JP2016075674A - Fine particle measurement system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the measurement accuracy of the fine particle amount in a fine particle measurement system.SOLUTION: The fine particle measurement system includes: an ion generation unit for generating ions by corona discharge; an electrification chamber for electrifying fine particles in a gas to be measured; a measurement signal generation circuit for generating a measurement signal correlated with the fine particle amount; a fine particle amount determination unit for determining the fine particle amount; and a particle size estimation unit for estimating the particle size of the fine particles in the gas to be measured. The fine particle amount determination unit performs correction by multiplying the measurement signal or the fine particle amount determined from the measurement signal by a coefficient related to the ratio between the estimated particle size and a reference particle size.SELECTED DRAWING: Figure 11

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.

  Conventionally, a fine particle measurement system for measuring 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 Documents 1 and 2). This fine particle measurement system generates ions by corona discharge, charges the fine particles contained in the exhaust gas by the generated ions, captures ions that are not used for charging the fine particles, and based on the amount of captured ions ( Conversely, the amount of fine particles contained in the exhaust gas is measured (based on the amount of ions that are charged and not captured). 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 contained in the exhaust gas. The amount of fine particles in the exhaust gas stream can be measured from the amount of ions.

Special table 2013-520669 gazette Special table 2014-501391 gazette

  However, the inventors of the present application show that the relationship between the measurement signal representing the current value of the current corresponding to the above-described ion amount and the amount of fine particles varies considerably due to the influence of the difference in the particle size of fine particles such as soot. Therefore, the new subject that a measurement precision fell will be discovered.

  In order to solve the above problems, the present invention can be realized as the following forms.

(1) According to one aspect of the present invention, an ion generation unit that generates ions by corona discharge; a charging chamber for charging at least some of the fine particles in the measurement gas using the ions; A capture unit that captures at least a part of the ions that are not used for charging the fine particles; and corresponds to a difference between the amount of ions generated from the ion generation unit and the amount of ions captured by the capture unit A measurement signal generating circuit that generates a measurement signal that correlates with the amount of fine particles in the measurement gas based on a current value; a fine particle amount determination unit that determines the amount of fine particles in the measurement gas based on the measurement signal A particulate measurement system is provided. The fine particle measurement system further includes a particle size estimation unit that estimates the particle size of the fine particles in the gas to be measured; the fine particle amount determination unit includes the estimated particle size and a reference particle size; Correction is performed by multiplying the measurement signal or the amount of fine particles determined from the measurement signal by a coefficient related to the ratio. According to the fine particle measurement system of this embodiment, the correction is performed by multiplying the measurement signal or the amount of fine particles determined from the measurement signal by a coefficient related to the ratio between the estimated particle size and the reference particle size. And the amount of fine particles, the influence of fluctuation due to the difference in particle size can be reduced, and the measurement accuracy of the amount of fine particles can be improved.

(2) In the fine particle measurement system, the fine particle amount determination unit may perform the correction according to the following formula to determine the mass concentration of the fine particles as the fine particle amount:
y = y ₀ × (B / A) ^N
Here, y is the corrected measurement signal or mass concentration of fine particles, y ₀ is the measurement signal or fine particle mass concentration before correction, A is the reference particle size, B is the estimated particle size, and N is It is an integer of 2 or more.
According to this configuration, the measurement accuracy of the mass concentration of the fine particles can be improved only by performing correction according to the above formula. By setting N = 2, the measurement accuracy of the mass concentration of the fine particles can be obtained with a sufficient calculation accuracy based on a simple arithmetic expression.

(3) In the fine particle measurement system, the fine particle amount determination unit may perform the correction according to the following formula to determine the mass concentration of the fine particles as the fine particle amount:
y = y ₀ × (A / B)
Here, y is the corrected measurement signal or particle number concentration, y ₀ is the corrected measurement signal or particle number concentration, A is the reference particle size, and B is the estimated particle size.
According to this configuration, it is possible to improve the measurement accuracy of the number concentration of the fine particles only by performing correction according to the above formula.

(4) In the fine particle measurement system, the fine particle measurement system may measure the amount of fine particles contained in exhaust gas of an internal combustion engine of a vehicle.
According to this configuration, it is possible to improve the measurement accuracy of the amount of fine particles contained in the exhaust gas of the internal combustion engine of the vehicle, and to accurately detect deterioration or abnormality of the filter device that captures the fine particles contained in the exhaust gas. It becomes.

