U.S. patent number 3,890,946 [Application Number 05/478,520] was granted by the patent office on 1975-06-24 for method and system to reduce noxious components in the exhaust emission from internal combustion engines with carburetor supply.
This patent grant is currently assigned to Robert Bosch G.m.b.H.. Invention is credited to Josef Wahl.
United States Patent |
3,890,946 |
Wahl |
June 24, 1975 |
Method and system to reduce noxious components in the exhaust
emission from internal combustion engines with carburetor
supply
Abstract
The carburetor for the engine is set to provide a slightly lean
mixture, for example at an air number of .lambda.=1.1. A fuel
injection valve is located in the induction tube, or inlet manifold
to the engine. The opening time of the valve is controlled in
dependence on inlet manifold pressure, or other operating
parameters (and may be non-linear to match non-linearities of the
carburetor) and, additionally, by sensed composition of the exhaust
gases from the engine to provide additional fuel so that the
overall fuel-air mixture, supplied by the carburetor as well as the
injected fuel will be just under the stoichiometric level, for
example at an air number of approximately 0.98, so that the exhaust
gases will be reducing and permit reduction of NO.sub.x compounds
in a catalytic converter with presence of minimum amounts of CO and
CH compounds in the exhaust.
Inventors: |
Wahl; Josef (Stuttgart,
DT) |
Assignee: |
Robert Bosch G.m.b.H.
(Gerlingen-Schillerhohe, DT)
|
Family
ID: |
5887646 |
Appl.
No.: |
05/478,520 |
Filed: |
June 12, 1974 |
Foreign Application Priority Data
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|
|
|
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Jul 21, 1973 [DT] |
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2337198 |
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Current U.S.
Class: |
123/684; 123/1A;
60/276; 123/1R; 123/698 |
Current CPC
Class: |
F02D
35/0092 (20130101) |
Current International
Class: |
F02D
35/00 (20060101); F02b 003/00 (); F02n 007/00 ();
F02d 005/00 () |
Field of
Search: |
;123/119R,119E,139AW,32EA,127,121,32ST,1 ;60/276,285 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Burns; Wendell E.
Attorney, Agent or Firm: Flynn & Frishauf
Claims
I claim:
1. Method to reduce noxious components in the exhaust from internal
combustion engines having a carburetor to supply a fuel-air mixture
to the engine, comprising the steps of
supplying fuel from the carburetor to the engine in a quantity less
than that forming a stoichiometric level to supply a lean fuel-air
mixture to the engine;
sensing the composition of the exhaust gases by testing oxygen
content therein, and providing a sensing signal representative of
oxygen in the exhaust gases;
intermittently injecting fuel to the fuel-air mixture being
supplied to the engine;
and controlling the injection time, for each injection of fuel, in
dependence on sensed composition of the exhaust gases by injecting
fuel during respectively longer, or shorter time intervals, as the
sensed composition of the exhaust gases changes between lean
(.lambda.>1) and rich (.lambda.<1) mixture to provide an
overall fuel-air mixture being applied to the engine which is just
below stoichiometric value.
2. Method according to claim 1, wherein the air number of the
fuel-air mixture being supplied to the engine by the carburetor has
an air number of about 1.1, and the step of intermittently
injecting fuel comprises adding fuel in such a a quantity that the
overall air number of the fuel-air mixture supplied to the engine
by both the carburetor and the fuel injection valve is about
0.98.
3. Method according to claim 1, wherein the step of controlling the
injection time comprises the step of sensing induction tube
pressure and said injection time is further controlled as a
function of the induction tube pressure.
4. Method according to claim 1, wherein the step of controlling the
injection time comprises the step of determining the relationship
of operating characteristics of the engine carburetor with respect
to the engine operating conditions and deriving an error function
representative of non-linearities in said relationship;
and modifying the injection time in accordance with a function
which compensates for said error function to provide an overall
fuel-air mixture being applied to the engine in which the relative
composition of fuel and air is essentially unvarying regardless of
engine operating conditions.
5. Method according to claim 1, wherein the step of injecting fuel
into the fuel-air mixture comprises
supplying fuel at a substantially constant pressure to an injection
valve to vary the quantity of fuel added by said injection step to
the fuel-air mixture derived from the carburetor substantially only
as a function of injection time of said valve.
