U.S. patent number 3,916,848 [Application Number 05/424,464] was granted by the patent office on 1975-11-04 for automotive-type internal combustion engine exhaust gas emission control system.
This patent grant is currently assigned to Robert Bosch GmbH. Invention is credited to Peter-Jurgen Schmidt.
United States Patent |
3,916,848 |
Schmidt |
November 4, 1975 |
Automotive-type internal combustion engine exhaust gas emission
control system
Abstract
A timing circuit is connected between a threshold switch
providing alternately voltages representative of excess, or absence
of oxygen in the exhaust emission from the engine, the timing
circuit measuring the time interval between change-over of the
threshold switch as determined by changes in the composition of the
exhaust emission; if the change-over is within a predetermined
timing range, a control switch is held in one position; if the
change-over rate drops, however, indicative of malfunction in the
exhaust emission sensor, or associated connected equipment, the
switch is placed into another state whereupon it will command a
fuel-air control amplifier to provide a control ratio of a
predetermined value and, if desired, additionally provide a sensed
output to control an alarm or other trouble indicator. Switching
change of the control switch can be overriden by other signals
available within the automotive vehicle.
Inventors: |
Schmidt; Peter-Jurgen
(Schwieberdingen, DT) |
Assignee: |
Robert Bosch GmbH
(Gerlingen-Schillerhohe, DT)
|
Family
ID: |
5868813 |
Appl.
No.: |
05/424,464 |
Filed: |
December 13, 1973 |
Foreign Application Priority Data
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Jan 12, 1973 [DT] |
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2301354 |
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Current U.S.
Class: |
123/688;
123/198D; 123/690 |
Current CPC
Class: |
F02D
41/1495 (20130101) |
Current International
Class: |
F02D
41/14 (20060101); F02B 003/00 () |
Field of
Search: |
;123/32EA |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Cangelosi; Joseph A.
Attorney, Agent or Firm: Flynn & Frishauf
Claims
I claim:
1. In an internal combustion engine exhaust emission control system
having
means (1) sensing the composition of the exhaust gases and
providing a sensed electrical signal,
an integrating control amplifier (29, 30) connected to said sensing
means (1) and providing an output signal (29') which is available
to command the relative mass ratio (.lambda.) of air-fuel applied
to the engine;
and a threshold switch (15), connecting the sensing means (1) to
the integrating control amplifier and operative to change switching
state above, and below its threshold level, said threshold switch,
upon normal operation of the system, cyclically switching between
its states,
a timing circuit (36) connected to the threshold switch (15) and
measuring the time intervals between change-over of switching state
of the threshold switch (15), as determined by changing output from
the sensing means (1) the timing circuit sensing the intervals
between change-over of the threshold switch (15'); and
a change-over switch (46; 47, 49) controlled by said timing circuit
(36) the timing circuit controlling said change-over switch to be
in a first state when the duration of the intervals between
change-over of the threshold switch are below a predetermined
timing interval, indicative of proper operation of the sensing
means and of the threshold switch, the timing circuit controlling
said change-over switch (46; 47, 49) to be in another state when
the switching interval since the last change-over of the threshold
switch is above said predetermined interval, said change-over
switch, when in the second state, providing an output signal (49')
indicative of excess time lapse between change-over of the
threshold switch (15) and representative of system malfunction.
2. System according to claim 1, further comprising a monostable
flip-flop (37, 39) connected between the threshold switch (15) and
the timing circuit (36) and triggered into unstable state by change
of state of the threshold switch (15);
and wherein said timing circuit comprises a capacitor (44)
connected to be charged during one state of the monostable
flip-flop (37, 39) and a discharge circuit (45) permitting
discharge of the capacitor during the other state of the monostable
flip-flop, said discharge circuit having a time constant which
prevents complete discharge of the capacitor when the switching
interval of the threshold switch (15) is within said predetermined
value to provide a residual charge on the capacitor (44), said
residual charge holding said change-over switch (46) in said state
indicative of proper operation.
3. System according to claim 2, wherein the capacitor (44) is
charged during the unstable state of the monostable flip-flop (37,
39) and discharged during the stable state thereof and said
discharge circuit has a high time constant and is connected to and
controlling said change-over switch (46) to change state indicative
of "trouble" operation upon discharge of the capacitor below a
predetermined level.
4. System according to claim 1, wherein the integrating control
amplifier comprises an operational amplifier (29);
and a coupling circuit (54) is provided between the output (49') of
the change-over switch (46) and the inverting input of the
operational amplifier (29) to modify the input signal applied
thereto.
5. System according to claim 4, wherein the coupling circuit
comprises a diode (54).