(5) In the fine particle measurement system, the particle size estimation unit may estimate the particle size based on a parameter related to driving of the internal combustion engine.
It is considered that the parameters relating to the driving of the internal combustion engine affect the particle size of the fine particles contained in the exhaust gas. Therefore, according to this configuration, it is possible to improve the estimation accuracy of the particle size and improve the measurement accuracy of the amount of fine particles.

(6) In the fine particle measurement system, the particle size estimation unit may estimate the particle size based on a plurality of different parameters.
According to this configuration, the accuracy of particle size estimation can be increased and the measurement accuracy of the amount of fine particles can be improved compared to a configuration in which the particle size is estimated based on one type of parameter.

(7) In the fine particle measurement system, it is preferable that the plurality of parameters different from each other include at least the rotational speed of the internal combustion engine and the fuel injection amount.
Since the rotational speed of the internal combustion engine and the fuel injection amount are considered to particularly affect the particle size of the fine particles contained in the exhaust gas, the measurement accuracy of the fine particle amount can be improved by using these parameters.

  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. FIG. 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 graph which shows an example of the particle size distribution of the microparticles | fine-particles S contained in waste gas. It is explanatory drawing which shows the example of the map of a particle size peak value. It is a graph which shows an example of the relationship between the mass concentration of microparticles | fine-particles S contained in waste gas, and a measurement signal. It is a graph which shows the result of having corrected by the above-mentioned formula (4) about the data of FIG. It is a graph which shows an example of the relationship between the number density | concentration of the microparticles | fine-particles S contained in waste gas, and a measurement signal. It is a graph which shows the result of having correct | amended by the said Formula (5) regarding the data of FIG. It is a flowchart which shows the procedure of fine particle amount determination processing.

A. Embodiment A-1. Device Configuration FIG. 1 is an explanatory diagram showing a schematic configuration of a vehicle to which a particulate measurement system according to 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 the exhaust gas discharged from the internal combustion engine 400 as a gas to be measured. 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 concept including operating condition parameters of the internal combustion engine 400 and environmental parameters that change as the internal combustion engine 400 operates. 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 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 are applicable. As an environmental parameter that varies depending on the operation of the internal combustion engine 400, for example, the exhaust gas temperature of the internal combustion engine 400 corresponds. These parameters relating to the driving of the internal combustion engine 400 are parameters that are considered to affect the particle size of the fine particles contained in the exhaust gas.

  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” is “the fine particle mass concentration” proportional to the mass of fine particles contained in the unit volume of exhaust gas, and “the fine particle amount” proportional to the number of fine particles contained in the unit volume of exhaust gas. It is measured as “number concentration”. Note that only one of “mass concentration of fine particles” and “number concentration of fine particles” may be measured. 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. 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. In the figure, the direction in which the exhaust gas flows is indicated by an arrow F.

  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 controls the electric circuit unit 700 and the air supply unit 800. The sensor control unit 600 includes a fine particle amount determination unit 610 and a particle size estimation unit 620. The fine particle amount determining unit 610 determines the amount of fine particles contained in the exhaust gas based on the signal input from the electric circuit unit 700. 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 particle size estimation unit 620 estimates the particle size of the fine particles contained in the exhaust gas. Specifically, as will be described later, the particle diameter of the fine particles is estimated based on signals relating to driving of the internal combustion engine 400 input from various sensors 406 to the vehicle control unit 420.

  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.

  The air supply unit 800 includes a pump (not shown), and supplies high-pressure air to the particulate sensor 100 via the air supply pipe 224 based on an instruction from the sensor control unit 600. 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, another type of gas may be supplied to the particle sensor 100.

  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 trapping unit 130 with the second electrode 132 as an anode and the casing CS constituting the charging chamber 121 and the trapping 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 as in the case of the cation PI alone, but the mass thereof is larger than that of the cation PI, so 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 fine particles contained in the exhaust gas based on the signal output from the fine particle sensor 100. A method for determining the amount of fine particles contained in the exhaust gas based on the signal output from the fine particle sensor 100 will be described later.

  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.