6. System to reduce the noxious components in the exhaust from an
internal combustion engine (15) having a carburetor (27) to supply
a fuel-air mixture to the engine, in which the carburetor supplies
a lean fuel-air mixture having an air number greater than unity
(.lambda.>1.0)
carrying out the method of claim 1, comprising
sensing means (37) responsive to the exhaust gases from the engine
and providing a sensing signal representative of oxygen in the
exhaust from the engine;
a fuel injection valve (30) in the induction system (20) to the
engine;
control means (31) connected to energize said injection valve for
intermittent opening, said sensing means (37) being connected to
said control means (31) to control the time of energization of said
injection valve, and hence the duration that said valve is open and
hence the quantity of fuel injected, as a function of sensed
composition of the exhaust gases.
7. System according to claim 6, wherein the control means (31)
comprises a monostable flip-flop (FF) (31) connected to and
controlled by said sensing signal to change the duration of the
unstable state of said monostable FF in dependence on sensed
composition of the exhaust gases.
8. System according to claim 7, wherein the control means further
comprises an integrating circuit (35) and a threshold switch (36),
the sensing signal being applied to said threshold switch which
changes state when the sensing signal exceeds a predetermined
reference limit, the output of the threshold switch being applied
to the integrator (35) to provide an integrated signal, varying in
positive or negative going direction, and depending on the time
that said sensing signal passes the threshold level of said
threshold switch.
9. System according to claim 6, further comprising means (46)
sensing pneumatic conditions in the induction tube (20) to the
internal combustion engine and further controlling the control
means (31) to vary time of energization of said injection valve,
and hence the duration that said valve is open, in dependence on
pneumatic conditions in said induction tube.
10. System according to claim 9, wherein the means sensing
pneumatic conditions in the induction tube comprises a pressure
transducer sensing vacuum in the induction tube.
11. System according to claim 9, wherein the pneumatic sensing
means comprises an air mass flow transducer responsive to air mass
flow in the induction tube of the engine.
12. System according to claim 7, further comprising transducer
means responsive to at least one of the pneumatic conditions in the
induction tube of the engine: vacuum; mass air flow;
said transducer means being connected to said monostable FF and
additionally controlling the unstable state of said monostable FF
(31) in dependence on pressure, or air flow conditions,
respectively, in said induction tube.
13. System according to claim 7, wherein said monostable FF stage
comprises at least one correction terminal input (33', 60) to
permit modification of the unstable time of the monostable FF (31)
as a function of a correction, or operating parameter of the
engine.
14. System according to claim 7, wherein the unstable state of the
monostable FF is controlled in dependence on position of the
throttle of the engine.
15. System according to claim 7, wherein the monostable FF includes
a variable circuit element (42, 43, 44) affecting the unstable
time, and hence the time of energization of said fuel injection
valve, and said sensing means (37) is connected to said FF to
provide for multiplicative modification of change in the unstable
time of said monostable FF, with respect to the variation of value
of said variable circuit element.
16. System according to claim 7, wherein the output of the
monostable FF is connected to the injection valve (30) to energize
the fuel injection valve when the monostable FF is in unstable
state, said fuel injection valve having fuel applied thereto at a
substantially constant pressure.
17. System according to claim 7, further comprising a trigger means
(34) connected to and controlled by the rotation of the engine and
triggering the monostable FF to change from stable to unstable
state in predetermined relationship to rotation of the engine.
18. System according to claim 7, wherein the monostable flip-flop
(31) is triggered from stable into unstable state by a pulse
source, the pulse repetition rate of which is dependent on loading
of the engine.
19. System according to claim 7, wherein the monostable FF includes
an inductive circuit (42), the inductivity of said circuit being
variable, and forming one control parameter determining the
unstable time of said monostable FF, the inductivity varying as a
function of an operating, or operation parameter of said
engine.
20. System according to claim 7, wherein the FF includes a
non-linear element (43; FIG. 4) and having variable characteristics
which change upon change in operating, or operation parameters of
the engine;
the carburetor (27) has a non-linear operating characteristic with
respect to change in an operation, or operating parameter of the
engine;
and the non-linearity of said element in said monostable FF being
selected to compensate for, and counteract non-linearities in the
characteristics of the carburetor upon change of a respective
operation, or operating parameter of the engine, said element
responding to operation, or operating parameters of the engine
which are affected by the non-linearities of the characteristics of
the carburetor.
