ES2996849A1 - NON-INTRUSIVE DIAGNOSTIC DEVICE FOR SPARK IGNITION SYSTEMS IN COMBUSTION ENGINES AND DIAGNOSTIC PROCESS USING IT (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Non-intrusive diagnostic device (1) for spark ignition systems in combustion engines comprising means for connection to the engine control circuit (3); a first power supply (5) for the device (1); means for acquiring and controlling the test (6); and a device for measuring the current in the primary circuit (7). Non-intrusive diagnostic process comprising supplying the logic circuit of the smart coil (15) by means of a sequence of pulses (8) for energization time values between an ETmin and an ETmax; an analysis (16) of the current response (11) in the primary circuit; a comparison of the percentage (17) of pulses (8) that generate a spark with calibration curves (13); an assessment of the condition of the spark plug (19) and/or a determination of the separation distance (18) between electrodes.

Description

description

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

Technical field of the invention

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

Background of the Invention

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 and fuel mixture inside the combustion chamber, thus generating enough energy for the engine to operate.

The ignition system of an internal combustion engine with spark ignition basically consists of a low voltage electrical circuit (primary circuit), a high voltage electrical circuit (secondary circuit) that includes the spark plug in which the spark jump occurs, and a control circuit whose signal comes from the electronic control unit of the engine.

It may happen that the spark plug has a factory defect and this will have an impact on the engine's poor performance, so it is very important to be able to detect it as soon as possible.

It may also happen that there is an incorrect gap between the spark plug electrodes, with a value outside the admissible dimensional tolerance between them, which would cause an abnormal spark, or even the absence of one, leading to a malfunction of the spark plug and, therefore, of the engine.

This failure in the value of the distance between electrodes 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 come closer together.

In the state of the art there are technologies that allow knowing 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 engine, it is an error that cannot be detected with current systems.

As an example of the state of the art, reference documents GB2416853, DE4116642, WO8909333, GB2257533, US6216678 and WO9825124 may be mentioned.

Reference document GB2416853 determines a system for diagnosing the performance of the ignition system of an internal combustion engine which acts by generating pulses on the secondary circuit of the ignition coil. The measurement of the feedback signal from the primary winding of the ignition coil, as well as the data transfer, are carried out entirely internally in the engine control unit and the spark duration of each cylinder is analysed and compared with other durations (relative reading) for each complete engine cycle via a scan tool connected to a data link connector.

This allows the spark plug to be diagnosed as defective or not, but does not provide a quantitative value for the gap between the electrodes. In addition, since this system acts on the secondary circuit, it is necessary to remove the engine wiring.

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 upwardly transformed ignition spark voltage of individual ignition events or attempts.

It is also unable to determine the exact value of the spark plug gap. This method focuses on checking the ignition system, but is not capable of quantifying the condition of the spark plug.

Reference document WO8909333 discloses a method and device for monitoring combustion in an internal combustion engine operating with spark ignition, in which the engine's exhaust system is used and the ignition voltage is monitored to determine whether combustion has occurred in the engine's combustion chamber.

With this system it is also not possible to obtain a quantitative value of the gap between the spark plug electrodes and, like the previous method, they focus on checking the ignition system, adding in this case a combustion control, but they have no way of quantifying the state of the spark plug.

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.

This system detects a short circuit or low impedance in a secondary circuit by comparing the spark discharge times with a given threshold value. To do this, two simultaneous sparks are generated in two of the engine's cylinders and the objective is to adapt the fuel injection in those cylinders in which the spark does not jump.

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

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

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

In reference to document W09825124, it determines a method for inspecting a spark plug installed in an engine by applying a voltage high enough to cause said spark plug to generate a spark, with the engine at rest and without supplying fuel to it.

This procedure is not obvious or immediate to carry out, as it requires disabling the fuel supply to the engine, which with current control systems can possibly cause fault warnings in the engine's electronic control unit (ECU).

Furthermore, it is not a system capable of determining the quantitative value of the spark plug's gap between electrodes.

It is therefore necessary to find a method and device that is capable of determining the problem existing in an ignition system, providing the quantitative value of the gap 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 assembly factories, without having to cause any type of special operation to the engine or modify its wiring.

Description of the invention

The non-intrusive diagnostic device (1) 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 an intelligent coil, and a control circuit whose signal comes from the electronic control unit of the engine, presented here, comprises means for connecting to the engine control circuit through a connector of said control circuit.

This device further comprises a first power supply for the device, means for acquiring and controlling the test, and a device for measuring the intensity in the primary circuit.

For their part, these acquisition and control means comprise a controller with software suitable for controlling and processing the data obtained, which comprises at least a first unit configured to generate a series of charge 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 actuation on the secondary circuit.

