EP1525386A2

EP1525386A2 - Device for determining the exhaust gas recirculation rate of an internal combustion engine

Info

Publication number: EP1525386A2
Application number: EP03764934A
Authority: EP
Inventors: Markus Amman; Nicholas Fekete; Dirk Herbstritt; Aleksandar Knezevic; Ralf MÜLLER; Carsten Plog
Original assignee: DaimlerChrysler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2002-07-23
Filing date: 2003-07-02
Publication date: 2005-04-27
Also published as: JP2005533957A; WO2004009981A3; US20050145022A1; US7100431B2; DE10233362A1; WO2004009981A2

Abstract

Disclosed is a device for determining the exhaust gas recirculation rate (AGR) of an internal combustion engine, comprising a tubular sensor unit which can be impinged upon by an exhaust gas atmosphere in a first area in an exhaust gas recirculation pipe and by an exhaust gas-fresh air atmosphere in a second area in an intake pipe of the internal combustion engine downstream from an inlet of the exhaust gas recirculation pipe. An inside of the sensor unit can be impinged upon by the exhaust gas atmosphere while an outside thereof can be impinged upon by the exhaust gas-fresh air atmosphere, or vice versa.

Description

Device for determining the exhaust gas recirculation rate of an internal combustion engine

The present invention relates to a device for determining the exhaust gas recirculation rate of an internal combustion engine according to the preamble of patent claim 1.

A known way to reduce NOX emissions in gasoline or diesel engines is exhaust gas recirculation (EGR). By adding exhaust gases to the fresh air before combustion, the temperature-dependent NOX emission is reduced in particular. Exhaust gas is usually added to an inlet line through an exhaust gas recirculation line from an exhaust line of the internal combustion engine. The recirculation rate of the exhaust gas, that is to say the amount of the exhaust gas stream proportionally mixed with the fresh air flow in the inlet line in relation to the amount of combustion air, is regulated by a controller unit by adjustment to setpoint values which are dependent on the operating point. An increase in the exhaust gas recirculation rate with the aim of further reducing the NOX emission is, for example, set a different limit depending on the operating point, namely by the soot or particle emission increasing above certain recirculation rates, the fuel consumption and the deterioration in the smooth running of the internal combustion engine. Carrying out a regulation of the exhaust gas recirculation rate requires the ongoing recording of the respective recirculation conditions when the internal combustion engine is operating.

From EP 057 46 14 AI a method for controlling the exhaust gas recirculation rate is known, which measures the pressure drop at a venturi nozzle in the exhaust gas recirculation channel to determine the actual value of the recirculated exhaust gas mass flow and determines the flow rate from the pressure difference.

A sensor unit for determining the exhaust gas recirculation rate of an internal combustion engine is known from DE 100 070 10 AI. The sensor unit is acted upon on the one hand by the exhaust gas atmosphere within the exhaust gas recirculation line, and on the other hand by the atmosphere of exhaust gas and fresh air present in the inlet line of the internal combustion engine after the exhaust gas recirculation line opens, the two gas atmospheres acting on the sensor unit being kept separate from one another.

DE 197 34 494 Cl discloses a method for operating an internal combustion engine with recirculation of exhaust gases from an exhaust gas line through an exhaust gas recirculation channel into an inlet line. In order to enable a maximum reduction in emissions through exhaust gas recirculation with the most accurate recording and control of the exhaust gas recirculation rates, it is provided that the respective oxygen content is measured in the gas streams before and after the exhaust gas recirculation channel flows into the inlet line by means of sensors and the controller unit from the measurement results the return rate is exactly determined.

To determine the EGR rate, it is necessary to respond as quickly as possible to changes in the concentration of a person get used sensor to regulate or limit the emission of pollutants with an engine control.

For use in a motor vehicle, a conventionally provided placement of a sensor on the wall of the intake manifold is a problem in that a sensor positioned in this way is not able to optimally react to rapid changes, for example a NOX concentration, because the flow rate of the gas to be detected on the wall of the elbow goes to zero. For this reason, among other things, a change in the gas composition will result in a time delay of the sensor signal, since the new or changed gas composition must flow against the entire sensor surface.

