Cylinder judging device for internal combustion engine

A rotating member is provided on an output rotating shaft of an internal combustion engine to generate a signal corresponding to a predetermined cylinder group and an identification signal for identifying the particular cylinder group, and based on these signals, the particular cylinder group is identified. At the time of the start of internal combustion engine, fuel cut mode, or steady constant-speed running, the fuel injection amount of the particular cylinder among said particular cylinder groups is made different from that of other cylinders at a group injection timing such that the particular cylinder assumed on the basis of the cylinder group identification result is the reference, whether the assumption is true or false is judged from the present rotational variation and the cylinder group identification result, and the stroke phase of each cylinder is discriminated to make cylinder discrimination. At this time, the controlled variable relating to the rotational speed is regulated for other cylinders.

TECHNICAL FIELD 
The present invention relates to a cylinder discriminating apparatus for an 
internal combustion engine, for reliably identifying, with a simple 
implementation, the stroke phase of each cylinder in a multiple cylinder 
type internal combustion engine with the internal combustion engine not 
being stopped. 
BACKGROUND ART 
In a multiple cylinder type internal combustion engine, which has a 
plurality of cylinders, the use of a so-called multi-point injection (MPI) 
system, in which an injector for fuel injection is arranged for each 
cylinder, is generally know. An MPI system provides a high degree of 
freedom of air intake system, and easily achieves a high output. For this 
reason, the MPI system attracts attention as a main system for electronic 
controlled fuel injection. 
An MPI system uses a group injection method in which a plurality of 
cylinders are grouped in advance and the injectors for each cylinder group 
are operated simultaneously to inject fuel, or a sequential injection 
method in which a plurality of injectors are operated independently to 
sequentially inject fuel into each cylinder. Whichever fuel injection 
method may be used, it is desirable to set the fuel injection timing so as 
to avoid a stroke having the possibility of deteriorated combustion and 
deteriorated exhaust gas, and, more particularly, the intake stroke. 
In order to set the fuel injection timing for each cylinder or each 
cylinder group so as to avoid the above mentioned problem of the intake 
stroke, it is important to determine in which stroke of the combustion 
cycle each cylinder of internal combustion engine is in. Specifically, a 
combustion cycle consisting of four strokes of intake, compression, 
combustion (expansion), and exhaust is repeated in each cylinder of 
internal combustion engine. For each cylinder, moreover, the timing is set 
in advance to enter the combustion stroke sequentially at equal intervals. 
Therefore, if it can be determined in which stroke the particular cylinder 
is, or inversely which cylinder is in the particular stroke, it can be 
known in which stroke each of the remaining cylinders is. 
The fuel injection described above before is controlled on the basis of 
such a cylinder discrimination result. At the start of the internal 
combustion engine, there scarcely arises a problem even if fuel is 
simultaneously injected into plural cylinders, so that, generally, it is 
necessary only that the cylinder discrimination is made after cranking is 
completed. 
However, the requirement for cylinder discrimination necessary to control 
the ignition system is very severe as compared with the cylinder 
discrimination necessary to control the fuel injection. Incidentally, a 
high voltage distribution system, which ignites cylinders in sequence by 
distributor, presents no problem because the cylinder operated by ignition 
is automatically selected by the distributor. For a low voltage 
distribution system, which does not use a distributor, it is necessary to 
make cylinder discrimination as quickly as possible at the engine start so 
as to determine which ignition coil (cylinder) should be energized. 
Conventionally, in order to control the ignition and fuel injection timing 
for each cylinder, and further to detect the rotational speed, a sensor is 
mounted on the rotating output shaft (crankshaft) of the internal 
combustion engine to detect the crank angle. Since the crankshaft rotates 
two turns in one combustion cycle, however, cylinder cannot be identified 
directly from the output of the crank angle sensor. A cylinder group 
consisting of two cylinders with a 360.degree. mutually different stroke 
phase can be identified from the output of the crank angle sensor, though. 
Conventionally, therefore, a sensor is also mounted on a camshaft rotating 
in connection with the crankshaft to determine a 360.degree. difference in 
stroke phase. Thus, the cylinder can be discriminated by using the signal 
from the cam sensor and that from the crank angle sensor. The camshaft, 
which opens and closes the intake and exhaust valves for each cylinder in 
the valve train, rotates one turn in synchronization with two turns of the 
crankshaft. 
However, if the cylinder discrimination is implemented by two signal 
systems consisting of the crank angle sensor and the cam sensor, the 
construction is generally becomes complicated and the cost is increased. 
Moreover, variations in phase inevitably occur between the signals 
obtained from the sensors due to the extension/contraction, deflection, 
etc. of a timing belt for connecting the crankshaft with the camshaft. For 
this reason, there are possibilities of a cylinder discrimination timing 
lag and mistaken discrimination. 
Unexamined Japanese Patent Publication No. 6-213052 discloses a special 
sensor that is mounted on the crankshaft to generate a preset reference 
angle signal and a rotating angle signal. According to this Publication, a 
method is disclosed in which based on the signal obtained from this 
sensor, a control signal for each crank angle of 360.degree. with the 
detection timing of the reference angle signal being the reference is 
obtained, and the group injection of fuel and group ignition for the 
plural cylinders are effected according to the control signal. 
This Publication also discloses the technology in which by stopping the 
fuel injection to one particular cylinder in the group injection/ignition 
mode, that cylinder is made to misfire intentionally, and a cylinder 
discrimination is made by determining whether or not the misfire is 
detected. Further, this Publication discloses a method in which the mode 
is switched into an independent injection/ignition mode in which after the 
cylinder discrimination is completed, fuel is injected independently to 
each cylinder for each crank angle of 720.degree. according to the 
cylinder discrimination result. 
With the method disclosed in this Publication, however, in order to make 
one particular cylinder misfire, the stopping of fuel injection to that 
cylinder must be repeated for each 360.degree. CA (crank angle) throughout 
plural cycles based on the above-mentioned control signal. Moreover, the 
cylinder discrimination cannot be made until the particular cylinder is 
thus made to misfire and the misfire is detected. In addition, in order to 
increase the reliability of cylinder discrimination, the aforesaid 
interruption of fuel injection and detection of misfire caused by this 
must be repeated. Therefore, the misfire state continues for a relatively 
long period of time, which is undesirable for an internal combustion 
engine. 
Also, with this conventional method, if a mistaken cylinder discrimination 
occurs at the engine start, the fuel injection control is carried out 
according to the mistaken cylinder determination result, and this state 
continues, so that a problem of deteriorated fuel consumption etc. arises. 
Further, the fuel injection is stopped compulsorily to cause misfire, by 
which rotational variation is produced. Therefore, there is a possibility 
of a problem arising in that the internal combustion engine stops when 
cylinder discrimination is made (engine stop). 
The present invention was made in view of the above situation, and 
accordingly a first object thereof is to efficiently produce cylinder 
discrimination at the start of an internal combustion engine. Also, a 
second object is to produce cylinder discrimination reliably and 
accurately even at a time other than at engine start. Further, a third 
object is to improve the reliability of cylinder discrimination, and a 
fourth object is to prevent a problem such as engine stopping from 
occurring when cylinder discrimination is produced. 
Still further, a fifth object of the present invention is to enable 
cylinder discrimination even when the internal combustion engine is 
running in a steady state, and a sixth object thereof is to prevent 
variations in the output of internal combustion engine when cylinder 
discrimination is produced. 
The present invention provides a cylinder discriminating scheme for an 
internal combustion engine which can achieve the above mentioned objects. 
DISCLOSURE OF THE INVENTION 
A cylinder discriminating method and apparatus in accordance with the 
present invention is provided in a multiple cylinder type of internal 
combustion engine which includes a plurality of cylinders having one 
combustion stroke per two turns of a crankshaft, i.e. a combustion cyccle 
and entering the combustion stroke in sequence at equal intervals. The 
apparatus basically comprises cranking detecting means for detecting the 
cranking state of the internal combustion engine; injection control means 
for controlling the actuation of a fuel injection valve provided in each 
of the cylinders; rotational variation detecting means for detecting a 
rotational variation of the internal combustion engine; identifying means 
for generating a signal for identifying a particular cylinder of the 
internal combustion engine; and cylinder discriminating means for 
discriminating the stroke phase of a cylinder in accordance with the 
output of the identifying means and the rotational variation detecting 
means. 
To achieve the above objects, in the cylinder discriminating apparatus in 
accordance with the present invention, the identifying means is configured 
as a sensing member which is provided on a rotating output shaft i.e., the 
crankshaft of the internal combustion engine and generates a signal 
corresponding to each cylinder or each cylinder group with a 360.degree. 
different stroke phase of the internal combustion engine and an 
identification signal for identifying a single particular cylinder or two 
particular cylinders with a 360.degree. different stroke phase in 
synchronization with the rotation of the rotating output shaft or 
crankshaft; and rotational variation imparting means is provided to 
produce a rotational variation to the internal combustion engine by 
controlling the operation of the injection control means when the cranking 
of the internal combustion engine is detected by the cranking detecting 
means. 
In particular, the rotational variation imparting means stops the operation 
of the fuel injection valve for a single particular cylinder or particular 
cylinder and a cylinder entering the combustion stroke continuously with 
this particular cylinder, or makes the fuel injection amount from the fuel 
injection valve to these cylinders different from the fuel injection 
amount from the fuel injection valve to other cylinders, thereby 
positively imparting a rotational variation to the internal combustion 
engine when the internal combustion engine has odd-numbered cylinders, and 
stops the operation of the fuel injection valve for either one of the two 
particular cylinders with a 360.degree. different stroke phase or either 
one of the two particular cylinders and a cylinder entering the combustion 
stroke continuously with this cylinder, or makes the fuel injection amount 
from the fuel injection valve to these cylinders different from the fuel 
injection amount from the fuel injection valve to other cylinders, thereby 
positively imparting a rotational variation to the internal combustion 
engine when the internal combustion engine has even-numbered cylinders. 
According to the present invention, a rotational variation is imparted to 
the internal combustion engine by making the fuel injection amount for a 
particular cylinder (cylinder group) different from the fuel injection 
amount for other cylinders (cylinder groups) at the start of the internal 
combustion engine, and the stroke phase of cylinder is discriminated in 
accordance with the present rotational variation and the cylinder group 
identification result detected by the identifying means, by which cylinder 
discrimination can be made even when the particular cylinder (cylinder 
group) does not misfire, the time taken for the cylinder discrimination 
can be shortened, and the reliability of discrimination result can be 
enhanced. 
Also, a cylinder discriminating apparatus in accordance with the present 
invention has controlled variable regulating means for regulating a 
controlled variable relating to the rotational speed of the internal 
combustion engine in order to keep the rotational speed at a predetermined 
speed or higher when the rotational variation imparting means is operated, 
for example, means for regulating the air amount at an idling time, by 
which the stopping of the internal combustion engine is prevented during 
cylinder discrimination. 
