JP4952374B2 - NOx purification system and control method of NOx purification system - Google Patents

Description

  The present invention relates to a NOx purification system including a NOx occlusion reduction type catalyst in an exhaust gas passage of an internal combustion engine and a control method for the NOx purification system.

  In a NOx purification system equipped with a conventional NOx occlusion reduction type catalyst (LNT catalyst), NOx occlusion reduction catalyst is used to store NOx and repeatedly desorb and decompose the occluded NOx and exhaust from the internal combustion engine. NOx in exhaust gas is reduced. Since this NOx occlusion amount has a limit determined by the capacity of the catalyst, the NOx occlusion function is maintained by desorbing and decomposing the occluded NOx and returning it to a fresh state. Therefore, in this NOx purification system, in order to maintain the NOx reduction function, the most important control is to desorb the stored NOx every certain period. This desorption of NOx is performed by reducing the oxygen in the catalyst atmosphere of the NOx storage reduction catalyst to zero.

  As a method of removing the surplus oxygen in the exhaust pipe, the oxygen concentration of the exhaust gas is measured, and the exhaust pipe injection for directly injecting the fuel into the exhaust pipe is performed to consume the surplus oxygen in the exhaust gas, In in-cylinder combustion of an internal combustion engine, post-injection in which fuel is injected into the cylinder is performed in the latter half of the combustion stroke, and excess oxygen is consumed in the cylinder.

  The frequency of this NOx desorption is once every several minutes (2 to 5 minutes). This desorption is performed from a state where there is surplus oxygen in the exhaust gas, that is, from a lean state where the excess air ratio in the exhaust gas exceeds 1, that is, from a state where there is no surplus oxygen in the exhaust gas. This is performed by shifting to the rich state (Rich) where the excess air ratio in the exhaust gas is 1 or less. This rich state is maintained for several seconds (about 3 to 5 seconds), and NOx occluded in the NOx occlusion reduction type catalyst is desorbed and decomposed in this rich state. The temperature of the exhaust gas during the NOx regeneration control is desirably secured at about 200 ° C. in order to decompose the desorbed NOx. After performing the NOx regeneration control for desorption and decomposition of NOx, the NOx occlusion capacity has been restored. Therefore, NOx is occluded again in the lean state of normal operation thereafter, and this is repeated, NOx is continuously purified.

  The NOx regeneration control for making the rich state is performed as follows, for example. First, the amount of NOx occluded in the NOx occlusion reduction catalyst is calculated instantaneously from the output values of the NOx concentration sensors provided before and after the NOx occlusion reduction catalyst, the intake air amount of the internal combustion engine, and the input fuel amount. The amount of NOx stored in the NOx storage-reduction catalyst is obtained by integrating the amount of NOx. When the NOx occlusion amount reaches a preset threshold value, it is determined that the NOx occlusion amount has reached the vicinity of the upper limit of the occlusion amount, which is the storable amount, and the time when regeneration is necessary has been approached.

  This regeneration control starts regeneration when the operating state of the internal combustion engine (engine rotational speed N0 and fuel amount Q0) is within a predetermined operating range (N1 <N0 <N2, Q1 <Q0 <Q2), and exhaust Tube injection or post injection is performed. The additional fuel injection amount ΔQ for this regeneration is determined by calculating from the air excess ratio λ and the intake air amount at that time so that the target air excess ratio λt (1 or less) is obtained. While correcting this additional fuel injection amount ΔQ with a value calculated from the detected value λm of the oxygen concentration sensor provided downstream of the regenerative fuel injection device, excessive air is applied for a predetermined time (about 3 to 5 seconds). The additional fuel injection is continued so that the rate λm becomes λt. When the operating state of the internal combustion engine deviates from the predetermined operating range, the additional fuel injection for this regeneration is stopped.

  However, in a vehicle equipped with an internal combustion engine, the engine speed N0 and the fuel amount Q0 of the internal combustion engine frequently change during traveling. Therefore, the excess air ratio λ in the exhaust gas changes from infinity at the time of motoring to around 1.0 when a turbo response delay occurs due to sudden acceleration or the like.

  Therefore, even if the fuel amount set to give the rich condition is additionally injected, the operating state of the internal combustion engine changes at the next moment, and the excess air ratio λ in the exhaust gas changes greatly. There are many cases. Moreover, it often passes through a predetermined operation range for regeneration. In such a case, even if additional fuel injection such as exhaust pipe injection or post injection is performed, a case where the regeneration excess air ratio λt is not reached frequently occurs, resulting in increased fuel wastage. As a result, fuel consumption deteriorates.

