Abstract:
An NH 3  applicator implement is equipped with a hitch arrangement for automatically effecting a connection with a tongue of an NH 3  nurse tank wagon. A quick-connect coupler assembly is provided for connecting the transfer hose of the nurse tank wagon to the supply hose of the implement. The quick-connect coupler assembly includes a first coupler section mounted to the applicator implement for powered, guided movement into engagement with a second coupler section mounted to the tongue of the nurse tank wagon. An electro-hydraulic control system including relay logic is used to first lock the fully coupled coupler sections together and then to engage the flow of NH 3  by remote actuation of a main on/off valve located at the nurse tank.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a hitch and coupling arrangement for automatically effecting hitch and quick-coupler connections between a nurse tank wagon carrying a tank of anhydrous ammonia (NH 3 ). 
     BACKGROUND OF THE INVENTION 
     Modern farming practices in North America require the application of fertilizer in order to maximize crop yields and, in turn, maximize profits. Currently, approximately 40% of this fertilizer is applied as anhydrous ammonia (NH 3 ) since it is the most cost effective per unit of nitrogen. However, despite this cost advantage, the use of NH 3  has not changed significantly in the past few decades due to safety issues and the extra labor involved in a applying the NH 3 . Historically, conventional knife injection applicators have been used to apply the NH 3  in the ground. These applicators generally tow a 1000-1500gallon NH 3  nurse tank. Multiple NH 3  wagons are used to support each applicator. When the tank borne by the wagon being towed by the applicator becomes empty, it is exchanged with a wagon bearing a full tank. A tender truck hooks up to the wagon bearing the empty tank in the field and transports it to a central fill station and then transports the wagon with the newly filled tank back to the field for the applicator to use. The current tank change operation is a multi-step process which requires the operator to physically dismount the tractor, put on NH 3  safety garb and/or, equipment and walk back to the just emptied tank to manually bleed and disconnect the tank. Typically, conventional applicators have to change tanks every 1 ½ hours and the process can take up to 15minutes with the operator, being exposed to a small amount of NH 3  vapor, hence the requirement for the safety garb and/or equipment. This manual tank change operation is inconvenient to the operator and reduces the overall productivity of the applicator. 
     It is a trend in farm equipment of various types to make units larger in order to more quickly cover the ground. However, an applicator which has the capability to apply NH 3  at nearly twice the speed of a conventional applicator would require the tanks to be exchanged nearly twice as often, or once every 45minutes. Employing the conventional manual change regimen, the down time involved in exchanging empty with full tanks would result in the large unit operating only at 75% efficiency. 
     The problems to be addressed then are those of reducing the amount of time required for exchanging empty with full tanks of NH 3  while reducing exposure of the operator to NH 3 . 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a hitch and coupling arrangement for effecting automatic towing hitch and fluid quick-coupler connections between an anhydrous ammonia nurse tank wagon and an anhydrous ammonia applicator implement. 
     It is an object of the invention to reduce the time necessary for exchanging an empty anhydrous ammonia tank towed by an anhydrous ammonia applicator implement with a full tank while minimizing the exposure of an operator to anhydrous ammonia that might be vented or spilled during the exchange process. 
     The aforementioned object is achieved by providing a remotely operable arrangement effecting decoupling of a fluid quick-coupler and implement hitch so as to disconnect the implement from an empty tank of NH 3  and for subsequently effecting coupling of the quick-coupler and implement hitch so as to connect the implement to a full tank of NH 3 . More specifically, there is provided a first coupler section of the quick-coupler that defines a receptacle for receiving an insert defined by a second coupler section of the quick-coupler, the first coupler section being mounted to a carriage mounted at the rear of the applicator implement for powered fore-and-aft movement toward and away from the second coupler section which is supported on the tongue of the NH 3  tank wagon. The quick-coupler sections include cooperating guide elements for guiding them together during coupling and are provided with cooperating, remotely operable, detent elements for selectively locking the coupled first and second coupler sections together or for releasing the detent elements for permitting the coupled sections to be separated from each other. The coupled sections can also be forcibly decoupled to prevent hose breakage and NH 3 , loss if for any reason, such as a broken hitch connection, for example, an excessive pull is exerted between the supply and transfer hoses. 
