JP5094702B2 - Particulate matter detector - Google Patents

Description

  The present invention relates to a particulate matter detection device. In particular, the present invention relates to a particulate matter detection device that detects the concentration of particulate matter in exhaust gas discharged from an internal combustion engine.

Conventionally, an exhaust pipe of an internal combustion engine is provided with a particulate matter detection device for detecting the concentration of particulate matter in the exhaust. As this particulate matter detection device, for example, in Patent Document 1, an electrode part is provided in an exhaust pipe, and particulate matter contained in exhaust gas is attached to the electrode part, and then the electrical part of the electrode part to which particulate matter has adhered is applied. It is shown that the concentration of particulate matter in exhaust gas in the exhaust pipe is detected by measuring the characteristic.
JP 2008-139294 A

  However, the particulate matter has a characteristic that its electrical properties change as the temperature changes. Therefore, as described above, in the particulate matter detection device that detects the concentration of the particulate matter based on the measurement of the electrical characteristics of the electrode part to which the particulate matter adheres, the operating state of the internal combustion engine and the temperature of the exhaust gas are detected. There is a possibility that the detected value also fluctuates according to the fluctuation.

  The present invention has been made in view of the above-described problems, and is a particulate matter detection device that detects the concentration of particulate matter in exhaust gas based on measurement of electrical characteristics of the particulate matter, and is an operation of an internal combustion engine. An object of the present invention is to provide a particulate matter detection device capable of stably detecting the concentration regardless of the state and the temperature of the exhaust.

In order to achieve the above object, an invention according to claim 1 has an electrode part (2) provided in an exhaust passage (EP) of an internal combustion engine, and the electric part of the electrode part to which particulate matter contained in the exhaust is adhered. Detection device (1) for detecting the concentration of particulate matter in the exhaust gas based on the physical characteristics, the parameter detecting means for detecting a parameter correlated with the temperature of the particulate matter attached to the electrode section (6, 8), the electrical characteristics of the electrode part to which the particulate matter has adhered are measured, and based on the measured electrical characteristics (ΔC) and the parameter (T _A ) detected by the parameter detection means And a concentration detection means (6) for detecting the concentration (D) of the particulate matter in the exhaust gas.

The invention according to claim 2 is the particulate matter detection device according to claim 1, wherein the electrical characteristics of the electrode part to which the particulate matter is attached and a parameter correlated with the temperature of the particulate matter; Storage means (6) storing data indicating the relationship between the concentration of particulate matter in the exhaust gas flowing through the exhaust passage is provided, and the concentration detection means uses the data stored in the storage means, The exhaust gas particulate matter concentration (D) is detected in accordance with the measured electrical characteristic (ΔC) and the parameter (T _A ) detected by the parameter detecting means.

  According to the first aspect of the present invention, the electrical characteristics of the electrode part to which the particulate matter is adhered are measured, and the parameter having a correlation between the measured electrical characteristics and the temperature of the particulate matter adhered to the electrode part. Based on the above, the concentration of particulate matter in the exhaust is detected. As a result, even when the operating state of the internal combustion engine and the temperature of the exhaust gas fluctuate and the electric physical properties of the particulate matter adhering to the electrode part fluctuate, the influence of the temperature of the electric physical properties of the particulate matter is taken into consideration However, the concentration of the particulate matter can be detected stably.

  According to the second aspect of the present invention, the data indicating the relationship between the electrical characteristics of the electrode portion, the parameter correlated with the temperature of the particulate matter, and the concentration of the particulate matter in the exhaust gas is stored in the storage means. In addition, this data is used to detect the concentration of the particulate matter in the exhaust gas according to the measured electrical characteristics and the detected parameters. Thereby, the concentration of the particulate matter can be detected more stably.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing a configuration of a particulate matter detection device (hereinafter referred to as “PM sensor”) 1 according to the present embodiment.