According to experiments conducted by the present inventors, since the operating state of the internal combustion engine changes after exhaust pipe injection with a set amount of fuel, the target excess air ratio λt can be reached or a predetermined amount When the target excess air ratio λt can be maintained during this time, it was shown to be less than expected. From these results, it was found that in actual traveling, fuel is often wasted even if NOx regeneration control is performed. Therefore, it is understood that by appropriately selecting the timing for performing the NOx regeneration control and increasing the probability that the rich state necessary for regeneration can be reached, wasteful consumption of fuel can be reduced and fuel consumption can be improved. It was. For that purpose, it is extremely important to predict a condition in which the load fluctuation of the engine is relatively small in the vehicle running state.

  According to the experiments by the present inventors, as a result of analyzing the change in the engine rotation speed and the change in the excess air ratio in the exhaust gas during the operation in the North American city driving mode in which the fluctuations in the engine rotation speed and the fuel load are severe, It was found that when the combustion (PCI combustion) is the main area and the gear of the transmission is 3rd speed or higher, the engine speed change is small and the period is long. It was also found that there was little change in the excess air ratio at this time, and that period often lasted for more than 5 seconds.

  On the other hand, when the gear of the transmission is 1st speed or 2nd speed, there are many chances to perform a shift change, so the engine rotation speed often changes abruptly. It was. Therefore, it has been found that the period suitable for the NOx regeneration control is when the gear of the transmission is 3rd speed or higher.

Based on these experimental data, the present inventor performs regeneration control when a diesel engine using a premixed compression ignition combustion system is operating in a premixed compression ignition combustion zone when the vehicle mission is at the third speed or higher. As a result, there was a time zone in which the change in the excess air ratio was small, and it was found that the probability of satisfying the regeneration conditions can be greatly improved. Furthermore, even if the amount of additional fuel injection is small, it is possible to specify the engine speed and engine load conditions that can generate a rich state suitable for NOx regeneration by setting the excess air ratio to 1 or less. This has minimized the deterioration of fuel consumption caused by.

  In order to prevent the deterioration of fuel consumption during NOx regeneration, the road gradient is calculated and stored based on the measured atmospheric pressure and GPS data, and the running state of the vehicle is predicted based on the stored road gradient. Exhaust gas purification catalytic reduction that performs reduction regeneration (NOx regeneration) when the minimum road gradient exceeds a predetermined slope to prevent the exhaust gas temperature from becoming lower than the reduction regeneration temperature and stopping before the reduction regeneration is completed A playback device has been proposed (see, for example, Patent Document 1).

However, the memory based on the road gradient and the control based on the road gradient are complicated, and the same traveling is not always performed. However, there is a problem that appropriate NOx regeneration control is not always performed.
JP 2006-125300 A

  The present invention has been made in order to obtain the above knowledge and solve the above problems, and an object of the present invention is to provide a NOx occlusion reduction type catalyst in an exhaust gas passage of an internal combustion engine mounted on a vehicle, and in the exhaust gas. In the NOx purification system for purifying NOx, the amount of fuel required for NOx regeneration control is minimized by appropriately selecting the timing of NOx regeneration control for recovering the NOx storage capacity of the NOx storage reduction catalyst. An object of the present invention is to provide a NOx purification system and a control method for the NOx purification system that can be reliably regenerated and can provide a clean engine of exhaust gas.

A NOx purification system for achieving the above object includes a NOx occlusion reduction type catalyst in an exhaust gas passage of an internal combustion engine mounted on a vehicle, and NOx for recovering the NOx occlusion capability of the NOx occlusion reduction type catalyst. In the NOx purification system including a regeneration control device that performs regeneration control, the regeneration control device shifts when the NOx storage amount exceeds a predetermined determination value set to 50% to 80% of the NOx allowable storage amount. The gear of the machine is 3rd speed or more, the combustion of the internal combustion engine is premixed compression ignition combustion, and the residual oxygen concentration of the exhaust gas discharged from the internal combustion engine is 5% or less and 1% or more when, performs the NOx regeneration control, in the NOx regeneration control, the amount of intake air and the fuel quantity of the operating state of the internal combustion engine, the additional fuel amount such that the excess air ratio of 1.0 or less The residual oxygen concentration of the exhaust gas flowing into the NOx occlusion reduction type catalyst is made zero with this calculated additional fuel amount, and whether the combustion of the internal combustion engine is in the premixed compression ignition combustion region or not is determined. Whether the residual oxygen concentration is within the range of 5% or less and 1% or more is also determined from the engine rotational speed and the fuel amount, and the regeneration control device is further configured to store the NOx. When the amount reaches the NOx allowable storage amount, NOx regeneration control different from the NOx regeneration control is performed .

