Method of diagnosing a mechanism for improving combustion in an internal combustion engine and apparatus therefor

In an internal combustion engine equipped with a mechanism for improving combustion such as a swirl control valve, the air-to-fuel ratio of the combustion mixture gas is increased until the stability of the engine reaches an allowable limit under the condition where the combustibility is to be improved by the mechanism for improving combustion. When the air-to-fuel rate at the allowable limit is equal to or smaller than a reference air-to-fuel ratio, whether or not the mechanism for improving combustion is defective is diagnosed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of diagnosing a mechanism for 
improving combustion in an internal combustion engine and an apparatus 
therefor. More specifically, the invention relates to a method of 
diagnosing whether or not a mechanism for improving combustion is property 
operating to realize lean burn as a result of improving combustibility in 
an engine, and to an apparatus for diagnosing such a mechanism. 
2. Related Art of the Invention 
In order to improve fuel efficiency in recent years, a lean burn engine has 
been proposed according to which the mixture gas is burned at an 
air-to-fuel ratio (e.g., 20 to 25) which is much higher than a 
stoichiometric air-to-fuel ratio. 
Such a lean burn engine is provided with a swirl control valve (hereinafter 
abbreviated as SCV) to ensure an ignition stability of a lean mixture gas, 
the SCV being closed during the lean burn to generate a strong swirl in a 
cylinder, so that the fuel and the air are mixed well together to form a 
homogeneous mixture gas to accomplish the lean burn (see Japanese 
Unexamined Patent Publication No. 6-101484). Similarly, a mechanism has 
heretofore been known for generating a tumble in the cylinders. 
A device has also been known according to which part of the intake air is 
introduced as assist air from an intake passage on the upstream side of 
the throttle valve to near an injection port of a fuel injection valve, 
and the assist air is brought into collision with the fuel injected from 
the fuel injection valve to atomize the fuel, so that the ignition 
stability of the lean mixture gas can be improved (see Japanese Examined 
Patent Publication No. 64-9465). 
The mechanism for improving combustion such as the above-mentioned SCV and 
the assist air-feeding mechanism are to realize lean burn. Therefore, in 
case such mechanisms fail to give swirling motion to the mixture gas or 
fail to atomize the fuel due to malfunctioning, the combustion efficiency 
deteriorates often causing the exhaust gas property and the engine 
operation to lose stability. 
It is therefore desired to provide a method and an apparatus for diagnosing 
the occurrence of malfunctioning in the mechanism for improving 
combustion. For example, whether the SCV properly opens or closes is 
detected by using a switch which turns on or off depending upon the 
opening or closure of the valve, and whether the assist air is properly 
fed or not is detected based on the output of a pressure sensor which 
detects the air pressure in the assist air-feeding passage, thereby 
enabling malfunctioning diagnosis. 
Since such diagnosing methods, however, require a special sensor and a 
switch for diagnosis, there are problems that the cost is raised and, 
further, space for installing the sensor and the like is required. 
Besides, even when the assist air is normally fed, there is a likelihood of 
a fault such that the fuel is not favorably atomized by the assist air. 
Therefore, it is desired to provide a method and apparatus capable of 
diagnosing whether an improvement in the combustibility which is the final 
object of the combustion improving mechanism has been accomplished or not. 
SUMMARY OF THE INVENTION 
The present invention was accomplished in view of the above-mentioned 
problems, and its object is to provide a method of diagnosing the 
occurrence of malfunctioning in a mechanism for improving combustion such 
as SCV and assist air feeding mechanism, and an apparatus therefor, 
without requiring any special sensor. 
Another object of the invention is to diagnose the malfunctioning of the 
mechanism for improving combustion relying upon whether an improvement in 
the combustibility which is the object of the invention has been 
accomplished or not. 
