METHOD AND DEVICE FOR CONTROLLING AND/OR MONITORING THE FUNCTION OF A SECONDARY AIR SUPPLY IN AN EMISSION CONTROL SYSTEM

Abstract

In a method and device for controlling and/or monitoring the function of a secondary air supply in an emission control system of an internal combustion engine, the emission control system includes at least two catalytic converters situated in succession in an exhaust duct, it being possible for the second catalytic converter to be implemented as a combination of catalytic converter and particulate filter. For a secondary air diagnosis and for secondary air control, a two-point lambda probe is situated, with respect to a direction of flow of exhaust gas, downstream of the first catalytic converter. Measures are applied for compensating tolerance and aging effects of the two-point lambda probe. This results in particular in cost advantages in emission control systems for fulfilling stricter emission requirements. In particular, this makes it possible to operate the particulate filter in optimized fashion.

Claims

1. A method for at least one of controlling and monitoring a function of a secondary air supply in an emission control system of an internal combustion engine, the emission control system, in its central section, including a first catalytic converter and a second catalytic converter situated in an exhaust duct in succession, a first lambda probe being situated, with respect to a direction of flow of exhaust gas, downstream of an engine block and upstream of the first catalytic converter, an exhaust gas probe being situated upstream of the second catalytic converter, air being introducible between the first and second catalytic converters by the secondary air supply for an optimized operation of the second catalytic converter, wherein a two-point lambda probe is situated downstream of the first catalytic converter and of the secondary air supply, the method comprising: using the two-point lambda probe for at least one of a secondary air diagnosis and a secondary air control; and applying to the two-point lambda probe measures that compensate tolerance and aging effects.

2. The method of claim 1, wherein: at least one particulate filter is situated downstream of the first catalytic converter and the secondary air supply or is part of the second catalytic converter; and the at least one of the secondary air diagnosis and the secondary air control is performed using the secondary air supply and the two-point lambda probe for the a least one particulate filter.

3. The method of claim 1, wherein the applying of the measures includes adapting an offset of a probe characteristic of the two-point lambda probe by an adjustment at high excess air while the internal combustion engine is running or is at a standstill.

4. The method of claim 3, wherein the applying of the measures includes applying a correction of a temperature-related shift of the probe characteristic with the aid of an active measurement of a sensor element temperature while the internal combustion engine is running or is at a standstill.

5. The method of claim 3, wherein the applying of the measures further includes applying a correction of a calculation of a lambda value, thereby taking into account a current exhaust-gas composition and a varying cross sensitivity vis-à-vis different exhaust-gas components.

6. The method of claim 1, wherein the applying of the measures includes shifting a lambda-one point of a probe characteristic of the two-point lambda probe via a tracking control of the second two-point lambda probe.

7. The method of claim 6, wherein the applying of the measures includes applying a correction of a temperature-related shift of the probe characteristic with the aid of an active measurement of a sensor element temperature while the internal combustion engine is running or is at a standstill.

8. The method of claim 1, wherein the applying of the measures includes: adapting an offset of a probe characteristic of the two-point lambda probe by an adjustment at high excess air while the internal combustion engine is running or is at a standstill; shifting a lambda-one point of the probe characteristic via a tracking control of the second two-point lambda probe; applying a correction of a temperature-related shift of the probe characteristic with the aid of an active measurement of a sensor element temperature while the internal combustion engine is running or is at a standstill; and applying a correction of a calculation of a lambda value, thereby taking into account a current exhaust-gas composition and a varying cross sensitivity vis-à-vis different exhaust-gas components.

9. The method of claim 1, wherein the internal combustion engine is part of a vehicle.

10. An emission control system of an internal combustion engine, the emission control system comprising: an engine control unit that includes a least one of a storage device and a comparator unit; and in a central section of the emission control system: a first catalytic converter situated in an exhaust duct; a second catalytic converter situated in the exhaust duct in sequence with the first catalytic converter; a lambda probe that is situated, with respect to a direction of flow of exhaust gas, downstream of an engine block and upstream of the first catalytic converter and that is configured to supply signals to the engine control unit; an exhaust-gas probe that is downstream of the first catalytic converter and of the second catalytic converter; a secondary air supply configured to introduce air between the first and second catalytic converters for optimized operation of the second catalytic converter; and a two-point lambda probe that is situated downstream of the first catalytic converter and of the secondary air supply and is configured to supply signals to the engine control unit; wherein the engine control unit is configured to: perform a catalytic converter diagnosis; use the signals from the two-point lambda probe to perform at least one of a secondary air diagnosis and a secondary air control of the secondary air supply; and apply to the two-point lambda probe measures that compensate tolerance and aging effects of the two-point lambda probe.

11. The device of claim 10, wherein at least one of the emission control system further comprises a particulate filter downstream of the first catalytic converter and of the secondary air supply.

12. The device of claim 10, wherein the second catalytic converter includes a particulate filter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The FIGURE is a schematic representation of an internal combustion engine having an emission control system by which the method of the present invention may be implemented, according to an example embodiment of the present invention.

DETAILED DESCRIPTION

[0032] The FIGURE shows in a schematic representation an internal combustion engine 1 that includes an engine block 10, an exhaust duct 20, a lambda probe 30 that is, with respect to the direction of flow of exhaust gas, downstream of the engine block 10 and that is, in an example embodiment, implemented as a wide-band lambda probe, and a first catalytic converter 40 situated downstream of the lambda probe 30. Lambda probe 30 makes possible lambda control 100 and is used for a first balancing 110 for diagnosing the storage capacity of the first catalytic converter.

