JP5965261B2 - Particle sensor - Google Patents

Description

  The present invention relates to a particle sensor.

  PM (Particulate Matter) discharged from a diesel engine is mainly composed of a soot component composed of carbonaceous matter and a SOF component (Soluble Organic Fraction) composed of high-boiling hydrocarbon components. The composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. It has been done conventionally.

  On the other hand, in recent years, on-vehicle type that monitors the occurrence of failure in the exhaust gas countermeasure system of the vehicle, lights up a warning light etc. when the failure occurs, notifies the driver of the occurrence of the failure, and records the failure content A failure diagnosis device (onboard diagnosis: OBD) is required in each country, and PM concentration in exhaust gas is detected on the outlet side of the particulate filter, resulting in poor performance of the particulate filter. Although the present inventors have been studying whether or not it is possible to monitor whether or not the exhaust gas has not been detected, the present inventors have been able to detect the PM concentration in the exhaust gas even at the inlet side of the particulate filter so as to monitor the engine state. I came to consider doing that.

  The prior art document information related to the present invention includes the following patent documents 1 and 2 and the like.

Japanese Utility Model Publication No. 64-50355 JP 2007-327936 A

  However, under the present circumstances, there are some experimental measuring instruments that measure the number of PM particles (amount) by detecting physical quantities such as weight, charge amount, light transmission (light scattering), and the like to obtain a concentration. These are the ones that take a predetermined amount of sample and perform batch measurement, and can be used as an in-vehicle particle sensor that can continuously detect the concentration of PM that changes every moment. It was not a thing.

  For this reason, development of an in-vehicle particle sensor capable of continuously detecting the concentration of PM that changes every moment is desired, and proposals of particle sensors such as the above-mentioned Patent Documents 1 and 2 have been made. However, particle sensors that can continue accurate measurement for a long period of time without being adversely affected by PM accumulation while being exposed to a flow of exhaust gas containing a large amount of PM have not yet been put into practical use. is there.

  The present invention has been made in view of the above circumstances, and is a particle sensor that can continuously detect the concentration of PM that changes every moment and can continue accurate measurement over a long period of time without being adversely affected by PM deposition. The purpose is to provide.

  The present invention is a particle sensor for detecting the concentration of PM contained in exhaust gas flowing through an exhaust pipe, and is inserted in the middle of the exhaust pipe so as to cross the flow of exhaust gas and in the direction of the flow of the exhaust gas. A pair of cylindrical electrodes arranged in parallel and facing each other so as not to line up, and one of the electrodes is a high voltage electrode and the other is a ground electrode, and a rectangular wave is generated so that partial discharge occurs between the electrodes. Pulse high voltage generating means for applying an AC high voltage, a capacitor interposed in an electric circuit for applying an AC high voltage between both electrodes by the pulse high voltage generating means, and measuring the terminal voltage of the capacitor Voltage measuring means, and a calculating means for converting the voltage value measured by the voltage measuring means into a PM concentration.

  In this case, when a rectangular AC high voltage is applied between the electrodes by the pulse high voltage generating means, a partial discharge occurs between the electrodes and the PM is charged, and the charged PM is applied to each of the electrodes. Capacitors are attached, but the gap between the electrodes is reduced due to the adhesion of the PM, and the surface area of the opposing surfaces is increased. As a result, the electric charge that moves through the space and the wall surface between the electrodes due to partial discharge and leakage current increases. While the amount of charge stored in the capacitor increases, the amount of charge stored in the capacitor also increases as the capacitance of the sensor part consisting of both electrodes increases, and the terminal voltage of the capacitor increases as the amount of charge increases. Therefore, it is possible to detect the PM concentration by measuring the voltage value with the voltage measuring means and converting with the calculating means.

  Furthermore, the charge accumulated in the capacitor is reset by the discharge of the capacitor that occurs when the polarity of the electric field is reversed by the application of a rectangular wave AC high voltage, and the PM adhering to each electrode is also Due to the reversal of the polarity of the electric field, it peels off by repelling the same charge as the electrode side, and PM is blown off by the flow of exhaust gas and reset, and then the charged PM is attached by a new electric field. Will start.

  Here, each of the electrodes has a cylindrical shape having no plane with respect to the flow of the exhaust gas, and is inserted in the middle of the exhaust pipe so as to cross the flow of the exhaust gas, and arranged in the direction of the flow of the exhaust gas. Since the exhaust gas is blown strongly from the direction close to the tangential direction, an environment in which PM does not stay is created, and the separation of the PM accompanying the reversal of the polarity of the electric field is created. Removal will be ensured.

