U.S. patent number 3,919,983 [Application Number 05/396,477] was granted by the patent office on 1975-11-18 for method and apparatus repetitively controlling the composition of exhaust emissions from internal combustion engines, in predetermined intervals.
This patent grant is currently assigned to Robert Bosch GmbH. Invention is credited to Peter Jurgen Schmidt, Josef Wahl, Richard Zechnall.
United States Patent |
3,919,983 |
Wahl , et al. |
November 18, 1975 |
Method and apparatus repetitively controlling the composition of
exhaust emissions from internal combustion engines, in
predetermined intervals
Abstract
Certain intervals are determined in which output signals from an
exhaust gas sensing device are sensed, and then applied to a
control circuit, to control the fuel supply system (carburetor, or
fuel injection system) in such a direction that a predetermined
ratio of fuel and air is being supplied to the engine to provide
exhaust gases of predetermined composition. The intervals are
determined by a logic circuit which has applied thereto engine
operating parameters such as operating time of the engine after
having been started, engine speed, engine power condition (idling,
or supplying power), engine temperature, or the like.
Inventors: |
Wahl; Josef (Stuttgart,
DT), Schmidt; Peter Jurgen (Schwieberdingen,
DT), Zechnall; Richard (Stuttgart, DT) |
Assignee: |
Robert Bosch GmbH (Stuttgart,
DT)
|
Family
ID: |
5856275 |
Appl.
No.: |
05/396,477 |
Filed: |
September 12, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Sep 14, 1972 [DT] |
|
|
2245029 |
|
Current U.S.
Class: |
123/680; 60/285;
60/276; 123/686; 123/687 |
Current CPC
Class: |
F02D
9/00 (20130101); F02D 41/2454 (20130101); F02D
41/1474 (20130101); F02D 2700/09 (20130101); F02D
2250/14 (20130101) |
Current International
Class: |
F02D
41/14 (20060101); F02D 9/00 (20060101); F02B
003/00 () |
Field of
Search: |
;123/32EA,32AE,119E,124,119R ;60/285,276 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Devinsky; Paul
Attorney, Agent or Firm: Flynn & Frishauf
Claims
We claim:
1. Method of controlling the composition of the exhaust gases from
internal combustion engines, including the step of
controlling the relative proportion (.lambda.) of air and fuel
being applied to the engine;
sensing operating parameters of the engine, comprising at least one
of: operating time of the engine upon starting, after having been
stopped; engine speed; engine operation under idling, or power
supplying condition; engine temperature;
sensing composition of the exhaust gases and providing an exhaust
output signal representative thereof;
sensing if a predetermined operating condition of the engine
prevails for a predetermined time limit;
comparing the exhaust sensed signal with a reference if said
operating conditions persisted beyond said predetermined time
limit;
generating a timing signal;
and controlling said relative proportion (.lambda.) of air and fuel
in accordance with sensed composition, as represented by the
exhaust signal, during said timing signal.
2. Method according to claim 1 wherein an exhaust sensing element
(15) is provided, further comprising the step of
exposing said sensing element to the exhaust gases for a time
period which is short with respect to the operating time of the
combustion engine.
3. Method according to claim 2 wherein said exposing step is
controlled by occurrence of said sensing signal.
4. Method according to claim 1 wherein an exhaust sensing element
is provided, further comprising the step of
continually exposing said sensing element (15) to the exhaust
gases.
5. Method according to claim 1 wherein step of sensing an operating
parameter of the engine comprises sensing that the engine is
operating under idling conditions, has reached a predetermined
temperature level, has a speed within a predetermined range, and
that these conditions pertain for the first time upon repeated
operation of the engine after it had been stopped.
6. Method of controlling the composition of the exhaust gases from
internal combustion engines, including the step of
controlling the relative proportion (.lambda.) of air and fuel
being applied to the engine;
generating an operating time signal having a limited time duration
with respect to operating time of the engine, after starting of the
engine subsequent to the engine having been stopped;
sensing operating parameters of the engine, comprising at least one
of: engine speed; engine operation under idling, or power supplying
condition; engine temperature; providing an indication signal of at
least one of said operating parameters having reached a
predetermined value;
sensing composition of the exhaust gases and providing an exhaust
output signal representative thereof;
and controlling the relative proportion of air and fuel in
dependence on said exhaust output signal upon conjunction of
occurrence of said timing signal and said indication signal, to
change, if required, said relative proportion, and only during
concurrent presence of the indication signal and said timing
signal.