In order to accomplish the above-mentioned objects, the present invention 
is concerned with a method and an apparatus for diagnosing a mechanism for 
improving combustion in an internal combustion engine, said mechanism for 
improving combustion including an operation unit operated by an actuator 
and controlling the supply of a combustion component into the internal 
combustion engine by means of said operation unit, thereby achieving the 
combustibility improvement, wherein, under a condition where the 
combustibility is to be improved by the mechanism for improving 
combustion, stability of the engine is sequentially detected and an 
air-to-fuel ratio of the combustion mixture gas is gradually increased 
until the stability of the engine reaches a previously set allowable 
limit, and, when the air-to-fuel ratio at a moment when the allowable 
limit is reached is equal to or smaller than a reference air-to-fuel 
ratio, a fault diagnosis signal indicating the occurrence of 
malfunctioning in the mechanism for improving combustion is output. 
That is, the above-mentioned mechanism for improving combustion is to 
realize lean burn by improving combustibility by atomizing the fuel and 
homogenizing the mixture gas. Therefore, in case the fuel is not atomized 
or the mixture gas is not homogenized due to malfunctioning, since 
stability in the combustion is deteriorated, stability is no longer 
maintained in a lean air-to-fuel ratio which could have maintained the 
engine stability to a sufficient degree during the normal operation. 
Therefore, the air-to-fuel ratio is gradually increased to find a limit of 
the lean burn, and whether the mechanism for improving combustion is 
operating as desired or not is diagnosed depending upon whether the limit 
of the lean burn has reached a predetermined lean air-to-fuel ratio. 
Here, the stability of the engine can be detected based upon a rate of 
change in the pressure in the engine cylinders or a rate of change in the 
rotational speed of the engine. 
According to the present invention, furthermore, an assist air-feeding 
mechanism which atomizes the fuel by bringing part of the intake air as 
assist air into collision with the fuel injected from a fuel injection 
valve, and has, as an operation unit, a valve for opening and closing an 
assist air-feeding passage may be the mechanism for improving combustion 
that is to be diagnosed. 
The assist air-feeding mechanism enhances the ignition stability by 
atomizing the fuel. When a trouble occurs such as interruption of the 
assist air feed due to a trouble in the valve (inclusive of both 
mechanical trouble and electrical trouble), the fuel is no longer atomized 
and a limit of lean burn decreases. 
An intake air control mechanism having, as an operation unit, an intake air 
control valve that opens and closes an air intake system for homogenizing 
the mixture gas by swirling the mixture gas, may be a combustion improving 
mechanism that is to be diagnosed. 
The intake air control mechanism improves the combustibility by 
homogenizing the mixture gas by causing the mixture gas to be swirled or 
tumbled. When the mixture gas is no longer swirled or tumbled due to a 
trouble in the intake air control valve, the mixture gas is no longer 
homogenized, and a limit of lean burn decreases. 
Other objects and advantages of the invention will become obvious from the 
following description of embodiments with reference to the accompanying 
drawings.

PREFERRED EMBODIMENTS 
FIG. 1 is a block diagram illustrating the fundamental constitution of an 
apparatus for diagnosing mechanism for improving combustion according to 
the present invention. 
In FIG. 1, a stability detecting means A detects the stability of an engine 
based upon a rate of change in the rotational speed or a rate of change in 
the pressure in a cylinder. An air-to-fuel ratio increasing means B 
increases the air-to-fuel ratio of a combustion mixture gas by controlling 
the amount of fuel injection until the stability of the engine as detected 
by the stability detecting means A reaches a previously set allowable 
limit under the condition where the combustibility has been improved by a 
mechanism C for improving combustion such as assist air-feeding mechanism 
or intake air control mechanism. 
When the air-to-fuel ratio is equal to or smaller than a reference 
air-to-fuel ratio at a moment when the stability of the engine has reached 
the allowable limit as a result of increasing the air-to-fuel ratio by the 
air-to-fuel ratio increasing means B, a malfunction diagnosing means D so 
judges that the fuel has not been atomized or the mixture gas has not been 
swirled due to malfunction of the mechanism C for improving combustion, 
and outputs a fault diagnosis signal. 