Further, in the above NOx purification system, the regeneration control device performs the NOx regeneration control at an engine speed lower than an engine speed at which premixed compression ignition combustion is possible when the engine speed of the internal combustion engine is 45% or more of the maximum output. And when the fuel injection amount is 26 mm ³ / st / liter or more and 40 mm ³ / st / liter or less.

  Further, in the above NOx purification system, when the regeneration control device performs the NOx regeneration control, the NOx is in a residual oxygen concentration range where the smoke generation amount is 1.0 or less and 0.0 or more in the Bosch number. It is comprised so that reproduction | regeneration control may be performed.

And the control method of the NOx purification system for achieving the above object includes a NOx occlusion reduction type catalyst in the exhaust gas passage of the internal combustion engine mounted on the vehicle, and the NOx occlusion reduction capability of the NOx occlusion reduction type catalyst. In a control method of a NOx purification system provided with a regeneration control device that performs NOx regeneration control for recovery, when the NOx occlusion amount exceeds a predetermined determination value set to 50% to 80% of the NOx allowable occlusion amount The gear of the transmission is 3rd speed or higher, the combustion of the internal combustion engine is premixed compression ignition combustion, and the residual oxygen concentration of the exhaust gas discharged from the internal combustion engine is 5% or less 1 % when the above, performs the NOx regeneration control, in the NOx regeneration control, the amount of intake air and the fuel quantity of the operating state of the internal combustion engine, the additional fuel amount is excess air ratio I to 1.0 With this additional fuel amount calculated, the residual oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst is made zero, and whether the combustion of the internal combustion engine is in the premixed compression ignition combustion region or not Whether the residual oxygen concentration is within the range of 5% or less and 1% or more is also determined by the engine rotation speed and the fuel amount, and the NOx occlusion amount is When the NOx allowable storage amount is reached, NOx regeneration control different from the NOx regeneration control is performed .

Further, in the above control method of the NOx purification system, the NOx regeneration control is performed at an engine speed of 45% or more of the maximum output at the maximum output and below an engine speed at which premixed compression ignition combustion is possible, and The method is started when the fuel injection amount is 26 mm ³ / st / liter or more and 40 mm ³ / st / liter or less.

  Further, in the control method of the NOx purification system, when the NOx regeneration control is performed, the NOx regeneration control is performed in a residual oxygen concentration range where the smoke generation amount is 1.0 or less and 0.0 or more in the Bosch number. It is characterized by performing.

  This premixed compression ignition combustion is a combustion called PCI (Premixed Compression Ignition) combustion, which is a system in which fuel and air are sufficiently mixed and then burned, and NOx and soot can be greatly reduced simultaneously. On the other hand, conventional normal combustion is diffusion combustion, in which the injected fuel is burned while being mixed and diffused with air. The rotation speed at the maximum output of the internal combustion engine is also called horsepower point rotation speed. Further, the fuel injection amount is a numerical value per cylinder per one liter of displacement and per stroke.

  In the NOx purification system and the control method for the NOx purification system, the NOx occlusion amount exceeds a predetermined determination amount. When NOx regeneration control is performed when the NOx occlusion amount is small, the NOx regeneration frequency increases. This is to prevent the fuel consumption from deteriorating. The predetermined determination amount in this case is set to about 50% to 80% of the NOx allowable storage amount with a considerable margin, not near the upper limit of the NOx storage amount. The NOx allowable storage amount can be obtained from experiments, and the predetermined determination amount is set based on the NOx allowable storage amount.

  The reason why the gear of the transmission is set to the third speed or more is that when the gear of the transmission is the third speed or more, the gear shift change is relatively small and the driving state is stable and the period is suitable for the NOx regeneration control. It is. On the other hand, when the gear is in the first speed or the second speed, there are many opportunities to perform a shift change, so the engine rotation speed often changes abruptly, and the change in the excess air ratio increases accordingly.

  The reason for the premixed compression ignition combustion is that, when diffusion combustion is mainly used, the residual oxygen concentration in the exhaust gas exhausted from the internal combustion engine cannot be reduced to 7% or less. This is because the oxygen concentration can be lowered to 5% or less, and NOx regeneration conditions, in other words, conditions for desorption and decomposition of NOx can be achieved with a small amount of additional fuel. Also, during premixed compression ignition combustion, the vehicle travel is often stable, there is little change in the operating state of the internal combustion engine, and the probability of reaching the NOx regeneration condition is increased.

  3 and 4 compare the exhaust gas temperature and residual oxygen concentration during premixed compression ignition combustion (PCI combustion) and conventional diffusion combustion when the engine speed of the internal combustion engine is 50% of the maximum output. The results are shown. The horizontal axis indicates the fuel amount Q0. From FIG. 3, it can be seen that in PCI combustion, the amount of fuel Q0 for reducing the residual oxygen concentration in the exhaust gas to 0% is small, and a low oxygen concentration state can be achieved. This is because a large amount of EGR is performed in the PCI combustion region, so that the residual oxygen concentration in the exhaust gas becomes very small compared to the diffusion combustion method. FIG. 4 also shows that PCI combustion can be performed at a temperature higher than 200 ° C. necessary for NOx regeneration, although the exhaust gas temperature is lower than that of diffusion combustion with a large amount of fuel Q0.

