U.S. patent number 3,636,931 [Application Number 04/815,320] was granted by the patent office on 1972-01-25 for fuel injection controlling system for internal combustion engine.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Masayuki Ishizaki, Seiji Suda.
United States Patent |
3,636,931 |
Suda , et al. |
January 25, 1972 |
FUEL INJECTION CONTROLLING SYSTEM FOR INTERNAL COMBUSTION
ENGINE
Abstract
A fuel injection controlling system for internal combustion
engines, wherein the various conditions of the internal combustion
engine are converted to signal currents, these signal currents are
superimposed upon a timing signal current, the magnitude of which
corresponds to a lapse of time, and then supplied to an input
terminal of a current level detecting circuit so that there is
produced an output pulse signal of which the duration is related to
the quantity of fuel required by the internal combustion engine,
and a fuel injection valve is opened in accordance with said output
pulse signal thereby to control the quantity of fuel supplied to
the internal combustion engine.
Inventors: |
Suda; Seiji (Hitachi-shi,
JA), Ishizaki; Masayuki (Hitachi-shi, JA) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JA)
|
Family
ID: |
26362799 |
Appl.
No.: |
04/815,320 |
Filed: |
April 11, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Apr 17, 1968 [JA] |
|
|
43/25206 |
Sep 11, 1968 [JA] |
|
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43/64960 |
|
Current U.S.
Class: |
123/485; 123/488;
123/483 |
Current CPC
Class: |
F02D
41/32 (20130101) |
Current International
Class: |
F02D
41/32 (20060101); F02m 051/02 () |
Field of
Search: |
;123/32,32E,32EI,119,139E |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goodridge; Laurence M.
Claims
We claim:
1. A fuel injection controlling system for internal combustion
engines having a fuel control apparatus including an
electromagnetic valve for controlling the amount of fuel delivered
by the fuel supply for the engine comprising:
first means for generating a plurality of signal currents each
being independent from one another having a magnitude corresponding
to a respective condition from which the quantity of fuel to be
supplied to said engine is determined;
second means for producing an output signal corresponding to an
algebraic summation of the magnitudes of said independent signal
currents; and
third means responsive to said output signal produced by said
second means for controlling the opening duration of said
electromagnetic valve, to thereby feed the proper quantity of fuel
to said engine.
2. A fuel injection controlling system according to claim 1,
wherein said first means includes a first circuit means for
producing independent condition signal currents corresponding to
the respective conditions of the engine operation, a second circuit
means for independently producing a timing signal current which
varies with a lapse of time from the starting point of fuel
injection and a third circuit means for resetting the value of said
timing signal current to a predetermined level at each starting
point of the fuel injection and said second means includes an input
terminal with a low input impedance for simultaneously receiving
said independent signal currents, and an output terminal for
producing said output signal corresponding to said algebraic
summation, and wherein said third means includes a discriminator
means for comparing the output signal produced by said second means
with a predetermined discriminating level and for closing said
electromagnetic valve at a desired time after the initiation of
fuel injection, when said output signal produced by said second
means reaches said predetermined level.
3. A fuel injection controlling system according to claim 2,
wherein each of said first circuit means and said second circuit
means includes a circuit having an output terminal for producing a
voltage corresponding to the relevant condition and a resistor
connected between said output terminal of said circuit and said
input terminal of said second means, said resistor having a
relatively high resistance higher than said input impedance of said
second means.
4. A fuel injection controlling system according to claim 3,
further including means for changing the resistance values of said
resistors in response to a predetermined value of the negative
pressure in the manifold of the engine.
5. A fuel injection controlling system according to claim 4,
further including a correction means for correcting for a
discontinuity in an input signal when said resistance values are
changed.
6. A fuel injection controlling system according to claim 2,
wherein said discriminator means comprises a transistor, the input
terminals of which are constituted by the base-emitter electrodes
thereof, and a tunnel diode connected between the base-emitter
electrodes of said transistor in the same polarity therewith,
whereby the transistor of said discriminator means which is
normally in its conducting state is rendered nonconductive at the
beginning of the fuel injection and is rendered conductive when an
input current reaches said predetermined level.
7. A fuel injection system according to claim 6, wherein the input
terminals of said discriminator means are connected with the power
source for said system through a capacitor so that a preparation
current is supplied therethrough whereby said transistor in said
discriminator means becomes conductive when said power source
voltage is imparted thereto.
8. A fuel injection system according to claim 2, wherein said
second means comprises an operation amplifier connected in series
with said third means.
9. A fuel injection system according to claim 8, further including
respective resistors for supplying said independent condition
signals produced from said first means to said operational
amplifier.
