JP2013072328A - Exhaust emission control system for internal combustion engine, internal combustion engine, and exhaust emission control method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system for an internal combustion engine, the internal combustion engine, and an exhaust emission control method for the internal combustion engine performing NOx increase control not involving large variation of behavior of engine operation when PM forced regeneration control is not performed, improving oxidation of PM, reducing frequency of PM forced regeneration control, and achieving both of improvement of emission control performance and prevention of deterioration of operability.SOLUTION: When an accumulation amount of PM of a catalyst carrier filter 13b is equal to or less than a control start amount set beforehand, normal control is performed in which urea water is supplied from a urea water supply device 15 according to an NOx amount discharged from the internal combustion engine. When the accumulation amount of PM exceeds the control start amount, NOx increase control is performed if exhaust gas temperature T of an inlet of an oxidation catalyst 13a is within a temperature range R1 set beforehand. When the accumulation amount of PM exceeds a capturing limit amount, PM forced regeneration control is performed.

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine, which can promote the oxidation removal of PM trapped in the DPF and reduce the frequency of the forced regeneration control of the PM without significant change in the operation behavior of the engine, the internal combustion engine, And an exhaust gas purification method for an internal combustion engine.

  In an internal combustion engine such as a diesel engine mounted on an automobile, exhaust gas contains PM (particulate matter) and NOx (nitrogen oxide), and an exhaust purification system including a catalyst-carrying filter and a NOx purification catalyst is used. Thus, these components are prevented from being released into the atmosphere.

  As one example of this exhaust purification system, there is a DPF (diesel particulate filter) device 13 that combines an oxidation catalyst (DOC) 13a and a catalyst-carrying filter 13b in the middle of an exhaust pipe 12 of an engine body 11 as shown in FIG. There is an exhaust purification system 10 that is provided and has a selective reduction catalyst (SCR) 14 for NO purification disposed behind it.

In this exhaust purification system 10, PM discharged from the engine body 11 is collected by a catalyst-carrying filter 13b carrying a catalyst. The PM collected and deposited on the catalyst-carrying filter 13b is subjected to a reaction of “2C + 2NO ₂ → 2CO ₂ + N ₂ ” or “C + NO ₂ → CO ₂ + NO” by nitrogen dioxide (NO ₂ ) in the exhaust gas G. Continuously oxidized and removed. A part of this nitrogen dioxide is contained in the exhaust gas G, but the nitrogen monoxide (NO) in the exhaust gas is converted to the temperature and nitrogen monoxide shown in FIG. 5 by the oxidation catalyst 13a in the previous stage (upstream side). It is oxidized to nitrogen dioxide according to the relationship with the conversion rate from nitrogen to nitrogen dioxide.

  However, under conditions where the exhaust gas temperature T is lower than the activation temperature of the oxidation catalyst 13a (T <Ta) or higher than the high temperature range (T> Tb), nitrogen dioxide is generated. Therefore, PM continues to accumulate on the catalyst-carrying filter 13b without continuous regeneration of PM oxidation by nitrogen dioxide.

  As countermeasures, for example, an oxidation catalyst, a DPF that collects PM in the exhaust gas G, and an exhaust gas temperature sensor that detects the exhaust gas temperature are arranged in the exhaust passage so that the exhaust gas temperature falls within a predetermined temperature range. A controller for controlling the air amount adjusting mechanism disposed in the intake passage is provided so that the PM collected in the DPF is surely burned and PM is not deposited in the entire operation region of the engine. An exhaust emission control device for a diesel engine has been proposed (see, for example, Patent Document 1).

  However, in actual vehicle operation, the internal combustion engine (engine) is operated under various operating conditions, and the exhaust gas temperature is controlled to a temperature within a predetermined range as in the exhaust purification device of the diesel engine described above. Is almost impossible and impractical. For example, in this exhaust purification device, it is proposed that when the temperature is higher than the set temperature, the turbocharger is driven to increase the air amount, and when the temperature is lower than the set temperature, the intake throttle is closed to reduce the air amount. If such a change occurs during driving under certain conditions, a large change in the engine behavior will occur, and the driver will feel uncomfortable due to the unexpected engine behavior, and the merchantability will be significantly impaired.

JP 2002-004838 A

  The present invention has been made in view of the above situation, and its purpose is to perform NOx increase control without significant change in the behavior of engine operation when PM forced regeneration control is not performed, and to oxidize PM. The internal combustion engine exhaust purification system, the internal combustion engine, and the exhaust purification of the internal combustion engine can improve both exhaust purification performance and prevent deterioration of operability by reducing the frequency of forced PM regeneration control It is to provide a method.

