DE102009012336B3 - Method for heating component of exhaust gas after-treatment device of internal combustion engine, involves converting oxygen and fuel contained in exhaust gas to increase temperature of component of exhaust gas after-treatment device - Google Patents

Abstract

The method involves converting oxygen and fuel contained in the exhaust gas to increase the temperature of the component of an exhaust gas after-treatment device. The opening time of the outlet valves of cylinders (3) of the internal combustion engine is adjusted such that the outlet valve does not open during the overlapping phase unlike as in the normal operation of the internal combustion engine.

Description

The The invention relates to a method for heating a component an exhaust aftertreatment device of an internal combustion engine according to the preamble of claim 1.

The Heating components of exhaust aftertreatment devices of internal combustion engines during of the regular Operation of the internal combustion engine can be done for a number of reasons. For example, it is common catalytic exhaust gas converters, such as oxidation catalysts of diesel internal combustion engines or three-way catalysts of Otto internal combustion engines after the start to heat the internal combustion engine to faster the so-called To achieve the light off temperature of the exhaust gas converter, d. H. the Temperature, in the exhaust gas contained unburned hydrocarbons and carbon monoxide are catalytically oxidized to carbon dioxide. Further It is also common particle filter of diesel internal combustion engines for the regeneration of the particulate filter to heat up the soot particles stored in the particle filter to burn. About that In addition, a heating is also in storage catalytic converters of gasoline internal combustion engines made to the exhaust gas temperature during the regeneration of the Lift storage catalytic converter. This can be done during the reduction of the Storage catalyst also stored nitrogen oxides to nitrogen for one Oxidation of sulfur can be taken care of while storing the nitrogen oxides together with these unintentionally stored in the storage catalyst becomes.

For heating the aforementioned components, such as exhaust gas converters, particulate filters or storage catalysts, there are a number of known methods that are used in practice mainly in the regeneration of particulate filters. For example, it is known for the regeneration of particulate filters, einzudösen before the catalytically coated particulate filter or an upstream oxidation catalyst in the exhaust gas, which is then catalytically oxidized by means of the residual oxygen in the exhaust gas, which causes sufficient for regeneration of the particulate filter increase the exhaust gas temperature. For the regeneration of particulate filters, however, methods are also known in which the combustion process in the combustion chamber itself is deliberately intervened in order to increase the exhaust gas temperature to a value required for regeneration. The intervention may include, for example, a targeted internal engine post fuel injection into the combustion chamber to increase the exhaust gas energy, which intervention may be accomplished by further measures, such as throttling the intake air or splitting the exhaust gas flow DE 39 09 932 A1 , the addition of an additive to the fuel according to EP 1 124 042 B1 or the measurement of the residual oxygen content in the exhaust gas can be supported.

Some of these measures But make structural changes on the internal combustion engine itself or on the exhaust tract or the installation of additional Sensors required while other measures, like internal engine measures, especially in internal combustion engines of motor vehicles often not without loss of comfort, like a noticeable Reduction of torque or other undesirable limitations the normal operation of the internal combustion engine, are feasible.

In the post-published older DE 10 2007 056 216 A1 is a method of the type mentioned for heating a catalyst in the exhaust system of a direct injection internal combustion engine and with an exhaust gas turbocharger described in which a reactive exhaust gas fuel-air mixture is generated in the exhaust system by increasing the valve overlap times of inlet and outlet valves the cylinder and a sufficient pressure gradient between the inlet and outlet side, an air portion of the reactive exhaust gas fuel-air mixture is supplied into the exhaust system exothermic reaction there with rich exhaust from the cylinders to the exhaust enthalpy and thus the energy transfer to the To increase turbine of the exhaust gas turbocharger. However, the method is only suitable for internal combustion engines with turbocharger.

From the JP 2007-291995 A It is also already known to heat a component of an exhaust aftertreatment device for regeneration by injecting fuel into the cylinder during a valve overlap phase during which an intake valve and an exhaust valve of a cylinder are simultaneously opened, and is supplied into the exhaust tract by scavenging air.

Next is from the DE 10 2007 039 613 A1 A method for operating a supercharged internal combustion engine is known in which, for the purpose of reducing a turbo lag, a valve overlap between the intake valve and the exhaust valve of each cylinder is set to overflow due to a pressure gradient between the intake side and the exhaust side.

Proceeding from this, the present invention seeks to improve a method of the type mentioned above, with which a component of an exhaust aftertreatment device by internal engine measures without additional sensors or loss of comfort or impairment of normal operation, to the effect that not only in internal combustion engines with turbocharger but also at Internal combustion engines without turbocharger, the generation of a positive pressure gradient can be promoted.