Another cylinder discriminating apparatus in accordance with the present 
invention further has fuel cut judging means for judging a fuel cut zone 
in vehicle deceleration where fuel injection is cut by the injection 
control means, by which the rotational variation imparting means is 
operated when the fuel cut zone is judged by the fuel cut judging means. 
In particular, in this case, when the internal combustion engine has 
odd-numbered cylinders, fuel corresponding to the fuel injection amount 
from the fuel injection valve for the single particular cylinder or the 
particular cylinder and a cylinder entering the combustion stroke 
continuously with this particular cylinder is injected by actuating the 
fuel injection valve, thereby positively producing a rotational variation 
to the internal combustion engine, and when the internal combustion engine 
has even-numbered cylinders, fuel corresponding to the fuel injection 
amount from the fuel injection valve for either one of the two particular 
cylinders with a 360.degree. different stroke phase or either one of said 
two particular cylinders and a cylinder entering the combustion stroke 
continuously with this cylinder is injected by actuating the fuel 
injection valve, hereby positively producing a rotational variation to the 
internal combustion engine. 
That is to say, in the fuel cut mode of the internal combustion engine, the 
fuel injection amount for the particular cylinder (cylinder group) is made 
different from the fuel injection amount for other cylinders (cylinder 
groups). Specifically, a rotational variation is produced to the internal 
combustion engine by injecting fuel to a particular cylinder (cylinder 
group) only, and cylinder discrimination is produced in accordance with 
the present rotational variation and the cylinder group identification 
result so that cylinder discrimination can be effected repeatedly by using 
the fuel cut mode time even at the time other than the start time of the 
internal combustion engine, by which the reliability of discrimination is 
enhanced. 
Also, a cylinder discriminating apparatus in accordance with the present 
invention further has speed change detecting means for detecting a speed 
change state of the vehicle to inhibit or stop cylinder discrimination 
made by the cylinder discriminating means when speed change is detected by 
the speed change detecting means. That is to say, because the rotational 
variation naturally increases when the vehicle speed changes, mistaken 
cylinder discrimination is prevented by inhibiting or stopping the 
cylinder discrimination during speed change. 
Further, a cylinder discriminating apparatus in accordance with the present 
invention has a first rotational variation imparting means which is driven 
at the start of the internal combustion engine and a second rotational 
variation imparting means which is driven in a fuel cut mode, and the 
injection control means has means for controlling the fuel injection for 
each cylinder on the basis of the cylinder discrimination result 
determined by the operation of the first rotational variation imparting 
means during the time from when the internal combustion engine is started 
to when the cylinder discrimination result is determined by the operation 
of the second rotational variation imparting means, and controlling the 
fuel injection for each cylinder on the basis of the cylinder 
discrimination result determined by the operation of the second rotational 
variation imparting means after the cylinder discrimination result is 
determined by the operation of the second rotational variation imparting 
means. 
That is to say, in the fuel cut zone at a start time and at a vehicle 
decelerating time, the fuel injection amount for a particular cylinder 
(cylinder group) is made different from that for other cylinders (cylinder 
groups) in accordance with the state, by which a rotational variation is 
positively made in the internal combustion engine, and the cylinder 
discrimination is made on the basis of the rotational variation at each 
time point and the cylinder group identification result. Thereby, cylinder 
discrimination is made stably and accurately while making the most of the 
advantages of both of the states, and without producing adverse effects on 
the internal combustion engine in each of the above states, and the fuel 
injection control based on the cylinder identification result is stably 
carried out. 
Another cylinder discriminating apparatus in accordance with the present 
invention further has steady running detecting means for detecting the 
steady running state of the internal combustion engine. When the steady 
running state is detected by the steady running detecting means, the 
rotational variation imparting means is operated to produce a rotational 
variation to the internal combustion engine. Thereby, when cylinder 
discrimination cannot be made at the start, or even when the fuel cut zone 
at the vehicle decelerating time is not detected after the start, cylinder 
discrimination can still be made in a stable running state of the vehicle. 
Moreover, when the multiple cylinder type internal combustion engine has 
even-numbered cylinders, the injection control means actuates the fuel 
injection valve for each cylinder in sequence in accordance with the 
output of a signal corresponding to each cylinder group from the 
identifying means before the rotational variation imparting means is 
operated and after an identification signal for identifying the particular 
cylinder is generated from the identifying means. Thereby, controlled 
variable regulating means for regulating a controlled variable relating to 
the rotational speed of the internal combustion engine is provided to keep 
said rotational speed at a predetermined speed or higher, so that the 
decrease in the output of internal combustion engine is prevented even 
when a cylinder is not yet discriminated. 
Also, a cylinder discriminating apparatus in accordance with the present 
invention further has injection amount setting means for setting the 
injection amount from the fuel injection valve, so that the transient 
correction information by the injection amount setting means is set 
separately at a time when the cylinder discrimination has been completed 
and a time when the cylinder discrimination is not yet completed, by which 
a proper fuel amount can be injected regardless of whether or not the 
cylinder discrimination result can be obtained.

BEST MODE OF CARRYING OUT THE INVENTION 
To explain the present invention in more detail, a cylinder discriminating 
apparatus in accordance with one embodiment of the present invention will 
be described below with reference to the accompanying drawings. 
In FIG. 1, reference numeral 1 denotes a rotating member that is mounted on 
a crankshaft (not shown), which is a rotating output shaft of a multiple 
cylinder type internal combustion engine having a plurality of cylinders, 
and rotates together with the crankshaft. This rotating member 1, called a 
crank angle sensor plate, constitutes an identifying means for generating 
a signal in synchronization with the rotation of crankshaft in cooperation 
with a sensing member 2 consisting of a Hall element arranged at the 
periphery thereof. The rotating member 1 has a vane structure such that a 
protrusion 1a for generating a signal corresponding to each cylinder or 
cylinder group of the internal combustion engine and a protrusion 1b for 
generating an identification signal necessary to identify the particular 
cylinder or the particular cylinder group consisting of two particular 
cylinders having a 360.degree. different stroke phase are formed in the 
circumferential direction thereof. 
For a four-cylinder type internal combustion engine, for example, the 
rotating member 1 has two protrusions 1a positioned symmetrically with 
respect to the center for generating two pulse signals for one rotation of 
the crankshaft by making the pulse signals correspond to each cylinder 
(cylinder group), the pulse signal having a trailing edge and a leading 
edge (FIG. 2) corresponding to timing of 5.degree. before the reference 
(B5.degree.) and 75.degree. before (B75.degree.) in terms of crank angle 
with the top dead center (TDC) of piston in each cylinder being a 
reference (0.degree.). Also, the rotating member 1 has a protrusion 1b on 
one side between the protrusions 1a for generating an identification 
signal for determining to which cylinder (cylinder group) the two pulse 
signals correspond. 
Although the details of an electronic control unit (ECU) 3, which 
constitutes the main part of the cylinder discriminating apparatus in 
accordance with this embodiment, will be described later, this electronic 
control unit 3 basically operates by receiving in a signal generated in 
synchronization with the rotation of the crankshaft by a signal generating 
means (identifying means) consisting of the rotating member 1 and the 
sensing member 2. It executes identification of a cylinder group, 
detection of variations in rotation of the internal combustion engine 
(crankshaft), and further cylinder discrimination. 
Specifically, the electronic control unit 3, as shown in FIG. 1 includes, a 
microprocessor, memory, etc. in terms of hardware, functionally has 
cylinder group identifying means 11, rotational variation detecting means 
12, first cylinder discriminating means 13, second cylinder discriminating 
means 14, cranking detecting means 15, first rotational variation 
imparting means 16, fuel cut judging means 17, second rotational variation 
imparting means 18, speed change detecting means 19, rotational speed 
control means 20, injection control means 21, and steady running detecting 
means 22, as shown in FIG. 1. The injection control means 21 actuates fuel 
injection valves 4a, 4b, 4c, and 4d provided so as to correspond to a 
plurality of cylinders, and controls fuel injection in each of these 
cylinders. Although not shown in FIG. 1, the electronic control unit 3, 
needless to say, incorporates an ignition control device for controlling 
ignition for each cylinder. 
First, a signal obtained by the signal generating means provided with the 
rotating member 1 and the cylinder group identification based on the 
signal will be described. 
When the internal combustion engine operates and the output rotating shaft 
(crankshaft) thereof rotates, the rotating member 1 rotates accordingly. 
Therefore, the sensing member 2 generates a signal series as shown in FIG. 
2 in accordance with the protrusions 1a and 1b of the rotating member 1. 
The four-cylinder type internal combustion engine is generally set so that 
the combustion stroke takes place at equal intervals in the sequence of 
first cylinder (#1), third cylinder (#3), fourth cylinder (#4), and second 
cylinder (#2). It is also configured so that each cylinder executes a 
series of combustion cycles consisting of intake, compression, combustion, 
and exhaust for every two turns of the crankshaft. One of the two 
protrusions 1a of the rotating member 1 generates a pulse signal 
indicating the crank angles of B5.degree. and B75.degree. corresponding to 
the first and fourth cylinders (#1-4) with the top dead center being the 
reference, and the other protrusion 1a generates a pulse signal indicating 
the crank angles of B5.degree. and B75.degree. corresponding to the second 
and third cylinders (#2-3) with the top dead center being the reference. 
The protrusion 1b generates an identification signal for determining 
whether the pulse signal of B5.degree. and B75.degree. obtained from the 
two protrusions 1a corresponds to the first and fourth cylinders or 
whether it corresponds to the second and third cylinders. By this 
identification signal, the pulse signal obtained after this identification 
signal is identified as one corresponding to the first and fourth 
cylinders, for example. 
The cylinder group identifying means 11 of this embodiment first determines 
which pulse in the signal series obtained from the signal generating means 
is the signal indicative of the crank angles of B5.degree. and B75.degree. 
corresponding to the cylinder (cylinder group) and which pulse is the 
identification signal. In accordance with the determination result, the 
signal corresponding to the particular cylinder group, specifically, the 
pulse signal corresponding to the first and fourth cylinder group (#1-4) 
is identified. Since the rotational speed of the crankshaft varies 
depending on the operating conditions of internal combustion engine, both 
of the signals cannot be distinguished even if only the pulse width of the 
signal series is simply monitored. As shown in FIG. 3, therefore, the 
cylinder group identifying means 11 measures the pulse width ratio (duty 
ratio) of each pulse signal (Step S1), and calculates, in sequence, the 
change rate of the sequentially measured pulse width ratio (Step S2). When 
the change rate of the pulse width ratio exceeds a preset value, this 
signal is detected as the pulse signal corresponding to the particular 
cylinder group (#1-4) emerging next to the identification signal (Step 
S3). 