  An exhaust gas purification system for an internal combustion engine according to the present invention for achieving the above object includes an oxidation catalyst, a catalyst-carrying filter, a urea water supply device, and a selective reduction catalyst in order from the upstream side in the exhaust passage of the internal combustion engine. In addition, in the exhaust gas purification system for an internal combustion engine that includes an internal combustion engine control device that controls the operation of the internal combustion engine and a urea water supply control device that controls the supply of urea water in the urea water supply device, the urea water supply control device includes: When the accumulation amount of PM accumulated on the catalyst-carrying filter is smaller than a preset control start amount, urea water is supplied from the urea water supply device according to the NOx amount discharged from the internal combustion engine, and NOx is reduced. The internal combustion engine control device performs a normal control to purify, and the exhaust gas temperature at the inlet of the oxidation catalyst is preset when the PM accumulation amount is equal to or greater than the control start amount. When the NOx increase control is performed to promote combustion removal of PM deposited on the catalyst-carrying filter when the temperature is within the temperature range, and the amount of PM exceeds the collection limit amount greater than the control start amount In other words, the catalyst-carrying filter is regenerated by performing PM forced regeneration control for forcibly removing PM.

According to this configuration, when the deposition amount of PM increases to some extent, it is a reducing agent for PM in a temperature range in which the conversion rate from nitric oxide (NO) to nitrogen dioxide (NO ₂ ) is high. By performing NOx increase control to increase nitrogen oxide (NOx), the oxidation of PM by nitrogen dioxide can be promoted and the PM deposited on the catalyst-carrying filter can be burned and removed efficiently, thereby suppressing the increase in the amount of accumulated PM. This can reduce the frequency of PM forced regeneration control.

  In addition, since the NOx increase control does not involve a large change in the operation behavior of the engine as compared with the method of changing the intake air amount (oxygen concentration), both improvement of exhaust gas purification performance and prevention of deterioration of operability are achieved. be able to.

  In the above exhaust gas purification system for an internal combustion engine, the internal combustion engine control device includes an advance angle of fuel injection timing in the cylinder, an EGR cut, and a control region having engine speed and torque or engine load as parameters. In addition, the NOx increase control is performed using a combination thereof.

  According to this configuration, in order to promote the oxidation of PM by increasing the amount of NOx, a method of performing a timing advance that is a change in injection timing or an EGR cut that stops EGR is used, so that the amount of oxygen is increased. In order to promote the oxidation of PM, the change in engine behavior should be reduced compared with the case where the air volume is increased by the turbocharger or the intake volume is decreased by the intake throttle. And the deterioration of drivability can be prevented.

  In the exhaust gas purification system for an internal combustion engine, the urea water supply control device maps in advance a NOx increase amount that is predicted to increase when NOx increase control is performed in addition to the NOx amount calculation map data during normal operation. The data is converted into NOx increase amount calculation map data and stored, and during NOx increase control, the NOx amount calculated based on the NOx amount calculation map data is added to the NOx increase amount calculation map data. When the urea water increase control for increasing the supply amount of urea water is performed with respect to the NOx emission amount obtained by adding the NOx increase amount calculated based on the above, the downstream (downstream side) selective reduction by the NOx increase control is performed. An adverse effect on the NOx purification rate of the type catalyst can be avoided.

  In the exhaust gas purification system for an internal combustion engine, the internal combustion engine control device measures a NOx amount flowing into the selective reduction catalyst at the time of NOx increase control by a NOx sensor, and the calculated NOx amount and the calculated NOx amount Comparing the emission amount, if the difference between the two exceeds a preset value, the map data for calculating the NOx increase amount is corrected. In addition, by correcting (rewriting) the map data of the NOx amount, the NOx purification rate of the selective catalytic reduction catalyst can be maintained, and the supply amount of urea water becomes an accurate amount, so that it is discharged downstream of the selective catalytic reduction catalyst. The amount of NOx that could not be reduced and the amount of surplus ammonia can be reduced.

  In order to achieve the above object, an internal combustion engine of the present invention comprises the above exhaust gas purification system for an internal combustion engine. With this configuration, the frequency of PM forced regeneration control can be reduced without significant changes in the behavior of the engine when PM forced regeneration control is not being performed, so both improvement of exhaust purification performance and prevention of deterioration of operability can be achieved. Can be planned.

