DE102011053419B4 - Method for controlling an exhaust system of a diesel engine and exhaust system of a diesel engine - Google Patents

Abstract

Method for controlling an exhaust gas system of a diesel engine, in which a sensor element is arranged, with which a soot load in the exhaust gas mass flow is determined, as a function of which a regeneration of a particulate filter is carried out, characterized in that a exhaust gas mass flow sensor (24, 34) is used as the sensor element, is switched at excessive soot load in a cleaning mode, wherein from the soot load of the exhaust gas mass flow sensor (24; 34) on a soot load of the particulate filter (9) is closed, over which the time for performing the regeneration of the particulate filter (9) is set, over a map the soot load of the particulate filter (9) from the soot load of the exhaust gas mass flow sensor (24; 34) and from the via an exhaust gas recirculation channel (10; 28) recirculated exhaust gas mass flow and calculated via an intake passage (22) of the diesel engine air mass calculated exhaust gas mass flow is determined.

Description

The invention relates to a method for controlling an exhaust system of a diesel engine, in which a sensor element is arranged, with which a soot load in the exhaust gas flow is determined, depending on a regeneration of a particulate filter is performed and an exhaust system of a diesel engine with an exhaust system in which a particulate filter is arranged, an exhaust gas recirculation channel, which branches off from the exhaust line, an exhaust gas cooler, which is arranged in the exhaust gas recirculation channel, an exhaust gas mass flow sensor, an exhaust gas recirculation valve, which is arranged in the exhaust gas recirculation channel and a control unit which is connected to the exhaust gas mass flow sensor and means for initiating the regeneration phase of the particulate filter.

Diesel engines with particulate filters are known. Regeneration phases are initiated at regular intervals or as a function of a measured pressure loss via the particle filter, in which the soot in the filter is burned off at a temperature of more than 500 ° C. For this purpose, for example, additional fuel is injected into the exhaust line, so that a temperature-increasing afterburning takes place.

However, these post-injections significantly increase fuel consumption. Since the intervals in which regeneration is necessary but especially for vehicles that are driven mainly in city traffic are quite short, it is important to perform the regeneration phase not purely time-dependent but depending on the actual soot load of the particulate filter.

For this purpose, it is known to arrange in each case a pressure sensor in front of and behind the particle filter so that the regeneration phase is carried out when a pressure difference limit value is exceeded. Such a constructed exhaust system is for example from the DE 103 26 784 A1 known. About this pressure difference is closed in a deposit calculation unit via different algorithms on a Schwebstoffablagerungsmenge and set the date of the regeneration phase.

Alternatively it is from the DE 10 2009 007 126 A1 known for measuring the soot load behind the particulate filter to provide a particle sensor element with which the soot loading of the exhaust gas is measured behind the filter, from which it is concluded on the functioning of the particulate filter.

Furthermore, from the DE 10 2005 061 548 B4 an exhaust gas mass flow sensor is known, which can be switched in response to its heating from a normal operating mode in a cleaning mode to burn its surface by increasing the temperature of deposits freely.

The US 2008/0282682 A1 discloses a sensor system for determining a loading of a particulate filter having two soot sensors, one of which is arranged in front of the particulate filter and a second behind the particulate filter. The first soot sensor measures an overall pouring mass flowing into the particulate filter, from which it is concluded that necessary regeneration has taken place. The second measures an escaping soot mass, which concludes the functionality of the particulate filter.

Also is from the AT 501 386 B1 a sensor known, which serves as a soot sensor for determining a soot amount in the exhaust gas. This can be used simultaneously as a sensor for determining an exhaust gas mass flow.

All these different exhaust systems have the disadvantage that the components used, whether exhaust gas sensors or pressure sensors, do not fulfill any additional function and cause correspondingly no additional costs. Therefore, very inexpensive sensors are often used, but often are not built sufficiently robust to ensure a sufficiently long life.

It is therefore an object to provide an exhaust system of a diesel engine and a method for controlling such an exhaust system, with which a regeneration phase for a particulate filter can be set without having to use additional components and yet to ensure that a regeneration is only performed when too high a load of the particulate filter with soot actually exists, so that no unnecessary increase in consumption takes place.

This object is achieved by a method for controlling an exhaust system of a diesel engine having the features of claim 1 and by an exhaust system of a diesel engine having the features of claim 5.