Described below are concrete embodiments of the apparatus and method of 
diagnosing the mechanism for improving combustion that has the 
above-mentioned fundamental constitution. 
Referring to FIG. 2 which illustrates the constitution of a system 
according to an embodiment, an internal combustion engine 1 intakes the 
air through a throttle valve 2, an intake manifold 3 and an intake valve 
4. 
The intake manifold 3 is provided at each branch portion thereof with a 
fuel injection valve 5 for each of the cylinders. The fuel injection valve 
5 is an electromagnetic fuel injection valve which opens when a current is 
supplied to a solenoid and closes when the supply of current is 
interrupted; i.e., the fuel injection valve 5 opens upon receiving an 
injection pulse signal from a control unit 16 that will be described later 
and injects into the engine 1 the fuel which is supplied from a fuel pump 
that is not shown and of which pressure is adjusted to a predetermined 
pressure by a pressure regulator. 
Each combustion chamber of the engine 1 is provided with an ignition plug 6 
which produces spark to ignite and burn the mixture gas. The engine 1 
discharges the exhaust gas through an exhaust valve 7, an exhaust manifold 
8a, an exhaust duct 8b and a catalytic converter 9. 
The control unit 16 is equipped with a microcomputer which is constituted 
by CPU, ROM, RAM, ND converter and input/output interface, and receives 
input signals from various sensors, calculates the fuel injection amount 
Ti through the fuel injection valve 5, and controls the operation of the 
fuel injection valve 5 based upon the fuel injection amount Ti. 
These variety of sensors include an air flow meter 10 for detecting the 
engine intake air flow amount Q, a crank angle sensor 11 for taking out a 
rotational signal from a crank shaft or a cam shaft, a cylinder pressure 
sensor 12 (cylinder pressure detecting means) for detecting the pressure 
in the cylinder of the engine, and the like sensors. 
By measuring the period of a detection signal output from the crank angle 
sensor 11 for each a predetermined crank angle or by measuring the 
frequency of generation of the detection signals within a predetermined 
period of time, it is made possible to calculate the rotational speed Ne 
of the engine. Therefore, the crank angle sensor 11 corresponds to a 
rotational speed detecting means. 
As disclosed in Japanese Unexamined Utility Model Publication No. 63-17432, 
furthermore, the cylinder pressure sensor 12 is a ring-like sensor which 
includes a piezoelectric element, and is mounted as a washer of the 
ignition plug 6. Upon receiving the combustion pressure, the ignition plug 
6 is lifted up, whereby the set load undergoes a change to output a signal 
that corresponds to the pressure in the cylinder. 
The CPU of the microcomputer incorporated in the control unit 16 is 
equipped with an air-to-fuel ratio map in which have been set target 
air-to-fuel ratios depending upon the engine load represented by a basic 
fuel injection amount Tp and the engine rotational speed Ne. In order to 
form a mixture gas of the target air-to-fuel ratio stored in the 
air-to-fuel ratio map, the CPU calculates a basic fuel injection amount Tp 
(=K.times.Q/Ne; K is a constant) based upon the intake air flow amount Q 
and the engine rotational speed Ne, and, further calculates a final fuel 
injection amount Ti by variously correcting the basic fuel injection 
amount Tp depending upon the operation conditions of the engine. The CPU 
outputs an injection pulse signal of a pulse width corresponding to the 
fuel injection amount Ti to each of the fuel injection valves 5 in 
synchronism with the intake stroke of each of the cylinders. 
The air-to-fuel ratio map contains, as a target air-to-fuel ratio, a lean 
air-to-fuel ratio (e.g., 20 to 25) which is very higher than a 
stoichiometric air-to-fuel ratio (14.7) for the region of low load and low 
rotational speed operations, and the region of high load and high 
rotational speed operations other than the above region of lean burn 
operations is made to be the region of an output combustion operations 
wherein, the stoichiometric air-to-fuel ratio, or an air-to-fuel ratio 
(e.g., about 13) which is slightly smaller than the stoichiometric 
air-to-fuel ratio is set as target air-to-fuel ratio. 
