DE19812829A1 - Control procedure for internal combustion engine - Google Patents

Abstract

The internal combustion engine (10) has an oxidation catalyser in the exhaust. The engine has self-ignition with fuel injection. At least one, two or one less than the total number of, cylinders is throttled so that in the exhaust at least one throttled cylinder gives an increased hydrocarbon and-or carbon monoxide emission. The increase is such that in the whole exhaust, a mean lambda value is obtained which is greater than 1.1, preferably greater than 1.3 and especially greater than 1.5. The fuel injection quantity of the throttled cylinder is changed so that despite the throttling of the remaining cylinders, it is compensated in its loading.

Description

The invention relates to a method for controlling an internal combustion engine n cylinders and a catalyst arranged in the exhaust gas flow and a device for controlling an internal combustion engine with n cylinders, each of which has a separate one Have intake duct.

The effectiveness of catalysts in lean engines, such as Lean Otto, DI Otto (direct injection) or DI diesel engine (direct injection) is by low exhaust gas temperatures are restricted because nitrogen oxides in particular are stored Catalysts are not always operated in the optimal temperature range can.

A temperature increase by throttling the engine via an intake manifold Throttle valve or an exhaust gas throttle does not bring the necessary success. This Measures reduce the air or exhaust gas mass flow and increase the Charge exchange work. The temperature increase that can be achieved by motor is at best at 50 degrees, but additionally, depending on the degree of throttling More consumption must be expected.

Another way of heating the catalytic converter is by converting it into the exhaust gas contained oxidizable pollutants CO and HC possible, provided there is sufficient oxygen for the oxidation reaction is available. This is particularly the case with diesel engines However, the pollutant content in the exhaust gas is very low, so that only slight temperature increases can be achieved in the catalyst from 5 degrees to 15 degrees.

With increasing throttling, the CO and HC content of the exhaust gas increases, in particular Falling below the threshold lambda = 1, strongly increasing. For example with a DI diesel engine  approx. 80% of the additional fuel introduced becomes CO and the remaining 20% HC transformed. However, without sufficient oxygen content in the exhaust gas, these can Emissions are partially implemented at most.

For this purpose, DE 195 22 165 A1 describes a device and a method for the control a spark ignition internal combustion engine proposed, one Exhaust catalyst device is heated to by a high temperature exhaust gas To remove cleanability reducing substances from the catalyst device. A lean combustion condition occurs in some cylinders and in the other cylinders initiated a fat burning. The fat is used for the fat burning cylinders Air-fuel ratio achieved in that the amount of air is reduced while the Fuel quantity remains constant. To regulate the flow rate of the air are Bypass lines between the corresponding cylinder of the engine and the upstream throttle valve provided.

This device has the disadvantage that the additional flow channels are expensive and their effects on the charge change in the cylinders are difficult to estimate and is usually negative, since there are no predictable or negative flow conditions. Furthermore, the "bypass lines" are inflexible due to their fixed cross section Control, should be designed differently for each engine and can not fluctuating operating conditions of the engine can be adapted.

The method associated with this device has the disadvantage that it is due to the Loss of performance and additional consumption only for the brief "outgassing" of the Catalyst due to a briefly increased temperature, but not for a long-term one Raising the operating temperature of the catalyst is suitable. With highly efficient Internal combustion engines, such as direct injection internal combustion engines and / or Diesel internal combustion engines is therefore the method known from the prior art Not insertable.

Furthermore, the bypass lines are throttled only by a predetermined amount optimal value of the air to fuel ratio around the combustion chamber. This however, combustion can fluctuate due to different  Operating conditions and load conditions with corresponding fluctuations in the Do not immediately consider the exhaust gas composition.

The present invention is therefore based on the object of a device and a Methods of the type mentioned above are available for highly efficient internal combustion engines make, the above disadvantages are overcome and a sufficiently high and long increase in the operating temperature of a downstream of the engine Catalyst is achieved.

This object is achieved according to the invention by a method of the above. Kind with the claim 1 characterized features and by a device of the above. Kind of with the in Claim 9 characterized features solved.

For this purpose, the method according to the invention provides that at least one or two or a maximum of n-1 cylinders are throttled individually in such a way that there is a lambda value of the individually throttled cylinder of 1.5 or less or an increase in CO and / or HC emission results, the fuel injection quantity of each individually throttled cylinder is advantageously increased such that each individually throttled cylinders in about the same power (or the power that he without Throttling would yield), like the other non-throttled cylinders.

