Patent Publication Number: US-9404235-B2

Title: Coupling arrangement

Description:
TECHNICAL FIELD 
     The present disclosure is directed to a coupling arrangement, more particularly to a coupling arrangement for coupling a work tool to a machine. 
     BACKGROUND 
     Work tools, such as shears, grabs, or buckets may be coupled with host machines, such as excavators, to perform work operations like cutting, grabbing or excavating. The work tools may be coupled to a boom or stick mechanism of the host machine via a fixed connection or a quick release connection. 
     A quick release connection allows for a relatively easy exchange of the work tool whereby the operator may connect or change a work tool without leaving the cab. The machine mounting bracket is arranged to slide into the work tool mounting bracket, when the work tool is positioned on the ground. After aligning the mounting bracket of the work tool and the mounting bracket of the machine, a locking device may be moved into a locked position to lock the work tool to the machine. 
     When connecting the work tool to the machine, the hydraulic hoses of the machine and work tool pressure fluid circuits may be connected for driving the work tool. Automatic hydraulic hose connection systems are known which may be activated by the operator from the cab for connection of the hydraulic hoses. Such systems may often be dependent on the connection of the work tool to the machine. Hydraulic hose couplers may be provided and arranged so that during connection of the work tool to the machine the hose couplers are also automatically connected. When the work tool mounting bracket is connected to the machine mounting bracket, the hose couplers may be contemporaneously connected. 
     However, aligning the hose couplers may require a higher level of accuracy than alignment of the mounting brackets. In practice, when a coupling arrangement is provided with such hose couplers, an operator may try to avoid relatively rough movements and high forces that are typical when connecting the work tool to the machine. Such actions may result in loss in efficiency. Nevertheless, a relatively high risk to cause damage to the hydraulic hose couplers remains due to the high forces and potential rough alignments between the mounting brackets. When the hose couplers are not aligned accurately, at connection of the machine and work tool pressure fluid circuits, pressurized fluid may escape or the couplers and/or hoses may need to be changed. As the hydraulic circuits of host machines may operate under relatively high pressures, any leakage may cause major spillage of hydraulic fluid and significant downtime. 
     EP1388616 discloses a coupling arrangement for coupling two ends of a pressurized hydraulic fluid circuit of a work tool and a machine. The coupling arrangement may comprise a quick release mounting bracket for coupling a work tool to a machine. The coupling arrangement may comprise a receiving fluid coupler and a moving fluid coupler, each coupler being connected to a hydraulic hose of a main hydraulic circuit. 
     One of the couplers may be arranged on the work tool and the other coupler may be arranged on the machine. Both couplers may be connected to each other for providing a fluid passage between the hydraulic hoses so that pressurised fluid may circulate between the fluid circuit of a work tool and a machine. The moving fluid coupler may be moved on a sledge to and from the receiving fluid coupler by an actuator. When the respective moving coupler is coupled to the receiving coupler, a locking notch may engage the moving coupler to keep both couplers coupled so that the actuator may release its pressure while fluid flows through the couplers. The locking notch requires significant space in the coupling arrangement. Moreover, after multiple engagements, the locking notch may become damaged, or may allow for play to occur which may cause leakage of fluid between the couplers. However, without the locking notch, the actuator would have to withstand significant forces that are exerted by the pressurised fluid flowing through the circuit, which may disengage the couplers. Furthermore, during movement of the coupler, the hydraulic hose that is coupled to the moving coupler may become wedged, caught, or trapped in or between the structure of the machine and/or the work tool. 
     WO2010062166, in the name of Caterpillar Work Tools B.V., discloses a coupling arrangement for coupling a work tool to a machine. The coupling arrangement may have a locking arrangement for locking the work tool to the machine. The locking arrangement may comprise a locking member which may be moved to a locked position where it abuts the locking member receiving elements. 
     The coupling arrangement further may have at least two fluid couplers arranged to be connected to each other for establishing a fluid passage between a main pressurized fluid circuit channel of a work tool and a main pressurized fluid circuit channel of a machine. The coupling arrangement may further have a driving arrangement for driving at least one of the fluid couplers for connection to the other fluid coupler, the driving arrangement being separate from the main pressurized fluid circuit. 
     The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of the prior art system. 
     BRIEF SUMMARY OF THE INVENTION 
     The present disclosure provides a coupling arrangement for fluid coupling a work tool to a machine comprising a plurality of coupler assemblies slideably mounted in a plurality of corresponding cavities for coupling a machine fluid circuit and a work tool fluid circuit, the coupler assembles partitioning the cavities to form chambers; and a rail circuit connecting the chambers. 