The engine 1 is provided with a swirl control valve (hereinafter 
abbreviated as SCV) 13 at a portion of each intake port of the intake 
manifold 3. The SCV 13 is a butterfly-type throttle valve with a notch. 
When the SCV 13 is closed, the flow of the intake air is deflected to 
produce a strong swirl (swirling motion in the transverse direction) in 
the cylinder, to enhance the ignition stability during the lean burn 
operation. 
Provision is made of a diaphragm 14 as an actuator for opening and closing 
the SCV 13. The SCV 13 can be driven to open and close by controlling the 
negative pressure of the engine introduced into a pressure chamber of the 
diaphragm 14 using an electromagnetic three-way change-over valve 15. 
An electric motor may be used as an actuator for opening and closing the 
SCV 13 which is the operation unit. 
The three-way change-over valve 15 is controlled by the control unit 16. In 
other words, in the lean burn operation region, the control unit 16 
controls the three-way change-over valve 15 to close the SCV 13 so as to 
give a swirling motion to the mixture gas (combustion component). 
As shown in the flow chart of FIG. 3, furthermore, the control unit 16 
diagnoses the occurrence of malfunction in the intake air control 
mechanism which is a mechanism for improving combustion constituted by the 
SCV 13, diaphragm 14 and three-way change-over valve 15. 
The function of the air-to-fuel ratio increasing means and the function of 
the malfunction diagnosing means are possessed in a software manner by the 
control unit 16 as shown in the flow chart of FIG. 3, and since the 
stability of the engine is detected based upon a rate of change in the 
pressure in the cylinder detected by the cylinder pressure sensor 12, the 
cylinder pressure sensor 12 corresponds to the stability detecting means. 
Referring to the flow chart of FIG. 3, it is, first, discriminated at step 
1 (expressed as S1 in FIG. 3, the same holds thereinafter) whether the 
three-way change-over valve 15 is so controlled as to close the SCV 13 to 
generate the swirling. 
When the SCV 13 is in the closed state, the program proceeds to step 2 
where a pressure in the cylinder detected by the cylinder pressure sensor 
12 is integrated over a predetermined crank angle range (e.g., TDC to ATDC 
100.degree. ) to obtain an integrated value Pi. 
At next step 3, the integrated value Pi is sampled for a predetermined 
period of time, and a plurality of the integrated values Pi obtained 
during the predetermined period of time are stored. 
At step 4, a deviation .DELTA.Pi (=Pimax-Pimin) is calculated between a 
maximum value Pimax and a minimum value Pimin among a plurality of 
integrated values Pi obtained within the predetermined period of time. 
At step 5, it is discriminated whether or not the deviation .DELTA.Pi (rate 
of change in the pressure in the cylinder) is equal to or smaller than a 
predetermined value that corresponds to the allowable limit value of 
stability of the engine. When the deviation .DELTA.Pi is equal to or 
smaller than the predetermined value, it is so presumed that the 
air-to-fuel ratio can be further increased yet maintaining the engine 
stability within the allowable range, and the program proceeds to step 6 
where the fuel injection amount is decreasingly corrected to gradually 
increase the air-to-fuel ratio. 
When the deviation .DELTA.Pi is in excess of the predetermined value, the 
program proceeds to step 7 where the fuel injection amount is increasingly 
corrected to gradually decrease the air-to-fuel ratio in order to recover 
the engine stability. 
As described above, the fuel injection amount is corrected by comparing the 
deviation .DELTA.Pi with the predetermined value, thereby increasing the 
air-to-fuel ratio up to the allowable limit. 
At step 8, the air-to-fuel ratio (lean limit air-to-fuel ratio) obtained as 
a result of controlling the air-to-fuel ratio based upon the deviation 
.DELTA.Pi is compared with a reference air-to-fuel ratio. 
