U.S. patent number 3,815,561 [Application Number 05/289,200] was granted by the patent office on 1974-06-11 for closed loop engine control system.
This patent grant is currently assigned to The Bendix Corporation. Invention is credited to William R. Seitz.
United States Patent |
3,815,561 |
Seitz |
June 11, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
CLOSED LOOP ENGINE CONTROL SYSTEM
Abstract
A closed loop engine control system for internal combustion
engines is described. The control system is responsive to signals
indicative of the presence or absence of oxygen in the exhaust gas
of the engine and is operative to generate an output signal for
receipt by a fuel delivery controller which will cause that fuel
delivery controller to increase fuel delivery in the presence of
oxygen molecules in the exhaust gas and to decrease fuel delivery
in the absence of oxygen molecules in the exhaust gas in order to
maintain the fuel delivery at the predetermined, and preferably the
stoichiometric, air/fuel ratio mixture point.
Inventors: |
Seitz; William R. (Farmington,
MI) |
Assignee: |
The Bendix Corporation
(Southfield, MI)
|
Family
ID: |
23110476 |
Appl.
No.: |
05/289,200 |
Filed: |
September 14, 1972 |
Current U.S.
Class: |
123/696; 327/323;
700/33; 700/68; 261/DIG.74; 60/276; 60/39.281; 307/127 |
Current CPC
Class: |
F02D
41/1479 (20130101); Y10S 261/74 (20130101) |
Current International
Class: |
F02D
41/14 (20060101); F02m 007/00 () |
Field of
Search: |
;60/285,276,39.28R
;123/32EA,119R,102,139E ;204/195S ;307/230,323,127,229 ;328/171
;235/183,150.1,150.21,151.35 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Hart; Douglas
Attorney, Agent or Firm: Benziger; Robert A. Flagg; Gerald
K.
Claims
I claim:
1. An internal combustion engine control system for modulating an
engine operating parameter substantially independently of
environmentally induced sensor output variations, said control
system comprising:
sensor means for examining an engine operating variable operative
to generate a sensor means signal having an environmentally
variable characteristic selected to be indicative of a quality of
the combustion process occurring within the engine said variable
characteristic being subject to environmentally induced
variations;
comparator means responsive to the sensor means signal operative to
generate a comparator means output signal having a predetermined
constant level signal established when said combustion process
quality is one of a greater or lesser quality than a predetermined
quality;
integrator means receiving said comparator output signal operative
to integrate said predetermined constant signal level to generate a
gradually changing output signal changing in one of two change
directions at a predetermined integrating rate as long as said
predetermined constant level signal is established; and
fuel delivery controller means receiving said gradually changing
output signal and operative to modulate fuel delivery in response
thereto;
whereby said predetermined constant level signal and said
predetermined integrating rate cause said fuel delivery modulation
to be substantially independent of said environmentally induced
variations in said sensor characteristic.
2. The system as claimed in claim 1 wherein said sensor means
signal variable characteristic varies with air/fuel ratio and
comprises a transitional band portion intermediate a relatively
high strength signal and a relatively low strength signal, said
transitional band portion being constant with variations in said
high and low strength signals induced by variations of at least one
environmental condition; and occurring substantially at a selected
air/fuel ratio;
wherein said system comprises reference level establishing means
operative to provide said comparator means with a set point level
within said sensor transitional band portion indicative of said
predetermined quality;
wherein said comparator means output signal comprises a second
constant signal level different from said predetermined constant
level signal, said second constant level signal being established
as long as said quality deviation is the other of said greater and
lesser qualities;
wherein said integrator means integrates said second constant
signal level to gradually change said gradually changing signal
level in the other of said two changes directions at said
predetermined integrating rates; and
wherein said fuel delivery controller means modulates fuel delivery
so as to gradually increase the air/fuel ratio when said comparator
output signal is established at one of said predetermined and
second constant levels signals and to otherwise gradually decrease
said air/fuel ratio when said comparator output signal is
established at the other of said predetermined and second constant
levels signals;
whereby said predetermined integrating rate and the difference
between said predetermined and second constant signal levels causes
said fuel delivery controller to vary the air/fuel ratio about said
selected air/fuel ratio within a range of air/fuel ratios
substantially independent of said variation of said at least one
environmental condition.
