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This is a continuation of application Ser. No. 08/634,561, filed Apr. 18, 1996, now U.S. Pat. No. 5,727,342. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to tool couplers for excavation, demolition and construction equipment. 
     Some types of construction equipment, such as backhoes and excavators, have a movable dipperstick (also referred to as an arm) to which a variety of tools, such as, for example, buckets and grapples, can be attached. A hydraulic linkage allows the equipment operator to pivot the tool from the free end of the dipperstick. To simplify the process of changing tool attachments, a universal coupler can be fixed to the dipperstick linkage. A selected tool can then be removably attached to the coupler, a process that typically involves manually positioning at least one latch pin between the coupler and the tool. 
     There is a trend in the industry to use an actuated coupler on the end of the dipper stick for connecting and disconnecting a tool from the linkage. A great advantage of these systems is that the operator can actuate the coupler to connect or disconnect a tool without the assistance of another worker and without having to leave the cab of the vehicle. 
     One type of actuated coupler first engages a crossbar formed in the tool with hooks depending from the coupler, and then engages a latch pin (or a block or a wedge) with a mating receptacle formed in a collar on the tool. A double-action hydraulic cylinder in line with the latch pin is positioned so that the cylinder extends to push the latch pin into the receptacle. In disengaging the tool from the coupler, the operator retracts the rod into the cylinder body, pulling the pin out of the receptacle. 
     SUMMARY OF THE INVENTION 
     The invention provides a coupling assembly for coupling a tool to a dipperstick, or arm, on an apparatus which has a hydraulic system for moving the tool. The coupling assembly includes a coupler body having a frame that defines a central cavity, and also having link structure for pivotally coupling to the dipperstick. An actuator assembly positioned within the central cavity includes a latch pin movable between an extended position and a retracted position. In the extended position, an end of the latch pin projects rearward from an opening in a rear end of the frame for engaging an aperture or receptacle defined by the tool. In the retracted position, the end of the latch pin is disengaged from the tool receptacle and positioned substantially within the frame. The actuator assembly also includes a hydraulic latch cylinder that has a movable part, and a fixed part. The movable part is coupled to the latch pin by a latch pin coupling assembly, which is structured and arranged such that, when the movable part is extended from the fixed part, the latch pin moves to the retracted position. 
     According to another aspect of the invention, the latch pin coupling assembly includes a bias member structured and arranged to apply a bias force that urges the latch pin towards the extended position. When a threshold level of hydraulic pressure is applied to the latch cylinder, the movable part of the cylinder overcomes the bias force and extends to move the latch pin to the retracted position and out of engagement with the tool. 
     Another feature of the invention is that the latch cylinder can be a single-action cylinder. 
     According to another feature of the invention, the latch cylinder can be positioned on an axis different from an axis defined by the latch pin, such as along side the latch pin. This feature provides a compact arrangement. The system is easily adaptable to any type of quick coupler type system due to the compactness and placement of the actuating cylinder. 
     According to another feature of the invention, the hydraulic pressure to the latch cylinder can be controlled by an electrically actuated valve assembly that hydraulically couples the dipperstick hydraulics to the latch cylinder. The valve assembly can include one or more solenoid valves that only allow hydraulic pressure to enter and remain in the latch cylinder when they are energized. 
     According to another feature of the invention, the valve assembly can be structured and arranged such that the dipperstick hydraulics must be approximately fully pressurized while extended to pressurize the latch cylinder. 
     According to another feature of the invention, the coupling assembly can also include a pin indicator that readily shows whether the latch pin is retracted. The indicator is located such that it can be viewed easily from the operator position. 
     According to another feature of the invention, a drop in hydraulic pressure in the latch cylinder below the threshold level allows the bias spring to push the coupling pin towards the extended position. An unexpected hydraulic pressure loss can be caused by a failure in the hydraulic system or by a failure in the valve assembly. The spring apply, hydraulic release system is safe in that it assures that an attached tool will not accidentally uncouple from the coupling assembly if there is a loss in hydraulic pressure in the latch cylinder. 
