Engine monitor/control microprocessor for continuously variable power train

Engine monitor/control microprocessor primarily effective to automatically adjust the engine power setting in a transmission power train in which the transmission drive reduction is variable in ratio, by step change or continuously so, such as for use in farm tractors. The microprocessor adjusts the position of the setting so that engine power set at all levels is produced at the right brake specific fuel consumption for substantially minimum pounds of fuel per horsepower hour, or within a band width thereof if not all that sensitive. Preferably, the microprocessor has a higher priority primary function of also automatically adjusting the transmission drive reduction ratio, for the same purpose but with high sensitivity.

CROSS REFERENCE TO RELATED CASES 
This application is a companion case to respectively coassigned U.S. Pat. 
No. 4,138,907 and Hennessey et al. U.S. Pat. No. 4,388,987 granted June 
21, 1983, the power train disclosures of both of which are incorporated in 
their entirety herein by reference. 
Also, this application is related to Cornell coassigned U.S. patent 
application Ser. No. 512,832 filed July 11, 1983, now U.S. Pat. No. 
4,594,666, relating to a power train automatic transmission control. This 
application embellishes the machinery of the power train with a further 
control which, briefly stated, amounts to an automatic power control which 
augments and is preferably used in conjunction with, the automatic 
transmission control disclosed in the above-identified Cornell patent 
application. 
BACKGROUND OF THE INVENTION 
The present invention is energy related, for the purpose of fuel 
conservation. It controls, as one part and only augmentally so, the engine 
power setting and further controls, as one part, the effective drive 
reduction ratio of a power train having a continuously variable or step 
change transmission, such as broadly used in agricultural and 
nonagricultural vehicles and machinery, especially an agricultural 
tractor. 
The invention specifically utilizes an engine and transmission, dual 
function monitor/control microprocessor for a variable ratio power train 
drive, primarily effective to automatically adjust both aspects of the 
drive so that engine power at all levels is produced at a brake specific 
fuel consumption (BSFC) of substantially minimum pounds (or Kg) of fuel 
per horsepower hour (or KWH). 
As background thereto, the material information includes but is not limited 
to U.S. Pat. Nos. 3,952,829, 4,180,979, 4,091,617, 4,158,290, and 
especially the (US) Society of Automotive Engineers Paper No. 780465 
relating to BSFC and also U.S. Pat. No. 3,914,938. 
SUMMARY OF THE INVENTION 
An object of the invention, therefore, is to consistently achieve 
substantially minimum or optimum brake specific fuel consumption in a 
self-powered vehicle, automatically by means of an engine and transmission 
monitor/digital-control microprocessor provided for a continuously 
variable or step change power train therein. 
The power train, in the drive line of which the invention is specifically 
embodied, includes a speed-adjustable engine and a range transmission and, 
between the engine and range transmission, a hydromechanical speed 
transmission equipped with pump and motor hydraulic units with variable 
displacement to vary the transmission ratio infinitely within limits. The 
range transmission has three or more speed ranges, at least some of which 
overlap, with infinitely variable speed characteristics because of the 
just mentioned speed transmission adjustments, incrementally ranging all 
the way from nominal speed afforded by the speed transmission reduction to 
much more speed reduction at a substantial ratio. 
Another object of the invention, providing for anti-lugging protection of 
the engine under a worsening load condition, is accomplished by 
automatically causing the speed transmission to progressively vary from 
essentially a 1:1 drive ratio to greater ratios and finally a maximum 
speed reduction ratio as the condition progressively increases rimpull 
loading. This objective is also accomplished secondarily at the same time 
by automatically causing the fuel rate of flow to increase and increase 
the power being made available from the engine. Under normal load 
conditions, the engine never lugs, being afforded more torque advantage by 
the speed transmission as indicated and perhaps at the same time more fuel 
depending on the amount of engine speed or transmission ratio deviation 
from the optimum. 
An additional object is the employment of the monitor/control 
microprocessor and its memory so as to provide thereto a data base for the 
engine comprising a predetermined consecutive series of desired engine 
speed values productive of substantially minimum brake specific fuel 
consumption for a range of power settings, and thereupon repetitively 
determining in the microprocessor, at frequent intervals, the desired 
minimum brake specific fuel consumption speed for the current power lever 
setting, thus constantly updating the objective of the system, always 
under easy access to the system, and ever present for due reference and 
response by the system. The provision of the data base is by simply a 
matter of known choices, namely, by table, or by other procedure such as 
an approximation equation. 
A more specific object of the invention, directed toward the accomplishment 
of a fuel-efficient drive system for a variable ratio power train, is the 
provision of an engine included therein which is adapted for automatic 
close control of available power and operating speed, an automatically 
controllable engine power lever operating the engine and having a 
plurality of operating positions, an operator controlled speed lever 
establishing a desired transmission output speed of said power train, a 
plurality of sensors for respectively sensing engine or transmission input 
speed, transmission output speed, power lever position, and speed lever 
position, an apparatus for automatically controlling the ratio of the 
transmission, and for automatically controlling the position of the power 
lever in response to said sensors, the control apparatus having a 
dedicated microprocessor programmed to establish a desired engine speed 
providing the least specific fuel consumption of said engine based on the 
position of said power lever, and, based on the position of the speed 
lever, vary the ratio of said transmission to maintain the desired engine 
speed upon increases in drive train load beyond that producing the desired 
engine speed for the specific power lever setting and to maintain the 
desired transmission output speed upon decreases in drive train load 
beyond that producing the desired engine speed for the specific power 
lever setting, said microprocessor further being programmed to establish a 
deadband in which the engine speed can exceed the desired speed without 
additional effect and upon the engine speed exceeding the deadband causing 
a decrease in the power lever setting thereby establishing a new desired 
engine speed, the microprocessor being still further programmed to 
establish a deadband in which the ratio of the transmission can be reduced 
without additional effect and upon the transmission ratio being reduced 
beyond the deadband, actuating the power lever to increase the power 
setting thereby increasing the desired engine speed while maintaining the 
desired transmission output speed.

A PREFERRED EMBODIMENT 
More particularly, as shown in FIG. 1, the power train 10 of a farm tractor 
12 supplies power for rimpull torque at the tractor drive wheel, of which 
the right rear wheel 14 is representative, through a path including an 
engine 16 controlled by a fuel injection pump 17 having a mechanical speed 
governor 19 of the well-known type manufactured by Robert Bosch Company 
under the designation "RSV" including a spring tensioned speed setting 
mechanism controlled through a linkage by a power lever 18 to change the 
governed speed setting by an appropriate change of spring tension. It will 
be appreciated that, in place of the mechanically controlled injection 
pump 17, an electronically controlled injection pump might be utilized 
wherein the fuel output of the injection pump, and thus the engine speed 
is varied in response to the signal 81 described hereinafter which in the 
preferred embodiment controls the power lever 18. 
There is further provided a hydromechanical speed transmission 20 
controlled indirectly with a speed lever 22 and an electrical hydraulic 
actuator 26 by way of a control module 24. A three-speed, reversible range 
transmission 28 controlled by a gear shift lever 30, a reduction gear and 
differential drive 32, a planetary final drive 34 for each drive wheel, 
and rear drive axles identified at 36 at one side and at 38 at one side 
connected between the differential 32 and final drive at that side and 
controlled by a steering brake 40 complete the power train. 
In the hydromechanical speed transmission 20, a drive gear 42 on the engine 
powered, transmission input shaft 44 continually meshes with a 
countershaft gear 46 which drives a swash-plate-controlled variable, axial 
piston hydrostatic pump 48 through an interconnecting countershaft 50. The 
actuator 26 tilts and holds a pump swash plate 52 so as to destroke it to 
zero pump displacement, and moves it therefrom through positive and 
negative angles for flow reversal by the pump at varying displacements. 
The countershaft gear 46 also continuously meshes with a gear 54 connected 
to the right gear 56 of a three element planetary gearset 58 not only 
providing one of two inputs but also providing two different drive modes, 
regenerative and split. A planetary carrier 60 serves as the element 
driving the planetary output shaft 62. 
A reversible fixed displacement axial piston motor 64 is mechanically 
connected to a planetary sun gear 66 by a sun gear shaft 68, and is 
hydraulically connected to the variable displacement pump 48 so as to be 
driven by the latter at varying speeds in opposite directions. But despite 
the sun gear 66 being rotatable in opposite directions, nevertheless the 
planetary ring gear 56, carrier 60, and planetary output shaft 62 always 
partake of rotation in the same direction as the transmission input shaft 
44. With the swash plate angle full negative and a reverse moving sun gear 
66, the effective hydromechanical gear reduction ratio provided at 58 is 
1:2.39, and with the swash plate angle full positive and forward sun 
rotation (i.e., in engine direction), the gear reduction ratio effectively 
obtainable is 1:1.005. 
A pinion 70 supported for rotation on and relative to the transmission 
input shaft 44 constantly meshes with a gear 72 secured to the same sun 
gear shaft 68 as the motor 64. The fixed ratio constraint thus imposed on 
pinion 70 causes it normally to rotate oppositely to the shaft 44, or to 
rotate in the same direction therewith but normally at a slower speed. 
Extremely strenuous transmission start up conditions and others can cause 
the pinion 70 to reach the same speed in the same direction as shaft 44, 
causing engagement of a one-way overspeed clutch 74 interposed between the 
pinion and shaft 44 so as to cause the pinion 70 to be a reaction member 
to sun 66 and motor 64; in that way, strenuous conditions can never make 
the motor 64 overspeed beyond the geared limits established by the 
reaction member, i.e., the pinion 70, and so the motor 64 cannot be 
damaged internally by excessive speed. For further details, reference can 
be made to the afore-mentioned U.S. Pat. No. 4,138,907. 
