EP1541839B1 - Method for controlling an internal combustion engine - Google Patents

Description

The invention relates to a method for operating an internal combustion engine having at least one four-stroke cylinder with controlled auto-ignition and spark ignition, wherein the four-stroke cylinder is operable at least in a controlled auto-ignition mode, having the features of the preamble of claim 1.

The internal combustion engine is, for example, a gasoline engine with one or more four-stroke cylinders. Gasoline engines are mainly operated with a stoichiometric mixture, which allow aftertreatment of exhaust gases. The fuel consumption loss at part load associated with throttling and stoichiometric operation may be reduced by lean operation, either by a homogeneous or stratified mixture by direct injection. In both cases, nitrogen emissions (NOx) can not be treated by conventional three-way catalysts (TWC). For this reason, lean nitrogen separators (LNT) have been developed that can treat the lean feed mixture. The disadvantage of these LNT-based systems is that they are much more expensive than conventional TWCs.

Low-nitrogen lean burn engines that eliminate the need for costly LNT aftertreatment have also been introduced. This was achieved by the controlled auto-ignition (CAI) in engines that were slightly modified in relation to currently produced engines. For this purpose, two proposals have been published ( Oakley et al. SAE Technical Paper 2001-01-1030 and Law et al. SAE Technical Paper 2001-01-251 ). In both proposals, this was achieved by using a valve control that causes the engine to have a high level of gas residue.

The controlled auto-ignition in four-stroke gasoline engines is a new development, which is constantly being developed with a rapidly changing state of the art.

The WO 01/46571 and the WO 01/46573 each relate to a method for operating a four-stroke internal combustion engine in which the combustion is achieved with a self-ignition. In addition, the internal combustion engine has a spark plug for spark ignition in order to supplement the auto-ignition process, in particular during the first ignition of the internal combustion engine. Preferably, the autoignition is used only in partial load ranges / low speed ranges, while the spark ignition is used at full load ranges / high speed ranges.

• einen Abgaskatalysator ;
• einen Luft/Kraftstoff-Verhältnis Detektor, um das Kraftstoff/Luft-Verhältnis stromaufwärts des Abgaskatalysators zu bestimmen; und
• einen NOx-Detektor,um NOx stromabwärts des Abgaskatalysators zu besimmen.

The US2003 / 0192305 deals with a control system which is capable of reducing deterioration of exhaust gas purification during the transition from spark ignition to auto ignition and vice versa. For this purpose, the tax system comprises:

• an exhaust gas catalyst;
• an air / fuel ratio detector to determine the air / fuel ratio upstream of the catalytic converter; and
• a NOx detector to purify NOx downstream of the exhaust catalyst.

For example, during the auto-ignition mode, deterioration of the combustion may be registered so that the combustion is very quickly switched from the auto-ignition mode to the spark ignition. This is intended to prevent deterioration of the exhaust gas cleaning performance even during the auto-ignition mode.

In the US 6,082,342 discloses a method of controlling auto-ignition in four-stroke engines. The conventional spark is maintained during the auto-ignition operation.

In two-stroke gasoline engines, the CAI technology is known, and has been used for example in motorcycle engines. In order to achieve a CAI, it is known from this experience that high internal exhaust gas recirculation conditions (internal EGR) and high mixture temperatures at the end of a compression stroke are necessary. As a result, it has been assumed that to obtain a CAI in a four-cycle engine, complex mixture heaters which can inhibit the regeneration-time responsiveness of the engine are necessary.

It has also been suggested that four-stroke CAI operation would have to be possible using direct injection and a fully variable valvetrain. The valvetrain provides early exhaust valve closing (EEVC) and late intake valve opening (LIVO) to separate residual gas in a combustion chamber with minimal heat loss.

For example, this describes EP 1 201 903 A1 a method of controlling the combustion process in a four-stroke engine having means for spark ignition, intake and exhaust valves in at least one cylinder. From one cycle to another, the spark igniters are activated or deactivated, with the exhaust valve being transitioned from an early close before the piston reaches its top dead center to a late close (near top dead center). In the transition from the spark ignition to the compression ignition, the exhaust valve closes much earlier than in the previous cycle, so that the fuel-air mixture is heated due to the residual gases.

This technology has been further investigated in EU projects. The Ford Consortium (Oakley et al., 2001) and others (Law et al., 2001) have demonstrated that stable CAI operation is possible with some type of cam control over a usable speed / load range. This has been achieved with little modified engines with conventional fuel injection (PFI) and conventional compression ratios (CR).

