Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to air fuel mixture
control apparatus for an internal combustion engine.
Various mathods have been proposed to control the
air fuel mixture ratio at the stoichiometric value utilizing
after-combustion data as obtained from an exhaust gas sensor,
for example, an oxygen sensor. Such an oxygen sensor is
constructed of a hallow tube of zirconium dioxide disposed in
the exhaust passage of the engine and provides an ou-tput
voltage with a very sharp characteristic change in amplitude
at the stoichiometric air fuel ratio. The output voltage
represents the amount of oxygen contained in the exhaust gas
when the oxygen sensor is operating ln the prescribed tempera-
ture range. ~owever, under low temperature environment which
might occur as a result of idling condition of the engine or
for any reason, the oxygen sensor becomes incapable of deliver-
ing a correct composition representative signal. Moreover,
a greater concentration of unburned gases is another factor
that can degrade the performance o~ the oxygen sensor. ~;
~herefore, the primary object of the present inven-
tion is to provide an air fuel mixture control apparatus in
which the data obtained from the exhaust gas sensor is disabled
during the time the engine is operating under conditions which
adversely affect the performance of the exhaust gas sensor.
. Another object of the invention is to change the
closed loop mode of air fuel mixture control system to the
open control mode whenever undesirable conditions have occurred ~-
. to the exhaust gas sensor.
A further object of the invention is to provide air
fuel mixture control apparatus which assures hiyh stability
in response to disturbances to the engine.
A further object of the invention is to prevent a
- catalytic convertor from being heated to an elevated ~empera~
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ture as it reacts with a greater concentration of unburned
fuel components.
Briefly described, the output voltage from the oxygen
sensor is compared with a desired voltage to provide an error
signal which is fed into a proportional-integral (PI) controller
for modulating the width of control pulses which deter~ine
the opening time of the fuel control valve. The error signal
takes a value which varies in amplitude representing the
difference in amount between the sensed composition and the
desired value. In one aspect of the present invention, an
abnormal condition detector is provided to detect the length
of interval between transitions of the error signal levels -
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ahove or below a predetermined level and provides an output ~
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when a predetermined period is reached. The output from the
abnormal condition detector thus indicates that the oxygen
sensor is not properly functioning and disables the PI controller
as long as the malfunctioning continues. In another aspect
of the invention, there is provided a detector to detect
idling condition of the engine and a timing circui~ coupled
to the detector in order to disable the PI controller at a
delayed timing from the instant the idling condition lS
detected. The timing circuit preferably provides another
delayed timing operation from the instant the engine is
started for cruising speed operation. The PI controller is
thus held disabled during the time from the instant the first
delayed interval has elapsed to the instant the vehicle has
moved some distance. Such timing intervals after the idling
and the cruising operations are effective for reducing noxious
exhaust emissions at the time of transitions from closed loop
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control to open loop control and vice versa. Other engine
operating condition detectors are provided which include a
deceleration condition detector and a low engine temperature
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detector to disable the controller. Such detectors provide
information well in advance that the performance of the oxygen
sensor begins to fail and serve to protect a catalytic convertor
from an excessive heat which might occur as a result of a
; rea~tion with unburne~ fuel components.
These and other objects and advantages will be
understood from the following ~escription when taken in
conjunction with the accompanying drawings, in wh:ich:
Fig. 1 is a schematic circuit diagram of air fuel
mixture control apparatus of the present invention,
Fig. 2 is a schematic diagram of an abnormal
condition detector employed in the circuit of Fig. l;
Fig. 3 is a schematic diagram of another embodiment
of the abnormal condition detector;
Fig. 4 is a schematic diagram of a preferred form
of the Fig. 1 circuit,
Figs. 5a and 5b are a circuit diagram of an idling
condition detector of the Fig. l circuit and a waveform diagram
in connection with the circuit of Fig. 5a, respectively, ~
Figs. 6a and 6b are a circuit diagram of a second j -
form of the idling condition detector and a waveform diagram
in connection with the circuit of Fig. 6a, respectively;
Figs. 7a and 7b are a circuit diagram of a third
form of the idling condition detector and a waveform diagram
in connection with the circuit of Fig. 7a, respectively,
Figs. 8a and 8b are a circuit diagram of a fourth
; form of the idling condition detector and a waveform diagram
in connection with the circuit of Fig. 8a, respectively, and
Fig. 9 is a circuit diagram of a proportional-
integral controller oE the circuit of Fig. 1.
