JP2012083121A - Particulate substance detection sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particulate substance detection sensor capable accurately controlling a temperature of a heating element for heating the particulate substance detection sensor which detects an amount of a particulate substance included in a measured gas by detecting an electric resistance formed by the particulate substance accumulated between a pair of electrodes facing each other leaving a prescribed interval between each other.SOLUTION: The particulate substance detection sensor 1 has a leak current detection means 40 for detecting a leak current signal (ΔV) which leaks to the detection electrodes 110 and 120 from the heat element 150 due to a decrease of an insulation resistance Rof heat-resistant insulating substrates 100 and 130 accompanying heating, as a temperature detection means for detecting a heating temperature of the heating element 150.

Description

  The present invention relates to an electric resistance type particulate matter detection sensor that is suitably used in, for example, an exhaust purification system of an internal combustion engine for a vehicle and detects the amount of particulate matter present in exhaust gas.

  In automobile diesel engines and the like, environmental pollutants contained in combustion exhaust, particularly particulate matter (Particulate Matter; hereinafter referred to as PM) as appropriate, mainly composed of soot particles and soluble organic components (SOF) are captured. In order to collect, a diesel particulate filter (hereinafter referred to as DPF as appropriate) is installed in the exhaust passage. The DPF is made of porous ceramics having excellent heat resistance, and traps PM by allowing combustion exhaust gas to pass through partition walls having a large number of pores.

If the amount of PM collected exceeds the allowable amount, DPF may cause clogging and increase pressure loss or increase PM slipping. It is recovering.
In the regeneration process of the DPF, high-temperature combustion exhaust gas is introduced into the DPF by heater heating or post injection, and PM is burned and removed.
In general, the regeneration timing of the DPF is determined by utilizing the fact that the pressure loss of the DPF increases due to the increase in the amount of collected PM. Therefore, the difference in detecting the pressure difference between the upstream and downstream of the DPF is detected. A pressure sensor is installed.

On the other hand, a PM detection sensor capable of directly detecting PM in combustion exhaust has been proposed. This PM detection sensor is installed downstream of the DPF, for example, measures the amount of PM that passes through the DPF, and monitors the operating state of the DPF, for example, cracks and breaks, in an onboard diagnosis (OBD). It can be used to detect abnormalities.
Alternatively, it has been studied to install a PM detection sensor upstream of the DPF, measure the amount of PM flowing into the DPF, and use it to determine the regeneration timing of the DPF instead of the differential pressure sensor.

As an example of such a PM detection sensor, Patent Document 1 discloses an electric resistance type smoke in which a pair of conductive electrodes are formed on the surface of an insulating substrate and a heating element is formed on the back surface or inside of the substrate. A sensor is disclosed.
This smoke sensor uses the fact that smoke (fine carbon) has electrical conductivity, and detects a change in electrical resistance caused by the deposition of smoke between electrodes serving as a detection unit.
In addition, there is a device that detects a change in electrostatic capacitance or a change in impedance of an element that changes depending on the amount of PM deposited on the detection unit (see, for example, Patent Document 2).
The heating element provided inside the sensor element heats the detection part of the sensor element to a desired temperature, measures the resistance between the electrodes at a certain temperature, then raises the heating temperature to burn off the attached smoke and detectability Is recovering.

In general, in a conventional electric resistance type PM detection sensor as disclosed in Patent Document 1, temperature is controlled based on a resistance value of a heating element when the smoke is burned out and reproduced by the heating element.
However, although the resistance value of the heating element changes linearly with respect to the temperature change, the absolute value of the resistance value change with respect to the temperature change is small and the sensitivity is low, and variations in the initial resistance value of the heating element and the detection circuit Is susceptible to variations in wiring resistance, etc., and the temperature control accuracy is low.
Further, the heating element is energized to regenerate the sensor by heating and removing the PM accumulated on the PM detection sensor, and when a certain time elapses when the sensor is heated, the PM detection signal oscillates as shown in FIG. Noise is detected.
This is because, as a result of diligent tests by the present inventors, the insulation resistance of alumina used as an electrical insulator is greatly reduced as the temperature of the heating element rises, and a conduction path is formed between the detection electrodes. It has been found.
When such a decrease in insulation resistance occurs, conduction is detected between the detection electrodes even though regeneration is completed and PM is not deposited between the detection electrodes, and the heat regeneration process is continued excessively. Even when the detection resistor is detected, there is a possibility that the energization pulse supplied to the heating element leaks to the detection electrode as noise and causes fluctuation in detection output.

  Therefore, in view of such circumstances, the present invention is used for detecting the amount of particulate matter contained in a gas to be measured such as combustion exhaust gas of an internal combustion engine, and according to the amount of particulate matter collected and deposited in the detection unit. Highly accurate particulate matter detection that enables high-precision temperature control by detecting the heating temperature at the time of regeneration control of particulate matter detection sensors that detect the changing electrical characteristics An object is to provide a detection sensor.

  According to a first aspect of the present invention, there is provided a detection unit on which particulate matter contained in a gas to be measured is deposited, and a heating element that is disposed between the detection unit via a heat-resistant insulating substrate and generates heat when energized. Detecting the electrical characteristics that change depending on the amount of particulate matter deposited on the detection unit to detect the amount of particulate matter contained in the gas to be measured, A particulate matter detection sensor that heats and removes the particulate matter deposited on the heating element, and as a temperature detection means for detecting the heating temperature of the heating element, the heat generation is caused by a decrease in insulation resistance of the heat-resistant insulating substrate accompanying heating. Leakage current detection means for detecting leakage current leaking from the body to the detection electrode is provided (claim 1).

  According to the first invention, since the leakage current depends on the temperature characteristic specific to the heat-resistant insulating substrate, the temperature of the heating element can be detected with high accuracy.

In the second invention, the heat-resistant insulating substrate is made of alumina. Alumina is widely used as an insulating material that is inexpensive and has stable insulating properties, and is very stably supplied.
However, as a result of diligent tests by the present inventors, a sudden change in resistance value from 100 GΩ to several tens of kΩ is shown with respect to a temperature change from room temperature to 1000 ° C., and the leakage current detection means is accompanied by this resistance value change. It has been found that the temperature of the heating element that can be detected by the detected leakage current can be detected with extremely high accuracy within ± 5 ° C.
On the other hand, when temperature control is performed by changing the resistance value of a conventional heating element irrespective of the present invention, the influence of wiring resistance is large, and a detection error of about ± 25 ° C. is caused for a change in wiring resistance of 0.1Ω. Further, it has been found that a measurement error of about ± 200 ° C. at maximum is caused by the influence of the variation in resistance value of the circuit and the variation between solids.

