WO2020099045A1

WO2020099045A1 - Particulate sensor with a test-gas flow propelled by ions

Info

Publication number: WO2020099045A1
Application number: PCT/EP2019/077703
Authority: WO
Inventors: Simon Schneider; Radoslav Rusanov; Oliver Krayl
Original assignee: Robert Bosch Gmbh
Priority date: 2018-11-16
Filing date: 2019-10-14
Publication date: 2020-05-22
Also published as: DE102018219726A1; EP3881053A1

Abstract

Proposed is a particulate sensor (12) comprising: a measuring chamber (30) having at least one test-gas inlet opening (32) and at least one test gas outlet opening (34), both the entire inlet cross-section of the test-gas inlet opening (32) and the entire outlet cross-section of the test-gas outlet opening (34) being smaller than a flow cross-section of the measuring chamber (30) perpendicular to the through-flow of said measuring chamber (30); a corona-discharge electrode (38) and a counter-electrode (40); and a device used to generate an electrical field between the corona-discharge electrode (38) and the counter-electrode (40), said field running from the corona-discharge electrode (38) to the counter-electrode (40) and generating a corona discharge. The particulate sensor (12) is characterised in that, other than the test-gas inlet opening (32) and the test-gas outlet opening (34), the measuring chamber (30) has no additional opening allowing the inflow or outflow of gas.

Description

description

title

Particle sensor with a sample gas flow driven by ions

State of the art

The present invention relates to a particle sensor according to the preamble of claim 1. Such a particle sensor is known both from EP 2 247 939 B1 and from EP 2 51 1 690 B1 and has a measuring chamber with at least one sample gas inlet opening and at least one

Sample gas outlet opening, wherein both the entire inlet cross section of the sample gas inlet opening and the entire outlet cross section of the

The sample gas outlet opening is smaller than a flow cross section lying perpendicular to the flow of measurement gas through the measurement chamber

Measuring chamber. In addition, such a sensor has a corona discharge electrode arranged in the measuring chamber and a counter electrode arranged in the measuring chamber and a device with which an electric field prevailing between the corona discharge electrode and the counter electrode can be generated which is directed from the corona discharge electrode to the counter electrode and which generates a corona discharge.

The known particle sensors work with a measuring principle, which is based on an electrical charge of the particles to be detected and by measuring the electrical charge discharged from the sensor with the particles. The particles are charged in an ionic current, which is generated by a corona discharge.

In the sensor known per se, in a flowing fluid

floating particles electrically charged. The particles are charged in an ionic current, which is generated by a corona discharge. A corona discharge is an electrical discharge at first

non-conductive medium in which free charge carriers are generated by ionizing components of the medium. The particles are charged by adhering ions. The charged particles are carried out of the particle sensor by the flowing fluid and take their electrical charge with them (escaping current). The charge is usually measured by measuring the mirror charge of the previously charged particles on a measuring electrode (Influenz) or by measuring the charge missing by leaving the previously charged particles, which is tracked on a virtual GND electrode to prevent charging of this electrode (escaping current). In both cases, the ions from the corona discharge, which do not adhere to a particle, are preferably filtered out beforehand by an electric field of an ion-trapping electrode. In the case of the influence sensor, the corona current is preferably generated in the form of a pulse train. The principle of evaluating an "escaping current" is explained in EP 2 824 453 A1.

EP 2 247 939 A1 describes one that works with an ejector principle

Particle sensor known. Compressed air is blown into the particle sensor from a nozzle, and exhaust gas serving as measuring gas is drawn in via the Venturi effect. The corona discharge takes place in an "ion generation section".

The ions generated in this way are blown into a "electric charge section" via a nozzle with pressurized air, to which sample gas is fed via a further inlet.

By using compressed air, the advantage of a big one

Measured gas flow through the particle sensor is achieved, which is largely independent of the flow velocity of the exhaust gas prevailing outside the particle sensor.

An ejector principle is used to guide the exhaust gas flow through the sensor in a controlled manner. For this purpose, compressed air is blown into the sensor from a nozzle and exhaust gas is sucked in via the Venturi effect. The corona burns in the compressed air chamber and ions get into the exhaust gas via the air flow. By using compressed air, a high flow through the sensor can advantageously be achieved, regardless of the external exhaust gas velocity in the exhaust pipe, as a result of which sufficiently high signal levels can also be achieved even with a low particle concentration. The disadvantage of this prior art is the use of compressed air, which has to be made available in a particularly complex manner. This applies analogously to the object of EP 2 511 690 B1, which also works with compressed air injection. Especially in particle sensors that are operated without a controlled sample gas supply, eg without a compressed air ejector pump, the sample gas volume flow in the sensor depends on external parameters. When used as

Exhaust gas sensor for internal combustion engines is the sample gas volume flow (here the exhaust gas volume flow) e.g. depending on the crank angle, the engine speed, the load, the condition of the particle filter or the temperature. In the extreme case of very low exhaust gas volume flows in the exhaust pipe, the flow through the sensor can dry up completely, whereby the sensor function is interrupted.

