JP2013204438A - Dpf regeneration method and exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DPF (Diesel Particulate Filter) regeneration method by which fuel consumption is minimized by accurately obtaining a temperature distribution within a DPF, and to provide an exhaust emission control system.SOLUTION: There is provided a DPF regeneration method in which DPF regeneration is started when a PM (Particulate Matter) depositing amount ΣPMin a DPF 13 exceeds a preset threshold value. In the DPF regeneration method, databases of PM combustion speeds r1, r2 or a PM removing amount ΔPMare prepared beforehand with PM depositing amounts and temperatures as parameters, and in DPF regeneration, a temperature distribution in the DPF 13 is calculated, the PM removing amount ΔPMwithin a preset time (t) is calculated based on any one of the databases and the temperature distribution in the DPF 13, a cumulative PM removing amount ΣPMfrom the DPF regeneration start is calculated by accumulating the calculated PM removing amounts ΔPM, and when the cumulative PM removing amount ΣPMbecomes equal to or more than the PM depositing amount ΣPMin DPF regeneration start, DPF regeneration is finished. An exhaust emission control system is also provided.

Description

  The present invention relates to a DPF regeneration method and an exhaust gas purification system in which fuel consumption is minimized by utilizing parameters (PM deposition amount and temperature) related to DPF regeneration.

  Particulate matter (PM) is contained in exhaust gas discharged from an internal combustion engine such as a diesel engine. Normally, this PM is collected by a diesel particulate filter (Diesel Particulate Filter; DPF) composed of various shapes and materials so as not to be discharged into the atmosphere.

  The amount of PM accumulated in the DPF is managed by a pressure difference measured by pressure sensors arranged before and after the DPF, and when a pressure difference of a certain level or more occurs, it is determined that a predetermined amount of PM has accumulated and DPF regeneration is performed ( For example, see Patent Document 1).

  In DPF regeneration, the temperature of the DPF is raised to a temperature at which PM can be combusted, and the state is maintained for a predetermined time, whereby the PM accumulated in the DPF is burned and removed. Thus, in an internal combustion engine equipped with a DPF, PM is not discharged into the atmosphere by repeating PM collection and DPF regeneration.

JP 2011-99378 A

  However, since the DPF regeneration is performed by setting the temperature and time under the same conditions every time, a certain amount of fuel is consumed regardless of whether the amount of accumulated PM is small or large. As a result, when the amount of accumulated PM is small, the amount of fuel used with respect to the amount of PM combustion increases, leading to deterioration in fuel consumption. Therefore, there is a need for a DPF regeneration method that minimizes fuel consumption using parameters related to DPF regeneration.

  Here, the temperature in the DPF during DPF regeneration changes temporally and spatially due to heat generated by PM combustion, heat loss to the DPF wall surface, and the like. Therefore, using the fact that the PM combustion rate during DPF regeneration depends on the temperature of the system and the PM deposition amount, the optimum DPF regeneration for minimizing the fuel consumption is performed using the temperature dependence formula. Therefore, it is necessary to accurately grasp the temperature distribution in the DPF.

  Therefore, an object of the present invention is to provide a DPF regeneration method and an exhaust gas purification system that can accurately grasp the temperature distribution in the DPF and minimize the fuel consumption.

  The present invention devised to achieve this object is a DPF regeneration method for starting DPF regeneration when the amount of PM deposition in the DPF exceeds a preset threshold value. A database of combustion speed or PM removal amount is created in advance, and during the DPF regeneration, the temperature distribution in the DPF is calculated, and the PM within the time set in advance based on one of the databases and the temperature distribution in the DPF When a removal amount is calculated, the calculated PM removal amount is accumulated to calculate a cumulative PM removal amount from the start of DPF regeneration, and when the accumulated PM removal amount is equal to or greater than the PM deposition amount at the start of DPF regeneration This is a DPF regeneration method for ending DPF regeneration.

  The temperature distribution in the DPF may be calculated based on a heat balance equation, a material balance equation, and a reaction rate equation in the DPF.

  Calculating a target temperature distribution that maximizes the PM combustion rate or PM removal amount with respect to the PM deposition amount during DPF regeneration, and controlling the temperature distribution in the DPF so that the temperature distribution in the DPF becomes the target temperature distribution; good.

  As the database, a first database when PM is mainly oxidized by nitrogen dioxide and a second database when PM is mainly oxidized by oxygen may be created in advance.

  A temperature range in which PM removal due to the amount of nitrogen dioxide is dominant in the DPF is defined as a first temperature range, and a temperature range higher than the first temperature range in which PM removal due to oxygen is dominant in the DPF is defined as a second temperature range. The first database is used when the temperature of the exhaust gas flowing into the DPF is within the first temperature range, and the second database when the temperature of the exhaust gas flowing into the DPF is within the second temperature range. Use a database.

  The first temperature region may be 200 ° C. or higher and lower than 500 ° C., and the second temperature region may be 500 ° C. or higher and 1000 ° C. or lower.

  Further, the present invention provides an exhaust gas purification system that includes a start determination unit that starts DPF regeneration when the amount of accumulated PM in the DPF exceeds a preset threshold value. A storage unit for storing a database of speed or PM removal amount, and calculating a temperature distribution in the DPF at the time of DPF regeneration, and within a preset time based on one of the databases and the temperature distribution in the DPF When calculating the PM removal amount, accumulating the calculated PM removal amount to calculate the cumulative PM removal amount from the start of DPF regeneration, and when the accumulated PM removal amount is equal to or greater than the PM deposition amount at the start of DPF regeneration And an end determination unit for ending DPF regeneration.

