Diagnostic method and device for checking the functionality of a component for exhaust-gas aftertreatment

Abstract

The invention relates to a diagnostic method for checking the functionality of a component for the exhaust-gas aftertreatment of an internal combustion engine. For this purpose, in an internal combustion engine, a secondary air supply is provided by means of which an excess of oxygen can be generated in the exhaust gas channel essentially independently of the operating conditions of the internal combustion engine, and wherein said excess of oxygen is utilized for the measurement of an oxygen storage capacity of the component or of a signal change at the component. It is provided that the component is subsequently subjected to a substoichiometric exhaust gas in order that the oxygen release capacity or the signal change upon a change from superstoichiometric exhaust gas to a substoichiometric exhaust gas is also taken into consideration in the diagnosis. The invention also relates to a device for exhaust-gas aftertreatment, which is designed to be able to carry out a method of said type.

Claims

1. A diagnostic method for checking the functionality of a particulate filter having a catalytic coating for the exhaust-gas aftertreatment of an internal combustion engine in an exhaust gas channel of the internal combustion engine, whereby the particulate filter is arranged in the exhaust-gas channel (12) downstream of a three-way catalytic converter, said method comprising the following steps: operating the internal combustion engine at a stoichiometric air-fuel ratio λ.sub.E=1, whereby the exhaust gas of the internal combustion engine is transported through the exhaust gas channel and a stoichiometric exhaust gas λ.sub.A=1 is fed to the particulate filter, feeding a superstoichiometric exhaust gas λ.sub.A>1 to the particulate filter, whereby the internal combustion engine is operated at a stoichiometric air-fuel ratio λ.sub.E=1 and additional secondary air is blown into the exhaust gas upstream from the particulate filter, determining a reaction of the particulate filter to the superstoichiometric exhaust gas, operating the internal combustion engine at a substoichiometric air-fuel ratio λ.sub.E<1, whereby a substoichiometric exhaust gas λ.sub.A<1 is likewise established at the particulate filter, and determining a reaction of the particulate filter to the substoichiometric exhaust gas, whereby the oxygen storage capacity (OSC) of the particulate filter is determined when the superstoichiometric exhaust gas is fed to the particulate filter, and the oxygen release capacity (RSC) from the particulate filter is determined during the substoichiometric operation of the internal combustion engine.

2. The diagnostic method according to claim 1, wherein the secondary air continues to be blown into the exhaust gas channel until a superstoichiometric exhaust gas is measured at a sensor downstream from the particulate filter.

3. The diagnostic method according to claim 1, further comprising switching the internal combustion engine to operation at a substoichiometric air-fuel ratio immediately after an oxygen breakthrough has been detected downstream from the particulate filter.

4. The diagnostic method according to claim 2, further comprising stopping to blow secondary air into the exhaust gas channel as soon as an oxygen breakthrough is ascertained at the sensor downstream from the particulate filter.

5. The diagnostic method according to claim 1, further comprising evaluating the functionality of the catalytic coating of the particulate filter on the basis of an integration of the oxygen mass flows during operation of the internal combustion engine with a substoichiometric exhaust gas as well with a superstoichiometric exhaust gas.

6. The diagnostic method according to claim 1, further comprising, before the secondary air is introduced, pre-conditioning the particulate filter by operating the internal combustion engine at a substoichiometric, rich air-fuel ratio λ.sub.E<1.

7. A device for the exhaust-gas aftertreatment of an internal combustion engine, comprising: an exhaust gas channel, a three-way catalytic converter arranged in the exhaust gas channel, a particulate filter with a catalytically active coating arranged downstream from the three-way catalytic converter, wherein the catalytically coating on the particulate filter is configured as a three-way catalytically active wash coat, a first lambda sensor arranged downstream from the particulate filter, an opening downstream from the three-way catalytic converter and upstream from the particulate filter, for the supply of secondary air into the exhaust gas channel of the internal combustion engine, and a control unit with a machine-readable program code for the execution of the method according to claim 1.

8. The device for the exhaust-gas aftertreatment according to claim 7, wherein the secondary air supply source comprises an electrically powered secondary air pump.