[0033] The internal combustion engine 1 further includes, downstream from first catalytic converter 40, a first two-point lambda probe 50 used for catalytic converter diagnosis-tracking control and for breakthrough detection for the diagnosis of first catalytic converter 40. The internal combustion engine 1 further includes a second catalytic converter 60 downstream of the first two-point lambda probe 50. The first two-point lambda probe 50 is additionally used for a balancing of the storage capacity of the second catalytic converter 60. The second catalytic converter 60 can be implemented as a combination block made up of the catalytic converter and the particulate filter or as a coated particulate filter. A separate particulate filter is also conceivable.

[0034] Downstream of the additional catalytic converter 60, the internal combustion engine 1 further includes a second two-point lambda probe 70 for breakthrough detection for the catalytic converter diagnosis 140 of the additional catalytic converter 60. Lambda probes 30, 50, and 70 are connected to an engine control unit 80, in which on the one hand the lambda control and on the other hand the diagnostic methods regarding the monitoring of the operability of the emission control system are implemented in hardware and/or software.

[0035] Additionally, a secondary air supply 90 into exhaust duct 20 is provided in this system between first catalytic converter 40 and first two-point lambda probe 50. In an example embodiment, the first two-point lambda probe 50 is used additionally for the secondary air diagnosis as well as for the air supply control (in the combination: tracking control/secondary air diagnosis 120 and second balancing/secondary air control 130).

[0036] For quicker heating of catalytic converter 60 having the particulate filter function to its operating temperature, an exothermic reaction is brought about in the coated particulate filter at a rich combustion chamber mixture by introducing secondary air via the secondary air supply 90 upstream from the particulate filter. In order to avoid unnecessary emissions, it is important for an average exhaust gas lambda of at least 1 to be maintained upstream from the particulate filter. At a sufficiently high temperature of the particulate filter, a burn-off of the soot charge and thus the regeneration of the particulate filter can be achieved by excess oxygen. For this purpose, a defined lean exhaust gas lambda is to be maintained upstream from the particulate filter.

[0037] A lambda probe is then suitable as a probe upstream from the coated particulate filter for adjusting the lambda in the event of the introduction of secondary air and for a diagnosis of the secondary air pump or the secondary air system if it has a sufficiently accurate lambda signal in a broad lambda range (typically at least between λ=1 und λ−1.2). A two-point lambda probe 50, 70 does not fulfill this requirement without additional measures.

[0038] This limitation applies also if the two-point lambda probe 50, as described in DE 10 2016 211 506.5, is to be used as a probe upstream from the catalytic converter for adjusting the lambda value in the rich preconditioning and for adjusting the lean lambda value as well as for balancing the entered oxygen quantity when measuring the oxygen storage capacity of the catalytic converter. Here in particular a sufficiently accurate lambda signal is required in a lambda range of typically between λ=0.95 und λ=1.05.

[0039] The use of a first (as shown in the FIGURE) two-point lambda probe 50 for the lambda control using secondary air or for its diagnosis presupposes the compensation of tolerance and aging effects, which result in a shift of the actual probe characteristic vis-à-vis the reference probe characteristic stored in the control unit or the engine control unit 80. Only then will the lambda signal of this first two-point lambda probe 50 fulfill the mentioned requirements regarding accuracy.

[0040] DE102012211687A1, DE102012211683A1, DE102013216595A1, DE102014210442A1, and DE102012221549A1 describe methods that allow for a compensation of tolerance and/or aging effects that result in such a characteristic curve shift. The methods described there, one or more of which, according to example embodiments of the present invention, are applied to the first two-point lambda probe 50 individually or in combination, include: adaptation of a constant offset of the probe characteristic by an adjustment at high excess air while the engine is running or is at a standstill; compensation of the shift of the lambda-one point of the probe characteristic via a tracking control using the second two-point lambda probe 50; compensation of a temperature-related shift of the probe characteristic with the aid of an active measurement of the sensor element temperature while the engine is running or is at a standstill; and taking into account the current exhaust-gas composition and different cross sensitivities of the probe vis-à-vis various exhaust-gas components in the conversion of the probe voltage into a lambda value.

[0041] In a particularly preferred variant of the method of the present invention, only a constant offset of the probe characteristic is adapted. This is possible to achieve in a comparatively simple manner by an adjustment at high excess air, such as occurs for example at an overrun fuel cutoff, and in many cases already results in a sufficient accuracy of the lambda signal so as to be able to use it for balancing the oxygen input and discharge for diagnosing the catalytic converter 60. At the same time, this adaptation improves the accuracy of the breakthrough detection in the diagnosis of first catalytic converter 40 and the accuracy of the tracking control 120 with the aid of the first two-point lambda probe 50.

[0042] By combining the adaptation of a constant offset of the probe characteristic with one or more of the above-mentioned methods, it is possible to improve the accuracy of the lambda signal of the first two-point lambda probe 50 downstream from first catalytic converter 40 further, in the event that even higher requirements are placed on the accuracy of this lambda signal.

[0043] Following the compensation, the lambda signal of the first two-point lambda probe 50 is used, as described above, for the lambda control using secondary air, in order to operate the particulate filter in optimized fashion. In addition, a corresponding diagnosis of a secondary air pump or of the secondary air system can be performed.

[0044] It is possible to apply the method according to the present invention analogously also to emission control systems that include more than two monitored catalytic converters or coated particle filters.