  If the frequency of the AC high voltage rectangular wave is lowered by the pulse high voltage generating means to increase the charging time of the capacitor per cycle, even when the concentration of PM contained in the exhaust gas is low, It becomes possible to realize the detection of the PM concentration by setting the amount of adhesion of PM as an amount having a significant difference.

  The present invention further includes a temperature sensor that detects the temperature of the exhaust gas in the exhaust pipe, applies temperature correction to the PM concentration calculated by the calculation means based on the exhaust temperature measured by the temperature sensor, and has a predetermined lower limit. It is preferable that the PM concentration can be detected only at the temperature or higher.

  In this way, it becomes possible to obtain a more accurate PM concentration in consideration of the fluctuation of the voltage value due to the exhaust temperature, and in a dew condensation environment with a low exhaust temperature that falls below a predetermined lower limit temperature. It is possible to avoid inaccurate detection.

  Furthermore, when carrying out the present invention more specifically, it is preferable that one of the pair of electrodes is composed of a wire and the other is composed of a rod that also serves as a support material for supporting the wire. By doing so, it is not necessary to separately install a support material, and the manufacture becomes easy, and the pressure loss with respect to the flow of exhaust gas can be reduced as much as the support material becomes unnecessary.

  According to the particle sensor of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, PM is adhered by devising the shape and arrangement of the electrodes and applying a rectangular wave AC high voltage to each of the electrodes by the pulse high voltage generating means. It is possible to detect the concentration of PM continuously changing from time to time, and to continue accurate measurement over a long period without being adversely affected by PM deposition. Furthermore, even if the concentration of PM contained in the exhaust gas is low by lowering the frequency of the rectangular wave of the alternating high voltage with the pulse high voltage generating means to increase the charging time of the capacitor per cycle. The PM concentration can be detected with the amount of PM adhering to each electrode as an amount having a significant difference.

  (II) According to the invention described in claim 2 of the present invention, it is possible to obtain a highly accurate PM concentration taking into account fluctuations in the voltage value depending on the exhaust gas temperature, and an exhaust gas temperature that falls below a predetermined lower limit temperature. Inaccurate detection under low condensation conditions can be avoided.

  (III) According to the invention described in claim 3 of the present invention, it is possible to facilitate the manufacture without using the support material, and to reduce the pressure loss with respect to the flow of the exhaust gas by the amount that the support material is unnecessary. can do.

It is the schematic which shows an example of the form which implements this invention. It is an arrow view of the II-II direction of FIG. It is sectional drawing which expands and shows the principal part of FIG. It is an electric circuit diagram of the particle sensor of this embodiment. It is a graph which shows the applied voltage to both electrodes, and the detection voltage of a voltage measuring device. It is explanatory drawing which shows typically the mode of adhesion and peeling of PM.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an exhaust pipe through which exhaust gas 2 from an engine flows, so that the flow of the exhaust gas 2 crosses in the middle of the exhaust pipe 1. Although a pair of electrodes 3 and 4 are inserted, in the example shown here, one of the pair of electrodes 3 and 4 is made of a stainless steel wire having a diameter of about 0.2 mm and the other is It is composed of a stainless steel rod having a diameter of about 5 mm that also serves as a support material for supporting the wire.

  Here, each of the electrodes 3 and 4 has a columnar shape arranged in parallel and facing each other, and can be constituted by a pair of wires. In this embodiment, a combination of a wire and a rod is used.

  1 shows the electrodes 3 and 4 arranged in the flow direction of the exhaust gas 2 for convenience of explanation, but in actuality, FIG. 2 is a view in the direction of the arrow II-II in FIG. It is necessary to arrange the electrodes 3 and 4 so as to cross the flow of the exhaust gas 2 so that they do not line up in the direction of the flow of the exhaust gas 2.

  At this time, each of the electrodes 3 and 4 is preferably inserted to the vicinity of the central portion in the radial direction of the exhaust pipe 1 so as to be exposed to the main flow of the exhaust gas 2. The detection of PM concentration is more accurate than the detection target of the flow near the inner wall of the exhaust pipe 1.

  FIG. 3 shows the detailed structure of each of the electrodes 3 and 4 in an enlarged view. The upper and lower ends of one electrode 3 formed of a wire are the upper and lower ends of the other electrode 4 formed of a rod. It is designed to be supported by insulators 5 and 6 attached to each other, and an interval w of about 5 mm is secured between them.

