JP4510655B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that temporarily captures NOx in exhaust gas discharged from the internal combustion engine and purifies the exhaust gas by reducing the captured NOx.

  In this type of exhaust gas purification device, an NOx trapping material is provided in the exhaust system of the internal combustion engine, and NOx discharged from the internal combustion engine is trapped by the NOx trapping material. Further, when the amount of trapped NOx increases, the trapped NOx is reduced by controlling the exhaust gas to a reduced state by increasing the amount of fuel or the like. Thereby, after purifying NOx, exhaust gas is discharged into the atmosphere, and the trapping ability of the NOx trapping material is recovered. As such an exhaust gas purifier, for example, one disclosed in Patent Document 1 is known. It has been.

  This exhaust gas purification device includes an EGR device in addition to the NOx trapping material (NOx purification catalytic converter) provided in the exhaust passage of the engine. This EGR device is provided in parallel between the exhaust passage of the engine and the upstream side of the NOx trapping material of the intake passage, and has a first EGR passage and a second EGR passage that respectively connect the passages. . The first EGR passage is provided with a first EGR cooler on the exhaust passage side and a first EGR valve on the intake passage side. Further, the second EGR passage is provided between the upstream side of the first EGR passage of the intake passage and the downstream side of the first EGR passage of the exhaust passage, and in order from the exhaust passage side to the second EGR passage, A diesel particulate filter (hereinafter referred to as “DPF”), a second EGR cooler, and a second EGR valve are provided. The engine is provided with a turbocharger, the turbine is provided between the first and second EGR passages of the intake passage, and the compressor is provided between the first and second EGR passages of the exhaust passage. Yes.

  In this exhaust gas purification device, an EGR operation is performed as follows by returning a part of the exhaust gas as EGR gas from the exhaust passage to the intake passage according to the operating state of the engine. That is, when the engine is in a low load state, the EGR operation is performed through the first EGR passage by opening the first EGR valve and closing the second EGR valve. Further, when the engine is in a high load state and the differential pressure between the intake air and the exhaust gas is small, the PM in the exhaust gas is collected by the DPF through the second EGR passage by opening the second EGR valve and closing the first EGR valve. While performing the EGR operation. As a result, EGR gas containing almost no PM is sucked into the downstream side of the intake passage along with outside air by the turbine, so that a necessary EGR amount is secured.

  However, this exhaust gas purification apparatus has the following problems. When the EGR passage is switched, first, EGR gas existing in the switched EGR passage is discharged into the intake passage, and then new EGR gas is recirculated from the exhaust passage. In addition, the EGR gas existing in the EGR passage before the switching is sufficiently cooled by the EGR cooler because the EGR gas stays in the EGR passage due to the EGR valve being closed, and becomes a lower temperature state. ing.

  For this reason, immediately after the switching of the EGR passage, the low-temperature EGR gas staying in the switched EGR passage is supplied to the combustion chamber by recirculation. Therefore, when the supply amount of fuel is increased in order to reduce NOx trapped in the NOx trapping material in such a state where the low-temperature EGR gas is recirculated, the temperature of the EGR gas is low. The ignitability of qi deteriorates and the combustion becomes unstable. In this case, misfire may occur. As a result, when the internal combustion engine is mounted on a vehicle, drivability may be deteriorated.

  The present invention has been made in order to solve the above-described problems. When the EGR passage having the high-temperature side and the low-temperature side passage is provided, even when the NOx reduction operation is performed when the EGR passage is switched, An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can ensure stable combustion of the internal combustion engine.

Japanese Patent Laid-Open No. 2004-162675 (Pages 5, 6 and 1)

In order to achieve the above object, an invention according to claim 1 is directed to an internal combustion engine (engine 3) having an intake system (intake pipe 4 in the embodiment (hereinafter the same in this section)) and an exhaust system (exhaust pipe 5). An exhaust gas purification apparatus 1 for an internal combustion engine that purifies exhaust gas discharged from a NOx trapping material (NO catalyst 17) that is provided in an exhaust system and traps NOx in the exhaust gas, and NOx trapped by the NOx trapping material NOx trapping amount calculating means (ECU 2, steps 31 and 32 in FIG. 8) that calculates the amount as a NOx trapping amount (NOx trapping amount integrated value S_QNOx), and the calculated NOx trapping amount to a predetermined value (determination value S_NOxREF) The NOx reduction means (injector 6, throttle valve 12) for reducing NOx trapped in the NOx trapping material when it reaches the exhaust system and the intake system is provided. An EGR passage (EGR pipe 14a) having a low temperature side passage 14d that recirculates a part of exhaust gas as EGR gas in the intake system at a lower temperature and a high temperature side passage 14c that recirculates at a higher temperature than the low temperature side passage 14d. An EGR passage switching means (EGR passage switching valve 15b) for switching the EGR passage to the low temperature side passage 14d and the high temperature side passage 14c, and a temperature state determination means (exhaust gas) for determining whether or not the EGR gas is in a predetermined high temperature state. In the case where the EGR passage is switched from the low temperature side passage 14d to the high temperature side passage 14c by the temperature sensor 37, ECU 2, step 26 in FIG. 7, step 72 in FIG. 12, step 86 in FIG. the temperature condition determining means only when the EGR gas is determined to be in a predetermined high-temperature state, by the NOx reduction means NOx reduction permission means for permitting the reduction of Ox, characterized in that it comprises a, and (ECU 2, step 39 in FIG. 8).

