Earth working – Processes
Reexamination Certificate
2002-10-28
2003-12-23
Novosad, Christopher J. (Department: 3671)
Earth working
Processes
C172S002000, C701S050000
Reexamination Certificate
active
06666279
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a control system for controlling an implement attached to an agricultural tractor, and, particularly, to a control system that will allow for variations in prevailing slip-pull data at progressively increasing implement draft levels.
The term, “tractor”, is meant to include any vehicle capable of propelling a ground or soil engaging implement for the purpose of processing the ground or soil, or objects (e.g. crops, forage, shellfish) lying on or in the ground or soil. Typically a tractor is a four wheel drive vehicle having a hitch for attachment of an implement behind the vehicle. It is also well known for tractors to push implements, such as furrow presses. The typical configuration of a tractor includes an operator cab mounted at the rear of the vehicle, and a forward-mounted engine and transmission system. However it is also known to provide a multi purpose vehicle, that may function as a tractor, having a forward mounted cab and underslung engine and transmission systems beneath a load carrying deck. Other forms of tractors include two wheeled, two wheel drive devices and tracked vehicles that may be coupled to pull or push implements. The instant invention relates to and embraces within its scope all such tractors.
Tractor/implement combinations are widely used in various processes in agriculture. One of the most common of these is plowing, in which a plow is towed behind a tractor. However, tractors may be used for a great variety of other operations such as spraying, furrow pressing, harrowing, raking, seeding and a number of specialized operations such as arise, for example, in vineyards and estuaries, in which specially designed ground-engaging implements are used. Consequently, “implement” as used herein includes but is not limited to plows, harrows, furrow presses, rakes, seed drills, and indeed virtually any article that may be attached to or operated by a tractor and that has the effect of increasing the energy demand of the tractor by virtue of engagement of the implement with the ground or soil or with objects thereon or therein.
Electronic control of the subsystems of tractors is becoming more and more common. For example European Patent Application No. 0838141 (the entire disclosure of which is incorporated herein by reference) discloses an integrated control system for tractors (designated by the trade mark “TICS” that is the subject of Community Trade Mark registration no. 1532696), by means of which a programmed microprocessor (or series of microprocessors) maximizes the work rate of a tractor, e.g. during plowing operations, by comparing the implement draft force against a steady state reference model, and performing implement working width and transmission ratio adjustments in order to maintain a maximal work rate while also maintaining a predetermined implement working depth.
There are four readily identifiable subsystems of a tractor/implement combination operating under the control of arrangement such as the aforementioned TICS. The subsystems influence the performance of the combination. They are the tractor engine; the tractor transmission; the implement; and the tire/soil interface. As disclosed in the aforementioned European Patent Application No. 0838141, it has in practice proved impossible successfully to carry out tractor/implement control using a dynamic reference model. The arrangement of the control system in European Patent Application No. 0838141 therefore includes a steady state reference model. In the use of such a model it is necessary for the control software to process accurately generated data on the influence of variables on the behavior and/or performance of the tractor/implement combination.
It is readily possible to obtain real-time data on the engine torque and governor setting, through use of sensors. One suitable form of engine torque sensor is disclosed, for example, in European Patent Application No. 0741286. It is also a straightforward matter to detect, using known transducers, the selected transmission ratio and generate a signal corresponding thereto for use by the control software. Prediction of the horizontally acting load resulting from engagement of the implement with the soil, or with other objects as noted above, is also possible. The method disclosed in European Patent Application No. 0838141 includes for this purpose an assessment of the prevailing soil strength value (or an equivalent thereto in the event of the implement engaging a medium other than soil) during calibration of apparatus included on the tractor/implement combination.
Heretofore, however, there has been no proposal for providing real-time information on the effect of the prevailing tire/soil interface on the performance of a tractor/implement combination. When a wheeled tractor propels an implement either by towing it or by pushing it, a degree of so-called “wheel slip” arises. Wheel slip, that is expressed as a percentage value, varies in dependence on numerous factors including the traction factors or conditions, that in turn depend on the soil type and density, the soil moisture conditions, and the presence at the soil surface of e.g. crop residues; and vehicle factors, including the tire size, the tire condition, the ballasting (weight distribution) of the tractor, and whether the tractor is a two wheel drive (2WD) or four wheel drive (4WD) vehicle.
The tire size and condition (that determine the area of the tire surface in contact with the soil) do not in practice vary during e.g. a plowing operation. Similarly the vehicle ballasting is, in Northern Europe at least, likely to be invariant during e.g. a plowing operation. This is because in Northern Europe the only factor that is likely to cause variations in the vehicle ballasting is the gradual depletion of fuel in the tanks of the tractor. This mass change is insignificant compared with the mass of the tractor. In North America it is known to inject nitrous ammonia during soil tilling operations. The nitrous ammonia is typically stored in a tank at the front of the tractor. Reduction of the level of nitrous ammonia during tilling may (depending on the mass of nitrous ammonia dispensed) have a noticeable effect on the ballasting of the tractor.
For a given tractor and implement combination it is possible to derive a so-called “slip-pull” curve that is a plot of the percentage wheel slip (y-axis) against the horizontally acting load resulting (referred to as the draft, in kN, when the tractor tows an implement) from engagement of the implement (x-axis). The term “slip-pull” is used even when the tractor is arranged to push rather than tow an implement.
In the past the possibility of variations in slip-pull characteristics have been largely ignored in the software responsible for predicting the performance of a tractor/implement combination. Instead it has been the practice simply to employ a one-dimensional lookup table, stored in a memory forming part of the control apparatus, that represents an idealized slip-pull curve of use of a tractor/implement combination in a “sandy loam stubble” (SLS) soil. This approach was generally acceptable for the following reasons:
(a) The SLS slip-pull curve is fairly conservative. Pull that can be generated at a given slip level (for the same tire size and vehicle mass) is dependent on inherent soil strength and the frictional nature of the surface. Hence while a sandy soil will return similar slip-pull characteristics over a wide range of moisture contents (until its bearing capacity is eventually reduced); a clay-based soil is inherently stronger and can therefore generate greater traction. However the range of moisture contents over which this can be achieved is narrower, increasing moisture causing a rapid increase in wheel slip. Consequently in the majority of field conditions in which plowing would be contemplated, the SLS curve returns an acceptable estimate (or possible underestimate) of the pull levels that can be generated at any given slip.
(b) Additionally a tire-soil traction syste
Lowe John Charles
Scarlett Andrew James
New Holland North America Inc.
Novosad Christopher J.
Stader John William
Webb Collin A.
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