Specifically, the cylinder group identifying means 11 sequentially 
determines the pulse width ratio of each pulse in the signal series 
obtained from the signal generating means as a ratio (T.sub.1 /T.sub.2) of 
a time width T.sub.1 from the leading edge to trailing edge of the pulse 
to a time width T.sub.2 from the leading edge to the leading edge of the 
next pulse. The change rate K of the pulse width ratio (T.sub.1 /T.sub.2) 
is sequentially determined as 
K.sub.n-1 =[(T.sub.1 /T.sub.2).sub.n -(T.sub.1 /T.sub.2).sub.n-1 ]/(T.sub.1 
/T.sub.2).sub.n-1 
from the pulse width ratio (T.sub.1 /T.sub.2).sub.n at the present time n 
and the pulse width ratio (T.sub.1 /T.sub.2).sub.n-1 of the time (n-1) one 
pulse before the present time. When this change rate K.sub.n-1 exceeds a 
preset value [0.3], for example, the pulse before that pulse is judged to 
be the pulse signal indicative of the particular cylinder (cylinder 
group), that is, the pulse signal that emerges next to the identification 
signal corresponding to the protrusion 1b added for cylinder group 
identification and indicates the cylinder group (#1-4) identified by the 
identification signal. 
More specifically, for example, when the rotational speed during the time 
when the crankshaft rotates one turn is constant, the pulse width ratios 
of pulse signals in the signal series shown in FIG. 2 are set as follows: 
(T.sub.1 /T.sub.2).sub.n-2 =0.389 
(T.sub.1 /T.sub.2).sub.n-1 =0.656 
(T.sub.1 /T.sub.2).sub.n =0.499 
Therefore, the change rate K of the pulse width ratio at each time point is 
determined sequentially as follows: 
K.sub.n-2 =0.686&gt;0.3 
K.sub.n-1 =-0.239.ltoreq.0.3 
K.sub.n =-0.220.ltoreq.0.3 
The change rate at the next pulse timing (n+1) is determined as 
K.sub.n+1 =0.0686&gt;0.3 
From this change rate K of the pulse width ratio, in this case, the pulse 
at the timing (n-2) is judged to be the pulse signal corresponding to the 
particular cylinder group (#1-4) emerging just after the identification 
signal. As a result, in the case of the signal series shown in FIG. 2, the 
pulse indicated by the timing (n-2) is signal [1] corresponding to the 
particular cylinder (cylinder group), and two pulses of the succeeding 
timing (n-1) and (n) are judged to be other signal [0]. 
The cylinder group identifying means 11 monitors three continuous judgment 
results in the signal series judged as described before. In this case, if 
the judgment result is correct, the judgment result of [1] indicative of 
the particular cylinder group always emerges only once in the three 
continuous judgment results. Therefore, the cylinder group identifying 
means 11 collates the series of judgment signals with three standard 
patterns indicated as the normal series as shown in FIG. 4, and when the 
series agrees with any one of these standard patterns, it recognizes that 
the cylinder group identification result is correct. Also, each time a new 
pulse is detected from the rotating member 1, the judgment signal series 
is shifted in sequence and updated. Therefore, the cylinder group 
identifying means 11 learns the judgment signal series in accordance with 
the shift pattern, and always obtains the up-to-date cylinder group 
identification information. 
By the above-mentioned cylinder group discrimination, the pulse 
corresponding to the cylinder group (#1-4) consisting of the first and 
fourth cylinders, which are the particular cylinders (cylinder group), is 
detected, and the timing of B5.degree. l and B75.degree. of the particular 
cylinder group (#1-4) is exactly detected from the leading and trailing 
edges of the pulse, respectively. 
When the cylinder group identification information judged as described 
above cannot be obtained, for example, the fuel injection or ignition for 
each cylinder is interrupted. 
For this apparatus, the particular cylinder is discriminated as described 
below on the basis of the cylinder group identification information 
determined based on the signal from the rotating member 1 attached to the 
crankshaft as described before. The cylinder discrimination is made while 
fuel is group injected at a preset timing for each cylinder group in 
accordance with the cylinder group identification information. Generally, 
the group injection is effected by dividing the cylinders into a cylinder 
group (#1-3) consisting of the first and third cylinders and a cylinder 
group (#4-2) consisting of the fourth and second cylinders in accordance 
with the sequence of combustion stroke that takes place in each cylinder. 
In this embodiment, however, the cylinders are divided into a cylinder 
group (#1-4) consisting of the first and fourth cylinders and a cylinder 
group (#2-3) consisting of the second and third cylinders so as to 
correspond to the signal (pulse) from the rotating member 1 described 
before, and for example, as shown in FIG. 5, each time the crankshaft 
rotates two turns for each combustion cycle, including intake (IN), 
compression (CP), combustion (CB), and exhaust (EX) strokes, fuel is group 
injected as indicated by the solid line cross hatching once for each 
cylinder. Alternatively, the fuel injection amount of one time is 
decreased to a half, and as shown in FIG. 6, each time the crankshaft 
rotates one turn, fuel is group injected dividedly. 
It is also possible that fuel is group injected at a timing indicated by 
the solid line and broken line cross hatching in FIG. 7, for example, for 
the two cylinder groups (#1-3) and (#4-2), which is a general group 
injection mode. In this case, however, only the particular cylinder group 
(#1-4) can be discriminated in the above-described cylinder group 
discrimination, so that there is a possibility that fuel injection is 
effected in each stroke of intake (IN) and compression (CP) as indicated 
by broken line cross hatching in FIG. 7. In particular, there is a 
possibility that fuel injection is effected at the timing at which the 
intake valve is open from the later half of intake (IN) stroke, which is a 
combustion deteriorated region, to the earlier half of the compression 
(CP) stroke. Such a fuel injection timing is undesirable for the so-called 
port injection type engine. For the in-cylinder direct injection type 
engine, however, group injection can be effected for the above-mentioned 
cylinder groups (#1-3) and (#4-2) because deterioration in combustion 
causes a big problem. It is also possible that the cylinder discrimination 
is made while fuel is injected simultaneously to all cylinders once for 
each combustion cycle at a timing based on the identification information 
of cylinder group (#1-4). 
Here, however, the following cylinder discrimination will be described 
assuming that fuel is group injected for the two cylinder groups (#1-4) 
and (#3-2) at the timing shown in FIG. 5. 
FIG. 8 is a flowchart showing a general procedure for cylinder 
discrimination in the apparatus of this embodiment. This procedure is 
started by initially setting the contents of two registers A-RAM and B-RAM 
for storing the cylinder discrimination result to [0] assuming that one of 
pulses indicating the cylinder group (#1-4) corresponds to the first 
cylinder (#1) and taking the B5.degree. timing as the reference timing 
(B5.degree. reference), in accordance with the above-mentioned cylinder 
group discrimination result (Step S11). Then, a first cylinder 
discrimination is executed by the first cylinder discriminating means 13 
(Step S12). 
This first cylinder discrimination step is executed by detecting the 
cranking completion of the internal combustion engine by the cranking 
detecting means 15 to activate the first rotational variation imparting 
means 16, driving the injection control means 21 under the control of the 
first rotational variation imparting means 16, and detecting the 
rotational variation of the internal combustion engine at this time by the 
rotational variation detecting means 12. In particular, this first 
cylinder discrimination step is executed by detecting the present 
rotational variation of the internal combustion engine by the rotational 
variation detecting means 12 while fuel injection to the first cylinder 
(#1) is stopped (fuel cut), or while the fuel injection amount is 
decreased. The first cylinder discrimination is made by judging whether 
the reference timing (B5.degree. reference) assumed as described above 
from the rotational variation truly corresponds to the first cylinder, or 
whether the assumption is inversely false and truly the reference timing 
corresponds to the fourth cylinder. When the above-mentioned assumption is 
judged to be true or false, the judgment result is stored in the register 
A-RAM, thereby completing the cylinder discrimination (Step S13). At this 
time, the control may transfer to a sequential injection mode on the basis 
of the cylinder discrimination result. Here, however, another cylinder 
discrimination step is further executed. 
Although the cylinder discrimination in Step S12 is described in detail 
later, the cylinder discrimination is basically made by forming an 
operating environment in which deterioration in combustion or misfire 
occurs in the first cylinder by decreasing the fuel amount injected to the 
first cylinder as compared with the fuel amount injected to the other 
cylinders in accordance with the B5.degree. reference assumed on the basis 
of the cylinder group identification result, and by determining whether or 
not rotational variation is produced due to this environment by using the 
rotational variation detecting means 12. When deterioration in combustion 
or misfire occurs in the first cylinder and the rotational variation is 
produced, the assumption is judged to be true and the data [40H] is stored 
in the register A-RAM. When rotational variation is not detected even if 
the fuel amount injected to the first cylinder is controlled, the 
assumption is judged to be false and the data [80H] is stored in the 
register A-RAM, thereby completing the judgment. 
When the judgment result that the assumption is true or false cannot be 
obtained in this cylinder discrimination step, that is, when judgment 
cannot be made, or when the reliability of judgment result is low, the 
first cylinder discrimination shown in Step S12 is stopped at that time. 
When the cylinder discrimination has been made by the first cylinder 
discrimination or the first cylinder discrimination has failed, a second 
cylinder discrimination, described below, is executed by using the second 
cylinder discriminating means 14 (Step S14). This second cylinder 
discrimination, which reconfirms the judgment result obtained by the 
aforementioned first cylinder discrimination, or executes cylinder 
discrimination from another viewpoint in case of the failure of the first 
cylinder discrimination, is made by using the fuel cut mode time for each 
cylinder group when the vehicle speed decreases. 
Although the second cylinder discrimination in Step S14 is described in 
detail later, the cylinder discrimination is basically made by detecting 
the fuel cut mode time for each cylinder (cylinder group) by the fuel cut 
judging means 17 to activate the second rotational variation imparting 
means 18, and by injecting fuel to the first cylinder (#1) only. That is, 
the cylinder discrimination is made by determining whether or not a 
rotational variation is produced by the rotational variation detecting 
means 12 by making the fuel injection amount for the first cylinder 
different from the fuel injection amount for other cylinders. When the 
rotational variation is detected and the assumption is judged to be true, 
the data [40H] is stored in the register B-RAM. On the other hand, when 
the rotational variation is not detected and the assumption is judged to 
be false, the data [80H] is stored in the register B-RAM, thereby 
completing the judgment (Step S15). Then, the control transfers to a 
sequential injection mode in accordance with the cylinder discrimination 
result. 
