DE112006002008B4 - Method for raising the exhaust gas temperature in an internal combustion engine - Google Patents

Abstract

Method for raising the exhaust gas temperature in an internal combustion engine with several differently operated cylinders, wherein at least a first cylinder, preferably a first group of cylinders, is operated with a rich air/fuel ratio, the air/fuel ratio and/or the load of each individual actively operated cylinder is set independently of the other cylinders, characterized in that the combustion in each cylinder individually adapted to the set fuel / air ratio, or the set load, preferably for the set fuel / air ratio, or the set load is optimized, with the combustion rate being adjusted by cylinder-specific metering of internal residual gas.

Description

The invention relates to a method for raising the exhaust gas temperature in an internal combustion engine with a plurality of differently operated cylinders, with at least a first cylinder, preferably a first group of cylinders, being operated with a rich fuel/air ratio, with the fuel/air ratio and/or the load of each actively operated cylinder is set independently of the other cylinders.

It is known to operate part of the cylinders rich and another part of the cylinders lean in order to generate an exothermic reaction in the catalytic converter, for example from publications JP H05-86848 A, WO 01/21950 A1 , U.S. 6,467,259 B1 , JP S56-113 009 A or the JP 2001-152844 A . This makes it possible to provide a combustible mixture on the catalytic converter. The availability of hydrocarbons and carbon monoxide at the catalytic converter is ensured by means of cylinders operated with a rich mixture. With the lean-operated cylinders, on the other hand, oxygen is made available at the catalytic converter. This leads to an exothermic reaction of hydrocarbons and oxygen in the catalyst, which significantly reduces the catalyst light-off time and thus minimizes fuel consumption and emissions. The disadvantage, however, is that the smooth running is worsened by the unequal distribution.

the DE 100 50 473 A1 describes a method for rapidly heating up an exhaust gas catalytic converter on a reciprocating internal combustion engine, which provides for the valve trains and/or the fuel injection device for at least one cylinder to be controlled in a targeted manner in such a way that working alternately in rich operation and in lean operation takes place.

A method for heating a catalyst of a direct-injection multi-cylinder Otto internal combustion engine is from DE 600 18 948 T2 known. A first group of cylinders is supplied with a lean and stratified mixture and a second group of cylinders with a rich and homogeneous mixture. During the heating of the catalyst, the power of all cylinders is unified by delaying the ignition of the cylinders of the second group.

From the DE 197 40 482 A1 a method for operating a multi-cylinder internal combustion engine with direct injection is also known, which provides that at times at least one cylinder is operated at a lambda value of less than 1.0 and at least one other cylinder at a lambda value of less than 1.0 for post-combustion of gasoline within the exhaust gas stroke. The method is used, among other things, to heat a catalytic converter.

the U.S. 2005/0126537 A1 discloses a method for controlling exhaust gas recirculation based on a combustion stability measurement. Incomplete combustion and misfires are detected by measuring the ion current. During the heating of the catalytic converter, the ignition angles in the individual cylinders are set as late as possible during the heating of the catalytic converter.

From the US 2001/0003971 A1 an engine control system for an internal combustion engine with electromagnetically actuated intake and exhaust valves is known.

It is the object of the invention to avoid the disadvantages mentioned and to improve the smooth running, or to intensify the effect of increasing the exhaust gas temperature.

According to the invention, this is achieved in that the combustion in each cylinder is individually adapted to the set fuel/air ratio or the set load, preferably individually optimized for the set fuel/air ratio or the set load Burning speed is adjusted by cylinder-specific metering of internal residual gas.

A preferred embodiment of the invention provides that at least one second cylinder, preferably a second group of cylinders, is operated with a lean fuel/air ratio. Due to the fact that the filling is adapted cylinder-selectively, cylinders can be operated with the same load (indicated mean effective pressure) despite the fact that some of the cylinders are operated rich and the rest of the cylinders are lean. This significantly increases smoothness. The filling status of each individual cylinder can be selected independently of the other cylinders.

