Method of monitoring the operation of an internal combustion engine

A method of monitoring the operation of an internal combustion engine, such as is usable in a motor vehicle, combines the recognition of ignition failures with recognition of combustion failures. In one embodiment combustion failures are detected by the faltering of torque delivered by the engine. Ignition failures are electrically detected in terms of spark voltage or spark duration. In a first embodiment the rate of ignition and combustion failures is first compared with a predetermined threshold and if neither threshold is exceeded, the detection of an individual ignition failure is deemed plausible and is registered if detected. Only a failure rate in excess of a threshold results in cylinder-specific remedial measures to protect a catalyst in the exhaust system. In a second embodiment, unlike the first, only an ignition failure results in a cylinder-selective remedial action.

This invention concerns monitoring internal combustion engines, 
particularly in a motor vehicle, with respect to ignition and combustion 
failures by a combination of procedures suited for different engine 
operation conditions so that at least one procedure operates effectively 
in each step of operating conditions. 
BACKGROUND AND PRIOR ART 
A method of monitoring the operation of an internal combustion engine is 
known from European patent document EP-0 344 349. In that method the spark 
duration is monitored electrically from the primary side of an ignition 
coil. Monitoring of an internal combustion engine for recognition of 
combustion failures can be done by two known methods, for example, the 
method which depends on recognizing faltering in the torque produced by 
the engine, disclosed in U.S. Pat. No. 4,691,288, and the determination of 
combustion failure, either by a lambda probe signal, disclosed in European 
patent document EP-0 387 254, or else by the monitoring of exhaust gas 
temperature. 
These known methods of combustion failure recognition have the 
disadvantage, however, that the recognition of individual or statistically 
distributed failures is difficult. Furthermore, the possibility of 
recognition of a combustion failure is limited to operation of an engine 
under very small load. Also, the recognition of faltering torque in 
particular has the disadvantage that mechanical vibrations of a motor and 
shaking of the vehicle by the roadway make the recognition of failures by 
that method most difficult. By a falter or faltering of the torque 
produced by an engine is meant irregular or uneven delivery of torque. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to combine a combustion failure 
recognition procedure with an electrical ignition monitoring procedure so 
that under every likely set of engine operation conditions, at least one 
of these procedures will provide useful information and possibilities of 
remedy. 
Briefly, in one embodiment of the method, if a combustion failure is 
detected in the initial step, it is then investigated whether in the same 
power stroke an ignition failure has been detected. If that inquiry has a 
negative answer, the combustion failure is registered and at most an 
overall precaution, such as a step to protect a catalyst in the exhaust 
system, is taken before there is a return to the first step for the next 
power stroke. If there is also an ignition failure, the cylinder 
correlation is obtained, the failure is registered and a cylinder-specific 
remedy is initiated such as the shut off of fuel to the cylinder, before 
returning the the first step. If no combustion failure is detected, a 
decision is then made as to whether an isolated ignition failure is 
detectable. If so, the cylinder correlation for the power stroke in 
question is obtained and if an individual ignition failure is electrically 
detected, the failure is registered before return to the first step. If no 
ignition failure is detected, registration of that factor is preferably 
done before return to the first step for the next power stroke. 
In another embodiment of the method, where the engine monitoring equipment 
includes a torque falter sensor for detecting combustion failure, the 
first step is to interrogate the engine operation condition data as to 
whether torque falter information is usable. If the answer to that 
question is in the affirmative the combustion monitoring device is 
interrogated as to whether the falter rate is greater than a predetermined 
threshold falter rate .alpha., and if another affirmative answer results, 
combustion failure is registered, and the cylinder corresponding to the 
power stroke in process has its fuel cut-off. 
