FR2842871A1 - Method of controlling combustion rates for internal combustion engine involves measuring two operating parameters of combustion only within set range of values - Google Patents

Abstract

The method of controlling combustion rates for an internal combustion engine (10) involves measuring an operating combustion influenced parameter (32) cyclically to determine the combustion rate, within a set measuring rate. The method involves determining a second cyclic parameter which also changes with the combustion rate. The combustion rate is determined only when the result from the second parameter is within a fixed range of values.

Description

Field of the Invention The present invention relates to a method of

  detection of misfire of an internal combustion engine according to which during engine operation, a para5 meter is cyclically determined using a physical measurement method, this parameter, being modified by a misfire, allows conclude that there is a misfire if an operating result of the measurement process is within

  outside or inside a predetermined value range.

  State of the art Misfire during the operation of an internal combustion engine results in an increase in the emission of pollutants and can also damage the catalyst of the vehicle exhaust. To detect misfire, condition to remedy this problem, we currently use

  mainly two engine control methods. These two methods are known: that of measuring the ion current and that of measuring the regularity of operation.

  According to the ion current measurement method, after ignition of the gas mixture in the cylinders of the internal combustion engine, a voltage is applied between the spark plug electrodes and the current generated by this voltage is measured as a parameter. As in the combustion operation, chemical and physical operations produce ionization of the gases and thus an increase in the conductivity of the gas mixture in the combustion chamber, the amplitude and the shape of the measured current make it possible to know whether the cycle of combustion which has just ended gave rise to combustion or not. Methods for measuring the ion current are known, among others according to the

  following documents: DE 196 49 278 Ai, DE 199 53 710 Ai, DE 199 15088 Al, DE 199 45 811 A1.

  As the combustion operation is a very dynamic operation influenced by boundary and variable conditions, it is not always easy to conclude that a misfire with good

detection quality.

  In the operating irregularity measurement method 35, the instantaneous angular velocity of the crankshaft is used as a parameter and from this measurement, a value is deduced from the operating irregularity of the engine. This value is then compared to a threshold

  predetermined to allow the conclusion of the existence of misfires of

  bustion in one of the cylinders. The methods for measuring operating irregularity are described in particular in documents DE 196641 916 Ai, DE 196 27 540 Ai, DE 199 46 873 Ai. Since the regularity of engine operation however also depends on other limiting conditions such as for example the load or the speed of rotation of the engine and that a misfire is also noticeable after the following combustions in the form of crankshaft oscillations , this process does not always make it possible to conclude that the detection quality is high

  of a misfire despite complicated mathematical calculations.

  In particular in engines having a large number of cylinders, the two methods reach the limit of their capacity for example for the detection of multiple misfires or combinations of misfires by the method of measuring irregularity of operation or the detection of a incomplete combustion by the ion current measurement process. As however the conditions fixed by the regulations for the quantity of polluting products emitted become more and more rigorous it is more and more important to obtain a very serious quality of detection. SUMMARY OF THE INVENTION The purpose of the present invention is to solve this problem and to this end relates to a method of the type defined above, characterized in that, using a different, different physical measurement method, it is determined cyclically another parameter which is also changed by a

  misfire, and a burnout 25 is only concluded if the operating result of the other measurement method is also outside or within a range of pre-set value.

  The method according to the invention considerably improves the quality of detection in that a misfire detected by the operation of one of the two methods is compared to a plausibility check by comparing with the result of the other. process; this means that an abnormal operating result from a measurement cycle of a measurement process will only be treated as a misfire if, for a synchronous measurement cycle or close to the other measurement process, a result

  abnormal operation is confirmed.

  According to a preferred development of the invention, for one of the two measurement methods, the procedure is analogous to that of the ion current measurement method in the engine cylinders while

  monitoring the ionic currents and then subjecting them to an exploitation and in that for the other (of the two measurement methods analogous to the method of measuring the regularity of operation), short variations of the rotational speed or speed are determined angular of a com5 posing driven in rotation by the internal combustion engine in particular the crankshaft of the engine because they are then two parameters completely independent of each other and which do not influence each other.

  Only then, if the results of the operation of the two measurement methods lie within or outside the ranges of predetermined measurement values can it be concluded that misfires ignition.

  As one of the two measurement methods is preferably used as the primary method, these measurement values will be determined essentially at each combustion cycle and will be used completely whereas with the other of the two measurement methods, an advantageously secondary method which only serves to confirm the plausibility of the measurement values of the primary method and, where appropriate, these values are not fully exploited if the primary measurement method provides unclear values situated at the limits of the range of predetermined measure or if it does not provide an unequivocal operating result.