  The reason why the residual oxygen concentration is 5% or less is that the amount of smoke (smoke) generated is minimized. If it exceeds 5%, the smoke increases rapidly, and if it is less than 5%, the increase in smoke is small and the residual oxygen concentration can be reduced to about 1%. Further, when the residual oxygen concentration exceeds 5.5% in PCI combustion, knocking is likely to occur.

  FIG. 5 shows the relationship between the residual oxygen concentration in the exhaust gas and the smoke generation amount (SM) indicated by the Bosch number (B.NO.) when the engine speed is 50% of the engine speed at the maximum output. (A line indicating the tendency of the experimental results). The horizontal axis indicates the residual oxygen concentration (%). The amount of smoke generated becomes the lowest at a residual oxygen concentration of 5% to 6%. A line A in FIG. 5 indicates a lower limit that facilitates knocking. If this line A (about 5.7%) is exceeded, it will be easy to knock. Further, a line B in FIG. 5 is a line indicating a range in which the exhaust gas temperature at the catalyst inlet exceeds 200 ° C. When the temperature becomes smaller than this line B (about 5.3%), the exhaust gas temperature at the catalyst inlet becomes smaller. It will exceed 200 ° C. Therefore, the margin is set to 5% or less with a margin.

  When the transmission is gear 3 or higher and the oxygen concentration is 5% to 1% in the premixed compression ignition combustion (PCI combustion) region, the temperature of the exhaust gas at the catalyst inlet can be relatively easily reduced to NOx. It can be about 200 ° C. required for regeneration.

  The reason for setting the engine speed to 45% or more is that the engine speed is 45% or more because if the engine speed is less than 45%, fuel consumption and smoke are relatively easy to change (sensitive). Is preferred. In addition, when it is 45% or more of the maximum output, the temperature of the exhaust gas at the catalyst inlet can be set to about 200 ° C. necessary for NOx regeneration relatively easily.

  FIG. 6 shows the result of comparing the residual oxygen concentration in the exhaust gas at the limit where the smoke generation amount (SM) does not exceed 1.0 in the Bosch number (B.NO.) between the PCI combustion method and the diffusion combustion method. . The horizontal axis indicates the engine speed as a ratio (%) of the engine speed at the maximum output. A line C in FIG. 6 is a line indicating a range in which the exhaust gas temperature at the catalyst inlet exceeds 200 ° C., and the exhaust gas temperature at the catalyst inlet can be set to 200 ° C. when the engine speed is 45% or more. I understand. The upper limit is determined by the restriction with the PCI combustion zone.

The reason why the fuel injection amount is set to 26 mm ³ / st / liter or more is to raise the temperature of the exhaust gas discharged from the internal combustion engine to about 200 ° C. and to reliably burn the fuel injected into the exhaust pipe. 40 mm ³ / st / liter or less is because of the limit of premixed compression ignition combustion.

  In addition, the NOx regeneration control is performed in the residual oxygen concentration range where the smoke generation amount is 1.0 or less and 0.0 or more in the Bosch number (B.NO.) because it is desired to reduce the smoke generation amount as much as possible. It is. This Bosch number is the soot concentration measured by a device called a Bosch type smoke meter.

  According to the NOx purification system and the control method of the NOx purification system according to the present invention, in a diesel engine using a premixed compression ignition combustion (PCI combustion) method, when the NOx occlusion amount exceeds a predetermined determination amount, the transmission When the gear is 3rd speed or more, the combustion of the internal combustion engine is performing premixed compression ignition combustion, and the residual oxygen concentration of the exhaust gas discharged from the internal combustion engine is 5% or less and 1% or more, Since the NOx regeneration control is performed, the probability of satisfying the regeneration condition can be greatly improved, and the fuel consumption can be improved by minimizing the amount of fuel necessary for the regeneration control of the NOx storage reduction catalyst. Moreover, since regeneration can be performed reliably, an internal combustion engine with clean exhaust gas can be provided.

  Hereinafter, the NOx purification system and the control method of the NOx purification system according to the embodiments of the present invention will be described with reference to the drawings, taking as an example a NOx purification system that purifies NOx of exhaust gas passing through an exhaust passage of a diesel engine. To do. FIG. 1 shows a configuration of a NOx purification system 1 according to an embodiment of the present invention.