In a third aspect of the invention, when the leakage current detection means is performed by pulse width modulation control that controls the amount of current supplied to the heating element by an on / off duty ratio, when the current supply pulse to the heating element is off, An off-time output signal (V _OFF ) detected in a state where particulate matter is not deposited between the pair of electrodes is detected.

  According to the third aspect of the invention, it is possible to detect in a stable state with a high leakage current that oscillates at a period inverted with respect to the on / off oscillation period of the energization pulse to the heating element, and has the highest sensitivity to temperature. It becomes easy to use for control. Therefore, it is possible to realize a highly reliable particulate matter detection sensor that detects the heating temperature with high accuracy and uses this to control the temperature with high accuracy.

In the fourth invention, the leakage current detection means includes an off-time output signal (V _OFF ) detected when the energization pulse is off and an on-time output signal (V _ON ) detected when the energization pulse is on. (V _OFF −V _ON ) is detected as a leakage current signal (ΔV).

  According to the fourth invention, the resistance value of the heat-resistant insulating substrate can be accurately calculated from the leakage current, and the temperature of the heating element can be set extremely high from the relationship between the resistance value of the heat-resistant insulating substrate and the temperature. It can be detected with high accuracy.

  According to a fifth aspect of the present invention, there is provided a heating element resistance value detecting means for detecting the resistance value of the heating element, and learning the relationship between the heating element resistance value and the temperature at the target temperature calculated by the leak current detecting means. A heating element resistance learning means is provided (claim 5).

  When the temperature is controlled only by the conventional heating element resistance, it is difficult to eliminate the influence of the wiring resistance of the control circuit or the like. According to the fifth invention, the high-temperature heating element resistance learning means Thus, by learning the relationship between the heating element resistance value and the temperature at the target temperature, it is possible to eliminate the influence of the resistance value variation of each particulate matter detection sensor and to control the temperature with higher accuracy.

  In a sixth aspect of the invention, the particulate matter detection sensor is disposed in the combustion exhaust passage of the internal combustion engine, and serves as an operating state detecting means for detecting the operating state of the internal combustion engine. The combustion exhaust temperature, the cooling water temperature, the oil temperature, A temperature sensor for detecting any one of the intake air temperature, the fuel temperature, or a plurality of temperatures selected from these, and temperature information immediately after starting the internal combustion engine detected by the temperature sensor and the heating element A low-temperature heating element resistance value learning means is provided for learning a relationship between the heating element resistance value and temperature in a low-temperature environment from the heating element resistance value detected by the resistance value detection means.

  The leakage current is detected only when the heating element generates heat above a certain temperature and the insulation resistance of the heat-resistant insulating substrate is lowered, and can be used for temperature control in a high temperature environment. According to the invention, by learning the relationship between the heating element resistance value and the temperature under a low temperature environment, it becomes possible to control the temperature with high accuracy not only at a high temperature but also over a wide temperature range.

  In the seventh invention, individual heat generation is performed from the high temperature heating element resistance learning value learned by the high temperature heating element resistance learning means and the low temperature heating element resistance learning value learned by the low temperature heating element resistance learning means. Temperature characteristic correcting means for correcting the temperature characteristic of the body is provided (claim 7).

  According to the seventh invention, not only the temperature of the heating element is accurately controlled by the temperature characteristic correcting means, but also the particulate matter detection sensor calculates the temperature of the gas to be measured from the resistance value of the heating element. It can be used as a temperature sensor, and can be used for control of the internal combustion engine, control of an exhaust gas purification device, and the like.

The block diagram which shows the outline | summary of the microparticle detection sensor in the 1st Embodiment of this invention. (A) is a developed perspective view showing an outline of a particulate matter detection element used in the particulate detection sensor of the present invention, and (b) is a perspective view showing an image of occurrence of leakage current used in the particulate detection sensor of the present invention. Figure. (A)-(c) is a characteristic view which shows the relationship between the temperature of a heat generating body, an oscillation pulse, and leakage current. (A) is an equivalent circuit diagram of the particulate matter detection sensor when the heating element energization pulse is turned on, and (b) is an equivalent circuit diagram of the particulate matter detection sensor when the thermal body conduction pulse is turned off. circuit diagram. (A)-(c) is a specific example which shows the detection result of the leakage current in each temperature of the fine particle detection sensor of this invention. (A) is a characteristic diagram showing resistance temperature characteristics of alumina used as a heat-resistant insulating substrate in the particulate matter detection sensor of the present invention, and (b) is used for temperature control of a conventional fine particle detection sensor shown as a comparative example. The characteristic view which shows the resistance temperature characteristic of a heat generating body. The effect of this invention is shown with a comparative example, (a) is a characteristic diagram which shows the temperature control error of the microparticle detection sensor of this invention, (b) is a characteristic diagram which shows the temperature control error of the conventional microparticle detection sensor. The effect of the particulate detection sensor of the present invention is shown, (a) is a characteristic diagram showing the correlation between the leakage current signal and the resistance of the heat-resistant insulating substrate, and (b) shows the correlation between the leakage current signal and the element temperature. Characteristic diagram. The block diagram which shows the outline | summary of the particulate matter detection sensor in the 2nd Embodiment of this invention. It is a characteristic view for explaining the control method of the particulate matter detection sensor of the present invention, (a) shows the change over time of the element temperature, (b) shows the change over time of the leakage current signal, v) shows the temporal change of the heating element resistance value. (A) uses a high-temperature heating element resistance learning means, and (b) uses the high-temperature heating element resistance learning means and the low-temperature heating element resistance learning means of the particulate matter detection sensor of the present invention. The characteristic view for demonstrating the correction method of resistance characteristics. The flowchart which shows the learning method of the heat generating body resistance value learning means at the time of high temperature used for the particulate matter detection sensor of this invention. The flowchart which shows an example of the electricity supply control method used for the particulate matter detection sensor of this invention. The flowchart in the case of using the particulate matter detection sensor of this invention as a temperature sensor. The flowchart which shows the learning method of the heating element resistance value learning means at the time of low temperature used for the particulate matter detection sensor of this invention. The characteristic view which shows the output oscillation condition which generate | occur | produces at the time of reproduction | regeneration of a microparticle detection sensor.

