JP2017015512A - Particulate substance detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particulate substance detection system capable of further correctly measuring the amount of particulate substances in exhaust gas.SOLUTION: The particulate substance detection system comprises a particulate substance sensor 2, a current measurement part 3 and a control circuit part 4. The control circuit part 4 performs switching control between a measurement mode and a burning mode. In the measurement mode, voltage Vs is added between a pair of electrodes 21 in a state of stopping energization to a heater 22 and measures current flowing between the electrodes 21 by the current measurement part 3. In the burning mode, the heater 22 is caused to generate heat and burns particulate substances accumulated in an accumulation section 20. If a measurement value of current I right after switching a mode from the burning mode to the measurement mode is higher than a predetermined threshold Ib, the control circuit part 4 determines that the particulate substances remain in the accumulation section 20 and performs the burning mode again.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a particulate matter detection system including a particulate matter sensor that measures the amount of particulate matter in exhaust gas, a current measurement unit connected to the particulate matter, and a control circuit unit connected to these.

  Particulate matter detection comprising a particulate matter sensor for measuring the amount of particulate matter (PM) in exhaust gas, a current measurement unit connected to the particulate matter sensor, and a control circuit unit connected to the current measurement unit A system is known (see Patent Document 1 below). The particulate matter sensor includes a pair of electrodes spaced apart from each other and a heater that heats the electrodes.

  The control circuit unit is configured to switch and control between the measurement mode and the combustion mode. In the measurement mode, a voltage is applied between the pair of electrodes of the particulate matter sensor. If it does in this way, a particulate matter will gather by electrostatic force and an electric current will flow between electrodes. By measuring this current value, the amount of particulate matter in the exhaust gas is calculated. If the measurement mode is continued for a while, a lot of particulate matter accumulates between the electrodes, and the current is saturated. Therefore, in this case, the mode is switched to the combustion mode, the heater is heated, and the accumulated particulate matter is combusted. Thus, the particulate matter sensor is configured to be regenerated.

JP, 2012-37373, A

  However, the particulate matter detection system may not be able to measure the amount of particulate matter sufficiently accurately. That is, in the particulate matter sensor, even when the combustion mode is performed, the particulate matter may not be sufficiently burned, and the particulate matter may remain between the electrodes. When switching to the measurement mode in this state, there is a possibility that the amount of the particulate matter cannot be accurately measured because the particulate matter sensor is not sufficiently regenerated.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a particulate matter detection system capable of more accurately measuring the amount of particulate matter in exhaust gas.

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 sensor;
A current measuring unit electrically connected to one of the pair of electrodes;
A control circuit unit connected to the particulate matter sensor and the current measurement unit,
The control circuit unit applies a voltage between the pair of electrodes in a state where energization to the heater is stopped, and measures a current flowing between the pair of electrodes by the current measuring unit, and Also, the heater is heated in a state where the voltage applied between the pair of electrodes is lowered, and the combustion mode in which the particulate matter deposited on the deposition portion is burned is controlled to be switched,
When the measured value of the current immediately after switching from the combustion mode to the measurement mode is higher than a predetermined threshold, the particulate matter remains in the deposition portion. And the particulate matter detection system is configured to perform the combustion mode again.

The particulate matter detection system determines that particulate matter remains in the deposition portion when the measured current value immediately after switching from the combustion mode to the measurement mode is higher than a predetermined threshold value. The combustion mode is performed again.
For this reason, if particulate matter remains in the deposition part due to insufficient combustion, the combustion mode is performed again, and the particulate matter in the deposition part is sufficiently combusted before measuring particulate matter in the exhaust gas. Done. Therefore, it is possible to suppress the measurement of particulate matter in the exhaust gas in a state where the particulate matter remains in the deposition portion, and it is possible to accurately measure the amount of particulate matter in the exhaust gas. Become.

  As described above, according to the present invention, it is possible to provide a particulate matter detection system that can measure the amount of particulate matter in exhaust gas more accurately.

