Title: Method for detecting misfiring in an internal combustion engine by analysing the angular acceleration of the drive shaft
Abstract: A method for detecting misfiring in an internal combustion engine by analysing the angular acceleration of the drive shaft, in which the value of the angular acceleration is estimated at predetermined angular positions of the drive shaft, the absolute value of the angular acceleration is compared with a predetermined threshold value, and the presence of a misfire is detected if the absolute value of the angular acceleration is greater than the predetermined threshold value; when the presence of a misfire is detected, a set of values of the angular acceleration subsequent to the value of the angular acceleration at which the misfire has been detected is filtered to eliminate the oscillation component generated by the misfire with respect to the value of the angular acceleration.
Patent Number: 7,024,303 Issued on 04/04/2006 to Sgatti, et al.
| Inventors:
|
Sgatti; Stefano (Imola, IT);
Siviero; Carlo (Bologna, IT);
Ponti; Fabrizio (Forli', IT)
|
| Assignee:
|
Magneti Marelli Powertrain S.p.A. (IT)
|
| Appl. No.:
|
773858 |
| Filed:
|
February 6, 2004 |
Foreign Application Priority Data
| Feb 07, 2003[IT] | B02003A0055 |
| Current U.S. Class: |
701/111; 701/29; 73/117.3 |
| Current Intern'l Class: |
G06F 19/00 (20060101) |
| Field of Search: |
701/111,29,102,34
73/116,117.3
|
References Cited [Referenced By]
U.S. Patent Documents
| 5377535 | Jan., 1995 | Angermaier et al.
| |
| 5504682 | Apr., 1996 | Shiraishi et al.
| |
| 5602331 | Feb., 1997 | Prevost.
| |
| 6055469 | Apr., 2000 | Shoji et al.
| |
| Foreign Patent Documents |
| 42 39 055 | Nov., 1992 | DE.
| |
| 0637738 | Aug., 1994 | EP.
| |
| 1 447 655 | Aug., 2004 | EP.
| |
Primary Examiner: Vo; Hieu T.
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb & Soffen, LLP
Claims
The invention claimed is:
1. A method for detecting misfiring in an internal combustion engine (
1)
by analysing the angular acceleration (acc) of the drive shaft (
4); the
method comprising the steps of:
estimating the value (acc) of the angular acceleration of the drive shaft (
4)
at predetermined angular positions of this drive shaft (
4);
comparing the absolute value (acc) of the angular acceleration of the drive shaft
(
4) with a predetermined threshold value (S);
detecting the presence of a misfire if the absolute value (acc) of the angular
acceleration of the drive shaft (
4) is greater than the predetermined threshold
value (S);
filtering, when the presence of a misfire is detected, when an absolute value
(acc) of the angular acceleration of the drive shaft (
4) exceeds the threshold
value (S), a set of values (acc) of the angular acceleration of the drive shaft
(
4) subsequent to the value (acc) of the angular acceleration of the drive
shaft (
4) at which the misfire has been detected to eliminate the oscillation
component generated by the misfire with respect to the value (acc) of the angular
acceleration of the drive shaft (
4); and
comparing only the filtered values (acc) of the angular acceleration of the drive
shaft (
4) with the threshold value (S) to detect the presence of any further
misfires subsequent to the misfire detected.
2. A method as claimed in claim 1, including filtering the values (acc) of the
angular acceleration of the drive shaft (
4) subsequent to the value (acc)
of the angular acceleration of the drive shaft (
4) at which the misfire
has been detected are filtered by algebraically adding to these values a corresponding
set of correction values obtained at the desigu and development stage of the engine
(
1) by analysing the oscillation generated by a misfire with respect of
the value (acc) of the angular acceleration of the drive shaft (
4).
3. A method as claimed in claim 2, including calculating the correction values
are calculated by subtracting a corresponding set of values (acc) of the angular
acceleration of the drive shaft (
4) in the presence of a misfire from a
set of values (acc) of the angular acceleration of the drive shaft (
4) in
standard conditions.
4. A method as claimed in claim 2, wherein the correction values are variable
as a function of the current engine point.
5. A method as claimed in claim 4, wherein, at the design stage of the engine
(
1), a plurality of salient engine points are identified, at each of which
the corresponding sample set of correction values is calculated, and during the
normal operation of the engine (
1), the set of correction values for the
current engine point is calculated by interpolating the sample sets of correction values.
6. A method as claimed in claim 4, wherein, at the design stage of the engine
(
1), a plurality of salient engine points are identified, at each of which
the corresponding sample set of correction values is calculated, and a single standard
reference set independent from the engine point is calculated from the sample sets
of correction values, and during the normal operation of the engine (
1),
the set of correction values for the current engine point is calculated from the
standard reference set.