  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. Here, 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 Iesc of formula (1) is approximately 1/10 of approximately ⁶ times the magnitude of the current flowing through the signal line 223 (Idc + Itrp), it is substantially ignored when monitoring the fluctuation of the input current Iin This is because it can. Since the current value of the input current Iin is equal to the current value of the corona current 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 current. From this, it can be said that the corona current measurement circuit 730 outputs a signal Sdc + trp indicating the current value of the corona current 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 value in accordance with the signal Sdc + trp input from the corona current measurement circuit 730. To do.

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. At this time, correction described later is executed.

A-2. 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 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. 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.

  The sensor control unit 600 determines the amount of fine particles contained in the exhaust gas based on the measurement signal Sesc supplied from the measurement signal generation circuit 740. As a method for determining the amount of particulates contained in the exhaust gas based on the measurement signal Sesc, for example, a method of referring to a map showing a correspondence relationship between the voltage value of the measurement signal Sesc and the amount of particulates contained in the exhaust gas, A method using a relational expression showing the relationship between the voltage value of the measurement signal Sesc and the amount of fine particles contained in the exhaust gas can be used. The sensor control unit 600 converts the voltage value of the measurement signal Sesc as an analog signal into a digital value with a predetermined resolution (for example, 8 bits).

A-3. FIG. 5 is a graph showing an example of the particle size distribution of the fine particles S contained in the exhaust gas. The horizontal axis is the particle size (diameter) (nm) of the fine particles, and the vertical axis is the number of particles (pieces / cm ³ ). The particle size of the fine particles S contained in the exhaust gas is not single, but shows a bell-shaped distribution curve in which the number of particles becomes maximum at a certain particle size. The particle size distribution of the fine particles S changes according to the operating conditions of the internal combustion engine 400, and the particle size peak value also changes accordingly. FIG. 5 shows the particle size distribution of the fine particles S when the operating conditions of the internal combustion engine 400 are three different conditions. The particle size peak values of the fine particles S under three kinds of conditions are 75 nm, 87 nm, and 97 nm, respectively.

  In the present embodiment, the “particle size peak value” refers to the particle size distribution of the fine particles S contained in the exhaust gas when the internal combustion engine 400 is operated under predetermined operating conditions (such as the rotational speed of the internal combustion engine 400 and the fuel injection amount). Means the value of the particle diameter having the largest number of particles. In the present embodiment, the particle size peak value corresponds to the particle size in the claims.

  The particle size estimation unit 620 estimates the particle size peak value of the fine particles S based on parameters relating to driving of the internal combustion engine 400 input from various sensors 406 to the vehicle control unit 420. In the present embodiment, the rotational speed of the internal combustion engine 400 and the fuel injection amount are used as parameters relating to the driving of the internal combustion engine 400. This is because these parameters are considered to particularly affect the particle size of the fine particles S contained in the exhaust gas.

  FIG. 6 is an explanatory diagram illustrating an example of a particle size peak value map. The map shown in FIG. 6 shows a correspondence relationship between the rotational speed and fuel injection amount of the internal combustion engine 400 and the particle size peak value of the fine particles S. In the present embodiment, the particle size estimation unit 620 estimates the particle size peak value of the fine particles S contained in the exhaust gas by referring to a two-dimensional map as shown in the figure. Instead of the map, a relational expression indicating the relationship between the rotational speed and fuel injection amount of the internal combustion engine 400 and the particle size peak value of the fine particles S contained in the exhaust gas may be used.

A-4. Correction of measurement results according to operating conditions A-4-1. Correction of Mass Concentration of Fine Particles FIG. 7 is a graph showing an example of the relationship between the mass concentration of the fine particles S contained in the exhaust gas and the measurement signal. The horizontal axis represents the mass concentration (mg / m ³ ) of the fine particles S contained in the exhaust gas, and the vertical axis represents the measurement signal Sesc. To be precise, the vertical axis is represented by the current value (pA) of the current Ic corresponding to the voltage level of the measurement signal Sesc. FIG. 7 shows the relationship between the mass concentration and the measurement signal for three types of conditions in which the particle size peak values of the fine particles S are different from each other. The particle size peak values of the fine particles S under the three types of conditions are 75 nm, 87 nm, and 97 nm, respectively, as in FIG. In the figure, for each of the three types of conditions, a first-order approximate expression y = a · x and a correlation coefficient R ² relating to measurement points obtained under each condition are shown. In general, as R ² is larger (that is, closer to 1), the degree of correlation is higher.