6. System according to claim 4, further comprising selectively
variable input resistance means (28, 31, 32) connected to the
coupling network and the operational amplifier (29, 30).
7. System according to claim 2, wherein the monostable flip-flop
(37, 39) comprises a transistor (37) having its emitter-collector
path connected in parallel to the capacitor (44) of the timing
circuit;
and a coupling capacitor (39) and a diode (38) coupling network
connecting the output of the threshold switch (15) to the control
electrode of the transistor (37).
8. System according to claim 1, wherein the timing circuit
comprises a capacitor (44);
and the change-over switch (46) comprises an emitter-follower input
transistor (47) connected to the timing capacitor (44), and a
switching output transistor (49) connected to and controlled by
said input transistor (47).
9. System according to claim 1, further comprising alarm circuit
means (53', 60, 61) connected to the output (49') of the
change-over switch (46) to provide an alarm output signal upon
sensing of "trouble" operation.
10. System according to claim 1, further comprising at least one
override connection terminal (52, 52') connected to the change-over
switch (46) to hold said switch in a position indicating proper
operation of the sensing means to override control of the
integrating control amplifier (29, 30) by said change-over switch
(46) upon energization of at least one of said override
terminals.
11. System according to claim 1, wherein the relative mass ratio
(.lambda.) of the air-fuel applied to the engine is controlled to
apply a lean mixture to the engine when the timing circuit has
sensed a time interval from the last change-over of the threshold
switch (15) which is above the time duration of the predetermined
interval.
Description
The present invention relates to a system to decrease the noxious
components in the emission from internal combustion engines, and
more particularly to such a system in which the mass ratio of fuel
and air of the mixture applied to the internal combustion engine is
controlled by means of an integrating controller which, in turn,
has input signals applied thereto representative of compliance
with, or deviation from sensed standards in the exhaust from the
engine.
Exhaust sensors located to be responsive to the composition of the
exhaust gases from an internal combustion engine, and providing
electrical output signals, have previously been proposed. To
control a mass ratio of air-fuel being applied to the internal
combustion engine, also called .lambda. control, fuel and air, in
suitable relationships, are applied by means of a carburetor or an
electronically controlled fuel injection system to the engine. The
control system maintains the mass ratio of fuel and air being
supplied at such a value that the exhaust from the engine has a
minimum of noxious components. This is the case if the exhaust is
just slightly reducing, that is, if the air-fuel mixture being
applied is maintained at a value which is just below stoichiometric
ratio. At this just slightly under stoichiometric value, this
exhaust gases will have a composition which will have a minimum of
noxious components, or can be limited to a minimum of noxious
components, if the exhaust system of the internal combustion engine
has a catalytic reactor to treat the exhaust gases.
The exhaust gas sensor may fail. This sensor, located in
gas-sensing relationship to the exhaust gases of the engine,
typically in the exhaust system thereof, will then no longer
provide an output signal. Failure of an output signal from a
typical sensor is, electrically, the equivalent of an indication
that the air-fuel mixture is lean. A control system connected
thereto will then control the input to the engine to compensate for
this -- erroneous -- "lean" mixture and command a rich fuel-air
mixture being applied to the engine.
It is an object of the present invention to provide a control
system in which failure of the sensing device, or at least a
portion of the control circuitry will provide an output indication
to the operator by commanding an alarm system, for example, and/or
changing the operating conditions of the internal combustion engine
to such an extent that the operator of the engine, typically of a
vehicle, cannot but fail to notice, and thus is forced to repair,
or have repaired the vehicle and particularly the exhaust system,
for example by replacing the sensor.
Control systems in which exhaust sensors are used and also
employing integrating amplifiers have output signals derived from
the sensors which jump between extreme values, indicative of
presence or absence of oxygen in the exhaust system. The
integrating amplifier then controls the system in such a manner
that, on the average, the oxygen being sensed is a minimum. The
system includes a threshold switch, which is responsive to changes
in output signals from the sensor.
SUBJECT MATTER OF THE PRESENT INVENTION
Briefly, a timing circuit is connected to the threshold switch, and
controls a switch which is held in a certain position when the
threshold switch has a change-over repetition rate indicative of
normal or ordinary operation, but permits, or causes change-over of
the switch if there is trouble, or malfunction in the sensor, or
the circuit connected thereto. The timing switch, then sensing a
different repetition rate of change-over of the threshold switch,
commands change of the switching position which, in turn, provides
an output signal which can be directly applied to the control
circuit of the integrating amplifier, to an alarm or warning
device, or to other apparatus to influence the operation 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 general, highly schematic circuit diagram and
illustrating an example of a .lambda.-control circuit and
supervisory circuit; and
FIG. 2 is a fragmentary portion of another embodiment of the
circuit of FIG. 1.