21. In combination with an internal combustion engine,
operating by carrying out the method of claim 1,
a fuel supply system comprising a carburetor set to provide an
air-fuel mixture at an air number greater than unity, in quantities
supplying the major portion of the air-fuel mixture requirements of
the engine;
a fuel injection valve in the induction system to the engine;
sensing means (37) responsive to the exhaust gases from the engine
and providing a sensing signal representative of oxygen in the
exhaust from the system;
and control means connected to energize said injection valve for
intermittent opening, said sensing means being connected to said
control means to control the time of energization of said injection
valve, and hence the duration that said valve is open as a function
of sensed composition of exhaust gases,
the quantity of fuel injected being a minor proportion of the fuel
necessary to provide a fuel-air mixture having an air number just
under unity.
22. Fuel supply system according to claim 21, wherein the fuel
supplied by the carburetor provides about 70-90% of the fuel
requirement of the fuel-air mixture required for operation of the
engine; and the fuel injected by the fuel injection valve comprises
the remaining 70-30% of total fuel requirements of the engine.
Description
Cross reference to related patents: U.S. Pat. Nos. 3,483,851,
3,782,347, and 3,759,232.
The present invention relates to a system to reduce the noxious
components of exhaust gases from internal combustion engines in
which the fuel-air mixture applied to the engine is provided by a
carburetor, normally set to supply a somewhat lean mixture.
It has previously been proposed to supply a somewhat lean mixture
to internal combustion engines by so setting the carburetor
controls that an excess of air is present. To obtain a
stoichiometric fuel-air mixture (.lambda.=1), a second carburetor
has been proposed which provides a rich fuel-air mixture. The two
mixtures are then mixed together, until a stoichiometric overall
mixture is provided. If the mixture applied to the internal
combustion engine is at the stoichiometric level (.lambda.=1) or
just below (for example .lambda. is approximately 0.98), the
overall emission from the internal combustion engine, including CO
and CH-compounds, becomes a minimum. The remaining NO.sub.x
compounds in the exhaust can be reduced in a catalytic reactor
connected to the exhaust from the internal combustion engine
itself. Such a device becomes expensive due to the use of two
carburetors, and the control of both carburetors, one of which is
controlled by a sensor in the exhaust system, is difficult to carry
out and additionally includes a substantial dead time which arises
in changing of mechanical control elements in the carburetor
itself. The accuracy of the setting and the composition of the
overall mixture applied to the engine is thus unfavorably
influenced.
It is an object of the present invention to provide a system and
method to reduce the noxious components in the exhaust gases of
internal combustion engines, to which fuel-air mixture is primarily
applied by a carburetor, reliably and inexpensively, that is, to so
influence the composition of the fuel-air mixture applied that an
approximately stoichiometric composition (or slightly rich
composition) can be readily obtained for supply to the engine, so
that the exhaust gases therefrom will have a minimum of noxious
components.
SUBJECT MATTER OF THE PRESENT INVENTION
Briefly, the inlet system of the engine, that is, for example the
induction type or the inlet manifold thereof, has a fuel injection
valve located therein which provides fuel to the engine, in
addition to the fuel-air mixture supplied by the carburetor. The
carburetor is set to supply a fuel-air mixture which is lean, that
is, .lambda.>1; fuel is added, in controlled measured
quantities, by the injection valve, just sufficient to bring the
fuel-air composition of the mixture actually applied to the
cylinders of the engine to just below stoichiometric value, under
control of a sensor located in the exhaust system of the internal
combustion engine.
The invention will be described by way of example with reference to
the accompanying drawings, wherein:
FIG. 1 is a graph illustrating the relative presence of quantities
of the components of the exhaust gases in dependence on the air
number .lambda. (abscissa);
FIG. 2 is a general block diagram of an engine system incorporating
the present invention;
FIG. 3 is a schematic circuit diagram of an inductively coupled
monostable flip-flop;
FIG. 4 is a schematic diagram illustrating operating
characteristics of a vacuum-induction transducer ussed in the
system of FIG. 3, in which the abscissa indicates pressure (or,
rather, vacuum) and the ordinate injection time of the fuel
injection valve, reflecting the operating characteristics of the
transducer; and
FIG. 5 is a schematic circuit diagram of an integral
controller.
The air number .lambda. is defined as having a value of unity (1)
if a stoichiometric composition of fuel and air is present. If
excess air is present, the value of .lambda. exceeds 1.0, the value
being determined by the mass ratio of air to fuel. Curve 10 (FIG.
