DE102010027984A1 - Method for operating exhaust system of internal combustion engine in motor vehicle, involves guiding fresh air by exhaust system, where fresh air is guided through exhaust duct during operating state of internal combustion engine - Google Patents

Abstract

The method involves guiding fresh air (41) by an exhaust system (10) associated with a fresh air supply (40). The fresh air is guided through an exhaust duct (12) during an operating state of an internal combustion engine in which injection and combustion of fuel does not occur. The fresh air is supplied for a certain time which corresponds to an oxygen content of exhaust gas in an environment of an exhaust gas probe. Independent claims are also included for the following: (1) a computer program ; and (2) a control and regulating device.

Description

State of the art

The invention relates to a method according to the preamble of claim 1, and a computer program and a control and / or regulating device according to the independent claims.

From the market, internal combustion engines with an exhaust system are known in which, for example, lambda sensors are used for the analysis of the exhaust gas. In order to ensure the required accuracy of a lambda probe or a NOx sensor, it is necessary to perform a calibration of the exhaust gas probes from time to time. This is achieved by supplying an environment of the exhaust gas probe with an exhaust gas, which has approximately an oxygen content, as it is found in an ambient air. Such an operating state of the internal combustion engine or of the exhaust system can be achieved if a vehicle driven by the internal combustion engine is in overrun operation for a specific minimum duration. Such a push operation is common for highway or highway driving. Thus, both a sufficient oxygen content of the exhaust gas can be expected, as well as a sufficient frequency of such phases. In such a state of the exhaust system, an adjustment of an exhaust gas probe, for example a lambda probe or a NO x probe can now be carried out. If, in contrast, a vehicle is operated under other conditions, for example in city traffic, then relatively long overshoot phases of the internal combustion engine, which are needed to adjust an exhaust gas probe, are comparatively rare or do not occur at all.

The DE 198 10 483 A1 describes a method for determining the sensor offset in HC and / or NOx sensors, wherein a sensor signal in operating states of the internal combustion engine and the catalytic converter, in which no HC and / or NOx emissions occur, read out and stored as an offset signal becomes.

Disclosure of the invention

The problem underlying the invention is achieved by a method according to claim 1 and by a computer program and a control and / or regulating device according to the independent claims. Advantageous developments are specified in subclaims. Features which are important for the invention can also be found in the following description and in the drawings, wherein the features, both alone and in different combinations, can be important for the invention, without being explicitly referred to again.

The inventive method has the advantage that an adjustment of exhaust gas sensors in internal combustion engines, which are designed as a gasoline engine or diesel engine, can be largely independent of a specific driving situation and thus not only possible on long downhill. The method allows a particularly accurate adjustment and is also advantageous for exhaust systems, which have their own control unit and therefore operate relatively independently.

The invention is based on the consideration that in the course of stricter emission limit values it is necessary to be able to carry out calibrations of exhaust gas probes even if no longer deceleration phases of the internal combustion engine are to be expected. Furthermore, it is considered that an adjustment of exhaust gas sensors only in an operating state in which an injection and combustion of fuel in the exhaust system does not take place, is possible or useful. For example, internal combustion engines, which are designed as a diesel engine, have in their exhaust system via a diesel particulate filter. A diesel particulate filter must be regularly cleaned of the particles accumulated during operation of a vehicle. This is done, for example, by the exhaust gas being heated in a controlled manner by means of a burner operated by fuel, so that the particles deposited in the diesel particle filter can burn. However, such a phase in which the diesel particulate filter is cleaned by injecting and burning fuel in an exhaust passage is poorly suited for balancing an exhaust gas probe provided in the exhaust system.

