Non-intrusive diagnostic device for spark-ignition systems in internal combustion engines and diagnostic method using the same

Abstract

The invention relates to a non-intrusive diagnostic device (1) for spark-ignition systems in internal combustion engines, comprising means for connecting to the engine control circuit (3); a first power supply (5) for the device (1); test acquisition and control means (6); and a device (7) for measuring the intensity in the primary circuit. The invention also relates to a non-intrusive diagnostic method comprising: supplying power to the logic circuit of the smart coil (15) via a sequence of pulses (8) for energisation time values ranging from ETmin to ETmax; analysing (16) the current response (11) in the primary circuit; comparing (17) the percentage of pulses (8) that generate a spark with calibration curves (13); assessing the spark plug condition (19) and / or determining the electrode gap (18).

Description

[0001] DESCRIPTION

[0002] Non-intrusive diagnostic device for spark ignition systems in combustion engines and diagnostic process using the same

[0003] Technical field of the invention

[0004] The present invention relates to the technical field of combustion engines, specifically to a non-intrusive diagnostic device for spark ignition systems in these engines and a diagnostic process.

[0005] Background of the Invention

[0006] The spark plug is an electrical component found in the ignition system of an internal combustion engine, and its main function is to provide the spark necessary to ignite the air-fuel mixture inside the combustion chamber, thus generating enough energy for the engine to run.

[0007] The ignition system of a spark-ignition internal combustion engine basically consists of a low-voltage electrical circuit (primary circuit), a high-voltage electrical circuit (secondary circuit) that includes the spark plug where the spark jumps, and a control circuit whose signal comes from the engine's electronic control unit.

[0008] It is possible that the spark plug has a factory defect, which will result in faulty engine behavior, so it is very important to detect it as soon as possible.

[0009] It can also happen that there is an incorrect separation between the spark plug electrodes, with a value outside the dimensional tolerance allowed between them, which would cause an abnormal spark, or even the absence of it, resulting in a malfunction of the spark plug and, therefore, of the engine.

[0010] This failure in the electrode gap value may be due to some circumstance that occurred during the assembly itself, since the spark plugs are assembled by hand and it may happen, for example, that the assembler accidentally hits the spark plug, causing the electrodes to move closer together.

[0011] In the state of the art, there are technologies that allow us to know if the electrodes are in contact, but they cannot know the distance between electrodes if they are not in contact, so if it is an incorrect distance that will surely cause a malfunction of the motor, it is an error that cannot be detected with current systems.

[0012] Examples of the state of the art include reference documents GB2416853, DE4116642, WO8909333, GB2257533, US6216678 and WO9825124.

[0013] Reference document GB2416853 defines a system for diagnosing the performance of an internal combustion engine's ignition system by generating pulses on the coil's secondary circuit. The measurement of the primary winding return signal of the ignition coil, as well as the data transfer, is performed entirely internally within the engine control unit. The spark duration of each cylinder is analyzed and compared to other durations (relative reading) for each complete engine cycle using a scan tool connected via a data link connector.

[0014] This allows for diagnosing whether the spark plug is faulty or not, but it doesn't provide a quantitative value for the electrode gap. Furthermore, because this system works on the secondary circuit, it requires disconnecting the engine wiring.

[0015] For its part, reference document DE4116642 defines a method of controlling an ignition system of an internal combustion engine by measuring in the primary winding of one or more ignition coils, not only the duration of the ignition spark, but also the up-transformed ignition spark voltage of individual ignition events or attempts.

[0016] It is also unable to determine the exact spark plug gap. This method focuses on checking the ignition system, but it cannot quantify the condition of the spark plug.

[0017] Reference document WO8909333 discloses a method and device for observing combustion in a spark-ignition-operated internal combustion engine, in which the engine's discharge system is used and the ignition voltage is monitored to determine whether combustion has occurred in the engine's combustion chamber.

[0018] This system also does not allow for obtaining a quantitative value of the spark plug electrode gap and, like the previous method, focuses on checking the ignition system, adding in this case a combustion control, but has no way of quantifying the condition of the spark plug.