3. The system as claimed in claim 1 wherein said fuel delivery
controller means comprises at least one timing capacitor and
current source means controllable to selectively charge said timing
capacitor at a controllable rate from an initial value determined
in accordance with a second engine operating variable to a
threshold value determine in accordance with a third engine
operating variable, said controllable rate being varied in
accordance with said gradually changing output signal to
controllably modulate the quantities of fuel delivered to the
associated engine independently of variations in fuel delivery
commanded to accommodate changes in said second and third operating
variables.
4. The system as claimed in claim 1 wherein said integrator measn
comprises an operational amplifier having an input terminal and an
output terminal and an integrating capacitor coupling said input
terminal and output terminal and determining asid predetermined
integrating rate.
5. The system as claimed in claim 2 wherein said relatively high
strength signal level comprises a minimum high strength signal
level and said relatively low strength sensor signal level
comprises a maximum low strength signal level, said minimum high
strength signal level and said maximum low strength signal level
each varying with the temperature and aging characteristics of said
sensor means and the difference between minimum high strength and
maximum lower strength signal levels defining said constant
transitional band so as to be substantially independent of the
aging and temperature characteristics of said sensor means so that
the fuel delivery controller means modulates fuel delivery
substantially independent of the aging and temperature
characteristics of said sensor means.
6. The system as claimed in claim 4 wherein said comparator means
comprises an operational amplifier having an input terminal and an
output terminal coupled by parallelly connected oppositely polled
semiconductor current conducting devices each having a
predetermined voltage drop when conducting, said predetermined
voltage drops establishing the magnitude of said constant signal
levels and permitting said comparator means to switch substantially
instantaneously from one of said constant signal levels to the
other when said sensor means signal passes through said set point
level so that the range in which said sensor means signal varies
about said set point level is determined substantially by said
magnitudes of said constant signal levels and said predetermined
rate at which said integrator means integrates said comparator
output signals.
7. An internal combustion engine controlling an engine parameter
varying with operating conditions of an internal combustion engine,
said control system comprising:
a. sensor means operatively connected with said engine to provide a
sensor means signal having a range of values varying with said
engine parameter;
b. reference level establishing means for providing a set point
level within said range of said sensor means signal;
c. comparator means connected to receive said sensor means signal
and said set point level operative to establish one of a constant
positive and negative polarity comparator output signal when said
sensor means signal is greater than said set point level and to
establish the other of said constant positive and negative polarity
comparator output signals when said sensor means signal is less
than said set point level;
d. integrator means operatively connected with said comparator
means to generate a control signal having a magnitude changing with
the integral of said constant positive polarity comparator output
signal when said constant positive polarity comparator output
signal is established and with the integral of said constant
negative polarity comparator output signal when said constant
negative polarity comparator output signal is established; and
e. control means operatively connecting said integrator means and
said engine for controlling said engine to vary said engine
parameter in accordance with said control signal,
whereby the integration of said constant positive and negative
polarity comparator output signals causes said control signal to
control said engine so as to vary said engine parameter so that
said sensor means signal is alternately increased and decreased
through said set point level.
8. The engine control system of claim 7 wherein said comparator
means comprises an operational amplifier having an input terminal
and an output terminal coupled by parallelly connected oppositely
polled semiconductor current conducting devices each having a
predetermined voltage drop when conducting, said predetermined
voltage drops establishing the magnitudes of said constant output
signals and permitting said comparator means to switch
substantially instantaneously from one of said constant positive
and negative output signals to the other when said sensor means
signal passes through said set point level so that said range in
which said sensor means signal varies about said set point level is
determined substantially by said magnitudes of said constant
positive and negative polarity comparator output signals and the
rate at which said integrator means integrates said comparator
output signals.
9. The apparatus of claim 8 wherein said semiconductor devices
comprise forward drops of said unidirectional current conducting
devices having nominal forward voltage drops establishing said
constant output signals.
10. The apparatus of claim 7 wherein said control means comprises
an operator controllable air/fuel delivery means for delivering
controllable air/fuel mixture to the engine, said control means
operative to control one of said air and fuel so as to vary the
air/fuel ratio in a predetermined range about a selected air/fuel
ratio.