When the judgment result that the assumption is true or false cannot be 
obtained in this cylinder discrimination step, that is, when judgment 
cannot be made, or when the reliability of judgment result is low, the 
second cylinder discrimination shown in Step S14 is repeatedly executed at 
a preset timing. When the second cylinder discrimination result stored in 
the register B-RAM differs from the first cylinder discrimination result 
stored in the register A-RAM, the second cylinder discrimination result is 
preferentially used and sequential injection is executed. 
Thus, in the apparatus of this embodiment, the cylinder discrimination for 
the cylinder groups (#1-4) and (#2-3) when fuel is group injected is 
executed by using the first cylinder discriminating means 13 and second 
cylinder discriminating means 14. However, it is, needless to say, 
possible to configure the apparatus so as to execute only the cylinder 
discrimination for one cylinder group. 
Next, the first and second cylinder discrimination will be described in 
more detail. 
In the first cylinder discrimination, as described above, after the 
cranking is completed at the engine start, the fuel injection amount for 
the first cylinder (#1) is decreased, or fuel is cut in an extreme case, 
and it is determined from the present variations in rotational speed 
whether or not this causes deterioration in combustion (misfire) in the 
first cylinder, by which cylinder discrimination is made. The cylinder 
discrimination is made by following the procedure shown in FIG. 9. 
This cylinder discrimination is started by initially setting two judgment 
result registers A.sub.(n) and B.sub.(n) to [0] and initially setting a 
control parameter KM corresponding to the combustion cycle to [0] (Step 
S21). Then, the cranking completion of the engine is judged by determining 
whether or not the engine rotational speed Ne at the start exceeds a 
predetermined rotational speed Ne0, for example, 1200 rpm, by means of the 
cranking detecting means 15 (Step S22). By this judgment, the cylinder 
discrimination in an unstable operation state of internal combustion 
engine in cranking is inhibited. 
When the stable state of engine is detected, it is determined whether or 
not the conditions for executing the first cylinder discrimination are met 
(Step S23). In this determination, it is determined whether the present 
water temperature is not lower than a predetermined value WT (for example, 
10.degree. C.) in order to inhibit cylinder discrimination at a low water 
temperature time at which there is fear of engine stall, it is determined 
whether the current engine rotational speed R.sub.2(n) is not lower than a 
predetermined rotational speed (for example, 700 rpm) at which there is 
fear of engine stall, and it is determined whether the cylinder 
discrimination is not completed in order to execute the first cylinder 
discrimination only once after engine start. When not all these conditions 
are met, that is, when even one condition is not met, the first cylinder 
discrimination scheduled to be executed subsequently is inhibited, and the 
control parameter KM is reset to [0] for the restart of the engine (Step 
S24). 
When the aforementioned conditions for cylinder discrimination are met, the 
first rotational variation imparting means 16 is activated to decrease the 
fuel injection amount for the first cylinder as compared with the other 
cylinders, and the present rotational speed is detected by the rotational 
variation detecting means 12. At this time, the control parameter KM is 
increased by one (Step S25). 
The decrease (cut) of fuel amount injected to the first cylinder by the 
first rotational variation imparting means 16 is effected at the group 
injection timing as shown by the solid line cross hatching in FIG. 10 by 
taking the B5.degree. timing when assuming that one of pulse signals 
indicative of the cylinder group (#1-4) corresponds to the first cylinder 
(#1) as the reference. That is, at the group injection timing of fuel set 
from the later half of the exhaust (EX) stroke to the earlier half of 
intake (IN) stroke of the first cylinder, the decrease (cut) of fuel 
amount injected to the first cylinder is executed. For the fourth cylinder 
at the timing from the later half of the compression stroke to the earlier 
half of the combustion (CB) stroke, however, fuel injection is effected as 
usual. When the above assumption is false, the timing of decrease (cut) of 
fuel amount injected to the first cylinder actually becomes the timing 
from the later half of the compression stroke to the earlier half of the 
combustion stroke of the first cylinder. However, to the fourth cylinder 
at the timing from the later half of the exhaust stroke to the earlier 
half of the intake stroke, a constant amount of fuel is injected without 
being decreased. 
The rotational variation detecting means 12 sequentially determines the 
engine rotational speed R.sub.1(n) in the combustion cycle at the time 
when the decrease (cut) of fuel amount injected to the first cylinder as 
R.sub.1(n) =60.times.1000000/T.sub.(n) [rpm] 
from, for example, the time taken for one rotation of crankshaft, that is, 
the time T.sub.(n) [.mu.sec] taken for one rotation of the aforesaid 
rotating member 1. For the rotational speed R.sub.2(n) used for judgment 
of cylinder discriminating conditions in the aforesaid Step 23, a value 
calculated, for example. as 
R.sub.2(n) =60.times.1000000/(T.sub.(n) +T.sub.(n-1))/2 [rpm] 
from the mean value of time taken for the crankshaft to continuously rotate 
two turns, (T.sub.(n) +T.sub.(n-1))/2, taking one combustion cycle to be a 
unit, may be used. 
The detection of the rotational speed R.sub.1(n) is repeatedly executed 
throughout three combustion cycles until the control parameter KM reaches 
a preset value [3] per the timing shown in FIG. 11 (Step S26). Each time 
the rotational speeds R.sub.1(n), R.sub.1(n-1), R.sub.1(n-2) for 
continuous three samples with the B5.degree. timing of the first cylinder 
(#1) being the reference are determined, the rotational variation 
detecting means 12 determines the present rotational variation as 
R.sub.1x(n-l) =R.sub.1(n-1) -{R.sub.1(n-2) +R.sub.1(n) }/2 
and determines whether the calculated value R.sub.1x(n-1) is positive or 
negative. If the calculated value R.sub.1x(n-1) is negative, the value 
A.sub.(n) of the judgment result register A-RAM is increased by one, and 
inversely if the calculated value R.sub.1x(n-1) is positive, the value 
B.sub.(n) of the judgment result register B-RAM is increased by one (Step 
S27). This operation is repeatedly executed throughout five combustion 
cycles until the control parameter KM reaches a preset value [5], for 
example, each time the rotational speeds for continuous three samples are 
determined (Step S28). 
The rotational variation detecting means 12 sequentially determines the 
rotational speed R.sub.1(n) at the B5.degree. timing for each rotation of 
crankshaft as described above to investigate the presence of rotational 
variation caused by decrease (cut) of fuel amount injected to the first 
cylinder at the time of group injection mode as shown in FIG. 5. FIG. 12 
schematically shows the principle of detection of rotational variation. As 
shown in this figure, the value R.sub.1x(n-1) is determined as an index of 
rotational variation. The R.sub.1x(n-1) is the difference between the mean 
value of the rotational speeds R.sub.1(n-2) and R.sub.1(n) of the first 
cylinder determined with the B5.degree. timing being the reference and the 
rotational speed R.sub.1(n-1) of the fourth cylinder at the B5.degree. 
timing, which lies at the intermediate position of R.sub.1(n-2) and 
R.sub.1(n). The mean value of the rotational speeds R.sub.1(n-2) and 
R.sub.1(n) is determined for the case where the rotational speed of engine 
does not change greatly. 
Referring to FIG. 12, the principle of detection of rotational variation 
will be described in more detail. When the B5.degree. reference of the 
first cylinder assumed as described above is correct, the timing at which 
the combustion of the first cylinder, in which injected fuel is decreased 
(cut) at the timing of B5.degree. reference, affects the rotational 
variation is just the timing of B5.degree. reference of the fourth 
cylinder. Inversely, the timing at which the combustion of the fourth 
cylinder affects the rotational variation is the timing of B5.degree. 
reference of the first cylinder. Therefore, the rotational speeds 
R.sub.1(n-2) and R.sub.1(n) at the timing (n--2) and (n) determined for 
each B5.degree. reference are the rotational speeds affected by the 
combustion of the fourth cylinder. Inversely, the rotational speeds 
R.sub.1(n-3) and R.sub.1(n-1) of the fourth cylinder determined at the 
B5.degree. timing (n-3) and (n-1), which are the intermediate timing of 
B5.degree. reference of the first cylinder, are the rotational speeds 
affected by the combustion of the first cylinder, in which injected fuel 
is decreased (cut). 
Accordingly, as shown in FIG. 12, the rotational speeds R.sub.1(n-2) and 
R.sub.1(n) determined for each B5.degree. reference depends on the 
combustion of the fourth cylinder. Also, the rotational speeds 
R.sub.1(n-3) and R.sub.1(n-1) of the fourth cylinder at the B5.degree. 
timing depends on the combustion of the first cylinder, in which fuel is 
decreased (cut), so that the rotational speed is decreased by the 
deterioration in combustion (misfire) caused by fuel decrease (cut). In 
this case, since the relationship of 
R.sub.1(n-1) &lt;R.sub.1(n-2), R.sub.1(n) 
holds, the difference R.sub.1x(n-1) in rotational speeds determined as 
described above is negative. 
When the above-mentioned assumption of the B5.degree. reference for the 
first cylinder is false, the rotational speeds R.sub.1(n-2) and R.sub.(n) 
determined by assuming that the rotational speeds depend on the combustion 
of the fourth cylinder for each B5.degree. reference actually depend on 
the first cylinder, and the fuel decrease (cut) for the first cylinder is 
effected in that combustion cycle, so that the rotational speed decreases. 
Also, the rotational speeds R.sub.1(n-3) and R.sub.1(n-1) of the fourth 
cylinder determined by assuming that the rotational speeds depend on the 
combustion of the first cylinder at the B5.degree. timing of the fourth 
cylinder actually depend on the fourth cylinder, so that the rotational 
variation depending on the fuel decrease (cut) does not occur. In this 
case, therefore, since the relationship of 
R.sub.1(n-1) &gt;R.sub.1(n-2), R.sub.1(n) 
holds, the difference R.sub.1x(n-1) in rotational speeds determined as 
described above is positive. 
In the detection of rotational variation in Step S27, if the difference 
R.sub.1x(n-1) in rotational speeds determined as described above is 
negative, the value A.sub.(n) of the judgment result register A-RAM is 
increased by one, and if the difference is positive, the value B.sub.(n) 
of the judgment result register B-RAM is increased by one. When the 
difference R.sub.1x(n-1) in rotational speeds is zero [0], it is judged 
that the judgment is impossible, and neither of the value A.sub.(n) of the 
judgment result register A-RAM nor the value B.sub.(n) of the judgment 
result register B-RAM is increased by one. Such a judgment is repeatedly 
executed throughout five combustion cycles in accordance with the control 
parameter KM. 
