CA2320082C - Process for detecting a misfire in an internal combustion engine and system for carrying out said process - Google Patents
Process for detecting a misfire in an internal combustion engine and system for carrying out said process Download PDFInfo
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- CA2320082C CA2320082C CA002320082A CA2320082A CA2320082C CA 2320082 C CA2320082 C CA 2320082C CA 002320082 A CA002320082 A CA 002320082A CA 2320082 A CA2320082 A CA 2320082A CA 2320082 C CA2320082 C CA 2320082C
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- misfire
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- engine
- sampled signal
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- 238000000034 method Methods 0.000 title claims abstract description 38
- 230000008569 process Effects 0.000 title claims abstract description 37
- 238000002485 combustion reaction Methods 0.000 title claims abstract description 7
- 238000005070 sampling Methods 0.000 claims abstract description 13
- 230000006870 function Effects 0.000 claims description 8
- 239000002826 coolant Substances 0.000 claims description 4
- 238000006243 chemical reaction Methods 0.000 claims 1
- 238000010586 diagram Methods 0.000 description 6
- 238000010304 firing Methods 0.000 description 6
- 238000007792 addition Methods 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 239000000446 fuel Substances 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 238000001514 detection method Methods 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 230000010355 oscillation Effects 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 241000518994 Conta Species 0.000 description 1
- 241001051742 Eacles Species 0.000 description 1
- 241001674048 Phthiraptera Species 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 230000009089 cytolysis Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M15/00—Testing of engines
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M15/00—Testing of engines
- G01M15/04—Testing internal-combustion engines
- G01M15/11—Testing internal-combustion engines by detecting misfire
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
- F02D41/1448—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an exhaust gas pressure
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
- F02D41/26—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using computer, e.g. microprocessor
- F02D41/28—Interface circuits
- F02D2041/286—Interface circuits comprising means for signal processing
- F02D2041/288—Interface circuits comprising means for signal processing for performing a transformation into the frequency domain, e.g. Fourier transformation
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D2200/00—Input parameters for engine control
- F02D2200/02—Input parameters for engine control the parameters being related to the engine
- F02D2200/10—Parameters related to the engine output, e.g. engine torque or engine speed
- F02D2200/1015—Engines misfires
Abstract
A process for detecting a misfire in one or more cylinders (3, 3') of an internal combustion engine, including the following operative steps: sampling the exhaust gas pressure values during at least one engine cycle, the sampling frequency being proportional to the crankshaft rotational speed; analyzing the sampled signal in the frequency domain; calculating a misfire index as a function of the results of said analysis; comparing said index with one or more threshold values. Said frequency domain analysis preferably includes a Fourier transform of the sampled signal. The present invention also relates to a system carrying out said process.
Description
"PROCESS FOR DETECTING A MISFIRE 1N AN INTERNAL COMBUSTION
ENGINE AND SYSTEM FOR CARRYING OUT SAID PROCESS"
The present invention relates to a process for detecting a misfire in an internal combustion engine, and in particular a process which can be used for detecting a misfire in one or more cylinders of an internal combustion engine. The present invention also relates to a system for carrying out said process.
It is known that in order to monitor the performance of an internal combustion engine, in particular a racing engine with a high number of cylinders, it is desirable to detect the occurrence of the misfire of the fuel mixture in ane or more cylinders. A
process for carrying out said detection, which is known from US-5576963 and presently plays an important role with respect to the ever stricter rules for the control of polluting exhausts, consists of measuring the sudden fluctuations in the rotational speed of the crankshaft by means of an electronic sensor located close to the fly-wheel.
This sensor is connected to the control unit positioned inside the car, which receives all the data concerning the engine and transmitted by suitable sensors. By calculating the fluctuations in the speed according to the delivered torque it is possible to identify a possible misfire in one cylinder of the engine. However, this process does not allow to precisely identify in which cylinder the misfire occurred and moreover has a quite high error probability, particularly in the case of the traveling car being subjected to sharp oscillations, e.g. caused by defects in the road surface, which temporarily affect the rotational speed of the crankshaft.
In order to overcome these drawbacks, US-5109825 devised t:o measure the fluctuations in time of the pressure of the engine exhaust gas. Though pressure sensors available on the market are very accurate and provide a response almost in real time, the known processes for detecting the misfire on the basis of the measurement of the pressure fluctuations in the exhaust gas are still very inaccurate and poorly reliable, particularly when applied to engines with a high number of cylinders.
Therefore the object of the present invention is to provide a process for detecting the misfire which is free from the above-mentioned drawbacks.
Another object of the present invention is to provide a system which carnes out s<~id process.
" CA 02320082 2005-06-06 These objects are achieved by means of a process and a system in which a misfire is identified from the analysis in the frequency domain of a signal obtained by sampling the exhaust gas pressure.
Thanks to the sampling and the subsequent frequency analysis of the pressure values detected in the exhaust pipes, the process according to the present invention provides a higher accuracy and reliability with respect to prior art processes. In fact, if the engine firing is regular, the periodical openings of the cylinder exhaust valves generate pressure pulses in the exhaust pipes having the same periodicity and similar waveforms. On the contrary, in the case of misfire in one of the cylinders, the corresponding pressure pulse is changed, thus changing the periodical pattern of the pressure values. The reference for the synchronization with the pulse frequency is readily derivable from the sensors detecting the rotational speed of the crankshaft and/or camshaft.
