Patent Publication Number: US-2013234415-A1

Title: Hydraulic hitch assembly

Description:
The present invention relates a hydraulic hitch assembly which includes a safety mechanism for preventing the unintentional release of an attachment. 
     BACKGROUND 
     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 (hereinafter referred to as a hydraulic hitch assembly). 
     One type of hydraulic hitch assembly is described in Australian patent 586124 and consists of a remotely operated 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 an 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. 
     The present invention seeks to provide a hydraulic hitch assembly including a safety mechanism that prevents the attachment from completely disengaging with the hydraulic hitch assembly even in the event of catastrophic mechanical and/or hydraulic failure. 
     SUMMARY 
     According to one aspect the present invention provides a hydraulic hitch assembly including oppositely directed jaws operable to releasably grip an attachment including two transverse hinge pins, wherein one of the oppositely directed jaws is fixed relative to the hitch assembly, and the other jaw is moveable between a withdrawn position, in which the oppositely directed jaws can be fitted between the two transverse hinge pins of the attachment, and an extended position, in which the two transverse hinge pins are gripped by the oppositely directed jaws, the hydraulic hitch assembly further including a safety mechanism including an arm moveable between an engaged position and a disengaged position, wherein when the arm is in the engaged poSition, the arm prevents the transverse hinge pin from being released from the fixed jaw. 
     In one form the fixed jaw has an acuate face for receiving a hinge pin of the attachment and the arm of the safety mechanism includes a contact face which is located on an opposing side to the acuate face of the fixed jaw when the arm is in the engaged position. 
     In one form the arm is moved between the engaged position and the disengaged position by moving about a pivot point. In one form the pivot point is fixed relative to the hydraulic hitch assembly. In one form the pivot point is located at a distal end of the arm from the contact face. 
     In one form the arm of the safety mechanism is moved between an engaged position and a disengaged position by an actuator positioned on the arm and moveable between an extended position and a retracted position. In one form the arm is in the disengaged position when the actuator is in the extended position. In one form the actuator moves the arm by extending from a retracted position and pushing upon a fixed point relative to the hydraulic hitch assembly. In one form the actuator is a hydraulic cylinder operable by a hydraulic fluid contained within a hydraulic circuit. 
     In one form the hydraulic hitch assembly includes a hydraulic ram to move the other jaw from a withdrawn position and an extended position and the hydraulic fluid is delivered to the hydraulic cylinder from the hydraulic ram. In one form the hydraulic ram includes a primary cylinder side and a rod side and the hydraulic fluid delivered to the hydraulic cylinder of the safety mechanism is delivered from the rod side of the hydraulic ram. 
     In one form the safety mechanism includes a mechanical bias to bias the arm towards the engaged position. In one form the mechanical bias is a compression spring. In one form a first end of the compression spring is fixed relative to the hydraulic hitch assembly and a second end of the compression spring is fixed to the arm. 
     In one form the hydraulic hitch assembly further includes a second safety mechanism, the second safety mechanism including a main body portion which moves between an engaged position, in which the main body portion is aligned to prevent the movement of the other jaw from the extended position to the withdrawn position, and a disengaged position in which the main body portion allows the movement of the other jaw from the extended position to the withdrawn position. 
     In one form, the second safety mechanism includes a mechanical bias to bias the main body portion to the engaged position and a hydraulic cylinder which when operated, acts against the mechanical bias to move the main body portion to the disengaged position. In one form the hydraulic piston of the second safety mechanism is operable by delivery of hydraulic fluid contained within a hydraulic circuit. In one form the hydraulic fluid is delivered from the rod side of the hydraulic ram of the hydraulic hitch assembly. 
     In one form the pressure of hydraulic fluid required to operate the hydraulic cylinder of the second safety mechanism to overcome the force of the mechanical bias and move the main body portion to the disengaged position is less than the pressure of the hydraulic fluid required to operate the hydraulic cylinder of the safety mechanism to move the arm to the disengaged position. 
