Method and apparatus for controlling width-adjustable tillage implement

In the field of agricultural tillage, there is a need for accurate, automated control of the widths of tilling implements, such as ploughs. The invention concerns methods of controlling a plough operatively combined with a vehicle such as a tractor, the methods including logging a series of values of the strength of soil encountered during a pass along a field; selecting the most frequently occurring soil strength value; and, for a subsequent pass of the tractor/plough combination along the field in the same direction, setting the width of the plough in dependence on the most frequently logged soil strength value. A microprocessor is provided to carry out the methods of the invention.

BACKGROUND OF THE INVENTION 
This invention concerns to improvements in or relating to tillage. In 
particular, the invention relates to a method and apparatus for 
controlling a width adjustable tillage implement such as a plough 
operatively combined with a powered vehicle such as a tractor or other 
multi-purpose agricultural vehicle. 
Conventionally a plough is secured to the three point hitch at the rear of 
a tractor. An operator of the tractor may use controls in the tractor cab 
to set the ploughing depth of the implement. This results in raising or 
lowering of the members of the three point hitch until the desired 
ploughing depth is obtained. Most ploughs are invertible by means of 
actuators also conventionally controlled from within the tractor cab. 
Inversion of a plough at the end of a first pass along a field ensures 
that the furrows ploughed during the next succeeding pass (during which 
the tractor travels in a direction opposite its direction during the first 
pass) face in the same direction as those ploughed during the first pass. 
The width of many ploughs is adjustable, by means of powered actuators 
mounted on the plough that are, conventionally, controllable from within 
the tractor cab. When a plough is adjusted to a wide setting the width of 
tillage increases correspondingly. Thus the workrate of the tractor/plough 
combination is potentially increased commensurately if the tractor 
maintains a constant forward speed. However, increasing the plough width 
increases the draught experienced by the tractor, ie. the force needed to 
pull the plough through the soil. This tends to increase the tractor's 
fuel consumption rate at a given speed, because of a need to fuel the 
tractor engine at a higher rate; or because of a need to shift 
transmission to a lower ratio; or both. In the alternative, the tractor 
may be driven at a lower speed to try and maintain a constant fuel 
consumption rate, but then the workrate improvement from the wider plough 
setting may be offset. There may in any event be an increase in fuel 
consumption, through running of the tractor engine at an inefficient 
speed. 
Any attempt to achieve compromise settings for the plough width, ploughing 
depth and engine governor that give rise to acceptable work rates without 
increasing the tractor's fuel consumption rate excessively are virtually 
impossible for a tractor operator alone to achieve in practice. This is 
primarily because the strength of soil (ie. its resistance to cultivation) 
varies over typically a range of eg. 30 kNm.sup.-2 to 60 kNm.sup.-2 from 
place to place in a field. The tractor operator is often unable to prevent 
wheel slip, over revving of the tractor engine or stalling of the engine 
when the plough encounters sudden changes in the soil strength. 
Patent application GB 9622087.6 discloses an automatic control apparatus 
and a control method for operating a tractor/implement combination in 
order to maintain a constant ploughing depth whilst simultaneously 
optimizing a performance parameter of the vehicle/implement combination. 
Typical such performance parameters include the workrate of the 
vehicle/implement combination; and the fuel consumption rate of the 
vehicle. 
SUMMARY OF THE INVENTION 
This invention provides a method and apparatus suitable for use in 
conjunction with the method of GB 9622087.6; and suitable for use in 
conjunction with other vehicle/implement automatic and semi-automatic 
control arrangements. 
According to a first aspect of the invention, there is provided a method of 
controlling a width adjustable tillage implement operatively combined with 
a powered vehicle, the method comprising: 
i. tilling with the implement for a first period; 
ii. obtaining a plurality of measured values of the strength of the soil 
tilled during the first period; 
iii. at the end of the first period, analyzing the measured soil strength 
values and selecting a first soil strength value characteristic of the 
soil strength values encountered during the first period; and 
iv. adjusting the width of the implement, in dependence on the first soil 
strength value, to a width for use during a subsequent tilling period. 