11. An internal combustion engine control system for modulating an
engine operating parameter substantially independently of
environmentally induced sensor output variations, said control
system comprising:
sensor means for examining an engine operating variable operative
to generate a sensor means signal having an environmentally
variable characteristic selected to be indicative of a quality of
the combustion process occurring within the engine said variable
characteristic being subject to environmentally induced
variations;
reference level establishing means for generating a set point level
having a value in the range of values of said sensor means
signal;
comparator means connected to said sensor means and said reference
level establishing means operative to provide a comparator signal
having first and second constant magnitudes when said sensor means
signal is respectively above and below said set point level;
integrator means operatively connected with said comparator means
operative to generate a control signal having a magnitude changing
at a first predetermined integrating rate when the magnitude of
said comparator signal is one of said first and second constant
magnitudes and a second predetermined integrating rate when the
magnitude of said comparison signal is the other of said first and
second constant magnitudes;
fuel delivery controller means receiving said gradually changing
output signal and operative to modulate fuel delivery in response
thereto;
whereby said first and second constant levels and said
predetermined integrating rate cause said fuel delivery modulation
to be substantially independent of said environmentally induced
variations in said sensor characteristic.
Description
BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention is related to the field of internal
combustion engine control systems in general and in particular to
that portion of the above noted field concerned with closed loop
control systems. In greater detail, the present invention is
concerned with a closed loop control system in which the exhaust
gases of an internal combustion engine are analyzed to indicate the
ratio of the air/fuel mixture being consumed by the engine and
through which signals are generated in order to modulate the fuel
delivery mechanism in order to provide a predetermined air/fuel
ratio mixture for the engine.
2. Description Of The Prior Art
Closed loop fuel control systems are well known in the internal
combustion engine art, in particular in that portion of the
internal combustion engine art which is devoted to the hot gas
turbine engine, to provide short term and long term input control
corrections. However, as applied to variable volume combustion
chamber type engines, such as the reciprocating piston or rotary
(Wankel) engine, closed loop fuel control systems are not well
known. One known system involves the use of an exhaust gas oxygen
concentration sensor one example of which is described in
co-pending commonly assigned patent application Ser. No. 284,386
filed Aug. 28, 1972 by Thomas J. Hemak and titled "Protective
Shield for Oxygen Sensor." This system relies upon the virtual step
function output signal of the oxygen concentration sensor (as
illustrated in FIG. 4) to directly effect the fuel delivery control
mechanism to increase or decrease the volume of fuel delivered as a
function of air being consumed by the engine with the magnitude and
speed of the correction being a function of the sensor output
signal. In working with a closed loop fuel control system based on
this sensor it has been observed that the sensor output signal
characteristic varies greatly as a function of sensor temperature
and also as a function of sensor age. While the sensor output
characteristic normally evidences a high to low transition at the
stoichiometric air/fuel mixture ratio point, the magnitude of this
transition (and hence the magnitude of the output signal) decreases
for an aging oxygen sensor and also is a direct function of sensor
temperature as illustrated in FIG. 4. This results in a closed loop
control system which is least effective during the engine warm-up
cycle and until the sensor reaches its normal operating
temperature. Since accurate fuel control during the warm-up cycle
is known to be important in reducing automotive exhaust emissions
it is therefore an object of the present invention to provide a
closed loop control system capable of examining engine exhaust and
controlling fuel admission to the engine which is not sensitive to
temperature induced variations in the sensor output signal. More
particularly it is an object of the present invention to provide
such a closed loop control system which is fully responsive to
sensor output signal variations having a minimal magnitude. In this
context. "minimal magnitude" is to be understood to mean a signal
magnitude of about 10 percent of the maximum signal magnitude. It
is also an object of the present invention to provide a closed loop
control system whose responsiveness is not altered by degradation
of the sensor device.