[0019] Reference document GB2257533 defines a method for detecting a low impedance short circuit in a secondary winding circuit of an ignition coil of an internal combustion engine having a distributorless ignition system.

[0020] This system detects a short circuit or low impedance in a secondary circuit by comparing spark discharge times to a predetermined threshold value. To do this, two simultaneous sparks are generated in two of the engine's cylinders, and the goal is to adjust fuel injection in the cylinders where the spark fails to fire.

[0021] It is not a method that aims to diagnose ignition systems to find the possible error, much less the quantitative assessment of the separation between the spark plug electrodes.

[0022] US6216678 discloses a method and apparatus for connecting to an engine ignition system to determine a misfire in a cylinder by monitoring the flow of current in the primary circuit.

[0023] This method attempts to identify engine cylinders with a lack of combustion due to a failure in the ignition system, but this does not allow for the determination of other possible problems in the ignition system, much less obtaining the numerical value of the spark plug electrode gap.

[0024] With reference to document WO9825124, it describes a method for inspecting a spark plug installed in an engine by applying a sufficiently high voltage to cause the spark plug to generate a spark, with the engine at rest and without fuel supplied. This procedure is neither obvious nor straightforward, as it requires disabling the fuel supply to the engine, which, with current control systems, could potentially trigger fault warnings in the engine's electronic control unit (ECU).

[0025] Furthermore, it is not a system capable of determining the quantitative value of the spark plug electrode gap.

[0026] It is therefore necessary to find a method and device that is able to determine the problem existing in an ignition system, providing the quantitative value of the separation between the spark plug electrodes, in the least invasive way for the engine, applicable both to the normal operation of the engine, as well as to the quality tests carried out in the assembly factories, without having to cause any special operation to the engine or modify its wiring.

[0027] Description of the invention

[0028] The non-intrusive diagnostic device for spark ignition systems in combustion engines comprising a low-voltage primary circuit, a high-voltage secondary circuit comprising a spark plug, both electromagnetically coupled by means of a smart coil, and a control circuit whose signal comes from the engine's electronic control unit, presented herein, comprises means of connection to the engine control circuit via a connector of said control circuit.

[0029] This device also comprises a first device power supply, test acquisition and control means, and a device for measuring the intensity in the primary circuit.

[0030] For their part, these acquisition and control means comprise a controller with suitable software for the control and processing of the data obtained, comprising at least a first unit configured to generate a series of load pulses on a logic circuit of the intelligent ignition coil and a second unit that allows a reading of the internal voltage of the spark plug and the current induced in the primary, as well as a control of the action on the secondary circuit.

[0031] This report also proposes a non-intrusive diagnostic process for spark ignition systems in combustion engines using a diagnostic device such as the one previously defined.

[0032] This process has a first phase consisting of connecting the device to the motor control circuit connector and a first power supply.

[0033] Next, a second phase is performed, consisting of powering the logic circuit of the system's intelligent coil with a sequence of charging pulses, repeating this sequence multiple times for specific spark plug energization time (ET) values. These energization time values ​​are within a certain ET range. m εn corresponds to an ET value that does not produce a spark in a spark plug for a nominal electrode gap, and ETmax corresponds to the ET capable of producing a spark in 100% of cases with an electrode gap greater than the nominal value. Both ETmax and ETn values m n are test parameters that are defined based on the expected range of separation between electrodes.

[0034] The third phase consists of an analysis of the current response in the primary circuit for each of the pulses, where the appearance of a peak in the current signal in the primary circuit determines the existence of a spark at the spark plug.

[0035] The fourth phase then takes place, obtaining the percentage of pulses that generate a spark for each ET value and comparing this value with calibration curves.

[0036] The fifth phase consists of assessing the condition of the spark plug based on the effect caused by the existence or absence of a spark and / or determining the specific value of the separation distance between the spark plug electrodes.

[0037] The non-intrusive diagnostic device for spark ignition systems in combustion engines and the process for such diagnosis proposed herein results in a significant improvement over the state of the art.

[0038] This is because a completely automated method is achieved in which the technician's role is limited to making the initial connection of the device to the motor control circuit connector, and the rest of the process is carried out in a fully automated way without human intervention.