This method advantageously provides a width adjustment technique suitable 
for use with the apparatus of GB 9622087.6. The method of the invention 
also advantageously makes use of the headland turn of a tractor/implement 
combination for determining and, as necessary, adjusting the plough width 
setting for a subsequent pass along a field. 
Preferably during the subsequent period, tilling occurs in generally the 
same direction as in the first tilling period. Thus, the method of the 
invention may be used to determine at the end of a first pass an optimal 
width setting for a subsequent pass along the field in the same direction. 
This is advantageous because (i) the strength of a given area of soil 
encountered by a plough may differ depending on the direction of approach 
of the plough; and also, of course, because (ii) many fields are inclined 
and hence give rise to different loadings on the vehicle/implement 
combination, depending on its direction of travel. Thus it is desirable 
that the method of the invention includes the sub-step of storing of an 
optimal value of the width setting determined from the average soil 
strength, until the vehicle/implement combination next tills in the same 
general direction. 
Conveniently the method includes: 
v. tilling with the implement for a second period; 
vi. obtaining a plurality of measured values of the strength of the soil 
tilled during the second period; 
vii. at the end of the second period, analyzing the measured soil strength 
values and selecting a second characteristic soil strength value 
characteristic of the soil strength values encountered during the second 
period; and 
viii. adjusting the width of the implement, in dependence on the second 
characteristic soil strength value, to a width for use during a further, 
subsequent tilling period. 
Thus the method permits optimization of the implement width, in dependence 
of average soil strength values, for a plurality of directions of travel 
in a field. 
Most fields are generally rectangular, so the number of different tilling 
directions to be accommodated in this way is usually limited to two (ie. 
representing passes in opposite directions along a field). 
Therefore, in preferred forms of the invention, in the further, subsequent 
period tilling occurs in generally the same direction as in the second 
period; and tilling in the first period occurs in generally the opposition 
direction to that of tilling in the second period. 
Nonetheless, it may be desirable to allow for more than two directions of 
travel during tilling. 
The method preferably includes: 
ix. inverting the tilling implement between consecutive tilling periods; 
and encoding of the measured soil strength values in dependence on the 
orientation of the tilling implement. This provides an advantageously 
simple method of ensuring that each width adjustment of the implement is 
determined from soil strength values detected during a previous pass along 
the field in the same direction. 
Conveniently the or each step of obtaining a plurality of measured soil 
strength values includes: 
xi. periodically measuring a variable of the vehicle/implement combination, 
the variable being proportional to the draft between the implement and the 
vehicle. This is particularly advantageous when the method is employed in 
a vehicle/implement combination including control apparatus as disclosed 
in GB 9622087.6. 
An advantageous frequency for measuring of the said variable of the 
vehicle/implement combination has been found to be equal to or greater 
than 4 Hz. 
Preferably the measured values of the variable are converted to values of 
soil strength and stored in a memory means as a histogram. Thus the 
inventive method is suitable for implementation by a microprocessor that 
may be installed in the vehicle. 
Preferably the soil strength values are rounded to the nearest 5 
kNm.sup.-2. This confers acceptable accuracy on the method without 
requiring lengthy processing times when the method of the invention is 
implemented by a microprocessor or other computing device. 
Conveniently the measured variable is or includes a static draft 
measurement. In particular, the measured value of the variable may be 
converted to a soil strength value using the formula: 
EQU D=(C1+C2.gs.sup.2).multidot.d.multidot.w.multidot.n. 
in which: 
D=draught (kN) 
C1=soil strength (kN/m.sup.2) 
C2=dynamic draught coefficient ([kN/m.sup.2 ]/[km/h].sup.2) 
gs=ground speed of the vehicle/implement combination (km/h) 
d=working depth of implement (m) 
w=width of implement (m) 
n=number of furrows 
The dynamic draft coefficient C2 may be derived from the measured draft 
value and the ground speed (gs) value. 