The object of the invention is to determine an EGR rate in the simplest possible manner with the greatest possible accuracy.

This object is achieved by a device with the features of patent claim 1.

By means of the measure according to the invention of using a sensor unit in the form of a tube, it is possible in a structurally simple manner to position the sensor-sensitive areas of the sensor unit at a distance from the wall areas of the respective flow lines, so that due to such an arrangement of the sensor-sensitive areas at locations of large flow rates Changes in gas concentrations compared to conventional solutions can be detected much faster. Pipe-shaped sensor units are also characterized by great mechanical stability. Conventional planar sensors were embedded gas-tight in an appropriate holder. In operation, planar sensors were exposed to thermocyclic changes in mechanical stress due to different thermal expansion coefficients of the holder and sensor material. Mechanical stresses caused thereby can lead to sensor failure due to crack formation. In the case of the EGR sensor unit, which is of tubular design according to the invention, crack formation due to thermocyclic load changes can be largely avoided. Furthermore, complex seals are not required in the case of a tubular sensor unit.

Advantageous embodiments of the device according to the invention are the subject of the subclaims.

It proves to be expedient for the sensor unit to have electrodes on the inside and / or outside using thin-film or thick-film technology. For example, by depositing a thin sensor layer on a porous carrier substrate, the manufacturing costs can be kept very low. As an example, the so-called dip-coating process from a sol is pointed out. This process is a wet chemical process for the production of ceramic thin layers that can be implemented very inexpensively. Attention is also drawn to EVD processes (electrochemical vapor deposition) and PVD processes (plasma vapor deposition).

It is preferred to provide the arrangement of the sensor unit essentially centrally in the inlet line, in particular an intake manifold. With this measure, the sensor-sensitive areas of the sensor unit can be easily positioned at locations of the greatest flow rates, which enables very precise measurements.

According to a preferred embodiment of the device according to the invention, an outside sensor sensor sensitive area of the sensor unit in the flow direction of at least one of the pressurizing atmospheres has a greater extent than an inside sensor-sensitive area. This requirement can be implemented, for example, by a cylindrical sensor unit, in which the sensor-sensitive area on the outside has a greater axial length than the sensor-sensitive area on the inside. In this way, an influence on an inside sensor-active material due to a backflow of an atmosphere acting on the outside of the sensor unit can be effectively avoided.

It has proven to be expedient to design the sensor unit on the inside and / or on the outside with an NO-selective membrane. Such a sensor-sensitive material proves to be relatively inexpensive to provide and enables precise measurements in a simple manner.

Finally, it is preferred to arrange a baffle plate in the area where the exhaust gas recirculation line opens into the inlet line. With such a plate, which meets the exhaust gas flowing into the inlet line, particularly good mixing of exhaust gas and fresh air can be achieved. The exhaust gas flowing into the inlet line expediently initially flows counter to the direction of flow of the fresh air and in the process hits the baffle plate.

The invention will now be further described on the basis of the accompanying drawing.

Show:

1 is a schematic side sectional view of a preferred embodiment of the inventive direction in which a sensor unit is applied to a carrier tube,

2 shows a schematic side view of the sensor unit according to FIG. 1 in a preferred positioning in an intake manifold, and

Fig. 3 shows a further preferred embodiment of the sensor unit according to the invention in a schematic side sectional view.

In FIG. 1, a sensor unit applied to a feed pipe 10 is denoted overall by 12. The outside of the sensor unit 12 is designed as an outer electrode 12a or first sensor, and the inside as an inner electrode 12b or second sensor. The respective electrodes are applied to a selectively ion-conducting material. An evaluation device that is operatively connected to the sensor unit or its sensors is not shown.

The membranes applied on the inside and outside are selectively conductive with respect to an ionized gas occurring in the atmospheres to be considered, as will now be explained with reference to FIG. 2.