A power lead 76 from the power lever 18 enables the module 24 to monitor 
the power setting, and a speed lead 78 from the speed control lever 22 
enables the module to monitor the transmission speed setting. The module 
24 is powered by +12 V DC as illustrated and, by an ouput cable 80, 
automatically controls the electrical hydraulic actuator 26 for the swash 
plate. 
By another interconnecting power output cable 81, the module 24 
automatically controls a DC motor 83 which is shaft connected, at the 
pivot of the power lever 18, to rotate the latter into desired spring 
tension setting positions for the governor mechanism 19, thus resetting 
injection pump 17 and controlling the engine speed and the available 
engine power. 
An engine speed lead afforded by a connection 82 from a transducer 84 
enables the control module 24 to monitor, via one gear 86 indicated on the 
engine powered, transmission input shaft 44, the actual engine rpm at the 
input to the hydromechanical speed transmission 20, i.e., before gear 
reduction. A similar transducer 90 and transmission speed connection 88 
enable the module 24 to monitor the drive side of a mid-mounted master 
clutch 92 for the transmission output rpm, i.e., after gear reduction. A 
valve controlled hydraulic actuator 94 causes internal multiple plates of 
the pressure-disengaged clutch 92 to disengage and to engage, 
respectively, under control of a tractor clutch pedal 96 when it 
correspondingly is depressed and released. Hydraulically connected to the 
actuator 94 is a normally open pressure switch 97 which, in response to an 
hydraulic pressure rise sufficient to disengage the clutch, closes its 
contacts. In other words, the driver closes the switch 97 by depressing 
the clutch pedal, and a closed circuit, not shown, signals that the clutch 
is decoupled. Switch 97 could also be a mechanical switch actuated by the 
clutch pedal, if desired. 
The clutch 92 decouples to allow gearshifts in the range transmission 28 
and can then recouple together the respective transmissions 20 and 28. 
The range transmission 28 has respective sets of speed changing gears 
mounted on the input and output shafts 98 and 100, respectively. When the 
lever 30 is shifted into the position marked HI a synchronized jaw clutch 
sleeve shifts on shaft 98 for establishing high range, and a shift of the 
lever 30 into the position marked M causes an opposite synchronized jaw 
clutch shift on shaft 98 for mid-range setting in the transmission. The 
sleeve 102 of a LO synchronized jaw clutch on output shaft 100 is employed 
for low range and additional means are provided for reverse, not shown, 
for the range transmission 28. 
Gear ratios are selected such that the range transmission 28 provides 
substantial overlap in its mid range M, so that the infinitely variable 
speeds otherwise available in the top of the LO range can be readily 
duplicated, without downshifting, while in the bottom of the mid range M. 
Similarly, the bottom of the HI range can be duplicated with infinite 
variability in the top of the mid range M, without need for upshifting 
while variations are made within such range of overlap. 
For purposes of discussions following immediately hereinafter, the range 
transmission 28 will be presumed to be in its mid range M which in 
practice covers the infinitely variable speeds at which the present 
tractor, and agricultural tractors generally, are utilized approximately 
90 percent of the time; those speeds are generally the ones used in actual 
field work. 
In accordance with the principles of the reaction member control in 
hydromechanical transmissions, the effective gear reduction ratio of speed 
transmission 20 is established by control of the sun gear 66 in its speed 
and relative direction of rotation, under the accurate direction of the 
pump swash plate 52 according to its angle of tilt. Carefully controlled 
actuator means 26 is provided for the purpose. 
ELECTRICAL HYDRAULIC ACTUATOR--FIG. 2 
The swash plate 52 is mounted transversely within the case of the pump 48 
so as to be centered in a span of bearings, a representative one of which 
is the tapered bearing 104 defining the plate tilt axis 106. The actuating 
means 26 comprises a double acting hydraulic cylinder 108 arranged with 
its housing guided in fixed motor slideways 110 and 112 and having a lug 
114 projecting through a window, not shown, cast as a long longitudinal 
slot in the side of the pump casing. A stud 116 held in screw threads in 
the swash plate 52 has a ball end 118 projecting laterally into, and 
closely confined within, a complementary slot in the lug 114. Accordingly, 
as the cylinder housing moves longitudinally along the side of the pump 
case as guided along a piston shaft axis 120 for the cylinder, the pump 
swash plate 52 changes its tilt and then stops within the angular swing 
range indicated about its tilt axis 106. 
In one physically constructed embodiment of the invention, the piston shaft 
122 defining the axis 120 of the double acting cylinder 108 projected 
through seals at opposite ends of the cylinder 108 and was fixed at anchor 
124 at the proximal end as viewed in FIG. 2. Connections were such that as 
the distal hydraulic service line 126 was pressurized so as to introduce 
fluid to the far side of the fixed piston, not shown, the housing of the 
cylinder 108 within slideways 110,112 retracted therein relative to 
proximal anchor 124 so as to tilt the swash plate for positive angularity 
and higher speed with less gear reduction. Conversely, pressurization of 
the proximal service line 128 caused advance of the housing of cylinder 
108 back toward the anchor to produce negative plate angularity and more 
gear reduction in the speed transmission, not shown. 
The actuating means 26 further comprises a two-way, closed center piloted 
valve 130 which hydraulically locks it, in response to a proportional 
pilot valve 132 commercially available. The microprocessor output cable 80 
through a proportional coil 134 automatically electrically controls the 
pilot valve 132, the pressure output of which is proportional to pulse 
width and direction of the signal electrically supplied through the cable 
80. 
Prior to instituting this automatic tilt angling operation the operator 
will set the range transmission, for example, in mid range M, and will 
also set the other controls for speed and power by close estimation 
according to his experience. 
OPERATOR CONTROLS--FIG. 3 
In this enlarged scale figure illustrating the operating console controls 
with greater particularity, all positions including park P for range shift 
lever 30 are shown, except for the unmarked neutral position N in which it 
is pivoted as actually illustrated. As shown in operative association with 
the lever 30, an out-of-neutral monitor microswitch 133 opens a circuit 
controlled thereby (not shown) signals that the range transmission is out 
of neutral N. The microswitch 133 is provided to indicate a neutral N 
setting and, similarly but not shown, a means is also provided to 
electrically indicate park P. The microswitch 133 is cammed closed by the 
lever pivot shaft 135 when in neutral N and thus interrupts the 
out-of-neutral signal. 
A manual out-in plunger switch 137 carried by the handle of the power lever 
18 has a spring biased, switch-open position when in its "out" position as 
illustrated. The power lever 18 takes the corresponding status of being 
manually operable by the driver, adjustable at will solely by him. But 
when thumb-depressed into the handle into its detented "in" position, not 
shown, the manual switch 137 closes, switching the power lever 18 into 
automatic operation to be disclosed hereinafter. It will be appreciated 
that if manual control of the engine field operating speed is not desired, 
the power lever 18 may be dispensed with and the module 24 could directly 
control the injection pump. A simple switch could be provided for shifting 
the engine between low idle and the operating range for automatic 
operation. 
In the field, the operator sets the power lever 18 somewhere above the LO 
idle position up to and including the so-called HI idle or wide open 
throttle position. The engine may be loaded or unloaded in the position 
set, depending upon tractor rimpull being required or not. 
At the same time, the operator sets the transmission output speed lever 22 
at a point between or including FAST and SLOW appoximating the effective 
gear reduction expected to be required in the speed transmission while the 
range transmission remains in its aforementioned mid-setting. Then the 
clutch pedal, meantime depressed, is released and the tractor proceeds, 
effectively handling the job as it goes and equally effectively being 
conserving of fuel as it goes. 
Novelty is felt to reside in the herein recognized utility for tractor fuel 
conservation and in the automatic module approach hereof for satisfying 
that utility as can be graphically appreciated. 
ENGINE RPM VS. LEVER POSITION--FIGS. 4A and 4B 
These figures are a graph of actual engine speed plotted against engine 
power lever or throttle setting, all in revolutions per minute. The 
particular engine is an International Harvester DTI-466B diesel engine. 
The power match curve 136 represents the lowest specific fuel consumption 
(BSFC) of the engine in pounds of fuel per horsepower-hour (or Kg/KWH) for 
each power lever setting. For example, point A is the minimum BSFC for a 
power lever setting of about 1950 rpm. The corresponding actual engine rpm 
is about 1800 rpm for the minimum BSFC point A, i.e., for that specific 
power lever setting. The curve 136 can theoretically never reach the no 
load condition curve 138 which shows higher speeds at all points because 
at no load BSFC is infinite. 
Each power lever setting in the available range from LO idle to HI idle 
will have its own least BSFC engine speed, thereby generating the power 
match curve 136. One example will typify the rest in the range. 
EXAMPLE I 
In this example for an engine power lever setting of 1950 rpm, by means of 
the automatic tilt angling of the swash plate as discussed above, the 
speed transmission establishes a lowest BSFC operating point A indicated 
on curve 136 resulting in an actual engine speed of about 1800 rpm due to 
the mechanical advantage afforded by the speed transmission. 
That advantage, let us assume, occurs with an effective 1:1.5 gear 
reduction in the speed transmission. The control module 24 has two modes 
depending upon the condition encountered. 
If the soil condition were, for example, to add more rimpull resistance to 
the tractor, a point B having an engine speed of, say 1700 rpm, might be 
reached for the 1900 rpm power lever setting. However, the control module 
24 immediately senses the underspeed and begins its primary or power 
limiting mode of operation. The effective gear reduction ratio in the 
speed transmission is automatically changed for more reduction, for 
example to 1:1.7, obviously giving the engine more of a mechanical 
advantage so it can speed back up to the actual desired speed A, to 
restore least BSFC operation but naturally at the expense of slowing the 
tractor ground speed somewhat. 
