DE10051675A1 - Operating method for IC engines has accumulator catalysts for nitrogen oxide storage in separate exhaust trains with individual regulation of rich/lean cycles - Google Patents

Abstract

Nitrogen oxide generated during lean burning of the engine is stored in an accumulator catalyst in the exhaust system. With increasing concentration, the fuel/air mixture is enriched to regenerate the accumulator catalyst. The rich/lean cycles for regeneration of accumulator catalyst located in several exhaust rains, are regulated separately for each train.

Description

The invention relates to a method for operating an internal combustion engine according to the Features of the preamble of claim 1.

In the case of engines with gasoline direct injection in particular, the so-called Stratified charge mode of fuel is injected shortly before the ignition, the supplied fuel-air mixture is very lean (air ratio λ <1). The excess air in so-called lean operation, however, creates nitrogen oxides, which are stored in a NOx Catalyst must be cached. Sets in the engine control integrated computing model or the one installed in or after the storage catalytic converter NOx sensor detects an increasing nitrogen oxide concentration, the engine control switches for seconds to a rich operation with air numbers λ <1 um. On the enrichment Hydrocarbons to be returned in the exhaust gas now bring about a reduction in the Storage catalytic converter stored nitrogen oxides. After the regeneration of the Storage catalytic converter, the engine can work in lean operation again in the partial load range and thus save fuel.

For engines with two or more cylinder banks (e.g. boxer or V engine) the two- or multi-line exhaust gas outlets in most cases merged into a common exhaust pipe. However, there are also multiple rows Internal combustion engines in which - for gas-dynamic reasons - one for each cylinder bank separate exhaust gas discharge is advantageous.

The object of the invention is therefore in the latter internal combustion engine Execution of an exhaust gas aftertreatment by NOx storage catalysts for everyone Provide exhaust system, the capacity of the storage catalysts optimal should be exploited.  

The problem is solved by the specified in claim 1 Process features.

Because of the rich / lean cycles for regeneration in the exhaust lines arranged storage catalytic converters are regulated separately, the Frequency of regeneration not after the "worse" storage catalyst, the for example, due to volume or manufacturing tolerances has less storage capacity than that arranged in the other exhaust line Storage catalyst. If there is first an increase in only one storage catalytic converter Nitrogen oxide concentration is detected, so the fuel-air mixture is only for that Accumulated cylinder bank row assigned to storage catalytic converter, d. H. it is about the Engine control "switched" from lean operation to rich operation. When petrol Direct injection, in which the fuel in the partial load range in the so-called Shift operation is only injected in the compression cycle, the would Fuel injection for those assigned to the "worse" storage catalytic converter Cylinder bank row already take place during the intake stroke. Through the separate Controlling the rich / lean cycles can achieve fuel consumption benefits because the other row of cylinder banks may continue to run lean for as long as necessary can work until there is also a signal to regenerate the cylinder bank row assigned NOx storage catalytic converter with the larger storage capacity is delivered.

An embodiment of the invention is in the following description and Drawing explained in more detail.

The single figure shows schematically a two-row internal combustion engine with one two-line separate exhaust gas discharge.  

Description of the embodiment

The internal combustion engine designed as a 6-cylinder engine in the present exemplary embodiment has two rows of cylinder banks 2 and 4 , each of which is followed by a separately designed exhaust gas outlet 6 and 8 . Both exhaust gas outlets 6 , 8 have an exhaust manifold part 10 or 12 , which merges into three exhaust manifolds 22 and 23 , respectively, via three individual manifold tubes 14 to 16 or 17 to 19 and via a distributor piece 20 or 21 . A precatalyst 24 or 25 , a storage catalytic converter 26 or 27 and a rear silencer 28 or 29 are arranged downstream of the two exhaust manifolds 22 , 23 as seen in the flow direction of the exhaust gases.