     The invention also provides a method of removing a tool from the coupler assembly having features as described above. An operator can remove a tool by the steps of applying hydraulic pressure to a latch cylinder that has a part fixed relative to the coupler body and a movable part rigidly coupled to the latch pin, extending the movable part from the fixed part, thereby urging the latch pin to the retracted position, engaging a cross member of the excavation tool with a hook structure depending and extending forward from the coupler body, rotating the coupler body toward the tool, aligning the latch pin with a mating receptacle formed in the excavation tool, reducing hydraulic pressure to the latch cylinder, and applying a bias force to the latch pin, urging the latch pin to the engaged position, thereby engaging the latch pin in the receptacle and securing the excavation tool to the coupler body. 
     According to another aspect of the invention, the method further includes the step of removing the tool from the coupler, including rotating the coupler body and the tool to a full forward position, again applying hydraulic pressure to the latch cylinder, again extending the movable part from the fixed part, thereby urging the latch pin to the retracted position and disengaging the latch pin from the receptacle, and disengaging the hook structure from the cross member of the excavation tool. 
     The latch cylinder extends using the more powerful head end to extract the latch pin, whereas coupling systems using an in-line dual-action cylinder and latch pin arrangement use the less powerful rod end for this purpose. This feature of the invention is important when extracting a frozen pin, which can require substantially more force than inserting a free moving pin. 
     Since, the hydraulic system uses a single-action latch cylinder, it only requires one hydraulic line between the valve assembly and the latch cylinder. This is simple and inexpensive compared with coupling systems that use a dual-action cylinder, and that require two hydraulic connections. 
     The rod of the latch cylinder is normally in the retracted position during the tool working period. Because the latch cylinder is retracted, the rod of the latch cylinder is not subject to damage from rocks and sharp objects. Normally, the only time the rod is extended, and thereby exposed to the elements and contaminants, is when a tool is being attached or detached from the coupling assembly. 
     A feature of the invention is that if there is a loss of either electrical or hydraulic power, the latch pin will extend or “insert” automatically. If electrical power inadvertently gets to the solenoid valves, the tool has to be fully rolled forward and inward in order for the pressure to build up in the latch cylinder to retract the latch pin. In this position, the coupler hooks are fully engaged and the likelihood of the tool falling off is minimized. One cannot simply throw the switch and have the tool fall to the ground. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of dipperstick with an attached coupling assembly, and a conventional bucket that can be attached to the coupling assembly. 
     FIG. 2 is a side view of a hydraulic coupling assembly shown coupling a conventional bucket to a dipperstick. 
     FIG. 3 is a top plan view of a coupling assembly, partially showing a bucket, with the latch pin in an unlatched, retracted position. FIG. 3A is a similar view, partially broken away, showing the latch pin in a latched, extended position. 
     FIG. 4 is a section view through line  4 — 4  of FIG.  3 . FIG. 4A is a similar section view through line  4 A— 4 A of FIG.  3 A. 
     FIG. 5 is a partial section view through line  5 — 5  of FIG.  3 . FIG. 5A is a similar partial section view through line  5 A— 5 A of FIG.  3 A. 
     FIG. 6 is a schematic diagram of a hydraulic system and an electrical system according to the invention. FIGS. 6A,  6 B and  6 C illustrate other embodiments of a valve assembly. 
    
    
     In the following detailed description of the invention, similar structures that are illustrated in different figures will be referred to with the same reference numerals. 
     It will also be noted that the figures are generally not drawn to scale. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIGS. 1 and 2, a hydraulic coupler assembly  10  according to the invention is attached to a conventional dipperstick or arm  12 . Only a free end of dipperstick  12  is illustrated in FIGS. 1 and 2. The other end of dipperstick  12  is pivotally coupled, typically via an intermediate articulation (not shown), to a base (not shown) that includes a hydraulic power system, and hydraulic and electric operator controls located in a cab. Coupler assembly  10  can be used for coupling the dipperstick  12  to any of a variety of tools, such as, for example, a conventional bucket  14 . 
