JP2013224618A - Dpf regeneration method and exhaust gas purification system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DPF regeneration method and an exhaust gas purification system capable of precisely obtaining a PM deposition amount upon the start of DPF regeneration processing to improve fuel economy.SOLUTION: An initial PM deposition amount upon the start of DPF regeneration control is calculated by integrating a carbon amount discharged from a DPF during the DPF regeneration control and by subtracting a carbon amount included in fuel inputted during the regeneration control from the integrated value.

Description

  The present invention relates to a DPF regeneration method and an exhaust gas purification system. More specifically, the present invention relates to a DPF regeneration method and an exhaust gas purification capable of improving the fuel consumption by accurately grasping the PM accumulation amount at the start of the DPF regeneration process. About the system.

  PM (particulate matter) called particulate matter is contained in exhaust gas discharged from an internal combustion engine mounted on a vehicle. Normally, this PM is collected by a DPF (diesel particulate filter) composed of various shapes and materials disposed in the exhaust passage of the internal combustion engine.

  The amount of PM collected in the DPF is managed by the pressure difference before and after the DPF detected by the pressure sensor, and it is determined that a predetermined amount of PM has accumulated when a pressure difference of a certain level or more occurs. Thus, reproduction processing is performed. In this regeneration process, the PM deposited on the DPF is burned and removed under the same conditions each time that the DPF is heated to a temperature at which PM is burned and maintained for a preset time. Thus, in the internal combustion engine provided with the DPF, the PM is not released into the atmosphere by repeating the collection of the PM and the regeneration process of the DPF.

  Since this DPF regeneration process is performed by maintaining the DPF at the same temperature for the same time each time, a certain amount of fuel is consumed each time. As a result, when the PM accumulation amount is small, there is a problem that a part of the fuel use amount with respect to the PM combustion amount is wasted, leading to deterioration of fuel consumption. Therefore, there is a need for a DPF regeneration method that minimizes fuel consumption using parameters related to DPF regeneration.

  In this connection, in order to be able to accurately determine the end timing of regeneration of the filter with a simple configuration, at the time of regeneration of the filter, a predetermined temperature (a temperature at which the filter is activated and PM is efficiently burned) An exhaust gas purifying apparatus that determines that regeneration is complete when the integrated value of the oxygen mass flow rate from when the filter temperature reaches 600 ° C. reaches a predetermined value corresponding to the amount of PM accumulated in the filter at the start of regeneration has been proposed. (For example, refer to Patent Document 1).

  In this exhaust gas purifying apparatus, the total combustion amount of PM is assumed to be equal to a value obtained by multiplying the integrated value of the oxygen mass flow rate by a predetermined coefficient C using the relationship between the combustion amount of PM and the oxygen mass flow rate. Since PM is burned and removed even before the temperature is raised to a predetermined temperature, and it is difficult to make the filter temperature maintained during the regeneration control completely constant depending on the situation of the internal combustion engine. There is a possibility that the time point at which PM is completely removed does not necessarily coincide with the time point at which regeneration is determined to end.

  Therefore, the present inventors calculate the PM removal amount within a preset time at the measured or estimated filter temperature based on the PM combustion rate or PM removal amount database during the regeneration control of the DPF, The accumulated PM removal amount is accumulated to calculate the accumulated PM removal amount of the PM that has been burned and removed from the start of the regeneration control, and the regeneration control is performed after the accumulated PM removal amount becomes the estimated PM accumulation amount at the start of the regeneration control. Proposed a method for regenerating DPF that ends.

  Here, in any of the above-described DFP regeneration methods, the PM deposition amount that serves as an index for starting the regeneration of the DPF is managed from the pressure difference (pressure loss) before and after the DPF. However, as shown in FIG. 12, there is a hysteresis relationship between the PM deposition amount and the pressure loss. For example, a case where the regeneration process is started even when the amount of PM collected is smaller than expected is expected. . In such a case, the amount of combustion used with respect to the PM combustion amount becomes excessive, resulting in a deterioration in fuel consumption. Therefore, it is desired to accurately grasp the PM accumulation amount at the start of the DPF regeneration process.

JP 2004-293340 A

  An object of the present invention is to provide a DPF regeneration method and an exhaust gas purification system capable of accurately grasping the PM accumulation amount at the start of the DPF regeneration process and improving fuel efficiency.

  The DPF regeneration method of the present invention that achieves the above object is an exhaust gas purification system that includes a DPF, and determines whether or not the PM deposition amount has reached the limit, and the PM deposition amount reaches the limit. In the DPF regeneration method of performing DPF regeneration control and performing DPF temperature rise control and DPF temperature maintenance control during the DPF regeneration control, the DPF is discharged from the DPF during the regeneration control. The amount of carbon generated by PM combustion is calculated by subtracting the amount of carbon contained in the fuel introduced during regeneration control from the integrated value, and the amount of PM collected in advance is set in advance. The PM combustion reaction rate constant and the PM combustion reaction rate are calculated using the Arrhenius equation, which is an equation for predicting the chemical reaction rate at a specific temperature with respect to the filter temperature, and the PM The amount of accumulated PM is calculated based on the amount of carbon generated by firing and the PM combustion reaction rate constant, and the PM combustion reaction rate is used to calculate the PM combustion reaction rate for each PM trapping amount and for each filter temperature. A database is set in advance, or a database of PM removal amount for each PM collection amount and filter temperature calculated using the PM combustion reaction rate is set in advance, and stored in the DPF regeneration control device, During the regeneration control of the DPF, the PM removal amount within a preset time at the measured or estimated filter temperature is calculated based on the database of the PM combustion reaction rate or the PM removal amount, and the calculated PM removal amount The accumulated PM removal amount of the PM removed by combustion from the start of regeneration control is calculated, and regeneration is performed after the accumulated PM removal amount reaches the calculated PM accumulation amount. It is characterized in that to terminate the control.