The invention provides that fresh air is supplied to the exhaust duct in a controlled manner in order to change the exhaust gas located in the surroundings of the exhaust gas probe and to enrich it with oxygen, so that an adjustment of one or more exhaust gas sensors is possible. For this purpose, one of the exhaust system associated fresh air supply is used, which sucks ambient air and feeds the exhaust duct. Preferably, the fresh air is introduced upstream of each exhaust gas probe to be adjusted. "Adjustment" is understood to mean a calibration (calibration) of the exhaust gas probe, so that the most precise possible connection between signals emitted by the exhaust gas probe and a respective measured variable specific to the exhaust gas probe can subsequently be established.

Preferably, fresh air is supplied at least until an oxygen content of the exhaust gas in an environment of the at least one exhaust gas probe corresponds approximately to an oxygen content of an ambient air. As a result, at least the environment of the exhaust gas probe can be sufficiently rinsed and advantageous conditions for a subsequent adjustment of the exhaust gas probe can be brought about. As a result, an adjustment of the exhaust gas probe can be done very accurately. This applies both to lambda probes, in particular broadband lambda probes, and to NOx sensors.

An embodiment of the invention provides that the desired duration of the supply of fresh air is determined empirically and / or depends on the previous operating state. This can be ensured in a simple manner that the conditions for balancing the exhaust gas probe for a sufficient time are available. In this case, on the one hand, an empirical determination can be used to determine a time duration for which these conditions are generally present. On the other hand, the required period of time can also be determined or more precisely determined by taking into account a previous operating state of the internal combustion engine or of the vehicle. For example, the duration of the fresh air supply can be reduced if an operating situation that was at least similar to a coasting operation of the vehicle preceded.

In addition, it is proposed that an injection of fuel be blocked until the adjustment is completed. This can be ensured that the adjustment of the exhaust probe takes place without interference.

• a) Betriebsphase vor und/oder während eines Starts der Brennkraftmaschine;
• b) Betriebsphase während und/oder nach einem Stopp der Brennkraftmaschine;
• c) Schubbetrieb der Brennkraftmaschine in einem Fahrzeug; und/oder
• d) Anforderung zur Durchführung des Verfahrens durch einen automatischen oder manuellen Eingriff.

An implementation of the method is particularly useful if at least one of the following conditions exists:

• a) operating phase before and / or during a start of the internal combustion engine;
• b) operating phase during and / or after a stop of the internal combustion engine;
• c) coasting of the internal combustion engine in a vehicle; and or
• d) Request to perform the procedure by automatic or manual intervention.

As a result, various operating phases are described in which the invention can be usefully used. In particular, unwanted constituents of the exhaust gas are less likely to be present before a start or after a stop of the internal combustion engine. These phases are therefore particularly suitable for balancing the exhaust gas probe. Furthermore, the method can be carried out as previously known in a coasting operation of the internal combustion engine. Likewise, the method can be performed when a request for implementation by means of an automatic intervention, for example by a control and / or regulating device of the internal combustion engine or the exhaust system is present. It is also possible to carry out the method according to the invention by a manual intervention, for example during a workshop diagnosis.

Furthermore, the invention provides that the fresh air is supplied by means of the fresh air supply of a burner associated with the exhaust system and / or by means of a secondary air blower. In many cases, such a fuel-powered burner for heating the exhaust gas is equipped with its own fresh air supply. The invention makes use of the fresh air supply of the burner, without operating the burner itself. Thus, advantageously, an existing embodiment of an exhaust system can be used to carry out the method according to the invention, additional costs are not incurred. The required for the cleaning of the particulate filter burner is switched off for an adjustment of the exhaust probes and only the fresh air supply turned on. Alternatively or additionally, it is provided to use a secondary air blower for the invention. This is useful, for example, if the exhaust system does not have a burner, as is often the case with gasoline engines.

The invention works better when the fresh air is supplied in close proximity to the exhaust gas probe. Such a particularly favorable arrangement for the method can be found in many prior art exhaust systems of motor vehicles, such as downstream of a turbocharger and upstream of a diesel oxidation catalyst. As a result, the method can be set up particularly cost-effectively, because no or little constructional adjustments - such as an adjustment of the fresh air supply of the burner - in the exhaust duct are required, but the process can be realized essentially by supplementing the existing control and / or regulating device ,

Hereinafter, an embodiment of the invention will be explained with reference to the drawings. In the drawing show:

1 a schematic representation of an exhaust system of a motor vehicle; and

2 a flow chart for the operation of the method in a computer program of a control and / or regulating device.