     Dipperstick  12  linkage includes a bucket guide link  16  pivotally attached to the dipperstick  12 , a bucket cylinder  18  for actuating the coupling assembly  10  and the bucket  14 , and a bucket link  20 . Extending bucket cylinder  18  rotates coupling assembly  10 , and any tool attached to coupling assembly  10 , inwardly in a forward direction. 
     Referring now also to FIGS. 3-5, coupling assembly  10  includes a frame  24  forming a central space  22 . Frame  24  includes side walls  26 , a bottom plate  28 , a coupler spreader plate  30  and a rear face plate  32 . Depending from side walls  26  are a pair of forward extending hooks  34  that are adapted to fit through an opening or recess  36  formed in a back sheet  38  of bucket  14  (see FIG.  1 ). The hooks  34  can then engage a cross tube  40  to support a forward end of bucket  14 . 
     Coupling assembly  10  has a pair of dipper pivot fixtures  42 , located near a forward end of side walls  26  for coupling to dipperstick  12 . A pair of link pivot fixtures  44  for coupling to bucket link  20  are located closer to the rear end of the frame  26 . A pair of link pivot fixtures  46  are also provided at an alternate location. 
     Bucket  14  is adapted to be coupled to dipperstick  12  with coupling assembly  10 . As noted above, a recess  36  is formed in back sheet  38  of the bucket for receiving hooks  34 . Once cross tube  40  is engaged by hooks  34 , the bucket can be lifted off the ground by raising the dipperstick  12 . This connection provides a first point of connection between coupling assembly  10  and bucket  14 . To enable the bucket  14  to rotate by operation of the bucket hydraulic cylinder  18 , a receptacle  50  formed in a latch collar  51  fixed to a plate  52  on the rear end of bucket  14  engages one end of a movable latch pin  48 . 
     Latch pin  48  slides within the bore of a bushing  60  welded to rear face plate  32  within frame  24 . On the other side of plate  32  there is an approximately semicircular-shaped coupler crescent  61  that fits over the top of latch collar  51  when bucket  14  is attached to coupling assembly  10 . 
     The latch pin  48  is part of an actuator assembly  54  that also includes a coil spring  56 , or other type of compression spring, for pushing the latch pin  48  through bushing  60  into engagement with the receptacle  50 , and a single-action latch pin hydraulic cylinder  58  that acts opposite the spring  56  to disengage the latch pin  48  from the receptacle  50 . Spring  56  is positioned approximately in line with latch pin  48 , and latch cylinder  58  is positioned on a parallel axis along side latch pin  48  and spring  56 . This arrangement allows the cylinder  58  to “push” the pin  48  out to retract. The spring  56  urges the pin  48  toward an engaged position with receptacle  50  when hydraulic pressure in the latch cylinder  58  is insufficient to overcome the spring force of spring  56 . The latch pin  48  is normally in the engaged position because latch cylinder  58  is normally not pressurized. 
     Coil spring  56  is kept in position by a latch spring assembly that forms part of actuator assembly  54 . One end of coil spring  56  bears against a pin block  62  that is welded to latch pin  48 . Pin block  62  includes an annular groove to receive coil spring  56 . The other end of coil spring  56 , towards the front of coupler  10 , bears against a winged end plate  64  and thereby holds the winged end plate  64  within the “V” formed by coupler spreader plate  30 . A spring guide rod  66  is positioned within the coils of spring  56 . Spring guide rod  66  extends transversely through a hole formed in end plate  64  and is welded thereto. A forward end of spring guide rod  66  includes a notch  68  that is positioned against an angled top edge  69  of coupler spreader plate  30  and held in place by the spring force from spring  56 . The other end of spring guide rod  66  acts as a stop for latch pin  48  in the retracted position (see FIG.  4 ). 
     The body  70  of latch cylinder  58  is fixed to pin block  62 . In the embodiment illustrated in FIGS. 3-5, body  70  has screw threads formed on its outer surface and screws into mating threads formed in a through hole in pin block  62 , and is held in place by a set screw  71 . The cylinder&#39;s extensible rod, or piston  72 , extends through the hole in pin block  62 . When hydraulic pressure coupled into cylinder  58  through hydraulic fitting  73  is increased, cylinder  58  extends and the free end of piston  72  bears against push plate  74 , which is welded to bushing  60 . 
