JP2014159781A - State detecting device of exhaust system, and control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively detect an exhaust humidity without using a humidity sensor, with respect to a state detecting device of an exhaust system.SOLUTION: A state detecting device includes a DPF (diesel particulate filter) 16 for collecting a PM (particulate matter), temperature sensors 31, 32, electrostatic capacity detection units 17a, 17b, 21 detecting an electrostatic capacity of the DPF 16, and an exhaust humidity calculating portion 23 for calculating an amount of water molecule corresponding to the temperatures detected by the temperature sensors 31, 32, and the electrostatic capacity detected by the electrostatic capacity detecting units 17a, 17b, 21, on the basis of a characteristic map in which the relationship of the temperature of the DPF 16, the electrostatic capacity of the DPF 16, and the amount of water molecule existing in a DPF portion, is determined in advance.

Description

  The present invention relates to an exhaust system state detection device and a control device.

  For example, a diesel particulate filter (hereinafter referred to as DPF) is known as a filter that collects particulate matter (hereinafter referred to as PM) in exhaust gas discharged from a diesel engine. Yes.

  Since the DPF has a limit in the amount of collected PM, it is necessary to perform forced regeneration by periodically burning and removing the accumulated PM. The forced regeneration is performed by supplying unburned fuel (HC) to the oxidation catalyst on the exhaust upstream side by in-pipe injection or post-injection, and raising the exhaust gas temperature to the PM combustion temperature by heat generated by oxidation. (For example, refer to Patent Document 1).

  In addition, an exhaust gas purification device for an internal combustion engine is also known that includes a humidity sensor that can detect whether or not condensed water exists in the exhaust gas (see, for example, Patent Documents 2 and 3).

JP 2011-247145 A JP 2002-50006 A JP 2003-193830 A

  Incidentally, some sensors attached to the exhaust pipe for detecting the air-fuel ratio and the nitrogen oxide concentration generally include an electric heater for raising the temperature to the operating temperature range. However, if the electric heater is operated in a state where moisture (condensed water) remains in the pipe, the adhered water causes a device crack and causes a failure.

  Since there is no on-board method for directly detecting the humidity in the exhaust pipe or the presence or absence of condensed water, generally the exhaust gas temperature and time at which no condensed water remains in the exhaust pipe is experimentally confirmed / mapped in advance, A method of determining the operation of the electric heater based on the result is used.

  However, when the exhaust pipe is submerged in a disaster such as a flood, the scale of the condensed water is different from that of the remaining condensed water. Therefore, the above estimation based on the gas temperature cannot be performed with sufficient accuracy.

  The present invention has been made in view of the above points, and an object thereof is to effectively detect the humidity of an exhaust system without using a humidity sensor.

  In order to achieve the above object, an exhaust system state detection device of the present invention is provided in an exhaust system of an internal combustion engine, a filter for collecting particulate matter in exhaust gas, and a temperature for detecting the temperature of the filter. A characteristic map obtained by preliminarily determining the relationship between the detection means, the capacitance detection means for detecting the capacitance of the filter, the temperature of the filter, the capacitance of the filter, and the water molecular weight present in the filter section. And a humidity calculating means for calculating a water molecular weight corresponding to the temperature detected by the temperature detecting means and the capacitance detected by the capacitance detecting means.

  Further, the capacitance detection means may include a pair of electrodes that are disposed opposite to each other with at least one partition wall in the filter and form a capacitor.

  Further, the exhaust passage on the upstream side and the downstream side of the filter is connected to bypass the filter, and the particulate matter in the exhaust gas that is provided in the bypass passage and flows through the bypass passage. And a second filter for collecting, and the pair of electrodes may be arranged to face each other with at least one partition wall interposed in the second filter.

  Further, when performing forced regeneration for burning and removing the particulate matter deposited on the second filter, the pair of electrodes may function as a heater.

