DE102009008248A1 - Method for preventing pre-ignition of cylinder of internal-combustion engine i.e. Otto engine, involves performing additional temporary or durable intervention on operating parameter of engine after defined amount of recognized pre-ignition - Google Patents

Abstract

The method involves recognizing knocking and pre-ignition of a cylinder with different algorithms and preventing ignition angle intervention of knocking regulation for retardation adjustment of ignition angle with contemporaneous recognition of knocking and pre-ignition. A fuel-rich fuel air mixture is produced for a preset time period. An additional temporary or durable intervention different from the intervention mass is performed on operating parameters of an internal-combustion engine on a part of an engine control after defined amount of recognized pre-ignition.

Description

The method serves to prevent Vorentflammungen in the combustion chambers of an Otto engine operated internal combustion engine. Pre-ignition is an irregular combustion in which parts of the fuel-air mixture are burned before the ignition is initiated via a spark plug. These spontaneous combustion of the fuel-air mixture occur before the actual ignition time, possibly even in the compression phase. The causes of pre-ignition are complex. Known causes, which lead to pre-ignition individually or in combination with one another, are spontaneous combustion in hot exposed areas in the combustion chamber, charge inhomogeneities and increased temperature level in the combustion chamber. Known influencing factors are the charge cycle control, influencing variables on the temperature level, fuel quantity, boost pressure, ignition angle setting, EGR control, etc. The prior art further describes a number of detection methods for the detection of pre-ignition. For example, describes DE 10 2006 015 662 A1 a detection method based on so-called knock sensors, which detect combustion noise via mechanical vibrations. Based on other influencing factors, eg. As the load detection, an extreme value monitoring is activated, which performs a shutdown of the cylinder / injection when detecting extreme knockers or Vorentflammungen. In the case of multiply occurring extreme values, the cylinder is switched off not only intermittently, but for the present driving cycle. This measure prevents mechanical damage, but also leads to performance and comfort losses.

Another method for the detection of Vorentflammungen is in the DE 10 2007 024 415 B3 specified. Here, the speed signal of the crankshaft is evaluated parallel to the signal of a knock sensor. By means of the evaluation of the speed signal during the power stroke, a delayed rotational movement is detected by comparison with a previous standard value and a pre-ignition is detected on the basis of this detection and a subsequent knock detection. In response to detected Vorentflammungen the fuel supply is interrupted, increases the boost pressure or cooled the corresponding cylinder with fuel.

Furthermore, it is already known from the DE 198 59 310 A1 To detect pre-ignition via a detection of the ion current, in which case the use of a control loop is described in which operating parameters of the internal combustion engine are controlled by the engine control based on detected pre-ignition. It is proposed, when the threshold value is exceeded for the measured ion current, to shift the firing angle in a controlled manner to later firing points and to return to a preset firing angle after elimination of the pre-firing. This method largely corresponds to the approach of a conventional knock control, which shifts the ignition angle at later firing times by an amount of several degrees crank angle abruptly when knocking events occur and then progressively gradually approaches the preset ignition angle. Such a method is for example from the DE 31 42 082 A1 known. Further improved methods evaluate the distance to the knock limit and / or use threshold value adaptations for knock detection and, based thereon, control of the ignition time (eg. DE 10 2007 007 641 A1 ). Knocking recognition in the prior art are based on structure-borne sound detection by knock sensors, cylinder pressure detection, ion current measurement or high-resolution speed considerations of the signal of the crankshaft speed.

Problematic on the detection of knocking and pre-ignition and the subsequent ones based on it Parameter settings are the detection algorithms that partly overlap in their results, covering both knocking and pre-ignition detect in parallel, but different approaches to Elimination of irregular combustion phenomena make necessary. Switching off the injection when detected Pre-ignition leads to the prevention of further pre-ignition, At the same time, however, it generates a non-circular run of the unit. One for the respective cylinder or the whole unit related, imperceptible to the driver reaction is desirable.