In other words, temporarily increased rimpull resistance would seem 
normally to demand reaction by the operator to advance his power lever 
setting and thus compensate with increased engine power output. But with 
automatic power limiting, and at optimum BSFC efficiency as described, the 
module automatically does the compensation without a requirement for 
operator intervention and without the engine being lugged down in speed by 
the temporarily increased load. 
When the rimpull resistance returns to the original value, the control 
module operates, in another phase of its power limiting logic mode, to 
sense the resulting tendency of the temporarily assumed actual drive 
reduction ratio to produce a higher engine speed than to the calculated 
optimum represented at point A. To counteract this tendency to operate 
with too much effective gear reduction ratio and too high engine speed, 
the module automatically decreases the effective gear reduction ratio from 
1:1.7 back to the initial lesser ratio of 1:1.5 appropriate to a higher 
tractor speed. That is to say, the engine is automatically afforded less 
of a mechanical advantage over the now-reduced load until the original 
condition is restored. It can handle a greater load at its power setting 
and is therefore loaded up to a greater amount, and the power match is 
restored right back to the least BSFC value. 
A contrasting cycle, completed under a different mode of operation of the 
module, is to be taken up in the example now to be considered. 
EXAMPLE II 
If, while operating at point A appearing in the graph shown in FIG. 4A, 
soil resistance stays the same but the tractor encounters a slight short 
downslope, as an example of a lightened load, the control module 24 enters 
into the second, or constant ground speed mode of operation. It does so 
because of the actual change of the operating point to point C, say, 1900 
rpm, again with a power lever setting of 1950 rpm and an effective 
transmission ratio of 1:1.5. Engine speed-up on such a short downslope 
tends to cause a finite increase of ground speed, and the speed 
transmission automatically causes more reduction ratio, e.g., 1:1.7, 
restoring the initial ground speed desired. The speed control logic mode 
perforce continues because, all the while, the primary power limiting 
logic mode has been satisfied, that is, both the engine speed and the 
output or ground speed are at or above their desired values. 
So the tractor compensates by reducing ground speed back down to the 
original ground speed whereupon, to continue with this example, the 
tractor then makes the transition by bottoming out at the end of the short 
slope. 
The cycle is completed because, at the end of the slope, the operating 
point A is resumed. That is, the module automatically adjusts the 
transmission setting for less gear reduction back to the originally 
assumed 1:1.5 ratio. Thus, from a former optimum setting condition A, the 
tractor without operator intervention immediately made adjustment to hold 
constant ground speed when on the downslope, and immediately readjusted to 
the former optimum setting condition to keep that same constant tractor 
speed when off the slope. 
The control module carefully monitors the power train and has means 
provided for programming it for the operating modes appropriate to the 
conditions being monitored. An explanation follows. 
MODULE--FIG. 5 
At the center of the control module 24 as shown in this figure is a 
microprocessor computer 140 having its own memory and proper programming 
for the operating modes required. 
Inputs include a power supply 142 for regulated +5 V input power, the 
magnetic transducer 84 adjacent gear 86 for engine speed rpm, the magnetic 
transducer 90 adjacent the clutch gear 92 for transmission output speed 
rpm, a +5 V potentiometer 144 for monitoring the setting of the power 
lever 18, and a speed potentiometer 146 for monitoring the transmission 
speed lever 22 for its setting. 
The outputs include the proportioning coil 134 for the swash plate pilot 
valve 132 for controlling the speed transmission and the power output 
cable 81 to the governor motor 83 for re-setting the power lever 18 
automatically when the operator has switched it for automatic operation as 
discussed above. 
B+ power is impressed on the +5 V power supply 142 and, by a connection 148 
is also impressed on a pulse width modulated swash plate drive circuit 
150m. A ferrite anti-noise bead 152 is present in the B+ lead to the power 
supply 142 and a tantalum capacitor 154 having one plate grounded is also 
present thereat to reduce high frequency electromagnetic interference from 
entering into the power supply 142. Also present is a series-connected 
reverse-polarity-detecting diode 156 to insure against damage in case the 
power supply is connected with wrong polarity to the source of B+. An 
electrolytic capacitor 158 having one plate grounded filters the B+ power. 
Also, a varistor 160 grounded at one side will, if optionally provided, 
protect against noise transients occurring from the B+ source from time to 
time. 
A resistor 162 leading from the B+power line is series connected to ground 
by a Zener diode 164 having a capacitor 166 parallel connected therewith 
and together serving as shunt series regulator to regulate voltage of the 
power supply. 
A resistor 168 impresses the Zener voltage on the base of an NPN transistor 
170 which, through its collector, delivers to the B+ power line electrons 
that its emitter is pumping from a junction 172 out of the base of a 
second NPN transistor 174. The NPN transistor 174 conducts electrons from 
the +5 V linear voltage regulated terminal 176 through its emitter to the 
B+ power line through a collector connection to the latter, and 
incorporates a base bias resistor 178. Two series connected resistors 180 
and 182 as supplemented by a paralleled capacitor 184 serve in conjunction 
with the transistors to define what the regulated linear output voltage 
will be at +5 V terminal 176. 
The transmission speed control 88 from the transducer 90 on speed 
transmission clutch output gear 92 transmits therein an essentially 
sinusoidal wave which first encounters in two stages of the circuit a pair 
of RC filters 184 and 186. The wave then encounters a pair of oppositely 
poled diode clippers 188 and 190 which clip off the waves so that they are 
flat on top and on bottom, limited to about 11/2 V peak to peak. Further 
RC filtering at 192 is followed by direction of the wave pulse as input to 
a schematically shown comparator 194. Full connections thereto are shown 
by way of a counterpart comparator 196 grounded at 198 and receiving +5 V 
through a terminal connected through a capacitor 200 to ground. The 
comparator 196 is connected to engine speed transducer 84 in the same 
manner. 
The regulated linear +5 voltage is supplied through a resistor 202 to the 
output junction 204 of comparator 194, whereas another similarly supplied 
resistor 206 is connected to the output junction 208 of the counterpart 
comparator 196. 
The output at junction 204 is the square wave indicated and, similarly, the 
output at the comparator junction 208 is such a square wave. Those waves 
in one physically constructed embodiment of the invention ranged in 
frequency from 10 Hz to 7000 Hz and had digital form for ease in computing 
shaft rpm. 
At the noted frequencies, the rpm signals of engine speed from 84 and 
transmission output speed from 90 are separately handled and analyzed by 
the microprocessor 140 by multiplexing, starting at their output junctions 
204 and 208, respectively. A pair of diodes 210 and 212 bridging therefrom 
are joined in series cathode to cathode and their junction is connected to 
a junction 214. 
A bias resistor 216 and base connector 218 from the junction 214 act in a 
way on an NPN transistor 220 so that, for example, the square wave pulses 
alone at 204 are ineffective to allow the transistor base to turn on 
transistor 220 through the diode 210. But the transistor 220 has a special 
inverter function connection 222 of its collector to a pin 224 on the 
microprocessor 140 and also to the linear voltage regulator's +5 V through 
a resistor 226. Thus, according to multiplexing procedure, the 
microprocessor 140 in order to measure engine rpm has a pin 228 go 
positive in readiness as to when the square wave causes junction 208 
linkwise to go positive. At that point of coincidence, the inverter 
transistor 220 by inversion causes the pin 224 to go low, starting a 
timing cycle within microprocessor 140. That cycle counts the interval 
until the next coincidence between the positive (high) pin 228 and the 
positive-going square wave at 208, which causes the pin 224 on 
microprocessor 140 to go low again so as to terminate the timing interval. 
The engine rpm is at once determined by microprocessor 140, whereupon it 
causes another pin 230 connected to junction 204 to go positive so that 
the microprocessor 140 can similarly determine the transmission output rpm 
from the tooth speed of the turning gear 92. 
The cycle then repeats, and does so about sixty times per second in the 
microprocessor. 
Transducers critically placed about the transmission and engine to provide 
appropriate electrical frequency signals to the speed connections 82 and 
88 can be selected from the group of a variable reluctance magnetic 
pickup, an optical pickup, and other magnetostrictive or other type 
pickups which provide a signal proportional, for example, to gear tooth 
frequency. 
The power lever 18 appearing in FIG. 5 has a mechanical linkage which has 
heretofore been described for making changes in the setting of the 
governor 19. Such changes can also be accomplished by electrical controls. 
Separately, the electrical connection by means of the potentiometer 144 
serves as the means of constantly monitoring the power lever position and 
hence the engine governor setting. 
A pull down resistor 232, appropriately grounded, provides for fault 
protection to the potentiometer power lead 76, as in the case of a broken 
wire, for example. Two stages 234,236 of RC filtering are present in the 
power lead, and also present are a pair of series connected clamping 
diodes 238,240 poled as shown to protect the power lead against noise 
spikes; finally, a current limiting resistor 242 leading from the clamping 
diodes' midjunction delivers the monitored power lever voltage setting 
signal to an analog to digital converter 244. The analog to digital 
converter 144 is commercially available under the National Semi-Conductor 
designation ADC0833 and is found to perform satisfactorily. Linear voltage 
as regulated to +5 V is supplied to the converter 244, suitably bypassed 
for noise and other protection purposes by a resistor 246, a filter 
capacitor 248, and an RC network 250. The converter 244 supplies input to 
the microprocessor 140 through the various pin leads 252 which are 
supplied through resistors 254 at +5 V by the linear voltage regulator. 
That input is digital input for ready consumption by the microprocessor 
140. 
The transmission speed lever 22 is not only digitally monitored in this 
same way by the converter 244, but is also served so as to supply its own 
digital command signal to the microprocessor 140 for direct control 
through pilot valve 132 over the swash plate tilt angle. The pilot valve 
132 is a commercially available electrohydraulic proportional servo valve. 
In other words, it has no mechanical connections similar to that of the 
power lever and hence relies exclusively on digital control over the swash 
plate. 
