Method and device for exhaust gas aftertreatment in an internal combustion engine

Abstract

A device for exhaust gas aftertreatment in an internal combustion engine can be connected to an outlet of the internal combustion engine. The device comprises an exhaust gas system with an exhaust gas channel in which a three-way catalytic converter is arranged, and an exhaust gas burner with which hot burner exhaust gases can be fed into the exhaust gas channel at a feed point upstream from the three-way catalytic converter. The three-way catalytic converter is configured as a lambda probe catalytic converter and comprises a first catalyst volume and a second catalyst volume, whereby a lambda probe is arranged downstream from the first catalyst volume and upstream from the second catalyst volume, whereby the first catalyst volume has a lower oxygen storage capacity than the second catalyst volume. A method for exhaust gas aftertreatment in an internal combustion engine has such an exhaust gas aftertreatment device.

Claims

1. A method for exhaust gas aftertreatment in an internal combustion engine having a device for exhaust gas aftertreatment, which device is adapted to be connected to an outlet of the internal combustion engine and comprises: an exhaust gas system with an exhaust gas channel in which a three-way catalytic converter is arranged, an exhaust gas burner, and a feed point for burner exhaust gases from the exhaust gas burner on the exhaust gas channel upstream from the three-way catalytic converter, wherein the three-way catalytic converter is configured as a lambda probe catalytic converter, and a lambda probe is arranged downstream from a first catalyst volume of the three-way catalytic converter and upstream from a second catalyst volume of the three-way catalytic converter, whereby the first catalytic volume has a lower oxygen storage capacity than the second catalyst volume, the method comprising the following steps: activating the exhaust gas burner, whereby a quantity of fuel fed to the exhaust gas burner and/or a quantity of fresh air fed to the exhaust gas burner is pilot-controlled, detecting the air-fuel ratio downstream from the first catalyst volume and upstream from the second catalyst volume of the three-way catalytic converter, and changing the quantity of fuel and/or the fresh air quantity when a rich blow-out or a lean blow-out is detected at the lambda probe, wherein, in a first operating state of the exhaust gas burner, the quantity of fuel of the exhaust gas burner is pilot-controlled in such a way that the exhaust gas burner is operated with a sub-stoichiometric air-fuel ratio (λ.sub.B<1), and wherein, in a second operating state of the exhaust gas burner, the quantity of fuel of the exhaust gas burner is pilot-controlled in such a way that the exhaust gas burner is operated with a super-stoichiometric air-fuel ratio (λ.sub.B>1), and wherein the exhaust gas burner is operated alternately with a sub-stoichiometric air-fuel ratio (λ.sub.B<1) and with a super-stoichiometric air-fuel ratio (λ.sub.B>1).

2. The method for exhaust gas aftertreatment according to claim 1, wherein the sub-stoichiometric air-fuel ratio (λ.sub.B) is pilot-controlled in the range from 0.93 to 0.98.

3. The method for exhaust gas aftertreatment according to claim 1, wherein the sub-stoichiometric air-fuel ratio (λ.sub.B) is pilot-controlled in the range from 1.02 to 1.07.

4. The method for exhaust gas aftertreatment according to claim 1, further comprising deactivating the exhaust gas burner once the three-way catalytic converter has reached a threshold temperature (T.sub.S).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained below on the basis of embodiments making reference to the accompanying drawings. In this context, identical components or components having the same function are provided with the same reference numerals in the various figures. The following is shown:

(2) FIG. 1 is a first embodiment of a schematically depicted internal combustion engine with a device according to the invention for exhaust gas aftertreatment;

(3) FIG. 2 is a second embodiment of an internal combustion engine with a device according to the invention for exhaust gas aftertreatment; and