Closed loop controls for variable volume combustion chamber
internal combustion engines utilizing the known oxygen sensors
provide a corrective signal which is directly related to the sensor
output signal. However, as the sensor ages, the magnitude of its
output signal decreases so that the closed loop control response
time will be gradually slowing thereby resulting in a long term
decrease in the responsiveness of the closed loop control system
rendering the known closed loop controls to be of little value. It
is therefore a further object of the present invention to provide a
closed loop control system whose output performance is not altered
or affected by age-induced changes in the sensor signal. It is a
more particular object of the present invention to provide a closed
loop control system which gives uniform response without regard to
variations in the magnitude of the input signal. It is a still
further object of the present invention to provide a closed loop
control system which provides uniform response without regard to
age or temperature of the sensor
SUMMARY OF THE PRESENT INVENTION
I have determined that the typical sensor output signal, regardless
of the sensor's age or operating temperature, will make a
high-to-low or a low-to-high signal excursion through at least one
intermediate sensor output signal voltage value which may be termed
the "transitional value." In some instances, a sensor may have a
"transitional band," comprised of a plurality of output signal
values each of which could be a transitional value. That is to say,
that the maximum low signal voltage value is less than the minimum
high signal voltage value and that between these two voltage values
there exists a nominal sensor output voltage value excursions
through which may advantageously be used to trigger a comparator
circuit so that whenever the sensor output signal is greater than
the transitional value, the comparator will generate an output
signal having a first predetermined constant magnitude which
magnitude will be uneffected by variations in sensor temperature or
age. Furthermore, whenever the sensor output signal is below the
transitional value, the comparator will generate an output signal
having a second predetermined constant magnitude different from the
first predetermined magnitude which again will not be influenced by
sensor, temperature or age. Thus, the comparator output signal may
be applied to the fuel delivery controller to increase or decrease
the quantity of fuel in the air/fuel mixture being provided to the
internal combustion engine in response to the sensor signals. This
system will therefore be rendered insensitive to variations which
may be due to variations in the temperature of the sensor or which
may result from aging of the sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the closed loop control system of the present
invention in a block diagram.
FIG. 2 illustrates an electronic circuit which may comprise a
portion of the block diagram of FIG. 1.
FIG. 3 illustrates an electronic circuit which may receive the
output signal of the circuit of FIG. 2.
FIG. 4 illustrates various voltage signal waveforms which may be
produced by the oxygen sensor of FIG. 1 in response to variations
in sensor temperature and/or age.
FIG. 5 illustrates the voltage output signal generated by the
comparator of FIG. 1.
FIG. 6 illustrates a full cycle of the voltage waveform as a
function of time generated by the circuit of FIG. 3 to control fuel
delivery.
FIG. 7 illustrates the output signal generated by the circuit of
FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, a block diagram of a closed loop control
system according to the present invention and intended for
association with a variable volume combustion chamber internal
combustion engine 10 is illustrated. The engine 10 produces an
exhaust gas stream through conduit 12 which stream is examined by
an exhaust sensor 20. The presently preferred embodiment
contemplates an oxygen sensor operative to determine the percentage
of oxygen concentration present within the exhaust gas stream.
According to the prior art this oxygen sensor would provide a
virtual step function output signal to be applied directly to a
fuel delivery controller 50. However, according to the present
invention, the output signal of the oxygen sensor is applied to a
summing device 30 which also receives the fixed value signal,
termed the set point value. The output of the summing device 30 is
then applied to comparator means 40 which generates an output
signal having a first relatively low fixed value when the output of
the oxygen sensor 20 exceeds the set point value and a second
relatively high fixed value when the output of the oxygen sensor 20
is less than the set point value. This output signal is applied to
the fuel delivery controller 50 to influence or modulate the amount
of fuel being provided to the engine 10. The engine 10 receives
various control inputs as illustrated at 60 which may be for
example an air consumption controlling input in the form of a
throttle setting (which may be operator controlled) as well as
other inputs which may or may not be controlled such as the load
placed upon the engine, ignition advance or retard signals or
modulation of exhaust gas recirculation (EGR). The fuel delivery
controller 50 also receives intelligence via communication link 70
which is indicative of the moment-to-moment operation of the
engine. For example, in the known fuel injection systems, this
intelligence may comprise information as to the speed of the
engine, the temperature of the engine coolant, the density of the
air being consumed by the engine, and such other input information
as may be of use to the fuel delivery controller 50 in providing a
gross fuel delivery control. The fuel delivery controller 50 would
then control the quantity of fuel to be delivered to the engine
through conduit 80 in accordance with these various sensed
parameters. The closed loop control would be operative to modulate
the gross fuel delivery control signal in accordance with a
correction factor determined by oxygen sensor 20. In this manner,
the system will automatically compensate for aging of the engine
and other components associated therewith such as the fuel delivery
mechanism, the EGR components, the engine valves and seals and any
other components which would directly or indirectly effect the
quantities of air and/or of fuel being measured, computed or
delivered.