Of the The present invention is therefore based on the object, a method to avoid pre-ignition, which enhances ride comfort as well as power and consumption of the internal combustion engine only as small as possible influences and at the same time a safe avoidance of further Vorentflammungen allows. The algorithm should be in an existing one Motor concept be incorporated by existing algorithms for Knock control can be used. Furthermore, a fast Elimination / "extinction" of pre-ignition done and a permanent reduction of Vorentflammungsneigung be achieved.

The Solution of the task is carried out according to the features of the main claim. Advantageous embodiments are the subclaims and the description.

For the method for preventing Vorentflammungen in cylinders of a Otto engine operated internal combustion engine, in which ge separated algorithms Vorentflammung and knocking is detected or predicted is carried out with simultaneous detection of Vorentflammungs- and knock events according to the invention advantageously blocking the knock control and thus preventing the default displacement of the ignition angle toward later ignition times. It has been shown that a retardation of the ignition at already detected or predicted pre-ignition can further increase the Vorentflammungsneigung, since later Zündwinkellagen a later combustion takes place, which leads to a higher temperature level in the cylinder at subsequent working cycles and thus further promotes the pre-ignition. Knock control and Vorentflammungsvermeidung thus work with regard to the ignition angle in different directions. In order to achieve deletion of the pre-ignition and a lowering of the tendency to knock despite the blocking of the ignition angle intervention of the knock control, an intervention takes place on the fuel mass to be injected, which is increased compared to the applied setpoint value, so that in the subsequent working cycle of the cylinder a fuel-rich fuel-air Mixture, preferably with a lambda value <0.9, is present. The intervention on the fuel mass is accurate to cycle realized, so that a rapid extinguishment of the pre-ignition can be done while reducing the tendency to knock. Furthermore, the occurrence frequency of the detected or predicted pre-ignition is evaluated by statistical methods, wherein in the simplest case, a counter is provided so that depending on the frequency of occurrence, additional, for fuel intervention additional and independent of this interventions to reduce the Vorentflammungsneigung done. These measures are preferably a limitation of the boost pressure and / or an adjustment of the desired position of the camshaft, preferably the intake camshaft. The position of the inlet camshaft and thus the start of opening of the intake valve and the boost pressure are decisive influencing factors for compression and combustion end pressure and thus determine the temperature level in the combustion chamber. Advantageously in accordance with the invention, a cycle-specific possible intervention - fuel mass adaptation - is thus combined with a slower adjustable engagement. Advantageously in accordance with the invention, the intervention on the fuel mass after a detected or predicted pre-ignition is only carried out for a short period in order to extinguish the pre-ignition on the one hand and to avoid unnecessary deterioration of the fuel consumption and / or exhaust gas values on the other hand. The adaptation of the fuel mass is deleted after the predefinable period of time, so that an originally intended for this operating point fuel-air mixture is set again.

In An embodiment of the invention is used for recognition / prediction the Vorentflammung continue the detection signal of the knock control used, so that a Vorentflammung always then recognized / predicted when the pre-ignition detection characteristics are present and additionally knocking of the same cylinder is detected.

As already described, in addition to the temporary Intervention on the fuel mass with repeated occurrence of Pre-ignition another intervention on the operating parameters the internal combustion engine, preferably by limiting the boost pressure and / or by specifying a new desired position value for the Camshaft whose position is changed, this intervention / interventions a second period of time can be made larger than the time span of the first intervention.

Of the further intervention on the operating parameters of the internal combustion engine (Adaptation), which occurs in the case of repeated occurrence of pre-ignition, is preferably up to the entire drive cycle to stop the internal combustion engine active. Furthermore, it is possible to carry out this adaptation up to a recognized refueling, so that an increase in pre-ignition tendency due to insufficient Fuel quality and associated adaptation to Refueling if necessary after elimination of the cause of increased Pre-ignition tendency is eliminated again. Another embodiment The invention leaves the adaptation value until the next one Workshop visit / service interval.

