Patent Publication Number: US-2009220326-A1

Title: Safety Device for Hydraulic Hitch Assembly

Description:
The present invention relates to a safety device for a hydraulic hitch assembly and in particular to a safety device that may be operated remotely from the hitch assembly. 
     BACKGROUND OF THE INVENTION 
     Large mobile machinery, such as excavators and the like, are commonly being fitted with various types of attachments to increase the versatility of the machine. Examples of such attachments include a bucket or rock hammer. Typically, these attachments are fitted to the articulated arm of the excavator through means of a quick change device, such as a hitch assembly or quick-coupler that is normally hydraulically activated. 
     One type of hydraulic hitch assembly is described in Australian patent 586124 and consists of a remotely operable pair of oppositely directed jaws which are adapted to move between an engaged position and a disengaged position. In the disengaged position, the jaws can fit between the internal transverse hinge pins of the attachment. The jaws are then moved away from each other through use of a hydraulic piston or ram into the engaged position where they grip the transverse hinge pins of the attachment and hold it in place for use. 
     Due to the risk of hydraulic failure where the hydraulic hitch assembly could potentially retract into the disengaged position almost immediately, hydraulic hitch assemblies are required to be fitted with a safety restraining device that would prevent the hitch assembly from disengaging from the attachment. These safety restraining devices are typically mechanical arrangements that require the operator of the machinery to engage and disengage the safety device at the site of the hitch assembly. As such, this means that each time the attachment is changed, the operator must descend from the cabin operating the machine to disengage the safety device. Thereafter, the operator is required to remount the cabin to operate the hydraulics driving the hitch assembly to replace the attachment of the hitch assembly, after which he must then once again descend from the cabin to re-engage the safety restraining device. 
     Accordingly, the present invention seeks to provide a safety device for use in hydraulic hitch assemblies and in particular seeks to provide a safety device that may be operated from the operating cabin of the machinery including the hitch assembly. 
     SUMMARY OF THE INVENTION 
     According to one aspect the present invention provides a safety device for a hydraulic hitch assembly operable between an engaged and a disengaged position, the safety device including:
         a main body portion moveable between an engaged position and a disengaged position, whereby when the main body portion is in the engaged position the safety device prevents the hydraulic hitch assembly from moving to a disengaged position;   a biasing means to bias the main body portion towards an engaged position; and,   a hydraulic piston which when operated acts against the biasing means and moves the main body portion to a disengaged position.       

     Preferably, the main body portion moves between an engaged position and a disengaged position about a pivot point. 
     Preferably the biasing means is provided by a mechanical arrangement such as for example a spring. 
     The hydraulic hitch assembly may be operable between a disengaged position and an engaged position by means of a hydraulic ram or piston. In this form, the hydraulic ram or piston is operated by a hydraulic circuit, wherein to move the hitch assembly into the engaged position hydraulic fluid is pumped under pressure into one side of the ram or piston to effect the movement. Once in the engaged position, the hydraulic ram or piston is prevented from moving the hitch assembly to the disengaged position by means of a valve assembly included in the hydraulic circuit. Preferably this valve assembly is in the form of a check valve. The valve assembly prevents movement of the ram or piston until a positive hydraulic pressure is applied to the valve assembly whereby the hydraulic ram or piston is released allowing the hitch assembly to return to the disengaged position. 
     Preferably the hydraulic piston of the safety device is also connected to the hydraulic circuit of the hitch assembly. More preferably, the positive pressure, applied to the valve assembly to release the hydraulic piston and/or ram to allow the hitch assembly to return to the disengaged position, is initially applied to the hydraulic piston of the safety device thereby moving the main body portion of the safety device to the disengaged position prior to the hitch assembly returning to a disengaged position. 
     According to another aspect the present invention provides a method of disengaging a hydraulic hitch assembly from an engaged position, the hydraulic hitch assembly including a safety device and wherein the method includes the following steps:
         (i) providing the hydraulic piston of the safety device with a positive pressure sufficient to overcome the biasing means and move the safety device from the engaged to the disengaged position; and,   (ii) moving the hydraulic hitch assembly into a disengaged position.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become better understood from the following detailed description of a preferred but non-limiting embodiment thereof, described in connection with the accompanying figures, wherein: 
         FIG. 1  is a schematic view of a safety device in accordance with one aspect of the present invention, 
         FIG. 2  is a schematic view of a hydraulic hitch assembly, 
         FIG. 3  is a schematic view of a hydraulic hitch assembly fitted with the safety device in the engaged position in accordance with one aspect of the present invention, and, 
         FIG. 4  is a schematic view of a hydraulic hitch assembly fitted with the safety device in the disengaged position in accordance with one aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The term “hydraulic hitch assembly” as used throughout the specification is intended to include quick couplers as well as any type of hydraulic assembly for attaching and detaching various attachments to large machinery. 