     Other features and advantages of the present disclosure will be apparent from the following description of various embodiments, when read together with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of the present disclosure will be more fully understood from the following description of various embodiments, when read together with the accompanying drawings, in which: 
         FIG. 1  is a side view of a machine and a work tool provided with a coupling arrangement according to the present disclosure; 
         FIG. 2  is a schematic representation of an embodiment of the coupling arrangement according to the present disclosure; 
         FIG. 3  is an isometric view of an embodiment of a coupling assembly according to the present disclosure; 
         FIG. 4  is a cross sectional view of a mounted coupling assembly of  FIG. 2  in a retracted position according to the present disclosure; and 
         FIG. 5  is a cross sectional view of a mounted coupling assembly of  FIG. 2  in an extended position according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure generally relates to a coupling arrangement  10  for coupling a machine hydraulic fluid circuit to a work tool hydraulic fluid circuit. 
       FIG. 1  illustrates a host machine  1 , as a hydraulic excavator, which may be provided with a hydraulic boom mechanism for driving a boom  2  and a work tool  3 . In this description, a boom  2  may be understood as comprising a hydraulic stick mechanism, or similar mechanisms. 
     Machine  1  may be a mobile machine such as for example an excavator, a back hoe, a digger, a loader, a knuckle boom loader, a harvester or a forest machine. 
     The work tool  3  may be coupled to the machine  1  through the boom  2 . In the embodiment shown, the work tool  3  may comprise a rotary cutter. In other embodiments, work tools  3  may for example include buckets, grapples, hammers and pulverizers. 
     The work tool  3  may comprise a frame that which carries multiple exchangeable and/or interchangeable tools. 
     The machine  1  may be provided with a coupling arrangement  10 . The coupling arrangement  10  may allow for fluid coupling between a machine bracket  12  and a work tool bracket  14 . The machine bracket  12  may be connected to the machine  1 . The work tool bracket  14  may be connected to the work tool  3 . 
     A pressurised fluid assembly  15  may extend along the boom  2  for moving the boom  2  and the work tool  3 . The pressurised fluid assembly  15  may comprise multiple hydraulic circuits, including a machine fluid circuit and an actuation fluid circuit. 
     The work tool  3  may comprise a work tool fluid circuit for the hydraulic control thereof. The machine fluid circuit may control fluid flow through the work tool fluid circuit. 
     The machine fluid circuit may be arranged to drive the boom  2  and to pivot the boom parts with respect to each other. The machine fluid circuit may be arranged to move the work tool  3 . For example, the machine fluid circuit may be arranged to pivot and/or rotate the work tool  3  or may be arranged to drive moving parts in the work tool  3 , such as rotary parts. The actuation fluid circuit may be arranged to enable fluid coupling between the machine fluid circuit and the work tool fluid circuit. 
       FIG. 2  illustrates an embodiment of a coupling arrangement  10  with hydraulic connections for connecting a machine bracket  12  to a work tool bracket  14  and for forming at least one fluid passage between the machine fluid circuit and the work tool fluid circuit. 
     The coupling arrangement  10  may comprise the machine bracket  12  which may be provided with at least one cavity  16 . The cavity  16  may extend through the machine bracket  12  and may have a cavity wide portion  18  and a cavity narrow portion  20 . 
     Cavity narrow portion  20  may be formed as a plurality of extensions of the wall of cavity  16 . In an embodiment, the cavity narrow portion  20  may be a single block extension of the wall of cavity  16 . A shoulder  22  may be formed between the cavity wide portion  18  and the cavity narrow portion  20 . 
     The coupling arrangement  10  may comprise a coupler assembly  24  movably mounted in the cavity  16 . Both the cavity  16  and the coupler assembly  24  may be correspondingly shaped to allow for the relative movement of the coupler assembly  24 . The coupler assembly  24  may be slidably mounted with at least portions thereof being in sliding engagement with the wall of the cavity  16 . The coupler assembly  24  may slide between a refracted position, where the coupler assembly  24  retracts fully or partially into the cavity  16 , and an extended position, where the coupler assembly  24  protrudes from the machine bracket  12  for engagement with a corresponding fluid coupler in the work tool bracket  14 . 
     The coupling arrangement  10  may comprise a chamber  26  provided in the cavity  16 . In an embodiment the chamber  26  may be formed in the cavity wide portion  18  and may be bounded by the wall of the cavity wide portion  18 , the shoulder  22  and the coupler assembly  24 . 
     The size of chamber  26  may vary through the movement of the coupler assembly  24  relative to the machine bracket  12 . The size of chamber  26  may be made to vary through the inflow and outflow of hydraulic fluid which may move the coupler assembly  24  relative to the machine bracket  12 . The changes in the size of the chamber  26  may effect the corresponding retraction and extension of the coupling assembly  24 . 
     In an embodiment the machine bracket  12  may be provided with a series of cavities  16 . Each cavity  16  may have a movably mounted coupler assembly  24  and a chamber  26 . For fluid coupling the machine bracket  12  to a work tool bracket  14 , the work tool bracket  14  may comprise fluid couplers which connect to corresponding coupler assemblies  24  mounted in the machine bracket  12 . Fluid coupling the machine bracket  12  to a work tool bracket  14  may be effected with the coupler assemblies  24  in the fully extended positions or the connect position. The coupler assemblies  24  may be in a disconnect position when refracted from the fully extended position. 
