JP6346577B2 - Fine particle measurement system - Google Patents

Description

  The present invention relates to a fine particle measurement system for measuring the amount of fine particles such as soot contained in a gas.

2. Description of the Related Art Conventionally, a fine particle measurement system that measures the amount of fine particles such as soot contained in exhaust gas of an internal combustion engine such as a diesel engine is known (Patent Document 1). The fine particle measurement system of Patent Document 1 generates ions by corona discharge, charges the fine particles in the exhaust gas with the generated ions, captures ions that are not used for charging the fine particles, and based on the amount of captured ions. (In other words, based on the amount of ions charged and not trapped in the fine particles), the amount of fine particles in the exhaust gas is measured. The amount of captured ions correlates with the amount of ions used for charging, and the amount of ions used for charging correlates with the amount of particulates in the exhaust gas. The amount of particulates in the exhaust gas stream can be measured from the amount. In such a fine particle measurement system, sufficient insulation is required between the electrode for corona discharge and the electrode for capturing ions not used for charging. Therefore, the insulation between the electrodes is ensured by surrounding the wiring connected to each electrode with a resin insulating member.

JP 2013-195069 A

However, the insulating member used in the fine particle measuring system of Patent Document 1 deteriorates with age due to, for example, soot and water adhering to the gas to be measured, and its insulating property is lowered. Therefore, the insulating member is connected to each electrode. There is a risk of leakage current between the wirings. When the leak current is generated, there is a problem in that the measurement accuracy of the amount of fine particles is lowered because the value of the current flowing through the electrode for capturing ions changes. For this reason, in such a case, it is required to calibrate by correcting the deviation of the measured value. However, in the past, the actual situation is that sufficient contrivance has not been made for calibration in the fine particle measurement system. Such a problem is not limited to the case where ions are generated by corona discharge to charge the particles, but is a common problem when ions are charged to the particles by any method.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, an ion generator for generating ions; at least a part of fine particles in exhaust gas of an internal combustion engine flows in, and the charged fine particles are charged using the ions A charging chamber; a gas supply unit that supplies a predetermined type of gas to the ion generation unit, sends the ions generated from the ion generation unit to the charging chamber, and promotes the inflow of the fine particles into the charging chamber; A gas supply control unit that controls the amount of the gas supplied by the gas supply unit; an ion trapping unit that traps at least a part of the ions that are not used for charging the fine particles; and generated from the ion generation unit was based on the current value corresponding to the difference between the amount of captured the ions to the amount and the ion trapping portion of the ion measurement signal to output a measurement signal which correlates to the quantity of particulate in the exhaust gas A fine particle measurement system comprising: a generation circuit; and a fine particle amount determination unit that determines the fine particle amount based on the measurement signal, wherein the measurement signal shift when the fine particle amount is zero, and the fine particle amount is A calibration execution unit that performs correction of any one of the deviations in the amount of fine particles specified based on the measurement signal when zero, and the calibration execution unit includes a supply amount of the gas Provides a fine particle measurement system that performs the correction when the supply amount satisfies a condition that does not allow the fine particles to flow into the charging chamber. According to the particulate measurement system of this aspect, when the gas supply amount is a predetermined amount that satisfies the condition that the particulates do not flow into the charging chamber, any one of the deviation of the measurement signal and the deviation of the particulate amount is eliminated. Since the correction is performed, the deviation can be corrected in a state where the charging to the fine particles in the exhaust gas is suppressed. The measurement signal output in such a state is inherently a measurement signal that correlates with the state in which the amount of fine particles in the exhaust gas is zero. Therefore, the measurement signal that correlates with the amount of fine particles other than zero is a decrease in the insulation of the insulating member. It is estimated that the leakage current value is caused by the above. For this reason, according to the fine particle measurement system of the above aspect, it is possible to accurately specify the deviation of the measurement signal or the deviation of the fine particle amount and perform the correction with high accuracy. For this reason, calibration of the particle measurement system can be executed to suppress a decrease in the measurement accuracy of the particle amount.

  (2) In the fine particle measurement system of the above aspect, the predetermined supply amount may be zero. According to the particulate measurement system of this embodiment, since the correction is performed when the gas supply amount to the ion generation unit is zero, the particulates to the charging chamber in a state where there is no pressure difference between inside and outside the charging chamber The possibility of inflow of water can be reduced.

  (3) In the fine particle measurement system according to the above aspect, the ion generation unit may generate the ions by corona discharge. According to the particulate measurement system of this embodiment, since ions are generated by corona discharge, very high insulation is required between the power supply circuit to the discharge electrode and the circuit through which a current corresponding to the difference in the amount of ions flows. . This is because leakage voltage tends to occur because the voltage fed (applied) to the discharge electrode in order to cause corona discharge is easily generated, while the current corresponding to the difference in ion amount is very large. This is because the influence of the leakage current on the current corresponding to this difference is large and it is necessary to prevent this influence from occurring. In such a configuration, even when the insulation between the circuits is deteriorated due to aging or the like, it is possible to suppress a decrease in the measurement accuracy of the amount of fine particles by performing the above-described correction.

  The present invention can be realized in various modes, and can be realized in the form of, for example, a particulate sensor, a particulate detection method, an internal combustion engine equipped with a particulate measurement system, and a vehicle equipped with the internal combustion engine. it can.

It is explanatory drawing which shows schematic structure of the vehicle to which the particulate-measurement system as one Embodiment of this invention is applied. 3 is an explanatory diagram schematically showing a schematic configuration of a tip end portion 100e of the particle sensor 100. 3 is a block diagram showing a schematic configuration of an electric circuit unit 700. FIG. 6 is a block diagram showing a configuration of a measurement signal generation circuit 740. FIG. It is a flowchart which shows the procedure of the fine particle amount determination and calibration process in this embodiment. It is a flowchart which shows the procedure of the fine particle amount determination process in this embodiment.