  An exhaust gas purification system of the present invention that achieves the above object is characterized in that, in an exhaust gas purification system configured to have a DPF, is provided with a regeneration control device that performs the above-described DPF regeneration method. is there.

  According to the DPF regeneration method and exhaust gas purification system of the present invention, it is possible to accurately grasp the initial PM accumulation amount accumulated in the DPF at the start of the regeneration process based on the carbon amount derived from PM combustion. As a result, deterioration of fuel consumption can be suppressed.

It is a figure which shows an example of the control flow of the regeneration method of DPF of embodiment which concerns on this invention. It is a figure which shows the detail of step S30 of FIG. It is a figure which shows the detail of step S33 of FIG. 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. It is a figure which shows the structure of the map data which shows PM removal amount which used PM deposition amount and catalyst temperature as a parameter. 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 graph which shows the relationship between PM deposition amount and pressure loss in DPF.

  Hereinafter, a DPF regeneration method and an exhaust gas purification system according to an embodiment of the present invention will be described. First, an exhaust gas purification system for carrying out the DPF regeneration method of the embodiment according to the present invention will be described.

  This exhaust gas purification system equipped with a DPF is a diesel particulate filter (DPF: Diesel Particulate Filter: hereinafter referred to as DPF) on which an upstream oxidation catalyst (DOC) carrier and a downstream oxidation catalyst are supported. And provided in the exhaust passage of the internal combustion engine. The exhaust gas purification system may be an exhaust gas purification system having a structure in which an oxidation catalyst (DOC) carrier is attached upstream and a DPF carrier without an oxidation catalyst is attached downstream.

During operation of the internal combustion engine, particulate matter (PM) contained in the exhaust gas may be oxygen or nitrogen dioxide (NO) in the exhaust gas depending on the temperature and composition of the exhaust gas. ₂ ) Part of the exhaust gas is oxidized in the exhaust gas or in the DPF, but depending on the temperature and composition of the exhaust gas, it is not oxidized in the exhaust gas or in the DPF, but is collected in the DPF of the exhaust gas purification system.

  If the amount of PM trapped in the DPF increases, the pressure loss of the DPF increases, which hinders the operation of the internal combustion engine. Therefore, the differential pressure before and after the DPF is measured or the previous regeneration is performed. When the accumulated amount of PM is estimated from the distance traveled from the process, fuel consumption, etc., and when the differential pressure across the DPF and the accumulated amount of PM exceed the respective threshold values, the filter temperature of the DPF is changed to the PM combustion temperature. And the temperature is maintained, and the DPF regeneration process is performed to burn and remove the PM trapped in the DPF. When raising the temperature of the filter and maintaining the temperature, a combination of multi-injection (multistage delay injection) in the cylinder, post injection, direct fuel injection in the exhaust pipe, intake throttle, exhaust throttle, EGR control, etc. is combined to raise the temperature of the exhaust gas. The high temperature is maintained, and the filter temperature is controlled by this high temperature exhaust gas.

  In the DPF regeneration method according to the embodiment of the present invention, in the exhaust gas purification system configured with the DPF, it is determined whether or not the PM accumulation amount has reached the limit from the differential pressure before and after the DPF. When the amount of accumulated PM has reached the limit, DPF regeneration control is performed, and the temperature of the DPF is monitored during the regeneration control of the DPF, while performing multi-injection (multistage delay injection) post-injection, etc. DPF temperature rise control and DPF temperature maintenance control are performed.

  Further, in this DPF regeneration method, using the Arrhenius equation, which is an equation for predicting the rate of a chemical reaction at a specific temperature, the PM calculated for a preset PM collection amount and a preset filter temperature A database of PM combustion rates by PM collection rate and by filter temperature is set in advance using the combustion rate, or by PM collection amount calculated by using this PM combustion rate and by filter temperature A PM removal amount database is set in advance, and this database is stored in the DPF regeneration control device.

  Then, during the regeneration control of the DPF, the PM removal amount within a preset time at the measured or estimated filter temperature is calculated based on the PM combustion speed or PM removal amount database, and the calculated PM removal amount Is accumulated to calculate the accumulated PM removal amount of the PM removed by combustion from the start of the regeneration control, and the regeneration control is terminated after the accumulated PM removal amount reaches the initial PM accumulation amount at the start of the regeneration control.

  In this DPF regeneration method, as a preliminary preparation, it is necessary to prepare a database of PM combustion rate or PM removal amount by PM collection amount and filter temperature. The PM combustion rate of PM accumulated in the DPF and the PM removal amount that is the amount burned and removed from the DPF will be described.

  In calculating the PM combustion rate and the PM removal amount, the PM combustion rate is calculated using the Arrhenius equation, and the PM combustion rate in the DPF differs depending on the filter temperature of the DPF.

  As shown in FIG. 4, while the temperature of the exhaust gas flowing into the DPF is low and the oxidation catalyst is lower than the activation temperature T1, PM cannot be combusted and removed. Wait until the temperature becomes equal to or higher than the first temperature T1, which is the activation temperature.