     For operation and control of the coupling arrangement  10  the hydraulic connections may be suitably provided. The machine fluid circuit may comprise hydraulic lines leading to the cavities  16  for connection to respective coupler assemblies  24 . In an embodiment, hydraulic lines A, B, C, D and L of the machine fluid circuit may allow flow of hydraulic fluid to and from the work tool fluid circuit when fluid coupling between the brackets  12 ,  14  are established. Hydraulic fluid may flow through the coupler assemblies  24  in the connect position to and from the corresponding fluid couplers in the work tool bracket  14 . 
     The coupling arrangement  10  may include hydraulic connections to a quick coupler mechanism for locking together brackets  12 ,  14 , such as a quick coupler wedge. 
     The actuation fluid circuit may be controlled independently from the machine fluid circuit. The actuation fluid circuit includes at least one actuator  28 . In an embodiment, the actuator may be a hydraulic cylinder. The actuator  28  may be connected contemporaneously to all the coupler assemblies  24 . The actuator  28  may be connected to the coupler assemblies  24  through suitable linkages such as through a connecting rod. 
     Refraction or extension of the actuator  28  may correspondingly retract or extend the coupler assemblies  24  to a disconnect position or to a connect position respectively. The coupler assemblies  24  may be uniformly retracted or extended by the actuator  28 . In an embodiment, a pair of actuators  28  may be provided to ensure an evenly balance load for fluid coupling or decoupling between the coupler assemblies  24  and the corresponding fluid couplers. 
     The operation of the actuation fluid circuit may be controlled by a bracket switch  30 . Bracket switch  30  may control hydraulic fluid flow for the extension of the coupler assemblies  24 . Bracket switch  30  may be suitably disposed in order to detect when a work tool bracket  14 , having at least one corresponding fluid coupler, is mounted to a machine bracket  12 . In an embodiment, the bracket switch  30  may be suitably positioned on the machine bracket  12 . The bracket switch  30  may not be activated if the work tool bracket  14  does not carry any corresponding fluid couplers and fluid coupling may not be effected as no flow of hydraulic fluid to extend the coupler assemblies  24  to the connect position is permitted by the bracket switch  30 . Bracket switch  30  may prevent actuation of the coupler assemblies  24  when no corresponding fluid couplers are present in the attached work tool bracket  14 . 
     The operation of the machine fluid circuit may be further controlled by a switch  32 . Switch  32  may control the flow of hydraulic fluid to a locking device  34  for the unlocking of the brackets  12 ,  14 . Switch  32  may be arranged to be activated only when the actuator  28  is in a fully retracted position. The switch  32  may be arranged not to be activated when the actuator  28  is in an extended position and unlocking of the brackets  12 ,  14  may not be effected as no flow of hydraulic fluid to actuate the locking device  34  is permitted by the switch  32 . Switch  32  prevents premature decoupling between the machine bracket  12  and the work tool bracket  14  when coupler assemblies  24  have not been retracted from the connect position. 
     In an embodiment the switches  30 ,  32  may be sensors connected to actuating mechanisms. In an embodiment the switches  30 ,  32  may be a solenoid or a hydro mechanical device. In an embodiment the switches  30 ,  32  may be hydromechnical switches which are activated upon physical contact with work tool bracket  14  and the actuator  28 . 
     The coupling arrangement  10  may further comprise a rail circuit  13 , denoted by a bold line in  FIG. 2 , which connects together each chamber  26 . The rail circuit  13  may be comprised of a single hydraulic line connected to each of the chambers  26  through further hydraulic lines. The rail circuit  13  may distribute the fluid pressure equally among the chambers  26 . Accordingly, the highest pressure in any one chamber  26  may generate the load required to effect the corresponding extension of the coupler assemblies  24  in the other chambers  26 . The chamber  26  having the highest working pressure may define the force presented to all coupler assemblies  24 . 
     The rail circuit  13  may be connected to the actuators  28 . In an embodiment, the rail circuit  13  may be connected to the piston side of the actuators  28 , provided as a hydraulic cylinder. 
     The coupling arrangement  10  may be connected to a hydraulic power circuit  35  for providing hydraulic pressure to lock and unlock machine bracket  12  to the work tool bracket  14 . Unlocking of the brackets  12 ,  14  by the hydraulic power circuit  35  may be controlled by the switch  32  through hydraulic connections between the hydraulic power circuit  35  and the switch  32 . 
     The hydraulic power circuit  35  may be connected to the actuator  28 . In an embodiment, the hydraulic power circuit  35  may be connected to the rod side of the actuator  28 , provided as a hydraulic cylinder. 
     The hydraulic power circuit  35  may be arranged to provide pressurised fluid to the rail circuit  13 . The bracket switch  30  may be disposed in the connection between the hydraulic power circuit  35  and the rail circuit  13 . 