A watchdog circuit 256 operates through a comparator and a NOT gate 258 as 
a timer to restart the microprocessor 140 in regular way in case something 
has meantime gone wrong. 
The microprocessor 140 receives through its input pin 262 the necessary 
power to run it from the +5 V linear voltage regulator. An adjacent pin 
264 is connected to the regulator by a decoupling capacitor 266 for 
blocking power source noise. Another adjacent pin 268 is connected by a 
resistor 270 to the +5 V linear voltage regulator for biasing the 
microprocessor 140 constantly to use its aforementioned internal memory. 
The required input crystal, a CPS Knight, which is connnected in standard 
way is omitted from the showing of the microprocessor 140 in FIG. 5. 
The transistors employed in the pulse width modulated swash plate drive 
circuit 150m of FIG. 5 are all of the NPN type except 292 and 314 which 
are of the PNP type. Of the two service connection junctions 272 and 274 
of that circuit, the junction 272 has among others, a connection to an 
output pin 276 on microprocessor 140, a connection through pull-up 
resistor 278 to the +5 V linear voltage regulator, and a connection to the 
base electrode of a transistor 280. The transistor emitter is connected to 
a ground line 282 and the collector is connected, in order, through a 
resistor 284, a junction 286, a resistor 288, thence to a B+ junction 290 
supplied by connection 148. 
The second transistor 292 (PNP), the base electrode of which is connected 
to junction 286, has the emitter connected through a resistor 294 to the 
B+ junction 290 and has the base connected through the respective 
cathode-anode of a diode 296 and the respective cathode-anode of a series 
connected diode 298 to the B+ junction 290; the elements 294, 296, and 298 
provide current limiting protection to the second transistor 292. A pair 
of series connected clamping diodes 299 and 300 provide a cathode to anode 
and another cathode to anode connection down from the B+ junction 290 to 
ground line 282; they protect against noise spikes and have an intervening 
junction 302 connected to the collector electrode of the second transistor 
292. 
In operation, microprocessor 140 causes pin 276 to go high at the same time 
that it causes junction 274 to go low. The pull-up resistor 278 goes to 
the same +5 V potential at its opposite ends and the correspondingly high 
junction 272 positively biases the base of transistor 280 so that it 
conducts. Accordingly, the resistor 284 goes less positive at its end 
connected to junction 286 and causes the base of the PNP second transistor 
292 to bias the latter into conducting. So a positive rectangular wave 
pulse, of modulated width determined by the microprocessor 140, is 
transmitted from the intervening junction 302 so as to be passed by the 
output cable 80 through the proportional coil 134 of the pilot valve 132. 
Suitable cable connectors are indicated in the cable at 304 and suitable 
anti-noise ferrite beads are indicated therein at 306. 
The circuit from coil 134 is completed to ground line 308 in the rest of 
the circuit in which, because service connection junction 274 is 
momentarily low, the circuit's respective transistors 310,312 (NPN) and 
314 (PNP) are base biased respectively negatively and positively so as not 
to conduct. A pull-up resistor 316 is connected between the +5 V linear 
voltage regulator and the base of a transistor 318 and, unimpeded, gives 
positive base bias to the transistor 218 causing it to conduct and 
discharge the positive rectangular wave through a resistor 320 thus 
completing the circuit to ground line 208. The transistor 318 is protected 
in the usual way by the resistor 320 in conjunction with another 
transistor 322 which together form a current limiter on the transistor 
318. 
The positive rectangular wave ceases when the pin 276 allows the service 
connection junctions 272 and 274 to reach the same potential levels. The 
next pulse starts after a predetermined interval, and so forth for the 
successive pulses in the positive direction as long as continued by the 
microprocessor. 
Negative pulses, in succession, are started with successive operation by 
the microprocessor 140 causing junction 274 to go high at the same time as 
junction 272 goes low. 
The cycles are repeated in either direction and, with pulse width 
modulation as determined by the microprocessor, the proportional coil 134 
receives an average positive current or negative current or no current as 
a proportional thing, causing proportional fluid directing action by the 
servo valve 132 acting as pilot valve. 
The purpose of the swash plate drive is to provide amplified electrical 
hydraulic actuation with precise control. The high-low microprocessor 
output means that the pin such as pin 276 is impressed with +5 V or OV at 
extremely low current carrying capacity. The B+ voltage impressed on the 
drive circuit 150m can fluctuate on the tractor at anywhere from 9 to 16 V 
whereas, despite the current amplification provided by the transistors, 
the proportional coil 134 is rated at only 7.5 V which is the most voltage 
ever impressed upon the coil terminals by the electrically amplifying 
transistors. Hydraulic amplification in the pilot valve 132 is shown in 
FIG. 5 greatly increases the force possible because of responsiveness of 
the piloted servo valve 130 which readily handles the moving and stopping 
load under which the swash plate is forced to operate. 
The control module 24 as shown in FIG. 5 is not confined to any set number 
of steps or inflexible sequence or order for its operation, although one 
flow chart for ease of understanding will be given, simply by way of 
example and not limitation. 
LOGIC FLOW CHART--FIG. 6A 
The starting point for the control module's automatic operation is the 
proportional control voltage picked off the potentiometer 146, varying 
with transmission speed control lever 22 as it positions the slider 
illustrated, and applied as monitored, according to block 324, is the 
desired transmission output speed command. The next block 326 of the FIG. 
6A flow chart indicates the monitoring of actual engine speed before gear 
reduction, depending at outset of the automatic operation strictly upon 
the operator's positional setting of the power lever and existing load on 
the tractor at the time. The converter block 328 next following represents 
an operation within the microprocessor of constantly recalculating a 
control parameter, the commanded speed reduction ratio of the speed 
transmission, determined as the quotient of commanded speed from block 324 
divided by actual speed from block 326. A further crucial block 330 
represents constant monitoring of the power lever setting as initially set 
by the operator at his desire for the general operation he seeks. 
The calculation block 332 next following in the sequence represents use of 
the power lever setting as parameter for the recalculations, updated sixty 
times per second, of the desired engine speed providing the least brake 
specific fuel consumption for that particular setting of the power lever; 
the basis is the Power Match curve of FIGS. 4A and 4B, which is the 
criterion for least BSFC. 
Next, diamond 334 represents the microprocessor's digital signal comparison 
of actual engine speed to the desired engine speed for least BSFC, as 
scaled numbers. The latter scaled number for want of a better identifying 
word is termed the computer's reference command whereas the actual speed 
scaled number compared thereto is termed the second signal. If the actual 
engine speed by comparison is equal, there will be no change at point of 
the diamonds 334 or 335 or in the desired speed command ratio being 
transmitted to block 336. However, if the actual engine speed drops below 
the desired engine speed, a Yes is generated which turns on modify block 
338. Specifically, the microprocessor is programmed automatically to 
modify the command ratio signal so as to call for more gear reduction, 
increasing the mechanical advantage and thereupon restoring actual engine 
speed to equivalence. 
To reach its signal modification step (338), the microprocessor 140 is 
programmed to detect some predetermined value of underspeed error reached 
at the preceding logic stage of simple digital comparison (334), before 
operating swash drive circuit 150m to produce the unmodulated or maximum 
width, DC rectangular wave pulses. Lesser or zero errors sensed by 
microprocessor 140 result in modulated drive wave pulses of digitally 
proportionally lesser or zero width, respectively. 
So the main speed command signal, modified or unmodified as appropriate, is 
transmitted (in ratio form as the command speed divided by sensed actual 
speed) on to the monitor block 336 which monitors and computes the actual 
ratio. Unimpeded, that command ratio as a digital signal will be 
transmitted through monitor block 336, to compare block 340, and thereupon 
utilized, if necessary, by blocks 350 and 352 or 360 to move the swash 
plate to bring the actual transmission reduction ratio (After Gear 
Reduction/Before Gear Reduction) and the command ratio (Desired Output 
Speed/Actual Engine Speed) into equivalence. 
So now the engine speed has been brought back to the desired speed and so, 
a "No" exists at diamond 334. However, because the command ratio is now 
less than the desired command ratio, i.e., the ratio based on the desired 
ground speed set by the speed lever 22, the system remains in power 
limiting logic mode. A "No" answer also results from compare diamond 335 
and so stable operation results, again at fuel efficiency. 
When the additional load is now reduced, the engine will have a tendency to 
speed up. So now a "Yes" answer will result in compare diamond 335 which 
leads to compare diamond 337 which asks if the commanded ratio is still 
modified, i.e., is it less than the desired command ratio. A "Yes" result 
here leads to modify block 339 which modifies the command ratio for less 
reduction to bring it closer to the desired command ratio. When it reaches 
equivalence with the desired command ratio, a "No" answer will result from 
diamond 337 and the microprocessor will shift into speed mode if the 
engine speed is still higher than the desired engine speed. Until that 
equivalence is satisfied, the microprocessor will be operating exclusively 
in its programmed power logic mode although, in the meantime, the 
suppressed, second speed logic mode earlier mentioned will be continually 
operating entirely subordinate to, and over-controlled by, the 
dominant-priority power logic mode. 
A means can be and preferably is provided in the power limiting logic to 
achieve yet finer control while satisfying the logic paths discussed 
above. This is by use of an integrator circuit to detect the engine speed 
changes indicated by compare diamonds 334 and 335. Thus, the integrator 
accumulates the difference between the actual engine speed and the desired 
engine speed from diamond 334 each time the microprocessor runs through 
its logic and creates a larger and larger negative error, and thus more 
and more modification by modify block 338 until the actual speed equals 
the desired speed and no further error is accumulated. When the compare 
diamond 335 is activated by the engine speed exceeding the desired speed 
and thus produces a positive error, this also is accumulated but reduces 
the negative error, and thus the command ratio modification, until the 
error becomes zero. As before, further positive error results in the 
microprocessor entering the speed mode. 