Another advantage of the process according to the present invention is that through the frequency analysis of the sampled signal it is possible to determine whether only one or more misfires occurred during a single engine cycle. In fact, the amplitude of the modulus of the various harmonics of the sampled signal depends on the number of cylinders wherein the misfire occurred.
A further advantage of the process according to the present invention is that through the frequency analysis of the sampled signal it is possible to determine not only the misfire, but also the position of the cylinder where it occurred. In fact, the knowledge of the cylinder firing sequence and the comparison of the ph~~se of the first harmonic of the sampled signal with the phase of the first cylinder provide a phase difference which indicates the position of the cylinder where the misfire occurred.
These and other advantages and characteristics of the process and system according to the present invention will be clear to those skilled in the art from the following detailed description of an embodiment thereof, with reference to the annexed drawings wherein:
- Figure 1 shows a diagrammatic view of the system according to the present invention;
- Figure 2 shows a flow chart of the process according to the present invention;
- Figures 3a, 3b and 3c show three diagrams of the pressure as a function of the crankshaft rotation;
- Figures 4a, 4b and 4c show otlier tliree diagrams of the pressure as a fiuection of the cr aeikshaft rotation;
- Figures Sa, Sb and Sc show three diagrams of the misfire index as a functivu of the number of engine cycles;
- Figure 6 shows a Fourier transform of the diagram of figwe 3 a; and - Figures 7a, 7b and 7c show three diagrams in polar coordinates of the main harmonic of the pressure in the diagrams of figures 3a, 3b and 3c.
With reference to figure 1, there is seen flint the system according to the present invention includes in a known manner a control unit 1 (indicated by a dotted line ) wliich in turn includes a pair of mutually connected electronic controllers 2.
2' eacle of wliich provides the control over one of two rows of cylinders 3, 3' of the engine. lie the present embodiment tliere is described a V 12 engine leaving two rows of six cylinders 3, 3' eacli, but in other embodiments the number of cylinders and/or rows may obviously change. The controllers 2, 2' are connected in a known mameer to a pair of coolant temperature sensors 4, 4' and to two pairs of sensors 5, 5' and 6, 6' respectively detecting the temperature and pressure ofthe air in the intake manifolds 7, 7'. The controllers 2, 2' are also connected to a pair of lambda sensors 8, 8' for analyzing the oxygen content in the exliaust pipes 9, 9', to two series of injectors 10, 10' whicli inject flee fuel into the intake pipes 11, 11' of the cylinders 3, 3', as weU as to a pair of ignition coils 12, 12'. Tlie exliaust pipes 9, 9' are preferably provided also witli a pair of temperature sensors 13, 13' connected to the controllers 2, 2'.
The system according to the present embodiment of the invention suitably includes a sensor 14 detecting the rotational speed of the fly wheel 15 integral wide the crankshaft and a fiuther pair of sensors 16, 16' detecting the rotation of the camshaft 17. These sensors 14, 16 and 16' are connected to the controllers 2, 2' so flint the latter, ou the basis of the received data, can calculate in real time the speed and angle of r otation of the cranksliaft during an engine cycle. Tlie presence of flee sensors 1 ~, 16 and 16' is made necessary by the fact flint the fly-wheel 15 in a four-stroke engine 30 makes two revolutions (720°) per cycle, wliereby the reference provided by the sensors 16, 16' allows to distinguisli the first revolution from the second one.
ENGINE AND SYSTEM FOR CARRYING OUT SAID PROCESS"
The present invention relates to a process for detecting a misfire in an internal combustion engine, and in particular a process which can be used for detecting a misfire in one or more cylinders of an internal combustion engine. The present invention also relates to a system for carrying out said process.
It is known that in order to monitor the performance of an internal combustion engine, in particular a racing engine with a high number of cylinders, it is desirable to detect the occurrence of the misfire of the fuel mixture in ane or more cylinders. A
process for carrying out said detection, which is known from US-5576963 and presently plays an important role with respect to the ever stricter rules for the control of polluting exhausts, consists of measuring the sudden fluctuations in the rotational speed of the crankshaft by means of an electronic sensor located close to the fly-wheel.
This sensor is connected to the control unit positioned inside the car, which receives all the data concerning the engine and transmitted by suitable sensors. By calculating the fluctuations in the speed according to the delivered torque it is possible to identify a possible misfire in one cylinder of the engine. However, this process does not allow to precisely identify in which cylinder the misfire occurred and moreover has a quite high error probability, particularly in the case of the traveling car being subjected to sharp oscillations, e.g. caused by defects in the road surface, which temporarily affect the rotational speed of the crankshaft.
In order to overcome these drawbacks, US-5109825 devised t:o measure the fluctuations in time of the pressure of the engine exhaust gas. Though pressure sensors available on the market are very accurate and provide a response almost in real time, the known processes for detecting the misfire on the basis of the measurement of the pressure fluctuations in the exhaust gas are still very inaccurate and poorly reliable, particularly when applied to engines with a high number of cylinders.
Therefore the object of the present invention is to provide a process for detecting the misfire which is free from the above-mentioned drawbacks.
Another object of the present invention is to provide a system which carnes out s<~id process.
" CA 02320082 2005-06-06 These objects are achieved by means of a process and a system in which a misfire is identified from the analysis in the frequency domain of a signal obtained by sampling the exhaust gas pressure.
