Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
1998-07-17
2001-01-23
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S298000, C123S606000
Reexamination Certificate
active
06176215
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a method for operation of a direct-injection spark-ignition internal combustion engine.
RELATED TECHNOLOGY
German Patent Application No. 43 24 642 A1 discloses a direct-injection spark-ignition internal combustion engine having one injector per cylinder, a combustible fuel/air mixture being formed in the respective combustion chamber with the injected fuel and the separately delivered combustion air. The electrodes of a spark plug project into the combustion chamber, and after application of an electrical flashover voltage between the electrodes, the mixture is ignited by sparking. In the known internal combustion engine, stratified-charge operation is provided for over large areas of the characteristics map by injection of fuel during the compression stroke of the working cycle of the respective cylinder. Charge stratification, with locally different fuel/air concentrations, considerably reduces the fuel consumption of the internal combustion engine, particularly under partial load. At full load, the known internal combustion engine operates with homogeneous mixture preparation.
In stratified charge operation, large portions of the volume of the combustion chamber charge are poorly combustible, since their mixture concentrations lie outside the ignition limits, i.e., the mixture between the electrodes of the spark plug is either too lean or too rich for ignition. Combustion chamber flow during charge exchange delivers to the electrodes of the spark plug mixture components with different concentrations, only portions of which lie within the ignition limits and are suitable for ignition by the ignition sparks. If what is located between the electrodes at the moment of ignition, at which an electrical flashover voltage is applied between the electrodes, is a mixture that is unsuitable for ignition, the ignition spark that jumps across cannot bring about ignition of the mixture. The transistorized ignition systems usually used to generate the flashover voltage cannot generate additional ignition sparks during the same working cycle, since the ignition coil charging time is too long for that. If the spark that is generated cannot bring about ignition, a misfire during that working cycle can no longer be avoided.
In addition, in the case of the known spark-ignition internal combustion engine, the electrodes of the spark plug project far into the combustion chamber in order to encounter rich mixture components, and are therefore continuously wetted with fuel, which causes the formation of deposits on the spark plug. Carbon bridges can cause sliding discharges of the flashover voltage onto the spark plug insulator. A misfire can thus occur which is additionally promoted by the reduced high-voltage output of the ignition system. In order to ignite leaner mixtures, a higher ignition energy must therefore often be provided by the ignition system. When, for example, capacitor ignition systems are used, though very high-energy ignition sparks can be generated, they often cannot ignite the mixture because of their very short duration. Misfires must be prevented in all circumstances, since ejecting the uncombusted mixture for that particular working cycle results in high exhaust emissions for the internal combustion engine.
SUMMARY OF THE INVENTION
It is an object of the present invention to create a method for operation of a direct-injection spark-ignition internal combustion engine which guarantees reliable mixture ignition and combustion, especially in stratified-charge operation.
The present invention therefore provides a method for operation of a direct-injection spark-ignition internal combustion engine (
1
), one injector (
6
) per cylinder (
3
) injecting fuel into the combustion chamber (
4
) and a combustible fuel/air mixture being formed along with separately delivered combustion air, that mixture being ignited, after application of an electrical flashover voltage between the electrodes (
10
,
11
) of a spark plug (
9
) projecting into the combustion chamber (
4
), by sparking. Stratified charge operation is provided over large areas of the characteristics map of the internal combustion engine (
1
) by injection of fuel during the compression stroke in the working cycle of the respective cylinder (
3
), wherein an ignition system (
15
) generates alternating voltage so that high voltage rapidly builds up between the electrodes (
10
,
11
) and triggers ignition sparks with a spark duration that can be defined as a function of an operating point.
An ignition system generates alternating voltage, and thus the ignition voltage, with a sufficiently high transformation rate and charges the ignition coil in such a way that the quantities of energy delivered in packaged fashion by the ignition coil generate practically a continuous ignition spark. The energy packages can be generated one after another by the ignition system in any quantity, so that an ignition spark of any desired spark duration can be formed between the electrodes, the spark duration being defined as a function of an operating point. If the ignition voltage that is applied does not lead to ignition of the mixture, for example due to sliding discharge of the spark via the spark plug insulator, a further ignition spark can then be triggered in the same working cycle, and the mixture can be reliably ignited.
Advantageously, a control unit generates a control signal having required information about the spark duration on the basis of at least one operating parameter of the internal combustion engine. The control signal, which is conveyed to the ignition system, may based on, for example, the engine speed, operating load, stratified-charge operation, exhaust gas recirculation, etc. The information for allocating the respective spark duration to the operating point of the internal combustion engine that has been determined can be stored in a characteristics map memory, and is taken from there by the control unit as necessary.
In particularly advantageous fashion, multiple ignition sparks can also be triggered one after another in one ignition interval during each working cycle, so that the probability that one of those ignition sparks will encounter combustible mixture concentrations between the electrodes, with a low utilization of energy by the ignition system, is increased.
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Baur Bernd
Hohner Peter
Karl G{umlaut over (u)}nter
Kemmler Roland
Argenbright Tony M.
Daimler - Benz Aktiengesellschaft
Kenyon & Kenyon
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