EP2085607A1 - Malfunction early recognition for a glow plug supplied with continuous consequence of tension pulses - Google Patents

Abstract

The method involves detecting of electrical resistances of a glow plug, during individual voltage pulses, which takes place within a predetermined time intervals. Comparison values are derived from the electrical resistances, and a condition for the comparison values is predetermined, where the comparison values represents gradient of the electrical resistances. Verification is made whether a comparison value fulfills the condition. A signal is outputted, when the comparison value fulfills the condition.

Description

State of the art

The present application relates to a method for early failure detection of at least one glow plug, which is supplied during at least one Glühzyklusses with a continuous train of voltage pulses of a respective electrical voltage, and a motor with at least one glow plug, which is adapted for the early failure detection of the glow plug for performing this method ,

Commonly referred to as glow plugs are electrical heating elements which are usually arranged to assist a cold start in the combustion chamber of internal combustion engines and heaters. Normally, a glow plug in a front part of a filament with a substantially temperature-independent resistor and in a rear part of a control coil whose resistance increases with temperature. As a result, a rapid heating of the front part of the glow plug and upon reaching certain temperature ranges, a feedback of the heating process is achieved.

As with all technical components, glow plugs also wear out over time, which can lead to malfunction or even total failure of the glow plug with increasing age. It is therefore desirable to recognize consumed glow plugs with a high probability of failure early. For this purpose it is known, the so-called cold resistance of To determine glow plug. For this purpose, in the first few seconds after the glow plug is switched on (as a rule within the first 60 s, but preferably 25 s), the current flowing through the glow plug is measured. From this measured current and a voltage assumed to be known, the cold resistance is calculated in a known manner. This is at unconsumed glow plugs, so glow plugs with low probability of failure, usually between 0.3 Ω and 1.0 Ω. If a higher cold resistance is determined because the current flowing through the glow plug drops, so this has according to experience on the early failure of the glow plug. If the measured cold resistance exceeds a specified threshold, the glow plug must be replaced.

In this known method, however, the current is measured without regard to the manner in which the candle is supplied with electrical voltage. In other words, known methods for failure detection of glow plugs measure the current flowing through the glow plug RMS and thus determine only an effective cold resistance of the glow plug. This also applies to glow plugs which are supplied with a pulse-width-modulated voltage, that is to say with a continuous series of voltage pulses of an electrical voltage. Pulse width modulated means that a duty cycle of the voltage pulses is modulated at a constant frequency. In motor vehicle engines, for example, a pulse-width-modulated voltage for supplying glow plugs by means of an electronic glow time control device is generated from the on-board voltage. So far, especially low-voltage glow plugs were supplied with an operating voltage of less than 11 V with a pulse width modulated voltage. Recently, such a power supply but more and more for on-board glow plugs with an operating voltage of 11 V and above is used.

In particular, for glow plugs operated with a pulse-width-modulated voltage, known methods for early failure detection of glow plugs prove to be less reliable.

Disclosure of the invention

It is the object of the present invention to provide a method for early failure detection of a supplied with a pulse width modulated voltage glow plug and an engine adapted to carry out such a method, in which the reliability of the early failure detection is increased.

This object is achieved by the method with the features of claim 1 and a motor having the features of claim 10.

In contrast to known methods, which only determine effective values for the measured current and thus only the effective cold resistance over many voltage pulses, in the method according to the invention the resistance of the glow plug is detected, which the glow plug shows during a single voltage pulse. In other words, the method of the present invention utilizes a higher resolution approach than known methods because it relies on the resistance of the glow plug during a single voltage pulse and not on a mean or rms value of cold resistance determined over many voltage pulses. This results in a much more accurate and reliable prediction of the probability of default than can be achieved by known methods. The type of glow plug for the process is irrelevant. For example, the method is equally suitable for a low-voltage glow plug as for an on-board glow plug or a ceramic glow plug.

It is possible in step (a) to record the time profile of the resistance during the respective voltage pulse. In such a case, the comparison value derived from the resistance in step (b) could be, for example, the mean value or an extreme value of the resistance during the voltage pulse. On the other hand, a time-dependent comparison value can be derived, provided z. B. in step (c) a condition for the temporal dependence of the comparison value is specified.

If a plurality of voltage pulses occur in the predetermined time interval, steps (a) to (e) can also be carried out repeatedly on different individual voltage pulses within the time interval, for example cyclically or sporadically.