  As described above, in the particulate measurement system 10 of this embodiment, the amount of particulates contained in the exhaust gas is determined based on the measurement signal Sesc. However, it can be seen from FIG. 7 that when the particle size peak values of the fine particles S are different from each other, the relationship between the mass concentration and the measurement signal is also different. Therefore, in this embodiment, by correcting the measurement signal Sesc based on the particle size of the fine particles S, the influence (measurement error) due to the difference in the particle size peak value on the relationship between the measurement signal Sesc and the mass concentration of the fine particles S. Reduce.

  By the way, it is considered that the particle size of the fine particles S contained in the exhaust gas discharged from the internal combustion engine 400 is in the range of 10 nm to 300 nm. In general, the fine particles S having a particle size within this range have a charge number that is approximately directly proportional to the particle size when charged by colliding with the cation PI, and the proportionality constant can be regarded as 1. it can. Therefore, for example, when the particle size of a certain fine particle is twice the particle size of another fine particle, the charge number becomes twice the charge number of other fine particles. When the particle size of a certain fine particle is twice that of the other fine particles, the mass thereof is eight times the mass of the other fine particles. As described above, the particle diameter of the fine particles S has a predetermined distribution. Hereinafter, the “particle diameter of the fine particles S” means the particle diameter peak value of the fine particles S.

In this embodiment, when determining the mass concentration of the fine particles S, the measurement signal Sesc is corrected according to the following equation (4).
y = y ₀ × (B / A) ^N (4)
In equation (4), y is the corrected measurement signal Sesc, y0 is the corrected measurement signal Sesc, A is the reference particle size peak value, B is the estimated particle size peak value, and N is an integer of 2 or more. (In this embodiment, N = 2) is shown respectively. The reference particle size peak value is set in advance by the user. When the corrected measurement signal Sesc is obtained, the mass concentration of the fine particles S is determined based on the above-described map and relational expression using the signal. The map and the relational expression used at this time (the map showing the correspondence between the voltage value of the measurement signal Sesc and the amount of fine particles contained in the exhaust gas, and the relational expression showing the correspondence) are used as reference particles. This is a map and relational expression derived when fine particles having a diameter peak value (hereinafter referred to as “reference fine particles”) are contained in the exhaust gas.

Here, the mass of the fine particles S having the estimated particle diameter peak value is (B / A) ³ times the mass of the reference fine particles. On the other hand, since the charge number of the fine particle S having the estimated particle size peak value is B / A times the charge number of the reference fine particle, the measurement signal Sesc before correction is output when the reference fine particle is included in the exhaust gas. The measured signal Sesc is B / A times. Accordingly, in the fine particles S and the reference particles having the estimated particle size peak value, the ratio of the uncorrected measurement signal Sesc becomes with respect to the mass ratio of the fine particles (B / A) ² times smaller value. Therefore, in this embodiment, the measurement signal Sesc and the fine particles are obtained by multiplying the measurement signal Sesc (the measurement signal Sesc when the fine particles S having the estimated particle size peak value are included in the exhaust gas) by (B / A) ^2. About the relationship with the mass concentration of S, the measurement error by the difference in a particle size peak value is reduced.

  FIG. 8 is a graph showing the result of correcting the data of FIG. 7 by the above equation (4). FIG. 8 shows the results of correction with the reference particle size peak value set to 75 nm and the estimated particle size peak values set to 87 nm and 97 nm. With this correction, it can be seen that the measurement error due to the difference in the particle diameter peak value is reduced in the relationship between the measurement signal Sesc and the mass concentration of the fine particles S. Thus, by performing the correction according to the above equation (4), the measurement accuracy of the mass concentration of the fine particles S can be improved.