  The two methods mentioned above are based on a different principle of operation or physical action, which is advantageous for checking the plausibility. Each of the measurement methods normally has weak points for which the quality of detection is relatively reduced, for example the detection of combinations of misfires in several cylinders by the method of measuring the irregularity of operation or the detection of a incomplete combustion by the ion current measurement process. Under these conditions, operating results are thus obtained which are very difficult to interpret, but in general this is not the case for the other measurement method if it is based on a physically different operating or action principle. Thus the meaning of unclear or unambiguous operating results given by one measurement method can be facilitated by the existence of clear and unequivocal operating results provided by the other method.

  According to another preferred development of the invention, this effect can be used to improve the quality of the detection by laying down more stringent conditions for the operating results of the secondary process by comparison with the state of the art, if the process primary education hardly achieves unclear results. As a realization of the motor control with two different measurement and operating methods, working in parallel would be very complicated both from the point of view of the material and the programs and can only be envisaged with difficulty for cost reasons, a another preferred development of the invention provides for a primary process constituted for example by the process for measuring the ion current which is completed by a secondary process, the measurement and operation of which uses components already fitted to the control of the engine such as sensors or the like, computers or control apparatus such as journey time calculators, interrupt calculators, peripherals or

analogous means.

  This is the case if in the secondary process, according to another preferred development of the invention, using an angle sensor used inter alia to measure the speed of rotation and the control device or the computer of the engine control, the time difference between the start and the end of a selected measurement window in an angular sector of the crankshaft or of another component driven in rotation by the engine is determined in order to be compared with a range of

  predetermined value resulting from normal engine operation.

  This predetermined value range can be a fixed predetermined value range depending on the speed of rotation of the motor or a value range which is calculated from the time differences between the

  start and end of the previous measurement window.

  Another preferred development of the invention provides for using a table of angular references or teeth intervals, this table being recorded in the memory of the engine control computer. This table contains the passage times of the teeth taken by the angle sensor for an angle sector for example of 1200 of the crankshaft and the calculator of which determines the sum to be used to calculate the instantaneous rotation speed of the engine once all the angular sector will have passed the angle sensor and after triggering

of an interruption.

  The start and end of each measurement window must always be located in the angular sector of the crankshaft, the teeth passage times of which are recorded in the table of passage times of tooth passage because this table is replaced by new durations of teeth after a rotation of the crankshaft by 1200. Within the angular sector, however, it is possible to select a duration and a practically any position of the measurement window, which makes it possible for example to modify this window according to the determined limit conditions of engine operation like for example the speed of rotation or the

engine load.

  The duration of the measurement window must however preferably be less than or maximum equal to 3600 divided by the number of cylinders in order to minimize in this way the influence of the contributions to the torque of several cylinders at the angular speed of the crankshaft and mi15 nimize thus the time difference measured between the start and the end of the

measurement window.

  Drawings The present invention will be described below in more detail with the aid of an exemplary embodiment shown in the accompanying drawings in which: - Figure 1 is a diagram of the technical environment of the invention, - the FIG. 2 is a detail view partially cut, on an enlarged scale of part X of FIG. 1, FIG. 3 is a diagram used to describe the operation of two measurement pro25 for the detection of a misfire, - Figure 4 is a schematic presentation of a signal form

  for one of the two methods and an array of time intervals used in this method.

  Description of embodiments

  The internal combustion engine 10 of a motor vehicle shown schematically and partially in Figure 1 comprises several cylinders 12 of which only one is shown. Each cylinder has a piston 14 reciprocating. The piston is connected by a connecting rod 16 to a crankshaft 18. To ignite the car35 burant / air mixture supplied to the cylinder 12, the engine 10 includes an ignition device 20 with an ignition coil 22 connected by lines

  ignition 24 to the spark plugs 26 of the cylinder heads 12.

  To detect misfires, the ignition circuit includes an installation for measuring the ionic current 32 between the secondary winding 30 of the ignition coil 22 and the spark plugs 26. This measurement installation 32 measures the current which is established in each cylinder 12 after the ignition of the fuel / air mixture, when the ignition coil 22 has supplied the electrodes of the spark plug 26 of the cylinder 12 concerned, a high voltage. This current is carried by an ionized gas which develops during combustion in the combustion chamber 34 of the cylinder 12. As it appears in FIGS. 1 and 3, the current measured by the measuring installation 32 is

  applied to a computer 36 of the engine control 38.

  As in the event of ignition failures in the combustion chamber 34 of the cylinder 12 there will be no ionized gas or only very little ionized gas, an ion current or only a very weak current cannot be measured there. If the ion current measured is thus below a predetermined value range, we conclude that there is a possibility of a misfire and the processing circuit 40 of the computer 36 supplies a signal to the AND gate 42. This gate controls a

  fault indicator 44 to display misfires.