       FIG. 3  illustrates a coupler assembly  24 . The coupler assembly  24  may comprise a hollow plunger  36 . Plunger  36  may have a suitable form and dimensions to be slidingly mounted within the cavity  16 . Plunger  36  may have a plunger narrow portion  38 , a gate portion  39  and a plunger wide portion  40 . In an embodiment, the gate portion  39  may be positioned within the plunger wide portion  40  and adjacent to the plunger narrow portion  38 . The gate portion  39  may be recessed from the plunger wide portion  40 . 
     The plunger narrow portion  38  may be in sliding engagement with the cavity narrow portion  20 . The plunger narrow portion  38  may be arranged to sealingly engage with cavity narrow portion  20  to restrict leakage of hydraulic fluid between the plunger narrow portion  38  and the cavity narrow portion  20 . 
     The plunger wide portion  40  may be in sliding engagement with the cavity wide portion  18 . The plunger wide portion  40  may be arranged to sealingly engage with cavity wide portion  18  to restrict leakage of hydraulic fluid between the plunger wide portion  40  and the cavity wide portion  18 . 
     The gate portion  39  may not be in contact with wall of the cavity wide portion  18 . 
     A fluid coupler  42  may be positioned within the plunger  36 . Plunger  36  may be provided with retaining structures to hold the fluid coupler  42  within the walls thereof. Fluid coupler  42  may have a through fluid channel  43  along the longitudinal axis of the plunger  36 . The fluid channel  43  may communicate with the hollow of the plunger  36 . 
     The fluid coupler  42  may couple with the corresponding fluid coupler, having a fluid channel disposed therein, in the work tool bracket  14 . Respective fluid channels form a fluid passage when the fluid couplers are connected. At fluid coupling hydraulic fluid from the machine fluid circuit may flow through the fluid channels to the work tool fluid circuit. Fluid coupler  42  may be formed as a male or female element for coupling to the fluid coupler with the corresponding form. 
     Extending laterally from the plunger  36  may be a pressure element  44 . In an embodiment the pressure element  44  may encircle the plunger  36  and may be formed as a rib or a protrusion. In an embodiment the pressure element  44  may extend from and encircle the plunger wide portion  40 . With the coupler assembly  24  mounted in the cavity  16 , the pressure element  44  may extend from the plunger  36  through the cavity  16  to slidingly engage the wall of the cavity wide portion  18 . The pressure element  44  may separate the chamber  26  from rest of the cavity wide portion  18 . 
     The pressure element  44  may be arranged to sealingly engage with the wall of the cavity wide portion  18  to limit leakage of hydraulic fluid between the wall of the cavity wide portion  18  and the pressure element  44 . The pressure element  44  may be suitably shaped or may be provided with a gasket to slidingly and sealingly engage cavity wide portion  18 . 
     The pressure element  44  may have a pressure surface  45  which, in an embodiment, may face the shoulder  22 . The dimensions and/or shape of the pressure surface  45  may be a function of the diameter of the coupler assembly  24 , the diameter of the fluid coupler  42 , the diameter of the corresponding fluid coupler in the work tool bracket  14  and/or the difference in the diameters of the fluid coupler  42  and the corresponding fluid coupler. The dimensions and/or shape of the pressure surface  45  may depend on the fluid dynamics of the fluid coupler  42  and the corresponding fluid coupler. Fluid dynamics may be dependent on the structure of fluid couplers, the type of hydraulic fluid and/or the fluid pressure used for the fluid coupling. 
     At least one bore  46  may be provided in the plunger  36  which may allow flow of hydraulic fluid from the exterior of the plunger  36  into the hollow thereof. The fluid channel  43  of the fluid coupler  42  may communicate through the hollow of the plunger  36  with the bore  46 . The bore  46  may be provided in the gate portion  39 . In an embodiment, the gate portion  39  may be provided with a plurality of bores  46 . Hydraulic fluid may flow around the gate portion  39  guided by walls formed by the plunger wide portion  40  and into the hollow through the plurality of bores  46 . 
     In an embodiment, a single bore  46  may be provided in the plunger  36 , not provided with a gate portion  39 . The bore  46  may be positioned between the pressure element  44  and the plunger wide portion  40 . 
     The size and the number of the bores  46  may be a function of the diameter of the coupler assembly  24 , the diameter of the fluid coupler  42 , the diameter of the corresponding fluid coupler in the work tool bracket and/or the difference in the diameters of the fluid coupler  42  and the corresponding fluid coupler. The dimensions and/or shape of the bore  46  may be dependent on the dimension and/or shape of the pressure surface  45 . The dimensions and/or shape of the bore  46  may depend on the fluid dynamics of the fluid coupler  42  and the corresponding fluid coupler. 