7. Method according to claim 6, wherein an exhaust sensing element
(15) is provided, further comprising the step of
intermittently exposing said sensing element to the exhaust gases
for a time period which is short with respect to the operating time
of the combustion engine.
8. Method according to claim 7 wherein the time period of said
exposing step is controlled by occurrence of said indication
signal.
9. Method according to claim 6, wherein an exhaust sensing element
is provided, further comprising the step of
continually exposing said sensing element (15) to the exhaust
gases.
10. Method according to claim 6, wherein the step of sensing
operating parameters of the engine comprises sensing that the
engine is operating under idling conditions, has reached a
predetermined temperature level, has a speed within a predetermined
range, and that these conditions pertain for the first time upon
repeated operation of the engine after it had been stopped.
Description
The present invention relates to a method and apparatus to decrease
the noxious components in the exhaust emission of internal
combustion engines, by supervising the exhaust, at preselected
intervals, and controlling the mass ratio of air-fuel being
supplied to the internal combustion engine in dependence on a
sensed output signal from a sensing element, sensing the
composition of the exhaust gases.
It is customary to adjust the air-fuel mixture being supplied to
internal combustion engines upon original manufacture, and then
from time to time, and various devices are provided in order to
supply the air-fuel mixture to the internal combustion engine.
These may be, for example, carburetors or fuel injection systems.
As the vehicle operates, various outside conditions influence the
operation and the relative proportion of air and fuel being
supplied to the internal combustion engine by the respective mixing
device may change. For example, the one or the other component may
be subject to drift; the internal combustion engine, itself, is
subject to changes during its operation, as a result of the
operating time and conditions thereof. All these changes may change
the composition of the exhaust gases being emitted from the engine,
so that these exhaust gases no longer comply with pollution control
requirements set by legislative or regulating bodies. The
adjustment of the fuel-air mixture supplying device, the
carburetor, or the fuel injection system, may be checked when the
engine is being serviced, or tuned, and can be changed to meet
requirements; the interval between service checks on the engines
becomes longer and longer, however, and thus the time during which
the vehicle may operate with an improperly adjusted fuel supply
system may be relatively long.
It is an object of the present invention to provide a method, and
an apparatus which carries out the method to monitor the
composition of the exhaust gases in intervals which are shorter
than those of the normal service intervals and, if necessary, to
change the ratio of fuel and air being supplied, so that the
exhaust emission from the engine will comply with legal
requirements.
In the method and in the apparatus according to the present
invention, it is assumed that the mass ratio of air to fuel
(expressed as the air number .lambda.) is set for approximately
stoichiometric value, which is to be maintained by the fuel supply
system. If the supply system is set for a value of .lambda. = 1,
corresponding to an air-to-fuel ratio of approximately 14.4:1, then
the exhaust emissions may be controlled to be a minimum. Such a
setting is provided for the engines, usually, when they are
new.
In the system and method according to the present invention, the
exhaust gas is analyzed by measuring partial oxidation pressure. In
accordance with a further object of the present invention, the
system which carries out the method should be simple and, itself,
not require servicing except possibly in very extended intervals,
and operate reliably and accurately even under the rough conditions
of random operation of motor vehicles.
Subject matter of the present invention
Briefly, certain intervals are determined in which the output
signal from an exhaust gas sensing device is sensed, and applied to
a control circuit which controls the fuel supply system
(carburetor, or fuel injection system), in such a direction that a
predetermined composition of exhaust gases is maintained. The
intervals themselves are determined by a logic circuit which has
applied thereto at least one of these engine operating parameters:
the operating time of the engine, after having once been started;
engine speed; whether the engine operates under idling, or power
supplying condition; engine temperature. In accordance with a
preferred embodiment, each time that the engine is started, a new
interval begins, and, upon logical conjunction of two or more of
the foregoing parameters, an output signal is provided which
effects connection of the sensing element in the exhaust gas system
of the engine, to provide a control signal if the sensing system
senses a deviation from a predetermined value, the control signal
operating a servo system which tends to re-establish the desired
exhaust composition.
In accordance with a feature of the invention, the apparatus
includes a first timing switch which is connected to a logic
circuit to start a timing interval, and a logic circuit being
controlled by at least one of the aforementioned operating
parameters; the first timing switch is connected over a second
logic circuit to a second circuit which controls a gate, which
connects the output signals of the exhaust gas sensing element to
the system, that is, which controls the gate to be conductive. When
the gate becomes conductive, the servo system which tends to reset
the fuel-air mixture applied to the input to re-establish proper
exhaust emission, is activated.