     Extension of cylinder  58  with sufficient force to overcome spring&#39;s  56  spring force thereby urges latch pin  48  to a retracted position since latch pin  48  is welded to pin block  62  and pin block  62  is fixed to cylinder body  70 . Release of pressure in cylinder  58  allows spring  56  to extend, urging pin block  62 , and thereby latch-pin  48 , toward a latched position wherein the latch pin  48  projects beyond rear face plate  32 . 
     Pin block  62  includes a cylindrical opening  76  that receives spring guide rod  66  when latch pin  48  is retracted by actuation of cylinder  58  (see FIG.  3 ). As mentioned above, spring guide rod  66  stops latch pin  48  from retracting beyond a predetermined point. When latch pin  48  is fully retracted, the end of spring guide rod  66  is inside the cylindrical opening  76  in pin block  62  and projects beyond the corresponding end of spring  56 . In this position, a transverse assembly hole  78  formed in the end of spring guide rod  66  is aligned with a U-shaped slot  80  formed in pin block  66 . An assembly pin (not shown) can be placed in assembly hole  78 . When pressure in cylinder  58  is released, latch pin  48  can be manually moved to the latched position, thereby releasing spring guide rod  66  from cylindrical opening  76  in pin block  62 . Assembly pin in hole  78  keeps spring  56  compressed on spring guide rod  66 . With pin block  62  out of the way, the assembled latch spring assembly, comprised of spring guide rod  66 , spring  56 , and winged end plate  64 , can be removed as a unit from coupler  10 . The latch spring assembly can be installed in coupler  10  by a reverse procedure. 
     Coupler  10  is structured to allow an operator in the control cab of the construction equipment to visibly assess whether the latch pin  48  is in the latched or retracted position, even when a tool is attached to coupler  10 . Back sheet  38  of bucket  14  extends forward only to the attachment point of hooks  34 , which leaves the forward portion of bucket  14  open between back sheet  38  and cross tube  40 . Bottom plate  28  of frame  24  forms a U-shaped indicator slot  82  positioned between hooks  34 . Indicator slot  82  is positioned such that pin block  62  is visible through the opening in bucket  14  and through indicator slot  82  when latch pin  48  is in the retracted position. When latch pin  48  is in the latched position, the operator&#39;s line of sight to pin block  62  is blocked by back sheet  38 . Pin block  62  can be made more noticeable by painting it a bright color. 
     Referring now also to FIG. 6, a hydraulic circuit  86  for operating latch cylinder  58  taps into the hydraulics of the excavator. A hydraulic pump  88  and a reservoir  90  are coupled to bucket cylinder  18  via a lever-operated, three-position, two-pole valve  92 . Pump  88 , reservoir  90  and valve  92  are located in the base  93  of the excavator. Hydraulic hoses  94 ,  96  connect between valve  92  and the rod end  98  and cylinder end  100  of bucket cylinder, respectively. Hydraulic hose  96  has a T-connection leading to one port of a valve assembly  102 . The T-connection can be conveniently made at the hydraulic fitting for the cylinder side  100  of bucket cylinder  18 . The other port of valve assembly  102  connects via hydraulic hose  104  to fitting  73  in latch cylinder  58 . Valve assembly  102  can be strapped, bolted or otherwise attached to a fixed part of bucket cylinder  18  or to an upper portion of dipperstick  12 . 
     Valve assembly  102  includes two solenoid actuated valves  108 ,  110 , each with a power connection controlled by a locking electrical toggle switch  111  located in the cab of the excavator. In an unlatch switch position the solenoids are energized and in a latch switch position the solenoids are shut off. When the solenoids are not energized (see FIG.  6 ), springs  112 ,  114  urge valves  108 ,  110 , respectively to a position wherein a check valve portion  116  of valve  108  and a through portion  118  of valve  110  are connected in series between lines  96  and  104 . When valves  108 ,  110  are energized (not shown), a through portion  120  of valve  108  and a check valve  122  portion of valve  110  are-placed in the circuit. 