(4) FIG. 3 is a diagram showing the course over time of the air-fuel ratio of the exhaust gas burner while a method according to the invention for exhaust gas aftertreatment is being carried out.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows an internal combustion engine 10 which has several combustion chambers 12 and whose outlet 18 is connected to an exhaust gas system 20. The internal combustion engine 10 is configured as a direct-injection gasoline engine. Each of the combustion chambers 12 has a spark plug 14 and a fuel injector 16 for purposes of injecting fuel into the appertaining combustion chamber 12 and igniting the fuel-air mixture. The exhaust gas system 20 comprises an exhaust gas channel 22 in which a turbine 24 of an exhaust gas turbocharger 54 and, downstream from the turbine 24, a three-way catalytic converter 26 are arranged in the direction in which exhaust gas from the internal combustion engine 10 flows through the exhaust gas channel. The three-way catalytic converter 26 is configured as a lambda probe catalytic converter 28. For this purpose, the three-way catalytic converter 26 has a first catalyst volume 38 and a second catalyst volume 40 arranged downstream from the first catalyst volume 38, whereby a lambda probe 34 is arranged in the housing of the three-way catalytic converter 26 downstream from the first catalyst volume 38 and upstream from the second catalyst volume 40. As shown in FIG. 1, the lambda probe 34 is preferably configured as a step change sensor 36 and can thus detect a change-over between a sub-stoichiometric and a super-stoichiometric exhaust gas. The oxygen storage means 42 of the first catalyst volume 38 is smaller than the oxygen storage means 44 of the second catalyst volume 40, so that the second catalyst volume 40 has a greater oxygen storage capacity than the first catalyst volume 38. The lambda probe 34 is arranged in the front section of the three-way catalytic converter 26, whereby the first catalyst volume 38 comprises about one-third while the second catalyst volume 40 comprises about two-thirds of the total catalyst volume of the three-way catalytic converter 26.

(6) The exhaust gas system 20 also comprises an exhaust gas burner 30 that is supplied with fresh air via a secondary air system 46 and with fuel via a fuel line. The exhaust gas burner 30 comprises a combustion chamber 56 into which a combustible fuel can be introduced by means of a fuel injector 48. Preferably, the fuel injector 48 of the exhaust gas burner 30 and the fuel injectors 16 of the internal combustion engine 10 are supplied with fuel from a shared tank. Downstream from the outlet 18 and upstream from the three-way catalytic converter 26, there is a feed point 32 on the exhaust gas channel 22 where the hot burner exhaust gas of the exhaust gas burner 30 is fed into the exhaust gas channel 22 in order to heat the three-way catalytic converter 26 up to its operating temperature after a cold start of the internal combustion engine 10. There can be additional catalytic converters upstream from the feed point 32 or downstream from the three-way catalytic converter 26. Moreover, the internal combustion engine 10 has an engine control unit 50 with which the quantity of fuel injected into the combustion chambers 12 can be regulated. Moreover, the exhaust gas burner 30 can be controlled by the engine control unit 50.

(7) After a cold start of the internal combustion engine 10, the exhaust gas burner 30 is activated by the engine control unit 50 so that the three-way catalytic converter 26 can be heated up as quickly as possible to the light-off temperature of the three-way catalytic converter 26 that is needed for a high conversion rate. During this active heating phase, the regulation of the lambda value is carried out in such a way that the gaseous emissions of the internal combustion engine 10 are as low as possible until the three-way catalytic converter 26 has reached its light-off temperature. In order to generate the smallest possible gaseous emissions during the active heating phase, it is necessary to regulate the mixed lambda value from the exhaust gas of the internal combustion engine 10 and from the burner exhaust gas of the exhaust gas burner 30 so as to obtain a stoichiometric ratio. This regulation takes place via the lambda probe 34 in the lambda probe catalytic converter 28. In order for the lambda probe 34 in the lambda probe catalytic converter 28 to be able to appropriately regulate the air-fuel ratio, the exhaust gas channel 22 is configured without an additional catalytic converter downstream from the feed point 32 and upstream from the lambda probe catalytic converter 28. The three-way catalytic converter 26 has an oxygen storage capacity (OSC). This oxygen storage capacity causes the deviation of the lambda signal in the direction of sub-stoichiometric or super-stoichiometric to be detected by the lambda probe 34 with a time delay. For this reason, the first catalyst volume 38 is configured to be smaller than the second catalyst volume 40. Consequently, the second catalyst volume can be used to prevent a blow-out in the direction of “rich” or “lean”. Moreover, the functionality of the three-way catalytic converter 26 can be diagnosed with the lambda probe 34, without a rich blow-out or lean blow-out occurring during the diagnosis by means of the lambda probe 34.

