Abstract:
A depth control system particularly useful for single point depth control on an agricultural implement includes a valve and actuator mounted directly to the pivotal connection areas of a hydraulic cylinder that controls height. Cylinder motion directly controls valve actuation independently of complicated linkages to reduce the size and cost of the system and substantially overcome hysteresis problems.

Description:
FIELD OF THE INVENTION 
     The present invention relates directly to lift systems on agricultural implements and, more specifically, to a depth control actuation system for such implements. 
     BACKGROUND OF THE INVENTION 
     Agricultural implements with hydraulically actuated depth or lift systems often include depth control systems such as shown in commonly assigned U.S. Pat. Nos. 5,427,184 and 5,988,293. A typical system may include a valve which is activated to stop vertical movement of the frame as the implement is lowered to a selected working position. 
     Many hydraulically controlled agricultural implements utilize a single point depth control system wherein implement depth is monitored and adjusted at a single location on the implement. Typically, a plunger bracket assembly is slidably mounted on an actuator tube operably connected to the implement rockshaft. A plunger on the assembly contacts a poppet valve to stop fluid flow from the hydraulic lift cylinders at a preselected depth. To adjust depth, a set screw on the bracket assembly is loosened, and the bracket assembly is slid along the tube. The screw is tightened to secure the assembly at the desired location along the tube. Normally the amount of depth adjustment is small. When the set screw is unthreaded, the bracket is loosened from the tube and slides on the tube, often to a wrong location. The bracket has to be manually moved, and the amount of adjustment has to be determined visually. When the set screw is tightened, the bracket often changes location. Several trials may be required to achieve the desired position. Therefore, depth adjustment is often imprecise, difficult to repeat, and time consuming. 
     In another type of depth control, which is the subject of commonly assigned U.S. Pat. No. 5,427,184, a long crank is provided to adjust a linkage adjacent the depth control cylinder. Although such a device has the advantage of directly monitoring cylinder extension and retraction, the valve and linkage components are more complicated, expensive and difficult to access, and are subject to damage by crops and soil passing through the machine. A further type of control is shown in commonly assigned U.S. Pat. No. 5,988,293. Although these types of devices have alleviated some of the problems associated with depth control structures, most require complicated and expensive linkages, particularly if the depth adjustment is conveniently located for the operator. Wear and hysteresis limit the ability of such structures to provide accurate and repeatable depth control functions. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an improved depth control system for an implement. It is a further object to provide such a system which overcomes most or all of the aforementioned problems. It is still another object to provide such a system which is particularly useful with single point depth control structures. 
     It is another object of the invention to provide an improved depth control system for an implement having reduced hysteresis and improved repeatability compared to at least most previously available systems. It is a further object to provide such a system which is less complicated, easier and less expensive to manufacture, and easier to access than most systems. 
     A depth control system includes a valve and actuator mounted directly to the pivotal connection areas of a hydraulic cylinder that controls height. Cylinder motion therefore directly controls valve actuation independently of complicated linkages to reduce the size and cost of the system and substantially overcome hysteresis problems. These and other objects, features and advantages of the invention will become apparent from the description below in view of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a portion of an implement with height control structure. 
     FIG. 2 is an enlarged perspective view of the height control structure on the implement of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2, therein is shown a portion of an agricultural implement  10  having a tool-supporting frame  12  supported for forward movement over a field by lift wheel structure  16 . Hydraulic cylinder structure  20  is connected through a lift linkage  22  to the wheel structure  16  to selectively raise and lower the frame  12 . Tools (not shown) can be mounted on the frame for vertical movement therewith between field-working and transport positions. Depth control for soil engaging elements is provided by the vertical movement of the frame  12 . 
     A rockshaft  24  extending transversely to the forward direction of the travel of the implement is rotatably mounted on the frame  12  by bearing block support structure  26 . A lever or arm  28  is fixed to and extends upwardly from the rockshaft  24  closely adjacent the support structure  26  for rotation with the rockshaft about a transversely extending axis. The lift linkage  22  includes a tension link  32  pivotally connected at a forward end  34  to the arm  28 . The link  32  includes an aft end  36  pivotally connected to an upright arm  38  on the wheel structure  16 . As the forward end  34  of the link  32  is moved in the fore-and-aft direction, the wheel structure  16  is pivoted relative to the frame  12  to raise and lower the frame. 