An oxygen sensor 1 is located in sensing relation to the exhaust
gases of an internal combustion engine (not shown). The output
sensor 1 provides an electrical signal which is a characteristic of
the composition of the gases within the exhaust from the internal
combustion engine. The oxygen sensor is, preferably, enclosed in a
shield, schematically indicated at 1'. The sensor, as well as the
control circuit, are powered from supply buses 3, 10, connected,
for example, to the battery circuit of an internal combustion
engine, or any other suitable d-c circuit which may be subject to
voltage fluctuations.
The electrical signal from sensor 1 is applied to the base of a
transistor 2 connected as an emitter follower. The collector of
transistor 2 is directly connected to bus 3; the emitter of the
transistor 2 is connected over a resistor 4 to a junction J1. The
collector-emitter path of transistor 2 and the series connected
resistor 4 form one leg of a first branch of a bridge 5. A second
leg of the branch of the bridge 5 is formed by the series circuit
of the collector-emitter path of a second transistor 6 and a
resistor 7. The base of transistor 6 is connected to a voltage
divider formed by resistors 8, 9, connected over a common resistor
12 between supply buses 10 and 3. Resistor 9 is adjustable. The two
resistors 8, 9 have a Zener diode 11 connected in parallel
thereto.
The third and fourth legs of the bridge 5, forming the second
branch, are formed by a resistor 13, connected to the common bus 3
and a resistor 14 connected to the common bus 10, both being
connected to junction J2, which forms, together with junction J1,
the diagonal connection of the bridge.
The diagonal of the bridge is connected to an operational amplifier
15, junction J2 being connected over coupling resistor 17 with the
non-inverting input, and junction J1 being connected over coupling
resistor 16 to the inverting input of the operational amplifier 15.
An output resistor 18 is connected to the output of the operational
amplifier 15, and connected to the common supply 10. The output of
the operational amplifier 15 is further connected to a junction
point of two base resistors 19, 20 for transistors 21, 22,
respectively. Transistors 21, 22 have their emitters connected to
respective tap points of two serially connected voltage dividers
formed of resistors 23, 24, 26, respectively. The transistors 21,
22 vary the transfer of the voltage swing derived from operational
amplifier 15, and thus can change the voltage difference of the
output signal being derived from the operational amplifier 15 and
further connected to an integrating amplifier. The emitter of
transistor 21 is connected to the junction between resistors 23,
24; the emitter of transistor 22 is connected to the junction
between resistors 25, 26. The collectors of the two transistors 21,
22 are connected together. The jointly connected collectors of
transistors 21, 22 are connected over a transfer switch 27 with an
input or coupling resistor 28 of an operational amplifier 29, which
functions as an integrator, having an integrating capacitor 30
connected between its output and its inverting input, to which the
coupling resistor 28 is likewise connected. Switch 27 can
selectively connect resistor 31, 32 as coupling resistors, rather
than the resistor 28 to the inverting input of operational
amplifier 29. The non-inverting input of operational amplifier 29
is connected over a coupling resistor 33 with the junction of
resistors 24, 25. The output of the operational amplifier 29 is
connected over a resistor 34 to the common supply bus 10 and,
further, to an output terminal 29'. The output terminal 29' can be
used to control, if necessary over an additional power amplifier,
the air-fuel mixture of an internal combustion engine, for example
by providing a position output which influences supply of fuel, or
air to the internal combustion engine, or by modifying the
injection period of fuel injection valves in the fuel injection
system.
Operational amplifier 15 is further connected by line 15' to a
timing circuit 36. The output line 15' is connected to a monostable
flip-flop (FF) which triggers the timing circuit 36. The monostable
FF includes a transistor 37, coupled over a coupling capacitor 39
and a diode 38, the cathode of diode 38 being connected to the base
of transistor 37. A resistor 40' connects to the common supply bus
3. The junction point of the anode of the diode 38 and capacitor 39
is connected to a resistor 41 which is connected to the common
supply bus 10. The emitter of transistor 37 is connected to the
common supply bus 3; the collector of transistor 37 is connected
over resistor 42 to supply bus 10; a diode 43 connects from the
collector of transistor 37 to one terminal of a capacitor 44, the
second terminal of which is connected to supply bus 3. Resistor 45,
of comparatively high value, is connected in parallel to the
capacitor 44. A coupling resistor 46' connects from the common
connection of capacitor 44, diode 43 and resistor 45 to the base of
an input transistor 47 of a control change-over switch 46.