The pre-catalysts 24 , 25 are connected to the storage catalysts 26 , 27 via an exhaust pipe 30 and 31, respectively; The storage catalytic converters 26 , 27 are in turn also connected to the rear silencers 28 , 29 via exhaust gas pipes 32 and 33, respectively. A short exhaust pipe 34 and 35 leads from the two rear silencers 28 , 29 , which at the same time forms the end piece of the exhaust gas discharge.

A lambda control probe 36 or 37 is installed in the pre-catalyst 24 or 25 to record the residual oxygen content. Seen in the flow direction of the exhaust gases, two temperature sensors 38 and 39 are mounted in the exhaust pipe 30 and 31 behind the pre-catalysts 24 , 25 for detecting the exhaust gas temperature. To detect the storage state of the two storage catalytic converters 26 , 27 , a NOx sensor 40 and 41 are arranged at the end of these catalytic converters, as seen in the flow direction of the exhaust gases. The lambda control probes 36 , 37 , the temperature sensors 38 , 39 and the two NOx sensors 40 and 41 are also connected to an engine control unit 42 .

The control method for the regeneration of the storage catalytic converters 26 , 27 , which is particularly suitable for engines with gasoline direct injection, is described in more detail below. With gasoline direct injection, the fuel is injected in the compression cycle of the piston in the partial load range. However, this stratified lean operation with excess air (λ <1), which is operated in the lower speed and torque range, produces nitrogen oxides, which are stored in the storage catalytic converters 26 and 27 by means of a chemical reaction. If an increase in the NOx concentration in the storage catalytic converters 26 , 27 is detected with the aid of the NOx sensors 40 , 41 arranged at the end of the storage catalytic converters 26 , 27 , the stratified mixture preparation with an air ratio λ <1 is established with the aid of the control unit 42 a homogeneous mixture preparation with an air ratio λ <1 "switched". For this purpose, the injection timing for homogeneous operation is shifted from the compression stroke to the intake stroke. At the same time, the throttle valve located in the intake tract of the engine is set from the "open" to "partially closed" position via the control unit 42 , so that the fuel-air mixture for the regeneration of the storage catalytic converters 26 , 27 is enriched in the desired sense. Homogeneous operation with λ = 1 can be monitored using the lambda probes 36 , 37 arranged in the exhaust pipe 22 , 23 . Since u. If the storage capacities of the two catalysts 26 , 27 are designed differently due to volume or manufacturing tolerances, or the raw emissions in the two rows of cylinder banks 2 , 4 are different, the storage capacity limit of both catalysts 26 , 27 can be reached at different times. If, for example, the storage catalytic converter 26 reaches its capacity limit first, only the regeneration of this catalytic converter 26 takes place via the cylinder bank row 2 , while the other cylinder bank row 4 can continue to work in lean operation, since the capacity limit of the storage catalytic converter 27 has not yet been reached.

As soon as the "poorer" storage catalytic converter 26 has been regenerated, a control signal to the control unit 42 again "switches" to the lean operation with an air ratio λ <1 for the relevant cylinder bank row 2 , provided that the engine continues to operate in part-load operation. In this way, the storage capacity of the “better” storage catalytic converter 27 can be fully utilized. This allows the fuel-saving lean operation in the part-load range of the engine to be maintained for longer.

The prescribed control procedure is not only for engines with petrol Direct injection applicable, but also for lean-burn engines with conventional Intake manifold injection applicable.

Claims (1)

Method for operating an internal combustion engine in which nitrogen oxides generated during lean operation are temporarily stored with the aid of a storage catalytic converter arranged in the exhaust gas system, and with increasing nitrogen oxide concentration in the storage catalytic converter, which is detected, for example, with the aid of a NOx sensor, with the aid of an engine control for regeneration of the Storage catalyst, the fuel-air mixture is enriched, characterized in that the rich / lean cycles for the regeneration of storage catalysts ( 26 , 27 ) arranged in two-line or multi-line exhaust systems are regulated separately in each exhaust line.