10. A fuel injection controlling system according to claim 1,
wherein said first means comprises a negative pressure detector, an
engine temperature detector, and a circuit for detecting the
rotational frequency of said engine, each detector circuit
producing an independent signal corresponding to a separate engine
parameter.
11. A fuel injection controlling system according to claim 10,
wherein said engine temperature detector comprises a
thermistor-resistor series circuit the output of which is connected
to a nonlinear clamping circuit whose output is, in turn, fed to
said second means, whereby a signal representative of a nonlinear
temperature sensitive characteristic is provided by said first
means.
12. A fuel injection controlling system according to claim 11,
wherein said rotational frequency detector comprises a monostable
multivibrator responsive to the interruption of primary current
flowing through a firing circuit, an integrating circuit connected
in series with said monostable multivibrator and a clamping circuit
connected in series with said integrating circuit, whereby a signal
representative of the rotational speed of said engine will be
delivered to said second means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a fuel injection controlling system for
internal combustion engines which is adapted to control the
quantity of fuel to be supplied, and more particularly it pertains
to improvements in or relating to a system of electrically
controlling the quantity of fuel to be injected.
2. Description of the Prior Art
Among the conventional methods of supplying fuel to an internal
combustion engine are the methods of sucking out fuel by making use
of a negative pressure existing in a suction pipe and the method of
injecting fuel by means of an injection nozzle. In the latter
method, the quantity of fuel to be supplied can be accurately
controlled in correspondence to the quantity of fuel required by
the internal combustion engine so that the efficiency of the
internal combustion engine is enhanced to provide an increased
output torque and the quantity of harmful exhaust gas is decreased.
Thus, this method is effectively utilized as means for supplying
fuel to the internal combustion engine for an automobile.
In most of the injection-type fuel feed systems, the various
conditions of the internal combustion engine are imparted to
electric elements in order that an electrical signal having a
magnitude corresponding to the quantity of fuel to be supplied to
the internal combustion engine may be produced by making use of a
change in the time constant of a time-constant circuit constituted
by such electric elements or a potential variation in a voltage
divider circuit, and an electromagnetic valve is actuated in
accordance with the electrical signal thus produced, thereby
controlling the quantity of fuel which is injected by an injection
nozzle. A typical example of such systems is a method opening an
electromagnetic valve by means of an electrical signal having a
required duration which is produced by the use of a monostable
flip-flop circuit. In this method, the values of the capacitor and
resistor serving as timing means in the monostable flip-flop
circuit are varied in accordance with the conditions of the
internal combustion engine thereby to change the duration of the
output. Such a system is disclosed in the U.S. Pat. No. 2,941,519
to Zechnall et al., filed Dec. 1, 1958, and U.S. Pat. No. 3,051,152
to Paule et al., filed Sept. 17, 1958, for example. In this system,
however, a limitation is put on the conditions of the internal
combustion engine from which the quantity of fuel is to be
determined, since difficulty is encountered in an attempt to
constitute the timing means by a number of electric elements in the
monostable flip-flop circuit. In order to determine the quantity of
fuel from a number of conditions, it will become necessary to
resort to the use of a complicated composite mechanism.
Another example is a system designed so that the various conditions
of the internal combustion engine are converted to resistance
values, a signal voltage is provided by an operational means
(voltage divider circuit) which is constituted by connecting a
combination of said resistance values between power source lines,
and that the open duration of an electromagnetic valve is
controlled in accordance with the signal voltage thus provided.
Such system is disclosed in U.S. Pat. No. 3,240,191, to Wallis,
filed May 29, 1963, for example. With the system using operational
means as described above, however, it is very difficult to change
the resistance characteristics corresponding to the various
conditions of the internal combustion engine since the absolute
values of such resistances have effect on the entire voltage
distribution. Thus, this makes it difficult to achieve the matching
between various types of internal combustion engines to which such
system as described above is applied. For internal combustion
engines for automobiles, such matching difficulty constitutes a
great disadvantage from the standpoint of mass production.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a system
capable of controlling the quantity of fuel to be supplied by
effecting an operation with respect to electric signals
corresponding to the various conditions of an internal combustion
engine in a very simple manner.
Another object of the present invention is to provide such a system
that can be matched to a plurality of types of internal combustion
engines having different characteristics merely by making minor
adjustments or design changes.
The system according to the present invention is characterized in
that the various conditions of an internal combustion engine from
which the required quantity of fuel is determined are converted to
independent electric signals respectively, a time signal is
produced which corresponds to the lapse of time from the moment
when the crankshaft reaches a predetermined position, these signals
are combined with each other and then supplied to a discriminator
circuit to produce an output signal having a time width
corresponding to the required quantity of fuel, and an
electromagnetic valve is operated in accordance with the output
signal thus produced.