The same reference numerals are used for functionally equivalent elements and sizes in all figures, even in different embodiments.

1 shows a schematic of an exhaust system 10 a motor vehicle with some other components. In the lower part of the 1 there is an exhaust duct 12 , in which an exhaust gas in Essentially passed from left to right and prepared. In the present case, it is an exhaust system 10 a diesel vehicle. The exhaust duct 12 has in a flow direction of the exhaust gas, a diesel oxidation catalyst 14 , a diesel particulate filter 16 , and an SCR catalyst 18 on. Upstream of the diesel oxidation catalyst 14 is a burner 20 and a valve 22 arranged for fuel injection. Downstream of the diesel particulate filter 16 is a valve 24 arranged, with the urea-based additives ("additives") can be introduced into the exhaust stream, which for the selective catalytic reduction ("SCR") in the SCR catalyst 18 needed. Furthermore, the exhaust duct 12 five temperature sensors 26 , two pressure sensors 28 , a lambda probe 30 , and two NOx sensors 32 on. Further, between the diesel particulate filter 16 and the SCR catalyst 18 a so-called mixer 34 arranged. Input of the exhaust duct 12 is also a precatalyst 36 (Pre-DOC).

Above the exhaust duct 12 are in the 1 from left to right a fresh air supply 40 , a fuel metering device 42 , a circuit breaker 44 and a heater 46 for heating the over the valve 24 injected additive. In the drawing of the 1 at the top there is a fuel supply from left to right 50 , An institution 52 for conditioning the valve 24 to conductive additives and a control and / or regulating device 54 , The control and / or regulating device 54 contains a computer program 55 and has a number of outgoing lines 56 and incoming wires 58 on. This electrical signals from and to the control and / or regulating device 54 guided. Two CAN buses 60 connect the control and / or regulating device 54 with rest in the 1 not shown devices of the internal combustion engine or the vehicle. Also included are the temperature sensors 26 , the lambda sensor 30 , the pressure sensors 28 and the NOx sensors 32 with the control unit 54 electrically connected. This is in the drawing of 1 but not shown.

A calibration of the lambda probe 30 or the NOx sensors 32 will be in the exhaust system 10 prepared as follows:
The control unit 54 Receives an automatic or manual statement to perform a match. The controller then determines 54 a current and a past operating state of the internal combustion engine or the vehicle. The control unit 54 now locks the valves 22 and 24 , so that no fuel or additive is introduced into the exhaust gas. Likewise, the burner 20 switched off or locked. The fresh air supply 40 now blows fresh air 41 over the switched off burner 20 into the exhaust gas. The fresh air 41 reaches the short distance downstream of the burner 20 arranged lambda probe 30 (Arrow 64 ). The state thus set is maintained for a period of time T1. The period T1 is from the controller 54 determined, wherein the current operating state of the internal combustion engine and the exhaust duct 12 as well as the past operating conditions are taken into account.

After expiry of the period T1, the adjustment of the lambda probe 30 and / or the NOx sensors 32 respectively. This is done according to previously known procedural rules and will not be explained here. The adjustment of the lambda probe 30 and the NOx sensors 32 is particularly accurate, because during the previous period T1, an oxygen content of the exhaust gas in an environment of the lambda probe 30 and the NOx sensors 32 corresponds approximately to an oxygen content of an ambient air. If necessary, the time period T1 from the controller 54 for a comparison of the NOx sensors 32 longer than for a calibration of the lambda probe 30 because the NOx sensors 32 downstream from the burner 20 are removed, as the lambda probe 30 ,

Is the adjustment of the lambda probe 30 or the NOx sensors 32 finished, so will the blockage of the burner 20 as well as the valves 22 and 24 from the controller 54 canceled. The exhaust duct 12 or the exhaust system 10 can now continue working in a normal operating mode.

