DE19810483A1 - Offset determination of hydrocarbon or nitrogen oxide sensor in catalyst-fitted engine exhaust system - Google Patents

Abstract

Hydrocarbon (HC) and/or nitrogen oxide (NOX) sensor offset is determined as the sensor signal when no hydrocarbon and/or nitrogen oxide emissions are present. The offset of HC and/or NOX sensors, in catalyst-fitted engine exhaust systems, is determined by reading the sensor signal in the engine (10) and catalyst (20) operating condition in which no HC and/or NOX emissions occur, the signal being stored as the offset signal.

Description

State of the art

The invention relates to a method for determining the Sensor offsets for HC and / or NOx sensors that are in the Exhaust system of an internal combustion engine with a catalytic converter gate are arranged.

HC and / or NOx sensors have been known for some time for monitoring the exhaust gas of internal combustion engines to use. Such sensors detect pollutant con centers and signal defects in the exhaust system, if predefinable threshold values of the sensor signals above be paced.

The problem here is that these sensors one Have offset. However, since it always depends on that of the sensor signal output to the sensors is decided, whether a catalyst is recognized as defective or not, there is considerable interest in pollutants, which are detected by such sensors, if possible exactly, d. H. to be determined without offset.

The invention is based on the problem of Offset to technically as easy to implement Way to determine.

Advantages of the invention

This problem arises in a method of determination the sensor offset for HC and / or NOx sensors that are in the Exhaust line of an internal combustion engine are arranged solved according to the invention in that the sensor signal in Operating states of the internal combustion engine in which none HC and / or NOx emissions occur, read out and as Offset signal is stored.

By reading out the sensor signal in the operating states of the Internal combustion engine in which no HC and / or NOx emissions ions occur and save this signal as Offset signal, an offset falsification can be very effective be completely eliminated, as this will cause the sensors to are advantageously adjustable to zero.

In principle, the most varied of operations come states of the internal combustion engine in which none HC and / or NOx emissions occur.

An advantageous embodiment provides that one Sensor signal from HC sensors with cold internal combustion engine ne and before starting the internal combustion engine reads out and saves as an offset signal.

In another advantageous embodiment Provided that the sensor signal from HC sensors preferably cold internal combustion engine in overrun mode  of a vehicle by the internal combustion engine is driven, reads and stores as an offset signal chert.

In both cases there is both the engine oil and also the catalyst of the internal combustion engine is not in the warm operating condition.

This ensures that neither the catalyst HC emissions are still emitted by the engine oil, which practically only when the catalytic converter is warm tors or engine oil occur. In overrun mode there are also almost no HC emissions.

To eliminate offset signals from NOx sensors advantageously provided that the sensor signal of NOx sensors when the engine is cold and before a start reads the gear of the internal combustion engine and as an offset signal saves.

In another advantageous embodiment provided that the sensor signal from NOx sensors after a regeneration phase of a NOx storage catalytic converter reads out with a rich air-fuel mixture and as Offset signal saves.

Even with these two operating states of the burner there are practically no NOx emissions, so that from the sensor in these operating conditions interpret the read signal as an offset signal is.

It is advantageously used to determine the Regeneration phase that of one behind the NOx storage tank  Talysator of the internal combustion engine arranged λ-probe read signal.

drawing

Further features and advantages of the invention are opposed stood the following description and the drawing cal representation of some embodiments.

The drawing shows:

Fig. 1 shows schematically the exhaust line of an internal combustion engine, in which the method making use of the invention is used;

Fig. 2 shows schematically the concentration of HC and NOx emissions plotted against the air ratio λ.

Description of the embodiments

A catalyst 20 is arranged in the exhaust line of an internal combustion engine 10 . This catalytic converter 20 can be, for example, a three-way catalytic converter or, in the case of an internal combustion engine that directly injects gasoline, a so-called NOx storage catalytic converter. Sensors 40 , 50 are arranged upstream and downstream of the catalytic converter 20 , the output signals of which are supplied to an electronic control unit 30 , in which injection times are determined depending on the values detected by the sensors 40 , 50 and are output to injection valves 14 . The sensors 40 can be, for example, λ probes, which are arranged in front of and behind the catalytic converter 20 . Sensor 50 is an HC or NOx sensor.

