DE102014223555A1 - Device with a sensor for measuring an NH3 concentration - Google Patents

Abstract

The invention relates to an apparatus (1) which can be used for experimental and research areas for measuring an NH 3 concentration in an SCR exhaust gas purification. The device (1) is used to arrange a sensor (3) in the exhaust gas flow of an exhaust end pipe (2) and is equipped for this purpose with a tubular connecting element (4) on which the sensor (3) is mounted. The fixing of the connecting element (4) to the exhaust end pipe (2) by means of a sealing against a peripheral portion (8) of the exhaust end pipe (2) can be applied coupling element (9) made of silicone, which due to its elastic and flexible material properties a simple and tool-free fixation to the Exhaust tailpipe (2) allowed.

Description

The invention relates to a device equipped with at least one sensor for measuring an NH ₃ concentration in an exhaust system equipped with an SCR catalytic converter on an exhaust gas end pipe of a motor vehicle.

Over the past few years, emissions standards for internal combustion engines have become increasingly stringent. The statutory maximum levels of NOx and particulates from internal combustion engines are so low that in many cases emission levels can not be met with improved combustion technologies. Therefore, the use of exhaust aftertreatment to eliminate the toxins and unburned fuel components produced during the combustion of fuel is indispensable.

The undesirable substances contained in the exhaust gas of a motor vehicle can be divided into two groups. For example, the term primary emission refers to chemical substances which are produced directly by the combustion process of the fuel in the engine and are already present in the so-called raw emission before passing through exhaust gas purification devices, for example unburned hydrocarbons, NOx, particles. As a secondary emission such chemical substances are referred to, which may be formed as by-products in the emission control system, such as NH ₃ or N ₂ O.

The undesirable gases carbon monoxide and hydrocarbon can be easily rendered harmless from the lean exhaust gas by oxidation on a suitable oxidation catalyst. The reduction of nitrogen oxides to nitrogen is much more difficult because of the high oxygen content in the exhaust gas of a lean-burn internal combustion engine. For the removal of particle emissions, the use of special diesel particulate filters has been unavoidable so far.

Known methods for removing nitrogen oxides from exhaust gases are on the one hand a method using nitrogen storage catalysts (NOx Storage Catalyst - NSC) and on the other hand, selective catalytic reduction (SCR) method using ammonia on a suitable catalyst, abbreviated SCR- Catalyst.

For example, this describes WO 99/39809 A1 an exhaust gas purification system in which an oxidation catalyst for the oxidation of NOx, a particulate filter, a metering device for a reducing agent and an SCR catalyst follow one another.

Depending on the engine design and design of the exhaust system, a distinction is made between "active" and "passive" SCR methods, with "passive" SCR processes in the exhaust system using specifically generated secondary ammonia emissions as reducing agents for the reduction of nitrogen oxides.

Such "passive" SCR processes have the disadvantage that one of their essential components is the provision of rich, ie oxygen-poor exhaust conditions, which are generally required for the in-situ generation of ammonia as a reducing agent.

In contrast, in "active" SCR process, the reducing agent is metered from an entrained additional tank by means of an injection nozzle in the exhaust line. As such, in addition to ammonia, an easily ammonia-decomposable compound such as urea or ammonium carbamate may also be used. Ammonia must be supplied to the exhaust gas at least in the stoichiometric ratio to the nitrogen oxides.

The exact dosage of ammonia causes great difficulties because of the highly fluctuating operating conditions of motor vehicles. This sometimes leads to significant ammonia breakthroughs after the SCR catalyst.