The comparison value may in general be any suitable comparison value. For example, the comparison value may be identical to the electrical resistance. Another suitable comparative value would be the gradient of the electrical resistance, ie the change with time of the resistor or its derivative with respect to time. A resistance gradient with a negative sign can be an indication of the increased probability of failure of a glow plug, because with old and used glow plugs above all the so-called hot resistance of the glow plug, which is usually measured after 25 s or 60 s after the start of Glühzyklusses, within a voltage pulse shows a declining tendency. For new glow plugs, a hot resistance of 0.6 Ω to 2.0 Ω is common. Like the cold resistance, the hot resistance tends to increase with age of the glow plug. The hot resistor offers another observable, which can be exploited to estimate the probability of failure of a glow plug.

In a preferred embodiment of the method, the beginning of the time interval coincides with the beginning of a Glühzyklusses the glow plug. In this case, the duration of the time interval is preferably 60 s and particularly preferably 25 s, so that the detected electrical resistance corresponds to the cold resistance of the glow plug. Or the time interval begins at least 25 s or preferably 60 s after the start of the annealing cycle, so that the detected electrical resistance corresponds to the hot resistance of the glow plug.

In a further preferred method, at least steps (a) and (b) are carried out for at least one voltage pulse within at least one further time interval, this further time interval and the first time interval being disjunct. In principle, both time intervals may be within the same annealing cycle, or both of the time intervals may be within different annealing cycles of the glow plug, with the sequence of voltage pulses being suspended between anneal cycles. For example, the validity of the method can be increased by detecting both the cold resistance and the hot resistance within a single annealing cycle by determining cold resistance and hot resistance, respectively, according to step (a) for respective disjoint time intervals during an annealing cycle, then respectively b) to perform (e). On the other hand, to detect sudden changes in the characteristics of the glow plug between annealing cycles, for example, cold resistance and / or hot resistance can be detected in successive annealing cycles, using comparative values obtained for each annealing cycle to specify the condition in the respective subsequent annealing cycle. In this connection, it is advantageous to store the comparative values obtained during execution of steps (a) and (b) during a first annealing cycle and during execution of steps (a) to (e) during a first annealing cycle subsequent second Glühzyklusses in step (c) read and use to specify the condition. Preferably, a so-called ring memory is used to store the comparison values, which stores the comparison values of a specific number of, preferably five, annealing cycles as data records in a stack. If the stack is filled, the data sets are successively overwritten with new records starting from the bottom record during execution of the process during the following annealing cycles.

Most preferably, in the execution of steps (a) and (b) during the very first Glühzyklusses the glow plug after their commissioning, the comparison value permanently stored and when performing steps (a) to (e) during subsequent annealing cycles in each step (c) respectively read out and used to specify the condition. In this way, a reference is provided with the original values of the glow plug, which allows an estimate of the absolute aging and wear of the glow plug. In particular, when performing step (c) during an annealing cycle, it is preferable to read both the comparison value of the very first annealing cycle and the comparison value of a respective annealing cycle immediately preceding the annealing cycle, and to use these to specify respective conditions for the comparison value of the current annealing cycle; d) checking whether these conditions are met, and wherein in step (e) the signal is output if the comparison value satisfies at least one of the conditions. In this way, the validity of the process is increased again.

The signal output in step (e) can be used to trigger different reactions, which can take place individually or in any desired combinations. Thus, the output signal, the operation of the glow plug to protect it at a predetermined voltage level, preferably the intended operating voltage, or below restrict or cause the glow plug to turn off. On the other hand, the signal may be responsible for the output of an optical, audible or haptic warning signal at a human machine interface (HMI). Further, the signal may cause a diagnostic message to be written to a fault memory that may be read out and further processed by a microprocessor.

Brief description of the drawings

Figur 1

stellt schematisch einen Motor eines Kraftfahrzeuges mit einer Glühkerze dar;

Figur 2

stellt nicht maßstabsgerecht Spannungspulse und Zeitintervalle für verschiedene Glühzyklen der Glühkerze dar;

Figur 3a)

ist ein Diagramm, das den zeitlichen Widerstandsverlauf während zweier einzelner Spannungspulse der kalten Glühkerze nach unterschiedlich vielen Glühzyklen zeigt;

Figur 3b)

ist ein Diagramm, das den zeitlichen Widerstandsverlauf während zweier einzelner Spannungspulse der heißen Glühkerze nach unterschiedlich vielen Glühzyklen zeigt; und

Figur 4

zeigt ein Flussdiagramm des erfindungsgemäßen Verfahrens.

The invention will be explained in more detail with reference to drawings.

