Abstract:
An agricultural tool for a tractor tool bar comprises a unit, such as a planter unit, that includes a ground contacting member for performing a working operation on the ground for changing the state of the soil, such as by opening a furrow to receive a seed from the planter unit. A downpressure system for the tool includes a two part telescopic air shock extending between the tool bar and a parallelogram linkage that attaches the unit to the tool bar. A sensor is operatively connected to the portion of the air shock that is attached to the parallelogram linkage for sending a signal representative of the length of the shock to an electronic controller. The controller operates through a feedback loop to attempt to maintain the air shock at a predetermined length which corresponds to a desired amount of downpressure.

Description:
TECHNICAL FIELD 
     This invention relates to agricultural tools that require downpressure to keep the tools properly engaged with the ground and/or to keep the tools working in a proper orientation or at a proper depth. 
     BACKGROUND OF THE INVENTION 
     Many agricultural tools used for soil tillage, planting and other purposes perform some type of working action on a farm field to change the state of the farm field. For example, soil tillage tools often use one or more rotary coulter discs that enter the soil to a desired depth to break up or till the soil to make the soil ready for planting. A large number of such soil tillage tools are usually mounted on an elongated, laterally extending tool bar that is coupled to the back of a tractor. This allows the soil to be tilled in a large swath behind the tractor as the tool bar and the soil tillage tools carried thereon are towed across a farm field by the tractor. The swath of tilled soil may be basically continuous across its width in a conventional tillage operation or may be separated by strips of untilled soil in a zone tillage operation depending upon the lateral spacing of the soil tillage tools relative to each other on the tool bar. 
     In some cases, soil tillage tools of the type described above are incorporated into a dedicated, single use tool whose only purpose is to break up or till the soil. After the soil is so tilled and when the farm field is ready for planting, the farmer will then use a separate planter tool to plant seeds into the tilled soil and to cover the planted seeds with soil. However, in other cases, the soil tillage tools may be incorporated into a planter unit such that the soil tillage and planting operations occur essentially at the same time. Regardless of whether the soil tillage and planting operations occur in a two step operation or in a single step operation, it is important that the tool act on or enter into the soil allow the soil to be properly tilled and/or the seeds to be properly planted at the right depth. In accomplishing this goal, most agricultural tools have some type of downpressure system that causes such tools to enter the soil to the proper depth and that attempts to retain the tools at such depth. 
     The aforementioned downpressure systems can be quite complex and expensive. Some of these systems use multiple mechanical springs or at least one bellows type air bag on each of the soil tillage tools in an attempt to provide sufficient downpressure. Such springs and air bags are exposed to the elements and can in certain situations become caked or fouled with dirt or debris from use, thereby decreasing their effectiveness in supplying the precise amount of downpressure required on the tools. This may result in some tools being located at the proper depth while other tools on the same tool bar are not at the proper depth. 
     In addition, variations in the soil compaction in the farm field can cause the amount of downpressure required on the tools to vary widely across the length of the tool bar or from one location to another in the farm field. Many downpressure systems known in the prior art are not able to adequately respond to such variations with the result again being that some tools may not be effectively maintained at the required depth. Thus, it would be an advance in the art to provide a downpressure system that is simple and inexpensive in nature, that is durable and is not prone to being fouled during use, and that effectively responds in a real time manner to changes in the downpressure that is required to thereby substantially continuously maintain the tools at the required predetermined depth. 
     SUMMARY OF THE INVENTION 
     One aspect of this invention relates to an agricultural tool for mounting on a tool bar, the tool bar being operatively carried on or attached to a tractor. The tool comprises a unit that performs an action on a farm field to change a state of the farm field as the unit is moved over the farm field. A linkage movably mounts the unit on the tool bar for up and down movement of the tool bar relative to the farm field. A system is provided for applying downpressure to the unit to maintain the unit in a desired operational position relative to the ground. The downpressure system comprises a fluid operated shock having first and second telescopic portions. The first portion of the shock is attached to the tool bar and the second portion of the shock is attached to the linkage. The shock is extensible and contractible in length dependent upon a pressure level of the fluid inside the shock. A source of pressurized fluid is provided. At least one valve is located between the source of pressurized fluid and the shock for supplying pressurized fluid to the shock or for removing the pressurized fluid from the shock. Finally, an electronic controller is connected to the valve for automatically operating the valve as the unit is moved over the farm field to add and remove as need be the pressurized fluid to the shock in a feedback control loop to substantially maintain the length of the shock at a predetermined length to establish and maintain a desired downpressure on the unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This invention will be described more specifically in the following Detailed Description, when taken in conjunction with the following drawings, in which like reference numerals refer to like elements throughout. 