Referring now to FIG. 2, the summing device 30 and the comparator
40 are illustrated in a representative, and preferred, electronic
embodiment. The summing device 30 is comprised of a pair of
interconnected resistors 32, 34 with the resistor 34 arranged to
receive the output signal from the exhaust sensor 20 and resistor
32 arranged to receive a fixed value voltage signal from
potentiometer 36. Resistors 32, 34 are interconnected at circuit
location 38. Circuit location 38 communicates with one input to an
operational amplifier 42. The other input to the operational
amplifier 42 is communicated to a fixed voltage reference which
represents the set point value. Oppositely directed diodes 44, 45
provide a feedback path around operational amplifier 42 to
establish maximum and minimum output signal levels. In the
illustrated embodiment the fixed voltage reference is established
by communicating a nonregulated source of voltage B+ through a
resistance 41 to the cathode of a zenner diode 43 whose anode is
communicated to ground. This source of regulated voltage is also
applied to the potentiometer 36 of the summing device 30 and to the
oxygen sensor to establish a reference voltage or middle ground at
the oxygen sensor. This will permit the oxygen sensor to generate
an output signal which is referenced to the middle ground value so
that, in the application of the present invention to an automotive
vehicle which uses a d.c. supply with chassis ground (positive or
negative) an intermediate voltage value will be used by the oxygen
sensor as its "ground" in order to provide both positive and
negative voltage values (relative to the middle ground) for the
amplifier 42. The potentiometer 36 should be adjusted so that
circuit location 38 will be at a voltage value equivalent to the
reference voltage established by zenner diode 43, the set point
value, when the output from the oxygen sensor 20 is at the
transitional value. That is, the set point value should be selected
to correspond to the selected transitional value of the exhaust
sensor. Alternatively, a voltage divider may be used in place of
potentiometer 36 where adjustability is not required.
With reference to FIG. 4, a graph is shown illustrating the output
signal characteristic of the typical oxygen sensor with three
output signal characteristic curves shown demonstrating a high to
low excursion at the stoichiometric air/fuel mixture ratio. The
curve identified as 1 corresponds to the maximum output signal
excursion which would be produced by a new sensor operating at its
maximum operating temperature. Curves 2 and 3 are illustrative of
the output signal characteristic evidenced by an oxygen sensor
operating at successively cooler temperatures or which is
successively older. The signal curve 1 evidences a maximum
excursion which, for way of example, would go from an output signal
value of approximately 1.0 volts to an output signal value of 0.1
volts for increasing air/fuel ratio with the excursion occurring
substantially at the stoichiometric mixture ratio. Extreme aging of
the device or operation of the device at a temperature far below
its normal operating temperature will result in a minimal signal
excursion of about 0.2 volts. In the case of the sensor whose
output signal characteristics are here illustrated, the signal
characteristics of the curves 1, 2, and 3 overlap for a narrow
region of output signal (of about 0.05 volts) centered at a value
of about 0.5 volts as the various signals demonstrate their
excursion characteristic. The "transitional band" for this sensor
is thus about 0.05 volts wide and a nominal value of 0.5 volts may
be selected as the representative "transitional value." The set
point value would then be selected to correspond to the
transitional value of 0.5 volts.
FIG. 5 illustrates the output of comparator device 40. The
comparator device output signal demonstrates a minimum to maximum
excursion of from -0.7 volts to +0.7 volts for increasing values of
the sensor output signal with the excursion occurring when the
sensor output signal equals the set point value, in this instance
0.5 volts. Thus, the output of the comparator device will be
independent of time based variations in the sensor output signal,
due for example to sensor aging, and will also be independent of
temperature band variations in the sensor output signal so long as
the minimum sensor signal excursion is occurring and is passing
through the selected transitional value.
Referring now to FIG. 3, an electronic circuit is illustrated which
accomplishes the general functions of the fuel delivery controller
50. The illustrated circuit includes a major portion of the
electronic fuel injection computer according to copending commonly
assigned patent application, Ser. No. 226,498 filed on Feb. 15,
1972 issued May 23, 1973 as U.S. Pat. No. 3,734,068 in the name of
J. N. Reddy and titled "Electronic Fuel Control System Including
Electronic Means For Providing A Continuous Variable Correction
Factor" and is intended to be illustrative of one method for
modulating fuel delivery in response to modulation commands of a
closed loop control. The circuit of this figure is comprised of a
pair of current sources 101, 102 which are alternately applied to a
pair of timing capacitors 103, 104 by a switching network 105
receiving triggering signals at terminals 51, 52. Also receiving
triggering signals at terminals 51, 52 (separately shown for
convenience) network 106 controls the level of the voltage on the
selected capacitor 103, 104 prior to generation of the injection
command signal. Threshold establishing circuit means 107 samples
the highest voltage appearing across capacitors 103, 104 and
compares this value with the level established by the signal
received at input port 53 to compute the fuel injection command
signal. This signal may be derived by various known techniques such
as illustrated in the co-pending Reddy application.