1) illustrates the relationship of the CO component in the exhaust
gases with respect to .lambda.. As is apparent, the value of the CO
component decreases at a value below .lambda.=1 and reaches a
minimum value just beyond .lambda.=1. Thereafter, the CO value is
essentially constant and very low. Curve 11 illustrates the
quantity of hydrocarbons (CH compounds) in the exhaust. Up to a
value of .lambda.=1.3, approximately, curve 11 has somewhat the
same shape as curve 10 for CO. Above .lambda.=1.3, the unburned
hydrocarbons in the exhaust rise rapidly. This is due to ignition
failures which occur from time to time--and more frequently as the
mixture becomes lean--so that unburned fuel will be present in the
exhaust.
Curve 12 illustrates the relationship of nitrogen-oxygen compounds
(NO.sub.x) in the exhaust. As can be seen, curve 12 has a shape
which is opposite to that of the curves 10 and 11. Curve 12 has a
maximum which is approximately at .lambda.=1.05. At higher and
lower values of air number .lambda., curve 12 drops rapidly.
NO.sub.x components arise at high combustion temperatures, since
the NO.sub.x components are generated by oxidation of the nitrogen
in the air. The combustion temperatures reach their maximum value
at approximately stoichiometric composition of the supplied
fuel-air mixture. Curve 12 shows the relationship of the NO.sub.x
components in the exhaust gases as derived from the cylinders of
the engine 15 (FIG. 2), that is, as they appear in the exhaust
manifold stubs 21, 22, 23, 24 which are connected to an exhaust
manifold 18, and hence to an exhaust collection line 25. By
connecting a catalytic reactor 26 to the exhaust line 25, the
relationship of NO.sub.x components in the exhaust downstream from
the catalytic reactor changes substantially, as illustrated by
broken curve 14. When the exhaust gas composition is reducing, that
is, at air numbers less than unity, the nitrogen-oxygen compounds
react in the catalytic reactor 13 with the carbon monoxide and with
the hydrogen in the unburned hydrocarbon remnants in the exhaust.
Thus, at air numbers less than unity, the output from the catalytic
reactor will have practically no NO.sub.x compounds.
If the air number exceeds unity, the exhaust gases are nno longer
reducing, but rather change to be oxidizing, that is, oxygen is now
present in the exhaust gas. The NO.sub.x compounds then no longer
can be reduced in the catalytic reactor 26, so that for air numbers
higher than unity, the two curves 12 and 14 will coincide.
The exhaust from the internal combustion engine, of course,
includes all the components referred to: CO, CH-compounds and
NO.sub.x compounds. These are the noxious components from the
exhaust which are to be minimized. Overall minimum noxious
components can be obtained at air numbers just below unity, for
example at an air number .lambda. of approximately 0.97 to 0.99,
for example of about 0.98. At this air number, the CO proportion is
low, although not yet at its absolute minimum; the CH component is
about to reach its minimum; and the NO.sub.x components can be
practically completely eliminated in a catalytic reactor. Thus,
operation of the internal combustion engine at an air number of
approximately 0.98 provides for effective overall minimum noxious
exhaust emission.
An internal combustion engine 15 (FIG. 2) has inlet manifold stubs
16, 17, 18, 19 connected to an induction tube 20. For purposes of
illustration, engine 15 is illustrated as a four-cylinder engine,
although the invention, of course, is applicable to an engine of
any number of cylinders. Exhaust manifold stubs 21-24 are connected
to a manifold line 25, the pipe of which connects to the catalytic
reactor 26. The exhaust from reactor 26 is conducted, for example,
through a muffler, to the tailpipe and then exhausted to ambient
air.
The fuel-air mixture for engine 15 is supplied by a carburetor 27.
The illustration is highly schematic, and the invention is
applicable to any type of commercially used carburetor. Hence, the
schematic illustration merely shows a nozzle extending into the
induction tube. Air is supplied to the induction tube through a
filter 28 and sucked in upon operation of the engine. A throttle 29
is located in convention manner, the throttle position being
controlled by a suitable linkage, shown in dotted line, by a
control element, for example an accelerator pedal 32.
In accordance with the present invention, a fuel injection valve 30
is provided which injects fuel into the induction pipe 20 of the
internal combustion engine 15. The injection valve 30 is located
behind throttle 29. Operation of the fuel injection valve 30 is
controlled by an electronic controller 31 which includes a
monostable flip-flop (FF) to be described below. During the
unstable state of the FF, the injection valve 30 is opened; during
the table state of the FF, the injection valve 30 is closed. Fuel
is supplied to injection valve 30 by a fuel line, schematically
indicated.