When the oxidation catalyst reaches or exceeds the first temperature T1 and enters the first temperature region R1, nitrogen monoxide (NO) in the exhaust gas is oxidized to generate nitrogen dioxide (NO ₂ ), and the combustion reaction of the formula (1a) According to the equation (chemical reaction equation), PM (C) collected in the DPF by nitrogen dioxide (NO ₂ ) is oxidized and removed. The activation temperature T1 is approximately 200 ° C. although it depends on the type of oxidation catalyst. In this first temperature region R1, nitrogen dioxide (NO ₂ ) is generated by the oxidation catalyst (DOC) upstream of the DPF, so that the amount of generated nitrogen dioxide is large, and the temperature region where PM oxidation by nitrogen dioxide is mainly performed. It is.

Further, when the oxidation catalyst is higher than the first temperature T1, becomes equal to or higher than the second temperature T2 at which nitrogen dioxide decreases, and enters the second temperature region R2, as shown in FIG. 5, the exhaust gas after contacting the oxidation catalyst The amount of nitrogen dioxide (NO ₂ ) in the catalyst is reduced, and PM (C) collected in the DPF is oxidized and removed by oxygen (O ₂ ) in the exhaust gas by the combustion reaction formula (1b). . That is, when nitrogen dioxide reaches the second temperature T2 or higher, the amount of production decreases as shown in FIG. 5, so that the rate of contribution to the PM combustion reaction decreases, and instead of this nitrogen dioxide, PM combustion with oxygen is mainly performed. It is an area to be called. Although this 2nd temperature T2 is based also on the kind of oxidation catalyst, it is about 500 degreeC in general.

  In this way, the PM combustion reaction varies depending on the temperature range of the oxidation catalyst, and therefore the combustion rate also varies.

As described above, the PM combustion reaction differs depending on the filter temperature, because there is a difference between oxidation by nitrogen dioxide (NO ₂ ) and oxidation by oxygen (O ₂ ), and the chemical reaction is different, so the PM combustion rate is also different. Using the filter temperature Tm, the PM combustion reaction is performed in a first temperature region R1 from the first temperature T1 to the second temperature T2 in the temperature raising process and a second temperature region R2 that is equal to or higher than the second temperature T2 in the temperature maintaining process. Classify into two temperature regions. The first temperature region R1 is a temperature range of 200 ° C. or more and 500 ° C. or less as a reference temperature, and the second temperature region R2 is a temperature range of 500 ° C. or more as a reference temperature. The upper limit of this second temperature region is the heat resistant temperature of the DPF, the highest predicted temperature of the exhaust gas, etc., and is set to 1000 ° C., for example. That is, the temperature range of the second temperature region of the database is set to 500 ° C. or more and 1000 ° C. or less.

  As described above, in the first temperature region R1 and the second temperature region R2, the oxidizer for burning PM is different, such as nitrogen dioxide and oxygen, and therefore, the reaction formula of the PM combustion reaction is different.

Next, PM combustion reaction formula (1a), PM combustion reaction rate formula (2a), reaction order determination formula (3a), reaction rate constant determination formula (4a), activation energy Ea1 and frequency factor A1 in the first temperature range Arrhenius equations (5a) and (6a) using the above, and a calculation equation (7a) for the PM removal amount ΔPMe1 burned and removed at time t are shown. In the following calculation, the reaction time (time of the control interval of the regeneration control of the DPF) is “t”, the initial PM deposition amount is “[C ₀ ]”, and the PM deposition amount after time t is “[C]”. The reaction rate is “v1, −d [C] / dt”, the reaction rate constant is “k1”, and the reaction order is “n1”.

The PM combustion reaction equation (1a) becomes the following equation (1a) in the first temperature region R1 from the first temperature T1 to the second temperature T2.

Next, the PM combustion reaction rate equation (2a) becomes the following equation.

The reaction order n1 is calculated from the PM combustion reaction rate equation (2a). This calculation is performed using a reaction order determination equation (3a) obtained by modifying the PM combustion reaction rate equation (2a).

Based on this reaction order determination formula (3a), as shown in FIG. 6, a linear curve is obtained by creating a graph with ln (V ₀ ) on the vertical axis and ln (C ₀ ) on the horizontal axis ( “Ln ()” represents the natural logarithm). Since the slope of this linear curve is the reaction order n1, the numerical value of the reaction order n1 is determined by setting the numerical value of this slope as the reaction order n1.

Next, the reaction rate constant k1 is calculated using the determined reaction order n1. This calculation is performed using a reaction rate determination equation (4a) obtained by modifying the PM combustion reaction rate equation and substituting the reaction order n1.

Based on this reaction rate determination formula (4a), as shown in FIG. 7, the vertical axis indicates “[1 / (− n + 1)] [(C ₀ ) ^{−n + 1} − (C) ^{−n + 1} ]”. A linear curve is obtained by creating a graph with time t on the horizontal axis, and the slope of this linear curve is the reaction rate constant k1, so that the value of this slope is the value of the reaction rate constant k1, The numerical value of the reaction rate constant k1 is determined.

On the other hand, if the gas constant is “R”, the reaction temperature (absolute temperature) is “T”, the activation energy (Arrhenius parameter) is “Ea1”, and the frequency factor that is a constant independent of temperature is “A1”. The Arrhenius equation that predicts the rate of chemical reaction at a certain temperature is “k1 = A1 · exp (−Ea1 / RT)”. The activation energy Ea1 and the frequency factor A1 of the Arrhenius equation are calculated from the previously determined reaction rate constant k1. When the Arrhenius equation is converted to a natural logarithm, (5a) and (6a) are obtained.