(8) Since the exhaust gas channel 22 is configured without an additional lambda probe upstream from the three-way catalytic converter 26, the burner mixture of the exhaust gas burner 30 cannot be regulated directly. The exhaust gas burner 30 is pilot-controlled and impinged with a forced amplitude. The lambda value of the exhaust gas burner 30 is pilot-controlled via the quantity of fuel metered into the combustion chamber 56. The forced amplitude is selected, for example, with a distance of 5% to a stoichiometric air-fuel ratio each time, so that the exhaust gas burner 30 alternates between operation at a sub-stoichiometric lambda value of 0.95 and a super-stoichiometric lambda value of 1.05. As soon as the oxygen storage means 42 of the first catalyst volume 38 has been cleared out during a sub-stoichiometric operation of the exhaust gas burner 30, the lambda probe 34 identifies a rich blow-out. At this point in time, the forced amplitude is adjusted to a super-stoichiometric lean operation. Starting at this point in time, the oxygen storage means 42 of the first catalyst volume 38 is filled up again and the lambda probe 34 detects a stoichiometric exhaust gas. As soon as the oxygen storage means 42 of the first catalyst volume 38 has been completely filled, the lambda probe 34 identifies a lean blow-out and the forced amplitude is once again adjusted to a sub-stoichiometric operation of the exhaust gas burner 30. In this process, the alternating change between a sub-stoichiometric and a super-stoichiometric air-fuel ratio of the exhaust gas burner 30 continues until the exhaust gas burner 30 is once again deactivated. At the earliest, this takes place once the three-way catalytic converter 26 has reached it light-off temperature.

(9) FIG. 2 shows an alternative embodiment of an internal combustion engine 10 with an exhaust gas system 20. Since this configuration is essentially the same as explained for FIG. 1, only the differences will be elaborated upon below. In this embodiment, the internal combustion engine 10 is configured as a naturally aspirated engine, so that the turbine 24 of the exhaust gas turbocharger 54 has been dispensed with. Moreover, in this embodiment, the lambda probe 34 is configured as a broadband probe 52, so that a quantitative determination of the exhaust gas lambda value in the three-way catalytic converter 26 is possible. Moreover, in this embodiment, the exhaust gas system 20 comprises a temperature sensor 58 with which the temperature of the three-way catalytic converter 26 can be determined at least indirectly.

(10) The method for heating up the three-way catalytic converter 26 is carried out analogously to the method described for FIG. 1. The method is ended as soon as the temperature of the catalytic converter 26 indicated by a model or by a temperature sensor 58 has reached or exceeded a threshold value.

(11) FIG. 3 shows the air-fuel ratio λ.sub.B of the exhaust gas burner 30 as well as the exhaust-gas air ratio λ.sub.S at the lambda probe 34. Here, the air-fuel ratio of the exhaust gas burner 30 alternates between a sub-stoichiometric air-fuel ratio and a super-stoichiometric air-fuel ratio. In this process, the oxygen storage means 42 of the first catalyst volume 38 of the three-way catalytic converter 26 is filled and cleared out, so that a stoichiometric exhaust gas λ.sub.S=1 is established during the entire heating phase at the lambda probe 34 downstream from the first catalyst volume 38.

(12) Thanks to the method for exhaust gas aftertreatment being proposed here, the three-way catalytic converter 26 can be heated up during the cold start phase of the internal combustion engine 10, a process in which the emissions are minimized during the heating of the three-way catalytic converter 26. During the heating phase of the three-way catalytic converter 26, the lambda regulation is carried out in such a way that the gaseous emissions of the internal combustion engine 10 are minimized until the three-way catalytic converter 26 has reached its light-off temperature and an efficient conversion of the gaseous emissions by the three-way catalytic converter 26 is ensured.

LIST OF REFERENCE NUMERALS

(13) 10 internal combustion engine

(14) 12 combustion chamber

(15) 14 spark plug

(16) 16 fuel injector

(17) 18 outlet

(18) 20 exhaust gas system

(19) 22 exhaust gas channel

(20) 24 turbine

(21) 26 three-way catalytic converter

(22) 28 lambda probe catalytic converter

(23) 30 exhaust gas burner

(24) 32 feed point

(25) 34 lambda probe

(26) 36 step change sensor

(27) 38 first catalyst volume

(28) 40 second catalyst volume

(29) 42 oxygen storage means of the first catalyst volume

(30) 44 oxygen storage means of the second catalyst volume

(31) 46 secondary air system

(32) 48 fuel injector

(33) 50 engine control unit

(34) 52 broadband probe

(35) 54 exhaust gas turbocharger

(36) 56 combustion chamber

(37) λ.sub.B air-fuel ratio of the exhaust gas burner

(38) λ.sub.E air-fuel ratio of the internal combustion engine

(39) λ.sub.m exhaust-gas air ratio downstream from the feed point

(40) λ.sub.S exhaust-gas air ratio at the lambda probe

(41) t time