Method of and device for regulating fuel-and-air mixture supplied to an internal combustion engine

Disclosed is a method and device for regulating the preparation of fuel-and-air mixture in a carburetor, fuel injection system and the like of an internal combustion engine. The device includes an oxygen probe directly communicating with the combustion chamber of the engine. Periodically fluctuating output signal of the probe is applied to an averaging circuit which produces an average output signal over a predetermined number of engine cycles. The shape and length of the averaged output signal is indicative whether the mixture ratio is lean or rich. The averaging can be made by means of a lowpass filter, an integrator or at least one counter counting in response to the angular position of the crankshaft or the predetermined time intervals. When the probe output voltage has the form of a hump or bulge, its length or area is used for determining the actual .lambda. value in the rich range of ratios of the mixture.

BACKGROUND OF THE INVENTION 
The present invention relates in general to an internal combustion engine, 
and in particular to a method of and a device for regulating fuel-and-air 
mixture supplied to a combustion chamber of an internal combustion engine 
via a mixture-preparing device having an oxygen probe which is placed 
directly in the combustion chamber to deliver an output signal indicative 
of the actual amount of oxygen in the mixture. 
In the German patent publication No. 3,028,359 a spark plug provided with 
an oxygen probe is described to be used in devices which control or 
regulate feeding of fuel to an internal combustion engine by means of 
immediate or so-called combustion chamber regulating process. This known 
spark plug is designed such that an oxygen probe is arranged in the 
insulator which surrounds the central spark electrode of the plug. The 
oxygen probe can be made of a number of materials and includes a 
comparison electrode, a solid electrolyte and a measuring electrode, 
whereby the comparison electrode and the measuring electrode are connected 
to a direct-current source to determine partial pressure of oxygen to be 
compared. Depending on whether at certain time points the partial pressure 
of oxygen in combustion chamber is interpreted in the sense of too rich or 
too lean a mixture supplied to the engine, the oxygen probe generates 
cyclic fluctuations of its output signal which immediately determines the 
condition in the combustion space. 
SUMMARY OF THE INVENTION 
A general object of the present invention is to provide a method and device 
which substantially improve the operation of the above described oxygen 
probe. 
More particularly, it is an object of the invention to provide an improved 
oxygen probe arrangement which permits, in addition to the immediate 
measurement of the combustion process, a very fast reaction of the fuel 
mixture regulating device, even when the so-called "cycle-to-cycle 
irregularities of fluctuation" interfere with the prompt regulation from 
one cycle to another one. 
Another object of this invention is to provide such an improved oxygen 
probe arrangement which substantially reduces the detection time of the 
constituents of fuel-and-air mixture supplied to the IC engine. In 
comparison with conventional arrangements of oxygen probe in the exhaust 
pipe, down times resulting from the expulsion of exhaust gases and their 
passage through the muffler are substantially reduced. 
Another object of this invention is to provide such an improved oxygen 
probe arrangement which operates even under extreme conditions of the 
fuel-and-air mixture, that is extremely rich or extremely lean, and 
detects the oxygen ratio after several machine cycles and initiates the 
corresponding reaction. 
In keeping with these objects and others which will become apparent 
hereafter, one feature of the invention resides, in a method of regulating 
fuel-and-air mixture supplied to a combustion chamber of an IC engine via 
a mixture-preparing device including an oxygen probe placed directly in 
the combustion chamber to deliver an output signal indicative of the 
actual amount of oxygen in the mixture, in the step of averaging the 
output signal of the probe from a predetermined number N of engine cycles 
depending on the rotary speed of the engine. The device for carrying out 
the novel method includes means for preparing the fuel-and-air mixture and 
an averaging circuit connected between the oxygen probe and the means for 
preparing the fuel-and-air mixture to average output signals from the 
probe over a predetermined number of engine cycles depending on the rotary 
speed of the engine. 