       FIGS. 4 and 5  illustrate a coupler assembly  24  slidingly mounted in the machine bracket  12 . In  FIG. 4  the coupler assembly  24  may be retracted to the disconnect position and in  FIG. 5  the coupler assembly  24  may be extracted to the connect position. The retraction of the coupler assembly  24  within the cavity  16  may be limited by the shoulder  22  which may abut pressure surface  45 . 
     Machine bracket  12  may have a machine circuit line  48 , which forms part of the machine fluid circuit, leading to the cavity  16 . Fluid from the machine fluid circuit may flow through the machine circuit line  48  to the cavity  16  through a port  49 . In the machine bracket  12  having plurality of cavities  16 , each cavity  16  may be separately connected to the machine fluid circuit through a plurality of corresponding circuit lines  48 . In an embodiment, hydraulic lines A, B, C, D and L may allow flow of hydraulic fluid to and from the ports  49  through respective machine circuit lines  48 . 
     Machine bracket  12  may have a rail circuit line  50 , which forms part of the rail fluid circuit, leading to the cavity  16 . In an embodiment the rail circuit line  50  leads to the chamber  26 . Fluid from the rail fluid circuit may flow through the rail circuit line  50  to the chamber  26 . 
     The chamber  26  in the cavity wide portion  18  may be bounded by the wall of the cavity wide portion  18 , the shoulder  22 , the pressure surface  45  and the plunger narrow portion  38 . The size of chamber  26  may depend on the inflow and outflow of hydraulic fluid through the rail circuit line  50 . Inflow of fluid into the chamber  26  may result in an increase in fluid pressure therein, as the chamber  26  may be fluid tight. The fluid pressure may act on the surfaces which bound the chamber  26 . The increasing fluid pressure acting on the pressure surface  45  may effect extraction of the coupler assembly  24  slidingly mounted in the machine bracket  12 . The coupler assembly  24  may be extracted to the connect position through continued inflow of hydraulic fluid under pressure to establish fluid coupling between the fluid coupler  42  and the corresponding fluid coupler in the work tool bracket  14 . 
     A diversion passage  52  may extend axially within the plunger  36  from the gate portion  39  toward the pressure element  44 . The diversion passage  52  may be axially aligned with the longitudinal axis of the plunger  36 . In an embodiment the diversion passage  52  may extend beyond the pressure element  44 . Hydraulic fluid flowing through the bores  46  may flow into the hollow of the plunger  36  and to the diversion passage  52 . 
     The dimensions and/or shape of the diversion passage  52  may be a function of the diameter of the coupler assembly  24 , the diameter of the fluid coupler  42 , the diameter of the corresponding fluid coupler in the work tool bracket and/or the difference in the diameters of the fluid coupler  42  and the corresponding fluid coupler. The dimensions and/or shape of the diversion passage  52  may be dependent on the dimension and/or shape of the bore  46 . The dimensions and/or shape of the diversion passage  52  may be dependent on the dimension and/or shape of the pressure surface  45 . The dimensions and/or shape of the diversion passage  52  may depend on the fluid dynamics of the fluid coupler  42  and the corresponding fluid coupler. 
     Extending from the diversion passage  52  may be a diversion line  54 . The diversion line connects the diversion passage  52  to the chamber  26 . In an embodiment the diversion line  54  may extend laterally from the diversion passage  52  to the chamber  26 . In an embodiment, the diversion line  54  may be disposed such that the pressure surface  45  is positioned between the bores  46  and the diversion line  54 . In an embodiment the diversion passage is a hose mounted externally to the plunger  36 . In an embodiment, the diversion line  54  may have a smaller diameter than diversion passage  52  such that the fluid pressure increases as the hydraulic fluid enters the diversion line  54 . Hydraulic fluid flowing into the bore  46  may flow through the diversion passage  52  and the diversion line into the chamber  26 . 
     A check valve  56  may be provided at the junction of the diversion passage  52  and the diversion line  52 . The check valve  56  may permit flow of fluid from the diversion passage  52  to diversion lines  54  and prevent flow of fluid from the diversion line  54  to diversion passage  52 . In an embodiment, check valve  56  may be disposed such that the pressure surface  45  is positioned between the bore  46  and the check valve  56 . 
     With reference to  FIG. 4  the coupler assembly  24  is retracted and may be disconnected from the corresponding fluid coupler. The gate portion  39  may be recessed into the cavity wide portion  18 . The gate portion  39  may be sealed from fluid entry by the cavity wide portion  18 . Port  49  of the machine circuit line  48  may be sealed by the plunger wide portion  40 . 
     In an embodiment, bore  46 , in the plunger  36  not provided with a gate portion  39 , may be recessed into the cavity wide portion  18  and may be sealed from fluid entry by the cavity wide portion  18 . 