A. First embodiment:
A1. System configuration:
FIG. 1 is an explanatory diagram showing a schematic configuration of a vehicle to which a particulate measurement system as an embodiment of the present invention is applied. FIG. 1A is an explanatory diagram illustrating a schematic configuration of a vehicle 500 on which the particulate measurement system 10 is mounted. FIG. 1B is an explanatory diagram illustrating a schematic configuration of the particulate measurement system 10 attached to the vehicle 500. The particulate measurement system 10 includes a particulate sensor 100, a cable 200, and a sensor driving unit 300, and measures the amount of particulates such as soot contained in exhaust gas discharged from the internal combustion engine 400. The internal combustion engine 400 is a power source of the vehicle 500 and is configured by a diesel engine or the like.

  The vehicle 500 includes various sensors 406 provided at various parts in the vehicle 500 in addition to the particle sensor 100. From these sensors 406, measured values of parameters relating to driving of the internal combustion engine 400 are supplied to the vehicle control unit 420. The parameters relating to the driving of the internal combustion engine 400 have a broad meaning including operating condition parameters of the internal combustion engine 400 and environmental parameters that change due to the operation of the internal combustion engine 400. The operating condition parameters of the internal combustion engine 400 include, for example, the rotational speed of the internal combustion engine 400, the fuel injection amount, the speed of the vehicle 500, the torque of the internal combustion engine 400, the exhaust pressure of the internal combustion engine 400, the intake pressure of the internal combustion engine 400, EGR This corresponds to the degree of opening / closing (when an EGR valve (Exhaust Gas Recirculation valve) is provided), the amount of intake air to the internal combustion engine 400, the ignition timing, and the like. Examples of the environmental parameter that changes due to the operation of the internal combustion engine 400 include the exhaust gas temperature of the internal combustion engine 400.

  The particulate sensor 100 is attached to an exhaust gas pipe 402 extending from the internal combustion engine 400, and is electrically connected to the sensor driving unit 300 by a cable 200. In the present embodiment, the particulate sensor 100 is attached to the exhaust gas pipe 402 on the downstream side of the filter device 410 (for example, DPF (Diesel particulate filter)). The fine particle sensor 100 outputs a signal correlated with the amount of fine particles contained in the exhaust gas to the sensor driving unit 300.

  The sensor driving unit 300 drives the particulate sensor 100 and measures the amount of particulate contained in the exhaust gas based on a signal input from the particulate sensor 100. In the present embodiment, “the amount of fine particles” means “the fine particle mass concentration” proportional to the mass of fine particles contained in the unit volume of exhaust gas and “the number of fine particles” proportional to the number of fine particles contained in the unit volume of exhaust gas. Measured as “concentration”. Note that only one of “mass concentration of fine particles” and “number concentration of fine particles” may be measured. In addition to these, for example, it may be measured as a value proportional to the surface area of the fine particles contained in the unit volume of the exhaust gas. The sensor driving unit 300 outputs a signal indicating the amount of fine particles contained in the exhaust gas to the vehicle control unit 420. The vehicle control unit 420 determines the combustion state of the internal combustion engine 400, the amount of fuel supplied from the fuel supply unit 430 to the internal combustion engine 400 via the fuel pipe 405, and the like in accordance with a signal input from the sensor drive unit 300. To control. The vehicle control unit 420 is configured to warn the driver of the vehicle 500 of deterioration or abnormality of the filter device 410, for example, when the amount of fine particles contained in the exhaust gas is larger than a predetermined upper limit (threshold value). May be. Here, the vehicle control unit 420 outputs a calibration start signal to the sensor driving unit 300 every time the vehicle 500 travels a predetermined distance (for example, 5000 kilometers) set in advance. The calibration start signal is a signal for instructing execution of calibration of a correction value used in fine particle amount determination and calibration processing described later. Electric power is supplied from the power supply unit 440 to the sensor driving unit 300 and the vehicle control unit 420.

  As shown in FIG. 1B, the particulate sensor 100 includes a cylindrical tip 100e. The tip 100e is inserted on the inside of the exhaust gas pipe 402 on the outer surface of the exhaust gas pipe 402. It is fixed. Here, the tip 100e of the particulate sensor 100 is inserted substantially perpendicular to the extending direction DL of the exhaust gas pipe 402. On the surface of the casing CS of the distal end portion 100e, an inflow hole 45 for taking in the exhaust gas into the casing CS and an exhaust hole 35 for discharging the taken in exhaust gas to the outside of the casing CS are provided. Part of the exhaust gas flowing through the exhaust gas pipe 402 is taken into the casing CS of the tip portion 100e through the inflow hole 45. The fine particles contained in the taken-in exhaust gas are charged by ions (here, cations) generated by the fine particle sensor 100. The exhaust gas containing the charged fine particles is discharged to the outside of the casing CS through the discharge hole 35. The internal configuration of the casing CS and the specific configuration of the particulate sensor 100 will be described later.

  A cable 200 is attached to the rear end portion 100r of the particle sensor 100. The cable 200 has a configuration in which a first wiring 221, a second wiring 222, a signal line 223, and an air supply pipe 224 are bundled. The first wiring 221, the second wiring 222, and the signal line 223 are electrically connected to an electric circuit unit 700 described later. The air supply pipe 224 is connected to an air supply unit 800 described later.

  The sensor driving unit 300 includes a sensor control unit 600, an electric circuit unit 700, and an air supply unit 800. The sensor control unit 600 and the electric circuit unit 700 and the sensor control unit 600 and the air supply unit 800 are electrically connected, respectively.

  The sensor control unit 600 includes a microcomputer and a memory, and controls the electric circuit unit 700 and the air supply unit 800. The sensor control unit 600 also includes a fine particle amount determination unit 610, a calibration execution unit 620, a map storage unit 630, a current value storage unit 640, a fine particle amount storage unit 650, a correction value storage unit 660, and an air supply. And a control unit 670.