     This and other objects of the invention will become apparent from a reading of the ensuing description together with the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a right rear perspective view showing an anhydrous ammonia applicator implement coupled for towing an anhydrous ammonia nurse tank wagon, and showing first and second coupler sections of a quick-coupler assembly prior to being automatically coupled together. 
         FIG. 2  is an enlarged view of that portion of  FIG. 1  which shows the mechanism for automatically effecting coupling of the first and second quick-coupler sections. 
         FIG. 3  is a side view of the mechanism for automatically effecting coupling of the first and second quick-coupler sections, with part of the guide track assembly broken away to reveal the cylinder connection with the carriage carrying the first coupler section. 
         FIG. 4  is a vertical sectional view taken lengthwise through the quick-coupler with the first and second coupler sections being shown in a separated condition occurring at initial contact of the first coupler section with the second coupler section during coupling the quick-coupling sections together. 
         FIG. 5  is a sectional view like  FIG. 4 , but showing the quick-coupler sections in a receiving locked position wherein the quick coupler sections are locked together, with the poppet valves being shown in a closed condition preventing flow through the quick-coupler. 
         FIG. 6  is a view like  FIG. 5 , but showing the quick-coupler sections in an operating position, with the poppet valves open permitting flow through the quick-coupler 
         FIG. 7  is a view showing the quick-coupler sections in an operating position like  FIG. 6 , but showing the quick-coupler sections in a breakaway condition wherein the detent balls are located at a release point. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , there is shown an anhydrous ammonia applicator implement  10  coupled for towing an anhydrous ammonia nurse tank wagon  80 . The applicator implement  10  is here shown as a winged implement including a center section  12 , having right- and left-hand wing sections  14  and  16 , respectively, hinged to its opposite sides for swinging vertically between lowered working positions, as shown, and raised transport positions, with right- and left-hand hydraulic lift cylinders  18  and  20  being provided for selectively moving the wing sections between their working and transport positions. 
     The center section  12  is equipped at its front with attachment points for a tractor three-point hitch, with only the upper attachment point  22  being visible. A transverse support beam  23  is fixed between a rear region of a pair of transversely spaced, longitudinally extending beams  24  of the center section  12  and a pair of ground wheels  25  are respectively caster-mounted to rear ends of the beam  24  Supported from a central region of the beam  23  is a towing hitch structure  26  which extends down and to the rear from the beam  23  and includes a generally funnel-shaped rearwardly opening tongue receptacle  28 . 
     Referring now also to  FIG. 2 , it can be seen that a flexible NH 3  supply hose  30  has one end coupled to a manifold arrangement  31  which is coupled to a plurality of individual feed lines (not shown) which respectively distribute the NH 3  to each of a plurality of soil opener arrangements  32  provided in transversely spaced relationship to each other across the width of the implement  10 . For a reason explained below, the supply hose  30  includes a relatively long length which is formed into a loop  33  that goes through an eye of a hose guide  34  located at a front, center region of the center section  12 . The supply hose  30  extends to the rear from the guide  34  and over a transversely extending, inverted U-shaped hose support  35  having legs fixed to a tool bar of the center section  12 , with the hose  30  extending first leftward at the front of guide  34  and then rearward beneath the hose support  35 . 
     A fluid quick-coupler assembly  100  ( FIGS. 4-7 ) is provided for interconnecting the fluid supply hose  30  to a flexible fluid transfer hose  36  leading from a nurse tank  38  carried by a wheeled wagon frame  40  of the nurse tank wagon  80 . The fluid quick-coupler assembly  100  includes a first fluid coupler section  110  connected to a rear end of the fluid supply hose  30 , and a second fluid coupler section  230  connected to a front end of the fluid transfer hose  36 . 
