Fuel-optimizing electronic control circuit for a fuel-injected marine engine or the like

A self-adaptive fuel control system for an internal combustion engine which provides maximum fuel economy by maintaining engine operation at a preselected point on the r.p.m. vs. fuel flow curve. Engine operation is maintained at the preselected point by sampling initial steady state engine speed, leaning the fuel mixture supplied to the engine until there is a predetermined drop in engine speed, enriching the fuel mixture to attain an increase in engine speed, resampling engine speed and then repeating the process.

FIELD OF THE INVENTION 
This invention relates to fuel control systems for internal combustion 
engines and more particularly to a self-adaptive fuel control system which 
provides maximum fuel economy for an internal combustion marine engine 
over all conditions of engine operation. 
BACKGROUND OF THE INVENTION 
Maximum fuel economy is now the primary goal for designers of internal 
combustion engines in view of the current and ever increasing cost of 
gasoline. 
The customary practice in designing and calibrating the fuel supply systems 
for internal combustion engines is to pre-schedule fuel flow according to 
some function of engine operating condition as measured on the engine 
during operation. On carburetor type engines the principal measured 
function is usually venturi pressure, and the fuel flow is primarily 
determined by this pressure (or depression) and secondarily the fuel flow 
may be determined by measuring various engine functions such as r.p.m., 
manifold vacuum, air flows, throttle position, etc., and controlling the 
fuel flow in accordance with some predetermined schedule. 
Fuel control systems of the type described above depend on prior knowledge 
of how the engine will perform under all possible conditions of load and 
environment. Such systems, even when relatively complicated and expensive, 
only obtain optimum performance in terms of fuel economy under a limited 
set of operating conditions. 
It is therefore a general object of the present invention to provide a 
self-adaptive fuel control system that does not depend on prior knowledge 
of engine performance. 
Self-adaptive fuel control systems per se are known and have been discussed 
by Draper and Li in a publication.* However, the Draper and Li system is 
designed to provide peak power output (maximum r.p.m.) for any given 
throttle setting and does not provide maximum fuel economy, as maximum 
fuel economy occurs near the border-line of lean misfire, not at maximum 
r.p.m. 
FNT *C. S. Draper and Y. T. Li, "Principles of Optimalizing Control Systems and 
the Application to the Internal Combustion Engine", American Society of 
Mechanical Engineers, 1951. 
It is therefore a further object of the present invention to provide 
maximum fuel economy for any given throttle setting on an internal 
combustion engine. 
A self-adaptive fuel control system that provides maximum fuel economy is 
described in a U.S. Patent Application entitled "Programmable Fuel Economy 
Optimizer For An Internal Combustion Engine" by H. E. Riordan, Ser. No. 
305,900, filed Sept. 25, 1981 and assigned to the same assignee as is the 
instant invention. The Riordan fuel economy optimizer provides maximum 
fuel economy by determining a rate of speed change versus fuel flow rate 
change and senses the lean limit of the engine on the basis of 
deceleration rate. This approach, although providing many advantages not 
possible with prior art fuel control systems, is not compatible with all 
types of two-cycle engines. 
It is therefore a further object of the instant invention to provide a 
self-adaptive fuel control system that operates with all engine types. 
It is another object of the instant invention to provide a self-adaptive 
fuel control system that provides an exact range of fuel mixture 
variation. 
It is a still further object of the instant invention to provide a 
self-adaptive fuel control system that has enhanced temperature stability. 
SUMMARY OF THE INVENTION 
In accordance with the invention an internal combustion engine is operated 
at or near a preselected point on the r.p.m. vs fuel flow curve, said 
preselected operating point providing maximum fuel economy during engine 
operation. 
It is a feature of the invention that engine operation is maintained at or 
near the preselected operating point by sampling the fuel mixture and 
engine r.p.m. while at or near a steady state operating condition. 
It is a further feature of the invention that the fuel mixture is leaned 
after the steady state operating condition is reached, allowing engine 
r.p.m. to decrease a first predetermined amount in reponse to the leaning 
operation. 
It is a still further feature of the invention that when engine r.p.m. has 
decreased the first predetermined amount, the fuel mixture is enriched a 
second predetermined amount, said second predetermined amount being 
designedly less than the degree of lean-out from the steady-state 
operating condition, thereby allowing engine r.p.m. to again increase to a 
new steady-state operating condition. 
The foregoing and other objects and features of this invention will be more 
fully understood from the following description of an illustrative 
embodiment thereof taken in conjunction with the accompaying drawings.