The setting of the combustion speed takes place, for example, via the turbulence in the combustion chamber. This can be done by varying the control times of the internal combustion engine, for example by varying the closing edge of at least one intake valve and/or the valve lift of at least one intake valve. With variable valve control, the relevant parameters can be changed over a wide range. By adjusting the combustion rate, preferably increasing it, the combustion can be retarded, which leads to an increased exhaust gas temperature. The cylinders can be operated with the same load (indicated mean effective pressure) but with different fillings.

After the individual cylinder exhaust gases have been combined, the air ratio of the exhaust gases from the entire engine can be stoichiometric, slightly lean or slightly rich.

It is also possible that the fuel/air ratio is set stoichiometrically in all cylinders, but the cylinders are operated with significantly different indicated mean effective pressures.

In a further embodiment of the invention, it can be provided that in at least one second cylinder, preferably a second group of cylinders, the injection of the fuel is completely switched off and a predefined quantity of secondary air is set via the control times of the intake and/or exhaust valves of this cylinder using fresh air pumped through . With cylinder deactivation true to the cycle, the internal torque of the fired cylinder is approximately doubled true to the cycle, which significantly improves combustion stability in the fired cylinders and significantly reduces raw emissions.

The increase in combustion stability can be used to significantly delay combustion, thereby increasing the exhaust gas temperature and heating up the catalytic converter with minimal untreated emissions.

This effect can be intensified if the deactivated cylinders pump fresh air to the catalytic converter. The amount of secondary air or the amount of fresh air pumped through is set via the control times of this cylinder. The cylinders that are not switched off can be operated with a rich fuel/air mixture. The measures to increase the exhaust gas temperature are preferably used during the warm-up phase until the light-off temperature of the catalytic converter is reached and/or in phases of low engine load to increase the temperature in the catalytic converter.

In order to keep the cylinder load as low as possible, it is advantageous if the unequal distribution of the fuel/air ratio and/or the load is exchanged at least once, preferably periodically, between the first group and the second group of cylinders during engine operation. As a result, the cylinder load can be thermally evened out and the cooling of a cylinder that is running at low or zero load can be prevented.

The invention provides that above and/or below a predefined total engine load and/or engine speed, the unequal distribution of the load and/or the filling between the cylinders is deactivated.

The measures for raising the exhaust gas temperature are preferably carried out as a function of the temperature of the internal combustion engine and/or the ambient temperature.

• 1 einen 4-Zylinder-Reihenmotor mit einflutigem Katalysator bei Parallelbetrieb;
• 2 einen 4-Zylinder-Reihenmotor mit einflutigem Katalysator bei Zyklusbetrieb;
• 3 einen 6-Zylinder-V-Motor mit doppelflutigem Katalysator für Parallelbetrieb;
• 4 einen 6-Zylinder-V-Motor mit doppelflutigem Abgaskatalysator bei Zyklusbetrieb;
• 5 einen 6-Zylinder-V-Motor mit einflutigem Katalysator bei Parallelbetrieb;
• 6 einen 6-Zylinder-V-Motor mit einflutigem Katalysator bei zyklischem Betrieb;
• 7 einen 6-Zylinder-Reihenmotor mit zweiflutigem Katalysator bei Parallelbetrieb;
• 8 einen 6-Zylinder-Reihenmotor mit zweiflutigem Katalysator bei Zyklusbetrieb;
• 9 einen 6-Zylinder-Reihenmotor mit einflutigem Katalysator;
• 10 einen 4-Zylinder-Reihenmotor mit einflutigem Katalysator mit Zylinderabschaltung; und
• 11 einen 6-Zylinder-V-Motor mit einflutigem Katalysator und Zylinderabschaltung.