9. The device for the exhaust-gas aftertreatment according to claim 7, wherein a first second lambda sensor is arranged downstream from the opening and upstream from the particulate filter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in greater detail below in embodiments making reference to the accompanying drawings. The following is shown:

(2) FIG. 1: an internal combustion engine with a device according to the invention for the exhaust-gas aftertreatment,

(3) FIG. 2: an exhaust gas channel of an internal combustion engine according to the invention,

(4) FIG. 3: a method diagram depicting the sequence of a diagnostic method according to the invention, and

(5) FIG. 4 a schematic diagram to depict the air-fuel ratio as well as the exhaust gas-air ratio during the individual phases of a diagnostic method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows an internal combustion engine 10 for a motor vehicle, comprising an exhaust gas channel 12 as well as a three-way catalytic converter 14 arranged in the exhaust gas channel 12. The internal combustion engine 10 is preferably configured as an externally ignited internal combustion engine 10 operating according to the Otto principle. Downstream from the three-way catalytic converter 14 as seen the flow direction of the exhaust gas, there is an opening 18 where secondary air can be introduced into the exhaust gas channel 12 of the internal combustion engine 10 by means of a secondary air supply source 16. Downstream from the opening 18, there are additional components 20 for the exhaust-gas aftertreatment, especially a particulate filter 22 with a three-way catalytically active coating, as well as lambda sensors 26, 28 that regulate the oxygen content in the exhaust gas channel 12 of the internal combustion engine 10. The lambda sensors 26, 28 are connected via signal lines 32 to a control unit 30 of the internal combustion engine 10.

(7) FIG. 2 again shows the exhaust gas channel 12 of the internal combustion engine 10. In the exhaust gas channel 12 downstream from the first three-way catalytic converter 14, there is another lambda sensor 36 with which the air-fuel ratio of the internal combustion engine 10 is regulated. The secondary air supply source 16 comprises a secondary air line 38 in which an electrically commutated secondary air pump 34 is installed. Between the secondary air pump 34 and the opening 18 of the secondary air line 38 in the exhaust gas channel 12, there is a shut-off valve 40 that can prevent a return flow of exhaust gas from the exhaust gas channel 12 in the direction of the secondary air pump 34. For purposes of regulation of the oxygen content in the exhaust gas channel 12, a first lambda sensor 26 is arranged upstream from the particulate filter 22 and a second lambda sensor 28 is arranged downstream from the particulate filter 22. In a simple execution variant, the first lambda sensor 26 upstream from the particulate filter 22 can be dispensed with.

(8) FIG. 3 shows a method diagram depicting the sequence of a diagnostic method according to the invention. During normal operation <100>, the internal combustion engine 10 is operated at an essentially stoichiometric air-fuel ratio λ.sub.E=1. In this process, the exhaust gas is purified by means of the first three-way catalytic converter 14 and by the catalytically coated particulate filter 22. During normal operation <100>, the secondary air pump 34 is switched off and the shut-off valve 40 is closed. Now, in order to carry out the diagnostic method, in a subsequent method step <120>, air is introduced into the exhaust gas 12 of the internal combustion engine 10 by means of the secondary air pump 34. The operation with secondary air as the conditioning phase is carried out continuously until the second lambda sensor 28 downstream from the particulate filter 22 detects an excess of air. In this phase, the internal combustion engine 10 continues to be operated at a stoichiometric air-fuel ratio so that a stoichiometric exhaust gas is fed at least to the first three-way catalytic converter 14, thus allowing an efficient conversion of the HC, CO and NO.sub.x emissions. If the second lambda sensor 28 situated downstream from the particulate filter 22 detects an oxygen breakthrough, the secondary air pump 34 is switched off in a subsequent method step <130>, the shut-off valve 40 is closed and the internal combustion engine 10 is operated at a substoichiometric air-fuel ratio. In this process, initially the oxygen stored in the first three-way catalytic converter 14 and—offset in time—the oxygen stored in the particulate filter 22 are released, until a rich breakthrough is measured at the second lambda sensor 28 downstream from the particulate filter 22. In this context, in method step <140>, the first lambda sensor 26 between the opening 18 of the secondary air line 38 or the other lambda sensor 36 can determine when a rich breakthrough occurs through the first three-way catalytic converter 14 and when the oxygen stored in the particulate filter 22 starts to be released.

