JP2017040214A - Particulate matter detection system - Google Patents

Abstract

Disclosed is a particulate matter detection system in which ash in exhaust gas hardly adheres to an electrode of a particulate matter detection sensor. A particulate matter detection system includes a particulate matter detection sensor, a control unit, and a temperature measurement unit. The control unit 4 performs a measurement mode and a heat generation mode. In the measurement mode, the amount of the particulate matter 3 in the exhaust gas g is measured by measuring the current flowing between the pair of electrodes 21a and 21b provided in the particulate matter detection sensor 2. In the heat generation mode, the heater 22 generates heat and the particulate matter 3 deposited on the deposition target portion 20 is removed. The controller 4 is configured to control the temperature of the deposition target portion 20 to 600 to 750 ° C. in the heat generation mode. [Selection] Figure 1

Description

  The present invention relates to a particulate matter detection system including a particulate matter detection sensor and a control unit connected to the particulate matter detection sensor.

  There is known a particulate matter detection system including a particulate matter detection sensor that measures the amount of particulate matter (PM) in exhaust gas, and a control unit connected to the particulate matter detection sensor (described below). Patent Document 1). The particulate matter detection sensor includes a portion to be deposited on which particulate matter in the exhaust gas is deposited, a pair of electrodes provided on the portion to be deposited, and a heater that heats the portion to be deposited. When particulate matter is deposited on the portion to be deposited, a current flows between the pair of electrodes. By measuring this current, the amount of particulate matter contained in the exhaust gas is measured.

  The control unit performs a measurement mode and a heat generation mode. In the measurement mode, the control unit measures the current flowing between the pair of electrodes, and calculates the amount of particulate matter in the exhaust gas based on the measured value. In the heat generation mode, the heater is heated to burn and remove the particulate matter deposited on the deposition target portion. Thus, the particulate matter detection sensor is configured to be regenerated.

  The particulate matter contains so-called ash. Ash is generated by oxidation of a metal component or the like contained in engine oil, and is made of an oxide such as P, S, or Ca. The melting point of ash is generally considered to be 900 ° C. or higher. Since ash is an insulator, when ash is fused to the surface of the electrode, it becomes difficult for current to flow between the pair of electrodes, and the performance of the particulate matter detection sensor is likely to deteriorate. Therefore, in order to prevent ash from fusing to the electrode surface, in the particulate matter detection system, the temperature of the deposited portion in the heat generation mode is set to 600 to 900 ° C. Since the melting point of ash is 900 ° C. or higher, it is considered that if the temperature of the deposited portion is 600 to 900 ° C., the ash is not melted and the ash can be prevented from being fused to the surface of the electrode.

JP 2012-12960 A

  However, even if the temperature of the deposited portion is 600 to 900 ° C., the ash may be melted and the ash may be fused to the surface of the electrode. In other words, ash generally has a melting point of 900 ° C. or higher, but when it becomes fine particles having a diameter of several nanometers, the melting point may be lowered due to a so-called quantum size effect. Moreover, when multiple types of ash are mixed, a eutectic reaction may occur and the melting point may be lowered. For these reasons, the melting point of ash may be 900 ° C. or lower. Therefore, when the temperature of the deposited portion is heated to 600 ° C. to 900 ° C. in the heat generation mode, the ash may melt and adhere to the electrode surface. Therefore, it becomes difficult for current to flow between the electrodes in the measurement mode, and there is a possibility that the amount of the particulate matter cannot be accurately measured.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a particulate matter detection system in which ash in exhaust gas hardly adheres to an electrode of a particulate matter detection sensor.

One embodiment of the present invention is a particulate form including a deposition portion on which particulate matter in exhaust gas is deposited, a pair of electrodes provided in the deposition portion and spaced apart from each other, and a heater that heats the deposition portion. A substance detection sensor;
A control unit connected to the particulate matter detection sensor;
A temperature measuring unit for measuring the temperature of the deposited part,
The control unit measures the current flowing between the pair of electrodes, thereby measuring the amount of the particulate matter contained in the exhaust gas, heats the heater, and deposits on the deposition portion. Perform a heat generation mode to burn and remove the particulate matter,
The control unit is in the particulate matter detection system configured to control the temperature of the deposition portion measured by the temperature measurement unit to be 600 to 750 ° C. in the heat generation mode.