Thanks to the sampling and the subsequent frequency analysis of the pressure values detected in the exhaust pipes, the process according to the present invention provides a higher accuracy and reliability with respect to prior art processes. In fact, if the engine firing is regular, the periodical openings of the cylinder exhaust valves generate pressure pulses in the exhaust pipes having the same periodicity and similar waveforms. On the contrary, in the case of misfire in one of the cylinders, the corresponding pressure pulse is changed, thus changing the periodical pattern of the pressure values. The reference for the synchronization with the pulse frequency is readily derivable from the sensors detecting the rotational speed of the crankshaft and/or camshaft.
Another advantage of the process according to the present invention is that through the frequency analysis of the sampled signal it is possible to determine whether only one or more misfires occurred during a single engine cycle. In fact, the amplitude of the modulus of the various harmonics of the sampled signal depends on the number of cylinders wherein the misfire occurred.
A further advantage of the process according to the present invention is that through the frequency analysis of the sampled signal it is possible to determine not only the misfire, but also the position of the cylinder where it occurred. In fact, the knowledge of the cylinder firing sequence and the comparison of the ph~~se of the first harmonic of the sampled signal with the phase of the first cylinder provide a phase difference which indicates the position of the cylinder where the misfire occurred.
These and other advantages and characteristics of the process and system according to the present invention will be clear to those skilled in the art from the following detailed description of an embodiment thereof, with reference to the annexed drawings wherein:
- Figure 1 shows a diagrammatic view of the system according to the present invention;
- Figure 2 shows a flow chart of the process according to the present invention;
- Figures 3a, 3b and 3c show three diagrams of the pressure as a function of the crankshaft rotation;
- Figures 4a, 4b and 4c show otlier tliree diagrams of the pressure as a fiuection of the cr aeikshaft rotation;
- Figures Sa, Sb and Sc show three diagrams of the misfire index as a functivu of the number of engine cycles;
- Figure 6 shows a Fourier transform of the diagram of figwe 3 a; and - Figures 7a, 7b and 7c show three diagrams in polar coordinates of the main harmonic of the pressure in the diagrams of figures 3a, 3b and 3c.
With reference to figure 1, there is seen flint the system according to the present invention includes in a known manner a control unit 1 (indicated by a dotted line ) wliich in turn includes a pair of mutually connected electronic controllers 2.
2' eacle of wliich provides the control over one of two rows of cylinders 3, 3' of the engine. lie the present embodiment tliere is described a V 12 engine leaving two rows of six cylinders 3, 3' eacli, but in other embodiments the number of cylinders and/or rows may obviously change. The controllers 2, 2' are connected in a known mameer to a pair of coolant temperature sensors 4, 4' and to two pairs of sensors 5, 5' and 6, 6' respectively detecting the temperature and pressure ofthe air in the intake manifolds 7, 7'. The controllers 2, 2' are also connected to a pair of lambda sensors 8, 8' for analyzing the oxygen content in the exliaust pipes 9, 9', to two series of injectors 10, 10' whicli inject flee fuel into the intake pipes 11, 11' of the cylinders 3, 3', as weU as to a pair of ignition coils 12, 12'. Tlie exliaust pipes 9, 9' are preferably provided also witli a pair of temperature sensors 13, 13' connected to the controllers 2, 2'.
The system according to the present embodiment of the invention suitably includes a sensor 14 detecting the rotational speed of the fly wheel 15 integral wide the crankshaft and a fiuther pair of sensors 16, 16' detecting the rotation of the camshaft 17. These sensors 14, 16 and 16' are connected to the controllers 2, 2' so flint the latter, ou the basis of the received data, can calculate in real time the speed and angle of r otation of the cranksliaft during an engine cycle. Tlie presence of flee sensors 1 ~, 16 and 16' is made necessary by the fact flint the fly-wheel 15 in a four-stroke engine 30 makes two revolutions (720°) per cycle, wliereby the reference provided by the sensors 16, 16' allows to distinguisli the first revolution from the second one.
In order to carry out the process according to the present invention, iu~ the two exliaust pipes 9, 9' there are properly arranged two liigli-precision pressure sensors 18, 18' connected to the controllers 2, 2', said sensors transmitting in real time au electric signal whose voltage is proportional to the measured pressure. Furtliervnore, the controllers 2, 2' are connected to a pair of warning lights 19, 19' positioned inside the car, to a port 20 for the connection to an external processor, as well as to a sensor 21 detecting the position of the engine throttle 22.
Referring now to figure 2, there is seen tliat the process according to the present invention includes, after a certain period of time from the engine start, a first step of periodical check, e.g. each second, of the engine running state. In fact, iu order to obtain reliable results from the process, it is preferable tliat the latter be carried out only if some engine parameters are within a preset range of values. Iu particular, the process according to the present invention is activated only wlieu the coolant temperature measured by sensors 4, 4', the air temperature measured by sensors 5, 5' and the au' pressure measured by sensors 6, 6' in the manifolds 7, 7' are above certain thresholds stored in the memory of the controllers 2, 2'. Moreover, these conta~ollers clieck tliat the revolutions per minute (rpm) detected by sensor 14 are within a preset range of values.
Table 1 hereunder shows an example of values meeting the conditions for the start of the process.
Minimum number of revolutions 990 rpm ~
Maximum number 7550 rpm of revolutions State check period 1 s Delay from engine start 10 s Minimum coolant temperature 20 C
Minimum air temperature 20 C
Minimum absolute pressure in manifolds250 mmHg 7, 7' Table 1: start conditions A fiutlier condition for starting the process may be reaching a certain opening of the tlu~ottle 22 as detected by sensor 21.
