AT520848B1 - METHOD OF CONTROLLING AN EXHAUST GAS TEMPERATURE OF A COMBUSTION ENGINE - Google Patents

Abstract

The invention relates to a method for controlling an exhaust gas temperature of an internal combustion engine (1) with at least a first group (A) and a second group (B) of cylinders (2), at least the first group (A) having a first exhaust manifold (6) an exhaust gas recirculation circuit (C1; C2) which fluidly connects the first exhaust manifold (6) to an intake manifold (4), and wherein the first exhaust manifold (6) and a second exhaust manifold (7) with a - in particular symmetrical - turbine (10) one Exhaust gas turbocharger (11) are flow-connected and a control element - in particular a flap (15) - is arranged in a flow connection of the first exhaust manifold (6), this control element being at least partially closed in at least a first partial load range of the internal combustion engine (1) and an injection quantity of the first group (A) of cylinders (2) is reduced to at least a subset of a first injection quantity. The object of the invention is to provide a method with which the exhaust gas temperature can be controlled in a simple manner. This object is achieved in that the method is triggered when the exhaust gas temperature falls below a critical lower limit and an injection quantity in cylinders (2) of the second group (B) is increased by a substantial part of the first injection quantity at least in the first partial load range, the injection quantity being increased is higher than a second injection quantity, which is injected at an exhaust gas temperature above the lower critical exhaust gas temperature.

Description

description

The invention relates to a method for controlling an exhaust gas temperature of an internal combustion engine with at least a first group and a second group of cylinders, wherein at least the first group with a first exhaust manifold has an exhaust gas recirculation circuit that fluidly connects the first exhaust manifold with an intake manifold, and wherein the first exhaust manifold and a second exhaust manifold are flow-connected to a - in particular symmetrical turbine of an exhaust gas turbocharger and a control element - in particular a flap - is arranged in a flow connection of the first exhaust manifold, this control element being at least partially closed in at least a first partial load range of the internal combustion engine and a The injection quantity of the first group of cylinders is reduced to at least a partial quantity of a first injection quantity, and the method, when the exhaust gas temperature falls below a lower critical level, is at least in the first partial load range an injection amount in cylinders of the second group is increased by a substantial part of the first injection amount, and the injection amount is higher than a second injection amount at the same load, which is injected at an exhaust gas temperature above the lower critical exhaust gas temperature.

DE 11 2015 003 446 T5 and DE 10 2016 006 676 A1 show such a method. The disadvantage here is that excess energy has to be generated in order to heat up the exhaust gas temperature, which energy has to be dissipated either via mechanical brakes or the like.

US 2011 13 19 78 A1 teaches a method with the purpose of heating a catalytic converter with a lean mixture with operation of two cylinders.

DE 10 2009 02 83 54 A1 shows a classic cylinder deactivation in which a group of cylinders is not fired. The gas in the cylinders is sent in a circle. Without injection, the proportion of nitrogen oxide in the exhaust gas is very high. The procedure is not suitable for a cold start.

From AT 503869 B1 an internal combustion engine with two groups of cylinders is known. In the case of an exhaust gas turbocharger with a sufficiently high flow rate in the lower speed range, an exhaust gas back pressure is provided that is large enough to recirculate exhaust gas. The exhaust gas damper is arranged between the branch of the exhaust gas recirculation line and the opening into the turbine of the exhaust gas turbocharger. Since it is not necessary to completely prevent the mass flow through the exhaust gas flap, it is proposed to reduce the installation size of the exhaust gas flap. The exhaust gas recirculation rate is regulated via an exhaust gas recirculation valve in the exhaust gas recirculation line. The reduced mass flow into the turbine of the exhaust gas turbocharger leads to a reduced boost pressure. The resulting lower air ratio increases the exhaust gas temperature. A cylinder deactivation is not provided.

In internal combustion engines with selective cylinder deactivation, a group of cylinders is deactivated at low load and idling. This lowers the temperature in the exhaust system, which in turn is disadvantageous for the exhaust gas aftertreatment system, since it requires a minimum temperature.