Transistor 47 is connected as an emitter-follower, and has its
collector connected to bus 10 and its emitter to bus 3, if
necessary over an emitter-resistor (not shown). The emitter of
transistor 47 is further connected over a resistor 48 to the base
of a switching transistor 49. A resistor 50 connects the base to
common line 3. The junction between resistor 48, resistor 50, and
base 49 has one or more resistors 51, 51' connected thereto, which,
in turn, are connected to respective terminals 52, 52'. Further
resistors similar to resistors 51, 51', and having further
terminals similar to terminals 52, 52', may be connected to the
same junction, and therefore the connection to resistor 51' and
terminal 52' is shown in dashed lines. The terminals 52, 52' . . .
may have various electrical signals applied thereto corresponding
to operating or operation parameters of the internal combustion
engine, and to influence the state of the switching transistor 49,
as will appear in detail below. The emitter of the switching
transistor 49 is connected to supply bus 3. The collector of
transistor 49 is connected to an output terminal 49'; further, the
collector is connected over a resistor 53 to common bus 10. A
connection line, including a diode 54, connects from the collector
of transistor 49, and hence output terminal 49', to the common line
connecting the collectors of transistors 21, 22, and further
forming the common switch terminal of switch 27.
OPERATION
The output sensing signal from sensor 1 is connected into the first
branch of the bridge 5 over transistor 2. This electrical signal,
which is representative of the composition of the exhaust gases of
the internal combustion engine, forms the actual value for the
control circuit. The sensors 1 have a high internal resistance when
the temperature in the exhaust gases is still low. Thus, the
control circuit must have high input resistance and, therefore,
transistor 2 is operated as an emitter-follower and, together with
its load resistor 4, provides the necessary input resistance for
the circuit.
The command value, that is, the value which the air number .lambda.
should have, and to which the air-fuel mixture is to be controlled
so that the exhaust gases from the engine will have a predetermined
composition, is formed by means of Zener diode 11. The resulting
signal is applied over the voltage divider formed of resistors 8, 9
and transistor 6 into the second arm of the branch of bridge 5. The
command value can be adjusted by adjusting resistor 9. Transistors
2 and 6, in the first branch of the bridge, are of opposite
conductivity type, and so connected that they are
temperature-compensating.
The comparison circuit for the command value and actual value is
connected as a bridge, and thus is essentially independent of
variations in supply voltage, supplied over the common lines 3, 10.
The bridge is in balance, that is, command and actual value are
equal, if the collector-emitter paths of transistors 2, 6 have the
same voltage thereacross. This is the case if the output signal
from sensor 1, and the commanded value which the signal should have
are equal. If the command value and actual value deviate, a voltage
will appear across the diagonal terminals J1, J2 of the bridge. Let
it be assumed that the output voltage of the sensing signal from
sensor 1, that is, the actual value is greater than the commanded
value. The inverting input to the operational amplifier 15 will
have a higher voltage applied than at the non-inverting input.
Operational amplifier 15, functioning as a comparator circuit,
provides an output signal which will be approximately at the
voltage of the supply line 3. In the opposite case, that is if the
actual value is smaller than the commanded value, the output signal
of operational amplifier 15 will jump to a voltage which
corresponds approximately to that of supply line 10.
The voltage swing or voltage jump at the input to integrator 29, 30
is decreased by an intermediately connected circuit 40, which
includes transistors 21, 22. The voltage jump is decreased and,
therefore, the value of integrating capacitor 30 can be decreased.
The output signal of operational amplifier 15 controls either the
one or the other of transistors 21, 22 to be in conductive
condition, the other, or the one transistor, then, being blocked. A
signal will be applied over the respectively conductive transistor
to the input network of the integrator 29, 30 which has a smaller
voltage swing than that of the output signal of the operational
amplifier.
Switch 27 is provided in order to change the time constant of the
integrator 29, 30. The output signal of the integrator 29, 30 then
controls a suitable control element in such a manner that the
air-fuel mixture applied to the internal combustion engine is so
changed that it corresponds to a predetermined commanded ratio,
resulting in exhaust of minimum noxious components. Switch 27 is
shown schematically; as referred to in U.S. Pat. Nos. 3,782,347 and
3,831,564, both assigned to the assignee of this application, the
actual construction of the switch can be different. The switch 27
can be a controlled semiconductor switch, for example transistors
in series with resistors corresponding to schematically indicated
resistors 28, 31, 32. The transistors are selectively rendered
conductive in accordance with desired integration time constants,
as explained in the cross-referenced applications.