  And the exhaust gas purification method for an internal combustion engine of the present invention for achieving the above-mentioned object is the oxidation catalyst, catalyst-carrying filter, urea water supply device for NOx and PM in the exhaust gas of the internal combustion engine in order from the upstream side to the exhaust passage. In the exhaust gas purification method for an internal combustion engine that purifies by an exhaust gas purification system in which a selective catalytic reduction catalyst is arranged, if the accumulated amount of PM deposited on the catalyst-carrying filter is smaller than a preset control start amount, the exhaust gas is discharged from the internal combustion engine. The internal combustion engine control device performs normal control to purify NOx by supplying urea water from the urea water supply device in accordance with the amount of NOx to be generated, and the internal combustion engine control device When the exhaust gas temperature at the inlet of the oxidation catalyst is within a preset temperature range, NOx increase control is performed to promote combustion removal of PM deposited on the catalyst-carrying filter, A method for regenerating the catalyst-carrying filter by performing PM forced regeneration control for forcibly burning and removing PM when the amount of PM becomes greater than a collection limit amount larger than the control start amount. It is.

  According to this method, when the deposition amount of PM increases to some extent, NOx increases nitrogen oxide as a reducing agent for PM in a temperature range in which the conversion rate from nitric oxide to nitrogen dioxide is high. By controlling the increase, PM oxidation by nitrogen dioxide can be promoted and PM deposited on the catalyst-carrying filter can be burned and removed efficiently, so the increase in the amount of accumulated PM can be suppressed and the frequency of PM forced regeneration control decreased. can do.

  In addition, since the NOx increase control does not involve a large change in the operation behavior of the engine as compared with the method of changing the intake air amount (oxygen concentration), both improvement of exhaust gas purification performance and prevention of deterioration of operability are achieved. be able to.

  According to the exhaust purification system for an internal combustion engine, the internal combustion engine, and the exhaust purification method for an internal combustion engine according to the present invention, NOx increase control without significant change in the behavior of the engine is performed in the case where the PM forced regeneration control is not performed. The frequency of PM forced regeneration control can be reduced by improving the oxidation of PM, and both improvement of exhaust purification performance and prevention of deterioration of drivability can be achieved.

It is a figure which shows the structure of the exhaust gas purification system of the internal combustion engine of embodiment of this invention. It is a figure which shows an example of the control flow of the exhaust gas purification method of the internal combustion engine of embodiment of this invention. It is a figure which shows an example of the control flow of NOx increase control and urea water increase control of FIG. It is a figure which shows the other example of the control flow of NOx increase control of FIG. 2, and urea water increase control. And the relationship between the conversion to nitrogen dioxide (NO ₂₎ from the temperature and the nitrogen monoxide (NO), shows a high conversion temperature range. The temperature in FIG. 2 from the temperature and the nitrogen monoxide (NO) which is shifted to the high temperature side to the relationship between conversion to nitrogen dioxide (NO _2), is a diagram illustrating a control start temperature range. It is a figure which shows the area | region for control in NOx increase control. It is a figure which shows the relationship between the time change of DPF differential pressure, and each control in the exhaust gas purification method of the internal combustion engine of this invention. It is a figure which shows the relationship between the time change of DPF differential pressure, and each control in the exhaust gas purification method of the internal combustion engine of a prior art.

  Hereinafter, an exhaust gas purification system, an internal combustion engine, and an exhaust gas purification method for an internal combustion engine according to embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, an exhaust gas purification system 10 for an internal combustion engine according to this embodiment is provided with a DPF device 13 in the middle of an exhaust passage (exhaust pipe) 12 of an engine main body 11, and in a subsequent stage (downstream side). The urea water supply device 15 and the selective reduction catalyst (SCR) 14 are arranged in this order. The DPF device 13 is configured by combining an upstream (front-stage) oxidation catalyst (DOC) 13a and a catalyst-carrying filter (filter) 13b carrying a downstream (rear-stage) catalyst.

  Further, a first temperature sensor 21 for detecting the exhaust gas temperature T at the inlet of the oxidation catalyst 13 a is disposed upstream of the oxidation catalyst 13 a, and the inlet of the selective reduction catalyst 14 is disposed upstream of the selective reduction catalyst 14. A second temperature sensor 22 for detecting the exhaust gas temperature Tx is arranged. Further, a NOx sensor 23 that can measure the amount of NOx flowing into the selective catalytic reduction catalyst 14 is disposed on the inlet side of the selective catalytic reduction catalyst 14. A differential pressure sensor (not shown) is provided before and after the catalyst-carrying filter 13b to monitor (monitor) the amount of PM accumulated in the catalyst-carrying filter 13b. Further, if necessary, a catalyst for ammonia oxidation (not shown) is disposed on the downstream side (rear side) of the selective catalytic reduction catalyst 14.