[0039] Since both the low- and high-voltage circuits of the ignition system are electromagnetically coupled, modifying the characteristics of the high-voltage circuit, such as the spark plug gap, also affects the electrical behavior of the primary circuit. Therefore, by analyzing what happens in the primary circuit, it is possible to deduce the type of system failure without needing to access the secondary circuit, apply any voltage to it, or take measurements. This results in a non-intrusive process that utilizes the instrumentation already installed in engines and vehicles to detect potential spark plug installation faults.

[0040] Thus, the monitoring and diagnostic process is carried out automatically and without interference with the engine, and is in principle designed for use on engine assembly lines in car factories, in the assembly of spark plugs in the engine.

[0041] Another advantage of this device is that, in addition to indicating the existence of a fault in the spark plug, based on the observation of the different reflection or response generated in the primary circuit, it is able to determine what type of fault is occurring in the secondary circuit, which can range from the existence of a defective spark plug, a total contact between the electrodes of the spark plug, or even a defective coil or a problem in the wiring.

[0042] But in addition to these pathologies, this device can determine the precise distance between electrodes, which is very advantageous because it allows for a direct measurement of the spark plug's performance in situ, enabling the evaluation and quantification of manufacturing and installation variations of the spark plug, in order to establish quantitative acceptance and rejection criteria during quality testing on engine manufacturing lines.

[0043] This diagnosis can be carried out either during the spark plug assembly process in the engine during the production process itself, thus preventing the defective engine from advancing on the manufacturing line, in workshops when carrying out maintenance inspections or in periodic tests carried out on the vehicle before or after driving it.

[0044] Therefore, it is a highly effective diagnostic device and process that allows for the analysis of an engine's spark plug, determining whether it is defective or has an abnormal gap between its electrodes. In this document, the word "comprises" and its variants are to be interpreted as open-ended expressions that do not exclude the possibility of other technical characteristics or components in addition to those explicitly mentioned. Furthermore, the word "comprises" includes the case "consists of," which is interpreted as a closed-ended expression limited solely to the technical characteristics or components explicitly mentioned. For those skilled in the art, other objects, advantages, and features of the invention will become apparent partly from the description and partly from the practice of the invention. Moreover, the present invention covers all possible combinations of embodiments indicated herein.

[0045] Brief description of the drawings

[0046] In order to aid a better understanding of the characteristics of the invention, according to a preferred embodiment thereof, a series of drawings are provided as an integral part of this description, where, for illustrative and non-limiting purposes, the following has been represented:

[0047] Figure 1 shows a schematic view of the assembly of a non-intrusive diagnostic device for a spark ignition system in combustion engines, according to a preferred embodiment of the invention.

[0048] Figure 2 shows a schematic view of a load pulse sequence of the non-intrusive diagnostic process of a spark ignition system in combustion engines, according to a preferred embodiment of the invention.

[0049] Figure 3 shows a schematic view of the received current response in the primary circuit for each of the pulses of the non-intrusive diagnostic process of a spark ignition system in combustion engines, according to a preferred embodiment of the invention.

[0050] Figures 4.1 and 4.2 show graphs of calibration curves and a characteristic curve for different electrode separations of the non-intrusive diagnostic process of a spark ignition system in combustion engines, according to a preferred embodiment of the invention.

[0051] Figure 5 shows a block diagram of the non-intrusive diagnostic process of a spark ignition system in combustion engines, according to a preferred embodiment of the invention.

[0052] Figure 6 shows an image of the samples prepared for study of the effect of the separation between the spark plug electrodes, according to a preferred embodiment of the invention.

[0053] Figures 7.1 and 7.2 show images of three graphs obtained from tests of spark plug behavior under laboratory conditions.

[0054] Figures 8.1 to 8.4 show waveform images for different charging times with a nominal spark plug.

[0055] Figure 9 shows the effect of load duration on spark intensity and delay for a nominal spark plug.

[0056] Figure 10 shows the ratio of successful spark events for different electrode distances and charging times.

[0057] Figure 11 shows the signal of an ignition with 5000 ps of coil charging time.