An outline of a particulate matter detection sensor (hereinafter referred to as PM detection sensor) 1 according to the first embodiment of the present invention will be described with reference to FIG. The PM detection sensor 1 of the present invention is provided in a combustion exhaust passage of an internal combustion engine and detects the amount of particulate matter in the measurement gas using the combustion exhaust as the measurement gas. Used for combustion control of internal combustion engines, regeneration of exhaust purification devices, abnormality diagnosis, and the like.
The PM detection sensor 1 is provided inside a particulate matter detection element (hereinafter referred to as PM detection element) 10, output detection means 20 for detecting an output signal from the PM detection element 10, and the PM detection element 10. A heating element energization control means 30 for controlling energization of the heating element 150, a leakage current detection means 40 for detecting a leakage current signal ΔV generated at a high temperature from the output signal _VOUT detected by the output detection means 20, and The heat generation temperature calculation means 50 calculates the temperature of the heating element 150 from the leak current signal ΔV detected by the leak current detection means 40.

The PM detection element 10 is formed on the surface of a heat-resistant insulating substrate 100 such as alumina, and is provided with a pair of detection electrodes 110 and 120 facing each other with a predetermined gap, and each of these detection electrodes 110 and 120 is externally output. A pair of output transmission leads 111 and 121 connected to the detection means 20 and the detection electrodes 110 and 120 and the output transmission leads 111 and 121 are disposed through the insulating substrate 100 so as to ensure insulation. And a pair of heating element energization leads 151 and 152 connecting the heating element 150 and the heating element energization control means 30 provided outside.
One output transmission lead 111 is connected to the control voltage V output transmission leads 111, 121, and the other output transmission lead 121 is connected to the output detection means 20.
When conductive particulate matter is deposited between the detection electrodes 110 and 120, electrical characteristics such as electrical resistance and impedance formed between the detection electrodes 110 and 120 change according to the amount of conductive fine particles deposited.

Output detection means 20 to detect a change in electrical resistance between the detection electrodes 110 and 120 due to the deposition of the particulate matter as a detection resistor _{R SEN,} by dividing resistors RDIV, by applying a control voltage _{V CC} min, detection a voltage dividing means 210 for detecting the resistance _{R SEN,} are provided with amplifying means 220 for amplifying the detection resistor _{R SEN} and dividing resistor Rdiv the output signal _{V OUT} which is divided by.
It should be noted that, by a similar current detection means such as a voltage dividing resistor Rdiv, the change in capacitance that changes according to the amount of PM deposited between the detection electrodes, the change in impedance of the element, and the combination of the detection resistor and capacitance An impedance change or the like may be detected.

Inside the PM detection element 10 is formed a heating element 150 that generates heat when energized and heats the detection electrodes 110 and 120. The heating element 150 is connected to the battery via the heating element energization leads 151 and 152. Supply and stop of the battery voltage V _B are controlled by an energization opening / closing means 31 connected to the voltage V _B and the heating element energization control means 30 and provided in the heating element energization control means 30.
The energization opening / closing means 31 is a heater control pulse signal that is oscillated to perform pulse width modulation control for controlling the energization amount to the heating element 150 according to the on / off duty ratio according to whether energization to the heating element 150 is necessary. Opening and closing is controlled by PWM.

The heating element 150 generates heat from 400 ° C. to 1000 ° C. when energized. When the particulate matter deposited between the detection electrodes 110 and 120 is removed by heating, the heating element 150 is controlled to a high temperature of 600 ° C. or higher and the detection condition is set to a constant temperature. In order to stabilize the temperature-dependent detection resistor R _SEN and improve the detection accuracy of the particulate matter, the temperature is controlled to a relatively low temperature of 600 ° C. or lower.

The insulation resistance _{R AL} of the insulating substrate 100 is at a low temperature of 400 ° C. or less, has a very high insulation 100GΩ from 100 M.OMEGA, increasing temperature of the heating element 150, the insulation resistance _{R AL} changes, 700 ° C. or higher Then, the electric resistance rapidly decreases, and at 1000 ° C., it decreases to about 100 kΩ.
For this reason, at a high temperature of 700 ° C. or higher, a conduction path is formed between the output transmission lead portions 111 and 121 and the heating element energization lead portions 151 and 152 through the insulating substrate 100, and leakage current is generated. Flowing.

PM detection sensor 1 of the present invention, as a temperature detecting means for detecting the heating temperature of the heating element 150, by a decrease in the insulation resistance _{R AL} of the heat-resistant insulating substrate 100 due to heat, the detection from the heating element 150 side electrode 1101,120 The leakage current detection means 40 for detecting the leakage current flowing into the detector is detected, and this leakage current is detected as a leakage current signal ΔV. Based on this leakage current signal ΔV, the heater temperature calculation means 50 determines the temperature of the PM detection element 10. The calculation is performed with high accuracy, and this is fed back to control the heating temperature of the heating element 150 with higher accuracy.

A specific configuration example of the PM detection element 10 will be described with reference to FIG. FIG. 2A is a developed perspective view of the PM detection element 10 to which the present invention can be applied.
A constant gap is provided on the surface of the insulating substrate 100 made of alumina formed in a substantially flat plate shape by a known molding method such as a doctor blade method by a known molding method such as thick film printing using platinum paste or the like. Opposing detection electrodes 110 and 120 are formed.
The detection electrode 110 and the detection electrode 120 are formed in a comb-like shape in which a plurality of electrodes protrude from the detection electrode lead portions 111 and 121, respectively, and are opposed to each other.
Further, an insulating protective layer 170 such as heat-resistant glass or alumina is formed so as to be laminated on the surface side of the detection electrodes 110 and 120 and cover the surfaces of the detection electrode lead portions 111 and 121, and the insulating protective layer 170. The detection electrodes 110 and 120 are exposed from the detection portion opening 170 provided in the electrode, and particulate matter is deposited between the detection electrodes 110 and 120.