     According to another aspect the present invention provides a method of releasing an attachment from a hydraulic hitch assembly as herein described the method including the following steps:
         a. moving the other jaw of the hydraulic hitch assembly to a withdrawn position;   b. moving the arm of the safety mechanism from an engaged position to a disengaged position; and,   c. releasing the hinge pin of the attachment from the fixed jaw of the hydraulic hitch assembly.       

    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES 
       The present invention will become better understood from the following detailed description of various non-limiting embodiments thereof, described in connection with the accompanying figures, wherein: 
         FIG. 1  is a schematic diagram of a hydraulic hitch assembly including a safety mechanism; 
         FIG. 2  is a schematic view of a safety mechanism in the engaged position; 
         FIG. 3  is a schematic view of a safety mechanism in the engaged position; 
         FIG. 4  is a schematic view of a safety mechanism in the disengaged position; and, 
         FIG. 5  is a schematic view from above of a safety mechanism; 
         FIG. 6  is a schematic view of a hydraulic hitch assembly including the safety mechanism in the engaged position and a second safety mechanism in the disengaged position; 
         FIG. 7  a schematic view of a hydraulic hitch assembly including the safety mechanism in the engaged position and a second safety mechanism in the engaged position; 
         FIG. 8  is a schematic view of a hydraulic hitch assembly including the safety mechanism in the disengaged position and a second safety mechanism in the disengaged position; 
         FIG. 9  is a cut away view of the chambers of the hydraulic ram of the hydraulic hitch assembly when the movable jaw is in the extended position; 
         FIG. 10  is a cut away view of the chambers of the hydraulic ram of the hydraulic hitch assembly when the movable jaw is in the withdrawn position; 
         FIG. 11   a  is a schematic view of an articulated arm including a hydraulic hitch assembly in preparation to engage an attachment in the form of a bucket; 
         FIG. 11   b  is a schematic view of an articulated arm including a hydraulic hitch assembly engaging an attachment in the form of a bucket; 
         FIG. 11   c  is a schematic view of an articulated arm including a hydraulic hitch assembly engaged with an attachment in the form of a bucket; and, 
         FIG. 11   d  is a schematic view of an articulated arm including a hydraulic hitch assembly disengaging an attachment in the form of a bucket. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS AND THE ACCOMPANYING FIGURES 
     The foregoing describes only some embodiments of the present invention, and modifications and/or changes can be made thereto without departing from the scope and spirit of the invention, the embodiments being illustrative and not restrictive. 
     In the context of this specification, the word “comprising” means “including principally but not necessarily solely” or “having” or “including”, and not “consisting only of”. Variations of the word “comprising”, such as “comprise” and “comprises” have correspondingly varied meanings. 
     Referring to the accompanying Figures, a hydraulic hitch assembly  10  is depicted in  FIG. 1  which is fitted with a safety mechanism  15  in accordance with certain embodiments. The hydraulic hitch assembly includes two oppositely directed jaws  21 ,  22  which are operable to releasably grip the transverse hinge pins  25 ,  26  of an attachment. The attachment may be any type of attachment that is commonly attached to heavy machinery using a hydraulic hitch assembly, such as for example a bucket or rock hammer. 
     The oppositely directed jaws  21 ,  22  include a fixed jaw  21 , which is fixed relative to the body of the hydraulic hitch assembly  10 , as well as a moveable jaw  22  that is capable of moving between a withdrawn position in which the two oppositely directed jaws  21 ,  22  can be fitted between the hinge pins  25 ,  26  of an attachment, and an extended position (as depicted in  FIG. 1 ) when the oppositely directed jaws are in a position where they grip the hinge pins  25 ,  26  of the attachment. The moveable jaw  22  moves in a linear fashion relative to the fixed jaw in a slidable arrangement. 
     The moveable jaw  22  is moved between the withdrawn position and the extended position by a hydraulic ram  23  that is operated by hydraulic fluid contained within a hydraulic circuit which is delivered to the bottom chamber of the hydraulic ram  23  by line  101  and rod side chamber of the hydraulic ram  23  line  102 . During typical operation, the hydraulic hitch assembly  10  may be attached to an attachment by fitting the oppositely opposing jaws  21 ,  22  between the hinge pins  25 ,  26  of the attachment when the moveable jaw  22  is in the withdrawn position and then moving the moveable jaw  22  into the extended position by operating the hydraulic ram  23  until the oppositely directed jaws  21 ,  22  grip the transverse hinge pins  25 ,  26  of the attachment. 
