Locomotive governor control

A digital processor implemented electronic governor for engine-generator units including a first control loop for producing a speed error and controlling fuel delivery setting as a function thereof and a second control loop for detecting rack error and producing a field excitation current control signal as a function thereof. Power dips and overruns are voided by modifying rack error as a function of engine acceleration. Means are provided for developing speed errors and rack control signals despite a breakdown in the rack position indicator. Open loop lower power setting controls are provided. Wheel-slip control, power limiting and variable acceleration functions are provided.

DESCRIPTION 
Technical Field 
This invention relates to control systems, often called "governors", for 
engine-generator units and particularly to an electronic governor which 
provides improved performance characteristics for engine-generator units. 
BACKGROUND OF THE INVENTION 
The term "engine-generator unit", as used in this patent specification, 
refers to the combination of a fuel burning engine and an electrical 
generator mechanically connected to the engine to be driven thereby. The 
engine may be a turbine, diesel or gas internal combustion engine, 
alcohol, methanol or mixed fuel engine or any other fuel burning engine, 
the speed and power output of which may be controlled through variations 
in the fuel delivery rate. The electrical generator may also vary 
considerably in physical characteristic, but in all cases is subject to 
output power control through field excitation level. 
Engine-generator units are found in numerous applications, including 
diesel-electric locomotives, trucks, earth-moving and off-road vehicles 
having traction motor drives and in stationary and mobile power generating 
stations. Although in some applications, relatively simple mechanical 
isochronous governors will suffice, engine-generator units which are used 
in applications presenting wide variations in load and frequent 
transitions between load and or speed settings present a complex control 
problem. For example, transitions between power settings and/or load 
requirements in a diesel locomotive often result in smoking due to a lack 
of proper correlation between fuel delivery rate and engine speed. In 
addition, a transition in power demand can and typically does produce a 
response such as a power dip or overrun which is opposite in sense to the 
operator-generated command. These and other adverse characteristics have 
been typical of prior art systems. 
SUMMARY OF THE INVENTION 
According to one aspect of the present invention an improved electronic 
governor characterized by improved efficiency in the operation of an 
engine-generator unit is provided. In general this is accomplished in a 
system which includes means such as an operator or program controlled 
device for establishing a power setting, a speed calculator for deriving a 
speed error signal as function of the power selector setting and the 
actual engine speed and for applying an output which is a function of the 
speed error signal to the fuel delivery rate control, and a power setting 
calculator for deriving a second error signal as a function of actual 
engine speed and actual fuel delivery rate control setting and for 
applying an output which is a function of the second error signal to the 
field current or field excitation control device. Throughout the following 
specification the first calculator is typically referred to as a "speed 
calculator" or "speed loop" and the second calculator is typically 
referred to as a "rack calculator" or a "power control loop". The overall 
result of the invention is a speed dominated system capable of producing 
optimum speed, fuel delivery and power settings at all times. 
According to a second aspect of the invention an electronic governor 
capable of providing improved objective operator response characteristics 
under changing load and changing power setting conditions is provided. In 
general this is accomplished in a system of the type described above by 
providing an input to the power control loop or rack calculator which is a 
function of engine acceleration and which modifies or overrides the actual 
fuel delivery rate setting to prevent power dips or overruns which are 
characteristic of prior art systems. 
According to a third aspect of the invention a control system or electronic 
governor capable of flexibility in accommodating the performance 
characteristics of a given engine-generator unit is provided. In general 
this is accomplished in a system of the type described above by 
implementing the calculators as digital processors capable of accessing a 
memory or combination of memories, storing appropriate control equations 
(loop transfer functions) and also a set of constants which are 
empirically determined from operation of each individual engine generator 
units. In the preferred form the memory or combination of memories is 
sub-divided physically so that the empirically determined constants may be 
added in a modular fashion to an otherwise complete and pre-programmed 
control system. 
In accordance with a fourth aspect of the invention irregularities in low 
power setting operation due to the switching on and off of parasitic 
(accessory) loads on the engine is avoided. This may be accomplished by 
means for sensing the existence of a low power setting in the operator or 
program controlled device and effectively bypassing the field current 
control loop and providing a fixed field excitation value which has been 
precalculated to correspond to a particular low power setting. 