Other objects, features and advantages of the present invention
will become apparent from the detailed description of the preferred
embodiments taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE INVENTION
FIG. 1a is a graph showing the relationship between the negative
pressure in the manifold and the quantity of fuel to be
supplied;
FIG. 1b is a graph showing the relationship between the rotational
frequency of the engine and the quantity of fuel to be supplied,
with the negative pressure in the manifold maintained constant;
FIG. 1c is a graph showing the relationship between the engine
temperature and the quantity of fuel to be supplied;
FIG. 2a is a circuit diagram showing an example of discriminator
means according to the present invention;
FIG. 2b is a view showing the input current characteristics of said
discriminator means;
FIG. 3a is a circuit diagram showing an example of arithmetic
operating means according to the present invention;
FIG. 3b is a view showing the characteristics thereof;
FIG. 4 is a circuit diagram showing the fuel injection controlling
system for internal combustion engines according to an embodiment
of the present invention;
FIGS. 5a and 5b are views showing characteristic curves useful for
explaining variations of fuel feed characteristics with the
negative pressure in the manifold, respectively;
FIG. 6a is a circuit diagram showing another example of
discriminator means according to the present invention; and
FIG. 6b is a view showing the characteristic curves thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred quantity Q.sub.p of fuel to be supplied in terms of
the negative pressure P in the manifold of the internal combustion
engine is as shown in FIG. 1a from which it will be seen that the
quantity Q.sub.p in terms of the negative pressure P is represented
by a continuous characteristic curve. However, it is difficult to
change the supplied fuel quantity Q.sub.p along such a
characteristic curve. In practice, therefore, such a characteristic
is approximated by polygonal line. The negative pressure P in the
manifold depends upon the opening degree of the throttle valve and
the rotational frequency N of the internal combustion engine. At a
predetermined rotational frequency N, if the negative pressure P in
the manifold is low, then it is required that the opening degree of
the throttle valve be increased to provide an increased output. In
this region, therefore, the characteristic is made such that the
supplied fuel quantity Q.sub.p is so selected as to produce a
maximum output in disregard of fuel cost. In case the negative
pressure P in the manifold is high, however, the opening degree of
the throttle valve is low. In this region, therefore, the
characteristic is modified so that the supplied fuel quantity
Q.sub.p is selected to make the fuel cost the lowest possible. The
modification point corresponds to the bent P. of the polygonal
line. Thus, the characteristic is divided into a power region and
an economic region, with this bent point as a boundary.
Referring now to FIG. 1b, there is shown the characteristic of the
proper supplied fuel quantity Q.sub.N in terms of rotational
frequency N of the engine. This characteristic also changes in the
form of a curve in terms of the rotational frequency N, with the
manifold negative pressure P as parameter. In practice, however, it
is difficult to achieve control along such curve. Therefore, it is
approximated by straight line.
FIG. 1c shows the characteristic of supplied fuel quantity Q.sub.t
in terms of engine temperature T. THis characteristic is also
approximated by a polygonal line since in some temperature region
the quantity Q.sub.t is proportional to the engine temperature
while in the opposite end regions there occur saturation
characteristics.
In order to control the quantity Q of fuel to be supplied in the
injection-type fuel feed system, two methods are conceivable, that
is, a method to change the quantity of fuel to be injected per unit
of time and a method to change the duration of the fuel injection.
In order to control such changes with the aid of an electromagnetic
valve, the latter method turns out to be advantageous. The system
according to the present invention may be applied to such a
control.
In such method, the quantity Q of fuel to be supplied and the
opening duration t of the electromagnetic valve are in
substantially linear relationship with each other. If the supplied
fuel quantity Q is represented in terms of duration t, then it may
be considered that the duration t is represented by a function
including as independent variables the manifold negative pressure
P, rotational frequency N and temperature T.
t=f.sub.1 (P)+f.sub.2 (N)+f.sub.3 (T) (1)
From manifold negative pressure P.sub.O corresponding to each bent
point, f.sub.1, f.sub.2 and f.sub.3 vary as follows:
When P.gtoreq.P.sub.O,
f.sub.1 (P)=r.sub.1 P+S.sub.1 (2)
f.sub.2 (N)=a.sub.1 N+b.sub.1 (3)
When P<P.sub.O,
f.sub.1 (P)=r.sub.2 P+S.sub.2 (4)
f.sub.2 (N)=a.sub.2 N+b.sub.2 (5)
When P.gtoreq.P.sub.O and T.sub.O .ltoreq.T.ltoreq.T.sub.1,
f.sub.3 (T)=kT+k' (6)
where T.sub.O represents the temperature corresponding to the
low-temperature bent point and T.sub.1 indicates the temperature
corresponding to the high-temperature bent point.