On the surface of the insulating substrate 140 made of alumina formed in a substantially flat plate shape, a heating element 150 is formed using platinum or the like at a position where the detection electrodes 110 and 120 can be heated, and further connected to the heating element 150 to generate a heating element. Lead portions 151 and 152 are formed.
The insulating base 140 made of alumina is provided on the back side of the insulating base 100 made of alumina and provided with the heating element 150 and the heating element leads 151 and 152 through the insulating base 130 made of alumina. These are integrally fired to form the PM detection element 10.

As shown in FIG. 4B, during regeneration, if the electric resistance of the insulating substrate 100 is lowered by the energization of the heating element 150 and becomes a certain temperature or more, the leakage from the heating element 150 side to the detection electrodes 110 and 120 side occurs. Current may flow.
For this reason, it has been found that the output signal _VOUT of the detection resistor R _SEN formed between the detection electrodes 110 and 120 oscillates in response to a change in the energization pulse to the heating element 150.
The present invention has been conceived to provide a particulate matter detection sensor that can positively utilize such a leak phenomenon and achieve higher temperature control.

  In addition, in the PM detection element 10 after completion, the insulating bases 100, 130, and 140 cannot be distinguished from each other. Therefore, in the following description, these are referred to as the insulating base 100 without distinction.

  Further, the PM detection element 10 that can be used in the present invention is a pair of detection electrodes 110, as shown in the present embodiment, as long as it detects an electrical resistance that changes in accordance with the amount of particulate matter deposited. It is not limited to what formed 120 in the shape of a comb-tooth, and what was comprised by a pair of parallel electrodes which provided a fixed gap | interval and comprised a several electrode pair by a porous electrode may be sufficient.

With reference to FIG. 3, the relationship between the change in the energization pulse to the heating element 150 and the detection voltage _VOUT will be described in detail. This figure shows an energization pulse and an output signal detected by the leak current signal detection means 40 when the temperature of the heating element 150 is raised to each temperature in a state where particulate matter is not deposited between the detection electrodes 110 and 120. This shows a change in _VOUT .
As shown in FIG. 5A, at 600 ° C., the detection signal _VOUT is below the detection limit and hardly changes.
However, as shown in FIG. 7B, at 800 ° C., the detection signal _VOUT is increased when the energization pulse is off, and the detection signal _VOUT is decreased when the energization pulse is on. detection signal V _OUT in the cycle inverted relative oN-oFF cycle of the energizing pulse is oscillated, as shown in the figure (c), at 900 ° C., the detection signal V _OUT even greater amplitude ([Delta] V) is oscillating .

さらに、本図（ｂ）に示すように、通電パルスがオフとなった状態では、本図左側に示すように、バッテリ電圧Ｖ_Ｂに対して発熱体１５０の発熱体抵抗ＲＨと絶縁性基体１００の絶縁抵抗Ｒ_ＡＬとが直列に接続され、これが、制御電圧Ｖ_ＣＣに対して直列に接続された検出抵抗Ｒ_ＳＥＮと並列に接続された状態となり、これらが分圧抵抗Ｒ_ｄｉｖと直列に接続された状態となっている。
ところが、発熱体の発熱体抵抗Ｒ_Ｈは、数Ω程度であるのに対して、絶縁抵抗Ｒ_ＡＬは高温時に抵抗値が下がった状態であっても数十ｋΩであるので、発熱体抵抗Ｒ_Ｈよりも遙かに大きく、本図右側に示すように発熱体抵抗Ｒ_Ｈを廃除した回路と等価である。
したがって、バッテリ電圧Ｖ_Ｂとオフ時出力信号Ｖ_ＯＦＦとの電位差（Ｖ_Ｂ−Ｖ_ＯＦＦ）によって絶縁抵抗Ｒ_ＡＬに流れる電流Ｉ１（＝（Ｖ_Ｂ−Ｖ_ＯＦＦ）／Ｒ_ＡＬ）と、制御電圧Ｖ_ＣＣとオフ時出力信号Ｖ_ＯＦＦとの電位差（Ｖ_ＣＣ−Ｖ_ＯＦＦ）によって検出抵抗Ｒ_ＳＥＮに流れる電流Ｉ_２（＝（Ｖ_Ｂ−Ｖ_ＯＦＦ）／Ｒ_ＳＥＮ）との和（Ｉ_１＋Ｉ_２）がオフ時出力信号Ｖ_ＯＦＦによって分圧抵抗Ｒ_ｄｉｖに流れる電流Ｉ_３（＝Ｖ_ＯＦＦ／Ｒ_ｄｉｖ）に等しく、これらの関係を整理するとオフ時出力信号Ｖ_ＯＦＦ、バッテリ電圧Ｖ_Ｂ、制御電圧Ｖ_ＣＣ、絶縁抵抗Ｒ_ＡＬ、検出抵抗Ｒ_ＳＥＮ、分圧抵抗Ｒ_ｄｉｖの間には、下記の関係が成り立つ。

さらに、オン時出力信号Ｖ_ＯＮとオフ時出力信号Ｖ_ＯＦＦとの差ΔＶ（＝Ｖ_ＯＦＦ−Ｖ_ＯＮ）とバッテリ電圧Ｖ_Ｂ、制御電圧Ｖ_ＣＣ、絶縁抵抗Ｒ_ＡＬ、検出抵抗Ｒ_ＳＥＮ、分圧抵抗Ｒ_ｄｉｖの間には、下記の関係が成り立つ。

これらの関係を変形すると、

となる。

したがって、絶縁抵抗ＲＡＬとバッテリ電圧Ｖ_Ｂからのリーク電流信号ΔＶとは反比例の関係にあり、リーク電流信号ΔＶを計測することによって絶縁抵抗Ｒ_ＡＬが検出できることが分かる。また、リーク電流ΔＶは、発熱体抵抗Ｒ_Ｈの影響を受けないことが分かる。 The reason why the output signal _VOUT oscillates at a cycle inverted with respect to the oscillation cycle of the energization pulse to the heating element 150 will be described with reference to FIG.
This figure (a) is an equivalent circuit diagram of the particulate matter detection sensor when the heating element energization pulse is turned on, and (b) is an equivalent circuit diagram of the particulate matter detection sensor when the heating element conduction pulse is turned off. It is an equivalent circuit diagram.
As shown in the figure (a), when energizing pulse is turned on, the insulation resistance R _AL of insulating substrate 100, since via the switching element 31 is grounded, with respect to the voltage dividing resistors Rdiv becomes parallel connection state, on-time output signal VON detected in a state in which current pulse is turned on, the combined resistance of the connected in parallel with the insulation resistance R _AL dividing resistor R _div (1 / (1 _{/ R a L + 1 / R} div)) and will prorated control voltage _{V CC} by the detection resistor _{R SEN} formed between the detection electrodes 110 and 120.
Therefore, the following relationship is established among the on-time detection signal V _ON , the control voltage V _CC , the insulation resistance R _AL , the detection resistance R _SEN , and the voltage _dividing resistance R _div .