  The PM sensor 1 includes the sensor electrode unit 2 provided in the exhaust pipe EP of the engine, the DC power supply 3 for dust collection connected to the sensor electrode unit 2, the impedance measuring device 4, and the temperature of the sensor electrode unit 2. A temperature control device 5 for controlling and an electronic control unit (hereinafter referred to as “ECU”) 6 for controlling them are configured. As will be described in detail below, the PM sensor 1 has an electrical characteristic of the sensor electrode unit 2 to which particulate matter (hereinafter referred to as “PM (Particulate Matter)”) contained in the exhaust gas flowing through the exhaust pipe EP is attached. And the concentration of particulate matter in the exhaust gas flowing through the exhaust pipe EP (hereinafter referred to as “PM concentration”) is detected based on the measured electrical characteristics.

  FIG. 2 is a diagram showing the configuration of the sensor electrode unit 2. More specifically, FIG. 2 (A) is a perspective view showing a configuration of the electrode plate 25 of the sensor electrode unit 2, and FIG. 2 (B) is configured to include two electrode plates 25 and 25. 5 is a perspective view showing a configuration of a sensor electrode unit 2.

As shown in FIG. 2A, the electrode plate 25 includes a substantially rectangular alumina substrate 251 and a tungsten conductor layer 252 formed on the surface of the alumina substrate 251. The tungsten conductor layer 252 includes a conductor portion formed in a substantially square shape at a substantially central portion of the alumina substrate 251 and a conductor portion extending linearly from the conductor portion to one end side of the alumina substrate 251. Consists of. Further, a tungsten printing portion 253 is formed on one end side of the alumina substrate 251 so as to be laminated on the conductive wire portion of the tungsten conductor layer 252.
Here, the thickness of the alumina substrate 251 is about 1 mm, and the length of one side of the conductor portion of the tungsten conductor layer 252 is about 10 mm.

  As shown in FIG. 2B, the sensor electrode unit 2 is configured by combining a pair of electrode plates 25 and 25 with plate-like spacers 26 and 26 interposed therebetween. The spacers 26 and 26 are provided on both end sides of each electrode plate 25, whereby a cavity 27 for collecting PM is formed in the conductor portion of the tungsten conductor layer 252 of each electrode plate 25. .

  Returning to FIG. 1, the dust collecting DC power source 3 and the impedance measuring device 4 are connected to the electrode plates 25 and 25 of the sensor electrode unit 2 via the changeover switch SW.

  The dust collection DC power source 3 operates based on a control signal transmitted from the ECU 6, and applies a predetermined voltage between the electrode plates 25, 25 of the sensor electrode unit 2 for a predetermined time. Thereby, PM contained in the exhaust gas flowing through the exhaust pipe EP is attached to the electrode plates 25 and 25.

  The impedance measuring device 4 operates based on the control signal transmitted from the ECU 6 and detects the capacitance between the electrode plates 25 and 25 of the sensor electrode unit 24 based on an AC signal having a predetermined measurement voltage and a measurement cycle. Then, a detection signal substantially proportional to the detected capacitance value is output to the ECU 6.

  The change-over switch SW operates based on a control signal transmitted from the ECU 6 and selectively switches the connection to the electrode plate 25 between the dust collection DC power source 3 and the impedance measuring instrument 4. As will be described in detail later, when collecting PM in the cavity 27 of the sensor electrode unit 2, the DC power source 3 for dust collection and the electrode plate 25 are connected, and the capacitance of the sensor electrode unit 2 is measured. In this case, the impedance measuring instrument 4 and the electrode plate 25 are connected.

The temperature control device 5 includes heaters 51, 51 provided in contact with the electrode plates 25, 25, and a heater DC power supply 52 that supplies power to the heaters 51, 51.
The heater DC power supply 52 operates based on a control signal transmitted from the ECU 6 and supplies a predetermined current to the heaters 51 and 51. The heaters 51 and 51 generate heat when the current is supplied from the heater DC power source 52 and heat the electrode plates 25 and 25. In addition, the sensor electrode unit 2 can be regenerated by heating the electrode plates 25 and 25 to burn and remove PM adhering to the electrode plates 25 and 25.