In accordance with the present invention, the aforementioned
manifold negative pressure P, rotational frequency N and
temperature T are converted to signal currents from which it is
attempted to determine the opening duration t of the
electromagnetic valve.
Description will now be made of the principle of an embodiment of
the present invention, with reference to FIGS. 2a, 2b and 3a,
3b.
Referring to FIG. 2a, there is shown a discriminator circuit
comprising an NPN-transistor 1 and a tunnel diode 2 connected
between the base electrode and the emitter electrode of the
transistor 1 in the same polarity and in parallel with the latter,
wherein the base electrode of the transistor 1 is connected with an
input terminal 3, and the collector electrode thereof is connected
with a power source terminal 5 through a load resistor 4. The
operation of this discriminator circuit will be explained with
reference to FIG. 2b. If an input current I.sub.in arriving at the
input terminal 3 is increased, then the overall current is enabled
to flow through the tunnel diode 2 because of the fact that the
tunnel diode represents a very low internal impedance when the
input current I.sub.in is lower than the maximum value I.sub.m of
the tunnel diode 2, so that the current is not caused to flow in
the base electrode of the transistor 1. Thus, the nonconductive
state is established between the emitter and the collector of the
transistor. However, if the input current I.sub.in exceeds the
maximum value I.sub.m, then the tunnel diode 2 is caused to enter
the negative region so that the current flowing therethrough is
decreased with the result that the terminal voltage builds up.
Consequently, the potential at the base electrode of the transistor
1 increases to cause a current I.sub.b to flow between the base
electrode and the emitter electrode. Thus, the conductive state is
established between the emitter electrode and the collector
electrode so that a collector current is caused to flow so that an
output signal is obtained across the load resistor 4.
In accordance with one embodiment of the present invention, an
attempt is made to effect operation with respect to the optimum
quantity of fuel to be supplied to the engine from the various
signal currents by making use of the aforementioned
characteristic.
FIG. 3a is a circuit diagram showing an example of operational
means adapted to form an output signal corresponding to a required
duration t by imparting the various conditions of the internal
combustion engine to the discriminator circuit described above in
connection with FIGS. 2a and 2b. Numeral 6 represents a signal
input terminal corresponding to the rotational frequency N of the
engine, 7 a signal input terminal corresponding to the manifold
negative pressure P, 8 a signal input terminal corresponding to the
temperature T, and 9 a signal input terminal corresponding to the
lapse of time. These signal input terminals are connected in common
to the input terminal of the discriminator circuit through the
resistors 10, 11, 12 and 13 respectively. A capacitor 14 and
resistor 15 constitute a differentiating circuit which is connected
in series between the power source terminal 5 and the input
terminal 3. This differentiating circuit is provided for the
purpose of imparting to the input terminal 3 a preparation signal
current I.sub.r having such a magnitude as to establish the
conductive condition between the emitter and the collector
electrodes of the transistor 1 when the power source is turned on.
Numeral 16 represents a reset signal input terminal for imparting a
negative trigger voltage to the transistor 1 to establish the
nonconductive condition between the emitter and the collector
electrodes of the transistor 1 when it is desired that the fuel
injection be started. This reset signal input terminal is also
connected with the input terminal 3. An output signal is taken from
between an output terminal 17 connected with the collector
electrode transistor 1 and the ground.
Next, the operation of the foregoing arrangement will be described
with reference to FIG. 3b. First of all, upon application of the
power source voltage to the power source terminal 5, the
preparation current I.sub.r is caused to flow into the input
terminal 3 through the capacitor 14 and resistor 15 so that a
current having a sufficient magnitude to establish the conductive
state between the emitter and the collector electrodes of the
transistor 1 is caused to flow into the base electrode thereof. At
this point, the potential at the collector electrode is so low that
no output signal is available from the output terminal 17.
Subsequently, if the engine is rotated by starter means (not
shown), then a negative pulselike reset current I.sub.s is supplied
from the input terminal 16 to the input terminal 3 when it is
desired that the fuel injection be initiated. This reset current
I.sub.s reduces the current flowing in the input terminal 3 so that
the potential at the base electrode of the transistor 1 is
decreased, while at the same time resetting the tunnel diode 2.
