Abstract:
A three-point hitch suitable for operation with wide implements is constructed by substituting a pair of flotation actuators for the usual drop links that are normally coupled between a pair of rocker arms and a pair of lower draft links. These drop links are coupled to a hydraulic circuit including, according to one embodiment, individual accumulators for each flotation actuator, and according to a second embodiment, both actuators are coupled to a single accumulator. The accumulator(s) act to cause a pre-selected lifting force to be exerted by the flotation actuators so that a predetermined amount of the weight of an implement mounted to the draft links is counterbalanced, leaving a desired ground pressure being exerted by the implement during operation. When using individual accumulators, a side-to-side weight balance can be achieved since different accumulator settings may be used.

Description:
[0001]    This is a continuation-in-part of U.S. patent application, Ser. No. 10/346,881, filed 16 Jan. 2003, now abandoned. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a tractor three-point hitch.  
         BACKGROUND OF THE INVENTION  
         [0003]    A variety of different implements are compatible with common three-point hitching systems. Many implements, such as mower-conditioners, snow plows, etc. need flotation in addition to height control to insure good performance and prevent damage. Presently, flotation is not available in common three-point hitching systems and must be designed into the implement.  
         SUMMARY OF THE INVENTION  
         [0004]    According to the present invention, there is provided an improved tractor three-point hitch.  
           [0005]    An object of the invention is to provide a tractor three-point hitch arrangement which provides flotation.  
           [0006]    A more specific object of the invention is to provide a three-point hitch arrangement which provides flotation and is achieved by making a relatively simple modification to a common three-point hitch arrangement.  
           [0007]    Yet a more specific object of the invention is to provide a three-point hitch arrangement wherein drop links are formed of flotation cylinders which are either coupled to respective accumulators or are both coupled to the same accumulator.  
           [0008]    These 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 DRAWINGS  
       [0009]    [0009]FIG. 1 is a perspective view of a tractor three-point hitch, which is representative of the prior art.  
         [0010]    [0010]FIG. 2 is a perspective view of the tractor three-point hitch shown in FIG. 1, but modified for forming a three-point hitch constructed in accordance with the principles of the present invention.  
         [0011]    [0011]FIG. 3 is a schematic view of a flotation control circuit constructed in accordance with a first embodiment.  
         [0012]    [0012]FIG. 4 is a schematic view of a flotation control circuit constructed in accordance with a second embodiment.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    Referring now to FIG. 1, there is shown a tractor three-point hitch assembly  10  which is representative of the prior art. The three-point hitch assembly  10  may be mounted at either the front or the rear of a vehicle and includes, as viewed in the drawing, right- and left-hand lower draft links or arms  12  and  14  mounted for pivoting vertically about a horizontal transverse axis defined by a transverse shaft  16  fixed to a frame  18  of the carrying vehicle. An upper third draft link or arm  20 , in the form of a length-adjustable turnbuckle has one end pivotally connected, as by a pin  22 , to a bifurcated end of a yoke  24 , and has its other end mounted for pivoting vertically about a horizontal transverse pin  26  coupled to a bracket  28  bolted to the vehicle frame  18  at a central location above and between the lower draft links  12  and  14 . A horizontal, transverse rock shaft  30  is mounted for rotation within a support member  32  secured to the vehicle frame  18  at a location spaced substantially vertically above the support shaft  16  for the lower draft links. Mounted to the right- and left-hand ends of the rocker shaft  30  are rocker arms  34  and  36 , respectively. A pair of lift links  38  and  40 , respectively, have upper ends pivotally coupled to free ends of the rocker arms  34  and  36 , as by horizontal transverse pins  42  and  44 , and have bottom ends pivotally coupled, as by horizontal transverse pins  46  and  48 , respectively, to yokes  50  and  52  having bifurcated lower ends coupled in straddling relationship to the draft links  12  and  14  by horizontal transverse pivot pins  54  and  56 , respectively. Right- and left-hand lift cylinders  58  and  60 , respectively, have upper ends pivotally coupled to the rocker arms  34  and  46 , as at pins  62  and  64 , and have lower ends pivotally coupled to the vehicle frame  18 , as at pins  66  and  68 .  
         [0014]    Referring now to FIG. 2, there is shown a three-point hitch assembly  70  incorporating the present invention, with components that are the same as those described above relative to FIG. 1, being given the same numeral call-outs. The only difference in the hitch assemblies  10  and  70  is that instead of the lift links  38  and  40  illustrated in FIG. 1, hydraulic float actuators  72  and  74  are provided. The hydraulic float actuator  72  includes a piston rod  76  having clevis at its lower end coupled to the lower draft link  12  by the pin  54  and a cylinder  78  having an upper end located between opposite lugs of a bifurcated free end of the right rocker arm  34  and coupled to the latter by the pin  42 . Similarly, the float actuator  74  includes a piston rod  80  having a lower end defined by a clevis coupled to the draft link  14  by the pivot pin  56 , and a cylinder  82  having an upper end located between lugs of a bifurcated free end of the rocker arm  36  and coupled thereto by the pin  44 .  