The exhaust emission itself can be measured in various ways, the
present invention being particularly directed to two of these.
One system to measure the exhaust emission utilizes a well known
and quite sensitive zirconium-dioxide sensor, having platinum
contacts. Such sensors have relatively short life if the fuel
includes lead. It is thus desirable to expose such a sensor to the
exhaust gases only for a short time and when measuring is actually
proceeding.
In accordance with a feature of the invention, the exhaust system
is formed with a bypass to the exhaust gases, the sensor being
located in the bypass, and the bypass itself being connected to the
exhaust gases, for example by means of a flap valve, only when
measurement of the exhaust gas is to be effected.
A second system to measure the composition of the fuel-air mixture
utilizes an exhaust gas measuring device which is substantially
immune to lead poisoning, or sensors having a platinum contact
arrangement within a protective sleeve. Such contacting may be
made, for example, with catalytically active, electron conductive
oxides. Sensors of this type have a relatively long response time,
however, that is, the output signal changes only after a certain
operating condition has persisted for a predetermined period of
time. It is therefore necessary that the apparatus provide a
constant operating condition for a predetermined time period, for
example idling conditions. Such sensors, which are insensitive to
lead contamination, but have a slow response time may be left
exposed to the exhaust gases at all times, since the contacting
system is immume to lead contamination or a protective sleeve is
provided.
The invention will be described by way of example with reference to
the accompanying drawings, wherein:
FIG. 1 is a general, schematic, block circuit diagram to illustrate
the system in accordance with the present invention;
FIG. 1a is a fragmentary portion of the system of FIG. 1, and
illustrating a modification;
FIG. 1b is a highly schematic diagram illustrating the use of a
lead sensitive sensor, in an exhaust bypass;
FIG. 2 is a schematic, more detailed diagram illustrating an
arrangement to change the fuel-air mixture in a system in which the
exhaust sensor is constantly exposed to the exhaust gases;
FIG. 3 is a timing diagram, having timing graphs a to g and showing
pulses arising in the system of FIG. 2; and
FIG. 4 is a second embodiment of the invention to change the
fuel-air mixture by control of the carburetor, or fuel injection
system in dependence on composition of the exhaust gases of an
automotive internal combustion engine.
An electrical logic circuit 10 (FIG. 1) is connected to a plurality
of sensors, providing output signals representative of operating,
or operation parameters of the internal combustion engine, which
includes: an engine temperature sensor 11; an idle condition sensor
12, a tachometer generator 13, providing a speed signal, ignition
switch 14, and exhaust gas sensors 15. The transducers 11, 12, 13,
14 and 15 provide electrical signals which are connected to the
logic circuit 10. The logic circuit 10 provides, at output terminal
10', an electrical signal which is applied to a signal-position
transducer 16, which converts the output signal from logic circuit
10, at terminal 10', to a physical displacement. The displacement
is available as a position change, schematically indicated by
junction point 16'. If the fuel-air mixture supplying device is a
fuel injection system, then the displacement at junction 16 is
applied, for example, as a displacement of a potentiometer 17,
which controls a control parameter in the fuel injection system 18,
supplying fuel, together with air, to the internal combustion
engine. The control is so connected, that the duration of injection
of fuel counteracts any deviation of sensed exhaust gas emission
from a set standard, by changing the duration and opening time of
the fuel, with respect to the then existing air flow. If the
fuel-air supply system is a carburetor 19 (FIG. 1a) then the
mechanical displacement available at point 16' is connected to an
air-fuel adjustment device in the carburetor, schematically
indicated as .lambda. control 20. In actual construction, the
.lambda. control 20 may, for example, be a control flap in a
bypass, or the like, which can be directly controlled from the
displacement available at point 16'. By changing the relative
bypassed air to carburetor 19, the relative proportion of air and
fuel of the air-fuel mixture provided by the carburetor 19 will be
changed, due to the addition of more, or less additional air to the
mixture.
Other systems and methods can be used to change the relative
composition of air and fuel; for example, it is possible to change
the fuel supply independently of air supply in the carburetor, by
turning a needle valve member supplying fuel, either through the
regular carburetor system, the idling jet, or an auxiliary jet;
likewise, the passage of air through the carburetor itself can be
changed by superimposing a deflection on the carburetor throttle as
commanded by the distance output from transducer 16, as
schematically indicated at point 16'.