The method of the invention may incorporate capturing data from a plurality 
of sensors located on or in the vehicle/implement combination in order to 
permit use of the above-identified formula. 
Conveniently the method includes tilling for one or more further tilling 
periods in which tilling occurs in directions generally parallel to that 
of the first and second periods, the number of periods of tilling being 
equivalent to the tilling of a predetermined area of land, the method 
including the step of mapping and storing in a memory the soil strength 
values occurring over the predetermined area. 
This advantageously permits subsequent analysis and/or manipulation of the 
soil strength data, for example in order to generate for a farmer a plot 
showing areas of a field requiring extra cultivation or the application of 
specialized chemicals in order to aid subsequent cultivation. 
The following definitions of optimal features of the invention relate to 
aspects thereof particularly suitable for when the method is practiced 
using the apparatus, or in conjunction with the method, of GB 9622087.6. 
When, as is usually the case, the tilling depth of the implement is 
adjustable, the method may optionally include: 
xii. adjusting one or more performance parameters of the vehicle during 
tilling, whereby to permit maintenance of a constant value of the tilling 
depth and to optimize a performance characteristic of the 
vehicle/implement combination. 
Preferably the one or more performance parameters are selected from: 
workrate; 
fuel consumption. 
Conveniently the step of adjusting the width of the implement in dependence 
on the average soil strength value includes the sub-steps of: 
xiii. measuring the value of the performance characteristic of the 
vehicle/implement combination; 
comparing the said measured value and a steady state reference model of the 
performance characteristic; and 
adjusting the implement width so as to minimize any difference between the 
said performance characteristic and the steady state reference model. 
This aspect of the method may include the further sub-steps: 
xiv. adjusting the implement width to a value predicted to minimize the 
difference between the measured value and the steady state reference 
model; 
xv. further tilling with the implement and measuring a further value of the 
said performance characteristic; 
xvi. comparing the further performance characteristic value and the steady 
state reference model; 
xvii. if necessary, further adjusting the implement width to minimize the 
difference between the performance characteristic and the steady state 
reference model; 
as necessary 
xviii. repeating steps xiv. to xvii. further to minimize the said 
difference; and, optionally, 
xviii. detecting one or more characteristics of the tilth; and 
xix. modifying the steady state reference model in dependence on the said 
detected tilth characteristics. 
For the avoidance of doubt, a "steady state" reference model is herein 
taken to mean a reference model in which the physical characteristics of 
the tractor/implement assembly are regarded as fixed with respect to any 
particular instant in time. Thus, for example, parameters such as the mass 
of the vehicle and the moments of inertia of various sub-components 
thereof are taken to be constant, even though such parameters will in 
reality vary during operation of the tractor. 
The method normally includes the steps of automatically adjusting the 
implement width to a value expected to be an optimal value for the 
prevailing values of the measured draft and for the prevailing setting of 
a variable performance parameter of the vehicle/implement combination. 
Under some circumstances the width of the implement may instead be adjusted 
to a predetermined value chosen by an operator of the vehicle/implement 
combination. A further, optional feature of the method may then include: 
xx. comparing a first performance characteristic of the vehicle/implement 
combination, when the implement width is adjusted to the predetermined 
value, against a further performance characteristic of the 
vehicle/implement combination when the implement width is adjusted to a 
value expected to be optimal for the prevailing values of the measured 
draft and for the prevailing settings of one or more variable performance 
parameters of the vehicle/implement combination and, if the difference 
between the first and further performance characteristics exceeds a 
predetermined maximum; 
xxi. transmitting a warning signal to an operator of the vehicle/implement 
combination. 
Thus if the setting selected by an operator of the vehicle/implement 
combination is too far removed from an optimal width setting that would 
normally be achieved under prevailing conditions by use of the method, the 
vehicle operator can be warned. 
In preferred embodiments, the tilling of the method is or includes 
ploughing, although other forms of tilling such as harrowing or operating 
a rotary cultivator are theoretically within the scope of the method of 
the invention. 