In Figure 2, a manifold pipe, in which the sensor unit according to the invention is arranged, is designated by 14. The arrow P 1 indicates that fresh air (from the left in the illustration in FIG. 2) enters the manifold tube 14. An exhaust gas recirculation line is designated 16, via which exhaust gases of an engine (not shown) can be returned to the intake tract or the manifold pipe 14. It can be seen that the recirculated exhaust gas (illustrated by arrow P3) via a first feed line 17a and a second feed line line 17b is introduced into the manifold tube 14. The exhaust gas flowing in via the feed line 17b flows (in a mouth region 17c) against a baffle plate 18 and mixes with the fresh air flowing in here.

At the end of the supply line 17a is the supply pipe 10, already described with reference to FIG. 1, to which the sensor unit 12 is applied.

It can be seen directly from FIG. 2 that the sensor unit 12 is acted upon on the outside by a fresh air exhaust gas atmosphere and on the inside by an exhaust gas atmosphere.

It should be noted that the sensor device according to the invention can use any type of sensor. In addition to the aforementioned sensors based on a selective ion conductor, reference should be made to resistive oxygen sensors, amperometric oxygen sensors, amperometric NOX sensors and other gas sensors which are selective for a component present in the exhaust gas.

As can also be seen from FIG. 2, the sensor unit 12 is arranged essentially centrally in the elbow pipe 14. As a result of this measure, the outside of the sensor is subjected to the maximum flow rate of the fresh air exhaust gas flow, which effectively reduces the response time of the sensor unit.

A preferred embodiment of the sensor unit according to the invention is finally described with reference to FIG. 3. One recognizes here the inside electrode 12b coated with an ion-selective membrane and the corresponding outside electrode 12a, which (for example in the case of a Arrangement, as described in Figure 2) on the inside by an exhaust gas atmosphere and on the outside by an exhaust gas fresh air atmosphere. In order to avoid that a backflow of the exhaust gas fresh air atmosphere contrary to the main flow direction (indicated here by arrow P4) back into the interior of the sensor unit leads to a falsification of the measurement result, the sensor-sensitive area of the inner electrode 12b is axial with respect to the outer electrode 12a, i.e. in Main direction of extension of the sensor unit 12 or in the flow direction P4, shortened. This ensures that the fresh air / exhaust gas mixture flowing back into the interior of the sensor unit does not influence the measurement result.

Claims

claims

1. Device for determining an exhaust gas recirculation rate (EGR) of an internal combustion engine, with a sensor unit (12), which in a first area with an exhaust gas atmosphere in an exhaust gas recirculation line (16, 17b), and in a second area with an exhaust gas fresh air atmosphere in an inlet line (14) of the internal combustion engine downstream of an opening (17c) of the exhaust gas recirculation line

(16) can be acted on, characterized in that the sensor unit (12) is tubular, with an inside (12b) of the sensor unit (12) with the exhaust gas atmosphere, and an outside (12a) of the sensor unit (12) with the exhaust gas fresh air Atmosphere can be acted upon or vice versa.

2. The device as claimed in claim 1, that the sensor unit has electrodes on the inside and / or outside which are produced using a thin-film or thick-film technique.

3. Device according to one of claims 1 or 2, characterized by an arrangement of the sensor unit (12) substantially centrally in the inlet line (14), in particular in an intake manifold tube.

4. Device according to one of the preceding claims, d a d u r c h g e k e n e z e i c h n e t that an externally formed sensor-sensitive area of the sensor unit in the flow direction of at least one of the pressurized atmospheres has a greater extent than an internally trained sensor-sensitive area.

5. Device according to one of the preceding claims, that the sensor unit (12) is coated on the inside and / or outside with an NO-selective membrane.

6. Device according to one of the preceding claims, g e k e n n z e i c h n e t d u r c h, in the region of the mouth (17c) of the exhaust gas recirculation line (17b) in the inlet line (14) provided baffle plate (18).