The control unit of the particulate matter detection system is configured to control the temperature of the deposition target part to be 600 to 750 ° C. in the heat generation mode.
Therefore, it can suppress that ash fuse | melts on the surface of an electrode. In other words, ash may have a melting point that is lowered to 900 ° C. or lower due to the quantum size effect or eutectic reaction, but is less likely to be 750 ° C. or lower as described later. Therefore, by setting the upper limit of the temperature of the deposited portion to 750 ° C., it is possible to suppress ash fusion on the surface of the electrode.

  In the particulate matter detection system, the lower limit value of the temperature of the portion to be deposited in the heat generation mode is set to 600 ° C. As will be described later, when the temperature of the deposited portion is 600 ° C. or less, the particulate matter may not burn and the particulate matter may remain between the electrodes. Substances can be burned sufficiently, and such problems can be suppressed.

  As described above, according to the above aspect, it is possible to provide a particulate matter detection system in which ash in the exhaust gas hardly adheres to the electrode of the particulate matter detection sensor.

1 is a conceptual diagram of a particulate matter detection system in Embodiment 1. FIG. FIG. 3 is a perspective view of a sensor main body in Embodiment 1. FIG. 3 is an exploded perspective view of the sensor main body according to the first embodiment. FIG. 3 is a cross-sectional view of the particulate matter detection sensor according to the first embodiment. The graph showing the relationship between the temperature and time of heat_generation | fever mode in Embodiment 1, and the presence or absence of PM adhesion. 3 is a graph showing the relationship between the temperature of the heat generation mode and the deterioration rate in the first embodiment. The graph for demonstrating the calculation method of the deterioration rate of FIG. FIG. 3 is a partial cross-sectional view of the particulate matter detection sensor in the measurement mode in the first embodiment. The expanded sectional view of FIG. The expanded sectional view of the particulate matter detection sensor after the particulate matter and ash are removed in the first embodiment. 2 is a flowchart of the particulate matter detection system in the first embodiment. 3 is a graph showing a temperature distribution of a deposition target portion in the first embodiment. The graph showing the relationship between the electrical resistance of a heater and temperature. The expanded sectional view of the particulate matter detection sensor in comparative form 1.

  The particulate matter detection system can be an on-vehicle particulate matter detection system to be mounted on a vehicle such as a diesel vehicle or a gasoline engine vehicle.

(Embodiment 1)
An embodiment according to the particulate matter detection system will be described with reference to FIGS. As shown in FIG. 1, the particulate matter detection system 1 of this embodiment includes a particulate matter detection sensor 2, a control unit 4, and a temperature measurement unit 5.

  As shown in FIGS. 2 and 3, the particulate matter detection sensor 2 includes a portion 20 to be deposited, a pair of electrodes 21 (21 a and 21 b), and a heater 22. The particulate matter 3 in the exhaust gas g is deposited on the portion 20 to be deposited. Further, the pair of electrodes 21a and 21b are provided in the deposition target portion 20 and are separated from each other. The heater 22 is provided for heating the portion 20 to be deposited.

As shown in FIG. 1, the control unit 4 is connected to the particulate matter detection sensor 2. The temperature measuring unit 5 measures the temperature of the deposition target part 20.
The control unit 4 performs a measurement mode and a heat generation mode. The measurement mode is a mode in which the amount of the particulate matter 3 contained in the exhaust gas g is measured by measuring the current flowing between the pair of electrodes 21a and 21b. The heat generation mode is a mode in which the heater 22 generates heat and the particulate matter 3 deposited on the deposition target portion 20 is burned and removed.

  The control unit 4 is configured to control the temperature of the deposition target portion 20 measured by the temperature measurement unit 5 to be 600 to 750 ° C. in the heat generation mode.

  The particulate matter detection system 1 of this embodiment is an on-vehicle particulate matter detection system that is mounted on a vehicle such as a diesel vehicle or a gasoline engine vehicle. As shown in FIG. 1, an exhaust pipe 11 through which exhaust gas g flows is connected to an engine 10 of a vehicle. The particulate matter detection sensor 2 is attached to the exhaust pipe 11. Further, a filter 6 that collects the particulate matter 3 is provided on the upstream side of the exhaust gas g from the particulate matter detection sensor 2.