  As shown in FIG. 1, the one electrode 3 made of wire is a high-voltage electrode connected to an in-vehicle battery 7 (DC power supply) via a switching circuit 8 and a booster circuit 9. The other electrode 4 composed of a rod is grounded via a capacitor 10 to form a ground electrode, and the pulse height comprising the battery 7, the switching circuit 8 and the booster circuit 9 is described above. A rectangular wave AC high voltage is applied by the voltage generating means 11 to generate a partial discharge between the electrodes 3 and 4. It is also possible to replace the battery 7, the switching circuit 8 and the booster circuit 9 with a single pulse generator to constitute the pulse high voltage generating means 11.

  Further, the terminal voltage of the capacitor 10 is measured by the voltage measuring device 12, and the measured voltage value is input to the control device 13 (calculation means) and converted into the PM concentration. ing.

  Here, particularly in the present embodiment, a temperature sensor 14 is provided at an appropriate position of the exhaust pipe 1 close to the position where the electrodes 3 and 4 are arranged, and the exhaust temperature measured by the temperature sensor 14 is supplied to the control device 13. A signal is input, and the control device 13 corrects the temperature of the PM concentration, and the PM concentration is detected only at a predetermined lower limit temperature (about 100 ° C.) or higher.

  Thus, in the case where the particle sensor is configured in this way, a partial discharge is generated between the electrodes 3 and 4 when the pulsed high voltage generator 11 applies a rectangular wave AC high voltage between the electrodes 3 and 4. PM is charged, and the charged PM adheres to each of the electrodes 3 and 4. As a result of the adhesion of this PM, the gap between the electrodes 3 and 4 is reduced and the surface areas of the opposing surfaces are increased. While the amount of charge moving in the space between the electrodes 3 and 4 and the wall surface due to partial discharge and leakage current increases, the amount of charge accumulated in the capacitor 10 increases, while the capacitance of the sensor portion comprising both electrodes 3 and 4 increases. Increasing the charge also increases the amount of charge accumulated in the capacitor 10, and the terminal voltage of the capacitor 10 increases as the amount of charge increases. The voltage value is measured by the voltage measuring device 12 and converted by the control device 13. Do It becomes possible to detect PM concentration in the.

Here, the reason why the amount of electric charge accumulated in the capacitor 10 increases as the capacitance of the sensor portion composed of both electrodes 3 and 4 increases will be described. The particle sensor of this embodiment is shown in FIG. When the sensor portion composed of the electrodes 3 and 4 is regarded like a capacitor, the capacitance can be expressed as the following equation (1).
[Equation 1]
C = εS / d (1)
C: Capacitance ε: Dielectric constant S: Surface area of the opposing surface of the electrode d: Gap between the electrodes

  Therefore, if the gap d between the electrodes 3 and 4 is reduced due to the adhesion of PM and the surface area S of the opposing surfaces is increased, the capacitance C of the sensor portion composed of the electrodes 3 and 4 increases.

And there exists a relationship like the following formula | equation (2) among the electric charge Q, the electrostatic capacitance C, and the applied voltage V. FIG.
[Equation 2]
Q = CV (2)

  Therefore, if the capacitance C increases with respect to the determined applied voltage V, the charge amount Q in the sensor portion composed of the electrodes 3 and 4 increases, and the charge amount in the capacitor 10 also increases. Since the capacitance at 10 is unchanged, the terminal voltage of the capacitor 10 increases.

  Further, the electric charge accumulated in the capacitor 10 is reset by the discharge of the capacitor 10 caused by reversing the polarity of the electric field by applying a rectangular wave AC high voltage, and is attached to the electrodes 3 and 4. Also, the PM is peeled off by repelling with the same charge as the electrodes 3 and 4 due to the reversal of the polarity of the electric field, and the PM is blown off by the flow of the exhaust gas 2 to be reset. The charged PM begins to adhere due to a strong electric field.

FIG. 5 is a graph showing the voltage V _in applied to both electrodes 3 and 4 by the pulse high voltage generating means 11 and the detection voltage V _out of the voltage measuring device 12. when applying an applied voltage V _in is the voltage, but the detection voltage V _out measured by the voltage measuring device 12 is detected as the waveform B, and dividing the time axis for each pulse of the applying voltage V _in, What is necessary is just to convert into the PM density | concentration by the control apparatus 13 by making the voltage value of the peak in the divided unit time, or an average voltage value into a measured value.

  Here, in the case of this embodiment, temperature correction is applied to the PM concentration calculated by the control device 13 based on the exhaust temperature measured by the temperature sensor 14, so that the voltage value variation due to the exhaust temperature is changed. In consideration of this, the control device 13 obtains a more accurate PM concentration.