In addition, an electrode temperature sensor 8 is connected to the ECU 6. The electrode temperature sensor 8 detects the temperature of the electrode plate 25 as a parameter correlated with the temperature of the PM attached to the sensor electrode unit 2 and outputs a detection signal to the ECU 6.
Here, the relationship between the temperature of the electrode plate 25 and the temperature of PM adhering to the electrode plate 25 will be described. The heat capacity of the electrode plate 25 is sufficiently larger than the heat capacity of PM adhering to the electrode plate 25. For this reason, even if PM having a temperature different from the temperature of the electrode plate 25 adheres to the electrode plate 25, the temperature of the PM becomes substantially equal to the temperature of the electrode plate 25. Therefore, in the following, it is assumed that the temperature of the electrode plate 25 and the temperature of PM adhering to the electrode plate 25 are substantially equal.

  The ECU 6 shapes an input signal waveform from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter referred to as “a processing unit”). CPU ”). In addition, the ECU 6 includes a storage circuit in which various arithmetic programs executed by the CPU and a control map shown in FIGS. 4 to 6 to be described later are stored, a dust collection DC power source 3, an impedance measuring device 4, a heater DC. And an output circuit for outputting a control signal to the power source 52 and the changeover switch SW.

  FIG. 3 is a flowchart showing a procedure for detecting the PM concentration of the exhaust gas by the PM sensor 1. This flowchart is executed by the ECU 6 after the engine is started.

In step S1, the PM sensor is warmed up, regenerated, and calibrated.
In step S2, detects the temperature of the sensor electrode unit by the electrode temperature sensor records the detected temperature as the initial electrode temperature T _I. Further, in this step, measuring the capacitance of the sensor electrode unit, and records the measured capacitance as an initial capacitance C _I.
In step S3, “0” is set to the total PM dust collection amount Y indicating the total amount of PM collected in the sensor electrode unit in response to the regeneration of the sensor electrode unit in step S1 described above.

In step S4, it is determined whether or not the sensor electrode portion is in a normal state. Specifically, in this step, first, a control map C ₀ (T) as shown in FIG. 4 that relates the capacitance C ₀ of the normal sensor electrode portion and the temperature T in a state where PM is not attached. ) To calculate the capacitance C ₀ (T _I ) of the sensor electrode unit according to the initial electrode temperature T _I of the sensor electrode unit. Further, it is determined whether or not the sensor electrode unit is in a normal state by determining whether or not the calculated capacitance C ₀ (T _I ) is substantially equal to the measured initial capacitance C _I. To do. If this determination is YES, the sensor electrode unit is determined to be in a normal state, and the process proceeds to step S6. If this determination is NO, it is determined that the sensor electrode portion is not in a normal state, and the process proceeds to step S15. The control map shown in FIG. 4 is created based on experiments performed in advance and stored in the storage circuit of the ECU.

In step S15, when it is determined that the sensor electrode unit is not in a normal state, the sensor electrode unit is regenerated, and a predetermined failure confirmation process is performed to check whether the sensor electrode unit has failed. The process proceeds to step S16.
In step S16, it is determined whether or not a failure of the sensor electrode unit has been confirmed. If a failure of the sensor electrode unit is confirmed, this process is terminated. If a failure of the sensor electrode unit is not confirmed, the process proceeds to step S1.

  In step S6, PM is collected on the sensor electrode portion by applying a predetermined dust collection voltage V to the sensor electrode portion over a predetermined dust collection time t. Thereby, an amount of PM corresponding to the PM concentration of the exhaust adheres to the sensor electrode portion.

In step S7, it detects the temperature of the sensor electrode unit by the electrode temperature sensor records the detected temperature as a dust collecting electrodes after the temperature T _A.