These The object is achieved by the Characteristics solved in the characterizing part of claim 1. After that, the opening time of at least one exhaust valve of another cylinder of the internal combustion engine adjusted so that the exhaust valve is different than normal Operation of the internal combustion engine does not open during the overlapping phase.

There during normal operation of the internal combustion engine, a positive pressure gradient during the overlapping phase and thus an overflow of fresh gas from the inlet side to the outlet side of the cylinder is undesirable, will be in normal operation during every overlapping phase the exhaust valve of another cylinder of the internal combustion engine open. By opening the exhaust valve of the other cylinder is in the exhaust tract Generated pressure surge (Vorlassstoß), the outlet side of the cylinder with the at least one open inlet and exhaust valve overpressure and thus causes a cancellation of the positive pressure gradient. In contrast, will According to the invention for increasing the Oxygen content and the fuel content in the exhaust avoided, an exhaust valve of another cylinder during each overlap phase the opening hours of the cylinder with the at least one opened inlet and outlet valve to open, so that generates in this case no discharge-side surge will that while the overlapping phase an overflow of Fresh gas from the inlet side through the at least one opened inlet valve, the combustion chamber and the at least one open exhaust valve of the cylinder with the at least one opened Inlet and exhaust valve could counteract in the exhaust system.

By the positive pressure gradient can while the overlap the opening hours Fresh gas containing both unburned fuel and oxygen through the open one Inlet valve, the combustion chamber of the cylinder and the open exhaust valve fed into the exhaust tract can be. The same applies to direct injection internal combustion engine, where by the positive pressure gradient during the overlap the opening hours the open one Inlet valve into the combustion chamber supplied fresh air along with a portion of the injected fuel through the opened exhaust valve can be introduced into the exhaust system.

Within the exhaust gas can then be the fuel in the internal engine supplied gas mixture with the oxygen and optionally contained in the exhaust residual oxygen be reacted in an exothermic oxidation reaction. The at this reaction released heat is then used to the desired Component, such as a particulate filter or a catalyst of Exhaust after-treatment device to heat up. The implementation of the Fuel and the oxygen in the exhaust tract can be heated before the Component done by the heat released the exhaust gas to a higher temperature heats up and the heated exhaust a part of the heat to the Issued aufheizende component. Preferably, the exothermic occurs Oxidation of the fuel, however, in the component to be heated itself, expediently through catalytic oxidation on a catalyst coated surface of the aufheizenden component to a larger part of the released Heat directly feed into the component to be heated.

With the method according to the invention can during normal operation of the internal combustion engine and without noticeable loss of comfort, the exhaust gas temperature so far raised be that a regeneration of a particulate filter or storage catalyst is possible. Depending on the operating point of the internal combustion engine is an increase in the Exhaust gas temperature or the temperature of the component to be heated by about 200 ° K up to about 400 ° K possible.

Around the amount of during the overlapping phase fed into the exhaust tract Increase fresh gas, It may be beneficial to the length of the overlap phase to enlarge by the Beginning of opening the at least one inlet valve, d. H. Beginning of intake, forward and / or the beginning of closing the at least one exhaust valve, d. H. Outlet end, to the rear is moved.

to Generation of a supply of fresh gas in the exhaust system promoting high positive pressure gradient while the gas exchange in a cylinder of the internal combustion engine is advantageous to carry out the heating only if either in a suction pipe of the internal combustion engine, a predetermined minimum intake manifold pressure is exceeded and / or the example with a turbocharger or a mechanical Loader equipped internal combustion engine works in charged mode. This avoids that the pressure drop through a low inlet side Pressure drops and thus during the overlapping phase the opening hours the intake and exhaust valves of the cylinder less fresh gas than desired in supplied to the exhaust tract becomes.

The fresh gas remaining in the cylinder after completion of the overlap phase is combusted conventionally, so that, unlike when the ignition is interrupted, there is no impairment conditions of normal operation of the internal combustion engine, such as misfiring, are noticeable.

The required for heating change the timing of the intake and exhaust valves, as described above, works particularly well with internal combustion engines with one of the Applicant developed, designated as AVS (Audi Valvelift system) Valve lift system, which not only the stroke of the valves but the location and duration of the opening or closing times changed cylinder-specific can be. in principle can however, other methods and devices are also used with which the location and the duration of the opening and closing times of inlet and / or exhaust valves can be changed as needed.