Conveniently the first and second characteristic soil strength values, for 
example, may be obtained by identifying the most frequently occurring soil 
strength value from a range of possible values during a said period of 
tilling. This step may advantageously employ storing of a histogram of 
soil strength values in eg. a microprocessor. When two soil strength 
values are encountered with equal frequency during a tilling period, the 
method may include the step of selecting the larger of the values as the 
characteristic soil strength value. 
According to a second aspect of the invention, there is provided a method 
of controlling a width-adjustable tillage implement operatively combined 
with a powered vehicle, the method comprising: 
i. tilling with the implement in a first direction for a first period; 
ii. obtaining a plurality of measured values of the strength of soil tilled 
during the first period; 
iii. subsequently tilling with the implement in a second direction for a 
second period; 
iv. subsequently adjusting the width of the implement in dependence on a 
first soil strength value characteristic of the soil strength values 
obtained during the first period; 
v. subsequently tilling, for a further period, in the first direction. 
This method may advantageously be used with many of the optional, preferred 
features of the first aspect of the invention defined herein. 
Alternatively, the step of selecting the characteristic soil strength value 
may include averaging of the soil strength values encountered during a 
said tilling period. 
According to a third aspect of the invention, there is provided an 
apparatus for controlling the width of a width-adjustable tillage 
implement operatively combined with a powered vehicle, the apparatus 
comprising one or more actuators for adjusting the width of the implement; 
one or more sensors for detecting the strength of soil previously tilled 
by the implement; and a processor for controlling the or each actuator in 
dependence on the detected soil strength values, wherein the processor 
stores detected soil strength values during a period of tilling and at the 
end of said period averages the stored values to obtain an average soil 
strength value, the processor subsequently controlling the or each 
actuator to adjust the width of the implement in dependence on the average 
soil strength value. 
Such an apparatus is advantageously suited for practicing of the method of 
the invention. 
In preferred embodiments the processor includes means for ensuring that 
such width adjustment of the implement occurs before subsequent tilling in 
generally the same direction as the direction of tilling during the first 
tilling period. Such means may for example include one or more means for 
receiving and recognizing sensor signals indicative of the orientation of 
an invertible plough, the orientation of which is uniquely associated with 
a chosen direction of travel of the vehicle/plough combination. 
Preferably the processor includes a memory for storing a histogram of soil 
strength values and means for comparing the most frequently occurring soil 
strength value against said histogram whereby to obtain the average soil 
strength value associated with the period of tilling. 
Alternatively, the apparatus may include means for averaging the soil 
strength values encountered during a said tilling period. 
Conveniently the apparatus may include one or more sensors for: 
detecting the width adjustment of the tillage implement and generating a 
width signal indicative thereof; and/or 
detecting the depth setting of the tillage implement and generating a depth 
signal indicative thereof, said signals being input to the processor. 
Preferably the implement is invertible and the apparatus includes one or 
more sensors for generating an orientation signal indicative of the 
orientation of the implement, the orientation signal being input to the 
processor. 
The processor may advantageously receive the width and depth signals in 
analogue form and the orientation signal in digital form. 
In preferred embodiments, the processor may include an interface for 
communicating with a CAN for controlling the actuators adjusting the or 
each performance parameter of the vehicle/implement combination; and/or 
maintaining a constant depth setting of the implement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, there is shown an agricultural tractor denoted 
by the reference numeral 10. In common with such vehicles in general, 
tractor 10 has front 11 and rear 12 pairs of driven wheels. Tractor 10 
also has an engine (not shown in the drawings), a transmission system 
including a gearbox, transfer box and appropriate differentials for the 
driven wheels; an operator cab 13 and a three point hitch 15 at the rear 
of the vehicle between the rear wheels for attachment of an adjustable 
implement, which in the embodiment shown is a plough 60. 
The ploughing width of reversible plough 60 shown is adjustable. 