Methods for selective cylinder deactivation serve to save fuel. They are usually only used in internal combustion engines with more than eight cylinders (V8 engines) in order to guarantee a certain degree of smoothness. This usually requires a variable valve drive, which increases the design effort and complexity of the internal combustion engine considerably.

A second injection quantity is injected into the still active cylinder during the time in which at least one group of the cylinders is deactivated.

The second injection quantity here denotes a set injection quantity that is also set for cylinder deactivation in normal operation. The power output remains the same as the power output before cylinder deactivation and the injection quantity is thus adjusted.

ensures that the efficiency is optimal.

In order to reduce nitrogen oxide emissions, systems for exhaust gas recirculation (EGR) are used in commercial vehicles and large engines, as well as in many passenger vehicles.

Exhaust gas temperature is understood here to mean the temperature reached by the exhaust gas in an exhaust gas aftertreatment system downstream of the turbine of the exhaust gas turbocharger. The exhaust gas mass flow back to the inlet is adjusted by a control element.

The control element can, for example, be a flap or a valve, this control element being suitable for partially closing the flow connection, that is to say that the flow connection is at least partially blocked and thus represents a flow resistance. The control element can advantageously also completely close off the flow connection.

The injection quantity is that at the moment in question, since it is variable over time.

A first injection quantity is to be understood here as an injection quantity of fuel which a group of cylinders injects into the combustion chambers at the design point.

If selective cylinder deactivation is envisaged, it is not readily possible to provide the required temperature of the exhaust gas aftertreatment system in the low load range or in idle within a short time. The exhaust gas aftertreatment system takes a relatively long time to heat up. If the exhaust gas temperature and, as a result, the exhaust gas aftertreatment system have not yet warmed up to the required temperature, there will be increased pollutant emissions. Cooling down through exhaust gas recirculation and cylinder deactivation during operation also have a negative impact on the effectiveness of the exhaust gas aftertreatment system.

The object of the invention is to provide a method that enables the exhaust gas aftertreatment system to be heated up quickly and / or prevents the exhaust gas aftertreatment system from cooling down.

This object is achieved according to the invention by a method mentioned at the beginning in that the amount injected into the cylinders of the first group is reduced to such an amount that the mean pressure of these cylinders of the first group is negative. In the suction tank of the internal combustion engine, the recirculated exhaust gases heat up the charge air. This is particularly advantageous in the case of a cold internal combustion engine.

This enables the first group of cylinders to be placed in a towing operation and thus the amount of energy required for heating does not have to be passed on to the output, but can be reduced in the first group of cylinders, and the fuel requirement is still low compared to the Normal operation.

The injection quantity is variable and adjustable for each group of cylinders or even for each cylinder. A first partial load range is understood here to mean a load range in which the internal combustion engine delivers less power than the full load range.

The method is used to control the exhaust gas temperature of an internal combustion engine. The internal combustion engine has several cylinders which are divided into a first group and a second group of cylinders. At least one exhaust gas recirculation circuit is provided, the exhaust gas recirculation circuit connecting the first exhaust manifold of the first group of cylinders to the intake manifold. An exhaust gas turbocharger is provided which is in flow connection with the first exhaust manifold and the second exhaust manifold. The second exhaust manifold can also be connected to the intake manifold and thus a second exhaust gas recirculation circuit can exist. The turbine of the exhaust gas turbocharger is ideally designed symmetrically. In the flow connection from the first exhaust manifold to the turbine, a control element is provided which can release, block and control the flow connection.

In the first partial load range, the control is at least partially closed and an injection amount of the first group of cylinders is at least a partial amount of one

first injection quantity reduced.

A symmetrical turbine of the exhaust gas turbocharger is understood here to mean that the flows to the turbine are designed to be the same.