Alternatively, this may be accomplished by measuring the parameters of 
power output of the generator to calculate an appropriate signal to the 
field current control loop which is not affected by the variations in 
parasitic loads. 
According to a fifth aspect of the invention a method of accurately and 
efficiently controlling the operation of an engine-generator unit of the 
type having rack position (fuel delivery rate) and field current controls 
is provided. In general this is accomplished in a method which comprises 
the steps of: 
(a) generating a power setting signal; 
(b) developing a desired speed signal; 
(c) developing a speed error from a comparison of the desired speed signal 
and an actual speed signal; 
(d) setting the rack control as a complex function of the speed error; 
(e) developing a desired rack signal from the actual speed; 
(f) developing a rack error signal from a comparison of desired rack and 
actual rack; and 
(g) setting field current as a complex function of the rack error. 
According to a sixth aspect of the invention a method of avoiding power 
dips and overruns due to power demand transitions in an engine-generator 
unit is provided. In general this is accomplished in a method which 
involves the steps of generating an error signal which controls field 
current setting from a combination of a desired rack signal derived from 
actual engine speed, an actual rack position signal and a signal 
proportional to engine acceleration, the latter signal being combined in 
opposition to the actual rack signal and in which the correct relationship 
to the desired rack signal is obtained. The result is a system response to 
a power increase command, for example, which produces an immediate field 
excitation increase despite the fact that engine inertia might produce a 
less rapid increase in the desired rack signal which is derived as a 
function of actual engine speed. During an increase in engine speed, the 
amount of rack required just to accelerate the system inertia is 
subtracted from the measured rack so that the resulting measured rack is a 
true representation of the net power being output by the engine. 
These and other features and advantages of the invention will be best 
appreciated and understood from a reading of the following specification 
which describes in detail an illustrative embodiment of the invention.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENT 
Referring to FIG. 1 a diesel fueled engine 10 having a rack actuator 12 for 
controlling fuel delivery rate setting is mechanically connected to drive 
a generator 14 having a variably excitable field winding 16 which controls 
the power output thereof. The generator is electrically connected to a 
variable electrical load 18 which, as hereinafter described, may take 
variety of forms ranging from traction motors to numerous other variable 
electrical loads. The engine 10 and generator 14 is hereinafter referred 
to as the engine generator unit 10,14. The engine generator unit 10,14 is 
connected to be controlled by an electronic governor 20 having a power 
setting device 22 which may be manually controlled by a human operator or 
automatically controlled by a program, or semi-automatically controlled 
using open loop inputs such as from trackside waystations or the like. The 
power setting of the device 22 is typically implemented to be advanced in 
steps or "notches" and may comprise a system of electrical switches which 
produce a mathematically encoded four-bit output signal for power settings 
from 0-8, 0-16, or whatever numerical sequence suits the particular 
application. The power setting device 22 can alternatively comprise a 
system which produces a signal proportional to the desired power setting 
as will be apparent to those skilled in the art using any number of known 
devices. Governor 20 further comprises a speed calculator or speed control 
loop 24 which controls the position of the rack actuator 12 and hence the 
fuel delivery rate. Governor 20 further comprises a rack calculator or 
power control loop 26 which calculates a field current setting and applies 
it to an amplifier 28 for establishing the value of the current through 
the generator field excitation winding 16. 