  From this equation (6a), a logarithmic graph (Arrhenius plot) having lnk1 on the vertical axis and reciprocal temperature (1 / T) on the horizontal axis as shown in FIG. A straight line that is a linear curve is obtained. Since the slope of this straight line is (−Ea1 / R), the value of this slope is taken as the value of the activation energy Ea1, and the value of the frequency factor A1 is calculated from the value of the intersection (intercept) lnA1 with the vertical axis.

  Since the activation energy Ea1 and the frequency factor A1 calculated by this method are values obtained by generalizing the PM combustion reaction in the first temperature range R1, the generalized PM combustion reaction rate is obtained by using these values. The constant k1 can be calculated.

Therefore, when the activation energy Ea1 and the frequency factor A1 are substituted into the Arrhenius equation, the equation (6a) is obtained, and the reaction rate constant k1 at each temperature T obtained by substituting the Arrhenius equation (6a) with ( The PM removal amount ΔPMe1 burned in t seconds can be calculated from (7a) which is substituted by the equation (2a) and deformed (7a).

The initial PM deposition amount [C ₀ ] ^{−n1 + 1} in the equation (7a) is predicted from the temperature during PM regeneration and the surplus carbon amount [C _IN (PM)] at that time. By subtracting the PM deposition amount (PM remaining amount) [C] ^{−n1 + 1} after t seconds from the initial PM deposition amount [C ₀ ] ^{−n1 + 1,} the PM removal amount ΔPMe1 burned in t seconds can be obtained. it can. Next, the PM removal amount ΔPMe1 can be calculated sequentially by treating this PM deposition amount [C] ^{−n1 + 1} as the initial deposition amount at the start of the next regeneration process. Therefore, by accumulating (accumulating) the PM removal amount ΔPMe1 burned in t seconds, it is possible to obtain the combustion time until the PM accumulation amount ΔPMc accumulated in the DPF is burned out.

That is, the reaction rate [v] is obtained in advance for each combination of the PM deposition amount [C ₀ ], [C] and the temperature [T] in an experiment such as a laboratory test and the like, and the Arrhenius plot is performed. The activation energy Ea1 and the frequency factor A1 in the equation can be calculated, and by fixing the activation energy Ea1 and the frequency factor A1, a general Arrhenius equation that can calculate a general combustion rate constant k in the PM combustion reaction can be calculated. The formula can be obtained.

The reaction rate constant k1m at a certain temperature Tm can be calculated from the Arrhenius equation specifying the activation energy Ea1 and the frequency factor A1, and the combustion rate v1m can be calculated from the reaction rate constant k1m. Therefore, further, the PM removal amount ΔPMe1m burned and removed during the control interval t by the reaction order n1 obtained in the process of these calculations is changed between the PM deposition amount [C ₀ ], [C] and the temperature [T]. It becomes possible to calculate for the combination.

As shown in FIG. 9, the PM removal amount [C ₀ i], [C] (corresponding to C1 to C4) and the PM removal during time t with respect to the temperature [Tj] (corresponding to T1 to T4) are calculated. The amount ΔPMe1m is stored as CTij (corresponding to CT11 to CT44) as a first database such as map data.

Similarly, PM combustion reaction formula (1b), PM combustion reaction rate formula (2b), reaction order determination formula (3b), reaction rate constant determination formula (4b), activation energy Ea2 and frequency in the second temperature region R2 An Arrhenius equation (5b) (6b) using the factor A2 and a calculation equation (7b) of the PM removal amount ΔPMe2 burned and removed at time t are shown. In the following calculation, the reaction time (time of the control interval of the regeneration control of the DPF) is “t”, the initial PM deposition amount is “[C ₀ ]”, and the PM deposition amount after time t is “[C]”. The reaction rate is “v2, −d [C] / dt”, the reaction rate constant is “k2”, and the reaction order is “n2”.

The PM combustion reaction formula (1b) becomes the following formula (1b) in the second temperature region R2 that is equal to or higher than the first temperature T2.

Next, the PM combustion reaction rate equation (2b) becomes the following equation.

The reaction order n2 is calculated from the PM combustion reaction rate equation (2b). This calculation is performed using a reaction order determination equation (3b) obtained by modifying the PM combustion reaction rate equation (2b).

Based on this reaction order determination formula (3b), a linear curve is obtained by creating a graph with ln (V ₀ ) on the vertical axis and ln (C ₀ ) on the horizontal axis, as in FIG. Since the slope of this linear curve is the reaction order n2, the numerical value of the reaction order n2 is determined by setting the numerical value of this slope as the numerical value of the reaction order n2.

Next, a reaction rate constant k2 is calculated using the determined reaction order n2. This calculation is performed using a reaction rate determination equation (4b) obtained by modifying the PM combustion reaction rate equation and substituting the reaction order n2.

Based on this reaction rate determination formula (4b), as in FIG. 7, “[1 / (− n + 1)] [(C ₀ ) ^{−n + 1} − (C) ^{−n + 1} ]” is plotted on the vertical axis. A linear curve can be obtained by creating a graph with time t on the horizontal axis, since the slope of this linear curve is the reaction rate constant k2, so that the reaction rate constant k2 can be used as the reaction rate constant k2. The numerical value of the speed constant k2 is determined.

On the other hand, if the gas constant is “R”, the reaction temperature (absolute temperature) is “T”, the activation energy (Arrhenius parameter) is “Ea2”, and the frequency factor, which is a constant independent of temperature, is “A2”. The Arrhenius equation, which is an equation for predicting the rate of chemical reaction at a certain temperature, is “k2 = A2 · exp (−Ea2 / RT)”. The activation energy Ea2 and the frequency factor A2 of the Arrhenius equation are calculated from the previously determined reaction rate constant k2. If the Arrhenius equation is in the form of a natural logarithm, equations (5b) and (6b) are obtained.