If torque falter information is not usable, the electrical ignition 
monitoring is consulted to find out if the ignition failure rate is 
greater than a predetermined ignition failure rate and if the answer to 
that inquiry is positive, an ignition error is registered, the cylinder 
correlation is consulted, and fuel is cut-off to the affected cylinder. If 
neither of the above mentioned failure rates exceeds the respective 
predetermined thresholds, it is investigated whether conditions are 
suitable for detection of an individual ignition failure. If the answer to 
that investigation is affirmative, it is determined whether an ignition 
failure has been detected in the current power stroke and if so an 
ignition error is registered but no remedy is applied. 
The methods of the invention has the advantage that in every likely set of 
engine operation conditions at least one method branch delivers usable 
results. It is particularly advantageous to phase out a method branch that 
delivers only inexact results when other method branches are operable. 
In the case of the second embodiment, when no error rate is above 
threshold, it is particularly advantageous to check for plausibility of a 
possible ignition failure in the power stroke being investigated in order 
to eliminate any serious risk of error when there is actually a normal 
ignition or combustion.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
FIG. 1 shows a preliminary program stage 1 of collecting values of various 
operating parameters of the internal combustion engines such as speed 
(rpm), torque, temperature, etc. so that all of these parameters can be 
available during each power stroke of the engine. These parameters are 
furnished in this case for determination in stage 2 whether the method of 
torque falter observation is usable for obtaining significant information 
with reference to combustion failures. A negative answer, indicating that 
this procedure is not usable, for example under extreme roadway conditions 
or when the engine has a very small load, leads to stage 3 in which the 
electrical monitoring of ignition failures is consulted regarding the 
ignition failure rate, and then to stage 4, which decides whether that 
rate exceeds a predetermined threshold rate .beta.. The electrical 
monitoring of ignition failures can conveniently be performed on the 
primary side of an ignition coil (not shown) either by monitoring the 
ignition voltage or the spark duration. The predetermined threshold rate 
.beta. is a rate above which a catalyst in the exhaust gas system might be 
damaged. If there is a risk of catalyst damage, in the program step 5 a 
cylinder-selective cut-off of fuel is performed and an ignition defect is 
registered. Then in the next program stage 6 there is a jump back to stage 
2 for another cycle, for example in the next power stroke. 
If in stage 2, it is determined that torque falter information is reliable 
enough to be usable, in program stage 7 of FIG. 1 the torque falter 
monitor is consulted to determine in program stage 8 whether the falter 
rate exceeds a predetermined threshold rate .alpha., which is again used 
to define a threshold above which there is risk of damage to a catalyst in 
the exhaust system. If the falter rate does exceed that threshold, 
cylinder fuel is cut-off from the affected cylinder and a combustion error 
is registered in stage 9, after which stage 6 produces a return to stage 2 
for another power stroke. 
If in stage 4 the ignition failure rate is found to be lower than the 
threshold critical for the catalyst, or if in stage 8, the torque falter 
rate, corresponding to a combustion failure rate, is below threshold 
.alpha., stage 10 of the method illustrated in FIG. 1 comes in to play. At 
this stage it is determined whether the engine operating conditions are 
suitable for reliable detection of individual ignition failures. The 
recognition of individual ignition failures is reliable only in operation 
of the engine between no load or negative load and a partial load 
threshold, a range of operation range conditions corresponding to a 
limited field of engine operating parameters. If the conditions for 
reliable recognition of individual ignition failures is not present, 
program stage 6 comes into play for returning to stage 2 for another power 
stroke. An affirmative answer in stage 10 leads to stage 11 in which it is 
observed whether an ignition failure has taken place in the power stroke 
under analysis. If the answer is "no" again, program step 6 provides a 
return to stage 2 for another power stroke, but if an ignition failure is 
recognized, an ignition failure is registered in stage 12, but cutting off 
of fuel injection is not necessary in this case, since sporatic individual 
ignition failures do not lead to damage of a catalyst in the exhaust 
system. After the registration of the ignition error, program step 6 leads 
to return to stage 2 for another power stroke. 