Describing the system of FIG. 1 in greater detail, the four-bit signal from 
the power setting device 22 or an appropriately converted signal from the 
proportional version of power setting device 22 is connected to a look-up 
table 30 preferably implemented using a read only memory (ROM) to generate 
a desired engine speed signal for each of the various notches or power 
settings available in the device 22. The desired speed signal which is 
output from look-up table 30 is applied to the positive input of a summer 
32 which forms a part of the speed calculator 24. The negative input to 
summer 32 is a measured engine speed signal and is derived from a 
tachometer 34 actuated by the diesel engine 10 and having an output line 
36. The difference between the desired and the measured speed signals is a 
speed error signal e.sub.N which is connected as the input to a digital 
processor 38 bearing the legend "speed computer". The speed computer 38 is 
a state of the art digital processor such as the Motorola 6803 and has a 
signal transfer characteristic which is a complex function of the speed 
error signal; i.e. "PID" function indicating an output signal which 
contains a component proportional to the speed error, a component 
proportional to the derivative of the speed error, and a component 
proportional to the integral of the speed error over time or iteration 
loops. Speed computer 38 is connected to access a memory 40 in which in 
the formula or results of calculations may be stored. The memory 40 is 
preferably sub-divided into a random access portion 40a and an add-on ROM 
40b which contains certain constants hereinafter defined which are unique 
to the particular engine 10 and generator 14 and which effectively tailor 
the governor 20 to the "personality" of the particular unit. Hence memory 
module 40b is hereinafter referred to as the "personality module". 
The output of the speed computer 38 is connected to control the rack 
actuator 12 to create a fuel delivery rate which will provide an output 
power which will maintain the engine speed corresponding to the speed 
demand signal created by device 22. As will be understood by those skilled 
in the art, the term "rack" is used to refer to a mechanical component of 
fuel delivery systems used in diesel engines. If other types of fuel 
burning engines are substituted for the diesel engine 10, the character of 
the rack actuator 12 will change accordingly. The position of the rack is 
indicated by a signal from rack position indicator 41. 
Tachometer 34 is also connected by way of signal line 42 to a second 
look-up table 44 which forms part of the rack calculator 26. Look-up table 
44 follows the table of FIG. 2 in providing a plurality of pre-programmed 
desired rack position signals which are known to result in optimum fuel 
efficiency in the diesel engine 10 under normal operating conditions. 
Interpolation between these fixed points is provided as hereinafter 
described. The result is an output from table 44 representing desired rack 
position. The signal is applied to a first positive input of a signal 
summer 46. A negative input to the summer 46 is received over line 48 from 
the rack actuator 12 and represents actual rack position. As will be 
apparent to those skilled in the art a signal representing the actual 
position of the mechanical device is readily generated using any number of 
known devices. A second positive input to the summer 46 is derived from 
the tachometer 34 and operated on to represent acceleration of the engine 
10. This signal is applied to the summer 46 in a sense which aids or adds 
to the desired rack signal and which opposes the actual rack signal to 
provide improved accelerational or transitional performance 
characteristics as hereinafter described. The output for the sum of the 
signals applied to the summer 46 appears on line 52 and represents rack 
error e.sub.R. This signal is applied to a rack computer 54 which is 
similar to the speed computer 38 in its physical implementation and is 
further similar in having a pre-programmed transfer characteristic which 
is a complex function comprising at least a first factor which is directly 
proportional to the rack error signal, a second factor which is 
proportional to the differential of the rack error signal, and a third 
factor which is proportional to the sum or integral of rack error over a 
number of iterations or loop calculations times. Computer 54, like 
computer 38, is connected to access the memory 40 and to obtain 
empirically determined constants from the personality module 40b for 
calculation purposes. It is to be understood that although the speed and 
rack computers 38 and 54 are shown as physically separate devices, they 
may also be implemented using concatenated processing times in a single 
processor. Similarly, while the memory 40 (including the personality 
module 40b) is shown as a single unit it may be implemented using two 
physically separate memories; however, this tends to defeat the advantage 
of the personality module 40b which is preferably added to the system as a 
single element at the time of installation. 
The output of rack computer 54 is a field excitation current control signal 
and is applied to an input of the amplifier 28 to control the current 
through the field winding 16 and, hence, the power output of the generator 
14 as previously described. 
FIG. 1 further illustrated an additional feature of the invention in the 
use of a low power control 58 which senses a "0" or a "1" setting or notch 
position in the device 22. It has been found preferable in view of 
unpredictable parasitic loads such as compressors, lights, and other 
accessory items which are powered either by engine 10 or generator 14 to 
operate open loop at very low power settings by switching in 
pre-determined and fixed field excitation levels under these conditions. 
