AT4705U1 - METHOD FOR OPERATING A PRIMED IGNITION ENGINE - Google Patents

Abstract

The invention relates to a method for operating a spark-ignited internal combustion engine with direct injection, with at least one NO`X storage catalytic converter in the exhaust line, the temperature of the NO`X storage catalytic converter and the load state of the internal combustion engine being determined continuously or discontinuously during engine operation, and wherein a maximum setpoint for the temperature of the NO`X storage catalytic converter is predefined. In order to improve fuel consumption and exhaust gas quality in the simplest possible way, it is provided that in unloaded operating states in which the temperature of the NO`X storage catalytic converter is above the predefined setpoint, the internal combustion engine is operated without throttling and the fuel supply to the combustion chamber is interrupted. The reinsertion after a load-free operating state also takes place without throttling.

Description

       

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  The invention relates to a method for operating a spark-ignition internal combustion engine with direct injection, with at least one NOx storage catalytic converter in the exhaust line, the temperature of the NOx storage catalytic converter and the load state of the internal combustion engine being determined continuously or discontinuously during engine operation, and a maximum setpoint or a setpoint map is predefined as a function of injection quantity and / or engine speed and / or load for the temperature of the NOx storage catalytic converter.



  NOx storage catalytic converters are used to reduce NOx emissions in direct-injection gasoline engines to the level prescribed by law. Storage or adsorber catalysts have a specific temperature window in which NOx storage can take place. This temperature window essentially determines the operating range of the direct-injection gasoline engine, in which it is possible to operate with an over-stoichiometric air-fuel ratio. After a certain mass of NOx has been stored, the engine must be operated with a substoichiometric value in order to reduce the stored NOx again, which increases fuel consumption.

   Storage catalytic converters are also sensitive to high temperatures and have an increased tendency to irreversible catalytic converter aging at exhaust gas temperatures that exceed a specific aging temperature. In order to avoid this damage, it is known, in order to protect the catalytic converter from exhaust gas temperatures that are too high, to bypass the exhaust gas with a bypass system at the adsorber or to switch over to a strongly substoichiometric engine operation when a specific exhaust gas temperature is exceeded.



  However, this has an adverse effect on the exhaust gas quality and / or the fuel consumption.



  AT 3,601 U1 has already proposed placing an exhaust gas cooler upstream of the NOx storage catalytic converter in order to reduce fuel consumption and exhaust gas emissions in the simplest possible manner and to provide effective protection for the NOx storage catalytic converter.



  It is also known to provide a bypassable cooling section between a pre-catalytic converter and a NOx storage catalytic converter in a spark-ignition internal combustion engine, the flow through the cooling section being able to be controlled via an exhaust gas flap. This enables temperature management of the NOx storage catalytic converter.

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  To further reduce fuel consumption and exhaust emissions, it is desirable to expand shift operation. In order to avoid an unacceptable increase in nitrogen oxide emissions, the known exhaust gas recirculation technology can be used. Internal exhaust gas recirculation can be accomplished by adjusting the timing. The disadvantage here, however, is the cost of the valve timing adjustment devices that are required for intake and exhaust valves. As a cost-effective alternative, the known external exhaust gas recirculation with flow control can be used, in which an exhaust gas recirculation line from the exhaust line opens into the inlet line.



  When lean operation is charged, however, the boost pressure increases in the intake manifold area and would hinder exhaust gas recirculation. In order to be able to recirculate enough external exhaust gas, it is necessary to apply a back pressure in the exhaust line upstream of the branch of the exhaust gas recirculation line. It is problematic, however, that in homogeneous operation with # = 1 high exhaust gas temperatures occur, which lie above the storage window of the NOx storage catalytic converter, as a result of which the nitrogen oxides produced can no longer be stored. In order to be able to drive as much as possible in fuel-efficient lean operation, it is necessary to take appropriate measures to keep the exhaust gas temperature down in front of the NOx storage catalytic converter.



  A particular problem here is the resumption of lean operation from an operating area with a high exhaust gas temperature. If the entire exhaust system is warmed up, it takes a relatively long time to bring the exhaust gas temperatures in front of the NOx storage catalytic converter back into the desired range, especially since the internal combustion engine is operated homogeneously during the blocking period of the NOx storage catalytic converter, and therefore significantly higher engine-side temperatures be generated. This problem cannot be solved satisfactorily by superficial cooling of the exhaust gas via pipes, for example by double-jacket cooling of the exhaust line.



  The object of the invention is to avoid these disadvantages and to reduce fuel consumption and exhaust gas emissions in the simplest possible manner in the case of a spark-ignition internal combustion engine. In particular, the period of reinsertion for lean operation from operating phases with high exhaust gas temperatures is to be shortened.



  According to the invention, this is achieved in that the internal combustion engine is operated without throttling and the fuel supply to the combustion chamber is interrupted in load-free operating states in which the temperature of the NOx storage catalytic converter is above the predefined setpoint. As

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 Load-free operating states are defined in overrun phases.

   In overrun phases above a reinstallation speed for the fuel supply - if the storage catalytic converter temperature measured or determined using a computing model is higher than the target value of the storage catalytic converter temperature - the internal combustion engine is throttled, i.e. with the throttle valve fully open, and operated without injection, so that a large amount of air is relatively cool flows through the inlet and outlet system and accelerates the cooling, especially of the entire catalyst structures.



  The drive train is closed, the engine is thus driven by the vehicle. The reinsertion speed is a function of gear and engine speed. As a result, the storage catalytic converter temperature can be reduced much faster and an earlier switch to fuel-efficient lean operation can be implemented. The reinstallation after such an overrun phase then also takes place in lean operation (shift operation), with only slight throttling being necessary. A rapid rise in temperature due to the otherwise necessary homogeneous operation with # = 1 can thereby be avoided.


    

Claims (3)

 CLAIMS 1. Method for operating a spark-ignition internal combustion engine with direct injection, with at least one NOx storage catalyst in the Exhaust line, whereby the temperature of the NOx Storage catalyst and the load state of the internal combustion engine is determined continuously or discontinuously, and being a maximum Setpoint or a setpoint map as a function of injection quantity and / or engine speed and / or load for the temperature of the NOx Storage catalyst is predefined, characterized in that in load-free operating states in which the temperature of the NOx Storage catalytic converter is above the predefined setpoint, which Internal combustion engine operated without throttling and the fuel supply to Combustion chamber is interrupted. 2. The method according to claim 1, characterized in that as a load-free Operating status overrun phases above a predefined Reinsertion speed can be defined. 3. The method according to claim 1 or 2, characterized in that after Termination of the no-load operating state and / or after the Temperature of the NOx storage catalytic converter to a predefined Resetting temperature, which corresponds at most to the setpoint, the The load operation in lean operation is restarted with an over-stoichiometric air-fuel ratio.