  The temperature distribution in the DPF may be calculated based on a heat balance equation, a material balance equation, and a reaction rate equation in the DPF.

  At the time of DPF regeneration, a target temperature distribution that maximizes the PM combustion rate or PM removal amount relative to the PM accumulation amount is calculated, and the temperature distribution in the DPF is controlled so that the temperature distribution in the DPF becomes the target temperature distribution. A temperature control unit may be further provided.

  The storage unit may store, as the database, a first database when PM is mainly oxidized by nitrogen dioxide and a second database when PM is mainly oxidized by oxygen.

  The termination determination unit sets a temperature region in which PM removal by nitrogen dioxide amount is dominant in the DPF as a first temperature region, and a temperature higher than the first temperature region in which PM removal by oxygen is dominant in the DPF. When the region is the second temperature region and the temperature of the exhaust gas flowing into the DPF is within the first temperature region, the first database is used, and the temperature of the exhaust gas flowing into the DPF is within the second temperature region. In such a case, the second database may be used.

  The first temperature region may be 200 ° C. or higher and lower than 500 ° C., and the second temperature region may be 500 ° C. or higher and 1000 ° C. or lower.

  ADVANTAGE OF THE INVENTION According to this invention, the DPF regeneration method and exhaust gas purification system which grasp | ascertain correctly the temperature distribution in DPF and can minimize fuel consumption can be provided.

It is a block diagram which shows an exhaust-gas purification system. It is a figure which shows a 1st temperature range and a 2nd temperature range. It is a figure which shows the relationship between the temperature of an oxidation catalyst, and the quantity of nitric oxide and nitrogen dioxide. It is a figure for calculating | requiring a reaction order. It is a figure for calculating | requiring a reaction rate constant. It is a figure for calculating | requiring activation energy and a frequency factor. It is a flowchart which shows a DPF regeneration method. It is a flowchart which shows the completion | finish judgment of DPF reproduction | regeneration. It is a figure which shows the model of a heat balance. It is a figure which shows the model of a material balance. It is a flowchart which shows the calculation method of PM removal amount.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  First, an example of an exhaust gas purification system for applying the DPF regeneration method according to the present embodiment will be described.

  As shown in FIG. 1, an exhaust gas purification system 10 is provided in an exhaust passage 12 that exhausts exhaust gas from an internal combustion engine 11 such as a diesel engine and carries an oxidation catalyst, and an upstream side or a downstream side of the DPF 13. An oxidation catalyst (Diesel Oxidation Catalyst; DOC) 14 provided in the exhaust passage 12 on the side (upstream side in FIG. 1), and an engine control unit (ECU) 15 for comprehensively controlling various devices. Prepare.

Most of the PM contained in the exhaust gas discharged from the internal combustion engine 11 is oxidized in the exhaust gas or in the DPF 13 by oxygen (O ₂ ) or nitrogen dioxide (NO ₂ ) in the exhaust gas. A part is collected and deposited in the DPF 13 of the exhaust gas purification system 10.

  When the amount of accumulated PM in the DPF 13 exceeds a preset threshold value, the pressure loss in the DPF 13 increases as the amount of accumulated PM in the DPF 13 increases, which may hinder the operation of the internal combustion engine 11. In addition, the DPF regeneration is performed in which the temperature in the DPF 13 is raised to a temperature at which PM can be combusted and the temperature is maintained, and the PM deposited on the DPF 13 is burned and removed.

  When the temperature in the DPF 13 is raised and maintained, exhaust gas is combined with multi-injection (multi-stage delay injection) or post-injection in the cylinder of the internal combustion engine 11, direct fuel injection in the exhaust pipe, intake throttle, exhaust throttle, EGR control, etc. The temperature in the DPF 13 is controlled by raising and maintaining the temperature.

  The PM accumulation amount in the DPF 13 is determined by measuring the differential pressure across the DPF 13 or estimating the PM accumulation amount from the travel distance, fuel consumption, etc. after the previous DPF regeneration. This is performed by determining that the PM deposition amount has exceeded a preset threshold when the front-rear differential pressure or the PM deposition amount exceeds a preset threshold.

  In the DPF regeneration method according to the present embodiment, when determining in the exhaust gas purification system 10 whether or not the PM accumulation amount in the DPF 13 has exceeded a preset threshold value, and determining that the PM accumulation amount has exceeded the threshold value The DPF regeneration is started, and the temperature in the DPF 13 is raised and maintained by multi-injection, post-injection, etc. while monitoring the temperature in the DPF 13 during the DPF regeneration.

  Also, in this DPF regeneration method, the PM combustion rate is calculated using the Arrhenius equation that predicts the rate of chemical reaction at a certain temperature, and the PM combustion with the PM deposition amount and temperature as parameters using this PM combustion rate. A database of speed or PM removal amount is created in advance.

  Then, during DPF regeneration, the temperature distribution in the DPF 13 is calculated, and the PM removal amount within a preset time is calculated based on either the PM combustion speed or PM removal amount database and the calculated temperature distribution in the DPF 13. The accumulated PM removal amount is accumulated to calculate the accumulated PM removal amount from the start of the DPF regeneration, and the DPF regeneration is terminated when the accumulated PM removal amount becomes equal to or greater than the PM accumulation amount at the start of the DPF regeneration.