DETAILED DESCRIPTION 
It is known that for a given engine, operating with continuously connected 
load, the r.p.m. vs fuel flow curves will exhibit a relatively constant 
shape on the lean side of the curve for any given throttle setting. The 
fuel control system of the instant invention takes advantage of this 
phenomenon and maintains the fuel delivery rate consistently near the lean 
limit while avoiding misfire. Since maximum fuel economy occurs near the 
lean limit, the instant invention is able to achieve maximum fuel economy 
over all conditions of engine operation. 
FIG. 1 shows a typical r.p.m. vs fuel flow curve for each of several 
settings of engine throttle opening. Points a, b and c on the top curve 
illustrate respectively the approximate conditions of over-lean fuel flow, 
maximum fuel economy, and maximum power. To the far right of each curve is 
the condition of fuel-rich limit, with resultant power loss. The fuel 
control system of the instant invention seeks to operate the associated 
internal combustion engine in a range slightly to the right of point b on 
the r.p.m. vs fuel-flow curve, where the slope of the curve is always 
positive but the offset from the lean limit and misfire is sufficient to 
provide smooth running. An operating range for the instant invention 
slightly to the right of point b provides maximum fuel economy yet is 
compatible with all engine types and enjoys great stability over a wide 
range of temperatures. 
The fuel control system of the instant invention is shown in FIG. 2. The 
system provides optimum fuel economy by sampling the initial steady-state 
engine r.p.m., leaning the amount of fuel supplied until the engine r.p.m. 
drops by a predetermined amount, such as 50 r.p.m., enriching the fuel 
mixture by a predetermined amount, such as 3%, resampling the engine 
r.p.m. and then repeating the entire process. The essential functions of 
circuit operation are r.p.m. sampling and fuel-flow sampling with the 
circuit sensing the lean limit of engine operation on the basis of a 
finite r.p.m. loss. 
Referring now in particular to FIG. 2, engine-r.p.m. information in the 
form of a tachometer signal is made available at terminal 100. The 
tachometer signal, is a d.c. level signal with a higher level d.c. signal 
indicating higher r.p.m. and a lower level d.c. signal indicating lower 
r.p.m. The tachometer signal is applied to comparators 107 and 112, to 
sample-and-hold circuit 104, and is also applied to terminal 148. 
The fuel control signals (E'fc) utilized to supply fuel mixture control 
information to the associated internal combustion engine, are applied to 
the engine via terminal 142. These signals are modified versions of 
incoming fuel control signals Efc applied to the circuit of FIG. 2 via 
terminal 141. The incoming fuel control signals are d.c. level signals 
generated by a resistor network (not shown). The d.c. level of the 
incoming fuel control signals is modified by the output signals of 
operational amplifier 136 in a manner to be discussed below. The fuel 
control output signals, which are changing in d.c. level, are applied to 
pulse generation circuitry (not shown) which in turn controls fuel flow 
controlling devices (not shown) such as a fuel injection system or a 
carburetor with electrically controllable metering. It is to be understood 
during the following description that a decrease in the d.c. level of 
signals E'fc will result in a leaner fuel mixture being applied to the 
associated internal combustion engine while an increase in the d.c. level 
of signal E'fc will result in a richer fuel mixture being applied to the 
associated internal combustion engine. 
The circuit of FIG. 2 is designed, for any throttle setting, to accommodate 
the condition of acceleration to an engine-r.p.m. level which maintains 
itself for a period of time. Once having achieved this "steady state" 
engine-r.p.m. level, the circuitry samples engine r.p.m. and fuel flow 
mixture to provide maximum fuel economy. Considering first the 
acceleration phase, assume that the associated internal combustion engine 
is accelerated to steady r.p.m., for a particular throttle setting. During 
acceleration, a high level d.c. tachometer signal is applied to the "+" 
terminal of comparator 112 via capacitor 108 and is also applied to 
terminal 148. Due to the bias network consisting of resistors 109, 110 and 
111, the magnitude of the signal at the "+" terminal of comparator 112 
exceeds the signal magnitude at the "-" terminal of comparator 112 
resulting in a high level d.c. output signal from comparator 112. This 
high level signal level permits capacitor 135 to charge during the 
acceleration interval via diode 134. 
The d.c. tachometer signal is also applied to the "-" input of comparator 
107. Switch 104, as well as switches 125, 126 and 143, are standard CMOS 
sample-and-hold switches which are open (OFF) when the voltage at the C 
(control) input is less than approximately 3 volts and closed (ON) when 
the C input is greater than 6 volts. During acceleration, switch 104 is ON 
which applies the tachometer signal to the "+" input of comparator 107. 