  The fine particle amount determination unit 610 determines the fine particle amount with reference to a fine particle amount map mp1 stored in the map storage unit 630 based on a signal (a measurement signal Sesc described later) input from the electric circuit unit 700. FIG. 1B schematically shows the setting contents of the fine particle amount map mp1. In the fine particle amount map mp1, a correspondence relationship between a signal input from the electric circuit unit 700 and the fine particle amount is set in advance. Details of the fine particle amount map mp1 and details of the method of determining the fine particle amount will be described later. In addition, the particulate amount determination unit 610 outputs a signal representing the amount of particulates contained in the exhaust gas to the vehicle control unit 420.

  The calibration execution unit 620 corrects the deviation of the signal input from the electric circuit unit 700 by executing a calibration process described later. Details of such signal shift will be described later. The current value storage unit 640 stores a current value derived from a signal input from the electric circuit unit 700 in a particle amount determination process described later. The fine particle amount storage unit 650 stores the fine particle amount determined in the fine particle amount determination process described later. The correction value storage unit 660 stores a correction value used in a particle amount determination process described later. The correction value storage unit 660 stores zero as an initial value of the correction value in advance. This correction value can be changed by a calibration process described later. The air supply control unit 670 controls the amount of high pressure air supplied by the air supply unit 800.

  The electric circuit unit 700 supplies power for driving the particle sensor 100 via the first wiring 221 and the second wiring 222. In addition, a signal correlating with the amount of fine particles contained in the exhaust gas is input from the fine particle sensor 100 to the electric circuit unit 700 via the signal line 223. The electric circuit unit 700 outputs a signal corresponding to the amount of fine particles contained in the exhaust gas to the sensor control unit 600 using the signal input from the signal line 223. Specific contents of these signals will be described later.

  Air supply unit 800 includes a pump (not shown), and supplies high-pressure air to particulate sensor 100 via air supply pipe 224 based on an instruction from sensor control unit 600 (air supply control unit 670). To do. The high-pressure air supplied from the air supply unit 800 is used when measuring the amount of fine particles by the fine particle sensor 100. Instead of supplying air by the air supply unit 800, other types of gas such as nitrogen gas may be supplied to the particle sensor 100. Further, a compressor may be used instead of the pump. In this case, for example, it may be used also as a compressor for supplying compressed air for braking.

  FIG. 2 is an explanatory diagram schematically showing a schematic configuration of the tip 100e of the particle sensor 100. As shown in FIG. The distal end portion 100e has a configuration in which an ion generation unit 110, an exhaust gas charging unit 120, and an ion trapping unit 130 are provided in a casing CS. That is, in the casing CS, the three processing units 110, 120, and 130 are arranged in this order from the base end side (upper side in FIG. 2) to the front end side (lower side in FIG. 2) of the tip end part 100e. Are lined up along the axial direction. The casing CS is formed of a conductive member, and is connected to the secondary side ground SGL (FIG. 3) via the signal line 223 (FIG. 1).

  The ion generation unit 110 is a processing unit for generating ions (here, cations) to be supplied to the exhaust gas charging unit 120, and includes an ion generation chamber 111 and a first electrode 112. The ion generation chamber 111 is a small space formed inside the casing CS. The air supply hole 55 and the nozzle 41 are provided on the inner peripheral surface, and the first electrode 112 protrudes inside. It has been. The air supply hole 55 communicates with the air supply pipe 224 (FIG. 1) and supplies high-pressure air supplied from the air supply unit 800 (FIG. 1) to the ion generation chamber 111. The nozzle 41 is a minute hole (orifice) provided in the vicinity of the central portion of the partition wall 42 that partitions the exhaust gas charging unit 120, and ions generated in the ion generation chamber 111 enter the charging chamber 121 of the exhaust gas charging unit 120. Supply. The first electrode 112 has a rod-like outer shape, and a base end portion thereof is fixed to the casing CS via the ceramic pipe 25 in a state in which the tip end portion is close to the partition wall 42. The first electrode 112 is connected to the electric circuit portion 700 (FIG. 1) via the first wiring 221 (FIG. 1).

  The ion generator 110 applies a DC voltage (for example, 2 to 3 kV) using the power supplied from the electric circuit unit 700 with the first electrode 112 as an anode and the partition wall 42 as a cathode. The ion generator 110 generates a positive ion PI by generating a corona discharge between the tip of the first electrode 112 and the partition wall 42 by applying this voltage. The positive ions PI generated in the ion generation unit 110 are jetted into the charging chamber 121 of the exhaust gas charging unit 120 through the nozzle 41 together with the high-pressure air supplied from the air supply unit 800 (FIG. 1). It is preferable that the jet speed of the air jetted from the nozzle 41 is about the speed of sound.

  The exhaust gas charging unit 120 is a part for charging the fine particles S contained in the exhaust gas with the cation PI, and includes a charging chamber 121. The charging chamber 121 is a small space adjacent to the ion generation chamber 111 and communicates with the ion generation chamber 111 via the nozzle 41. The charging chamber 121 communicates with the outside of the casing CS via the inflow hole 45 and communicates with the trapping chamber 131 of the ion trapping unit 130 via the gas flow path 31. The charging chamber 121 is configured such that when air containing positive ions PI is ejected from the nozzle 41, the inside becomes negative pressure, and exhaust gas outside the casing CS flows through the inflow hole 45. The air containing the cation PI ejected from the nozzle 41 and the exhaust gas flowing in from the inflow hole 45 are mixed inside the charging chamber 121. At this time, the cation PI supplied from the nozzle 41 is charged to at least a part of the fine particles S contained in the exhaust gas flowing in from the inflow hole 45. The air containing the charged fine particles S and the cations PI that have not been charged is supplied to the trapping chamber 131 of the ion trap 130 via the gas flow path 31.