  An internal combustion engine control device 30 called an ECU (engine control unit) is provided. In addition to the information from the sensors 21, 22, 23, the internal combustion engine weir device 30 obtains information from an engine operating status determination means for determining the operating status of the engine not shown in FIG. Performs overall control of the internal combustion engine.

  Further, a urea water supply control device 31 called a DCU (dosing unit) connected to the internal combustion engine control device 30 is installed. In response to the command from the urea water supply control device 31, the urea water supply device 15 purifies NOx by the selective catalytic reduction catalyst 14, and the exhaust passage from an apparatus (not shown) necessary for the supply of the urea water tank and the like. 12 is supplied with urea water.

  Next, an exhaust gas purification method for the internal combustion engine in the exhaust gas purification system 10 for the internal combustion engine will be described. In the exhaust gas purification method for an internal combustion engine according to the embodiment of the present invention, when the amount of PM deposited on the catalyst-carrying filter 13b is equal to or less than a preset control start amount, that is, the differential pressure P across the catalyst-carrying filter 13b. When the normal control is smaller than the control start differential pressure value Ps, no special control is performed.

In this normal control state, with respect to the catalyst-carrying filter 13b, the exhaust gas temperature T detected by the first temperature sensor 21, which indicates the temperature of the oxidation catalyst 13a, is within the high conversion temperature range (Ta or higher Tb) shown in FIG. In the case of R1 below, the conversion from nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ) corresponding to the exhaust gas temperature T is performed with a high conversion rate, and the nitrogen dioxide in the exhaust gas However, if the exhaust gas temperature T deviates from the high conversion temperature range R1 shown in FIG. 5, the PM deposition amount increases and the front-to-back differential pressure P also increases. This high conversion temperature range R1 is closely related to the activation temperature range of the catalyst supported on the oxidation catalyst 13a, and is, for example, within a temperature range of 250 ° C. to 400 ° C. with respect to the exhaust gas temperature T at the inlet of the oxidation catalyst 13a. The That is, Ta = 250 ° C. and Tb = 400 ° C.

At this time, with respect to the selective catalytic reduction catalyst 14, NO _x is purified by normal control according to the amount of exhausted NO _x . That is, information on the engine operating state (engine speed, torque or engine load) is obtained from the engine operating state determining means, and the NOx emission amount corresponding to the engine operating state is set in advance, and the urea water supply control device 31. The urea water supply device calculates the urea water supply amount that can be calculated by referring to the map data for calculating the NOx amount during normal operation stored in the internal combustion engine control device 30 and can reduce the calculated NOx emission amount. 15, NOx flowing out from the DFP device 13 is reduced by the selective reduction catalyst 14 using ammonia generated from the urea water. The ammonia that cannot be consumed in the reduction is oxidized and rendered harmless by a downstream ammonia oxidation catalyst (not shown).

  As the time elapses or the travel distance increases, the amount of PM accumulated on the catalyst-carrying filter 13b increases and the front-rear differential pressure P increases. FIG. 9 shows an outline of an increase in front-to-back differential pressure (DPF differential pressure) in the prior art. When the front-rear differential pressure P reaches the preset limit differential pressure value Pk, PM forced regeneration control (forced regeneration) is performed to reduce the pressure loss of the catalyst-carrying filter 13b. As shown in FIG. 9, when the initial pressure of the front-rear differential pressure P when no PM is accumulated in the catalyst-carrying filter 13b is P0, the front-rear differential pressure value P0k after the forced regeneration has a relationship of P0 ≦ P0k. . After the first forced regeneration, when the front-rear differential pressure value P0k increases from the front-rear differential pressure value P0k and reaches the limit differential pressure value Pk, the PM forced regeneration control is repeated.

  On the other hand, in the control of the exhaust gas purification method for an internal combustion engine of the present invention, as shown in FIG. 8, after the front-rear differential pressure P reaches the control start differential pressure value Ps exceeding the front-rear differential pressure P0k after forced regeneration, Accordingly, NOx increase control is performed. That is, when the amount of PM deposited on the catalyst-carrying filter 13b exceeds a preset control start amount, NOx increase control is performed according to the situation, and further, the amount of PM deposited is the collection limit amount (limit deposition). (PM) is configured to perform PM forced regeneration control.

  The exhaust gas purification method for an internal combustion engine of the present invention will be described with reference to the control flow of FIG. The control flow of FIG. 2 is called and executed from the upper control flow when the internal combustion engine is started, and is repeatedly called and executed after returning to the upper control flow, and at the end of the operation of the internal combustion engine. , Shown as ending with the upper control flow.