1 is a circuit diagram of a particulate matter detection system in a measurement mode in Embodiment 1. FIG. 1 is a circuit diagram of a particulate matter detection system in a combustion mode in Embodiment 1. FIG. 1 is an exploded perspective view of a particulate matter sensor in Embodiment 1. FIG. 3 is a flowchart of a control circuit unit in the first embodiment. The flowchart following FIG. The graph of the temperature of a heater, the voltage of a 1st electrode, the measured value of a 1st electric current measurement part, and the measured value of a 2nd electric current measurement part in Example 1 when a particulate matter fully burned. The graph of the temperature of a heater, the voltage of a 1st electrode, the measured value of a 1st electric current measurement part, and the measured value of a 2nd electric current measurement part in Example 1 when combustion shortage of a particulate matter arises . 3 is a graph showing the relationship between the heater temperature and electrical resistance in Example 1. FIG. 10 is a part of a flowchart of a control circuit unit in the second embodiment. In Example 2, when the first wiring and the second wiring are short-circuited to GND, the heater temperature, the voltage of the first electrode, the measured value of the first current measuring unit, and the measured value of the second current measuring unit And graph. 10 is a part of a flowchart of a control circuit unit in the third embodiment. The graph of the temperature of a heater, the voltage of a 1st electrode, the measured value of a 1st electric current measurement part, and the measured value of a 2nd electric current measurement part when the 1st wiring in Example 3 is disconnected. The graph of the temperature of a heater when the heater fails in Example 3, the voltage of a 1st electrode, the measured value of a 1st electric current measurement part, and the measured value of a 2nd electric current measurement part. The graph of the temperature of a heater, the voltage of a 1st electrode, the measured value of a 1st electric current measurement part, and the measured value of a 2nd electric current measurement part when the insulating member in Example 3 deteriorates. 9 is a part of a flowchart of a control circuit unit in the fourth embodiment. FIG. 10 is a circuit diagram of a particulate matter detection system in a heat generation mode in the fifth embodiment.

  The particulate matter detection system can be a particulate matter detection system for a diesel vehicle to be mounted on a diesel vehicle.

Example 1
Examples relating 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 example includes a particulate matter sensor 2, a current measuring unit 3, and a control circuit unit 4. As shown in FIG. 3, the particulate matter sensor 2 includes a portion 20 to be deposited, a pair of electrodes 21 (21 a and 21 b), and a heater 22. Particulate matter in the exhaust gas is deposited on the portion 20 to be deposited. The pair of electrodes 21 are provided in the portion 20 to be deposited and are separated from each other. The heater 22 is provided for heating the portion 20 to be deposited.

The electrode 21 includes a first electrode 21a and a second electrode 21b. As shown in FIG. 1, the second electrode 21 b is connected to the current measuring unit 3. The first electrode 21a is connected to an auxiliary current measuring unit 3 ′ described later.
The control circuit unit 4 is connected to the particulate matter sensor 2 and the current measurement unit 3.

The control circuit unit 4 is configured to switch between a measurement mode (see FIG. 1) and a combustion mode (see FIG. 2). In the measurement mode, as shown in FIG. 1, the voltage Vs is applied between the pair of electrodes 21 in a state where energization to the heater 22 is stopped. Thereby, an electric field is generated between the electrodes 21a and 21b, and the particulate matter is collected by electrostatic force. When particulate matter is deposited between the electrodes 21a and 21b, a current I flows. This current I is measured by the current measuring unit 3.
In the combustion mode, the heater 22 is heated while the voltage applied between the pair of electrodes 21 is lower than that in the measurement mode, and the particulate matter deposited on the deposition target portion 20 is combusted.

  When the measured value of the current I immediately after switching from the combustion mode to the measurement mode is higher than the predetermined threshold value Ib, the control circuit unit 4 determines that the particulate matter remains in the deposition target portion 20. The combustion mode is performed again.

  The particulate matter detection system 1 of this example is used by being mounted on a diesel vehicle. The control circuit unit 4 is configured by a microcomputer. A plurality of A / D converters are formed in the microcomputer. Further, the particulate matter detection system 1 of the present example includes a high voltage circuit 11, a switch 6, an auxiliary current measurement unit 3 ′, a heater drive circuit 12, and a heater current detection circuit 13.