  The ion trap 130 is a part for trapping ions that have not been used for charging the fine particles S, and includes a trap chamber 131 and a second electrode 132. The capture chamber 131 is a small space adjacent to the charging chamber 121 and communicates with the charging chamber 121 via the gas flow path 31. Further, the capture chamber 131 communicates with the outside of the casing CS via the discharge hole 35. The second electrode 132 has a substantially rod-shaped outer shape whose upper end is tapered, and the longitudinal direction of the second electrode 132 is in the casing CS such that the longitudinal direction is along the flow direction of the air flowing through the gas flow path 31 (the extending direction of the casing CS). It is fixed. The second electrode 132 is connected to the electric circuit portion 700 (FIG. 1) via the second wiring 222 (FIG. 1). A voltage of about 100 V is applied to the second electrode 132 and functions as an auxiliary electrode that assists in capturing positive ions that have not been charged by the fine particles S. Specifically, a voltage is applied to the ion trap 130 with the second electrode 132 as an anode and the casing CS constituting the charging chamber 121 and the trap chamber 131 as a cathode. As a result, the positive ions PI that have not been used for charging the fine particles S receive a repulsive force from the second electrode 132 and are deflected in a direction away from the second electrode 132. The positive ions PI whose traveling direction is deflected are captured by the capture chamber 131 functioning as a cathode and the inner peripheral wall of the gas flow path 31. On the other hand, the fine particles S charged with the cation PI receive a repulsive force from the second electrode 132 in the same manner as the simple cation PI. However, since the mass is larger than that of the cation PI, the degree of deflection due to the repulsive force is Smaller than a single cation PI. Therefore, the charged fine particles S are discharged from the discharge hole 35 to the outside of the casing CS according to the flow of the exhaust gas.

  The fine particle sensor 100 outputs a signal indicating a change in current according to the amount of positive ions PI captured by the ion capturing unit 130. The sensor control unit 600 (FIG. 1) determines the amount of particulates contained in the exhaust gas based on the signal output from the particulate sensor 100.

  FIG. 3 is a block diagram illustrating a schematic configuration of the electric circuit unit 700. The electric circuit unit 700 includes a primary power supply circuit 710, an insulating transformer 720, a corona current measurement circuit 730, a measurement signal generation circuit 740, a first rectifier circuit 751, and a second rectifier circuit 752. ing.

  The primary power supply circuit 710 boosts the DC voltage supplied from the power supply unit 440 and supplies the boosted DC voltage to the insulation transformer 720 and drives the insulation transformer 720. The primary power supply circuit 710 includes a discharge voltage control circuit 711 and a transformer drive circuit 712. The discharge voltage control circuit 711 includes a DC / DC converter, and the supply voltage to the insulation transformer 720 can be arbitrarily changed under the control of the sensor control unit 600. For example, the supply voltage is controlled such that the current value of the input current Iin supplied to the first electrode 112 of the particle sensor 100 via the first wiring 221 becomes a target current value (for example, 5 μA). Practically done. This control method will be described later. Thereby, in the ion generation part 110, the generation amount of the cation PI generated by corona discharge can be made constant.

  The transformer drive circuit 712 includes a switch circuit capable of switching the direction of the current flowing through the primary coil of the insulation transformer 720, and drives the insulation transformer 720 by switching the switch circuit. In this embodiment, the transformer drive circuit 712 is configured as a push-pull circuit, for example, but may be configured as a circuit of another system such as a half-bridge system or a full-bridge system.

  The insulation transformer 720 performs voltage conversion on the power supplied from the primary side power supply circuit 710 and supplies the converted power (here, AC power) to the secondary side rectifier circuits 751 and 752. The insulation transformer 720 can set different amplification factors for the power supplied to the first rectifier circuit 751 and the power supplied to the second rectifier circuit 752 depending on the secondary coil configuration. Is possible. The insulation transformer 720 of this embodiment is configured such that the primary side coil and the secondary side coil are not in physical contact and are coupled magnetically. The primary side circuit of the insulating transformer 720 includes the sensor control unit 600 and the power supply unit 440 in addition to the primary side power supply circuit 710. The secondary side circuit of the insulating transformer 720 includes the particle sensor 100 and rectifier circuits 751 and 752. The corona current measurement circuit 730 and the measurement signal generation circuit 740 are circuits that extend between the primary side circuit and the secondary side circuit of the isolation transformer 720, and are electrically connected to both circuits, respectively. . As will be described later, the corona current measurement circuit 730 has a gap between a circuit portion electrically connected to the primary side circuit of the isolation transformer 720 and a circuit portion electrically connected to the secondary side circuit. It is physically insulated. Here, the ground (ground potential) indicating the reference potential of the primary side circuit is also referred to as “primary side ground PGL”, and the ground indicating the reference potential of the secondary side circuit is also referred to as “secondary side ground SGL”. The end of the primary side coil of the insulating transformer 720 is connected to the primary side ground PGL, and the end of the secondary side coil is connected to the secondary side ground SGL. The casing CS of the particle sensor 100 is connected to the secondary side ground SGL via the signal line 223 and the shunt resistor 230. In the particulate measurement system 10, the primary side ground PGL and the secondary side ground SGL are electrically insulated by an insulating member. Such an insulating member is made of, for example, ceramic or resin, and has high insulating properties (for example, about 1 teraohm).

  The rectifier circuits 751 and 752 convert the AC power output from the insulating transformer 720 into DC power. The first rectifier circuit 751 is connected to the first electrode 112 of the particle sensor 100 via the first wiring 221 and the short protection resistor 753. The second rectifier circuit 752 is connected to the second electrode 132 of the particle sensor 100 via the second wiring 222 and the short protection resistor 754.

  The corona current measurement circuit 730 is connected to both ends of the shunt resistor 230 on the signal line 223 through wirings 761 and 762, and is connected to the sensor control unit 600 through the wiring 763. The corona current measurement circuit 730 outputs a signal Sdc + trp indicating the current value of the current (Idc + Itrp) flowing on the signal line 223 from the casing CS toward the secondary side ground SGL to the sensor control unit 600. Here, the “signal indicating the current value” is not limited to a signal directly indicating the current value, but also a signal indirectly indicating the current value. For example, a signal that can specify a current value by applying an arithmetic expression or a map to information obtained from the signal is also included in the “signal indicating the current value”.

  The sensor control unit 600 controls the discharge voltage control circuit 711 according to the signal Sdc + trp input from the corona current measurement circuit 730. The outline of control of the discharge voltage control circuit 711 by the sensor control unit 600 will be described later.