  Therefore, the ECU 15 includes a start determination unit 16 that starts DPF regeneration when the amount of PM accumulated in the DPF 13 exceeds a preset threshold, a temperature control unit 17 that raises and maintains the temperature in the DPF 13, and a PM A storage unit 18 for storing a database of PM combustion rate or PM removal amount using the deposition amount and temperature as parameters, and a temperature distribution in the DPF 13 is calculated during DPF regeneration, and one of the databases and the temperature distribution in the DPF 13 The PM removal amount within a preset time is calculated based on the above, the calculated PM removal amount is accumulated to calculate the cumulative PM removal amount from the start of DPF regeneration, and the cumulative PM removal amount is the PM at the start of DPF regeneration. And an end determination unit 19 that ends the DPF regeneration when the amount exceeds the accumulation amount.

  In the DPF regeneration method applied to the exhaust gas purification system 10, as described above, it is necessary to create a database of the PM combustion rate or the PM removal amount using the PM accumulation amount and the temperature as parameters. The combustion speed and PM removal amount will be described.

  When calculating the PM combustion rate and the PM removal amount, the PM combustion rate is calculated using the Arrhenius equation. However, since the chemical reaction differs depending on the temperature, the PM combustion rate in the DPF 13 also varies depending on the temperature region.

As shown in FIG. 2, when the temperature of the exhaust gas flowing into the DPF 13 is low and the oxidation catalyst is lower than the activation temperature, PM cannot be burned and removed. wait until a first temperature above T ₁ is the activation temperature.

When the oxidation catalyst becomes equal to or higher than the first temperature T _{1 and} reaches the first temperature region R ₁ , nitrogen monoxide (NO) in the exhaust gas is oxidized to generate nitrogen dioxide, and the chemical reaction formula (1) ( As shown in the chemical reaction formula of PM combustion reaction, PM (C) collected in the DPF 13 is oxidized and removed by nitrogen dioxide.

The first temperature T ₁ is approximately 200 ° C., although it depends on the type of oxidation catalyst. In the first temperature region R _{1 that} is equal to or higher than the first temperature T _1, nitrogen dioxide is generated by the DOC 14 provided on the upstream side of the DPF 13, so that the amount of nitrogen dioxide generated is large, and PM oxidation mainly by nitrogen dioxide is performed. Done.

In addition, as shown in FIG. 3, when the oxidation catalyst is higher than the first temperature T _{1 and} becomes equal to or higher than the second temperature T _{2 at which} nitrogen dioxide decreases, and after entering the second temperature region R ₂ , The amount of nitrogen dioxide in the exhaust gas is reduced, and the PM collected in the DPF 13 is oxidized by oxygen in the exhaust gas as shown in the chemical reaction formula of Formula (2) (chemical reaction formula of PM combustion reaction). Removed.

The second temperature T ₂ is about 500 ° C., although it depends on the type of oxidation catalyst. In the second temperature region R _{2 that} is equal to or higher than the second temperature T ₂ , the amount of nitrogen monoxide (NO) increases and the amount of nitrogen dioxide produced decreases, so the rate at which nitrogen dioxide contributes to the PM combustion reaction decreases. Then, PM combustion is mainly performed by oxygen.

  As described above, the chemical reaction as the PM combustion reaction differs depending on the temperature, whether it is mainly oxidized by nitrogen dioxide or mainly oxidized by oxygen (the oxidizing agents are different). Accordingly, the PM combustion rate also varies.

Therefore, the PM combustion reaction and the PM combustion speed, the first temperature region R ₁ of the second lower than temperature T ₂ first temperature above T ₁ is a Atsushi Nobori process, the second temperature T ₂ above the temperature maintained Process The temperature is classified into two temperature regions, ie, two temperature regions R ₂ .

For example, a first temperature region R ₁ is lower than 200 ° C. or higher 500 ° C., the second temperature region R ₂ is 500 ° C. or higher 1000 ° C. or less. The upper limit of the second temperature region R ₂ is set according to the maximum predicted temperature of the heat-resistant temperature and the exhaust gas DPF 13. In the present embodiment, as an example, the upper limit of the second temperature region R ₂ is 1000 ° C., and the temperature range of the second temperature region R ₂ is 500 ° C. or more and 1000 ° C. or less.

In the first temperature region R ₁ , the chemical reaction formula of the PM combustion reaction is expressed by the following formula (1), and the reaction rate formula of the PM combustion reaction is expressed by the following formula (3).

Here, “r ₁ ” is the PM combustion rate (reaction rate), “t” is the reaction time (time of the DPF regeneration control interval), and “[C]” is the PM deposition amount (PM remaining amount) after time t. , “K ₁ ” is a reaction rate constant, and “n ₁ ” is a reaction order.

When the equation (3) is transformed, the following equation (4) which is a reaction order determining equation is obtained. The reaction order n ₁ is determined using this equation (4).

Here, “r ₁₀ ” is the initial PM combustion speed, “ln ()” is the natural logarithm, and “[C] ₀ ” is the initial PM deposition amount.

As shown in FIG. 4, when a graph having “ln (r ₁₀ )” on the vertical axis and “ln ([C] ₀ )” on the horizontal axis is created based on the equation (4), a linear curve is obtained. . The reaction order n ₁ is determined from the slope of this linear curve.

Then, the reaction rate constant k ₁ is determined using the determined reaction order n ₁ . This determination is performed using the following equation (5), which is a reaction rate constant determination equation obtained by modifying equation (3) and substituting reaction order n ₁ .