  According to the exhaust gas purification apparatus for an internal combustion engine, NOx in the exhaust gas discharged from the internal combustion engine to the exhaust system is captured by the NOx trapping material provided in the exhaust system. Further, the amount of NOx trapped in the NOx trapping material is calculated as the NOx trapping amount by the NOx trapping amount calculating means, and when the calculated NOx trapping amount reaches a predetermined value, the trapped NOx is reduced to NOx. After being purified by reduction by means, it is discharged into the atmosphere.

  Also, a part of the exhaust gas is recirculated from the exhaust system to the intake system via the EGR passage as EGR gas by the EGR means, and is sucked into the combustion chamber together with fresh air, thereby lowering the combustion temperature. , NOx emissions are reduced. Further, the EGR passage is switched by the EGR passage switching means to a low temperature side passage that recirculates the EGR gas at a lower temperature and a high temperature side passage that recirculates the EGR gas at a higher temperature than the low temperature side passage.

Further, when the EGR passage is switched from the low temperature side passage to the high temperature side passage, the NOx reduction permission means reduces NOx only when the temperature state determination means determines that the EGR gas is in a predetermined high temperature state. Is permitted and NOx reduction is performed. When the EGR passage is switched from the low temperature side passage to the high temperature side passage, the response delay of the EGR gas immediately after the switching or the lower temperature EGR gas staying in the low temperature side passage returns to the intake system. It takes time for the EGR gas actually sucked into the combustion chamber to reach a high temperature state. Therefore, as described above, when it is determined that the EGR gas is in the predetermined high temperature state, the NOx reduction is allowed in a state where the EGR gas is in the predetermined high temperature state by permitting the execution of the NOx reduction means. Can be executed. As a result, stable combustibility of the air-fuel mixture can be ensured, and misfire during the reduction of NOx can be reliably avoided. Further, when the internal combustion engine is mounted on a vehicle, good drivability can be ensured.

  Hereinafter, an exhaust gas purification apparatus according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an exhaust gas purification apparatus 1 to which the present invention is applied, together with an internal combustion engine 3. The internal combustion engine (hereinafter referred to as “engine”) 3 is, for example, a four-cylinder (only one is shown) diesel engine mounted on a vehicle (not shown).

  A combustion chamber 3c is formed between the piston 3a of the engine 3 and the cylinder head 3b. An intake pipe 4 (intake system) and an exhaust pipe 5 (exhaust system) are connected to the cylinder head 3b, and a fuel injection valve (hereinafter referred to as “injector”) 6 (NOx reducing means) is connected to the combustion chamber 3c. It is attached to face.

  The injector 6 is disposed at the center of the top wall of the combustion chamber 3c, and is connected in turn to a high-pressure pump and a fuel tank (both not shown) via a common rail. The fuel injection amount TOUT, which is the valve opening time of the injector 6, and the injection timing are controlled by a drive signal from the ECU 2 (see FIG. 2).

  A magnet rotor 30a is attached to the crankshaft 3d of the engine 3, and the crank angle sensor 30 is constituted by the magnet rotor 30a and the MRE pickup 30b. The crank angle sensor 30 outputs a CRK signal and a TDC signal, which are pulse signals, to the ECU 2 as the crankshaft 3d rotates.

  The CRK signal is output every predetermined crank angle (for example, 30 °). The ECU 2 obtains the rotational speed NE (hereinafter referred to as “engine rotational speed”) NE of the engine 3 based on the CRK signal. The TDC signal is a signal indicating that the piston 3a of each cylinder is at a predetermined crank angle position near the TDC (top dead center) at the start of the intake stroke, and in this example of the 4-cylinder type, every crank angle of 180 °. Is output.

  The intake pipe 4 is provided with a supercharging device 7, which is a supercharger 8 constituted by a turbocharger, an actuator 9 connected thereto, and a vane opening control valve 10. It has.

  The supercharger 8 includes a rotatable compressor blade 8a provided in the intake pipe 4, a rotatable turbine blade 8b provided in the exhaust pipe 5, and a plurality of rotatable variable vanes 8c (only two are shown). And a shaft 8d for integrally connecting these blades 8a and 8b. The turbocharger 8 pressurizes the intake air in the intake pipe 4 by rotationally driving the compressor blade 8a integrated therewith as the turbine blade 8b is rotationally driven by the exhaust gas in the exhaust pipe 5. Perform supercharging operation.

  The actuator 9 is of a diaphragm type that is operated by negative pressure, and is mechanically connected to each variable vane 8c. A negative pressure is supplied to the actuator 9 from a negative pressure pump through a negative pressure supply passage (both not shown), and a vane opening degree control valve 10 is provided in the middle of the negative pressure supply passage. The vane opening control valve 10 is composed of an electromagnetic valve, and the negative pressure supplied to the actuator 9 changes when the opening is controlled by a drive signal from the ECU 2, and accordingly, the variable vane 8c The supercharging pressure is controlled by changing the opening degree.