Accordingly, control 58, which may be implemented as part of the rack 
computer 54, senses a 0 or 1 position in the device 22 and effectively 
bypasses or disables the computer 54 to provide fixed field excitation 
values to the amplifier 28. 
Briefly describing the operation of FIG. 1 a notch setting in the device 22 
results in the generation of a desired speed signal by table 30 and the 
development of a speed error e.sub.N from summer 32. Assuming a transient 
condition in which the speed error signal has not yet settled out to zero, 
an input to the speed computer 38 is generated and an output or control 
signal depending upon the particular formula which is solved by the 
computer 38 is generated and applied to the rack actuator 12. The actuator 
12 is advanced or retracted to increase or decrease engine speed. The 
integral factor of the PID transfer function in computer 38 accumulates 
small speed errors over time so the speed error eventually goes to zero. 
Assuming the power setting at device 22 is neither notch 0 or notch 1, the 
actual or measured speed signal on line 42 from tachometer generator 34 is 
applied to the look-up table 44 and results in a desired rack signal being 
applied to the positive input of summer 46. An actual rack position signal 
is applied to the negative input by way of line 48. Under steady state 
conditions these two signals alone are summed and a rack error e.sub.R is 
applied to the input of the rack computer 54. Under conditions of 
acceleration or deceleration, an additional positive input is applied to 
the summer 46 over line 50 representing instantaneous acceleration value 
of the engine 10. If a command is for positive acceleration (increasing 
speed per unit time) it is entirely possible in the implementation of the 
system as shown in FIG. 1 that the acceleration of the engine will require 
significantly more rack than is called for from the table due to engine 
inertia and produce a negative rack error when in fact a power output 
increase is called for. This "dip" is highly undesirable from the 
standpoint of objective operator performance characteristic and is 
eliminated by temporarily adding in the acceleration signal via line 50 to 
compensate for the lag in the desired rack signal. The constant multiplier 
(hereinafter referred to as K.sub.11) is empirically derived from engine 
testing and the same or a different K.sub.11 factor may be used for 
deceleration control purposes to avoid an overrun or actual power increase 
when a contemporaneous power decrease command is generated. In any event 
the output of the summer 46 is applied to the rack computer 54 and the 
transfer function thereof iterates a field excitation current setting 
which is applied to amplifier 28 to control the current through the 
winding 16. 
As previously mentioned, a notched setting of 1 or 0 effectively results in 
a bypass of the rack computer 54 and the generation of an appropriate 
field winding excitation setting by control 58 in an open loop fashion. 
Referring now to FIG. 3 additional features of the invention as found in 
the preferred embodiment will be described. It is to be understood that 
the diagram of FIG. 3, like the block diagram of FIG. 1, is arranged 
partly on a functional basis and partly on a physical basis because of the 
"best mode implementation" in the form of one or more digital processors 
having pre-determined programs stored in memory. As will be apparent to 
those skilled in the art, this implementation results in one or more very 
small and compact electronics devices performing a number of functions 
which in less sophisticated implementations might be performed by known 
and physically distinct devices. The invention is intended to embrace not 
only the digital processor implementation but also other less 
sophisticated implementations calling for a wide spectrum in the number of 
individually implemented functions as suits the particular user. The 
diagram of FIG. 3 is best understood when considered in conjunction with 
the software or flowcharts of FIG. 4 and the table of terms given at the 
end of the specification. The flow chart functions are expressed in 
generic functional terms so that the programmer might implement these 
functions using hardware and software formats of his own choosing. 
Referring now to FIGS. 3 and 4B the same basic arrangement of functions as 
was described with reference to FIG. 1 will be found. However, certain 
additional control functions as well as additional details of the basic 
control functions are illustrated in FIG. 3. As a first item, the 
fundamental implementation of the look-up table 30 is identified by the 
correspondingly numbered function box in FIG. 4B. As will be apparent to 
those skilled in the art the conversion from a four-bit signal input (from 
the notched device 22) to a digital number is a straight-forward matter of 
look-up in a read only memory. A signal proportional to desired power from 
a proportional version of the power setting device 22 can likewise be 
converted to a digital number in straight-forward matter to be used in the 
look-up table. This output is applied to a ramp rate generator 60 which is 
part of the calculator 24 to smooth out transitions in desired speed 
numbers caused by a movement of the operator-controlled level in the 
device 22. Ramp rate generator 60 causes the desired speed signal to 
undergo a transition between numbers having a plurality of stairstep type 
incremental increases or decreases, each increment being of fixed time. 