  As shown in FIG. 1, the current measurement unit 3 includes a current-voltage conversion circuit 31 and a voltage measurement circuit 32. The current-voltage conversion circuit 31 includes an op-op OP and a resistor R. The resistor R is connected between the inverting input terminal 39 and the output terminal 37 of the operational amplifier OP. Further, the voltage measurement circuit 32 is configured by an A / D converter 320. The voltage measurement circuit 32 measures the output voltage Vo of the operational amplifier OP.

  The non-inverting input terminal 38 of the operational amplifier OP is held at a predetermined voltage (hereinafter also referred to as non-inverting input terminal voltage Va). Due to the virtual short circuit which is a characteristic of the operational amplifier OP, the voltage of the inverting input terminal 39 (hereinafter also referred to as the inverting input terminal voltage Va ′) becomes substantially equal to the non-inverting input terminal voltage Va.

In the measurement mode, the control circuit unit 4 of this example stops energization of the heater 22 and controls the switch 6 to connect the first electrode 21a to the high voltage circuit 11 as shown in FIG. Therefore, the voltage Vs is applied between the electrodes 21, the particulate matter is collected, and the current I flows between the electrodes 21. This current I is measured by the current measuring unit 3. Thereby, the amount of particulate matter contained in the exhaust gas is measured.
The current I does not flow into the inverting input terminal 39 of the operational amplifier OP but flows through the resistor R. Therefore, the voltage drops at the resistor R by RI. Therefore, the output voltage Vo of the operational amplifier OP becomes a value represented by the following expression.
Vo = Va′−RI
By transforming this equation, it can be seen that the current I is expressed by the following equation (1).
I = (Va′−Vo) / R (1)

  The control circuit unit 4 stores the value of the inverting input terminal voltage Va ′ and the resistance R. Then, the current I is calculated from the above equation (1) using the value of the output voltage Vo measured by the voltage measurement circuit 32. Thereby, the amount of particulate matter in the exhaust gas is calculated.

  The auxiliary current measuring unit 3 ′ has the same configuration as the current measuring unit 3. The voltage at the inverting input terminal 39 of the auxiliary current measuring unit 3 ′ is held at Vb ′. The inverting input terminal voltage Vb ′ of the auxiliary current measuring unit 3 ′ is substantially equal to the inverting input terminal voltage Va ′ of the current measuring unit 3.

  On the other hand, as shown in FIG. 2, the control circuit unit 4 of this example controls the switch 6 and connects the first electrode 21a to the auxiliary current measuring unit 3 'in the combustion mode. In this state, the heater drive circuit 12 is driven to cause the heater 22 to generate heat.

Further, the particulate matter detection system 1 of this example includes a temperature measurement unit 5 that measures the temperature of the heater 22. The temperature measurement unit 5 includes three A / D converters 33 to 35 and a heater current detection circuit 13. The temperature measurement unit 5 measures the heater resistance _RH , which is the electric resistance of the heater 22, and calculates the temperature of the heater 22 using this measured value. As shown in FIG. 8, there is a certain relationship between the temperature of the heater 22 and the heater resistance _RH . Therefore, the temperature of the heater 22 can be calculated by measuring the heater resistance _RH .

A method for measuring the temperature of the heater 22 will be described in more detail. As shown in FIG. 2, a wiring resistance Rp is parasitic on the heater wirings 229a and 229b. The lengths of the two heater wires 229a and 229b are equal. Therefore, the wiring resistances Rp parasitic on the two heater wirings 229a and 229b are equal to each other.
In this example, the third A / D converter 33 and the fifth A / D converter 35 are used to measure the voltage V _H between the two terminals 226 and 227 connected to the heater wiring 229. Further, the current i flowing through the heater 22 is measured using the heater current detection circuit 13. Then, using the measured values of the voltage V _H and the current i, the total resistance Ra of the heater resistance _RH and the two wiring resistances Rp is measured. The total resistance Ra can be expressed by the following formula (2).
Ra = V _H / i = R _H + 2Rp (2)