  In this embodiment, the particulate matter 3 in the exhaust gas g is collected using the filter 6, and the amount of the particulate matter 3 that has passed through the filter 6 is measured by the particulate matter detection sensor 2. When the filter 6 is clogged with the particulate matter 3, the particulate matter 3 cannot be sufficiently collected. Therefore, the amount of the particulate matter 3 measured by the particulate matter detection sensor 2 increases. In this embodiment, when the amount of the particulate matter 3 in the exhaust gas g exceeds a predetermined value, it is determined that the filter 6 is clogged, and a filter heater (not shown) is caused to generate heat and collected by the filter 6. The particulate matter 3 formed is burned. Thus, the filter 6 is configured to be regenerated.

  As shown in FIG. 2, the particulate matter detection sensor 2 includes a sensor body 23 having a quadrangular plate shape. The electrodes 21 a and 21 b are exposed from the end surface 200 of the sensor body 23. In this embodiment, the particulate matter 3 is deposited on the end surface 200 of the sensor main body 23. That is, the end surface 200 is the portion to be deposited 20.

  As shown in FIG. 3, the sensor main body 23 includes a plurality of insulating plates 24 made of ceramic. Between the plurality of insulating plates 24, the first electrode 21a and the second electrode 21b are interposed. A plurality of first electrodes 21a and second electrodes 21b are provided. The plurality of first electrodes 21 a are connected to each other by connection plugs (not shown) formed on the insulating plate 24. Similarly, the plurality of second electrodes 21b are also connected to each other by a connection plug. The sensor body 23 is provided with a heater 22.

  When the heater 22 is energized to generate heat, the electrical resistance of the heater 22 changes. As shown in FIG. 13, there is a certain relationship between the temperature of the heater 22 and the resistance of the heater 22. In this embodiment, the electrical resistance of the heater 22 is measured by the control unit 4, and the temperature of the heater 22, that is, the temperature of the deposition target portion 20 is calculated using the measured value.

  The particulate material 3 is mainly composed of carbon and has electrical conductivity. Therefore, as shown in FIG. 8, when the particulate matter 3 is deposited on the deposition target portion 20, a current flows between the electrodes 21a and 21b. The control unit 4 is configured to measure this current and calculate the amount of the particulate matter 3 in the exhaust gas g using the measured value.

  When the particulate matter 3 is excessively deposited on the portion 20 to be deposited, the amount of current flowing between the electrodes 21a and 21b is saturated. Therefore, the amount of the particulate matter 3 in the exhaust gas g cannot be calculated. Therefore, in this case, the control unit 4 generates heat from the heater 22 (see FIG. 3), and burns and removes the particulate matter 3. Thereby, the particulate matter detection sensor 2 is regenerated.

As shown in FIG. 9, ash 7 is attached to the particulate matter 3. Ash 7 is obtained by oxidizing P, S, Ca, etc. contained in the engine oil. The ash 7 is made of, for example, CaSO ₄ , Ca ₃ (PO ₄ ) ₂ , Ca ₂ P ₂ O ₇ , ZnO, Zn ₃ (PO ₄ ) _2, or the like. The melting point of these substances is usually 900 ° C. or higher, but may be 900 ° C. or lower when the quantum size effect or eutectic reaction occurs. For example, when the ash 7 becomes fine particles having a diameter of several nanometers, the melting point of the ash 7 is lowered due to the quantum size effect. Moreover, when multiple types of ash 7 are mixed, melting | fusing point of ash 7 falls by eutectic reaction. For these reasons, the melting point of ash 7 may be 900 ° C. or lower.

  Therefore, when the heating mode is performed, that is, when the heater 22 generates heat and the particulate matter 3 is burned and removed, if the temperature of the heater 22 is raised to about 900 ° C., the ash 7 is melted and shown in FIG. As described above, the ash 7 may be fused to the surface of the electrode 21. Since the ash 7 is an insulator, when the surface of the electrode 21 is covered with the ash 7, no current flows between the pair of electrodes 21a and 21b. Therefore, there is a possibility that the amount of the particulate matter 3 in the exhaust gas g cannot be accurately measured. Therefore, in this embodiment, when the heat generation mode is performed, the temperature of the heater 22, that is, the temperature of the deposition target portion 20 is set to 600 to 750 ° C. In this case, the upper limit value of the temperature of the portion 20 to be deposited is 750 ° C., which is lower than the melting point of the ash 7 when the quantum size effect or the like occurs, so that the ash 7 can be prevented from melting in the heat generation mode. . Therefore, as shown in FIG. 10, the ash 7 can be prevented from being fused to the surface of the electrode 21.