7. A method as claimed in claim 6, including expressing the set of values (acc)
of the angular acceleration of the drive shaft (
4) and the set of correction
values as angular acceleration of the drive shaft (
4) as a function of the
angular position of the drive shaft (
4), the standard reference set being
expressed as a ratio between angular acceleratfon of the drive shaft (
4)
and engine load (
1) as a function of time.
8. A method as claimed in claim 7, wherein the engine load (
1) is indicated
by the flow of fresh air supplied to the engine (
1).
9. A method as claimed in claim 1, including filtering a set of eight values
(acc) of the angular acceleration of the drive shaft (
4) are filtered from
the value (acc) of the angular acceleration of the drive shaft (
4) at which
the misfire has been detected.
10. A method as claimed in claim 1, wherein the threshold value (S) for the detection
of the misfire is a function of the current engine point.
11. A method as claimed in claim 1, wherein, for each complete rotation of the
drive shaft (
4), as many values (acc) of the angular acceleration of the
drive shaft (
4) are estimated as there are cylinders (
2) performing
combustion during a complete rotation of the drive shaft (
4).
12. A method as claimed in claim 1, wherein, in each complete rotation of the
drive shaft (
4), as many angular measurement sections having the same amplitude
are identified as there are cylinders (
2) performing combustion during a
complete rotation of the drive shaft (
4), the time taken by the drive shaft
(
4) to travel each angular measurement section being measured, and the value
(acc) of the angular acceleration of the drive shaft (
4) at the ith instant
being calculated by applying the following formula:
##EQU2##
in which:
acc
i is the angular acceleration of the drive shaft (
4) at
the i-th moment;
T
i+1 is the time used by the drive shaft (
4) to pass over the
(i+1)-th angular measurement line;
T
i is the time used by the drive shaft (
4) to pass over the
i-th angular measurement line.
13. A method as claimed in claim 12, including measuring the time taken by the
drive shaft (
4) to travel each angular measurement section is measured using
the signal supplied by the phonic wheel (
5) which is provided with a disc
having 60 teeth (
6), each angular measurement section having an angular
amplitude equal to a number of teeth (
6) of the phonic wheel (
12)
of between 3 and 12.
14. A method as claimed in claim 12, wherein each angular section is at least
partially superimposed with respect to the expansion stroke of a respective piston (
3).
15. A method as claimed in claim 12, wherein each angular section substantially
coincides with the expansion stroke of a respective piston (
3).
Description
The present invention relates to a method for detecting misfiring in an internal
combustion engine by analysing the angular acceleration of the drive shaft.
BACKGROUND OF THE INVENTION
In an internal combustion engine with controlled ignition, the term misfire or
misfiring indicates a phenomenon of incorrect combustion within one or more cylinders;
the misfire is in particular known as an ignition misfire when it is due to the
inadequate or lacking energy of the spark generated by the spark plug, and is known
as an injection misfire when it is due to a fuel supply which is inadequate or lacking.
The presence of a misfire is particularly damaging since incorrect combustion
is detrimental to engine performance, increases the level of pollutant emissions
from the engine and may cause permanent damage to the catalyst. For this reason,
European standards on automobile vehicle emission limits require misfiring to be
detected efficiently and for drivers to be informed of the presence of a misfire
by means of an indicator light disposed on the dashboard. In particular, it is
necessary, under European regulations on automobile vehicle emission limits, to
indicate an increase in pollutant emission levels when the number of misfires in
a first interval (for instance 1000 TDC—top dead centres) exceeds a first
threshold, and to indicate permanent deterioration of the catalyst when the number
of misfires in a second interval (for instance 200 TDC—top dead centres)
exceeds a second threshold.
At present, misfiring is detected indirectly, i.e. by analysing the instantaneous
value of the angular acceleration of the drive shaft or the instantaneous value
of the drive torque, as a direct analysis of combustion by means of sensors disposed
inside each cylinder is not practicable for reasons of cost.
The most widespread method for detecting misfiring involves analysing the angular
acceleration of the drive shaft; in particular, the signal supplied by the phonic
wheel is used to calculate the value of the angular acceleration of the drive shaft
at predetermined angular positions of this drive shaft, and misfiring is detected
if the absolute value of the angular acceleration of the drive shaft is higher
than a predetermined threshold value.
It has been observed, however, that this method is not very reliable as the absolute
value of the angular acceleration of the drive shaft may also exceed the threshold
value as a result of causes unconnected with misfiring, such as, for instance,
the coupling or uncoupling of the compressor of the air conditioning plant, the
roughness of the road, or even abrupt decelerations. Moreover, in the case of a
single misfire, the value of the angular acceleration of the drive shaft may be
supplemented by torsional oscillations which cause the absolute value of the angular
acceleration of the drive shaft to exceed the threshold value at several successive
instants; in this case, a single misfire is erroneously detected as a plurality
of successive misfires.