So in properly subdued tone, the monitor blocks 330 and 332 for the power 
logic as indicated continually monitors the desired engine speed and, as 
represented by compare diamonds 334 and 335, the comparison is continually 
being made to sense when the power logic mode modified signal to the 
transmission has brought the actual engine speed back up to the desired 
engine speed (satisfying the point of least BSFC) and the command ratio up 
to the desired command ratio (satisfying the speed lever 22). When that 
point is sensed, and when the desired engine speed is exceeded with the 
power logic mode remaining satisfied, the microprocessor goes into its 
speed logic mode, bypassing block 338. 
Because the rpms of actual transmission output speed and actual engine 
speed are constantly known, the block 336 representing constant monitoring 
of the actual speed reduction ratio functions in the same way as block 328 
for the command ratio. Therefore, the actual speed reduction ratio from 
block 336 and the command speed reduction ratio from block 328, when 
compared at the step represented by diamond 340, will in the ideal case 
find equivalence of digital signal when the main command signal is 
modified just right. So the cycle will be repeated rapidly again, and 
again, just as soon as the repeat paths 342 and 344, the exit path 346, 
and thence path 348 leading through the microprocessor make their first 
completion. 
In case the engine would speed up beyond its desired speed, as in the 
tractor encountering a downslope, the speed logic mode reacts through the 
blocks 326, 328, 336, compare diamond 340, diamond 350, and modify block 
352 to cause more gear reduction; in other words, the engine speed-up, 
causing point C (FIG. 4A) to be reached, decreases the command ratio by 
raising the denominator, engine speed, so that by comparison the actual 
reduction ratio by staying the same becomes the greater ratio of the two, 
relatively speaking. 
Therefore, as caused by the slight downslope of Example II, the greater 
effective gear reduction required in block 352 is achieved by 
appropriately modifying the actual ratio at that point and the thus 
modified actual ratio signal is transmitted as the new output in path 
354,356 thus changing the proportional coil 134 and swash-plate tilt angle 
into some less positive angular direction to increase the reduction to 
account for the higher engine speed. So the constant ground speed is 
sustained as desired on the slight downslope. If the engine speed 
decreases, as when the tractor levels out, the command ratio will then 
exceed the actual ratio and the signal will go from compare diamond 350 to 
modify block 360 which will modify the ratio to less reduction. To 
maintain the constant ground speed, this operation continues until the 
engine speed comes down to an equilibrium point. 
In contast, consider the foregoing Example I situation in which a higher 
ground speed at the initial 1:1.5 gear reduction ratio was automatically 
temporarily slowed because of an assumed extreme but momentary rimpull 
overload. The predominant primary or power limiting logic caused more gear 
reduction to maintain the engine speed, and suppressed the speed mode 
which would have required less reduction to maintain ground speed. Then 
with the tractor overload past and gone, and with the initial (lower) 
rimpull restored, the microprocessor, still in its power limiting mode, 
because the ground speed is less than the desired speed set by the speed 
lever 22, operates to restore the initial engine speed in the expected 
way, by means of less effective gear reduction (diamond 350, block 360) 
until the initial 1:1.5 is reached, restoring the former BSFC stability. 
The modify block 352 and the just mentioned modify block 360 are referred 
to later in aspects to be discussed of the speed control logic mode of the 
control module. 
MIN. BSFC CURVE--FIG. 7 
The wide open throttle torque curve indicated at 362 in this figure is 
representative of automotive diesel engines in general use, is a 
simulation of the operating characteristics of a commercial International 
Harvester DTI-466B engine. The points JKL indicated on the curve bear 
noting. 
In the prior art, the peak torque point J is crucial to known anti-stall 
controls, whose straightforward purpose is to avoid passing that point of 
operation during engine slowdown because the immediate torque dropoff 
thereafter will stall out the engine and cause it to lose the load. 
Terming that purpose straightforward is for the reason that it is strictly 
negative, to avoid actually reaching the single overload point by 
automatically, just beforehand, downshifting the transmission and slowing 
the vehicle. See "Earth Movers Dig Into Computers," Chilton's Truck & 
Off-Highway Industries, January-February, 1983, pp 33-35 and inset 
article. 
Another prior art notion in vogue in the tractor art is to shift up and 
throttle back, thus going in the direction of losing the load but actually 
stopping short of the torque peak so as to meantime keep safe and yet save 
some fuel. 
The direction taken by the present invention is not so much for merely 
avoiding a single taboo operating point, or for upshifting. The direction 
will be recognized from the power limiting mode hereof as somewhat the 
opposite, to keep down-shifting a variable transmission as it loads up to 
stay on the least BSFC curve as well as for readjusting the power lever 
when needed so that the engine will actually positively follow rather than 
avoid, all points defined by a least BSFC curve. The result is reduced 
fuel consumption. For example, the essentially straight portion of torque 
curve 362 defined at rated power by points K and L will be seen closely to 
parallel the constant 180 HP (135 kW) broken line and the constant 200 HP 
broken line appearing in the FIG. 7 graph. But operating at full-throttle 
as indicated at point K (approximately 190 HP) would consume excess fuel, 
according to the graph. 
What is significant and more desirable, is operating the same way but 
automatically at point L which in some instances will be accomplished at a 
5 percent fuel saving, nevertheless developing about the same 190 HP. That 
fuel saving has been observed in one or more tractors embodying the 
present invention. 
Superimposed on the graph of FIG. 7 are the diagonally upwardly and 
leftwardly extending straight governor curves, starting from the bottom 
for instance as 1000 engine rpm, 1500 engine rpm, 2000 rpm, etc., 
corresponding to different settings of the power lever 18. 
Also superimposed are the known, seemingly concentric constant brake 
specific fuel comsumption curves, rather much centering in regular way 
about the 0.35 curve indicative of 0.35 pounds (0.16 kg) of fuel consumed 
by the engine per horsepower hour. Radially outwardly therefrom appear the 
surrounding curves marked for respectively 0.36 pounds, 0.37 pounds, 0.38 
pounds, 0.40 pounds, 0.42 pounds, and 0.45 pounds (0.20 kg) per horsepower 
hour. 
Returning to the constant horsepower lines (broken), we can perceive that 
the 60 horsepower line is closest to the 0.38 pound curve at only one 
point, the 80 horsepower line is closest to the 0.37 pound curve at only 
one point, and so forth. That resulting pattern of points establishes the 
locus of points for a smooth broken line curve 364 joining all such points 
and being essentially coincident at the upper right end with the 0.35 
pound curve which is the most saving of all in effective fuel utility. It 
follows that such curve 364 is truly representative of near-minimum brake 
specific fuel consumption for the engine throughout the entire range of 
horsepowers enveloped by the wide open throttle torque curve 362 for the 
engine. 
That same locus of points once established according to a figure such as 
FIG. 7 readily transfers to a figure, such as FIG. 4 preceding, as a 
conveniently smooth curve 136 in the latter figure approximating the least 
brake specific fuel consumption and vital to the present control module. 
That curve 136 of FIGS. 4A and 4B represents simply a predetermined 
consecutive series of desired engine speed values productive of 
substantially minimum brake specific fuel consumption for a range of 
engine power settings; so it can be stored in the microprocessor memory as 
a rough table if the memory is somewhat restrictive. With extensive memory 
capability of the microprocessor, the table can be stored with only 
incremental differences in the speed values not requiring interpolation. 
However, with average memory assigned, as contemplated for the present 
microprocessor, reducing the curve 136 in known way to a simple engine 
speed equation will enable the microprocessor constantly to resolve the 
equation for solutions in precise digital terms for each and every setting 
to which the power lever 18 is adjusted. So actual speed becomes a 
function of the power lever setting in the equation, the setting 
constituting the variable control parameter of which the changing values 
are constantly being entered in the equation by the computer for 
recalculation of same. 
The wide open throttle curve of the torque of a combined 
engine-transmission train having infinite variability actually consists of 
an infinite number of curves constituting a family which keeps peaking 
more and more with more speed reduction in the infinitely variable 
transmission; the reason is the torque capability naturally becomes higher 
and higher with succeeding increases in transmission gear reduction ratio. 
POWER TRAIN CURVES--FIG. 8A 
In the graph of this figure with transmission output torque plotted against 
transmission output speed, only three curves appear of the wide open 
throttle torque for the overall engine-transmission combination. 
At the transmission's least speed reduction ratio which is essentially 1:1, 
the torque curve 366 therefor closely approximates the torque curve of the 
engine alone and would be identical thereto if the transmission happened 
to be geared to deliver an exact 1:1 ratio. In the manner as done 
previously, the least BSFC broken line curve 368 is readily superimposed, 
effective during only the approximately 1:1 reduction ratio transmission 
setting. 
Visibly distinct, the overall torque curve 370 is shown constructed for a 
transmission reduction ratio of 1:1.5, which happens conveniently to occur 
when the sun gear, previously discussed, is hydraulically locked against 
retrograde or forward movement. The broken line least BSFC curve 372 is 
readily superimposed appropriate only to that transmission reduction 
ratio. 
Finally, for visual comparison at the other extreme, the overall train 
torque curve 374 represents the condition of the transmission providing 
maximum gear reduction of 1:2.39 for greatly multiplying torque and 
rimpull. The appropriate least BSFC curve is plotted in broken lines at 
376. A pattern of points WXY emerges establishing the locus of least fuel 
consumption points connected by a smooth average curve 378 for the entire 
reduction range of the present speed transmission. 
As viewed in FIG. 8A, the diagonally upwardly and leftwardly directed 
straight broken lines represent the engine governor limited portion of the 
individual overall drive train torque curves of the engine-transmission 
train. As will be seen, during automatic operation, the transmission 
output speed or ground speed does not follow the portion of the curve 
(although the engine does). 