A-4-2. Correction of Number Concentration of Fine Particles FIG. 9 is a graph showing an example of the relationship between the number concentration of fine particles S contained in exhaust gas and the measurement signal. The horizontal axis represents the number concentration (1 million particles / m ³ ) of the fine particles S contained in the exhaust gas, and the vertical axis represents the measurement signal Sesc. To be precise, the vertical axis is represented by the current value (pA) of the current Ic corresponding to the voltage level of the measurement signal Sesc. FIG. 9 shows the relationship between the number concentration and the measurement signal for three types of conditions in which the particle size peak values of the fine particles S are different from each other. The particle size peak values of the fine particles S under the three types of conditions are 75 nm, 87 nm, and 97 nm, respectively, as in FIG. In the figure, for each of the three types of conditions, a first-order approximate expression y = a · x and a correlation coefficient R ² relating to measurement points obtained under each condition are shown. Similar to the mass concentration described above, according to FIG. 9, it can be seen that when the particle size peak values of the fine particles S are different from each other, the relationship between the number concentration and the measurement signal is also different.

In this embodiment, when determining the number concentration of the fine particles S, the measurement signal Sesc is corrected according to the following equation (5).
y = y ₀ × (A / B) (5)
In the formula (5), y is the measurement signal Sesc corrected, y ₀ is the uncorrected measurement signal Sesc, particle size peak value A as a reference, B is the estimated particle size peak value, respectively. The reference particle size peak value is the same as the reference particle size peak value in the above-described equation (4). When the corrected measurement signal Sesc is obtained, the number concentration of the fine particles S is determined based on the above-described map and relational expression using the signal.

  As described above, since the charge number of the fine particles S having the estimated particle size peak value is B / A times the charge number of the reference fine particles, the measurement signal Sesc before correction includes the reference fine particles in the exhaust gas. In this case, it is B / A times the measurement signal Sesc output. Therefore, the ratio of the measurement signal Sesc before correction between the fine particle S having the estimated particle size peak value and the reference fine particle is B / A times larger than the number ratio of the fine particles. Therefore, in this embodiment, by multiplying the measurement signal Sesc by A / B, which is the reciprocal of B / A, the measurement error due to the difference in the particle size peak value is obtained for the relationship between the measurement signal Sesc and the number concentration of the fine particles S. Reduce.

  FIG. 10 is a graph showing the result of correcting the data of FIG. 9 by the above equation (5). FIG. 10 shows the result of correction with the reference particle size peak value set to 75 nm and the estimated particle size peak values set to 87 nm and 97 nm. With this correction, it can be seen that the measurement error due to the difference in particle diameter peak value is reduced in the relationship between the measurement signal Sesc and the number concentration of the fine particles S. Thus, by performing the correction according to the above equation (5), the measurement accuracy of the number concentration of the fine particles S can be improved.

A-5. Fine Particle Amount Determination Processing A fine particle amount determination method based on the correction of the measurement signal Sesc described above will be described with reference to FIG. FIG. 11 is a flowchart showing the procedure of the fine particle amount determination process. In the fine particle measurement system 10, when the ignition is turned on in the vehicle 500, the fine particle amount determination process is executed. The sensor control unit 600 waits until the internal combustion engine 400 is turned on (step S905). When the internal combustion engine 400 is turned on (step S905: YES), the sensor control unit 600 determines whether it is necessary to determine the amount of fine particles (step S910). If it is determined that determination of the amount of fine particles is not necessary (step S910: NO), the process returns to step S905.

  On the other hand, when it is determined that the determination of the amount of fine particles is necessary (step S910: YES), the fine particle amount determination unit 610 acquires the measurement signal Sesc of the fine particle sensor 100 (step S915), and the measurement signal Sesc. Is stored (step S920). The particle size estimation unit 620 receives the signal from the sensor 406, and acquires the rotational speed and the fuel injection amount of the internal combustion engine 400 (step S925). The particle size estimation unit 620 estimates the particle size peak value of the fine particles S by referring to the map (step S930). The fine particle amount determination unit 610 corrects the measurement signal Sesc by the above-described method using the particle size peak value of the fine particles S estimated by the particle size estimation unit 620 (step S935). The fine particle amount determination unit 610 determines the fine particle amount (mass concentration and number concentration of the fine particles S) based on the corrected measurement signal Sesc (step S940). When the amount of fine particles is determined, the process returns to step S905 described above.