     The safety mechanism  15  operates with respect to the fixed jaw  21  of the hydraulic hitch assembly  10  and the front transverse hinge pin  25  of the attachment. The safety mechanism  15  includes an arm  20  that is moveable between an engaged position and a disengaged position.  FIGS. 1 to 3  each show the arm  20  of the safety mechanism  15  in the engaged position where a contact face  31  of the arm  20  together with the arcuate face  30  of the fixed jaw  21  prevent the transverse hinge pin  25  of the attachment from being released from the hydraulic hitch assembly  10  even when the moveable jaw  22  is in the withdrawn position and the other transverse hinge pin  26  of the attachment is released from the hydraulic hitch assembly  10 . 
     The arm  20  of the safety mechanism  15  is moveable between an engaged position shown in  FIGS. 1 ,  2  and  3  and a disengaged position as shown in  FIG. 4  where the contact face  31  of the arm  20  is no longer on the opposing side of the hinge pin  25  to the arcuate face  30  of the fixed jaw  21  such that the hinge pin  25  is able to be released freely from the hydraulic hitch assembly. 
     The arm  20  of the safety mechanism  15  is able to move between the engaged position and the disengaged position by moving about, or pivoting from, a pivot point  24  which is fixed relative to the hydraulic hitch assembly  10 . The pivot point  24  is located at a distal end from the contact face  31  of the arm  20  and is provided by a pin passing through an opening in the body of the arm  20  which is then secured to the body of the hydraulic hitch assembly  10 . 
     Turning to  FIG. 2  there is shown a mechanical bias in the form of a compression spring  42  that is part of the safety mechanism  15 . The compression spring  42  acts to bias the arm  20  towards the engaged position shown in  FIGS. 1 to 3 . The compression spring is fixed at one end  43  to a flange portion of the hydraulic hitch assembly  44  and fixed at the other end  46  to a flange  45  located on the arm  20  of the safety assembly  15 . In order to move the arm  20  from the engaged position to the disengaged position the biasing force of the compression spring  42  pushing the arm into the engaged position must be overcome such that the arm  20  may move upwards about the pivot point  24  thereby compressing the body of the compression spring  42  towards the flange  44 . 
     In order to engage a transverse hinge pin  25  onto the fixed jaw  21  of the hydraulic hitch assembly  10 , the hinge pin  25  is placed into contact with face  61  of the arm  20  of the safety mechanism  15  whereby the contact force of the hinge pint  25  abutting against face  61  is sufficient to overcome the biasing force of compression spring  42  to move the arm  20  whereby it pivots about the pivot point  24  compresses the compression spring  42  and moves from the engaged position to the disengaged position. The hinge pin  25  is then freely able to move into place and abut the acuate face  30  of jaw  21  at which point there is no longer a force acting on face  61  of the arm  20  of the safety device  15  whereby the biasing force of the compression spring  42  pushes the arm  20  back into the engaged position with the hinge pin  25  safely locked between the contact face  31  and the acuate face  30  of the fixed jaw  21 . 
     The contact face  31  is concave in shape and includes cupping points  52 ,  51  at either end of the contact face  31 . Such a concave shape and cupping points  52 ,  51  assist in contacting and containing the hinge pin  25  between the arm  20  of the safety assembly  15  and the fixed jaw  21  when the arm  20  is in the engaged position. 
     A further structural feature of the design of the safety mechanism  15  is associated with the shape of the arm  20 . The arm  20  is itself shaped with in an elbow configuration which provides two points of contact  60 ,  65  depicted in  FIGS. 2 and 3  where the arm  20  is in contact with the main body of the hydraulic hitch assembly  10  when in the engaged position. The first point of contact  65  provides that the arm  20  is in contact with a horizontally aligned flange  66  on the main body of the hydraulic hitch assembly  10  located underneath the pivot point  24 . A protrusion extending from the arm and ending in contact point  65  separates the arm from the contact point on the flange  66 . This provides that the arm  20  does not rotate further beyond the engaged position around pivot point  24  under the biasing force of the compression spring  42 . 