The invention enables monitoring a multi-cylinder engine in average, 
whereby the measuring results in respective cylinders are evaluated in 
series according to the ignition sequence. In addition, this invention 
enables a simultaneous monitoring of each individual cylinder. The latter 
possibility has the advantage that deviations of the fuel-air mixture 
composition in the cylinders can be individually removed. In prior-art 
regulating devices of this kind, it may happen that one engine on average 
operates at a fuel-and-air mixture value .lambda.=1 but the individual 
cylinders, however, may operate with extremely rich and extremely lean 
mixture. This condition increases fuel consumption and exhaust gas 
emission, inasmuch as the consumption and exhaust gas characteristics in 
the range of .lambda.=1 are not linear. Hence, the monitoring of 
individual cylinders always produces better overall results when 
regulating the engine at .lambda.=1 of mixture value, or at a value which 
slightly deviates in the direction towards leaner mixtures. 
In the preferred embodiments of this invention, the averaging of the oxygen 
probe output signals over several engine cycles can be made either by 
means of lowpass filtering circuit, by a time integration of integer 
cycles, or by time period measurements so as to determine the measure of 
the excessively rich mixture in the cycles under examination, that is not 
only a general indication whether the mixture is too rich or too lean. In 
combining for example the measurement of time intervals with averaging 
over several cycles, for example over integral multiples of 720.degree. of 
crankshaft angle, a substantial improvement of regulating possibilities is 
achieved. The invention enables not only a measurement which is faster 
then according to conventional methods based on the measurement in the 
exhaust pipe but also improves the speed of regulation. 
The novel features which are considered characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
conjunction with the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The idea of this invention resides in averaging over a plurality of engine 
cycles the output signals from a combustion space-.lambda. measuring probe 
or oxygen probe. These signals, normally subject to strong fluctuations, 
are now applicable for the regulation of ratio of constituents of a 
fuel-air mixture of an engine which is faster, more precise and more 
effective for the preparation of the fuel-and-air mixture and producing an 
optimum composition of the constituents of the mixture under all 
operational conditions of the internal combustion engine. 
Referring firstly to FIG. 1, there is illustrated the construction of a 
combustion space-.lambda. value measuring probe. Such probes, which have 
already been devised in a miniature leaf-like form for measuring 
.lambda.=1, can be designed in the form of a spark plug socket or can be 
installed directly in a spark plug and screwed into the wall of the 
combustion chamber. 
In FIG. 1, reference numeral 1 denotes a .lambda.- or oxygen probe which in 
the following description will be referred to as probe. The probe includes 
a metal socket 3 provided with an outer thread 3a, a sealing seat 3b, and 
a hexagonal nut 3c. The threaded socket 3 is screwed in a corresponding 
threaded hole in wall 2 of a combustion chamber in the IC engine. 
Socket 3 supports a cylindrical electrically insulating and 
pressure-resistant holding body 4 made preferably of ceramic material and 
having at its end directed to the combustion chamber a projecting nose 4a. 
The holding body 4 is provided with a central axial passage 4b preferably 
of rectangular cross section in which an oxygen-sensing leaf 5 is 
arranged. The construction of the sensing leaf 5 is known from prior art 
and will not be discussed in detail. The interspace between the probe leaf 
5 and the inner wall of central passage 4b acts as a channel 5a for 
reference air. In the example illustrated in FIG. 1, this reference 
channel 5a, which extends throughout the insulating holder 4, communicates 
with the outer atmosphere so that it can apply outer air to the sensing 
leaf 5. The probe or sensing leaf 5 can be secured in the ceramic holder 4 
either by a suitable putty or by soldering with a glass solder. In the 
same manner, the ceramic holder can be attached to the metal socket 3 or 
can be secured in position by a flange joint. 