After the detection of rotational variation throughout five continuous 
combustion cycles is completed, it is determined whether the value 
A.sub.(n) of the judgment result register A-RAM or the value B.sub.(n) of 
the judgment result register B-RAM is not lower than a preset value, for 
example, [4] (Step S29). If any one of the value A.sub.(n) of the judgment 
result register A-RAM and the value B.sub.(n) of the judgment result 
register B-RAM is not lower than [4], specifically, if the value A.sub.(n) 
of the judgment result register A-RAM is not lower than [4], it is judged 
that the B5.degree. reference of the first cylinder assumed as described 
above is correct. Inversely, if the value B.sub.(n) of the judgment result 
register B-RAM is not lower than [4], it is judged that the B5.degree. 
reference of the first cylinder assumed as described above is mistaken and 
actually the correct B5.degree. reference corresponds to the fourth 
cylinder, and the cylinder discrimination is completed (Step S30). At this 
time, the control parameter KM is reset to [0] for the next cylinder 
discrimination (restart of that engine). If neither the value A.sub.(n) of 
the judgment result register A-RAM nor the value B.sub.(n) Of the judgment 
result register B-RAM reaches [4], it is judged that the cylinder 
discrimination could not be made exactly, and the cylinder discrimination 
is stopped. 
In the above-described first cylinder discrimination, it is preferable that 
the controlled variable relating to the rotational speed be adjusted by 
operating, for example, the rotational speed control means 20, and more 
specifically, the air-fuel ratio be adjusted by clipping the intake air 
amount in idling operation at the predetermined lower limit value, and 
control be carried out so that the rotational speed exceeds the target 
idle rotational speed, thereby taking measures against engine stall etc. 
According to the above-described first cylinder discrimination, since the 
cylinder discrimination is made by decreasing the fuel injected to the 
first cylinder immediately after the engine start, a state in which the 
cylinder discrimination is not made can be effectively prevented from 
continuing for a long period of time. Moreover, since the cylinder 
discrimination is executed in a short period of time just after the start 
of internal combustion engine, there is no possibility that driving 
feeling is adversely affected. 
According to the above-described detection of rotational variation, since 
the evaluation value R.sub.1x(n) is determined as a negative value in the 
cylinder of deteriorated combustion (misfire), and as a positive value in 
the combustion cylinder, the judgment level can be defined as zero [0], 
and no complicated matching operation etc. are needed. Accordingly, the 
cylinder discrimination based on the rotational variation can be executed 
simply and reliably. 
Further, since only the fuel injection amount for the particular cylinder 
has to be decreased to an extent that the rotational variation occurs, the 
cylinder can be discriminated without complete misfire of the particular 
cylinder, so that the deterioration in driving feeling does not occur. 
Also, since complete misfire does not take place, the activation of a 
catalyst for exhaust system is not affected adversely, so that the 
cylinder discrimination can be made reliably. 
The second cylinder discrimination is made by the procedure, for example, 
shown in FIG. 13. This procedure s started by initially setting the values 
C.sub.(n) and D.sub.(n) of two judgment result registers C-RAM and D-RAM, 
respectively, to [0], and by initially setting two control parameters KM 
and KK corresponding to the combustion cycle to [0] (Step S31). 
Subsequently, it is determined whether or not the conditions for executing 
the cylinder discrimination are met (Step S32). 
This determination is made, for example, by determining whether or not the 
vehicle is being decelerated and the injection of fuel to the engine is 
cut by using the fuel cut judging means 17, and whether or not the vehicle 
speed is being changed by using the speed change detecting means 19. 
Specifically, it is determined whether or not the air amount regulating 
means (for example, a throttle valve) is fully closed, and the engine 
rotational speed R.sub.2(n) at that time is higher than the predetermined 
rotational speed (for example, 1500 rpm) at which the operating condition 
in a fuel cut mode is realized. Also, the determination is made by making 
sure that the change in rotational speed at that time is not so great as 
the change in rotational speed at the speed change time, and further by 
making sure whether the cylinder discrimination had not been completed 
already. When not all these conditions are met, that is, when even one 
condition is not met, the second cylinder discrimination scheduled to be 
executed subsequently is inhibited, and the control parameter KN is reset 
to [0] for the next cylinder discrimination in a fuel cut mode (Step S33). 
When the above-mentioned conditions for the second cylinder discrimination 
are met, the second rotational variation imparting means 18 is then 
activated to inject fuel to the first cylinder (#1) only, and the current 
rotational speed is detected by the rotational variation detecting means 
12. Then, the control parameter KN, which indicates that the fuel 
injection amount is increased, is increased by one (Step S34). 
The control of the increase in fuel amount injected to the first cylinder 
by the second rotational variation imparting means 18 is carried out, as 
with the case of the above-described first cylinder discrimination, at the 
group injection timing by taking the B5.degree. timing when assuming that 
one of pulse signals indicative of the cylinder group (#1-4) corresponds 
to the first cylinder (#1) as the reference. That is, at the group 
injection timing of fuel set from the later half of the exhaust stroke to 
the earlier half of intake stroke of the first cylinder, the injection of 
fuel to the first cylinder is executed. For the fourth cylinder at the 
timing from the later half of the compression stroke to the earlier half 
of the combustion stroke, however, the fuel cut state is kept as usual. 
When the above assumption is false, the timing of fuel injection to the 
first cylinder actually becomes the timing from the later half of the 
compression stroke to the earlier half of the combustion stroke of the 
first cylinder. However, for the fourth cylinder at the timing from the 
later half of the exhaust stroke to the earlier half of the intake stroke, 
the fuel cut state is maintained. 
The rotational variation detecting means 12 sequentially determines the 
rotational speed R.sub.1(n) in the combustion cycle at the time when fuel 
is injected to the first cylinder only on condition that the control is in 
a fuel cut mode. 
The detection of the rotational speed R.sub.1(n) at this time is repeatedly 
executed for a period such that the control parameter KN reaches a preset 
value [3], that is, throughout three continuous combustion cycles (Step 
S35). Each time the rotational speeds R.sub.1(n), R.sub.1(n-1), 
R.sub.1(n-2) for continuous three samples with the B5.degree. timing of 
the first cylinder (#1) being the reference are determined, the rotational 
variation detecting means 12 determines the present evaluation value 
R.sub.1x(n-1) for rotational variation as described before, and determines 
whether the calculated value R.sub.1x(n-1) is positive or negative. If the 
calculated value R.sub.1x(n-1) is positive, the value C.sub.(n) of the 
judgment result register C-RAM is increased by one, and inversely if the 
calculated value R.sub.1x(n-1) is negative, the value D.sub.(n) of the 
judgment result register D-RAM is increased by one (Step S36) 
This operation is repeatedly executed throughout fifty combustion cycles 
while the control parameter KK is increased incrementally until the value 
thereof reaches a preset value [50], for example, each time the rotational 
speeds for continuous three samples are determined (Step S37). 
The rotational variation detecting means 12 sequentially determines the 
rotational speed R.sub.1(n) at the B5.degree. timing for each rotation of 
crankshaft as described above to investigate the presence of rotational 
variation caused by fuel injection to the first cylinder as described 
above in a fuel cut mode. The difference R.sub.1x(n-1) between the mean 
value of the rotational speeds R.sub.1(n-2) and R.sub.1 (n) of the first 
cylinder determined with the B5.degree. timing being the reference and the 
rotational speed R.sub.1(n-1) of the fourth cylinder at the B5.degree. 
timing, which lies at the intermediate position of R.sub.1(n-2) and 
R.sub.1(n), is determined as an index of rotational variation. 
Next, the operation of the detection of rotational variation will be 
described in more detail. When the B5.degree. reference of the first 
cylinder assumed as described above is correct, the timing affected by the 
combustion of the first cylinder, to which fuel is injected at the timing 
of B5.degree. reference, is just the B5.degree. timing of the fourth 
cylinder. Inversely, the timing affected by the combustion of the fourth 
cylinder is the B5.degree. timing (B5.degree. reference) of the first 
cylinder. Therefore, the rotational speeds R.sub.1(n-2) and R.sub.1(n) at 
the timing (n-2) and (n) determined for each B5.degree. reference are the 
rotational speeds affected by the combustion of the fourth cylinder. The 
rotational speeds affected by the combustion of the first cylinder, to 
which fuel is injected at the time of fuel cut, are detected as the 
rotational speeds R.sub.1(n-3) and R.sub.1(n-1) determined at the 
B5.degree. timing (n-3) and (n-1) of the fourth cylinder, which is the 
intermediate timing of B5.degree. reference of the first cylinder. 
As shown in FIG. 12, therefore, the rotational speeds R.sub.1(n-2) and 
R.sub.1(n) determined for each B5.degree. reference of the first cylinder 
depend on the fourth cylinder in a fuel cut state, so that rotational 
variation does not occur. However, the rotational speeds R.sub.1(n-3) and 
R.sub.1(n-1) determined at the B5.degree. timing of the fourth cylinder 
are higher than the rotational speed at the ordinary fuel cut time because 
they depend on the combustion of the first cylinder to which fuel is 
injected. In this case, therefore, 
R.sub.1(n-1) &gt;R.sub.1(n-2), R.sub.1(n) 
so that the difference R.sub.1x(n-1) in rotational speed determined as 
described above becomes positive. 
If the assumption of the B5.degree. reference of the first cylinder 
described above is false, the rotational speeds R.sub.1(n-2) and 
R.sub.1(n) determined for each B5.degree. reference assuming that they 
depend on the fourth cylinder in a fuel cut state actually depend on the 
combustion of the first cylinder to which fuel is injected, so that the 
rotational speed is increased by the combustion of fuel. Also, the 
rotational speeds R.sub.1(n-3) and R.sub.1(n-1) determined at the 
B5.degree. timing of the fourth cylinder assuming that they depend on the 
combustion of the first cylinder actually depend on the fourth cylinder in 
a fuel cut state. In this case, therefore, 
R.sub.1(n-1) &lt;R.sub.1(n-2), R.sub.1(n) 
so that the difference R.sub.1x(n-1) in rotational speed determined as 
described above becomes negative. 
In the detection of rotational variation in Step S36, if the difference 
R.sub.1x(n-1) in rotational speeds determined as described above is 
positive, the value C.sub.(n) of the judgment result register C-RAM is 
increased by one, and if the difference is negative, the value D.sub.(n) 
of the judgment result register D-RAM is increased by one. When the 
difference R.sub.1x(n-1) in rotational speeds is zero [0], it is judged 
that the judgment is impossible, and neither of the value C.sub.(n) of the 
judgment result register C-RAM nor the value D.sub.(n) of the judgment 
result register D-RAM is increased by one. Such a judgment is repeatedly 
executed throughout fifty combustion cycles in accordance with the control 
parameter KK. 