Furthermore, as shown in the figure (b), when the energizing pulse is turned off, as shown in the figure the left, heating element resistance RH and insulating substrate 100 of the heating element 150 with respect to the battery voltage V _B of the insulation resistance R _AL are connected in series, this control voltage in a state of being connected in parallel with the sense resistor R _SEN connected in series with the V _CC, connect to the voltage dividing resistor R _div series It has become a state.
However, the heating element resistance R _H of the heating element is about several Ω, whereas the insulation resistance R _AL is several tens of kΩ even when the resistance value is lowered at high temperature. _It is much larger than _H and is equivalent to a circuit in which the heating element resistance _RH is eliminated as shown on the right side of the figure.
Therefore, the potential difference between the battery voltage _{V B} and the OFF time of the output signal _{V OFF (V B -V OFF)} by the current flowing through the insulation resistance _{R AL I1} and _{(= (V B -V OFF)} / R AL), the control voltage V _CC and the potential difference between the off time of the output signal _{V oFF (V CC -V oFF)} current flowing through the detection resistor _{R SEN} by _{I 2 (= (V B -V} oFF) / R SEN) and the sum of _(I 1 _{+ I} 2) There equal to the current _I 3 flowing through the off-time of the output signal _{V oFF} voltage dividing resistors _{R div (= V oFF / R} div), and rearranging these relationships off time of output signal _{V oFF,} the battery voltage _{V B,} the control voltage V The following relationship is established among _CC , insulation resistance R _AL , detection resistance R _SEN , and voltage _dividing resistance R _div .

Further, the difference ΔV (= V _OFF −V _ON ) between the output signal V _ON at the _ON time and the output signal V _OFF at the _OFF time, the battery voltage V _B , the control voltage V _CC , the insulation resistance R _AL , the detection resistance R _SEN , and the voltage division The following relationship is established between the resistors _Rdiv .

When these relationships are transformed,

It becomes.

Therefore, is inversely proportional to the leakage current signal [Delta] V from insulation resistance RAL and the battery voltage V _B, it can be seen that can detect insulation resistance R _AL by measuring the leakage current signal [Delta] V. It can also be seen that the leakage current ΔV is not affected by the heating element resistance _RH .

In the above embodiment, the difference between the off-time output signal V _OFF and the on-time output signal V _ON is used as the leakage current signal ΔV. However, the leakage current signal ΔV is on compared with the change in the off-time output signal V _OFF due to the temperature change. The change in the hour output signal V _ON is considered to be small and almost constant, and as a simple method, the leak current signal ΔV may be calculated by comparing the off-time output signal V _OFF with a constant offset potential.

A specific leak signal detection result will be described with reference to FIG.
As shown in FIG. 6A, at 600 ° C., for example, the battery voltage V _B = 14 v, the control voltage V _CC = 5 v, Assuming that the resistance R _H = 4.70 Ω, the insulation resistance R _AL = 0.5 GΩ, the detection resistance R _SEN = 1 GΩ, and the voltage dividing resistance R _div = 10 kΩ, the output signal V _ON = 0.05 mV when output, and the output when OFF The signal V _OFF = 0.05 mV and the leak current signal ΔV = 0.00 mV, and the leak current signal ΔV is not detected.
Furthermore, as shown in this figure (b), at 800 ° C., the battery voltage V _B = 14 v, the control voltage V _CC = 5 v, the heating element resistance R _H = 5.60Ω, the insulation resistance R _AL = 5.3 MΩ, Assuming that the detection resistor R _SEN = 1 GΩ and the voltage dividing resistor R _div = 10 kΩ, the output signal V _ON = 0.05 mV, the output signal V _OFF = 26.27 mV, and the leak current signal ΔV = 26.2 mV when calculated. The actual detection result was ΔV = 33.0 mV.
Furthermore, as shown in this figure (c), at 900 ° C., battery voltage V _B = 14 v, control voltage V _CC = 5 v, heating element resistance R _H = 6.05Ω, insulation resistance R _AL = 0.8 MΩ, Assuming that the detection resistor R _SEN = 1 GΩ and the voltage dividing resistor R _div = 10 kΩ, the output signal V _ON = 0.05 mV when turned on, the output signal V _OFF when _{turned off} 170.89 mV, and the leakage current signal ΔV = 170.8 mV, The actual detection result is ΔV = 179.5 mV, and the calculated value and the actual detection result are in good agreement.

The effect of the present invention will be described with reference to FIG.
This figure (a) shows the resistance-temperature characteristics of alumina, and the points indicated by ● in the figure are the results of detection of the leak current detection signal ΔV using alumina as the insulating substrate 100 as an example of the present invention. The calculated insulation resistance _RAL is shown.
Since the insulation resistance of alumina changes exponentially with respect to a temperature change, the resistance value changes rapidly even with a slight temperature change.
For example, the wiring resistance when a copper wire having a wiring diameter of 0.5 mm ² and a specific resistance of 0.0336 Ω / m is used for two positive and negative lines of 5 m is 0.336 Ω. kΩ much smaller relative to the number MΩ is resistance R _AL of the insulating substrate 100 from, corresponds to a temperature error of 0.1 ° C. or less, the wiring resistance effect is negligible.
Accordingly, as shown in the figure (a), the temperature characteristic value of the alumina, and good agreement with the leakage current detection signal ΔV insulation resistance R _AL calculated from detected by using the PM detection sensor 1 of the present invention, By measuring the leakage current detection signal ΔV, it can be expected that the heating temperature of the heating element 150 can be accurately controlled.
On the other hand, as shown in FIG. 5B, the heating element resistance _RH changes linearly with respect to a temperature change from 0 ° C. to 800 ° C., but the change width of the resistance value is 2.0Ω to 5.6Ω. A measurement error is likely to occur for a slight change in resistance value, and a temperature difference from the target temperature is likely to occur when the heating element resistance _RH of the conventional heating element 150 is detected and temperature controlled.
In addition, for example, R _H = 0.0045Ω / ° C. × t ° C. + 2.0Ω (t is the temperature of the heating resistor)
Since the absolute value of the heating element resistance _RH is low, if there is the same wiring resistance of 0.36Ω as described above, the influence on the detected temperature is large, resulting in a temperature error corresponding to 75 ° C.
In addition, when the temperature is detected by measuring only the conventional heating element resistance _RH , the influence of the circuit variation cannot be ignored, and a temperature difference of about 200 ° C. is generated when the influence of the circuit error is taken into consideration.
Note that the temperature characteristics of the insulation resistance _RAL of the actual insulating substrate 100 and the heating element resistance temperature coefficient α of the heating element 150 cause individual differences, and thus are measured in advance for individual particulate matter detection elements. A chip on which data on the temperature characteristics of the insulation resistance _RAL and the heating element resistance temperature coefficient α is recorded is mounted for each element, and is read by the leakage current signal detection means 40 to be used for correction of the control temperature. good.