     As can best be seen in  FIG. 3 , guide track assembly  42  is mounted to a central location of the support beam  23  so as to be centered above the hitch assembly  26 . The guide track assembly  42  comprises right- and left-hand parallel, vertical plates  44  and  46 , respectively, which are each provided with a forward end region  48 , which is generally rectangular and has a lower out-turned flange  50  which overlies the support beam  23  and is secured thereto by a U-bolt  52 . Each plate  44  and  46  further includes a rear region  54  having only about one-third of the height of the front region  48  and being joined to and inclined downwardly and to the rear from an upper rear part of the front region  48 . Fixed to each of confronting faces of the plates  44  and  46  is an edge of a guide track  56  including a horizontal section spaced a short distance below an upper edge of forward end region  48  and a downwardly and rearwardly inclined section .space a short distance below an upper edge of the inclined rear region  54 . A transverse plate  58  is fixed to the top edge of the plates  44  and  46 , and, fixed to an inside region of the inclined portion of each transverse plate  58  is a vertical guide strap  60 . The respective guide tracks  56  are spaced from each other so as to define a gap between them. A carriage  62  comprising a channel-shaped body  64  disposed with depending flanges at its opposite sides, with front and rear sets of rollers  66  being mounted to the flanges is mounted for rolling fore-and-aft along the guide tracks  56 . Movement of the carriage  62  along the guide tracks  56  is selectively achieved by operation of an extensible and retractable hydraulic actuator  68  having its rod end coupled to a connecting ear  70  provided at a front underside location of the carriage  62  so as to extend downwardly through the gap provided between the guide tracks  56 . The cylinder end of the actuator  68  is coupled to a frame member  72  of the center section  12  of the applicator implement  10 . When the actuator  28  is retracted, the carriage  62  is positioned on the horizontal section of the guide tracks  56 ,  56  where it holds the first coupler section  110  for transport, as shown in  Figs. 2 and 3 , or holds the coupled coupler sections  110  and  230  for field operation. 
     The first fluid coupler section  110  is connected, in a manner described below, to a vertical mounting plate  74  of an L-shaped mounting structure  76  having a horizontal mounting plate  78  joined to the bottom of vertical plate  74  and overlying and being fixed to the carriage  62 . Thus, extension of the actuator  68  from its retracted position shown in  FIGS. 2 and 3  will result in the carriage  62  rolling forwardly along the guide tracks  56 ,  56  so as to carry the first coupler section  110  down the inclined section of the guide tracks  56 ,  56  for being aligned with, and coupled to, the second coupler section  230 , in a manner described below. 
     The nurse tank wagon  80  includes a tongue  82  coupled at the forward end of the wagon frame  40 , the tongue  82  including a forward end defined by a circular coupling ring  84  located within the tongue receptacle  28  and receiving a retractable hitch pin (not shown) located within a clevis structure  86 . A single-acting hydraulic actuator  87  is coupled to a linkage, partially shown at  88 , which is attached to the hitch pin, with retraction of the actuator effecting the withdrawal of the hitch pin from the coupling ring  84 , with a compression spring (not shown) being located within the actuator cylinder and acting against the piston to extend the rod so as to normally retain the pin in its hitching position within the coupling ring  84 . A support stand  89  is pivotally coupled to the tongue  82  by a pivot pin  90  located adjacent a bottom lip  91  of the tongue receptacle  28 , the lip  91  acting to fold the stand  89  from an upright, support position, wherein a foot of the stand is in ground engagement, to an elevated stored position, as shown, wherein the stand  89  extends backward along an underside of the tongue  82  from the pivot pin  90 . Fixed to, and extending above, the tongue  82  is a hose support structure  92  including a base defining an upright receptacle receiving a post  93  having a connecting bracket  94  at its top to which opposite side straps  95  of a hose cradle  96  are is pivotally connected as at pivot connections  97 , which define a transverse horizontal pivot axis. Defining a front end of the cradle  96  is a front, generally U-shaped rod  98  having upwardly diverging legs fixed to forward ends of the straps  95 . Similarly, a rear end of the cradle  96  is defined by a rear, generally U-shaped rod  99  having diverging legs fixed to rearward ends of the side straps  95 . The cradle  96  is sloped upwardly towards the front so as to have an inclination approximately the same as that of the inclined section of the guide tracks  56 . The supply hose  36  in the hose cradle  96 , with the fluid coupler section  230  being located just in front of the U-shaped rod  98  at the forward end of the cradle so as to be substantially axially aligned with the coupler section  110  when the latter, together with the carriage  62 , is positioned on the sloped part of the guide track  56 ,  56  by extension of the actuator  68 . In a manner described in more detail below, the hydraulic actuator  68  may be operated remotely during the process for effecting the coupling and decoupling of the quick-coupler assembly  100  by respectively bringing the coupler section  110  into engagement with the coupler section  230 , or by separating the coupler section  110  from the coupler section  230 . 