After the detection of rotational variation throughout fifty combustion 
cycles is completed, it is determined whether the value C.sub.(n) of the 
judgment result register C-RAM or the value D.sub.(n) of the judgment 
result register D-RAM is not lower than a preset value, for example, [40] 
(Step S38). If either of the value C.sub.(n) of the judgment result 
register C-RAM and the value D.sub.(n) of the judgment result register 
D-RAM is not lower than [40], specifically, if the value C.sub.(n) of the 
judgment result register C-RAM is not lower than [40], it is judged that 
the B5.degree. reference of the first cylinder assumed as described above 
is correct. Inversely, if the value D.sub.(n) of the judgment result 
register D-RAM is not lower than [40], it is judged that the B5.degree. 
reference of the first cylinder assumed as described above is mistaken and 
actually the correct B5.degree. reference corresponds to the fourth 
cylinder, and the cylinder discrimination is completed (Step S39). When 
this cylinder discrimination is completed, the control parameter KN is 
reset to [0] for the next cylinder discrimination. 
If both of the value C.sub.(n) of the judgment result register C-RAM and 
the value D.sub.(n) of the judgment result register D-RAM are lower than 
[40], it is judged that the cylinder discrimination cannot be made, and 
the cylinder discrimination is stopped (Step S40). In this case, the 
aforesaid value C.sub.(n) of the judgment result register C-RAM and value 
D.sub.(n) of the judgment result register D-RAM and the control parameters 
KN and KK are reset to [0] for the next cylinder discrimination. 
In the second cylinder discrimination as well, it is preferable that the 
controlled variable relating to the rotational speed be adjusted by 
operating, for example, the rotational speed control means 20, and more 
specifically, the air-fuel ratio be adjusted by clipping the intake air 
amount in idling operation at the predetermined lower limit value, or the 
manifold pressure be increased, thereby taking measures against engine 
stall etc. Also, the fuel injection in the fuel cut mode may be limited so 
that the fuel injection is not executed unless the injected fuel burns 
actually. If such measures are taken, the rotational variation detecting 
accuracy is improved, and the catalyst provided in the exhaust system is 
preferably protected. 
According to this second cylinder discrimination, fuel is injected to the 
particular cylinder only at the time of fully closed fuel cut to the 
engine, and the cylinder is discriminated from the present rotational 
variation, so that the accuracy of cylinder discrimination can be enhanced 
sufficiently. Moreover, the fuel injection to the particular cylinder at 
the fuel cut time can be considered to be precedent to the return of 
combustion mode for each cylinder, so that the driving feeling is scarcely 
affected adversely. Further, if the intake air amount during fuel cut is 
increased in advance, the range in which combustion can be possible can be 
set so as to be wide, so that the rotational speed data of a predetermined 
sample can be obtained in a short period of time. If such consideration is 
given, the cylinder discrimination can be completed in a short period of 
time. In particular, the fuel cut time continues over a relatively long 
time, and therefore, if the detection of rotational variation is 
repeatedly executed, for example, using this period, the reliability of 
cylinder discrimination can easily be statistically increased. That is, 
the period for giving rotational variation is set long equivalently, by 
which the reliability of cylinder discrimination can be enhanced. 
Like the aforementioned case of first cylinder discrimination, since the 
evaluation value R.sub.1x(n) is determined as a negative value in the 
cylinder of deteriorated combustion (misfire), and as a positive value in 
the combustion cylinder, the judgment level can be defined as zero [0]. 
Therefore, no complicated matching operation etc. are needed, and the 
cylinder discrimination based on the rotational variation can be reliably 
executed. Also, as described above, by interrupting cylinder 
discrimination at a speed change time, the erroneous judgment factors of 
rotational vibration resulting from speed change are eliminated, so that a 
possibility that the internal combustion engine is operated over a long 
period of time while the erroneous judgment result is kept can be 
prevented. 
Assuming that as shown in the procedure in the above embodiment, the first 
cylinder discrimination is executed for a short period of time just after 
the start of engine, and the second cylinder discrimination is executed 
for a relatively long period of time at the subsequent fuel cut mode time, 
if, for example, the first cylinder discrimination fails, this failure can 
be compensated effectively by the subsequent second cylinder 
discrimination. Even when cylinder discrimination can be made by the first 
cylinder discrimination, the judgment result in the first cylinder 
discrimination can be reconfirmed by the subsequent second cylinder 
discrimination. If the judgment result in the first cylinder 
discrimination is erroneous, this error can be corrected reliably by the 
judgment result of the second cylinder discrimination. Therefore, reliable 
cylinder discrimination can be made in a short period of time just after 
the start by making the most of the advantages of the first and second 
cylinder discrimination, so that an effect that the transfer to sequential 
injection after cylinder discrimination can be facilitated is achieved. 
The present invention is not limited to the above embodiment. For example, 
it is, needless to say, possible to configure the control unit so that 
only one of the aforementioned first and second cylinder discriminations 
is executed. When only the first cylinder discrimination is executed, the 
group injection mode should be set at the engine start, and it should be 
transferred to the sequential injection mode quickly at the time when 
cylinder discrimination is made. When only the second cylinder 
discrimination is executed, the all-cylinder simultaneous injection mode 
or the group injection mode should be set at the engine start, and it 
should be transferred to the sequential injection mode quickly at the time 
when the cylinder discrimination is made. Even when the aforesaid divided 
group injection shown in FIG. 6 is effected, the first and second cylinder 
discrimination can basically be executed in the same manner. 
Although in the above embodiment, the description was made in connection 
with four-cylinder type internal combustion engine, in the case of 
three-cylinder type internal combustion engine, cylinder discrimination 
can be executed in the same manner by the method described below. 
In the case of three-cylinder type internal combustion engine, the 
combustion cycle for each cylinder is set at crank angle intervals of 
240.degree. in the order of the first, third, and second cylinders as 
shown in FIG. 14. Therefore, the apparatus is so configured that the 
reference pulses can be obtained for each 120.degree. from the rotating 
member 1 (signal generating means) attached to the crankshaft, and an 
identification signal that can identify the first cylinder can be obtained 
from the rotating member 1 (identifying means). When the reference pulse 
indicative of the first cylinder is obtained from this signal generating 
means, fuel is injected simultaneously to the second and third cylinders 
assuming that the first cylinder is at the exhaust top position. The 
status of rotational variation at this time is detected, and it is 
determined whether the piston of the first cylinder is at the compression 
top position or at the exhaust top position by the same method as that for 
the aforementioned first and second cylinder discrimination. 
Specifically, fuel is injected simultaneously to the -second and third 
cylinders as shown in FIG. 14 by the cross-hatching (solid and broken 
line) at a timing assuming that the first cylinder is at the exhaust top 
position, and the rotational variation between the reference pulse signals 
for the first cylinder is detected. It is necessary only that it is 
determined whether the above assumption is correct or not according to the 
rotational variation detected at this time, and it is determined whether 
the piston of the first cylinder is at the compression top position or at 
the exhaust top position from this determination result. In this case as 
well, like the above-described embodiment, determination is executed only 
when the conditions for executing a predetermined cylinder discrimination 
are met, by which the occurrence of unwanted engine stall should 
preferably be prevented. After the determination result is obtained, the 
mode should be transferred to the sequential injection mode quickly. 
In the case of four-cylinder type internal combustion engine (even-numbered 
cylinders), explanation was given as to an example in which cylinder 
discrimination is made by making the injection amount of one cylinder (the 
first cylinder in the above embodiment) of the particular cylinder group 
(#1-4) having 360.degree. different stroke phase from each other different 
from that of other cylinders. When the operation of this cylinder 
discrimination is considered, for example, by giving attention to the 
particular cylinder (for example, the first cylinder), the above-mentioned 
identification of the particular cylinder group substantially corresponds 
to the determination of whether the first cylinder is at the compression 
top position or at the exhaust top position. Thus, cylinder discrimination 
is made by making the injection amount of the particular cylinder 
different from that of other cylinders. It can therefore be said that the 
aforesaid cylinder discrimination in the case of even-numbered cylinders 
is based on the same concept as that of the cylinder discrimination for 
three-cylinder type internal combustion engine. Therefore, substantially, 
in the even-numbered cylinder type internal combustion engine, like the 
cylinder discrimination for three-cylinder type internal combustion 
engine, the 360.degree. different stroke phases (for example, compression 
top and exhaust top) of the particular cylinder are identified, and the 
fuel injection amount for the particular cylinder is made different from 
that of other cylinders assuming that one of the stroke phases is 
positive, whereby the cylinders may be discriminated. 
The cylinder discriminating apparatus of the present invention is not 
restricted by the number of cylinders of internal combustion engine. If 
the internal combustion engine has odd-numbered cylinders of three and 
more, the cylinder discrimination may be made by the above-mentioned 
method for cylinder discrimination for three-cylinder type internal 
combustion engine. Also, if the internal combustion engine has 
even-numbered cylinders of four and more, the cylinder discrimination may 
be made by the above-mentioned method for cylinder discrimination for 
four-cylinder type internal combustion engine. 
Although the cylinder discrimination has been made immediately after the 
start of internal combustion engine or by detecting the fuel cut mode in 
vehicle deceleration in the above description, it also can be executed by 
detecting the state in which the vehicle is running at a constant speed. 
Specifically, the running of vehicle is started immediately after the 
start of internal combustion engine and the first cylinder discrimination 
cannot be made, and subsequently, when the vehicle transfers to the steady 
running mode, the second cylinder discrimination cannot be made quickly. 
That is, the cylinder discrimination result cannot be obtained, despite 
the fact that the steady running state is established, until the fuel cut 
mode by deceleration is detected, so that the simultaneous injection of 
all cylinders or the group injection at the start of internal combustion 
engine is continued. 
Accordingly, in the present invention, as shown in the general control 
procedure of fuel injection mode of FIG. 15, even when the fuel cut mode 
by deceleration is not detected, the constant running state is detected 
and the rotational variation is given positively by making the fuel 
injection amount for the particular cylinder different from that for other 
cylinders, whereby the cylinder discrimination is executed. 
Specifically, as shown in FIG. 15, after the engine is started (Step S41), 
the simultaneous injection mode is set for all cylinders or cylinder 
groups (Step S42). In this state, the fuel cut mode caused by deceleration 
is detected, and the aforesaid second cylinder discrimination is executed 
(Step S43). Alternatively, if the fuel cut mode is not detected, the 
steady constant-speed running mode of the vehicle (internal combustion 
engine) is detected by the steady running detecting means 22, and the 
third cylinder discrimination is executed (Step S44). This third cylinder 
discrimination is basically the same as the aforesaid first cylinder 
discrimination. It is executed by making the fuel injection amount for the 
particular cylinder (first cylinder) different from that for other 
cylinders by driving the first rotational variation imparting means 16. 
The control system is configured so that when the cylinder discrimination 
result is obtained by the aforesaid second cylinder discrimination in the 
fuel cut mode, or when the cylinder discrimination result is obtained by 
the third cylinder discrimination in the steady constant-speed running 
mode, the normal sequential injection mode (Step S45) is executed 
according to the cylinder discrimination result. 