The invention is explained in more detail below with reference to the figures. Show it:

• 1 a 4-cylinder in-line engine with a single-flow catalytic converter in parallel operation;
• 2 a 4-cylinder in-line engine with a single-flow catalyst in cycle operation;
• 3 a 6-cylinder V engine with double-flow catalyst for parallel operation;
• 4 a 6-cylinder V-engine with double-flow catalytic converter in cycle operation;
• 5 a 6-cylinder V engine with a single-flow catalyst in parallel operation;
• 6 a 6-cylinder V-engine with a single-flow catalyst with cyclic operation;
• 7 a 6-cylinder in-line engine with a double-flow catalyst with parallel operation;
• 8th a 6-cylinder in-line engine with double flow catalyst in cycle operation;
• 9 a 6-cylinder in-line engine with a single-flow catalytic converter;
• 10 a 4-cylinder in-line engine with a single-flow catalytic converter with cylinder deactivation; and
• 11 a 6-cylinder V engine with a single-flow catalytic converter and cylinder deactivation.

the 1 until 11 show various internal combustion engines for use of the method according to the invention.

Cycle operation refers to operation in which the charge and/or load is swapped between the first and second groups of cylinders from one engine cycle to another for a predefined number of cycles. Parallel operation is understood to mean operation with an unequal distribution of charge and/or load between the first and second group of cylinders, in which there is no change in charge or load between the groups of cylinders.

The individual cylinders are denoted by reference numbers 1, 2, 3, 4, 5, 6 in the figures. Two groups of exhaust gas lines L1, L2 lead from the individual cylinders to single- or double-flow or to separate catalytic converters K.

Cylinders that are operated with F are denoted by M, cylinders that are operated lean.

the in the 1 until 9 The arrangements shown have in common that one group of cylinders is operated rich and another group of cylinders is operated lean. Rich operation ensures that hydrocarbons and carbon monoxide are made available for catalytic converter K. Lean operation, on the other hand, ensures that oxygen (O ₂ , O) is made available at the catalytic converter.

This creates an exothermic reaction of hydrocarbons and oxygen in the catalyst, which leads to a significant reduction in the catalyst light-off time while minimizing fuel consumption and emissions, or which prevents the catalyst from cooling down too far during operation at the lowest load.

At the in 1 internal combustion engine shown, the first and third cylinders 1, 3 are rich and the second and fourth cylinders 2, 4 are operated lean. As a result, an overall air ratio λ _K ≧0.9 is established in the area of the catalytic converter K. The typical firing order is 1-3-4-2. In the 2 The variant shown differs from the one in 1 indicated parallel operation in that the groups of lean-operated cylinders and rich-operated cylinders alternate cyclically. In a first cycle I, for example, cylinder 1 and cylinder 3 are operated rich and cylinders 2 and 4 are operated lean. In the second cycle II, cylinders 1 and 3 are operated lean, but cylinders 2 and 4 are operated rich. Here, too, an overall air mixture λ _K ≥ 0.9 occurs in the area of the catalytic converter K in each cycle. The delivered cylinder torque is adjusted accordingly (control times) and is the same for all cylinders.

3 and 4 show internal combustion engines with six cylinders and double-flow catalysts K. In 3 shows the situation for a 6-cylinder internal combustion engine with two exhaust lines L1 and L2 and two catalytic converters K for parallel operation. Cylinders 1, 4 are operated rich, cylinders 3, 6 are operated lean. The air ratio λ _K for cylinders 2, 5 is made up as the mean value of the air ratios λ _K for cylinders 1, 3 and 4, 5, respectively. The typical firing order 1-4-3-6-2-5 is indicated by the dashed arrows. The internal load is the same for all cylinders. In the area of the catalytic converters K, the overall air ratio is λ _K ≧0.9.