     With reference to  FIG. 5  the coupler assembly  24  is extended and may be connected to the corresponding fluid coupler. The gate portion  39  may be positioned to be in fluid communication with the port  49  of the machine circuit line  48 . Fluid may flow from the machine circuit line  48  through port  49  and into the gate portion  39 . Hydraulic fluid may flow around the gate portion  39  and into the hollow of plunger  36  through the plurality of bores  46 . 
     In an embodiment, when the gate portion  39  is in fluid communication with machine circuit line  48  the coupler assembly  24  may be at a fully extended position. In an embodiment, the gate portion  39  may have dimension and/or shape which corresponds to the port  49 . 
     In an embodiment with plunger  36  not provided with a gate portion  39 , when the coupler assembly  24  is extended the bore  46  may be positioned to be in fluid communication with the port  49  of the machine circuit line  48 . Fluid may flow from the machine circuit line  48  through port  49  and into the bore  46 . Hydraulic fluid may flow into the hollow of plunger  36  through the bore  46 . 
     In an embodiment, the bore  46  may have dimension and/or shape which corresponds to the port  49 . In an embodiment, when the bore  46  is in fluid communication with machine circuit line  48  the coupler assembly  24  may be at a fully extended position. 
     With reference to  FIG. 2 , the operation of the coupling arrangement  10  may be initiated by coupling a machine bracket  12  to a work tool bracket  14 . The hydraulic power circuit  35  may be activated to actuate the locking device  34  to lock machine bracket  12  to the work tool bracket  14 . The locking device  34  may be actuated to lock the brackets  12 ,  14  through increased fluid pressure through line X. In an embodiment, the increased fluid pressure may act on the rod side of the locking device  34 . 
     Upon locking of the brackets  12 ,  14 , pressure in the hydraulic lines may increase further. A pressure regulator  58  may be connected to line X. Pressure regulator  58  may open only when the locking pressure in the locking device  34  is higher than a preset value. In an embodiment, the value is selected from the range of 60 bar-90 bar. In an embodiment, the value is 70 bar. Flow of hydraulic fluid to the bracket switch  30  and the rail circuit  13  may be prevented before the brackets  12 ,  14  are mechanically locked. 
     Hydraulic fluid may flow to the bracket switch  30  when the pressure regulator  58  opens to permit fluid flow. Bracket switch  30  may be activated if the work tool bracket  14 , carrying a corresponding fluid coupler, is coupled to the machine bracket  12 . Activation of the bracket switch  30  may effect the actuation of a valve  60  to permit flow of fluid to check valve  62 . 
     Check valve  62  may permit fluid to flow into the rail circuit  13  and through rail circuit lines  50  to the chambers  26 . Increased flow of fluid in the chambers  26  results in increased fluid pressure therein. The fluid pressure may act on the pressure surfaces  45  of the coupler assemblies  24  effecting extension from the disconnect position to an extended position at which a fluid coupling between the fluid couplers  42  and the corresponding fluid couplers in the work tool bracket  14  is established. The build up of pressure in chamber  26  may not enter the hollow of plunger  36  as a result of the check valve  56  which blocks the flow of fluid from the diversion line  54  to the diversion passage  52 . 
     In an embodiment, check valve  62  may permit fluid to flow through the rail circuit  13  to the piston side of the actuators  28 . Increased flow of fluid into the piston side chambers of the actuators  28  may result in increased fluid pressure therein to effect extension of the actuators  28 . The actuators  28  may be connected to the coupler assemblies  24  and may effect a corresponding extension of the coupler assemblies  24 . The extension of the coupler assemblies  24  through extension of the actuators  28  may be optional or may be in addition to the extension effected by the action of the pressurised fluid on the pressure surface  45 . 
     Extraction of the coupler assemblies  24  through the pressure build up in the chambers  26  and/or extension of the actuators  28 , may connect lines A,B,C,D and L through respective lines  48  and ports  49  to the hollows of plungers  36  to allow fluid flow from the machine fluid circuit into the hollow of plunger  36 . If the machine fluid circuit is not actuated, fluid inside the hollow of plunger  36  may remain at atmospheric or tank pressure. Upon actuation of the machine fluid circuit the pressure in the lines  48  and the hollow of plunger  36  may increase. 
     At fluid coupling between the fluid couplers  42  and the corresponding fluid couplers, the gate portions  39  may be in fluid communication with ports  49  allowing fluid to flow through machine circuit lines  48  into the hollow of plunger  36 . Fluid may then pass through fluid channels  43  in the fluid couplers  42  to the respective channels in the corresponding fluid couplers. 
     In an embodiment, at fluid coupling between the fluid couplers  42  and the corresponding fluid couplers, the bores  46  of each plunger  36  may be in fluid communication with ports  49  allowing fluid to flow through machine circuit lines  48  into the hollow of plunger  36 . Fluid may then pass through fluid channels  43  in the fluid couplers  42  to the respective channels in the corresponding fluid couplers. 