As shown in FIG. 5, based on the equation (5), the vertical axis indicates “(1 / (− n ₁ +1)) ([C] ₀ ^{−n1 + 1−} [C] ^{−n1 + 1} )”, horizontal Creating a graph with “t” on the axis gives a linear curve. The reaction rate constant k ₁ is determined from the slope of this linear curve.

  On the other hand, the Arrhenius equation is expressed by the following equation (6).

Here, “A ₁ ” is a frequency factor (a constant independent of temperature), “R” is a gas constant, “T” is a temperature (reaction temperature) as an absolute temperature, and “E ₁ ” is an activation energy (Arrhenius parameter). ).

The activation energy E ₁ and the frequency factor A ₁ are calculated from the previously determined reaction rate constant k ₁ . Then, when equation (6) is in the form of a natural logarithm, equations (7) and (8) are obtained.

As shown in FIG. 6, when a logarithmic graph (Arrhenius plot) having the vertical axis “ln (k ₁ )” and the horizontal axis “1 / T” is created based on the equation (8), A curve is obtained. The activation energy E ₁ is determined from the slope of this linear curve, and the frequency factor A ₁ is determined from the intercept.

Since the activation energy E ₁ and the frequency factor A ₁ determined by this method are values that generalize the PM combustion reaction in the first temperature region R ₁ , the generalized PM combustion is obtained by using these values. It is possible to calculate the reaction rate constant k ₁ of the reaction.

Therefore, when the activation energy E ₁ and the frequency factor A ₁ are substituted into the equation (7), the equation (8) is obtained, and the reaction rate constant k ₁ at each temperature T obtained by the substitution into the equation (8) is obtained by the equation By substituting into (3) and deforming, the following equation (9) is obtained, and the PM removal amount ΔPM _e1 burned and removed within the time t can be calculated from the equation (9).

Here, the initial value of PM accumulation amount (PM accumulation amount at the start of DPF regeneration) [C] ₀ −n1 ^{+ 1} is estimated from the differential pressure across the DPF 13 measured by the pressure sensors arranged before and after the DPF 13. By subtracting the PM deposition amount [C] ^{−n1 + 1} after time t from the initial value [C] ₀ ^{−n1 + 1} of the PM deposition amount, the PM removal amount ΔPM _e1 that is burned and removed within the time t is obtained. be able to. By treating this PM deposition amount [C] ^{−n1 + 1} as the initial PM deposition amount at the start of the next DPF regeneration, the PM removal amount ΔPM _e1 can be calculated sequentially.

Accordingly, by accumulating (accumulating) the PM removal amount ΔPM _e1 that is burned and removed within the time t, it is possible to obtain the time until the PM accumulated in the DPF 13 is burned out.

That is, in an experiment such as a laboratory test, the activation energy E ₁ and the frequency are obtained by obtaining the PM combustion rate r ₁ for each combination of the PM deposition amounts [C] ₀ , [C] and the temperature T and plotting the Arrhenius plot. Factor A ₁ can be calculated, and by fixing this activation energy E ₁ and frequency factor A ₁ , Formula (8), which is a general formula that can calculate the reaction rate constant k ₁ of the generalized PM combustion reaction, Can be obtained.

From this equation (8), the reaction rate constant k ₁ at a certain temperature T can be calculated, and the PM combustion rate r ₁ can be calculated from the reaction rate constant k ₁ . Further, the PM removal that is burned and removed within the time t with respect to the combination of the PM deposition amount [C] ₀ , [C] and the temperature T by the reaction order n ₁ obtained in the calculation process. The amount ΔPM _e1 can be calculated.

  As shown in Table 1, this calculation result is expressed as a PM removal amount (corresponding to CT11 to CT44) within a time t using the PM deposition amount (corresponding to C1 to C4) and the temperature (corresponding to T1 to T4) as parameters. First database such as map data is created.

On the other hand, in the second temperature region R ₂ , the chemical reaction formula of the PM combustion reaction is expressed by the following formula (2), and the reaction rate formula of the PM combustion reaction is expressed by the following formula (10).

Here, “r ₂ ” is the PM combustion rate (reaction rate), “t” is the reaction time (time of the control interval for DPF regeneration), and “[C]” is the PM deposition amount (PM remaining amount) after time t. , “K ₂ ” is a reaction rate constant, and “n ₂ ” is a reaction order.

When the equation (10) is transformed, the following equation (11) which is a reaction order determining equation is obtained. The reaction order n ₂ is determined using this equation (11).

Here, “r ₂₀ ” is the initial PM combustion speed, “ln ()” is the natural logarithm, and “[C] ₀ ” is the initial value of the PM deposition amount.

Similar to FIG. 4, a linear curve is obtained by creating a graph with “ln (r ₂₀ )” on the vertical axis and “ln ([C] ₀ )” on the horizontal axis based on Expression (11). The reaction order n ₂ is determined from the slope of this linear curve.

Then, the reaction rate constant k ₂ is determined using the determined reaction order n ₂ . This determination is performed using the following equation (12), which is a reaction rate constant determination equation obtained by modifying equation (10) and substituting reaction order n ₂ .

Similarly to FIG. 5, based on the formula (12), the vertical axis ^indicates “(1 / (− n ₂ +1)) ([C] ₀ ^{−n2 + 1−} [C] ^{−n2 + 1} )”, and the horizontal axis. If a graph with “t” taken is created, a linear curve is obtained. The reaction rate constant k ₂ is determined from the slope of this linear curve.