4 shows a similar 6-cylinder V-type internal combustion engine as in 3 , whereby the air ratios of the cylinders 1, 3 on the one hand and 4, 6 on the other hand are changed cyclically. This means that in a first cycle I, cylinders 1, 4 are operated rich and cylinders 3, 6 are operated lean. In a second cycle II, the charges between cylinders 1, 4 and 3, 6 are swapped over, so that cylinders 1, 4 are operated lean and cylinders 3, 6 are operated rich. In the next cycle, the unequal distribution again corresponds to the situation of the first cycle I. The fuel/air ratio of cylinders 2, 5 is again made up as the mean value of the fuel/air ratios of cylinders 1, 3 and 4, 6, respectively. Here too, in the area of the double-flow catalytic converter K, there is a total air ratio λ _K ≧0.9.

the 5 and 6 show 6-cylinder V-type internal combustion engines, with the two exhaust lines L1, L2 opening into a single-flow catalytic converter. 5 shows the situation for parallel operation. Cylinders 1, 2 and 3 are operated rich, while cylinders 4, 5 and 6 are operated lean. The typical firing order 1-4-3-6-2-5 is indicated with dashed lines. In the area of the catalytic converter, the total air ratio is λ _K ≥ 0.9.

6 shows the in 5 internal combustion engine shown with cyclic operation. In a first cycle I, cylinders 1, 2 and 3 are operated rich and cylinders 4, 5 and 6 are operated lean. In a second cycle II, cylinders 1, 2 and 3 are operated lean and cylinders 4, 5 and 6 are operated rich. A total air ratio λ _K of at least 0.9 again results in the area of the catalytic converter K.

the 7 and 8th show 6-cylinder in-line internal combustion engines with two exhaust lines L1 and L2 and two-flow catalytic converters K. When in 7 In the parallel operation shown, cylinders 1, 4 are operated rich and cylinders 2, 6 are operated lean. The fuel/air ratios for cylinders 3, 5 result from the mean values of the fuel/air ratios for cylinders 2, 4 and 4, 6. The firing order can be 1-4-2-6-3-5, for example . In the area of the catalytic converter K, there is a total air ratio λ _K of at least 0.9.

8th shows the situation for cyclic operation. In a first cycle I, cylinders 1, 4 are operated rich and cylinders 2, 6 are operated lean. In the second cycle II, cylinders 1, 4 are operated lean and cylinders 2, 6 are operated rich. The fuel/air ratios for cylinders 3, 6 result from the mean values of the fuel/air ratios for cylinders 2, 4, or 4 and 6. In the area of the catalytic converters K, a total air ratio λ results for each cycle I, II _K of at least 0.9.

9 shows the situation for a 6-cylinder in-line internal combustion engine with a single-flow catalytic converter K. In parallel operation, half of the cylinders, for example cylinders 1, 3, are operated rich and the other half of the cylinders, for example 4, 5 and 6, are operated lean. If the internal combustion engine is operated cyclically, three cylinders are operated alternately rich and lean. For example, in a first cycle I, cylinders 1, 2 and 3 are operated rich, while cylinders 4, 5 and 6 are operated lean. in one In the second cycle II, on the other hand, cylinders 1 to 3 are operated lean and cylinders 4 to 6 are operated rich.

An 8-cylinder engine can also be operated in parallel or cyclically in the same way. The basic condition is that for the respective catalytic converter K, a lean and rich mixture is supplied alternately in the ignition sequence. The resulting mixture on the catalyst then adjusts to the desired mean value.

the 10 and 11 show internal combustion engines in which one group of cylinders is operated rich and another group of cylinders is deactivated. The deactivated cylinders are denoted by reference character A.

With fully variable, highly flexible valve train systems, it is possible to carry out cylinder deactivation processes that are true to the cycle when the engine is started. With cylinder deactivation, the internal torque of the fired cylinder is approximately doubled with the same alternating torque, which significantly improves combustion stability and significantly reduces raw emissions. The increase in combustion stability can be used to significantly delay combustion, so that the catalytic converter K can be heated up with minimal untreated emissions.

This effect can be intensified if the deactivated cylinders pump fresh air to the catalytic converter K, while the fired cylinders transport the fuel in the form of HC and CO emissions to the catalytic converter K due to rich engine operation.

the 10 shows an arrangement with a single-flow catalytic converter K. The cylinders 1 to 4 open into a single exhaust line L1, which leads to the catalytic converter K. Here, a group of cylinders, namely cylinders 1, 3, is operated rich and cylinders 2, 4 are switched off, which is indicated by reference character A.