     Check valve  116  blocks a hydraulic flow from bucket cylinder  18  to latch cylinder  58 , but is set to permit flow in the other direction when there is an over-pressure condition in the latch cylinder  58  relative to the cylinder side  100  of bucket cylinder  18 . Check valve  122 , on the other hand, blocks any back flow from latch cylinder  58  to bucket cylinder  18 , and is set to permit the latch cylinder  58  to be pressurized when the cylinder side  100  of bucket cylinder  18  is fully pressurized. With the cylinder side  100  fully pressurized, bucket cylinder  18  will be fully extended and the coupling assembly  10  will be rotated fully forward. 
     Referring now to FIG. 6A, another embodiment of a valve assembly  102 ′ includes valve  108  in series with check valve  124  between lines  96  and  104 . Check valve  24  prevents back flow from line  104  to  96 . A drain line  126  normally connects between line  104  and reservoir  90  via through portion  128  of solenoid valve  130 . When valves  108  and  130  are energized, drain line  126  is blocked by check valve portion  132  of valve  130 , and through portion  120  is positioned in series connection with check valve  124  between lines  96  and  104 . Check valve  124 , similar to check valve portion  122 , is set to permit pressurization of line  104  and latch cylinder  58  when full hydraulic pressure is applied to extend bucket cylinder  18 . 
     Referring to FIG. 6B, in a third embodiment, valve assembly  102 ″ is configured with solenoid valves  108  and  110 , similar to the arrangement of valve assembly  102 . In addition, a drain line  134  connects between valves  108  and  110 . Flow through drain line  134  to reservoir  90  is limited by an orifice  136  flow limiter. 
     Referring now to FIG. 6C, a fourth embodiment of a valve assembly  102 ′″ includes solenoid valves  138  and  110 . In the normal, non-energized configuration shown in the drawing, cylinder  58  drains to reservoir  90  via through portion  118  of valve  110  and lower through portion  140  of valve  138 . When valves  110 ,  138  are energized, pressure line  96  is coupled to cylinder  58  via upper through portion  142  of valve  138  and check valve portion  122  of valve  110 . 
     Valve assemblies  102 ′,  102 ″ and  102 ′″ can be safer than valve assembly  102 , especially in high back pressure systems, because of the drain connections to reservoir  90 , however, the drain connections require an additional hydraulic hose. 
     Referring again to FIG. 6, indicator lights  148  and an audible indicator  144 , such as a beeper sound device, located in the cab alert the operator that the switch  111  is in the energized, unlatch position. A warning lamp  146  mounted on the dipperstick  12  lights or flashes to help to alert surrounding personnel that the switch  111  is in the unlatch mode and that the latch pin  48  could be retracted. Of course, audible indicator  144  can be configured to be audible outside the operator cab. 
     A single operator in the cab of the excavation equipment can detach a tool, such as bucket  14 , to the coupling assembly  10  and attach a new tool to the coupling assembly without any assistance, as described in detail below. Some particulars of the following recitation of steps for coupling and removing a tool are made with reference to the embodiment of valve assembly  102  illustrated in FIG.  6 . It will be understood that the embodiments of valve assemblies  102 ′,  102 ″, and  102 ′″ illustrated in FIGS. 6A,  6 B, and  6 C, respectively, will function in much the same manner, and the operator will make essentially the same sequence of steps to attach or detach a tool. 
     To decouple a tool from coupling assembly  10 , the latch pin  48  must be moved to the retracted position. The operator first throws switch  111  in the cab to the unlatch position. The indicator lamps  148  and warning lamps  146  then light up, and the audible indicator  144  sounds. The solenoids becomes energized, which moves solenoid valves  108 ,  110  in valve assembly  102  to their unlatch position. Check valve  116  is moved out of hydraulic circuit  89  and check valve  122  is moved into hydraulic circuit  89 . This, by itself, is insufficient to retract latch pin  48 . Check valve  122  is set to prevent passage of hydraulic fluid and thus prevent latch cylinder  58  from being pressurized until the pressure on the cylinder side  100  of bucket cylinder  18  is greater than a predetermined value. 