  A water-cooled intercooler 11 and a throttle valve 12 (NOx reduction means) are provided downstream from the supercharger 8 of the intake pipe 4 in order from the upstream side. The intercooler 11 cools the intake air when the temperature of the intake air rises due to the supercharging operation of the supercharging device 7 or the like. The throttle valve 12 is connected to an actuator 12a made of, for example, a DC motor. The opening degree TH of the throttle valve 12 (hereinafter referred to as “throttle valve opening degree”) TH is controlled by controlling the duty ratio of the current supplied to the actuator 12a by the ECU 2 in accordance with a target throttle valve opening degree THCMD described later. The

  The intake pipe 4 is provided with an air flow sensor 31 upstream of the supercharger 8 and a supercharging pressure sensor 32 between the intercooler 11 and the throttle valve 12. The first airflow sensor 31 detects the intake air amount QA, the supercharging pressure sensor 32 detects the supercharging pressure PACT in the intake pipe 4, and those detection signals are output to the ECU 2.

  Further, the intake manifold 4a of the intake pipe 4 is partitioned into a swirl passage 4b and a bypass passage 4c from the collecting portion to the branch portion, and each of the passages 4b and 4c is connected to each combustion chamber 3c via an intake port. Communicating with

  A swirl device 13 for generating a swirl in the combustion chamber 3c is provided in the bypass passage 4c. The swirl device 13 includes a swirl valve 13a, an actuator 13b for opening and closing the swirl valve 13a, and a swirl control valve 13c. The actuator 13b and the swirl control valve 13c are configured similarly to the actuator 9 and the vane opening control valve 10 of the supercharging device 7, respectively, and the swirl control valve 13c is connected to the negative pressure pump. With the above configuration, when the opening degree of the swirl control valve 13c is controlled by the drive signal from the ECU 2, the negative pressure supplied to the actuator 13b changes, and the opening degree of the swirl valve 13a changes. The strength of the is controlled.

  The engine 3 is provided with an EGR device 14 having an EGR pipe 14a (EGR passage) and an EGR control valve 14b. The EGR pipe 14 a is connected between the intake pipe 4 and the exhaust pipe 5, specifically, so as to connect the swirl passage 4 b of the collecting portion of the intake manifold 4 a and the upstream side of the supercharger 8 of the exhaust pipe 5. Has been. Through this EGR pipe 14a, a part of the exhaust gas of the engine 3 is recirculated to the intake pipe 4 as EGR gas, thereby reducing the combustion temperature in the combustion chamber 3c, thereby reducing NOx in the exhaust gas. .

  The EGR control valve 14b is composed of a linear electromagnetic valve attached to the EGR pipe 14a, and the valve lift amount VLACT is linearly controlled by a duty-controlled drive signal from the ECU 2, thereby the EGR gas amount. Is controlled.

  The EGR pipe 14a is branched downstream of the EGR control valve 14b into a high temperature side passage 14c and a low temperature side passage 14d, and an EGR passage switching valve 15b (EGR passage switching means) is provided at the branch portion. ing. The high temperature side passage 14c and the low temperature side passage 14d merge before the intake pipe 5, and an EGR cooler 15c is provided in the middle of the low temperature side passage 14d. The EGR passage switching valve 15b is controlled by the ECU 2 in accordance with the load state of the engine 3, so that the portion of the EGR pipe 14a on the downstream side of the EGR passage switching valve 15b is changed to the low temperature side passage 14d and the high temperature side passage 14c. Selectively switch.

  With the above configuration, when the EGR passage switching valve 15b is switched to the low temperature side passage 14d, the EGR gas is cooled by the EGR cooler 15c by passing through the low temperature side passage 14d, and then the intake pipe 4 To reflux. On the other hand, when the EGR passage switching valve 15b is switched to the high temperature side passage 14c, the EGR gas returns to the intake pipe 4 as it is without being cooled through the high temperature side passage 14c.

  Further, a three-way catalyst 16 and a NOx catalyst 17 (NOx trapping material) are provided on the exhaust pipe 5 downstream of the supercharger 8 in order from the upstream side. The three-way catalyst 16 purifies the exhaust gas by oxidizing HC and CO in the exhaust gas and reducing NOx under a stoichiometric atmosphere. The NOx catalyst 17 captures (absorbs) NOx in the exhaust gas when the oxygen concentration in the exhaust gas is high, and reduces the captured NOx with a reducing agent in the exhaust gas in a reducing atmosphere with a low oxygen concentration. , Purify the exhaust gas. The NOx catalyst 17 is provided with a NOx catalyst temperature sensor 36 for detecting its temperature (hereinafter referred to as “NOx catalyst temperature”) TLNC, and its detection signal is output to the ECU 2.