The advantages of torque falter recognition and other recognition of 
combustion failures (i.e. not only in cases of electrical ignition 
failure) are hereby complemented by the advantages of electrical ignition 
failure recognition. Electrical ignition failure recognition has good 
recognition possibilities for statistically distributed individual 
failures in engine operation under no load or negative load and up to a 
certain partial load on the engine, as well as at low speeds. At the same 
time, the disadvantages of torque falter recognition under the influence 
of extraneous mechanical shaking can to a large extent be compensated, 
since the electrical ignition failure recognition still remains operative 
during disturbed torque falter detection. 
FIG. 2 shows another embodiment of a method according to the invention 
combining recognition of combustion failures with electrical recognition 
of ignition failures. As in the case of FIG. 1, the engine operation data 
to be interrogated is obtained in stage 1 and is periodically renewed at 
intervals suitable for the particular data. In this case the first 
interrogation is shown at stage 13, where it is determined whether a 
combustion failure has been detected from the data available in stage 1. 
In the embodiment of FIG. 2, instead of the torque falter recognition of a 
combustion failure which was described in connection with FIG. 1, two 
other procedures are available, either an evaluation of the exhaust gas 
composition by means of a lambda signal or monitoring the exhaust gas 
temperature. If both of these methods are provided, the selection of one 
or both of them and the evaluation takes place in stage 13 and is not 
shown elsewhere in FIG. 2. The choice of one of these methods may depend 
upon the data of stage 1 that has been interrogated, so that one will be 
preferred during certain conditions of engine operation and the other 
under other conditions of engine operation, and perhaps sometimes both of 
them in parallel, with a correlation between them provided by a 
plausibility stage not shown in FIG. 2. Both of these methods have the 
advantage that they are not limited to recognizing ignition failures and 
are capable of recognizing combustion failures from various other causes. 
With these methods, however, no correlation with the power strokes in the 
several cylinders can usually be carried out and the detection of isolated 
combustion failures is problematic and may be impossible to carry out 
because of great inertia in the system. 
If no combustion failure is recognized, which means that the question of 
stage 13 is answered with "no", stage 14, in a manner dependent upon the 
operating parameters of the engine, takes up the question whether 
recognition of individual ignition failures is possible. If recognition of 
isolated ignition failures is found not be possible, stage 15 then 
registers absence of failure recognition. This registration may be coupled 
with shutting off previously initiated protective measures. After stage 
15, stage 16 directs a jump back to stage 13 as soon as new data is 
available from stage 1, or as soon as a next interval for interrogation 
has arrived. 
If in the program stage 14 a positive answer has been found for the 
question whether conditions are favorable for detection of isolated 
ignition failures, stage 17 is activated to identify the cylinder which is 
in a power stroke, by reference to the firing order of the cylinders. Then 
in stage 18, it is determined electrically whether an individual ignition 
failure has occurred. If that inquiry is answered in the negative, stage 
15 again registers the absence of ignition failure and return to stage 13 
is provided by stage 16. If an individual ignition failure is detected in 
stage 18, that result is registered and a diagnosis lamp is lighted, after 
which stage 16 is then ultilized to return to stage 13 for another cycle. 
If stage 13 determines affirmatively that a combustion failure has been 
detected, stage 20 is activated for the determination of whether ignition 
failures can be recognized. At the same time a statistically derived 
ignition failure rate is determined. If in stage 20 an ignition failure is 
recognized, for example by detecting the spark voltage by observing the 
primary side of an ignition coil and/or determining by the current in the 
secondary of an ignition coil the duration of the spark, a correlation is 
then made with the cylinder firing order to identify the cylinder affected 
by the ignition failure. Then follows the already described stage 19 in 
which the ignition failure is registered and a diagnosis lamp lighted, but 
in this case it is appropriate in stage 22 to apply remedial measures that 
are cylinder-selective, for example, in the case of sequential fuel 
injection, the shutting off of fuel injection from the particular 
cylinder. Thereafter stage 16 again returns the program to stage 13. 