Let it be assumed that the sensor 1 and the connected circuit are
functioning properly. Operational amplifier 15 will change over,
that is, will change state in relatively short time intervals, the
output voltage of the operational amplifier 15 switching between
the voltage of supply line 10 and supply line 3, periodically. The
output of the operational amplifier 15 thus provides, in short
intervals, positive and negative pulses. Upon each negative jump,
monostable FF, that is transistor 37, is triggered by transfer of a
pulse over capacitor 39, that is, transistor 37 is blocked by a
period of time determined by capacitor 39. When transistor 37
blocks, resistor 42 and diode 43 will have no current flowing
thereover, and capacitor 44 can charge. The time, determined by
capacitor 39, is so selected that the capacitor 44 can be fully
charged. After this time has elapsed, and when transistor 37 again
becomes conductive, capacitor 44 can discharge over the
high-resistance resistor 45 and the input of transistor 47,
operated as an emitter-follower. The discharge time of the storage
capacitor 44 is so selected that, assuming proper operation of the
control system and of the sensor 1, a residual charge will always
remain in capacitor 44 and capacitor 44 will never completely
discharge, but always retain a certain minimum charge. Thus, the
switch 46, formed by transistors 47, 49, is not changed over.
Switching transistor 49 is held in conductive state by transistor
47.
Let it be assumed that sensor 1 fails, or that the control system
fails, that is, that no output signal will be available at the
output of operational amplifier 15. Capacitor 44 can now discharge
completely. This blocks transistor 49. The air-fuel mixture which
is applied to the internal combustion engine is then controlled in
such a manner, by output from integrating amplifier 29, 30, that
the mixture will go to the lean direction. This is obtained by
transferring a signal over diode 54 which applies its signal to the
resistors 28 (or 31, 32, respectively, if connected) in such a
direction that the integrator 29, 30 will integrate in the
direction to command a lean mixture. The operating performance of
the internal combustion engine will become worse, forcing the
operator of the engine, usually a motor vehicle, to engage in
maintenance and repair, that is, typically to replace sensor 1.
The output signal available at the collector of transistor 49, and
hence the terminal 49', can be used in other ways than to connect a
signal over diode 54, as shown. It may be applied, for example, at
other points in a fuel-air mixture supply system, or elsewhere in
the vehicle, for example by interfering with proper electrical
operation of the electrical components of the system, in order to
inhibit normal operation of the engine and to provide an indication
to the operator. The output signal can also be used to control a
warning device, which informs the driver that the sensor 1, or a
portion of the control system, has failed.
Referring to FIG. 2, the resistor 53 can be omitted and the
circuit, otherwise identical to that shown in FIG. 1, can be broken
at terminals X-X'. Instead of resistor 53, the coil 53' of a relay
is connected between terminals X-X', which, when energized, pulls
in a relay contact 60 to energize an alarm 61, for example an alarm
lamp, connected with the switch 60 between buses 3 and 10. Alarm
system 61 can be used in lieu of, or in combination with diode 54,
or to interfere in any other way with the operation of the motor
vehicle electrical system, or, by control of other parameters, with
any other element, in addition to providing a warning signal.
The monostable FF is controlled by the negative going flank, due to
the presence of diode 38, and uses a single transistor. It can be
replaced by the well-known monostable FF circuits with two
transistors, so that the positive as well as the negative switching
flank from the output of the operational amplifier 15 will trigger
the timing circuit to charge capacitor 44 twice as often. The size
of capacitor 44 can thus be decreased, at the cost of an additional
transistor.
The control systems to influence the operation of the internal
combustion engine, that is, to control the air-fuel mixture, should
not be effective under some operating conditions of the internal
combustion engine. Some of such typical conditions are: when the
exhaust sensor 1 is still cold, that is, upon starting, upon
warm-up of the internal combustion engine; or upon full-load
operation of the engine; or upon idling operation of the engine. In
all these instances, electrical signals can be applied over
terminals 52, 52' . . . to the junction of resistors 48, 50, over
appropriate coupling resistors 51, 51' . . . , which electrical
signals are characteristic of the one or the other operating
condition under which the transistor 49 is to be held in conductive
condition, so that the control circuit and a warning device (FIG.
2), if used, is disabled; in other words, the normal operation of
transistor 49 is overriden, so that no output signal will be
available from transistor 49 at terminal 49'. The operating
conditions of the internal combustion engines will, under such
override conditions, not be affected, since, under those operating
conditions, the control system is not operating but, due to the
special conditions then pertaining, normal operation of the
internal combustion engine, without malfunction or trouble
indication, is desired.
Various changes and modifications may be made in accordance with
the inventive concept.
* * * * *