     In the illustrated embodiments, check valve  122  is set such that the coupling assembly  10  and attached tool  14  must be rotated fully forward and approximately full pressure must be applied in line  96  to bucket cylinder  18  to open check valve  122 . This assures that accidentally throwing switch  111  will not, by itself, be sufficient to retract latch pin  48 . 
     Once the pressure in latch cylinder  58  is great enough to overcome the spring force of spring  56 , latch cylinder  58  extends and thereby retracts latch pin  48 . The operator can confirm that the latch pin  48  is retracted if he sees the pin block  62  in the retracted position. While the switch  111  is still in the “tunlatch” position, the latch pin  48  will be held back retracted. 
     Alternatively, to bring the latch pin  48  to the retracted position, the operator can first rotate coupling assembly  10  forward, fully pressurize bucket cylinder  18 , and then throw switch  111  to the unlatch position. 
     At this point, solenoid valves  108 ,  110  are still energized and in the unlatch position, and check valve  122  retains pressure in latch cylinder  58 . The operator can then use free hands to maneuver the vehicle to disengage the hooks  34  from cross member  40  to uncouple the tool. 
     If the equipment is to remain idle for a period of time, the operator throws toggle switch  111  to the latch position, de-energizing the solenoid valves in valve assembly  102 , and lowers hydraulic pressure in line  96 . This allows pressure to drop in latch cylinder  58  such that spring  56  urges latch pin  48  to the engaged, or latched position, thereby bringing the piston  72  of cylinder  58  to a protected position retracted into cylinder body  70 . 
     To attach a new tool, with the latch pin  48  still in the retracted position and the valves in the valve assembly  102  still energized, the operator adjusts pressure in the bucket cylinder  18  and maneuvers the coupling assembly  10  to insert hooks  34  into the recess  36  of the new tool and engage cross tube  40 . The operator then lifts the tool off the ground, and rolls coupling assembly  10  forward by extending bucket cylinder  18 . Coupler crescent  61  engages an upper side of latch collar  51 , thus bringing latch pin  48  into alignment with receptacle  50  on bucket  14 . The operator knows that the coupler crescent  61  has engaged latch collar  51  when he sees the bucket  14  visibly begins to roll forward. Less than full pressurization of the bucket cylinder  18  is typically required to bring the coupling assembly to this position. 
     The operator then throws switch  111  to the latch position. This de-energizes solenoid valves  108 ,  110  and moves check valve  122  out of hydraulic circuit  86  and check valve  116  into hydraulic circuit  86 . Check valve  116  is set to open at a low differential pressure, such that hydraulic pressure will be released from the latch cylinder  58  when the back pressure in bucket cylinder  18  is much less than full pressure but great enough to rotate coupling assembly forward so that the coupling crescent engages the tool latch collar  50 . 
     When the hydraulic pressure in latch cylinder  58  is released, spring  56  moves latch pin  48  into the engaged position with receptacle  50 . The position of pin block  62  gives the operator a visible signal that the pin  48  is latched and the tool secured. Check valve  116  thereafter prevents the latch pin assembly from being inadvertently pressurized. 
     Other embodiments of the invention are within the scope of the following claims.

Summary:
The invention provides a coupling assembly and method for coupling a tool to a dipperstick, or arm, on an apparatus which has a hydraulic system for moving the tool. The coupling assembly includes a coupler body having link structure for pivotally coupling to the dipperstick. A latch member is movable between an engaged position for engaging the tool and a disengaged position for disengaging from the tool. A spring is arranged to provide a spring force to urge the latch member to the engaged position. A hydraulic motor has a part that is stationary relative to the coupler body and a movable part that can be extended relative to the stationary part when hydraulic pressure is applied to one end of the hydraulic motor. The movable part is coupled to the latch member such that extension of the movable part urges the latch member to the retracted position in opposition to the spring force.