  On the other hand, the Arrhenius equation is expressed by the following equation (13).

Here, “A ₂ ” is a frequency factor (a constant independent of temperature), “R” is a gas constant, “T” is a temperature as absolute temperature (reaction temperature), and “E ₂ ” is an activation energy (Arrhenius parameter). ).

The activation energy E ₂ and the frequency factor A ₂ are calculated from the previously determined reaction rate constant k ₂ . Then, when equation (13) is in the form of a natural logarithm, equations (14) and (15) are obtained.

Similar to FIG. 6, when a logarithmic graph (Arrhenius plot) having “ln (k ₂ )” on the vertical axis and “1 / T” of the temperature on the horizontal axis is created based on Expression (15), a linear curve Is obtained. The activation energy E ₂ is determined from the slope of this linear curve, and the frequency factor A ₂ is determined from the intercept.

Since the activation energy E ₂ and the frequency factor A ₂ determined by this method are values that generalize the PM combustion reaction in the second temperature region R ₂ , the generalized PM combustion is obtained by using these values. The reaction rate constant k ₂ of the reaction can be calculated.

Therefore, when the activation energy E ₁ and the frequency factor A ₁ are substituted into the equation (14), the equation (15) is obtained, and the reaction rate constant k ₂ at each temperature T obtained by the substitution into the equation (15) is represented by the equation By substituting into (10) and deforming, the following equation (16) is obtained, and the PM removal amount ΔPM _e2 that is burned and removed within the time t can be calculated from the equation (16).

Here, the initial value of the PM accumulation amount (PM accumulation amount at the start of DPF regeneration) [C] ₀ ^{−n2 + 1} is estimated from the differential pressure across the DPF 13. By subtracting the PM deposition amount [C] ^{−n2 + 1} after time t from the initial value [C] ₀ ^{−n2 + 1} of the PM deposition amount, the PM removal amount ΔPM _e2 that is burned and removed within the time t is obtained. be able to. By ^treating this PM deposition amount [C] ^{−n2 + 1} as the initial PM deposition amount at the start of the next DPF regeneration, the PM removal amount ΔPM _e2 can be calculated sequentially.

Accordingly, by accumulating (accumulating) the PM removal amount ΔPM _e2 burned and removed within this time t, it is possible to obtain the time until the PM accumulated in the DPF 13 is burned out.

That is, in an experiment such as a laboratory test or the like, the activation energy E ₂ and the frequency are obtained by obtaining the PM combustion rate r ₂ for each combination of the PM deposition amount [C] ₀ , [C] and the temperature T and plotting the Arrhenius plot. Factor A ₂ can be calculated, and by fixing this activation energy E ₂ and frequency factor A ₂ , Formula (15), which is a general formula that can calculate the reaction rate constant k ₂ of the generalized PM combustion reaction, is Can be obtained.

The reaction rate constant k ₂ at a certain temperature T can be calculated from this equation (15), and the PM combustion rate r ₂ can be calculated from the reaction rate constant k ₂ . Further, the PM removal that is burned and removed within the time t with respect to the combination of the PM deposition amount [C] ₀ , [C] and the temperature T by the reaction order n ₂ obtained in the process of these calculations. The amount ΔPM _e2 can be calculated.

  Similar to Table 1, the calculation result is defined as the PM removal amount (corresponding to CT11 to CT44) within the time t using the PM deposition amount (corresponding to C1 to C4) and the temperature (corresponding to T1 to T4) as parameters. A second database such as map data is created.

  As described above, the first database when the oxidation of PM by nitrogen dioxide is the main and the second database when the oxidation of PM by oxygen are the main are created in advance and stored in the storage unit 18 as the databases. Keep it.

That is, in the DPF regeneration method according to the present embodiment, the temperature range in which PM removal due to the amount of nitrogen dioxide is dominant in the DPF 13 is the first temperature range R _1, and PM removal due to oxygen is dominant in the DPF 13. If the temperature range higher than the first temperature range R ₁ is the second temperature range R ₂ and the temperature of the exhaust gas flowing into the DPF 13 is within the first temperature range R ₁ , the first database is used to flow into the DPF 13. temperature of the exhaust gas in the case of the second temperature region R ₂ is to use a second database.

  The DPF regeneration method using these databases will be specifically described.

  As shown in FIG. 7, the DPF regeneration method is started by being called from the upper control flow when the internal combustion engine 11 is started. In step S101, the differential pressure ΔP before and after the DPF 13 is measured, and in step S102, the start determination is made. The unit 16 determines whether or not the differential pressure ΔP across the DPF 13 exceeds a preset first threshold value ΔP1.

  If it is determined in step S102 that the differential pressure ΔP before and after the DPF 13 does not exceed the first threshold value ΔP1 (No), the process returns to step S101 because there is a margin in the amount of PM accumulated in the DPF 13, and the DPF 13 captures the PM. Continue collecting.

  On the other hand, if it is determined in step S102 that the differential pressure ΔP before and after the DPF 13 exceeds the first threshold value ΔP1 (Yes), it is determined that there is no more margin in the PM accumulation amount in the DPF 13 and the process proceeds to step S103. Then, DPF regeneration for burning and removing the PM deposited on the DPF 13 is started.

  In step S104, the temperature controller 17 raises and maintains the temperature of the exhaust gas flowing into the DPF 13 using a known technique in order to burn and remove the PM accumulated in the DPF 13.