[0058] Figures 12.1 and 12.2 show the spark success rate for nominal spark plugs and for different spark plugs with modified gaps, respectively.

[0059] Figures 13.1, 13.2 and 13.3 show the effect of total failures due to connection failure, continuity problems between the coil and the spark plug or missing or defective spark plug, and short circuit in the spark plug, respectively.

[0060] Detailed description of a preferred embodiment of the invention

[0061] As shown in the figures provided, it can be observed that in a preferred embodiment of the invention, the non-intrusive diagnostic device (1) for spark ignition systems in combustion engines proposed herein relates to systems comprising a low-voltage primary circuit and a high-voltage secondary circuit comprising a spark plug, both electromagnetically coupled by means of a smart coil (2), and a control circuit whose signal comes from the engine's electronic control unit (3). Figure 1 depicts an engine (3) with two smart coils (2).

[0062] This diagnostic device (1) comprises means for connecting to the engine control circuit via a connector (4) in said control circuit.

[0063] As shown in Figure 1, the device (1) also has a first power supply (5) for the device, acquisition and control means (6) and a measuring device (7) for the intensity in the primary circuit.

[0064] The power supply can power the device at 12V (automotive) or 24V (industrial). A 5V power supply module is also used for the logic stage to amplify the signal obtained in real time to control the spark plug controller.

[0065] For its part, the means of acquisition and control (6) of testing comprise a controller with suitable software for the control and processing of the data obtained, which has a first unit (6.1) and a second unit (6.2).

[0066] The device is controlled by instrumentation with real-time control capabilities and high-frequency communication. This stage of the equipment generates a digital actuation output with a frequency of at least 20 MS / s, which must trigger the spark plug.

[0067] Thus, the first unit (6.1) is configured to generate a series of load pulses (8) on the logic circuit of the smart coil (2), and comprises a power controller whose function is to amplify the pulse train (8), while the second unit (6.2) comprises in this case a first and a second analog input that allow a reading of the internal voltage of the spark plug and the current induced in the primary, respectively, and analog and digital outputs for control of the action on the secondary circuit.

[0068] The software allows, through dialogue screens with the operator, the input of the particular configuration of the system to be diagnosed.

[0069] As shown in Figure 1, in this preferred embodiment of the invention, the diagnostic device further comprises a second power source (9) that can be connected to the primary circuit via the connector (4) of the engine control circuit (3), for cases where it is necessary to diagnose an engine (3) that does not have a battery connected. Thus, this device (1), by having this second power source (9), can test spark plugs in engines that are not yet connected to a battery and, therefore, the smart coil (2) of the ignition system must be powered in addition to the diagnostic device (1).

[0070] In this embodiment, the controller is suitable for real-time data processing. Furthermore, the device (1) comprises an interface (10) that allows its connection to external software for data collection and processing upon completion of the tests.

[0071] In this preferred embodiment of the invention, the measuring device (7) for the primary circuit current consists of a clamp meter. In other embodiments, this measuring device may consist of one or more shunt resistors.

[0072] This document also proposes a non-intrusive diagnostic process for spark ignition systems in combustion engines (3) using a diagnostic device as previously defined.

[0073] As shown in Figure 5, this process comprises a first phase consisting of a connection (14) of the device (1) to the connector (4) of the motor control circuit (3) and to a first power source (5).

[0074] The second phase consists of a power supply to the logic circuit of the intelligent coil (15) of the system by means of a sequence of load pulses (8), as shown in Figure 2, which represents the action on the intelligent coil (2) by means of a series of pulses (8) over time.

[0075] A plurality of repetitions (R) are performed for specific spark plug energization time (ET) values. These energization time values ​​are between an ET value. mn corresponds to a value that does not produce a spark in a spark plug for a nominal electrode gap, and ETmax corresponds to the ET capable of producing a spark in 100% of cases with an electrode gap greater than the nominal value. In this case, the supply is initiated with a first repetition (R1) of pulses (8) for an ET value m The process begins with a 40 ps repetition, and continues with the sequence of repetitions (R) for different ET values, searching for the duration for which the spark jumps stochastically, until ending with a final repetition (R2) corresponding to the ETmax value, which in this embodiment is considered to be 600 ps. Alternatively, in other embodiments, the feed can begin in the opposite direction, that is, with a first repetition for the ETmax value and ending with a final repetition for the ET value. m n.