According to the invention, an increase in the injection quantity by a substantial part of the first injection quantity represents an increase which is suitable for increasing the exhaust gas temperature so that it is above the lower critical exhaust gas temperature.

This solution enables the exhaust gas aftertreatment system to be heated up quickly and easily. Furthermore, no cooling for the exhaust gas recirculation and no asymmetrical turbine is required.

Furthermore, the invention makes it possible to increase the pressure on the exhaust side. For this purpose, the flap / control element is completely closed and the exhaust gas from the cylinders of the first group is passed through the first exhaust gas recirculation circuit into the intake manifold and at the same time the exhaust gas recirculation valve is at least partially closed.

It is advantageous if the injection quantity into the cylinders of the second group is increased to twice, preferably more than twice, the first injection quantity. As a result, the exhaust gas temperature can be raised very quickly due to the heat released during the combustion of the fuel.

It is advantageous if the injection quantity into the cylinders of the first group is reduced essentially to zero, since this leads to a lower consumption.

With an activated first group of cylinders, the exhaust gas temperature can be increased or reduced when the control element a first amount of the exhaust gas, or with deactivated injection of the air that flows through the exhaust gas recirculation circuit of the first group of cylinders, adjusted as required and the Amount of hot or cooler gas to the exhaust aftertreatment system can be controlled or regulated.

The first amount is to be understood as a subset of an entirety of the exhaust gas from the first group of cylinders.

In order to bring the internal combustion engine faster to its operating temperature, or to keep the operating temperature from falling, it is provided in a special variant of the method that the control is closed in the first partial load range and the first amount of exhaust gas or air Represents the entirety of the exhaust gas or the air from the first group of cylinders, which flows via the exhaust gas recirculation circuit.

In a further advantageous embodiment, the amount injected into the cylinders of the second group is set to such an amount that the mean pressure of these cylinders of the second group is positive and in particular essentially corresponds in terms of amount to the negative mean pressure of the cylinders of the first group.

It is advantageous if a second exhaust gas recirculation circuit connects the second exhaust manifold to the intake manifold. This has the advantage that the pollutant emissions can be further reduced.

In order to be able to react more flexibly to load changes, it is advantageous if the second exhaust gas recirculation circuit has an exhaust gas recirculation valve and, as a second amount, conveys at least a portion of exhaust gas to the intake manifold, the second amount being set via the exhaust gas recirculation valve.

The second amount here denotes a partial amount of the exhaust gas from the second group of cylinders that is returned into the intake manifold.

It is advantageous if the exhaust gas recirculation valve is fully opened outside of the first partial load range.

A particularly advantageous operating point in the first partial load range with regard to the exhaust gas temperature for the exhaust gas aftertreatment system arises when the first amount as

a proportion of the total mass flow that flows through the intake manifold is set in the range from approximately 30% to 50%, and the second amount is set as a proportion of the total mass flow in the range from 5% to 15%.

The total mass flow that flows through the intake manifold represents the sum of the mass flows to the first group and to the second group of cylinders.

In order to make the control more flexible, it is advantageous if the exhaust gas recirculation circuit of the first group of cylinders and the flow connection to the turbine can be connected to one another via a 3/2-way valve as a control element.

It is advantageous if a second line with an EGR cooler is provided parallel to the exhaust gas recirculation circuit of the first group of cylinders, the exhaust gas recirculation circuit and the second line being arranged to be connectable to one another via a 3/2-way valve. Thus, the two exhaust gas recirculation circuits can be flown through in parallel.

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

1 shows an internal combustion engine according to the invention in a first embodiment in a schematic representation; and

2 shows an internal combustion engine according to the invention in a second embodiment in a schematic representation.

1 shows an internal combustion engine 1 with at least two groups A, B of cylinders 2, which are connected via gas ducts 3 to an intake manifold 4 into which an inlet line 5 opens.

An exhaust manifold 6, 7 emanates from each group A, B of cylinders 2, the two exhaust manifolds 6, 7 opening via connecting lines 18 into a respective flood of a symmetrical turbine 10 of an exhaust gas turbocharger 11. A compressor of the exhaust gas turbocharger 11, which is arranged in the inlet branch 5, is designated by reference number 12.