     Referring now to  FIG. 4 , the quick-coupler  100  is shown in an uncoupled condition with the first and second coupler sections  110  and  230  being in axial alignment with, but with fluid conveying parts being separated from, each other. Specifically, the first coupler section  110  includes a central fluid passage  112 . Starting from the left in  FIG. 4 , the first coupler section  110  comprises a control collar arrangement support  114  and a valve housing  116 , which are configured substantially as cylindrical tubes and have ends screwed together to form a single unit. The interior of the valve housing  116  is provided with an annular inward projection defining a leftwardly facing valve seat  118  and a rightward facing bottom of a cylindrical receptacle  120  having an annular seal lip  121  at its right end, the receptacle being adapted for receiving an end portion of the second coupler section  230 , as described in further detail below. Located centrally within the valve housing  116  is a poppet valve head  122  including a bulbous left end section  124  joined to a rightwardly projecting stem section  126  and carrying an annular seal  128  held in sealed engagement with the seat  118  by a coil compression spring  130  acting between a bottom end of a blind bore  132  extending axially in the left end section  124  of the valve head  122  and a valve head guide  134  received in the bore and anchored to a guide support  136  retained within a right end region of the lock arrangement support  114  by a snap ring  138 . 
     The exterior of the control collar arrangement support  114  includes a left end region  140  having a first diameter, a middle region  142  having a second diameter slightly smaller than that of the left end region, and a right end region  144  having a third diameter substantially less than that of the middle region thereby defining an annular stop surface  146  facing rightward. A control collar locking arrangement  150  is mounted for shifting axially along the support  114  and valve housing  116  and includes a lock control collar  152  received on the support  114  and having an interior surface including a left end region  154  and a middle region  156  respectively sized for sliding along the left end and middle regions  140  and  142  of the support  114 . Since the inside surface of the left end surface region  154  is stepped outwardly from the inside diameter of the middle surface region  56 , an axially facing surface  158  is defined at the juncture of the different inside diameters. A fluid passage  160  extends between a port  162  located in an end surface of the support  114  and an exit point located at the juncture of the different outside diameter surfaces of the left and middle regions  140  and  142  of the support  114 . Leakage of fluid along the respective interfaces between the left and middle region of the support  114  and the left and middle regions  154  and  156  of the collar  152  is prevented by appropriate seals (not numbered) received in annular grooves provided in the left and middle regions of the support  114 . Thus, when a source of pressurized fluid is coupled to the port  162 , the pressure will act against the surface  158  and cause the dollar  152  to shift to the right, as shown in  FIGS. 4  and  5 , for example. The collar  152  further includes a relatively short right end region  164  having an inside diameter that is less than that of the middle region  156 , thereby defining an annular, leftward facing stop surface  166  located in confronting relationship to the stop surface  146  provided on the locking arrangement support  114 , with the stop surfaces  146  and  166  becoming engaged with each other, as shown.  FIG. 6 , by the action of the spring  172  in the absence of fluid pressure at the port  162 . 
