Abstract
The present disclosure relates to exhaust gas emissions in motor vehicles. The teachings thereof may be embodied in soot sensors. For example, a soot sensor may include: a first electrode; a second electrode; an insulation body between the first electrode and the second electrode configured to allow soot particles to pass with a gas flow into a space defined between the first electrode and the second electrode; a meter evaluating a current between the first electrode and the second electrode resulting from an electrical voltage applied between the first electrode and the second electrode; and elements concentrating the electric field strength formed on at least one of a surface of the first electrode or a surface of the second electrode.
Claims
1. A soot sensor comprising: a first electrode; a second electrode; an insulation body between the first electrode and the second electrode configured to allow soot particles to pass with a gas flow into a space defined between the first electrode and the second electrode; a meter evaluating a current between the first electrode and the second electrode resulting from an electrical voltage applied between the first electrode and the second electrode; and elements concentrating the electric field strength formed on at least one of a surface of the first electrode or a surface of the second electrode.
2. The soot sensor as claimed in claim 1, wherein the first electrode comprises a rod-shape.
3. The soot sensor as claimed in claim 1, wherein the second electrode comprises a cylindrical shape.
4. The soot sensor as claimed in claim 2, wherein the cylindrical second electrode is arranged concentrically around a rod-shaped first electrode.
5. The soot sensor as claimed in claim 1, wherein the elements comprise spike-like tips.
6. The soot sensor as claimed in claim 1, wherein the elements comprise triangular tips.
7. The soot sensor as claimed in claim 1, wherein the elements comprise grooves in one of the surfaces.
8. The soot sensor as claimed in claim 1, wherein that the elements comprise nanostructures on the surface of the first electrode or the surface of the second electrode.
Description
[0018] In the drawings:
[0019] FIG. 1 shows a soot sensor,
[0020] FIG. 2 shows a soot sensor according to the invention,
[0021] FIG. 3 shows a further embodiment of the soot sensor according to the invention,
[0022] FIG. 4 shows a further embodiment of the soot sensor known from FIG. 3,
[0023] FIG. 5 shows a further embodiment of the soot sensor according to the invention.
[0024] FIG. 1 shows a soot sensor 1. The soot sensor 1 is composed of a first electrode 2, which is arranged in the interior of a second electrode 3. The exhaust gas, which contains soot particles 4, of the internal combustion engine is situated between the first electrode 2 and the second electrode. It is sought to measure the concentration of the soot particles 4 in the exhaust gas by means of the soot sensor. In other words, it can be stated that it is sought to determine the soot content in the exhaust gas by means of the soot sensor. For this purpose, a measurement voltage is applied between the first electrode 2 and the second electrode 3 by the voltage supply 6. The first electrode 2 is electrically insulated with respect to the second electrode 3 by means of the insulation body 5. The insulation body 5 may be constructed as a disk composed of a ceramic material. Furthermore, it can be seen in FIG. 1 that an ohmic resistance 7 is connected between the voltage supply and the second electrode 3, which ohmic resistance exhibits high impedance in order to measure the relatively small currents that can form between the first electrode 2 and the second electrode 3 owing to the soot particles 4. The measurement of said currents is realized by means of the current measurement element 8, which is connected to evaluation electronics 9. Such soot sensors 1 are used for on-board diagnosis in motor vehicles with diesel engines.
[0025] The voltage that must be applied between the first electrode 2 and the second electrode 3 in order to obtain evaluable measurement currents is relatively high. Such a voltage may amount to 2 to 3 kV and is thus relatively cumbersome to monitor. It is therefore advantageous, in order to generate easily evaluable measurement currents, to use the embodiments according to the invention of the first electrode 2 and/or of the second electrode 3, as described below.
[0026] FIG. 2 shows a soot sensor 1 according to the invention with a first electrode 2 and with a second electrode 3. The first electrode 2 is electrically insulated with respect to the second electrode 3 by means of an insulation body 5, and an electrical voltage, which is generated by the electrical voltage supply 6, is applied between the first electrode 2 and the second electrode 3. It is sought to measure the concentration of the soot particles 4 in the exhaust gas by means of the soot sensor 1 according to the invention. It is thus also sought to determine the soot content in the exhaust gas by means of the soot sensor 1 according to the invention.