It can be seen that from the zero torque point U on the transmission 
output-speed axis that an increase of torque straight up to point X on the 
reduction range curve 378 will result in minimum brake specific fuel 
consumption for the transmission setting of 1:1.5 speed reduction. If 
increased ground resistance to wheel speed causes the control module 
hereof automatically to provide more gear reduction in the speed 
transmission, the transmission can readily accommodate as the operating 
point viewed graphically rises up the curve 378 toward Y thereon. 
The starting point W for the overall train torque curve WXY can be 
considered typical and represents specifically the assumed initial 
condition of a steady load, a speed lever setting fixed for a 1:1 ratio, 
and a power lever setting fixed for 2000 rpm so that the engine under 
automatic minimum BSFC operation is being run at the corresponding minimum 
BSFC speed of approximately 1650 rpm. To hold to the latter speed, despite 
increases in the steady load, is to hold to near-minimum specific fuel 
consumption. Because BSFC curve 368 has an infinite number of points W 
thereon available as starting points, depending on the power lever 
setting, the family of overall drive train torque curves akin to WXY is of 
infinite number and not attempted to be illustrated. 
EXAMPLE III 
An extreme example now given brings out the full adjustment capability of 
the present automatic power matching train operation. Speed logic is a 
straightforward way of establishing the stabilized initial condition just 
set forth. So in speed logic mode and despite governor droop, and from a 
transmission ratio of roughly 1:1.2 at point V on the FIG. 8A graph, the 
constant ground speed or second mode of operation will continue to change 
the transmission ratio maintaining a constant transmission output speed as 
the torque increases straight up toward operating point W as rimpull load 
is increased. Meanwhile, the engine speed is being slowed by the load to 
the above-assumed 1650 rpm. Thereafter, the power limiting logic mode goes 
into effect automatically as result of the tractor's reaching its load and 
a very slight undershoot of the 1650 rpm point and maintains the tractor 
operating at W as desired on the WXY curve 378. 
Specifically on the reduction range curve 378 for the speed transmission, 
already producing minimum BSFC in the engine, the transmission upon 
encountering increased resistance is caused automatically to introduce 
more gear reduction and, at reaching of the operating point X, the 
transmission will again have the engine operating with minimum BSFC still 
at 1650 rpm, but at an adjusted transmission ratio of 1:1.5. Further 
resistance increase of the tractor load shifts the operating point to 
approach Y, progressing thereto smoothly and always along the reduction 
range curve 378. And the full multiplication of torque, with a torque rise 
by 2.39 times, occurs with the reaching of point Y. 
The significance is that, while on the WXY portion, the engine does not 
lug; it operates always and only on points on the curve WXY at the least 
BSFC, speed, 1650 rpm, and entirely automatically with the same power 
setting and with no change from or intervention by the operator. 
The return pattern, on the same curve W,X,Y equally efficiently, begins as 
soon as the resistance no longer requires the extreme of 2.39 torque 
multiplication for sufficient rimpull of the tractor. The striking part to 
the operator, however, is progress in direction of the arrows on the 
reduction range, smooth curve 378 where he never detects the engine 
laboring even though tractor speed naturally slows during a stretch of 
highly burdensome soil resistance. It will be appreciated from the 
contrasting operation, that in constant ground speed mode, as from point V 
to W, for example, least BSFC is not maintained. 
EXAMPLE IV 
There is a relationship between the modify block 360 of flow diagram FIG. 
6A and the transition indicated by arrows from point V straight up to 
point W in FIG. 8A. The control module operates in the second constant 
ground speed mode beginning at point V where it compares actual ratio with 
the command ratio and finds that, under increasing torque loading and as 
the engine slows down, the actual ratio is the lesser. So less actual gear 
reduction is required than the existing 1:1.2 ratio and the transmission 
moves toward establishing a 1:1 gear reduction ratio by the time the 
operating point W is reached, all progressively so as to maintain constant 
speed in the speed mode for reaching point W, FIG. 8A. Therefore, the 
so-called governor droop illustrated by the natural, broken line, diagonal 
governor curves is avoided because there is no droop in the constant 
ground-speed mode of the microprocessor. 
EXAMPLE V 
The transmission in its secondary speed mode also desirably operates in the 
opposite direction, and autoically does so according to modify block 352 
in flow chart FIG. 6A, in going through the opposite transition from point 
W straight down at constant speed toward the aligned zero torque point V, 
FIG. 8A. The circumstance is the gradual removal of appreciable 
torque-loading on the transmission and a thus increased engine speed so 
that the actual ratio sensed is greater than the command ratio and is 
readily determined according to the notation between compare diamond 350 
and modify block 352, FIG. 6A. So, counter to the direction of the arrows, 
and with constant ground speed maintained between W and V, FIG. 8A, the 
automatic operation changes the transmission from 1:1 at W to a 1:1.2 at V 
for more gear reduction to counteract the natural loss-of-load speed-up of 
the engine; the slowing-down transmission and unloaded engine speed-up 
will offset one another, with constant ground speed maintained all during 
the transition. 
By flow chart, FIG. 6A, the step represented by block 352 is to modify the 
command ratio starting at that point W and the thus modified command ratio 
signal is transmitted as new output in paths 354 and 356, thus changing 
the proportioning coil 134 and swash plate tilt angle into some less 
positive angular direction for more effective gear reduction. 
EXAMPLE VI 
This example is merely cumulative to Example II preceding, but importantly 
illustrates what can be carried to an extreme situation very possibly 
encountered. Let it be assumed that the present tractor is proceeding 
easily on a slight slope with a heavy wagon lightly in tow, with the power 
train automatically operating with practically no reduction, let us say a 
ratio of 1:1 for simplicity. The tractor and tow immediately encounter an 
extended severe downhill condition so as to operate at some unmarked point 
vertically over point C, FIG. 4A; such point in fact would be a motoring 
point above no load curve 138, that is, the wagon is pushing the tractor. 
The power mode is fully satisfied because the control sensors of the 
microprocessor serve only to assure it, while in that mode, that the 
actual engine speed is kept up to desired speed or, in graphical terms, 
that speed remains on or above the power match curve 136 in FIG. 4A and 
the ground speed is at the desired speed. 
Due, therefore, to the relative decrease of command ratio in this assumed 
situation, the actual ratio by comparison becomes the larger of the two 
and gives rise to a signal which can be represented by the reaction of 
block 352 as required in the FIG. 6A flow chart. Consequently, as the 
rolling wagon tends to force the tractor downhill faster, a modified 
command ratio signal from block 352 is transmitted in paths 354,356 to 
cause the swash plate to establish more and more effective gear reduction 
up to approximately a 1:2 or perhaps a 1:2.39 ratio. The engine is thus 
being motored to increasing speeds through the transmission by the wagon 
and tractor due to their downhill coast. So the full braking capability of 
the engine is brought to bear automatically in the speed mode to ensure 
positive vehicle control. 
By way of departure from the earlier presumption of the range transmission 
always being in the medium or mid range M, it remains entirely in the 
operator's province to upshift and downshift at will (FIG. 3), as when the 
speed transmission is approaching full positive angularity in its speed 
overlap with the HI range or full negative angularity in overlapping the 
LO range (FIG. 2). So when the load becomes such that the speed 
transmission's range can no longer automatically accommodate to achieve 
near-minimum BSFC, the way is always open for the operator readily to 
restore the speed transmission to within its effective speed ratio range 
by shifting into HI for the lesser rimpull loadings or into LO for any 
excessive loadings. 
Or an easier way is open, for effecting rather substantial changes, through 
power lever adjustment which can readily be brought about automatically to 
restore the near-minimum BSFC and constant ground speed operation desired. 
Novelty is felt to reside in the herein recognized utility to set power 
according to requirements in terms of its specific fuel consumption and 
the maintenance of constant ground speed and in the automatic module 
approach herein for automatically satisfying that utility as can be 
graphically appreciated. 
AUTOMATIC POWER SETTING FOR MINIMUM BSFC 
FIG. 4B enlarges a portion of the FIG. 4A graph of actual engine speed 
plotted against engine power lever or throttle setting. On the power match 
curve 136, the illustrative point A represents the power match point at 
which a power lever setting of 1950 rpm produces an engine speed of about 
1800 rpm if sufficiently loaded to be in the power limiting mode. This 
steady match between load power required and engine power delivery at 
minimum BSFC is ideally desired and would hold, except that some 
operational variable will inevitably change. 
EXAMPLE VII 
If, while the power train graphed is operating at matched power point A, a 
significant decrease in soil resistance or a moderate downslope or both 
are encountered, the control module 24 is capable of entering into an 
operating mode reducing the power lever setting. This occurs automatically 
when the speed of the more lightly loaded engine increases toward the no 
load condition curve 138 toward point E, which is entirely outside, on the 
high speed side, of a power lever deadband 380 graphically appearing as a 
cross-hatched envelope above, and parallel with, the power match curve 
136. The so-called width of the deadband is illustratively shown as 
amounting to about +50 above all corresponding points on the curve 136. 
The deadband does not extend below the curve 136. 
More particularly, as the sensed engine speed increases above the deadband 
380 for the power lever, and at the same time that the speed mode is 
adjusting the transmission ratio to maintain constant tractor ground 
speed, the control module 24 also begins to cause a power lever setting 
reduction which continues until the engine reaches that reduced setting 
where the load is precisely sufficient to bring engine speed directly down 
into intersection with the deadband 380 as indicated at the desired point 
F. 
At or just below this new operating point F, the module 24 continues in its 
regular speed mode of operation to keep the transmission adjusted for the 
new power setting, to maintain constant tractor ground speed at the 
desired speed as long as the engine speed is no lower than its point of 
intersection with the closely adjacent power match curve 136. The control 
module 24 is rendered more sensitive in its speed mode for doing all the 
fine tuning so to speak, that is, while automatically adjusting the 
transmission ratio in incremental amounts within the range graphed. It 
should be noted that the point E can only be reached transiently and is 
not a steady state operating point. 