     Referring to  FIG. 1 , there is shown a safety device which may be attached to a hydraulic hitch assembly. The safety device  10  includes a main body portion  12  which is substantially elongate and includes an engagement tip  85  and pivoting point  15 . The safety device  10  also includes a spring  20  which in the instant diagram is biased against retaining block  45  which is fixed relative to the main body portion of a hydraulic hitch assembly (not shown in  FIG. 1 ). The safety device  10  also includes a hydraulic piston  35  with hydraulic fluid space  25  to receive hydraulic fluid under pressure in order to operate the hydraulic piston  35 . The hydraulic piston is shown resting against retaining block  40  which would also be attached and fixed relative to the main body portion of the hitch assembly and not attached to the main body portion  12  of safety device  10 . In an alternative embodiment the retaining block may be attached to the body portion of the hydraulic ram  70  associated with the hydraulic hitch assembly. 
     Referring now to  FIG. 2 , there is shown generally a hydraulic hitch assembly indicated by  51  used for attaching an attachment such as a bucket or rock hammer to heavy machinery such as for example an excavator. The hitch assembly  51  includes two remotely operable oppositely directed jaws  60 ,  65  which are able to move between an engaged position (as depicted in  FIG. 2 ) and a disengaged position. In the disengaged position, the opposing jaws  60  and  65  are able to fit between the transverse hinge pins  50  and  55  of a particular attachment thereby releasing the attachment. Upon engaging with the attachment, the jaws  60  and  65  are pushed apart by means of a hydraulic ram  70  operable from the cabin of the machinery, which pushes apart jaws  60  and  65  until the attachment is securely fastened to the hitch assembly  51 . 
     Although not shown in  FIG. 2 , the hydraulic ram  70  is operated via a hydraulic circuit through which operation pumps hydraulic fluid into the hydraulic ram  70  which in turn pushes jaw  65  away from  60  to engage with the attachment, at which point the hydraulic fluid is shut off from a main hydraulic circuit by means of check valve, thereby maintaining jaws  65  and  60  in an engaged state. In order to release the check valve and thereby disengage the hydraulic hitch assembly  51 , a positive pressure must be applied to the check valve in order to release the hydraulic ram  70  thus allowing jaw  65  to return to the disengaged state. 
     Referring now to  FIG. 3 , there is shown a safety device  10  fitted in conjunction with a hydraulic hitch assembly. The safety device  10  as well as the hydraulic hitch assembly are shown in the engaged position, whereby an attachment is securely fastened to the hitch assembly. In the event of a hydraulic failure, the hydraulic ram  70  would release thereby allowing jaw  65  to contract towards jaw  60 . In this event, the engagement point  85  of the safety device would engage with engagement crevasse  80  of the hitch assembly  51  thereby preventing jaws  60  and  65  from moving together beyond a distance that would allow the attachment to disengage from the hitch assembly. 
     The safety device  10  is hinged at a fixed point  15  relative to the hitch assembly  51  where it may rotate about point  15  between an engaged and disengaged position. Whilst the hydraulic hitch assembly  51  is in the engaged position, the spring  20  of the safety device  10  is biasing the safety device into the engaged position by pushing against retaining block  45  attached and fixed relative to the hitch assembly  51 . 
     In order to disengage the safety device from this position it is necessary to supply hydraulic fluid under pressure to cavity  25  of the hydraulic piston  35  located in the safety device  10 . Upon applying fluid with sufficient pressure, the hydraulic piston  35  pushes down onto retaining block  40 , also attached and fixed relative to the main body portion of the hitch assembly, and thereby pushes the safety device against the biasing force of the mechanical spring  20 . Once the force of the hydraulic piston  35  pushing against retaining block  40  is greater than the resilient force of the spring  20 , the safety device is caused to rise and move about hinged point  15  such that the device moves to the disengaged position. 