Different rates for desired speed signal increases are used for desired 
speed signal decreases and the generator may be implemented with two or 
more different increase and decrease rates so that the acceleration or 
response time of a locomotive used for both yard and mainline work may be 
adjusted to suit the operator and the application. The flowchart boxes 
identified by reference numeral 60 provide the implementation for ramp 
generator 60 in the preferred embodiment using digital computer 
implementation. The left side of the flowchart area 60 is for ramping up 
and the right side is for ramping down as will be apparent from an 
interpretation of the various legends. 
Summer function 32 is correspondingly numbered in FIG. 4B and, as is 
apparent, involves an arithmetic combination of two numbers. 
Looking now to the calculator block 38 of FIG. 3 it can be seen that the 
transfer characteristic from speed error e.sub.N to the voltage V which is 
applied to the rack actuator 12 is a complex function involving four 
factors, the multipliers or coefficients for the four factors being 
K.sub.1, K.sub.2, K.sub.3, and K.sub.4 respectively. These factors will be 
referred to in the following paragraphs by the respective coefficients 
alone. The last or bottom line in block 38 of FIG. 3 simply indicates that 
the voltage must be within the limits of available potential. The 
calculation blocks are correspondingly numbered with reference numeral 38 
in FIG. 4B. 
The first or K.sub.1 factor of the transfer function is the speed error 
itself; i.e. this is the "direct" in the transfer function. The second 
factor or K.sub.2 factor is the change in speed error as between two 
consecutive loop times. The third or K.sub.3 factor is a summed or 
integrated factor so that a steady state voltage V is produced after the 
transient has passed and the speed error e.sub.N has gone to 0. The fourth 
or K.sub.4 factor is proportional to the change in desired speed and may 
be considered optional although desirable. As will be apparent the K.sub.4 
factor is essentially an acceleration factor and tends to advance or 
retract rack faster if a very large speed increase is commanded and slower 
if a small increase is commanded. This use of an acceleration figure tends 
to improve the objective operator performance characteristics of the 
system as previously described. 
FIG. 3 further illustrates a function block 62 which is illustrated in FIG. 
4A. This is essentially the generation of a filtered or loop-averaged 
measured engine speed signal to be applied to the negative input of the 
summer 32. The effect of this function is essentially the same as that of 
an averaging device so that the actual speed signal applied to the summer 
is a more accurate function of actual engine speed than one measured over 
several engine revolutions. 
Referring now to FIGS. 3 and 4D, a backup function in the event of a rack 
position sensor failure; i.e., an electrical or mechanical failure in the 
position sensor, is provided. Function block 64 in FIG. 3 and Flowchart 
area 64 in FIG. 4D indicate an approach to a determination that a rack 
position sensor failure has occurred. In this case it is simply a matter 
of indicating the rack position has failed to change by some 
pre-determined amount in the face of a rack position change command. Under 
these circumstances, function block 66 in FIG. 3 indicates on the left 
side a software implemented operation on measuring four rack potentiometer 
readings and averaging them and storing the resulting average rack 
potentiometer signal in a particular storage location referred to as a 
"table" in memory 40. The right side of FIG. 4D is an indication that in 
the event of an indicated rack position sensor failure, the calculator 24, 
in function block 66, uses the last recorded rack actuator position 
average as the basis for generating a measured rack position signal. 
Referring now to FIGS. 3 and 4C a second measured engine speed signal is 
generated by a filter function block 68 which may be implemented in either 
calculator 24 or 26 but in this instance is implemented in the field 
control loop or calculator 26. The purpose of the routine shown in the 
flowchart of FIG. 4C is to generate a measured engine speed signal for 
application to the look-up table 44 over one or more revolutions of engine 
10 to dramatically increase the response time and stability of the field 
control loop 26. 