  Further, a first LAF sensor 33 and a second LAF sensor 34 are respectively provided immediately upstream and downstream of the three-way catalyst 16 in the exhaust pipe 5. The first and second LAF sensors 33 and 34 linearly detect the oxygen concentrations VLAF1 and VLAF2 in the exhaust gas in a wide range of air-fuel ratios from the rich region to the lean region, respectively. Based on the oxygen concentration VLAF1 detected by the first LAF sensor 33, the ECU 2 calculates an actual air-fuel ratio A / FACT representing the air-fuel ratio of the actual gas burned in the combustion chamber 3c. Further, an exhaust temperature sensor 37 (temperature state determining means) for detecting the exhaust temperature TEXH is provided between the EGR pipe 14a of the exhaust pipe 4 and the supercharger 8, and the detection signal is output to the ECU 2. . The ECU 2 further outputs a detection signal indicating an operation amount (hereinafter referred to as “accelerator opening”) AP of an accelerator pedal (not shown) from the accelerator opening sensor 35, and the outside air temperature sensor 38 determines the outside air temperature TAT. A detection signal is output.

  In the present embodiment, the ECU 2 constitutes a NOx trapping amount calculation means, a temperature state determination means, and a NOx reduction permission means, and is constituted by a microcomputer comprising an I / O interface, CPU, RAM, ROM, and the like. (Neither shown). The detection signals from the various sensors 30 to 38 described above are each input to the CPU after A / D conversion and shaping by the I / O interface.

  In accordance with these input signals, the CPU determines the operating state of the engine 3 according to a control program stored in the ROM and the like, and includes an engine including fuel injection amount control and intake air amount control according to the determined operating state. 3 control is executed. Further, as a reduction operation for reducing the NOx trapped by the NOx catalyst 17, it is determined whether or not a rich spike should be executed, the temperature of the EGR gas is estimated, and the estimated temperature of the EGR gas is estimated. Perform a rich spike. As will be described later, this rich spike is discharged from the combustion chamber 3c by increasing the fuel injection amount TOUT and decreasing the intake air amount QA to enrich the actual air-fuel ratio A / FACT. This is done by including unburned components in the exhaust gas.

  Next, the switching control process for the EGR pipe 14a will be described with reference to FIG. This process is for determining whether to switch the EGR pipe 14a to the low temperature side passage 14d or the high temperature side passage 14c according to the load state of the engine 3, and is executed at predetermined time intervals.

  First, in step 1 (illustrated as “S1”, the same applies hereinafter), whether or not the engine 3 is in a low load state is determined by searching a map according to the engine speed NE and the required torque PMCMD. As shown in FIG. 4, in this map, the engine 3 is divided into a low load region and a high load region according to the rotational speed of the engine 3 and the required torque PMCMD. Basically, the smaller the required torque PMCMD, the lower the load on the engine 3. It is determined that it is in a state. The requested torque PMCMD is a torque required for the engine 3 and is obtained by searching a map (not shown) according to the engine speed NE and the accelerator pedal opening AP.

  If the answer to step 1 is YES and the engine 3 is in a low load state, the passage switching flag F_EGRHOT is set to “1” (step 2), and this process is terminated. Thus, when the passage switching flag F_EGRHOT is set to “1”, the EGR passage switching valve 15b switches the EGR pipe 14a to the high temperature side passage 14c, and the EGR gas recirculates through the high temperature side passage 14c. Thereby, in a low load state, the EGR gas is refluxed as it is without being cooled, so that the combustion temperature is higher than when refluxing via the low temperature side passage 14d, thereby ensuring stable combustibility, Misfire is prevented.

  On the other hand, if the answer to step 1 is NO and the engine 3 is in a high load state, the passage switching flag F_EGRHOT is set to “0” (step 3). As described above, when the passage switching flag F_EGRHOT is set to “0”, the EGR pipe 14a is switched to the low temperature side passage 14d, and the EGR gas is recirculated through the low temperature side passage 14d. Thereby, in a high load state, the EGR gas is cooled by the EGR cooler 15c, so that the temperature of the EGR gas is lower than when the EGR gas is recirculated through the high temperature side passage 14c, thereby suppressing an increase in the combustion temperature. Thus, the amount of NOx generated can be reduced.

  Next, the EGR gas temperature estimation process will be described with reference to FIG. In this process, the temperature of the EGR gas is estimated according to the switching state of the EGR pipe 14a set in the process of FIG. 3, and is set as the estimated temperature TEGR, and is executed at predetermined time intervals.

  First, in step 10, it is determined whether or not the passage switching flag F_EGRHOT is “1”. When this answer is NO and the EGR pipe 14a is switched to the low temperature side passage 14d, the TCOOLER map shown in FIG. 6 is searched according to the difference between the exhaust gas temperature TEXH and the outside air temperature TAT and the exhaust gas volume SV. Thus, the cooling temperature TCOOLER is obtained (step 11). The cooling temperature TCOOLER represents the extent to which the EGR gas temperature (exhaust temperature TEXH) is cooled by the EGR cooler 15c, that is, the temperature range of the EGR gas that can be lowered by cooling by the EGR cooler 15c. . In the TCOOLER map, the cooling temperature TCOOLER is set to a larger value because the EGR gas is more easily cooled as the difference between the exhaust gas temperature TEXH and the outside air temperature TAT is larger and the exhaust gas volume SV is smaller. Yes. The exhaust gas volume SV is obtained by searching a map (not shown) according to the engine speed NE and the intake air amount QA.