A further preferred embodiment of the method according to the invention provides that the increase of the oxygen content according to the invention and the fuel content in the exhaust gas is always made when a need for heating a component of the exhaust aftertreatment device is detected. This need can be, for example, in the case of a Particulate filter can be determined by measuring a pressure difference in the exhaust tract upstream and downstream of the particulate filter, the loading of the Particle filter determined and when exceeding a predetermined Pressure difference on the need for regeneration of the particulate filter is closed while in the case of a storage catalytic converter, the need for regeneration Measurement of the NOx content detected behind the storage catalyst can be.

Provided currently no other operating states with higher priority required become after the determination of the need by the engine control unit on the one hand the timing of the intake and exhaust valves during the subsequent gas changes so changed, that an overlap their opening hours guaranteed is while on the other hand for the positive pressure gradient is taken care of. This condition is preferred by a model in the Engine control maintained until either an operating condition with higher priority is required or the purpose of the heating has been achieved, such as a full one Regeneration in the case of a particulate filter or a storage catalyst or an overrun the light-off temperature of an oxidation or three-way catalyst.

in the The following is the invention with reference to an illustrated in the drawing embodiment explained in more detail. It demonstrate:

1 a schematic representation of a 4-cylinder internal combustion engine with an exhaust gas turbocharger;

2 a perspective view of parts of a Ventilhubschaltsystems for controlling gas exchange valves of the cylinders of the internal combustion engine;

3 a simplified sectional view of parts of a cylinder of the internal combustion engine during a gas exchange;

4 an illustration of timing of an intake and exhaust valve of the cylinder and of control times of an exhaust valve of another cylinder of the internal combustion engine during a gas exchange during the heating of a component of an exhaust aftertreatment device.

In the 1 illustrated 4-cylinder internal combustion engine 1 includes an intake tract 2 for the intake of fresh air into the cylinders 3 the internal combustion engine 1 , an exhaust tract 4 for the removal of exhaust gas from the cylinders 3 the internal combustion engine 1 , as well as an exhaust gas turbocharger 5 with one in the exhaust tract 4 arranged turbine 6 and one in the intake tract 2 arranged compressor 7 , The internal combustion engine 1 is from an engine control unit 8th controlled. The exhaust tract contains one behind the turbine 6 the exhaust gas turbocharger 5 arranged exhaust gas aftertreatment device 9 containing an oxidation catalyst 10 and a downstream particle filter 11 includes.

Every cylinder 3 the internal combustion engine 1 has two inlet valves 12 and two exhaust valves 13 on, of which in 2 one on each side of a spark plug 14 in the cylinder head 15 is shown. The intake valves 12 allow one to supply fresh gas into the cylinder 3 certain inlet channel 16 to open and close while the exhaust valves 13 to serve a for the removal of exhaust gas from the cylinder 3 in the exhaust tract 4 certain outlet channel 17 to open and close.

The operation of the inlet valves 12 and the exhaust valves 13 takes place in each case by valve trains, one of which 18 in 3 partially shown. The valve train 18 includes for each cylinder 3 a cam piece 19 standing on an overhead ground camshaft 20 axially displaceable between two end positions and can be locked in the end positions. The cam piece 19 carries at its opposite front ends in each case a pair of cams 21a . 22a such as 21b . 22b with different cam contours. Every pair of cams 21a . 22a respectively. 21b . 22b can be achieved by the axial displacement of the cam piece 19 optionally with a roll 23 an associated roller cam follower 24 from one of the two intake valves 12 (or exhaust valves 13 ) of the cylin DERS 3 bring to bear by the different cam contours the stroke and / or the timing, ie the opening and closing times, the intake valves 12 (or exhaust valves 13 ) of each cylinder 3 independent of those of other cylinders 3 to adjust.

In order to reduce the emission values of the internal combustion engine, the oxidation catalyst should 10 after a cold start of the engine 1 be heated as quickly as possible to heat it above its light-off temperature. When the loading of the particulate filter 11 With soot particles exceeds a predetermined threshold, must also the particulate filter 11 be heated to regenerate it by burning the accumulated soot particles. In both cases, the heating is carried out by increasing the temperature of the exhaust gas and / or the catalyst 10 or of the particulate filter 11 by the exhaust gas is enriched by internal engine measures with fuel and oxygen and then by within the oxidation catalyst 10 the fuel is catalytically oxidized by the oxygen. The released during the exothermic oxidation reaction causes after a cold start of the engine 1 in that the oxidation catalyst 10 heats up faster while in normal operation of the internal combustion engine 1 ie with heated oxidation catalyst 10 , causes an increase in the exhaust gas temperature. This increase in the exhaust gas temperature is depending on the operating point of the internal combustion engine 1 between about 200 ° K and 400 ° K and is enough to the particle filter 11 to regenerate during operation without sacrificing comfort.