  Further, the control device of the present invention further includes the state detection device and heater control means for controlling a heater for heating built in a sensor provided in the exhaust system, and the heater control means starts the internal combustion engine. Sometimes, when the exhaust humidity calculated by the humidity calculating means is equal to or higher than a predetermined threshold value indicating dew condensation, the operation of the heater for heating is suspended until the exhaust humidity becomes lower than the threshold value.

  According to the exhaust system state detection device and the control device of the present invention, water molecules contained in the exhaust gas passing through the DPF and water molecules adsorbed on the filter are effectively detected without using a humidity sensor. be able to.

It is a typical whole block diagram which shows the state detection apparatus and control apparatus of an exhaust system which concern on one Embodiment of this invention. It is a figure which shows the characteristic map used for calculation of exhaust humidity in the exhaust-system state detection apparatus which concerns on one Embodiment of this invention. It is a flowchart which shows the control content by the state detection apparatus of the exhaust system which concerns on one Embodiment of this invention. It is a flowchart which shows the control content by the control apparatus which concerns on one Embodiment of this invention. It is a typical whole block diagram which shows the state detection apparatus and control apparatus of the exhaust system which concern on other embodiment.

  Hereinafter, an exhaust system state detection device and a control device according to an embodiment of the present invention will be described with reference to FIGS. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  As shown in FIG. 1, a diesel engine (hereinafter simply referred to as an engine) 10 is provided with an intake manifold 10a and an exhaust manifold 10b. An intake passage 11 for introducing fresh air is connected to the intake manifold 10a, and an exhaust passage 12 for releasing exhaust gas to the atmosphere is connected to the exhaust manifold 10b. Further, an air-fuel ratio sensor 34, a NOx sensor 35, an exhaust pipe injection device 13, an exhaust aftertreatment device 14, a DPF inlet temperature sensor 31, and a DPF outlet temperature sensor 32 are provided in the exhaust passage 12 in order from the exhaust upstream side. Yes.

  The exhaust pipe injection device 13 injects unburned fuel (HC) into the exhaust passage 12 in response to an instruction signal output from an electronic control unit (hereinafter, ECU) 20. In addition, when using the post injection by the multistage injection of the engine 10, this in-pipe injection device 13 may be omitted.

  The exhaust aftertreatment device 14 is configured by arranging an oxidation catalyst 15 and a DPF 16 in order from the exhaust upstream side in a case 14a.

  The oxidation catalyst 15 is formed by, for example, supporting a catalyst component on the surface of a ceramic carrier such as a cordierite honeycomb structure. When the unburned fuel (HC) is supplied by the in-pipe injection device 13 or post injection, the oxidation catalyst 15 oxidizes this to raise the temperature of the exhaust gas.

  The DPF 16 is formed, for example, by arranging a large number of cells partitioned by porous ceramic partition walls along the exhaust gas flow direction, and alternately plugging the upstream side and the downstream side of these cells. . The DPF 16 collects PM in the exhaust gas in the pores and surfaces of the partition walls, and performs so-called forced regeneration that burns and removes the PM when the PM accumulation amount reaches a predetermined amount. The forced regeneration is performed by supplying unburned fuel (HC) to the oxidation catalyst 15 by the exhaust pipe injection device 13 or post injection, and raising the DPF 16 to the PM combustion temperature (for example, about 600 ° C.).

  In addition, the DPF 16 of the present embodiment is provided with a pair of electrodes 17a and 17b that are disposed to face each other with at least one partition wall therebetween to form a capacitor. The pair of electrodes 17a and 17b are electrically connected to the ECU 20, respectively.

The DPF inlet temperature sensor 31 detects the temperature of exhaust gas flowing into the DPF 16 (hereinafter referred to as inlet temperature T _IN ). The DPF outlet temperature sensor 32 detects the temperature of exhaust gas flowing out from the DPF 16 (hereinafter referred to as outlet temperature T _OUT ). The inlet temperature T _IN and the outlet temperature T _OUT are output to the electrically connected ECU 20.

  The air-fuel ratio sensor 34 detects the air-fuel ratio λ in the exhaust gas exhausted from the engine 10. The NOx sensor 35 detects the nitrogen compound (NOx) concentration in the exhaust gas discharged from the engine 10. Each of the air-fuel ratio sensor 34 and the NOx sensor 35 incorporates an electric heater for heating (not shown).