  In this NOx purification system 1, a NOx occlusion reduction type catalyst (LNT catalyst) 4 is disposed in the exhaust gas passage 3 of the diesel engine (E) 2. The NOx occlusion reduction type catalyst 4 is formed of a monolithic catalyst, and a catalyst coat layer such as aluminum oxide or titanium oxide is provided on a support such as a cordierite honeycomb, and platinum (Pt), palladium (Pd) is provided on the catalyst coat layer. ), And a NOx occlusion material (NOx occlusion material) such as barium (Ba).

  The NOx occlusion reduction type catalyst 4 purifies NOx in the exhaust gas by the NOx occlusion material occludes the NOx in the exhaust gas when the oxygen concentration is high, that is, in the lean air-fuel ratio state. In the exhaust gas state where the oxygen concentration is low or zero, that is, in the rich air fuel ratio state or the stoichiometric air fuel ratio state, the stored NOx is released and the released NOx is reduced by the catalytic action of the catalytic metal. This prevents NOx from flowing out into the atmosphere.

  In addition, fuel is injected into the exhaust pipe upstream of the NOx storage reduction catalyst 4 during NOx regeneration control, so that the oxygen concentration in the exhaust gas flowing into the NOx storage reduction catalyst 4 is lowered to form a reducing atmosphere. The fuel injection valve 5 is provided.

  Further, an exhaust gas temperature sensor 6, an excess air ratio sensor (λ sensor: oxygen concentration sensor) 7, and a first NOx sensor (NOx concentration detection sensor) 8 are disposed upstream of the NOx storage reduction catalyst 4, and store NOx. A second NOx sensor (NOx concentration detection sensor) 9 is disposed downstream of the reduction catalyst 4. Using the detected values of the first NOx sensor 8 and the second NOx sensor 9, the NOx occlusion amount occluded by the NOx occlusion reduction type catalyst 4 is estimated.

  Furthermore, a regeneration control device 10 is provided, and this regeneration control device 10 performs NOx regeneration control for recovering the NOx storage capability of the NOx storage reduction catalyst 4, sulfur regeneration control for recovering from sulfur poisoning, and the like. The regeneration control device 10 is usually incorporated in a control device called an ECU (engine control unit) that controls the overall operation of the engine 2. The regeneration control device 10 detects the operating state of the engine 2 (for example, the engine speed N0, the load (fuel injection amount) Q0, etc.), the intake air amount Va, and the first and second NOx sensors 8 and 9. The NOx concentrations Cn1 and Cn2, the exhaust gas temperature Tg, the oxygen concentration Co (excess air ratio λm), and the like are input.

  In this NOx purification system 1, NOx in the exhaust gas G discharged from the engine 2 is occluded in the NOx occlusion material of the NOx occlusion reduction type catalyst 4 in the lean air-fuel ratio state that is the normal operation state of the diesel engine 2. To be purified. Further, in the rich air-fuel ratio state in the NOx regeneration control for recovering the NOx occlusion capacity of the NOx occlusion reduction type catalyst 4, NOx occluded in the NOx occlusion material of the NOx occlusion reduction type catalyst 4 is released and the NOx occlusion capacity is obtained. Is recovered, and the released NOx is reduced and purified by the catalytic action of the catalytic metal of the NOx storage reduction catalyst 4. The purified exhaust gas Gc passes through the exhaust gas passage 3 and is released into the atmosphere.

  In the present invention, in these NOx purification systems 1, the regeneration control device 10 performs the following control according to the control flow illustrated in FIG. The control flow of FIG. 2 is repeatedly called and executed from the control flow for controlling the operation of the engine 2 when the operation of the engine 2 is started. When the operation of the engine 2 is completed, the operation control of the engine 2 is performed. It is shown as ending with the control flow to be performed.

  When the control flow of FIG. 2 is called, the process starts. In step S11, data necessary for determining the start of the reproduction control is input. As this data, the NOx concentrations Cn1 and Cn2 before and after the NOx storage reduction catalyst 4, the intake air amount Va, and the fuel amount Q0 are input, and the exhaust gas amount Vg is calculated from the intake air amount Va and the fuel amount Q0. , NOx occlusion amount Vn (= Vg × (Cn1−Cn2) × Δt) within Δt time is calculated from NOx concentrations Cn1 and Cn2, and this is integrated every Δt time to obtain NOx occlusion amount Vns (= ΣVn). Is calculated.

  In the next step S12, it is determined whether or not the NOx occlusion amount Vns is larger than a predetermined determination amount Vc. If it is small (NO), there is still a great demerit that the fuel consumption deteriorates even if the NOx regeneration control is performed, so the process goes to the return without performing the NOx regeneration control.