The current source 101 is comprised of transistor 108 whose base is
connected to the junction of a pair of voltage dividing resistors
110, 111 and whose emitter is connected to resistor 112. The
resistors 110 and 112 are connected to a source of potential
identified as B+ and resistor 11 goes to ground. Current source 102
is similarly comprised of a transistor 109 whose base is coupled to
the junction of voltage divider resistors 114, 115 and whose
emitter is connected to resistor 116 which is also connected to the
B+ source. The base of transistor 109 is also connected to a
modulating network 118 to be described hereinbelow. This
arrangement is operative to establish readily calculable levels of
current flow in the collectors of transistors 108, 109,
respectively. The collector of transistor 108 is then connected in
a parallel fashion to the collectors of a pair of transistors 131,
132. Similarly, the collector of transistor 109 is connected in
parallel to the collectors of a pair of transistors 133, 134. The
bases of transistors 131 and 134 are connected together through
resistances 141, 142 while the bases of transistors 132, 133 are
connected by way of resistances 143, 144. The junction of
resistances 141, 142 is connected to terminal 51 while the junction
of resistances 143, 144 is connected to terminal 52. The emitters
of transistors 131 and 133 are connected to capacitor 103 while the
emitters of transistors 132 and 134 are connected to capacitor 104.
This circuit is arranged to provide the current flow from current
source 101 through transistor 131 to capacitor 103 and the current
from source 102 through transistor 134 to capacitor 104 whenever a
high voltage signal appears at terminal 51 and a low voltage signal
appears at terminal 52. Whenever a low voltage signal is present at
terminal 51 and a high voltage signal is present at terminal 52,
the current from source 101 will flow through transistor 132 to
capacitor 104, while the current from source 602 flows through
transistor 133 to capacitor 103
The threshold establishing circuit receives a signal indicative of,
for example, an engine operating parameter such as the manifold
pressure at terminal 53 and this signal is applied to the base of
transistor 172. The base of transistor 171 receives, by way of
diodes 161, 162, the signal from the one of capacitors 103, 104
whose accumulated charge, or voltage, is highest. As the emitters
of transistors 171, 172 are coupled together, one of these
transistors will be in conduction depending upon which has a base
residing at a higher voltage value. When the value appearing on the
base of transistor 171 exceeds the value appearing on circuit input
170, transistor 171 will go into conduction and transistor 172 will
drop out of conduction. Termination of conduction of transistor 172
will consequently terminate conduction of transistor 173. While
transistor 172 was conducting, transistor 173 was also conducting
and a relatively high voltage signal, as illustrated in FIG. 7, was
present at terminal 54 due to the voltage divider action of
resistors 182, 183. However, termination of conduction of
transistor 173 will result in a substantially zero or ground level
signal appearing at circuit location 174 due to the lack of current
flow through the resistors 182, 183. This output signal may be
applied to any of the known injector valve driver circuits one of
which is illustrated in Ser. No. 130,349 -- Junuthula N. Reddy --
"Control Means For Controlling The Energy Provided To The Injector
Valves Of An Electronically Controlled Fuel System" to constitute
an injection command signal.
The timing capacitor discharging and initial charge controlling
circuitry 106 is comprised of a plurality of reference level
establishing means 210, 212, and 214, a pair of discharging means
216, 218, switching means 220 and a current source means 222. The
reference level establishing means 210, 212, and 214 are connected
to the source of energy indicated as B+ and are comprised of
voltage divider means 224, 226, and 228, respectively, and voltage
signal communicating transistor means 230, 232, and 234
respectively. The voltage communicating transistor means 230, 232
and 234 are arranged to have their bases communicated to a portion
of the voltage divider means so that a known level of voltage may
appear thereon and their emitters are connected to a common point.
The collectors of the transistors 230 and 232 are coupled together
and are communicated to ground through a diode means 236 while the
collector of transistor 234 is communicated to ground through a
separate diode means 238. The collector/diode junction of the
transistors 230, 232 and diode means 236 is communicated to the
discharging means 216 while the collector/diode junction of
transistor 234 and diode means 238 is communicated to the
discharging means 218.