  The measurement signal generation circuit 740 measures a current Ic corresponding to the current Iesc (hereinafter referred to as “leakage current Iesc”) of the positive ion PI that has flown outside without being captured by the ion trap 130. The measurement signal generation circuit 740 is connected to the secondary-side signal line 223 via the wiring 771 and is connected to the primary-side sensor control unit 600 via the wiring 772. Further, the measurement signal generation circuit 740 is connected to the primary side ground PGL via the wiring 773. The measurement signal generation circuit 740 outputs the measurement signal Sesc to the sensor control unit 600. The measurement signal generation circuit 740 may generate a low sensitivity measurement signal and a high sensitivity measurement signal and output them to the sensor control unit 600, respectively. In this case, one of the low sensitivity measurement signal and the high sensitivity measurement signal may be the measurement signal Sesc.

The relationship of the following formula (1) is established between the currents flowing through the tip 100e of the particle sensor 100.
Iin = Idc + Itrp + Iesc (1)
Here, Iin is an input current of the first electrode 112, Idc is a discharge current flowing through the casing CS via the partition wall 42, and Itrp is a trap corresponding to the charge amount of the cation PI trapped in the casing CS. Iesc is a leakage current corresponding to the charge amount of the cation PI that has flown outside without being captured by the ion trap 130.

Since the discharge current Idc and the trapping current Itrp flow from the casing CS to the secondary side ground SGL via the signal line 223, the total current (Idc + Itrp) flows through the shunt resistor 230 on the signal line 223. Here, the current value of (Idc + Itrp) is substantially equal to the current value of the input current Iin. Leakage current I esc of formula (1) is approximately 1/106 times the magnitude of the current flowing through the signal line 223 (Idc + Itrp), because when the substantially negligible monitors the variation of the input current Iin It is. Since the current value of the input current Iin is equal to the current value of the corona discharge of the ion generator 110, it can be said that the current value of the current (Idc + Itrp) flowing through the signal line 223 is substantially equal to the current value of the corona discharge. From this, it can be said that the corona current measurement circuit 730 outputs a signal Sdc + trp indicating the corona discharge current value of the ion generator 110 to the sensor controller 600. In response to this, the sensor control unit 600 controls the discharge voltage control circuit 711 so that the current value of the input current Iin becomes the target current in accordance with the signal Sdc + trp input from the corona current measurement circuit 730. .

The leakage current Iesc is equal to the difference between the input current Iin and the current flowing through the shunt resistor 230 (Idc + Itrp).
Iesc = Iin− (Idc + Itrp) (2)
A current Ic corresponding to the leakage current Iesc flows through the measurement signal generation circuit 740. The measurement signal generation circuit 740 generates a measurement signal Sesc corresponding to the current Ic and outputs it to the sensor control unit 600. The particle amount determination unit 610 of the sensor control unit 600 determines the amount of particles contained in the exhaust gas based on the measurement signal Sesc.

A2. Configuration example of measurement signal generation circuit:
FIG. 4 is a block diagram illustrating a configuration of the measurement signal generation circuit 740. The measurement signal generation circuit 740 includes an amplifier circuit 741, a negative feedback resistor 742, and a resistor 743. An operational amplifier can be used as the amplifier circuit 741. The inverting input terminal of the amplifier circuit 741 is connected to the secondary side ground SGL via the resistor 743, the wiring 771, and the signal line 223. As shown in FIG. 3, the signal line 223 is connected to the casing CS of the particle sensor. A power supply Vref that applies a constant reference voltage (for example, 0.5 V) to the primary side ground PGL is connected to the non-inverting input terminal of the amplifier circuit 741 via a wiring 773. In the following description, the same reference numeral “Vref” is used to represent the reference voltage of the power supply Vref. When the reference voltage Vref is input to the non-inverting input terminal of the amplifier circuit 741, the potential difference between the two input terminals of the amplifier circuit 741 is brought close to a potential difference range where errors (such as errors due to bias current and offset voltage) are unlikely to occur. Can be adjusted. As will be described in detail later, a current Ic corresponding to the leakage current Iesc (FIG. 3) of the particle sensor 100 flows through the inverting input terminal of the amplifier circuit 741. This current Ic is converted into a voltage E1 by the amplifier circuit 741. The signal Sesc indicating the voltage E1 is supplied as a measurement signal to the sensor control unit 600 via the wiring 772.

  The reason why the current Ic flowing through the inverting input terminal of the amplifier circuit 741 becomes a current corresponding to the leakage current Iesc of the particle sensor 100 is as follows. When the leakage current Iesc is generated, the reference potential of the secondary side ground SGL is lower than the reference potential of the primary side ground PGL according to the magnitude of the leakage current Iesc. This is because energy (power) supplied to the particle sensor 100 from the primary circuit including the primary power supply circuit 710 (FIG. 3) and energy (power) output from the particle sensor 100 via the signal line 223. This is because a difference in energy corresponding to the leakage current Iesc occurs. If a difference occurs between the reference potential of the secondary ground SGL and the reference potential of the primary ground PGL due to the generation of the leakage current Iesc, the compensation current Ic corresponding to this difference is applied to the inverting input terminal of the amplifier circuit 741. Flows. This compensation current Ic is equal to the leakage current Iesc and is a current that compensates for the difference between the reference potential of the secondary side ground SGL and the reference potential of the primary side ground PGL. Therefore, the measurement signal generation circuit 740 can generate the voltage E1 (and the measurement signal Sesc) representing the leakage current Iesc by performing IV conversion of the compensation current Ic.

The output voltage E1 of the amplifier circuit 741 is given by the following equation (3).
E1 = Ic × R1 + Vref (3)
Here, Ic is a compensation current, R1 is a resistance value of the negative feedback resistor 742, and Vref is a reference voltage of the amplifier circuit 741.