Sensor 15, depending on its construction, may be connected in the
exhaust system of the internal combustion engine at all times, or
may be exposed to the exhaust gases only temporarily. FIG. 1b
illustrates a system in which the sensor or transducer 15 is
connected only temporarily. The exhaust pipe 52 has a bypass 53
connected therein, which can be selectively closed off by a flap
valve 54. Sensor 15 is located in the bypass, and electrically
connected by output line 15'. The position of the flap 54 is
controlled by a linkage 55 from a magnet 51 which is energized from
an output of logic circuit 10, connected to junction 10'. In any
case, that is whether the sensor 15 is of the slow acting type
permanently exposed to exhaust gases, or of the rapid acting type
only temporarily exposed to exhaust gases, logic circuit 10
provides output signals which are utilized to control the relative
proportion of air and fuel being supplied to the internal
combustion engine either by a fuel injection system 18 or by a
carburetor 19, by controlling either the air flow, fuel flow, or
fuel injection time, as the case may be.
Referring now to FIG. 2 which shows details of logic circuit 10; a
first bistable flip-flop (FF) controls 21 a first timing circuit,
over a logic circuit formed as AND gate 22. The timing circuit is a
monostable multivibrator (MMV) 23. FF 21 is connected to the
ignition switch 14 over a differentiating network formed by a
capacitor 25 and resistor 24. Ignition switch 14 is turned ON, when
the internal combustion engine (not shown) is started. FF 21 has a
second input which is connected to the output of a threshold switch
26, which includes an operational amplifier 27, having one input
connected to engine temperature sensor 11.
The second input of the AND gate 22 is connected to an idle sensing
switch 12. This switch is closed only when the accelerator control
of the engine is not operated, that is, when the engine is idling.
When the engine is not idling, switch 12 is open. The third input
to the AND gate 22 is connected to a speed sensing switch 9, which
has its input connected to a tachometer generator 13. When the
speed is at a certain value, an output is derived from switch
9.
The output of the AND gate 22 is connected to the input of MMV 23.
The idle switch 12 is further connected to an input of a second FF
28. The output of the second FF 28 is connected to the input
terminal 30 of a logic AND gate 29, the first input 31 of which is
connected to the first output of MMV 23. The second output of MMV
23 is connected to an input of FF 28. A further input of the FF 28
is connected to the output of the R/C circuit 24, 25 of the
differentiator connected to the ignition switch 14. The output of
the AND gate 29 is connected to the input of a second timing switch
formed as MMV 32. The first output of MMV 32 is connected to an
input of the first FF 21; a second output of MMV 32 is connected to
the signal/position transducer 16.
The signal/position transducer 16 has an input gate 33 which has
two AND gates 34, 35. One input, each, of the AND gates 34, 35 is
connected to the output of the MMV 32. AND gate 34 is connected
directly to the output of an amplifier 36; AND gate 35 is connected
to the amplifier 36 over an inverting input. Amplifier 36 is a
threshold amplifier and provides a signal when the signal from the
exhaust gas sensor 15 reaches a certain value. The output of the
AND gate 34 is connected to the control electrode of a transistor
39; the output of the AND gate 35 is connected to the control
electrode of a transistor 37. The transistors 37, 39 have their
respective emitters grounded; their collectors are connected to a
motor 38 which can be connected to a source of potential over one,
or the other of the transistors.
Operation (with reference to FIGS. 2 and 3): upon turning the
ignition switch 14 ON, the output from switch 14 will be the signal
as indicated in line a of FIG. 3; the lines which carry the
respective signals have been given the same letters in FIG. 2 as
the graph letters in FIG. 3. Differentiator 24/25 provides a pulse
to one input of the FFs 21, 28 which will change state to be set.
When temperature sensor 11 senses a temperature of the internal
combustion engine above a predetermined value, threshold switch 26
provides an output signal and FF 21 is reset. The output of the FF
21 is shown in graph b of FIG. 3. Since the output from FF 21 is
connected at its inverted side, a 1-signal is on line b and will be
applied to AND gate 22. If idle switch 12 provides an output
indicating that the engine is idling, the second input of AND gate
22 will have a 1-signal. If, further, the engine speed is such that
the engine is at idling speed, as sensed by tachometer generator 13
and switch 9, a 1-signal will be on the third input of AND gate 22
which provides an output 1-signal to the MMV 23 which will be
triggered into unstable state. As MMV changes, the second FF 28
will be set. It will be immediately reset as soon as the idle
switch 12 opens. This means that only if the idle switch 12 remains
closed during the unstable state of the MMV 23, the second MMV 32
can be triggered into unstable condition over the AND gate 29, that
is, upon enabling of terminal 30.