  When the control flow of FIG. 2 is called and started, in step S11, whether or not the amount of PM deposited on the catalyst-carrying filter 13b has exceeded a preset control start amount is determined. Judgment is made based on whether or not P is equal to or greater than the control start differential pressure value Ps.

  If the front-rear differential pressure P is smaller than the control start differential pressure value Ps in step S11 (NO), in step S30, the normal control is related to a predetermined time set in advance (the determination interval in step S11). After the time) Δt1, the process returns to step S11 and waits for the front-rear differential pressure P to be equal to or greater than the control start differential pressure value Ps.

  If it is determined in step S11 that the front-rear differential pressure P has reached the control start differential pressure value Ps or more (YES), the process goes to step S12 and is detected by the first temperature sensor 21 that indicates the temperature of the oxidation catalyst 13a. It is determined whether or not the exhaust gas temperature T is within a control start temperature range (T1 or more, T2 or less) R2 as shown in FIG.

  This control start temperature range R2 may be set to be the same as the high conversion temperature range R1, but is set to fall within the high conversion temperature range (Ta or more, Tb or less) R1 when NOx increase control is performed. It is preferable to keep it. That is, since the exhaust gas temperature T in the case of performing NOx increase control decreases, keep track whether advance degree decreases experiment or the like, according to the operating state of the engine, previously reduced temperature .DELTA.Ta, the ΔTb Predicting, it is preferable that T1 = Ta + ΔTa and T2 = Tb + ΔTb.

Thereby, the temperatures ΔTa and ΔTb that decrease in the NOx increase control are estimated in advance, and the reducing agent for PM is located near the peak of the conversion rate using the control start temperature range R2 that has moved higher than the high conversion temperature range R1. By increasing NO ₂ , PM oxidation in the catalyst-carrying filter 13b can be further promoted.

  If it is determined in step S12 that the exhaust gas temperature T is not within the control start temperature range R2, a predetermined time set in advance (the time related to the determination interval in step S11 and the determination interval in step S12). ) After Δt2, the process returns to step S11 and waits for the exhaust gas temperature T to fall within the control start temperature range R2. If it is determined in step S12 that the exhaust gas temperature T falls within the control start temperature range R2, the process proceeds to step S13, and NOx increase control and urea water increase control (NOx increase control) are performed in parallel.

  This NOx increase control is called in step S13 of the control flow of FIG. 2, and when the control flow of FIG. 3 starts, in step S21, NOx increase control is performed by the same determination of T1 ≦ T ≦ T2 as in step S12. Is determined to be started (ON) or not (control OFF) (NO), in step S32, normal control is set in advance for a predetermined time (in step S21). After a period of time (Δt3 related to the determination interval), the process returns to step S21 and waits until the NOx increase control can be started.

  If it is determined in step S21 that the NOx increase control may be started (control ON) (YES), in the next step S22, the engine speed Ne and the torque Trq (or engine Trq) obtained from the engine operating state detecting means are determined. Based on the load), it is determined which of the control areas (zones) A, B, and C shown in FIG. 7 is used as a parameter, and in each of the following steps S23 to S25, Control corresponding to the control areas A, B, and C is performed. The control regions A, B, and C are divided according to the relationship with the conversion rate of nitrogen monoxide to nitrogen dioxide, which is closely related to the exhaust gas temperature T.

  In the case of the control region A, the conversion rate at which nitric oxide is converted to nitrogen dioxide on the low temperature side is a slightly low region, and therefore the engine is driven by the timing advance that advances the fuel injection timing in the cylinder in step S23. The NOx discharged from the main body 11 is increased. Further, in the case of the control region B, since the conversion rate at which nitric oxide is converted into nitrogen dioxide is also a high region, it is determined from the engine body 11 by both the timing advance angle and the EGR cut that stops EGR in step S24. Significantly increases NOx emissions. Further, in the control region C, the torque required on the high temperature side increases (engine load also increases), so in step S25, the engine main body 11 is discharged by EGR cut instead of timing advance. NOx to be increased.

  In FIG. 7, the control region is related to the temperature region, and each region (zone) A, B, C is shown in a form surrounded by a straight line. However, the display in FIG. In the actual case, each control such as timing advance angle and EGR cut, which is determined in advance, is written in the map data and stored in the internal combustion engine control device 30, and the map data is referred to for control. Timing advance angle, EGR cut, etc. are selected and controlled.

