Abstract:
Self-propelled liquid dispensing equipment having ground engaging wheels and an active trailing link suspension system in which either suspension struts or air struts control suspension travel. A liquid pressure transducer is connected to a liquid reservoir to provide a control input that varies the assist given by the suspension struts or air strut in direct proportion to the quantity of liquid. A given suspension travel is maintained regardless of the quantity of liquid carried by the equipment.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to liquid dispensing equipment, and, more particularly, to suspension systems for such equipment. 
     2. Description of the Related Art 
     For many years, liquid dispensing equipment has been part of the agricultural field. The liquid dispensing equipment is used to distribute liquid fertilizer and/or insecticides or herbicides onto the ground of a field for agricultural purposes. Usually, such equipment takes the form of a mobile wheeled vehicle with significant clearance height so as to clear crops that have partially matured. The equipment usually consists of a power unit for self propulsion, an operator cab and a liquid reservoir. Liquid is dispensed using articulated booms that are retracted for transport to the field and then extended laterally to distribute the liquid onto the field. 
     One of the requirements of such a device may be to have a controllable, substantially constant, suspension travel so that the equipment, and thus the spray boom, is at a constant level above the field surface. This is done to ensure uniform distribution and coverage of the material being sprayed. 
     Many liquids solutions utilize water as a base and are thus relatively dense. As a result, the full and empty weight of the equipment is substantially different and this could be reflected in the variation of suspension travel, thus producing inconsistent coverage. 
     In an attempt to counter this effect, active suspension systems have been proposed similar to suspension systems in the automotive field. These include a suspension strut mounted within suspension springs and operable, through pressurized hydraulic fluid, to raise or lower the suspension travel. In the prior art, suspension systems have utilized relatively expensive components to physically measure the distance of the frame from the field thus reflecting suspension travel. With systems of this type there is a significant cost of the sensor components and the potential of exposure to the debris and other material normally experienced when traversing a field. 
     Accordingly, it is an object of the present invention to provide a simplified and reliable way to provide an active suspension for liquid dispensing equipment. 
     SUMMARY OF THE INVENTION 
     The present invention provides a simplified active suspension system for liquid dispensing self-propelled equipment. The present invention also provides the simplified active suspension by using a low cost sensor for determining liquid load on the equipment. 
     In one form, the invention is a suspension system for self-propelled liquid application equipment having a reservoir for liquid and ground engaging wheels. The suspension system includes articulated suspension links for each wheel enabling up and down travel. A spring is connected to the suspension links to urge the suspension system to an extended travel. A suspension strut is connected to the suspension links and is responsive to pressurized fluid inputs to vary the travel of the suspension system. A controller receives control inputs and provides the pressurized fluid input to the suspension strut. A liquid pressure transducer is fluidly connected to the liquid reservoir and provides a control input to the controller proportional to the amount of liquid in the reservoir so that the suspension strut maintains the travel of the suspension system at a given length, irrespective of the amount of liquid in the reservoir. 
     In another form, the invention is a suspension system for self-propelled liquid application equipment having a reservoir for liquid and ground engaging wheels. The suspension system includes articulated suspension links for each wheel enabling up and down travel. An air strut is connected to the suspension links to urge the suspension system to an extended travel and is responsive to pressurized fluid inputs to vary the travel of the suspension system. A controller receives control inputs and provides the pressurized fluid input to the air strut. A liquid pressure transducer is fluidly connected to the liquid reservoir and provides a control input to the controller proportional to the amount of liquid in the reservoir so that the air strut maintains the travel of the suspension system at a given length, irrespective of the amount of liquid in the reservoir. 
     In yet another form, the invention is embodied in self-propelled liquid dispensing equipment including a frame, a plurality of ground engaging wheels for ground movement and a power unit supported by the frame and driving at least a portion of the ground engaging wheels. Articulated suspension links are provided for each ground engaging wheel enabling up and down travel relative to the frame. Springs are connected to the frame and to each of the suspension links to urge the suspension system to an extended travel. A suspension strut is connected to at least a portion of the suspension links and is responsive to pressurized fluid inputs to vary the travel of the suspension system. A controller on the frame receives control inputs and provides pressurized fluid to the suspension strut. A liquid reservoir is mounted on the frame for liquid to be applied. A pumping mechanism is fluidly connected to the fluid reservoir for applying liquid to the ground. A liquid pressure transducer is fluidly connected to the liquid reservoir and provides a control input to the controller proportional to the amount of liquid in the reservoir so that the suspension strut maintains the travel of the suspension system at a given length, irrespective of the amount of liquid in the reservoir. 
     An advantage of the present invention is a simplified and cost effective sensor for determining load in a liquid dispensing system. 
     Another advantage is that the sensor for an active suspension system is positioned out of the debris path for such equipment traversing a field. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a side view of liquid dispensing equipment embodying the present invention; 
         FIG. 2  is a portion of the equipment shown in  FIG. 1  showing the interconnection in schematic fashion with the suspension system of  FIG. 1 ; 
         FIG. 3  shows a portion of the suspension system of the equipment shown in  FIG. 1 ; and 
         FIG. 4  is a schematic diagram of an alternate embodiment of the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates embodiment of the invention and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to  FIG. 1 , there is shown liquid dispensing equipment  10  including a frame  12  which supports a power unit  14 . Power unit  14  is used for propulsion across the ground in a field and, in addition, provides power for auxiliary components of the equipment  10 . An operator cab  16  is mounted on frame  12  and provides an operator space and includes controls for liquid dispensing and directional movement of the equipment  10 . The equipment  10  includes wheel assemblies  18 , each having a relatively large diameter, to enable high clearance through a crop field during the time in which crops are progressing towards maturity. The equipment also includes a spray boom  20 , shown in simplified fashion, which receives liquid from a reservoir  22  for dispensing liquid onto the ground through nozzles  24 , only one of which is shown. 