The reference air-to-fuel ratio has been set to be smaller than the lean 
limit air-to-fuel ratio of when the SCV 13 is actually closed and a strong 
swirl is generated in the cylinder, and to be larger than the lean limit 
air-to-fuel ratio when the SCV 13 is not closed despite it is so 
controlled as to be closed and a strong swirl is not generated (see FIG. 
4). 
Therefore, when it is discriminated at step 8 that the lean limit 
air-to-fuel ratio obtained as a result of controlling the air-to-fuel 
ratio based on the deviation .DELTA.Pi is equal to or smaller than the 
reference air-to-fuel ratio, the program proceeds to step 9 where it is 
judged that, since the intake air control mechanism constituted by the SCV 
13, diaphragm 14 and three-way change-over valve 15 is malfunctioning, the 
swirling is not generated as desired and the lean limit air-to-fuel ratio 
has decreased. Accordingly, a fault diagnosis signal is output. 
Malfunction in the intake air control mechanism includes mechanical defect 
of the SCV 13, diaphragm 14 and three-way change-over valve 15, as well as 
electrical defect such as disconnection and short-circuit of control line 
to the three-way change-over valve 15. 
When the fault diagnosis signal indicating the occurrence of malfunctioning 
of the intake air control mechanism is output, a fail safe control is 
executed such as inhibiting the lean burn or warning the occurrence of 
malfunction in the intake air control mechanism. 
On the other hand, when it is discriminated at the step 8 that the lean 
limit air-to-fuel ratio obtained as a result of controlling the 
air-to-fuel ratio based upon the deviation .DELTA.Pi is larger than the 
reference air-to-fuel ratio, the program proceeds to step 10 where it is 
judged that, since the intake air control mechanism is properly operating 
and the SCV 13 is closed as controlled, a strong swirl is generated as 
desired, and the combustibility is improved. 
Here, the cylinder pressure sensor 12 can also be used for diagnosing 
misfire. Therefore, malfunctioning in the intake air control mechanism can 
be diagnosed without driving up the manufacturing cost provided the engine 
is equipped with the cylinder pressure sensor 12 for diagnosing misfire. 
In the foregoing description, the pressure in the cylinder was integrated 
over a predetermined crank angle range. It is, however, also allowable to 
employ a constitution in which a rate of change in the maximum pressure in 
the cylinder or a rate of change in the pressure in the cylinder at a 
predetermined crank angle is calculated as a parameter for indicating 
stability. 
In the foregoing description, furthermore, the stability of the engine was 
detected based on the rate of change in the pressure in the cylinder. It 
is, however, also possible to judge the stability of the engine based upon 
a rate of change in the rotational speed Ne of the engine. Electronic 
control of the ignition timing and the fuel injection requires data 
related to the rotational speed Ne of the engine. Therefore, a system for 
detecting the stability based upon a rate of change in the rotational 
speed Ne of the engine can be constituted without requiring any special 
sensor and without driving up the manufacturing cost. 
The flow chart of FIG. 5 illustrates another embodiment for diagnosing 
malfunction in the intake air control mechanism by discriminating the 
stability based on the rate of change in the rotational speed Ne of the 
engine. In this embodiment, since the stability is discriminated based on 
the rate of change in the rotational speed Ne of the engine as described 
above, the crank angle sensor 11 which is a rotational speed detecting 
means corresponds to means for detecting stability. 
Referring to the flow chart of FIG. 5, it is discriminated at step 21 
whether or not the three-way change-over valve 15 is so controlled as to 
close the SCV 13 to generate the swirling. 
When the SCV 13 is in the closed state, the program proceeds to step 22 
where the rotational speed Ne of the engine is calculated based upon 
detection signals from the crank angle sensor 11. 
At step 23, the rotational speed Ne of the engine is sampled over a 
predetermined period of time. 