A first solution to the problems discussed above is disclosed in European Patent
Application EP-0637738-A1 which discloses a method for detecting misfiring in an
internal combustion engine by analysing the angular acceleration of the drive shaft;
in order to try to eliminate the influence of disturbances, the value of the angular
acceleration of the drive shaft is processed by creating a so-called cyclicity
index which, compared with appropriate thresholds, indicates the presence of misfiring.
However, the method for detecting misfiring as disclosed in European Patent
Application EP-0637738-A1 also tends erroneously to detect a plurality of successive
misfires rather than a single misfire as a result of the oscillations of the value
of the angular acceleration of the drive shaft triggered by a single misfire.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method for detecting misfiring
in an internal combustion engine by analysing the angular acceleration of the drive
shaft, which is free from the drawbacks described above and, in particular, is
simple and economic to produce and is able to reduce to a minimum the percentages
of incorrect and failed detections of misfiring.
The present invention relates to a method for detecting misfiring in an internal
combustion engine by analysing the angular acceleration of the drive shaft as set
out in claim 1.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described with reference to the accompanying
drawings, which show a non-limiting embodiment thereof, in which:
FIG. 1 is a diagrammatic view, in lateral elevation and cross-section, of an
internal combustion engine provided with a control unit which implements the method
for detecting misfiring of the present invention;
FIG. 2 is a diagram showing the variation of the value of the angular acceleration
of the drive shaft as a function of the angular position of this drive shaft in
the presence of a single misfire;
FIG. 3 is a diagram showing a set of eight correction values used by the control
unit of FIG. 1;
FIG. 4 is a diagram showing the variation of the value of the angular acceleration
of the drive shaft of FIG. 2 after the application of a filtering process using
the eight correction values of FIG. 3;
FIG. 5 is a diagram showing the variation of the value of the angular acceleration
of the drive shaft as a function of the angular position of this drive shaft in
the presence of a double misfire;
FIG. 6 is a diagram showing the variation of the value of the angular acceleration
of the drive shaft of FIG. 5 after the application of a filtering process using
the eight correction values of FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, a petrol-driven internal combustion engine is shown overall by
1
and comprises four cylinders
2, each of which houses a respective piston
3 mechanically connected to a drive shaft
4 in order to transmit
the force generated by the combustion of the petrol in the cylinder
2 to
the drive shaft
4. A phonic wheel
5 provided with 60 teeth
6
and coupled to a sensor
7 adapted to detect the time interval between the
passage of two consecutive teeth
6 is keyed on the drive shaft
4.
The engine
1 further comprises a control unit
8, which is connected
to the sensor
7 and is adapted to detect misfiring in the cylinders
2.
The methods used by the control unit
8 to detect misfiring, using the
information supplied by the sensor
7 coupled to the phonic wheel
5,
are described below.
For each complete rotation of the drive shaft
4 (and therefore of the
phonic wheel
5), as many values acc of the angular acceleration of the drive
shaft
4 are estimated as there are cylinders
2 performing combustion
during a complete rotation of the drive shaft
4; with reference to the engine
1 shown in FIG. 1, two values acc of the angular acceleration of the drive
shaft
4 are therefore estimated for each complete rotation of the drive
shaft
4.
In each complete rotation of the drive shaft
4, two (equal to the number
of cylinders
2 performing combustion during a complete rotation of the drive
shaft
4) angular measurement sections having the same amplitude are identified,
the time taken by the drive shaft
4 to travel each angular measurement section
is measured, and the value acc of the angular acceleration of the drive shaft
4
at the ith instant is calculated by applying the following formula:
##EQU1##
in which:
acc
i is the angular acceleration of the drive shaft
4
at the ith instant;
T
i+1 is the time taken by the drive shaft
4 to
travel the (i+1)th angular measurement section;
T
i is the time taken by the drive shaft
4 to travel
the ith angular measurement section.
The time taken by the drive shaft
4 to travel each angular measurement
section is measured using the signal supplied by the phonic wheel
5; by
way of indication, each angular measurement section has an angular amplitude equal
to a number of teeth
6 of the phonic wheel
5 of between 3 and 12.
Preferably, each angular measurement section coincides substantially with the expansion
stroke of a respective piston
3 or is at least partially superimposed on
the expansion stroke of a respective piston
3.
FIG. 2 is a diagram showing the variation of the value acc of the angular acceleration
of the drive shaft
4 as a function of the angular position of this drive
shaft
4 in the presence of a single misfire. FIG. 5 is a diagram showing
the variation of the value acc of the angular acceleration of the drive shaft
4
as a function of the angular position of this drive shaft
4 in the presence
of a double misfire.