The outer end of sensing leaf 5 is provided with electrical contacts 6 
adjoining from opposite sides the leaf 5 and being connected via 
conductive webs to electrical terminals of a cable 7. A protective tube 8 
is secured to the upper rim of the socket 3 and protects the projecting 
part of sensing leaf 5 and the wires of the cable 7. Due to the direct 
communication of the lower tip of probe leaf 5 with the combustion space 
of a cylinder of the engine, the output signal delivered by the probe 
differs substantially from the output signal of the probe when the latter 
is installed in the exhaust pipe of the engine, namely when a 
quasi-homogeneous fuel-air mixture reaches the oxygen probe in the exhaust 
pipe, then a corresponding probe in the combustion chamber is subject to a 
mixture which rapidly undergoes changes both in time and in place. During 
the suction and compression cycle, a fuel-air mixture is present which 
cannot bring the probe into a balanced condition and is not supposed to do 
so, inasmuch as the establishment of a balance is bound to an exothermic 
reaction and could occur only in response to an undesired ignition of the 
mixture at these time points. Only after ignition and inflammation of the 
mixture in the combustion chamber is the probe brought into its balanced 
condition. 
The probe needs a certain period of time to detect the ratio of the 
mixture, and thus it does not respond to the thin flame front when the 
latter passes by. Under the assumption that the flame front leaves behind 
a residue of gas with unburned components resulting from the lack of air 
during the combustion, that is the value .lambda. is less than 1 (rich 
mixture), then the probe operates as a fuel cell. Oxygen is sucked in 
through the reference air channel 5a and burned in the control path of the 
probe. In this case the probe generates a measurable voltage in the form 
of a voltage pulse which due to its relative width is called a voltage 
bulge . This voltage bulge lasts the longer, the more unburned component 
particles are present in the residual gas. The duration or length of the 
voltage bulge can range up to the time point of the exhaust cycle. 
FIGS. 2a and 2b illustrate time behavior of pressure in the combustion 
chamber and of the output signal of the probe, based on actual 
oscillographic measurements. The upper curve I in FIG. 2a represents 
pressure in combustion chamber, and the curve II is the time plot of the 
output signal from the probe in the case of a rich mixture having its 
.lambda. value of about 0.9. 
In the case of a lean mixture (surplus air in the residual gas), the probe 
voltage is essentially at a voltage level zero and exhibits only a few 
short voltage pulses of higher amplitude, the latter pulses occurring 
statistically due to the mixture preparation and combustion and are called 
"cycle-to-cycle fluctuations or irregularities". Such fluctuations of the 
probe output signal are practically unpredictable. According to this 
invention, the output signals from a combustion space probe, before being 
evaluated as an actual signal for controlling the composition of the 
fuel-and-air mixture, are subjected to an averaging process. 
The upper curve I' in FIG. 2b shows pressure condition in combustion space 
and the curve II' shows the time plot of the output signal from the probe 
when the fuel-air mixture is leaner or of a value .lambda. of about 1.0. 
The averaging of output signals from the probe can be made in different 
ways, for instance by lowpass filtering, by integration over a time period 
corresponding to a multiple of integer engine cycles, or by measuring the 
time period. The aforementioned averaging methods will be discussed in 
greater detail below. 
In interpreting output signals from a combustion space probe by means of 
lowpass filtering, the output signals of the probe are amplified, then 
preferably subjected to an impedance adjustment, and then applied to a 
lowpass filter. The averaged output signal U has a relationship to the 
ratio of the fuel-air mixture .lambda. depicted in FIG. 2c. 
Another method of analyzing the output signals of the probe is based on 
their integration either over a time interval or a predetermined 
crankshaft angle, and thereupon holding the integrated value in a store. 
The integration period may be either an integral number of engine cycles 
or an integral multiple of crankshaft cycles, for example 720.degree. of 
crankshaft rotation. In the case of time-integration using steady time 
constants of the integrator, the obtained result must be related to the 
number of rotations (divided by the number of rotations) because the 
output signal of the probe is dependent upon the rotary speed of the 
engine. 
In still another embodiment, the output signals of the probe can be 
interpreted by measuring time periods (real time units or in degrees of 
crankshaft angle) during which the probe voltage has exceeded a 
predetermined voltage level. This time measurement necessitates, similarly 
as in the preceding example, a correction depending on the rotary speed. 