Disclosure of the invention

The present invention differs from this prior art by the characterizing features of claim 1, according to which the

Apart from the measuring gas inlet opening and the measuring gas outlet opening, the measuring chamber does not have any further opening allowing an inflow or outflow of gas. The particle sensor according to the invention in particular has no opening serving for the supply of compressed air.

By means of the invention, a sample gas flow through the, which is driven or at least supported solely by the movement of the ions, is achieved

Measuring chamber generated. It is driven by shocks from

Sample gas molecules with the ions that drift in the electrical field between the corona discharge electrode and the counter electrode to the counter electrode, which is also referred to as the ion wind. The invention uses this ion wind to actively drive measurement gas through the sensor. The sensor function is thus maintained with sufficient sensitivity even when there is no sample gas movement without such an ion wind. The invention

Particle sensor generates a signal that is compared to signals from others

Particle sensors, which work without such an ion wind and without a differently driven sample gas stream, have a lower dependence on the speed of the sample gas stream passing the particle sensor on the outside.

In particular when used for particle detection in the exhaust gas of internal combustion engines, in which the exhaust gas volume flow is subject to strong fluctuations, this results in an adequate measurement sensitivity even with small exhaust gas volume flows. Unwanted interruptions in the Sensor function with small exhaust gas flows in the exhaust pipe can be largely avoided. There is also an expansion of the measuring range, especially for small concentrations. The lower detection limit is advantageously shifted down. There are also cost advantages since, for example, no pressurized gas sources such as pumps are required to compress the sample gas or air.

A preferred embodiment is characterized in that the corona discharge electrode is arranged closer to the measurement gas inlet opening than the counter electrode and that the counter electrode is closer to the

Sample gas outlet opening is arranged as the corona discharge electrode.

It is also preferred that the particle sensor has an outer protective tube and an inner protective tube arranged inside the outer protective tube, the outer cross section of which is so much smaller than an inner cross section of the outer protective tube that a flow cross section is present between the inner protective tube and the outer protective tube. that the inner protective tube projects beyond the outer protective tube at a first end, and that the outer protective tube projects beyond the inner protective tube at an end opposite the first end, and that the measuring chamber is arranged at the second end outside the inner protective tube.

It is further preferred that the measuring chamber is an interior of a metallic housing which has a first end and a second end, the at least one measuring gas inlet opening being closer to the first end than the measuring gas outlet opening and the at least one measuring gas outlet opening being closer to the second end than the measuring gas inlet opening and that a dielectric carrier element is arranged in the measuring chamber, to which the corona discharge electrode is arranged adhering and wherein the housing has at least one indentation serving as counter electrode, which is closer to the second end than the corona Discharge electrode.

A further preferred embodiment is characterized in that the indentation is a constriction encircling the housing.

It is also preferred that the dielectric carrier element consists of ceramic. A further preferred embodiment is characterized in that the measuring chamber is an interior of a ceramic housing which has a first end and a second end, the at least one

Sample gas inlet opening is closer to the first end than that

Measuring gas outlet opening and wherein the at least one measuring gas outlet opening is closer to the second end than the measuring gas inlet opening and that a dielectric carrier element is arranged in the measuring chamber.

It is also preferred that the first end is covered by a porous cover.

A preferred embodiment is characterized in that a counter electrode is arranged adhering to an inner wall of the ceramic housing.

It is also preferred that at least one further electrode is arranged adhering to an inner wall of the ceramic housing.

Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the description below. The same reference numerals in different figures designate the same or at least functionally comparable elements. When describing individual figures, reference may also be made to elements from other figures. In each case in schematic form:

Figure 1 shows a first embodiment of an inventive

Particle sensor;

FIG. 2 shows an electrode arrangement to clarify the measuring principle;

Figure 3 shows another embodiment of an inventive

Particle sensor; and

Figure 4 shows another embodiment of an inventive

Particle sensor. 1 shows a particle sensor unit 10, the one

Particle sensor 12, which is connected via a cable harness 14 to a control device 16 of the particle sensor unit 10.