Operation of the fuel injection valve 30, controlled by the control
unit 31, is governed by various operating parameters of the
internal combustion engine. One of these operating parameters is
pressure (or, rather, vacuum) in the induction pipe 20; another
parameter is engine speed; another parameter, in accordance with
the present invention, is composition of the exhaust gases. Other,
further parameters may be used to influence the open-time of the
fuel injection valve 30.
A pressure sensing device 46, such as a diaphragm chamber, is
connected in pressure sensing relationship to the induction pipe
20, to control the duration of the unstable state of the FF 31.
Circuit 31 further has a correction input 33. The circuit 31 is
triggered by a pulse source 34 which may, for example, be
controlled from the crankshaft of the engine 15. The pulse source
may, also, be an external pulse source, such as an astable
multivibrator operating at a frequency which is dependent on
loading of the engine, for example by sensing air flow. The
monostable FF 31 has a further input, connected to an integral
controller 35 which, in turn, is supplied by signals from a
threshold switch 36, which is connected to an exhaust gas
composition sensor 37. Sensor 37 is sensitive to the presence of
oxygen in the exhaust gases and located in the exhaust manifold, or
exhaust pipe 25 between the engine 15 and the catalytic reactor
26.
Basic operation: The carburetor 27 is so adjusted that in any
usually encountered operating condition, the fuel-air composition
supplied thereby will be lean, that is, the air number will be
greater than unity. Preferably, the setting may be such that the
air number is, on the average, approximately 1.1. This ensures that
under all ordinary operating conditions of an internal combustion
engine used, for example, in automotive applications, the mixture
will be lean. Additional fuel is added to this lean mixture
supplied by carburetor 27 by selectively opening the fuel injection
valve 30. The quantity of fuel supplied by injection valve 30 is so
controlled, or so measured that the overall total fuel-air mixture
which is supplied to the cylinders of engine 15 will have an air
number of just under unity, and preferably about 0.98.
The necessary additional fuel supplied by the injection valve 30
should bring the mixture as close to the desired air number as
possible. Its operation, therefore, should be matched to the
operating characteristics of the carburetor, and any variations or
non-linearities in the fuel-air composition supplied by the
carburetor under varying operating conditions of the engine should
be balanced by the fuel injection valve. This balancing can be
essentially obtained, in accordance with the present invention,
since the quantity of fuel to be added by the injection valve will
be small; thus, any variations in quantity of fuel to be supplied
will be small, so that the control swing, or control range to which
the injection valve 30 will be subjected will be small. The coarse
adjustment, and the coarse supply and matching of fuel to air,
according to requirements of engine 15 under varying operating
conditions, is carried out by carburetor 27.
In accordance with a feature of the invention, the integral
controller provides output signals which influence the fuel supply
added by the injection valve in multiplicative relationship.
The electronic control unit 31 (FIG. 3) includes a monostable FF
which, specifically, has an input transistor 37 and an output
transistor 39, the base of which is connected over resistor 38 to
the collector of transistor 37. The collector of output transistor
39 is connected to a common positive bus 40 over the primary
winding 41 of a transformer 42. Transformer 42 has a movable core
43, which is suitably connected by a linkage, schematically shown
at 44, with the membrane 45 of a diaphragm chamber unit 46.
Diaphragm chamber unit 46 is connected pneumatically to the
induction pipe 20 (FIG. 2) of the engine 15 by a branch stub
located behind the throttle 29.
In quiescent condition, input transistor 37 of the monostable FF is
held in conductive condition by resistor 47 connected between the
base of the transistor 37 and positive bus 40. The secondary
winding 49 of transformer 42 is connected to the base of the
transistor 37 over diode 48; the other terminal of the secondary
winding 49 is connected to the tap, or division point of a voltage
divider formed of resistors 50, 51 which are connected across
positive bus 40 and negative bus 53 of the system. The correction
input terminal 33 is also connected to the tap point between
resistors 50, 51.
A control cam, connected to rotate in synchronism with the
crankshaft of the internal combustion engine 37, as illustrated by
arrow 52, opens and closes a switch 54 which has one terminal
connected to the common, or negative, or ground, or chassis bus 53
of the supply source (not shown, and typically the battery of an
automotive vehicle). A load resistor 55 and one electrode of a
coupling capacitor 56 are further connected to the switch 54. The
other electrode of capacitor 56 is connected to a second load
resistor 57 and then to the negative bus 53. A diode 58 connects to
the base of the transistor 37.