     At fluid coupling between the fluid couplers  42  and the corresponding fluid couplers and flow of pressurised fluid through the respective fluid channels, separation forces may be generated which act on the fluid couplers. The separation forces may be countered by the fluid pressure acting on the pressure surface  45  and/or the actuators  28 . In an embodiment, pressure in the chamber  26  may be sufficient to generate a force on the pressure surface  45  to maintain fluid coupling between the fluid couplers. In an embodiment, fluid coupling between the fluid couplers may be maintained through the pressure in the actuators  28  and the pressure in the chamber  26  acting on the pressure surface  45 . 
     The separation forces generated may be dependent on the pressure of the fluid in the machine circuit. In an embodiment, an increase in the machine fluid circuit pressure may result in a higher separation force between the fluid couplers. The pressure surface  45  may be provided such that the difference in the ratio between the fluid coupler surfaces and pressure surface  45  is greater than 1 so that force acting on pressure surface  45  is greater than the separation force. 
     The chamber  26  may be connected to the machine fluid circuit via the check valve  56  mounted in the plunger  36 . If pressure in the machine fluid circuit is higher than the pressure in the chamber  26 , the fluid in the hollow of the plunger  36  may be at a higher pressure value and may flow to the chamber  26  where the fluid pressure has a lower pressure value. The fluid at a higher pressure will flow from the hollow of the plunger  36  through the diversion passage  52 , the check valve  56  and the diversion line  54  into the chamber  26 . The flow of fluid may continue till the pressure in the chamber  36  and pressure in the hollow of the plunger  36  equalise. 
     As the pressure in the chamber  26  generates a force on the pressure surface  45 , the force acting on the pressure surface  45  may be equal to the separation forces generated by the fluid flowing from the hollow of plunger  36  through the fluid channels and which act on the fluid couplers. The equalising of pressures in the chamber  26  and the hollow of plunger  36  may serve to lock the coupler assemblies  24 . As all chambers  26  are connected through the rail circuit  13 , a higher pressure load in one chamber  26  may be distributed to the other chambers  26 , even if the pressures in the hollow of the respective plungers  36  may be at a lower pressure value. 
     As fluid may not flow from the chamber  26  to the hollow of plunger  36 , due to the check valve  56 , the pressure in the chamber  26  may remain even when the pressure in the machine fluid circuit drops to a pressure value lower than the pressure value in the chamber  26 . The pressure level may be available in the chambers  26  independent of the pressure in the hydraulic lines A, B, C, D and L of the machine circuit. As all chambers  26  are connected through the rail circuit  13 , a balanced pressure load may be present to all coupler assemblies  24 , even if the machine circuit pressure is lower or absent. 
     In an embodiment, check vale  62  may be pilot operated to block inflow of fluid having potentially damaging fluid pressures so as to avoid damage to components that may not be designed to withstand a high pressure. The check valve  62  may block high pressure in the rail circuit  13  from reaching the locking device  34 . 
     In an embodiment, a pressure relief valve  64  may connect the rail circuit  13  to machine fluid circuit. The pressure relief valve  64  may be an adjustable pilot operated valve that is mounted to remove excessive pressure peaks generated in the machine fluid circuit that may be transmitted to the chambers  26  through the check valve  56  and the rail circuit  13 . The pressure relief valve  64  may have pressure setting that is significantly higher than the maximum pressure tolerable in the chambers  26  and the rail circuit  13  to avoid unintended loss of force needed to maintain fluid coupling. In an embodiment, the pressure relief valve  64  may have pressure setting selected from the range of 390 bar-420 bar. In an embodiment, the pressure setting is 420 bar. 
     With reference to  FIG. 2 , operation of the coupling arrangement  10  to decouple machine bracket  12  from the work tool bracket  14  may be initiated by relieving pressure in the chambers  26  and the rail circuit line  50  through the rail circuit  13 . 
     In an embodiment, a primary drain circuit for the rail circuit  13  may be provided through a normally-open drainage switch  66  and primary drainage check valves  68 ,  70 . Drainage switch  66  may close to block the drain function, only when the chambers  26  and the rail circuit line  50  are pressurised. 
     Primary drainage check valves  68 ,  70  may be connected to the machine fluid circuit. In an embodiment primary drainage check valves  68 ,  70  may be connected to lines A and B, wherein either one of these lines may be depressurized to allow return fluid to flow back to the tank. The return fluid may consist of a fluid volume in the piston side of the actuators  28  and in the chambers  26 . 
     In an embodiment, further primary drainage check valves may be provided which are connected to the other hydraulic lines. 
     Pressure in line X may relieved while line Y may be pressurised though the hydraulic power circuit  35 . Fluid from line Y may flow into the rod side of the actuators  28 . Increase in pressure in the rod side and the reduction of pressure in the piston side may effect a retraction of the actuators  28 . As the actuators  28  are connected to the coupler assemblies  24 , the coupler assemblies  24  may be correspondingly retracted and disconnected from fluid coupling. The full retraction of the actuators  28  may correspondingly effect complete retraction of the coupler assemblies  24  into the machine bracket  12 . 
