U.S. patent number 3,916,170 [Application Number 05/463,369] was granted by the patent office on 1975-10-28 for air-fuel ratio feed back type fuel injection control system.
This patent grant is currently assigned to Nippondenso Co., Ltd.. Invention is credited to Susumu Harada, Hideaki Norimatsu.
United States Patent |
3,916,170 |
Norimatsu , et al. |
October 28, 1975 |
Air-fuel ratio feed back type fuel injection control system
Abstract
A fuel injection control system comprising an air-fuel ratio
feedback control in combination with an electronically controlled
fuel injection system. In this system, the concentration of oxygen
contained in the engine exhaust gases is compared with a
predetermined value in a comparator whereby whether the fuel
injection quantity is to be corrected in a direction to increase it
or in a direction to decrease it is determined in accordance with
the output of the comparator, and the rate of change of the
correction is controlled in accordance with a sum output produced
by adding a detected value of engine rpms and a detected value of
engine intake state. When the air-fuel control cannot operate
properly, for example because of a low exhaust temperature or under
deceleration conditions, a holding circuit is connected to the
integrater output to maintain the integrated output at a value
intermediate the fluctuating range thereof. The system has an
excellent follow-up characteristic to respond to rapid changes in
the operating conditions of an engine and it is capable of
maintaining the air-fuel mixture ratio at a predetermined
value.
Inventors: |
Norimatsu; Hideaki (Kariya,
JA), Harada; Susumu (Oobu, JA) |
Assignee: |
Nippondenso Co., Ltd. (Kariya,
JA)
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Family
ID: |
26387658 |
Appl.
No.: |
05/463,369 |
Filed: |
April 23, 1974 |
Foreign Application Priority Data
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Apr 25, 1973 [JA] |
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48-47486 |
Jun 28, 1973 [JA] |
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48-73454 |
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Current U.S.
Class: |
701/103; 701/109;
701/123; 123/493; 123/682 |
Current CPC
Class: |
F02D
41/1482 (20130101); G06G 7/57 (20130101); F02D
41/123 (20130101); F02D 41/149 (20130101) |
Current International
Class: |
G06G
7/00 (20060101); G06G 7/57 (20060101); F02D
41/14 (20060101); F02D 41/12 (20060101); G06G
007/70 (); F02M 007/00 () |
Field of
Search: |
;235/150.2,150.21,151.34
;123/32AE,32EA |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
J G. Rivard, "Closed-Loop Electronic Fuel Injection Control of the
Internal-Combustion Engine," Society of Automotive Engineers,
International Automotive Engineering Congress, Jan. 8-12, 1973, pp.
1-9..
|
Primary Examiner: Morrison; Malcolm A.
Assistant Examiner: Smith; Jerry
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
We claim:
1. An air-fuel ratio feedback type fuel injection control system
comprising a main feedback circuit and a holding means; said main
feedback circuit including:
an oxygen concentration sensor for detecting the concentration of
oxygen contained in the exhaust gases of a vehicle internal
combustion engine;
a comparator for comparing the output of said oxygen concentration
sensor with a first predetermined value to generate an output;
an adder circuit for adding at least a first detected value
representing an intake state in said engine and a second detected
value of the number of revolutions of said engine and generating a
sum output thereof;
an inverter connected to said adding circuit to generate an
inverted output of said sum output;
a switching circuit connected to said comparator, said adder
circuit and said inverter and responsive to the output of said
comparator for selecting and generating either of said sum output
and said inverted output as an output thereof;
an integrating circuit connected to said switching circuit for
integrating the output of said switching circuit to generate an
integrated output;
an electronically controlled fuel injection means connected to said
integrating circuit and said engine and adapted for injecting a
fuel amount corresponding to at least one of operating parameters
of said engine, whereby fuel amount to be injected is corrected in
accordance with the output of said integrating circuit; and
said holding means being connected to said integrating circuit and
said fuel injection means, and maintaining said integrated output
at a second predetermined value except upper and lower saturation
values of said integrated output when the correction of the
injection fuel amount by said main feedback circuit is
terminated.