Operation: The monostable FF is controlled, once for each rotation
of the cam, as illustrated by arrow 52, for example once for each
rotation of the crankshaft, to switch into astable state. When the
switch 54 is open--as illustrated in FIG. 3--capacitor 56 can
charge to the operating voltage between lines 40 and 53 through the
two resistors 55, 57. When the control arm 54 is switched by the
cam, upon rotation thereof (arrow 52) against the fixed contact
connected to negative bus 53, the positively charged electrode of
capacitor 56 is connected to the negative terminal, and the base of
transistor 37 will receive a strong negative voltage. This blocks
transistor 37 which, in turn, controls output transistor 39 to
change to conductive state. The collector current, flowing over
primary winding 41 of transformer 42 induces a voltage in the
secondary 49, which continues to hold the input transistor 37 in
blocked state. The duration of this voltage which holds the input
transistor blocked is determined by the induced voltage which
depends on the position of the core 43 in the transformer 42, and
hence on the pressure (or, rather, vacuum) in the induction pipe 15
of the engine to which the vacuum diaphragm chamber 46 is
connected. If pressure drops sharply below ambient atmospheric
pressure, for example when the throttle 29 is closed, or almost
closed, membrane 46 moves the iron core 43 downwardly (FIG. 3) to
increase the air gap in transformer 42, thus substantially
decreasing the inductivity of the primary 41. Due to the low
induced voltage, input transistor 37 will rapidly change to its
quiescent conductive state and, thus, rapidly block the output
transistor 39. The pulse which is derived from the collector of
output transistor 39, and applied over resistor 59, will thus be
only of short duration. If the accelerator 32 is substantially
completely depressed, so that throttle 29 is open, or almost open,
the air pressure in the induction pipe will be only slightly less
than that of ambient atmospheric air. Core 43 is then moved
downwardly only slightly. The primary winding will have a high
inductivity, causing slow rise of the collector current in the
primary winding 41, and resulting in a long pulse from the resistor
59 connected to the collector of transistor 39.
The correction input 33 may have signals of various input
parameters connected thereto; for example, the setting signal of
integral controller 35 may be connected at this terminal, as well
as other correction parameters, for example correction parameters
representing speed of the engine. Changing the voltage at the tap
point of the voltage divider, changes the duration of the pulse,
since the voltage applied to the base of the transistor will be
changed. This change is multiplicative. It is also possible to
apply correction parameters to the input 60, which will also effect
multiplicative change of the pulse duration of the monostable FF.
If this is done, it is desirable to include a resistor in the line
between the connection from the lower terminal of primary 41 and
the supply voltage line 40.
The invention has been described in connection with an inductively
coupled FF. It is, of course, also possible to use R/C coupled
flip-flops, or other circuits. Rather than using vacuum in the
induction manifold, other control parameters may be used, for
example a parameter representative of air flow through the
induction tube obtained, for example, as an output voltage from a
potentiometer, the slider position of which is controlled by a
deflection member in the induction tube leading to the internal
combustion engine. Such a deflection element will provide an output
signal which is also representative of load on the engine since, in
effect, flow of air-fuel mixture to the cylinders of the engine is
measured. The vacuum diaphragm chamber will also respond, to some
extent, to loading on the engine since, when the throttle is open
and at high speed of the engine, the pressure in the induction tube
is practically the same as that of ambient air pressure. It is an
important feature of the present invention that the correction
parameter so affects the unstable time of a monostable FF that the
effect is multiplicative.
FIG. 4 is a diagram of voltage or, rather, injection time ti, in
milliseconds, of the injection valve 30 with respect to induction
tube vacuum. The normal injection time--vacuum characteristic of
the transducer 46 is illustrated by solid line 61. By suitably
shaping core 43 of the transformer 42, the essentially linear
relationship can be distorted to obtain the relationship
illustrated in broken line 62. A similar distortion of the linear
relationship can be obtained by utilizing non-linear resistors in
the circuit of FIG. 3, or by placing a non-linear mechanical
linkage between the membrane 45 of transducer 46 and core 43.
Shaping the core 43, however, to be non-linear is a simple
solution. The non-linearity of the core 62 compensates
non-linearities of the carburetor.