  In addition, when the temperature of the deposition target portion 20 in the heat generation mode is less than 600 ° C., the particulate matter 3 cannot be burned sufficiently, and the unburned particulate matter 3 may remain in the deposition portion 20. Further, as described above, when the temperature exceeds 750 ° C., the ash 7 is easily fused to the electrode 21. For these reasons, in this embodiment, the temperature of the portion 20 to be deposited in the heat generation mode is set to 600 to 750 ° C.

  Next, description will be given of experimental data which is the basis for the temperature range (600 to 750 ° C.). First, an experiment was conducted to confirm the lower limit value (600 ° C.) of the temperature of the portion 20 to be deposited in the heat generation mode. In this experiment, first, the particulate matter detection sensor 2 was attached to the exhaust pipe 11 (see FIG. 1), and the engine 10 was started to generate exhaust gas g. Thereby, the particulate matter 3 in the exhaust gas g was deposited on the portion 20 to be deposited. Thereafter, the heater 22 was heated for a certain time. At this time, as shown in FIG. 5, the temperature of the deposition target portion 20 was changed to 550 ° C., 600 ° C., 650 ° C., 700 ° C., and 750 ° C. Further, the exothermic time was varied for 5 to 80 seconds. Then, the portion 20 to be deposited was observed to confirm whether the particulate matter 3 could be removed.

  As shown in FIG. 5, when the temperature of the portion 20 to be deposited is 600 ° C. or 650 ° C., the particulate matter 3 can be removed by heating for 20 seconds or more. Moreover, if the temperature of the part 20 to be deposited is 700 ° C., the particulate matter 3 can be removed by heating for 10 seconds or more. On the other hand, when the temperature of the portion to be deposited 20 is 550 ° C., the particulate matter 3 cannot be removed even if heated for 80 seconds. From this experimental result, it can be seen that the temperature of the deposition target portion 20 needs to be 600 ° C. or higher in order to sufficiently remove the particulate matter 3.

  Next, another experiment was conducted to confirm that the temperature of the deposition target portion 20 in the heat generation mode needs to be 750 ° C. or lower. In this experiment, an acceleration test was performed so that the same amount of ash 7 as that generated when the vehicle traveled 300,000 km was generated. And the temperature of the to-be-deposited part 20 in heat_generation | fever mode was set to 600-900 degreeC conditions as shown in FIG. A method for calculating the deterioration rate will be described later.

  In the experiment, the filter 6 was removed from the exhaust pipe 11 (see FIG. 1), and a large amount of the particulate matter 3 reached the particulate matter detection sensor 2 in a short time. Further, the sulfated ash content of the engine oil was 1.34% (usually 0.8%), and the amount of ash 7 generated was increased. As a result, the same amount of ash 7 as when the vehicle traveled 300,000 km reached the particulate matter detection sensor 2 in a short time.

  Further, the heat generation mode and the measurement mode were alternately repeated while exposing the particulate matter detection sensor 2 to the exhaust gas g. The heating time for each sample in the exothermic mode was 210 seconds per cycle. Further, a plurality of samples of the particulate matter detection sensor 2 are prepared. As shown in FIG. 6, the temperatures of the deposited portions 20 in the heat generation mode are 600 ° C., 700 ° C., 750 ° C., 800 ° C., 850 ° C., 900 Set to ° C.

  After generating particulate matter 3 and ash 7 equivalent to 300,000 km from engine 10, each sample is exposed to normal exhaust gas g in the concentration of particulate matter 3, and the current flowing between the pair of electrodes 21a and 21b is measured. The time change was measured. As shown in FIG. 7, for example, in a sample in which the temperature is set to 700 ° C. in the heat generation mode, current starts to flow between the electrodes 21a and 21b in a relatively short time after the measurement is started. This is presumably because the ash 7 is hardly fused on the surface of the electrode 21, so that a current flows between the electrodes 21 a and 21 b even if the particulate matter 3 is slightly deposited. On the other hand, in the sample in which the temperature is set to 800 ° C. in the heat generation mode, current does not start to flow unless a longer time elapses after the measurement starts than the sample at 700 ° C. This is presumably because the ash 7 is fused to the surface of the electrode 21 in the 800 ° C. sample.