The tachometer signal magnitude at the "-" input of comparator 107 is 
greater than the tachometer signal magnitude at the "+" input of 
comparator 107, due to the voltage divider network consisting of resistors 
102, 103 and 105 and therefore the d.c. output signal level of comparator 
107 is low during acceleration. The low signal level output of comparator 
107 turns switch 126 OFF which in turn results in a high level voltage 
(VDD) being applied to the C terminal of switch 143, turning this switch 
ON, and applying the output signal from amplifier 136 to the "+" terminal 
of comparator 145 and also to capacitor 144, thus allowing this capacitor 
to charge as E'fc increases. 
Due to the bias network consisting of resistors 137 and 139, the output of 
operational amplifier 136 tracks the voltage level at the amplifier's "+" 
input terminal and is slightly greater in magnitude than the voltage 
present on capacitor 135 (Ec). However the output of amplifier 136 is 
limited in value to the voltage present on terminal 141, i.e. the voltage 
level of the incoming fuel control signals Efc. During acceleration, the 
voltage across capacitor 135 (Ec) will increase until it exceeds Efc and 
at this time the output of comparator 145 will go low as the voltage 
magnitude at the "+" terminal of comparator 145 (Ec) exceeds the voltage 
magnitude at the "-" terminal of comparator 145 (Ed). The low output of 
amplifier 145 turns transistor 124 OFF which in turn places a high voltage 
level at the C terminal of sample and hold circuit 104. 
As acceleration progresses, capacitor 106 begins to charge, from the high 
level output signal of sample and hold circuit 104. The charge being 
stored in capacitor 106 is indicative of engine r.p.m. as it is a sample 
of the tachometer signal E't. 
At the conclusion of acceleration, a steady-state r.p.m. level is reached, 
with steady state r.p.m. being defined as that engine speed at which the 
d.c. level of the tachometer signal remains constant for a period of 
approximately 10 seconds. Upon reaching steady-state r.p.m., the 
tachometer signal applied to the "-" terminal of comparator 112 exceeds 
the magnitude of the tachometer signal being appled to the "+" terminal of 
comparator 112 through capacitor 108. When this occurs, the output of 
comparator 112 switches low and capacitor 135 begins to discharge through 
transistor 120, resistor 121 and the output of amplifier 107 which is low 
at this time. 
As capacitor 135 continues to discharge, a point will be reached where the 
charge present across capacitor 144 (Ed) will exceed the charge present 
across capacitor 135 (Ec). When this occurs, the output of comparator 145 
goes high, turning transistor 124 ON, which in turn places sample-and-hold 
switch 104 in the hold mode. Capacitor 106 at this point is charged to a 
value representative of a new level of engine steady-state r.p.m., speed 
and this value is retained since sample-and-hold circuit 104 has been 
placed in the hold mode. 
Now that the engine has reached steady-state r.p.m., the fuel mixture will 
be leaned until engine r.p.m. drops a predetermined amount. During the 
leaning circuit operation, capacitor 135 continues to discharge, as 
described above, and the output of amplifier 136 (E'fc), which tracks the 
decline of the charge across capacitor 135 also declines in value. This 
declining signal is applied to terminal 142, and from there to the 
associated fuel control devices (not shown), to lean the fuel mixture 
applied to the associated internal combustion engine. As the fuel mixture 
becomes progressively leaner, engine r.p.m. begins to drop. 
Recall from the previous description that when steady-state r.p.m. was 
reached, sample and hold circuit 104 was placed in the hold mode, 
maintaining a charge across capacitor 106 indicative of steady-state 
r.p.m. This voltage value (Eb) is applied to the "+" input of comparator 
107. As engine r.p.m. decreases, the magnitude of the tachometer signal 
applied to the "-" terminal of comparator 107 (Ea) also decreases until it 
is less than the voltage value stored in capacitor 106 (Eb). The amount of 
decline in engine r.p.m. necessary to reach this point can be readily 
predetermined through proper selection of the value of resistors 101, 102, 
103, and 154. An exemplary decline in engine r.p.m. for the embodiment of 
the invention described herein is 50 r.p.m. 
At the time engine r.p.m. drops the predetermined amount, the output of 
comparator 107 will go high to commence enriching the engine fuel mixture. 