2 shows a flowchart of the method for a computer program 55 which is in the control and / or regulating device 54 the exhaust system or the internal combustion engine ("engine control unit") is executable. The processing takes place in the drawing of 2 essentially from top to bottom.

Starting from a start block 70 in which a request for an adjustment of an exhaust gas probe ( 30 ; 32 ) - for example, the lambda probe 30 - present, is in a block 72 detects an operating condition of the vehicle. In the following block 74 become the valve 22 for injection of fuel and the valve 24 blocked for the addition of additives in the exhaust gas. Likewise, the burner 20 blocked.

In the block 76 becomes the fresh air supply 40 switched on. Then it is in the block 78 waited for a period T1, so that one for the adjustment of the lambda probe 30 sufficient oxygen content in the exhaust duct 12 can adjust. After that takes place in a block 80 the actual adjustment of the lambda probe 30 ,

After adjustment of the lambda probe 30 becomes the fresh air supply 40 switched off again and the blocking of the valves 22 and 24 as well as the burner 20 canceled. In the end block 84 ends in the 2 described procedure.

The procedure may be in the start block 70 be called in particular when a start of the internal combustion engine is performed or imminent or during or after a stop of the internal combustion engine. Likewise, the method can be carried out in a coasting operation of the internal combustion engine or of a vehicle. Also an automatic request by the control and / or regulating device 54 or manual intervention is possible.

The time period T1 is determined from the operating state of the vehicle and from previously empirically determined values stored in a memory of the control and / or regulating device 54 are stored, determined. In an adjustment of the NOx sensors 32 If necessary, the time period T1 can be greater than when the lambda probe is adjusted 30 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19810483 A1 [0003]

Claims (9)

Method for operating an exhaust system ( 10 ) of an internal combustion engine, wherein at least one parameter of the in an exhaust passage ( 12 ) flowing exhaust gas from an exhaust gas probe ( 30 ; 32 ) is detected, characterized in that during an operating state of the internal combustion engine, in which an injection and combustion of fuel does not take place, the exhaust duct ( 12 ) upstream of the exhaust gas probe ( 30 ; 32 ) by means of one of the exhaust system ( 10 ) associated fresh air supply ( 40 ) Fresh air ( 41 ) and during and / or after the exhaust gas probe ( 30 ; 32 ) is adjusted. Method according to claim 1, characterized in that fresh air ( 41 ) is supplied at least until an oxygen content of the exhaust gas in an environment of the at least one exhaust gas probe ( 30 ; 32 ) corresponds approximately to an oxygen content of an ambient air. A method according to claim 2, characterized in that the duration is determined empirically and / or depends on the previous operating state. Method according to at least one of the preceding claims, characterized in that an injection of fuel is blocked until the adjustment is completed. Method according to at least one of the preceding claims, characterized in that it is carried out when at least one of the following conditions is present: - Operating phase before and / or during a start of the internal combustion engine; - Operating phase during and / or after a stop of the internal combustion engine; - Pushing operation of the internal combustion engine in a vehicle; and or - Request to perform the procedure by automatic or manual intervention. Method according to at least one of the preceding claims, characterized in that the fresh air ( 41 ) by means of the fresh air supply ( 40 ) one of the exhaust system ( 10 ) associated burner ( 20 ) and / or supplied by means of a secondary air blower. Method according to at least one of the preceding claims, characterized in that the fresh air ( 41 ) in the immediate vicinity of the exhaust gas probe ( 30 ; 32 ) is supplied. Computer program ( 55 ), characterized in that it is suitable for carrying out the method according to one of claims 1 to 7. Control and regulating device ( 54 ), characterized in that a computer program ( 55 ) is executable according to claim 8.

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