  By this NOx increase control, NOx in the exhaust gas G discharged from the engine body 11 to the exhaust passage 12 increases, and from nitric oxide to nitrogen dioxide at a conversion rate according to the exhaust gas temperature T flowing into the oxidation catalyst 13a. Is converted by the oxidation catalyst 13a, and the nitrogen dioxide in the exhaust gas increases. This nitrogen dioxide promotes the oxidation of PM deposited on the catalyst-carrying filter 13b.

  In steps S23 to S25, urea water increase control is performed together with the NOx increase control. In this urea water increase control, the amount of NOx flowing into the selective catalytic reduction catalyst 14 is increased by the NOx increase control as compared with the normal control in which the NOx increase control is not performed. Therefore, it is necessary to process this increased NOx. Because there is.

  This urea water increase control is a control to increase the urea water corresponding to the increase in NOx, and the amount of increase in NOx by the NOx increase control is performed by the processing corresponding to each control region A, B, C in FIG. Because it is different, NOx that will be discharged when NOx increase control is performed in that control region is known in advance, and it increases when NOx increase control is performed in addition to the map data for NOx amount calculation during normal operation Then, the predicted NOx increase amount is converted into map data in advance to create NOx increase amount calculation map data, which is stored in the urea water supply control device 31 (or the internal combustion engine control device 30), and during NOx increase control, Based on the NOx increase amount calculation map data, urea water increase control for increasing the supply amount of urea water is performed.

  That is, referring to the NOx increase amount calculation map data during NOx increase control stored in the urea water supply control device 31, the NOx increase amount is calculated, and the urea water supply capable of reducing the calculated NOx increase amount The amount is increased and supplied from the urea water supply device 15, and NOx flowing out from the DFP device 13 is reduced by the selective reduction catalyst 14 using ammonia generated from the urea water. The ammonia that cannot be consumed by the reduction is oxidized and rendered harmless by a downstream ammonia oxidation catalyst (not shown). Thereby, it is possible to avoid an adverse effect on the NOx purification rate in the selective reduction catalyst 14 of the NOx increase control.

  This NOx increase control and urea water increase control are performed for a predetermined time Δt4 set in advance, the process returns, the process returns to step S13 in FIG. 2, and the process proceeds to the next step S14.

  In this step S14, it is determined whether or not the PM deposited on the catalyst-carrying filter 13b has reached the collection limit amount based on whether or not the differential pressure P before and after becomes equal to or greater than the limit differential pressure value Pk. If it is determined that the front-rear differential pressure P is greater than or equal to the limit differential pressure value Pk (YES), PM forced regeneration control is performed in step S40, and the process returns. If it is determined in step S14 that the front-rear differential pressure P is not greater than or equal to the limit differential pressure value Pk (NO), the process goes to step S15.

  In step S15, it is determined whether or not the exhaust gas temperature T is within the high conversion temperature range R1. If it is determined in step S15 that the exhaust gas temperature T is within the high conversion temperature range R1, in step S16, the same NOx increase control and urea water increase control as in step S13 are set for a predetermined time (in step S13). For a period of time (t different from the predetermined time Δt4) Δt5, and the process returns to step S14.

  The predetermined time Δt4 in step S13 is a time when the exhaust gas temperature T is predicted to be reduced by the amount of temperature decrease ΔT previously predicted by the NOx increase control, while the predetermined time Δt5 in step S16 is the exhaust gas. This is the time related to the temperature range check interval in step S15 after the temperature T decreases.

  If it is determined in step S15 that the exhaust gas temperature T is not within the high conversion temperature range R1, the process goes to step S31, where normal control without NOx increase control and urea water increase control is performed for the same time as the predetermined time Δt4 in step S16. And return to step S14.

  After steps S15, S16, and S17, in step S11, after the front-rear differential pressure P becomes equal to or higher than the control start differential pressure value Ps, and after the exhaust gas temperature T enters the control start temperature range R2, In addition, only when the exhaust gas temperature T is within the high conversion temperature range R1 until the front-rear differential pressure P becomes equal to or higher than the limit differential pressure value Pk and the PM forced regeneration control is started, in other words, depending on the situation. Then, NOx increase control and urea water increase control are performed, and the oxidation of PM deposited on the catalyst-carrying filter 13b is promoted by nitrogen dioxide, so that PM is efficiently burned and removed. As a result, as shown in FIG. 8, it is possible to lengthen the time until the PM forced regeneration control as compared with the case where the normal control and the PM forced regeneration control in FIG. 9 are repeated, thereby reducing the frequency of the forced regeneration control. be able to.