The unstable time of the second MMV 32 is comparatively short. The
output signal of sensor 15 will thus be applied over the AND gates
34, 35 to transistors 37, 39, controlling the motor 38 only during
this unstable time period, in order to cause motor 38 to operate,
for example by changing the tap point of a variable resistor,
included in the control portion of an electronic fuel injection
system; or to change the angular position of a flap valve in a
carburetor fuel supply system. While the second MMV 32 is in its
unstable state, transistor 37 commands rotation of motor 38 in one
direction, and transistor 39 commands rotation of the motor in the
other direction, depending upon the respective output from
amplifier 36 which, in turn, will depend upon whether the values
applied to the amplifier 36 are above, or below a reference
determined by a voltage divider connected to a reference potential
R. Output voltage of the sensor is compared over a line 15' with
the voltage of the reference. Depending on the relative polarity of
the output voltage of the sensor with respect to the reference,
either transistor 37 or 39 will be rendered conductive, thus
causing operation of the motor in one direction or the other.
The timing diagram makes the operation clear. When the threshold
switch 26 responds, its output will be a signal as indicated in
graph c. Assuming that the engine is idling, switch 12 will provide
the output indicated in graph d. Thus, if switch 26 has reset FF
21, if idling conditions pertain, and the proper speed is present,
MMV 23 will change into unstable state, as seen in graph e. Graph f
shows the output signal of the second FF 28, in which a 1-signal is
provided when the idle switch 12 (graph d) is closed and
simultaneously the first MMV 23 is in unstable state (graph e). The
second MMV 32 is operated only when the first FF 28 provides a
1-signal beyond the unstable switching state of the MMV 32 (graph
e) to provide a short pulse, graph g, so that the operating circuit
can change the relative ratio of air and fuel being supplied to the
internal combustion engine.
The direction of rotation of servo motor 38 of signal-position
transducer 16 is determined by the amplifier 36, which is an
operational amplifier connected as a threshold switch. The output
signal of the sensor 15 is compared with a predetermined reference
R; depending on the result, one or the other of the AND gates 34,
35 will be enabled, to control transistors 37, 39, respectively, to
be conductive.
Upon switch-over of the MMV 32 into unstable state, the first FF 21
is set into its original state, so that the next time that a change
in the relative proportion of air and fuel can be controlled by
motor 38 can occur only when switch 14 is again operated, that is,
if the other conditions pertain and, further, the engine is again
started. The set terminal of the second FF 28 is connected to the
first MMV 23, to be set upon return of the first MMV 23 to its
original state, unless, of course, either the ignition switch is
operated, or the idle signal (graph d) from transducer 12
persists.
FIG. 4 illustrates a modified embodiment, in which similar, or
similarly operating parts have been given the same reference
numerals and will not be described again in detail. R/C
differentiator 24, 25 connects ignition switch 14 to FF 21, and the
temperature threshold switch 26 connects the reset terminal of the
FF 21. Differing from the circuit of FIG. 2, the output of AND gate
29 is connected to the input of a third FF 40. The FF 40 is further
connected to the idle switch 12 and to the output of operational
amplifier 36, connected as a threshold switch. One output of FF 40
is connected to a first input of an AND gate 41, the second input
of which is connected to the output of the second FF 28. The second
output of the FF 40 is connected to the common inputs to the AND
gates 34, 35, the other inputs of which are connected to the
operation amplifier 36, directly, or over an inverting input, as in
the example of FIG. 2.
Operation of circuit of FIG. 4: when switch 14 is connected, the
two FFs 21, 28 will be changed to set state. When the temperature
has reached a predetermined level, as determined by switch 26, FF
28 will change state to be reset, so that AND gate 22 will have a
1-signal at a first terminal. If idle switch 12 and speed switch 9
also provide 1-signals, MMV 23 is changed to unstable state, which
changes over the second FF 28, and over AND gate 29, third FF 40
will be set. When the FF 40 is set, the motor 38 of the
signal-position transducer will operate until the output from
sensor 15, on line 15', balances the value set by the voltage
divider connected between reference source R and has reached its
proper value. As soon as operational amplifier 36 changes
potential, or if idle switch 12 should open, motor 38 is
disconnected since FF 40 will again change state. Resetting of the
first FF 21 is obtained over AND gate 41 when the third FF 40
changes state upon failure of the signal from either operational
amplifier 36 or the idle switch 12, provided that the second FF 28
is still maintained in its previous position by the idle switch 12.