Thus the tractor/implement combination 10 may be regarded as comprising a 
plurality of controllable sub-systems, each of which influences the 
performance of the tractor in dependence on the prevailing conditions. The 
sub-systems include the engine (adjustable in one of two ways, ie. by 
means of a throttle setting or by means of an engine governor setting, 
depending on the engine type); the transmission (adjustable by virtue of 
selection of gear ratios); the three point hitch 15; and the plough 60 
adjustable in a manner described below by adjustment of one or more 
actuators. 
Tractor/implement combination 10 includes a plurality of slave controllers 
for the sub-systems, in the form of microprocessors 41, 42, 43 and 48. 
Certain parameters of the engine performance are controlled by means of an 
engine management system including microprocessor 41 that optimizes engine 
performance in dependence on the throttle or engine governor settings 
input either by the tractor operator using suitable control members, or 
from a programmable controller constituted as a further microprocessor 21 
(described in greater detail in GB 9622087.6) located in the cab of the 
FIG. 1 vehicle. The engine management system operates by adjusting various 
parameters, such as the metering volume of a fuel injection system, the 
timing of the fuel injection system, the boost pressure of a turbocharger 
(if present), the opening of engine valves and the opening of portions of 
the vehicle exhaust system, via suitable powered actuators such as 
solenoids. 
Tractor 10 includes a semi-automatic transmission system in which the 
transmission ratio selected is determined by a slave controller in the 
form of microprocessor 42 acting on one or more solenoids to engage and 
disengage gear sets of the gear box and/or gears of the transfer box, in 
dependence on the settings of a plurality of gear levers in the operator's 
cab or in dependence on signals from microprocessor 21. 
The FIG. 1 embodiment includes hitch microprocessor 43 and plough control 
microprocessor 48. 
Microprocessor (slave controller) 43 controls the positions of the elements 
of the implement (three point) hitch 15. Again, the microprocessor 43 
controls a number of actuators such as solenoids in dependence on the 
settings of control levers in the operator's cab 13, on signals received 
from microprocessor 21, or in dependence on its own programming. 
Microprocessor 48 is operatively connected to actuators, eg. hydraulic 
actuators, for adjusting the width of the plough and for reversing the 
plough at the end of each furrow and operates in dependence on signals 
received from microprocessor 21; from lever settings in cab 13; or 
according to its own programming. 
Plough 60 is a fully-mounted, reversible plough 60. By "fully mounted" is 
meant an implement the depth of which is adjusted by the tractor implement 
hitch, and not by actuators on the implement itself. (The latter class of 
implement is generally referred to as a "semi-mounted" implement.) Thus 
the FIG. 2 implement is fully mounted notwithstanding the presence of a 
stabilizer wheel 49. However the ploughing depth may in alternative 
embodiments also be adjusted by virtue eg. of support wheels and/or remote 
actuators. 
A further embodiment of the invention, not shown in the drawings, may be 
similar to the FIG. 1 embodiment except that the implement hitch has 
attached thereto a semi-mounted plough. Numerous other implements may 
equally well be secured to either the front or the rear of the tractor. 
Microprocessor 21 in the embodiment shown lies within the cab 13 and is 
operatively connected to an operator interface/control unit 22. 
Preferably, although not essentially, microprocessor 21 includes in its 
NVM or a removable memory module a steady-state reference model of the 
operation of the tractor/implement combination when carrying out a variety 
of tasks under a variety of different field conditions. The reference 
model can be updated through use of the tractor/implement combination, in 
order to take account of contemporaneously prevailing field conditions 
such as soil strength and tractive efficiency. Thus the reference model 
may include some data that varies each time the vehicle is used; and some 
data, such as the mass of the vehicle hardware (i.e. those components 
whose masses do not alter during use of the tractor), the transmission 
ratios, the engine output at given engine speeds and torque loads, and so 
on, that are fixed. 
A communication bus 23 interconnects the microprocessor 21 and the 
microprocessors 41, 42, 43 and 48 associated with the adjustable 
sub-systems. 