FIG. 1

schematically illustrates an engine of a motor vehicle with a glow plug;

FIG. 2

does not scale to voltage pulses and time intervals for different annealing cycles of the glow plug;

FIG. 3a)

is a diagram showing the time course of resistance during two individual voltage pulses of the cold glow plug after different number of Glühzyklen;

FIG. 3b)

is a diagram showing the time course of resistance during two individual voltage pulses of the hot glow plug after different number of Glühzyklen; and

FIG. 4

shows a flowchart of the method according to the invention.

Embodiments of the invention

According to FIG. 1 a glow plug 1 protrudes into the combustion chamber 2 of an engine 3 of a motor vehicle, not shown. An electronic Glühzeitsteuergerät 4 supplies the glow plug 1 with a pulse width modulated voltage, which generates it from the on-board voltage. A microcontroller 5 with an evaluation unit 6 is provided for measuring the current flowing through the glow plug 1 and for determining its resistance by means of the known voltage applied to the glow plug. The microcontroller 5 is connected to a human-machine interface or HMI 7, which is set up to output an optical and / or audible warning signal, and to a fault memory 19.

The course of the pulse width modulated voltage is shown in the diagram of FIG. 2 highly simplified and not to scale symbolized as a result of rectangular voltage pulses along a time axis. An annealing cycle of the glow plug 1 is understood to be the time during which the glow plug 1 is continuously supplied with a sequence of voltage pulses of a respective electrical voltage in order to support a cold start of the motor. The power supply of the glow plug 1 and the annealing cycle end as soon as the engine 3 no longer requires support by the glow plug 1, where as the driving cycle, the time between starting and stopping the engine 3 is understood regardless of whether the vehicle is actually moving. Because the glow plug 1 assists the cold start of the engine 3 and the engine 3 usually does not cease operation at the end of the glow cycle of the glow plug 1, the start of a drive cycle coincides with the beginning of a respective glow cycle of the glow plug 1, but the drive cycle lasts usually longer than the annealing cycle.

FIG. 2 now shows three consecutive annealing cycles 8, 9, 10 of the glow plug 1, the respective driving cycles of the motor 3 correspond and may be of different duration. Because the start of each of the annealing cycles 8, 9, 10 coincides with the beginning of a respective driving cycle, a respective driving cycle ends at a time between two respective ones of the annealing cycles 8, 9, 10 so that the engine 3 immediately before the start of each annealing cycle 8, 9, 10 is switched off, wherein the time between the driving cycles or the annealing cycles 8, 9, 10 is generally irregular and arbitrary.

For the annealing cycle 8 is in FIG. 2 a time interval 11 is drawn, whose beginning is identical to the beginning of the Glühzyklusses 8 and whose duration is less than 25 s. During this time interval 11, the glow plug 1 has not yet reached its operating temperature. Accordingly, a resistance determined by the microcontroller 5 during a voltage pulse 17 in the time interval 11 is a cold resistance of the glow plug 1 FIG. 2 a time interval 12 is drawn in, the earliest 60 s after the start of the Glühzyklusses 8 begins. In the time interval 12, the glow plug 1 has reached its operating temperature, and a resistance determined by the microcontroller 5 during a voltage pulse in the time interval 12 is accordingly a hot resistance of the glow plug 1.

In the FIG. 3a ) are in a resistance-time diagram to see the time course of the cold resistance of the glow plug 1 after 3000 annealing cycles and after 10,000 annealing cycles during two individual successive voltage pulses, wherein the graph provided with the reference numeral 13 represents the cold resistance 13 of the glow plug 1 after 3000 annealing cycles while the graph provided with the reference numeral 14 represents the cold resistance 14 of the glow plug 1 after 10000 annealing cycles. As in FIG. 3a ), the cold glow resistor 13 of the younger glow plug rises steeply to a resistance of more than 0.4 Ω immediately after the onset of the first voltage pulse at time t = 0, and stays in during the duration of the voltage pulse of slightly more than 0.02 second slightly increasing trend above the value During the subsequent voltage pulse, the cold resistance 13 reaches almost the value of 0.5 Q right at the beginning of the voltage pulse, and then drops first in the further course of the voltage pulse and towards the end of the voltage pulse to easily exceed the value of 0.5 Ω. In contrast, the cold resistance 14 of the older glow plug exceeds the value of 0.5 Ω already at the beginning of the first voltage pulse and grows in the further course of the voltage pulse to above 0.6 Ω, while in the course of the second voltage pulse with slight slope values between 0 , 5 Ω and 0.6 Ω.