2. An air-fuel ratio feedback type fuel injection system according
to claim 1, wherein said second predetermined value is set at a
substantial midpoint of the fluctuating range of said integrated
output.
3. A fuel injection control system including a computing section
for computing an optimum amount of fuel to be injected in
accordance with parameters concerning operational conditions of an
internal combustion engine in a vehicle, and fuel supplying means
for injecting the fuel into said internal combustion engine in
response to an output of said computing section, said computing
section comprising:
a. a main feedback circuit including air-fuel ratio detecting means
for measuring an air-fuel ratio of gas mixture by detecting at
least one component of exhaust gases of an internal combustion
engine; integration constant generating means for generating a
positive integration constant and a negative integration constant;
selecting means connected to said air-fuel ratio detecting means
and said integration constant generating means for selecting, in
response to the output of said air-fuel ratio detecting means, one
of said positive and negative constants in accordance with the
output of said air-fuel ratio detecting means; and an integrating
circuit connected to said selecting means for integrating said one
of said positive and negative constants selected by said selecting
means to produce an integrated output, thereby correcting the fuel
amount to be injected; and
b. holding means connected to said integrating circuit for
maintaining the integrated output of said integrating circuit in
said main feedback circuit at a predetermined value intermediate
within a fluctuating range of said integrated output when there
occurs in said internal combustion engine a condition that the
correction function of the fuel amount by said integrating circuit
in said main feedback circuit is terminated.
4. A fuel injection control system according to claim 3, wherein
said holding means includes condition detecting means for detecting
the occurrence of said condition in said internal combustion engine
to produce a condition detected output, and an auxiliary feedback
circuit connected to said condition detecting means and in response
to said condition detected output for feeding said integrated
output back to an input terminal of said main feedback circuit to
thereby maintain said integrated output at said predetermined value
intermediate with the fluctuating range of said integrated
output.
5. A fuel injection control system according to claim 4, wherein
said condition detecting means detects the occurrence of the
condition in that said air-fuel ratio detecting means cannot
operate normally.
6. A fuel injection control system according to claim 3, wherein
said air-fuel ratio detecting means includes an oxygen
concentration sensor for detecting the concentration of oxygen
contained in the exhaust gases of said internal combustion
engine.
7. A fuel injection control system according to claim 6, wherein
said holding means maintains said integrated output delivered by
said integrating circuit in said main feedback circuit at said
predetermined value when the temperature of the exhaust gases of
said engine is below an allowable temperature at which said oxygen
concentration sensor begins to operate normally.
8. A fuel injection control system according to claim 7, wherein
said holding means includes condition detecting means for detecting
the occurrence of a condition that the temperature of the exhaust
gases of said engine is below said allowable temperature to produce
a condition detected output, and an auxiliary feedback circuit
connected to said condition detecting means and in response to said
condition detected output for feeding said integrated output back
to an input terminal of said main feedback circuit to thereby
maintain said integrated output at said second predetermined value
intermediate within the fluctuating range of said integrated
output.
9. A fuel injection control system according to claim 3, wherein
said holding means includes condition detecting means for detecting
the occurrence of the condition that the supply of the fuel is cut
off during deceleration of the vehicle to produce a condition
detected output, and an auxiliary feedback circuit connected to
said condition detecting means and in response to said condition
detected output for feeding said integrated output back to an input
terminal of said main feedback circuit to thereby maintain said
integrated output at said predetermined value intermediate within
the fluctuating range of said integrated output.
10. A fuel injection control system according to claim 3, wherein
said selecting means in said main feedback circuit includes a
comparator connected to said air-fuel ratio detecting means for
delivering a comparison output when the output of said air-fuel
ratio detecting means attains the predetermined air-fuel ratio, an
adder circuit for adding at least a first detected value
representing an intake state in said engine and a second detected
value representing the number of revolutions of said engine and
delivering a sum output thereof, and a selection circuit connected
to said integration constant generating means for alternatively
selecting, in accordance with the comparison output of said
comparator, either one of said plus and minus integration
constants.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel injection control system
which provides an additional air-fuel ratio feedback control for an
electronically controlled fuel injection system.