EXAMPLE VIII 
In this contrasting example, and from operating point A at the outset, let 
us assume the plowing resistance of the soil increases which would cause 
engine speed to drop transiently toward the level point B, below the power 
match curve 136. The control module 24, in its power limiting mode 
described above, immediately begins to change the transmission ratio for 
more reduction to raise the engine speed to its optimum BSFC point A, 
which effectively reduces the transmission output speed or ground speed. 
The control module 24 further senses the change in transmission ratio 
beyond a deadband 381 (FIG. 8B) and causes a power setting advance. 
When the power lever setting is advanced, the engine accelerates and the 
engine speed exceeds the power match curve 136 shifting the command module 
into the speed mode which increases the transmission reduction to account 
for the increased engine speed. Within the deadband envelope 381, the 
desired transmission output or ground speed becomes equal to the actual 
output or ground speed and so a new steady state operating point H is 
reached at the left side of the deadband 381 shown in FIG. 8B with the 
engine operating at a new minimum BSFC point H on the power match curve 
FIG. 4B. 
If, from this stable operating point, the load decreases slightly, the 
control module 24 will shift into power limiting mode and cause the drive 
train to first cross the deadband to the desired speed line VW in FIG. 8B 
and then shift into the speed mode as described above. When the automatic 
power lever setting is engaged, the drive train will not follow the curve 
WXY of FIG. 8A beyond the width of the deadband. Rather, it will adjust 
for increased loads by increasing the power lever setting until it reaches 
the maximum setting at point Z' at which point, the drive train will 
follow, as indicated by the arrows in FIG. 8B, the curve 374 or Z'Y' upon 
further increases in load. Once beyond the point Z', a decrease in load 
will cause the drive train to follow the path Y'ZWV with the power lever 
setting automatically adjusting down as the engine speed increases above 
the deadband 380 of FIG. 4B as explained in the preceding example. 
Again, incremental adjustments will be fine tuned into the power train 
through appropriate incremental transmission ratio changes by the module, 
which is more sensitive in its power limiting and speed modes compared to 
when it causes power setting changes. 
Because it constantly monitors actual engine speed and constantly monitors 
the nominal power setting, the control module 24 can not only program the 
power setting for minimum BSFC but also is provided with power means for 
automatically changing the power lever position at least part way toward 
such a setting. 
POWER LEVER MOTOR CONTROL--FIGS. 1 and 5 
As shown electrically connected to the output leads 81 of the control 
module 24, a preferred power means is a reversible DC motor 83 which is 
shaft-connected to mechanically pivot the power lever 18 into various 
positions throughout its range of power settings. A manual switch MS, 
identified by reference numeral 137 in FIG. 5, when closed connects B+ 
power to energize a motor circuit 150n controlling the output leads 81 to 
the motor. When the manual switch 137 is open, the power lever is only 
manually controlled as described above. The motor control circuit 150n is 
to be considered substantially identical to the companion circuit 150m for 
the swash plate control. 
The built-in protection and safeguards described for circuit 150m as it 
accurately controls the swash plate tilt angle afford the same benefits to 
the identical circuit 150n as it equally accurately controls the pivot 
angle of the power lever. 
In actual practice, however, the power lever will have a motor control 
circuit, not shown, and a reversible, single speed slow DC motor, of 
greatly simplified design compared to control circuits 150m and 150n. The 
reason is the requirement in practice that the microprocessor 140 have 
high sensitivity in the power and speed modes and that the proportionally 
moving swash plate actuator 26 have correspondingly high responsiveness, 
i.e., in 0.3 seconds, execute full travel from one extreme tilt angle to 
the opposite extreme, and vice versa. On the other hand the power lever 18 
will take 10 seconds, motor time, to be driven thereby at constant speed 
through full travel, either way; hence due to this relative insensitivity 
and more deliberate response, the simplified circuit just suggested and 
not shown, can operate a simple DC reversing switch to the lever motor but 
the circuit preferably will incorporate the same protection and safeguards 
previously mentioned, and be rendered fool-proof to a like extent. 
The high responsiveness of the swash plate actuator 26 to change the 
transmission ratio compared to the slow response of the power lever 
control motor 83 establishes a priority in the manner in which the control 
apparatus as a whole adjusts to varying conditions of load and/or desired 
ground speed. Thus, when a sufficiently large deviation in ground speed 
from the desired value exists, the control apparatus will simultaneously 
adjust the transmission ratio, in the power limiting mode described above, 
as well as the power lever setting to reduce the deviation. Because of the 
relative response times, the transmission ratio adjustments will bear the 
brunt of this correction. When the deviation results in an increase of 
engine speed beyond the desired value, the speed mode of the transmission 
control will maintain a constant ground speed while the power lever 
control will correct engine speed deviation, both controls acting 
relatively independently. 
Exhibiting flexibility in the same vein as in its power and speed modes of 
operation, the control module 24 as shown in FIG. 5 is not confined to any 
set number of steps or sequence or order for automatic power lever 
operation, although for ease of understanding, the flow chart approach 
will now be used, simply by way of one example and not limitation. 
POWER CONTROL FLOW CHART--FIGS. 6A+6B COMBINED THRU 344 RE-ROUTE PATH 
Devoted exclusively to showing the automatic power lever control logic, 
FIG. 6B is outlined by the referred to non-involvement path 342,344,346 
representing the condition in which the power lever adjustment logic 
remains fully satisfied, manifested by the power lever marking time. But 
by following path 342 through interconnecting diamonds 382 and 384, by way 
of just noting them in passing, thence to underratio comparison diamond 
386, one can see from the legend identifying the latter 386 the capability 
of the microprocessor to constantly monitor the command ratio for every 
deviation of more than 2 percent below the command ratio for the desired 
ground speed, i.e., the desired command ratio, that is, 2 percent of the 
possible range of the transmission ratio. 
Continuing by following the path from 386 through interconnecting diamonds 
388 and 390, by way of noting them in passing, thence to overspeed 
comparison diamond 392, one can see from the labeling on the latter, the 
further capability of the microprocessor to constantly monitor actual 
engine speed for every deviation in speed in excess of 50 rpm above the 
desired speed being calculated. The mentioned deviations, both ways, 
permitted by the automatic power control for each power setting establish 
the previously discussed deadbands 381 and 380 respectively now to be 
treated in detail. 
OPERATION UTILIZING POWER SETTING DEADBAND--FIG. 6B 
So long as underratio comparison in diamond 386 by the microprocessor shows 
the command ratio to be below but within the 2 percent (based on the ratio 
range) of the desired command ratio determined by the microprocessor, then 
according to the No answer from comparison diamond 386, the automatic 
power control will be satisfied and not activate. On the other hand, with 
the underratio detected as going more than 2 percent below the desired 
command ratio, the microprocessor logic from diamond 386 follows the Yes 
path 394 through an interconnecting throttle diamond 396, by way of just 
noting it in passing, thence to the increase throttle block 398. According 
to the flow chart, therefore, the step represented by the block 398 is for 
the microprocessor to signal for a greater power setting. So the 
microprocessor is programmed to run the lever motor to pivot the throttle 
or power lever 18 for sufficient power increase to eliminate the degree of 
underratio back to at least within 2 percent of the desired command ratio. 
According to the No answer, FIG. 6B, from the overspeed comparison diamond 
392, the automatic power control logic remains satisfied so long as the 
actual engine speed stays within 50 rpm of the desired speed. But with 
each overspeed in excess of 50 rpm, the microprocessor logic conforms to 
the Yes path 402 from diamond 392 through interconnecting diamonds 
404,408, by way of just noting them in passing, thence to throttle 
decrease block 410. So the microprocessor is programmed to run the lever 
motor and reduce throttle or power lever 18 until excess overspeed is 
eliminated down to within 50 rpm above the desired engine speed. 
The microprocessor 140 has further utility now to be explained. 
FIG. 6B--PROGRAMMED SAFEGUARDS IN MICROPROCESSOR LOGIC 
The consecutively connected gear diamond 382 and clutch diamond 384, 
together with their respective No and Yes paths for the logic involved, 
are operatively associated respectively with the out-of-neutral switch 133 
shown in FIG. 3, and the normally open, clutch pressure switch 97 shown in 
FIG. 1. The switch input, by appropriate but unshown input connections to 
the microprocessor 140, is constantly monitored by the latter as one of 
its important safeguard functions presently to be considered. 
When either or both of the switches 135 and 97 dictate it, the 
microprocessor puts the automatic power control in inactive status, i.e., 
because of switch 135 closing to indicate a neutral transmission 28 or 
because of switch 97 closing to indicate a disengaged master clutch 92. In 
other words, the logic path is No from gear diamond 382 or from clutch 
diamond 384, or both, and so the normal power lever control logic is 
overruled and must be so overruled because the engine cannot be loaded 
through the interrupted power train. If allowed at this point to become 
active, the automatic power control would keep sensing overspeed in the 
engine running free of load, and keep slowing it down, ultimately to 50 
rpm above low idle despite the operator desiring a higher speed, for 
example, to set the tractor in motor from standstill. 
A Yes answer in the logic path from gear diamond 382 in conjunction with a 
Yes answer in the logic path from clutch diamond 384 represents the right 
combination of conditions for automatic power control, that is, the 
out-of-neutral switch 133 opens to indicate the range transmission is in 
gear and the normally open pressure switch 97 opens to indicate release of 
the clutch pedal and full clutch engagement. So the power lever requires 
control, now that the engine is coupled to load. 