  The above description of the current measurement process

  ionic to detect misfire is a very description

  simplified because the precise nature of the process is not of particular interest here. Other particular details and embodiments of such ion current measurement methods will be found in the documents cited in the preamble, namely: DE 196 49 278 Ai, DE 199 53 710 Ai,

DE 199 15 088 Ai, DE 199 45 811 Ai.

  To measure the speed of rotation, the motor 10 comprises a measuring installation composed, in a known manner, of an angle sensor wheel or a speed of rotation 50 integral in rotation with the crankshaft 30 and an angle sensor 48 cooperating inductively with this wheel. This sensor comprises a permanent magnet 52 with a soft iron core 54 and a copper winding 56 as it appears better in FIG. 2. The tone wheel 50 made of magnetic material has a

  outer periphery subdivided into 60 arc segments, equal of which 58 35 segments each carry a tooth 52 projecting in the radial direction.

  The 58 teeth are interrupted at a location by 2 neighboring segments leaving an interval L. When the motor 10 is running, the tone wheel 50 passes in front of the angle sensor 48. As the flanks of the teeth 52 pass, the magnetic flux changes in the soft iron core 54 of the angle sensor

  48 which induces a tension in the winding 56.

  This voltage is applied in the form of an analog voltage signal to a sensor 58 of the computer 36 of the engine control 38 as it appears better in FIG. 3. The signal is then transformed into a digital signal in which the passage of a tooth 52 corresponding to level "1" and between two neighboring teeth there will be level "0". By combining the digital signals obtained we have the curve

  of the signal shown in Figure 4.

  The computer 36 includes a clock 60, an operating circuit 62 and a program 64. The clock 60 increases its counting state by one unit in each time interval, for example by a few ps such as 3.6 gs. When a tooth 52 preferably passes the rear flank or negative flank of the tooth in front of the angle sensor 48 unilts an interruption. This interruption produces the entry of the current counting state of the clock 60 and its recording in a table of teeth 66, in a direct access memory (RAM), of the computer 36; in other words, this signal is stored in memory. From the times recorded in table 66, after each rotation of the one-year crankshaft 20 gle of 120, the operating circuit 62 and the program 64 calculate the duration necessary for the rotation and from this the speed of instantaneous rotation of the motor 10. This information is then transmitted by the control of the motor 38 to a device for measuring the speed of rotation.

  (not shown) or towards the control of an injection pump.

  In addition and unlike current methods of detecting misfires, the times recorded in the table of teeth 66 are also used to assess the plausibility of the measurement results.

  and operating the ion current measurement method described above.

  As shown in FIG. 4, a measurement window MF is fixed in an angular sector WS of 1200 and the start and end of which are indicated by the references TR; in this sector there will be 20 teeth 52. The beginning and the end of the window are indicated by the references MFB and MFE; these references preferably always correspond to the negative side of a tooth 52. The angular sector indicated corresponding to 120 depends on the completion of the control 38 of the motor and can be either higher or lower. Duration and position of the MF measurement window

  are essentially free to choose so that trials allow

  try to determine the duration and the optimal position for each application. If necessary, the length and position of the MF measurement window can also be modified as a function of the load or the speed of rotation of the motor 10 since it is possible to shift the measurement window to MF during engine operation. 10 according to conditions

  limits predetermined by the computer 36.

  For the signal curve shown in FIG. 4, the measurement window MF is located substantially in the middle of the angular sector WS; the start of the MF window is located 48 upstream of the ZOT ignition top dead center 10 and the end of the MFE measurement window is 120 behind the OT point of the ZOT ignition point, so that the length of the MF measurement window is 60; this window is fixed unequivocally with respect to the rotation of the crankshaft 18.

  To detect misfires, each rotation of 15 120 of the crankshaft 18 is calculated from the durations recorded in the

  tooth durations table 66, the time difference MFD and between the start of the MFB window and the end of the MFE window. This time difference MFD depends firstly on the speed of rotation of the motor 10 calculated by the computer 36 based on the table of the passage times 20 of teeth 66. On the other hand, this time difference is extended by a misfire in the cylinder 12 which has just been triggered because the piston 16 of this cylinder 12 does not add to the torque of the crankshaft 18 and thus the instantaneous angular speed slows down slightly.

  The calculated time difference MFD between the start MFB and the end MFE of the measurement window MF is applied to a comparison circuit 68 to compare this difference with a predefined range of value recorded in a memory of the comparison circuit, the difference MFD time in front is within this value range if the motor 10 is running quietly. If the calculated MFD time difference is greater than the range and thus exceeds the range of values in memory, it can be concluded that a misfire is possible and a signal is then applied to the AND gate 42 of the computer 36 .

  If at the same time the two inputs of the AND gate 42 of the computer 36 receive a signal, the fault indicator 44 of the dashboard of the vehicle is lit or a fault signal is signaled in another way. Another possibility of carrying out the method of measuring the operating irregularity is given in the following documents:

  DE 196 41 916 Ai, DE 196 27 540 Ai, DE 199 46 873 Ai.