To enrich the exhaust gas with fuel and with oxygen, the cylinder is changed during a gas or charge change near the end of the exhaust stroke and the beginning of the intake stroke 3 each one of the two intake valves 12 and one of the two exhaust valves 13 every cylinder 3 so controlled that over a predetermined crankshaft angle range to an overlap of the opening times of the valves 12 and 13 comes, as in 4 represented by a hatched area. The overlap of the opening times means that over this crankshaft angle range, both the inlet valve 12 as well as the exhaust valve 13 are partially open, so that during the overlapping phase fuel and oxygen-containing fresh gas from the inlet channel 16 through the partially opened inlet valve 12 , the combustion chamber 25 of the cylinder 3 and the partially opened exhaust valve 13 in the outlet channel 17 and from there to the exhaust tract 4 is supplied as in 2 represented by arrows, if at the same time for a positive pressure gradient between the inlet channel 16 and the outlet channel 17 is taken care of. That in the exhaust tract 4 supplied fresh gas there ensures that for heating the oxidation catalyst 10 or of the particulate filter 11 required enrichment of the exhaust gas with fuel and oxygen.

To ensure the positive pressure gradient, the heating of the oxidation catalyst takes place 10 or of the particulate filter 11 whenever one of a pressure sensor 26 measured and to the engine control unit 8th transmitted intake manifold pressure in a suction tube 27 designated part of the intake 2 behind the compressor 7 the exhaust gas turbocharger 5 exceeds a predetermined pressure or when the exhaust gas turbocharger 5 is operated in the loading mode, so that in the inlet channel 16 a certain minimum pressure is present.

In addition, the pressure differential is also affected by exhaust side measures, as with reference to FIG 4 is explained with reference to three lift curves, of which the lift curve displayed as a broken line that of the intake valve 12 and the stroke curve shown as a solid line that of the exhaust valve 13 from one of the cylinders 3 shows that in 4 is designated as cylinder A, while the lift curve indicated as a dotted line that of an exhaust valve 13 from another the cylinder shows in 4 is designated as cylinder B. All three lift curves show the condition during a period when the exhaust gas is heating up the oxidation catalyst 10 or the particulate filter 11 enriched with fuel and with oxygen. How out 4 it can be seen, the exhaust valve 13 of in 4 Cylinder B designated cylinder 3 the internal combustion engine 1 so controlled that it during this period only after completion of the overlapping phase (hatched area) of the opening times of the intake valve 12 and the exhaust valve 13 of in 4 cylinder referred to as cylinder A 3 opens, so that during the overlapping phase, a positive pressure gradient counteracting outlet pressure surge (Vorlassstoß) is avoided.

In contrast, during normal operation of the internal combustion engine 1 the outlet valve 13 of in 4 Cylinder B designated cylinder 3 so controlled that it already during the overlapping phase (hatched area) of the opening times of the inlet valve 12 and the exhaust valve 13 of in 4 cylinder referred to as cylinder A 3 opens. By opening the exhaust valve 13 of the designated as cylinder B cylinder 3 will be in the exhaust tract 4 generates a pressure surge, so that in the designated cylinder A cylinder 3 with the opened inlet valve 12 and the opened exhaust valve 13 does not come to the formation of a positive pressure gradient. This will in normal operation of the internal combustion engine 1 during an overlap phase an undesirable supply of fresh gas in the exhaust tract 4 through the opened inlet valve 12 , the combustion chamber 25 and the opened exhaust valve 13 avoided.

The heating of the oxidation catalyst 10 by the previously described internal engine supply of fuel and oxygen into the exhaust gas tract 4 will after a cold start of the engine 1 always made when, first, the pressure sensor 26 measured and to the engine control unit 8th transmitted pressure in the intake manifold 27 exceeds a predetermined minimum value or the exhaust gas turbocharger 5 in charging mode, if second, that of a temperature sensor 28 measured and to the engine control unit 8th transmitted temperature of the oxidation catalyst 10 is below the light-off temperature, and thirdly, if no request for another operating state with a higher priority goes to the engine control unit. The heating will continue until the temperature sensor 28 measured and to the engine control unit 8th transmitted temperature of the oxidation catalyst 10 exceeds the light-off temperature or to the engine control unit 8th higher priority, the setting of another operating state is required.

The heating of the particle filter 11 by the above-described internal engine supply of fuel and oxygen containing fresh gas in the exhaust tract 4 is always done when the pressure difference between one of a pressure sensor 29 in front of the particle filter 11 measured exhaust pressure and one of a pressure sensor 30 measured ambient pressure exceeds a predetermined value, which indicates a substantial loading of the particulate filter with soot particles. In this case, the heating of the particulate filter 11 as long as continued until either the difference of the pressure sensors 29 . 30 measured pressures a complete regeneration of the particulate filter 11 or from the engine control unit 8th higher priority, the setting of another operating state is required.