  Next, in step 12, a value obtained by subtracting the cooling temperature TCOOLER from the exhaust temperature TEXH is set as the estimated temperature TEGR of the EGR gas recirculated to the intake pipe 4.

  On the other hand, when the answer to step 10 is YES and the EGR pipe 14a is switched to the high temperature side passage 14c, the EGR gas recirculates as it is without being cooled from the exhaust pipe 4, so that the exhaust temperature TEXH is set to the estimated temperature TEGR. (Step 14).

Next, in step 13, the annealing process of the estimated EGR gas temperature TEGR obtained in step 12 or 14 is performed by the following equation (1), and then the present process is terminated.
TERG ← αTEGR (n) + (1-α) TEGR (n−1) (1)
Here, α is a predetermined annealing coefficient less than 1.0. As is clear from this equation (1), a weighted average value of the current value TEGR (n) of the estimated temperature TEGR and the previous value TEGR (n-1) is calculated as the current estimated temperature TEGR.

  Next, the EGR temperature condition determination process will be described with reference to FIG. This process determines the temperature condition of the EGR gas, which is one of the execution conditions of the rich spike, according to the estimated temperature TEGR of the EGR gas calculated in the process of FIG. 5, and is executed every predetermined time. The

  First, in step 20, it is determined whether or not the passage switching flag E_EGRHOT is “1”. If the answer is NO and the EGR pipe 14a is switched to the low temperature side passage 14d, the temperature condition flag F_RICHEGR is set to “1” to indicate that the EGR gas temperature condition is satisfied. (Step 21).

  Next, in step 22, the passage switching flag F_EGRHOOT is shifted to the previous value F_EGRHOTZ, and then this process is terminated.

  On the other hand, when the answer to step 20 is YES and the EGR pipe 14a is switched to the high temperature side passage 14c, it is determined whether or not the passage switching flag F_EGRHOT is equal to the previous value F_EGRHOTZ (step 23). When this answer is NO and the previous value F_EGRHOTZ is “0”, that is, immediately after the EGR pipe 14a is switched from the low temperature side passage 14d to the high temperature side passage 14c, the time obtained in step 13 of FIG. Is set as the initial value TEGR0 of the EGR gas temperature (step 24).

  Next, in step 25, in order to indicate that the temperature condition of the EGR gas is not satisfied, the temperature condition flag F_RICHEGR is set to “0”, and then step 22 is executed.

  On the other hand, if the answer to step 23 is YES and the passage switching flag F_EGRHOT and its previous value F_EGRHOTZ are both “1”, that is, not immediately after the EGR pipe 14a is switched to the high temperature side passage 14c, the estimation at that time It is determined whether or not the value obtained by subtracting the initial value TEGR0 from the temperature TEGR is equal to or higher than a predetermined value TREF (for example, 0.7 times the cooling temperature TCOOLER) (step 26).

  When this answer is NO and TEGR-TEGR0 <TREF, that is, when the increase in the estimated temperature TEGR of the EGR gas after the EGR pipe 14a is switched to the high temperature side passage 14c does not reach the predetermined value TREF, Assuming that the temperature condition of the EGR gas has not yet been established, the above step 25 and subsequent steps are executed, and the temperature condition flag F_RICHEGR is maintained at “0”.

  On the other hand, when the answer to step 26 is YES and the increase in the estimated temperature TEGR after the EGR pipe 14a is switched to the high temperature side passage 14c reaches a predetermined value TREF, the EGR gas is switched after the EGR pipe 14a is switched. Assuming that the temperature condition is satisfied, the above steps 21 and after are executed to switch the temperature condition flag F_RICHEGR to “1”.

  As described above, when the EGR pipe 14a is switched from the low temperature side passage 14d to the high temperature side passage 14c, it is determined that the EGR gas temperature increase (TEGR-TEGR0) after the switching is equal to or greater than the predetermined value TREF. When this occurs (step 26: YES), it is determined for the first time that the temperature condition of the EGR gas, which is one of the rich spike execution conditions, is satisfied (step 21). That is, when the rich spike is executed at the time of switching to the high temperature side passage 14c of the EGR pipe 14a, the execution of the rich spike is not immediately permitted after the switching, and the temperature of the EGR gas thereafter corresponds to the predetermined value TREF. Waiting for only the rise, the execution of rich spike is allowed.

  Next, rich spike execution condition determination processing will be described with reference to FIG. This process is executed every predetermined time. First, in step 30, it is determined whether or not the timer value TMRICH of the rich timer is zero. The rich timer measures the execution time of the rich spike, and the timer value TMRICH is reset to 0 when the engine 3 is started.