Characterized in that as the sensor element, an exhaust gas mass flow sensor is used, which is switched to a high soot load in a cleaning mode, wherein from the soot load of the exhaust gas mass flow sensor is closed on a soot load of the particulate filter, about which the time is set for performing the regeneration of the particulate filter, wherein via a Map the soot load of the particulate filter from the soot load of the exhaust gas mass flow sensor and from the It is not necessary to use an additional sensor to determine the regeneration phase, as the exhaust gas mass flow recirculated via an exhaust gas recirculation channel and the exhaust gas mass flow calculated via an intake duct of the diesel engine are determined. Depending on the installation location, either a discharged or an exhaust gas quantity recirculated to the intake manifold is measured via the exhaust gas mass flow sensor, which exhaust gas is used, for example, for controlling or regulating the exhaust gas recirculation valve or the exhaust gas flap. Since, regardless of the installation location of the exhaust gas mass flow sensor, it is always supplied with exhaust gas whose soot content per mass unit essentially corresponds to the carbon black fraction with which the particle filter is charged, it can be deduced from the soot loading of the exhaust gas mass flow sensor on the soot load of the particulate filter. It would also be conceivable to conclude from a change in the soot load on an exhaust gas mass flow sensor arranged behind the particulate filter to the loading of the particulate filter.

These advantages can be used with an exhaust system in which a characteristic map is stored in the control unit, via which a soot load of the particulate filter in dependence on the soot load of the exhaust gas mass flow sensor and the exhaust gas mass flow recirculated via the exhaust gas recirculation channel and the calculated exhaust gas mass flow via the intake duct of the diesel engine is determinable. This means that the soot load of the particulate filter from the soot load of the exhaust gas mass flow sensor and the exhaust gas mass flow is determined via a characteristic map and, if appropriate, a start of the regeneration phase of the particulate filter follows from this result.

Preferably, a map is stored in the control unit, via which a soot load of the exhaust gas cooler in dependence on the Rußbelastung the exhaust gas mass flow sensor and the exhaust gas mass flow is determined so that the soot load of an exhaust gas cooler from the soot load of the exhaust gas mass flow sensor and the exhaust gas mass flow is determined via the map. In this way, an optimal time for burning the exhaust gas cooler can be determined. If appropriate, this can be done simultaneously with the regeneration of the particulate filter. In this case, the time can be set without having to attach additional sensors, so that the component cost for the regeneration of the particulate filter and the burning of the exhaust gas cooler is minimized.

Preferably, the exhaust gas mass flow sensor operates on the principle of hot film manometry. This means that the sensor has heating resistors which are heated, whereby the generated heat of these heating resistors is delivered to the flowing medium by convection. The resulting temperature change of the heating resistor or the additional power consumption to obtain the Heizwiderstandstemperatur are a measure of the existing mass flow. These sensors are very reliable. Only deposits on the surfaces are to be avoided, so that when used in the exhaust system usually additional heating wires for burning off the deposits are provided. This is also done on the basis of parameters to be defined, which serve as a measure of the layer thickness and thus of the soot content in the exhaust gas.

In particular, it is concluded from the heating time on the soot load of the exhaust gas mass flow sensor. A larger soot load has an increase in the heating time result, so that with constant measurement of the heating time on the respective layer thickness and on the respective layer thickness changes on the. Soot loading of the exhaust gas can be closed. Accordingly, this heating time can serve as a measure of the loading of the particulate filter with appropriately stored map.

It is particularly advantageous to measure the temperature of the exhaust gas upstream of the particle filter, which is additionally taken into account in the determination of the soot load of the particle filter. Accordingly, a temperature sensor is preferably arranged in front of the particle filter, which is connected to the control unit. In this way, it can be considered whether, during normal engine operation, temperatures may possibly be reached which already result in regeneration of the particulate filter or of the exhaust gas cooler. Furthermore, the particle filter tends to grow faster at lower temperatures, so that the temperature can also be stored in the map or can be taken into account in an appropriate algorithm reproducing the map.

In a further embodiment, the exhaust gas mass flow sensor is arranged downstream of the exhaust gas cooler in the exhaust gas recirculation channel. This reduces the thermal load of the exhaust gas mass flow sensor and increases the measurement accuracy of the sensor.