If the conditions above are met, at the beginning of an engine cycle, corresponding to a certain position of the camshaft 17 as detected by sensors 16, 16', the controllers 2, 2' start sampling the electric signals transmitted by sensors 18, 18' and proportional to the pressure inside the exliaust pipes 9, .9'. These analogue signals are converted in a known manner into digital form and tlien stored in a buffer memory within each controller 2, 2'. The sampling frequency is suitably synchronized witli the rotational speed of the fly-wheel 15 as detected by sensor 14, so tliat at the end of the engine cycle, detected tlirougli sensors 16 and 16', tliere is stored a preset nmuber, e.g. 64, of pressure samples. Though the response of the pressure sensors 18, 18' is almost immediate, in order to synchronize precisely witli the engine, the controllers 2, 2' take into account the lag, almost constant, caused by the time required by the pressure pulse to travel from the exhaust valves of the cylinders 3, 3' to the pressure sensors 18, 18' along the exhaust pipes 9, 9'. Thanks to the temperature sensors 13, 13' it is possible to compensate for the very small fluctuations in said lag caused by the fluctuations in the temperature within the pipes 9, 9'.
After liaving been sampled, the presswe values corresponding to au engine cycle are processed by the controllers 2, 2' which, at the same time, sample another series of pressure values which are stored in a further buffer memory for a subsequent processing.
Referring now to figure 2, there is seen tliat the process according to the present invention includes, after a certain period of time from the engine start, a first step of periodical check, e.g. each second, of the engine running state. In fact, iu order to obtain reliable results from the process, it is preferable tliat the latter be carried out only if some engine parameters are within a preset range of values. Iu particular, the process according to the present invention is activated only wlieu the coolant temperature measured by sensors 4, 4', the air temperature measured by sensors 5, 5' and the au' pressure measured by sensors 6, 6' in the manifolds 7, 7' are above certain thresholds stored in the memory of the controllers 2, 2'. Moreover, these conta~ollers clieck tliat the revolutions per minute (rpm) detected by sensor 14 are within a preset range of values.
Table 1 hereunder shows an example of values meeting the conditions for the start of the process.
Minimum number of revolutions 990 rpm ~
Maximum number 7550 rpm of revolutions State check period 1 s Delay from engine start 10 s Minimum coolant temperature 20 C
Minimum air temperature 20 C
Minimum absolute pressure in manifolds250 mmHg 7, 7' Table 1: start conditions A fiutlier condition for starting the process may be reaching a certain opening of the tlu~ottle 22 as detected by sensor 21.
If the conditions above are met, at the beginning of an engine cycle, corresponding to a certain position of the camshaft 17 as detected by sensors 16, 16', the controllers 2, 2' start sampling the electric signals transmitted by sensors 18, 18' and proportional to the pressure inside the exliaust pipes 9, .9'. These analogue signals are converted in a known manner into digital form and tlien stored in a buffer memory within each controller 2, 2'. The sampling frequency is suitably synchronized witli the rotational speed of the fly-wheel 15 as detected by sensor 14, so tliat at the end of the engine cycle, detected tlirougli sensors 16 and 16', tliere is stored a preset nmuber, e.g. 64, of pressure samples. Though the response of the pressure sensors 18, 18' is almost immediate, in order to synchronize precisely witli the engine, the controllers 2, 2' take into account the lag, almost constant, caused by the time required by the pressure pulse to travel from the exhaust valves of the cylinders 3, 3' to the pressure sensors 18, 18' along the exhaust pipes 9, 9'. Thanks to the temperature sensors 13, 13' it is possible to compensate for the very small fluctuations in said lag caused by the fluctuations in the temperature within the pipes 9, 9'.
After liaving been sampled, the presswe values corresponding to au engine cycle are processed by the controllers 2, 2' which, at the same time, sample another series of pressure values which are stored in a further buffer memory for a subsequent processing.
Tliis processing carried out by each processor of the controllers 2, 2' suitably includes an aua.lysis in the frequency domain, and iu particular a Fourier transform of the sampled signal, tlirougli whicli tliere are obtained two series of coeffcients cowesponding to the real pan and the imaginary part of the frost harmonics of the signal. In particular, iu the present embodiment there are calculated the coel~cients of the first 32 liarmonics of the sampled signal, but in other embodiments it is obviously possible to calculate a different number of harmonics according to the needs.
These coefficients are used to calculate iu a known way the modulus of the :frost harmonics, e.g. the first three, and then, by combining the values of these moduli, to obtain au index which allows to detect a misfire in one or more of the cylinders 3, 3'.
This misfire index can be calculated in various ways, e.g. by adding or multiplying the moduli of the hamnonics. Prior to tliis addition or multiplication, the moduli may possibly be multiplied or raised to a power with a different coeff cient for each liarmonic, so as to obtain a weighed addition or multiplication. In the present embodiment, the misfire index is calculated by simply adding the moduli of the first three harmonics.
Once said index has been calculated, it is compared with preset tliresliold values stored in the controllers 2, 2'. Table 2 hereunder shows an example of threshold values of the misfire index experimentally obtained as a function of the engine rpm detected by sensor 14 and of the pressure in the manifolds 7, 7' as detected by sensors 6, 6'.
rpm mmHg ~. ~
Table 2: Threshold values of the misfire index The controller 2 or 2' whicli detects the exceeding of said threshold, iuclicates _7_ tlirough the warning light 19 or 19' that a misfire occurred in the corresponding row of cylinders 3 or 3'.