  When the answer to step 30 is YES and TMRICH = 0, the NOx emission amount QNOx is obtained by searching a map (not shown) according to the engine speed NE and the required torque PMCMD (step 31). The NOx emission amount QNOx is an estimate of the NOx amount in the exhaust gas at that time. In this map, the larger the engine speed NE and the larger the required torque PMCMD, the larger the exhaust gas volume SV. Is set to a value.

  Next, a value obtained by adding the calculated NOx emission amount QNOx to the current NOx emission amount integrated value S_QNOx is updated as the current NOx emission amount integrated value S_QNOx (NOx trapping amount) (step 32). This integrated NOx emission amount S_QNOx corresponds to the amount of NOx trapped by the NOx catalyst 17 (hereinafter referred to as “NOx trapped amount”).

  Next, it is determined whether or not the accelerator opening AP is substantially 0, that is, whether or not the accelerator pedal is in a fully closed state (step 33). When the answer is YES, that is, when the vehicle is decelerating or idling, it is determined that the rich spike execution condition is not satisfied, and the rich spike flag F_RICH is set to “0” (step 34). Exit. Accordingly, the rich spike is not executed, and the engine control for normal time is executed in the fuel injection amount control process and the intake air amount control process described later.

  On the other hand, if the answer to step 33 is NO and the vehicle is neither decelerating nor idling, it is determined whether or not the NOx emission amount integrated value S_QNOx obtained in step 32 is greater than or equal to a determination value S_QNOxREF (predetermined value). A determination is made (step 35).

  This determination value S_QNOxREF is calculated by searching the table shown in FIG. 9 according to the NOx catalyst temperature TLNC. In the table, the determination value S_QNOxREF is set to the first determination value SQ1 when TLNC ≦ first predetermined value T1 (eg, 200 ° C.), and NOx catalyst temperature when T1 <TLNC <second predetermined value T2 (eg, 400 ° C.). The higher the TLNC, the larger the value is set linearly. When TLNC ≧ T2, the second determination value SQ2 is set larger than the first determination value SQ1. This is because the NOx reduction rate decreases as the NOx catalyst temperature TLNC decreases and as the amount of NOx trapped increases.

  If the answer to step 35 is NO and S_QNOx <S_QNOxREF, the amount of NOx trapped is relatively small. Therefore, it is determined that the rich spike execution condition is not satisfied, and step 34 is executed.

  On the other hand, if the answer to step 35 is YES and S_QNOx ≧ S_QNOxREF, it is determined whether or not the temperature condition flag F_RICHEGR set in the process of FIG. 7 is “1” (step 36).

  When this answer is NO, the temperature condition of the EGR gas is not satisfied, and the rich spike execution condition is not satisfied, so that the step 34 is executed and the rich spike flag E_RICH is set to “0”. On the other hand, if the answer to step 36 is YES and the EGR gas temperature condition is satisfied, it is determined that the rich spike execution condition is satisfied, and the next step 37 and subsequent steps are executed.

  In this step 37, the NOx emission integrated value S_QNOx is reset to the value 0, and then the timer value TMRICH of the rich timer is set to a predetermined time TRO (for example, 5 sec) (step 38). Next, the rich spike flag F_RICH is set to “1” to indicate that the rich spike execution condition is satisfied (step 39). Along with this, engine control for rich spike is executed in a fuel injection amount control process and an intake air amount control process, which will be described later, whereby a rich spike is executed. The predetermined time TRO is set to a time sufficient to reduce NOx by the rich spike.

  Next, the timer value TMRICH of the rich timer is counted down (step 40), and this process is terminated. The timer value TMRICH is down-counted only by this step 40.

On the other hand, the answer to step 30 is NO when the above step 38 is executed. In this case, the smoothed value APAVE of the accelerator opening is calculated by the following equation (2) (step 41).
APAVE ← α ・ AP + (1-α) APAVE ...... (2)
Here, α is a predetermined annealing coefficient less than 1.0.

  Next, it is determined whether or not the calculated annealing value APAVE is substantially 0 (step 42). When this answer is NO, the step 39 and the subsequent steps are executed, the rich spike is continued, and the timer value TMRICH is counted down.

  On the other hand, when the answer to step 42 is YES and the annealing value APAVE calculated as described above is substantially zero, that is, during execution of the rich spike, the accelerator opening AP is fully closed, When the state continues, it is determined that the condition for executing the rich spike is not satisfied, assuming that the engine 3 is decelerated or idling. Then, after setting the rich spike flag F_RICH to “0” (step 43), the present process is terminated.

  Next, the fuel injection amount control process and the intake air amount control process will be described. These processes are performed according to the success or failure of the rich spike execution condition determined in the process of FIG.

  FIG. 10 shows the fuel injection amount control process. In this process, the fuel injection amount TOUT is controlled in accordance with the success or failure of the rich spike execution condition. First, in step 50, it is determined whether or not the rich spike flag F_RICH is “1”.

  If the answer to this question is NO and the rich spike execution condition is not satisfied, a normal time map (not shown) is searched according to the engine speed NE and the required torque PMCMD, so that The fuel injection amount TOUTN is obtained (step 51), and in the subsequent step 52, the normal fuel injection amount TOUTN obtained in step 51 is set as the fuel injection amount TOUT, and this process is terminated.