This high value output signal is applied to sample-and-hold circuit 126 
which functions as an invertor and applies a low level signal to the 
control terminal of sample-and-hold circuit 143, placing this circuit in 
the hold mode. When this occurs, the last value of signal E'fc is stored 
in capacitor 144 (Ed) which represents the amount the internal combustion 
engine has been leaned since reaching steady state r.p.m., as described 
above. 
The high level output of comparator 107 is also applied to transistor 119 
and to transistor 124. The application of the high level signal to 
transistor 119 serves to commence charging capacitor 135 through 
transistor 119. As the voltage across capacitor 135 (Ec) increases, the 
output of the amplifier 136 experiences a corresponding increase. This 
increasing signal is applied to terminal 142, and to the associated fuel 
control devices (not shown), to begin enriching the fuel mixture applied 
to the associated internal combustion engine. As the fuel mixture is 
enriched, engine r.p.m. begins to increase. The application of the high 
level output signal from comparator 107 to transistor 124 turns this 
transistor OFF, which in turn places sample-and-hold circuit 104 back in 
the sample mode so that capacitor 106 can begin sampling the increasing 
engine r.p.m. in the manner previously described. 
The fuel mixture will continue to be enriched and engine r.p.m. will 
continue to increase until the charge across capacitor 135 (Ec) exceeds 
the previously stored charge across capacitor 144 (Ed). The amount the 
fuel mixture is enriched is determined by the gain of amplifier 136 and is 
preferably 3%. The output of comparator 145 will go low when the mixture 
has been enriched 3% and initiate the next leaning cycle in the manner 
described above. 
Referring now to FIGS. 3A-3F, it can be seen that the fuel control circuit 
of the instant invention progresses through a series of discrete intervals 
(1-5) which have been described in detail above. Interval 1 is the initial 
acceleration interval during which the internal combustion engine is 
advanced toward steady-state r.p.m., for the particular throttle setting. 
During this interval, the voltage across capacitor 135 (Ec) rises to the 
value of VDD (FIG. 3D) and then levels off. 
Steady-state r.p.m. is reached in interval 2 at which time voltage Ec 
beings to decrease in the manner described above, which serves to lean the 
fuel mixture being applied to the internal combustion engine. When voltage 
Ec decreases below the level of the voltage across capacitor 144 (voltage 
Ed, FIG. 3D), the output of amplifier 145 goes high (FIG. 3E) and switch 
104 is placed in the hold mode (FIG. 3C). Leaning the engine fuel mixture 
continues (FIG. 3D) until the engine r.p.m. drops a predetermined amount. 
The drop in engine r.p.m. is indicated in FIG. 3A when voltage Ea ("-" 
input of comparator 107) falls below voltage Eb ("-" input of comparator 
107). 
When engine r.p.m. drops the predetermined amount, the transition is made 
from interval 2 to interval 3. At this time, device 104 is placed in the 
sample mode (FIG. 3B), device 143 is placed in the hold mode (FIG. 3F), 
the output of comparator 107 goes high (FIG. 3B), and Ec beings to 
increase (FIG. 3D), which serves to enrich the fuel mixture and increase 
engine r.p.m. 
Engine r.p.m. continues to increase until voltage Ec again reaches the 
value of voltage Ed at the boundary between intervals 3 and 4 (FIG. 3D). 
At this time, the output of comparator 107 goes low (FIG. 3B), device 104 
returns to the hold mode (FIG. 3C,) the output of comparator 145 goes low 
(FIG. 3E), device 143 returns to the sample mode (FIG. 3F), and the 
voltage Ec begins to decrease (FIG. 3D), thereby initiating another 
leaning cycle as described above. 
Interval 5 repeats interval 3 and this process of selective speed sampling 
and fuel-flow sampling will continue as long as the engine is maintained 
at the same throttle setting. 
The circuit of FIG. 2 is designed for maximum fuel economy for any throttle 
setting within a large range of operating r.p.m.; however, it not intended 
to control the fuel mixture at idle or at very large throttle openings. 
More particularly, at idle, the tachometer signal applied to terminal 148 
serves to hold the output of comparator 112 low, which disables the 
described automatic circuit operation. Similarly, at very large throttle 
openings (greater than 50%) device 125 is enabled, which in turn disables 
comparator 107 and serves to inhibit the lean cycle described above. The 
remaining components shown in FIG. 2, not specifically referred to during 
the foregoing description, are standard bias and divider networks and will 
not be discussed in detail as their function is clearly understood to one 
skilled in this technical area. 
Although a specific embodiment of this invention has been shown and 
described, it will of course be understood that various modifications may 
be made without departing from the spirit of this invention.