At this moment, the controller 2 or 2' which detected the misfire preferably compares the modulus of each of the first three harmonics with preset thresliold values 5 also stored as a function of the engine rpm and of the pressure in the corresponding manifold 7 or 7'. If all tliree moduli are witliin a range of values between a muiimum thresliold and a maximum tliresliold, a single misfwe is detected, i.e. a misfire occurred in one only of the cylinders 3 or 3', otlierwise a multiple misfire is detected, i.e. a misfire occurred iu at least two of the cylinders 3 or 3' belonging to a row.
10 Tlie following tables 3.1, 3.2, 4.1, 4.2, 5.1 and 5.2 show examples of ~ruuimun~
values and amplitudes of the tlireshold ranges for the moduli of the first tln~ee harmonics.
__ rpm mmHg ~ ~.
15 Table 3.1: Minimum threshold values for the modulus of the first liarmonic rpm mmHg .~ ~.
Table 3.2: Range amulitude for the modulus of the first liarmonic _g_ rpm mmHg ~ ~.
Table 4.1: Minimum tlireshold values for the modulus of the second harmonic _ rpm mmHg ~- ~
GOOU
Table 4.2: Rank litude for the modulus of the second harmonic rpm mmHg ~ ~.
Table 5.1: Minimum thresliold values for the modulus of the third liarmonic rpm mmHg ~ ~
Table 5.2: Range amulitude for the modulus of the third liarmonic 5 If a misfire is detected in only one of the six cylinders 3 or 3', the relevant controller 2 or 2' can determine the position of the cylinder wliere the misfire occurred by first calculating iu a known manner the plisse of the first harmonic.
Tliereafter, by subtracting the phase of the first liarmonic from the plisse of the first cylinder of the engine cycle, stored iu the controllers 2, 2' by means of a table as a function of the engine rpm, there is obtained a phase difference wliicli approximately cowesponds to the phase of the cylinder wliere the misfire occurred.
For example, if at given engine rpm the phase of the first cylinder of the engine cycle is 210°, a misfire occurred in the first, second, third, fourth, fifth or si.~ctla cylinder in firing order when the phase of the first liarmonic is respectively between 180° and 15 240°, 120° and 180°, 60° and 120°, 0° and 60°, 300° and 360° or 240° and 300°.
Table 6 hereunder sliows the relationship between the engine rpm and the phase of the first cylinder in order to determine the position of the cylinder where the misfire occurred.
rpm phase Table 6: relationship between engine rpm and phase of the first cylinder Each detection of a misfn~e in one of the engine cylinders, as well as the corresponding cylinder position in case of single misfire, is stored in suitable counters in the memory of controllers 2, 2'. Tliis memory can be read througli port 20 by an external processor during the car servicing, so as to diagnose possible engine failures.
Referring now to figures 3a to 3c, there is seen, tlirough measurements made in experimental tests where misfires were caused in the tested engine, liow the signal transmitted by sensors 18, 18' clianges as a function of the misfire in one of the cylinders 3, 3'. In particular, figure 3a sliows that at about 2000 rpm witli an engine load around 15%, the voltage (given in Volts) at the terminals of the pressure sensors 18, 18' proportional to the pressure in the exliaust pipes 9, 9' is almost regular with six periodical oscillations during au engine cycle (indicated by the cranksliaft rotation angle fi~om -180° to 540°). This voltage is indicated by a thin line, whereas a tliick line indicates the voltage in the case of misfire in the first cylinder. In this case, it is clearly seen tliat the voltage pattern has a first ii~~egularity around 240°
and a second irregularity around 480°. However, figure 3b sliows that at about 4000 rpm with an engine load approximately at 100%, the voltage pattern iu case of regular firv~g is more complicated witli respect to the preceding case. Nonetlieless, the voltage pattern in case of misfire iu the first cylinder (still indicated by the tliick lice) moves away around 400° fiom the regular fn7ug voltage pattern (still indicated by the thin line).
Also figure 3c shows tliat at about 6000 rpm with an engine load approximately at 100%, the voltage pattern of the pressure sensors 18, 18' is different in the case of misfwe in the ~u~st cylinder, in particular around 470°.
Similarly, with reference to figures 4a to 4c, tliere is seen, still. tlirough measurements made in experimental tests, vow the signal transmitted by the pressure sensors 18, 18' clianges as a fimction of the misfire v~ one of the cylinders 3, 3', regardless of the misfire being caused by a lack of fuel injection or ignition in the cylinder. In fact, tliere is seen tliat the voltage pattern in case of lack of injection (indicated by the thick line) is substantially equal to the voltage pattern in case of lack of ignition (indicated by the dotted line). This correspondence can be found both at low rpm, i.e. at about 2000 rpm with an engine load around 15% (figure 4a), at intermediate rpm, i.e. at about 4000 rpm with an engine load around 55%
(figure 4b), and at liigli rpm, i.e. at about 6000 rpm with an engine load approximately at 100%
(figure 4c).
Referring now to figures 5a to 5c, there is seen tliat the misfire index measured as a function on the engine cycles (indicated on the horizontal axis) sliows readily detectable peaks, whicli correspond to the moments when a misfire was expei~uentally caused in one oftlie engine cylinders. This can be found botli at low rpm, i.e. at about 1000 rpm witli an engine load around 15% {figure 5a), at intermediate ipnn, i.e. at about 3000 rpm witli an engine load around 55% (figure Sb), and at liigli rpm, i.e. at about 5000 rpm witli an engine load approximately at 100% (figure 5c).