  On the other hand, if the answer to step 50 is YES and the rich spike execution condition is satisfied, a map for rich spike (not shown) is searched according to the engine speed NE and the required torque PMCMD. Thus, the fuel injection amount TOUTRICH for the rich spike is obtained (step 53). The fuel injection amount TOUTRICH for the rich spike is set to a value larger than the fuel injection amount TOUTN for the normal time.

  Next, in step 54, the fuel injection amount TOUTRICH for rich spike obtained in step 53 is set as the fuel injection amount TOUT, and this process is terminated.

  Next, the intake air amount control process will be described with reference to FIG. In this process, the intake air amount QA is controlled by controlling the throttle valve opening TH in accordance with the success or failure of the rich spike execution condition. First, in step 60, it is determined whether or not the rich spike flag F_RICH is “1”.

  If the answer to this question is NO and the rich spike execution condition is not satisfied, the target throttle valve opening degree TMCMD is set to the full opening degree THWOT (step 61), and this process ends.

  On the other hand, if the answer to step 60 is YES and the rich spike execution condition is satisfied, the target throttle valve opening THCMD for the rich spike is determined according to the operating state of the engine 3 (step 62). This process is terminated.

  As described above, the rich spike increases the fuel injection amount TOUT and decreases the intake air amount QA by controlling the throttle valve 12 in the fuel injection amount control process and the intake air amount control process. Is done by. The intake air amount QA may be controlled by controlling the supercharging device 7, the swirl device 12, and the EGR device 14 instead of or in addition to the control of the throttle valve 12 as described above.

  As described above, according to the exhaust gas purification apparatus of the present embodiment, when the EGR pipe 14a is switched from the low temperature side passage 14d to the high temperature side passage 14c, the estimated temperature TEGR of the EGR gas is a predetermined value from the initial value TEGR0. When the temperature rises by TREF (step 26: YES), it is determined that the temperature condition of the EGR gas is satisfied (step 21), and execution of rich spike is permitted when other conditions are satisfied. (Step 39). As a result, since the rich spike is executed in a state where the EGR gas is surely at a predetermined high temperature state, stable ignitability and combustion of the air-fuel mixture can be ensured, so misfire during the execution of the rich spike can be ensured. It can be avoided and good drivability can be secured.

  Next, the EGR temperature condition determination process according to the second embodiment will be described with reference to FIG.

  In this determination process, first, in step 70, it is determined whether or not the passage switching flag E_EGRHOT set in the process of FIG. 3 is “1”. If the answer is NO and the EGR pipe 14a is switched to the low temperature side passage 14a side, the temperature condition flag F_RICHEGR is set to “1” on the assumption that the temperature condition of the EGR gas is satisfied (step 71). This process is terminated.

  On the other hand, if the answer to step 70 is YES and the EGR pipe 14a is switched to the high-temperature side passage 14c, it is determined whether or not the estimated temperature TEGR of the EGR gas is equal to or higher than a predetermined temperature TREF2 (for example, 250 ° C.). (Step 72).

  If the answer is NO and the estimated temperature TEGR has not yet risen to the predetermined temperature TREF2, the temperature condition flag F_RICHEGR is set to “0” (step 73), and this process is terminated.

  On the other hand, if the answer to step 72 is YES and the estimated temperature TEGR reaches the predetermined temperature TREF2, the temperature condition flag F_RICHEGR is set to “1”, assuming that the temperature condition of the EGR gas is satisfied, and step 71 is executed. To do.

  As described above, in the first embodiment described above, when the increase in the estimated temperature TEGR after the switching of the EGR pipe 14a is equal to or higher than the predetermined value TREF, it is determined that the EGR gas temperature condition is satisfied. On the other hand, in the present embodiment, when the estimated temperature TEGR itself after switching the EGR pipe 14a reaches the predetermined temperature TREF2, the temperature condition of the EGR gas is satisfied, assuming that the temperature of the EGR gas has reached a predetermined high temperature state. The rich spike is allowed to be executed. Therefore, also in this embodiment, the same effect as the first embodiment described above can be obtained.

  Next, an EGR temperature condition determination process according to the third embodiment will be described with reference to FIG. As is clear from comparison with FIG. 7, the determination process of this embodiment differs from that of the first embodiment only in part of the processing content, so the same execution content as in the first embodiment. The same step number will be assigned to and the description will be made with a focus on the different execution contents.

  In this determination processing, if the answer to step 23 is NO and the EGR pipe 14a is immediately after the low temperature side passage 14d is switched to the high temperature side passage 14c, the timer value TMDLY of the downcount delay timer is set to the predetermined time TDO ( For example, after setting to 1 sec) (step 84), step 25 is executed. On the other hand, when the answer to step 23 is YES and not immediately after the EGR pipe 14a is switched to the high temperature side passage 14c, it is determined whether or not the timer value of the delay timer TMDLY is 0 (step 86).