For a sample whose temperature was set to 700 ° C. in the heat generation mode, the time To until the current between the electrodes 21a and 21b reached a predetermined threshold value Io was measured. For other samples (samples in which the temperature was set to 600 ° C., 750 ° C., 800 ° C., 850 ° C., and 900 ° C. in the heat generation mode), the time Tx until the current reached the threshold value Io was measured. And the degradation rate d of each sample was computed using the following formula | equation.
d = (Tx−To) / To × 100 (%)
In the heat generation mode, the sample having a temperature of 700 ° C. had a deterioration rate d of 0%. The deterioration rate d of each sample is shown in FIG.

  From FIG. 6, it can be seen that the deterioration rate d is almost 0% when the temperature of the deposited portion 20 in the heat generation mode is 750 ° C. or lower. It can also be seen that when the temperature exceeds 750 ° C., the deterioration rate d increases. This is because when the temperature in the heat generation mode exceeds 750 ° C., the ash 7 is fused to the electrode 21, so that the current hardly flows between the electrodes 21 a and 21 b, and the current starts to flow after starting the measurement mode. This is probably because it takes a long time to complete.

  From the above experiment, in the heat generation mode, in order to prevent the particulate matter 3 from remaining in the deposition target portion 20 and the ash 7 from fusing to the electrode 21, the temperature of the deposition target portion 20 is set to 600 ° C. It turns out that it is necessary to control to 750 ° C.

  Next, the structure of the particulate matter detection sensor 2 will be described in more detail. As shown in FIG. 4, the particulate matter detection sensor 2 includes the sensor main body portion 23, a holding portion 81, a housing 25, and a fixing portion 26. The holding part 81 is made of an insulating material such as ceramics. The sensor main body 23 is held in the holding portion 81. Further, the holding portion 81 is disposed in the housing 25.

  The housing 25 is inserted into the fixing member 26. A male screw portion 261 of the fixing member 26 is screwed into a female screw portion 110 formed in the exhaust pipe 11. Thereby, the particulate matter detection sensor 2 is fixed to the exhaust pipe 11.

  As shown in FIG. 4, a shoulder 251 is formed on the housing 25. A spring member 83 is disposed on the tip side of the shoulder portion 251. By crimping the shoulder portion 251, the enlarged diameter portion 811 of the holding portion 81 is pressed against the reduced diameter portion 252 of the housing 25 using the applied pressure of the spring member 83. Thereby, the exhaust gas g is prevented from leaking from between the enlarged diameter portion 811 and the reduced diameter portion 252.

  The particulate matter detection sensor 2 includes an electrode wiring 291 and a heater wiring 292. These wirings 291 and 292 are provided in pairs. The electrode wiring 291 is electrically connected to the electrodes 21 a and 21 b in the sensor main body 23. The heater wiring 292 is electrically connected to the heater 22.

  The tip of the sensor body 23 is protected by two covers 27 and 28, an inner cover 27 and an outer cover 28. The outer cover 28 includes a bottom portion 282 and a side wall portion 281. Through holes 283 and 284 are formed in the side wall portion 281 at positions close to the bottom portion 282.

  In addition, a through hole (inner side through hole 273) is also formed in the inner cover 27. An opening 272 is formed in the inner cover 27. The opening 272 is formed between the deposition target portion 20 and the bottom portion 282 and opens in the longitudinal direction (Z direction) of the sensor main body 23. The inner cover 27 is formed with a guide plate 271 for guiding the exhaust gas g.

  The exhaust gas g passes through the inner side through hole 273 after passing through the upstream side through hole 283 of the outer cover 28, hitting the side wall portion 281, and changing its direction. At this time, the exhaust gas g is guided to the portion 20 to be deposited by the guide plate 271. As a result, more exhaust gas g hits the portion 20 to be deposited. Thereby, the responsiveness of the particulate matter detection sensor 2 is enhanced.

  After the exhaust gas g hits the deposition target portion 20, the exhaust gas g passes through the opening portion 272, further passes through the downstream side through-hole 284, and is discharged to the outside of the outer cover 28.