In FIG. 3b ) are shown for comparison, the hot resistance of the glow plug 1 also after 3000 Glühzyklen and after 10,000 annealing cycles during two individual successive voltage pulses, the glow plug 1 after 3000 annealing cycles, the hot resistor 15 and after 10000 annealing cycles has the hot resistor 16. It is striking that the younger glow plug 1 after 3000 Glühzyklen during both voltage pulses has a nearly constant resistance between 1.2 Ω and 1.4 Ω, while the older glow plug after 10000 Glühzyklen at the beginning of each voltage pulse has a higher resistance of over 1.4 Ω, which drops in the course of the voltage pulse, however. Accordingly, the older glow plug 1 is characterized by a falling course of the hot resistor 14 during a voltage pulse. In other words, the change with time or the gradient of the hot resistor 14 is negative.

In the method according to the invention, the different resistance characteristic during a single voltage pulse is now utilized in newer and older glow plugs 1.

By means of the flowchart of FIG. 4 the procedure is explained in more detail. After the method has started in step S1, the cold resistance of the glow plug 1 during a single voltage pulse 17 is determined by the microcontroller 5 in step S2 detected within the time interval 11 of the Glühzyklusses 8. From this cold resistance, a comparison value is derived by the evaluation unit 6 in the subsequent step S3, which in the simplest case is identical to the cold resistance. From the evaluation unit 6, a condition for the comparison value is specified in step S4. Again, in the simplest case, this condition consists of a threshold that must not be exceeded by the comparison value. For example, in the case of FIGS. 3a ) and 3b ) a threshold value of 0.6 Ω can be specified. If this threshold value is exceeded by the cold resistance, then this is an indication that the glow plug 1 has reached a critical age and that due to this a rapid failure of the glow plug 1 can be expected. Therefore, it is checked in step S5 whether the comparison value or the cold resistance satisfies the predetermined condition, ie in the present case whether the cold resistance of the glow plug 1 is greater than 0.6 Ω. If this is the case, signals are output from the microcontroller 5 to the glow time control device 4 and to the HMI 7 in step S6 to cause the glow time control device 4 to supply the glow plug 1 with only a predetermined operating voltage in the following, while the HMI 7 for Issue of an optical and / or audible warning signal is caused. Furthermore, an entry is made in the error memory 19 of the motor 3, which can later be read out and utilized by a controller, not shown for this purpose. The method then ends with step S7. If, on the other hand, it is determined in step S5 that the cold resistance is less than 0.6 Ω, no signal is output by the microcontroller 5 and the method ends with step S8.

In another embodiment of the method according to the invention in step S2 instead of the cold resistance of the glow plug 1 whose hot resistance is measured, for example, during a single voltage pulse 18, which is within the in the FIG. 2 shown time interval 12 of the Glühzyklusses 8 is located. In such case, in step S3, the Gradient of the hot resistance derived from this and used as a reference. Since a glow plug 1 shortly before failure has a negative hot resistance gradient during a voltage pulse, it is expedient in step S4 to predetermine for the comparison value as a condition that the comparison value must be negative or less than zero. In the subsequent step S5 then the sign of the comparison value is checked. If this is negative, ie if the hot resistance has a negative gradient, steps S6 and S7 take place successively. On the other hand, if the sign is zero or positive, step S8 occurs.

The two described methods can also be combined by detecting both the cold resistance during the voltage pulse 17 and the hot resistance during the voltage pulse 18 and, as explained above, the cold resistance and the gradient of the hot resistance are derived as respective comparison values and respective conditions for these comparison values be explained above. In step S5, these conditions are then checked for both the cold resistance and the gradient of the hot resistance, and steps S6 and S7 are carried out as far as either the cold resistance or the gradient of the hot resistance or both satisfy the respective condition. Accordingly, the method can be executed with any number of comparison values and respective conditions for these comparison values. As comparison values, in addition to the cold resistance and the gradient of the hot resistance, the hot resistance itself and / or the gradient of the cold resistance can be used alternatively or in combination in particular.

According to a further embodiment of the invention, when carrying out the method, the measured resistances and / or the comparison values are stored in order to enable them during execution of the method during a subsequent annealing cycle for specifying the condition in step S4 use. Are the steps S1-S3 in the FIG. 4 for example, during the Glühzyklusses 9 of FIG. 2 executed, the measured cold and hot resistances and / or the comparative values derived therefrom such as cold resistance, hot resistance and gradient of the cold resistance and gradient of the hot resistance are stored in a ring memory. When the process is executed again in the subsequent annealing cycle 10, the stored comparison values of the previous annealing cycle 9 are read from the ring memory in step S4. These read-out comparison values are used to specify suitable conditions for the comparison values obtained during the annealing cycle 10. For example, one possible condition would be that the difference in the cold resistances of the annealing cycles 9 and 10 should not exceed a predetermined threshold. In this way, sudden changes in resistance of the glow plug 1 between individual annealing cycles 8, 9, 10 can be detected. The differences between the comparison values of the annealing cycles 9 and 10 are written into the ring memory as additional comparison values with the remaining comparison values of the annealing cycle 10, in order to be read out in a subsequent annealing cycle as described in step S4 and used to specify suitable conditions.

