DE102009008248B4 - Method for preventing pre-ignition in cylinders of an Otto engine operated internal combustion engine - Google Patents

Abstract

A method for preventing Vorentflammungen in cylinders of a Otto engine operated internal combustion engine, in which with different algorithms both knocking and Vorentflammungen be detected or predicted and at the same time detecting / predicting knock and Vorentflammung the Zündwinkeleingriff the knock control is retarded for retarding the ignition angle and parallel for a predefinable time period via a change in the injected fuel mass, a fuel-rich fuel-air mixture is generated in the combustion chamber and after a defined number of other detected or predicted Vorentflammungen another, the intervention on the injected fuel mass different, temporary or permanent intervention on operating parameters of the engine by the engine control, which minimizes the pre-ignition tendency.

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.

From the EP 1 715 179 A2 Furthermore, a method for avoiding premature combustion events in an internal combustion engine is previously known, wherein in the simplest possible way for the internal combustion engine dangerous knocking phenomena should be detected and avoided. For this, at least one knock sensor is provided for detecting knock events in the combustion chamber, wherein when a knock event occurs, a test step is first performed to distinguish between spark-induced normal knocking and premature combustion, and at least one premature combustion prevention measure is performed if the knocking event is premature Incineration is identified.

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 up detect both knocking and pre-ignition in parallel, but different approaches to the elimination of irregular combustion phenomena necessary do. Switching off the injection when detected pre-ignition leads to prevention more Vorentflammungen, but at the same time produces a non-round Course of the unit. One for the respective cylinder or the whole unit related, for the driver imperceptible reaction is desirable.

The present invention is therefore based on the object to provide a method for preventing Vorentflammungen, which affects the ride comfort and power and consumption of the internal combustion engine as little as possible and at the same time a safe avoidance of others Pre-ignition possible. The algorithm should be able to be incorporated into an existing engine concept by using existing knock control algorithms. Furthermore, a quick elimination / "deletion" of the pre-ignition should take place and a permanent reduction of Vorentflammungsneigung be achieved.

The solution the task is carried out according to the features of the main claim. Advantageous embodiments are the dependent claims and to take the description.

For the procedure to prevent pre-ignition in cylinders of an Otto engine operated internal combustion engine, in which with separate algorithms Pre-ignition and knocking is detected or predicted takes place with simultaneous detection of pre-ignition and knocking events According to the invention advantageous a blocking of the knock control and thus a prevention of the standard relocation the ignition angle towards later Ignition points. It has been shown that retarding the ignition at already identified or predicted pre-ignition the Vorentflammungsneigung continue to increase can, as with later Zündwinkellagen a later one Combustion occurs, which in subsequent work cycles too a higher temperature level in the cylinder leads and thus the pre-ignition further favors. Knock control and pre-ignition prevention work with it with regard to the ignition angle in different directions. In spite of the blocking of the Zündwinkeleingriffes the knock control a delete the pre-ignition and lowering the tendency to knock, an intervention takes place on the fuel mass to be injected, which is increased compared to the applied setpoint, so that in the following Working cycle of the cylinder a fuel-rich fuel-air mixture, preferably with a lambda value <0.9, is present. The procedure over The fuel mass is accurate to the cycle, so that a fast Clear the pre-ignition while reducing the tendency to knock can be done. Furthermore, with the help of statistical methods the frequency of occurrence evaluated or predicted pre-ignition, where in the simplest case, a counter is provided so that in dependence from the frequency of occurrence further, for fuel intervention additional and independent of this intervention to reduce the Vorentflammungsneigung done. These measures are preferably a limitation of the boost pressure and / or an adjustment the target position of the camshaft, preferably the intake camshaft. The position of the intake camshaft and thus the beginning of the opening of the intake valve and the boost pressure are significant influencing factors for compression and Combustion pressure and thus determine the temperature level in the Combustion chamber. According to the invention advantageous is thus a cycle exactly possible intervention - fuel mass adaptation - with a slower adjustable intervention combined. According to the invention advantageous is done after detected or predicted pre-ignition Engaged in the fuel mass only a short period of time to on the one hand to extinguish the Vorentflammung and on the other hand no unnecessary Deterioration of fuel consumption and / or exhaust gas values. The adaptation of the fuel mass is after the predefinable Deleted time, so that one originally For this Working point provided 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 a knocking of the same cylinder is detected.