  In subsequent step S105, the end determination unit 19 determines whether or not an end signal permitting the end of DPF regeneration has been received, and repeats step S104 until it is determined that the end signal has been received (No). If it is determined that it has been received (Yes), the process proceeds to step S106 and DPF regeneration is terminated.

  Then, PM collection by normal operation of the internal combustion engine 11 is resumed, and steps S101 to S106 are repeated. When the operation of the internal combustion engine 11 is ended, an interrupt is generated in step S107 and the control flow of the DPF regeneration method is ended, and then the control flow returns to the upper control flow. Thereafter, the upper control flow ends.

By the way, although the end signal is also transmitted by the end determination unit 19, specifically, as shown in FIG. 8, first, in step S201, the PM accumulation amount ΣPM accumulated on the DPF 13 from the differential pressure ΔP before and after the DPF 13 _c is calculated. The PM accumulation amount ΣPM _c is obtained in advance through experiments or the like to obtain a relationship between the differential pressure ΔP across the DPF 13 and the PM accumulation amount ΣPM _c in the DPF 13 and stored in the storage unit 18 as a third database such as map data. Thus, it can be easily calculated based on the actually measured differential pressure ΔP of the DPF 13 and the third database. Furthermore, initialized to zero the accumulated PM removal amount [sum] Pm _e in step S201.

In a succeeding step S202, various measurement data necessary for calculating the temperature distribution in the DPF 13 is read. Specifically, the DPF inlet temperature T _in measured by the temperature sensor provided at the inlet of the DPF 13, the DPF wall surface temperature T _wall measured by the thermocouple provided at the wall surface of the DPF 13, and the air provided in the intake passage The intake air flow rate measured by a flow rate (Mass Air Flow; MAF) sensor and the fuel injection amount output from the ECU 15 are read.

Then, in step S203, the temperature distribution in the DPF 13 is calculated, and in the subsequent step S204, PM within the time t set in advance based on either the first database or the second database and the temperature distribution in the DPF 13 calculated in step S203. The removal amount ΔPM _e is calculated.

In step S205, the calculated PM removal amount .DELTA.PM _e and spatially and temporally accumulated in step S204, to calculate the cumulative PM removal amount [sum] Pm _e from the time of DPF regeneration start _{(= ΣPM e + ΔPM e)} .

Then, in step S206, if the cumulative PM removal amount [sum] Pm _e is determined whether a PM accumulation amount [sum] Pm _c above, the cumulative PM removal amount [sum] Pm _e is less than the PM deposit amount ΣPM _c (No), Returning to step S202, it is determined that the PM deposited on the DPF 13 has not been removed, and steps S202 to S205 are repeated.

On the other hand, if the cumulative PM removal amount [sum] Pm _e is determined to be the PM deposition amount [sum] Pm _c than proceeds to step S207 as was removed PM deposited on (Yes), DPF 13.

In step S207, performs a measurement of the differential pressure [Delta] P of the DPF 13, it is determined whether the differential pressure [Delta] P at the next step S208 DPF 13 is the second threshold value [Delta] P ₂ below.

If it is determined in step S208 that the differential pressure ΔP before and after the DPF 13 is higher than the second threshold value ΔP ₂ (No), it is determined that the PM accumulated in the DPF 13 has not been completely removed, and the time set in advance in step S209. The process waits for (a time related to the determination interval in step S208) and returns to step S207.

On the other hand, if it is determined in step S208 that the differential pressure ΔP before and after the DPF 13 is equal to or less than the second threshold value ΔP ₂ (Yes), it is determined that the PM accumulated in the DPF 13 has been completely removed, and the process proceeds to step S210.

  In step S210, a DPF regeneration end signal is transmitted assuming that DPF regeneration has been completed.

  Here, the method for calculating the temperature distribution in the DPF 13 in step S203 will be specifically described.

  In this step S203, the temperature distribution in the DPF 13 is calculated by modeling the heat balance, the mass balance, and the reaction rate equation in the DPF 13. For this purpose, a temperature sensor and an oxygen concentration sensor are provided on the upstream side of the DPF 13. Hereinafter, the model formula will be described.

(1) Heat balance The amount of heat and heat loss generated in the DPF 13 are expressed by the following equations (17) and (18), respectively.

Here, “Q _reaction ” is the amount of heat generated in the DPF 13, “Q _A ” is the heat of reaction, “ρ _B ” is the DPF bulk density, “r _Aw ” is the reaction rate, “π” is the pi, and “D ”Is the DPF diameter,“ l ”is the distance from the inlet of the DPF 13,“ dl ”is the minute distance,“ Q _loss ”is the heat loss,“ α ”is the heat transfer coefficient,“ T ”is the exhaust gas temperature,“ T _wall "Is the DPF wall surface temperature.

As shown in FIG. 9, a part of the heat quantity Q _reaction generated in the DPF 13 moves through the DPF wall surface and becomes a heat loss Q _loss . Therefore, a temperature distribution is also generated in the radial direction of the DPF 13. Considering the average temperature as the exhaust gas temperature T, the heat balance of the DPF 13 is expressed by the following equation (19).

Here, "c _p" is the exhaust gas average specific heat, "F _0" is the exhaust gas flow, "dT" is the temperature difference between the DPF inlet temperature T _in the DPF outlet temperature T _out in a minute distance dl.