  The ECU 20 performs various controls such as fuel injection of the engine 10 and the exhaust pipe injection device 13, and includes a known CPU, ROM, RAM, input port, output port, and the like. In addition, the ECU 20 includes an electrostatic capacity calculation unit 21, a PM accumulation amount estimation unit 22, an exhaust humidity calculation unit 23, a dew point determination unit 24, and an electric heater control unit 25 as some functional elements. Each of these functional elements will be described as being included in the ECU 20 which is an integral hardware, but any one of these may be provided in separate hardware. In the present embodiment, the capacitance calculation unit 21 and the pair of electrodes 17a and 17b constitute the capacitance detection means of the present invention.

  The electrostatic capacity calculation unit 21 calculates the electrostatic capacity C between the pair of electrodes 17a and 17b. Capacitance C is based on the relationship of Equation 1 below, where the dielectric constant ε of the medium between the electrodes 17a and 17b, the area S of the electrodes 17a and 17b, and the distance d between the electrodes 17a and 17b, It changes as the dielectric constant ε and the distance d change due to changes in temperature.

The PM accumulation amount estimation unit 22 is based on the inlet temperature T _IN detected by the DPF inlet temperature sensor 31 and the capacitance C calculated by the capacitance calculation unit 21. Estimate the deposition amount PM _DEP . For the estimation of the PM deposition amount PM _DEP , an approximate expression or a map obtained in advance by experiments can be used.

The exhaust humidity calculation unit 23 determines the humidity of the exhaust gas flowing into the DPF 16 (hereinafter referred to as exhaust humidity H _EG ) based on the capacitance C calculated by the capacitance calculation unit 21 and the DPF inlet temperature T _IN. Is calculated. Specific calculation of the exhaust humidity _HEG by the exhaust humidity calculation unit 23 will be described in detail below.

The ECU 20 stores a plurality of capacitances (hereinafter referred to as a reference capacitance C ₀ ) measured in advance by changing the PM accumulation amount and the exhaust gas temperature in an exhaust gas dry state by experiments or the like. Further, the ECU 20 stores a three-dimensional characteristic map (see FIG. 2) that defines the relationship among the capacitance deviation ΔC, the DPF average temperature T _AVE, and the exhaust humidity H _EG that has been obtained in advance through experiments or the like. First, the exhaust humidity calculation unit 23 calculates the current capacitance (hereinafter, actual capacitance C _A ) calculated by the capacitance calculation unit 21, the current PM deposition amount PM _DEP and the DPF average temperature T _AVE . A deviation (capacitance deviation ΔC) from the corresponding reference capacitance C ₀ is calculated. Then, the exhaust humidity calculation unit 23 calculates the current exhaust humidity H _EG by applying the calculated current capacitance deviation ΔC and the DPF average temperature T _AVE to the three-dimensional characteristic map (see FIG. 2). .

The calculation of the exhaust humidity H _EG is preferably performed when the DPF average temperature T _AVE is lower than around 100 ° C. Further, the temperature used for calculating the exhaust humidity H _EG is not necessarily the DPF average temperature T _AVE , and either the inlet temperature T _IN or the outlet temperature T _OUT may be used. Also, when the exhaust pipe is inundated due to a disaster such as a flood, or when the DPF absorbs water due to the accumulation of condensed water, the water molecules exist in a liquid state and therefore exist in a gaseous state. As a result, the capacitance C is overwhelmingly large and therefore appears as an extremely high capacitance C value. Therefore, in comparison with the value of the capacitance C at the end of the previous operation, the presence or absence of water immersion or condensed water in the stopped exhaust pipe may be detected.