[0076] Regarding the spacing between pulses, sufficient time must be allowed to prevent overheating of the coil and to give the system time to respond. For example, with a 10 ms spacing, it is possible to perform 200 pulses in 2 seconds, allowing testing of 10 energization time levels with 20 pulses for each level.

[0077] Depending on the electrode gap, the spark begins to become unstable after a certain energization time. For example, with a nominal electrode gap, the spark becomes unstable with an ET of less than 200 ps, ​​while an abnormally low electrode gap allows a spark to be established with 150 ps.

[0078] Next, a third phase takes place in which an analysis (16) of the current response (11) in the primary circuit is performed for each of the pulses (8). The response (11) is shown in Figure 3, and it reveals the appearance of a peak (12) in the current signal in the primary circuit in some pulses (8), where this peak (12) indicates the presence of a spark at the spark plug.

[0079] Detection is made possible by the oscillatory effects that occur during the discharge of the current pulse (8) in the logic circuit of the smart coil (2). Since the spark plug electrode gap is strongly related to instabilities in the coil's discharge current, by analyzing the "reflected" current in the primary circuit, variations in the secondary circuit can be deduced with respect to initial operating conditions or reference conditions, such as, for example, abnormal spark plug electrode gaps.

[0080] The fourth phase consists of obtaining the percentage (17) of pulses (8) that generate a spark for each ET value, as well as comparing this value with calibration curves (13) determined for each spark plug electrode gap, such as those shown in Figures 4.1 and 4.2.

[0081] Figure 4.1 shows the percentage of spark events (Y-axis) as a function of the ET value (X-axis), and the curves are obtained for different electrode gap values. Specifically, a first calibration curve (C1) corresponding to insufficient spark plug electrode gap, a second calibration curve (C2) corresponding to a nominal electrode gap, and a third calibration curve (C3) for excessive electrode gap are shown schematically.

[0082] Figure 4.2 shows the variation of the ET value with which 50% of spark events are achieved (X-axis) as a function of the distance between the electrodes (Y-axis).

[0083] The fifth phase then takes place, which consists of an assessment of the condition of the spark plug (19) based on the effect caused by the existence or absence of a spark and, based on the result, the specific value of the separation distance (18) between the electrodes of the spark plug is also determined.

[0084] This specific value can be obtained by finding the energization time value from which the spark plug spark begins to fail, having as a known data the energization time value for which the spark plug spark begins to be unstable for a nominal separation between the electrodes, and for other electrode separation values, such as the aforementioned calibration curves (13).

[0085] In other embodiments, when the device is connected to a motor (3) without a connected battery, the process includes an additional step of connecting the primary circuit (14.1) to a second power source (9) already provided by the device (1). This additional step occurs after the device (1) is connected to the motor control circuit connector (4) and to a first power source (5).

[0086] As shown in Figure 5, in this proposed embodiment, the fifth stage of spark plug condition assessment (19) first analyzes the presence or absence of current (20) in the primary circuit. If the absence of current (20.1) is determined, this indicates problems in the secondary circuit due to a disconnected or defective coil (21).

[0087] Likewise, if the presence of current is detected (20.2), the value of this current must be analyzed (22) to determine if it is a different value from the nominal value (22.1) of current in said primary circuit, in which case the assessment of the condition of the spark plug also determines a coil not connected or defective (21).

[0088] If, on the other hand, there is current (20.2) but its value corresponds to the nominal value (22.2), the absence or presence of a spark (23) in the spark plug must be studied.

[0089] In the event of the presence of a spark (23.2), the specific value of the separation distance (18) between the spark plug electrodes is determined, obtaining the value of the energization time from which the spark plug spark begins to fail, as previously indicated.