If NOx occlusion amount Vns is greater than the predetermined determination amount Vc (YES) in step S12, is better the NOx regeneration control was performed when the conditions for NOx regeneration is in place, since the fuel consumption is improved, the NOx regeneration control Go to step S13 to check the conditions.

  In step S13, it is determined whether or not the gear (gear stage) of the transmission (mission) is in the third speed or higher. If it is not in the third speed or higher in this determination (NO), the control goes to return without performing NOx regeneration control. If it is determined that the vehicle is in the third speed (YES), it is determined whether or not it is in the premixed compression ignition combustion (PCI combustion) region in step S15 through step S14 in which the engine speed N0 and the engine fuel amount Q0 are input. . In the case of entering the third speed or higher, the engine rotational speed N0 is 45% or more of the engine rotational speed (horsepower rotational speed) Nmax at the maximum output, and in this state, the exhaust at the catalyst inlet is relatively easy. The temperature of the gas can be about 200 ° C. required for NOx regeneration.

In step S15, it is determined whether or not the premixed compression ignition combustion (PCI combustion) region is N0 <N2 and Q0 <Q2. If the determination is not PCI combustion (NO), the control goes to return without performing NOx regeneration control. If this determination is PCI combustion (YES), go to step S16. Although depending on the type and model of the engine 2, the upper limit engine speed N2 of the premixed compression ignition combustion (PCI combustion) is an engine speed capable of premixed compression ignition combustion, and the upper limit engine fuel amount Q2 is In terms of the displacement per liter, per stroke, per cylinder, it is about 40 mm ³ / st / liter.

In step S16, it is checked whether or not the operating state is such that the range of the excess air ratio λ falls within a predetermined range, and it is determined whether or not the NOx regeneration control can be started. This determination is based on whether N1 <N0 and Q1 <Q0. Within this range, the residual oxygen concentration Co is equal to or less than the predetermined determination value Coc (5%), that is, the excess air ratio λ is equal to or less than the predetermined determination value λc (1.3). If the determination in step S16 is not within this range (NO), the process returns without performing NOx regeneration control. If it is within this range (YES), go to step S17 to perform NOx regeneration control. Depending on the type and model of the engine 2, the lower limit engine speed N1 is about 45% of the maximum output, and the lower limit engine fuel amount Q1 is about 26 mm ³ / st / liter.

  In step S16, the oxygen concentration Co detected by the excess air ratio sensor 7 may be checked to determine whether or not the NOx regeneration control may be started. In this determination, if the oxygen concentration Co is not less than or equal to the predetermined determination value Coc (5%) (NO), the process returns without performing NOx regeneration control. If the oxygen concentration Co is less than or equal to the predetermined determination value Coc in this determination (YES), the process goes to step S17 to perform NOx regeneration control. When the excess air ratio λm is used instead of the oxygen concentration Co, the predetermined determination value λc is 1.3 corresponding to the oxygen concentration of 5%.

  In step S17, an additional fuel amount ΔQ to be performed by exhaust pipe injection (or post injection) is calculated from the intake air amount Va and the fuel amount Q0. This additional fuel amount ΔQ is calculated as a value such that the excess air ratio λ is 1.0 or less.

  In the next step S18, exhaust pipe injection (or post injection) is performed with this additional fuel amount ΔQ, and rich control for NOx regeneration is performed for a predetermined time (time related to each determination interval). As a result, the residual oxygen concentration of the exhaust gas flowing into the NOx occlusion reduction catalyst 4 is made zero, the NOx occluded from the NOx occlusion reduction catalyst 4 is desorbed, and this desorbed NOx is removed from the NOx occlusion reduction type. The catalyst 4 is reduced with the catalyst. As a result, the NOx storage capacity of the NOx storage reduction catalyst 4 is recovered.

  In the next step S19, it is determined whether or not NOx regeneration is completed. This determination is made based on whether or not the rich control for NOx regeneration in step S18 has passed a predetermined time, or is determined from the NOx concentrations Cn1 and Cn2 before and after the NOx storage reduction catalyst 4 or the like.

  If NOx regeneration has not been completed (NO) in step S19, the process returns to step S13. If NOx regeneration has been completed (YES), the process goes to step S20 to perform NOx regeneration end work. Go, return.

  When the NOx regeneration control in step S20 is completed, the process returns to the advanced control flow that called the control flow of FIG. 2, and is called again from this advanced control flow and the control flow of FIG. 2 is repeatedly executed. . If the engine key is turned off in the middle of this control flow and the engine operation is terminated, an interruption occurs due to the engine key off, the NOx regeneration end operation in step S20 is performed, and the process returns. Finish with.