Continuing with the detailed description of the field control loop or rack 
calculator 26, the notch number from device 22 is fed to open loop control 
58 which functions to determine whether the operator has called for notch 
position "0" or notch position "1". If, as previously described, the 
operator had called for one or the other of these low notch positions, the 
field current setting will be made on a fixed and open loop basis. To this 
end, function block 70 performs a measurement and logical determination to 
determine whether the "0" notch position has been commanded. If this is 
the case, function block 72 sets the field current and two mathematical 
terms to prescribed low levels for control of source relay 28 and the 
generator field coil 16. The rack computer 54 is effectively inoperative; 
i.e., in the preferred implementation as indicated in FIG. 4E, the 
computational functions indicated by blocks 70 and 72 are preferably 
combined with the computational functions of block 54 in a common digital 
processor which, of course, remains operative at all times. 
If device 22 calls for notch position "1" the decision block 70 passes the 
analytical function to block 74 which detects the presence of the "1" 
notch position and activates function block 76 to set a second set of 
field current and mathematical values in accordance with previously 
calculated field current figures. Again, block 76 pre-empts the function 
of the rack computer 54. 
FIG. 4E illustrates the open loop field current calculation function of 
blocks 70, 72, 74, and 76. 
Assuming that a higher notch position is commanded through device 22 the 
determination of the desired rack signal for application to summer 46 is 
passed on to the look-up table 44. As previously mentioned, the device 22 
is provided with a fixed number of notch positions or power settings and 
does not, in itself, provide any proportional control between those 
settings in the locomotive case being described. In the case of 
proportional input from device 22 the look-up table functions the same. 
However, measured engine speed obviously varies relatively smoothly 
between settings in a proportional or infinitely variable fashion and it 
is desirable to produce desired rack signals which are proportional to 
measured engine speed between the optimum operating points shown in FIG. 
2; i.e., the desired rack signal will follow straight line segments 
between the optimum operating points of FIG. 2. As will be apparent to 
those skilled in mathematics, this proportional control calls for an 
interpolation function which is represented in the function blocks of 
flowchart 4E in the area of referenced numeral 44. 
In accordance with a further feature of the invention the desired rack 
signal is adjusted in the presence of a wheel-slip condition; i.e., in the 
application to traction motor powered vehicles it is desired to reduce the 
power applied to the traction motors by the generator 14 in the event that 
the driving wheels lose traction and begin to spin. The mechanism for 
detecting wheel-slip is represented by function block 78 in FIG. 3. As 
will be apparent to those skilled in the art, the physical implementation 
of a wheel-slip detector can take a variety of forms including, for 
example, a comparator receiving rate signals from driven and idler wheels 
or a comparator receiving rate signals from each of several driven wheels 
on different axles. Referring further to FIG. 3 and to FIG. 4F, the 
detection of a wheel-slip condition in function block 78 results in a 
downramping of the desired rack signal as indicated by function blocks 80 
in FIGS. 3 and 4F. Through summer 46 this results in a field current 
reduction which cures the wheel-slip condition and restores traction. Once 
the wheel-slip has been eliminated, function block 82 operates to ramp the 
desired rack signal back up to the setting commanded by look-up table 44 
in response to the measured engine speed signal from filter 68. 
Continuing with the description of FIGS. 3 and 4F in the area of the summer 
46 and the rack computer 54, the summing function involves three input 
signals; viz., desired rack, engine acceleration multiplied by the 
constant K.sub.11 and measured rack. As will be apparent to those skilled 
in the computer art a three input summing function is actually carried out 
in two steps. The first of which is the subtraction of the acceleration 
factor on line 50 from the measured rack signal on line 48, and the second 
of which is the summing of the result of the first step calculation with 
the desired rack signal to produce the rack error e.sub.R. 
Looking now to the rack computer 54 the details of calculations for this 
area are illustrated by the legend in block 54 of FIG. 3 and also in the 
function blocks of the flowchart, FIG. 4F. As previously described the 
transfer function of computer 54 is of the PID (proportional, integral, 
differential) type consistent with established control theory. The 
constants K.sub.8, K.sub.9, and K.sub.10 and empirically determined and 
retrieved from the personality module 40b which makes up the computer 
memory shown in FIG. 1. 