     The second point of contact  60  is between an outside elbow surface of the arm  20  and a vertically aligned flange  67  located on the main body of the hydraulic hitch assembly. The second contact point  60  provides added structural integrity to the arm  20  such that if the hinge pin  25  is pushed onto the contact face  31  of the arm  20 , the full force is not transferred to the pivot point  24  but rather onto the main body of the hydraulic hitch assembly  10 . 
       FIGS. 3 and 4  show an actuator  53  of the safety assembly  15  that is able to be moved from a retracted position shown in  FIG. 3  to an extended position shown in  FIG. 4 . The actuator  53  is moved as part of a hydraulic cylinder  28  that is operated by a hydraulic fluid contained which is delivered via line  57  of a hydraulic circuit. The action of the hydraulic fluid onto the actuator  53  of the hydraulic cylinder  28  forces the actuator  57  into the extended position shown in  FIG. 4  where the force of the actuator pushing onto a fixed part of the main body of the hydraulic hitch assembly  10  is sufficient to overcome the biasing force of the compression spring  42  to enable the actuator to move the arm  20  from the engaged position to the disengaged position. 
     If it is desired to remove the hinge pin  25  of the attachment from the fixed jaw  21  of the hydraulic hitch assembly, then pressure exerted by the hydraulic fluid delivered by the hydraulic circuit  57  onto the hydraulic cylinder  28  forces the actuator  53  to extend onto the fixed point on the main body of the hydraulic hitch assembly  10  pushing the arm  20  to move in a pivotable relation around point  24  and overcoming the biasing force of the compression spring  42  thereby moving contact face  31  from the opposing side of the arcuate face  30  of the fixed jaw  21 . The hinge pin  25  of the attachment may then be removed freely from the hydraulic hitch assembly. 
       FIG. 5  is an alternate view of the safety assembly  15  showing the arm  20  in relation to the hydraulic cylinder  28  and compression spring  42  and pivoting point  24 . 
     The safety mechanism  15  is able to retain the transverse hinge pin  25  of the attachment at the fixed jaw  21  end of the hydraulic hitch assembly  10  to prevent the disengagement of the attachment from the hydraulic hitch assembly  10  due to catastrophic mechanical and/or hydraulic failure. In such an event, the safety mechanism  15  will retain the transverse hinge pin  25  of the attachment in the front fixed jaw  21  of the hydraulic hitch assembly  10 . The attachment may rotate around the retained hinge pin  25  if the moveable jaw  22  of the hydraulic hitch assembly is in the withdrawn position, however, it will not dislodge from the hydraulic hitch assembly  10  altogether. 
     The safety mechanism  15  also has the added advantage that it is easy to use when engaging an attachment whereby the arm  20  in the engaged position will be moved to the disengaged position when the face of the arm  61  which makes contact with the hinge pin  25  of the attachment is pushed into the disengaged position against the biasing force of the compression spring  42 . Once the hinge pin  25  has been placed adjacent the fixed jaw  21  or the arcuate surface  30  of the fixed jaw  21 , the arm  20  of the safety assembly  15  will spring back under the mechanical bias of the compression spring  42  into the engaged position. 
     The safety mechanism  15  may be released by moving the arm  15  into the disengaged position by a single acting hydraulic cylinder  28  which may source its hydraulic fluid from the rod side of the primary hydraulic ram  23  used to push the moveable jaw  22  from the withdrawn to the extended position. 