     The control collar arrangement  150  further includes a hollow, cylindrical spring housing  168  having a left end wall defined by a circular ring  169  having an inside diameter engaged with a cylindrical outer surface of the collar  152 , with a snap ring  170  being mounted in a groove provided in the collar  152  adjacent its left end for the purpose of engaging the ring  169  and causing the housing  168  to be shifted rightward when the collar is shifted rightward. A spring abutment ring  171  is received on, and secured to, the support  114  at a location adjacent the valve housing  116 . A coil compression spring  172  is located in the housing  168 , with opposite ends of the spring  172  being in engagement with the end wall ring  169  and the abutment ring  171 . The housing  168  extends axially to the right from the snap ring  170  and has a right end wall defined by a support hub  174  received on the valve housing  116  and having a threaded right end screwed onto a threaded left end of a tubular detent ball carrier  176  that projects to the right beyond a right end of the valve housing  116 . A plurality of angularly spaced funnel-shaped, detent ball receptacles  178  are arranged in a vertical plane traversing the ball carrier  176  at a location adjacent its right end, and each receptacle  178  contains a detent ball  180 . An exterior surface of the ball carrier  176  includes a left end region  182  having a diameter slightly less than that of a right end region  184 , the later containing the ball receptacles  178 . A detent ball lock/release collar  186  includes respective interior surface regions  188  and  190 , sized for respectively sliding along the exterior surface regions  182  and  184 , with it being noted that due to the fact that the surface region  188  is at a lesser diameter than the surface region  190 , an annular, rightwardly facing surface  192  is defined at the juncture of the two regions. A port  194  is provided in the collar  186  in communication with the surface  192 . Leakage of fluid along the respective interfaces between the left and right end regions  182  and  184  of the ball carrier  176  and the left and right end regions  188  and  190  of the lock/release collar  186  is prevented by appropriate seals (not numbered) received in annular grooves provided in the left and right regions of the ball carrier  176 . An annular ball-release groove  196  is provided in the interior surface region  190  of the collar  186  at a location adjacent its right end. When a source of pressurized fluid is coupled to the port  194 , the collar  186  is shifted to a leftward, ball release position, as shown in  FIG. 4 . wherein the ball-release groove  196  is positioned in register with the detent balls  180  so as to permit them to move freely radially outward. When the detent ball lock/release collar  186  is in its release position, shown in  FIG. 4 , a coil compression spring  198 , which encircles the hub  174 , is compressed between the collar  186  and the hub  174 . Upon pressurized fluid being released through the port  194 , the spring will act to shift the collar  186  to the right to a locking position wherein the right end of the collar  186  is shifted into engagement with a snap ring  200  provided in a groove located adjacent the right end of the ball carrier  176 , the ball-release groove  196  then being in a locking position, as shown in  FIG. 5 , wherein it is misaligned to the right of the detent balls  180 . 
     A valve coupler section alignment arrangement  202  is supported at the left end region of the detent ball lock/release collar  186 . Specifically, the left end of the collar  186  is defined by a flange  204  and the alignment arrangement  202  includes the vertical support plate  74  of the mounting structure  76 , the plate  74  being received on the collar and clamped against the flange  204  by a threaded ring  208  engaged with a threaded section of the exterior of the collar. Three identical, axially extending, cylindrical rod guides  210  (only one shown in  FIGS. 4 - 7 ) are equally spaced from each other angularly about the collar  186  and have reduced diameter end sections  212  inserted, from the right, through holes  214  provided in the support plate  74 . The reduced diameter end sections  212  of each rod guide  210  is threaded and receives a retaining nut  216  which secures the rod guide to the plate. Extending axially through each rod guide  210  is a bore  218  in which a rod  220  is received for sliding, with a nut  222  being threaded onto the left end of the rod for preventing it from being withdrawn rightward from the rod guide  210 . Each of the rods  220  has a threaded right end engaged with a threaded bore provided in a centering plate  224  that is disposed parallel to the support plate  74 . The centering plate  224  has a thickened center region that is provided with a frusto-conical opening  226  oriented with its large diameter to the right. Received on each of the rods  220  and having a left end portion encircling each of the rod guides  210  is a coil compression spring  228  having its opposite ends engaged with the plates  74  and  224 , the arrangement of the rods  220  and springs  228  permitting the guide plate  224  to be resiliently shifted axially relative to the plate  74  during the operation of aligning the first and second sections  110  and  230  of the quick-coupler arrangement  100  with each other, in a manner described below in further detail. 
     The second quick-coupler section  230  includes a central fluid passage  232  and is comprised of a centering guide  234  and a valve housing  236  having threaded ends screwed together to form a single unit. Located at a central region between opposite ends of the centering guide  234  is a frusto-conical guide surface  238 , which has a small diameter end joined to a step which defines an axially facing, annular abutment surface  240 . The exterior of the valve housing  236  is provided with an annular detent groove  242  spaced a predetermined distance from the abutment surface  240 . The guide surface  238  is shaped complementary to the opening  226  provided in the guide plate  224  carried by the first quick-coupler section  110 . 
     The valve housing  236  is formed substantially as a cylindrical tube having an exterior wall which is stepped between its opposite ends so as to define a cylindrical insert section  244  sized to fit closely within the receptacle  120  of the first quick-coupler section  110 , the insert section  244  terminating at an axially facing, annular seal  246  with an o-ring secured in position by an attachable o-ring keeper  247 . The seal  246  is disposed for contacting an end surface of the receptacle  120 , with the keeper  247  acting as a stop for being engaged by a right end surface of the receptacle  120  when the quick-coupler is in the operating condition illustrated in  FIG. 6   
     An annular valve seat  248  is formed on an interior surface of the valve housing  236  at a location where the insert section  244  joins the remainder of the valve housing  236 . 