Preferably, the control unit is connected to an injection valve, via which fuel for regeneration of the particulate filter in the exhaust line can be injected. This allows the direct control of the injection valve for timely and rapid regeneration of the particulate filter.

Thus, a method is provided for controlling an exhaust system and an exhaust system for a diesel engine, in which the particulate filter at an optimum time, that is, only regenerated at actually present to high particle load, without having to use additional sensors. This reduces costs. In this case, the already existing soot measurement can be used on the exhaust gas mass flow sensor, if appropriate maps are stored in the engine control.

An embodiment of an exhaust gas recirculation system according to the invention is shown in the figure and will be described as well as the associated method in the following.

The figure shows a schematic diagram of two alternative or jointly usable embodiments of an exhaust system according to the invention.

The exhaust system according to the invention consists of an engine block 2 in which combustion of a fuel-air mixture with supplied exhaust gas takes place in a known manner. From the engine block 2 leads an exhaust system 4 initially in the form of an exhaust manifold to an exhaust outlet 6 , Upstream to the exhaust outlet 6 is in the exhaust system 4 an exhaust flap 8th is arranged. Upstream of the exhaust flap 8th and downstream of a diesel particulate filter 9 who is also in the exhaust system 4 is arranged branches off the exhaust line 4 a low pressure exhaust gas recirculation channel 10 from.

This low pressure exhaust gas recirculation channel 10 is located in the low pressure region of the internal combustion engine that is downstream of an exhaust gas turbine 12 an exhaust gas turbocharger 14 , In low-pressure exhaust gas return channel 10 are a first exhaust gas recirculation valve 16 and a first exhaust gas cooler 18 arranged, by means of which the temperature of the exhaust gas and the desired amount of exhaust gas in Niederdruckabgasrückführkanal 10 can be adjusted. The low pressure exhaust gas return channel 10 opens upstream of a compressor 20 of the turbocharger 14 in a suction channel 22 of the internal combustion engine, ie in a low pressure region before compression of the exhaust air-air mixture.

In the flow direction of the exhaust gas before the first exhaust gas recirculation valve 16 and in front of the first exhaust gas cooler 18 is in the low pressure exhaust gas return channel 10 an exhaust gas mass flow sensor 24 thus arranged downstream of the diesel particulate filter 9 is arranged. This is used in a known manner to determine the recirculated exhaust gas mass flow and is equipped with a control unit 25 connected, which the data of the exhaust gas mass flow sensor 24 processed and, for example, for optimized adjustment of the exhaust gas recirculation valve 16 uses. The position in front of the exhaust gas cooler 18 and the exhaust gas recirculation valve 16 reduces the tendency to form condensate in the area of the exhaust gas mass flow sensor 24 , because in front of the exhaust gas cooler, the highest temperatures in the low pressure exhaust gas return duct 10 present, wherein the temperature of the exhaust gas compared to the temperature at the outlet of the engine block 2 already significantly lower. The arrangement in front of the exhaust gas recirculation valve 16 prevents disturbances of the flow through the exhaust gas recirculation valve 16 Have an influence on the measurement.

The exhaust gas mass flow sensor 24 is a working according to the principle of Heißfilmenemometrie sensor having, for example, a heating resistor, which serves to burn off deposits on the ceramic body in a cleaning mode, so as to ensure proper functioning of the exhaust gas mass flow sensor 24 to ensure. This burn-off takes place, for example, as a function of the heating duration of the heating resistors of the exhaust gas mass flow sensor 24 , In the present case, the exhaust gas mass flow sensor 24 downstream to the particle filter 9 arranged so that it can be assumed that a relatively low soot load, but with heavy loading of the particulate filter 9 due to the sinking capacity will increase. Accordingly, via a in the control unit 25 stored map from the soot load of the exhaust gas mass flow sensor 24 , which results, for example, from the heating time or the heating time change and the actual exhaust gas mass flow to an excessive carbon black loading of the particulate filter 9 getting closed. If this is detected, a regeneration phase of the particulate filter 9 initiated by adding additional fuel through the injector 27 in the exhaust system 4 is injected, whereby an afterburning arises, by which the temperature is increased so far that the particulate filter 9 is burned. Of course, via the control unit 25 also the other units for carrying out the regeneration phase in a known manner. The exhaust gas mass flow can be calculated from the recirculated exhaust gas mass flow and the intake air quantity.