     In one form of this embodiment the rod side of the hydraulic ram  23  may be capable of three states of hydraulic pressure. The first is when the pressure is applied to the primary cylinder of the hydraulic ram  23  such that the rod side of the hydraulic ram  23  has theoretically zero pressure. From this state and once pressure is applied to the rod side of the hydraulic ram  23  it will initially have a pilot check valve  128  release pressure which is 1:3 ratios to the captive pressure of the primary cylinder side. Once the check valve  128  release pressure is reached this will activate the pilot check valve  128  which will then release the captive pressure in the primary cylinder of the hydraulic ram  23 . The pressure required to release the check valve  128  is also the same hydraulic pressure required to activate the main a hydraulic piston of a second safety mechanism (as described in PCT application PCT/AU2006/001884) to move to the disengaged position before the moveable jaw  22  retracts. Once the primary cylinder side of the hydraulic ram  23  has retracted completely and bottoms out, the rod side goes to an increased or full system pressure. An increased or full system pressure is the preferred pressure required to activate the hydraulic cylinder  28  to act against the compression spring  42  and move the arm  20  of the safety assembly  15  to the disengaged position. In a preferred form, pilot pressure directed to the hydraulic cylinder  28  is insufficient to overcome the biasing of the compression spring and the arm  20  will not move under such conditions and remain in the engaged state preventing the hinge pin  25  from being released from the hitch assembly. 
     What this means is that when detaching an attachment from a hydraulic hitch assembly  10  the flow of the hydraulic fluid is reversed from the primary cylinder and sent to the rod side of the hydraulic ram  23  at an initial pilot pressure which operates the check valve  128  releasing the pressure on the cylinder side of the hydraulic ram  23 . Pilot pressure lifts the main body portion of the second safety mechanism and the moveable jaw  22  then retracts freeing the hinge pin  26  of the moveable jaw. 
     Once the hydraulic ram  23  has fully retracted the rod side of the hydraulic cylinder then goes to full system pressure. This full system pressure is used to lift the arm  20  of the safety mechanism  15  which provides a sufficient amount of hydraulic pressure to the hydraulic cylinder of the safety mechanism  15  to overcome the biasing force of the compression spring. Once the full system pressure has stopped being applied, even when the hydraulic ram  23  is in the retracted position, the arm  20  of the safety assembly moves to the engaged position under the force of the compression spring. 
     Reference is made to  FIGS. 6 to 10  in order to better illustrate the embodiment when the hitch assembly includes the safety mechanism in addition to the second safety mechanism as described in PCT/AU2006/001884. 
     Like numerals have been used in these embodiments to illustrate the various features of the safety mechanism  15  in conjunction with a hitch assembly  10 . In addition, a second safety mechanism  110  is depicted which includes a main body portion  115  which is moveable between an engaged position shown in  FIG. 7  and a disengaged position shown in  FIGS. 6 and 8 . In the engaged position shown in  FIG. 7  the main body portion  115  prevents the moveable jaw  22  retracting to the withdrawn position by being in alignment with a notch  155  located on the body of the moveable jaw  22  on the side facing the fixed jaw. The main body portion  115  of the second safety mechanism  110  is able to pivot about pivot point  121  which moves the main body portion  115  to the disengaged state shown in  FIGS. 6 and 8  wherein the moveable jaw  22  may move to a position  22   b  which is the withdrawn position allowing the attachment pin  26  to be released from the hitch assembly  10 . The second safety mechanism  110  also includes a mechanical bias in the form of a compression spring  116  which acts to bias the main body portion  115  into the engaged position in alignment with the notch  155  located on the moveable jaw  22 . A hydraulic cylinder  117  which is operable by means of a hydraulic fluid delivered via line  118  from a hydraulic circuit can be operated to act against the biasing force of a compression spring  116  pushing against a fixed point  120  relative to the hitch assembly  10  and thereby biasing the main body portion  115  to the disengaged position shown in  FIGS. 6 and 8 . 
     Referring now to  FIGS. 6 ,  7 ,  8 ,  9 ,  10  and  FIGS. 11   a  to  11   d , the various steps associated with attaching an disengaging an attachment including pins  25  and  26  will be described. 
     Referring to  FIGS. 6 ,  10  and  11   a  the hitch assembly  10  attached to an articulated arm  200  is lowered with the moveable jaw  22  of the hitch assembly  10  in the withdrawn position wherein the hydraulic ram  23  with primary cylinder  151  and rod side cylinder  150  with theoretically zero hydraulic pressure. With the hydraulic ram  23  in such a state, the arm  20  of the safety mechanism  15  biased into the engaged position under the force of the compression spring  42 . The fixed jaw  21  of the hydraulic hitch, assembly is lowered to meet the attachment such that contact surface  61  of the arm  20  meets the attachment pin  25  whereby the attachment pin pushes against contact surface  61  thereby compressing the compression spring  42  which moves arm  20  to the disengaged position allowing the pin  25  to seat within the arcuate face  30  of the fixed jaw  21 . In this position, the compression spring moves the arm  20  back into the engaged position once the contact surface  61  is no longer being forced upwards by the attachment pin  25  which provides that attachment pin  25  is now prevented from being released from the fixed jaw  21  by the arm  20  of the safety mechanism  15 . 