         [0015]    Referring now to FIG. 3, there is shown a flotation control circuit  84  constructed in accordance with a first embodiment for controlling the operation of the floatation actuators  72  and  74 . The circuit  84  includes a right-hand accumulator  86  coupled to the rod end of the actuator  72  by a supply/return line  90 , and includes a left-hand accumulator  88  coupled to the rod end of the actuator  74  by a left-hand supply /return line  92 . A further right-hand supply/return line  91  is coupled to the piston end of the actuator  72 , and a further left-hand supply/return line  93  is coupled to the piston end of the actuator  74 . A pressure fluid supply line  94  is coupled to the output of a pressure-compensated supply pump  96  having its input coupled to a sump or reservoir  98 . A right-hand, four-position, four-way directional control valve  100  has a set of supply/return ports respectively coupled to the supply/return lines  90  and  91 , and has a supply port and a return port respectively coupled to a first branch of the supply line  94  and to a return line  97 , which extends to the sump  98 . Similarly, a left-hand, four-position, four-way directional control valve  102  has a set of supply/return ports respectively coupled to the supply/return lines  92  and  93 , and has a supply port and a return port respectively coupled to a second branch of the supply line  94  and to a return line  99 , which is coupled to the sump  98 .  
         [0016]    A control circuit  104 , constructed in accordance with a second embodiment, is illustrated in FIG. 4. The control circuit  104  is a simplification of the circuit  84  in that it includes only one accumulator  106  and only one directional control valve  110 , which is a three-position, four-way directional control valve, that, as explained below, has one less function than do each of the valves  100  and  102 . Specifically, the accumulator  106  is coupled to a branched supply/return line  108  coupled between a supply/return port of the control valve  110  and the rod end of each of the actuators  72  and  74 . A second branched supply/return line  112  is coupled between a second supply/return port of the control valve  110  and the piston ends of the actuators  72  and  74 . The pressure fluid supply line  94  is coupled between the outlet of the pump  96  and a supply port of the valve  110 , while the return line  99  is coupled between the sump  98  and a return port of the valve  110 .  
         [0017]    In operation, assume the three-point hitch assembly  70  to be connected to an implement such as a wide area mower or the like, and for the flotation circuit  84  to be in use. When the work site is reached, the servo valve (not shown) for controlling the lift actuators  58  and  60  is actuated to lower the implement and place the actuators in a float mode. The direction control valves  100  and  102 , which up to now have been in a lock-out position (indicated at the top of the valves) are shifted to respective working positions (the position illustrated in FIG. 3). Fluid flow to and from the piston ends of the actuators  72  and  74  will then be prevented and a lifting force, as determined by the pressure in the accumulators  86  and  88  will act to counterbalance the weight of the implement. Because the pump  96  is pressure-compensated, its displacement will be zero whenever the direction control valves  100  and  102  block flow to the actuators  72  and  74 . A pump which is not pressure-compensated could be used, but in that case, the valves  100  and  102  would have to be replaced with valves having open centers that provide a path back to the sump  98  any time the valves are positioned to block flow to the actuators  72  and  74 . Normally, the desired pressure exerted by the accumulators  86  and  88  will be such that only a small portion of the weight of the implement bears on the ground during operation. If the implement is not balanced in weight from side-to-side, then the accumulators  86  and  88  will be set at different pressures so that a balance in side-to-side ground pressure results for operation. Then, during operation, undulations in the work surface will result in the supports of the implement, usually skits or the like, to follow the ground contour with fluid being forced from the piston end of the cylinders  78  and  82  to the sump  98  when the rods  76  and  80  are forced upwardly, and with fluid being drawn into the piston ends of the cylinders  78  and  82 , when the piston rods  76  and  80  move downwardly. The amount of the lifting or weight counterbalance force exerted by the accumulators can be increased by shifting the valves  100  and  102  upward by one position from the illustrated working position shown wherein the rod end is connected to the pump  96  and the piston end is connected to the sump  98 . The lifting force exerted by the accumulators  86  and  88  can be decreased by shifting the valves  100  and  102  to their upper most positions wherein the rod ends of the actuators  72  and  74  are connected to the sump  98  and the piston ends are connected to the pump  96 . When it is desired the actuators  72  and  74  be prevented from extending or retracting, the valves  100  and  102  are shifted to their lowermost positions wherein the flow of fluid to and from the cylinders  78  and  82  is prevented. The operation is essentially the same if the control circuit  104  is used instead of the circuit  84 , but here only the accumulator  106  is used so no side-to-side compensation can be made for differences in weight of the implement at opposite sides of the longitudinal centerline of the implement. Furthermore, the control valve  110  omits the lockout function. In any event, when it is desired to once again raise the implement for transport, the cylinders of the actuators  58  and  60  are pressurized so as to effect a lifting action on the rocker arms  34  and  36  such that they act through the float actuators  72  and  74  to lift the links  12  and  14 .  
         [0018]    Thus, it will be appreciated that by simply modifying a conventional three-point hitch assembly  10  by substituting hydraulic actuators for the lift links and providing a control circuit embodying accumulators for causing these actuators to have a desired float characteristic, a three-point hitch assembly having individually floating draft links suitable for operating with a wide implement is created.  
         [0019]    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.