  Next, the flowchart of the control part 4 in this form is demonstrated. As shown in FIG. 11, the control unit 4 first measures the current between the electrodes 21a and 21b of the particulate matter detection sensor 2, and calculates the amount of the particulate matter 3 in the exhaust gas g based on the measured value. (Step S1; measurement mode).

  Next, the control unit 4 determines whether or not it is necessary to regenerate the filter 6 (step S2). If it is determined YES, the process proceeds to step S3. Then, the filter heater is heated to burn the particulate matter 3 collected by the filter 6. Thereby, the filter 6 is regenerated.

  Thereafter, the control unit 4 determines whether or not the current value between the electrodes 21a and 21b exceeds a predetermined value, that is, whether or not the current is saturated. If it is determined YES, the process proceeds to step S5. Here, the heater 6 is heated to burn and remove the particulate matter 3 deposited on the deposition target portion 20 (heat generation mode). At this time, the control unit 4 sets the temperature of the heater 22, that is, the temperature of the deposited portion 20 to 600 to 750 ° C.

Next, the temperature distribution of the portion 20 to be deposited in the heat generation mode will be described. As shown in FIG. 12, the temperature in the deposition target part 20 is not uniform, and there are a part where the temperature is high and a part where the temperature is low. In the present embodiment, the difference between the maximum temperature T _max and the minimum temperature T _min in the deposition target portion 20 is set to 100 ° C. or less. That is, the difference between the average temperature T _typ and the maximum temperature T _max is within 50 ° C., and the difference between the average temperature T _typ and the minimum temperature T _min is within 50 ° C.

Next, the effect of this form is demonstrated. In this embodiment, the temperature of the deposition target portion 20 is controlled to 600 to 750 ° C. in the heat generation mode.
Therefore, it is possible to suppress the ash 7 from being fused to the surface of the electrode 21. That is, as described above, the ash 7 may have a melting point of 900 ° C. or lower due to the quantum size effect or eutectic reaction, but hardly reaches 750 ° C. or lower. Therefore, by setting the upper limit of the temperature of the deposited portion to 750 ° C., it is possible to suppress ash fusion on the surface of the electrode.

  In the present embodiment, the lower limit value of the temperature of the deposited portion in the heat generation mode is set to 600 ° C. Therefore, in the heat generation mode, the problem that the particulate matter does not burn and the particulate matter remains between the electrodes 21a and 21b can be suppressed.

As shown in FIG. 12, in this embodiment, the temperature difference (T _max −T _min ) between the highest temperature portion and the lowest temperature portion in the deposition target portion 20 is set to 100 ° C. or less. Therefore, there can be a margin between the maximum temperature T _max and 750 ° C. and between the minimum temperature T _min and 600 ° C., and any part of the deposited portion 20 can be reliably set to 600 to 750 ° C. become. The temperature of the depositing part 20 is likely to change depending on the temperature and flow rate of the exhaust gas g. However, if T _max −T _min ≦ 100 (° C.), even if the temperature and flow rate of the exhaust gas g change suddenly in the heat generation mode. It becomes easy to make all the parts of the portion 20 to be deposited 600 to 750 ° C.

  In this embodiment, as shown in FIG. 2, the sensor main body 23 of the particulate matter detection sensor 2 is formed in a quadrangular plate shape. The end surface 200 of the sensor main body 23 is a deposition target portion 20. Therefore, the area of the deposition target portion 20 can be reduced, and the temperature variation in the deposition target portion 20 can be reduced. Therefore, in the heat generation mode, all the portions of the deposition target portion 20 are easily set to 600 to 750 ° C.

  As shown in FIG. 4, in this embodiment, a guide plate 271 that guides the exhaust gas g to the deposition target part 20 is formed on the inner cover 27 of the particulate matter detection sensor 2. Therefore, the exhaust gas g is likely to hit the portion 20 to be deposited, and the responsiveness of the particulate matter detection sensor 2 can be improved. In this way, the particulate matter 3 is likely to be deposited on the portion 20 to be deposited, and the ash 7 is also likely to be deposited on the portion 20 to be deposited together with the particulate matter 3 (see FIG. 8). However, in this embodiment, since the upper limit value of the temperature of the portion 20 to be deposited in the heat generation mode is set to 750 ° C., the ash 7 is melted and fused to the electrode 21 even when the amount of ash 7 deposited is increased. Is unlikely to occur.