1

Internal combustion engine

2

intake system

3

cylinder

4

exhaust tract

5

turbocharger

6

turbine

7

compressor

8th

Engine control unit

9

exhaust treatment device

10

oxidation catalyst

11

particulate Filter

12

intake valve

13

outlet valve

14

spark plug

15

cylinder head

16

inlet channel

17

exhaust port

18

valve train

19

cam piece

20

base camshaft

21a, 21b

cam

22a, 22b

cam

23

role

24

Roller cam

25

combustion chamber

26

pressure sensor

27

suction tube

28

temperature sensor

29

pressure sensor

30

pressure sensor

Claims (14)

Method for heating at least one component ( 10 . 11 ) an exhaust aftertreatment device ( 9 ) an internal combustion engine ( 1 ), in which for increasing the temperature of the exhaust gas and / or the component ( 10 . 11 ) in the exhaust gas contained oxygen and fuel are reacted, wherein for increasing the oxygen content and the fuel content in the exhaust gas during a gas exchange in at least one cylinder ( 3 ) of the internal combustion engine ( 1 ) Opening times of at least one inlet valve ( 12 ) and at least one outlet valve ( 13 ) are adjusted so that they overlap, and wherein by a positive pressure gradient between a suction pipe ( 27 ) and an exhaust tract ( 4 ) of the internal combustion engine ( 1 ) during the overlap phase fresh gas from the cylinder ( 3 ) in the exhaust tract ( 4 ), characterized in that the opening time of at least one outlet valve ( 13 ) of another cylinder ( 3 ) of the internal combustion engine ( 1 ) is adjusted so that the exhaust valve ( 13 ) unlike in normal operation of the internal combustion engine ( 1 ) does not open during the overlap phase. Method according to claim 1, characterized in that the heating of the at least one component ( 10 . 11 ) of the exhaust aftertreatment device ( 9 ) is only carried out when in the intake manifold ( 27 ) a predetermined intake manifold pressure is exceeded. Method according to claim 1, characterized in that the heating of the at least one component ( 10 . 11 ) of the exhaust aftertreatment device ( 9 ) is only made when the internal combustion engine ( 1 ) is in charged operation. Method according to one of the preceding claims, characterized in that the length the overlapping phase is increased by the beginning of the opening of the at least one inlet valve ( 12 ) forward and / or the beginning of the closing of the at least one exhaust valve ( 13 ) is moved backwards. Method according to one of the preceding claims, characterized in that after the overlapping phase in the cylinder ( 3 ) remaining fresh gas is conventionally ignited and burned. Method according to one of the preceding claims, characterized in that the fuel and oxygen contained in the exhaust gas in the component to be heated ( 10 ) are catalytically reacted. Method according to one of the preceding claims, characterized in that the component to be heated, an oxidation or three-way catalyst ( 10 ), in which the fuel and oxygen contained in the exhaust gas are catalytically converted to after a cold start of the internal combustion engine ( 1 ) faster a light-off temperature of the catalyst ( 10 ) to reach. Method according to one of claims 1 to 7, characterized in that the component to be heated, a particulate filter ( 11 ) and that the fuel and oxygen contained in the exhaust gas before the particulate filter ( 11 ) or in the catalytically coated particulate filter in order to remove the particulate filter ( 11 ) to regenerate. A method according to claim 8, characterized in that a loading of the particulate filter ( 11 ) is monitored with soot particles and that the fuel content and the oxygen content in the exhaust gas are increased when the loading of the particulate filter ( 11 ) exceeds a predetermined threshold. A method according to claim 9, characterized in that the loading of the particulate filter ( 11 ) by determining a pressure difference between two points in front of and behind the particle filter ( 11 ) is monitored. Method according to one of claims 1 to 10, characterized that the component to be heated is a storage catalyst, and that the fuel and oxygen contained in the exhaust before the storage catalyst or implemented in the catalytically coated storage catalyst to regenerate the storage catalyst. Method according to claim 11, characterized in that that monitors a loading of the storage catalytic converter with NOx and that the fuel content and the oxygen content in the exhaust gas increase, when the loading of the storage catalyst exceeds a predetermined threshold. Method according to claim 12, characterized in that that the loading of the storage catalyst by measuring a NOx content monitored behind the storage catalytic converter becomes. Method according to one of the preceding claims, characterized characterized in that the heating is continued until the purpose the heating has been achieved or another with a higher priority Operating status is requested.