DE10354978B4 - Knock-resistant multi-cylinder combustion engine - Google Patents

Abstract

Internal combustion engine with several cylinders, with at least one ignition spark generating device, a fuel supply device and a knock detection system being provided on each cylinder, and with a control device which, when the internal combustion engine is operating essentially stoichiometrically, when a knock signal is scanned on at least one cylinder by the knock detection system, the individual The amount of fuel supplied to the cylinders is changed as follows: - the control device operates the knocking cylinders, each time enriched by a predetermined amount of fuel, - the control device operates the remaining, non-knocking cylinders, each leaned by a predetermined amount of lean fuel, the control device for the knock detection system having a time measuring device , which detects how long no knocking was detected, the control device each of the remaining cylinders by one operates leaned predetermined lean amount of fuel in which knocking has not been detected for the longest time.

Description

The invention relates to an internal combustion engine with a plurality of cylinders.

At such internal combustion engines often spark-generating devices and a fuel supply device are provided. In operation, the condition sometimes arises that a so-called "knocking" is sensed.

The EP 0 725 893 B1 teaches that such knocking can be remedied by adjusting the spark timing of a knocking cylinder "late". In addition, according to the enrichment of the individual cylinders fed EP 0 725 893 B1 Fuel mixture are made dependent on the retardation value.

The DE 42 39 842 A1 discloses a method for controlling the supply of air to an internal combustion engine, by which also a knocking sensibility of the engine is to be reduced.

From the DE 39 05 498 C2 It is known to reduce the tendency to knock by suitable variation of various parameters such as ignition timing, air / fuel ratio or precompression. At least one knock sensor is provided for detecting the knocking.

The US 5,365,908 A discloses a method for reducing knocking in which the ignition timing is retarded while simultaneously decreasing the amount of fuel supplied to the cylinders. A similar procedure is also from the GB 2 262 615 A known.

A shift of the ignition point later to reduce the knocking, optionally combined with an enrichment of the fuel mixture depending on the shift is also from the DE 29 30 540 C2 and from the DE 28 52 715 C2 and Bosch: Automotive Handbook, 3rd Edition, Dusseldorf, VDI-Verlag, 1993, page 360-361 known.

In operation, it is disadvantageous that occasionally component failure occurs in such equipped engines.

The invention is based on the task of providing an always reliably operating internal combustion engine, an improved control device for such an internal combustion engine and a method for operating such an internal combustion engine, for example in a motor vehicle.

The object is solved by the independent claims. Advantageous developments emerge from the respective dependent claims.

The knock limit depends on gasoline engines u. a. also from different fuel qualities (octane number) and engine tolerances (compression ratio). Therefore, these are equipped with a knock control, so that optimal torque and optimum performance can be achieved. The actual ignition timing may change by up to eight degrees crank angle in a full throttle point when operating with 91 RON fuel versus 98 RON. At full load, there is a relatively linear dependency of approximately 5 to 10 K per degree crank angle between the exhaust gas temperature and the ignition point. Especially with catalytic converters arranged close to the engine, the mixture has to be enriched in full load at high engine speeds under the optimum performance air ratio of about lambda = 0.9, so that the catalyst does not overheat. According to the o. G. Depending on temperature protection functions, the ignition returns of the knock control or corrections of the ignition timing as a function of engine and intake air temperature are taken into account in order to only grease to such an extent that the permissible maximum temperature is maintained.

The dependence of the knock limit on the air ratio (at lambda = 1, the tendency to knock is the strongest) is taken into account in the invention. The invention makes use of the possibility of reducing the tendency to knock by fattening or leaning.

If the knock limits of the individual cylinders of an engine are different (eg because of structural tolerances, air, fuel, blow-by, oil suction or poor "EGR distribution" = different exhaust gas recirculation rates for the individual cylinders) the engine is replaced by a Cylinder-specific enrichment much better protected than by a global enrichment. The approach of not only modifying the mixture of knocking cylinders but also of oppositely modifying the mixture of possibly non-knocking cylinders avoids increased exhaust emissions and increased fuel economy.

The concrete embodiment of the exemplary embodiments is based on the finding according to the invention that the exhaust valves torn off in the combustion tests known in the prior art are due, inter alia, to excessive exhaust gas temperatures of the relevant cylinder as a result of ignition cancellations of the knock control.

The invention provides three very effective methods depending on the mode of operation of the engine, two of which are alternative to one another can be applied. It is envisaged to use one of the two alternative methods to be used together with a third method according to the invention.