FIG. 5 illustrates a circuit diagram of an integral controller, for
example the integral controller 35 of FIG. 2, as well as the
arrangement of the threshold switch 36 (FIG. 2). The output sensor
37 is connected over a separable connector, shown schematically at
37', over a coupling resistor 65 to the inverting input of an
operational amplifier 63 which, by virtue of its feedback resistor
69, is connected to provide for proportional amplification of the
output signal from the sensor 37. The direct input of operational
amplifier 63 is connected over coupling resistor 66 to the tap
point of a voltage divider, formed by adjustable resistor 67 and
resistor 68 and connected across buses 40, 53. The value of the
feedback resistor 69 determines the amplification factor of the
operational amplifier. The output of the operational amplifier is
connected to common positive bus 40; the power supply connections
to the amplifier 63 have been omitted for clarity.
The output of the operational amplifier 63 is connected over a
coupling resistor 71 to the inverting input of a second operational
amplifier 64, forming the integral controller. The direct input of
the operational amplifier 64 is connected over coupling resistor 75
to the tap point of a voltage divider formed of serially connected
resistors 73, 74, respectively connected across buses 40, 53. The
feedback circuit of operational amplifier 64 includes capacitor 75
which, then, causes the operational amplifier 64 to operate as an
integrating amplifier. The output of operational amplifier 64 is
connected to a load resistor 64', and then to positive bus 40. An
output resistor 76 connects the output of operational amplifier 64
to output terminal 77, which is connected to the correction input
terminal 33 of the monostable FF of circuit 31 (FIGS. 2, 3).
Operation of circuit of FIG. 5: The sensor 37 which, preferably, is
a known oxygen sensor, described in more detail in co-pending
applications Ser. Nos. 259,134; 316,008; 447,475, assigned to the
assignee of the present application, is amplified in operational
amplifier 63. The operational amplifier 63, as is apparent from the
diagram of FIG. 5, is connected as an inverting amplifier. The
output voltage will, then, have a negative value when the sensor 37
provides an output. The output voltage derived from amplifier 63
jumps between discrete threshold levels, in dependence on whether
the voltage at its inverting input is above, or below the voltage
at the direct input. The voltage at the direct input is determined
by the setting of the voltage divider formed by resistors 67, 68,
and such other signals connected to the tap point between resistors
67, 68 to form correction signals representative of selected
parameters (not shown). Operational amplifier 63, then, operates as
an inverter, and the output signal therefrom is connected to the
inverting input of operational amplifier 64. Operational amplifier
64, due to the presence of integrating capacitor 75, integrates
when the input voltage is negative, in positive direction. The
voltage at the output terminal 77 then shifts slowly in positive
direction, the rate of shift being determined by the integrating
constants of the circuit. The output voltage of operational
amplifier 64 shifts in negative direction, that is, the operational
amplifier integrates in negative direction if the output from
operational amplifier 63 is positive, representative of a rich
air-fuel mixture.
The voltage at terminal 77, connected to terminal 33 (FIG. 3) and
hence to the tap point of the voltage divider formed by resistors
50, 51 then modifies the unstable time of the monostable FF, and
hence the open time duration ti of the fuel injection valve 30
(FIG. 2) by introducing an additional signal at the tap point
between resistors 50, 51, so that the actual open time ti of the
fuel injection valve will be additionally modified over that shown
in the relationship of FIG. 4, depending on sensed composition of
the exhaust gases, as determined by sensor 37. The composition of
the exhaust gases can, therefore, be maintained in the reducing
range, that is, at an air number just below unity so that the
engine will operate with a just slightly rich mixture and just to
the left of the steep portion of curve 14, FIG. 1, resulting in
minimum overall noxious components in the exhaust of the
engine.
Various changes and modifications may be made within the scope of
the inventive concept and the invention may be used with features
described in the co-pending applications, the disclosure of which
is hereby incorporated. The timing of the astable time of
multivibrator 31 can be modified also, for example, by connecting a
variable resistor 33a in parallel to terminal 33', so that the
voltage division ratio of voltage divider 50, 51 is modified. The
extent of variation of resistor 33a can be controlled by a selected
engine operating parameter. For example, resistor 33a can be a
potentiometer, the slider of which is coupled to the gas pedal 32
(FIG. 2). The transformer 42 then may have a fixed value of
inductions, so that the pressure-displacement transducer 46 need
not be coupled to the movable core 43.
* * * * *