As shown in FIG. 16, the aforesaid third cylinder discrimination determines 
in sequence, on condition that the cylinder discrimination by the fuel cut 
mode in deceleration is not finished (Step S51), whether the water 
temperature of engine coolant is not lower than a predetermined 
temperature (for example, 80.degree. C.) (Step S52), whether the vehicle 
speed is not lower than a predetermined value (for example, 50 km/h) (Step 
S53), whether the gear ratio is a predetermined high-speed ratio (for 
example, third gear) or higher (Step S54), whether the throttle opening is 
constant (Step S55), and whether the manifold pressure is not lower than a 
predetermined value (Step S56). If all of these conditions are met, the 
steady cylinder discrimination is executed (Step S57). That is to say, the 
steady cylinder discrimination is started on condition that the vehicle is 
in the ordinary running state, the throttle opening is kept constant with 
the accelerator not operated, and the manifold pressure does not change 
greatly (in other words, changes in a predetermined range). 
If any one of the above conditions is not met, the steady cylinder 
discrimination is not executed, and even if the execution of steady 
cylinder discrimination is started, when the accelerator or brake is 
operated in the course of execution, the discrimination is stopped 
immediately. That is, only when the internal combustion engine is operated 
at a constant speed under certain conditions, the steady cylinder 
discrimination is made. 
This steady cylinder discrimination, as shown in an example of procedure of 
FIG. 17, is first started by detecting the operation state by means of 
various sensors mounted on the internal combustion engine and vehicle 
(Step S60). Based on the detected operation state, in starting the 
cylinder discrimination described below, the air-fuel ratio (A/F) of the 
particular cylinder is read from, for example, a data map set in advance 
(Step S61). In accordance with the detected air-fuel ratio, the fuel 
injection amount for the first cylinder, which is the particular cylinder, 
is decreased gradually to make it different from the fuel injection amount 
for other cylinders (Step S62). 
Then, the intake air amount is increased to compensate the decrease in 
internal combustion engine output caused by the decrease in fuel injection 
amount for the first cylinder, and the air-fuel ratio (A/F) for other 
cylinders is regulated to keep the overall rotation output (specifically, 
torque) of internal combustion engine constant (Step S63). The intake air 
amount is increased by regulating the bypass passage area, for example, by 
increasing the opening degree of a bypass valve for bypassing the throttle 
valve. 
After the control for decreasing the fuel injection amount for the first 
cylinder is carried out and the accompanying control of air-fuel ratio for 
other cylinders is carried out (tailing), a predetermined time elapse is 
allowed (Step S64), and the information about the rotational variation 
detected as described before is extracted throughout, for example, 50 
combustion cycles (Step S65). It is determined throughout 50 cycles 
whether or not the rotational variation is caused by the decrease in fuel 
injection amount for the first cylinder, and it is determined whether the 
timing truly corresponds to the first cylinder or inversely corresponds to 
the fourth cylinder (Step S66). The algorithm for this determination is 
the same as that for the aforesaid first cylinder discrimination. 
Subsequently, after the stroke phase of each cylinder is identified by 
determining the cylinder discrimination result as described above, the 
control transfers to the sequential injection mode in accordance with the 
cylinder discrimination result (Step S67). When the timing assumed as 
B5.degree. reference truly corresponds to the first cylinder, this 
transfer to the sequential injection mode is carried out while gradually 
increasing the fuel amount to return the fuel injection amount for the 
first cylinder to the original fuel injection amount before the start of 
cylinder discrimination. Alternatively, when the assumption is wrong, and 
the timing assumed as B5.degree. reference corresponds to the fourth 
cylinder, the transfer is carried out while gradually increasing the fuel 
injection amount for the fourth cylinder (Step S68). At this time, as the 
fuel injection amount for the first or fourth cylinder increases, the 
intake air amount regulated as described above is gradually returned to 
the original amount (Step S69). Since the rotation output increases as the 
fuel injection amount for the first or fourth cylinder is increased to 
return it to the original amount, in order to compensate it to keep the 
rotation output constant, the control transfers to the normal sequential 
injection mode while reducing the intake air amount and regulating the 
air-fuel ratio of other cylinders. 
Thus, if the cylinder discriminating apparatus is configured so that the 
cylinder discrimination is executed by giving rotational variation 
positively even at the time of steady constant-speed running, even when 
the fuel cut state due to deceleration does not take place, the stroke 
phase of each cylinder can be identified effectively in the constant-speed 
running state in which the throttle opening is constant. Therefore, the 
control can transfer to the normal sequential injection mode quickly. 
Moreover, when the fuel injection amount for the particular cylinder is 
decreased, rotational variation is given while compensating the decrease 
in rotation output of internal combustion engine by increasing the intake 
air amount and regulating the air-fuel ratio for other cylinders, so that 
the deterioration in drivability due to torque variation is not caused. 
Therefore, together with the aforesaid cylinder discrimination at the time 
of fuel cut, an exact cylinder discrimination result can be obtained in a 
relatively short period of time after the engine start. Accordingly, a 
problem in that the internal combustion engine is unwillingly operated in 
the all-cylinder simultaneous injection mode, group injection mode, etc. 
for a long period of time caused by unidentified stroke phase of each 
cylinder is effectively prevented. 
In the above embodiments, immediately after the rotational variation 
imparting means is operated, the rotational variation is detected. 
However, after the rotational variation imparting means is operated, the 
detection timing is delayed by several cycles (for example, two cycles), 
and when a rotational variation caused by receiving the influence of 
rotational variation impartment appears surely, the rotational variation 
is detected, by which the detection accuracy of rotational variation may 
be improved. In the embodiments, the calculated value R.sub.1x(n-1), which 
is an index for rotational variation, is determined for cylinder 
discrimination. However, for example, after the particular cylinder is 
discriminated, the pulse widths for every two strokes after the rotational 
variation impartment are accumulated alternately, and it may be determined 
whether the particular cylinder is compression top or exhaust top from the 
relationship of, for example, 
T.sub.1 +T.sub.3 +T.sub.5 + . . . &gt;T.sub.2 +T.sub.4 +T.sub.6 + . . . 
by the magnitude of pulse width. 
In the above embodiments, explanation has been given assuming that the 
all-cylinder simultaneous injection or group injection is effected for the 
internal combustion engine for the period until the cylinder 
discrimination is completed, that is, for the period for which the 
cylinder is unidentified. However, from the viewpoint of combustion 
efficiency etc., the following injection mode may be set. 
For four-cylinder internal combustion engines, the normal sequential 
injection timing of fuel for each cylinder is set as the exhaust (EX) 
stroke of each cylinder as indicated by the solid line cross hatching in 
the combustion cycle schematically shown in FIG. 18. More specifically, 
the fuel injection timing for each cylinder is set from the later half of 
the exhaust (EX) stroke to the early time of the succeeding intake (IN) 
stroke. However, if fuel is injected simultaneously at the timing as shown 
in FIGS. 5 to 7 for the period until the cylinder discrimination is 
completed, even if the fuel injection amount is increased by the 
accelerating operation (operation of accelerator) during that time, the 
increased fuel amount is not always immediately used for combustion. For 
example, even if acceleration is effected in the compression (CP) stroke 
of the first cylinder shown in FIG. 5, some delay occurs before the 
increase in fuel because the timing of group injection of fuel is the 
exhaust (EX) stroke, which is two strokes after the compression (CP) 
stroke. 
In the present invention, therefore, as shown in FIGS. 19 and 20, an 
interim injection mode is set in which fuel is injected (solid 
cross-hatching) in sequence to each cylinder in the reverse order of the 
normal sequential injection mode. In this interim injection mode, while 
the ignition control for each cylinder is carried out in the same manner 
as the ordinary sequential injection mode, only the injection timing of 
fuel is set in the reverse order. Specifically, as shown in FIG. 19, fuel 
is injected in the exhaust (EX) stroke of the first and fourth cylinders 
so that the injection timing for the first and fourth cylinders is 
correct. Meanwhile, for the third and second cylinders, the injection 
timing is set so that fuel is wrongly injected in the compression (CP) 
stroke. Alternatively, as shown by the solid line cross-hatching in FIG. 
20, for the first and fourth cylinders, fuel is injected in the 
compression (CP) stroke so that the injection timing is intently wrong, 
and inversely, for the third and second cylinders, the timing is set so 
that fuel is injected correctly in the exhaust (EX) stroke. It can be said 
that this is an abnormal sequential injection mode with respect to the 
normal sequential injection mode. 
In either of the modes shown in FIGS. 19 and 20, in this interim injection 
mode, fuel is injected in the normal exhaust stroke for two cylinders 
having a 360.degree. different stroke phase. The fuel injection for the 
remaining two cylinders is effected in the compression stroke. 
According to this interim injection mode, even if accelerating operation is 
performed in the compression (CP) stroke of the first cylinder in the 
combustion cycle shown in FIG. 19, the fuel injection amount for the 
fourth cylinder entering the exhaust (EX) stroke is increased, so that the 
speed of internal combustion engine is rapidly increased. Also, even if 
accelerating operation is performed when the first cylinder is in the 
combustion (CB) stroke in the combustion cycle shown in FIG. 19, fuel can 
be increased at the fuel injection timing in the exhaust (EX) stroke after 
one stroke phase, so that the acceleration response can be ensured 
sufficiently. The acceleration response can be enhanced in the interim 
injection mode as compared with the case where conventional all-cylinder 
simultaneous injection or group injection is carried out. 
When the interim injection mode is set at the timing shown in FIG. 20 as 
well, the correct injection timing is set for the remaining two cylinders 
as described above, so that the increase in speed of internal combustion 
engine can be achieved due to the rapid increase in fuel injection amount 
in response to the accelerating operation like the case of interim 
injection timing shown in FIG. 19. 
When the interim injection mode is employed, therefore, the fuel injection 
for the internal combustion engine should be controlled by following the 
procedure shown in FIG. 21, for example. Specifically, when the cranking 
of internal combustion engine is started by the activation of a starter 
switch as shown in FIG. 21 (Step S71), or when the series data of cylinder 
discrimination result determined already is reset for any reason (Step 
S72), the internal combustion engine is operated in a state in which fuel 
is not injected to the internal combustion engine, or in a state in which 
ignition is not effected (Step S73). At this time, in accordance with the 
aforesaid specific pulse in the series of the pulse signals obtained from 
the rotating member (signal generating means) 1 mounted on the crankshaft, 
which is the output rotating shaft, the pulse signal for the particular 
cylinder or the particular cylinder group consisting of two cylinders 
having different a 360.degree. stroke phase is identified, and the pulse 
signal series is identified (Step S74). 