The particle sensor 12 protrudes into an exhaust pipe 18, which carries exhaust gas as the measurement gas 20, and has a protruding into the flow of the measurement gas 20

Pipe arrangement of an inner metallic tube 22 and an outer metallic tube 24. Such a tube arrangement is used in a preferred embodiment of the invention, but is not an essential element of the invention.

The two metallic tubes 22, 24 preferably have a general one

Cylindrical shape or prism shape. The base areas of the cylindrical shapes are preferably circular, elliptical or polygonal. The cylinders are preferably arranged coaxially, the axes of the cylinders lying transversely to the flow direction of the measurement gas 20 which flows in the exhaust pipe 18 outside the pipe arrangement. The inner metallic tube 22 protrudes beyond the outer metallic tube 24 into the flowing measurement gas 20 at a first end 26 of the tube arrangement facing away from the installation opening in the exhaust gas tube 18. The outer metallic tube 24 projects beyond the inner metallic tube 22 at a second end 28 of the two metallic tubes 22, 24 facing the installation opening in the exhaust pipe 18. The inside diameter of the outer metallic tube 24 is preferably so much larger than the outer diameter of the inner one

metallic tube 22 that there is a first flow cross-section or a gap 5 between the two metallic tubes 22, 24. The clear width W of the inner metallic tube 22 forms a second flow cross section.

The result of this geometry is that measurement gas 20 is above the first

Flow cross section enters the tube arrangement at the first end 26, then changes its direction at the second end 28 of the tube arrangement, enters the inner metallic tube 22 and is sucked out of the measuring gas 20 flowing past. This results in a laminar flow in the inner metallic tube 22. This tube arrangement of tubes 22, 24 is with a preferred embodiment of an inventive

The particle sensor is fastened transversely to the flow direction of the measurement gas 20 in the exhaust pipe 18 and protrudes laterally into the flow of the measurement gas 20, the interior of the metallic pipes 22, 24 is preferably sealed from the surroundings of the exhaust pipe 18. The attachment is preferably carried out with a screw connection.

The particle sensor 12 has a measuring chamber 30 which has at least one measuring gas inlet opening 32 and at least one measuring gas outlet opening 34, both the entire inlet cross section of the

Sample gas inlet opening 32 and the total outlet cross section of the sample gas outlet opening 34 are each smaller than one perpendicular to the

Flow of measuring gas 33 lying through measuring gas 20

Flow cross section 36 of the measuring chamber 30. A corona discharge electrode 38 and a counter electrode 40 are arranged in the measuring chamber 30. The control device 16 has a device with which an electrical field 42 prevailing between the corona discharge electrode 38 and the counter electrode 40 can be generated, which is directed from the corona discharge electrode 38 to the counter electrode 40 and that generates a corona discharge 44. The device is a voltage source that generates a high voltage sufficient to generate the corona discharge. The measuring chamber 30 has, apart from the measuring gas inlet opening 32 and the measuring gas outlet opening 34, no further opening allowing an inflow or outflow of gas. The corona discharge electrode 38 is arranged closer to the measurement gas inlet opening 32 than the counter electrode 40, and the counter electrode 40 is arranged closer to the measurement gas outlet opening 34 than the corona discharge electrode 38. The measuring chamber 30 is arranged at the second end 28 outside the inner metallic tube 22. In the example shown, the electrodes are arranged adhering to a ceramic, planar carrier element 50. In the example shown, an ion-trapping electrode 46 and a measuring electrode 48 are also arranged adhering to the ceramic carrier element 50. The counter electrode 40 can also be arranged on a wall of the measuring chamber 30. The wall of the measuring chamber 30 can consist entirely of metal and thus serve as the counter electrode 40.

FIG. 2 shows a cross section of a ceramic carrier element 34 of a particle sensor, which carries various electrodes, and is used for

Illustration of the working principle of a planar particle sensor working with a corona discharge 44. A corona discharge electrode 38, a ground electrode as counter electrode 40 and an ion trap electrode 46 are arranged on the electrically insulating ceramic carrier element 50. In the exemplary embodiment shown, the ceramic carrier element 50 additionally carries a measuring electrode 48, which serves as a particle charge detection electrode, but which is not absolutely necessary.