Thus in the embodiment shown the controller 21 is able to control each of 
the microprocessors controlling the adjustable sub-systems. Microprocessor 
21 may be regarded as hierarchically the primary microprocessor of the 
vehicle shown. However it is theoretically possible for the reference 
model and the control algorithms present in microprocessor 21 to be 
distributed among a number of microprocessors. In such an arrangement a 
specific, primary processor 21 may be dispensed with. The invention is 
considered to include such embodiments. 
The mode of control may be adjusted, as desired. For example, the 
microprocessor 21 may include stored therein a control algorithm that 
seeks to optimize the workrate of the tractor 10 when carrying out a 
chosen task. 
Another algorithm representing another control mode may seek to minimize 
the specific or actual fuel consumption of the tractor. 
A further algorithm may be selected to return control of at least some of 
the tractor sub-systems to the operator, who may then use the conventional 
cab-mounted levers and controls of the vehicle. Such a mode is necessary 
e.g. when the tractor 10 is driven on roads between field operations; and 
when turning in the headland at the end of a field, where it is thought 
that automatic control of the entire tractor/plough combination would 
offer no benefits. When such a mode is selected, the microprocessor 21 
ceases to influence the microprocessors 41, 42, 43 and 48 until an 
automatic control mode is again engaged, but the microprocessors 41, 42, 
43 and 48 may remain active throughout this period in order to provide 
independently controllable sub-systems. The control of the microprocessor 
48 during turning in the headland is described hereinbelow. 
The various modes of operation need not be stored in any of the 
microprocessors. Indeed, there may be some benefit in providing the 
software for the various control modes in removable memory devices such as 
diskettes, so that a tractor user can purchase only the software that is 
of use to him. Similarly, modified versions of the reference model may be 
supplied in removable memory devices so that the control apparatus may be 
tailored to a farmer's individual requirements. 
Referring now to FIG. 2, there is shown a flow diagram representative of 
the headland mode subroutine that is operated by microprocessors 43 and 48 
when microprocessor 21 relinquishes control of them to permit turning of 
the tractor 10 in the headland. 
In the FIG. 2 method during tilling operations the control software 
constantly calculates the implement draft in kN, by the formula: 
EQU D=(C1+C2.multidot.gs.sup.2).multidot.d.multidot.w.multidot.n) (1) 
in which: 
D=draft (kN) 
C1=static draught coefficient (kN/m.sup.2) or soil strength 
C2=dynamic draught coefficient ([kN/m.sup.2 ]/[km/h].sup.2) 
gs=ground speed (km/h) 
d=working depth (m) 
w=furrow width (m) 
n=no. of furrows 
C2 is derivable from C1, that in turn is available from sensor 
measurements. In preferred embodiments of the invention, the transmission 
ratio, engine speed and (optionally) the implement settings are adjustable 
to take account of variations in the draft value D in order eg. to 
optimize workrate, minimize fuel consumption or otherwise control the 
performance of the vehicle/implement combination. 
In the presently most preferred embodiment, in which the implement is a 
plough, the control software will maintain the plough depth constant 
throughout the ploughing operation. Thus adjustment of the implement is 
limited to width adjustments only--although (as is explained in more 
detail below) the software is such as not to permit width adjustments to 
occur while the plough tills the soil. This feature ensures that the 
resulting furrows do not vary in width from one end to the other. 
As is apparent from block 140, the headland mode subroutine is called from 
a "disengaging mode" subroutine programmed into microprocessor 21, that 
controls the vehicle/implement combination while the plough rises from the 
soil at the end of a pass along the field. The disengaging mode subroutine 
returns control of the engine governor to the vehicle operator while 
turning occurs. 
At block 141, the headland mode subroutine searches a soil strength 
histogram acquired during the previous pass in the direction about to be 
ploughed, and identifies the most frequently occurring soil strength 
range. This is achieved through analysis of the recorded soil strength 
values. The soil strength values are in the preferred embodiment stored as 
a histogram in microprocessor 21. If two soil strength values occur with 
equal frequency, the software identifies the higher of the two as the 
"most frequently occurring" value, to ensure that the draft of the plough 
remains within acceptable limits. 