1st method:

Specifically, according to the invention, in a substantially stoichiometrically operated internal combustion engine, when a knock signal is sensed on at least one cylinder or cylinder group, the knocking cylinder or groups are respectively enriched by a predetermined amount of fuel enrichment with simultaneous ignition cancellation. The remaining non-knocking are each emaciated by a predetermined amount of lean fuel.

It is provided according to the invention that the other cylinders or cylinder groups are operated so emaciated that in the exhaust gas originating from all cylinders or cylinder groups, a substantially stoichiometric composition is present. This makes it possible to effectively cool a particular cylinder or cylinder group, thereby avoiding knocking. By leaning out the remaining cylinders or cylinder groups, a mixture is thereby provided in the exhaust gas which can be easily stoichiometrically converted by a downstream catalytic converter.

In a four-cylinder engine with z. B. worse cooled and thus knock sensitive middle cylinders could according to cylinders 1 and 4 without knocking activities with a middle mixture of z. B. Lambda = 1.03, cylinder 2 (knock the strongest, latest ignition) with lambda = 0.96 and cylinder 3 with lambda = 0.98 run. The thermal or mechanical loading of components of the individual cylinders is correspondingly more uniform. Due to the lower average necessary retardation on the same time by the enrichment faster burning middle cylinders deteriorates also the overall motor efficiency less.

In an embodiment of this method, preferably that or those other cylinders or cylinder groups is operated in each case emaciated, in which or in which the longest no knocking has been detected. With these cylinders, it is expected that an additional leaning operation will not produce additional knocking.

2nd method:

In the method according to the invention provided as an alternative to the above method designs, a leaning operation is effected when a knock signal is sampled in the case of essentially stoichiometric operation of the internal combustion engine at that cylinder or at that cylinder group at which knocking is detected. By leaning the knock tendency is slightly reduced. Regardless of and also in addition, the knocking cylinder or groups of cylinders may be operated at a later ignition point than cylinders or cylinder groups in which no knock signal has been sensed.

Since a temperature rise in the catalyst occurs in both methods, it must be ensured that the maximum permissible catalyst temperature is not exceeded, for example by temporarily providing substoichiometric operation (lambda <1) either for each individual cylinder or averaged over all cylinders.

3rd method:

An alternative to the two methods explained above provides according to the invention that in substantially substoichiometric operation of the engine, the knocking cylinder or cylinder groups are each additionally lubricated, the knocking cylinders or cylinder groups being operated at the same ignition timing as those Cylinders or cylinder groups in which no knock signal is sampled.

Generally, to achieve the max. Torque or the max. Achievement will be provided for enrichment. To protect cylinder-specific components such. As the exhaust valves or the exhaust system can also be used to enrichment for lowering the temperature. In this case, in knock events to increase the knock limit only the mixture of the cylinder in question additionally, briefly enriched to prevent knocking. The pre-ignition remains unchanged.

In conventional systems, redemptions are usually active for a period of 5 to 60 seconds. In a cylinder-specific enrichment to increase the knock limit only a few injection pulses are necessary to safely avoid further knock events, because the combustion chamber and all affected components are cooled immediately. Accordingly, the engine power remains virtually unchanged, resulting in an efficiency advantage over methods with spark timing.

The above-described methods according to the invention can also be operated in combination with one another.

1 shows a program flowchart, which is adhered to in a control according to the invention in connection with an internal combustion engine, and

2 shows a diagram, with the curves of the cylinder-specific air ratios λ of a 6-cylinder engine and the associated, cylinder-specific ignition angle.

In the control device according to the invention is a commercially available industrial control, a predetermined computer program as in 1 displayed repeats periodically at a mark "start". In this case, contents of memory variables can be transferred from one program run to the next. This is known to the person skilled in the art and will not be explained in more detail here. In addition, the control device according to the invention can process signals from sensors, not shown here, wherein the sensor values are expressed in variable contents.

It is possible to use a plurality of control devices instead of a single control device, for. B. a control device for the ignition, another control device for the injection and another higher-level control device for the measurement and overall control.