An exhaust gas recirculation line 13 extends from a first exhaust manifold 6 and opens into the intake manifold 4 and forms a first exhaust gas recirculation circuit C1. Reference numeral 14 denotes an exhaust gas recirculation valve.

In that exhaust manifold 6 from which the exhaust gas recirculation line 13 branches off, a flap 15 is arranged between the branch of the exhaust gas recirculation line 13 and the opening into the turbine 10. The turbine 10 of the exhaust gas turbocharger 11 is followed by an exhaust gas aftertreatment system 16.

FIG. 2 shows an exhaust gas recirculation circuit C, through which different cylinders 2 are connected to the intake manifold 4. The first group A of cylinders 2 is connected to the intake manifold 4 via a first exhaust gas recirculation circuit C1 and the second group B of cylinders 2 is connected to the intake manifold 4 via a second exhaust gas recirculation circuit C2. In the embodiment shown, the first group A has three cylinders 2 and the second group B also has three cylinders 2. An injection quantity can be set differently from cylinder 2 to cylinder 2.

The internal combustion engine 1 sucks in cold ambient air via an air line 5 and via the intake manifold 4, a compressor and a charge air cooler can be connected upstream.

In a first operating scenario for one of the exemplary embodiments according to FIGS. 1 or 2, the cylinders 2 of the first group A suck in 50% of the amount of air from the intake manifold 4 and compress the air. No fuel is injected into these cylinders 2 of the first group A. There is no combustion and the amount of gas expands into the first exhaust manifold 6. Due to the losses during compression and in the gas exchange, the air in the first exhaust manifold 6 is moderately heated.

To the arrangement according to the invention even with high engine load or in the conventional engine operating mode with "symmetrical", the same injection quantity over all cylinders 2, and

To be able to operate with low fuel consumption, a connecting line 18 is provided between the first exhaust manifold 6 and the turbine 10.

This connecting line 18 can be controlled either by a 2/2-way valve 19 upstream of the turbine 10 or by a 3/2-way valve 20 which divides the mass flow between the connecting line 18 and the first exhaust gas recirculation circuit C1.

In order to generally regulate the exhaust gas recirculation circuits C1 and C2 and to be able to switch off the exhaust gas recirculation (EGR), exhaust gas recirculation valves 14 are again provided.

EGR coolers 22 can advantageously be arranged in the exhaust gas recirculation circuits C1 and / or C2. This is shown by way of example in the exhaust gas recirculation circuit C1 in FIG. 2. These are advantageously only switched on during operation with a high engine load (that is, in the conventional engine operating mode without the need to raise the exhaust gas temperature). The regulation takes place here, for example, via a 2/2-way valve 23a or via a 3/2-way valve 23b.

When the 2/2-way valve 19 is closed, the first exhaust manifold 6 is not connected to the turbine 10 via the connecting line 18, but only via the first exhaust gas recirculation circuit C1 in a short circuit to the intake manifold 4.

As a result, the temperature in the suction pipe 4 rises. In the assumed example of the exemplary embodiment, the temperature in the first exhaust manifold 6 with deactivated cylinders 2 of the first group A is approximately 100.degree.

In order to achieve the desired engine output, more fuel is injected into the remaining cylinders 2 (cylinder 2 of the second group B), in particular more than twice the amount per cylinder 2 - compared to conventional, ie with the same fuel injection in all cylinders 2, motor operated at the same load. The exhaust gas temperature of these fired cylinders 2 of the second group B and the downstream exhaust manifold 7 rises sharply as a result. A part of this hot exhaust gas - 230 ° C in the assumed example of the exemplary embodiment (in the exemplary embodiment 12% of the amount of gas pumped through the intake manifold 4) is returned uncooled via the second exhaust gas recirculation circuit C2 to the intake manifold 4 and further increases the gas temperature there.