In step S8, a capacitance change amount ΔC as an electrical characteristic of the sensor electrode unit is measured. Here, first, by measuring the capacitance of the sensor electrode unit after particulate collection of PM, and recorded as a post-PM collection capacitance C _A. Next, the capacitance of the sensor electrode part before dust collection, that is, C ₀ (T _A ) is calculated using the control map shown in FIG. 4 described above, and before dust collection from the capacitance C _A after dust collection. Is obtained by subtracting the capacitance C ₀ (T _A ) and recorded as capacitance change amount ΔC (= C _A −C ₀ (T _A )).

In step S9, a PM dust collection amount X indicating the amount of PM collected in the sensor electrode unit is calculated. More specifically, based on a control map shown in Figure 5 relating the variation amount of capacitance ΔC and the dust collecting electrodes after the temperature T _A and the PM particulate collection amount X, the measured capacitance change amount ΔC calculating the PM particulate collection amount X corresponding to preparative collector and dust after the electrode temperature T _a.

FIG. 5 is a diagram illustrating a relationship between the capacitance change amount ΔC and the PM dust collection amount X, and is a diagram illustrating an example of the above-described control map. FIG. 5 shows only the correlation between the capacitance change amount ΔC and the PM dust collection amount X when the post-dust collection electrode temperature T _A is T _A1 , T _A2 , T _A3 .
As shown in FIG. 5, when the PM dust collection amount X increases, the capacitance change amount ΔC of the sensor electrode portion also increases. Further, correlation between such an electrostatic capacitance variation ΔC and PM particulate collection amount X varies depending on the dust-collecting electrodes after the temperature T _A. The control map shown in FIG. 5 is created based on, for example, an experiment for grasping the temperature characteristics of the capacitance described later, and is stored in the storage circuit of the ECU.

  Returning to FIG. 3, in step S10, the PM concentration D of the exhaust gas is detected. In this step, specifically, the PM concentration of the exhaust gas according to the calculated PM dust collection amount X based on the control map as shown in FIG. 6 that relates the PM dust collection amount X and the PM concentration D of the exhaust gas. D is calculated.

FIG. 6 is a diagram showing the relationship between the exhaust gas PM concentration and the PM dust collection amount of the sensor electrode section.
As shown in FIG. 6, the PM concentration D of the exhaust increases as the PM dust collection amount X increases. The control map shown in FIG. 6 is created based on experiments performed in advance and stored in the storage circuit of the ECU.

  Returning to FIG. 3, in step S11, the total PM dust collection amount Y is updated. Specifically, the total PM dust collection amount Y is updated by adding the calculated PM dust collection amount X.

In step S12, the total PM particulate collection amount Y is determined whether a predetermined maximum precipitator amount Y _MAX or more. If this determination is YES, the process proceeds to step S13, and if NO, the process proceeds to step S14.
In step S13, the sensor electrode unit is regenerated and “0” is set to the total PM dust collection amount Y, and the process proceeds to step S14.
In step S14, it is determined whether or not the PM concentration detection is to be terminated. If this determination is YES, this process ends. If NO, the process moves to step S6.

[Capacitance temperature characteristics experiment]
Next, a capacitance temperature characteristic grasping experiment for grasping the temperature characteristic of the capacitance of the sensor electrode unit will be described.
FIG. 7 is a diagram illustrating a configuration of the experimental apparatus 110.
The experimental apparatus 110 includes an engine 111, a normal DPF 112 and a damaged DPF 113 provided downstream of the engine 111, a switching valve 114 that switches exhaust discharged from the engine 111 between the normal DPF 112 and the damaged DPF 113, a normal DPF 112, and a damaged DPF 113. And a test PM sensor 115 provided on the downstream side of the DPF 113.

The normal DPF 112 is a filter that collects PM contained in the exhaust discharged from the engine 111. Therefore, the PM concentration in the exhaust downstream of the normal DPF 112 is almost zero. The damaged DPF 113 is a product in which the normal DPF 112 is intentionally damaged. Therefore, exhaust gas having a predetermined PM concentration flows downstream of the damaged DPF 113.
As the test PM sensor 115, a sensor having the sensor electrode unit 2 having the same configuration as that of the above-described embodiment was prepared.