Since due to statistical fluctuations in the mixture a "cycle-to-cycle 
regulation" is inapplicable, the probe voltage is measured over still more 
cycles before an interpretation of the average condition in the combustion 
space of the tested cylinder is made. 
If the averaging is made over a number of consecutive time intervals or 
consecutive cycles, then the aforementioned possibilities of time 
measurement and of integration over a test cycle are applied to a 
predetermined fixed number of individual engine cylces, and the final 
result is an average value of the selected number of individual engine 
cycles. In averaging over consecutive time intervals the actual values 
evidently occur always at certain time points. Accordingly, in another 
embodiment of this invention it is of advantage to perform calculation 
simultaneously with or parallel to the consecutive time intervals. For 
instance, the averaging process over consecutive or serial time intervals 
is made twice, whereupon it is reduced to half the number of individual 
engine cycles under consideration. In this manner it is made possible that 
fast changes occurring within the fixed number of individual engine cycles 
are not detected only after the runoff of the selected number of engine 
cycles, but are detected either immediately or after the runoff of half 
the number of selected cycles. 
In averaging by means of time interval measurements or by integration over 
the testing cycle, signal values pertaining to individual engine cycles 
can also be averaged and prepared by the lowpass filtering and digital 
processing in such a manner that they fled in a shift register of a 
predetermined length. After each testing cycle, the average value of the 
individual signal values stored in the shift register is computed. In this 
way it is achieved that information about actual .lambda.-values is 
obtained after each individual engine cycle and not only after the runoff 
of the selected number of such cycles. In addition, in this averaging 
process by means of lowpass filtering it is also possible to weight the 
measured values in such a manner that the last stored engine cycle value 
obtains the largest weight whereas the oldest value stored in the register 
obtains the least weight. Another preferred method of evaluating and 
averaging the output signals from an oxygen or combustion space probe is 
the so-called counting method. In this case there are provided two 
counters interconnected in such a manner as to count the number of rich 
cycles following a first rich cycle and the other counter counting the 
number of lean cycles. After the runoff of a predetermined number of 
engine cycles, a balance of the two counts is made and the difference or 
ratio of the two counted values is used for computing the average actual 
.lambda.-value. For this purpose a calibration curve is prepared which 
indicates the count state as a function of .lambda. as will be explained 
in more detail below. 
According to still another embodiment of the latter method there is 
provided a single counter only, which at the beginning of each counting 
process is set to zero and starts counting either the rich or the lean 
cycles, inasmuch as the difference relative to a predetermined number of 
such cycles of necessity corresponds to the number of cycles which have 
not been counted by the single counter. 
This counting method can be with advantage supplemented with secondary 
conditions. For instance, provided that before the runoff of the total 
number N of engine cycles a number n.sub.f of consecutive rich cycles 
(n.sub.f &lt;N) occurs and the fuel-and-air mixture has become too rich, and 
corresponding regulating steps can be immediately performed to correct the 
mixture ratio. Similarly, in the event that before the runoff of all 
cycles N, a series of consecutive n.sub.m lean cycles will occur (n.sub.m 
&lt;N), then the mixture is too lean and counteracting regulating measures 
can be immediately introduced. Such a secondary condition thus takes over 
the function of a fast monitoring of limit values and offers the 
possibility to react to deviations before the runoff of the total number N 
of selected cycles because n.sub.f and n.sub.m &lt;N. 
Plot diagrams according to FIGS. 3a and 3b show graphically the 
aforementioned method. Assuming that the total number N of selected cycles 
equals 8 and n.sub.f =n.sub.m =4, then it is possible already after the 
half of the predetermined 8 cycles to determine that the mixture is too 
rich (FIG. 3a) or too lean (FIG. 3b). 
From experimentation it has been recognized that particularly in the range 
of rich mixture values (.lambda.&lt;1), the signal voltage hump or bulge is 
the longer, the richer is the mixture. This finding enables the 
introduction of an interesting secondary condition or of an additional 
regulating possibility, in which the intervention the regulating means is 
not made dependent solely on the averaging of a predetermined number N of 
engine cycles but is additionally responsive to the determination of the 
size of the specific voltage bulges. For instance, by suitable circuits 
the time constant of regulation can be additionally made shorter or 
longer. 