  In the sensor control unit 600, the fine particle amount determination unit 610 determines the fine particle amount contained in the exhaust gas with reference to the fine particle amount map mp1 based on the measurement signal Sesc supplied from the measurement signal generation circuit 740. As shown in FIG. 1B, the fine particle amount map mp1 is a two-dimensional map showing the correspondence between the measurement signal Sesc and the fine particle amount. In FIG. 1B, the horizontal axis indicates the amount of fine particles, and the vertical axis indicates the measurement signal Sesc. More precisely, the vertical axis indicates the current value of the current Ic corresponding to the voltage level of the measurement signal Sesc. As shown in the fine particle amount map mp1, the measurement signal Sesc and the fine particle amount are proportional to each other. When the amount of fine particles is zero, the current value of the measurement signal Sesc is zero. The fine particle amount determination unit 610 can determine the amount of fine particles by specifying a current value corresponding to the supplied measurement signal Sesc and referring to the fine particle amount map mp1 based on the current value.

  However, if the insulating property of the insulating member disposed between the primary side ground PGL and the secondary side ground SGL decreases due to aging or the like, leakage occurs between the primary side ground PGL and the secondary side ground SGL. An electric current can be generated. When the leak current is generated, the difference between the reference potential of the secondary side ground SGL and the reference potential of the primary side ground PGL changes from the initial value, so that the value of the leakage current Iesc changes. As a result, the magnitude (voltage) of the measurement signal Sesc deviates from the original value, and an error occurs in the determined amount of fine particles. For example, although the fine particles are not present in the exhaust gas, the leakage current Iesc is detected as a non-zero value, and the detected fine particle amount may not become zero. Further, since the insulating property of the insulating member changes with time, the value of the leakage current Iesc also changes with time, and as a result, the amount of deviation in the magnitude of the measurement signal Sesc also changes with time. Therefore, the measurement error of the amount of fine particles may gradually increase. Therefore, in the fine particle measurement system 10 of the present embodiment, a fine particle amount determination and calibration process described later is executed and corrected using a current value derived based on the measurement signal Sesc, and the correction value used for the correction is updated. By doing so, a decrease in the measurement accuracy of the amount of fine particles is suppressed.

  The air supply control unit 670 described above corresponds to the gas supply control unit in the claims. The air supply unit 800 corresponds to a gas supply unit in claims.

A3. Fine particle amount determination and calibration process:
FIG. 5 is a flowchart showing the procedure of the fine particle amount determination and calibration processing in the present embodiment. FIG. 6 is a flowchart showing the procedure of the fine particle amount determination process in the present embodiment. In the fine particle amount determination and calibration processing, processing for determining the amount of fine particles such as soot contained in the exhaust gas discharged from the internal combustion engine 400 and a correction value used in the determination are set (updated) to appropriate values. Processing. In order to set the correction value to an appropriate value, in this embodiment, the deviation of the measurement signal Sesc when the amount of fine particles in the exhaust gas is essentially zero is specified, and a correction value that cancels this deviation is determined. . In the fine particle measurement system 10, when an ignition-on signal is received from the vehicle control unit 420, fine particle amount determination and calibration processing are executed.

  The fine particle amount determination unit 610 executes a fine particle amount determination process (step S105). Specifically, as shown in FIG. 6, the fine particle amount determination unit 610 identifies the current value of the current Ic corresponding to the voltage level of the measurement signal Sesc and stores it in the current value storage unit 640 (step S205). The fine particle amount determination unit 610 corrects the current value specified in step S205 using the correction value stored in the correction value storage unit 660 (step S210). As described above, the initial value of this correction value is zero, and the correction value can be updated by fine particle amount determination and calibration processing. By setting this correction value to an appropriate value, a signal corresponding to the original amount of fine particles can be obtained even if the measurement signal Sesc shifts due to a decrease in insulation properties of the insulating member.

  The fine particle amount determining unit 610 refers to the fine particle amount map mp1 to determine the fine particle amount based on the corrected current value (step S215). The fine particle amount determination unit 610 stores the fine particle amount determined in step S215 in the fine particle amount storage unit 650 (step S220).

  As shown in FIG. 5, after the fine particle amount determination process (step S110) is completed, the air supply control unit 670 is on standby until a calibration start instruction signal is received from the vehicle control unit 420 (step S110). When the start instruction signal is received (step S110: YES), the pump of the air supply unit 800 is stopped (step S115). As described above, the vehicle control unit 420 outputs a calibration start signal every time the vehicle 500 travels a predetermined distance set in advance, and therefore, the procedure after step S115 is set in advance for the vehicle 500. It is executed every time a predetermined distance is traveled. The supply of high-pressure air to the ion generation chamber 111 is stopped by stopping the driving of the pump in step S115. For this reason, cations PI generated in the ion generation chamber 111 are suppressed from being sent to the charging chamber 121. In addition, since the air containing the cation PI is not jetted from the nozzle 41 into the charging chamber 121, it is possible to suppress the inside of the charging chamber 121 from becoming a negative pressure. For this reason, the inflow of the exhaust gas into the charging chamber 121 through the inflow hole 45 is suppressed. For these reasons, the execution of step S115 suppresses charging of the fine particles in the exhaust gas, and the measurement signal Sesc can be regarded as zero.

  After the completion of step S115, the fine particle amount determination unit 610 continuously specifies a current value of the current Ic corresponding to the voltage level of the measurement signal Sesc and stores it in the current value storage unit 640 a predetermined number of times (N times). The calibration execution unit 620 acquires the stored current values for the predetermined number of consecutive times (step S120). The predetermined number of continuous times in step S120 can be set to an arbitrary number. Further, the accuracy of calibration can be improved by setting the predetermined number of continuous times to a larger number.

  The calibration execution unit 620 calculates the average value of the N current values acquired in step S120 (step S125). When step S125 is executed, the pump remains stopped, so that charging of the fine particles in the exhaust gas is suppressed, and the state in which the amount of fine particles can be regarded as zero remains. For this reason, the current value is essentially zero. However, when a leak current is generated due to a decrease in insulating properties of the insulating member, a current corresponding to the leak current is detected. In addition, by obtaining the average value of N times, it is possible to accurately specify the current value corresponding to the leakage current without errors.