[0027] Soot particles 4 which are transported in an exhaust-gas flow from an internal combustion engine through an exhaust tail pipe can enter the soot sensor 1 which is integrated in the exhaust tail pipe. The soot particles 4 pass into an electric field which forms owing to the electrical voltage applied between the first electrode 2 and the second electrode 3. To generate an easily measurable electrical current between the first electrode 2 and the second electrode 3, elements 15 for concentrating the electric field strength are formed on the surface of the first electrode 2 and/or on the surface of the second electrode 3. In this example, the first electrode 2 is in the form of a rod-shaped threaded bar, wherein the elements 15 for concentrating the electric field strength are formed by the thread flights, between which triangular tips are formed. The electric field is concentrated at these tips, whereby the electric field strength becomes very high in the region of the tips. The intense increase in the electric field strength in the region of the tips can exceed the breakdown field strength of the gas in said region. In the event of the breakdown field strength of the gas being exceeded, electrically charged particles are formed which are accelerated in the direction of the opposite electrode and, owing to impact ionization events, lead to an avalanche-like formation of charge carriers. When said charge carrier avalanche reaches an electrode surface, a very high current can be measured, which can be easily evaluated and which is proportional to the number of charged particles in the exhaust gas.
[0028] FIG. 2 however also shows an ohmic resistance 7, which is advantageous in order to be able to measure, by means of the evaluation electronics 9, the electrical current that flows between the first electrode 2 and the second electrode 3. Furthermore, FIG. 2 shows a protective cap 10 which serves for the targeted guidance of the exhaust-gas flow through the soot sensor 1. The exhaust gases may for example into the soot sensor 1 through a first opening 11, where the soot content in the exhaust gas can be measured between the first electrode 2 and the second electrode 3. Thereafter, the exhaust-gas flow exits the soot sensor 1 through the second opening 12 formed in the second electrode 3, and is conducted back into the main exhaust-gas flow via the third opening 13.
[0029] FIG. 3 shows a further embodiment of the soot sensor 1 according to the invention. Here, the soot sensor 1 is of rotationally symmetrical form about a central axis 14. The first electrode 2 is in the form of a rod-shaped electrode. The cylindrical second electrode 3 is formed concentrically around the second electrode. The second electrode 3 is thus in the form of a hollow cylinder. The insulation body 5, which in this case is in the form of a disk, electrically separates the first electrode 2 from the second electrode 3. A voltage can be applied between the first electrode 2 and the second electrode 3 by means of the voltage supply 6. The elements 15 for field concentration formed on the inner surface of the second electrode 3 are in this case in the form of triangles. The tips of the triangles lead to a very high field strength in the region of the tips of the triangles. Owing to said high field strength, the breakdown field strength in the exhaust gas can be exceeded, whereby, owing to avalanche-like impact ionization, a high measurement current can be generated, which can be easily registered by means of the evaluation electronics 9.
[0030] FIG. 4 shows a further embodiment of the soot sensor 1 known from FIG. 3. The first electrode 2 is equipped with elements 15 for concentrating the electric field strength, which elements are in the form of spike-like tips. The second electrode 3, on its inner surface, has semicircular elements 15 for concentrating the electric field strength. A multiplicity of possible surface structures of the first electrode 2 and of the second electrode 3 are conceivable, whereby targeted modeling of the field distribution in the interior of the soot sensor 1 is possible.
[0031] FIG. 5 shows a further embodiment of the soot sensor 1 according to the invention. Here, both the first electrode 2 and the second electrode 3 are formed as rod-shaped elements. Triangular elements 15 for concentrating the electric field strength are formed both on the first electrode 2 and the second electrode 3. The first electrode 2 and the second electrode 3 are electrically insulated with respect to one another by means of the insulation body 5. A protective cap 10 is formed over the first electrode 2 and over the second electrode 3. The protective cap 10 again, by means of the first opening 11, the second opening 12 and the third opening 13, allows the exhaust gas and the soot particles to flow into the interior of the soot sensor 1 and thus also between the first electrode 2 and a second electrode 3. The second electrode 3 may, in the context of the disclosure of FIGS. 1 to 5, be in the form of a hollow cylinder.