In this example, the fourth A / D converter 34 and the fifth A / D converter 35 are used to measure the voltage Vp applied to the wiring resistance Rp parasitic on one heater wiring 229b. Using the measured values of the voltage Vp and the current i, the wiring resistance Rp parasitic on one heater wiring 229b can be calculated from the following equation (3).
Rp = Vp / i (3)

  A sensing wiring 228 is connected to the fourth A / D converter 34. The sensing wiring 228 is connected in the vicinity of the heater 22. The fourth A / D converter 34 measures the voltage Vp applied to one heater wiring 229b via the sensing wiring 228. Although resistance is also parasitic on the sensing wiring 228, almost no current flows through the sensing wiring 228. Therefore, the voltage drop due to the sensing wiring 228 is so small that it can be ignored, and the voltage Vp can be accurately measured.

The temperature measurement unit 5 of this example measures the total resistance Ra and the wiring resistance Rp using the above formulas (2) and (3), and further calculates the heater resistance _RH using the following formula. . That is, the two wiring resistances Rp are subtracted from the total resistance Ra. Thus, an accurate value of the heater resistance _{RH that is} not affected by the wiring resistance Rp is obtained, and the temperature of the heater 22 is accurately calculated.
R _H = Ra-2Rp

  Next, the operation of the control circuit unit 4 will be described. As shown in FIG. 4, the control circuit unit 4 first determines whether to regenerate the particulate matter sensor 2 (step S1). Here, for example, the current I flowing between the electrodes 21 is measured, and if the value is saturated, it is determined to be regenerated (Yes). If it is determined Yes in step S1, the process proceeds to step S2 to switch to the combustion mode. That is, the switch 6 is controlled so that the first electrode 21a is connected to the auxiliary current measuring unit 3 '(see FIG. 2) and the heater 22 generates heat.

  Next, the process proceeds to step S3, and it is determined whether or not the temperature of the heater 22 has sufficiently increased. Here, the temperature of the heater 22 is measured by the temperature detector 5, and it is determined whether or not the measured value is higher than a predetermined value Tb. If YES is determined in step S3, the process proceeds to step S4. Here, it is determined whether or not a predetermined time has elapsed. In this way, the particulate matter 2 deposited on the deposition target portion 20 is burned by maintaining the heater 22 at a sufficiently high temperature for a predetermined time.

  When it is determined Yes in step S4, the process proceeds to step S5, and energization of the heater 22 is stopped. And it progresses to step S6 and it is judged whether the temperature of the heater 22 fell sufficiently. That is, when the heater 22 is energized for a short time, the temperature of the heater 22 is measured by the temperature detection unit 5 and it is determined whether or not the measured value is lower than a predetermined value Ta. If it is determined YES, the process proceeds to step S7.

  In step S7, switching to the measurement mode is performed. That is, the switch 6 is switched to connect the first electrode 21a to the high voltage circuit 11 (see FIG. 1), and the current I is measured using the current measuring unit 3. Thereafter, as shown in FIG. 5, the process proceeds to step S8. Here, it is determined whether or not the current I immediately after switching to the measurement mode is greater than a predetermined threshold value Ib. That is, when the particulate matter is not sufficiently burned in the combustion mode and the particulate matter remains in the portion 20 to be deposited, a large current flows between the electrodes 21a and 21b when switching to the measurement mode. Based on this current value, it is determined whether or not particulate matter remains.

  If YES in step S8, that is, if it is determined that the particulate matter remains, the process proceeds to step S10. Here, it is determined whether or not the combustion mode has been continuously performed more times than a predetermined number. When it is determined No in step S10, the process proceeds to step S2 and the combustion mode is performed again. As described above, in this example, when it is determined in Step S8 that the particulate matter remains (Yes), the combustion mode is performed again to burn the remaining particulate matter. Thus, the measurement mode is performed after the particulate matter is sufficiently combusted. Moreover, in step S10, when the combustion mode is performed N times continuously (Yes), it is determined that the heater 22 of the particulate matter sensor 2 has failed. Then, the process proceeds to step S11, and a failure signal is generated. This prompts the user or the like to replace the particulate matter sensor 2.