According to the invention, there is an oxidation catalytic converter or another catalytic converter in the exhaust system which is able to store NOx. Under certain operating conditions, the NOx is released and converted again, whereby the nitrogen oxides, in particular to nitrogen, water and CO ₂ , are broken down. The storage takes place here when there is an excess of oxygen in the exhaust gas; the release at high temperatures and / or at lambda 1 and less, ie in particular in the presence of HC, H ₂ and / or CO in the exhaust gas. The problem here, however, is that the NOx storage, in particular an absorber, for example based on alkali, alkaline earth, La or Se, can be poisoned. Common poisoning components are sulfur oxides. These poisoning substances can be removed at very high temperatures, and if necessary the lambda can be set to ≦ 1 before or after reaching the high temperature in the exhaust gas stream. The invention relates in particular to achieving the high regeneration temperature.

In contrast to the prior art, not all cylinders are throttled and at bypassing some cylinders reduces the effect of throttling, but rather it only individual cylinders - not all - by assigned - not to all cylinders acting - throttles (even only one throttle) throttled.

This has the advantage that in one or individual cylinders in addition to a reinforced one CO formation also at least partially oxidized or cracked the more stable HC molecules , which tends to reduce the pollutant content after the catalytic converter, because a Oxidation of this pollutant mixture is easier and the operating temperature of the Catalyst is permanently increased, with the other cylinders in their full Performance and controllability remain fully intact.

Furthermore, the CO oxidation starts at lower temperatures than the HC reaction a, so that this method is advantageous even at lower Catalyst temperatures than can be effective with a pure late injection.

The throttling is expediently carried out in such a way that a lambda value of 1 or less, especially 0.95 or less in the throttled cylinder.

For an almost complete CO and HC oxidation, the Lambda _DR value is set such that a Lambda _Ges value of the total exhaust gas of at least 1, in particular of at least 1.1. The number of throttled cylinders and their air ratio Lambda depend on the desired Lambda _Ges value.

With a 4-cylinder DI diesel engine (1.9 l, turbocharger) at the operating point at 2000 rpm 2 bar internal pressure results in a catalyst temperature increase of 230 degrees that a cylinder is throttled to a lambda value of 0.8. This can be done in can be used advantageously for a short heating of the catalyst.

Temperature monitoring upstream and / or downstream of the catalytic converter can ensure that throttling is only possible if the catalyst temperature is sufficient he follows. Throttling takes place only when the exhaust gas or the catalytic converter has a  Minimum temperature at which he pollutants (CO and HC) can also implement; especially at ≧ 180 ° C.

A brief electrical heating of the catalytic converter is also advantageous To trigger pollutant conversion once. The reaction then runs because of the high Pollutant concentration continues independently.

Increased H ₂ formation in the throttled cylinder advantageously also lowers the minimum temperature for the catalytic converter.

In the device it is provided according to the invention that in at least one, in two or a maximum of n-1 separate intake channels, an additional throttle valve is provided.

This has the advantage of being simple but at the same time flexible and effective Throttling so that the proportion of oxidizable pollutants in the exhaust gas is throttled Cylinder for a subsequent oxidation reaction with corresponding heating of the Catalyst is increased while at the same time the unthrottled cylinder is sufficient Provide oxygen for catalytic conversion and reliable engine control.

In a particularly advantageous embodiment, before and / or after an im Exhaust gas flow arranged catalyst temperature sensors arranged, which with a Control device for the throttle valve are connected (reason see above).

The device advantageously contains the features described in the method or Measures (individually and in sum) - and vice versa. Other features, advantages and advantageous embodiments of the invention result from the dependent claims, and from the following description of the invention with reference to the accompanying Drawing.

This shows a preferred embodiment of a schematic representation device according to the invention.

A direct injection diesel engine 10 has four cylinders 12 to 18 . These are supplied with fuel via injection nozzles 20 and with air via intake valves 22 from an intake manifold 24 . The intake manifold 24 is divided into four separate flow channels 26 to 32 for each of the cylinders 12 to 18 .

Exhaust valves 34 and an exhaust manifold 36 exhaust gas flows away from the cylinders 12 to 18 and a possibly electrically heated NOx storage catalytic converter or oxidation catalytic converter 38 .