  From this equation (6b), a logarithmic graph (Arrhenius plot) having lnk2 on the vertical axis and the reciprocal of temperature (1 / T) on the horizontal axis is created as in FIG. A straight line that is a curve is obtained. Since the slope of this straight line is (−Ea2 / R), the numerical value of this slope is taken as the numerical value of the activation energy Ea2, and the numerical value of the frequency factor A2 is calculated from the numerical value of the intersection (intercept) lnA2 with the vertical axis.

  Since the activation energy Ea2 and the frequency factor A2 calculated by this method are values obtained by generalizing the PM combustion reaction in the second temperature range R2, the generalized PM combustion reaction rate is obtained by using these values. The constant k2 can be calculated.

Therefore, when the activation energy Ea2 and the frequency factor A2 are substituted into the Arrhenius equation, the equation (6b) is obtained, and the reaction rate constant k2 at each temperature T obtained by substituting into the Arrhenius equation of (6b) is expressed as ( The PM removal amount ΔPMe2 burned in t seconds can be calculated from (7b) which is substituted by the equation (2b) and deformed (7b).

The initial PM deposition amount [C ₀ ] ^{−n2 + 1} in the equation (7b) is predicted from the temperature during PM regeneration and the surplus carbon amount [C _IN (PM)] at that time. By subtracting the PM deposition amount (PM remaining amount) [C] ^{−n2 + 1} after t seconds from the initial PM deposition amount [C ₀ ] ^{−n2 + 1,} the PM removal amount ΔPMe2 burned in t seconds can be obtained. it can. Next, the PM removal amount ΔPMe2 can be calculated sequentially by treating this PM deposition amount [C] ^{−n2 + 1} as the initial deposition amount at the start of the next regeneration process. Therefore, by accumulating (accumulating) the PM removal amount ΔPMe burned in t seconds, it is possible to obtain the combustion time until the PM accumulation amount ΔPMc accumulated in the DPF burns out.

That is, the reaction rate [v] is obtained in advance for each combination of the PM deposition amount [C ₀ ], [C] and the temperature [T] in an experiment such as a laboratory test and the like, and the Arrhenius plot is performed. The activation energy Ea2 and the frequency factor A2 in the equation can be calculated, and by fixing the activation energy Ea2 and the frequency factor A2, a general Arrhenius equation that can calculate a general combustion rate constant k in the PM combustion reaction can be calculated. The formula can be obtained.

The reaction rate constant k2m at a certain temperature Tm can be calculated from the Arrhenius equation specifying the activation energy Ea2 and the frequency factor A2, and the combustion rate v2m can be calculated from the reaction rate constant k2m. Therefore, further, the PM removal amount ΔPMe2m burned and removed during the control interval t based on the reaction order n2 obtained in the process of these calculations is converted into the PM deposition amount [C ₀ ], [C] and the temperature [T]. It becomes possible to calculate for the combination.

As shown in FIG. 9, the PM removal amount [C ₀ i], [C] (corresponding to C1 to C4) and the PM removal during time t with respect to the temperature [Tj] (corresponding to T1 to T4) are calculated. The amount ΔPMe2m is stored as CTij (corresponding to CT11 to CT44) as a second database such as map data.

In the DPF regeneration method according to the embodiment of the present invention, the PM deposition amounts [C ₀ i], [C] and the temperature [C] are applied to both the first temperature region R1 and the second temperature region R2. PM removal amounts ΔPMe1m and ΔPMe2m during t time with respect to Tj] are stored in a database as CTij, and a catalyst temperature index that changes according to the progress of the DPF regeneration process based on this database during the DPF regeneration process The regeneration control is not terminated until the PM removal amount ΔPMem with respect to the temperature Tm is obtained and cumulatively calculated until the cumulative PM removal amount ΣPMem reaches the PM deposition amount ΣPMcm estimated at the start of regeneration of the DPF.

  This DPF regeneration method is performed by a control flow as shown in FIGS. In this control flow, when the operation of the internal combustion engine is started, the control flow is started from the upper control flow, and the differential pressure across the DPF is measured in step S11. At this time, PM in the exhaust gas generated in the internal combustion engine is collected by the DPF at the start of the operation of the internal combustion engine. In the next step S12, it is determined whether or not the differential pressure ΔPm across the DPF exceeds a predetermined first determination differential pressure (threshold value) ΔP1.

  If it is determined in step S12 that the differential pressure ΔPm across the DPF does not exceed the first determination differential pressure ΔP1 (NO), it is determined that there is a margin in the PM collection capability of the DPF, and the process returns to step S11. Continue to collect. Further, if the determination in step S12 indicates that the differential pressure ΔPm across the DPF exceeds the first determination differential pressure ΔP1 (YES), it is determined that the DPF PM trapping capacity has no room, and step S13 To start the DPF regeneration control for burning and removing the PM trapped in the DPF.

  When the DPF regeneration control is started, the control flow in step S20 and the control flow in step S30 are performed in parallel. In the control flow of step S20, the temperature rise control of the exhaust gas flowing into the exhaust gas purification device and the temperature maintenance control of the exhaust gas are performed for the combustion removal of the PM deposited on the DPF. Since the exhaust gas temperature raising control and the exhaust gas temperature maintenance control can be performed using a well-known technique in the prior art, details are not described here.