(2) Mass Balance As shown in FIG. 10, the amount generated by the reaction in the DPF 13 is expressed by the difference between the input and output before and after the microvolume, that is, the following equation (20).

Here, “r _j ” is a reaction rate, “S” is a DPF cross-sectional area, “dV” is a minute volume, “F _j ” is an input amount, and “F _j + dF _j ” is an output amount.

  Focusing on a certain component A and rearranging the equation (20) using the rate of change as a variable, the following equation (21) is obtained.

Here, “x _A ” is the rate of change of component A, and “z _A ” is the concentration of component A.

(3) Reaction rate equation When oxygen is considered as an oxidant for PM and the component of PM is treated as solid carbon, equation (22), which is an oxidation rate equation, is expressed as follows.

Here, “A” is a frequency factor, “p _A ” is a PM partial pressure, “p _O2 ” is an oxygen partial pressure, “E” is activation energy, and “R” is a gas constant.

  The following formulas (23) to (25) are obtained from the above formulas (17) to (22).

  Based on these formulas (23) to (25), the temperature distribution in the DPF 13 is calculated.

The reaction heat Q _A is known to be a reaction in the oxidation reaction of carbon, and is a numerical value that is also known in advance for the DPF bulk density ρ _B. The DPF wall surface temperature T _wall is grasped by measuring with a thermocouple as a temperature sensor installed on the DPF wall surface.

The exhaust gas flow rate F ₀ is calculated as the sum of the intake air flow rate and the fuel injection amount. This is measured by signals output from the MAF sensor and ECU 15 installed in the intake passage.

Exhaust gas average specific heat c _p is a known function of exhaust gas temperature. A thermocouple as a temperature sensor for measuring the exhaust gas temperature is provided at the inlet of the DPF 13. Thus, the temperature T at the initial value V = 0 (DPF inlet) is defined.

The oxygen concentration in the exhaust gas is calculated from the exhaust gas flow rate F ₀ and the amount of oxygen in the exhaust gas. At this time, the amount of oxygen in the exhaust gas is calculated by subtracting the amount of oxygen necessary for complete combustion of the injected fuel from the amount of oxygen in the intake air.

The concentration z _A of the component A (PM) is previously stored in the ECU 15 as a map in accordance with the operating conditions. That is, when the engine speed and the fuel injection amount are determined, the PM amount discharged from the internal combustion engine 11 is grasped.

From the above information, first, the reaction amount of PM is calculated from the reaction rate of component A (PM) at the DPF inlet by the equation (25), and then using the obtained r _Aw and the equations (23) and (24). The concentration change (dx _A / dV) and the temperature change (dT / dV) when the exhaust gas moves in a minute volume (axial direction) are calculated.

  By using the calculated temperature distribution, the efficiency of fuel consumption at the time of DPF regeneration is improved as compared with the case where the end determination of DPF regeneration is performed using only the DPF inlet temperature.

Next, a method for calculating the PM removal amount ΔPM _e in step S204 will be specifically described.

As shown in FIG. 11, in step S204, first, the temperature T in the DPF13 is determined whether a first temperature T ₁ or more at step S301, when the temperature T in the DPF13 is lower than the first temperature T ₁ (No), the temperature T in the DPF 13 is too low and PM deposited on the DPF 13 cannot be burned and removed, and the process proceeds to step S205, where the temperature T in the DPF 13 is equal to or higher than the first temperature T ₁ . If it is determined that there is (Yes), the process proceeds to step S302.

In step S302, it is determined whether the temperature T of the DPF13 is the second temperature T ₂ above, when the temperature T in the DPF13 is lower than the second temperature T ₂ (No), the temperature T in the DPF13 there proceeds to step S303 as in the first temperature region R _1, if the temperature T of the DPF13 is determined to be the second temperature T ₂ above (Yes), the temperature T in the DPF13 second temperature the process proceeds to step S304 as in the region R _2.

In step S303, based on the first database of the first temperature region R for _1, is burned calculates been PM removal amount .DELTA.PM _e removed in time t in the temperature distribution in the DPF13 calculated in step S203, step The process proceeds to S205.

On the other hand, in step S304, on the basis of the second database of the second temperature region R for _two, it is burned to calculate the removed PM removal amount .DELTA.PM _e in time t in the temperature distribution in the DPF13 calculated in step S203 The process proceeds to step S205.

The PM removal amount ΔPM _e calculated in step S204 takes into account the temperature distribution in the DPF 13, and is more realistic than, for example, a value calculated as the DPF inlet temperature Tin in the representative temperature _in the DPF 13. The value is close to the environment.

Cumulative PM removal amount [sum] Pm _e calculated using the PM removal amount .DELTA.PM _e is intended to accurately represent actual amount of PM removed is burned by the DPF regeneration, the accumulated PM removal amount [sum] Pm _e and DPF by comparing the PM accumulation amount [sum] Pm _c at the time of reproduction start, it is possible to perform the termination judgment of the DPF regeneration properly.

  That is, since the temperature at the time of combustion of PM changes, it is inappropriate to control the DPF regeneration at the fixed representative temperature. Therefore, by calculating the temperature distribution in the DPF 13 based on the model base, That is, by calculating the heat balance of temperature rise due to reaction heat and heat loss on the DPF wall surface, the mass balance as the amount of change of PM, and the reaction rate equation, the temperature change in the axial direction of the DPF 13 is calculated accurately. Therefore, it is possible to grasp the temperature change of a simple system and perform highly accurate DPF regeneration.