2. Description of the Prior Art
Fuel injection systems are known in the art in which the amount of
air drawn into an engine is measured, and the amount of fuel
predetermined in relation to the measured air quantity is
programmed in terms of the injection time of electromagnetic
valves, whereby the fuel injection quantity is regulated in
accordance with the program.
A disadvantage of fuel injection systems of this type is that while
various engine parameters such as the intake manifold vacuum and
engine temperatures may be detected to control the fuel injection
quantity, it is extremely difficult to correct for constantly
changing operating conditions of the engine, the variations
according to the type of engine, i.e., the variations with
different engines, etc., and this particularly gives rise to
serious difficulties when the vehicle is equipped with a catalytic
exhaust gas cleaning system or the like for exhaust emission
control purposes.
SUMMARY OF THE INVENTION
With a view to overcoming the foregoing difficulty, it is an object
of the present invention to provide an air-fuel ratio feedback type
fuel injection control system wherein the concentration of oxygen
contained in the exhaust gases is detected by a sensor to correct
the fuel injection quantity in accordance with the sensor output,
and the feedback follow-up characteristic of the system during
transient periods is improved, whereby permitting the engine to
operate at a predetermined air-fuel mixture ratio.
In accordance with the present invention, there is thus provided an
air-fuel ratio feedback type fuel injection control system
comprising a comparator for comparing the detected output of an
oxygen concentration sensor with a predetermined value, an adding
circuit for adding a detected value of intake state and a detected
value of engine rpms to produce a sum output, and correction means
for determining the sense of correction in accordance with the
output of the comparator and generating an error output having a
correction factor varied in accordance with the sum output. A great
advantage of this arrangement is that since the sense of correction
is determined in accordance with the comparator output, the
air-fuel mixture ratio indicated by the concentration of oxygen in
the exhaust gases which is detected by the oxygen concentration
sensor is controlled to a predetermined value, and moreover the
correction factor of the error output is controlled in accordance
with the sum output of the detected values of the intake state and
engine rpms to thereby ensure improved feedback follow-up
characteristic during transient perieds when the operating
conditions of the engine vary over a wide range or rapidly.
When the air-fuel control cannot operate properly, for example
because of a low exhaust temperature or under deceleration
conditions, a holding circuit is connected to the integrater output
to maintain the integrated output at a value intermediate the
fluctuating range thereof.
In accordance with another form of the invention, the system
further comprises stopping means for terminating the correction of
the fuel injection quantity by the feedback control system when the
supply of fuel is cut off during the deceleration periods. A great
advantage of this arrangement is that by stopping the correction of
the fuel injection quantity under the deceleration driving
conditions, it is possible to eliminate the danger of supplying an
abnormally rich mixture when the fuel injection is started again
upon termination of the deceleration driving conditions.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram showing an embodiment of an air-fuel
ratio feedback type fuel injection control system according to the
present invention.
FIG. 2 is a wiring diagram showing a detailed circuit diagram of
the principal part of the embodiment shown in FIG. 1.
FIG. 3 is an input-output characteristic diagram of the manifold
vacuum sensor in the system of FIG. 2.
FIG. 4 is an input-output characteristic diagram of the engine rpm
sensor in the system of FIG. 2.
FIG. 5 is an input-output characteristic diagram of the adding
circuit in the system of FIG. 2.
FIG. 6 is a wiring diagram showing a detailed circuit diagram for
the principal part of another embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in greater detail with
reference to the illustrated embodiments.
Referring first to FIG. 1 showing a first embodiment of the
invention, numeral 1 designates an integration constant generating
adding circuit wherein the engine rpm, intake manifold vacuum,
inlet air quantity, etc. may be detected, and the detected voltage
is converted into an error from a reference voltage V.sub.B /2
having half the value of a supply voltage to produce a negative
voltage integration constant output (the voltage smaller than the
reference voltage V.sub.B /2 is hereinafter designated as a
negative voltage and the greater one as a positive voltage).