On the other hand, step S30 is a control flow for determining the end of regeneration control of the DPF. As shown in FIG. 2, in the first step S31, measurement of the exhaust gas at the DPF outlet is started in step S31a, and the total exhaust carbon amount [C _t ] is obtained. Next, in step S31b, the surplus carbon amount [C _IN (PM)] is estimated by subtracting the carbon amount [C _F ] contained in the fuel introduced at the time of regeneration from the total exhausted carbon amount [C _t ]. This injected fuel is used for driving the engine and raising the temperature of the filter by post injection or the like. Therefore, the surplus carbon amount [C _IN (PM)] is derived from PM combustion. In step S31c, the PM deposition amount ΣPMcm deposited on the DPF is calculated using the equation (7a) or (7b). In step S31c, the cumulative PM removal amount ΣPMem is set to zero.

  In the next step S32, the temperature distribution T in the DPF is calculated as the filter temperature. In the next step S33, the PM removal amount ΔPMem during the control time t for the temperature distribution T in the DPF is calculated. This step S33 has a control flow as shown in FIG. 3, which will be described later. In the next step S34, the PM removal amount ΔPMem is cumulatively calculated to calculate a cumulative PM removal amount ΣPMem (ΣPMem = ΣPMem + ΔPMem).

  In the next step S35, it is determined whether or not the accumulated PM removal amount ΣPMem exceeds the PM accumulation amount ΣPMcm. If the accumulated PM removal amount ΣPMem does not exceed the PM deposition amount ΣPMcm (NO) in step S35, the process returns to step S32 and repeats steps S32 to S35, assuming that PM deposited on the DPF has not been removed. . If the accumulated PM removal amount ΣPMem exceeds the PM accumulation amount ΣPMcm (YES) in step S35, it is determined that the PM accumulated in the DPF has been removed, and the process goes to step S14.

  In step S14, the front-rear differential pressure ΔPm of the DPF is measured, and in the next step S15, it is determined whether the front-rear differential pressure ΔPm of the DPF is equal to or lower than a predetermined second determination differential pressure (threshold value) ΔP2. To do. If it is determined in step S15 that the differential pressure ΔPm across the DPF is not equal to or lower than the second determination differential pressure (threshold value) ΔP2 (NO), it is determined that the PM accumulated in the DPF has not been completely removed. The process waits for the time set in advance in S16 (the time related to the determination interval in step S15), and returns to step S14. If it is determined in step S15 that the differential pressure ΔPm across the DPF is equal to or lower than the second determination differential pressure (threshold value) ΔP2 (YES), it is assumed that the PM accumulated in the DPF can be completely removed. Go to S17.

  In step S17, assuming that the regeneration control has been completed, a regeneration control end signal is transmitted to the control flow in step S20 performed in parallel, the control flow in step S20 is stopped, and the process proceeds to step S11. Return. On the other hand, in the control flow of step S20 that receives the signal for the completion of the reproduction control, the reproduction process is terminated, the control flow of step S20 is terminated, and the process returns to step S11.

  As described above, in the control flow shown in FIGS. 1 to 3, when returning to step S11, PM collection by the normal operation of the internal combustion engine is resumed, and steps S11 to S17 are repeated. Then, when the operation of the internal combustion engine is ended, an interruption occurs, and in step S18, an end process is performed, and then the control flow returns to the upper control flow, and the control flow of FIG.

  Here, the method for calculating the temperature distribution T in the DPF in step S32 will be specifically described below.

  In step S32, the temperature distribution in the DPF is calculated by modeling the heat balance, material balance, and reaction rate equation in the DPF. For this purpose, a temperature sensor and an oxygen concentration sensor are provided on the upstream side of the DPF. The model formula will be described as follows.

ここで、「Ｑ_reaction」はＤＰＦ内で発生した熱量、「Ｑ_A」は反応熱、「ρ_B」はＤＰＦかさ密度、「ｒ_Aw」は反応速度、「π」は円周率、「Ｄ」はＤＰＦ直径、「ｌ」はＤＰＦの入口からの距離、「ｄｌ」は微小距離、「Ｑ_loss」は熱損失、「α」は熱伝達率、「Ｔ」は排気ガス温度、「Ｔ_wall」はＤＰＦ壁面温度である。 (1) Heat balance The amount of heat and heat loss generated in the DPF are expressed by the following equations (8) and (9), respectively.

Here, “Q _reaction ” is the amount of heat generated in the DPF, “Q _A ” is the heat of reaction, “ρ _B ” is the DPF bulk density, “r _Aw ” is the reaction rate, “π” is the circumference, “D ”Is the DPF diameter,“ l ”is the distance from the DPF inlet,“ 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.

ここで、「ｃ_p」は排気ガス平均比熱、「Ｆ₀」は排気ガス流量、「ｄＴ」は微小距離ｄｌでのＤＰＦ入口温度Ｔ_inとＤＰＦ出口温度Ｔ_outとの温度差である。 As shown in FIG. 10, the heat quantity Q _reaction generated in the DPF partly 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. Considering the average temperature as the exhaust gas temperature T, the heat balance of the DPF is expressed by the following equation (10).

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.

ここで、「ｒ_j」は反応速度、「Ｓ」はＤＰＦ断面積、「ｄＶ」は微小体積、「Ｆ_j」は入量、「Ｆ_j＋ｄＦ_j」は出量である。 (2) Mass Balance As shown in FIG. 11, the amount generated by the reaction in the DPF is expressed by the difference between the amount of input and output before and after the minute volume, that is, the following equation (11).

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.

ここで、「ｘ_A」は成分Ａの変化率、「ｚ_A」は成分Ａの濃度である。 Focusing on a certain component A and rearranging equation (11) using the rate of change as a variable, the following equation (12) is obtained.