As indicated by function blocks 54a, 54b and 54c in flowchart FIG. 4F, 
means are provided to detect and deal with an engine overload condition in 
which summer 32 indicates that the system is below desired speed and that 
speed is decreasing. Under this condition the field current is reduced by 
the K.sub.12 factor. Note that while flowchart function block 54b 
indicates the addition of the K.sub.12 factor to the generator field 
current IGF, the ND figure is greater than NMF figure and changes the sign 
of the K.sub.12 factor to produce a negative rack error. As indicated by 
function block 54c in flowchart 4F and K.sub.8, K.sub.9 and K.sub.10 
factors are effectively eliminated from the transfer function and field 
current is reduced despite the fact that normal load control operation 
continues to call for an increase in field current. 
FIG. 4G illustrates an optional field current control system in which 
maximum current and voltage levels are established for all power settings 
and means are provided to prevent the unit from exceeding these values. To 
implement this control function it is, of course, necessary to provide 
measuring devices such as current shunts and voltage meters in the main 
generator output of the engine generator unit to provide actual current 
and voltage signals to the computer 54. 
If, as shown in FIG. 4G, the main generator current exceeds the 
pre-established maximum (function block 54d) the desired rack or RD and RC 
figures are recalculated and used to control field current. Similarly if 
the main generator voltage is outside of the upper limit, the desired rack 
signal is again recalculated on the basis of the allowable maximum and 
used to control the amplifier 28. Another optional field current control 
system in which constant power from the engine-generator unit can be 
provided in the lower notches by using the information from measuring 
devices in the main generator circuit instead of using the fixed 
excitation method previously described. To implement this control function 
the actual current and voltage signals to the computer 54 are required. If 
as shown in FIGS. 4I through 4L the constant power function is selected 
then the associated desired power is determined from the look-up table. A 
desired rack which would equate to the limit for either field current or 
field voltage is calculated. The minimum desired rack from that calculated 
from either the wheel slip ramp rate logic, the current limit or voltage 
limit is then selected in the control equation. 
INDUSTRIAL APPLICABILITY 
Referring now to FIGS. 5 and 6 the application of the governor of the 
present invention will be described as applied to the control of an engine 
10 and generator 14 in a diesel electric locomotive having traction motors 
82, 84, 86 and 88 connected to receive power from the generator 14. As 
shown in FIG. 5 an operator-controlled notch device 22 is provided for the 
programming of power commands. This device is connected to a digital 
processor 24, 26, 40 having a personality module 40b which is a ROM having 
the constants K.sub.1 through K.sub.13 which are peculiar to the engine 10 
and generator 14 permanently stored therein. The operator controls/signals 
further include a shut-down switch 90 which preferably includes a 
"generator unload" capability so that the locomotive may be idled with no 
power going to the traction motors 82, 84, 86, and 88 regardless of engine 
speed. The generator unload switch may optionally be located within a 
high-voltage locker 96 which is within the physical confines of the diesel 
locomotive. Operator controls/signals further include a yard/main switch 
92 which sets the ramp rates of ramp rate generator 60 so as to produce 
rapid acceleration performance capabilities for yard work and less rapid 
smoother acceleration characteristics for main line work. Finally, a 
diagnostic lamp 94 is provided to indicate that the rack 
measurement/default system of FIG. 4D has determined the rack position 
sensor 12 to be inoperative and that the engine is running on previously 
stored rack position/speed numbers stored in table 66 over some period of 
time. This is an indication that normal performance cannot be expected and 
that service is required upon reaching a service station. 
As shown in FIG. 5 the processor 24, 26, 40 is connected to receive rack 
position and engine speed signals from the engine 10 and is connected to 
deliver a rack actuator current to the fuel controlled mechanism 
associated with the engine 10; i.e., the rack actuator identified by 
reference numeral 12 in FIG. 1. Similarly the generator 14 is connected to 
deliver generator voltage and generator current signals to the processor 
24, 26, 40 for the purpose of implementing the power limited load control 
options of FIGS. 4G and 4I. The generator is connected to receive the 
field excitation current to control the power applied to the traction 
motors 82, 84, 86 and 88. 