FIG. 7A shows a change in the insulation resistance _{RAL in} the vicinity of 800 ° C. when alumina as an example of the present invention is used as the insulating substrate 100. As shown in this figure, for example, even if there is a detection error of ± 5% in the measurement of the insulation resistance _RAL , the temperature difference that can occur as a result is within ± 5 ° C.
On the other hand, when a detection error of ± 5% occurs in the detection of the heating element resistance _RH shown as a comparative example in FIG. 5B, the temperature error becomes ± 62 ° C.
Therefore, the control accuracy is greatly improved by controlling the heating temperature of the heating element 150 by detecting the insulation resistance _RAL of the insulating substrate 100.

It shows the relationship between the particulate matter detected by the detection sensor the leakage current detection signal [Delta] V and the element temperature T _SEN measured values and leakage current detection signal element temperature calculated from [Delta] V T _SEN of the present invention in FIG.
As shown in the figure, the element temperature T _SEN changes logarithmically with respect to the leakage current detection signal ΔV, and the measured value and the calculated value of the element temperature T _SEN are in good agreement. According to the particulate matter detection sensor, the temperature can be controlled with extremely high accuracy.

With reference to FIG. 9, the PM detection sensor 1a in the 2nd Embodiment of this invention is demonstrated.
In the above embodiment, heating is performed with extremely high accuracy by detecting the leakage current detection signal ΔV generated when the PM detection element 10 is heated to a high temperature in a state where particulate matter is not deposited between the detection electrodes 110 and 120. Although it has been described that the temperature can be controlled, in the above-described embodiment, the effect is exerted for temperature control at a high temperature of 700 ° C. or higher where leakage current occurs.
Therefore, in this embodiment, in addition to the same configuration as the above embodiment, it is possible to perform temperature control with high accuracy even at a low temperature where leakage current does not occur or is difficult to detect even if leakage current occurs. The difference is that a heating element resistance value detecting means 32 for detecting the resistance value _RH of the heating element 150 is provided.
In the conventional particulate matter detection sensor, the heating temperature of the heating element 150 is controlled by detecting the resistance value _RH of the heating element 150. However, as described above, the influence of wiring resistance and circuit variation is large. Detection error is likely to occur.
However, in the present embodiment, not only the resistance value _RH of the heating element 150 is detected, but also the wiring of the individual PM detection sensor 1a is determined based on the detection result and the detection result of the leak current detection signal ΔV detected at a high temperature. The error is corrected and temperature control can be performed with high accuracy. A specific correction method will be described later.
In addition, about the structure similar to the said embodiment, since the same code | symbol was attached | subjected, description is abbreviate | omitted.

Here, a specific temperature control method using the leakage current detection signal ΔV of the PM detection sensors 1 and 1a of the present invention will be described with reference to FIG.
This figure (a) shows change with time of element temperature T _SEN (° C.) and insulation resistance R _AL of the insulating substrate 100. The insulation resistance R _AL, as shown in the high insulating property of several GΩ level at low temperatures, with increasing element temperature T _SEN, changes abruptly becomes more than the predetermined temperature T _{1 (e.g.,} 600 ° C.), for example up to several kΩ descend.
As shown in the figure (b), the leakage current detection signal ΔV is detected when a predetermined temperature above T _1.
At this time, as described above, the leakage current detection signal ΔV (mV) rises while oscillating at a cycle inverted with respect to the opening / closing cycle of the energization pulse to the heating element 150.
Leakage current detection signal ΔV is, when it reaches the preset F / B target value, it is considered that the element temperature TSEN has reached the target temperature T _2, as the leakage current detection signal ΔV is constant The duty ratio of the energization pulse to the heating element 150 is controlled.
At the same time, as shown in FIG. 3C, the heating element resistance R _H (Ω) that rises as the element temperature T _SEN increases is measured, and the heating element resistance R _H at the target leakage current is learned.

FIG. 11A is a characteristic diagram when the resistance characteristic of the heating element 150 is corrected by the heating element resistance learning value R _LRN .
As described above, the heating element resistance _RH is easily affected by wiring resistance and circuit variation, and there is a variation range in which a temperature difference occurs as shown by dotted lines in FIGS.
Therefore, as described above, the heater characteristics of the actual PM detection element 10 are corrected by the heating element resistance learning value R _LRN learned when the F / B target value is reached.
Specifically, compared with the leakage current detection signal element temperature calculated from [Delta] V T _SEN and device temperature was calculated from a heater resistor R _H T _SEN, more precise temperature control by correcting the difference It becomes possible.
For example, in the relationship between the heating element resistance _RH and the element temperature T _SEN as shown in FIG. 5A, the heating element resistance at 20 ° C. is R _20, and the resistance when the temperature rises from 20 ° C. to 800 ° C. When the rate of change (slope of the straight line) is the heating element resistance temperature coefficient α ₂₀ , the heating element resistance Rt at t ° C. is given by R _t = R ₂₀ {1 + α ₂₀ (t−20)}. Correction is performed based on the difference from the heating element resistance learning value R _LRN learned at the F / B target value based on the leakage current detection signal ΔV.
This figure (b) makes the above-mentioned heating element resistance learning value R _{LRN the} high temperature side heating element learning value R _LH, and the resistance characteristic of the heating element 150 by two points of the low temperature side heating element learning value R _LL described later. It is a characteristic view in the case of performing temperature detection with higher accuracy by correcting.