  As the measurement of the angular movement of the crankshaft 18 and the measurement of the ion current are done using completely different physical measurement methods and that the signal deduced from the measurement of the angular movement of the crankshaft 18 or the signal deduced from the measurement of the ion current in the combustion chamber 34 are not influenced in the same way by other boundary conditions, other than misfires, the method for measuring operating irregularities last described above is well suited to confirm the

  plausibility of the ion current measurement method described above.

  In a motor vehicle which carries out the detection of misfires mainly by a method for measuring operating irregularities, it is however possible to reverse the plausibility check of the operating results of this primary measurement method according to FIG. 1 by having in plus an ion current measurement installation 32 connected to each spark plug 26 in series, this installation being placed in the ignition circuit of the ignition device 20; the measured values will be evaluated and compared with the evaluated values

  of the primary measurement method for operating irregularities.

  To avoid overstressing the calculation capacities of the motor control 36, provision may be made in this case for recording the measurement values of the ion current measurement installation 32 or, where appropriate, the operating results of the process. measurement by ion current in a memory of the computer 36 and call these values for a plausibility check of the measurement values of the primary measurement method of operating irregularities only if the operating results of this method are nearby an edge, that is to say just inside or outside the range of predetermined values and which could give the conclusion that there is a misfire

  without allowing precise recognition of the misfire.

  In order to have a high detection quality which makes it possible to conclude with a very high probability of the existence of a failure in combustion, it is also possible to set more stringent conditions than usual for the operating results of the measurement method of the secondary ion current. This means that the operating result of the primary process, which makes it possible to conclude with a certain probability that a

  misfire, will only be confirmed by the secondary process and the fault signal will only be triggered if the operating result of the secondary process is unequivocal and is for example close to the middle of the predefined angular range or within a range of limited value more narrowly than usual.

Claims (7)

CLAIMS) Method for detecting misfire of an internal combustion engine according to which during engine operation, a parameter is cyclically determined using a physical measurement method, this parameter being modified by a misfire combustion, leads to the conclusion that there is a misfire if an operating result of the measurement process is outside or inside a value range fixed beforehand, characterized in that using from another different physical measurement method, another parameter is cyclically determined which is also changed by a misfire, and we only conclude that a misfire exists if the operating result of the Another measurement method is also outside or inside a value range fixed beforehand.   2) Method according to claim 1, characterized in that two independent and non-influencing parameters are determined reciprocally.   ) Method according to claim 1, characterized in that one of the two measurement methods is a primary measurement method, the parameters of which are determined mainly at each combustion cycle of the engine (10), they are used, and the other measurement method is a secondary measurement method, the parameters of which are completely exploited in order to use them in order to confirm the plausibility of the parameter obtained by the first measurement method,   only completely if the operating result of the primary measurement process is close to the marginal zone of the previously determined value range.   4) Method according to claim 3, characterized in that one concludes that there is a misfire only if the result of the operation of the secondary measurement process is located near the   middle of the value range set beforehand.    ) Method according to claim 1, characterized in that one of the two methods is a direct method according to which a parameter is measured and used in the combustion chamber (34) of the cylinders (12) of the engine (10). ) Method according to claim 5, characterized in that   the parameter measured and used is an ion current.   7) Method according to claim 1, characterized in that one of the two measurement methods is an indirect method for which an external parameter of the combustion chamber (34) of the cylinders (12) of the engine (10).   8) Method according to claim 7, characterized in that the determined parameter is a period during which a component (18,   50) driven by the motor (10) rotates by a predetermined angular measurement.   9) Method according to any one of claims 7 or 8,   characterized in that an angular sensor (48) detects angle marks (52) of a tone wheel (50) connected in rotation to the crankshaft (18) of the engine (10) and the time interval is determined between the passage of two landmarks corner (52).   100) Method according to claim 9, characterized in that a measurement window (MF) is fixed between two angle marks (52), this window being located inside a predetermined angle sector of the crankshaft (18) and the time interval between the passage of the   two angle marks (52) in front of the angle sensor (48).   1 10) Method according to claim 10, characterized in that one determines the duration between two neighboring corner marks (52) inside the corner sector and this duration is recorded in a table (66) and at from the durations recorded in the table (66), the time interval between the passage of the two angle marks (52) of the measurement window (MF) is determined.   ) Method according to any one of claims 10 or 11,   characterized in that the length and / or position of the measuring window (MF) is changed   according to the limit conditions of engine operation.   ) Method according to any one of claims 10 to 12,   characterized in that the angular interval between the start and the end of the measurement window (MF)   is s 360 '/ n, n being the number of cylinders (12).