  Therefore, the efficiency of DPF regeneration is improved, and it becomes possible to realize low fuel consumption.

Furthermore, in the DPF regeneration method described above, the temperature control unit 17 calculates a target temperature distribution that maximizes the PM combustion rate r ₁ , r ₂ or the PM removal amount ΔPM _e with respect to the PM deposition amount ΣPM _c by the DPF regeneration, The temperature distribution in the DPF 13 may be controlled so that the temperature distribution in the DPF 13 becomes the calculated target temperature distribution.

  In this way, paying attention to the fact that the PM combustion rate during DPF regeneration depends on the PM deposition amount and temperature, by optimizing the relationship between the time and temperature required for DPF regeneration, that is, the reaction related to PM combustion By calculating the relationship between time and temperature required for PM to burn from parameters (reaction order, activation energy, and reaction rate constant), and executing DPF regeneration under the most convenient conditions, DPF regeneration can be performed under conditions that suppress deterioration.

  As described above, according to the present invention, it is possible to provide a DPF regeneration method and an exhaust gas purification system that can accurately grasp the temperature distribution in the DPF and minimize the fuel consumption.

10 exhaust gas purification system 11 internal combustion engine 12 exhaust passage 13 DPF
14 DOC
15 ECU
16 Start determination unit 17 Temperature control unit 18 Storage unit 19 End determination unit

Claims (12)

In the DPF regeneration method for starting the DPF regeneration when the PM accumulation amount in the DPF exceeds a preset threshold value,
Create a database of PM combustion rate or PM removal amount with PM deposition amount and temperature as parameters,
During the regeneration of the DPF, the temperature distribution in the DPF is calculated, the PM removal amount within a preset time is calculated based on any of the databases and the temperature distribution in the DPF, and the calculated PM removal amount is accumulated. Then, a cumulative PM removal amount from the start of DPF regeneration is calculated, and DPF regeneration is terminated when the cumulative PM removal amount becomes equal to or greater than the PM deposition amount at the start of DPF regeneration.   The DPF regeneration method according to claim 1, wherein the temperature distribution in the DPF is calculated based on a heat balance, a mass balance, and a reaction rate equation in the DPF.   At the time of DPF regeneration, a target temperature distribution that maximizes the PM combustion rate or PM removal amount relative to the PM accumulation amount is calculated, and the temperature distribution in the DPF is controlled so that the temperature distribution in the DPF becomes the target temperature distribution. The DPF regeneration method according to claim 1 or 2.   The database according to any one of claims 1 to 3, wherein a first database in the case where the oxidation of PM by nitrogen dioxide is the main database and a second database in the case of the oxidation of PM by oxygen are mainly prepared as the database. The DPF regeneration method as described in 2.   A temperature range in which PM removal due to the amount of nitrogen dioxide is dominant in the DPF is defined as a first temperature range, and a temperature range higher than the first temperature range in which PM removal due to oxygen is dominant in the DPF is defined as a second temperature range. The first database is used when the temperature of the exhaust gas flowing into the DPF is within the first temperature range, and the second database when the temperature of the exhaust gas flowing into the DPF is within the second temperature range. The DPF regeneration method according to claim 4, wherein a database is used.   The DPF regeneration method according to claim 5, wherein the first temperature region is 200 ° C or higher and lower than 500 ° C, and the second temperature region is 500 ° C or higher and 1000 ° C or lower. In the exhaust gas purification system including the start determination unit that starts the DPF regeneration when the PM accumulation amount in the DPF exceeds a preset threshold value,
A storage unit for storing a database of PM combustion rate or PM removal amount with PM deposition amount and temperature as parameters;
During the regeneration of the DPF, the temperature distribution in the DPF is calculated, the PM removal amount within a preset time is calculated based on any of the databases and the temperature distribution in the DPF, and the calculated PM removal amount is accumulated. A cumulative PM removal amount from the start of DPF regeneration, and an end determination unit that terminates the DPF regeneration when the cumulative PM removal amount is equal to or greater than the PM deposition amount at the start of DPF regeneration;
An exhaust gas purification system comprising:   The exhaust gas purification system according to claim 7, wherein the temperature distribution in the DPF is calculated based on a heat balance, a mass balance, and a reaction rate equation in the DPF.   At the time of DPF regeneration, a target temperature distribution that maximizes the PM combustion rate or PM removal amount relative to the PM accumulation amount is calculated, and the temperature distribution in the DPF is controlled so that the temperature distribution in the DPF becomes the target temperature distribution. The exhaust gas purification system according to claim 7 or 8, further comprising a temperature control unit.   The said memory | storage part memorize | stores the 1st database when the oxidation of PM by nitrogen dioxide is main as the said database, and the 2nd database when the oxidation of PM by oxygen is main. The exhaust gas purification system according to any one of 9.   The termination determination unit sets a temperature region in which PM removal by nitrogen dioxide amount is dominant in the DPF as a first temperature region, and a temperature higher than the first temperature region in which PM removal by oxygen is dominant in the DPF. When the region is the second temperature region and the temperature of the exhaust gas flowing into the DPF is within the first temperature region, the first database is used, and the temperature of the exhaust gas flowing into the DPF is within the second temperature region. The exhaust gas purification system according to claim 10, wherein the second database is used in some cases.   The exhaust gas purification system according to claim 11, wherein the first temperature region is 200 ° C or higher and lower than 500 ° C, and the second temperature region is 500 ° C or higher and 1000 ° C or lower.