Witli reference to figure 6, there is seen tliat the modulus of the first ten liarmonics of the signal (in Volts) transmitted by sensors 18, 18' clianges duite apparently from the case of regular firing iu all cylinders (indicated by the wliite bars) to the case of misfwe in the first cylinder {indicated by the grey bars). Tlie figure shows the modulus of the first ten hamnonics calculated with the engine at 2000 ihm and a load around 15%, i.e. the case sliown in figure 3a and figure 4a. Tlie figure clearly 5 sliows tliat in the case of regular fn-ing the modulus of the sixtli harmonic is much higlier tlian au otlier moduli, whereas in the case of misfwe in the first cylinder there is also a significant contribution of the moduli of the first liarmonics, iu particular of the first three. It is clear tliat the contribution of the modulus of eacli liarmonic depends on some factors whicli have to be considered wlien setting the tliresliold values of the misfire index. These factors include, for example, the shape of the exhaust pipes 9, 9', the number and the firing sequence of the cylinders 3, 3' of each row.
Finally refernng to figures 7a to 7c, there is seen that the phase of the fwst liarmonic changes as a function of the position of the cylinder where th.e misfire occurred. In fact, it is possible to identify six separate' areas, each area corresponding 15 to an engine cylinder, where the polar coordinates of the modulus and phase of the first liai7nonic at the moment of the misfire are concentrated. In pairticular, there is seen tliat said coordinates concentrate in six sectors having an extension of 60° each, wliose sequence is defined by the cylinder firing sequence, which in the present embodiment is 1-4-2-6-3-5 for the row of cylinders 3. Taking into account the engine 20 pliase, this correspondence can be found botli at low rpm, i.e. at about 2000 rpm with an engine load around 15% (figure 7a), at intermediate rpm, i.e. at about 4000 rpm witli an engine load approximately at 100% (figure 7b), and at high rpm, i.e.
at about 6000 rpm with an engine load approximately at 100% (figu.re 7c).
Possible additions and/or modifications may be made by tliose skilled in the art 25 to the above-described and illustrated embodiment, yet witliout departing from the scope of the invention. In fact it is obvious tliat the type of sampling, frequency analysis and particularly the method for calculating the misfwe index may cliange according to the type of engine to be monitored. Similarly, also the threshold values may cliange according to the experimental tests carried out on each type of engine.
30 Finally, it is obvious tliat the process according to the present invention can be used iu combination witli one or more prior art processes.
These coefficients are used to calculate iu a known way the modulus of the :frost harmonics, e.g. the first three, and then, by combining the values of these moduli, to obtain au index which allows to detect a misfire in one or more of the cylinders 3, 3'.
This misfire index can be calculated in various ways, e.g. by adding or multiplying the moduli of the hamnonics. Prior to tliis addition or multiplication, the moduli may possibly be multiplied or raised to a power with a different coeff cient for each liarmonic, so as to obtain a weighed addition or multiplication. In the present embodiment, the misfire index is calculated by simply adding the moduli of the first three harmonics.
Once said index has been calculated, it is compared with preset tliresliold values stored in the controllers 2, 2'. Table 2 hereunder shows an example of threshold values of the misfire index experimentally obtained as a function of the engine rpm detected by sensor 14 and of the pressure in the manifolds 7, 7' as detected by sensors 6, 6'.
rpm mmHg ~. ~
Table 2: Threshold values of the misfire index The controller 2 or 2' whicli detects the exceeding of said threshold, iuclicates _7_ tlirough the warning light 19 or 19' that a misfire occurred in the corresponding row of cylinders 3 or 3'.
At this moment, the controller 2 or 2' which detected the misfire preferably compares the modulus of each of the first three harmonics with preset thresliold values 5 also stored as a function of the engine rpm and of the pressure in the corresponding manifold 7 or 7'. If all tliree moduli are witliin a range of values between a muiimum thresliold and a maximum tliresliold, a single misfwe is detected, i.e. a misfire occurred in one only of the cylinders 3 or 3', otlierwise a multiple misfire is detected, i.e. a misfire occurred iu at least two of the cylinders 3 or 3' belonging to a row.
10 Tlie following tables 3.1, 3.2, 4.1, 4.2, 5.1 and 5.2 show examples of ~ruuimun~
values and amplitudes of the tlireshold ranges for the moduli of the first tln~ee harmonics.
__ rpm mmHg ~ ~.
15 Table 3.1: Minimum threshold values for the modulus of the first liarmonic rpm mmHg .~ ~.
Table 3.2: Range amulitude for the modulus of the first liarmonic _g_ rpm mmHg ~ ~.
Table 4.1: Minimum tlireshold values for the modulus of the second harmonic _ rpm mmHg ~- ~
GOOU
Table 4.2: Rank litude for the modulus of the second harmonic rpm mmHg ~ ~.
Table 5.1: Minimum thresliold values for the modulus of the third liarmonic rpm mmHg ~ ~
Table 5.2: Range amulitude for the modulus of the third liarmonic 5 If a misfire is detected in only one of the six cylinders 3 or 3', the relevant controller 2 or 2' can determine the position of the cylinder wliere the misfire occurred by first calculating iu a known manner the plisse of the first harmonic.