With reference to FIG. 12, an example of the heating element resistance learning method applied to the particulate matter detection sensor of the present invention will be described.
In the particulate matter deposition presence / absence determination step in step S100, the detection signal _VOUT is compared with a predetermined threshold value _VREF . When the detection signal _VOUT is smaller than the threshold value _VREF , the detection resistance R _SEN is large and the detection electrode It is determined that the particulate matter is not deposited between 110 and 120, the determination is Yes, and the process proceeds to the leakage current determination process in step S110.
On the other hand, when the detection signal V _OUT is equal to or higher than the threshold value V _REF , the detection resistance R _SEN is small, and it is determined that particulate matter is accumulated between the detection electrodes 110 and 120. Proceed to the process and restart from step S100.
Next, in the leakage current determination process in step S110, the leakage current detection signal ΔV is compared with a preset F / B target value, and when the leakage current detection signal ΔV is equal to or greater than the F / B target value. It is determined that the target temperature has been reached, the determination is Yes, and the process proceeds to the heating element resistance learning process in step S130.
On the other hand, when the leak current detection signal ΔV has not reached the F / B target value, the determination is No, the process proceeds to the end step, and the process restarts from step S100.
In step S130, a heating element resistance learning process, the heating element resistance _RH at the F / B target temperature obtained from the leak current detection signal ΔV is detected by the heating element resistance detection means 32, and the heating element resistance learning value is stored in a recording medium such as a memory. Record and save as R _LRN .
The learning result is used for correction of the next temperature control of the heating element 150. When learning of the heating element resistance _RH is completed, the process proceeds to an end step.

With reference to FIG. 13, an example of a method for controlling the temperature of the heating element 150 using the learning result of the heating element resistance at the F / B target value described above will be described.
In the target heating element resistance calculation process of step S200, the target heater temperature T _TRG (° C.) is calculated from the corrected heating element resistance characteristic α obtained from the previously learned heating element resistance learning value R _LRN and the resistance temperature coefficient α _20. ) To calculate the target heating element resistance R _TRG (Ω).
Next, in the heating element resistance determination process in step S210, it is determined whether or not the detected heating element resistance R _DTC detected by the heater detection means 32 is equal to the target heating element resistance _RTRG .
If the detected heating element resistance R _DTC is smaller than the target heating element resistance _RTRG, it is determined No, and it is determined that there is a risk of overcurrent or overheating if the energization is maintained as it is. Proceed to energization suppression process.
In the energization suppression process of step S220, the duty ratio is lowered to suppress the energization amount, and the process proceeds to the end process.
On the other hand, if the detected heating element resistance _RTDC and the target heating element resistance _RTRG are equal in the heating element resistance determination process in step S210, the determination is Yes and the target temperature has been reached or the amount of energization is appropriate. Therefore, the process proceeds to the energization maintaining process in step S230.
In the energization amount maintaining process in step S230, the duty ratio is maintained as it is to maintain the temperature, and the process proceeds to the end process.
Further, in the heating element resistance determination process in step S210, if the detected heating element resistance R _DTC is smaller than the target heating element resistance _RTRG , the determination is No and the target temperature has not been reached, or the energy supply It is determined that the amount is insufficient, and the process proceeds to an energization amount increasing process in step S240.
In the energization amount increasing process of step S240, the duty ratio is increased in order to increase the energization amount and reach the target temperature at an early stage, and the process proceeds to the end process.
By repeating steps S200 to S240, the temperature of the heating element 150 is accurately maintained at the target temperature.

An example of a control method when the particulate matter detection sensor of the present invention is used as a temperature sensor will be described with reference to FIG.
In the heating element resistance detection process in step S300, the detected heating element resistance R _DTC is detected by the heating element resistance detection means 32.
In the heater temperature estimation step in step S210, the heater temperature T _EST is estimated based on the corrected heating element resistance R _AMD corrected with the heating element resistance learning value R _LRN and the resistance temperature coefficient α.
When the estimation of the heater temperature is completed, the process proceeds to the end step.
As described above, by correcting the heating element resistance at the high temperature by the leakage current signal ΔV, the temperature detection accuracy estimated from the heating element resistance at the low temperature is also improved.
Therefore, the estimated heater temperature T _EST estimates the temperature of the gas to be measured from the resistance of the heating element not only in the temperature control of the heating element 150 but also in the state where the heating element 150 is not energized, and the combustion of the engine It can also be used for control and control of an exhaust purification device.

Referring to FIG. 15, the particulate matter detection sensor of the present invention is provided in the combustion exhaust passage of the internal combustion engine, and the combustion exhaust temperature or the cooling water temperature is detected as an operation state detection means for detecting the operation state of the internal combustion engine. An example in which a low-temperature heating element resistance learning unit is provided in addition to the above-described high-temperature heating element resistance learning unit in order to perform temperature control with higher accuracy using a temperature sensor will be described. In the learning condition establishment determination process in step S400, a temperature sensor that detects engine cooling water temperature _TW or combustion exhaust temperature, oil temperature, intake air temperature, fuel temperature, or a plurality of temperatures selected from these temperatures. It is determined whether or not the detected temperature and the sensor temperature T _SEN are substantially equal.
For example, example, immediately after or if the beginning of startup has passed sufficient time since the last engine stop, the engine coolant temperature T _W and the sensor temperature T _SEN and the determination Yes and is approximately equal conditions, the temperature detection process in step S410 move on.
On the other hand, in the context in which it is determined that such as when restarting in a short time from the shutdown, a large temperature difference between the engine coolant temperature T _W and the element temperature T _SEN, judgment becomes No termination stroke without cold side learning Proceed to
In the temperature detection process of step S410, the engine coolant temperature _TW is detected as temperature information by the water temperature sensor, and the heating element resistance _RH of the particulate detection sensor of the present invention is detected by the heating element resistance detection means 32.
Next, in the low temperature learning process in step S420, the engine coolant temperature _TW and the measured gas temperature, that is, the element temperature T _SEN are considered to be equal, and the heating element resistance _RH detected at this time and the engine coolant are detected. and a temperature T _W, the low temperature heating element resistance learning value R _LL is recorded in a memory or the like, is stored.
When learning of the low-temperature heating element resistance learning value _RLL is completed, the process proceeds to an end step.
In the present embodiment, as the temperature characteristic correction means for correcting the temperature characteristics of the individual heating elements, the heating element resistance learning value R _LRN learned at the F / B target value by the high temperature heating element resistance learning means described above is used as the high temperature. Two points are used: the heating element resistance learning value R _LH during low temperature and the low temperature heating element resistance learning value R _LL learned by the low-temperature heating element learning means described above.
With the two learning values obtained in this way, as shown in FIG. 11B, the heating element resistance temperature coefficient α is further increased with respect to the relationship between the heating element resistance value _RH and the element temperature T _SEN. Correction can be made with high accuracy.
As described above, the leak current signal ΔV is detected only when the heating element 150 generates heat above a certain temperature (T ₁ ) and the insulation resistance R _AL of the heat-resistant insulating substrate 100 is lowered, and the temperature in a high temperature environment is detected. It can be used for control.
However, the relationship between the heating element resistance value _RH and the temperature T _{SEN in} a low temperature environment by using temperature information obtained by temperature information detection means for detecting temperature information such as a water temperature sensor or an oil temperature sensor. By learning the above, it becomes possible to accurately control the temperature not only at high temperatures but also over a wide temperature range.