     Located centrally within the valve housing  236  is a poppet valve head  250  including a bulbous right end section  252  joined to a leftwardly projecting stem section  254  and carrying an annular seal  256  held in sealed engagement with the seat  248  by a coil compression spring  258  acting between a bottom end of a blind bore  260  extending axially in the right end section  252  of the valve head  250  and a valve head guide  262  received in the bore and anchored to a guide support  264  retained within a left end region of the centering guide  234  by a snap ring  266 . 
     In operation, assume that an operator of a tractor hitched to the applicator implement  10  is notified by a signal sent by a tank pressure sensor, for example, of the fact that the nurse tank wagon  80  being towed by a semi-mounted applicator implement  10  has just become depleted of NH 3 . Also assume that a tender truck operator has left a filled exchange nurse tank wagon  80  in a generally level exchange site in the field and has opened the main on-off NH 3  valve on the wagon to prepare for connecting the tank to the applicator implement  10 . The operator will then drive the tractor to the exchange site and, without leaving the seat of the tractor, will actuate the hydraulic actuator  68  causing it to extend to move the carriage  62 , together with the attached quick-coupler assembly  100 , rearwardly from the operating/transport position on the horizontal section of the guide track  56 ,  56  to the inclined section of the guide track, with hydraulic fluid pressure at the same time being routed to the port  162  of the valve section  110  causing the control collar  152  to be shifted to the right carrying with it the spring housing.  168  and the detent ball carrier  176 , with the latter engaging the centering guide  234  and causing it to move riqhtwardly so as to permit the poppet valve heads  122  and  150  to move to their closed positions, as shown in  FIG. 5 . Fluid pressure is then coupled to the port  194  so as to cause the detent ball lock/release collar  186  to be shifted to the left against the bias of the springs  198  to a release position wherein the ball release groove  199  is in register with the balls  180 . Gravity will then cause the coupler section  230  and its attached hose  36  to fall away from the coupler section  110  and into the hose cradle  96  with a rearwardly directed surface of the centering guide  234  of the coupler section  230  abutting the U-shaped rod  98  which defines the front of the cradle  96 . At this time, the hitch pin actuator  87  is actuated to withdraw the hitch pin from the drawbar coupling ring  84 , after which the operator will pull forward, and the support stand  89  of the nurse wagon hauling the depleted tank  38  will drop to support the ring  84  in position for automatic coupling to the tender truck hitch. The operator will then drive away from the depleted tank while actuating the hydraulic cylinder  68  causing it to retract and move the carriage  62  up the inclined section to the horizontal section of the guide track  56 ,  56 . At the same time, pressure fluid will be exhausted from the ports  162  and  194 . The tender truck driver closes the main on-off NH 3  valve on the depleted wagon upon pick up for refilling. 
     Next, the operator will back the tractor together with the applicator implement  10  so as to receive the coupling ring  84  at the front of the tongue  82  of the replacement nurse tank wagon  80 . The lip  91  raises the stand  89  into the-storage position. At this point the coupling ring  84  will be properly located in the clevis structure  86  for having the hitch pin installed and this will be done by operating a control valve for relieving the pressure from the actuator  87 , with its internal spring acting to insert the hitch pin through the coupling ring to secure the ring to the clevis structure  86 . The operator then drives the tractor back towards the field location where application of NH 3  stopped. At the same time, the hydraulic control valve for the actuator  68  is actuated to effect extension of the actuator  68  so as to cause the coupler section  110  to be carried rearward by the carriage  62 . At the same time, the coupler section  110  will be readied for coupling, as shown in  FIG. 4 , by pressurized fluid being routed to the ports  162  and  194 . As the carriage  62  travels down the inclined portion of the guide track  56 ,  56 , the centering plate  224  will eventually come into contact with the guide surface  238  of the centering guide  234 . Any slight misalignment of the coupler sections  110  and  230  will be accommodated by the centering plate  224  being deflected by the interaction of the centering guide surface  238  and the frusto-conical opening  226  of the centering plate  224 , with the coupler section  230  tilting, if necessary, about the axis defined by the connection pins  97 . Upon the guide surfaces  226  and  238  becoming engaged with each other, as shown in  FIG. 4 , the coupler sections  110  and  230  will be properly aligned for being connected together. 