         FIG. 1  is a perspective view of a portion of the downpressure system of this invention, particularly illustrating one of the downpressure applying devices of this invention connected to the pivotal linkage extending between an agricultural tool bar and one planter row unit connected to the tool bar for applying downpressure to the planter row unit; 
         FIG. 2  is a perspective view similar to  FIG. 1 , particularly illustrating a four row planter with each planter row unit having its own separate downpressure applying device of the type shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of another portion of the downpressure system of this invention, particularly illustrating an air supply and control system for providing pressurized air to the downpressure applying devices shown in  FIGS. 1 and 2 ; 
         FIG. 4  is an enlarged perspective view of a valve block used in the air supply and control system of  FIG. 3 ; and 
         FIG. 5  is an enlarged perspective view of a portion of a downpressure applying device that can be used as part of this invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIGS. 1 and 2 , a laterally elongated agricultural tool bar is generally illustrated as  2 . Tool bar  2  is of the type that is commonly attached to tractors or the like in order to mount a plurality of agricultural tools in a side-by-side manner across the length of the tool bar. For example, as shown in  FIG. 2 , the agricultural tools can comprise four planter row units generally illustrated as  4 . Planter row units  4  are designed to open a furrow in a farm field, to drop the seeds of a row crop (e.g. corn or soybeans) into such furrow, and to close the furrow as the tractor propels the tool bar  2  and planter row units  4  across the farm field. Each planter row unit  4  is attached to tool bar by a parallelogram pivot linkage having a pair of laterally spaced upper pivotal link arms  6  and a pair of laterally spaced lower link arms  8  which underlie the upper link arms  6 . 
     This invention relates to a system  10  for applying controlled downpressure to planter row units  4  to ensure that planter row units  4  are maintained in a desired operational position on the ground. System  10  is not limited for use with planter row units  4  or with a particular number of planter row units  4 . System  10  can be used with just one planter row unit  4  or as many planter row units  4  as one wishes to mount on or as can be mounted on tool bar  2 . System  10  can also be used with agricultural tools other than planter row units which require downpressure to work properly, such as closing wheels, floating trash wheels, tillage tools, etc. One desirable characteristic of system  10  is that the downpressure on each planter row unit  4  can be controlled and maintained individually in an automatic fashion during operation of planter row units  4  without requiring manual adjustment or control by the operator. 
     As shown most clearly in  FIG. 1 , one portion of system  10  is a mechanical device, such as an air shock  12 , which has an upper end pivotally connected to an upwardly extending post  3  on tool bar  2  by a pivot pin  14 . The lower end of air shock  12  is secured to a cross member  16  with cross member  16  extending between lower link arms  8  of the parallelogram linkage for planter row unit  4 . The opposite ends of cross member  16  are pivotally connected to lower link arms  8  by aligned pivot pins  18  (only one of which can be seen in  FIG. 1 ). Thus, the upper and lower ends of air shock  12  are free to pivot about horizontal axes defined by pivot pins  14  and  18  as air shock  12  applies downpressure to planter row unit  4 . 
     Air shock  12  is a conventional device in the automotive art that combines downpressure air bag type technology with a shock absorber. A suitable air shock  12  is commercially available from Ridetech of Jasper, Ind. In addition, a suitable air shock  12  is shown in U.S. Pat. No. 6,581,918, which patent is hereby incorporated by reference. 