11 shows a 6-cylinder V-type internal combustion engine with a single-flow catalytic converter K. One possible strategy is to run cylinders 1, 2 and 3 rich and to switch off cylinders 4, 5 and 6.

Claims (19)

Method for raising the exhaust gas temperature in an internal combustion engine with several differently operated cylinders, wherein at least a first cylinder, preferably a first group of cylinders, is operated with a rich air/fuel ratio, the air/fuel ratio and/or the load of each individual actively operated cylinder is set independently of the other cylinders, characterized in that the combustion in each cylinder individually adapted to the set fuel / air ratio, or the set load, preferably for the set fuel / air ratio, or the set load is optimized, with the combustion rate being adjusted by cylinder-specific metering of internal residual gas. procedure after claim 1 , characterized in that the adjustment of the combustion via the combustion rate takes place by varying the control times of at least one intake valve. procedure after claim 1 or 2 , characterized in that the adjustment of the combustion rate is carried out by cylinder-specific variation of the closing edge of at least one intake valve. Procedure according to one of Claims 1 until 3 , characterized in that the adjustment of the combustion rate is carried out by cylinder-specific variation of the valve lift of at least one inlet valve. Procedure according to one of Claims 1 until 4 , characterized in that the adjustment of the combustion takes place via the combustion position, preferably by cylinder-specific adjustment of the ignition point. Procedure according to one of Claims 1 until 5 , characterized in that the adaptation of the combustion takes place by cylinder-specific variation of the injection time and/or the injection duration. Procedure according to one of Claims 1 until 6 , characterized in that the indicated mean pressure is kept the same in all cylinders during the measures to raise the exhaust gas temperature. Procedure according to one of Claims 1 until 7 , characterized in that the air ratio of the exhaust gas in the region of a catalytic converter after the exhaust gases of the individual cylinders have been combined is between 0.9 and 1.1. Procedure according to one of Claims 1 until 6 or 8th , characterized in that the fuel/air ratio is set stoichiometrically in all cylinders, but the cylinders have different indicated mean pressures. Procedure according to one of Claims 1 until 9 , characterized in that at least a second cylinder, preferably a second group the cylinder is operated with a lean fuel/air ratio. Procedure according to one of Claims 1 until 10 , characterized in that in at least one second cylinder, preferably in a second group of cylinders, the injection of the fuel is switched off completely and a predefined quantity of secondary air and/or quantity of fresh air pumped through is set via the control times of the intake and/or exhaust valves of this cylinder. procedure after claim 10 or 11 , characterized in that the exhaust valves of at least one deactivated cylinder are kept closed. Procedure according to one of Claims 10 until 11 , characterized in that the intake valves of at least one deactivated cylinder are kept closed. Procedure according to one of Claims 1 until 13 , characterized in that the fuel/air ratio and/or the load is reversed at least once, preferably periodically, between the first group and the second group of cylinders during engine operation. Procedure according to one of Claims 1 until 14 , characterized in that the combustion position is thermodynamically unfavorable late shifted to increase the exhaust gas temperature. Procedure according to one of Claims 1 until 15 , characterized in that the measures for raising the exhaust gas temperature are carried out during the warm-up phase until the light-off temperature of the catalyst is reached. Procedure according to one of Claims 1 until 16 , characterized in that the measures for raising the exhaust gas temperature are applied in phases of lower engine load to increase the temperature in the catalytic converter. Procedure according to one of Claims 1 until 17 , characterized in that the measures for raising the exhaust gas temperature take place as a function of the temperature of the internal combustion engine and/or the ambient temperature. Procedure according to one of Claims 1 until 18 , characterized in that above and/or below a predefined total engine load and/or speed the unequal distribution of the load and/or the fuel/air ratio between the groups of cylinders is deactivated.

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