Thus, the base current of the transistor 1 is interrupted so that
the nonconductive condition is established between the emitter and
the collector electrodes thereof. As a result, the potential at the
collector electrode increases, and thus an output signal
E.sub.output appears at the output terminal 17. At the same time, a
sawtooth wave signal voltage which increases with the lapse of time
is applied to the signal input terminal 9 so that a time-lapse
signal current I.sub.v is caused to flow through tHe input terminal
by way of resistor 13. Further, voltages corresponding to the
various conditions of the engines are applied to the other signal
input terminals 6, 7 and 8, and signal currents I.sub.n, I.sub.p
and I.sub.t are supplied to the input terminal 3 through the
resistors 10, 11 and 12 respectively. Because of the very low input
impedance of the input terminal 3, these signal currents are
algebraically combined with each other so that there is obtained a
combined current I.sub.in which in turn flows in the input terminal
3. Such combined current I.sub.in is selected to be lower than the
maximum value I.sub.m of the tunnel diode 2. The combined current
I.sub.in increases with an increase of the time-lapse signal
current I.sub.V, but when it is in the region below the maximum
value I.sub.m, it is caused to flow to the ground through the
tunnel diode 2, so that no current is made to flow in the base
electrode of the transistor 1. Thus, the nonconductive condition is
established between the emitter and the collector electrodes, and
therefore in such region, the output signal available at the output
terminal 17 is preserved. After the lapse of predetermined time t,
however, the combined current I.sub.in flowing in from the input
terminal 3 exceeds the maximum value I.sub.m of the tunnel diode 2,
so that the internal impedance of the tunnel diode 2 is increased
with the result that the terminal voltage is increased.
Consequently, the potential at the base electrode of the transistor
increases to enable a base current to flow therein so that the
conductive condition is established between the emitter and the
collector electrodes. Thus, the potential at the collector
electrode decreases so that the output signal at the output
terminal disappears. By operating the fuel injection control value
in accordance with the output signal available at the output
terminal 17, therefore, it is possible to feed fuel for the
aforementioned duration t. This duration t depends upon the
magnitudes of the signal currents I.sub.n, I.sub.p and I.sub.t
which depend upon the conditions of the engine, and therefore the
quantity Q of fuel to be supplied can be controlled to correspond
to the required fuel quantity by changing these signal currents in
accordance with predetermined characteristics. That is, since the
time-lapse signal current I.sub.v varies at a constant gradient
irrespective of the conditions of the engine whereas the composite
current I.sub.in flowing in the input terminal 3 varies like
I.sub.in1, I.sub.in2, I.sub.in3, . . ., the duration t in which the
maximum value I.sub.m of the tunnel diode 2 is reached varies like
t.sub.1, t.sub.2, t.sub.3. . . . .
Referring now to FIGS. 5a and 5b, description will be made of the
present invention as embodied under the following conditions.
a. Injection is simultaneously effected with respect to respective
two cylinders of a four-cylinder, four-stroke-type engine.
b. Injection timing is set such that the injection is started by
means of primary current interrupter contact associated with a
firing coil and additionally provided with two contacts when these
contacts are made.
c. A sawtooth wave voltage which builds up with the lapse of time
is used as a signal to detect time variations.
d. It is assumed that the required fuel feed characteristics of the
engine are as shown in FIGS. 1a, 1b and 1c, and that such
characteristics can easily be changed.
In FIG. 4, numeral 18 represents the aforementioned operational
circuit, 19 a sawtooth wave generating circuit adapted for
providing a time-lapse signal, and 20 a reset circuit adapted to
provide a negative trigger voltage in synchronism with the
generation of the sawtooth wave. Numeral 21 indicates a circuit for
detecting a negative pressure in the engine suction manifold, which
consists of a combination of a diaphragm and a potentiometer type
resistor, 22 an engine temperature detecting circuit, and 23 a
circuit for detecting the rotational frequency of the engine.
Numeral 24 denotes a selector circuit for selecting that one of the
electromagnetic valves to which the output signal of the
operational circuit is to be supplied, and 25 a switching circuit
for flowing a driving current through the electromagnetic valve
thus selected.