  Further, in the NOx regeneration control flow of FIG. 2, when the NOx occlusion amount Vns reaches a certain level, the engine operating state is in the premixed compression ignition combustion (PCI combustion) operation region and the engine speed N0 is a predetermined value. When the determination value is N1 (45%) or more, rich control for NOx regeneration is performed, and the NOx control flow performed when the NOx storage amount Vns reaches the limit is complemented. Accordingly, in the control flow of FIG. 2 only, the NOx occlusion amount Vns reaches the limit in the premixed compression ignition combustion (PCI combustion) operation region and the engine speed N0 does not exceed the predetermined determination value N1. Cannot handle. Therefore, by performing NOx regeneration control or sulfur poisoning regeneration control when the NOx storage amount Vns reaches the NOx allowable storage amount (limit) in cooperation with a control flow different from FIG. The NOx storage reduction catalyst 4 can be effectively regenerated while suppressing fuel consumption.

  With the control method of the NOx purification system 1 according to the control flow of FIG. 2 described above, the NOx storage reduction catalyst 4 is provided in the exhaust gas passage 3 of the engine 2 mounted on the vehicle, and the NOx storage reduction catalyst 4 is stored. In the NOx purification system 1 including the regeneration control device 10 that performs NOx regeneration control for recovering the capacity, when the NOx occlusion amount Vns exceeds a predetermined determination amount Vc, the combustion of the engine 2 is predicted to have a large EGR amount. When the mixed compression ignition combustion (PCI combustion) is performed and the residual oxygen concentration Co of the exhaust gas discharged from the engine is 5% or less and 1% or more, the NOx regeneration control in step S18 can be performed.

Further, the NOx regeneration control is performed so that the engine rotation speed N0 of the engine 2 is 45% or more of the maximum output and is equal to or less than the engine rotation speed at which premixed compression ignition combustion is possible, and the fuel injection amount Q0 is 26 mm ³ / st / It can be carried out when it is not less than liter (Q1) and not more than 40 mm ³ / st / liter.

  In addition, when NOx regeneration control is performed, the amount of smoke generated is Bosch NO. NOx regeneration control can be performed in a residual oxygen concentration range of 1.0 or more and 0.0 or more.

  7 and 8 show the relationship between the engine speed and the fuel consumption deterioration rate in premixed compression ignition combustion (PCI combustion) and diffusion combustion. FIG. 7 and FIG. 8 are graphs showing experimental results, and it can be seen that PCI combustion is remarkably less deteriorated than diffusion combustion. In addition, it can be seen that the deterioration of fuel consumption is further reduced when the residual oxygen concentration in the exhaust gas is minimized (black circle) than when the residual oxygen concentration in exhaust gas is 5% (white circle).

  Therefore, according to the above-described NOx purification system 1 and the control method of the NOx purification system, when the NOx occlusion amount Vns exceeds the predetermined determination amount Vc in the diesel engine 2 using the premixed compression ignition combustion (PCI combustion) method. In addition, the gear of the transmission is 3rd speed or more, the combustion of the engine 2 is premixed compression ignition combustion, and the residual oxygen concentration Co of the exhaust gas G discharged from the engine 2 is 5% or less. Since the NOx regeneration control is performed at 1% or more, the probability of satisfying the regeneration condition can be greatly improved, and the fuel consumption can be improved by minimizing the amount of fuel required for the regeneration control of the NOx storage reduction catalyst 4. Can do. In addition, since the regeneration can be performed reliably, the engine 2 with clean exhaust gas can be provided.

It is a figure showing typically composition of a NOx purification system of an embodiment concerning the present invention. It is a figure of the control flow which shows an example of the control method of the NOx purification system which concerns on this invention. It is a figure which shows the relationship between the fuel amount and the residual oxygen concentration in exhaust gas in PCI combustion and diffusion combustion. It is a figure which shows the relationship between the fuel quantity and exhaust gas temperature in PCI combustion and diffusion combustion. It is a figure which shows the relationship between the residual oxygen concentration in exhaust gas, and the amount of smoke generation in PCI combustion. It is a figure which shows the relationship between an engine speed and the residual oxygen concentration in exhaust gas in PCI combustion and diffusion combustion. It is a figure which shows the relationship between an engine speed and the fuel consumption deterioration rate in PCI combustion and diffusion combustion. FIG. 8 is a partially enlarged view of FIG. 7 showing a relationship between engine rotation speed and fuel consumption deterioration rate in PCI combustion.