It will be appreciated from FIGS. 2 and 5 that, following a misfire, the value
acc of the angular acceleration of the drive shaft
4 presents a sequence
of high values which tend gradually to fade, i.e. have a curve of a damped oscillatory type.
The norm (or absolute value) of each value acc of the angular acceleration of
the drive shaft
4 is compared with a predetermined threshold value S which
is preferably a function of the current engine point; the presence of misfiring
is detected if the absolute value acc of the angular acceleration of the drive
shaft
4 is greater than the predetermined threshold value S. When misfiring
is detected, i.e. when an absolute value acc of the angular acceleration of the
drive shaft
4 exceeds the threshold value S, a set of eight values acc of
the angular acceleration of the drive shaft
4 subsequent to the value acc
of the angular acceleration of the drive shaft
4 at which misfiring has
been detected are filtered in order to eliminate the oscillation component caused
by the misfire with respect to the value acc of the angular acceleration of the
drive shaft
4; only the eight filtered values acc of the angular acceleration
of the drive shaft
4 are then compared with the threshold value S to detect
the presence of any subsequent misfires following the misfire detected.
It will be appreciated that the number of values acc of the angular acceleration
of the drive shaft
4 to which filtering is applied may be other than eight
and is generally between three and twelve; eight are preferably chosen bearing
in mind that, in general, the oscillatory phenomenon of the value acc of the angular
acceleration of the drive shaft
4 dies out within this duration.
The eight values acc of the angular acceleration of the drive shaft
4
following the value acc of the angular acceleration of the drive shaft
4
at which the misfire has been detected are filtered by algebraically adding a corresponding
set of eight correction values to these values; these correction values are obtained
at the design and development stage of the engine
1 by analysing the oscillation
generated by a misfire with respect to the value acc of the angular acceleration
of the drive shaft
4. The correction values may for instance be calculated
by subtracting a corresponding set of values acc of the angular acceleration of
the drive shaft
4 in the presence of a misfire from a set of values acc
of the angular acceleration of the drive shaft
4 in standard conditions.
By way of example, FIG. 3 is a diagram showing a set of eight correction values
as a function of the angular position of the drive shaft
4.
In other words, the method described above to improve the ability to diagnose
misfiring entails the isolation of the oscillatory disturbance which takes place
with respect to the value acc of the angular acceleration of the drive shaft
4
following a single misfire and the successive use of this oscillatory disturbance
to filter a set of eight values acc of the angular acceleration of the drive shaft
4 following each misfire.
FIG. 4 is a diagram showing the variation of the value acc of the angular acceleration
of the drive shaft
4 of FIG. 2 after the application of the filtering process,
i.e. after the eight correction values of FIG. 3 have been algebraically added
to the values acc of the angular acceleration of the drive shaft
4 of FIG.
2. FIG. 6 is a diagram showing the variation of the value acc of the angular acceleration
of the drive shaft
4 of FIG. 5 after the application of the filtering process,
i.e. after the eight correction values of FIG. 3 have been algebraically added
to the values acc of the angular acceleration of the drive shaft
4 of FIG. 5.
It will be appreciated from an examination of FIGS. 4 and 6 that the filtering
method described above enables error-free detection of single or multiple misfires;
in practice, the above-descried filtering makes it possible to eliminate the possibility
of the control unit
8 confusing a single misfire with a multiple misfire.
In order to ensure that the detection of misfires is very reliable, the correction
values have to be variable as a function of the engine point. For this reason,
at the design stage of the engine
1, a plurality of salient engine points
are identified, at each of which the corresponding sample set of correction values
is calculated; during normal operation of the engine
1, the set of correction
values corresponding to the current engine point is calculated by interpolating
the sample sets of correction values. As an alternative, at the design stage of
the engine
1, a plurality of salient engine points are identified, at each
of which the corresponding sample set of correction values is calculated, and a
single standard reference set independent from the engine point is calculated from
the sample sets of correction values; during normal operation of the engine
1,
the set of correction values corresponding to the current engine point is calculated
from the standard reference set. In particular, the set of values acc of the angular
acceleration of the drive shaft
4 and the set of correction values are expressed
as angular acceleration of the drive shaft
4 as a function of the angular
position of this drive shaft
4, while the standard reference set is expressed
as a ratio between angular acceleration of the drive shaft
4 and engine
load
1 as a function of time. The engine load
1 is preferably indicated
by the flow of fresh air supplied to the engine
1.
Experimental tests have shown that the use of a standard reference set
of correction values in place of a plurality of sample sets of correction values
makes it possible considerably to reduce the memory occupation of the control unit
8 without substantial effects on the reliability and accuracy of the filtering method.
*