As further shown schematically in FIG. 1, the internal combustion engine 10 also has an oil pan 16 which is connected to the intake manifold 12 of the internal combustion engine 10 via a crankcase ventilation line 18 .

The method for determining the sensor offset of an HC and / or NOx sensor 50 is described below with reference to FIG. 1 in conjunction with FIG. 2.

In FIG. 2, the concentration of HC and NOx Emissio NEN over the air ratio λ applied. As can be seen from FIG. 2, HC concentrations occur predominantly with a rich mixture, ie with a value of the air ratio λ <1, whereas NOx emissions occur predominantly with a lean mixture, ie with an air ratio λ <1.

The basic idea of the invention is to operate such conditions in which only HC or NOx emissions occur, for determining the sensor offset of the HC or To use NOx sensors.

The determination of the sensor offset using the example of a HC sensor is described in more detail below.

The sensor offset of the HC sensor is determined when the engine is cold and the vehicle is overrun, which is driven by the internal combustion engine 10 , and the values determined in this way are stored as an offset signal.

In this way it is ensured that neither HC emissions from the warm catalyst 20 nor from the warm engine oil are emitted into the exhaust line of the internal combustion engine, the HC emissions emitted by the engine oil via the oil pan 16 , the crankcase ventilation line 18 and the intake pipe 12 Internal combustion engine 10 supplied and in this way get into the exhaust line.

In addition, no HC emissions occur in the overrun mode of the vehicle, which is driven by the internal combustion engine 10 , so that signal falsification is not to be expected as a result and an adjustment to the value zero is possible.

It is understood that such elimination of the Sensor offsets every time the vehicle is pushed by new can be made.

Another embodiment of the method provides that the sensor signal of the HC sensor 50 is read out when the internal combustion engine is cold and before the internal combustion engine is started and is stored as an offset signal. In this operating state of the internal combustion engine 10, it is also ensured that 20 HC emissions are not emitted either by the internal combustion engine itself or by the engine oil or the catalyst.

In a gasoline direct injection internal combustion engine, a so-called NOx storage catalyst is used as the catalyst 20 . Such a NOx storage catalytic converter picks up NOx emissions, that is, stores NOx emissions, until a concentration is reached which requires regeneration of the NOx storage catalytic converter. Here, the NOx storage catalyst is operated briefly with a rich fuel-air mixture, ie with an air ratio λ <1. In this operating state of the internal combustion engine 10 there are practically no NOx emissions (see FIG. 2). In one embodiment of the method, the determination of the offset signal of a NOx sensor 50 , which is arranged behind the catalytic converter 20 , is therefore carried out after such a regeneration phase of the NOx storage catalytic converter with a rich fuel-air mixture.

In another embodiment, for eliminating the sensor offset signal at a NOx sensor 50 is provided that reads the sensor signal of the NOx sensor 50 downstream of the catalyst 50 when the engine is cold and before a starting process of the internal combustion engine and stores it as offset signal . In this case too, it is ensured that no NOx emissions are emitted by the NOx storage catalytic converter, by warm engine oil or by the internal combustion engine itself.

Claims (5)

1. A method for determining the sensor offset in HC and / or NOx sensors which are arranged in the exhaust line of an internal combustion engine with a catalyst, characterized in that the sensor signal in operating states of the internal combustion engine ( 10 ) and the catalyst ( 20 ), in which no HC and / or NOx emissions occur, read out and stored as an offset signal. 2. The method according to claim 1, characterized in that one reads the sensor signal from HC sensors when the internal combustion engine is cold ( 10 ) and before a starting operation of the internal combustion engine ( 10 ) and stores it as an offset signal. 3. The method according to claim 1, characterized in that one reads the sensor signal from HC sensors in front of preferably cold internal combustion engine in overrun mode of the vehicle, which is driven by the internal combustion engine ( 10 ), and stores it as an offset signal. 4. The method according to claim i, characterized in that that the sensor signal from NOx sensors when cold  Engine and before starting the internal combustion engine reads out the machine and stores it as an offset signal. 5. The method according to claim 1, characterized in that the sensor signal from NOx sensors after a Regeneration phase of a NOx storage cat with a rich one Reads air-fuel mixture and as offset Stores signal.