As already described, in addition to Temporary intervention on the fuel mass in repeated occurrence 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 their situation changed with this intervention (s) being performed for a second period of time, the bigger than that Period of the first intervention is.

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 for the entire driving cycle until the engine stops active. Furthermore, it is possible to perform this adaptation until a recognized refueling, so that An increase in Vorentflammungsneigung by inadequate fuel quality and thus accompanying adaptation after new refueling possibly after the omission of the Cause of the 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 description of the figures refer to.

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. The occurrence of knock events, the pre-ignition prediction, the ignition angle, the lambda value, a pre-ignition counter value and a corresponding counter value as well as the charge pressure limitation are shown in temporal relation to each other.

in the top diagram are occurring with the respective markers Knock events shown. The knock detection takes place as known in the art. Detected knock events lead Knock Knockfregelungen known to a retardation of the ignition angle. The late adjustment of the firing angle is recognizable in the illustrated diagram on the basis of the ignition angle jump, followed by a gradual approach to the original firing angle takes place as long as no further knocking events are detected. In another knock event, the adjustment of the ignition angle takes place in an 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, even if parallel a knocking event has been detected. A detection of the pre-ignition leads to a Intervention on the fuel mass, so that through an adaptation of the fuel mass to be injected a fuel-rich fuel-air mixture in the combustion chamber is produced. The fourth diagram from above shows this procedure the predetermined desired lambda value in the combustion chamber is shown, which is implemented by a corresponding fuel injection. With the occurrence of pre-ignition, the pre-ignition counter is set to 1. The counter value remains below the threshold in this example. The Detection or prediction of the 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 particularly preferred method for evaluating the pre-ignition hereby represents the high-resolution Analysis of the speed signal. A connected to the crankshaft Donor 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 of the crankshaft. From these so-called teeth times, a high-resolution speed signal for the respective Circulation of the encoder wheel are obtained, which a number of speed signals during the Working game supplies. From the individual successive 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 position and a high value of Gradients of the speed signal are indicative of a pre-ignition. Here you can these values are evaluated on the basis of past work cycles and in case of deviation in characteristic magnitudes, a recognition / prediction of the Pre-ignition. Furthermore, it is possible to talk about the evolution of this Values over previous work games a prediction of pre-ignition to allow before their occurrence. in this connection can several evaluation procedures take place in parallel. A validation of a Predicted pre-ignition by means of the signal of 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. The lower diagram shows that at the time of exceeding the threshold value by the repeatedly occurring Knocking and Vorentflammungsereignisse the boost pressure setpoint 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 the compression stroke 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.

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 for late adjustment the ignition angle locked will and in parallel for a predetermined period of time change the injected fuel mass a fuel-rich fuel-air mixture in the combustion chamber is generated and after a defined number of further recognized or predicted pre-ignition another, from the intervention on the injected fuel mass of different, temporary or Permanent intervention on operating parameters of the internal combustion engine done by the engine control, which the Vorentflammungsneigung decreases. 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 characterized in that statistically the number of recognized / predicted Pre-ignition over One cycle is recorded and based on this number of others Intervention takes place on the operating parameters of the engine. Method according to one of the preceding claims, characterized characterized in that at a detected or predicted Vorentflammung the temporary first intervention on the fuel mass after expiration a predetermined first period of time is withdrawn. Method according to one of the preceding claims, characterized characterized in that the further intervention on the operating parameters the engine control in case of repeated occurrence of Vorentflammungen for the Duration a second period of time is performed, the second Time span greater than the first period of the first intervention is. Method according to one of the preceding claims, characterized 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 working point leads, in which the Vorentflammung was recognized / predicted, where this adaptation at least one driving cycle until the engine stops or for recognized refueling or permanently at least until next service for the further operation of the internal combustion engine is maintained.