This paper also proposes a non-intrusive diagnostic process for spark ignition systems in combustion engines using a diagnostic device as defined previously.

This process presents a first phase consisting of a connection of the device to the connector of the motor control circuit and to a first power supply.

The second phase is then carried out, consisting of supplying the logic circuit of the system's smart coil with a sequence of charging pulses, performing a plurality of repetitions for certain spark plug energisation time (ET) values. These energisation time values are between an ETmin value corresponding to an ET value that does not produce a spark in a spark plug for a nominal value of electrode gap, and an ETmax value corresponding to the ET capable of producing a spark in 100% of the cases with an electrode gap value greater than the nominal value. Both ETmax and ETmin values are test parameters that are defined based on the expected range of electrode gap.

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 in the spark plug.

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

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.

The non-intrusive diagnostic device for spark ignition systems in internal combustion engines and the process for such diagnosis proposed here provide a significant improvement in the state of the art.

This is because a completely automated method is achieved in which the technician's actions are 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 completely automated manner without human intervention.

Since both the low and high voltage circuits of the ignition system are electromagnetically coupled, changing the characteristics of the high voltage circuit, such as the gap between the spark plug electrodes, also has an effect on the electrical behaviour of the primary circuit. In this way, by analysing what happens in the primary circuit it is possible to deduce the type of fault in the system, without having to access the secondary circuit, or to apply any voltage to it or to take measurements, thus achieving a non-intrusive process that takes advantage of the instrumentation already installed in engines and vehicles to detect possible faults in the assembly of the engine spark plugs.

The monitoring and diagnostic process is therefore carried out automatically and without interference with the engine, and is primarily designed for use on engine assembly lines in car factories, when assembling spark plugs into the engine.

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

In addition to these pathologies, this device can determine the specific distance between electrodes, which is very advantageous because it provides a direct measurement of the spark plug's operation in situ, allowing the manufacturing and installation dispersion of the spark plug to be evaluated and quantified, in order to establish quantitative acceptance and rejection criteria during quality tests on engine manufacturing lines.

This diagnosis can be carried out either during the assembly process of the spark plugs in the engine, in the production process itself, thus preventing the defective engine from moving forward 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 is therefore a very effective diagnostic device and process that can be used to analyse the condition of an engine's spark plug, determining whether it is defective or has an abnormal distance between its electrodes.

In this document, the word "comprises" and its variants are to be interpreted as open-ended expressions that are not intended to exclude the possibility of other technical features or components in addition to those explicitly mentioned. Furthermore, the word "comprises" includes the case "consists of", being interpreted as a closed-ended expression that is limited only to the technical features or components explicitly mentioned. For those skilled in the art, other objects, advantages and features of the invention will be apparent partly from the description and partly from the practice of the invention. Furthermore, the present invention covers all possible combinations of embodiments indicated herein.

Brief description of the drawings

In order to assist in a better understanding of the characteristics of the invention, in accordance with a preferred example of its practical implementation, a series of drawings is provided as an integral part of said description, where, for illustrative and non-limiting purposes, the following has been represented:

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

Figure 2.- Shows a schematic view of a sequence of charge pulses of the non-intrusive diagnostic process of a spark ignition system in combustion engines, according to a preferred embodiment of the invention.

Figure 3.- Shows a schematic view of the response received from the current 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.

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

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.

Figure 6.- Shows an image of the samples prepared for studying the effect of the separation between the spark plug electrodes, according to a preferred embodiment of the invention.

Figures 7.1 and 7.2 show images of three graphs obtained during tests of spark plug behavior under laboratory conditions.

Figures 8.1 to 8.4 show images of waveforms for different charging times with a nominal spark plug.

Figure 9.- Shows the effect of load duration on spark intensity and delay for a nominal spark plug.

Figure 10.- Shows the ratio of successful spark events for different electrode gaps and charging times.

Figure 11.- Shows the signal of an ignition with 5000 qs of coil charge time.

Figures 12.1 and 12.2 show the spark success ratio for nominal spark plugs and for different spark plugs with modified gaps, respectively.

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

Detailed description of a preferred embodiment of the invention

In view of the figures provided, it can be observed how in a preferred embodiment of the invention, the non-intrusive diagnostic device (1) for spark ignition systems in combustion engines proposed here, refers to systems comprising a low voltage primary circuit and a high voltage secondary circuit comprising a spark plug, both electromagnetically coupled by means of an intelligent coil (2), and a control circuit whose signal comes from the electronic control unit of the engine (3).

Figure 1 shows a motor (3) with several smart coils (2).