[0090] Furthermore, if there is no spark (23.1), it must be analyzed whether or not there is a backflow (24) of energy in the primary circuit, that is, a discharge of magnetic energy back into the primary circuit. If there is a backflow of energy (24.1) through the primary circuit, the assessment of the spark plug's condition establishes a defect in that spark plug (25) or its absence.

[0091] Finally, if obtaining the percentage (17) of pulses (8) that generate a spark determines the absence of a spark (23.1) at the spark plug and also determines an absence of energy return (24.2) to the primary circuit, the assessment of the spark plug's condition establishes a short circuit (26) in it due to contact between its electrodes. In this case, with total contact between the spark plug electrodes, pulse generation is prevented in all cases, but the discharge occurs directly through the spark plug.

[0092] Table 1 also provides an example of the diagnostic logic in detecting pathologies based on measuring the current in the primary, the ability to generate sparks with high and low ET, and the existence of magnetic energy discharges back to the primary.

[0093] Table 1 As can be seen in Table 1, in addition to detecting the abnormal distance between electrodes, other failure modes can be detected.

[0094] Thus, for example, when there is a charge intensity, but a total absence of spark is detected, even with high ET values, a short circuit is determined in the spark plug due to total contact between the electrodes.

[0095] If, on the other hand, there is a charge intensity but an absence of spark is detected, but when the charge or energization time (ET) is sufficiently increased, an induced discharge appears in the primary, then the spark plug is determined to be defective or absent, the latter meaning that there is a bad contact between the spark plug and the intelligent coil.

[0096] Finally, as shown in Table 1, if there is no load consumption, it is determined to be defective or not connected, usually due to a problem in the wiring.

[0097] In a practical example of carrying out this process, a first sample preparation was performed.

[0098] Thus, for the study of failures in the ignition system, various failure cases were studied.

[0099] First, to study the effect of the spark plug electrode gap, samples were prepared in which the distance between the electrodes was modified by mechanical deformation. Figure 6 shows an image of the samples prepared for this purpose.

[0100] These samples are prepared so that each one has a different separation between the electrodes.

[0101] In addition, the effect of total failures was studied: connection failures, non-functional coils, short circuit of the spark plug electrodes and spark plug not present or unable to make the spark (open end).

[0102] Next, prototypes of the device were developed. Two versions of the device were implemented in this stage.

[0103] Table 2

[0104] Prototype 1 was used in the initial tests, and in it, the test signals were processed offline once the tests were completed.

[0105] Prototype 2, on the other hand, offers complete automation of the test, and the different pulses are processed in real time, making it possible to detect the distance between electrodes in real time during the test. Table 2 shows the components used in each device prototype.

[0106] The next step is obtaining the experimental results.

[0107] Prototype 1:

[0108] Initially, tests were performed off-engine. In the laboratory study, a measurement point with the engine grounded was used to determine if the spark could be detected indirectly from the primary current. The acquired data were automatically transferred to a PC, allowing for automated data collection of thousands of ignition events, up to the 22,369 individual measurements summarized in Table 3.

[0109] Table 3

[0110] Table 3 shows the laboratory tests performed. This table provides data for spark plugs 1 to 8, which are shown in Figure 6. The numbers in the table between 0 and 1 refer to the electrode gap, with 1 being the nominal value and 0 being full contact.

[0111] Prototype 2:

[0112] In a later phase of the study, tests were carried out on the developed test bench, with the spark plugs implanted in the engine, studying more than 4500 points in total.

[0113] The main conclusions of the studies are detailed below:

[0114] 1- Behavior of nominal spark plugs, under laboratory conditions.

[0115] The current measured across the shunt resistor in the primary allows for spark detection if the signal is measured at a high frequency (at least 20 MS / s). Although a 1 MHz acquisition is capable of adequately detecting the waveform, it fails to detect ignition events, as shown in Figures 7.1 and 7.2.

[0116] The raw signal (in gray) and the 1 MHz filtered signal can be seen in the upper graph of Figure 7.1, while the spectral signature of the signal is shown in the lower graph of Figure 7.1. Figure 7.2 depicts the automatic segmentation and response model adjustment system.