The dew point determination unit 24 determines the presence or absence of condensation based on the exhaust humidity _HEG calculated by the exhaust humidity calculation unit 23 when the DPF inlet temperature T _IN or the like is 100 ° C. or less (hereinafter also referred to as dew point determination). I do. The ECU 20 stores in advance a humidity threshold value _HDP that indicates the presence or absence of condensation. The dew point determination unit 24 determines that the filter is wet (or has condensation) when the calculated exhaust humidity H _EG is equal to or higher than the humidity threshold H _DP when the DPF inlet temperature T _IN is 100 ° C. or lower. To do. Even if it is below the dew point (H _EG is below H _DP ), if the humidity of the exhaust gas is high, high humidity is defined as H _{0 and} the high humidity state of the exhaust humidity H _EG is determined. Good.

The electric heater control unit 25 controls the operation of an electric heater (not shown) built in the air-fuel ratio sensor 34 and the NOx sensor 35 based on the dew point determination of the dew point determination unit 24. For example, if the air-fuel ratio sensor 34 or the NOx sensor 35 that has been wetted by condensation is heated by an electric heater, there is a risk of causing element cracking. In order to prevent this element cracking, the electric heater control unit 25, when the exhaust humidity H _EG is equal to or higher than the humidity threshold H _DP at the start of the engine 10, until the exhaust humidity H _EG becomes lower than the humidity threshold H _DP. It is comprised so that the operation | movement of may be suspended.

  Next, based on FIGS. 3 and 4, a control flow by the exhaust system state detection device and the control device of the present embodiment will be described. First, the control flow by the exhaust system state detection device shown in FIG. 3 will be described.

In step (hereinafter, the step is simply referred to as S) 100, it is determined whether or not the DPF inlet temperature T _IN or the like is 100 ° C. or less. When the DPF inlet temperature T _IN or the like is 100 ° C. or lower, the control proceeds to S110.

In S110, the current actual capacitance C _A is calculated, and the current PM deposition amount PM _DEP and DPF average temperature T _AVE are calculated. Further, in S120, the reference capacitance C ₀ corresponding to the PM deposition amount PM _DEP and the DPF average temperature T _AVE calculated in S110 is read.

In S130, a deviation between the actual capacitance C _A calculated in S110 and the reference capacitance C ₀ read in S120, that is, a capacitance deviation ΔC is calculated. Thereafter, in S140, the exhaust gas humidity H _EG is calculated by applying the capacitance deviation ΔC calculated in S130 and the DPF average temperature T _AVE calculated in S110 to the three-dimensional characteristic map (see FIG. 2).

  Next, based on FIG. 4, the control flow by the control apparatus of this embodiment is demonstrated. This control starts simultaneously with the start of the engine 10 (ignition key ON). Moreover, since each step from S200 to S240 is the same control as S100 to 140 shown in FIG. 3, detailed description is omitted.

In S250, the exhaust humidity H _EG calculated in S240 whether there is more than the humidity threshold H _DP indicating the condensation is determined. If the exhaust humidity H _EG is equal to or higher than the humidity threshold H _DP (H _EG ≧ H _DP ), the control proceeds to S255. If the exhaust humidity H _EG is higher than the high humidity H ₀ , heating by the electric heater is suspended in S260. If the exhaust humidity H _EG is less than the high humidity H ₀ , heating by the electric heater is started in S270 and the process returns. On the other hand, when the exhaust humidity H _EG is less than the humidity threshold H _DP (H _EG <H _DP ), the present control proceeds to S260, where the heating by the electric heater is suspended and the process returns.

  Next, effects of the exhaust system state detection device and the control device according to the present embodiment will be described.

  2. Description of the Related Art Conventional exhaust gas purification apparatuses are known that include a humidity sensor that can detect humidity in exhaust gas. The sensor element of the humidity sensor has problems that unburned components and the like in the exhaust gas are attached and frequently heated with high-temperature exhaust gas, which causes a decrease in detection accuracy due to deterioration over time. Moreover, in order to suppress deterioration with the passage of time, it is necessary to improve the durability of the sensor element, and there is a problem of increasing the manufacturing cost.