During CAI operation, the ignition can usually be switched off. The CAI operation requires compliance with certain limits, such as a relatively high proportion of residual gas and a certain temperature of the mixture, which depends on the composition of the mixture. If the factors mentioned below fall below the required limit, this can lead to a Misfire lead. A misfire causes the four-stroke cylinder to permanently fail because the preheated residual gases are not available for the following engine cycles. Such a case FIG. 1 in this FIG. 1 For example, cycles n-4 through n-1 are shown, showing normal CAI operation. This is shown in each case with a dickliniertem square in which a mixing ratio of fresh fuel / air mixture and residual gas is located. The fresh fuel / air mixture is obliquely hatched, the residual gas is characterized as a bar. If the above limits are exceeded, it will be a misfire. This is in FIG. 1 denoted by n. The four-stroke cylinder is still in CAI mode. In the cycles n + 1 to n + 4 is clearly shown that the proportion of residual gas relative to the fresh fuel / air mixture proportion is always lower, with no residual gas content is present in the cycles n + 3 and n + 4. This causes the four-stroke cylinder to fail. The cycles n-1 to n-4 respectively represent a cycle performed before the misfire, where n + 1 to n + 4 each represent a cycle following the misfire.

The invention has for its object to provide an improved method for operating an internal combustion engine, in particular a gasoline engine available, which can continue to operate after a misfire occurring in CAI operation.

This is achieved by a method having the features of claim 1 according to the invention.

Thus, an internal combustion engine with a four-stroke cylinder is provided, which is re-ignited after a occurring in CAI operation misfire by igniting a following on the misfire cycle in the spark mode and can continue to operate.

Fig. 1

schematisch einen üblichen CAI-Betrieb,

Fig. 2

schematisch einen CAI-Betrieb mit einem Wiederzünden in einem Funkenzündungsmodus.

Further advantageous embodiments of the invention are disclosed in the dependent claims and in the FIG. 2 following description of the figures described. Show it:

Fig. 1

schematically a usual CAI operation,

Fig. 2

schematically a CAI operation with a re-ignition in a spark ignition mode.

In FIG. 2 For example, the inventive method of operating an internal combustion engine having at least one four-stroke controlled auto-ignition (CAI) cylinder and spark ignition is illustrated, wherein the four-stroke cylinder is operable at least in a controlled auto-ignition mode. FIG. 2 represents cycles n-4 to n-1, which show a normal CAI mode with normal ignition and normal torque. The normal ignition is shown in each case with a dickliniertem square 1, in which a ratio of fresh fuel / air mixture 2 and residual gas 3 is located. The fresh fuel / air mixture 2 is obliquely hatched, wherein the residual gas 3 is marked as a bar. The CAI mode requires compliance with certain limits, such as a relatively high level of residual gas and a certain temperature of the mixture. If the specified limits are exceeded, there is a misfire. The misfire is in FIG. 2 denoted by n (arrow 4). The time is shown by the arrow 5.

In a cycle n + 1 is clearly shown that the residual gas content 3 based on the fresh fuel / air mixture proportion 2 is lower. In the cycle n + 1, the four-stroke cylinder is re-ignited by spark ignition. In cycle n + 2, the four-stroke engine returns to CAI mode. The four-stroke cylinder continues to operate in this mode, as clearly indicated by cycles n + 3 and n + 4.

Cycles n-1 through n-4 each represent a pre-misfire cycle, where n + 1 through n + 4 each represent a misfire cycle.

The four-stroke cylinder is operated at moderate load and engine speeds with a significant portion of residual gas 3 being separated or recycled from the previous cycle, thereby initiating the CAI.

Claims (3)

1. Method for operating an internal combustion engine having at least one four-stroke cylinder with controlled auto-ignition and spark ignition, it being possible for the four-stroke cylinder to be operated at least in a controlled auto-ignition mode, wherein after a misfire occurring in the controlled auto-ignition mode, the four-stroke cylinder is re-ignited, in the cycle following the misfire, in a spark-ignition mode by virtue of more fuel being injected into the four-stroke cylinder,
   characterized in that
   the ignition remains activated during the controlled auto-ignition mode, wherein after the re-ignition, that is to say after the spark-ignition mode, the four-stroke cylinder is returned into the controlled auto-ignition mode, and continues to be operated in said mode, in the cycle directly following the cycle in the spark-ignition mode.
2. Method according to Claim 1,
   characterized by
   a pre-ignition setting selected such that the ignition is optimized in such a way that the same engine torque is obtained in the case of spark ignition as in CAI operation.
3. Method according to Claim 1 or 2,
   characterized in that
   in the re-ignition cycle, in the case of the engine having direct injection, a stratified injection of the fuel takes place shortly before the ignition.

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