  The calibration execution unit 620 overwrites the correction value stored in the correction value storage unit 660 with the average value calculated in step S125 (step S130). Therefore, when the fine particle amount determination and calibration processing is executed after the execution of step S130, the current value can be corrected using the latest correction value in step S210. That is, the latest leakage current can be canceled and the current value caused by the fine particles in the exhaust gas can be accurately derived. After completion of step S130, the air supply control unit 670 activates the pump of the air supply unit 800 that has been stopped (step S135), and the fine particle amount determination and calibration processing ends.

  According to the particle measurement system 10 of the first embodiment described above, the current value obtained while the supply of high-pressure air to the ion generation unit 110 (ion generation chamber 111) by the air supply unit 800 is stopped. Then, a correction value is obtained, and the current value of the current Ic corresponding to the voltage level of the measurement signal Sesc is corrected using the correction value. Since the charging of the fine particles in the exhaust gas is suppressed by stopping the supply of high-pressure air to the ion generator 110, the current value obtained in such a state is essentially zero. However, when the current value is a value other than zero, this current value is not a current value caused by fine particles in the exhaust gas but is estimated to be a leak current value caused by a decrease in insulating properties of the insulating member. In the particulate measurement system 10, the current value of the current Ic corresponding to the voltage level of the measurement signal Sesc is corrected based on the leakage current value. Therefore, the leakage current value is canceled and the current value caused by particulates in the exhaust gas is accurately obtained. Can be derived. For this reason, it can suppress that the detection accuracy of the amount of particulates in exhaust gas falls. Further, by obtaining the average value of the current values for N times, it is possible to specify the current value corresponding to the leakage current with high accuracy without errors.

  Further, in the fine particle measurement system 10, since ions are generated by corona discharge, a member having a very high insulating property (resistance value) is required as an insulating member between the primary side ground PGL and the secondary side ground SGL. As described above, even if the insulating property of the insulating member is deteriorated due to aging or the like, according to the particle measuring system 10 of the present embodiment, the amount of particles in the exhaust gas can be obtained with high accuracy.

  In the fine particle amount determination and calibration processing, the procedure from step S115 is performed every time a calibration start signal is received from the vehicle control unit 420. In other words, the vehicle 500 is set to a predetermined distance (for example, 5000 kilometers). ) And the correction value is updated each time the vehicle is driven. When the vehicle 500 travels a predetermined distance, there is a high possibility that the insulating member disposed between the primary side ground PGL and the secondary side ground SGL has deteriorated over time and the insulating property thereof has decreased. Therefore, with the configuration of the above embodiment, the correction value can be updated at an appropriate timing with a high possibility that the correction value has changed.

B. Variations:
B1. Modification 1:
In the embodiment, the cation PI is generated by corona discharge, and the fine particle S is charged by mixing the cation PI with the exhaust gas flowing into the charging chamber. However, the present invention is not limited to this. For example, the present invention is applied to a fine particle measuring system 10 having a charged portion in a sensor body that makes charged particles charged with fine particles S by attaching particles on the surface of the electrode and applying a high voltage to the electrode. (See, for example, US Patent Publication US2012 / 0312074A1 and US Patent Publication US2013 / 0219990A1).

B2. Modification 2:
In the embodiment, the fine particle amount determination and the calibration process are executed in the sensor control unit 600, but at least a part of the process may be executed in the vehicle control unit 420. For example, step S105 (particulate amount determination processing) may be executed by the sensor control unit 600 (particulate amount determination unit 610), and steps S110 to S135 may be executed by the vehicle control unit 420. In this configuration, in step S <b> 120, the vehicle control unit 420 may acquire N current values from the sensor control unit 600. In step S130, the vehicle control unit 420 transmits the average value calculated in step S125 to the sensor control unit 600, and the sensor control unit 600 overwrites and stores the received average value in the correction value storage unit 660. That's fine. In this configuration, the vehicle control unit 420 corresponds to a calibration execution unit in claims.

B3. Modification 3:
In the embodiment, the calibration start instruction signal is output every time the vehicle 500 travels a predetermined distance (for example, 5000 kilometers) set in advance, but the present invention is not limited to this. It is not limited to 5000 kilometers and may be output every time the vehicle travels an arbitrary distance. Further, for example, it may be output when a predetermined switch arranged on an instrument panel or the like in the vehicle 500 is turned on by a driver or the like. With such a configuration, the driver can calibrate the correction value at any desired timing. Further, for example, it may be output when the integrated value of the operation time has reached a predetermined threshold. This configuration also has the same effect as the configuration triggered by the above-described travel distance reaching a predetermined threshold. Further, for example, it may be configured such that time is measured by a timer (not shown) and is periodically output when a predetermined period (for example, 30 days) elapses.

B4. Modification 4:
In the embodiment, the correction of the current value of the measurement signal Sesc and the update of the correction value used for the correction are performed in the fine particle amount determination and calibration processing, but the present invention is not limited to this. For example, in the fine particle amount determination process, the fine particle amount may be determined based on the current value of the measurement signal Sesc, the determined fine particle amount may be corrected, and a correction value used to correct the fine particle amount may be updated. . In this configuration, for example, the amount of fine particles is obtained based on the current value obtained with the pump stopped, and the amount of fine particles is determined as a correction value. Since the amount of fine particles obtained in this state is essentially zero, the amount of fine particles obtained as a value other than zero corresponds to the amount of fine particles corresponding to an error obtained due to a cause such as a leak current. Therefore, in the fine particle amount determination process, the fine particle amount can be obtained with high accuracy by subtracting the fine particle amount corresponding to the error from the fine particle amount determined based on the current value of the measurement signal Sesc.

B5. Modification 5:
In step S215 of the fine particle amount determination process of the embodiment, the fine particle amount is determined with reference to the fine particle amount map. Instead of the map, a relational expression indicating the relationship between the voltage value of the measurement signal Sesc and the fine particle amount is used. The amount of fine particles may be determined by calculating using.