     The cylinder  20  includes a rod end  40  pivotally connected by elongated cylinder pin structure  42  to the rockshaft arm  28  rearwardly and below the pivotal connection at the forward end  34  to the arm  28 . The cylinder  20  includes a base end  44  pivotally connected by a second elongated cylinder pin structure  46  to an aft end of a cylinder support bracket structure  48 . The cylinder support bracket  48  includes an angle support  50  having a forward end connected to the bearing block support structure  26 . The aft end of bracket  48  is connected by a U-bolt assembly  52  to a transversely extending frame tube  12   t.    
     The rod and base ends of the cylinder  20  are connected by hydraulic lines  56  and  58 , respectively, to a controlled source of hydraulic fluid for extending and retracting the cylinder. The base end line  58  is connected to a lower output port on a control valve  60  which is mounted directly on the rod end cylinder pin structure  42 . The control valve  60  includes a forwardly directed inlet port connected through a manual lock-up valve  66  and fluid line  68  to a controlled source of hydraulic fluid on the towing vehicle (not shown). The control valve  60  includes an outwardly biased valve actuator  70 , which when in the position shown in FIG. 2 allows generally unrestricted flow between the base end of the cylinder  20  and the source. The actuator  70 , when depressed against the bias, blocks flow between the cylinder  20  and the source. The valve  66  is normally open during field operations but can be closed to lock the cylinder  20  in a selected position such as the extended position during transport of the implement  10 . 
     Valve actuator structure  80  is supported from the rod and base ends  40  and  44  of the cylinder  20  and includes a tube or guide  82  slidably received through mating apertures in the cylinder pin structures  42  and  46 . A spring  84  is captured on the base end of the guide  82  between pin and washer structure  86  and the pin structure  46 , and an aft end pin  88  prevents the guide  82  from sliding forwardly out from the aperture in the pin structure  46 . The forward end of the guide  82  extends through and freely slides within the aperture in the rod end pin structure  42  while the base end of the guide normally remains fixed relative to the base end pin structure  46 . In case of binding, over-retraction of the cylinder  20  or improper adjustment of the actuator structure  80 , the spring  84  can compress to allow the guide  82  to slide rearwardly relative to the pin structure  46  to prevent bending or breaking of the actuator structure  80 . 
     The actuator structure  80  includes a plate or contact member  90  slidably supported on the guide  82 . An adjustment rod  94  is rotatably supported from the guide  82  by a forward rod bracket  96  and an aft rod bracket  98  below and parallel to the guide  82 . The guide  82  is supported generally parallel to cylinder axis  20   a  and remains parallel to the cylinder axis with extension and retraction of the cylinder. The rod  94  has a threaded central portion received through a threaded aperture at the lower end of the contact member  90 . By rotating the rod  94 , the contact member  90  can be adjustably positioned along a central portion of the guide  82 . Indices  102  are provided along the central portion to provide the operator with a visual indication of the adjusted position of the contact member  90 . As the cylinder  20  is retracted by opening the hydraulic line  68  to reservoir, the frame  12  lowers. The valve  60  moves with the rod end pivot structure  42  rearwardly relative to the contact member  90  as the forward end of the guide slides through the pin structure  42 . The valve  60  and contact member  90  converge generally along a straight path parallel to the cylinder axis  20   a  until the member  90  depresses the valve actuator  70  and blocks flow from the base end of the cylinder  20  through the line  58  to establish an adjusted frame position dependent on the adjusted position of the contact member  90  along the guide  82 . To raise the frame, the operator pressurizes the line  68  using a control valve on the towing vehicle and a one-way check valve (not shown) in the valve  60  allows hydraulic fluid to enter the base end of the cylinder  20  to extend the cylinder rod and raise the frame. 
     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.