Alternatively, microprocessor 21 may at block 141 simply generate an 
average soil strength value from the recorded values, instead of 
identifying the most frequently occurring value. Nonetheless, for economy 
the latter term is used herein to cover either method of identifying a 
soil strength value characteristic of the previous pass along the field. 
Subsequently (block 142) the software runs a prediction algorithm in 
respect of the most frequently encountered soil strength over the 
potential transmission gear range and over the available implement working 
width range. This results in a set of performance curves (workrate versus 
implement width in each gear) that is stored in the memory of the CPU. 
At block 143, these performance curves are searched for the absolute best 
implement working width (ie. over the entire range of adjustment of 
implement working widths); and the best implement working width within 
(optional) operator-set limits (if they differ from the broad range 
referred to hereinabove). 
A determination is then made (block 144) whether the absolute best working 
width lies within the operator-set limits. If the result of this 
determination is affirmative, or if the tractor operator has not specified 
his preferred plough width, at block 146 the software simply waits for the 
plough to turn over, tests whether this has occurred (block 147), sets the 
plough working width to "absolute best" value (block 148) (through 
operation of one or more adjustment actuators mounted on plough 60) and 
(block 149) reverts to an idle mode preparatory to running of subroutines 
(described in GB 9622087.6) for engaging the plough with the soil for 
tilling; and for controlling the operation of the tractor/plough 
combination during ploughing. 
If the determination, of whether the absolute best working width is within 
the operator-set limits, is negative, the software then calculates whether 
the loss of workrate, resulting from failure to use the "absolute best" 
working width, is greater than a predetermined percentage (step 150). If 
the result of this determination is negative, the software waits for the 
plough to turn over, checks for plough turn over, sets the plough width to 
the best within operator-set limits value and reverts to the idle mode 
(blocks 146, 147, 151 and 149). 
If on the other hand the loss of work rate determined at step 150 is 
excessive, a warning indication is made (eg. via the operator display 22 
in the preferred embodiment) to the operator (block 152) that the 
potential performance loss is great. The operator is then given the option 
of overriding the operator-set working width limits in order to optimize 
workrates. The override may take the form of re-specifying the 
operator-set working width, or of allowing the software to calculate and 
implement an "absolute best" optimal width. 
If (block 153) the operator overrides the previous operator-set width, 
steps 146, 147, 148 and 149 are repeated. If this results in an acceptable 
absolute best working width calculation, the subroutine reverts to idle 
mode preparatory to running of the engaging and operational subroutines 
mentioned above. 
If the operator chooses not to override the previous operator-set limits at 
block 153, the software waits for the plough to turn over (block 146), 
checks for plough turnover (block 147); sets the plough working width to 
the best available working width within the range of operator-set limits 
(block 151) and reverts to idle mode preparatory to engagement of engaging 
and then engaged modes. 
The steps of FIG. 2 are repeated each time the tractor/plough combination 
completes a pass along the field. The characteristic soil strength value 
obtained each time is derived from the histogram of soil strength values 
recorded during the last pass in the same direction as that about to be 
ploughed. 
The bits of data corresponding to the respective directions of travel of 
the tractor/plough combination would of course be encoded in dependence on 
the orientation of the plough, since the plough is inverted by the control 
software each time the tractor changes direction. The plough may include a 
sensor 90 (FIG. 3) generating encoding signals indicative of its 
orientation. 
During passes along the field, the software acquires data on the soil 
strength by measuring the draft experienced between the tractor and the 
plough, preferably at a sampling rate of equal to or greater than 4 Hz. 
This sampling rate has been found to provide adequate reaction times for 
the apparatus of the invention when eg. sudden changes in soil strength 
are encountered. 
In addition to their function of providing a steady state model for setting 
of the implement width, a plurality of histograms of soil strength may 
also be stored in memory in, for example, microprocessor 48 or 
microprocessor 21, or in a removable memory device in order to provide a 
map of soil strength values in a field. The stored map may be 
appropriately electronically labelled to identify it to a particular 
field, and may be used by a farmer in subsequent operations on the field 
such as harrowing, furrow pressing and even the application of specialized 
chemicals in order to take account of variations in the soil strength in 
order to produce a more consistent crop. 