The first-discussed secondary condition, namely the consecutive occurrence 
of richer or leaner individual cycles differing from the total number N of 
selected cycles, can be also supplemented with the following secondary 
condition: Provided that there are n.sub.f rich cycles, then the width of 
the voltage bulge of the output signal of the probe of the area of this 
voltage bulge can be determined approximately by computation from time 
measurements or from integration. The computation result then indicates 
whether the n.sub.f rich cycles were insufficiently or excessively rich. 
An example is illustrated in FIG. 4a which depicts such a voltage bulge 
pertaining to a rich mixture related to the angular position of the 
crankshaft. The abscissa is divided into sections .DELTA..alpha. which 
need not be of the same length. FIG. 4b illustrates an integration 
.intg.U.sub.S d.alpha..apprxeq..SIGMA.U.sub.i .DELTA..alpha. of the 
voltage bulge pertaining to a rich mixture. It shows the integration for 
two different shapes of the voltage bulge, namely for the case, indicated 
by full lines, of excessively rich mixture and for the case of a normally 
rich mixture, as indicated by dashed lines. The plot diagram indicated in 
FIG. 4c shows the computation result for the two different shapes of the 
probe output voltage, indicated as "rich angular sections .DELTA..alpha.". 
If one conceives the whole diagram as a continuation of n.sub.f cycles, 
then the integral value .SIGMA.U.sub.i .DELTA..alpha. increases always by 
an amount illustrated in FIG. 4b. The same is valid for the "rich counter 
state", so that after reaching the number n.sub.f of rich cycles the total 
value .SIGMA.U.sub.i .DELTA..alpha. or .SIGMA..DELTA..alpha. is a measure 
of the richness of the mixture. From the above examples, it will be 
recognized that the immediate evaluation of fuel and air mixture in the 
combustion chamber by a single probe only not only provides information 
whether the mixture is rich or lean, but also a measure is obtained how 
rich the mixture has become at a time point of measurement. Such 
information cannot be obtained from a single probe installed in the 
exhaust pipe. 
The curve according to FIG. 5, similarly as the curve of FIG. 2c, indicates 
the averaged probe voltage for different .lambda. values. The qualitative 
relationship between and the total number n.sub.F of fat cycles is thus 
established. The number n.sub.F differs from the number n.sub.f inasmuch 
as the former may include also interposed lean cycles. At the rich side of 
the mixture n.sub.F &gt;n.sub.f and in the case of extremely rich mixtures 
n.sub.F =N, that is it corresponds to the total number of selected cycles. 
On the basis of the aforediscussed various evluation possibilities of 
output signals from the probe in the combustion chamber, an overall 
regulating circuit can be constructed utilizing corresponding control of 
the mixture-preparing device in the engine. Such a regulating circuit is 
illustrated in a simplified block diagram in FIG. 6. The regulating path 
includes a mixture-preparing device 10 which in practice can be any fuel 
dosing device controllable by a feedback signal corresponding to the 
actual .lambda. value, so that at any time point the dosing action and the 
amount of fuel mixture supplied to the engine are regulated in the desired 
direction. Such fuel mixture-preparing devices can be electrical, 
electronic, electromechanical or mechanical fuel-injecting installations 
which control carburetor or the like fuel-preparing systems for the 
engine. Reference numeral 11 indicates combustion chamber or an internal 
combustion engine of several combustion chambers each provided with a 
separate oxygen probe. In the latter case, each probe has a separate 
regulating path for its supply of fuel-and-air mixture. Combustion 
chamber-or oxygen probe 12 delivers a variable output voltage U.sub.S 
which is to be evaluated in accordance with this invention. In the 
regulating circuit according to FIG. 6 there are indicated three different 
evaluation methods, which may be employed either alternatively or in an 
arbitrary combination with one another so as to achieve the desired 
regulating operation. The first evaluation process, indicated by A, 
provides a threshold circuit 13, a counter 14 and converter 18, connected 
in series to the output of the probe 12. Counter 14 is set to a selected 