α_z

Basiszündwinkel

Δα_z,j

zylinderindividuelle Abweichung von α_z

Δα_zd

Zundwinkeländerung zur schrittweisen Rückführung auf α_z pro Loop

λ_ges

Luftverhältnis, gemittelt über alle Zylinder

λ_j

Luftverhältnis des Einzelzylinders j

λ_Lim

zylinderindividuelle Magergrenze

Δλ_j

zylinderindividuelle Abweichung von λ_ges

Δλ_d

Luftverhältnisänderung zur schrittweisen Rückführung auf λ_ges pro Loop

n

Anzahl Zylinder

i

Anzahl der Zylinder, deren Gemisch/Zündwinkel momentan von der Klopfregelung beeinflusst werden

The controller according to the invention uses the following variables:

α _z

basic ignition

Δα _{z, j}

cylinder-specific deviation from α _z

Δα _zd

Angle change for gradual return to α _z per loop

λ _ges

Air ratio, averaged over all cylinders

λ _j

Air ratio of the single cylinder j

λ _Lim

cylinder-specific lean limit

Δλ _j

cylinder-specific deviation of λ _ges

Δλ _d

Air ratio change for the stepwise return to λ _ges per loop

n

Number of cylinders

i

Number of cylinders whose mixture / ignition angle is currently affected by the knock control

The controller scans in the first step after the field "Start" whether a knock has been detected on the internal combustion engine. It also determines which of the n cylinders is knocking. For this purpose, a knock sensor of a knock detection system is used, the z. B. based on ion current measurement or evaluation of the cylinder pressure signal.

If a knock has been detected, then the controller goes into a polling state in which it is determined whether the engine is operated stoichiometrically at λ _ges = 1 or substoichiometrically at λ _ges <1.

In stoichiometric operation with λ _ges = 1, both the angle of the pre-ignition and the cylinder-specific λ is adjusted in a particular embodiment of the invention. In the program in 1 In the first query "Knock recognized?", the query branches to "λ _ges = 1?". This condition is met in stoichiometric operation, so that the branch "yes" is passed.

In the present case, the value λ is set to the value λ _ges - Δλ _j . The value λ _{1 .. (ni)} is set to the value (λ _ges + (Σ _1..i Δλ _j ) / (ni)), and this value should always be kept <λ _Lim (cylinder individual lean limit). In the present case λ = 1, so that λ _{j is} calculated to be 1 - Δλ _j and λ _{1 .. (ni)} = (1 + (Σ _1..i Δλj) / (ni)).

By the Zündrücknahme and by the above-described simultaneous enrichment of the combustion mixture of the knocking cylinder while maintaining the component temperature limits for the one or more knocking cylinder effectively reduces the tendency to knock. The other cylinders are emaciated by an amount of (Σ _1..i Δλ _j ) / (ni), whereby a λ _ges of 1 is obtained.

If it is recognized at the next pass that there is no more knock, then both the cylinder-specific deviation Δα _{z, j} and the cylinder-specific deviation Δλ _{j are} withdrawn. This is done in the "Knock Detected?" Branch equal to "No". Alternatively, the program can also set the value for Δα _zd and / or Δλ _d to "0" for a certain time and thus provide a holding time for the ignition angle adjustment and / or enrichment. This option is not detailed in the program flowchart.

2 FIG. 10 illustrates the retraction of ignition with the value Δα _{z, j} together with the enrichment of the knocking cylinder over the value λ _j = 1-Δλ _j, for example, on a six-cylinder internal combustion engine. As you can see very well, at the time t = 6 sec. sampled at the cylinder 1 that knocking is present. The internal combustion engine is operated stoichiometrically with λ _ges = 1 up to this time. As a result, the ignition angle is adjusted to "late", starting from a value α = 30 ° to a value α = 20 °. At the same time, the air ratio λ _{zyll is enriched} to a value of 0.93. In the present case, therefore, the air ratio of a knocking cylinder per 10 ° crankshaft angle at Zündzeitpunktspätverstellung by a value Δλ _j of 0.07 is lowered. The value λ _zyll then remains at the value 0.93. To the same extent, the air ratios for the cylinders numbered 2 to n = 6 are raised to a value _greater than 1, each by a value of (Σ _1..i Δλ _j ) / (ni) = 0.07 / 5 = 0.014. This results in the result that the air ratio, averaged over all six cylinders, is equal to the value 1, which corresponds to a stoichiometric combustion. The unburned fuel used in the cylinder 1 for cooling is stoichiometrically reacted in a cylinder-installed catalyst together with the excess combustion air of the cylinders 2 to n = 6.

In 2 is in addition to the time t = 10 sec. found that cylinder # 2 starts to knock. As a result, the ignition angle is retarded from a value of 30 ° to a value of 25 °. To the same extent, the air ratio for the cylinder 2 is set to a value of 0.965.