In the above embodiment, the case where alumina is used as the insulating substrate 100 has been described. However, as the first invention, the insulating substrate is not limited to alumina, and the heat resistance insulation whose resistance temperature characteristics are known. For materials, it is speculated that oxide ceramic materials such as titania and mullite, and non-oxide ceramic materials such as silicon nitride, silicon carbide, and aluminum nitride can also be used.
In addition, it has been found by intensive studies by the present inventors that zirconia is not suitable as a material for the insulating substrate of the present invention because it produces high conductivity at high temperatures.
In the above embodiment, the particulate matter detection element that detects the electrical resistance formed on the pair of opposing detection electrodes as an electrical characteristic has been described as an example. However, in the present invention, the particulate matter detection element detects the electrical resistance. The target electrical characteristics are not limited to the electrical resistance formed in the detection unit, and the capacitance component that detects the capacitance that varies depending on the amount of particulate matter deposited on the detection unit may be used. It is also possible to detect a change in impedance of the combined impedance of the detection resistor and the capacitance.
By detecting a leak current signal generated when the insulation resistance of the insulating substrate decreases when the heating element provided via the insulating substrate is energized as a regeneration means of the PM detection element, the intrinsic resistance of the insulating substrate is detected. The technical idea of the present invention, which detects the temperature of the PM detection element from the temperature characteristic with extremely high accuracy and is used for temperature control of the PM detection element, detects any electrical characteristic as a method for detecting PM in the gas to be measured. It can also be adopted as appropriate.

1 particulate detection sensor 10 particulate matter detection element 100 heat resistant insulating substrate (alumina substrate)
110, 120 Detection electrodes 111, 121 Output transmission lead 150 Heating element 151, 152 Heating element energization lead 20 Output detection means 210 Voltage dividing means 220 Amplifying means 30 Heating element energization control means 31 Energization switching means (FET)
40 Leakage current detection means 50 Heating element temperature calculation means R _AL insulation resistance R _H heating element resistance value R _SEN detection resistance R _div voltage dividing resistance V _B battery voltage V _CC control voltage

JP 59-197847 A JP 2008-066421 A

Claims (7)

The detector comprises a detector that deposits particulate matter contained in the gas to be measured, and a heating element that is disposed between the detector and a heat-resistant insulating substrate and generates heat when energized, and is deposited on the detector. The particulate matter deposited between the detection electrodes by energizing the heating element while detecting the amount of particulate matter contained in the gas to be measured by detecting electrical characteristics that change depending on the amount of particulate matter A particulate matter detection sensor for removing heat by heating,
As temperature detection means for detecting the heating temperature of the heating element, there is provided leakage current detection means for detecting leakage current leaking from the heating element to the detection electrode due to a decrease in insulation resistance of the heat-resistant insulating substrate accompanying heating. A particulate matter detection sensor. The particulate matter detection sensor according to claim 1, wherein the heat-resistant insulating substrate is made of alumina. When the leakage current detection means is performed by pulse width modulation control that controls the amount of current supplied to the heating element according to an on / off duty ratio, the current flowing between the pair of electrodes is turned off when the current supply pulse to the heating element is off. The particulate matter detection sensor according to claim 1 or 2, wherein an off-time output signal ( _VOFF ) detected in a state where particulate matter is not deposited is detected. The leak current detecting means, the difference (V _OFF between the off time of the output signal which the current pulse is detected in the off (V _OFF) and the on-time of the output signal which the current pulse is detected when the ON (V _ON) the particulate matter detection sensor as claimed in any one of claims 1 to 3 for detecting the -V _oN) as leakage current signal ([Delta] V). A high-temperature heating element resistance learning means having a heating element resistance value detection means for detecting the resistance value of the heating element and learning the relationship between the heating element resistance value and the temperature at the target temperature calculated by the leak current detection means The particulate matter detection sensor according to any one of claims 1 to 4, further comprising:   The particulate matter detection sensor is disposed in the combustion exhaust passage of the internal combustion engine, and as an operation state detection means for detecting the operation state of the internal combustion engine, the combustion exhaust temperature, cooling water temperature, oil temperature, intake air temperature, fuel temperature are detected. A temperature sensor for detecting any temperature or a plurality of temperatures selected from these is provided, and detected by the temperature information immediately after the start of the internal combustion engine detected by the temperature sensor and the heating element resistance value detecting means. The particulate form according to any one of claims 1 to 5, further comprising low-temperature heating element resistance learning means for learning a relationship between the heating element resistance value and temperature in a low-temperature environment from the generated heating element resistance value. Substance detection sensor. The temperature characteristics of individual heating elements are corrected from the high temperature heating element resistance learning value learned by the high temperature heating element resistance learning means and the low temperature heating element resistance learning value learned by the low temperature heating element resistance learning means. The particulate matter detection sensor according to claim 6, further comprising a temperature characteristic correcting unit.

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