Explanation of symbols

1 NOx purification system 2 Diesel engine (E)
3 Exhaust gas passage 4 NOx storage reduction catalyst (LNT catalyst)
5 Fuel Injection Valve 6 Exhaust Gas Temperature Sensor 7 Excess Air Ratio (λ) Sensor 8 First NOx Sensor (NOx Concentration Detection Sensor)
9 Second NOx sensor (NOx concentration detection sensor)
10 Reproduction control device (ECU)
Cn1, Cn2 NOx concentration Co O2 concentration Coc Predetermined determination value G Exhaust gas Gc Purified exhaust gas N1 Lower limit value of engine rotation speed N2 Upper limit value of engine rotation speed N0 Engine rotation speed Nmax Engine rotation speed at maximum output Q0 Fuel Injection amount (load)
Q1 Lower limit value of engine fuel amount Q2 Upper limit value of engine fuel amount tc Predetermined determination value ts NOx regeneration time Tg Exhaust gas temperature Va Intake air amount Vc Predetermined determination amount Vg Exhaust gas amount Vn NOx occlusion amount Vns NOx occlusion Amount Δt Time λ Excess air ratio λc Predetermined judgment value

Claims (6)

In a NOx purification system including a NOx storage reduction catalyst in an exhaust gas passage of an internal combustion engine mounted on a vehicle, and a regeneration control device that performs NOx regeneration control for recovering the NOx storage capability of the NOx storage reduction catalyst,
When the regeneration control device determines that the NOx occlusion amount exceeds a predetermined judgment value set to 50% to 80% of the NOx allowable occlusion amount, the gear of the transmission is 3rd speed or more, and the internal combustion engine NOx regeneration control is performed when the combustion of is premixed compression ignition combustion and the residual oxygen concentration of the exhaust gas discharged from the internal combustion engine is 5% or less and 1% or more ,
In the NOx regeneration control, the additional fuel amount is calculated as a value such that the excess air ratio is 1.0 or less from the intake air amount and the fuel amount in the operating state of the internal combustion engine, and the calculated additional fuel amount The residual oxygen concentration of the exhaust gas flowing into the NOx occlusion reduction type catalyst is set to zero, and it is determined whether the combustion of the internal combustion engine is in a premixed compression ignition combustion region based on the engine speed and the fuel amount, and Whether the residual oxygen concentration is within the range of 5% or less and 1% or more is also determined by the engine speed and the fuel amount,
Furthermore, when the NOx occlusion amount reaches the NOx allowable occlusion amount, the regeneration control device performs NOx regeneration control different from the NOx regeneration control . The regeneration control device performs the NOx regeneration control at an engine rotational speed of 45% or more of the maximum output at the maximum output and below an engine rotational speed capable of premixed compression ignition combustion, and a fuel injection amount is 26 mm. ^2. The NOx purification system according to claim 1, wherein the NOx purification system starts when it is ³ / st / liter or more and 40 mm ³ / st / liter or less.   When the regeneration control device performs the NOx regeneration control, the NOx regeneration control is performed in a residual oxygen concentration range in which a smoke generation amount is 1.0 or less and 0.0 or more in a Bosch number. The NOx purification system according to claim 1 or 2. Control of a NOx purification system including a NOx storage reduction catalyst in an exhaust gas passage of an internal combustion engine mounted on a vehicle and a regeneration control device for performing NOx regeneration control for recovering the NOx storage capability of the NOx storage reduction catalyst In the method
When the NOx occlusion amount exceeds a predetermined judgment value set to 50% to 80% of the NOx allowable occlusion amount, the gear of the transmission is 3rd speed or more, and the combustion of the internal combustion engine is premixed compression When the ignition combustion is performed and the residual oxygen concentration of the exhaust gas discharged from the internal combustion engine is 5% or less and 1% or more, the NOx regeneration control is performed,
In the NOx regeneration control, the additional fuel amount is calculated as a value such that the excess air ratio is 1.0 or less from the intake air amount and the fuel amount in the operating state of the internal combustion engine, and the calculated additional fuel amount The residual oxygen concentration of the exhaust gas flowing into the NOx occlusion reduction type catalyst is set to zero, and it is determined whether the combustion of the internal combustion engine is in a premixed compression ignition combustion region based on the engine speed and the fuel amount, and Whether the residual oxygen concentration is within the range of 5% or less and 1% or more is also determined by the engine speed and the fuel amount,
Further, when the NOx occlusion amount reaches the NOx allowable occlusion amount, NOx regeneration control different from the NOx regeneration control is performed . In the NOx regeneration control, the engine rotation speed of the internal combustion engine is 45% or more of the maximum output and the engine rotation speed is less than the engine rotation speed capable of premixed compression ignition combustion, and the fuel injection amount is 26 mm ³ / st / liter or more. 5. The NOx purification system control method according to claim 4, wherein the control method is started when it is 40 mm ³ / st / liter or less.   6. The NOx regeneration control is performed in a residual oxygen concentration range in which a smoke generation amount is 1.0 or less and 0.0 or more in a Bosch number when the NOx regeneration control is performed. NOx purification system control method.

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