  Further, instead of the control flow of FIG. 3, the internal combustion engine controller 30 uses the control flow of FIG. 4 to which step S26 and step S27 are added to perform the selective reduction catalyst 14 in step S26 during NOx increase control. The inflow NOx amount is measured by the NOx sensor 23, and the NOx amount by measurement, the NOx amount calculated from the NOx amount calculation map data during normal operation, and the NOx increase amount calculated by the NOx increase amount calculation map data are calculated. The sums are compared to determine whether or not the difference between the two is within a preset correction value. If the difference between the two does not exceed the correction value in this determination (YES), the process returns. If the difference between the two exceeds the correction value in the determination in step S26 (NO), the process returns to step S27. Then, the NOx increase amount calculation map data is rewritten and corrected, and then the process returns.

  When the control flow of FIG. 4 is used, the NOx purification rate of the selective catalytic reduction catalyst 14 can be maintained by comparing with the monitoring of the NOx amount and rewriting of the map data, and it flows out of the selective catalytic reduction catalyst 14. NOx that cannot be reduced and excess ammonia can be reduced.

  And the internal combustion engine of embodiment which concerns on this invention is provided with the exhaust gas purification system 10 of said internal combustion engine.

  Therefore, in the exhaust gas purification system 10 for an internal combustion engine, the internal combustion engine, and the exhaust gas purification method for the internal combustion engine configured as described above, the urea water supply control device 31 performs control in which the amount of PM deposited on the catalyst-carrying filter 13b is set in advance. In the case where it is equal to or less than the start amount, that is, when the front-rear differential pressure P is smaller than the control start differential pressure Ps, urea water is supplied from the urea water supply device 15 according to the amount of NOx discharged from the internal combustion engine, and NOx. The internal combustion engine control device 30 performs the normal control to purify the catalyst, and the internal combustion engine control device 30 performs the oxidation catalyst when the PM accumulation amount exceeds the control start amount, that is, when the front-rear differential pressure P is equal to or greater than the control start differential pressure Ps. When the exhaust gas temperature T at the inlet of 13a is within a preset temperature range R1 (or R2), NOx increase control is performed to promote combustion removal of PM deposited on the catalyst-carrying filter 13b, and the amount of PM is increased. Control open When the collection limit amount larger than the amount is exceeded, that is, when the front-rear differential pressure P is greater than or equal to the limit differential pressure value Pk, PM forced regeneration control for forcibly burning and removing PM is performed to perform catalyst-carrying filter Play 13b.

Therefore, when the amount of PM deposited increases to some extent, nitrogen is a reducing agent for PM in the temperature range R1 or R2 where the conversion rate from nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ) is high. By performing NOx increase control to increase oxide (NOx), it is possible to promote the oxidation of PM by nitrogen dioxide and efficiently burn and remove the PM deposited on the catalyst-carrying filter 13b, thereby suppressing an increase in the amount of accumulated PM. This can reduce the frequency of PM forced regeneration control.

  In addition, since the NOx increase control does not involve a large change in the operation behavior of the engine as compared with the method of changing the intake air amount (oxygen concentration), both improvement of exhaust gas purification performance and prevention of deterioration of operability are achieved. be able to.

  Further, the internal combustion engine control device 30 determines the advance angle of the fuel injection timing in the cylinder, EGR cut, for each of the control areas A, B, and C using the engine speed Ne and the torque Trq (or engine load) as parameters. , And combinations thereof, NOx increase control is performed.

  Therefore, in order to increase the amount of oxygen and promote the oxidation of PM, the engine is increased as compared with the case where the method of increasing the amount of air by the supercharger or decreasing the amount of intake by the intake throttle is adopted. A change in behavior can be reduced, and deterioration in drivability can be prevented.

Further, the urea water supply control device 31 pre-maps the NOx increase amount predicted to increase when the NOx increase control is performed in addition to the map data for NOx amount calculation during the normal operation to calculate the NOx increase amount. Map data is created and stored, and during NOx increase control, the NOx increase amount calculated based on the NOx increase amount calculation map data is added to the NOx amount calculated based on the NOx amount calculation map data. The urea water increase control for increasing the supply amount of urea water is performed with respect to the added NOx discharge amount. Accordingly, it is possible to avoid an adverse effect on the NO _x purification rate of the selective reduction catalyst 14 in the subsequent stage (downstream side) due to the NOx increase control.