In this embodiment, as shown in FIG. 1, a filter 6 is provided on the upstream side of the exhaust gas g from the particulate matter detection sensor 2. The filter 6 has a particulate matter 3 collection efficiency of 98% or less.
Therefore, the pressure loss of the exhaust gas g can be reduced. That is, the collection efficiency of the filter 6 is generally 99.9% or more. Therefore, as long as the filter 6 does not fail, the amounts of the particulate matter 3 and the ash 7 that reach the particulate matter detection sensor 2 are very small. However, such a filter 6 having a high collection efficiency has a high pressure loss of the exhaust gas g, and the fuel consumption of the engine 10 is likely to decrease. Therefore, it has been studied to reduce the collection efficiency of the filter 6 and reduce the pressure loss of the exhaust gas g. When the collection efficiency of the filter 6 is 98% or less as in the present embodiment, the pressure loss of the exhaust gas g can be reduced, and the reduction in fuel consumption can be suppressed.
Note that when the collection efficiency of the filter 6 is reduced, the amount of the particulate matter 3 and the ash 7 that reach the particulate matter detection sensor 2 increases. In this embodiment, the temperature of the deposition target portion 20 in the heat generation mode is increased. Since the upper limit of 750 ° C. is set, even if the amount of ash 7 increases, it is possible to suppress the fusion of a large amount of ash 7 to the electrode 21.

  The collection efficiency of the filter 6 is preferably 80% or less. When the collection efficiency is 80% or less, the pressure loss of the filter 6 can be further reduced, and the fuel consumption can be further suppressed.

  The collection efficiency of the filter 6 is more preferably 60% or less. When the collection efficiency is 60% or less, the pressure loss of the filter 6 can be further reduced, and the fuel consumption can be further suppressed.

  As described above, according to the present embodiment, it is possible to provide a particulate matter detection system in which ash in the exhaust gas hardly adheres to the electrode of the particulate matter detection sensor.

  In this embodiment, the control unit 4 and the temperature measurement unit 5 are integrated. That is, the electrical resistance of the heater 22 is measured by the control unit 4, and the temperature of the heater 22, that is, the temperature of the deposition target portion 20 is calculated using the measured value. However, the present invention is not limited to this, and a dedicated temperature sensor may be provided as the temperature measuring unit 5.

DESCRIPTION OF SYMBOLS 1 Particulate matter detection system 2 Particulate matter detection sensor 20 Deposited part 21 Electrode 22 Heater 3 Particulate matter 4 Control part 5 Temperature detection part

Claims (5)

A deposition part (20) in which particulate matter (3) in the exhaust gas is deposited, a pair of electrodes (21) provided in the deposition part (20) and spaced apart from each other, and the deposition part (20) A particulate matter detection sensor (2) having a heater (22) for heating;
A control unit (4) connected to the particulate matter detection sensor (2);
A temperature measuring part (5) for measuring the temperature of the deposition part (20),
The controller (4) measures a current flowing between the pair of electrodes (21), thereby measuring the amount of the particulate matter (3) contained in the exhaust gas, and the heater (22 ) Is heated, and a heating mode for burning and removing the particulate matter (3) deposited on the deposition target part (20) is performed,
The controller (4) is configured to control so that the temperature of the deposition target (20) measured by the temperature measurement unit (5) is 600 to 750 ° C. in the heat generation mode. Particulate matter detection system (1).   The particulate matter detection system (1) according to claim 1, wherein the temperature difference between the highest temperature part and the lowest temperature part in the deposition target part (20) is 100 ° C or less.   A filter (6) for collecting the particulate matter (3) contained in the exhaust gas is provided on the upstream side of the exhaust gas with respect to the particulate matter detection sensor (2), and the filter (6 3) The particulate matter detection system (1) according to claim 1 or 2, wherein the collection efficiency of the particulate matter (3) is 98% or less.   The particulate matter detection system (1) according to claim 3, wherein the collection efficiency of the filter (6) is 80% or less.   The particulate matter detection system (1) according to claim 3 or 4, wherein the collection efficiency of the filter (6) is 60% or less.

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