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

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.

The power supply can supply the equipment at 12 V (automotive) or 24 V (industrial). A 5 V power supply module is also used for the logic stage, in order to amplify the signal obtained in real time to act on the spark plug controller.

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

The device is controlled by means of instrumentation with real-time control capacity and high-frequency communications. This stage of the equipment generates a digital output with a frequency of at least 20 MS/<s> that must cause the spark in the spark plug.

Thus, the first unit (6.1) is configured to generate a series of charge 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 controlling the performance on the secondary circuit.

The software allows, through dialogue screens with the operator, to enter the particular configuration of the system to be diagnosed.

As shown in Figure 1, in this preferred embodiment of the invention, the diagnostic device also comprises a second power supply (9) that can be connected to the primary circuit through the connector (4) of the engine control circuit (3), for those cases in which it is intended to obtain the diagnosis of an engine (3) that does not have a battery connected. Thus, this device (1), by having this second power supply (9), can test spark plugs in engines that are not yet connected to a battery and, therefore, the intelligent coil (2) of the ignition system must be supplied in addition to the diagnostic device (1).

In this embodiment, the controller is suitable for real-time data processing. In addition, the device (1) comprises an interface (10) that allows its connection to external software for data collection and processing at the end of the tests.

In this preferred embodiment of the invention, the device (7) for measuring the intensity of the primary circuit is formed by ammeter clamps. In other embodiments, said intensity measuring device may be formed by one or more shunt resistors.

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

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 supply (5).

The second phase consists of supplying the logic circuit of the smart coil (15) of the system by means of a sequence of charging pulses (8), as shown in Figure 2, in which the action on the smart coil (2) is represented by a series of pulses (8) over time.

A plurality of repetitions (R) are carried out for certain spark plug energization time (ET) values. These energization time values are between an ETmin value corresponding to a value that does not produce a spark in a spark plug for a nominal value of separation between electrodes, and an ETmax value corresponding to the ET capable of producing a spark in 100% of the cases with a value of separation between electrodes greater than the nominal value. In this case, the supply is started with a first repetition (R1) of pulses (8) for an ETmin value of 40 qs, and the sequence of repetitions (R) continues for different ET values, searching for the duration for which the spark jumps stochastically, until ending with a last repetition (R2) corresponding to the ETmax value, which in this embodiment is considered to be 600 qs. On the other hand, in other embodiments, feeding can be started in the opposite direction, that is, with a first repetition for the ETmax value and ending with a last repetition for the ETmin value.

Regarding the separation between pulses, sufficient time must be allowed to avoid overheating of the coil and to give the system time to respond. Thus, for example, if they are separated by 10 ms, it is possible to make 200 pulses in 2 s, which allows testing 10 levels of energization time with 20 pulses for each level.

Depending on the electrode gap, the spark starts to be unstable at a certain energization time value. For example, for a nominal electrode gap the spark starts to be unstable with an ET less than 200 μs, while an abnormally low electrode gap allows spark establishment with 150 μs.

Next, a third phase takes place in which an analysis (16) of the current response (11) in the primary circuit is carried out for each of the pulses (8). The response (11) is represented in Figure 3 and it shows the appearance of a peak (12) in the current signal in the primary circuit in some pulses (8), where this peak (12) determines the existence of a spark in the spark plug.

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 gap between the spark plug electrodes is strongly related to the instabilities in the coil discharge current, by analysing the “reflected” current in the primary circuit, variations in the secondary circuit with respect to initial operating conditions or reference conditions can be deduced, such as: abnormal gap between the spark plug electrodes.

The fourth phase consists of obtaining the percentage (17) of pulses (8) that generate spark for each ET value, as well as the comparison of this value with calibration curves (13) determined for each value of separation between the spark plug electrodes, such as those shown in Figures 4.1 and 4.2.

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 values of separation between the electrodes. Specifically, a first calibration curve (C1) corresponding to an insufficient separation of the spark plug electrodes, a second calibration curve (C2) corresponding to a nominal separation between the electrodes, and a third calibration curve (C3) for an excessive separation between the electrodes are shown schematically.

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

The fifth phase then takes place, which consists of an assessment of the state 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 spark plug electrodes is also determined.

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

In other embodiments, when the device is connected to a motor (3) without a battery connected, the process has an additional phase of connecting the primary circuit (14.1) to a second power source (9) that this device (1) already has. This additional phase takes place after the phase of connecting the device (1) to the connector (4) of the motor control circuit and to a first power source (5).

As shown in Figure 5, in this embodiment proposed here, in the fifth phase of assessment of the state of the spark plug (19), the existence or not of current (20) in the primary circuit is first analyzed. If the absence of current (20.1) is determined, this determines the existence of problems in the secondary circuit due to a non-connected or defective coil (21).

