is blocked which in turn prevents the flow of fluid from the first rod chamber  24 . 
         [0020]    The closed tank poppet valve  66  prevents fluid from flowing out of the first rod chamber  24  to the tank  45 . The closed tank poppet valve  66  prevents fluid from flowing from the first head chamber  26 , second rod chamber  32 , and second head chamber  34  back to the supply tank  45  as well. Therefore, closing the poppet valve  66  prevents undesirable movement of the implement  12  when the main stage pilot valve  58 , the middle-stage pilot valve  48 , the main stage poppet valve  60 , or the main stage poppet valve  62  is stuck in position. Closing the tank poppet valve  66  provides an additional safety feature to prevent movement of the implement  12  until the pilot valve  48 , the first spool valve  60 , or the second spool valve  62  can be repaired. 
         [0021]    As can be seen, the first head controller  38 , second rod controller  40 , and the second head controller  42  also each include a pilot valve  58 , a middle-stage pilot valve  48 , a main stage poppet valve  60 , and a main stage poppet valve  62 . Therefore, the first head controller  38 , the second rod controller  40 , and the second head controller  42  may each detect a stuck valve in a similar manner as that of the first rod controller  36 . Additionally, if any of the pilot valve  58 , the middle-stage pilot valve  48 , the main stage poppet valve  60 , or the main stage poppet valve  62  are stuck at the same time as another the pilot valve  58 , the middle-stage pilot valve  48 , the main stage poppet valve  60 , or the main stage poppet valve  62  the tank controller  44  may close the tank poppet valve  66  in a similar manner. 
         [0022]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.