At step 24, a deviation .DELTA.Ne (=Nemax-Nemin) is calculated between a 
maximum value Nemax and a minimum value Nemin among the rotational speeds 
Ne of the engine sampled within the predetermined period of time. 
At step 25, the deviation .DELTA.Ne (rate of change in the rotational 
speed) is compared with a predetermined value. When the deviation 
.DELTA.Ne is equal to or smaller than the predetermined value, the 
air-to-fuel ratio is gradually increased at step 26. When the deviation 
.DELTA.Ne is larger than the predetermined value, on the other hand, the 
air-to-fuel ratio is gradually decreased at step 27 to recover the 
stability. 
Hereinafter, like in the steps 8 to 10 shown in the flow chart of FIG. 3, 
the air-to-fuel ratio obtained as a result of accomplishing the lean limit 
air-to-fuel ratio is compared with the reference air-to-fuel ratio, 
thereby diagnosing malfunction in the intake air control mechanism (steps 
28 to 30). 
The above-mentioned embodiments have dealt with the engine equipped with an 
intake air control mechanism which generates swirling (or tumbling) in the 
cylinder as a mechanism for improving combustion. As shown in FIG. 6, 
however, the engine may be provided with an assist air-feeding mechanism 
in which part of the intake air is brought as assist air into collision 
with the fuel injected from the fuel injection valve 5 to atomize the 
fuel, as a mechanism for improving combustion. In FIG. 6, the same 
elements as those of FIG. 2 are denoted by the same reference numerals and 
their description is omitted. 
The engine 1 shown in FIG. 6 is provided with an assist air passage 21 
which bypasses the throttle valve 2 and is opened near the injection port 
of each of the fuel injection valves 5. The air (hereinafter referred to 
as assist air) introduced due to the pressure difference between the 
upstream and downstream of the throttle valve 2, is injected near the 
injection port of the fuel injection valve 5 so as to come into collision 
with the injected fuel, so that the injected fuel is atomized. 
A normally-closed electromagnetic valve 22 is provided on the way of the 
assist air passage 21 to open the assist air passage 21 in a 
turned-on/turned-off manner. The electromagnetic valve 22 is turned on or 
off by the control unit 16 based upon data such as cooling water 
temperature Tw, etc., and change-over controls the supply or interruption 
of the assist air that is injected near the injection port as part of the 
air intaken by the engine. That is, the valve body of the electromagnetic 
valve 22 corresponds to the operation unit and the electromagnetic coil 
corresponds to the actuator thereby to control the supply of the assist 
air which is part of the intake air that is the combustion component. 
Here, the control unit 16 diagnoses the occurrence of malfunctioning in the 
assist air-feeding mechanism which comprises the assist air passage 21 and 
the electromagnetic valve 22 according to the same procedure as that of 
the flow chart of FIG. 3 or 5. 
That is, the content of processing at step 1 in the flow chart of FIG. 3 or 
at step 21 in the flow chart of FIG. 5 is changed into the processing for 
discriminating whether the electromagnetic valve 22 is in the open state 
or not (step 1a or step 21a) in the flow chart of FIG. 7 or 8, thereby 
diagnosing the malfunctioning in the same manner as the aforementioned 
embodiments. 
When the assist air-feeding mechanism malfunctions and fails to feed the 
assist air although the electromagnetic valve 22 is opened due to clogging 
in the assist air passage 21 or adhesion of the electromagnetic valve 22 
in the closed state, the fuel is not atomized by the assist air and the 
lean limit air-to-fuel ratio decreases. Therefore, whether the assist 
air-feeding mechanism is malfunctioning or not can be diagnosed by 
discriminating whether the air-to-fuel ratio is a value that is expected 
in a state where the assist air is normally fed, the air-to-fuel ratio 
having been increased to a degree with which the stability of the engine 
is on the verge of the allowable limit as discriminated based upon the 
rate of change in the cylinder pressure or in the rotational speed of the 
engine.