Finally, in a further embodiment of the invention, the comparative values of this very first annealing cycle are permanently stored as a so-called "primary vector" for the entire service life of the glow plug when the method is performed during the very first annealing cycle immediately after startup of the glow plug. As an alternative or in addition to the above-described procedures, this initial vector is read out during the execution of the method during each subsequent annealing cycle and used to specify conditions for the comparison values of the respective annealing cycle. As a possible condition can be set for the comparison values be that they may not deviate from a given value of corresponding components of the original vector. Is it, for example, in the annealing cycle 8 in the FIG. 2 around the very first annealing cycle of the glow plug 1, the comparison values derived in step S3 during the annealing cycle 8 are permanently stored as the original vector. When the method is carried out during the subsequent annealing cycles 9 and 10 and all further annealing cycles, this initial vector is read out in step S4 and the condition is specified that the comparison values of the respective annealing cycle may not deviate from the comparison values in the original vector by more than predefined threshold values , If it is determined in step S5 that the deviation of a comparison value from the corresponding comparison value of the original vector exceeds the predetermined threshold value, steps S6 and S7 are executed.

Claims (10)

Method for early failure detection of at least one glow plug (1) which is supplied with a continuous series of voltage pulses (17, 18) of a respective electrical voltage during at least one annealing cycle (8, 9, 10) of the glow plug (1), comprising the steps of: (A) detecting an electrical resistance (13, 14, 15, 16) of the glow plug (1) during a single voltage pulse (17, 18), which takes place within a predetermined time interval (11, 12); (b) deriving at least one comparison value from the electrical resistance (13, 14, 15, 16); (c) specifying a condition for the comparison value; (d) checking if the comparison value satisfies the condition; and (e) outputting at least one signal if the comparison value satisfies the condition. Method according to Claim 1, in which at least one comparison value is identical to the electrical resistance (13, 14, 15, 16) and / or at least one comparison value is a gradient of the electrical resistance (13, 14, 15, 16). Method according to one of claims 1 or 2, wherein the beginning of the time interval (11) coincides with the beginning of a Glühzyklusses (8, 9, 10) of the glow plug (1), or wherein the time interval (12) at least 25 s or 60 s after Beginning of the annealing cycle (8, 9, 10) begins. Method according to one of the preceding claims, in which at least steps (a) and (b) are carried out for at least one voltage pulse (17, 18) within at least one further time interval (11, 12), this further time interval (11, 12) and the time interval (11, 12) are disjoint. Method according to claim 4, wherein both time intervals (11, 12) are within the same annealing cycle (8, 9, 10) or wherein both time intervals (11, 12) are within different annealing cycles (8, 9, 10), wherein between the Annealing cycles (8, 9, 10) the sequence of voltage pulses (17, 18) is exposed. Method according to claim 5, wherein during the execution of steps (a) and (b) during a first annealing cycle (8, 9, 10) the comparison value is stored and during execution of steps (a) to (e) during a subsequent second annealing cycle (8 , 9, 10) in step (c) and used to specify the condition. A method according to claim 6, wherein during the execution of steps (a) and (b) during the very first annealing cycle (8) of the glow plug (1) after commissioning the comparison value is stored permanently and during execution of steps (a) to (e) during the following Annealing cycles (9, 10) in each step (c) each read and used to specify the condition. Method according to claim 7, wherein during the execution of step (c) during an annealing cycle (9, 10) both the comparison value of the very first annealing cycle (8) and the comparison value of a respective annealing cycle (9, 10) immediately preceding the annealing cycle (9, 10) ) and used for specifying respective conditions for the comparison value of the Glühzyklusses (9, 10), wherein in step (d) is checked whether these conditions are met and wherein in step (e) the signal is output when the comparison value at least one of the conditions met. Method according to one of the preceding claims, wherein the signal output in step (e) operation of the glow plug (1) at a predetermined voltage level and / or turning off the glow plug (1) and / or the output of an optical warning signal and / or the output an acoustic warning signal and / or the output of a haptic warning signal and / or the writing of a diagnostic message in a fault memory (19) causes. Motor (3) with at least one glow plug (1), which is set up for early failure detection of the glow plug (1) for carrying out a method according to one of the preceding claims.

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