The remaining hot exhaust gas mass flow of the cylinders 2 of the second group B flows out of the exhaust manifold 7 via the connecting line 18 to the turbine 10 and to the exhaust gas aftertreatment system arranged after the turbine 10.

In the assumed example for the first operating scenario, the proportion of the amount of cold fresh air drawn in is 38% (62% is recirculated, uncooled gas). The fresh air is drawn in from the environment at ambient temperature (20 ° C). The intake manifold temperature in the lowest partial load operation can be increased to 80 ° C, the exhaust gas temperature at the turbine 10 rises to 230 ° C.

This heating effect can be further increased by activating an engine braking device (decompression brake) of the cylinder 2 that is not fired in the first operating scenario. The decompression increases the losses of the braked cylinder 2, the fired cylinder 2 compensates for the increased "internal engine friction" through higher injection quantities and thus a higher quantity of burned fuel.

In a second advantageous operating scenario for one of the exemplary embodiments according to FIG. 1 or 2, the flap 15 between the branch of the first exhaust gas recirculation circuit C1 and the opening into the turbine 10 is completely closed. The entire exhaust gas of the cylinders 2 of the first group A is thus conducted into the intake manifold 4 through the first exhaust gas recirculation circuit C1. In contrast to the first operating scenario, so much fuel is injected into the cylinders 2 of the first group A that when the exhaust gas recirculation valve 14 is partially closed, the combustion in these cylinders 2 of the first group A results in a negative mean pressure. The negative mean pressure results from the high gas pressure in the first exhaust manifold 6.

The second operating scenario is particularly advantageous when the internal combustion engine is cold. In

A specific example, in which the component temperature of the internal combustion engine is 25 ° C, results in a negative mean pressure in the cylinders 2 of the first group A of -2.38 bar at low engine speed, especially when idling, since these cylinders 2 counteract a counter pressure have to push out in the first exhaust manifold 6 of 3.3 bar. As a result, the exhaust gas from cylinders 2 of the first group A is heated to 296 ° C. As a result, an advantageously elevated temperature of 135 ° C. is established in the suction pipe 4.

The second operating scenario, which is advantageous for a cold start of the internal combustion engine, can advantageously be further developed in that so much fuel is injected into the cylinder 2 of the second group B that the negative mean pressure of the cylinder 2 of the first group A is compensated and that the Internal combustion engine is prevented. Here, the exhaust gas from the second exhaust manifold 7 is advantageously routed to the turbine 10 of the exhaust gas turbocharger 11.

In the above example, there is a positive mean pressure of +2.38 bar in the cylinders 2 of the second group B and, with the same number of cylinders 2 in the first and second groups A, B, a total mean pressure of 0 bar (idle) .

The exhaust gas of the cylinder 2 of the second group B is much hotter than in normal engine operation due to the increased injection quantity and the increased charge air temperature. The exhaust gas temperature upstream of the exhaust gas aftertreatment system 16 rises sharply as a result. In the above example it is 222 ° C. This advantageously enables the urea metering to be activated in the SCR catalytic converter shortly after the cold start. The advantage of this solution according to the invention is that an external burner and / or a variable valve drive can be dispensed with in order to provide this heating function after the engine has started. In addition, due to the recirculated exhaust gas of the cylinder 2 of the first group A, the nitrogen oxide emission of the cylinder 2 of the second group B is reduced by this method.

When operating in the partial load range, so much more fuel is injected into the cylinder 2 of the second group B in the second operating scenario that a positive mean pressure greater than 2.38 bar and thus a positive total mean pressure is established.