In the fine particle measurement system 10 of the present embodiment described above, the particle size peak value of the fine particles S contained in the exhaust gas is estimated, and the coefficient (the coefficient relating to the ratio between the estimated particle size peak value and the reference particle size peak value ( The measurement signal Sesc is corrected by multiplying the measurement signal Sesc by (B / A) ^N (N = 2 in this embodiment) or A / B). For this reason, measurement errors due to differences in particle size peak values can be reduced, and the measurement accuracy of the amount of fine particles can be improved. Further, since the particle size peak value is estimated based on two types of parameters (the rotational speed of the internal combustion engine 400 and the fuel injection amount) related to the driving of the internal combustion engine 400, the particle size peak value is estimated based on one type of parameter. Compared to the configuration, the estimation accuracy of the particle size peak value can be increased, and the measurement accuracy of the amount of fine particles can be improved. In addition, since the rotational speed and fuel injection amount of the internal combustion engine 400 are considered to particularly affect the particle size of the fine particles S contained in the exhaust gas, using these parameters increases the estimation accuracy of the particle size peak value. And the measurement accuracy of the amount of fine particles can be improved. Furthermore, by using the particle size peak value as the particle size of the fine particles S, a map for estimating the particle size can be easily constructed. In addition, since the measurement accuracy of the amount of fine particles contained in the exhaust gas of the internal combustion engine 400 of the vehicle 500 can be improved, it is possible to accurately detect deterioration or abnormality of the filter device that captures the fine particles contained in the exhaust gas. Become.

B. Modifications Note that the present invention is not limited to the above-described embodiment, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

B-1. Modification 1
The configuration of the particle measurement system 10 described in the embodiment is an exemplification, and the present invention can be realized by a configuration other than the particle measurement system 10 described in the embodiment. For example, the fine particle measurement system 10 may not include the second electrode 132. In the fine particle measurement system 10, the ion generation unit 110 may be configured separately from the fine particle sensor 100 instead of inside the fine particle sensor 100. Further, the first electrode 112 is disposed in the charging chamber 121 so as to penetrate the front and rear of the partition wall 42, and a corona discharge is generated between the distal end portion of the first electrode 112 and the inner wall surface of the charging chamber 121. May be. In this case, the ion generation unit 110 and the exhaust gas charging unit 120 are integrated. The measurement signal generation circuit 740 may be any circuit as long as it can generate a signal indicating the amount of fine particles, and various configurations other than the configurations described in the above-described embodiments can be employed.

B-2. Modification 2
The fine particle measurement system 10 of the above-described embodiment is configured to generate cations between the first electrode 112 and the partition wall 42 by corona discharge, but the fine particle measurement system 10 generates anions by corona discharge. It is good also as a structure.

B-3. Modification 3
In the embodiment, the measurement signal Sesc is corrected. However, instead of the measurement signal Sesc, the mass concentration and the number concentration of the fine particles S determined based on the measurement signal Sesc may be corrected. Also in this case, in the above equation (4), a correction equation in which y is the mass concentration of the fine particle S after correction and y ₀ is the mass concentration of the fine particle S before correction can be used. Similarly, in the above equation (5), it is possible to use a correction equation in which y is the number concentration of the fine particles S after correction, and y ₀ is the number concentration of the fine particles S before correction. Even in this case, the measurement accuracy of the amount of fine particles can be improved by simple correction. In the above formula (4), N = 2 is used in the present embodiment, but the measurement accuracy of the mass concentration of the fine particles using an integer greater than 2 as the value of N according to the use environment of the fine particle sensor 100 or the like. You may make it improve.

B-4. Modification 4
In the embodiment, the particle size peak value of the fine particles S is estimated based on the parameters of the rotational speed of the internal combustion engine 400 and the fuel injection amount, but the present invention is not limited to this. Instead of the rotational speed of the internal combustion engine 400 and 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, the EGR opening / closing degree, the intake to the internal combustion engine 400 Other operating condition parameters such as air amount, ignition timing, etc. may be used. Further, instead of the operating condition parameter, an environmental parameter (such as the exhaust gas temperature of the internal combustion engine 400) that changes due to the operation of the internal combustion engine 400 may be used. This is because these parameters are considered to affect the particle size of the fine particles S contained in the exhaust gas. In the embodiment, the particle size peak value of the fine particle S is estimated based on two types of parameters. However, the particle size peak value of the fine particle S is calculated using one type of parameter or a plurality of three or more types of parameters. It may be estimated.