The DE 10 2010 029 740 A1 relates to a method of monitoring an SCR catalyst in which the NH ₃ storage capability of the SCR catalyst is monitored. The method is based on continuously detecting and evaluating the measured NOx conversion during the overdosage phase to detect the formation of NH ₃ slip. Thus, a corresponding signal can be generated selectively even at very low NH ₃ concentrations downstream of the SCR catalyst. To detect NH ₃ slippage indicative of the transition from the overdosage phase to the underdosage phase, a variable characterizing NO x conversion is continuously detected during the overdosage phase and it is concluded, with a drop in NO x conversion, that NH ₃ slippage is present , This allows a very fast and early detection of NH ₃ slippage, so that the occurring NH ₃ emissions can be kept as small as possible. This is particularly advantageous in view of the harmful effects of released ammonia.

The US 2010/0024393 A1 relates to a method of controlling NOx with an SCR catalyst using ammonia storage and slip control. The NH ₃ , which flows into the SCR catalyst is, by means of an NH ₃ sensor detected at a Abgasendrohrauslass. The NH ₃ sensor at the exhaust tailpipe outlet aids in the measurement and control of exhaust tailpipe NH ₃ slip by providing information about exhaust tailpipe NH ₃ slip. For example, the urea dosing rate is controlled on this basis.

In addition, from the WO 2014/066214 A1 nor an exhaust gas monitoring device of an SCR catalyst known, in particular sensors for pressure and temperature measurement and the detection of NOx data has.

The aim of applying an SCR dosing strategy is to set an NH ₃ storage level under given boundary conditions for an optimum NO x conversion rate without NH ₃ slip after the catalyst.

Typically, the application of the SCR dosing strategy is performed on a test bench for an engine exhaust system configuration. The transmission of the measurements thus determined to the operation of the motor vehicle under real driving conditions is often only possible to a limited extent. Therefore, it makes sense to carry out a measurement of variables such as NOx conversion or NH ₃ slip immediately during operation of the motor vehicle.

According to the current state of the art, the measuring sensors required for this purpose are integrated into the existing exhaust system, in particular by introducing openings for the measuring sensors.

A disadvantage is the associated effort, which is mainly caused by the at least partial disassembly of the exhaust system. Furthermore, a considerable additional effort is also incurred in a later dismantling, so often dispensed with the expansion of the sensors. In addition, the introduced openings can close again only with great effort.

Against this background, the invention has the object to provide a device for measuring an NH ₃ concentration, which allows a measurement under real operating conditions without a substantial interference with the exhaust system of the motor vehicle. In particular, the device should be fast and flexible, especially for different vehicles, ready for use and also can be removed without permanent changes of the motor vehicle.

This object is achieved with a device according to the features of claim 1. The subclaims relate to particularly expedient developments of the invention.

The sensor of the device according to the invention is in particular a sensor for measuring an NH ₃ concentration.

According to the invention, therefore, the device has a tubular connecting element for releasably fixing to the exhaust gas end pipe by means of a sealing element engageable against a peripheral portion of the exhaust end pipe coupling element, wherein the connecting element is equipped with a support for the sensor such that the sensor extends into the free flow cross-section of the connecting element, wherein the connection element has an exhaust gas outlet behind the sensor in the flow direction of the exhaust gas. As a result, a particularly tool-free installation of the sensor on the exhaust pipe end without changing the existing exhaust system is possible in a surprisingly simple manner by the device is arranged in extension of the exhaust pipe end. By the exhaust system during the measurement without interference with the exhaust stream, in particular without a caused by the sensor impairment of the exhaust gas flow within the pipeline is ready, unwanted and the measurement result falsifying interactions between the sensor and the exhaust system, in particular the SCR catalyst avoided , In addition, the device of the invention allows universal use without special adjustments and can be removed at any time without residue.

By the coupling element is equipped with a sealing element for gas-tight contact with the exhaust tailpipe, unwanted flow losses are reliably avoided. In this case, the sealing element may in particular be designed such that only small flow losses occur in the transition region between the exhaust gas end pipe and the coupling element and the free flow passage is not reduced.