Referring to FIG. 6 a typical operating condition and the response of the 
system shown in FIGS. 1, 3, 4 and 5 will be described. The diesel electric 
locomotive is assumed to be operating at a desired engine speed correlated 
with notch position 2 in device 22. The operator advances the device 22 to 
notch position 4 calling for an increase in engine speed and an increase 
in power delivered to the traction motors 82, 84, 86 and 88. The dynamics 
of the rack actuator 12 are such as to exhibit entirely different (much 
shorter) time constants than the dynamics of the engine 10. Accordingly, 
the actual rack position may be very quickly advanced by the now extant 
speed error e.sub.N while the measured speed signal and, hence, the 
desired rack signal applied to summer 46 changes quite slowly. As a 
result, the system of FIGS. 1 and 3 might ordinarily generate a large 
negative rack error which would reduce power at the same time the operator 
is calling for a power increase. To overcome this condition, K.sub.11 
factor or engine acceleration factor is applied to the summer 46 to aid 
the desired rack signal and actually boost rack (and power) beyond that 
theoretically needed to ramp from the first to the second speed positions 
as shown in the upper diagram of FIG. 6; i.e., the lower diagram of FIG. 6 
illustrates the effect of the K.sub.11 factor to produce an artificial 
rack boost during the acceleration time to prevent the power dip usually 
associated with notch position increases in diesel electric locomotives. 
Note also in the lower diagram of FIG. 6 that as the engine reaches the 
newly commanded speed position associated with notch 4, the K.sub.11 
factor goes negative and avoids an overshoot condition which would 
otherwise exist in the control loop until damped out by return to a stable 
system operating position. 
The following table provides definitions for the factors illustrated in 
FIGS. 3 and 4 to assist the user of the present invention in developing 
commands for the implementation of the invention according to the best 
mode. 
TABLE 1 
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FLOWCHART DEFINITIONS 
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NM = measured engine speed (loop average filtered) 
KN = engine speed vs. mag pick-up pluse time 
conversion constant 
NN = notch engine speed 
ND = desired engine speed at any instant 
SP = control sample period 
Rd = speed change ramp rate in decreasing 
direction (adjustable) 
Ru = speed change ramp rate in increasing 
direction (adjustable) 
e.sub.N = 
speed error 
e.sub.NL = 
speed error during previous sample period 
E.sub.1,E.sub.2 
engine speed control equation 
software integrators 
K.sub.1,K.sub.2, = 
speed control equation constants 
K.sub.3, K.sub.4 
sized for application 
I.sub.MIN = 
minimum rack actuator current 
I.sub.MAX = 
maximum rack actuator current 
IA = rack actuator current 
.DELTA. e.sub.N = 
change in speed error since last 
sample period 
I(NP) = table value for rack actuator current at 
given notch position 
R(NP) = table value for desired rack position 
at given notch position 
m,b = rack vs actuator current conversion 
coefficients 
RM = measured rack 
NP = notch position 
IGF = generator field current 
I1 = open loop field current for notch 1 
NR = speed valve used for determination of 
desired rack 
N(NP) = table value for notch speed 
R = desired rack before rate of change limits 
RN = rate of change limited desired rack 
.DELTA. RMAX = 
maximum allowable rate of rack change 
in one sample period 
RD = wheel slip limited desired rack 
RC = measured rack corrected for engine 
acceleration 
e.sub.R = 
rack error 
A &, B = load control equation software integrators 
K.sub.8,K.sub.9,K.sub.10 = 
load control equation constants; 
K.sub.12 = 
sized for application 
VGMAX = generator output voltage limit (optional) 
IGMAX = generator output current limit (optional) 
IGFMIN = generator field current minimum value 
IGFMAX = generator field current maximum value 
K.sub.11 = 
rack acceleration correction factor 
during accel. 
rack acceleration correction factor 
during deceleration 
KR = generator power to rack position conversion 
factor 
IG = generator output current (optionally measured) 
VG = generator output voltage (optionally measured) 
NMT = measured engine speed (torsional average 
filtered) 
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