Referring now to Fig. 1, an air-fuel mixture control ;~
system of the present invention for an internal combustion
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engine is shown and comprises an o~ygen sensor 10 constructed
of a hollow tube of zirconium dioxide which reacts with the
amount of oxyg~n in the exhaust gases and provides an output
voltage with a very sharp characteristic change in amplitude
at the stoichiometric air fuel ratio. The output from the -
oxygen sensor 10 is coupled to a comparator 14 which may be
a differential amplifier and compares it with the desired
value. The difference between the values represents an error
signal which is modified by a proportlonal-integral controller
; 10 18. The modified signal is used to determine the width of
^ pulses to control the opening time of electromechanical valves
as represented by an air-fuel mixture means ~20. The control
pulse may be obtained by a pulse width modulator 21 which
modulates the width of pulses supplied from a pulse generator
; 23 in accordance with the signal from the PI controller 18.
,~` Therefore, the air-fuel mixture ratio is controlled by the
...
'- output from the oxygen sensor.
'r; Connected to the output of the comparator 14 is an
,~ abnormal condition detector 16 which measures the length
of interval between transitions of signal level of the output
. and provides an output when that interval exceeds a prede-
termined period. The occurrence of signal at the output of the
detector 16 indicates that an abnormal condition exists in the
control loop and is used to disable the PI controller 18. Such
abnormal condition may be triggered ~y a malfunctioning of
the oxygen sensor 10 because of its inability to operate at
temperatures below the prescribed value during the time of
idling. In addition, the oxygen sensor 10 is not able to
operate satisfactorily when the exhaust emissions contain
much unburned gases. Such high concentration of unburned
gases occurs during the time of deceleration.
In order to de-tect undesirable conditions, engine
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parameter sensors are provided which include an engine speed
sensor 24, a throttle position sensor 26 and an engine tempera-
ture sensor 28. The output from the speed sensor 24 is coupled
to comparators 30 and 32. The comparator 30 compares the
output voltage from sensor 24 with a desired value and provides
an output when the engine speed is higher than the prede-
termined speed. Throttle position sensor 26 provides an
output when the throttle valve is fully closed. The outputs
from the comparator 30 and throttle position sensor 26 are
applied to an AND gate 33. ~ high level at the output of
AND gate 34 indicates that the vehicle is under decelerating
condition. The comparator 32 on the other hand compares
; the speed sensor output with a desired value and provides
an output when the engine speed is below the predetermined
speed. The outputs from the throttle position sensor 26 and
the comparator 32 are connected to an AND gate 36 to deliver a
high level output which indicates that the vehicle is under
the idling condition. The decelerating and idling condition
signals are applied to the PI controller 18 via the OR gate
22 to disable the same.
In order to disable the PI controller 18 when the
engine te~perature is low to thereby save the system from
; the malfunctioning oxygen sensor 10, an engine temperature
sensor 28 is provided. The temperature-related signal from the
temperature sensor 28 i9 compared with a desired value by
a comparator 33 which provides an output when the engine ~
temperature is below the predetermined temperature. The output `~ -
from the comparator 33 is connected to the PI controller 18
via the OR gate 22 to disable the same.
Fig. 2 illustrates a circuit required to perform
the function of the abnormal condition detector 16. The
signal from the comparator 14 is coupled to an integrating
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circuit 201 on one hand and to an integrator 203 via an
invertor 202 on the other. Comparators 204 and 205 are
connected to the output circuits of integrators ~01 and 203 r
; respectively. The integrator 201 integrates the comparator
output while it remains high, while the integrator 203
integrates the comparator output while it remains low. Each
of the comparators 204 and 205 compares the input voltage
with a predetermined voltage delivered from a reference voltage
source 207 and provides an output to the PI controller 18 via
the OR gate 22.
An alternative circuit of the abnormal condition
detector 16 is shown in Fig. 3. The high level output from
the comparator 14 enables an AND gate 301 to pass clock pulses
to a counter 302 which provides an output when the count
reaches a predetermined nur~ber, while the low level signal
is polality inverted by an invertor 303 to enable an AND gate
304 which passes the clock pulses to a counter 305' which in like
manner counts the clock to provide an output when the same
, count is reached as in counter 302. ,The outputs from the
counters 302 and 305 are applied to the set terminal of a flip-
flop 307 via an OR gate 306" the Q output of flip-flop 307
going high to disable the PI controller 18 via OR gate 22
and to operate an alarming device 308. In order to bring
the PI controller 18 into closed circuit again when the
abnormal condition disappears, a change-of-state detector 310
is connected to the output of comparator 14. The detector
310 includes two flip-flopes311 and 312 and two monostable
rnultivibrators 313 and 314 connected to the Q output terminals
of flip-flops 311 and 312, respectively. The flip-flop 311
has its set terminal connected to the output of comparator 14
and its reset terminal connected thereto via an invertor
315, while the flip-flop 312 has its set terminal connected ~ ,
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to the comparator ou-tput via the invertor 315 and its reset
terminal connected directly thereto. When the low level
signal at the input to flip-flop 311 changes to high, mono-
stable multivibrator 313 is caused to produce a pulse which
is coupled to the counter 305 in which a count may have been
reached during the interval the low level signal continued.
Thus, a change of state from low to high level signals is
detected and the counter 305 is cleared. In like manner, when
a high level signal changes to low, flip-flop 312 is set by the
inverted signal and causes monostable multivibrator 314 to
produce an output which is applied to the counter 302, and
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-~ thus a change of state from high to low is detected and the
counter 302 is cleared. When the detector 16 is in the
automatic mode, the outputs from the change-of-state detector
,~ 310 are connected to the reset terminal of flip-flop 307 via
the "AUTO" position of an "AUTO-MANUAL" transfer switch 316 to
;j remove the high level si~nal from the Q output terminal
of flip-flop 307. In the manual mode, the switch 316 is
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transferred to the manual position, and the flip-flop 307 is ;
; 20 reset by a manual reset switch 317. -
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The circuit of Fig. 1 is modified by the provision
of a timing circuit 400 connected between the output of AND
gate 36 and the input of OR gate 22, as shown in Fig. 4. A
first form of the timing circuit 400 comprises, as shown in
Fig. 5a, a monostable multivibrator 501 and an in~ertor 502
are connected in series between one input of an AND gate 503
and the input terminal 504 to which the output from t~he AND
gate 36 is applied. The AND gate 503 has its other input
terminal connected directly to -the input terminal 504. The
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operation of the circuit of Fig. 5a will be explained ~n
connection with Fig. 5b. Upon occurrence of a signal
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(Fi~. 5b-1) from the idling condition detector which comprises
the speed sensor 24, throttle position sensor 26, comparator
32 and AND gate 36, ~the monostable multivibrator 501 produces
a pulse havlng a duration o~ T (Fig. 5b-2). This pulse is
, inverted in polarity by the invertor 502 and coupled to
and inhibit the AND gate 503. Therefore, the output of AND
gate 503 goes high at the trailing edge of the pulse produced
by the multivibrator 501 (Fig~ 5b-3) and applied to the
controller 18 via the output terminal 505 and OR gate 22.
As shown in Fig. 5b, when the temperature within the exhaust
passage begins to fall at the instant idling condition begins,
the multivibrator 501 is triggered to produce the pulse T.
As the idling condition continues the t~mperature in the
exhaust passage falls below the temperature at which the
oxygen sensor 10 is not capable of operating satisfactorily, ;~
as indicated by dashed lines. The output from the timing
circuit 400 occurs after the temperature in the exhaust
passage falls below the lower limit temperature for the oxygen
sensor 10.
A second form of the timing circuit 400 is shown
in Fig. 6a. The sensed idling signal (Fig. 6b-l) from the
AND gate 36 of the idling detector is applied to a monostable
multivibrator 602 via an OR gate 601. A first pulse having a
duration of "T" (Fig. 6b-2) is produced and inverted by an
invertor 603 to disable an AND gate 604 while the multivibrator
output remains high. The AND gate 604 places a high level
input (Fig. 6b-3) to the set terminal of flip-flop 605 at
the trailing edge of the pulse. The high level Q output is
connected to an AND gate 606. The idling signal at the
input terminal 607 is also coupled to an invertor 610
and inverted thereby. The inverted signal is passed through
` AND gate 606 and OR gate 601 to the monostable multivibrator
602 to produce a second pulse
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(Fig. 6b-2). This second pulse appears at the output terminàl
608 via an AND gate 609 since it is enabled by the high level
signal at the output of invertor 610 while resetting the flip-
flop 605 (Fig. 6b-4).
In this embodiment, the PI controller 18 is inhibited
during time "T" from the instant the vehicle begins to cruise.
The temperature in the exhaust passage falls to a temperature
below the lower limit for the oxygen sensor 10 until it rises
again as the vehicle gathers speed.
` lO A third form of the timing circuit 400 .is shown
` in Fig. 7a. The sensed idling signal (Fig. 7b-1) applied
- to the input terminal 700 triggers an monostable multivibrator
702 via an OR gate 701 -to produce a pulse having a duration
"T" (Fig. 7b-2) which is inverted by an invertor 703 and
applied to an AND gate 70S to which is also coupled the signal - -
on input terminal 700. The AND gate 705 produces a high level
signal when the time "T" has elapsed (Fig. 7b-3). The high
level output from the AND gate 705 is connected to the output
terminal 704 via an OR gate 706 and at the same time applied
to one input of an AND gate 707 to which is also applied the
inverted of signal on input terminal 700. The AND gate 707
produces a high level signal when the idling signal goes low
as the vehicle begins to move at cruising speeds, this high
output from AND gate 707 being coupled to the monostable
multivibrator 702 via OR gate 701 to,trigger a second pulse~ ;
The second pulse is applied to an AND gate 708 and passed there-
through to the output terminal 704. Therefore, it will be
noted that the PI controller 18 is inhibited from the trailing
edge of the first timing pulse "T" to the trailing edge of
the second timing pulse. ~ -
A forth form of the timing circuit 400 is shown in
; Fig. 8a. The idling signal (Fig. 8a-1) at the input terminal
.
800 is inver-ted by an invertor 801 and applied to an operational
integrating circuit ~02. The integrated signal (Fig. ~b-2)
is co~pared with a desired value by a comparator 803 which
` provides an output which lasts from the instant the integrated
signal is above the desired voltage level (Fig. 8b-3). The
idling signal is also applied to the output terminal 805 via
an inhibit gate 804. The output from the compara-tor 803 is
used to inhibit the gate 804 so that the output terminal 805
goes low at the instant which is delayed by time Tl from the
end of idling condition and goes high again at the instant ~ -
delayed by time T2 from the instant an idling con~ition
occurs again (Fig. 8b-4).
- The integrating circuit 802 may preferably be of a ;
variable rate integration type and constructed an operational
amplifier 810 having its inverting input coupled to the outpu-t
of invertor 801 via the input resistor 811. This input resistor
has a parallel, shunt connection formed of the emitter-
collector path of a transistor 812 and a resistor 813. The
base electrode of the transistor 812, which is an npn switching
transistor, is connected over lead 814 to the output of a
-~ coincidence circuit 806. The coincidence circuit 806 has
two input terminals, one being connected to the input terminal
800 and the other connected to the output terminal 805. When
the two input signals coincide with each other, the coincidence
circuit 806 produces an output which is applied to the base
of transistor 812. Transistor 812 conducts and places resistor
813 in parallel to resistor 811 and thus changing the inte-
~ gration rate of operational amplifier 810, as shown in Fig.
; 8a 5. The change in the rate of integration occurs both at
the leading and trailing edges of the inhibit pulse. This
arrangement is particularly advantageous when the vehicle
experiences a rapid succession of idling and cruising conditions
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which is likely to tale place during a congested traffic, since
under such conditi~ns the integrator 802 would begin integra-
tion in opposite direction before the integrated voltage
reaches its saturation voltage.
The timing circuit 400 as described above provides
various timing operations which allow delayed switching to
change from closed to open control and vice versa. The
delayed switching permits transition to occur more smoothly
than otherwise because there exists a delayed time from the
10 instant a disturbance to the system occurs to the instant
a response is observed.
Another important factor that influence the smooth
transition of operation from open to closed loop control is
the amplitude of error signal provided at the output of PI
controller 18 when switching is to be made; if the signal
amplitude is high when the closed loop control is resumed,
oscillation would occur in the closed loop, thus adversely
affecting the system performance.
In order to avoid such undesirable consequences,
the integrating gain of the integral control amplifier~of
the PI controller 18 is held to a minimum in response to the
occurrence of the disabling signal applied to the controller
~l 18.
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Fig. 9 shows a circuit which is required to perform
the aforesaid purpose. The PI controller 18 comprises a
proportional control amplifier 901, an integrating control
amplifier 902 and an àdder circuit 903. The proportional and ~ -
integrating control amplifier 901 and 902 have their inputs
connected in common to the output of comparator 14 and their
- 30 outputs connected in common to one input of the adder 903.
The proportional control amplifier 901 comprises an operational
amplifier 904 and has its inverting input terminal connected
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to the output of comparator 14 via a resistor 905 and further
connected to its output via a resistor 906 and its noninverting
input connected to ground reference. The output of the
proportional amplifier 901 is coupled to the inverting terminal
of an operational amplifier 907 of adder 903 via an input
resistor 908 and a normally closed relay contact 909. The
integrating amplifier 902 comprises an operational amplifier
910 having its inverting terminal connected to the output of
com?arator 14 via a resistor 911 and further connected to its
output terminal via an integrating capacitor 912 which is
shunted by a normally open relay contact 9I3, and its non-
inverting terminal connected to ground. The output of the
integrating amplifiex 910 is coupled to the inverting terminal
of amplifier 907 via an input resistor 914. The amplifier
907 of adder 903 has its noninverting terminal connected
ii
to a reference voltage provided at the junction between
resistors 915 and 916 connected together in series across a
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, voltage source Vcc and ground. The two signals from the
proportional and integrating control amplifiers 901 and 902
are added up and connected to the input of the pulse width
modulator 21. The relay contacts 909 and 913 are simultaneously
operated when relay 917 is energized by the disabling signal
from OR gate 22. The operation of relay 917 disconnects the
output circuit of proportional controller 901, while short-
circuiting the integrating capacitor 912 of controller 902
thus bringing the output potential to zero. It will be noted
therefore that when the closed loop control is resumed, i.e.
when the disabling signal is removed, the voltage at the
~! input to the adder 903 is at a minimum and thus no output
, 30 will be delivered to the pulse width modulator 21.
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