Numeral 1A designates a vacuum sensor for generating a vacuum
voltage corresponding to the intake manifold vacuum representing
the intake state, 1B an rpm sensor for generating an rpm voltage
corresponding to the number of revolutions of an engine, 1C an
adder for producing the sum of the vacuum voltage and the rpm
voltage. Numeral 2 designates an inverting amplifier for inverting
the integration constant with respect to the reference voltage
V.sub.B /2 to generate a positive voltage inverted output. Numeral
3 designates an oxygen concentration sensor consisting of a solid
electrolyte such as zirconium oxide which is mounted in an exhaust
pipe 14 to detect the concentration of oxygen in the exhaust gases,
whereby when the exhaust gas temperature exceeds an allowable
temperature in the range between 450.degree. to 600.degree.C, the
sensor comes into normal operation in response to the oxygen
concentration and generates a concentration detecting signal.
Numeral 4 designates a temperature sensor consisting of a
thermistor for detecting the exhaust gas temperature, 5 an
allowable temperature detecting circuit responsive to the output
signal of the temperature sensor 4 for generating an output when
the exhaust gas temperature reaches the allowable temperature.
Numeral 6 designates a gating circuit whereby in the absence of the
output signal from the allowable temperature detecting circuit 5,
that is, when the exhaust gas temperature is lower than the
allowable temperature, the circuit is closed to prevent the passage
of the concentration signal from the oxygen concentration sensor 3,
whereas when the detecting circuit 5 generates an output, the
circuit is opened to permit the concentration signal to pass
therethrough. Numeral 7 designates a comparator for normally
comparing the concentration signal from the oxygen concentration
sensor 3 with a predetermined air-fuel ratio setting value V.sub.H
to generate a 1 or 0 level output signal. Numeral 8 designates a
switching circuit responsive to the output signal of the comparator
7 for determining the sense of correction to pass to the output
thereof either the negative voltage integration constant from the
integration constant generating adding circuit 1 or the positive
voltage inverted output from the inverting amplifier 2. Numeral 9
designates an integrator for integrating the negative voltage
integration constant or the positive voltage inverted output to
vary the correction factor thereof. The fuel injection quantity is
corrected in accordance with the output of the integrator 9.
Numeral 10 designates an output holding feedback circuit which
constitutes a correction stopping means and by which the output of
the integrator 9 is received as an input and fed back through the
gating circuit 6 when there is no output from the allowable
temperature detecting circuit 5, whereby the output of the
integrator 9 is held at the reference voltage V.sub.B /2 to stop
the correction of the fuel injection quantity. Numeral 11
designates the computing section of a conventional electronically
controlled fuel injection control system for generating injection
pulses having a time duration corresponding to an engine parameter
such as the intake manifold vacuum or engine temperature, whereby
the time duration of the injection pulses is corrected in
accordance with the difference between the integrated output of the
integrator 9 and the reference voltage V.sub.B /2. Numeral 12
designates electromagnetic valves which are opened by the injection
pulses from the computing section 11 to inject the required fuel
quantity, 13 an internal combustion engine, 14 the exhaust pipe of
the engine 13.
With the construction described above, the operation of the first
embodiment is as follows. The system is prearranged so that when
the integrated output of the integrator 9 becomes equal to the
value of the reference voltage V.sub.B /2, the amount of correction
by the feedback control system which applies feedback in accordance
with the oxygen concentration of the exhaust gases is reduced to
zero and a predetermined basic fuel quantity required is injected.
Assuming now that the exhaust gas temperature is below the
allowable detecting temperature, the oxygen concentration sensor 3
does not respond and thus it produces no output. This situation
corresponds to a weak mixture detecting condition so that the
output signal of the allowable temperature detecting circuit 5 acts
in such a manner that the gating circuit 6 prevents the passage of
the output of the oxygen concentration sensor 3. In other words,
the temperature sensor 4 and the allowable temperature detecting
circuit 5 detects that the exhaust gas temperature is below the
allowable temperature and thus an output for actuating the gating
circuit 6 is generated. Consequently, the output holding feedback
circuit 10 comes into operation to maintain the integrated output
of the integrator 9 at the value of the reference voltage V.sub.B
/2 and the computing section 11 generates the injection pulses
corresponding to the basic fuel requirement to inject and supply
the fuel into the engine 13 through the electromagnetic valves
12.