(9) In a subsequent method step <150>, an evaluation of the superstoichiometric oxygen mass flows and of the substoichiometric oxygen mass flows can be used to make an assessment of the oxygen storage capacity (OSC) or of the oxygen release capacity (RSC) of the particulate filter. Moreover, in another method step <160>, the signal gradient is measured at the first lambda sensor 26 or at the second lambda sensor 28 when a change is made from a substoichiometric exhaust gas to a superstoichiometric exhaust gas, and on this basis, a conclusion can be drawn about the functionality of the lambda sensors 26, 28. In order to diagnose the particulate filter 22 and the lambda sensors 26, 28, either the introduction of secondary air when the particulate filter 22 is being heated up can be employed to oxidize the soot particles held back in it or else the secondary air pump 34 can be activated specifically for the diagnosis only. As an alternative, the introduction of secondary air following a regeneration of the particulate filter 22 can be prolonged until the diagnosis of the particulate filter 22 or of the lambda sensors 26, 28 has been ended. Once the diagnosis of the functionality of the particulate filter 22 or of the lambda sensors 26, 28 has been completed, in a subsequent method step <160>, the internal combustion engine 10 is once again run in normal operation at the stoichiometric air-fuel ratio and with the introduction of secondary air switched off.

(10) In order to carry out a diagnosis of the particulate filter 22 and/or of the lambda sensors 26, 28 that is as trouble-free as possible, it can be advantageous if the internal combustion engine 10 is briefly operated in an intermediate method step <110> at a substoichiometric air-fuel ratio between the stoichiometric normal operation and the start of the secondary air supply in order to completely empty the oxygen storage unit in the first three-way catalytic converter 14 and in the particulate filter 22, thereby ensuring a pre-conditioning of the catalytic converters 14, 22.

(11) FIG. 4 shows the air-fuel ratio λ.sub.E of the internal combustion engine 10 as well as the exhaust gas-air ratio upstream from the particulate filter 22 (at the position of the first lambda sensor 26) as well as downstream from the particulate filter 22 (at the position of the second lambda sensor 28). During normal operation I, the internal combustion engine 10 is operated at a stoichiometric air-fuel ratio λ.sub.E=1, while a stoichiometric exhaust gas λ.sub.A=1 is found in the exhaust gas channel 12 upstream from the particulate filter 22 as well as downstream from the particulate filter 22. In the pre-conditioning phase II, the internal combustion engine 10 is operated at a substoichiometric air-fuel ratio λ.sub.E<1, as a result of which, due to the oxygen storage capacity of the first three-way catalytic converter 14, a substoichiometric exhaust gas λ.sub.A<1 is established with a time delay in the exhaust gas channel 12 upstream from the particulate filter 22 and then once again with a time delay, a substoichiometric exhaust gas λ.sub.A<1 is also established downstream from the particulate filter 22. In phase III, if a substoichiometric exhaust gas is detected at the second lambda sensor 28, the internal combustion engine 10 is once again operated at a stoichiometric air-fuel ratio λ.sub.E=1 and the secondary air introduction is activated. In this process, initially a superstoichiometric exhaust gas λ.sub.A>1 is established in the exhaust gas channel 12 upstream from the particulate filter 22 and, corresponding to the oxygen storage capacity (OSC) of the particulate filter 22, a superstoichiometric exhaust gas λ.sub.A>1 is established with a time delay downstream from the particulate filter 22. If a superstoichiometric exhaust gas λ.sub.A>1 is measured at the second lambda sensor 28, the secondary air introduction is discontinued again and the internal combustion engine 10 is operated in phase IV at a substoichiometric air-fuel ratio λ.sub.E<1. In this process, a substoichiometric exhaust gas λ.sub.A<1 is established in the exhaust gas channel 12 upstream from the particulate filter 22 and, corresponding to the oxygen release capacity (RSC) of the particulate filter 22, a substoichiometric exhaust gas λ.sub.A<1 is also established downstream from the particulate filter 22. In phase V, the diagnostic method is concluded and the internal combustion engine 10 is again operated at a stoichiometric air-fuel ratio λ.sub.E=1, a process in which a stoichiometric exhaust gas λ.sub.A=1 is established in the exhaust gas channel 12.

LIST OF REFERENCE NUMERALS

(12) 10 internal combustion engine

(13) 12 exhaust gas channel

(14) 14 three-way catalytic converter

(15) 16 secondary air supply source

(16) 18 opening

(17) 20 component

(18) 22 particulate filter with a catalytic coating

(19) 24 sensor

(20) 26 first lambda sensor

(21) 28 second lambda sensor

(22) 30 control unit

(23) 32 signal line

(24) 34 secondary air pump

(25) 36 additional lambda sensor

(26) 38 secondary air line

(27) 40 shut-off valve

(28) λ.sub.E air-fuel ratio

(29) λ.sub.A exhaust gas-air ratio