     Referring now to  FIG. 4 , there is shown the safety device  10  in the disengaged position whereby the hydraulic piston  35  of the safety device  10  has pushed against retaining block  40  attached to the hitch assembly thereby moving the safety device  10  to the disengaged position. In the disengaged position it can be seen that the engagement point  85  of the safety device  10  is no longer aligned with the corresponding engagement crevasse  80  of the hitch assembly thereby allowing jaws  60  and  65  to retract once the hydraulic ram of the hitch assembly is allowed to release and move the hydraulic hitch assembly  51  into the disengaged position. 
     A clear advantage of the safety device  10 , is that in order to release the device and allow the jaws  60  and  65  of the hitch assembly  51  to retract to the disengaged position, the hydraulic piston  35  of the safety device  10  may be operated from a point that is remote from the hitch assembly such as for example from the cabin of the heavy machinery. 
     As an additional advantage of this arrangement, the hydraulic fluid operating the hydraulic piston  35  may be part of the hydraulic circuit associated with the hydraulic hitch assembly  51 . In this form, the reverse pressure applied to the checking valve to release the hydraulic. ram  70  of the hitch assembly  51  is initially directed to the hydraulic piston of the safety device  10  thereby moving the safety device to the disengaged position just prior to releasing the hydraulic ram  70  of the hitch assembly  51 . In this way, the safety device IO can be manipulated from the cabin of an excavator or the like and thereby not requiring the operator to descend from the cabin in order to disengage the safety device to remove and attach various attachments to the hydraulic hitch assembly  51 . 
     Furthermore, this arrangement also provides the additional safety advantage that if there is indeed a hydraulic failure causing the hydraulic hitch assembly to retract, the safety device cannot be moved to the disengaged position as it would require hydraulic pressure to do so. 
     Thus, the safety device would always be in the engaged position in the event of a hydraulic failure. 
     In order to assist an operator of an excavator or the like which is equipped with the safety device of the present invention to determine whether the safety device  10  is in an engaged or a disengaged position, the safety device may also be fitted with display means (not shown in the figures). According to one form, the display means may be in the form of two flanges, one extending from the engagement end of the safety device  10  and the other extending from the end adjacent the pivoting point  15 . When the safety device is in the engaged position, the flanges are arranged so as to be in a particular configuration when viewed from the cabin of the excavator such that the operator can be assured the safety device is in the engaged position. Once the safety device is moved to the disengaged position, the flanges are no longer aligned in said particular configuration, indicating that the safety device is no longer in the engaged position. In an alternative embodiment, a display means may be located in the actual cabin of the excavator or the like and be in the form of a light for example which when operated provides the operator with an indication of whether the safety device is in the engaged or disengaged state. 
     An example of an embodiment of the invention is described as follows: 
     A check valve associated with a hydraulic ram of a typical hydraulic hitch assembly operates at a 3:1 ratio, that is the check valve can provide a captive pressure of 3000 PSI, which will maintain the hydraulic hitch assembly in an engaged position. As the check valve operates at a 3:1 ratio, it requires a reverse pressure of 1000 PSI to release after which the hydraulic hitch assembly will retract into the disengaged position. In this example the 1000 PSI of reverse pressure is provided to the hydraulic piston of the safety device before being applied to the check valve and this pressure is sufficient to operate the hydraulic piston to overcome the force of the biasing means thereby moving the safety device into the disengaged state and allowing the hitch assembly to move into the disengaged position. 
     The captive pressure holding the hydraulic ram of the hitch assembly may drop due to a number of reasons such as for example, there is a bypass of hydraulic pressure, the seals of the hydraulic ram are damaged, or there is contamination in the hydraulic fluid. In this instance, the required pressure to release the check valve will also fall according to the 3:1 ratio whereby the pressure required to release the check valve will not be sufficient to for the hydraulic piston of the safety device to overcome the force of the biasing means (eg a spring). This means that the safety device cannot be moved into the disengaged position, and thereby constantly monitors the safe working condition of the hydraulic hitch assembly. 
     Finally, it can be understood that the inventive concept in any of its aspects can be incorporated in many different constructions so that generality of the preceding description is not to be superseded by the particularity of the attached drawings. Various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements of parts without departing from the spirit or ambit of the invention.