  Further, the internal combustion engine control device 30 measures the NOx amount flowing into the selective catalytic reduction catalyst 14 with the NOx sensor 23 during the NOx increase control, and compares the measured NOx amount with the calculated NOx emission amount, When the difference between the two exceeds a preset value, the NOx increase amount calculation map data is corrected. Accordingly, the NOx purification rate of the selective catalytic reduction catalyst 14 can be maintained, and the amount of urea water supplied is an appropriate amount, so the amount of NOx that cannot be reduced and is discharged downstream of the selective catalytic reduction catalyst 14. And the amount of excess ammonia can be reduced.

  According to the exhaust purification system of an internal combustion engine, the internal combustion engine, and the exhaust purification method of the internal combustion engine of the present invention, when it is not PM forced regeneration control, NOx increase control without significant change in the behavior of the engine is performed, By improving the oxidation of PM and reducing the frequency of PM forced regeneration control, it is possible to achieve both improvement of exhaust purification performance and prevention of deterioration of drivability. Available.

DESCRIPTION OF SYMBOLS 10 Exhaust gas purification system 11 Internal combustion engine 12 Exhaust passage (exhaust pipe)
13 DPF device 13a Oxidation catalyst (DOC)
13b Catalyst support filter 14 Selective reduction type catalyst (SCR catalyst)
15 urea water supply device 21 first temperature sensor 22 second temperature sensor 23 NOx sensor 30 internal combustion engine control device 31 urea water supply control device

Claims (6)

An exhaust passage of the internal combustion engine includes an oxidation catalyst, a catalyst-carrying filter, a urea water supply device, and a selective reduction catalyst in order from the upstream side, and an internal combustion engine control device that controls the operation of the internal combustion engine and urea in the urea water supply device In an exhaust gas purification system for an internal combustion engine equipped with a urea water supply control device for controlling the supply of water,
When the amount of PM accumulated on the catalyst-carrying filter is smaller than a preset control start amount, the urea water supply control device is configured to release urea from the urea water supply device according to the amount of NOx discharged from the internal combustion engine. Perform normal control to purify NOx by supplying water,
When the PM accumulation amount is equal to or greater than the control start amount, the internal combustion engine control device performs NOx increase control when the exhaust gas temperature at the inlet of the oxidation catalyst is within a preset temperature range. Promote combustion removal of PM deposited on the catalyst-carrying filter,
When the accumulation amount of the PM becomes equal to or greater than the collection limit amount larger than the control start amount, the catalyst-carrying filter is regenerated by performing PM forced regeneration control for forcibly burning and removing the PM. An exhaust purification system for an internal combustion engine.   The internal combustion engine control device performs NOx increase control using advance angle of fuel injection timing in a cylinder, EGR cut, and a combination thereof for each control region having engine speed and torque or engine load as parameters. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein:   In addition to the NOx amount calculation map data during normal operation, the urea water supply control device converts the NOx increase amount that is predicted to increase when NOx increase control is performed into map data in advance to generate NOx increase amount calculation map data. The NOx increase amount calculated based on the NOx increase amount calculation map data is added to the NOx amount calculated based on the NOx amount calculation map data during NOx increase control. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2, wherein urea water increase control for increasing the supply amount of urea water is performed with respect to the NOx emission amount.   The internal combustion engine control device measures the amount of NOx flowing into the selective catalytic reduction catalyst with a NOx sensor during NOx increase control, compares the measured NOx amount with the calculated NOx emission amount, and determines the difference between the two. 4. The exhaust gas purification system for an internal combustion engine according to claim 3, wherein when NO exceeds a preset value, the NOx increase amount calculation map data is corrected.   An internal combustion engine comprising the exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 4. In an exhaust gas purification method for an internal combustion engine, NOx and PM in the exhaust gas of the internal combustion engine are purified by an exhaust gas purification system in which an oxidation catalyst, a catalyst-carrying filter, a urea water supply device, and a selective catalytic reduction catalyst are arranged in order from the upstream side in the exhaust passage. ,
When the amount of PM deposited on the catalyst-carrying filter is smaller than a preset control start amount, urea water is supplied from the urea water supply device in accordance with the NOx amount discharged from the internal combustion engine to purify NOx. Perform normal control,
When the PM accumulation amount is equal to or greater than the control start amount, the internal combustion engine control device performs NOx increase control when the exhaust gas temperature at the inlet of the oxidation catalyst is within a preset temperature range. Promote combustion removal of PM deposited on the catalyst-carrying filter,
When the accumulation amount of the PM becomes equal to or greater than the collection limit amount larger than the control start amount, the catalyst-carrying filter is regenerated by performing PM forced regeneration control for forcibly burning and removing the PM. An exhaust purification method for an internal combustion engine.

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