The response of the switches 28, and 40 may be different.
The adjustment device in accordance with the present invention
provides an electronically controlled supervision of exhaust gases,
and adjustment of the air-fuel ratio (air number .lambda.) upon the
logical conjunction of certain operating conditions. Each time,
when the engine is started, the logic circuit is activated, that
is, is set to be operated. After the engine has exceeded a certain
temperature, for example has reached normal operating temperature,
logic circuits provide for sensing of the exhaust gas sensors, for
comparison with a reference value. This occurs only, however, if
the operating state of the internal combustion engine remained, for
a certain period of time, without interruption in idling
conditions, and only the first time after the desired operating
temperature has been exceeded. The adjustment is provided by
changing a suitable element in the air/fuel supply to the engine,
driven by a motor 38, for example changing the setting of a
potentiometer in the control circuit of the fuel injection system,
or the setting of a link, valve, or flap in the air, or fuel supply
to the internal combustion engine, or in connection with the
carburetor. Depending on the polarity of the deviation of the
sensed exhaust signal from the reference, the motor rotates to the
right, or to the left, to re-establish balance. The operating
period of the motor, itself, is limited. Thus, adjustment will be
slow and the first time that a deviation is sensed, the adjustment
may not entirely compensate for the deviation, since MMV 32 (FIG.
2) may reset before full compensation has been obtained, or because
idling condition may no longer pertain (FIG. 4). Yet, limiting the
extent of resetting permits gradual and very exact matching to the
desired value, without hunting or overshoot.
If the embodiment of FIG. 4 is selected, and idling persists, the
motor will operate until balance is obtained, and provided that the
operating parameters, logically permitting energization of the
motor continue. It is also possible to so connect the logic circuit
that the motor will continue to operate until balance is obtained
even though the time period during which measurement is initiated
has terminated. In both instances, the readjustment may be limited
to occur only when the motor changes from cold to warm condition,
that is, each time that the motor is started after prolonged
shut-down. The readjustment may also be made each time that a
plurality of conditions continue to persist, for example motor at
operating temperature, a definite operating state of the engine
(for example idle), a predetermined speed.
It is not necessary to select idling speed of the internal
combustion engine as one of the parameters; other parameters may be
used, provided that, in ordinary operation, they persist for a
sufficiently long period of time so that oxygen sensors which are
subject to delay in response, can reach balance. Such oxygen
sensors usually require several seconds for electrical balance with
the gases being sensed. Thus, any parameters which remain in this
condition for a time sufficient for the sensor to respond may be
selected, such as speed, throttle position, pressure (or rather,
vacuum) in the intake manifold, air flow, or air/fuel flow to the
engine, or any other operating, or operation condition of the
engine which can be clearly defined, and which is apt to recur in
definite intervals.
The bypass (FIG. 1b) in which the sensor 15 is located if, for
example, it is subject to contamination by lead, may be operated by
a flap, controlled from a solenoid 51 which is connected to
terminal 10', the output of the logic circuit. Terminal 10' is
shown in FIGS. 2 and 4, and provides an output which is independent
of the sensor itself. The solenoid 51 can also be connected to be
operated when the FF 21 provides a 1-signal on its output line, in
order to provide some pre-heating time to the sensor 15 so that
heat balance can be achieved before the actual measurement is made,
which will control the motor 38 (compare graphs b and g in FIG. 3),
the flap valve 54 being closed as soon as FF 21 is again set. This
flap valve will remain closed until the engine is again started,
and another measuring cycle can commence.
If the fuel-air supply is provided by a fuel injection system,
which is entirely electronic, then the output at terminal 10' need
not be applied to a system including a servo motor 38 to control a
potentiometer, to change the electronic circuit controlling the
fuel injection time, but, rather the output at terminal 10' can be
used to electronically control the operating times, for example by
connecting transistors 37, 39, selectively, in a shunt circuit to a
timing element in the electronic fuel injection circuit, such as
capacitor, or the like, to change the discharge, or charge rate of
the capacitor, and thus change the timing of the injection duration
of fuel by the fuel injection circuit. Such a system, without the
motor 38, however, then is the electronic equivalent of a
combination of transducers 16, 17, taken together.
Various changes and modifications may be made within the scope of
the inventive concept.
* * * * *