There is an operating point, for example, point W on FIGS. 8A or 8B, at 
which the speed transmission reaches its maximum commanded ratio 
condition, i.e., producing least effective gear reduction occurring at 
+17.degree. swash angle, and the sensing of which is represented by the 
commanded diamond 388 is interrelated with underratio comparison diamond 
386, directly in the latter's No. path, and is also interrelated with 
overspeed comparison diamond 392 by way of the immediately intervening 
high idle safeguard diamond 390. Therefore when the underratio function 
has a satisfied condition (No from 386) sending out no signal, the 
next-in-logic-sequence commanded ratio, diamond 388 will be afforded the 
Yes path as illustrated leading through safeguard diamond 390, path 394, 
throttle diamond 396, thence to throttle increase block 398; the resulting 
increased throttle increases the engine speed and causes the speed mode in 
the microprocessor to react by increasing the gear reduction to maintain 
constant ground speed, deswashing the speed transmission back from the 
+17.degree. extreme tilt angularity, thereby providing some range for 
future change in the transmission ratio. 
To explain it graphically by returning momentarily to FIG. 8a, with the 
increase in throttle, the points WXY and the curve between them shifts 
parallelly upward along the curves 368,372,376. However, since the load on 
the tractor and the desired ground speed have not changed, the drive train 
operating point remains in the same position on the graph as before, on 
the vertical line VW, but is now slightly below a newly established power 
limiting logic curve WXY and is therefore in the speed mode. 
The effect of commanded block 388 is limited, on the one hand, by its 
resolution, i.e., how close does the commanded ratio have to be to the 
maximum commanded ratio to get a Yes, and, on the other hand, by block 392 
which will automatically reduce the power lever setting if the engine 
speed exceeds 50 rpm over the desired engine speed. 
The reason for the assurance that engine speed stays below, or at most at, 
2700 rpm, the sensing of which is represented by high idle diamond 390 
that is in safeguard position to commanded diamond 388, is to establish 
maximum engine operating speed which, for the engine in question, is 2700 
rpm. So as illustrated, the Yes path from diamond 388 indicating extreme 
(+17.degree.) plate angularity requires that engine speed simultaneously 
be less than the 2700 allowed maximum rpm in order for the Yes path from 
safeguard diamond 390 to show a call for increased throttle to speed up 
the engine. Of course, the 2700 rpm could be some number over high idle to 
prevent transient actuation of diamond 390. 
The No path from commanded diamond 388 and the No path from high idle 
diamond 390 are illustrated to indicate that overspeed logic becomes 
effective, as represented by overspeed comparison diamond 392, as soon as 
either one has a No; that is to say, the commanded ratio relationship is 
compatible with slowing the engine by being less than maximum ratio or, if 
already at maximum, the (overriding) attainment by the engine of its top 
allowable operating speed will find full compatibility to an engine being 
slowed in speed, for whatever reason the programming might call for. 
Thereupon the microprocessor as programmed can start applying its 
overspeed logic for appropriately decreasing throttle to alleviate the 
overspeed conditions when they occur. 
The intervening swash diamond 404 as shown located in FIG. 6B between 
overspeed diamond 392 and the block 410, representing throttle decrease, 
evidences that the microprocessor logic requires that the commanded ratio 
sensed be less than maximum in order for the Yes path from diamond 404 to 
allow the overspeed control to decrease the throttle. In other words, the 
overspeed condition is not allowed to throttle down the engine, at the 
same time that the swash angle reading being monitored by the 
microprocessor shows the speed transmission to be then running at maximum 
commanded ratio (least mechanical advantage) at high idle speed while the 
microprocessor is operating in speed mode. 
The rpm diamond 406, representing the engine safeguard logic which protects 
when the engine is being motored, as by a trailer in a downhill condition 
such as example VI above, has a No path which according to FIG. 6B goes to 
the right and exits with no signal, when engine speed is below 2800 rpm. 
Yet the Yes path from 406 indicates that the throttle decrease step 
represented by block 410 goes on automatically until the motoring of the 
engine reduces to a speed below 2800 rpm. 
The No path from overspeed comparaison diamond 392 and the No path from 
swash diamond 404 properly indicate that the motored top speed logic limit 
becomes effective, as represented by the 2800 rpm diamond 406, as soon as 
either one is sensed as the first No to occur; that is to say, the 
overspeed comparison finds compatibility with motored overspeeding by 
being less than the +50 rpm in excess or, if already in excess by more 
than the +50 rpm, the (overriding) attainment by the commanded ratio 
reaching maximum (minimum effective gear reduction ratio) will find full 
compatibility with motored overspeeding and the need to throttle down the 
engine. Thereupon the microprocessor as programmed retards (at 410) the 
power lever to avoid adding fuel to the engine which is being motored 
thereby enhancing its engine braking. 
The reason for throttle monitoring as represented by maximum throttle 
diamond 396 and by minimum throttle diamond 408 in their No and Yes paths 
of association ahead of the powered throttle change blocks 398,410, 
respectively, can be explained in a few words. The microprocessor logic 
herein requires no unnecessary act, and so no throttle increase or 
decrease signals will be allowed when the power lever already occupies the 
maximum or minimum settings, respectively. 
The overspeed comparison and underratio comparison programming described so 
far has required the microprocessor internally to have a main overspeed 
circuit and a main underratio circuit, each operating on three counts 
which corresponds to the 50 rpm and 2 percent deviations, for accuracy 
which has proven satisfactory in the field. Reaching the third count, 
either upward from power match curve 136, FIG. 4B, or leftward from 
transmission output speed line VWZ in FIG. 8B means that the deadband 380 
or 381 is no longer effective because it has been crossed. So there will 
be automatic power control with any further deviation in engine or 
transmission output speed respectively, to bring the operating point back 
to the adjacent edge of the deadband on the graph. 
From the foregoing it can be appreciated that the automatic power control 
is merely augmental to the much more sensitive power limiting mode or 
speed mode, both operating from four principal signals. The power lever is 
the source of the first signal because its setting is being constantly 
monitored, and the speed lever is the source of the second signal because 
its setting, too, is being constantly monitored. The third signal 
developed is proportional to the common engine-transmission-input speed, 
and these three signals enable the microprocessor accurately to dictate 
how the transmission speed reduction ratio is changed in response to a 
speed error detected between the third speed signal and a desired engine 
speed signal computed as a constant recalculation by the computer; the 
fourth signal, of course, is the conveniently taken transmission output 
speed value digitally necessary in the computer for determining the 
commanded ratio which the changed speed reduction ratio must match and its 
deviation from the desired commanded ratio. 
Then, from a less sensitive and less responsive area of operation, not only 
dominated by transmission control priority requirements but also dominated 
by a conspicuous deadband system, the automatic power control comes on, 
due to the four signals enabling the microprocessor accurately to dictate 
how the automatic power control is to change the power lever setting in 
response to the speed band error or the commanded ratio error. 
Besides applying torque to the rest of the power train including the drive 
axles illustrated herein, the engine of the present power train separately 
but equally effectively drives the conventional single speed or dual speed 
power take-off (PTO) shaft of the tractor, now shown. The control module 
does not affect the PTO output although the effect of the PTO and air 
conditioning and other loadings about the tractor is included in the 
control module's operation. In other words, the two sensors of speed and 
other sensors hereof take into account all engine loading for engine 
optimization automatically with the sequential transmission ratio setting 
and automatic power setting. 
The load on the farm tractor, from the auxiliaries just mentioned and on 
the drawbar, varies considerably with the nature of the work which 
includes, of course, merely towing a wagon or idle machinery. On a long 
downslope where the drawbar pull becomes negative and the tow and tractor 
develop a momentum motoring the tractor engine, the electrical circuit of 
the power lever motor 83 and the electrical hydraulic circuit of the swash 
actuator 26, FIG. 1, automatically establish cooperation offsetting 
excessive engine speeds, as exemplified below. 
EXAMPLE IX 
The effect of sustained rolling downgrade by the tow and tractor is to 
increase engine speed and ground speed. Programmed to keep the ground 
speed constant in speed mode in the manner described, the automatic 
transmission control sets the ratio eventually for maximum; the ultimate 
effect is that the tractor axles are forced to drive the engine through 
equivalent step-up gearing at an effective speed increasing ratio of 
2.39:1. And by its desired complementary action, the automatic power 
control sets the engine throttle eventually to a low fuel rate for some 
minimum rate of engine rpm. The engine braking, due primarily to pumping 
losses, affords positive vehicle control because the tractor axles in 
order to turn are forced to drive a persisting load and must do so only 
through high ratio step-up gearing. 
EXAMPLE X 
Drawbar pull can require in cases 50% to 80% of engine power in a farm 
tractor, as in drawing a disk harrow, or a much less percentage in a level 
towing operation. The automatic transmission control can, within the range 
of drawbar power requirements herein contemplated, automatically establish 
near-minimum BSFC at infinitely adjustable speeds within the range of 
approximately 3 to 8 miles per hour (mph) ground speed or 4.8 km/hr. to 
12.8 km/hr., all in a mid range setting of the range transmission, now 
shown. The synergistic effect of the automatic power control when coupled 
therewith is to afford infinite speed adjustability within the larger 
ground speed range of approximately 1.5 to 8 mph (2.4 to 12.8 kM/hr.); 
this effect, with a constant view to achieving least BSFC, is obviously 
separate in its view from the synergism apparent in preceding Example X, 
which is accomplished with an eye toward positive vehicle control during 
sustained coasting, without the least regard to BSFC. 
It is evident the invention applies equally to other continuously variable 
transmissions (CVT's) including the lower horsepower, belt drive type, 
continuously variable mechanical transmissions. Also the present 
principles apply with equal force to further engine-CVT power trains, 
hydrostatic and hydromechanical and others. Although perhaps not ideal for 
maintaining the engine exactly on the least BSFC curve, the invention can 
also be applied to step change power shift transmissions. Indeed, given 
enough gears, a power shift transmission eventually approaches a 
continuously variable transmission.