  On the other hand, if it is determined No in step S8, that is, no particulate matter remains, the process proceeds to step S9 and the measurement mode is continued. And it returns to step S1 (refer FIG. 4).

  Next, with reference to FIG. 6 and FIG. 7, the time change of the temperature of the heater 22, the voltage of the first electrode 21 a, the measured value of the auxiliary current measuring unit 3 ′, and the measured value of the current measuring unit 3 is shown. The represented graph will be described. FIG. 6 is a graph when the particulate matter is sufficiently burned in the combustion mode. As shown in the figure, the temperature of the heater 22 is relatively low in the measurement mode. At this time, since the first electrode 21a is connected to the high voltage circuit 11 (see FIG. 1), the voltage of the first electrode 21a becomes equal to the voltage Vs of the high voltage circuit 11. Further, in the measurement mode, the auxiliary current measurement unit 3 ′ is not connected to the first electrode 21 a, so that no current is measured by the auxiliary current measurement unit 3 ′. When the measurement mode is continued for a while, the particulate matter gradually accumulates on the deposition target portion 20, so that the current flowing between the electrodes 21 increases. Therefore, the measured value of the current measuring unit 3 gradually increases.

When the measurement mode is ended and the mode is switched to the combustion mode, the temperature of the heater 22 starts to rise. When the temperature of the heater 22 rises sufficiently, the particulate matter deposited on the deposition target portion 20 burns. Further, when the temperature of the heater 22 rises, the temperature of the insulating member 23 (see FIG. 3) disposed between the heater 22 and the electrode 21 also rises, and the electrical resistance of the insulating member 23 decreases. Therefore, a leakage current I _L (see FIG. 2) flows from the heater 22 to the electrodes 21a and 21b. The leakage current _IL is measured by the current measuring unit 3 and the auxiliary current measuring unit 3 ′.

  As shown in FIG. 6, when the combustion mode ends, the temperature of the heater 22 gradually decreases. After the temperature of the heater 22 is sufficiently lowered, the mode is switched to the measurement mode. When the particulate matter is sufficiently burned in the combustion mode and no particulate matter remains in the portion 20 to be deposited, the current I does not flow suddenly even when the measurement mode is switched as shown in FIG. After switching to the measurement mode, when the particulate matter accumulates with time, the current I starts to flow gradually.

  On the other hand, as shown in FIG. 7, when the particulate matter is not sufficiently burned in the combustion mode, the current I suddenly flows when the measurement mode is switched. This is because the particulate matter having conductivity remains between the electrodes 21 and the voltage Vs is applied between the electrodes 21. This current I is measured by the current measuring unit 3. The value of the measured current I exceeds the threshold value Ib.

The effect of this example will be described. As shown in FIG. 5, when the measured value of the current I immediately after switching from the combustion mode to the measurement mode is higher than a predetermined threshold value Ib, the control circuit unit 4 of this example causes the deposition target 20 to It is determined that the particulate matter remains and the combustion mode is performed again (steps S8, S10, S2).
Therefore, when the particulate matter remains in the depositing part 20 due to insufficient combustion, the combustion mode is performed again, and after the particulate matter in the depositing part 20 has sufficiently combusted, the particulate matter in the exhaust gas Measurement is performed. Therefore, it is possible to suppress the measurement of the particulate matter in the exhaust gas in a state where the particulate matter remains in the depositing portion 20, and it is possible to accurately measure the amount of the particulate matter in the exhaust gas. become.

Further, as shown in FIG. 5, the control circuit unit 4 of this example determines that particulate matter remains in the deposition target part 20 and performs the process of performing the combustion mode again more times than a predetermined number of times, When it carries out continuously, it is comprised so that it may judge that the particulate matter sensor 2 is out of order (step S8, S10).
Therefore, it is possible to detect that the particulate matter sensor 2 has failed, and to prompt the user or the like to replace the particulate matter sensor 2.