According to the invention advantageous there is an adaptation of the setpoint of the boost pressure or the target position the camshaft in at least the operating point, in which the pre-ignition was recognized / predicted.

Further advantageous embodiments are the figures and the associated Figures description to take.

in this connection demonstrate:

1 a schematic representation of the deletion of a pre-ignition,

2 a schematic representation of an adaptation to reduce Vorentflammungsneigung.

1 shows a schematic representation of the procedure for deleting a pre-ignition. Timed to each other are the occurrence of knock events, the pre-ignition prediction, the ignition angle, the lambda value, a pre-ignition counter value and an associated counter value, and the boost pressure limit shown.

in the top diagram are occurring with the respective markers Knock events shown. The knock detection takes place as known in the art. Detect knock events in known knock control to a retardation the ignition angle. The retardation of the ignition angle is in the illustrated diagram based on the Zündwinkelsprungs recognizable, followed by a gradual approach to the original ignition angle, as long as no further knock events are detected. At another Knock event occurs the adjustment of the ignition angle in analogous way. If a pre-ignition is detected or predicted (Marking in the second diagram v. O.), So deviates from the reaction the knock control no adjustment of the ignition angle, too if a knock event was detected in parallel. A detection of Pre-ignition leads to an intervention on the fuel mass, so that by an adaptation of the fuel mass to be injected generates a fuel-rich fuel-air mixture in the combustion chamber becomes. In the fourth diagram from above this intervention is based on the given predetermined lambda value in the combustion chamber, which is implemented by a corresponding fuel injection. As the pre-ignition occurs, the counter becomes pre-ignition set to 1. The counter value remains in the present Example below the threshold. The detection or prediction of Pre-ignition takes place as described in the prior art by analysis of the structure-borne sound signal, the ionic current signal or by evaluation of cylinder pressure or speed signals. A special preferred method for evaluating the Vorentflammung here the high-resolution analysis of the speed signal associated with the crankshaft encoder wheel and an associated Sensor generate during the circulation of the sender wheel at the times of Passing the respective encoder wheel marks / teeth position signals the crankshaft. From these so-called teeth times can be a high-resolution Speed signal for the respective revolution of the sender wheel be obtained, which a number of speed signals during of the working game supplies. From the single consecutive Speeds and their differences, which occur in the working and compression stroke, the characteristics characterizing combustion can be isolated. It has been shown that, for example, an early location and a high value of the gradient of the speed signal indicative of are a Vorentflammung. These values can be based on past working cycles are evaluated and in case of deviation in characteristic orders of magnitude can be a recognition / prediction of Pre-ignition. Furthermore, it is possible over the development of these values through previous work cycles to allow prediction of pre-ignition before it occurs. in this connection Several evaluation procedures can be carried out in parallel. A Validation of a predicted pre-ignition by means of the signal the knock sensor or the evaluation of the knock control is also possible.