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

ここで、「Ａ」は頻度因子、「ｐ_A」はＰＭ分圧、「ｐ_O2」は酸素分圧、「Ｅ」は活性化エネルギ、「Ｒ」はガス定数である。 (3) Reaction rate equation When oxygen is considered as an oxidizing agent for PM and the component of PM is treated as solid carbon, the equation (13), 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.

これら（１４）〜（１６）式に基づいて、ＤＰＦ内の温度分布を算出する。 The following formulas (14) to (16) are obtained from the above formulas (8) to (13).

Based on these equations (14) to (16), the temperature distribution in the DPF 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 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. 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 as a map according to the operating conditions. That is, if the engine speed and the fuel injection amount are determined, the amount of PM discharged from the internal combustion engine is known.

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 (16), and then using the obtained r _Aw and the equations (14) and (15), _A concentration change (dx _A / dV) and a temperature change (dT / dV) when the exhaust gas moves in a minute volume (axial direction) are calculated.

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

  Next, step S33 for calculating the PM removal amount ΔPMem during the control time t with respect to the temperature distribution T in the DPF will be described with reference to the control flow shown in FIG. In step S33, it is determined whether or not the temperature distribution T in the DPF is equal to or higher than a predetermined first determination temperature T1 in the first step S33a. In step S33a, if the temperature distribution T in the DPF is smaller than the first determination temperature T1 (NO), it is determined that the temperature distribution T in the DPF is too low to burn and remove the PM collected in the DPF. go to. In step S33a, if the temperature distribution T in the DPF is equal to or higher than the first determination temperature T1 (YES), the process goes to step S33b.

  In step S33b, it is determined whether or not the temperature distribution T in the DPF is equal to or higher than a predetermined second determination temperature T2. In step S33b, if the temperature distribution T in the DPF is smaller than the second determination temperature T2 (NO), the temperature distribution T in the DPF is in the first temperature region R1, and the process goes to step S33c. In step S33b, if the temperature distribution T in the DPF is equal to or higher than the second determination temperature T1 (YES), the temperature distribution T in the DPF is in the second temperature region R2, and the process goes to step S33d.

  In step S33c, using the first database of the PM removal amount ΔPMe1 burnt and removed in t seconds for each temperature distribution T in the DPF calculated using the activation energy Ea1 and the frequency factor A1 in the first temperature region R1. The PM removal amount ΔPMem burned and removed in t seconds in the temperature distribution T in the DPF is calculated. Then, it goes to step S34.

  In step S33d, using the second database of the PM removal amount ΔPMe2 burnt and removed for t seconds for each temperature distribution T in the DPF calculated using the activation energy Ea2 and the frequency factor A2 in the second temperature region R2. The PM removal amount ΔPMem burned and removed in t seconds in the temperature distribution T in the DPF is calculated. Then, it goes to step S34.

  According to this DPF regeneration method, in an exhaust gas purification system configured with a DPF, it is determined whether or not the PM accumulation amount ΔPMc has reached a limit from the differential pressure ΔPm across the DPF, and the PM accumulation amount ΔPMc. Is reached, the DPF regeneration control is performed, and the temperature distribution T in the DPF is monitored during the regeneration control of the DPF, and the DPF temperature rise control by the post injection and the DPF temperature maintenance control are performed. In the DPF regeneration method, the PM burning rate calculated with respect to a preset PM trapping amount ΔPMc and a preset filter temperature by using the Arrhenius formula, which is a formula for predicting the rate of a chemical reaction at a specific temperature. A database of PM combustion rates for each PM collection amount and for each filter temperature using v1 and v2, or a PM collection amount calculated using this PM combustion rate In addition, a PM removal amount database for each filter temperature is set in advance and stored in the DPF regeneration control device, and is calculated based on the PM combustion speed or PM removal amount database during DPF regeneration control. The PM removal amount ΔPMem within a preset time in the temperature distribution T is calculated, and the calculated PM removal amount ΔPMem is accumulated to calculate the accumulated PM removal amount ΣPMem of the PM removed by combustion from the start of regeneration control. The regeneration control can be terminated after the accumulated PM removal amount ΣPMem reaches the PM accumulation amount ΣPMcm estimated at the start of the regeneration control.

  Furthermore, in the DPF regeneration method described above, the amount of PM trapped during regeneration during the regeneration control of the DPF in the “DPF regeneration process end determination” in step S30 of the control flow of FIGS. The target temperature distribution is added to ΔPMc by adding a step of calculating a target temperature distribution Tt at which the PM combustion speed v1, v2 or PM removal amount ΔPMe is maximized based on a database of PM combustion speed or PM removal amount ΔPMe. If Tt is output to the “DPF regeneration process” in step S20 and the temperature increase control of the DPF and the temperature maintenance control of the DPF are controlled so that the temperature distribution T in the DPF becomes the target temperature distribution Tt, Reaction order n1, n2, activation energy Ea1, Ea2, reaction rate constant k1 of Arrhenius equation related to PM combustion rate v1, v2 or PM removal amount ΔPMe From the reaction parameters k2, etc., to calculate the relationship between the temperature and the time required for PM is burned, it is possible to perform the reproduction in the most convenient conditions. Thereby, the efficiency of the reproduction process can be improved. Note that the PM removal amount ΔPMe increases as the target temperature distribution Tt increases.

  According to the above DPF regeneration method, the initial PM accumulation amount accumulated in the DPF at the start of the regeneration process is accurately grasped based on the carbon amount derived from PM combustion. Deterioration can be suppressed.