Referring now to FIG. 3, the relationship between microprocessor 48 and the 
remainder of the components of FIG. 1 is shown in more detail. 
Microprocessor 48 comprises a central processor or microcomputer 48a, 
having a digital input interface 48b and an analogue input interface 48c. 
Microprocessor 48a receives power via a voltage regulator 48d from the 12 
volt power supply of the tractor. Microprocessor 48a can output signals 
via a solenoid driver 48e. There is also an input/output interface 48f 
with the controller area network (CAN) of the tractor/plough combination. 
The primary component of the CAN is microprocessor 21. 
The digital interface 48b receives signals, including signals indicative of 
the orientation of plough 60 from a signal generator in the form of a pair 
of microswitches, indicated by reference numeral 90, that generate signals 
uniquely identifying the orientation of plough 60. The microswitches are 
physically secured to an ultrasonic depth sensor 91 that generates 
analogue signals (input via the analogue interface 48c to microprocessor 
48a) indicative of the depth of ploughing. Thus the depth sensor provides 
feedback data on the ploughing depth for comparison against the set point 
ploughing depth calculated by microprocessor 21 during ploughing 
operations. 
During ploughing, the draught values (that are proportional to the soil 
strength) are recorded in microprocessor 21, and encoded by microprocessor 
48a using data from the microswitches 90 indicative of the orientation of 
plough 60. 
Further feedback of the operation of plough 60 during ploughing operations 
is accomplished by a furrow width transducer 92 that provides feedback 
data on the actual width ploughed, for comparison against the set point 
plough width determined by microprocessor 21. 
FIG. 3 includes an optional, manual control box 93 that may be used eg. for 
adjusting the width setting of plough 60 in the absence of signals from 
the CAN. 
Finally, the solenoid driver 48e of controller 48 is operatively connected 
to a solenoid valve indicated schematically by reference number 94 for 
adjusting the width setting of the plough 60. 
Solenoid valve 94 is shown schematically, since in practice the actual 
width adjustment arrangement may take a variety of different forms, and 
may be constituted as a plurality of actuators. 
The sensor that provides data on the draft experienced during ploughing may 
be located on the three point hitch 15, or on a member of the plough 60 
secured to three point hitch 15. Other locations for this sensor are also 
possible. 
In use of the apparatus and method of the invention, the plough width and 
ploughing depth are maintained constant by microprocessor 21 (in 
accordance with the principles described in GB 9622087.6), and parameters 
of the tractor are varied eg. in order to maximize work rate or to 
minimize fuel consumption. If during ploughing the soil strength should 
increase, the microprocessor 21 responds by temporarily boosting the 
engine power output (if possible) and/or selecting a lower transmission 
ratio. Conversely, a reduction in soil strength would cause the 
microprocessor 21 to shift the transmission to a higher gear. At the 
headland turn after completion of a pass along the field, the furrow width 
is adjusted in accordance with the FIG. 2 method by microprocessors 21 and 
48 after reversing (inversion) of the plough. The plough is adjusted to a 
furrow width that according to the determination made in microprocessor 21 
at step 143 is most likely to provide an optimal work rate during the 
return pass down the field. This particular value is, as explained above, 
preferably determined by logging soil strength values during the previous 
pass along the field in the same direction, analyzing their distribution, 
and selecting the most frequently occurring value. 
It will be understood that changes in the details, materials, steps and 
arrangements of parts which have been described and illustrated to explain 
the nature of the invention will occur to and may be made by those skilled 
in the art upon a reading of this disclosure within the principles and 
scope of the invention. The foregoing description illustrates the 
preferred embodiment of the invention; however, concepts, as based upon 
the description, may be employed in other embodiments without departing 
from the scope of the invention. Accordingly, the following claims are 
intended to protect the invention broadly as well as in the specific form 
shown.