In addition, these values of the exhaust gas mass flow sensor 24 also for burning the exhaust gas cooler 18 or the exhaust gas recirculation valve 16 be used, for which either a separate map is deposited to close on a necessary burning or each with the regeneration of the particulate filter 9 also a regeneration of the exhaust gas cooler 18 is initiated. When depositing a separate map is of course directly the measured recirculated exhaust gas mass flow with the soot load of the exhaust gas mass flow sensor 24 depending on the soot load of the exhaust gas cooler 18 deposited.

To further improve this control is in front of the particulate filter 9 a temperature sensor 29 arranged, which is also connected to the control unit and whose values can also be taken into account in the map. In particular, this temperature sensor is suitable 29 to determine whether temperatures are occurring during operation that may make regeneration unnecessary.

Alternatively, this regeneration can also be dependent on the measured values of a second exhaust gas mass flow sensor 34 carried out in a high-pressure exhaust gas recirculation channel 28 is arranged and thus upstream of the particulate filter 9 is arranged.

The intake channel 22 leads from the mouth of the low pressure exhaust gas recirculation channel 10 over the compressor 20 of the turbocharger 14 to a charge air cooler 26 in which the compressed air-exhaust gas mixture is cooled to improve the combustion. From here, the intake duct leads 22 to the engine block 2 , wherein in this flow path, a branch is arranged, at which the high-pressure exhaust gas return passage 28 in the intake channel 22 empties.

This high pressure exhaust gas return channel 28 branches off the exhaust duct 4 upstream of the turbine 12 of the turbocharger 14 from. In this high pressure exhaust gas return channel 28 is a second exhaust gas recirculation valve 30 for controlling the exhaust gas mass flow and a second exhaust gas cooler 32 arranged to control the temperature of the exhaust gas. The exhaust gas mass flow sensor 34 , which also operates on the principle of hot film manometry, is downstream of the exhaust gas cooler 32 arranged. Here is a not so high exhaust gas temperature as at the entrance of the high-pressure exhaust gas recirculation channel 28 in front. This allows a more accurate measurement because these sensors are not designed and calibrated for the extremely high exhaust gas temperatures. So can for both exhaust gas recirculation channels 10 . 28 same sensors 24 . 34 be used. About this exhaust gas mass flow sensor 34 can also directly and accurately the exhaust gas mass flow in the high-pressure exhaust gas return duct 28 as well as the soot load of the exhaust gas mass flow, for example, measured over the heating time and the control unit 25 for controlling this second exhaust gas quantity and for inferring the soot load of the particulate filter 9 to provide. In contrast to the first embodiment for the arrangement of the exhaust gas mass flow sensor in the present case, the exhaust gas mass flow sensor 34 subjected to the same soot loading per unit volume of the exhaust gas as the particulate filter 9 , Accordingly, from the soot load this exhaust gas mass flow sensor 34 to a soot load of the particulate filter 9 be closed and thus a time to perform the regeneration of the particulate filter 9 be determined. This can in turn via a map in the control unit 25 carried out in the soot loading of the particulate filter 9 above the soot loading of the exhaust mass flow sensor 34 is determined as a function of the exhaust gas mass flow. In this case, in turn, conclusions can be drawn from the intake air mass flow and the recirculated exhaust gas mass flow to the discharged exhaust gas mass flow.

Incidentally, the method proceeds in the same way as already described for execution in the low pressure range, so that here, for example, the exhaust gas cooler can be regenerated if necessary, which will be necessary here less often because of the high temperatures.

It is thus possible without additional measuring means to determine the soot loading of the particulate filter and thus initiate a regeneration phase at the optimum time. By saving further measuring means incurred in comparison to known designs lower costs. Fuel is saved compared to versions where regeneration takes place at fixed intervals.

It should be understood that the scope of the present application is not limited to the described embodiments. Both the exhaust system with a pure low pressure or a pure high-pressure channel but also systems with two exhaust gas recirculation channels are suitable for the described method. Also different working exhaust gas mass flow sensors can be used. The map or the maps can be stored either in a separate control unit or in the engine control unit. Optionally, instead of a characteristic field, a corresponding algorithm can also be stored in order to reproduce the dependency of the values. The maps are to be determined for the engines in advance by tests.