The ceramic carrier element 50 is arranged with its longitudinal direction parallel to the direction of the measuring gas 20 flowing there in the measuring chamber 30 of FIG. 1. Via this arrangement of corona discharge electrode 38, counter electrode 40, ion trap electrode 46 and possibly also measuring electrode 48, measuring gas 20 flows with the one indicated by the direction of the arrow

Flow direction. The corona discharge 44 takes place between the corona discharge electrode 38 and the counter electrode 40. The corona discharge 44 is traversed by measuring gas 20 loaded with particles. The measuring gas 20 present there is partially ionized in the corona discharge 44. The particles then take up ions and thus an electrical charge.

The voltage required to generate the corona discharge 44 between the corona discharge electrode 38 and the counter electrode 40 is generated by a high-voltage source integrated in the control device 16.

The ion trap electrode 46 traps ions that do not adhere to the heavier and therefore more inert particles transported with the measurement gas 20. In the case of a metallic design or coating, the wall of the measuring chamber 30 can also serve as a counter-electrode for the ion-trapping electrode 46. The measurement of the electrical charge carried with the soot particles either takes place by means of charge influence on the measuring electrode 48 serving as the particle charge detection electrode, or it is carried out using the "escaping currenf" principle.

In the following, reference is again made to FIG. 1. In the

Flow through the two protective tubes changes the measurement gas flow at the second end 28. The measuring gas inlet opening of the measuring chamber 30 is arranged there. A portion of the measurement gas 20 is diverted there into the measurement chamber 30 by the suction effect of the ion wind. The counter electrode 40 is placed in this redirected part of the flow of the measurement gas 20 downstream of the corona discharge electrode 38, so that the electric field 42 and thus also the ion wind from the sample gas inlet opening 32 to

Measuring gas outlet opening 34 has direction. This creates a pressure drop in the measuring chamber 30, which is associated with the above-mentioned suction effect. Further downstream are the ion-trapping electrode 46 and the possibly existing measuring electrode 48 and the measuring gas outlet opening 34, via which the measuring gas 20 flows out of the measuring chamber 30 and, for example, re-enters an exhaust gas flow in a main exhaust pipe.

Would, e.g. due to very low sample gas volume flows in the vicinity of the particle sensor 12, a sample gas flow through the metallic tubes 22, 24 does not arise, so the vacuum created by the ion wind would still suck in sample gas and conduct it into the measuring chamber 30, so that the

Sensor function would be guaranteed.

Figure 3 shows a further embodiment of an inventive

Particle sensor 12. A metallic housing 52 is also provided

Sample gas inlet openings 32 used at the first end 26, which is at ground potential, and thus serves as a counter-electrode for the corona discharge electrode ion-capture electrodes 46. The alignment of the ion wind is shaped by the alignment of the corona discharge electrode (e.g. with a needle-shaped tip) and the shape of the metallic housing 52 such that the ion flow of the corona discharge sucks in sample gas through the sample gas inlet openings. Subsequently, the charging of the particles, the filtering of the excess ions and the detection of the charged particles as well as the discharge of the measuring gas from the measuring gas outlet openings 34 take place. It would also be conceivable for a further protective tube to enclose the metallic housing 52 cylindrically at a certain radial distance. This prevents the development of an undesirable back pressure for the sample gas flow driven by the ion wind.

The corona discharge electrode 38 and the ion trap electrode 46 are preferably arranged adhering to a dielectric, preferably ceramic, carrier element 50.

The measuring chamber 30 is here an interior of the metallic housing 52, which has a first end 26 and a second end 28. The at least one measurement gas inlet opening 32 is closer to the first end 26 than that Sample gas outlet opening 34. The at least one sample gas outlet opening 34 is closer to the second end 28 than the sample gas inlet opening 32. The housing 52 has at least one indentation 54 serving as a counter-electrode, which is closer to the second end 28 than the corona discharge - Electrode 38. The indentation 54 is preferably a constriction encircling the housing. At the second end 28, the housing 52 is closed by a seal 56 arranged between the carrier element 50 and the housing 52, so that gas exchange between the measuring chamber 30 and an external environment of the housing only through the sample gas inlet opening (s) and the sample gas outlet opening (s). through it.

FIG. 4 shows a further exemplary embodiment of a particle sensor 12 according to the invention. In comparison to the subject of FIG. 3, a ceramic housing 60 is used here. Otherwise, the structure and operation are very similar to the subject of Figure 3. The ceramic housing can e.g. by means of ceramic injection molding (CIM) with in-mold labeling.