With reference to FIG. 6, a complete cycle of a voltage waveform on
the capacitors 103, 104 is illustrated. The portion of the wave
from a to f represents the voltage attributable to the current
I.sub.1 from source 101 while the portion identified as 4
represents the portion attributable to the current I.sub.2 from
source 102. The various level changes and slopes present in the
I.sub.1 initial portion of the waveform are attributable to the
action of the reference level establishing means 210, 212, 214 and
the charging and discharging characteristics of the capacitors
under the influence of the current I.sub.1 and the discharging
means 106, 216, 218. A similar wavefrom 180 degrees out of phase
with this waveform is generated on the other of the capacitors 103,
104 so that the initial points a and f of the first and second
portions of the waveforms on the capacitors 103, 104 coincide in
time and also coincide with the receipt of mutually exclusive
triggering signals received on terminals 51, 52. Receipt of a
relatively high signal at terminal 51 will result in a rapid
dumping of the energy stored in capacitor 103 and the resultant
application of current I.sub.1 to the capacitor 103 to charge that
capacitor. The voltage appearing on that capacitor as a result of
the application of current I.sub.1 and as modulated by the action
of the reference level establishing means 210, 212 will result in a
voltage waveform appearing on capacitor 103 substantially as shown
in FIG. 6 from points a through b, c, d, e and to point f on the
curve in FIG. 6. At the point in time corresponding to point f, the
triggering inputs received at input terminals 51, 52 will be
reversed so that capacitor 103 will receive the current I.sub.2.
The value of current I.sub.2 will be a function of the voltage
appearing on the base terminal of transistor 109 and will charge
capacitor 103 as shown on the portion of the curve identified as 4
of FIG. 6. A representative threshold value is illustrated in FIG.
6 as the dashed line 5 and the second portion of the curve, 4,
crosses the threshold 5 at a point in time identified as T.sub.3.
The circuit of FIG. 3 would therefore be operative to provide a
flow of fuel to the engines in accordance with the teachings of the
above-noted pending applications for the time period between
T.sub.1 and T.sub.3.
With reference now to FIG. 3, modulating network or means 118 is
illustrated as communicating with the base of transistor 109
through resistance 119. As illustrated, the modulating means 118 is
comprised of an operational amplifier 120 having a capacitor 121 in
its feedback loop communicating with the inverting input which also
communicates through resistor 122 with a terminal 123. This
terminal communicates directly with a similarly designated terminal
of the comparator device 40 of FIGS. 1 and 2. Upon receipt of a
comparator device output signal as illustrated in FIG. 5, the
operational amplifier will be operative to generate at the base of
transistor 109 an output voltage which will either be gradually
increasing in the case of a negative input signal from comparator
40 or will be gradually decreasing in the case of a positive input
from the comparator 40 so as to add or subtract incremental units
of base drive for transistor 109. This will result in increasing or
decreasing the magnitude of the current I.sub.2 and hence changing
the slope of the ramp voltage generated at the capacitor 103, 104
receiving this current. Again with reference to FIG. 6, this will
result in a curve identified as 4b for decreasing values of current
I.sub.2 and the curve 4a for increasing values of I.sub.2. For
convenience, the deviations between curves 4a, 4b, and 4 have been
greatly exaggerated. With reference now to FIG. 7, the circuit of
FIG. 3 and the curve 4a would generate a fuel injection command
pulse having a duration from T.sub.1 to T.sub.2 while the curve 4
would generate a fuel injection command pulse having a duration
from T.sub.1 to T.sub.3 and the curve 4b would generate the fuel
injection command pulse subsisting from time T.sub.1 to T.sub.4. It
can thus be seen, that for a given set of operating conditions for
the engine, exemplified by the fact that threshold curve 5 in FIG.
4 is unchanging, the quantity of fuel delivered to the engine may
be varied by the closed loop control system of the present
invention to maintain the air/fuel ratio at the predetermined
value.
It will be seen that the present invention accomplishes its stated
objectives. By providing a comparator responsive to the sensor with
fixed maximum and minimum values, and switchable therebetween in
response to sensor signal excursions through the selected
transitional value, the characteristic of the closed loop control
signal applied to the fuel delivery controller is rendered
independent of variation in the characteristic of the sensor signal
so that the fuel delivery controller response is uniform and will
only respond to variations in engine performance with respect to
the set point.
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