  Also, paying attention to the fact that the PM combustion speed v1m, v2m or PM removal amount ΔPMe1m, ΔPMe2m during the regeneration process of the DPF depends on both the PM collection amount (PM deposition amount) ΔPMc and the filter temperature, By monitoring, more accurate PM combustion speeds v1m and v2m or PM removal amounts ΔPMe1m and ΔPMe2m can be calculated, and a more appropriate reaction end timing (timing) can be calculated.

Note that the total amount of carbon discharged [C _t ] and the amount of carbon [C _F ] contained in the fuel input at the time of regeneration can be calculated by the following equations by measuring each gas with a sensor. However, [Fuel] indicates the amount of fuel input.

  The exhaust gas purification system according to the embodiment of the present invention is an exhaust gas purification system configured to include an upstream oxidation catalyst and a downstream DPF, and the DPF regeneration method according to the above embodiment. It is configured with a playback control device for performing.

A1, A2 Frequency factor [C], PM deposition amount after t time [C ₀ ] Initial PM deposition amount [C] ^{−n1 + 1} PM deposition amount after t seconds (PM remaining amount)
[C ₀ ] ^{−n1 + 1} PM initial deposition amount [C ₀ i], [C], C1 to C4 PM deposition amount
[C _t ] Total carbon emissions
[C _F ] Amount of carbon contained in fuel input during regeneration
[C _IN (PM)] Excess carbon amount Ea1, Ea2 Activation energy (Arrhenius parameter)
k1, k2 Reaction rate constant n1, n2 Reaction order R Gas constant R1 First temperature region R2 Second temperature region T Reaction temperature (absolute temperature)
T1 First temperature T2 Second temperature [Tj], T1 to T4 Temperature distribution Tt in temperature T DPF Target temperature distribution t Reaction time (time of control interval of regeneration control of DPF)
v1, v2, -d [C] / dt reaction rate (PM combustion rate)
ΔP, ΔPm Differential pressure across the DPF ΔP1 Differential pressure for first determination (threshold)
ΔP2 Differential pressure for second determination (threshold)
ΔPMc PM deposition amount ΔPMe, ΔPMe1, ΔPMe2 PM removal amount ΔPMem, ΔPMe1m, ΔPMe2m, CTij, CT11 to CT44 PM removal amount during t time ΣPMcm PM deposition amount estimated at the start of regeneration of DPF ΣPMem Cumulative PM removal amount

Claims (7)

In the exhaust gas purification system configured with the DPF, it is determined whether or not the PM accumulation amount has reached the limit. If the PM accumulation amount has reached the limit, the regeneration control of the DPF is performed. In a DPF regeneration method for performing DPF temperature rise control and DPF temperature maintenance control during DPF regeneration control,
The amount of carbon generated by PM combustion is calculated by integrating the amount of carbon discharged from the DPF during DPF regeneration control, and subtracting the amount of carbon contained in the fuel introduced during regeneration control from the accumulated value,
The PM combustion reaction rate constant and PM combustion reaction rate are calculated using the Arrhenius equation, which is a formula for predicting the rate of chemical reaction at a specific temperature, with respect to a preset amount of PM collected and a preset filter temperature. ,
Calculate the PM deposition amount based on the amount of carbon generated by the PM combustion and the PM combustion reaction rate constant,
Using the PM combustion reaction rate, a PM combustion reaction rate database for each PM collection amount and for each filter temperature is set in advance, or according to the PM collection amount calculated using the PM combustion reaction rate. In addition, a database of PM removal amount by filter temperature is set in advance and stored in the DPF regeneration control device.
During regeneration control of the DPF, based on the database of PM combustion reaction rate or PM removal amount, calculate the PM removal amount within a preset time in the separately calculated temperature distribution in the DPF,
By accumulating the calculated PM removal amount, the cumulative PM removal amount of the PM removed by combustion from the start of the regeneration control is calculated, and the regeneration control is performed after the accumulated PM removal amount reaches the calculated PM deposition amount. A method for regenerating a DPF, comprising: ending.   2. The method for regenerating a DPF 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.   During the regeneration control of the DPF, a target temperature distribution that maximizes the PM combustion rate or the PM removal amount is calculated with respect to the amount of PM collected during regeneration, and the calculated temperature distribution in the DPF is the target temperature distribution. The DPF regeneration method according to claim 1, wherein the temperature rise control of the DPF and the temperature maintenance control of the DPF are controlled so that   The database is divided into a first database in which the oxidation of PM by nitrogen dioxide is the main and a second database in which the oxidation of PM by oxygen is the main. The numerical value of the activation energy and the frequency factor of the Arrhenius equation The method for regenerating a DPF according to claim 1, wherein the PM combustion rate is calculated by changing a numerical value. The exhaust gas temperature or the filter 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 in the temperature range above the first temperature range, PM due to oxygen in the DPF The temperature range of the exhaust gas or the filter temperature where the removal becomes dominant is the second temperature range,
When the temperature of the exhaust gas flowing into the DPF or the filter temperature is within the first temperature range, the first database is used, and the temperature of the exhaust gas flowing into the DPF or the filter temperature is within the second temperature range. 5. The DPF regeneration method according to claim 4, wherein the PM combustion rate is calculated using the second database.   6. The method for regenerating a DPF according to claim 5, wherein the first temperature region is 200 ° C. or more and 500 ° C. or less, and the second temperature region is 500 ° C. or more and 1000 ° C. or less.   An exhaust gas purification system comprising a DPF, comprising an regeneration control device for performing the DPF regeneration method according to any one of claims 1 to 6.

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