In this temperature characteristic grasping experiment, the relationship between the capacitance of the sensor electrode part and the temperature of the sensor electrode part was measured under a plurality of conditions using the experimental apparatus 110 configured as described above. .
FIG. 8 shows the results of this experiment. In FIG. 8, the horizontal axis indicates the temperature of the sensor electrode unit, and the vertical axis indicates the capacitance of the sensor electrode unit.

  Specifically, first, the switching valve 114 was set on the normal DPF 112 side, and the capacitance of the sensor electrode portion was measured while exhaust gas discharged from the engine 111 was allowed to flow into the normal DPF 112. Here, the capacitance of the sensor electrode portion was measured while changing the temperature of the sensor electrode portion by continuously changing the operating conditions of the engine 111. Thereby, the temperature characteristic of the electrostatic capacitance of the sensor electrode part in a state where PM is not attached is measured. The measurement result is shown by a solid line 8a in FIG.

Next, the switching valve 114 is set on the damaged DPF 113 side, and a predetermined dust collection voltage is applied to the sensor electrode portion for a predetermined dust collection time while exhaust exhausted from the engine 111 flows into the damaged DPF 113. PM of exhaust gas was collected on the electrode part. Here, after collecting PM of exhaust gas in the sensor electrode part, the capacitance of the sensor electrode part was measured while changing the temperature of the sensor electrode part by continuously changing the operating conditions of the engine 111. .
Further, in this experiment, by changing the degree of damage of the damaged DPF 113, PM is collected in the sensor electrode part under a plurality of types of PM concentrations, and the capacitance of the sensor electrode part with different PM dust collection amounts is collected. Temperature characteristics were measured. These measurement results are shown by three broken lines 8b, 8c and 8d in order from the one with the smallest amount of PM dust collection in FIG.

  As shown in FIG. 8, under a certain temperature of the sensor electrode unit, the capacitance of the sensor electrode unit increases as the PM dust collection amount of the sensor electrode unit increases. Further, as the temperature of the sensor electrode portion increases, the capacitance of the sensor electrode portion increases. Further, when the amount of PM dust collection is different, the temperature characteristics of the capacitance of the sensor electrode portion also change.

  Here, the relationship between the measurement results as described above and the control maps shown in FIGS. 4 and 5 will be described.

As described above, FIG. 4 is a control map that relates the capacitance C ₀ of the sensor electrode unit and its temperature T when no PM is attached. Therefore, the control map shown in FIG. 4 is created based on the measurement result shown by the solid line 8a in FIG.

Further, FIG. 5 is a control map showing the relationship between electrode temperature T _A and the PM particulate collection amount X after the variation amount of capacitance ΔC and dust collection. Therefore, the electrode temperature T _A after dust collection corresponds to the temperature of the sensor electrode unit of the horizontal axis in FIG. 8. Further, the capacitance change amount ΔC corresponds to a value obtained by subtracting the capacitance of the sensor electrode portion in a state where the PM shown by the solid line 8a is not attached from the capacitance on the vertical axis in FIG. Thereby, the control map shown in FIG. 5 can be created from the measurement results shown in FIG.

According to this embodiment, there are the following effects.
(1) According to the present embodiment, the capacitance change amount ΔC of the sensor electrode unit 2 to which PM is attached is measured, and the measured capacitance change amount ΔC and the post-dust collection electrode temperature of the sensor electrode unit 2 based on the T _a, it detects the PM concentration D of the exhaust. As a result, even when the operating state of the engine and the temperature of the exhaust gas fluctuate and the electric property of the PM adhering to the sensor electrode unit 2 fluctuates, the effect of the temperature of the electric property of this PM on the temperature can be considered stably. Thus, the PM concentration D can be detected.