A Lambda _DR value denotes a lambda value of the exhaust gas of an individual throttled cylinder, while a Lambda _Ges value denotes a lambda value of the total exhaust gas. In addition, temperatures upstream of the catalyst 38 T _{before cat} and downstream of the catalyst 38 T _{after cat} are advantageously measured.

In the preferred embodiment shown, an additional individual throttle valve 40 is provided in the flow channel 24 of the cylinder 12 . With this throttle valve 40 , the cylinder 12 can be throttled independently of the other (not throttled cylinders) 14 to 18.

The throttling of the cylinder 12 causes a possibly drastic increase in the proportion of oxidizable pollutants in the exhaust gas of the cylinder 12 and the value Lambda _{DR of} this cylinder 12 can be set individually and independently of the other cylinders 14 to 18 which are not throttled. The remaining cylinders 14 to 18 continue to work in a lean state and thus supply enough oxygen in their exhaust gas so that a sufficient to complete catalytic conversion of the additional pollutants CO and HC can take place on the catalyst.

This intensified oxidation reaction heats the catalyst 38 in the desired manner so that it can operate at an optimal operating point for regeneration, although the exhaust gases from the lean operation would not actually allow this. Overall, the engine 10 can continue to run in lean operation without the need for additional permanent heating of the catalyst 38 .

On the other hand, a brief (in particular electrical) heating of the catalyst 38 to initiate the catalytic oxidation can be advantageous. After the start of the reaction, however, the additional electrical heating can be switched off, since the waste heat from the reaction automatically keeps the catalytic conversion going.

This process is particularly suitable for nozzle-controlled direct injectors, such as pump-nozzle and pump-line-nozzle systems. Also result in common rail systems there are advantages over the purely late or post-injection that has so far been common.

Overall, the pollutant content after the catalytic converter 38 drops because regeneration of the NOx storage catalytic converter is more easily possible using the method according to the invention.

Reference list

10th

engine

12th

cylinder

14

cylinder

16

cylinder

18th

cylinder

20th

Injector

22

Inlet valve

24th

Intake manifold

26

Flow channel

28

Flow channel

30th

Flow channel

32

Flow channel

34

Exhaust valve

36

Exhaust manifold

38

catalyst

40

Single throttle valve

Claims (10)

1. A method for controlling an internal combustion engine with n cylinders and an oxidation catalyst arranged in the exhaust gas stream, characterized in that the internal combustion engine is a self-igniting internal combustion engine with fuel injection, in which at least one, two or a maximum of n-1 cylinders are throttled in such a way that there is in the exhaust gas stream at least one throttled cylinder results in an increase in HC and / or CO emissions. 2. The method according to claim 1, characterized in that the increase in HC / CO- Emission is only such that an average λ ≧ 1.1, advantageous ≧ 1.3 and in particular ≧ 1.5. 3. The method according to claim 1 or 2, characterized in that the Fuel injection quantity of the throttled cylinder is changed in such a way that the throttled cylinder in its performance despite the throttling other cylinders is aligned. 4. The method according to any one of the preceding claims, characterized in that the throttling takes place in such a way that a lambda _DR value of 1 or less, in particular of 0.95 or less, results in the exhaust gas flow of the individually throttled cylinder. 5. The method according to any one of the preceding claims, characterized in that the fuel injection is nozzle-controlled, in particular via a Pump-nozzle, pump-line-nozzle, common rail or distributor pump with Magnetic valve.   6. The method according to any one of the preceding claims, characterized in that the throttling depending on a temperature of the exhaust gas flow downstream and / or upstream of the catalyst. 7. The method according to any one of the preceding claims, characterized in that the catalyst is briefly electrical before and / or during throttling is heated. 8. The method according to any one of the preceding claims, characterized in that the throttling takes place in such a way that an additional H ₂ formation takes place in the self-igniting combustion. 9. Device for controlling a self-igniting internal combustion engine with n cylinders ( 12 , 14 , 16 , 18 ), each having a separate intake duct ( 26 , 28 , 30 , 32 ), characterized in that in at least one of the separate intake ducts ( 26 , 28 , 30 , 32 ) a throttle valve ( 40 ) is provided, and that at least one or a maximum of n-1 cylinders can be throttled via the control device such that there is an increase in HC and / or CO emissions in the exhaust gas flow of at least one throttled cylinder results. 10. The device according to claim 8, characterized in that a temperature sensor which is connected to the control device for the throttle valve ( 40 ) is arranged before and / or after a catalyst ( 38 ) arranged in the exhaust gas stream.