In 2 is shown in a schematic diagram of the procedure for the adaptation of parameters in multiple occurring pre-ignition. The temporally first section until the first dotted timestamp is similar to 1 described procedure. If, as indicated by the first mark in the upper diagram, knocking is detected without a pre-ignition being predicted / detected, the ignition angle shift takes place at later ignition times and the subsequent approach to the previous ignition angle. As time passes, knocking and pre-ignition are simultaneously predicted / detected at the same time. As already too 1 described, with simultaneous prediction / detection of Vorentflammungen the Zündwinkeleingriff the knock control is disabled and there is no late shift of the ignition angle, but the Solllambda value is shifted (for example, from 0.95 to 0.8 - as shown), resulting in an increased injection quantity in the next Working cycle leads. The detected pre-ignition counter is set to 1. Subsequently, again a detection of pre-ignition and knock, in which the procedure described is repeated. The Zündwinkeleingriff is disabled, there is the described intervention via the fuel injection and the counter is increased by 1. At the next occurrence of knocking and predicted / detected pre-ignition (fourth dotted timestamp), the counter exceeds the threshold. The ignition angle, in turn, remains unchanged and the pre-ignition is extinguished by the intervention on the fuel injection. Due to the multiple recognized / predicted Vorentflammungen another intervention to reduce the Vorentflammungsneigung done. It can be seen in the lower diagram that at the time the threshold is exceeded by the repeated occurrence of knocking and pre-ignition events, the boost pressure set point is reduced. The actual value follows this time-delayed. The adaptation value for the supercharging pressure setpoint remains for further working cycles, even if the adaptation of the fuel quantity via the lambda setpoint adaptation is canceled again. Equivalent to the boost pressure setpoint adjustment is the adjustment of the camshaft position, in particular the intake camshaft possible. Here are different effects, which must be considered in an adjustment to reduce the Vorentflammungsneigung. A later opening of the intake valve by a retarded camshaft position leads to a lower effective compression ratio in Kom Pressionshub and therefore influences the compression end pressure and ultimately the temperature in the combustion chamber. At the same time, however, flow effects are promoted by an advance of the camshaft, which lead to a flushing of the combustion chamber with fresh air at the intersection of inlet and outlet valve opening, which ultimately leads to a cooling of the combustion chamber. Depending on the operating point, an adjustment of the position of the intake camshaft may be effective after early or late to reduce the Vorentflammungsneigung. The adjustment direction must therefore be modeled or specified based on determined experimental data operating point-dependent.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 102006015662 A1 [0001]
• - DE 102007024415 B3 [0002]
• - DE 19859310 A1 [0003]
• DE 3142082 A1 [0003]
• DE 102007007641 A1 [0003]

Claims (8)

Method for preventing pre-ignition in cylinders of an Otto engine operated internal combustion engine, in which with different algorithms both tapping and Pre-ignition can be detected or predicted and at the same time Detecting / predicting knock and pre-ignition the ignition angle intervention the knock control prevents retardation of the ignition angle and in parallel for a predefinable period of time Change in the injected fuel mass a fuel-rich Fuel-air mixture is generated in the combustion chamber and after a defined number of further detected or predicted pre-ignition another, from the intervention on the injected fuel mass various, temporary or permanent interference with operating parameters of Internal combustion engine is made by the engine control, which the Minimizes pre-ignition tendency. Method according to claim 1, characterized in that that a pre-ignition is detected / predicted when at the same time Knocking the same cylinder is detected. Method according to claim 1 or 2, characterized that further intervention on the operating parameters of the engine control occurs at repeated occurrence of Vorentflammungen and this by boost pressure limitation and / or adjustment of the position of the camshaft he follows. Method according to claim 3, characterized that the position of the intake camshaft is adjusted. Method according to one of the preceding claims, characterized in that statistically the number of recognized / predicted Pre-ignition is recorded over a cycle and on Based on this number of further intervention on the operating parameters of the Motors done. Method according to one of the preceding claims, characterized in that at a recognized or predicted Pre-ignition of the temporary first intervention on the fuel mass withdrawn after a predefinable first period of time becomes. Method according to one of the preceding claims, characterized in that the further intervention on the operating parameters the engine control in case of repeated occurrence of Vorentflammungen a second period of time is performed for the duration is, with the second period being greater than the first Period of the first intervention is. Method according to one of the preceding claims, characterized in that the further intervention on the operating parameters the engine control in case of repeated occurrence of Vorentflammungen to an adaptation of the boost pressure or the position of the camshaft in at least the operating point leads, in which the Vorentflammung was recognized / predicted, this adaptation being at least one Driving cycle until the engine shutdown or recognized Refueling or permanently at least until the next service for the further operation of the internal combustion engine upright is obtained.