Claims (10)

Claims 1. A method for controlling an exhaust gas temperature of an internal combustion engine (1) with at least a first group (A) and a second group (B) of cylinders (2), at least the first group (A) having an exhaust gas recirculation circuit with a first exhaust manifold (6) (C +), which fluidly connects the first exhaust manifold (6) to an intake pipe (4), and wherein the first exhaust manifold (6) and a second exhaust manifold (7) with a - in particular symmetrical - turbine (10) of an exhaust gas turbocharger (11) are flow-connected and a control element - in particular a flap (15) - is arranged in a flow connection of the first exhaust manifold (6), this control element being at least partially closed in at least a first partial load range of the internal combustion engine (1) and an injection quantity of the first group (A ) of cylinders (2) is reduced to at least a partial amount of a first injection amount, and the method when the exhaust gas falls below a lower critical level temperature is triggered and at least in the first partial load range an injection amount in cylinders (2) of the second group (B) is increased by a substantial part of the first injection amount, the injection amount being higher than a second injection amount at the same load that at an exhaust gas temperature is injected above the lower critical exhaust gas temperature, characterized in that the amount injected into the cylinders (2) of the first group (A) is reduced to such an amount that the mean pressure of these cylinders (2) of the first group (A) is negative. 2. The method according to claim 1, characterized in that the injection quantity into the cylinders (2) of the second group (B) is increased to twice, preferably more than twice, the first injection quantity. 3. The method according to claim 1 or 2, characterized in that the injection quantity into the cylinders (2) of the first group (A) is reduced substantially to zero. 4. The method according to any one of claims 1 to 3, characterized in that the control element sets a first amount of the exhaust gas or the air that flows through the exhaust gas recirculation circuit (C +; C2) of the first group (A) cylinder (2). 5. The method according to claim 4, characterized in that the control is closed in the first partial load range and the first amount of exhaust gas or air represents the entirety of the exhaust gas or air from the first group (A) of cylinders (2), which is via the Exhaust gas recirculation circuit (C +; C2) flows. 6. The method according to any one of claims 1 to 5, characterized in that the injection quantity into the cylinders (2) of the second group (B) is set to such an amount that the mean pressure of these cylinders (2) of the second group (B) is positive and in particular corresponds in terms of amount to the negative mean effective pressure of the cylinders (2) of the first group (A) substantially. 7. The method according to any one of claims 1 to 6, wherein the internal combustion engine (1) has a second exhaust gas recirculation circuit (C ») which connects the second exhaust manifold (7) to the intake manifold (4), characterized in that the second exhaust gas recirculation circuit (C2 ) has an exhaust gas recirculation valve (14) and conveys at least a portion of exhaust gas to the intake manifold (4) as a second quantity, the second quantity being set via the exhaust gas recirculation valve (14). 8. The method according to claim 7, characterized in that the exhaust gas recirculation valve (14) is fully opened outside of the first partial load range. 9. The method according to claims 4 and 8, characterized in that the first amount is set as a proportion of the total mass flow that flows through the suction pipe (4) in the range of approximately 30% to 50%, and the second amount is set as a Share of the total mass flow is set in the range from 5% to 15%. 10. Internal combustion engine (1) with at least a first group (A) and a second group (B) of cylinders (2), wherein at least the first group (A) with a first exhaust manifold (6) has an exhaust gas recirculation circuit (C +) which the first exhaust manifold (6) flow-connected to an intake pipe (4), and wherein the first exhaust manifold (6) and a second exhaust manifold (7) are flow-connected to an - in particular symmetrical - turbine (10) of an exhaust gas turbocharger (11) and in a flow connection of the first exhaust manifold (6) a control element - in particular a flap (15) - is arranged with the exhaust gas recirculation circuit (C +;) of the first group (A) cylinder (2) and the flow connection to the turbine (10) via a 3/2-way valve (20) can be connected to one another as a control element, and the internal combustion engine can be operated according to a method according to one of claims 1 to 9, characterized in that parallel to the exhaust gas recirculation circuit (C1; C2) of the first group (A) Z ylinder (2) a second line with an EGR cooler (22) is provided, wherein exhaust gas recirculation circuit (C +; C2) and the second line are arranged such that they can be connected to one another via a 3/2-way valve (23). For this purpose 2 sheets of drawings