B6. Modification 6:
In the embodiment, in step S115 of the fine particle amount determination and calibration process, the pump is stopped and the supply of high-pressure air to the ion generator 110 is stopped. However, the present invention is not limited to this. For example, in a state where the supply of high-pressure air by the air supply unit 800 is stopped, when the atmospheric pressure in the charging chamber 121 is higher than the atmospheric pressure in the exhaust gas pipe 402, high-pressure air is supplied by the air supply unit 800. However, the atmospheric pressure in the charging chamber 121 may be relatively high. In such a case, the air supply unit 800 may be driven to supply high-pressure air to the ion generation unit 110. However, in this case, it is required to supply air to such an extent that the exhaust gas (fine particles) in the exhaust gas pipe 402 does not flow into the charging chamber 121. That is, in general, the calibration execution unit 620 preferably executes the calibration process when the supply amount of high-pressure air to the ion generation unit 110 is a predetermined supply amount that satisfies the condition that fine particles do not flow into the charging chamber 121. .

B7. Modification 7:
In the embodiment, when step S115 (pump drive stop) is completed, the current value acquisition (step S120) for a predetermined number of times has been performed. However, a standby period is maintained between these two steps S115 and S120 for a predetermined period. You may provide the step to do. When there is a cation PI that is not charged by the fine particles S and not captured by the casing CS in the charging chamber 121 at the time when the pump is stopped, the cation PI then enters the fine particles in the charging chamber 121. By charging S, a measurement signal Sesc (leakage current Iesc) due to charging of the fine particles can be generated. In this case, there is a possibility that the leakage current due to the decrease in insulation cannot be accurately specified. On the other hand, by waiting for a predetermined period after step S115, the calibration process can be executed in a state where the amount of cations PI that are not charged with the fine particles S and not captured by the casing CS is reduced. For this reason, the leak current can be specified with high accuracy.

B8. Modification 8:
In the embodiment, the fine particle measurement system 10 is mounted on the vehicle 500 and measures the amount of fine particles contained in the exhaust gas of the internal combustion engine 400, but the present invention is not limited to this. Fine particles contained in the exhaust gas of any other internal combustion engine such as an internal combustion engine mounted on an arbitrary moving body such as a ship or a stationary internal combustion engine may be measured.

  The present invention is not limited to the above-described embodiments and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments and the modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10 ... Fine particle measurement system 25 ... Ceramic pipe 31 ... Gas flow path 35 ... Discharge hole 41 ... Nozzle 42 ... Partition wall 45 ... Inflow hole 55 ... Air supply hole 100 ... Fine particle sensor 100e ... Tip part 100r ... Rear end part 110 ... Ion generation Part 111 ... Ion generation chamber 112 ... First electrode 120 ... Exhaust gas charging part 121 ... Charging chamber 130 ... Ion trap part 131 ... Trapping chamber 132 ... Second electrode 200 ... Cable 221 ... First wiring 222 ... Second Wiring 223 ... Signal line 224 ... Air supply pipe 230 ... Shunt resistance 300 ... Sensor drive part 400 ... Internal combustion engine 402 ... Exhaust gas pipe 405 ... Fuel pipe 406 ... Sensor 410 ... Filter device 420 ... Vehicle control part 430 ... Fuel supply part 440 ... Power supply unit 500 ... Vehicle 600 ... Sensor control unit 610 ... Fine particle amount determination unit 620 ... Calibration Execution unit 630 ... Map storage unit 640 ... Current value storage unit 650 ... Particle amount storage unit 660 ... Correction value storage unit 670 ... Air supply control unit 700 ... Electric circuit unit 710 ... Primary power supply circuit 711 ... Discharge voltage control circuit 712 ... Transformer drive circuit 720 ... insulation transformer 730 ... corona current measurement circuit 740 ... measurement signal generation circuit 741 ... amplification circuit 742 ... negative feedback resistor 743 ... resistor 751 ... first rectifier circuit 752 ... second rectifier circuit 753 ... for short circuit protection Resistance 754... Short protection resistance 761, 763... Wiring 771 to 773 .. wiring 800 .. air supply CS .. casing DL .. extension direction E1 ... voltage F ... arrow Ic ... current and compensation current Idc ... discharge current Iin ... input current Iesc ... current, leakage current Itrp ... trapping current PI ... positive ion PGL ... primary side ground S ... fine particle S esc ... Measurement signal Sdc + trp ... Signal SGL ... Secondary side ground Vref ... Power supply, reference voltage

Claims (3)

An ion generator for generating ions;
A charging chamber for charging at least some of the fine particles in the exhaust gas of the internal combustion engine, and charging the flowing fine particles using the ions;
A gas supply unit that supplies a predetermined type of gas to the ion generation unit, sends the ions generated from the ion generation unit to the charging chamber, and promotes the inflow of the fine particles into the charging chamber;
A gas supply control unit for controlling a supply amount of the gas by the gas supply unit;
An ion trapping part for trapping at least a part of the ions not used for charging the fine particles;
Based on the current value corresponding to the difference between the amount of captured the ions to the amount and the ion trapping portion of the ions generated from the ion generating unit, it outputs a measurement signal which correlates to the quantity of particulate in the exhaust gas A measurement signal generation circuit to
A fine particle amount determining unit that determines the fine particle amount based on the measurement signal;
A particulate measurement system comprising:
Correction of any of the deviation of the measurement signal when the amount of fine particles is zero and the deviation of the amount of fine particles specified based on the measurement signal when the amount of fine particles is zero. A calibration execution unit for executing the calibration;
The calibration execution unit executes the correction when the supply amount of the gas is a predetermined supply amount that satisfies a condition that the fine particles do not flow into the charging chamber.
A fine particle measuring system characterized by that. The fine particle measurement system according to claim 1,
The predetermined supply amount is zero;
A fine particle measuring system characterized by that. The fine particle measurement system according to claim 1 or 2,
The ion generator generates the ions by corona discharge.
A fine particle measuring system characterized by that.

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