The measuring chamber 30 is an interior of the ceramic housing 60. The ceramic housing 60 has a first end 26 and a second end 28. The first end 26 is covered by a porous cover 62 which, owing to its permeability to the measurement gas, forms a measurement gas inlet opening 32. Due to the non-permeable components of the cover 62, the total inlet cross section of the measurement gas inlet opening is smaller than a flow cross section of the measurement chamber 30 lying perpendicular to the flow of measurement gas through the measurement chamber 30. The measurement gas inlet opening 32 is also closer to the first end 26 than the measurement gas outlet opening 34, and that at least one measuring gas outlet opening 34 is closer to the second end 28 than the measuring gas inlet opening 32. In the measuring chamber 30 there is a dielectric one

Carrier element 50 is arranged, which carries at least the corona discharge electrode 38 and the ion trapping electrode 46. Counter electrodes 40 are arranged adhering to an inner wall of the ceramic housing 60.

It would also be conceivable to place a measuring electrode on the inside of the ceramic housing 60 downstream of a counter electrode of the ion-trapping electrode, so that only on the ceramic carrier element 50 High-voltage electrodes are located and only the low-voltage electrodes are located on the inner wall of the ceramic housing 60.

This invention speaks of particles and exhaust gas as the measurement gas. This is done only as an example for simplification or illustration. The

Invention always relates generally to particles, with particles

Floating particles are meant which can be solid or liquid (droplets) and which float in a fluid, in particular a gas.

Claims

Expectations

1. Particle sensor (12) with a measuring chamber (30), the at least one

Has sample gas inlet opening (32) and at least one sample gas outlet opening (34), both the entire inlet cross section of the

Sample gas inlet opening (32) and the total outlet cross section of the sample gas outlet opening (34) are each smaller than a perpendicular to the

Flow of measuring gas (20) through the measuring chamber (30)

Flow cross section of the measuring chamber (30), and with one in the

Measuring chamber (30) arranged corona discharge electrode (38) and a counter electrode (40) arranged in the measuring chamber (30), and with a device with which a between the corona discharge electrode (38) and the counter -Electrode (40) prevailing electric field can be generated, which is directed from the corona discharge electrode (38) to the counter electrode (40) and which generates a corona discharge, characterized in that the measuring chamber (30) in addition to the

Sample gas inlet opening (32) and the sample gas outlet opening (34) has no further opening allowing an inflow or outflow of gas.

2. Particle sensor (12) according to claim 1, characterized in that the corona discharge electrode is arranged closer to the measurement gas inlet opening than the counter electrode and that the counter electrode is arranged closer to the measurement gas outlet opening than the corona discharge electrode .

3. Particle sensor (12) according to claim 1 or 2, characterized in that the particle sensor has an outer protective tube and an inner protective tube arranged within the outer protective tube, the outer cross section of which is so much smaller than an inner cross section of the outer protective tube that between the inner protective tube and the outer protective tube is a flow cross-section that the inner protective tube protrudes at a first end over the outer protective tube, and that the outer protective tube at a first end

opposite end protrudes beyond the inner protective tube, and that the measuring chamber is arranged at the second end outside the inner protective tube.

4. Particle sensor (12) according to claim 1 or 2, characterized in that the measuring chamber is an interior of a metallic housing which has a first end and a second end, the at least one measuring gas inlet opening being closer to the first end than that

Sample gas outlet opening and wherein the at least one

Sample gas outlet is closer to the second end than that

Sample gas inlet opening and that a dielectric carrier element is arranged in the measuring chamber, to which the corona discharge electrode is arranged adhering and wherein the housing has at least one indentation serving as counter-electrode, which is closer to the second end than the corona discharge -Electrode.

5. Particle sensor (12) according to claim 4, characterized in that the indentation is a constriction encircling the housing.

6. Particle sensor (12) according to claim 4 or 5, characterized in that the dielectric carrier element consists of ceramic.

7. Particle sensor (12) according to claim 1 or 2, characterized in that the measuring chamber is an interior of a ceramic housing which has a first end and a second end, the at least one measuring gas inlet opening being closer to the first end than that

Sample gas outlet opening and wherein the at least one

Sample gas outlet is closer to the second end than that

Sample gas inlet opening and that a dielectric carrier element is arranged in the measuring chamber.

8. Particle sensor (12) according to claim 7, characterized in that the first end is covered by a porous cover.

9. particle sensor (12) according to claim 8, characterized in that a counter-electrode (40) is arranged adhering to an inner wall of the ceramic housing (60).

10. Particle sensor (12) according to claim 9, characterized in that

at least one further electrode is arranged adhering to an inner wall of the ceramic housing (60).