Tliereafter, by subtracting the phase of the first liarmonic from the plisse of the first cylinder of the engine cycle, stored iu the controllers 2, 2' by means of a table as a function of the engine rpm, there is obtained a phase difference wliicli approximately cowesponds to the phase of the cylinder wliere the misfire occurred.
For example, if at given engine rpm the phase of the first cylinder of the engine cycle is 210°, a misfire occurred in the first, second, third, fourth, fifth or si.~ctla cylinder in firing order when the phase of the first liarmonic is respectively between 180° and 15 240°, 120° and 180°, 60° and 120°, 0° and 60°, 300° and 360° or 240° and 300°.
Table 6 hereunder sliows the relationship between the engine rpm and the phase of the first cylinder in order to determine the position of the cylinder where the misfire occurred.
rpm phase Table 6: relationship between engine rpm and phase of the first cylinder Each detection of a misfn~e in one of the engine cylinders, as well as the corresponding cylinder position in case of single misfire, is stored in suitable counters in the memory of controllers 2, 2'. Tliis memory can be read througli port 20 by an external processor during the car servicing, so as to diagnose possible engine failures.
Referring now to figures 3a to 3c, there is seen, tlirough measurements made in experimental tests where misfires were caused in the tested engine, liow the signal transmitted by sensors 18, 18' clianges as a function of the misfire in one of the cylinders 3, 3'. In particular, figure 3a sliows that at about 2000 rpm witli an engine load around 15%, the voltage (given in Volts) at the terminals of the pressure sensors 18, 18' proportional to the pressure in the exliaust pipes 9, 9' is almost regular with six periodical oscillations during au engine cycle (indicated by the cranksliaft rotation angle fi~om -180° to 540°). This voltage is indicated by a thin line, whereas a tliick line indicates the voltage in the case of misfire in the first cylinder. In this case, it is clearly seen tliat the voltage pattern has a first ii~~egularity around 240°
and a second irregularity around 480°. However, figure 3b sliows that at about 4000 rpm with an engine load approximately at 100%, the voltage pattern iu case of regular firv~g is more complicated witli respect to the preceding case. Nonetlieless, the voltage pattern in case of misfire iu the first cylinder (still indicated by the tliick lice) moves away around 400° fiom the regular fn7ug voltage pattern (still indicated by the thin line).
Also figure 3c shows tliat at about 6000 rpm with an engine load approximately at 100%, the voltage pattern of the pressure sensors 18, 18' is different in the case of misfwe in the ~u~st cylinder, in particular around 470°.
Similarly, with reference to figures 4a to 4c, tliere is seen, still. tlirough measurements made in experimental tests, vow the signal transmitted by the pressure sensors 18, 18' clianges as a fimction of the misfire v~ one of the cylinders 3, 3', regardless of the misfire being caused by a lack of fuel injection or ignition in the cylinder. In fact, tliere is seen tliat the voltage pattern in case of lack of injection (indicated by the thick line) is substantially equal to the voltage pattern in case of lack of ignition (indicated by the dotted line). This correspondence can be found both at low rpm, i.e. at about 2000 rpm with an engine load around 15% (figure 4a), at intermediate rpm, i.e. at about 4000 rpm with an engine load around 55%
(figure 4b), and at liigli rpm, i.e. at about 6000 rpm with an engine load approximately at 100%
(figure 4c).
Referring now to figures 5a to 5c, there is seen tliat the misfire index measured as a function on the engine cycles (indicated on the horizontal axis) sliows readily detectable peaks, whicli correspond to the moments when a misfire was expei~uentally caused in one oftlie engine cylinders. This can be found botli at low rpm, i.e. at about 1000 rpm witli an engine load around 15% {figure 5a), at intermediate ipnn, i.e. at about 3000 rpm witli an engine load around 55% (figure Sb), and at liigli rpm, i.e. at about 5000 rpm witli an engine load approximately at 100% (figure 5c).
Witli reference to figure 6, there is seen tliat the modulus of the first ten liarmonics of the signal (in Volts) transmitted by sensors 18, 18' clianges duite apparently from the case of regular firing iu all cylinders (indicated by the wliite bars) to the case of misfwe in the first cylinder {indicated by the grey bars). Tlie figure shows the modulus of the first ten hamnonics calculated with the engine at 2000 ihm and a load around 15%, i.e. the case sliown in figure 3a and figure 4a. Tlie figure clearly 5 sliows tliat in the case of regular fn-ing the modulus of the sixtli harmonic is much higlier tlian au otlier moduli, whereas in the case of misfwe in the first cylinder there is also a significant contribution of the moduli of the first liarmonics, iu particular of the first three. It is clear tliat the contribution of the modulus of eacli liarmonic depends on some factors whicli have to be considered wlien setting the tliresliold values of the misfire index. These factors include, for example, the shape of the exhaust pipes 9, 9', the number and the firing sequence of the cylinders 3, 3' of each row.
Finally refernng to figures 7a to 7c, there is seen that the phase of the fwst liarmonic changes as a function of the position of the cylinder where th.e misfire occurred. In fact, it is possible to identify six separate' areas, each area corresponding 15 to an engine cylinder, where the polar coordinates of the modulus and phase of the first liai7nonic at the moment of the misfire are concentrated. In pairticular, there is seen tliat said coordinates concentrate in six sectors having an extension of 60° each, wliose sequence is defined by the cylinder firing sequence, which in the present embodiment is 1-4-2-6-3-5 for the row of cylinders 3. Taking into account the engine 20 pliase, this correspondence can be found botli at low rpm, i.e. at about 2000 rpm with an engine load around 15% (figure 7a), at intermediate rpm, i.e. at about 4000 rpm witli an engine load approximately at 100% (figure 7b), and at high rpm, i.e.
at about 6000 rpm with an engine load approximately at 100% (figu.re 7c).