These circuits will be described in further detail below. The
sawtooth wave generating circuit 19 is constituted by a bootstrap
circuit. When either one of timing contacts 26 and 27 is made, a
current which has been flowing through a resistor 29 by way of a
resistor 28 is now made to flow to the ground through diode 30 or
31, so that a transistor 32 is rendered nonconductive. At this
point, a capacitor 35 begins to be charged through a diode 33 and a
resistor 34. As a result, the potential at the base electrode of a
transistor 36 is increased so that the conductivity between the
collector and the emitter electrodes thereof is increased. Thus, an
increasing current is caused to flow from the emitter electrode to
a resistor 37, so that the potential at the emitter electrode
builds up gradually. By virtue of the fact that the transistor 32
is rendered nonconductive when the sawtooth wave generating circuit
19 starts the generation of the sawtooth wave, the reset circuit 20
is adapted to establish the conducting state between the emitter
and the collector electrodes of a transistor 39 by connecting the
collector electrode of the transistor 32 with the base electrode of
the transistor 39 through a resistor 38, and impart a negative
trigger voltage to the reset signal input terminal 16 of the
operational circuit by discharging charges stored at a capacitor 40
when the transistor 39 is in the nonconducting state. The engine
manifold negative pressure detecting circuit 21 is constituted by
the diaphragm adapted for movement in accordance with the manifold
negative pressure and potentiometer type resistor 41 actuated by
the diaphragm, wherein a voltage which builds up with an increase
in the manifold negative pressure is obtained at a slidable contact
42. The engine temperature detecting circuit 22 is constituted by a
series circuit of a temperature-sensitive element 43 and resistor
44, wherein a signal voltage is obtained at the connection point of
the series circuit. In the case where as temperature-sensitive
element 43 use is made of a thermistor, the resistance value of the
temperature-sensitive element 43 decreases with temperature
increase, while the potential at the output point thereof
increases. The lowest voltage is clamped by resistors 45 and 46 and
diode 47, and the highest voltage is clamped by resistors 48 and 49
and diode 50. Thus, there is obtained the characteristic
represented by the polygonal line in FIG. 1c. The engine rotational
frequency detecting circuit 23 is constructed by the use of a
monostable flip-flop circuit which is triggered with the aid of a
breaker contact 52 for interrupting the primary current flowing
through a firing coil 51, in order to reduce the pulsation of the
output voltage and improve the response characteristic. The voltage
at the connection point between the firing coil 51 and the breaker
contact 52 builds up when the contact 52 is in the open state. This
voltage is differentiated by a capacitor 53 and resistor 54 and
then imparted to the base electrode of a transistor 56 of the
monostable flip-flop circuit through a diode 55. Further, this
voltage is imparted to the base electrode of a transistor 58
through a resistor 57, thus establishing the conductive condition
between the emitter-collector electrodes of the transistor 58. The
collector electrode of the transistor 58 is connected with a
conductor 60 through a resistor 59 and also grounded through a
capacitor 61 and resistor 62. Thus, if the voltage which has been
imparted to the base electrode of the transistor 58 becomes extinct
due to the closure of the breaker contact 52, then the transistor
58 is rendered nonconductive so that the potential at the collector
electrode thereof increases. This voltage variation is
differentiated by a capacitor 61 and resistor 62, and then imparted
to the base electrode of the aforementioned transistor 56 through a
diode 63. The transistor 56 constitutes the monostable flip-flop
circuit together with a transistor 64, resistors 65, 66 and 68 and
capacitor 69. The transistor 56 is rendered nonconductive when the
monostable flip-flop circuit is in the stable state, and it has its
collector electrode connected with an integrating circuit
constituted by a resistor 70 and capacitor 71. At this capacitor
71, there occurs a voltage of which the magnitude corresponds to
the rotational frequency N of the engine. This voltage is applied
to the base electrode of a transistor 72 to change the conductivity
between the emitter and the collector electrodes thereof so that a
voltage appearing at the connection point between resistors 73 and
74 connected in series with each other is varied in accordance with
the rotational frequency N of the engine. Series resistors 75 and
76 constitute a clamping circuit together with a diode 77, which is
adapted to clamp the maximum value of the voltage appearing at said
connection point. The selector circuit 24 consists of a bistable
flip-flop circuit constituted by transistors 78 and 79 and
resistors 80, 81, 82 and 83. The transistors 78 and 79 are
connected in such a manner as to be controlled by the
aforementioned timing contacts 26 and 27. Those terminals of the
contacts 26 and 27 which are opposite to the grounded ones are
connected with the conductor 60 through resistors 84 and 85
respectively, and also with the base electrodes of transistors 88
and 89 through resistors 86 and 87 respectively. The transistors 88
and 89 have their emitter electrodes grounded and the collector
electrodes thereof connected with the conductor 60 through
resistors 90 and 91 and further with the base electrodes of the
transistors 78 and 79 of the aforementioned bistable flip-flop
circuit through resistors 101, 102 and diodes 103, 104
respectively. Thus, the transistors 78 and 79 are rendered
conductive by the fact that their base electrodes are biased at a
high voltage when one of the contacts 26 and 27 is closed so that
one of the transistors 88 and 89 is rendered nonconductive.