After the pulse signal series is identified by this operation, the internal 
combustion engine is operated in the aforesaid interim injection mode in 
accordance with the timing of pulse signal corresponding to the first and 
fourth cylinders (#1-4), for example (StepS75). After the operation of 
internal combustion engine is started in the interim injection mode, it is 
determined whether or not the fuel full closed conditions, for example, 
due to deceleration are met (Step S76). If the fuel full closed conditions 
are met, fuel cut operation is executed to stop the injection of fuel to 
each cylinder (Step S77). In this state, it is determined whether or not 
the aforesaid second cylinder discrimination can be executed (Step S78). 
This discrimination is made by checking that the throttle opening is [0] 
and fuel injection is stopped to each cylinder under the condition that 
the rotational speed of internal combustion engine is not lower than a 
predetermined value. If the cylinder discrimination conditions are met, 
the cylinder discrimination mode executed as described above is set, and 
cylinder discrimination is made (Step S79). 
If the stroke phase of each cylinder is identified by the cylinder 
discrimination, and the cylinder discrimination is finished (Step S80), 
the control transfers to the sequential injection mode in accordance with 
the cylinder discrimination result (Step S81). However, if the cylinder 
discrimination result is not identified, or if the acceleration or 
deceleration of internal combustion engine is effected in the course of 
the cylinder discrimination and the cylinder discrimination is stopped, 
the procedure from Step S76 is repeatedly executed again while detecting 
the running state (Step S82). 
According to this procedure, until the stroke phase of each cylinder is 
exactly identified by cylinder discrimination, that is, until the cylinder 
discrimination is made, the fuel injection for the internal combustion 
engine can be controlled in accordance with the interim injection mode, so 
that even if acceleration or deceleration operation is performed by the 
operation of accelerator or brake during this time, the operation of 
internal combustion engine can be controlled efficiently by following 
this. Therefore, even if the cylinder discrimination is not completed, the 
drivability can be ensured sufficiently. Also, while the fuel injection 
mode for the internal combustion engine is controlled in the interim 
injection mode that can follow the driving operation, the fuel injection 
mode for the particular cylinder is made different from that of other 
cylinders, by which the cylinder discrimination can be made efficiently, 
and the control can transfer to the sequential injection mode quickly. 
Although the case in which the interim injection mode is applied to the 
second cylinder discrimination was explained in FIG. 21, the interim 
injection mode may, needless to say, be applied to the case in which the 
cylinder discrimination is not executed by determining the fuel cut 
conditions in deceleration, but the cylinder discrimination is executed by 
detecting the aforesaid steady constant-speed running state. Needless to 
say, it may be applied to the case in which the cylinder discrimination is 
executed in accordance with the detection state while monitoring both of 
the fuel cut state and the steady constant-speed running state. 
In the above-mentioned first and second cylinder discrimination, when the 
fuel injection amount for the particular cylinder was made different from 
that of other cylinders, the total output of internal combustion engine 
was kept constant by increasing the intake air amount and by regulating 
the air-fuel ratio for other cylinders. When a significant output 
variation in the internal combustion engine is restrained by regulating 
the controlled variable relating to the rotational speed of internal 
combustion engine and by keeping the rotational speed at a constant value 
or more, the intake air amount etc. may be adjusted and controlled in 
accordance with the tables configured as shown in FIGS. 22A and 22B. 
Specifically, when a rotational variation is given by injecting fuel to the 
particular cylinder only in the aforesaid fuel cut mode, the throttle 
opening is close to the fully closed state and the intake air amount is 
very small, so that there is a possibility that the combustion due to fuel 
injection and the increase in rotational speed are not expected. In this 
case, therefore, for example, the intake air amount is increased to make 
the combustion of the particular cylinder normal and the output is 
increased, by which the detection accuracy should be enhanced. 
In such a case, a table showing the lower limit flow rate of idle intake 
air amount set in accordance with the rotational speed of internal 
combustion engine, for example, as shown in FIG. 22A should be used to 
clip control the lower limit value. Further, a correction factor set in 
accordance with the cooling water temperature of internal combustion 
engine as shown in FIG. 22B should be used to correct the idle intake air 
amount. At this time, in order to regulate the idle intake air amount with 
good response, it is preferable to use a linear solenoid type control 
valve. 
Thus, not only the idle intake air amount is lower-limit clip controlled in 
accordance with the rotational speed of internal combustion engine, but 
also the idle intake air amount is corrected in accordance with the engine 
water temperature, by which the aforesaid cylinder discrimination can be 
executed effectively while easily preventing the unwilling stop of 
internal combustion engine. Specifically, by multiplying the idle intake 
air amount determined in accordance with the rotational speed by a 
correction factor determined in accordance with the engine water 
temperature, a proper rotational variation in cylinder discrimination 
should be obtained, and an optimum idle intake air amount that can obtain 
good deceleration feeling should be determined. At this time, if the 
correction value of inherent idle intake air amount of internal combustion 
engine is determined as a learning value for idle intake air amount of 
internal combustion engine, for example, at the fuel cut time, and the 
intake air amount in cylinder discrimination is further corrected by using 
the correction value (learning value), the variations regarding the 
individuality of internal combustion engine are corrected, so that better 
control can be carried out. 
If the cylinder discrimination cannot be made at the start of internal 
combustion engine, the fuel cut mode in deceleration or the steady 
constant-speed state is detected as described before, and the cylinder 
discrimination is executed. Before the completion of cylinder 
discrimination, fuel injection is controlled in accordance the 
all-cylinder simultaneous injection or group injection as described above 
or the abnormal sequential injection mode described in FIGS. 19 and 20. 
After the completion of cylinder discrimination, fuel injection is 
controlled in the normal sequential injection mode in accordance with the 
cylinder discrimination result. 
However, the acceleration and deceleration of internal combustion engine is 
effected despite whether or not the cylinder discrimination is completed. 
Also, the degree of acceleration and deceleration is varied. The fuel 
control of internal combustion engine, which governs the acceleration and 
deceleration, is usually executed on the assumption that the internal 
combustion engine is operated in the normal sequential injection mode 
based on the cylinder discrimination result. However, the fuel injection 
timing naturally differs between the time when the cylinder discrimination 
has been completed at which the sequential injection mode is executed and 
the time when the cylinder discrimination is not yet completed, so that it 
is thought that the fuel control mode in the sequential injection mode 
used as it is presents a problem. 
Specifically, the fuel injection timing differs when the cylinder 
discrimination is not yet completed, and for example, fuel is injected in 
the compression or combustion stroke, so that there arises a problem in 
that the sticking amount of the fuel to the intake port wall surface 
varies and the like problems. Further, a difference in calculation value 
of fuel amount to be injected is prone to be caused by the difference in 
injection timing. Such a fuel control error appears as a cause for 
deterioration in transient response to acceleration or deceleration or an 
excessive reaction, resulting in impaired drivability. 
Accordingly, in the present invention, the transient correction fuel 
control data used for fuel control in acceleration and deceleration is set 
separately at a time when the cylinder discrimination has been completed 
and the at a time when the cylinder discrimination is not yet completed, 
and the transient correction fuel control data is used selectively in 
accordance with the fuel injection mode of internal combustion engine. The 
transient correction fuel control data set separately include a water 
temperature correction factor, rotational speed correction factor, 
acceleration tailing factor, etc. which are transient correction data 
regarding the acceleration increase amount of fuel in acceleration. These 
correction factors etc. should be given as the map information with the 
rotational speed of internal combustion engine and engine water 
temperature being parameters as shown in FIGS. 23A, 23B, and 23C. 
Similarly, the transient correction data regarding the deceleration 
decrease amount of fuel in deceleration include a water temperature 
correction factor, rotational correction factor, pressure correction 
factor, deceleration tailing factor, etc. These factors should be set 
separately as the map information with engine water temperature and 
rotational speed, and manifold pressure being parameters. 
When the fuel injection amount is increased by asynchronously increasing 
the fuel injection pulse in accordance with the throttle opening in 
acceleration when the cylinder discrimination is not yet completed, the 
fuel injection amount varies greatly in accordance with the number of 
injection pulses. Therefore, for example, as shown in FIGS. 25A, 25B, and 
25C, a water temperature correction factor, rotational speed correction 
factor, and base fuel injection amount per one injection pulse should be 
set separately as the map information with the engine water temperature 
and rotational speed, and throttle opening being parameters. 
If the transient correction fuel control data (correction factor etc.) for 
fuel control when the cylinder discrimination is not yet completed are set 
in this manner separately from the transient correction fuel control data 
used in the normal sequential injection mode, the control of fuel 
injection amount can be carried out in accordance with the fuel injection 
mode when the cylinder discrimination is not yet completed, so that the 
transient response to acceleration and deceleration is made good, and the 
drivability can be stabilized. In particular, at the injection timing in 
accordance with the fuel injection mode when the cylinder discrimination 
is not yet completed, a proper fuel amount according to acceleration or 
deceleration can be injected, so that smooth acceleration and deceleration 
control can be executed favorably as compared with the case where the 
normal sequential injection control is carried out. 
INDUSTRIAL APPLICABILITY 
As described above, according to the cylinder discriminating apparatus for 
an internal combustion engine in accordance with the present invention, a 
signal corresponding to each cylinder or each cylinder group with a 
360.degree. different stroke phase is obtained from the signal generating 
means mounted on the output rotating shaft of internal combustion engine, 
and an identification signal capable of identifying the single particular 
cylinder or the particular cylinders with a 360.degree. different stroke 
phase is obtained, so that the stroke phase of a particular cylinder or a 
particular cylinder group that can be used as the reference for cylinder 
discrimination with correct timing can be identified. 
After the cranking of internal combustion engine is completed, or in the 
fuel cut mode, or when the steady constant-speed running state is 
detected, the fuel injection amount for the particular cylinder or the 
particular cylinder group is made different from the fuel injection amount 
of other cylinders to positively produce a rotational variation in the 
internal combustion engine, and the stroke phase of each cylinder is 
discriminated in accordance with the present rotational variation and the 
cylinder group identification result, so that a particular cylinder 
(cylinder group) can be accurately discriminated in a short period of time 
without causing complete misfire. 
When the amount of fuel injection for a particular cylinder or the 
particular cylinder group is made different from the fuel injection amount 
of the other cylinders to produce a rotational variation, the controlled 
variable relating to the rotational speed of internal combustion engine is 
regulated to keep the rotational speed at a predetermined speed or higher, 
so that an accident such as engine stall in cylinder discrimination can be 
prevented, and large output variations of internal combustion engine can 
be effectively restrained effectively. Moreover, the cylinder 
discrimination can be made without the deterioration in driving feeling, 
and the reliability of cylinder discrimination can be increased.