On the other hand, the state detection device of the present embodiment detects the electrostatic capacitance C using the electrodes 17a and 17b provided in the DPF 16, and based on the detected electrostatic capacitance C and the DPF average temperature T _AVE . The exhaust humidity _HEG is calculated.

Therefore, according to the state detection device of the present embodiment, the exhaust humidity _HEG can be detected with high accuracy without using a humidity sensor, and the manufacturing cost can be effectively reduced.

  In addition, a conventional exhaust purification device that includes an air-fuel ratio sensor, a NOx sensor, or the like is known. Although these air-fuel ratio sensors and NOx sensors have a built-in heating electric heater, there is a risk of element cracking if the electric heater is operated in a state where it is wetted by condensation.

On the other hand, in the control device of the present embodiment, when the engine 10 is started, the exhaust humidity H _EG calculated from the capacitance C and the DPF average temperature T _{AVE is} equal to or higher than the humidity threshold H _DP indicating high condensation and the high humidity H _0. In this case, heating by the electric heaters of the air-fuel ratio sensor 34 and the NOx sensor 35 is suspended.

  Therefore, according to the control device of the present embodiment, it is possible to reliably prevent element cracking of the air-fuel ratio sensor 34 and the NOx sensor 35.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, as shown in FIG. 5, a bypass passage 18 that bypasses the DPF 16 may be connected to the exhaust passage 12, and the bypass passage 18 may be provided with a measurement DPF 16 a (second filter) having a small capacity. In this case, it is preferable that the pair of electrodes 17a and 17b are arranged opposite to each other with at least one partition wall in the measurement DPF 16a, and an orifice 18a (throttle) for adjusting the flow rate of the exhaust gas is provided in the bypass passage 18. . Further, when the forced regeneration of the measurement DPF 16a is executed, a voltage may be applied to the pair of electrodes 17a and 17b so as to function as a heater.

DESCRIPTION OF SYMBOLS 10 Engine 12 Exhaust passage 13 Exhaust pipe injection apparatus 14 Exhaust after-treatment apparatus 15 Oxidation catalyst 16 DPF (filter)
20 ECU
21 Capacitance calculation unit (capacitance detection means)
22 PM deposition amount estimation unit 23 Exhaust humidity calculation unit (humidity calculation means)
24 Dew point determination unit 25 Electric heater control unit (heater control means)
31 Inlet temperature sensor (temperature detection means)
32 Outlet temperature sensor (temperature detection means)
34 Air-fuel ratio sensor 35 NOx sensor

Claims (5)

A filter provided in an exhaust system of an internal combustion engine for collecting particulate matter in the exhaust;
Temperature detecting means for detecting the temperature of the filter;
Capacitance detecting means for detecting the capacitance of the filter;
The temperature detected by the temperature detection means based on the characteristic map obtained in advance for the relationship between the temperature of the filter, the capacitance of the filter, and the water molecular weight present in the filter section, and the capacitance detection means And a humidity calculating means for calculating a water molecular weight corresponding to the capacitance detected by the exhaust system. The exhaust system state detection device according to claim 1, wherein the capacitance detection unit includes a pair of electrodes that are disposed to face each other with at least one partition wall interposed in the filter, and form a capacitor. A bypass passage that bypasses the filter by connecting the exhaust passage upstream and downstream of the filter;
A second filter that is provided in the bypass passage and collects particulate matter in the exhaust gas flowing through the bypass passage;
The exhaust system state detection device according to claim 2, wherein the pair of electrodes are disposed to face each other with at least one partition wall interposed in the second filter. The exhaust system state detection device according to claim 3, wherein when performing forced regeneration for burning and removing the particulate matter deposited on the second filter, the pair of electrodes function as a heater. The state detection device according to any one of claims 1 to 4,
A heater control means for controlling a heater for heating built in a sensor provided in the exhaust system,
When the exhaust gas humidity calculated by the humidity calculating unit is equal to or higher than a predetermined threshold value indicating dew condensation when the internal combustion engine is started, the heater control unit is configured to turn on the heater until the exhaust humidity becomes lower than the threshold value. A control device characterized in that the operation is suspended.

Images