Further, as shown in FIG. 4, the control circuit unit 4 of the present example is configured so that the temperature of the heater 22 measured by the temperature detection unit 5 becomes lower than a predetermined value Ta after the combustion mode is finished. The measurement mode is switched (steps S6 and S7).
In the state where the temperature of the heater 22 is high, the leak current _IL flows from the heater 22 to the electrode 21 as described above. Thus, flow high temperature of the heater 22, switching to the measurement mode with the leakage current I _L flows, the current value measured by the current measurement unit 3, or by the leakage current I _L, between electrodes 21 Whether it is due to the current I cannot be distinguished. Therefore, the value of the current I flowing between the electrodes 21 cannot be measured accurately, and it becomes difficult to determine whether or not particulate matter remains unburned in the deposition target portion 20. In contrast, as in this example, be switched to the measurement mode from the lowered sufficiently temperature of the heater 22, the leakage current I _L does not flow hardly, if the current I flows between the electrodes 21, the value Can be measured accurately. Therefore, it can be accurately determined whether or not particulate matter remains in the portion 20 to be deposited.

  As described above, according to this example, it is possible to provide a particulate matter detection system that can measure the amount of particulate matter in exhaust gas more accurately.

  In this example, the temperature of the heater 22 is measured by measuring the electrical resistance of the heater 22, but the present invention is not limited to this. That is, a dedicated temperature sensor may be provided separately.

(Example 2)
In the following embodiments, the same reference numerals used in the drawings among the reference numerals used in the drawings represent the same components as in the first embodiment unless otherwise specified.

  In this example, the operation of the control circuit unit 4 is changed. FIG. 9 shows a flowchart of the control circuit unit 4 of this example. This flowchart continues from step S7 described in FIG. Since steps S8 to S11 are the same as those in the first embodiment, detailed description thereof is omitted. In this example, when it is determined No in step S8, that is, when it is determined that the current I immediately after switching to the measurement mode is lower than the threshold value Ib and there is no particulate matter remaining in the deposition target portion 20, Proceed to S81. Here, it is determined whether or not the wiring 24 (see FIG. 3) of the particulate matter sensor 2 is short-circuited to GND. That is, as shown in FIG. 1, the inverting input terminal 39 of the operational amplifier OP included in the current measuring unit 3 is held at a positive voltage (inverting input terminal voltage Va ′). Therefore, when the wiring 24 is short-circuited to GND, the current I flows in the direction opposite to the normal direction. For example, as shown in FIG. 10, when the first wiring 24a is short-circuited to GND at a certain time t1, the measured value of the auxiliary current measuring unit 3 'becomes a negative value. Similarly, when the second wiring 24b is shorted to GND at time t2, the measured value of the current measuring unit 3 becomes a negative value.

As shown in FIG. 9, in step S <b> 81, it is determined whether or not the current I flows in the reverse direction and becomes a value lower than a predetermined value −Ia. If YES is determined here, the process proceeds to step S82, and it is determined that the wiring 24 is short-circuited to GND. Then, it moves to step S11 and generates a failure signal. This prompts the user or the like to replace the particulate matter sensor 2.
In addition, the configuration and operational effects similar to those of the first embodiment are provided.

(Example 3)
In this example, the operation of the control circuit unit 4 is changed. The control circuit unit 4 of this embodiment, the combustion mode or the like, using a current measuring unit 3 or the like, and measuring the leakage current I _L that flows from the heater 22 to the electrode 21, using the measured value, the particulate matter sensor It is configured to determine whether 2 is out of order. For example, if, when the first wire 24a of the particulate matter sensor 2 (see FIG. 3) is disconnected, the leakage current I _L does not flow to the first wire 24a. Therefore, as shown in FIG. 12, during the combustion mode, the leakage current _IL is not measured by the auxiliary current measuring unit 3 ′ and becomes lower than the predetermined determination value Ic. In this case, it can be determined that the first wiring 24a is disconnected.

Further, if the heater 22 of the particulate matter sensor 2 has failed, the temperature of the heater 22 does not rise sufficiently during the combustion mode, and the temperature of the insulating member 23 does not rise sufficiently. Therefore, not lowered sufficiently the electrical resistance of the insulating member 23, as shown in FIG. 13, the leakage current I _L does not flow sufficiently during the combustion mode. Therefore, the leakage current I _L during the combustion mode becomes the value lower than the determination value Ic predetermined. The value of the leakage current I _L measured respectively by the current measurement unit 3 and the auxiliary current measurement unit 3 'is, when both lower than the determination value Ic, it can be determined that the heater 22 has failed.