Possible additions and/or modifications may be made by tliose skilled in the art 25 to the above-described and illustrated embodiment, yet witliout departing from the scope of the invention. In fact it is obvious tliat the type of sampling, frequency analysis and particularly the method for calculating the misfwe index may cliange according to the type of engine to be monitored. Similarly, also the threshold values may cliange according to the experimental tests carried out on each type of engine.
30 Finally, it is obvious tliat the process according to the present invention can be used iu combination witli one or more prior art processes.
Claims (15)
1. A process for detecting a misfire in one or more cylinders (3,3') of an internal combustion engine, characterized in that it includes the following operative steps:
- generating a sampled signal by sampling an exhaust gas pressure during at least one engine cycle at a sampling frequency proportional to rotational speed of a crankshaft;
- analyzing said sampled signal in the frequency domain;
- calculating a misfire index from said analysis;
- comparing said index with at least one threshold value; and - identifying a misfire based on said comparison of said index with said at least one threshold value.
- generating a sampled signal by sampling an exhaust gas pressure during at least one engine cycle at a sampling frequency proportional to rotational speed of a crankshaft;
- analyzing said sampled signal in the frequency domain;
- calculating a misfire index from said analysis;
- comparing said index with at least one threshold value; and - identifying a misfire based on said comparison of said index with said at least one threshold value.
2. A process according to claim 1, characterized in that said frequency domain analysis includes a Fourier transform of the sampled signal.
3. A process according to claim 2, characterized in that the calculation of the misfire index includes the combination of the modulus of some harmonics of the sampled signal.
4. A process according to claim 3, characterized in that the calculation of the misfire index includes the addition of the modulus of at least the first three harmonics of the sampled signal.
5. A process according to any one of claims 1 to 4, characterized in that the sampling of the pressure values is started at the beginning of an engine cycle.
6. A process according to any one of claims 1 to 5, characterized in that it includes the comparison of the modulus of at least one harmonic of the sampled signal with one or more threshold values.
7. A process according to claim 6, characterized in that it includes the calculation of the phase of the first harmonic of the sampled signal, and the calculation of the difference between said phase and the phase of at least one engine cylinder (3,3').
8. A system for carrying out the process according to any one of claims 1 to 7, characterized in that it includes at least one sensor (18,18') detecting the pressure in the exhaust pipes (9,9') and at least one sensor (14) detecting the crankshaft rotation, said sensors (14, 18, 18') being connected to at least one control unit (1,2,2') including means for the analogue-to-digital conversion of the electric signal transmitted by the sensor (18, 18') detecting the pressure in the exhaust pipes (9, 9'), means for sampling the signal converted into digital form, memory means for storing the sampled signal, as well as means for analyzing the sampled signal in the frequency domain, calculating a misfire index as a function of the results of said analysis and comparing said index with one or more threshold values.
9. A system according to claim 8, characterized in that it includes at least one sensor (16,16') detecting the camshaft (17) rotation.
10. A system according to claim 8 or 9, characterized in that it comprises means for controlling the sampling frequency of said sampling means according to the signal transmitted by the sensor (14) detecting the crankshaft rotation.
11. A system according to any one of claims 8 to 10, characterized in that it comprises at least one sensor (4, 4') detecting the coolant temperature, and at least two sensors (5, 5', 6, 6') respectively detecting the temperature and pressure of the air in the intake manifolds (7, 7'), said sensors (4, 4', 5, 5', 6, 6') being connected to said control unit (1, 2, 2').
12. A system according to any one of claims 8 to 11, characterized in that it comprises at least one warning light (19, 19') indicating a misfire in at least one engine cylinder, said warning light (19, 19') being connected to said control unit (1, 2, 2').
13. A system according to any one of claims 8 to 12, characterized in that it comprises a sensor (21) detecting the position of the engine throttle (22), said sensor (21) being connected to said control unit (1, 2, 2').
14. A system according to any one of claims 8 to 13, characterized in that it comprises at least one sensor (13, 13') detecting the temperature in the exhaust pipes (9, 9'), said sensor (13, 13') being connected to said control unit (1, 2, 2').
15. A car characterized in that it includes a system according to any one of claims 8 to 14 for detecting a misfire in one or more engine cylinders (3, 3').
Applications Claiming Priority (3)
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IT98MI000363A IT1298944B1 (en) | 1998-02-24 | 1998-02-24 | PROCEDURE FOR DETECTING FAILED EXPLOSION IN AN INTERNAL COMBUSTION ENGINE AND SYSTEM THAT PERFORMS THIS |
ITMI98A000363 | 1998-02-24 | ||
PCT/IT1998/000233 WO1999044028A1 (en) | 1998-02-24 | 1998-08-17 | Process for detecting a misfire in an internal combustion engine and system for carrying out said process |
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US5935189A (en) * | 1997-12-31 | 1999-08-10 | Kavlico Corporation | System and method for monitoring engine performance characteristics |
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1998
- 1998-02-24 IT IT98MI000363A patent/IT1298944B1/en active IP Right Grant
- 1998-08-17 EE EEP200000490A patent/EE04248B1/en not_active IP Right Cessation
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2000
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2001
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