[0117] Thus, it can be seen that when the primary power supply is cut off (point A in Figure 7.2), an oscillation appears, and after a delay, the spark occurs (point B1 in Figure 7.2). Some of the energy is returned to the primary, causing a second oscillation of the system.

[0118] The magnitude of this energy backflow and the measured delay depend on the intensity, i.e., the primary charging time, as shown in Figures 8.1 to 8.4, in which the spark plugs are designated with the numbers 1 to 4.

[0119] In addition, routines for segmentation and automatic adjustment of a response model were developed, as shown in Figure 7.2.

[0120] For very short charging times, the spark plug exhibits spark generation stability problems, as shown in the tests with less than 500 µs of energization time in Figure 9. The graphs on the left and right of Figure 9 show the effect of charging time on spark intensity and delay (d), measured in ps, respectively. As will be shown later, this instability is strongly dependent on the spark plug electrode gap, which is used for diagnostic purposes. - Behavior of off-specification spark plugs under laboratory conditions.

[0121] The electrode gap of the spark plugs was modified as shown in Figure 6, and the spark plug performance curves were re-examined. Although no significant differences were found in the long charging time cases, it was observed that for short charging times, the percentage of success in spark generation is inversely proportional to the electrode gap, as can be seen in Figure 10.

[0122] Figure 10 shows the success rate of spark events for different electrode gaps (x-axis) and the spark plug firing times (in ps) on each graph. The spark plug firing frequency is shown on the y-axis. This is the basis of the method for diagnosing electrode gap performance: a nominal spark plug should successfully generate a spark for longer firing times but should fail to produce a spark for shorter firing times.

[0123] 3- Engine study

[0124] In a subsequent phase, the behavior of the ignition system with the spark plugs installed in the engine was studied. The installation conditions differed significantly from the laboratory work, as the metallic environment provided by the cylinder head and block influenced the spark plug inductance, and the engine's ability to act as a ground for the system differed from the laboratory setup. Although the general signal characteristics remained the same, the spark generation delay was much lower than in the previous cases, as shown in Figure 11.

[0125] Despite this difference in behavior, it is still possible to diagnose the electrode gap based on the spark success rate for short ignition times. Thus, Figures 12.1 and 12.2 show that spark plugs with reduced electrode gaps are able to generate a spark adequately for times below 150 ps, ​​while those with the nominal gap cannot.

[0126] Finally, extreme faults were studied, such as connection errors and a poorly connected, missing, or defective spark plug. Figures 13.1 to 13.3 illustrate some of the tests carried out with different charging times and significant faults in the ignition system.

[0127] Figure 13.1 shows a fault in the spark plug connection, Figure 13.2 shows a continuity problem between the coil and the spark plug, or a missing or defective spark plug, while Figure 13.3 shows a case of a short circuit in the spark plug. In this last figure, some saturation is reflected in the oscilloscope reading.

[0128] The study concludes that it is possible to diagnose the condition of the spark plug and ignition system by measuring the primary current. Table 1 summarizes the differences between the cases studied. One aspect to consider is that diagnosing short circuits and out-of-specification electrode gaps requires spark detection, thus necessitating measurement speeds in the region of 20 MHz. - Real-time integration and cycle time validation.

[0129] Based on the previous results, prototype 2 was developed. The objective of this prototype is to integrate all functionalities into a compact and industrializable device. To achieve this, the following changes were made:

[0130] The first pulse generation unit was replaced with one with sufficient nominal current to act directly on the smart coil (for this purpose the NI-9477 card was used).

[0131] An acquisition card capable of acquiring at 20 MS / s was used to directly measure the analog signals in the real-time system (NI-9775 card).

[0132] Current clamps were used as an alternative to shunt resistors so as not to affect the reference voltage level.

[0133] The testing process, as shown in Figures 2 and 3, consists of executing a pulse train and analyzing the resulting current. The test time is determined by the system's ability to acquire and process this information in real time. Unlike prototype 1, in prototype 2 the data is analyzed in real time. Laboratory tests have determined the feasibility of performing the 'charge-trigger-measurement-signal analysis' cycle in 5 ms per spark, allowing for the execution of 200 pulses / s. This makes it possible to test 10 ET levels with 50 pulses per level in 2.5 s, enabling the verification of a 4-cylinder engine in 10 s.