Description will now be made of the operational circuit 18. The
quantity of fuel to be supplied which depends upon the engine
manifold negative pressure P and rotational frequency N differs
between when the manifold negative pressure P is P P.sub.0 and when
P< P.sub.0. Therefore, the gradient of the characteristic is
changed by changing the resistors 10, 11 to resistors 10', 11'
which are connected with input terminals 6 and 7 through switches
SW2-1 and SW2-2 which are operated when the manifold negative
pressure P is equal to P.sub.0. The state shown in the drawing
corresponds to that in which the manifold negative pressure P is P
P.sub.0. The values of the resistors 10 and 11 are selected to be
lower than those of the resistors 10' and 11', and the gradient of
the characteristic is so set up that variations in the current
flowing in the input terminal 3 become greater as compared with
those in the manifold negative pressure, as shown in FIG. 5a. By
changing the values of the resistors, the gradient of the
characteristic is changed as described above, but the absolute
value is also varied at the same time. If it is left as it is, the
quantity of injected fuel in terms of the manifold negative
pressure P is changed in a jumping manner when P= P.sub.0. Such
phenomenon is undesirable. Therefore, the design is made such that
this jumping phenomenon is prevented by switching from a resistor
108 to a resistor 108' a bias current flowing in the input terminal
3 through a switch SW2-3 from an input terminal 107 to which is
applied a fixed bias voltage available from the connection point
between the series resistors 105 and 106 as input. The output
terminal 17 of the operational circuit 18 is coupled to the base
electrode of a transistor 110 through a resistor 109. The
transistor 110 which is adapted to serve as amplifier has its
collector electrode connected with the conductor 60 through a
resistor 111 and its emitter electrode connected with the base
electrode of a transistor 112 for driving an electromagnetic valve.
The collector electrode of the transistor 112 is connected with the
conductor 60 through electromagnetic coils 113 and 114, and the
emitter electrode thereof is grounded. On the other hand, the
output terminal 17 is connected with the base electrode of a
transistor 116 through a resistor 115. This transistor 116 which is
also adapted to serve as amplifier has its collector electrode
connected with the conductor 60 through a resistor 117 and its
emitter electrode connected with the base electrode of a transistor
for driving an electromagnetic valve. The collector electrode of
the transistor 118 is connected with the conductor 60 through
electromagnetic coils 119 and 120, and the emitter electrode
thereof is grounded. Further, the base electrodes of the two
amplifier transistors 110 and 116 are connected with the collector
electrodes of the transistors 78 and 79 of the aforementioned
discriminator circuit 24 through diodes 121 and 122 respectively.
SW1 is a power source switch connected between the conductor 60 and
a battery 123.
Next, the operation of the present system will be fully described.
First of all, by closing the power source switch SW1, the voltage
of the battery is applied to the entire circuit arrangement so that
the latter is brought into the active state. In the operational
circuit, when the voltage at the power source terminal 5 builds up,
the preparation current I.sub.r is caused to flow in the input
terminal 3 through the capacitor 14 and resistor 15 to render the
transistor 1 conductive so that no output voltage appears at the
output terminal 17. Thus, none of the transistors 110 and 116 can
be rendered conductive, and therefore the electromagnetic valves
remain closed. At the same time, signal voltages corresponding to
the engine manifold negative pressure P, rotational frequency N and
temperature T and imparted to the input terminals 6, 7 and 8
respectively, so that currents corresponding to these voltages are
supplied to the input terminal 3. When the engine is started,
either one of the timing contacts 26 and 27 is made at a point of
time when it is desired that the fuel injection be initiated. In
case the timing contact 26 is made for example, the bias current
which has been flowing from the conductor 60 to the transistor 32
through the resistors 28 and 29 is now caused to flow to the ground
through the diode 30 and timing contact 26, so that the transistor
32 is rendered nonconductive. As a result, the potential at the
collector electrode of the transistor 32 increases to render the
transistor 39 conductive so that the electric charges which have
been stored at the capacitor 40 are discharged to the input
terminal 16 of the operational circuit 18. The polarity of the
current resulting from this discharge is negative, and therefore
the current I.sub.in flowing in the input terminal 3 is reduced so
that the transistor 1 is rendered nonconductive and the tunnel
diode 2 is shifted to the characteristic region below the maximum
value I.sub.m. When the transistor 1 is rendered nonconductive, the
potential at the collector electrode thereof increases, with the
result that an output voltage appears at the output terminal 17.