     With reference to  FIG. 4 , continued extension of the actuator  68  will cause the mounting plate structure  76  to travel towards the coupler section  230  with the result that the mounting plate  74 , together with the rod guides  210 , are slid to the right along the rods  220  against the action of the springs  228 , while the detent ball carrier  176  moves along the exterior of the valve housing  236  until the end of the carrier  176  engages the abutment surface  240  of the centering guide  234 , at which time the detent balls  180  come into alignment with, and drop into, the detent ball groove  242 . 
     At this point, fluid pressure is exhausted from the port  194 , thus permitting the loaded springs  198  to shift the lock/release collar  186  to its rightward locking position, shown in  FIG. 5 , wherein it retains the detent balls  180  in the ball groove  242 . At this point, fluid pressure is exhausted from port  162 , whereupon the spring  172  acts to cause relative axial movement between the receptacle section  120  of the valve housing  116  and the insert section  244  of the valve housing  236  resulting in the right end of the housing  116  coming into engagement with the seal keeper  247  and seal  246 . 
     During this movement, which begins with the receptacle section  120  and insert section  244 , as illustrated in  FIG. 5 , and ends with the receptacle section  120  and insert section  244  positioned, as illustrated in  FIG. 6 , the stems  126  and  254 , respectively of the poppet valve heads  122  and  250  become engaged with each other and cause the valve heads  122  and  250  to be moved from their closed positions shown in  FIG. 5  to their open positions shown in  FIG. 6 . It is to be noted that once the coupler sections  110  and  230  are locked together, as shown in  FIG. 5 , the valve controlling the hydraulic actuator  68  is actuated to cause the actuator  68  to retract so as to place the carriage  62 , together with the coupler  100 , at the horizontal section of the guide track  56 ,  56 . 
     In the event that an excessive pulling force is exerted between the coupler sections  110  and  230  when they are locked together, as shown in  FIG. 6 , for example, the coupler arrangement  100  is designed to separate with the valve heads  122  and  250  immediately shifting to closed positions to prevent leakage of anhydrous ammonia from the hoses  30  and  36 , such separation also preventing hose breakage. Specifically, with reference to  FIG. 7 , there the coupler arrangement  100  is shown in a breakaway condition where the detent balls  180  have just been forced out of the detent ball groove  242  by a force which has overcome the retaining force exerted by the springs  198 , with it being noted that the compressed springs  228  between the support plate  74  and centering plate  224  subtract from the retaining force exerted by the springs  198 . Further separation of the first and second coupler sections  110  and  230  from each other will result in the valve heads  122  and  250  moving into respective closed positions for preventing ammonia leakage. 
     It will be appreciated then that an operator can easily and quickly exchange an empty nurse tank wagon  80  for a full nurse tank wagon, while minimizing the exposure of the operator to any anhydrous ammonia liquid or gas during the exchange process. Further it will be appreciated that the coupling structure described above provides for automatic decoupling and to prevent hose breakage and NH 3  loss if for any reason, such as a broken hitch connection, an excessive pull is exerted between the transfer and supply hoses. As can be appreciated from the description, no hydraulic pressure is required at the coupler arrangement  100  to maintain the latter in its locked conditions, nor is hydraulic pressure required to maintain the hitch pin in its installed position so that hydraulic system pressure loss does not result in implement hitch or fluid coupler disconnection. Because the hitch coupling structure is activated before the hose coupling structure, relative hose positions are well defined and repeatable for a uniform, predictable coupling procedure. The coupling structure provides a unique integrated hydraulic control of the coupler flow and hose attachment. The actual final fluid connection between the hoses can be completed while the operator drives from the exchange site to the field position to thereby decrease the amount of time necessary to make the exchange. Because the volume between the coupler portions on the hoses is relatively small, only a few milliliters (about nine cubic inches) of NH 3  will be exhausted to atmosphere during coupling and uncoupling. However, a shield may be placed adjacent the couplers to prevent the exhaust from traveling in a particular direction. 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.