     As shown in  FIG. 2 , the reservoir  22  has appropriate fill locations and a sight glass tube  28  which extends from the sump of the reservoir  22  to the top and thus provides a visual indication of the liquid within the reservoir  22 . A liquid pumping mechanism shown at  26  receives liquid from reservoir  22  and directs it through liquid conduits (not shown) to nozzle  24  for distribution on to a field. 
     Referring now to  FIG. 3 , there is an illustration of the suspension system for the wheel assemblies  18 , herein shown for a single wheel. The suspension system includes articulated trailing links  30  made up of an upper link  32  connected to frame  12  and a lower link  34  pivoted to the upper link  32  at  36 . The wheel of the wheel assembly  18  is journaled and mounted to the lower link  34  so that it moves relative to the frame  12  as the lower link  34  pivots. A spring  38  abuts lower link  34  and a portion of the base of upper link  32  to provide a yieldable mounting and to support a significant portion of the weight of equipment  10 . Positioned within coil spring  38  is a suspension strut  40  that, like active suspension systems, receives pressurized hydraulic flow from lines  42  to increase or decrease the travel of the lower link  34  relative to frame  12  and thus the travel of the suspension system of the equipment  10 . 
     Referring back to  FIG. 2 , the hydraulic connections  42  extend from suspension strut  40  to a hydraulic pressurization unit  44  that provides a controlled pressure to suspension strut  40 , urging it in the direction of suspension travel so that a higher pressure is translated into a larger travel. The hydraulic pressurization unit  44  usually consists of a hydraulic pump and valve mechanism (not shown), responsive to direct the flow from the pump to and from the suspension strut  40 . The hydraulic pressurization unit  44  receives a control input via control line  46  from an electronic control unit (ECU)  48  that may also function as the equipment and/or power unit controller. The hydraulic pressurization unit  44  and the ECU are referred to collectively as a controller for the suspension strut  40 . The ECU  48  receives additional control inputs via control line  52  providing an operator input control  50  as well as other inputs such as GPS. 
     In accordance with the present invention, the ECU  48  receives another control sensor signal input through line  54  from a pressure transducer  56  that is fluidly connected to reservoir  22  at or near its lowest point via a T-connection  58  in sight glass tube  28 . Although the connection is shown through the sight glass tube  28 , it should be apparent to those skilled in the art that it may be provided in other forms to fluidly connect with the reservoir  22 . 
     As stated above, the liquid being dispensed is a dense material and has a significant, but predictable weight. The pressure sensed by transducer  56  ends up being directly proportional to the quantity of liquid, and thus the load, in the reservoir  22 . The output of pressure transducer  22  may be in any one of number of forms but, as herein illustrated, is a voltage output directly proportional to the pressure sensed. The pressure sensed by transducer  56  is used as a control input to the ECU  48  to vary the assist given by the suspension strut  40  to the suspension system  30 . When the liquid pressure is at its maximum, the load is greatest and the suspension strut  40  applies its maximum assistance to the suspension system  30 . Accordingly, as liquid is dispensed and the pressure goes down, the assistance the suspension strut  40  gives to the suspension system  30  is reduced, thus maintaining the travel of the suspension system  30  at a given length, irrespective of the amount of liquid in said reservoir. 
     Referring to  FIG. 4 , there is shown, in schematic fashion, an alternate embodiment of the present invention. Like reference numerals are used to designate unchanged components. The pressure sensor  56  generates a signal through line  54  to ECU  48  that is proportional to the quantity of liquid in reservoir  22 . Additional control inputs are provided from operator input control  50  and other inputs such as GPS. The control signal from ECU  48  is fed by line  46  to a fluid pressurization unit  60 . Unit  60  generates controlled pneumatic pressure connected via fluid lines  62  to an air strut  64 , sometimes referred to as an air bag or air spring. The fluid pressurization unit  60  and the ECU  48  are referred to collectively as a controller for the air strut  64 . 
     Air strut  64  is positioned between frame  12  and suspension system  30  to support the entire weight of equipment  10  at a suspension travel governed by the pressure maintained by fluid pressure unit  60 . Typically, fluid pressurization unit  60  includes an air compressor and valves to direct the compressor output to the air strut  64 . The signal from pressure sensor  56  corrects the output from fluid pressurization unit  60  to reflect the depletion of liquid in reservoir  22 , and thus the overall weight, as the equipment  10  is operated. 
     Pressure transducers are inexpensive, simplified devices that enable the initial cost of the system to be reduced. In addition, the pressure sensor is substantially isolated from the environment debris as the unit  10  traverses the ground in a field. This minimizes the potential adverse effect on reliability that would occur on devices that have mechanical parts exposed to the outer portion of the suspension system. The uniformity of the liquid being distributed and the reliability of the pressure sensor  58  produce a highly accurate and reliable way of utilizing an active suspension system. 
     While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.