Such state corresponds to that in which the timing contact 26 is
closed. When this timing contact 26 is closed, the transistor 88 is
rendered nonconductive, so that the potential at the collector
electrode thereof increases, with the result that the potential at
the base electrode of the transistor 79 incorporated in the
selector circuit 24 is increased so that the transistor 79 is
rendered conductive. Thus, the amplifier transistor 116 provided in
the switching circuit 25 has its base electrode grounded through
the diode 122. At this point, the transistor 78 which constitutes
the bistable flip-flop circuit together with the transistor 79 is
in the nonconducting state, and the amplifier transistor 110 is
rendered conductive with an output voltage appearing at the output
terminal 17 of the operational circuit 18. Further, the transistor
112 is also rendered conductive to flow a current through the
electromagnetic coils 113 and 114 so that the valve is opened to
make the fuel injection possible. Simultaneously, the transistor 32
is rendered nonconductive with the result that the potential at the
collector electrode thereof increases so that the capacitor 35
begins to be charged so that the terminal voltage thereof is
increased to shift the transistor 36 from the nonconducting state
to the conducting state. Thus, the potential at the emitter
electrode of the transistor 36 is gradually increased in accordance
with a lapse of time. This time-lapse signal voltage is imparted to
the input terminal 9, resulting in a current which flows to the
input terminal 3 through the resistor 13. In case the current
I.sub.in which is a combination of the signal current corresponding
to the various conditions of the engine and the time-lapse signal
current is lower than the maximum value I.sub.m of the tunnel diode
2, then all the input currents I.sub.in are made to flow to the
ground through the tunnel diode 2, and thus in this region the
transistor 1 is maintained in the nonconducting state so that the
fuel injection is continued. However, if the input current I.sub.in
exceeds the maximum value I.sub.m of the tunnel diode 2, then the
latter is brought into the negative region so that the internal
impedance thereof increases to increase the terminal voltage. As a
result, the potential at the base electrode of the transistor 1 is
increased so that the conductive condition is established between
the emitter and the collector electrodes thereof. At this point,
the output voltage at the output terminal 17 becomes extinct. Thus,
the transistors 110 and 112 are rendered nonconductive so that the
currents flowing through the electromagnetic coils 113 and 114 are
interrupted. Consequently, the valve is closed to interrupt the
fuel injection. The time t in which the fuel injection is ended
corresponds to that in which the input current I.sub.in reaches the
maximum value I.sub.m of the tunnel diode 2. It depends upon the
signal current which varies depending upon the various conditions
of the engine. In this way, the quantity of injected fuel turns out
to be a proper one which meets the various conditions of the
engine.
When the crank shaft of the engine is rotated to a certain degree,
the timing contact 26 is broken and subsequently the other timing
contact 27 is made. Thus, the fuel-injecting operation is performed
in a manner similar to that described above. In this case, the
transistor 78 of the selector circuit 24 is rendered nonconductive
while the transistor 79 is made conductive, so that the
electromagnetic coils 119 and 120 are energized to open the
valve.
In the foregoing embodiment, use was made of NPN-transistors, but
it will be readily apparent to those skilled in the art that it is
also possible to use PNP-transistors.
Description will now be made of the case where use is made of an
operational amplifier, with reference to FIGS. 6a and 6b. This
operational amplifier is of the ordinary type, and therefore
detailed description thereof will be omitted. Applied to the signal
input terminals are signal voltages which are obtained in
accordance with the various conditions of the engine, and they are
so set up as to decrease with increases in the rotational frequency
N of the engine, the manifold negative pressure P and the
temperature T. Further, the sawtooth wave voltage applied to the
time-lapse signal input terminal 9 is one which rapidly drops to a
negative voltage of a high magnitude upon the initiation of the
input and thereafter gradually changes toward zero. Numeral 123
represents an operational amplifier, and 124 resistor.
In the aforementioned setup, normally the transistor 1 is rendered
conductive with an input signal voltage which is obtained depending
upon the various conditions so that no output voltage is available
at the output terminal 17. However, if a negative voltage of a high
magnitude is imparted to the time signal input terminal 39 at a
point of time t.sub.0 when it is desired that the fuel injection be
started, then the summed value becomes lower than the barrier
voltage of the transistor 1 so that the latter is rendered
nonconductive with the result that an output voltage appears at the
output terminal 17. On the other hand, if the summed value becomes
higher than the barrier voltage of the transistor 1 as a result of
the gradual decrease of the time-lapse signal voltage, the
transistor 1 is then rendered conductive so that the output voltage
at the output terminal 17 becomes extinct. The time is changed like
t.sub.1, t.sub.2, t.sub.3 depending upon the magnitude of the input
signal voltage corresponding to the various conditions, and thus
the quantity of fuel to be supplied can be controlled as in the
aforementioned embodiment.
* * * * *