Further, if the insulating member 23 has deteriorated, as shown in FIG. 14, even if the combustion mode ends and the temperature of the heater 22 decreases, a large leak current _IL flows. Therefore, after the combustion mode has been completed, if the value of the leakage current I _L measured respectively by the current measurement unit 3 and the auxiliary current measurement unit 3 'are both higher than a predetermined value Id, the insulating member 23 can be judged to be deteriorated.

Next, the operation of the control circuit unit 4 of this example will be described using the flowchart of FIG. The flowchart of FIG. 10 continues from step S3 described in FIG. After it is determined Yes in step S3, the process proceeds to step S31, and the leakage current _IL is measured. Then, it moves to step S32 and it is judged whether the particulate matter sensor 2 is out of order. For example, among the values of the leakage current I _L measured respectively by the current measurement unit 3 and the auxiliary current measurement unit 3 ', one of the values is lower than the determination value Ic, the wiring 24 is disconnected Judge. Further, both the measured leakage current I _L is lower than the determination value Ic, it is determined that the heater 22 has failed. Then, the process proceeds to step S33, and a failure signal is generated. This prompts the user or the like to replace the particulate matter sensor 2.

In Step S32, if No, that is, if it is determined that the particulate matter sensor 2 has not failed, Steps S4 and S5 are performed, and then Step S51 is performed. Here, it is determined whether or not the temperature of the heater 22 has become lower than a predetermined value Tc (see FIG. 14). Here it determined Yes moves to step S52, again measure the leakage current _{I L.} Thereafter, the process proceeds to step S53. Here, the value of the leakage current I _L measured respectively by the current measurement unit 3 and the auxiliary current measurement unit 3 'are both to determine higher or not than a predetermined value Id (see FIG. 14) . If it is determined Yes, the process moves to step S54, and it is determined that the insulating member 23 has deteriorated. Then, it progresses to step S33 and a failure signal is generated. If it is determined No in step S53, the process proceeds to step S6 (see FIG. 4).

The effect of this example will be described. By performing the failure determination by using the measured value of the leakage current I _L, and when the wiring 24 is broken, when the heater 22 has failed, or the like when the insulation member 23 is deteriorated, the particulate matter sensor 2 for various reasons This can be detected even if the device fails. Therefore, it can be detected more reliably that the particulate matter sensor 2 has failed.
In addition, the configuration and operational effects similar to those of the first embodiment are provided.

Example 4
In this example, the operation of the control circuit unit 4 is changed. FIG. 15 shows a flowchart of this example. The flowchart of this example continues from step S8 described in FIG. As shown in FIG. 15, in this example, step S83 is performed after step S8 is performed. Here, the inverting input terminal voltage Va ′ of the operational amplifier OP (see FIG. 2) is measured. That is, when step S83 is performed, step S6 (see FIG. 4) has already been performed, and the temperature of the heater 22 is sufficiently lowered. Therefore, at this time, the leakage current _IL hardly flows unless the insulating member 23 is deteriorated. Therefore, does not flow the leakage current I _L to the resistor R of the current measuring unit 3, the voltage does not drop at the resistor R. For this reason, the output voltage Vo of the operational amplifier OP is substantially equal to the inverting input terminal voltage Va ′. Therefore, by measuring the output voltage Vo using the voltage measurement circuit 32, the inverting input terminal voltage Va ′ (= Vo) can be accurately measured.

  After performing Step S83, the process proceeds to Step S84. Here, the value of the inverting input terminal voltage Va ′ in the above equation (1) is changed. Thereafter, the process proceeds to step S9 (see FIG. 5). In step S9, the measurement mode is continued and the current I is calculated using the above equation (1).