predetermined number N of engine cycles. This predetermined number N is 
controlled by a sensor 11a coupled to engine 11 to feed the counter 
signals corresponding to individual engine cycles. The branch A of the 
regulating circuit operates as follows: If the variable probe voltage 
U.sub.S exceeds a predetermined threshold voltage set by the threshold 
circuit 13, then a signal corresponding to a rich cycle is applied to the 
counter 14 which is incremented according to the applied engine cycle 
signals and after the preset number N of cycles is stopped. The counting 
result corresponds to the value N-n.sub.F , that is in the total number N 
of engine cycles the residual cycles which have not been counted as rich, 
are recognized as lean cycles. The converting member 18, adjusted 
practically according to the characteristic curve of FIG. 5, converts the 
counting results to the actual .lambda. value and applies a corresponding 
signal to a comparison point 19 in which the actual .lambda. value signal 
is compared with a desired .lambda. value signal generated by another 
threshold circuit or a general desired value generator 19a. The resulting 
regulating deviation is fed via regulator 20 to the control input of the 
fuel mixture-preparing device 10. 
An alternative or a supplement to the method A is the method indicated in 
FIG. 6 by B, in which the probe output voltage is also applied to an 
integrator 15 where it is integrated in accordance with the plot diagrams 
of FIGS. 4a, 4b and 4c. In still another alternative or supplement, 
indicated by C, the output signal U.sub.S is applied to a comparator 16 
where it is compared with a predetermined threshold level and if the 
threshold is exceeded, the signal is counted in angular increments 
.DELTA..alpha. in the subsequent counter 17. The .DELTA..alpha.-counter 17 
is connected to the generator 11a which delivers a .DELTA..alpha. signal 
in accordance with the angular position of the crankshaft or camshaft. 
The block diagram according to FIG. 7 shows in greater detail a 
modification of the circuit for evaluation of output signals from the 
combustion chamber probe to obtain an information about the lean or rich 
ratio of the fuel-and-air mixture. Output voltage from probe 12 is applied 
to the subsequent comparators 13a and 13b set to different threshold 
levels to determine whether the probe voltage is indicative of lean or 
rich ratio. The connection of circuit elements at the output of each 
comparator is identical, so that only one signal circuit, namely for the 
evaluation of "rich" signals is illustrated in FIG. 7. A storing device 21 
operating as a sample-and-hold member is connected between the output of 
comparator 13a for "rich" signals and stores the "rich" signals for the 
whole period of the testing cycles. The output of the sample-and-hold 
circuit 21 is connected to one input of an AND-gate 22 whose other input 
is directly connected to the output of the threshold circuit 13a. 
Accordingly, a logic high or "1" signal appears at the output of the 
AND-gate 22 when both the preceding and the momentarily measured engine 
cycles have a rich mixture. In this case, counter 23 is decremented. In 
the event that the subsequent new cycle has a lean mixture, then a "0" 
signal is generated at the output of AND-gate 22 and is applied to an 
inverting input of OR-gate 24. Counter 23 is loaded with a predetermined 
number n.sub.f (consecutive rich cycles). This loading occurs also in the 
case when the counter 23 is reset by the signal from the recognition 
member 25. If the counter 23 is reset in response to the recognition 
member 25, then this condition is indicative that the consecutive number 
n.sub.f of cycles must have been reached, and consequently the recognition 
member 25 immediately generates and applies to the mixture-preparing 
device a -.DELTA..lambda. signal to counteract the detected results. As 
mentioned before, the same circuit operates for the comparator 13b 
adjusted for detecting "lean" signals, only the output signal 
+.DELTA..lambda. is generated by the recognition member 25 to introduce an 
opposite reaction in the mixture-preparing device. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in 
specific examples of fuel-and-air regulating circuits, it is not intended 
to be limited to the details shown, since various modifications and 
structural changes may be made without departing in any way from the 
spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.