For this purpose, preferably, the sealing element has limited elastic and / or flexible material properties, so that a reliable seal is achieved without an additional fixative. For example, sealing elements made of silicone, which at the same time have good temperature resistance, are suitable for such purposes. The sealing element can be designed as a spout, sleeve or even sections as a bellows.

In addition, by the sealing element also has a sufficient dimensional stability, so at the same time the holding function for the coupling element can be realized by the sealing element. In addition, the connection element by means of such a flexible or elastic seal on Almost any Abgasendrohrformen, especially so also deviating from the circular shape outlet openings are easily adapted. For example, the sealing element can also be attached to oval exhaust tailpipes without changes.

The coupling element could for this purpose be introduced into the outlet-side opening of the exhaust end pipe. In contrast, an embodiment of the method in which the coupling element can be positioned by means of a fixing means in a force-fitting manner on an outer circumferential section of the exhaust gas end pipe is particularly practical, so that the free outlet cross section of the exhaust gas end pipe is not restricted by the device.

In another, also particularly useful embodiment of the invention, the carrier has a receptacle for particular radial fixation of the sensor, wherein the radial position, for example by means of a thread of the carrier can be adjusted so that the sensor into the region of a fluid axis or a geometric center of the outlet opening of the exhaust end pipe extends.

According to a further particularly expedient embodiment of the invention, the at least one sensor with a particular vertical orientation is fixed in a hanging arrangement on the carrier, so that it is largely protected from environmental influences, in particular liquid accumulations, arranged in the connection element.

In addition, it proves to be particularly practical if at least one sensor is interchangeable fixed to the carrier and therefore can be easily solved in a possible damage or for control purposes of the carrier and thus of the connection element. For this purpose, for example, a carrier with an internal thread, in which the sensor can be screwed with an external thread, wherein at the same time, the axial position and the angular position with respect to the flow direction can be variably adjusted.

In this case, a particularly reliable fixation and at the same time an improved sealing effect can be achieved in that the fixing means comprises at least one pipe clamp. In this way, a predetermined clamping force can be adjusted. In addition, such clamps are also suitable for fixing to non-rotationally symmetrical exhaust tailpipes.

The connecting element could be realized in a simple embodiment by a pipe section. Moreover, an embodiment in which the coupling element has a first line cross-section adapted to the exhaust end pipe and a second line cross-section for the connection element that has been widened with respect to the first line cross-section is particularly useful. A transition region with a continuous region exists between the first line cross-section and the second line cross-section Cross-sectional extension is provided. As a result, the coupling element is also suitable for large outlet cross sections of an exhaust end pipe, for example in commercial vehicles. In addition, in the region of the second line cross section, the flow velocity is reduced, which leads to an improvement in the measured value acquisition. An impairment or error influences on the measurement due to the cross-sectional widening are excluded, however, because the concentration is measured by means of the sensor.

Furthermore, it is advantageous if the sensor is designed for continuous, cyclical and / or discontinuous measurement in order to be able to reliably evaluate the course of the measured value detection in conjunction with a multiplicity of operating parameters of the internal combustion engine.

The device preferably has an interface for wireless data transmission of acquired measured values. This makes it possible to dispense with the laying of signal lines for the transmission of the detected measured values to a control unit. Rather, the device is immediately ready for operation after attachment to the exhaust pipe end, with optionally an electrical energy supply in the form of an energy storage device is attached to the connection element.