  The effect of this example will be described. The inverting input terminal voltage Va ′ of the operational amplifier OP does not exactly match the non-inverting input terminal voltage Va, and they are different by the offset voltage ΔV. Further, the offset voltage ΔV changes depending on the temperature or the like. Therefore, the inverting input terminal voltage Va ′ is not always a constant value but a value that varies depending on the temperature or the like. In this example, the inverting input terminal voltage Va 'is measured, and the measured value is used when calculating the value of the current I. Therefore, the current I can be accurately calculated.

In particular, in this example, the inverting input terminal voltage Va ′ is measured after the temperature of the heater 22 has sufficiently decreased. Therefore, in a state in which the leakage current I _L does not flow through resistor R, it can measure the inverting input terminal voltage Va '(= Vo). In this example, when measuring the inverting input terminal voltage Va ′, the first electrode 21a is connected to the inverting input terminal 39 ′ of the auxiliary operational amplifier OP ′ (see FIG. 2). The inverting input terminal voltage Vb ′ of the auxiliary operational amplifier OP ′ is substantially equal to the inverting input terminal voltage Va ′ of the operational amplifier OP. Therefore, the potential difference between the pair of electrodes 21 is almost 0 V, and the current I hardly flows between the electrodes 21 even if the particulate matter remains. Thus, in this embodiment, in a state where the current I and the leakage current I _L between the electrodes 21 hardly flows, the output voltage Vo, that is, by measuring the inverting input terminal voltage Va '. Therefore, the voltage does not drop at the resistor R, and the inverting input terminal voltage Va ′ can be accurately measured.
In addition, the configuration and operational effects similar to those of the first embodiment are provided.

(Example 5)
In this example, the connection method between the first electrode 21a and the auxiliary current measuring unit 3 ′ is changed. As shown in FIG. 16, in this example, the first electrode 21a is always connected to the auxiliary current measuring unit 3 ′. Further, a switch 6 is provided between the connection point 109 and the high voltage circuit 11. In this example, when the combustion mode is set, the switch 6 is turned off. When the measurement mode is set, the switch 6 is turned on and the first electrode 21 a is connected to the high voltage circuit 11. Thereby, the voltage Vs of the high voltage circuit 11 is applied between the pair of electrodes 21a and 21b, and particulate matter in the exhaust gas is collected.
In addition, the configuration and operational effects similar to those of the first embodiment are provided.

DESCRIPTION OF SYMBOLS 1 Particulate matter detection system 2 Particulate matter sensor 20 Deposited part 21 Electrode 22 Heater 3 Current measuring part 4 Control circuit part I Current

Claims (3)

A deposition part (20) on which particulate matter in the exhaust gas is deposited, a pair of electrodes (21) provided in the deposition part (20) and spaced apart from each other, and a heater for heating the deposition part (20) A particulate matter sensor (2) having (22);
A current measuring unit (3) electrically connected to one of the pair of electrodes (21);
A control circuit unit (4) connected to the particulate matter sensor (2) and the current measurement unit (3);
The control circuit section (4) applies a voltage between the pair of electrodes (21) in a state where energization to the heater (22) is stopped, and generates a current (I) flowing between the pair of electrodes (21). The heater (22) generates heat while the measurement mode measured by the current measurement unit (3) and the voltage applied between the pair of electrodes (21) are lower than in the measurement mode, and the deposition target (20 ) To switch between combustion modes for burning the particulate matter deposited in
When the measured value of the current (I) immediately after switching from the combustion mode to the measurement mode is higher than a predetermined threshold (Ib), the control circuit unit (4) It is judged that the particulate matter remains in (20), and the particulate matter detection system (1) is configured to perform the combustion mode again.   The control circuit unit (4) determines that the particulate matter remains in the deposition target part (20), and performs the combustion mode again for a number of times more than a predetermined number of times. The particulate part chamber detection system (1) according to claim 1, characterized in that, if performed, the particulate matter sensor (2) is determined to be faulty.   A temperature detection unit (5) for detecting the temperature of the heater (22) is provided, and the control circuit unit (4), after finishing the combustion mode, detects the heaters (5) detected by the temperature detection unit (5). The particulate matter detection according to claim 1 or 2, wherein the temperature is changed to the measurement mode after the temperature of 22) becomes lower than a predetermined value (Ta). System (1).

Images