In order to further ensure a total air ratio of λ _ges = 1, the cylinders 3 to n = 6 must be further emaciated to compensate for the enrichment of cylinder 2, and in total by a value of (0.07 + 0.035 / 6-2) = 0 , 02625 to λ _{1 .. (ni)} = 1.02625

In a further embodiment, not shown here, analogous to 1 it is also provided in the case "λ _ges = 1", the cylinder or cylinder as a knocked scored cylinder with respect to their cylinder-individual air ratio so lean that the tendency to knock is reduced.

In the event that the internal combustion engine and each individual cylinder is operated substoichiometrically, ie λ _ges <1, Δα _{z..j is set} to 0, ie there is no Zündwinkelrücknahme (see 1 ). In this case, the control device is influenced so that Δλ _j to a value of z. B. is set to about 0.1 to avoid repeated knock sure. This value can be made dependent on the knock intensity in a particular embodiment and thus adapted to the respective prevailing conditions and also be different from cylinder to cylinder.

In the next run of the program is again checked whether the corresponding change has already caused a disappearance of knocking. Optionally, the enrichment is further increased to z. B. Δλ _j about 0.15. If knocking has stopped at the cylinder in question, then the program branches according to 1 at the first query on the branch "no". Then it is checked whether Δλ _j is still> 0. If so, the next injection quantity is determined so that the next Δλ _j results from the difference between the instantaneous Δλ _j and the value Δλ _d . Alternatively, the program may also set the value for Δλ _d to "0" for a certain time, thus providing a hold time for enrichment. This option is not detailed in the program flowchart.

If Δλ _d already has the value 0 in this check, then the loop is continued at "Start" without changing Δλ _j .

In this way, it is always ensured in sub-stoichiometric operation that follow-up knocking is avoided, with an adjustment of the instantaneous ignition angle not taking place.

Of course, according to 1 all changes made in the branch "Knocking recognized?" = "No" gradually returned to the initial value when knocking is no longer detected.

Claims (23)