  Here, as schematically shown in FIG. 6, each of the electrodes 3 and 4 has a cylindrical shape having no plane with respect to the flow of the exhaust gas 2, and the exhaust gas 2 is disposed in the middle of the exhaust pipe 1. Are disposed so as to cross the flow of the exhaust gas 2 and are arranged so as not to line up with the flow direction of the exhaust gas 2, and in particular, the opposed surfaces of the electrodes 3, 4 are from the direction in which the exhaust gas 2 is close to the tangential direction. An environment in which PM is hard to stay by blowing strongly is created, and separation and removal of PM accompanying the reversal of the polarity of the electric field is surely performed.

  Incidentally, if the frequency of the AC high voltage rectangular wave is lowered by the pulse high voltage generating means 11 to increase the charging time of the capacitor 10 per cycle, each of the cases where the concentration of PM contained in the exhaust gas 2 is low. The PM concentration can be detected with the amount of PM adhering to the electrodes 3 and 4 as an amount having a significant difference.

  Therefore, according to the above-described embodiment, the shape and arrangement of the electrodes 3 and 4 are devised, and the pulse high voltage generation means 11 applies a rectangular AC high voltage to each of the electrodes 3 and 4 to thereby prevent the adhesion of PM. It is possible to detect the concentration of PM that changes from time to time by reliably performing peeling, and to continue accurate measurement over a long period of time without being adversely affected by PM deposition. Is a case where the concentration of PM contained in the exhaust gas 2 is low by lowering the frequency of the rectangular wave of the alternating high voltage by the pulse high voltage generating means 11 and increasing the charging time of the capacitor 10 per cycle. However, the PM concentration can be detected by setting the amount of PM adhering to each of the electrodes 3 and 4 as an amount having a significant difference.

  Further, a temperature sensor 14 for detecting the temperature of the exhaust gas 2 in the exhaust pipe 1 is further provided, and the PM concentration calculated by the control device 13 is subjected to temperature correction based on the exhaust temperature measured by the temperature sensor 14, and a predetermined value is obtained. Since the PM concentration can be detected only at the lower limit temperature or higher, it is possible to obtain a highly accurate PM concentration that takes into account fluctuations in the voltage value due to the exhaust temperature, and to fall below a predetermined lower limit temperature. Inaccurate detection in a condensation environment with a low exhaust temperature can be avoided.

  Furthermore, since one of the pair of electrodes 3 and 4 is composed of a wire and the other is composed of a rod that also serves as a support material for supporting the wire, the support material is not required, and the manufacture is facilitated. In addition, the pressure loss with respect to the flow of the exhaust gas 2 can be reduced by the amount that the support material is unnecessary.

  The particle sensor of the present invention is not limited to the application to the entrance side of the particulate filter as in the above-described embodiment, but may be applied to any location in the exhaust pipe. Of course, various modifications can be made without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1 Exhaust pipe 2 Exhaust gas 3 Electrode 4 Electrode 10 Capacitor 11 Pulse high voltage generation means 12 Voltage measuring device (voltage measurement means)
13 Control device (calculation means)
14 Temperature sensor

Claims (3)

  A particle sensor for detecting the concentration of PM contained in exhaust gas flowing through an exhaust pipe, which is inserted in the middle of the exhaust pipe so as to cross the flow of exhaust gas and not aligned with the flow direction of the exhaust gas A pair of cylindrical electrodes arranged in parallel and facing each other, and one of the electrodes as a high voltage electrode and the other as a ground electrode, and a rectangular wave AC high voltage so that partial discharge occurs between the electrodes. Pulse high voltage generating means to be applied, a capacitor interposed in an electric circuit for applying an alternating high voltage between both electrodes by the pulse high voltage generating means, and voltage measuring means for measuring the terminal voltage of the capacitor A particle sensor comprising: a voltage value measured by the voltage measuring means; and a calculating means for converting the voltage value into a PM concentration.   A temperature sensor for detecting the temperature of the exhaust gas in the exhaust pipe is further provided, and the PM concentration calculated by the calculation means is subjected to temperature correction based on the exhaust temperature measured by the temperature sensor, and the PM concentration is detected only at a predetermined lower limit temperature or more. The particle sensor according to claim 1, wherein the particle sensor is configured to perform detection.   3. The particle sensor according to claim 1, wherein one of the pair of electrodes is constituted by a wire and the other is constituted by a rod that also serves as a support material for supporting the wire.

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