     Referring still to  FIG. 1 , a pivot linkage  20  comprising a lower pivot arm  22  and an upper pivot arm  24  pivotally connects cross member  16  with a rotary sensor  26  carried on a post  3  of tool bar  2 . Sensor  26  can take many different forms, but one suitable sensor  26  is a rotary electrical potentiometer. Lower pivot arm  22  is pivotally connected at its lower end to cross member  16  and at its upper end to the lower end of upper pivot arm  24 . The upper end of upper pivot arm  24  is non-rotatably connected to the rotary input shaft or the like of sensor  26  such that up and down movement of upper pivot arm  24  rotates the rotary input shaft of sensor  26  in concert therewith. The purpose of pivot linkage  20  and sensor  26  is to detect up and down motion in the parallelogram linkage that supports planter row unit  4  on the ground by detecting changes in the distance between the pivot connection to cross member  16  and the fixed location of sensor  26 . Sensor  26  provides a voltage signal to an electronic controller  28  that varies as the parallelogram linkage pivots up and down and as the distance between cross members  16  and sensor  26  changes correspondingly. Sensor  26  can be external to air shock  12  as shown herein or could also be built as part of air shock  12 . 
     Referring now to  FIGS. 3 and 4 , the remaining portion of system  10  is an air supply and control system that comprises an electronic, microprocessor based controller  28  and a compressor  30  that is driven by a power source carried on tool bar  2  or on the tractor. When powered, compressor  30  is used to supply pressurized air to an air tank  32 . Compressor  30  can run as needed so that air tank  32  functions as a large reservoir of pressurized air that is maintained at a predetermined pressure. Air tank  32  will supply pressurized air therefrom to each air shock  12  through a valve block  34 . 
     Valve block  34  has an individual air valve (not shown but contained within valve block  34 ) for each air shock  12  such that valve block  34  will have as many air valves as there are air shocks  12 . Each air valve within valve block  34  is connected to the air inlet of one of the air shocks  12  by a flexible air supply hose  36 . Each air valve is connected both to air tank  32  as well as to an air exhaust port. 
     The air valve for each air shock  12  has three states. The first state is an off state of the air valve in which pressurized air neither passes into or out of supply hose  36  to air shock  12 . This maintains the downpressure being supplied by air shock  12  on planter row unit  4  at its current level. The second state is an inlet state of the air valve in which air tank  32  is opened to air supply hose  36  to allow pressurized air to flow from air tank  32  into air shock  12  to increase the internal air pressure in air shock  12  to thereby increase the downpressure on planter row unit  4 . The third state is an outlet state of the air valve in which air supply hose  36  is now connected to an exhaust port of the air valve to allow the internal air pressure in air shock  12  to bleed out through hose  36  and through the exhaust port to allow the internal air pressure in air shock  12  to decrease to thereby decrease the downpressure on planter row unit  4 . The air valve will be automatically placed into these various states as need be by the operation of electronic controller  28 . 
     Referring to  FIG. 4 , valve block  34  has two electrical control solenoids for each air valve, i.e. an air increase solenoid  38  and an air decrease solenoid  40 . Electronic controller  28  electrically activates solenoids  38  or  40  to selectively put the air valve into either the air inlet or air outlet states thereof. When neither solenoid  38  or  40  is activated, the air valve is maintained in its off state. 
     Electronic controller  28  is connected in some fashion, i.e. either directly or through CANBUS communication, to the output of sensor  26  to receive a voltage signal therefrom. Electronic controller  28  is programmed to store a reference sensor voltage that corresponds to the downpressure in air shock  12  that is required to keep planter row unit  4  in a predetermined desired operational position relative to the ground. For example, when planter row unit  4  is in engagement with the ground and is at what the operator considers to be a proper working depth, the corresponding voltage being reported by sensor  26  can be assigned as the reference voltage. Let&#39;s assume for the sake of the following example that the reference voltage is 2.5 volts. 