An internal combustion engine having a plurality of cylinders, the cylinders each having at least one ignition device, a fuel supply device and a knock detection system, and a control device which, in substantially stoichiometric operation of the internal combustion engine, senses a knock signal to at least one cylinder through the knock detection system Cylinders supplied fuel quantity changed as follows: The control device operates each of the knocking cylinders by a predetermined amount of enrichment of fuel, The controller operates the remaining non-knocking cylinders at a predetermined leaning amount of fuel, the knocking detection system control means having a time measuring means which detects how long knocking has not been detected, the control means for each of the remaining cylinders being a predetermined amount of leaning emptied of fuel for which no knock has been detected for the longest time. Internal combustion engine according to claim 1, characterized in that the control device operates the other cylinders so emaciated that in the coming of all cylinders exhaust gas is a stoichiometric composition. Internal combustion engine according to one of the preceding claims, characterized in that the control device operates the knocking cylinder with a later ignition timing as a cylinder in which no knock signal is sampled. An internal combustion engine having a plurality of cylinders, the cylinders each having at least one ignition device, a fuel supply device and a knock detection system, and a control device which, in substantially stoichiometric operation of the internal combustion engine, senses a knock signal to at least one cylinder through the knock detection system The quantity of fuel supplied to individual cylinders is changed either as follows: the control device lubricates the knocking cylinders respectively by a predetermined amount of enrichment of fuel, the control means empties the remaining non-knocking cylinders respectively by a predetermined amount of leaning fuel or changes them as follows: the control means operates the knocking cylinders in each case by a predetermined Abmagerungsmenge of fuel, - and in substoichiometric operation of the Ve engine, upon sensing a knock signal on at least one cylinder by the knock detection system, changes the amount of fuel supplied in each cylinder as follows: the controller lubricates the knocking cylinders respectively by a predetermined amount of fuel enriched, the controller operates the knocking cylinders at the same ignition timing as the cylinders where no knock signal is sampled. Internal combustion engine according to claim 4, characterized in that the control device operates the remaining cylinders so emaciated that in the exhaust gas from all cylinders there is a stoichiometric composition. An internal combustion engine according to claim 4 or 5, characterized in that the knock detection system control means comprises a time measuring means which detects how long knocking has no longer been detected, the control means operating each of the remaining cylinders by a predetermined leaning amount of fuel at which no knock was detected longest. Internal combustion engine according to one of claims 4 to 6, characterized in that the control device operates the knocking cylinder with a later ignition timing than in cylinders in which no knock signal is sampled. A control device for an internal combustion engine having a plurality of cylinders, wherein at least one ignition spark generating means, a Kraftstoffstoffzuführeinrichtung and a knock detection system is provided on the cylinders, and wherein the control means in substantially stoichiometric operation of the internal combustion engine when sensing a knock signal to at least one cylinder by the knock detection system in the individual cylinders supplied fuel quantity changed as follows: The control device operates each of the knocking cylinders by a predetermined amount of enrichment of fuel, - The control device operates the remaining cylinders each emaciated by a predetermined amount of lean fuel, wherein the knock detection system control means comprises a time-measuring means which detects how long knocking has not been detected, the control means operating each of the remaining cylinders by a predetermined lean amount of fuel at which knocking has not been detected the longest. Control device according to claim 8, characterized in that the control device operates the other cylinders so emaciated in such a way that there is a stoichiometric composition in the exhaust gas from all cylinders. Control device according to claim 8 or 9, characterized in that the control device operates the knocking cylinder with a later ignition timing as a cylinder in which no knock signal is sampled. A control device for a multi-cylinder internal combustion engine, the cylinders each having at least one spark generator, one fuel injector, and a knock detection system, the controller, upon substantially stoichiometric operation of the internal combustion engine, sensing a knock signal on at least one cylinder through the engine The knock detection system varies the amount of fuel supplied in each cylinder either as follows: the controller drives the knocking cylinders each by a predetermined amount of fuel enriched, the controller drives the remaining, non-knocking cylinders respectively by a predetermined amount of lean fuel or changes as follows In the case of substoichiometric operation of the internal combustion engine, when a knock signal is sensed on at least one cylinder by the knock detection system, the amount of fuel supplied in each cylinder is changed as follows: - the control device operates each of the knocking cylinders is enriched by a predetermined amount of enrichment of fuel; the controller operates the knocking cylinders with the same ignition timing as the cylinders where no knock signal is sampled. Control device according to claim 11, characterized in that the control device operates the other cylinders so emaciated in such a way that there is a stoichiometric composition in the exhaust gas originating from all the cylinders. A control device according to claim 11 or 12, characterized in that the knock detection system control means comprises a time measuring means which detects how long knocking has no longer been detected, the control means operating each of the remaining cylinders as depleted by a predetermined amount of leaning of fuel at which no knock was detected longest. Control device according to one of claims 11 to 13, characterized in that the control device operates the knocking cylinder with a later ignition timing as a cylinder in which no knock signal is sampled. Motor vehicle with an internal combustion engine according to one of claims 1 to 7. A method of operating a multi-cylinder internal combustion engine, wherein, upon sensing a knock signal on at least one cylinder, the knocking cylinders are each operated to fuel a predetermined amount of fuel enrichment, the remaining cylinders each being depleted by a predetermined amount of lean fuel, with the remainder Cylinders are each abmagert operated by a predetermined Abmagerungsmenge of fuel in which the longest no knocking is detected. A method according to claim 16, characterized in that the remaining, non-knocking cylinders are operated so emaciated, that in the exhaust gas from all cylinders, there is a substantially stoichiometric composition. Method according to one of claims 16 or 17, characterized in that the knocking cylinders are operated at a later ignition timing than the cylinders in which no knock signal is sampled. A method of operating a multi-cylinder internal combustion engine, wherein - At substantially stoichiometric operation of the internal combustion engine when sensing a knock signal to at least one cylinder, the knocking cylinder either - Are operated each enriched by a predetermined Befettungsmenge of fuel, the other cylinders are operated emaciated respectively by a predetermined Abmagerungsmenge of fuel, or - Are operated emaciated at a predetermined Abmagerungsmenge of fuel, and - In substoichiometric operation when sensing a knock signal to at least one cylinder, the amount of fuel supplied in the individual cylinders is changed as follows: - The knocking cylinders are each operated by a predetermined enrichment amount of fuel enriched, - The knocking cylinders are operated at the same ignition timing as cylinders where no knocking is sensed. A method according to claim 19, characterized in that those other cylinders are each operated by a predetermined lean-off amount of fuel deposited, in which the longest no knocking is detected. Method according to one of claims 19 or 20, characterized in that the knocking cylinders are operated at a later ignition timing than the cylinders in which no knock signal is sampled. A computer program for implementation in a microprocessor-based control device for a multi-cylinder internal combustion engine, each of the cylinders having at least one spark generator, fuel supply, and knock detection system, the computer program being adapted to perform a method according to any one of claims 16 to 21 , Data carrier with a computer program according to claim 22.

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