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 value different from the nominal value (22.1) of current in said primary circuit, in which case the assessment of the state of the spark plug also determines a non-connected or defective coil (21).

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

In the event that a spark is present (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.

On the other hand, in the event of an absence of spark (23.1), it must be analyzed whether or not there is a return (24) of energy in the primary circuit, that is, a discharge of magnetic energy back to the primary circuit. In the event that there is a return of energy (24.1) through the primary circuit, the assessment of the state of the spark plug establishes a defect in said spark plug (25) or its absence.

Finally, if obtaining the percentage (17) of pulses (8) that generate spark determines the absence of spark (23.1) in the spark plug and an absence of return (24.2) of energy to the primary circuit is also determined, the assessment of the state of the spark plug establishes a short circuit (26) in it by contact between its electrodes. In this case with total contact between the spark plug electrodes, the generation of pulses is avoided in all cases, but the discharge occurs directly through the spark plug.

Table 1 also provides an example of the diagnostic logic in the detection of pathologies based on the measurement of 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.

Table 1

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

Thus, for example, when there is load intensity, but a total absence of spark is detected, even with high ET, a short circuit in the spark plug is determined by total contact between the electrodes.

If, on the other hand, when there is a load intensity, the absence of spark is detected, but when the load or energization time (ET) increases sufficiently, an induced discharge does appear in the primary, then the spark plug is determined to be defective or absent, the latter meaning that there is poor contact between the spark plug and the smart coil.

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

In a practical example of carrying out this process, a first sample preparation was carried out.

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

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

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

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 spark (open end).

The prototypes of the device were then created. In this embodiment, two versions of the device were implemented.

Table 2

Prototype 1 was used in initial testing and the test signals were processed offline once the tests were completed.

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

The next step is to obtain the experimental results.

Prototype 1:

Initially, the tests were carried out off-engine. In the laboratory study, a measurement point with the engine grounded was used to identify whether the spark could be detected indirectly from the primary current. The acquired data were automatically transferred to a PC, so that the data collection could be automated to make several thousand ignition events, up to the 22,369 individual measurements summarized in Table 3.

Table 3

Table 3 reflects the tests carried out in the laboratory. This table provides the data for spark plugs 1 to 8 shown in Figure 6. The number in the table between 0 and 1 refers to the distance between electrodes, with 1 being the nominal value and 0 being full contact.

Prototype 2:

In a later phase of the study, tests were carried out on the developed test bench, with the spark plugs installed in the engine, studying more than 4,500 points in total.

The main conclusions of the studies are as follows:

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

The current measured across the shunt resistance in the primary allows the detection of the spark if the signal is measured at a high frequency (at least 20 MS/<s>). Although a 1 MH<z> acquisition is able to adequately detect the waveform, it fails to detect the ignition events, as shown in Figures 7.1 and 7.2.

The raw signal (in grey) filtered at 1 MH<z> 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 shows the automatic segmentation and adjustment system of the response model.

It can thus be seen that, at the moment the power supply to the primary is cut off (point A in Figure 7.2) an oscillation appears and after a delay time the spark occurs (point B1 in Figure 7.2). Part of the energy is returned to the primary causing a second oscillation of the system.

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

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

For very short values of charge times, the spark plug presents stability problems in spark generation, as shown by the tests with less than 500 us of energization time in Figure 9. The graphs on the left and right of this Figure 9 show the effect of the charge duration on the intensity and the delay of the spark for the case of delay (d), measured in qs, respectively. As will be shown later, this instability strongly depends on the distance between the spark plug electrodes, which is used for diagnosis.

2- Behavior of spark plugs out of specification, under laboratory conditions.

The gap between the electrodes of several spark plugs was modified as shown in Figure 6 and the spark plug performance curves were studied again. Although no significant differences could be found in the cases of long charging times, it was found that for short charging times the percentage of success in spark generation is inversely proportional to the gap between the electrodes, as can be seen in Figure 10.

In this Figure 10, the ratio of events with successful spark for different distances between electrodes (gap) is represented on the abscissa axis and the spark plug charge times are indicated on each graph in qs. The spark plug frequency is displayed on the ordinate.

This is the basis of the method for diagnosing the electrode gap: a nominal spark plug must be successful in generating the spark for long charging times but, at the same time, must not be able to produce the spark for short charging times.