(2) According to the present embodiment, the variation amount of capacitance ΔC of the sensor electrode unit 2, and the electrode temperature T _A after dust collection, the PM particulate collection amount X of the sensor electrode unit, and the PM concentration D of the exhaust, The control maps shown in FIGS. 5 and 6 showing the relationship are stored in the storage circuit of the ECU 6. Further by using these control maps, to detect the PM concentration D of the exhaust gas corresponding to the measured variation amount of capacitance ΔC and dust collecting electrodes after the temperature T _A. As a result, the PM concentration D can be detected more stably.

  In the present embodiment, the electrode temperature sensor 8 and the ECU 6 constitute parameter detection means, the ECU 6 constitutes concentration detection means, and the ECU 6 constitutes storage means. More specifically, the means relating to execution of step S7 in FIG. 3 constitutes a parameter detection means, and the means relating to execution of steps S1 to S16 in FIG. 3 constitutes a concentration detection means.

The present invention is not limited to the above-described embodiment, and various modifications can be made.
In the above embodiment, the temperature of the electrode plate 25 is detected by the electrode temperature sensor 8 as a parameter having a correlation with the PM attached to the sensor electrode unit 2, but the present invention is not limited to this. The exhaust gas temperature may be detected as a parameter correlated with the PM adhering to the sensor electrode unit 2.

It is a schematic diagram which shows the structure of PM sensor which concerns on one Embodiment of this invention. It is a perspective view which shows the structure of the sensor electrode part which concerns on the said embodiment. It is a flowchart which shows the procedure which detects PM density | concentration of exhaust_gas | exhaustion by PM sensor which concerns on the said embodiment. It is a figure which shows an example of the control map which concerns on the said embodiment. It is a figure which shows an example of the control map which concerns on the said embodiment. It is a figure which shows an example of the control map which concerns on the said embodiment. It is a figure which shows the structure of the experimental apparatus of the temperature characteristic grasping | ascertainment experiment which concerns on the said embodiment. It is a figure which shows the result of the said experiment.

Explanation of symbols

1 ... PM sensor (particulate matter detector)
2. Sensor electrode part (electrode part)
DESCRIPTION OF SYMBOLS 25 ... Electrode plate 3 ... DC power supply for dust collection 4 ... Impedance measuring instrument 5 ... Temperature control apparatus 6 ... ECU (parameter detection means, concentration detection means, storage means)
8 ... Electrode temperature sensor (parameter detection means)
EP ... Exhaust pipe (exhaust passage)

Claims (2)

Particles of exhaust gas having an electrode portion provided downstream of a filter that collects particulate matter in an exhaust passage of an internal combustion engine, and based on the electrical characteristics of the electrode portion to which particulate matter contained in the exhaust adheres A particulate matter detection device for detecting the concentration of particulate matter,
Parameter detection means for detecting a temperature parameter correlated with the temperature of the particulate matter attached to the electrode part;
Measuring means for measuring electrical characteristics of the electrode part;
First data indicating the correlation between the value of the electrical characteristic of the electrode portion and the value of the temperature parameter in the initial state, the amount of change in the electrical characteristic during a predetermined time, the value of the temperature parameter, and the exhaust Storage means storing second data indicating the correlation of the concentration of the particulate matter in the exhaust gas flowing through the passage;
Obtaining the detected value of the temperature parameter and the measured value of the electrical characteristic after the dust collection time has elapsed from the initial state, and using the detected value of the temperature parameter as an argument, the electrical characteristic based on the first data A change amount calculating means for calculating a change amount of the electrical characteristics by subtracting the initial value from the measured value;
Concentration detection means for detecting the concentration of particulate matter in the exhaust based on the second data with the detected value of the temperature parameter and the change amount of the electrical characteristic as arguments. Detection device. 2. The particulate matter detection device according to claim 1 , wherein a dust collection voltage is applied to the electrode section until the dust collection time elapses from the initial state .

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