     Importantly, this invention does not envision that electronic controller  28  would immediately correct for any variations of the sensor voltage from 2.5 volts. Instead, the operator has the ability to provide electronic controller  28  with three settings. The first setting is the amount of change in the voltage level from the reference voltage that is required before the electronic controller  28  would attempt a correction. The operator could pick from a plurality of preset settings, e.g. 5, 10, 15, 20, 25, 30, 40, 50, 60, or 70 millivolts, or input his or her own setting. Let&#39;s suppose the operator picked 5 millivolts as the voltage change threshold. Thus, the voltage reported by sensor  26  to controller  28  would have to change at least 5 millivolts up or down from the reference voltage of 2.5 volts before controller  28  would activate either the air increase solenoid  38  or air decrease solenoid  40  depending upon the direction of the voltage change relative to the reference voltage. For added flexibility, the user could pick or input different separate settings for the voltage change threshold depending upon whether controller  28  would be executing an air increase or air decrease, e.g. the voltage change threshold for an air increase could be 5 millivolts but could be 15 millivolts for an air decrease. 
     However, even if controller  28  detects a voltage change that meets the selected threshold, i.e. the voltage from sensor  26  has changed at least 5 millivolts up or down from the reference voltage of 2.5 volts in the example above, controller  28  would not immediately take corrective action. The second setting of controller  28  is how long the voltage change must be maintained, i.e. a voltage time threshold, before controller  28  takes action. Again, the operator could pick from a plurality of preset settings, e.g. 0, 10, 25, 50, 100, 200, 300, 500, 1000, or 3000 thousandths of a second, or input his or her own setting. In the example above, let&#39;s further suppose the operator has additionally picked 200 thousandths of a second as the voltage time threshold which equates to two tenths of a second. Thus, controller  28  will initiate corrective action only if both the voltage change threshold and the voltage time threshold are met, i.e. only if the voltage change is at least 5 millivolts higher or lower than the reference voltage of 2.5 volts and only if this voltage change is maintained for at least 200 thousandths of a second. If these two conditions are met, then controller  28  will activate either the air increase solenoid  38  or the air decrease solenoid  40  depending upon whether the voltage change was above or below the reference voltage. 
     The third setting of controller  28  is to allow the operator to pick an on time for how long the solenoids  38  or  40  are left open by controller  28 . Once again, the operator can pick from a plurality of settings, i.e. 10, 20, 30, 40, 50, 75, 100, 150, 200, 300 hundredths of a second, or input his or her own setting. Thus, if the operator picks 150 hundredths of a second for the valve on time setting, then controller  28  will activate one of the solenoids  38  or  40  for 1.5 seconds. If operation within this valve on time setting does not restore the voltage reading to the reference voltage of 2.5 volts, then controller  28  will repeat the steps noted above in a closed loop control fashion until the reference voltage is restored. Thus, system  10  of this invention maintains a desired level of downpressure on each of the air shocks  12  and on each of the planter row units  4  automatically without any operator input other than for the selection of the three settings, i.e. the voltage change threshold, the voltage time threshold and the valve on time, described above. 
     Air shock  12  could be replaced by other types of downpressure applying devices, such as a bellows type air bag or by a hydraulic cylinder. If hydraulic cylinders replace air shocks  12 , then a hydraulic fluid supply and control system for supplying pressurized hydraulic fluid to the hydraulic cylinders would be used in place of the air supply and control system with controller  28  having the same control methodology and settings. In the case of a hydraulic system, the hydraulic fluid supply and control system would return the pressurized fluid to the main hydraulic fluid reservoir during a pressure decreasing operation rather than exhausting to atmosphere as is done with air. A single air shock  12  could be replaced by dual air shocks with one air shock  12  pushing down on the parallelogram linkage  6 ,  8  and the other air shock  12  pushing up on the parallelogram linkage. In this dual air shock system, controller  12  would simultaneously increase the pressure in one air shock  12  and decrease the pressure in the other air shock  12  when making a correction. Moreover, the parallelogram linkages that support planter row units  4  could be replaced with other types of pivotal or non-pivotal linkages that permit movement of units  4  up and down relative to tool bar  2 . 
     Various other modifications of this invention would be apparent to those skilled in the art. Thus, this invention is not limited to the details of the preferred embodiment described herein.