3- Study in motor

In a later phase, the behaviour of the ignition system with the spark plugs installed in the engine was studied. The implementation conditions differ significantly from the laboratory work, since the metallic environment provided by the cylinder head and the block influences the spark plug inductance, and the engine's capacity as a system ground is different from the laboratory device. Although the general characteristics of the signal are maintained, the delay found in the generation of the spark is much lower than in the previous cases, as shown in Figure 11.

Despite this difference in behaviour, it is still possible to diagnose the gap from the percentage of spark success for low energisation times. Thus, Figures 12.1 and 12.2 show that spark plugs with reduced gaps are able to generate the spark adequately for times below 150 qs, while those with the nominal gap cannot.

Finally, extreme failures were studied, such as incorrect connections and poorly connected, missing or defective spark plugs. Figures 13.1 to 13.3 illustrate some of the tests carried out with different load times and significant failures in the ignition system.

Figure 13.1 shows a faulty 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. This last figure shows some saturations in the oscilloscope measurement.

From the study it can be concluded that it is possible to diagnose the condition of the spark plug and the ignition system by measuring the primary current. Table 1 summarizes the differences between the cases studied. One aspect to consider is that the diagnosis of the case of short circuit and gap between electrodes out of specification requires the detection of the spark, so measurement speeds in the range of 20 MHz are required.

4- Real-time integration and cycle time validation.

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

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

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

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

The test process, as shown in Figures 2 and 3, consists of executing a pulse train and analysing the resulting current. The test time is determined by the system's capacity to acquire and process this information in real time. Unlike what happened in prototype 1, in the case of prototype 2 the data is analysed in real time. Laboratory tests have determined the feasibility of carrying out the 'load-trigger-measure-signal analysis' cycle in 5 ms per spark, which allows the execution of 200 pulses/s. In this way, it is possible to test 10 ET levels with 50 pulses per level in 2.5 s, which allows a 4-cylinder engine to be tested in 10 s.

Claims (1)

1- Non-intrusive diagnostic device (1) for spark ignition systems in combustion engines, where this system comprises a low voltage primary circuit and a high voltage secondary circuit comprising a spark plug, both electromagnetically coupled by means of an intelligent coil (2), and a control circuit whose signal comes from the electronic control unit of the engine (3), characterized in that it comprises: - means for connecting to the motor control circuit (3) through a connector (4) in said control circuit; - a first power supply (5) of the device (1); - test acquisition and control means (6) comprising a controller with software suitable for controlling and processing the data obtained, comprising at least a first unit (6.1) configured to generate a series of charge pulses on a logic circuit of the smart coil (2) and a second unit (6.2) allowing 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) of the intensity in the primary circuit. 2- Device according to claim 1, comprising a second power source (9) capable of connection to the primary circuit through the connector (4) of the motor control circuit (3) for a motor (3) without a connected battery. 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 at the end of the tests. 5- Device according to any of the preceding claims, wherein the measuring device (7) of the intensity of the primary circuit is formed by one or more shunt resistors. Device according to any of claims 1 to 4, wherein the device (7) for measuring the intensity of the primary circuit is formed by ammeter clamps. Non-intrusive diagnostic process for spark ignition systems in combustion engines by means of a diagnostic device (1) as defined in claims 1 to 6, characterized in that it comprises: - a connection (14) of the device (1) to the connector (4) of the motor control circuit (3) and to a first power supply (5); - a supply of the logic circuit of the intelligent coil (15) of the system by means of a sequence of charging pulses (8), performing a plurality of repetitions (R) for certain values of energization time (ET) of the spark plug, where these energization time values are between an ETmin value corresponding to a value that does not produce a spark in a spark plug for a nominal value of separation between electrodes, and an ETmax value corresponding to the ET capable of producing a spark in 100% of the cases with a value of separation between electrodes greater 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 in the spark plug; - obtaining the percentage (17) of pulses (8) that generate spark for each ET value, and a comparison of 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 gap (18) between the spark plug electrodes. Process according to claim 7, comprising an additional phase of connecting the primary circuit (14.1) to a second power supply (9), after the phase of connecting (14) the device (1) to the connector (4) of the motor control circuit (3) and to a first power supply (5), for a motor (3) without a connected battery. Process according to any of claims 7 or 8, where if 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 state of the spark plug (19) establishes problems in the secondary circuit due to a non-connected or defective coil (21). 10- Process according to any of claims 7 or 8, where if obtaining the percentage (17) of pulses (8) that generate spark determines the presence of current with a nominal value (22.2), absence of spark (23.1) in the spark plug and presence of energy return (24.1) through the primary circuit, the assessment of the state 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, where 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) in the spark plug and absence of energy return (24.2) towards the primary circuit, the assessment of the state of the spark plug (19) establishes a short circuit (26) in it by contact between its electrodes.