If no ignition failure is recognized at stage 20, the combustion failure 
detected in stage 13 cannot be related to a particular cylinder, so that 
after the following stage 19 registers the combustion failure, only an 
overall remedial measure is carried out in stage 23, for example, shutting 
off a bank of cylinders supplied through one fuel injection channel of the 
engine. After stage 23, stage 16 again returns the program to stage 13. 
FIG. 3 shows the basic construction of means for determining the necessary 
magnitudes for the monitoring of an internal combustion engine. An 
ignition coil 24 has its primary winding 25 connected at one end to the 
battery voltage UB and at the other end to a control transitor 26 through 
which the ignition coil is connected to ground or chassis. A voltage 
measuring circuit 23 senses through the primary winding 25 the spark 
voltage as transformed to a voltage U.sub.p across the primary winding 25 
and supplies that voltage to a microcomputer 28. The control transistor 26 
has its base electrode likewise connected to the microcomputer 28 which, 
among other things, controls the interruption time for the energizing 
circuit of the primary winding 25. 
The secondary winding 29 of the ignition coil 24 is connected with a 
distributor that assures that the high voltage is supplied, in accordance 
with the cylinder firing order, to the respective spark plugs (not shown) 
of four cylinders 31 to 34. An engine speed (rpm) sensor 35 monitors the 
engine speed for torque falters and provides its output to the 
microcomputer 28. All the operating parameters of the engine that are of 
interest are made available to the microcomputer 28, which then operates 
according to one of the programs respectively described in FIGS. 1 and 2, 
or some modification thereof, so that deficient operation of the internal 
combustion engine will be recognized and appropriate remedial measures 
initiated. 
FIG. 4 shows a method of monitoring an internal combustion engine which 
combines features of the methods explained with respect to FIGS. 1 and 2. 
The rectangle 100 at the top of FIG. 4, like the rectangles 1 in FIGS. 1 
and 2, represents the furnishing of parameters of the operation of the 
internal combustion engine during the monitoring. Again, these parameters 
may be registered at the start of every cycle of the kind diagramed in 
FIG. 4 until a new cycle is ready to begin at which time they are updated, 
or they may be updated at times or even gradually in accordance with the 
operation of the engine. 
In FIG. 4 the stages 101 and 102 are entered simultaneously, or they could 
be entered sequentially provided that the first one to be entered does not 
go out of this stage until the other one is ready to exit this stage. 
Stage 101 determines whether a type I fault detection method is reliable. A 
type I fault detection method comprises at least one ignition fault 
detection system, so that at least one ignition fault detection method is 
applied to determine, at this stage, only whether a type I fault detection 
method is reliable in view of the engine operating parameters that are 
available and consulted in stage 101. A type II fault detection method 
comprises at least one combustion fault detection system and involves the 
performance of at least one combustion fault detection method for 
determining, in stage 102, only whether a type II method and system is 
reliable under the circumstances defined by the engine operating 
parameters which are available and consulted at that time. 
If stages 101 and 102 reveal that both type I and type II systems and 
methods are reliable under the circumstances found in unit 100, both 
systems and methods are utilized in parallel and this is shown in stage 
201 of FIG. 4. 
If only type I methods and systems are reliable under the circumstances 
that were found, only one or more methods and systems which detect an 
ignition fault are primarily used. This is shown by stage 103 in FIG. 4. 
Conversely, if only one or more type II methods and systems are reliable 
under the current conditions, stage 104 is activated and only systems and 
methods for detecting combustion faults are primarily used. Of course only 
one of stages 201, 103 and 104 is activated by the results of stage 101 
and 102, but at the same time stage 105 or 106, or both stages 105 and 
106, are activated. The engine operating parameters of unit 100 may 
indicate through stages 105 and 106 that either ignition fault detection 
or combustion fault detection is not only unreliable but is actually worse 
than useless because of the errors likely to result under these engine 
operation conditions. If that is the case, the operation of ignition fault 
detection (I) or that of combustion fault detection (II), or both, are 
suppressed or blocked (stages 107 and 108). On the other hand, if in a 
previous cycle one or both kinds of systems and methods were suppressed or 
blocked, a determination at stage 105 or 106, or both, that the particular 
kind of system and method is not worse than useless causes the termination 
of suppression or blocking of a particular type or types (I or II or both) 
fault detection. This is indicated by the stages 207 and 208 which are 
labelled "RESTORE IF SUPPRESSED". 