On the other hand, when the exhaust gas temperature exceeds the
allowable temperature, the oxygen concentration sensor 3 operates
in response to this temperature and the gating circuit 6 opens to
pass the output signal of the oxygen concentration sensor 3. In
this condition, if the oxygen concentration of the exhaust gases is
high and the mixture is weak, the concentration detecting signal
from the oxygen concentration sensor 3 is at the low level and this
low level output signal is applied to the comparator 7 through the
gating circuit 6. Consequently, the comparator 7 compares this
signal with the air-fuel ratio setting value V.sub.H and generates
a 0 level signal which is utilized to cause the switching circuit 8
to perform the selecting function and thereby to introduce the
positive voltage inverted output of the inverting amplifier 2 into
the integrator 9. As a result, the integrator 9 integrates this
inverted output and generates an integrated output voltage which
decreases gradually. In response to this integrated output voltage,
the time duration of the injection pulses from the computing
section 11 is increased and an increased amount of fuel is injected
to supply an enriched mixture. Continuation of this process causes
the oxygen concentration of the exhaust gases to decrease
gradually. When the oxygen concentration eventually drops to a
predetermined value, the output signal of the oxygen concentration
sensor 3 goes to the high level and this high level output signal
is applied to the comparator 7 by way of the gating circuit 6. When
this high level signal becomes higher than the air-fuel ratio
setting value V.sub.H, the 1 level signal from the comparator 7
causes the selecting operation of the switching circuit 8 to
introduce the sum output or the negative voltage integration
constant output of the adding circuit 1 into the integrator 9. The
integrator 9 integrates this integration constant output and
generates an integrated output voltage which rises gradually. This
integrated output voltage decreases the time duration of the
injection pulses from the computing section 11 and the fuel
injection quantity is decreased to control the oxygen concentration
to approach a predetermined value which corresponds to the optimum
air-fuel mixture ratio. Further, in the above-described feedback
control, the integration constant output by which the air-fuel
mixture ratio or the oxygen concentration at the higher exhaust gas
temperature than the allowable temperature is controlled to the
predetermined value, is the sum output from the added 1C which
produces the sum of the output voltages of the vacuum sensor 1A and
the rpm sensor 1B. In this way, any time delay due to the influence
of the velocity of exhaust gases or the response speed of the
oxygen concentration sensor 3 during the time between the
correction of the fuel injection quantity and the response of the
sensor 3 is compensated for. In other words, when the amount of air
drawn into the engine is increased greatly or in the high engine
rpm ranges, the value of the integration constant is increased to
increase the absolute value for the slope of the integrator output,
whereas when the inlet air quantity is decreased greatly or in the
low engine rpm ranges, the value of the integration constant is
decreased to decrease the absolute value for the slope of the
integrator output. In this way, it is possible to improve the
control response characteristic of the feedback control system
which maintains the air-fuel mixture ratio at a predetermined value
during transient periods when the engine operating conditions
change rapidly or over a wide range.
FIG. 2 shows the principal individual circuits of the embodiment
which perform the abovedescribed operations. In FIG. 2 showing the
individual circuits designated by numerals 1 through 10 in FIG. 1,
numerals 1a.sub.1, 1a.sub.2, 1a.sub.3, 2a, 5a, 7a, 9a and 10a
designate operational amplifiers, 1e.sub.1 and 1e.sub.2 diodes,
6b.sub.1, 6b.sub.2, 6b.sub.3, 8b.sub.1 and 8b.sub.2 transistors, 9c
and integrating capacitor, 6d.sub.1 and 6d.sub.2 relays, V.sub.B a
supply terminal to which a positive voltage is applied, G a
grounding terminal, A a voltage divider for reducing the supply
voltage to one half to supply the reference voltage V.sub.B /2 to
the circuits 2, 5, 9 and 10.