  When this answer is NO, that is, when the predetermined time TDO has not elapsed after the EGR pipe 14a is switched to the high temperature side passage 14c, the step 25 is executed and the temperature condition flag F_RICHEGR is maintained at "0". To do.

  On the other hand, if the answer to step 86 is YES and the EGR pipe 14a is switched to the high-temperature side passage 14c and the predetermined time TDO has elapsed, the temperature of the EGR gas has risen sufficiently to assume a predetermined high-temperature state. Step 21 is executed to switch the temperature condition flag F_RICHEGR to “1”.

  As described above, in the above-described embodiment, it is determined that the temperature condition of the EGR gas is satisfied when the increase in the estimated temperature TEGR after the switching of the EGR pipe 14a reaches the predetermined value TREF. In the embodiment, after the EGR pipe 14a is switched, when the predetermined time TDO elapses, it is determined that the temperature condition of the EGR gas is satisfied, assuming that the temperature of the EGR gas sufficiently rises and reaches a predetermined high temperature state. Allow the execution of rich spikes. Therefore, also in this embodiment, the same effect as the first embodiment described above can be obtained.

  In addition, this invention can be implemented in various aspects, without being limited to the described embodiment. For example, in the embodiment, the EGR cooler 15c is provided only in the low temperature side passage 14d of the EGR pipe 14a. However, the present invention is not limited to this, and the temperature difference of the EGR gas is set between the high temperature side and the low temperature side passages 14c and 14d. Anything is possible. For example, an EGR cooler 15c having a large cooling capacity may be provided in the low temperature side passage 14d, and an EGR cooler having a small cooling capacity may be provided in the high temperature side passage 14c. In the embodiment, the cooling temperature TCOOLER is obtained according to the difference between the exhaust temperature TEXH and the outside air temperature TAT. However, the present invention is not limited to this, and when the EGR cooler 15c is a water-cooled type, for example, the outside temperature You may obtain | require according to the difference of temperature TAT and cooling water temperature.

  Further, the present invention can be applied not only to a diesel engine mounted on a vehicle but also to a gasoline engine such as a lean burn engine. In addition, the present invention can be applied to various industrial internal combustion engines including a marine vessel propulsion engine such as an outboard motor having a crankshaft arranged in a vertical direction. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

1 is a diagram showing a schematic configuration of an exhaust gas purification apparatus of the present invention and an internal combustion engine to which the exhaust gas purification apparatus is applied. It is a figure which shows a part of exhaust gas purification apparatus. It is a flowchart which shows an EGR channel | path switching process. It is a figure which shows an example of the map for discriminating the engine load used by the process of FIG. It is a flowchart which shows an EGR gas temperature estimation process. It is a figure which shows TCOOLER used by the process of FIG. It is a flowchart which shows the EGR temperature condition determination process by 1st Embodiment. It is a flowchart which shows a rich spike execution determination process. It is a figure which shows an example of the S_QNOxREF table used by the process of FIG. It is a flowchart which shows fuel injection amount control. It is a flowchart which shows intake air amount control. It is a flowchart which shows the EGR temperature condition determination process by 2nd Embodiment. It is a flowchart which shows the EGR temperature condition determination process by 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification apparatus 2 ECU (NOx trapping amount calculation means, temperature state determination means, NOx reduction permission means)
3 Engine (Internal combustion engine)
4 Intake pipe (intake system)
5 Exhaust pipe (exhaust system)
6 Injector (NOx reduction means)
12 Throttle valve (NOx reduction means)
14a EGR pipe (EGR passage)
14c High temperature side passage 14d Low temperature side passage 15b EGR passage switching valve (EGR passage switching means)
17 NOx catalyst (NOx trapping material)
37 Exhaust temperature sensor (temperature state determination means)
S_QNOx NOx emission amount integrated value (NOx trapping amount)
S_QNOxREF judgment value (predetermined value)

Claims (1)

An exhaust gas purification device for an internal combustion engine that purifies exhaust gas discharged from an internal combustion engine having an intake system and an exhaust system,
A NOx trap that is provided in the exhaust system and traps NOx in the exhaust gas;
NOx trapping amount calculating means for calculating the NOx trapped by the NOx trapping material as the NOx trapping amount;
NOx reduction means for reducing NOx trapped by the NOx trapping material when the calculated NOx trapping amount reaches a predetermined value;
A low-temperature side passage provided between the exhaust system and the intake system and configured to recirculate a part of exhaust gas from the exhaust system to the intake system as EGR gas at a lower temperature; and at a temperature higher than the low-temperature side passage. An EGR passage having a high temperature side passage for reflux;
EGR passage switching means for switching the EGR passage to the low temperature side passage and the high temperature side passage;
Temperature state determining means for determining whether or not the EGR gas is in a predetermined high temperature state;
When the EGR passage is switched from the low temperature side passage to the high temperature side passage by the EGR passage switching means, only when the EGR gas is determined to be in the predetermined high temperature state by the temperature state determination means. NOx reduction permission means for permitting NOx reduction by the NOx reduction means;
An exhaust gas purifying apparatus for an internal combustion engine, comprising:

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