     In this point, and referred to  FIG. 11   b  the moveable jaw  22  is in position  22   b  where the main body portion  115  of the second safety mechanism  115  is in the disengaged position. The articulated arm  200  is then moved such that the hitch assembly  10  is rotated upwards whereby the second pin  26  of the attachment is moved into alignment adjacent the moveable jaw  22 . The hydraulic cylinder  210  that rotates the articulated arm  200  to this position includes a non-rod side which will be in excess of 3,000 psi when fully bottomed out. By means of a directional control valve this high pressure may be diverted to port  101  of the hydraulic ram  23  of the hitch assembly  10 . This high hydraulic pressure moves the hydraulic ram  23  thereby moving the moveable jaw  22  into the extended position which thereby allows the main body portion  115  of the second safety mechanism  110  to move into the engaged position where it is an alignment with a notch  155  located on the moveable jaw. The hinge pins of the attachment are now fully attached to the hitch assembly  10  and the pressure located in the primary side of the hydraulic ram  23  is shut off by means of the check valve  128  to maintain the hinge pins of the attachment locked in place to the hydraulic hitch assembly  10  for use. This state is depicted with reference to  FIGS. 7 ,  9  and  11   c.    
     With reference to  FIGS. 9 and 10  the check valve  128  has a 3:1 release pressure ratio in this embodiment which means that if the captured hydraulic pressure is 3,000 psi in the primary cylinder  151  the check valve  128  release pressure will be 1,000 psi. 1,000 psi is referred to herein as a low pressure. 
     In the event that there is a hydraulic failure, the second safety mechanism  115  will remain in the engaged position thereby preventing the moveable jaw  22  from retracting thereby maintaining the attachment hinge pins within the moveable jaws. 
     Furthermore, if there is a further mechanical failure the fixed jaw maintains its grip around the hinge pin  25  as the arm  20  of the safety mechanism prevents release of the hinge pin. 
     In order to release the hinge pins of the attachment from the hitch assembly  10 , an initial reversal of hydraulic pressure is diverted to port  102  by bottoming out the main hydraulic cylinder of the articulated arm  200 . The hydraulic pressure directed to port  102  into the rod side of the hydraulic ram  23  is then also directed through ports  118  and  57  which lead to the hydraulic cylinder  117  of the second safety device and the hydraulic cylinder  28  of the safety mechanism  15 . 
     The first initial low pressure pilot check valve  128  release pressure of up to 1,000 psi in this embodiment is sufficient to operate hydraulic cylinder  117  to overcome the biasing force compression spring  116  thereby moving the main body  115  of the second safety mechanism  110  to the disengaged portion. However, the pilot check valve  128  release pressure, or low pressure of up to 1,000 psi is insufficient to operate hydraulic cylinder  28  in order to overcome the biasing force of spring  42  in order to move the arm  20  of the safety mechanism  15  to the disengaged position to allow the release of hinge pin  25  from the fixed jaw  21  of the hitch assembly  10 . This state can be seen depicted in  FIG. 11   d.    
     Once the check valve  128  pressure of 1,000 psi has been reached and the main body portion  115  of the second safety mechanism  110  has been moved to the disengaged position the moveable jaw  22  retracts as the pressure in chamber  150  then goes to high pressure of 3,000 psi which is delivered via port  57  to hydraulic cylinder  28  thereby providing a force sufficient to overcome the biasing force of the compression spring  42  which lifts the arm  20  of the safety mechanism  15  allowing the release of the hinge pin  31  from the fixed jaw  21  of the hitch assembly  10 . The attachment may then be removed entirely from the hydraulic hitch assembly. 
     Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention.