U.S. patent number RE31,906 [Application Number 06/382,692] was granted by the patent office on 1985-06-04 for control system for internal combustion engine.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Yutaka Nishimura, Yoshishige Oyama, Teruo Yamauchi.
United States Patent |
RE31,906 |
Oyama , et al. |
June 4, 1985 |
Control system for internal combustion engine
Abstract
A control system including a microprocessor for controlling the
controlled variables of an internal combustion engine, especially,
the flow rate of fuel is disclosed. An air flow meter provides an
output signal having such a non-linear characteristic relative to
the flow rate of intake air that the signal level increases in the
region of the small flow rate of intake air. The microprocessor
carries out necessary digital computation on the basis of the
output signal of the air flow meter to provide a fuel flow rate
control signal. This digital control signal is converted into a
signal having a linear characteristic proportional to the flow rate
of intake air, or after having been produced from the
microprocessor, converted into a signal including information
proportional to the flow rate of intake air.
Inventors: |
Oyama; Yoshishige (Katsuta,
JP), Yamauchi; Teruo (Katsuta, JP),
Nishimura; Yutaka (Katsuta, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
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Family
ID: |
12729204 |
Appl.
No.: |
06/382,692 |
Filed: |
May 27, 1982 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
899159 |
Apr 24, 1978 |
04205377 |
May 27, 1980 |
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Foreign Application Priority Data
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Apr 22, 1977 [JP] |
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52-45795 |
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Current U.S.
Class: |
701/108; 123/480;
123/494; 123/694; 73/204.18 |
Current CPC
Class: |
F02D
41/1479 (20130101); F02D 41/24 (20130101); F02D
41/187 (20130101); F02D 41/182 (20130101) |
Current International
Class: |
F02D
41/14 (20060101); F02D 41/18 (20060101); F02D
41/00 (20060101); F02D 41/24 (20060101); G06F
015/20 (); F02D 033/00 () |
Field of
Search: |
;364/431.04,431.05,431.06 ;123/475,480,483,484,485,486,494,589
;73/204 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Datametrics Bulletin: Heated Sensor Finds Wide Applications in
Fluid Flow Measurements, Publication of 1971..
|
Primary Examiner: Gruber; Felix D.
Attorney, Agent or Firm: Antonelli, Terry & Wands
Claims
We claim:
1. A control system for an internal combustion engine comprising:
an air flow meter for metering the flow rate of intake air supplied
to the engine and for producing an output signal relative to the
flow rate of intake air; a plurality of sensors for detecting
different conditions of engine operation; a microprocessor for
carrying out digital computation on the basis of the output signal
of said air flow meter and the output signals of said sensors
thereby providing a plurality of control signals for controlling
the controlled variables of the engine; fuel supply means for
supplying fuel to the engine; and fuel flow rate control means for
controlling the flow rate of fuel supplied by said fuel supply
means according to a fuel flow rate control signal among the
control signals; wherein said air flow meter includes means for
producing, as said output signal relative to the flow rate of
intake air, a non-linear signal having a
.Iadd.continually-increasing .Iaddend.non-linear characteristic
.Iadd.with increase in flow rate .Iaddend.such that the changing
rate of said signal with respect to the flow rate of intake air is
greater in a predetermined region in which the flow rate of intake
air is small than in other regions of the flow rate of intake air,
said microprocessor being supplied with said non-linear signal in a
digital form for carrying out digital computation on the basis of
said non-linear signal.
2. A control system for an internal combustion engine as claimed in
claim 1, wherein the output signal of said air flow meter provides
a desired resolution for intake air over the entire range of the
flow rate of intake air when said output signal is processed with a
limited number of bits required for said microprocessor for the
control of the controlled variables of the engine.
3. A control system for an internal combustion engine as claimed in
claim 1, wherein the output signal X of said air flow meter is
substantially expressed as X=K.sub.1 log Q+K.sub.2 where Q is the
flow rate of intake air and K.sub.1 and K.sub.2 are constants.
4. A control system for an internal combustion engine as claimed in
claim 1, wherein the output signal X of said air flow meter is
substantially expressed by a function of the liquadratic root of Q,
where Q is the flow rate of intake air.
5. A control system for an internal combustion engine as claimed in
claim 1, wherein said non-linear signal producing means comprises a
heater means disposed in the flow of intake air, the temperature of
said heater means changing according to the flow rate of intake
air; a sensing means for producing an output signal in accordance
with a change in the temmperature of said heater means; an
integrating means for integrating the output signal of said sensing
means; and a square-root circuit means receiving an output of said
integrating device for producing said non-linear signal on the
basis of the output of said integrating means.
6. A control system for an internal combustion engine as claimed in
claim 1, wherein said non-linear signal producing means comprises
heater means disposed in the flow of intake air, the temperature of
said heater means changing according to the flow rate of intake
air; sensing means for producing an output signal in accordance
with a change in the temperature of said heater means; a control
signal producing means for producing a control signal in response
to the output signal of said sensing means; a current control means
for controlling a current flowing through said heater means in
accordance with the control signal of said control signal producing
means to maintain the temperature of the heater means constant; and
an output means for producing said non-linear signal on the basis
of the controlled current.
7. A control signal as claimed in claim 6, wherein said non-linear
signal producing means further comprises detecting means for
detecting the signal produced from said output means and producing
an output signal when detecting a predetermined level of said
detected signal, and an adjusting means for adjusting the sensing
level of said sensing means, in accordance with the output signal
of said detecting means.
8. A control system for an internal combustion engine as claimed in
claim 1, 2, 3, 4, 5, 6, or 7 wherein said fuel flow rate control
means includes a magnetic means energized in accordance with said
fuel flow rate control signal produced from said microprocessor,
and said fuel supply means includes a valve means disposed in a
flow path of the fuel and operating in response to the energization
of said magnetic means.
9. A control system for an internal combustion engine as claimed in
claim 1, 2, 3, 4, 5, 6, or 7 wherein said microprocessor carries
out digital computation to obtain said fuel flow rate control
signal as a signal having said non-linear characteristic, and said
control system further comprises means for converting said fuel
flow rate control signal into a linear signal proportional to the
flow rate of intake air.
10. A control system for an internal combustion engine as claimed
in claim 9, wherein said converting means includes means delimiting
an opening allowing flow of fuel to be supplied to the engine, a
cam means having a profile determined according to said non-linear
characteristic and driven in accordance with said fuel flow rate
control signal, and a movable means driven by said cam means for
adjusting the area of the opening in accordance with the profile of
said cam means.
11. A control system for an internal combustion engine as claimed
in claim 9, wherein said converting means includes means delimiting
an opening allowing flow of fuel to be supplied to the engine and
having a profile determined according to said non-linear
characteristic, a cam means driven in accordance with said fuel
flow rate control signal, and a movable means driven by said cam
device for at least partially closing the opening. .Iadd.
12. A control system for an internal combustion engine comprising:
an air flow meter for metering the flow rate of intake air supplied
to the engine and for producing an output signal relative to the
flow rate of intake air; a plurality of sensors for detecting
different conditions of engine operation; a microprocessor for
carrying out digital computation on the basis of the output signal
of said air flow meter and the output signals of said sensors
thereby providing at least one control signal for the engine; fuel
supply means for supplying fuel to the engine; and fuel flow rate
control means for controlling the flow rate of fuel supplied by
said fuel supply means according to said control signal; wherein
said air flow meter includes means for producing, as said output
signal relative to the flow rate of intake air, a non-linear signal
having a continually-increasing non-linear characterstic with
increase in flow rate such that the changing rate of said signal
with respect to the flow rate of intake air is greater in a
predetermined region in which the flow rate of intake air is
smaller than in other regions of the flow rate of intake air, said
microprocessor being supplied with said non-linear signal in a
digital form for carrying out digital computation on the basis of
said non-linear signal. .Iaddend. .Iadd.
13. A control system for an internal combustion engine comprising:
an air flow meter for metering the flow rate of intake air supplied
to the engine and for producing an output signal relative to the
flow rate of the intake air; a plurality of sensors for detecting
different conditions of engine operation; a microprocessor for
carrying out digital computation on the basis of the output signal
of said air flow meter and the output signals of said sensors
thereby providing a plurality of control signals for controlling
the controlled variables of the engine, fuel supply means for
supplying fuel to the engine; and fuel flow rate control means for
controlling the flow rate of fuel supplied by said fuel supply
means according to a fuel flow rate control signal among the
control signals; wherein said air flow meter includes means for
producing, as said output signal relative to the flow rate of
intake air, a non-linear signal having a continually-increasing
non-linear characteristic with increase in flow rate such that the
changing rate of said signal with respect to the flow rate of
intake air is greater in a predetermined region in which the flow
rate of intake air is small than in other regions of the flow rate
of intake air, said control system further comprising means for
converting said non-linear signal to a digital form, said
microprocessor being supplied with said non-linear signal in a
digital form for carrying out digital computation on the basis of
said non-linear signal. .Iaddend. .Iadd.14. A control system for an
internal combustion engine comprising: an air flow meter for
metering the flow rate of intake air supplied to the engine and for
producing an output signal relative to the flow rate of intake air;
a plurality of sensors for detecting different conditions of engine
operation; a microprocessor for carrying out digital computation on
the basis of the output signal of said air flow meter and the
output signals of said sensors thereby providing at least one
control signal for the engine; fuel supply means for supplying fuel
to the engine; and fuel flow rate control means for controlling the
flow rate of fuel supplied by said fuel supply means according to
said control signal; wherein said air flow meter includes means for
producing, as said output signal relative to the flow rate of
intake air, a non-linear signal having a non-linear characteristic
such that the changing rate of said signal with respect to the flow
rate of intake air is greater in a predetermined region in which
the flow rate of intake air is smaller than in other regions of the
flow rate of intake air, said control system further comprising
means for converting said non-linear signal to a digital form, said
microprocessor being supplied with said non-linear signal in a
digital form for carrying out digital computation on the basis of
said non-linear signal. .Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to a system for controlling an internal
combustion engine, and more particularly to a control system in
which the signals representing the amount of air supplied to an
internal combustion engine, the temperature of the engine, the
rotating speed of the engine, the load of the engine, and the
composition of exhaust gases from the engine are processed by a
microprocessor to obtain various control signals so that these
control signals can be used for the control of the controlled
variables of the engine, especially, for the control of the amount
of fuel supplied to the engine.
A known disclosure, for example, U.S. Pat. No. 3,969,614 discloses
a method for controlling an internal combustion engine in which a
digital computer is used to control the controlled variables of the
engine, including the amount of fuel supplied to the engine, the
ignition timing and the amount of exhaust gases recirculated
through the engine, on the basis of the results of detection on the
amount of intake air supplied to the engine, the temperature of the
engine, the rotating speed of the engine, the load of the engine,
and the composition of exhaust gases from the engine.
In the steady running condition of a motor vehicle driven by an
internal combustion engine, the amount of intake air supplied to
the engine is the most important factor for controlling the amount
of fuel supplied to the combustion chamber of the engine. The flow
rate of intake air is detected by an air flow meter disposed
upstream of the throttle valve, and an output signal representing
the detected flow rate of intake air is delivered from the air flow
meter.
In a fuel supply system in which fuel is supplied to an internal
combustion engine in synchronous relation with the engine
crankshaft position, a method is generally employed according to
which the open period of the fuel valve is controlled to control
the amount of fuel supplied to the engine. In this case, the open
period of the fuel valve is controlled to lie approximately within
the range of 2.5 ms to 9 ms. When a digital signal is used as this
control signal for controlling the open period of the fuel valve, a
binary-coded decimal signal of 12 bits (=4.times.3) will be enough
to ensure the accuracy of control within 1%. Suppose that the
minimum open period 2.5 ms of the fuel valve corresponds to a
binary-coded decimal number 100. Then, the maximum open period 9 ms
of the fuel valve will be less than a binary-coded decimal number
400, and the number of bits of the binary-coded decimal signal will
be as many as 11 bits (=3+4+4). Suppose further that the digital
signal is a binary-coded signal, and 256 (=2.sup.8) corresponds to
the maximum open period 9 ms of the fuel valve. Then, the minimum
open period 2.5 ms of the fuel valve will correspond to about 50,
and a digital signal of 8 bits will be enough to ensure the
accuracy of control within .+-.1% (=.+-.0.5/50). Therefore, a
digital control signal having a limited number of bits as above
described can be sufficiently used for the desired control of the
amount of fuel supplied to the engine.
However, due to the fact that the output signal of the air flow
meter has a level which is generally approximately proportional to
the detected flow rate of intake air, the output signal of the air
flow meter has a low level when the flow rate of intake air is
small. Thus, when the output signal of such a low level is
converted into a digital signal of a limited number of bits to be
used for digital processing, a change in the flow rate of intake
air in this region cannot be represented with high accuracy. In
other words, the resolution of the flow rate of intake air is
degraded in the small flow rate region when such a flow rate is
represented by the digital signal of the limited number of bits.
This fact will be discussed in more detail. Generally, the metering
range of the air flow meter metering the flow rate of intake air is
from about 0.1 m.sup.3 /min to about 5 m.sup.3 /min which is about
50 times the value of 0.1 m.sup.3 /min. Suppose that the flow rate
of intake air is represented by a binary-coded signal of 10 bits,
and the maximum flow rate of intake air 5 m.sup.3 /min is
represented by 2.sup.10 =1024, then, the minimum flow rate of
intake air which is about 0.1 m.sup.3 /min is represented by
1024/507/8207/82.sup.4 =16. Therefore, a high resolution of about
1/1000.times.100=0.1% is obtained in a region where the flow rate
of intake air is large or close to its maximum, and a change in the
flow rate of intake air can be indicated with high accuracy in such
a region. However, the resolution is only about 1/20.times.100=5%
in a region where the flow rate of intake air is small or close to
its minimum, and a change in the flow rate of intake air within 5%
cannot be indicated in such a region.
Therefore, in an engine control system in which the output signal
of an air flow meter is converted into a digital signal of a
limited number of bits and is then subjected to digital processing
by a microprocessor to obtain a control signal for controlling the
amount of fuel supplied to the combustion chamber of the engine,
the control signal contains an insufficient amount of information
when the flow rate of intake air is small, and the accuracy of
control of the amount of fuel supplied to the combustion chamber of
the engine is reduced in the region where the flow rate of intake
air is small or close to its minimum. The control of the air-fuel
ratio to maintain it at a proper value in the region of the small
flow rate of intake air, that is, during driving a vehicle at low
speeds is especially important from the viewpoint of obviating
environmental pollution by the toxic components of engine exhaust
gases, and such a reduction in the accuracy of control of the
amount of fuel supplied to the combustion chamber of the engine
must be avoided as much as possible. It is necessary to increase
the number of bits of the digital signal representing the flow rate
of intake air detected by the air flow meter in order to prevent
the undesirable reduction in the accuracy of control in the region
of the small flow rate of intake air. To this end, the
microprocessor must have a parallel processing capacity with an
increased number of bits, or the arithmetic processing time in the
microprocessor must be extended when the parallel processing
capacity of the microprocessor is not increased. The former is
disadvantageous from the economical standpoint, and the latter is
also disadvantageous from the standpoint of the control response,
hence, the accuracy of control.
The prior art proposals have failed to refer to the problem of the
forementioned reduction in the accuracy of control of the internal
combustion engine in the region of the small flow rate of intake
air, especially, the problem of the undesirable reduction in the
accuracy of control of the amount of fuel supplied to the
combustion chamber of the engine in such a region, and have also
failed to provide any concrete solution for this problem.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a
control system of the kind including a microprocessor for
controlling an internal combustion engine, especially, for
controlling the amount of fuel supplied to the combustion chamber
of the engine on the basis of a principal control factor which is
the flow rate of intake air, which system is novel and improved
over the prior art systems in that no increase is required in the
parallel processing capacity of the microprocessor, and the
arithmetic processing time need not be unnecessarily extended.
It is an important feature of the engine control system according
to the present invention that the air flow meter provides an output
signal having such a non-linear characteristic relative to the flow
rate of intake air that the signal level increases in the region of
the small flow rate of intake air, and on the basis of such an
output signal, the microprocessor carries out necessary digital
processing to provide a control signal used for the control of the
internal combustion engine, especially, for the control of the
amount of fuel supplied to the combustion chamber of the
engine.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram of an embodiment of the control
system for an internal combustion engine according to the present
invention.
FIG. 2 is a graph showing various output signals of the air flow
meter in FIG. 1 relative to the flow rate of intake air.
FIG. 3 is a graph showing a most ideal output signal of the air
flow meter relative to the flow rate of intake air.
FIG. 4 shows schematically the structure of one form of the air
flow meter preferably employed in the present invention.
FIG. 5 is a graph illustrating the output signal of the air flow
meter shown in FIG. 4.
FIG. 6 shows schematically the structure of another form of the air
flow meter preferably employed in the present invention.
FIG. 7 shows schematically the structure of still another form of
the air flow meter preferably employed in the present
invention.
FIG. 8 is a graph illustrating the output signal of the air flow
meter shown in FIG. 7.
FIG. 9 shows schematically the structure of yet another form of the
air flow meter preferably employed in the present invention.
FIG. 10 illustrates how an ideal output signal can be provided by
the air flow meter shown in FIG. 9.
FIG. 11 is a diagrammatic view of one form of the fuel flow rate
control unit of continuous metering type preferably employed in the
present invention.
FIGS. 12 and 13 illustrate how a proper amount of fuel can be
supplied by the fuel flow rate control unit shown in FIG. 11.
FIG. 14 is a diagrammatic view of one form of the fuel flow rate
control unit of intermittent metering type preferably employed in
the present invention.
FIG. 15 is a schematic block diagram of part of another form of the
fuel flow rate control unit of intermittent metering type
preferably employed in the present invention.
FIG. 16 illustrates the operation of the control unit shown in FIG.
15.
FIG. 17 is a schematic block diagram of part of still another form
of the fuel flow rate control unit of intermittent metering type
preferably employed in the present invention.
FIG. 18 is a schematic block diagram of a fast idling device.
FIG. 19 is a graph showing the relation between the amount of
intake air and the amount of air charged into the combustion
chamber of the engine.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in detail with
reference to the accompanying drawings. Referring to FIG. 1, an air
flow meter 100 is disposed upstream of a throttle valve 104 in an
intake duct 102 of an internal combustion engine 105. The air flow
meter 100 generates an output signal representing the flow rate of
air supplied into the intake manifold of the engine 105 depending
on the opening of the throttle valve 104. This output signal of the
air flow meter 100 is a most important factor for the control of
the amount of fuel to be supplied to the combustion chamber of the
engine 105. The amount of supplied fuel should be varied depending
on the operating condition of the engine 105, and means are
provided for this purpose which include a throttle position sensor
106 detecting the opening of the throttle valve 104, an intake air
pressure sensor 108 detecting the air pressure in the intake
manifold, a crank angle sensor 110 detecting the angular position
of rotation of the engine crankshaft, a temperature sensor 112
detecting the temperature of the engine cylinder head and/or the
temperature of the engine crankshaft, and an oxygen sensor 116
detecting the exhaust gas composition in an exhaust manifold 114,
especially, the concentration of oxygen contained in the engine
exhaust gases. A fuel flow rate control unit 120 is provided for
controlling the flow rate of fuel injected into the intake manifold
from a fuel injection unit 118. A sensor 122 sensing the operation
of the fuel flow rate control unit 120 is provided to correct the
amount of fuel injected from the fuel injection unit 118 when the
control unit 120 is incorrectly active. The output signals of the
air flow meter 100 and sensors 106, 108, 110, 112, 116 and 122 are
applied to a microprocessor 128 through a multiplexer 124 and an
analog-to-digital (A-D) converter 126. In response to the
application of these digital input signals, the microprocessor 128
carries out necessary digital processing of these inputs using
various constants and functions previously stored in an associated
memory unit 130 and delivers through an output unit 132 various
control signals required for the control of the operation of the
engine, such as the control of the amount of supplied fuel, control
of the ignition timing and control of the exhaust gas
recirculation. A timer 134 is provided so that such control signals
can be applied to the various control units during the desired
period of time.
In FIG. 1, the multiplexer 124 and A-D converter 126 are shown
included in the system since it is supposed that the air flow meter
100 and various sensors 106, 108, 110, 112, 116 and 122 generate
analog output signals. When, however, the air flow meter and
sensors are designed to generate digital output signals, the
multiplexer 124 and A-D converter 126 may be replaced by an input
unit used generally for a digital computer. The fuel injection unit
118 is shown injecting fuel to a point downstream of the throttle
valve 104 in the intake duct 102, as it is associated with the
so-called continuous metering type adapted for supplying fuel
without regard to the rotation phase of the engine. However, in
case of the so-called intermittent metering type adapted for
supplying fuel in synchronous relation with the rotation phase of
the engine, the fuel injection unit 118 is disposed as shown, or
otherwise on the cylinder head of the engine. It is apparent that
various other sensors than those shown in FIG. 1 may be provided as
required. The multiplexer 124, A-D converter 126, microprocessor
128, memory unit 130 and output unit 132 may be disposed on a
single substrate or printed circuit board.
FIG. 2 shows the level of the output signal X of the air flow meter
100 relative to the flow rate Q of intake air. The output signal X
appearing from the air flow meter in the prior art is as shown by
the curve A or B in FIG. 2, and it will be seen that the output
signal X has a level approximately linearly proportional to the
metered flow rate Q of intake air, and the resolution for the flow
rate Q of intake air is reduced in the region of the small flow
rate of intake air when this signal X is converted into a digital
signal of a limited number of bits to be subjected to digital
processing in the microprocessor 128. This problem can be solved
when the level of the signal X relative to the flow rate Q of
intake air in the region of the small flow rate of intake air is
increased as shown by the curve C, D or E in FIG. 2. In the case of
the curve E, the signal X has a low level in the region of the
large flow rate of intake air, and the resolution for the metered
flow rate of intake air is reduced in such a region, resulting in a
corresponding reduction in the accuracy of control of the amount of
fuel supplied to the combustion chamber of the engine. However, in
the region in which the flow rate of intake air is large, that is,
when the vehicle is running at high speeds, the air-fuel ratio need
not be so strictly determined as the engine exhaust gases do not
contain toxic components in such a large amount which will give
rise to the problem of environmental pollution.
Suppose that the relation between the flow rate Q of intake air and
the output signal X of the air flow meter 100 is expressed as
Differentiation of the equation (1) gives the following
equation:
Suppose then that .DELTA.Q/Q and .DELTA.X are constant, then, the
following equation holds:
where K is a constant.
X is expressed as
where K.sub.1 and K.sub.2 are constants. It is thus known that,
when the signal X represented by the equation (4) is obtained for
the flow rate Q of intake air, .DELTA.X is constant when the
.DELTA.Q/Q is constant, that is, the level of the signal X changes
always at a constant rate when the flow rate Q of intake air
changes at a constant rate. This proves the fact that the same
resolution is obtained over the entire range of the flow rate Q of
intake air which is converted into a digital signal. The relation
between the flow rate Q of intake air and the output signal X of
the air flow meter 100, which relation is expressed by the equation
(4), corresponds to the curve C in FIG. 2 and is shown by the curve
F in FIG. 3. Suppose that 1 m.sup.3 of air has a weight of 1.5 Kg,
then, the aforementioned flow rate of 0.1 to 5 m.sup.3 /min is
converted approximately into 9 to 450 Kg/h. Suppose then that
K.sub.1 =1 and K.sub.2 =0 in the equation (4), then, the value of
the signal X ranges from 2.2 (=log 9) to 8.3 (=log 450). Thus, the
output signal X of the air flow meter 100 can be converted into a
digital signal of a small number of bits since the maximum value
8.3 is only about 4 times as large as the minimum value 2.2. The
equation (4) representing the relation between the flow rate Q of
intake air and the output signal X of the air flow meter 100
provides an ideal relation. For the purpose of the present
invention, the relation between the flow rate Q of intake air and
the output signal X of the air flow meter 100 is not limited to
that represented by the equation (4) and may be as that represented
by the curve D or E in FIG. 2.
FIG. 4 shows schematically the structure of one form of the air
flow meter 100 preferably employed in the present invention. The
air flow meter shown in FIG. 4 is of the thermal type having a
heater 10 including fixed resistors 11 and 12. This heater 10
constitutes a resistance bridge circuit together with fixed
resistors 13, 14 and a variable resistor 15. A change in the flow
rate of intake air results in a corresponding change in the
temperature of the heater 10, and a voltage corresponding to the
change in the heater temperature appears across the bridge
terminals 16 and 17. This voltage is applied to an operational
amplifier 18 to be integrated, and the resultant control signal is
applied from the operational amplifier 18 to a current control
circuit 19. In response to the application of the control signal to
the current control circuit 19, it acts to increase the current
value supplied to the heater 10 to compensate the temperature drop
in the heater 10, while it acts to decrease the current value
supplied to the heater 10 to compensate the temperature rise in the
heater 10, so that the bridge circuit can be balanced always. This
change in the current value is derived as a change in the voltage
across a resistor 20, and the output signal X thus obtained for the
metered flow rate Q of intake air is applied to the microprocessor
128.
From the balance between the quantity of heat generated by the
heater 10 and the degree of cooling of the heater 10 depending on
the flow rate Q of intake air, the following equation holds:
where I is the current value supplied to the heater 10 to maintain
constant the temperature of the heater 10, R is the resistance
value of the resistor 11 in the heater 10, A and B are constants
determined from the theory of thermal conduction, T.sub.w is the
temperature of the heater 10, and T.sub.a is the temperature of
intake air. It will be apparent from the equation (5) that the
current I, hence, the output signal X of the flow meter is a
function of the biquadratic root of the flow rate Q of intake air
and is approximate to the curve F shown in FIG. 3. In FIG. 5, such
a curve F is shown by the one-dot chain line, and the curve G shown
by the solid line corresponds to the relation given by the equation
(5).
Another method may be used to obtain a curve approximate to the
curve F. According to this method, the bridge circuit is balanced
when the flow rate Q of intake air is zero, and with the increase
in the flow rate Q of intake air, the current I supplied to the
heater 10 is increased in a relation corresponding to the voltage
appearing across the bridge terminals 16 and 17. This voltage is
proportional to the square root of the flow rate Q of intake air.
Thus, when this voltage is applied to a square-root circuit 21
after being integrated in the operational amplifier 18, and the
output of the square-root circuit 21 is derived as the signal X,
this signal X is a function of the biquadratic root of the flow
rate Q of intake air and can be approximated to the curve F. The
dotted curve H in FIG. 5 represents the output of the operational
amplifier 18 in this case.
The air flow meter shown in FIG. 4 further includes a detection
circuit 22 which detects the value of the signal X and generates
its output signal when a predetermined value is detected, and a
control circuit 23 including an element such as a servomotor which
operates to adjust the resistance value of the variable resistor 15
in response to the application of the output signal of the
detection circuit 22 thereto, so that the curve G can be further
approximated to the curve F in the region in which the flow rate Q
of intake air is small. The control circuit 23 adjusts the
resistance value of the variable resistor 15 so as to increase the
heater temperature T.sub.w in the region in which the flow rate Q
of intake air is small. The reference numerals 24 and 25 designate
temperature sensors detecting the intake air temperatures at points
upstream and downstream respectively of the heater 10 in the intake
duct 102, and the numeral 26 designates a switch used for varying
the resistance value of the heater 10.
FIG. 6 shows schematically the structure of another form of the air
flow meter 100 preferably employed in the present invention. The
air flow meter shown in FIG. 6 is of the thermal type similar to
that shown in FIG. 4. Referring to FIG. 6, temperature sensitive
resistances are used as intake air temperature sensors 24 and 25
which constitute a bridge circuit together with fixed resistors 27
and 28. The bridge voltage appearing across the bridge terminals 29
and 30 is applied to an operational amplifier 31 to be integrated
to provide a control signal applied to a current control circuit
32. When the current control circuit 32 controls the current
supplied to a heater 10 composed of resistors 11 and 12 so as to
provide zero bridge voltage across the bridge terminals 29 and 30,
the following reation holds:
where C.sub.p is the specific heat at constant pressure, and
.DELTA.T is the difference between the intake air temperatures
detected by the temperature sensors 24 and 25. The temperature
difference .DELTA.T is constant when the bridge voltage appearing
across the bridge terminals 29 and 30 is zero. Therefore, the flow
rate Q of intake air is found by measuring the power consumption
RI.sup.2 of the heater 10. A constant-voltage circuit 33 is
connected between the current control circuit 32 and the heater 10
to apply a constant voltage across the heater 10. Thus, the heater
current I is proportional to the flow rate Q of intake air.
Therefore, detection of the heater current I provides the signal X
representing the flow rate Q of intake air, as in the case of the
air flow meter structure shown in FIG. 4. In the region in which
the flow rate of intake air is small, the resistor 11 in the heater
10 is used alone by disconnecting the resistor 12 by turning off a
switch 26. On the other hand, in the region in which the flow rate
of intake air is large, the switch 26 is turned on to connect the
resistor 12 in parallel with the resistor 11 thereby decreasing the
resistance value of the heater 10. In this manner, a non-linear
characteristic similar to that shown by the curve D in FIG. 2 can
be obtained.
In the air flow meter structure shown in FIG. 6, the bridge voltage
is proportional to the temperature difference .DELTA.T, hence,
inversely proportional to the flow rate Q of intake air when the
heater current I is maintained constant. In such a case, therefore,
the signal X obtained by integrating the bridge voltage in the
operational amplifier 31 has a non-linear characteristic as shown
by the curve E in FIG. 2.
FIG. 7 shows schematically the structure of still another form of
the air flow meter 100 preferably employed in the present
invention. The air flow meter shown in FIG. 7 is of the so-called
multi-stage type, and two throttle valves 34 and 35 are disposed in
the intake duct 102. The throttle valve 34 is first rotated through
a linkage 80, and after the throttle valve 34 has been rotated to a
selected angular position, the throttle valve 35 is then rotated
through the linkage 80. Air flow meter units 36 and 37 are disposed
upstream of the throttle valves 34 and 35 respectively and may be
conventionally known ones each having a linear characteristic as
shown by the curve B in FIG. 2. In the region in which the flow
rate of intake air is small, the throttle valve 34 is rotated while
the throttle valve 35 is held from rotation, so that the flow rate
Q of intake air is detected by the air flow meter unit 36, and its
output signal X is proportional to the flow rate Q of intake air.
Subsequently, the throttle valve 35 is rotated, and the stream of
intake air is divided into two portions passing through the
throttle valves 34 and 35, so that the output signal X of the air
flow meter unit 36 is reduced to a level lower than that
proportional to the flow rate Q of intake air. FIG. 8 shows the
characteristic of the air flow meter shown in FIG. 7, and the
rotation of the throttle valve 35 starts at a point a. The curve M
in FIG. 8 represents the characteristic of the air flow meter unit
36, and the line N represents that of the air flow meter unit 37.
By suitably determining the proportional constants of the linear
characteristics of the air flow meter units 36 and 37, the curve M
in FIG. 8 can be substantially approximated to the curve C shown in
FIG. 2.
FIG. 9 shows the structure of yet another form of the air flow
meter 100 preferably employed in the present invention. The air
flow meter shown in FIG. 9 is of the so-called area type. Referring
to FIG. 9, a vane 38 rotates through an angle .theta. corresponding
to the flow rate Q of intake air to define a restricted opening 40
between it and a ridge portion 39. A pointer 41 is fixed to the
vane 38 for making swinging movement with the rotation of the vane
38, and thus, the movement or displacement of the pointer 41 is
proportional to the rotating angle .theta. of the vane 38. A
potentiometer 42 is associated with the pointer 41 to convert the
displacement of the pointer 41 into a corresponding voltage, so
that the output voltage of the potentiometer 42 provides the signal
X. A vacuum actuated servo 43 is operatively connected with the
vane 38, and the setting of the servo 43 is controlled by a control
valve 44 so as to adjust the sensitivity of the air flow meter. A
bypass 45 is provided to bypass a portion of intake air as
required, and a bypass adjusting screw 46 is provided to adjust the
amount of air bypassing through the bypass 45. A damper 47 is
provided to prevent pulsating movement of the vane 38 due to
pulsation of intake air supplied into the intake manifold of the
engine.
FIG. 10 illustrates how the level of the output signal X of the air
flow meter shown in FIG. 9 can be increased in the region of the
small flow rate of intake air. Suppose that the area A.sub.op of
the restricted opening 40 is expressed as A.sub.op =C.sub.A
.multidot.e.theta.(C.sub.A: constant). Then, the angle .theta.,
hence, the output signal X is a function of the logarithm of the
area A.sub.op of the restricted opening 40, hence, the flow rate Q
of intake air, and the ideal characteristic C described with
reference to FIG. 2 can be obtained. The area A.sub.op of the
restricted opening 40 can be expressed as
where A.sub.va is the area of the vane 38, H is the height of the
vertical section of the intake duct 102 (the length of the vane 38
between its pivoted point and its free end being equal to the
height of the vertical section of the intake duct 102 and given by
H), x is the horizontal distance of the vane 38 between the pivoted
point and the free end along the longitudinal axis of the intake
duct 102 when the rotating angle of the vane 38 is .theta., and h
is the height of the ridge portion 39 at the point of the distance
x. From the equation (7), the height h of the ridge portion 39 is
given by ##EQU1## since A.sub.op is supposed to be A.sub.op
=C.sub.A .multidot.e.theta. as above described. Due to the fact
that x=H sin .theta., the height h of the ridge portion 39 is
expressed as a function of x as follows: ##EQU2## Thus, when the
shape of the ridge portion 39 is determined to satisfy the relation
given by the equation (9), the aforementioned relation A.sub.op
=C.sub.A .multidot.e.theta. can be obtained, and therefore, the
ideal relation between the flow rate Q of intake air and the output
signal X of the air flow meter can be obtained.
In the manner above described, the level of the signal X
representing the flow rate Q of intake air can be increased in the
region of the small flow rate of intake air without increasing the
signal level in the region of the large flow rate of intake air.
Such a characteristic of the signal X relative to the flow rate Q
of intake air will be referred to as a non-linear characteristic in
this specification. The non-linear characteristic referred to
herein is limited to the above meaning and does not include the
non-linearity such as that of the curve B in FIG. 2. It is apparent
from the previous description on the ideal non-linear
characteristic that the resolution for the flow rate Q of intake
air in the region of the small flow rate of intake air can be
improved without increasing the capacity of parallel processing of
information bits by the microprocessor, when the signal X having
such a so-called non-linear characteristic is generated by the air
flow meter and converted into a digital signal to be subjected to
digital processing in the microprocessor. The information of the
flow rate Q of intake air obtained as a result of arithmetic
processing of the signal X having the non-linear characteristic in
the microprocessor does not naturally exactly correspond to the
practical flow rate Q of intake air. Thus, the proper air-fuel
ratio cannot be obtained when the amount of fuel supplied to the
combustion chamber of the engine is directly controlled on the
basis of such information. It is therefore necessary to suitably
convert the air flow rate information for the accurate control of
the amount of supplied fuel in order that the specific information
output of the microprocessor can exactly correspond to the detected
flow rate Q of intake air.
FIG. 11 shows schematically the structure of one form of the fuel
flow rate control unit 120 in the continuous metering type system
preferably employed in the present invention. Referring to FIG. 11,
a motor 48 operates according to the air flow rate information
signal applied from the microprocessor 128 to drive a cam member
49. The rotation of the cam member 49 causes corresponding sliding
movement of a metering piston 50 within a cylinder 51 thereby
changing the open area of a metering slit 52 provided in the side
wall of the cylinder 51. Fuel is supplied into the cylinder 51
through a fuel supply port 53. A differential pressure control
valve 54 acts to maintain constant the fuel pressure differential
across the metering slit 52 so that the flow rate of fuel flowing
through the metering slit 52 is proportional to the open area of
the metering slit 52. The fuel in an amount proportional to the
open area of the metering slit 52 is fed through the differential
pressure control valve 54 to the fuel injection unit 118, thence
into the intake duct 102. The motor 48 may be a servomotor when the
air flow rate information output signal of the microprocessor 128
is the digital signal to be subjected to D-A conversion. The motor
48 may be a pulse motor when the air flow rate information output
signal of the microprocessor 128 is applied in the form of the
digital signal which does not require the D-A conversion.
The air flow rate information output signal of the microprocessor
128 is converted in the fuel flow rate control unit 120 shown in
FIG. 11 in a manner as described with reference to FIGS. 12 and 13.
It is supposed herein that the output signal X of the air flow
meter is given by the equation (4).
Referring to FIG. 12, the open area As of the metering slit 52 is
increased or decreased in proportional relation to the retracting
or advancing stroke Sp of the piston 50, and the flow rate of fuel
flowing through the metering slit 52 is also proportional to the
stroke Sp of the piston 50. Therefore, the flow rate of fuel is
proportional to the flow rate of intake air when the piston 50
urged in either direction according to the air flow rate
information output signal of the microprocessor 128 is displaced in
such a relation that its stroke Sp is proportional to the detected
flow rate Q of intake air. Thus, for the signal X given by the
equation (4), the piston 50 makes its stroke Sp in proportional
relation to the detected flow rate Q of intake air when the piston
stroke Sp is selected to satisfy the following equation:
ti X=K.sub.1 ' log S.sub.p +K.sub.2 ' (10)
where K.sub.1 ' and K.sub.2 ' are constants. The stroke S.sub.p of
the piston 50 satisfying the equation (10) is obtained by suitably
selecting the profile of the cam member 49.
Referring to FIG. 13, the piston 50 is adapted to be urged by a
lever 55 driven by the motor 48, instead of being urged by the cam
member 49, so that the piston 50 makes its stroke S.sub.p in
proportional relation to the air flow rate information provided by
the output signal of the microprocessor 128. In such a case, the
information can be converted in a manner as described below by
similarly suitably selecting the shape of the metering slit 52. The
stroke S.sub.p of the piston 50 is expressed, in this case, as
where K.sub.1 " and K.sub.2 " are constants. Therefore, the open
area As of the metering slit 52, hence, the flow rate of fuel
through the metering slit 52 can be made proportional to the
detected flow rate Q of intake air when the shape of the metering
slit 52 is determined to satisfy the following relation:
where K.sub.1 '" and K.sub.2 '" are constants. The information
output signal of the microprocessor 128 may be converted into an
analog signal by a non-linear D-A converter to attain the desired
D-A conversion of the information.
FIG. 14 shows schematically the structure of one form of the fuel
flow rate control unit 120 used in the so-called intermittent
metering type system, preferably employed in the present invention.
In the so-called intermittent metering type system, fuel is
supplied into the combustion chamber 57 of the cylinder in
synchronous relation with the rotation phase of the engine.
Referring to FIG. 14, a switch circuit 58 which may be a transistor
circuit of Darlington connection is turned on during a limited
period of time corresponding to the high level of the information
output signal of the microprocessor 128. In response to the turn-on
of the switch circuit 58, current is supplied from a power source
59 to the electromagnetic coil 62 of the fuel value 61 through a
resistor 60. The fuel valve 61 is held open during the period of
time of energization of the coil 62 thereby supplying fuel into the
combustion chamber 57. (Actually, the mixture of atomized fuel and
air is supplied into the combustion chamber 57.) Therefore, the
amount of fuel supplied to the combustion chamber 57 is
proportional to the period of time .DELTA.t.sub.p during which the
fuel valve 61 is held in its open position.
This open period of time .DELTA.t.sub.p of the fuel valve 61 is
determined to be proportional to the detected flow rate Q of intake
air and inversely proportional to the rotating speed n of the
engine. Therefore, when the rotating period of the engine T.sub.a,
the following relation holds:
hence,
Introducing the equation (4) into the equation (14), log
.DELTA.t.sub.p is expressed as follows:
where K.sub.3 and K.sub.4 are constants. The equation (15)
indicates the fact that the open period of time .DELTA.t.sub.p of
the fuel valve 61 can be computed on the basis of X given by the
equation (4). Therefore, in lieu of converting the air flow rate
information provided by the output signal of the microprocessor
128, the valve open time .DELTA.t.sub.p may be computed in the
microprocessor 128 according to the equation (15), and the
resultant output signal of the microprocessor 128 may be used
directly for turning on the switch circuit 58 so as to supply the
proper amount of fuel to the combustion chamber 57.
FIG. 15 is a schematic block diagram of part of another form of the
fuel flow rate control unit 120 of the intermittent metering type
preferably employed in the present invention. In the modification
shown in FIG. 15, the signal proportional to Q.multidot.T.sub.a in
the expression (13) is derived from a unique circuit in lieu of
carrying out the computation of the equation (15) in the
microprocessor 128. Referring to FIG. 15, a pulse of a signal
synchronous with the rotation phase of the engine is applied to an
input terminal 64 at time A in FIG. 16. A monostable multivibrator
65 is triggered to actuate a constant-current circuit 66, and a
constant current charges a capacitor 67. In response to the
application of the next pulse of the synchronous signal to the
input terminal 64 at time B in FIG. 16, the monostable
multivibrator 65 actuates a current control circuit 69, and the
capacitor 67 starts to discharge. Therefore, the voltage value at
time B in FIG. 16 is proportional to the rotating period T.sub.a of
the engine. The discharge current I.sub.d of the capacitor 67 has a
constant value which is inversely proportional to the information
of the detected flow rate Q of intake air provided by the
information signal applied to the current control circuit 69 from
the microprocessor 128. Therefore, the relation
holds since the discharge period of time t.sub.d between time B and
time C in FIG. 16 is proportional to T.sub.a /I.sub.d, and I.sub.d
is inversely proportional to Q. The signal representing t.sub.d is
applied from an output terminal 68 to the switch circuit 58 shown
in FIG. 14 to turn on the same.
FIG. 17 is a schematic block diagram of part of still another form
of the fuel flow rate control unit 120 of the intermittent metering
type preferably employed in the present invention. In the
modification shown in FIG. 17, the signal representing the open
period of time .DELTA.t.sub.p of the fuel valve 61 is obtained when
the signal X having a non-linear characteristic inversely
proportional to the flow rate Q of intake air, such as that
represented by the curve E in FIG. 2, is applied to the
microprocessor 128. From the equation (13), the valve open time
.DELTA.t.sub.p is expressed as
where Y=K.sub.y /Q. The value of (n.multidot.Y) lies approximately
within the range of 0.4 to 0.1 since the valve open time
.DELTA.t.sub.p is about 2.5 ms to 9 ms as described hereinbefore.
The microprocessor 128 computes (n.multidot.Y) and applies its
output signal representing the result of computation to a
multipliable D-A converter 72 through an input terminal 78. The
signal representing Ky is applied to a comparator 70 through
another input terminal 71 to be compared with the output signal of
the D-A converter 72. The comparator 70 continues to generate its
output signal until coincidence is reached between these two input
signals. A control circuit 73 operates in response to the output
signal of the comparator 70 to alter the content of a register 74.
When Ky/(n.multidot.Y) is finally registered in the register 74, an
output signal representing
(Ky/n.multidot.Y).times.(n.multidot.Y)=Ky appears from the
multipliable D-A converter 72. The comparator 70 ceases to generate
its output signal, and the content of the register 74 is fixed at
Ky/(n.multidot.Y). The signal representing this Ky/(n.multidot.Y)
appears at an output terminal 75 to be applied to the switch
circuit 58 shown in FIG. 14.
It is necessary to change the amount of fuel supplied to the
combustion chamber of the engine in order to provide the proper
air-fuel ratio corresponding to the operating condition of the
engine. For this purpose, the output signal X of the air flow meter
must be corrected depending on the factors including the
temperature, rotating speed and load of the engine and the
composition of exhaust gases. The amount .DELTA.X required for
correcting the output signal X of the air flow meter for the
purpose of providing the proper air-fuel ratio is given by the
following equation:
where q is the amount of fuel supplied to the combustion of fuel
supplied to the combustion chamber of the engine. Therefore, the
air-fuel ratio of the air-fuel mixture supplied to the combustion
chamber of the engine can be controlled by sensing the engine
temperature, engine rotating speed, engine load and exhaust gas
composition by the various sensors 106 to 116 shown in FIG. 1,
applying these sensor output signals to the microprocessor 128 and
computing .DELTA.X using the functions and constants stored
previously in the memory unit 130. That is, the signal representing
.DELTA.X=log Q/q is added to the output signal X of the air flow
meter 100 to obtain the signal used for controlling the amount q of
supplied fuel. In this case, the air-fuel ratio can be controlled
with high accuracy by a digital signal of a small number of bits
since both the signals X and .DELTA.X are the function of log
Q.
In the case of correction of the output signal X of the air flow
meter 100 on the basis of the result of detection of oxygen in the
engine exhaust gases by the oxygen sensor 116 using the zirconia
element, the value .DELTA.X is negative and positive when the outpt
signal of the oxygen sensor 16 is higher and lower than a
predetermined level respectively. The value of .DELTA.X is such
that it will not cause hunting of the system. Although the oxygen
sensor 116 using the zirconia element has a high sensitivity, and
its output signal fluctuates incessantly, the output signal of the
oxygen sensor 116 is integrated in the microprocessor 128 or in an
integrating circuit for a suitable period of time so that the
average value thereof can be compared with the aforementioned
predetermined level. Further, the microprocessor 128 may generate,
during its computation processing time, a servomotor control signal
in synchronous relation with the crank angle or at a rate of a
constant time interval faster than the response time of the
servomotor 48. In such a case, the control signal is averaged so as
to accurately control the movement of the piston 50. Further, the
control signal controlling the servomotor 48 may be held as a
digital quantity during the computation processing time of the
microprocessor 128. Thus, the output signal X of the air flow meter
can be corrected in synchronous relation with the crank angle or at
constant time intervals.
For the correction of the output signal X of the air flow meter 100
on the basis of the result of detection of the engine temperature
by the temperature sensor 112, the output signal .theta. of the
temperature sensor 112 is applied to the microprocessor 128 which
computes .DELTA.X as a function of .theta.. This correction is
carried out when the detected engine temperature lies in the low
range.
For the correction of the output signal X of the air flow meter 100
on the basis of the results of detection of the rotating speed and
load of the engine, the output signal of the crank angle sensor 110
detecting the rotating speed of the engine is applied to the
microprocessor 128 together with the output signal of the throttle
position sensor 106 and/or the intake air pressure sensor 108
detecting the load and acceleration or deceleration of the engine,
and the microprocessor 128 computes the value of .DELTA.X using the
functions and constants stored previously in the memory unit 130.
During deceleration, the supply of fuel can be shut off. Further,
the timer 134 is operated as required during, for example, starting
or accelerating stage of the engine so as to correct the output
signal X of the air flow meter 100 during such a stage only.
When the temperature of the engine is low as in the starting stage
of the engine, the engine is rotated in the idling mode while
reducing the flow rate of intake air. In the idling mode of the
engine, enough air-fuel mixture is not supplied to the combustion
chamber resulting in irregular rotation of the engine. A fast idle
device is provided for ensuring uniform rotation of the engine and
increasing the rotating speed of the engine in the idling mode. As
shown in FIG. 18, the fast idle device comprises a bypass 79, a
bypass valve 76, and a control unit 77 controlling the opening of
the bypass valve 76. The control unit 77 includes generally a heat
responsive member such as a bimetal element or wax. The control
unit 77 may be in the form of an electrical actuator such as an
electromagnetic solenoid, a stepping motor, a PWM type
electromagnetic member or a servomotor which is controlled by the
output signal of the microprocessor 128. In this case, feedback
control for the rotating speed of the engine can be attained by
detecting the rotating speed of the engine by the crank angle
sensor 110, comparing the detected value with the predetermined
setting previously programmed in the memory unit 130, and actuating
the control unit 77 on the basis of the result of comparison
thereby controlling the flow rate of air flowing through the bypass
75. This feedback control is carried out when the output signal of
the throttle position sensor 106 is detected to lie within the
idling range of the engine. It is apparent that the output signal X
of the air flow meter structure shown in FIGS. 4, 6, 7 or 9 has a
non-linear characteristic relative to the flow rate Q of intake air
supplied by the fast idle device. The control unit 77 may be
arranged to directly control the throttle valve 104.
When the engine is operating steadily, the flow rate of air charged
in the engine is approximately equal to the flow rate of intake
air. However, these flow rates are not equal during the
acceleration of the engine, and the flow rate Q of intake air is
larger than the flow rate P of charged air with respect to time as
shown in FIG. 19. Thus, the amount of supplied fuel should be
determined on the basis of the flow rate P of charged air.
Therefore, the amount of fuel supplied to be mixed with the charged
air at time n in FIG. 19 must be controlled on the basis of the
flow rate Q of intake air at time m. Considering the computation
processing time of the microprocessor 128, the relation between the
time m and the time n can be determined by suitably selecting the
sequential order of signal transmission by the multiplexer 124 or
selecting the processing program of the microprocessor 128.
The operation of the air flow meter 100 is affected by pulsation of
intake air being supplied to the engine. It is therefore necessary
to provide the damper 47 shown in FIG. 9 or to suitably determine
the factors such as the volume, elasticity and length of the air
intake duct 102 so as to eliminate the adverse effect due to
pulsation of intake air. Further, the output signal X of the air
flow meter 100 may be applied to the microprocessor 128 after being
averaged for a suitable period of time or may be integrated to be
averaged after being applied to the microprocessor 128 so as to
eliminate the adverse effect due to pulsation of intake air. Such
an adverse effect can be also obviated by sampling the output
signal X of the air flow meter 100 at only a predetermined crank
position.
* * * * *