Now let it be assumed that both ignition fault detection and combustion 
fault detection are reliable. Stage 201 then activates stage 202 to 
determine any fault is to be found. If none is found, the absence of fault 
is registered in stage 130, after which there is a return to 101 and 102 
for a new cycle. If at least one fault is found at stage 202 all data of 
significance are detected and registered in stage 203, after which any 
failures and their nature are stored, in stage 204, where the acroynm REM 
stands for "register error in memory." 
If stage 103 is activated by stages 101 and 102, the possible presence of 
an ignition fault is detected at stage 109. If none is found stages 130 
and 133 are entered as before so that return for a new cycle thereafter 
takes place. If an ignition fault is found, stage 111 is activated to 
determine whether there is also a combustion fault. This means that even 
if stage 103 is activated, stage 104 must be activated, as well as stage 
110 in order to satisfy stage 111 if that stage is called upon to 
determine whether there is a combustion fault. For this reason two 
different ways of activating stages 109 and 110 are shown in FIG. 4, so 
that if stages 103 and 109 are primarily used, stage 110 will give its 
information only to stage 111 and, likewise if stages 101 and 102 select 
stage 104 for primary use, stage 109 will activate stage 112, but will not 
also activate stage 111. 
According to whether a combustion fault information is available, stage 111 
causes stage 113 or stage 115 to register the ignition fault or faults. 
Stage 117 or stage 119 registers the error in memory, after which the 
process goes to stage 133 for return to stages 101 and 102 for the next 
cycle. FIG. 4 does not show any remedial measures applied or specify 
lighting of a lamp to indicate a fault. These are left out to simplify the 
diagram and references is made to FIGS. 1 and 2 and their description for 
indicating when a lamp should be lighted, when fuel to a particular 
cylinder should be shut off and when an overall precaution which is not 
cylinder-selective should be applied to protect a catalyst in the exhaust 
system. 
When stages 101 and 102 favor the use of type II detection systems and 
methods, stage 104 activates stage 110 to determine if a combustion error 
is found. If not, stages 130 and 133 are sequentially activated, with a 
return to stages 101 and 102 for a new cycle thereafter. If a combustion 
fault is found, stage 112 is activated to determine whether an ignition 
fault might also be found. No ignition fault can be found if stage 105 has 
determined that ignition fault detection under the contemporary conditions 
is worse than useless, the ignition fault information then being 
suppressed, but unless that information is suppressed, stage 109 will 
supply the ignition fault information in stage 112. Stage 112 will then 
cause the registration of faults in either in stage 114 if no ignition 
fault is also clearly present or in stage 116 if an ignition fault has 
been recognized as well as a combustion fault. At stages 114 and 116 the 
registering of the error or errors in memory is activated in respective 
stages 118 and 120, followed by return for a new cycle through stage 133. 
FIG. 4 and its description indicate that it may be useful to have more than 
one ignition fault detection system and more than one combustion fault 
detection system, since some ignition fault dectection systems are more 
suitable at certain engine operation conditions and another ignition fault 
detection system ma be useful under some other engine operating 
conditions. The same applies to combustion fault detection systems. In 
some cases it may be desirable to utilize information about the rate of 
faults of one kind or the other and under other conditions it may be 
important to determine isolated faults regardless of the rate at which 
such faults have occurred in the past. These considerations have already 
been mentioned with reference to the methods of FIG. 1 and FIG. 2. 
Although the invention has been described with reference to particular 
illustrative examples of the method of the invention, it will be 
understood that variations and modifications may be made and features of 
one of these examples introduced into the other, within the inventive 
concept.