FIG. 3 illustrates an intake manifold vacuum versus vacuum voltage
characteristic diagram showing the input-output characteristic of
the vacuum sensor 1A. In FIG. 3, designated as P.sub.D is a
critical vacuum for preventing the integration constant from
decreasing excessively when the intake manifold vacuum increases
greatly, whereby when the manifold vacuum exceeds the critical
vacuum, the vacuum voltage is clamped to an anode voltage V.sub.D
of the diode 1e.sub.2. In FIG. 4, there is illustrated an engine
rpm versus rpm voltage characteristic diagram showing the
input-output characteristic of the rpm sensor 1B. In FIG. 5, there
is illustrated an intake manifold vacuum versus integration
constant characteristic diagram using the engine revolutions of the
adding circuit 1 as an parameter. With the integration constants
according to this characteristic diagram, the above-described
correction of the fuel injection quantity with improved response
characteristic during transient periods is ensured.
Referring now to FIG. 6, there is illustrated a wiring diagram
showing the principal circuits of another embodiment of the system
according to the invention. The circuits constitute second stopping
means whereby the correction of the fuel injection quantity by the
feedback control system is terminated when the supply of fuel is
cutoff during deceleration periods. In FIG. 6, numeral 100
designates a cutoff condition sensor whereby when the sum of the
outputs of a thermistor 100a for detecting the coolng water
temperature and the engine rpm sensor 1B exceeds a predetermined
value, a transistor 100b is turned off to generate a cutoff
condition signal. Numeral 200 designates a cutoff switch circuit
whereby when the accelerator pedal is released for deceleration
driving, a cutoff switch 200a is closed and a transistor 200b is
turned off to generate a cutoff switch signal. Numeral 300
designates an AND circuit whereby when both cutoff condition signal
and the cutoff switch signal are on, a transistor 300a is turned
off to generate a cutoff signal. Numeral 400 designates a cutoff
signal conversion circuit whereby when the cutoff signal is
generated, the output voltage of the temperature sensor 4 is raised
to forcibly create a condition which indicates that the engine
temperature is lower than the allowable temperature.
With the construction described above, when the supply of fuel is
cutoff, the exhaust gas temperature is high, the oxygen
concentration sensor 3 is in the normal operating condition and
there is no injection of fuel. Consequently, the oxygen
concentration sensor 3 continues to generate the low level output
signal indicative of the fact that the concentration of oxygen
contained in the exhaust gases is high and the mixture is weak. In
this case, therefore, the feedback control system serves in such a
manner that the amount of correction of the fuel injection quantity
for enriching the mixture is prevented from increasing abnormally.
In other words, during deceleration due to the releasing of the
accelerator pedal, the cutoff condition sensor 100 generates a
cutoff condition signal and the cutoff switch circuit 200 generates
a cutoff switch signal with the result that the AND circuit 300
generates a cutoff signal. This cutoff signal brings the cutoff
signal conversion circuit 400 into operation to forcibly raise the
output voltage of the temperature sensor 4. Consequently, the
output voltage of the sensor 4 indicates that the engine
temperature is lower than the allowable temperature, and thus the
output of the integrator 9 is held at the reference voltage V.sub.B
/2 and the correction of the fuel injection quantity is stopped
through the action of the previously mentioned allowable
temperature detecting circuit 5, the gating circuit 6 and the
output holding feedback circuit 10. The cutoff signal generating
means shown in FIG. 6 and comprising the cutoff condition sensor
100, the cutoff switch circuit 200 and the AND circuit 300 is
incorporated in the computing section 11 of the conventional
electronically controlled fuel injection control system. In this
case, therefore, it is necessary to add only the cutoff signal
conversion circuit 400 to the circuitry of FIG. 2 and the circuit
construction of this embodiment is thus greately simplified.
Further, while, in the second embodiment described above, the
second stopping means is designed to forcibly raise the output
voltage of the temperature sensor 4, it is of course possible to
use other means such as operating the gating circuit 6 with the
cutoff signal.
* * * * *