The invention allows numerous embodiments. To further clarify its basic principle, one of them is shown in the drawing and will be described below. This shows an exploded view of a deployable especially in experimental and research field device 1 for measuring an NH ₃ concentration in an exhaust system equipped with an SCR catalytic converter, not shown, on an exhaust gas end pipe 2 a motor vehicle not shown. The device 1 serves to arrange a sensor designed as a probe 3 in the exhaust stream of the exhaust end pipe 2 and is for this purpose with a tubular connecting element 4 fitted. At the connection element 4 is a carrier corresponding to an aperture 5 with an internal thread 6 on an upper side of the connecting element 4 fixed in which the sensor 3 with an external thread 7 detachable and adjustable in the radial direction and in terms of its angular position can be fixed. The fixation of the connection element 4 to the tailpipe 2 takes place by means of a sealing against a peripheral portion 8th the exhaust end pipe 2 engageable coupling element 9 Made of silicone, which due to its elastic and flexible material properties a simple and tool-free fixation on the exhaust pipe 2 allowed. In addition, two fixing clamps are used 10 the non-positive attachment of the coupling element 9 on the exhaust pipe 2 on the one hand and the connecting element 4 on the other hand. In this case, the free flow cross-section of the connection element 4 on the largest in practice flow cross-section of commercial exhaust tailpipes 2 matched, so that the coupling element 9 one to the exhaust pipe 2 adapted first line cross-section 11 and one opposite to the first line cross section 11 extended second cable cross-section 12 for the connection element 4 having. For data transmission of acquired measured values is the sensor 3 with a line 13 connected to a control unit, not shown, in which the detected measured values are evaluated.

LIST OF REFERENCE NUMBERS

1

 contraption

2

 tailpipe

3

 sensor

4

 connecting element

5

 carrier

6

 inner thread

7

 external thread

8th

 peripheral portion

9

 coupling member

10

 fixer

11

 Wire Gauge

12

 Wire Gauge

13

 management

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

• WO 99/39809 A1 [0006]
• DE 102010029740 A1 [0011]
• US 2010/0024393 A1 [0012]
• WO 2014/066214 A1 [0013]

Claims (10)

One with at least one sensor ( 3 ) equipped device ( 1 ) for measuring an NH ₃ concentration in an exhaust system equipped with an SCR catalytic converter on an exhaust gas end pipe ( 2 ) of a motor vehicle, characterized in that the device ( 1 ) a tubular connecting element ( 4 ) for releasably fixing to the exhaust gas end pipe ( 2 ) by means of a sealing against a peripheral portion ( 8th ) of the exhaust end pipe ( 2 ) engageable coupling element ( 9 ), wherein the connecting element ( 4 ) with a carrier ( 5 ) for the sensor ( 3 ) is equipped such that the sensor ( 3 ) in the free flow cross-section of the connecting element ( 4 ). Contraption ( 1 ) according to claim 1, characterized in that the coupling element ( 9 ) with a sealing element for gas-tight connection to the exhaust end pipe ( 2 ) Is provided. Contraption ( 1 ) according to claim 2, characterized in that the sealing element has at least partially elastic and / or flexible material properties. Contraption ( 1 ) according to at least one of the preceding claims, characterized in that the coupling element ( 9 ) by means of a fixing agent ( 10 ) frictionally connected to the outer peripheral portion ( 8th ) of the exhaust end pipe ( 2 ) is positionable. Contraption ( 1 ) according to at least one of the preceding claims, characterized in that the carrier ( 5 ) a receptacle for fixing the sensor ( 3 ) having. Contraption ( 1 ) according to at least one of the preceding claims, characterized in that at least one sensor ( 3 ) with a particular vertical orientation in a suspended arrangement on the support ( 5 ) is fixed. Contraption ( 1 ) according to at least one of the preceding claims, characterized in that at least one sensor ( 3 ) exchangeable on the carrier ( 5 ) is fixed. Contraption ( 1 ) according to at least one of the preceding claims, characterized in that the fixing agent ( 10 ) comprises at least one pipe clamp. Contraption ( 1 ) according to at least one of the preceding claims, characterized in that the coupling element ( 9 ) a first, to the exhaust pipe end ( 2 ) customizable cable cross-section ( 11 ) and one opposite the first line cross-section ( 11 ) extended second line cross-section ( 12 ) for the connection element ( 4 ) having. Contraption ( 1 ) according to at least one of the preceding claims, characterized in that the device ( 1 ) has an interface for wireless data transmission of acquired measured values.

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