B-5. Modification 5
In the embodiment, the particle size peak value of the fine particles S is used as the particle size used for determining the amount of fine particles. However, instead of the particle size peak value, an average value of the particle sizes of the fine particles S may be used. Even in the configuration using the average value of the particle size, a map for estimating the particle size can be easily configured. In this case, the average value of the particle diameter of the fine particles S corresponds to the particle diameter in the claims.

B-6. Modification 6
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. Also, the amount of particulates contained in the flue gas in the factory chimney may be measured, or the amount of soot and other arbitrary particulates contained in a certain space may be measured as an environmental monitor in an office or road. Good.

DESCRIPTION OF SYMBOLS 10 ... Fine particle measurement system 31 ... Gas flow path 35 ... Discharge hole 41 ... Nozzle 42 ... Partition 45 ... Inflow hole 100 ... Fine particle sensor 110 ... Ion generation part 111 ... Ion generation chamber 112 ... 1st electrode 120 ... Exhaust gas charging part 121 DESCRIPTION OF SYMBOLS ... Charging chamber 130 ... Ion capture part 131 ... Capture chamber 132 ... Second electrode 221 ... First wiring 222 ... Second wiring 223 ... Signal line 230 ... Shunt resistance 300 ... Sensor drive part 400 ... Internal combustion engine 402 ... Exhaust gas Pipe 405 ... Fuel pipe 410 ... Filter device 420 ... Vehicle control unit 430 ... Fuel supply unit 500 ... Vehicle 600 ... Sensor control unit 610 ... Fine particle amount determination unit 620 ... Particle size estimation unit 700 ... Electric circuit unit S ... Fine particle

Claims (7)

An ion generator that generates ions by corona discharge;
A charging chamber for charging at least some of the fine particles in the gas to be measured using the ions;
A capturing section that captures at least a part of the ions that were not used for charging the fine particles;
Based on the current value corresponding to the difference between the amount of ions generated from the ion generator and the amount of ions trapped by the trap, a measurement signal that correlates with the amount of fine particles in the gas to be measured is generated. A measurement signal generation circuit to
A fine particle measurement system comprising: a fine particle amount determination unit that determines a fine particle amount in the measurement gas based on the measurement signal;
Furthermore, a particle size estimation unit for estimating the particle size of the fine particles in the gas to be measured is provided,
The fine particle amount determination unit performs correction by multiplying the measurement signal or the fine particle amount determined from the measurement signal by a coefficient related to a ratio between the estimated particle size and a reference particle size,
A fine particle measuring system characterized by that. The fine particle measurement system according to claim 1,
The fine particle amount determination unit performs the correction according to the following formula, and determines the mass concentration of the fine particles as the fine particle amount:
y = y ₀ × (B / A) ^N
Here, y is the corrected measurement signal or mass concentration of fine particles, y ₀ is the measurement signal or fine particle mass concentration before correction, A is the reference particle size, B is the estimated particle size, and N is An integer greater than or equal to 2,
A fine particle measuring system characterized by that. The fine particle measurement system according to claim 1,
The fine particle amount determination unit performs the correction according to the following formula, and determines the number concentration of the fine particles as the fine particle amount:
y = y ₀ × (A / B)
Here, y is the corrected measurement signal or the number concentration of fine particles, y ₀ is the measurement signal or the number concentration of fine particles before correction, A is the reference particle size, and B is the estimated particle size.
A fine particle measuring system characterized by that. The fine particle measurement system according to any one of claims 1 to 3,
The fine particle measurement system measures the amount of fine particles contained in exhaust gas of an internal combustion engine of a vehicle.
A fine particle measuring system characterized by that. The fine particle measurement system according to claim 4,
The particle size estimation unit estimates the particle size based on a parameter relating to driving of the internal combustion engine.
A fine particle measuring system characterized by that. The fine particle measurement system according to claim 5,
The particle size estimation unit estimates the particle size based on a plurality of different parameters.
A fine particle measuring system characterized by that. The fine particle measurement system according to claim 6,
The plurality of parameters different from each other include at least the rotational speed and fuel injection amount of the internal combustion engine,
A fine particle measuring system characterized by that.