Claims

CLAIMS 1- Non-intrusive diagnostic device (1) for spark ignition systems in combustion engines, wherein this system comprises a low-voltage primary circuit and a high-voltage secondary circuit comprising a spark plug, both electromagnetically coupled by means of a smart coil (2), and a control circuit whose signal comes from the engine's electronic control unit (3), characterized in that it comprises: - means of connection to the motor control circuit (3) via a connector (4) in said control circuit; - a first power source (5) for the device (1); - a test acquisition and control means (6) comprising a controller with suitable software for controlling and processing the data obtained, comprising at least a first unit (6.1) configured to generate a series of load pulses on a logic circuit of the smart coil (2) and a second unit (6.2) that allows a reading of the internal voltage of the spark plug and the current induced in the primary and a control of the actuation on the secondary circuit; and - a measuring device (7) for the intensity in the primary circuit. 2- Device according to claim 1, comprising a second power source (9) capable of being connected to the primary circuit through the connector (4) of the motor control circuit (3) for a motor (3) without a battery connected. 3- Device according to any of claims 1 or 2, wherein the controller is suitable for processing data in real time. 4- Device according to any of the preceding claims, comprising an interface (10) that allows its connection to external software, for data collection and processing upon completion of the tests. 5- Device according to any of the preceding claims, wherein the measuring device (7) of the primary circuit current is formed by one or more shunt resistors. 6- Device according to any of claims 1 to 4, wherein the measuring device (7) of the intensity of the primary circuit is formed by an ammeter clamp. 7- Non-intrusive diagnostic process for spark ignition systems in combustion engines using a diagnostic device (1) as defined in claims 1 to 6, characterized in that it comprises: - a connection (14) from the device (1) to the connector (4) of the motor control circuit (3) and to a first power source (5); - a supply of the intelligent coil logic circuit (15) of the system by means of a load pulse sequence (8), performing a plurality of repetitions (R) for certain spark plug energization time values ​​(ET), where these energization time values ​​are between an ET value m n corresponding to a value that does not produce a spark in a spark plug for a nominal electrode gap, and an ETmax value corresponding to the ET capable of producing a spark in 100% of cases with an electrode gap higher than the nominal value; - an analysis (16) of the current response (11) in the primary circuit for each of the pulses (8), where the appearance of a peak (12) in the current signal in the primary circuit determines the existence of a spark at the spark plug; - obtaining the percentage (17) of pulses (8) that generate a spark for each ET value, and comparing this value with calibration curves (13); - an assessment of the condition of the spark plug (19) based on the effect caused by the presence or absence of a spark, and / or a determination of the specific value of the separation distance (18) between the electrodes of the spark plug. 8- Process according to claim 7, comprising an additional step of connecting the primary circuit (14.1) to a second power source (9), after the step of connecting (14) the device (1) to the connector (4) of the motor control circuit (3) and to a first power source (5), for a motor (3) without a battery connected. 9- Process according to any of claims 7 or 8, wherein obtaining the percentage (17) of pulses (8) that generate a spark determines in the primary circuit an absence of current (20.1) or a presence of current (20.2) with a value different from the nominal value (22.1), the assessment of the condition of the spark plug (19) establishes problems in the secondary circuit due to a coil not connected or defective (21). 10- Process according to any of claims 7 or 8, wherein obtaining the percentage (17) of pulses (8) that generate a spark determines the presence of current with a nominal value (22.2), absence of spark (23.1) at the spark plug and presence of energy return (24.1) through the primary circuit, the assessment of the condition of the spark plug (19) establishes a defect in said spark plug (25) or absence thereof. 11- Process according to any of claims 7 or 8, wherein if obtaining the percentage (17) of pulses (8) that generate a spark determines the presence of current with a nominal value (22.2), absence of spark (23.1) at the spark plug and absence of energy return (24.2) to the primary circuit, the assessment of the condition of the spark plug (19) establishes a short circuit (26) in it by contact between its electrodes.

Images