     A secondary drain circuit may consist of check valve  62  and secondary drainage check valve  72 . The valves  62  and  72  may allow fluid to flow back to the tank through line X but only if line Y is pressurised. The return fluid may consist of a fluid volume in the piston side of the actuators  28  and in the chambers  26 . 
     Switch  32  may detect the position of the actuators  28 . Switch  32  may be normally closed and may block flow of fluid from the hydraulic power circuit  35  through line Y to locking device  34 . At complete retraction of the actuators  28  the switch  32  may effect the actuation of the valve  73  to permit flow of fluid from the hydraulic power circuit  35  to the piston side of the locking device  34  to unlock the brackets  12 ,  14 . This is a safety measure to avoid unintended operation of the locking device  34  if the coupler assemblies have not been retracted completely into the machine bracket  12 . 
     A relief valve  74  may be provided in the hydraulic line connecting line Y and the rod sides of the actuators  28  to avoid any unintended drift of the actuators  28  in the disconnected position. The relief valve  74  may be pilot operated. The fluid in the rod side of the actuators  28  may be trapped unless chambers  26  and the lines  50  are pressurized to such level as to pressure regulator  58 . 
     The skilled person would appreciate that foregoing embodiments may be modified to obtain the apparatus of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     This disclosure describes a coupling arrangement  10  for coupling a machine hydraulic fluid circuit to a work tool hydraulic fluid circuit. In a machine  1 , work tools  3  may be used for handling heavy materials. Work tools  3  may demolish, drill, dig, plow, cut, grab and/or carry heavy materials which may include sand, stone, metal, and more. Work tools  3  may be coupled to and powered by machines  1 , in particular mobile host machines. The machine  1  may be provided with transmissions, hydraulic equipment, booms  2  and/or sticks for driving the work tool  3 . Work tool operations may be controlled by the operator via an operating panel in the cab of the machine  1 . 
     The coupling arrangement  10  may have at least one hollow plunger  36  provided with a check valve  56 . The hollow plunger  36  may connect the machine fluid circuit to the rail fluid circuit through diversion passage  52  and diversion line  54 . The fluid pressure in the machine fluid circuit may be used to retain the fluid coupling of the fluid couplers. The check valve  56  may restrict the fluid flow from the rail fluid circuit to the machine fluid circuit. 
     In operation of the coupling arrangement  10 , pressure in the chambers  26  may be provided from either the rail fluid circuit, during the connection process, or the machine fluid circuit, during operation of the work tool. Check valves  56  and  62  may allow pressure to build up in the chambers  26 . The prevailing pressure value in the chambers  26  may be the higher of the pressure values of the machine fluid circuit or the rail fluid circuit. This pressure in the chambers  26  may remain even if the pressure source is no longer available. Pressure relief valve  64  may protect the chambers  26 , the rail circuit line  50  and the rail circuit  13  against damage as a result of excessive pressure. 
     The coupling arrangement  10  may have at least one hollow plunger  36  provided with a gate portion  39  having a plurality of bores  46  or a bore  46 . When the coupler assemblies  24  are retracted to a disconnect position, the chambers  26  may be sealed from the hydraulic lines of the machine fluid circuit. At disconnection, the coupler assembly  24  may not be actuated unintentionally as a result of pressure build up in the hydraulic lines of the machine fluid circuit when fluid coupling has not yet been established. 
     The coupling arrangement  10  may have a rail fluid circuit to ensure a balanced load on the coupler assemblies  24 . All chambers  26  may be connected through the rail fluid circuit to allow the highest pressure in any of the hydraulic lines of the machine fluid circuit or of the rail fluid circuit to generate the load required to retain fluid coupling between the fluid couplers. 
     The coupling arrangement  10  may have a bracket switch  30  to detect whether the work tool bracket  14  carries a corresponding fluid coupler. Bracket switch  30  may not permit fluid pressurisation of the rail fluid circuit when a work tool bracket  14  carrying a corresponding fluid coupler is not detected. The bracket switch  30  may avoid inefficient coupling present in devices wherein fluid connections are established simultaneously at mechanical coupling of the machine bracket and the work tool bracket. 
     The coupling arrangement  10  may have a switch  32  to detect whether the actuators  28  are fully retracted. The activation of switch  32  determines whether the locking device  34  may be actuated to unlock the brackets  12 ,  14  without the risk of potential damage to the fluid couplers and/or couplers assemblies  24 . 
     The industrial applicability of the coupling arrangement  10  as described herein will have been readily appreciated from the foregoing discussion. 
     Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein. 
     Where technical features mentioned in any claim are followed by references signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, neither the reference signs nor their absence have any limiting effect on the technical features as described above or on the scope of any claim elements. 
     One skilled in the art will realise the disclosure may be embodied in other specific forms without departing from the disclosure or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the disclosure described herein. Scope of the invention is thus indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.