Claims (10)

Method for controlling an exhaust gas system of a diesel engine, in which a sensor element is arranged, with which a soot load in the exhaust gas mass flow is determined, as a function of which a regeneration of a particulate filter is carried out, characterized in that a exhaust gas mass flow sensor ( 24 ; 34 ) is used, which is switched to too high soot load in a cleaning mode, wherein from the soot load of the exhaust gas mass flow sensor ( 24 ; 34 ) to a soot load of the particulate filter ( 9 ), what is the time to perform the regeneration of the particulate filter ( 9 ) is determined, wherein via a characteristic map the soot load of the particulate filter ( 9 ) from the soot load of the exhaust gas mass flow sensor ( 24 ; 34 ) and from the via an exhaust gas recirculation channel ( 10 ; 28 ) returned Exhaust gas mass flow as well as via an intake duct ( 22 ) of the diesel engine intake air quantity calculated exhaust gas mass flow is determined. Method for controlling an exhaust system of a diesel engine according to claim 1, characterized in that via a characteristic map the soot load of an exhaust gas cooler ( 18 . 32 ) from the soot load of the exhaust gas mass flow sensor ( 24 . 34 ) and the exhaust gas mass flow is determined and at too high soot load of the exhaust gas cooler ( 18 . 32 ) This is burned free. Method for controlling an exhaust system of a diesel engine according to one of the preceding claims, characterized in that in front of the particle filter ( 9 ) the temperature of the exhaust gas is measured, which additionally in the determination of the soot load of the particulate filter ( 9 ) is taken into account. Method for controlling an exhaust system of a diesel engine according to one of the preceding claims, characterized in that from the heating time on the soot load of the exhaust gas mass flow sensor ( 24 . 34 ) is closed. Exhaust system of a diesel engine with an exhaust line ( 4 ), in which a particulate filter ( 9 ), an exhaust gas recirculation channel ( 10 . 28 ), which from the exhaust line ( 4 ), an exhaust gas cooler ( 18 . 32 ), which in the exhaust gas recirculation channel ( 10 . 28 ), an exhaust gas mass flow sensor ( 24 . 34 ), an exhaust gas recirculation valve ( 16 . 30 ), which in the exhaust gas recirculation channel ( 10 . 28 ) is arranged, a control unit ( 25 ), which with the exhaust gas mass flow sensor ( 24 . 34 ) as well as funds ( 27 ) for initiating the regeneration phase of the particulate filter ( 9 ), characterized in that in the control unit ( 25 ) a map is stored, via which a soot load of the particulate filter ( 9 ) as a function of the soot load of the exhaust gas mass flow sensor ( 24 ; 34 ) and from the via the exhaust gas recirculation channel ( 10 ; 28 ) recirculated exhaust gas mass flow and the via the intake duct ( 22 ) of the diesel engine sucked air quantity calculated exhaust gas mass flow can be determined. Exhaust system of a diesel engine according to claim 5, characterized in that in the control unit ( 25 ) a map is stored, via which a soot load of the exhaust gas cooler ( 18 . 32 ) as a function of the soot load of the exhaust gas mass flow sensor ( 24 . 34 ) and the exhaust gas mass flow can be determined. Exhaust system of a diesel engine according to one of claims 5 or 6, characterized in that the exhaust gas mass flow sensor ( 24 . 34 ) works on the principle of hot film manometry. Exhaust system of a diesel engine according to one of claims 5 to 7, characterized in that the exhaust gas mass flow sensor ( 24 . 34 ) downstream of the exhaust gas cooler ( 18 . 32 ) in the exhaust gas recirculation channel ( 10 . 28 ) is arranged. Exhaust system of a diesel engine according to one of claims 5 to 8, characterized in that in front of the particulate filter ( 9 ) a temperature sensor ( 29 ) arranged with the control unit ( 25 ) connected is. Exhaust system of a diesel engine according to one of claims 5 to 9, characterized in that the control unit ( 25 ) with an injection valve ( 27 ), via which fuel for regeneration of the particulate filter ( 9 ) in the exhaust line ( 4 ) is injectable.

Images