JP7024470B2 - Engine control - Google Patents

Description

The present invention relates to an engine control device.

Patent Document 1 discloses an engine provided with a NOx catalyst that occludes NOx and reduces and purifies it in an exhaust passage, and a PM filter that collects fine particle substances.

Since the NOx catalyst occludes the sulfur component in the exhaust gas in addition to the NOx, so-called S poisoning occurs in which the occlusable amount of the NOx decreases by the amount of the occluded sulfur component. In order to maintain a high NOx occlusion and reduction function by the NOx catalyst, it is necessary to desorb the sulfur component from the NOx catalyst to eliminate S poisoning. In the NOx catalyst regeneration control that desorbs the sulfur component from the NOx catalyst, the air-fuel ratio of the exhaust is set richer than the theoretical air-fuel ratio, and the sulfur component is released from the NOx catalyst by the unburned fuel supplied as a reducing agent for reduction. Let me.

On the other hand, in order to maintain the performance of the PM filter, it is necessary to prevent excessive deposition of fine particle substances. In the PM filter regeneration control that removes fine particles from the PM filter, oxygen and unburned fuel are supplied to the PM filter by performing post-injection with the air-fuel ratio of the exhaust as lean from the stoichiometric air-fuel ratio, thereby supplying fine particles. The substance is burned and removed from the PM filter.

Patent No. 4241032

In the engine of Patent Document 1, if the accumulated amount of particulate matter of the PM filter becomes excessive during the implementation of NOx catalyst regeneration control, the PM filter regeneration control is switched to, and the PM filter regeneration control has the accumulated amount of particulate matter. It is carried out until it becomes less than a predetermined amount. In this case, the NOx catalyst will be exposed to high temperature conditions until the PM filter regeneration control is completed.

Here, the inventor of the present application states that when the NOx catalyst is exposed to a high temperature condition, the occlusion agent carried on the NOx catalyst aggregates and the sulfur component becomes difficult to react with the reducing agent. In this case, it was found that it is difficult to desorb the sulfur component from the NOx catalyst even by controlling the regeneration of the NOx catalyst. Furthermore, the inventor of the present application further promotes the aggregation of the occlusion agent in the NOx catalyst as the time for controlling the regeneration of the PM filter becomes longer and / or the temperature becomes higher, and the sulfur component becomes more difficult to react with the reducing agent. It was confirmed.

The present invention has been made based on the above findings, and an object of the present invention is to provide an engine control device and a control method capable of more efficiently eliminating S poisoning of a NOx catalyst.

In order to solve the above problems, the present invention is characterized in that it is configured as follows.

One aspect of the present invention according to claim 1 of the present application is
In a lean state where the air-fuel ratio of the exhaust gas is leaner than the theoretical air-fuel ratio, which is provided in the exhaust passage of the engine and is provided integrally with the oxidation catalyst that can oxidize the unburned fuel in the exhaust or on the downstream side thereof. A NOx catalyst that absorbs NOx in the exhaust gas and reduces the stored NOx when the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, and fine particles in the exhaust gas provided on the downstream side of the oxidation catalyst. An engine control device equipped with a PM filter capable of collecting state substances and a fuel injection valve for introducing fuel into the cylinder of the engine.
A rich step in which the air-fuel ratio of the exhaust gas introduced into the NOx catalyst is set to a rich state where the air-fuel ratio is richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, and a lean air-fuel ratio and unburned fuel from the stoichiometric air-fuel ratio are the oxidation catalysts. A NOx catalyst regeneration control unit that performs NOx catalyst regeneration control for removing the sulfur component stored in the NOx catalyst by repeating a rich lean cycle including a lean step for setting the lean state to be introduced into the NOx catalyst.
The air-fuel ratio of the exhaust gas introduced into the PM filter is set to be leaner than the stoichiometric air-fuel ratio and the unburned fuel is introduced into the oxidation catalyst, and the collected fine particle-like substance is transferred from the PM filter. The PM filter regeneration control unit that implements the PM filter regeneration control to be removed,
Equipped with
In the NOx catalyst regeneration control, at least during the rich step, the main injection for injecting fuel for obtaining engine torque into the cylinder and the fuel being injected into the cylinder at a time retarded from the main injection. Additional injection is carried out,
The NOx catalyst regeneration control unit controls the fuel injection valve so that the injection timing of the additional injection is on the advance side in the cycle in which the execution time is earlier than in the cycle in which the execution time is later among the plurality of cycles. It is characterized by that.

The invention according to claim 2 is the engine control device according to claim 1.
Among the plurality of cycles, the NOx catalyst regeneration control unit has the fuel injection valve so that the cycle in which the execution time is earlier is gradually advanced to the injection timing of the additional injection than the cycle in which the execution time is later. It is characterized by controlling.

The invention according to claim 3 is the engine control device according to claim 1 or 2.
The NOx catalyst regeneration control unit is characterized in that after repeating the rich lean cycle for a predetermined number of cycles, the fuel injection valve is controlled so that the injection timing of the additional injection in the rich step becomes constant.

The invention according to claim 4 is the engine control device according to any one of claims 1 to 3.
The engine supplies an SCR catalyst provided on the downstream side of the NOx catalyst to the exhaust passage, and an SCR reducing agent composed of a raw material of NH ₃ or NH ₃ between the NOx catalyst and the SCR catalyst. Further equipped with a reducing agent supply means for SCR,
In the control device, the more the injection timing of the additional injection in the rich step is set to the advance side in the NOx catalyst regeneration control, the more the SCR reducing agent supply means is supplied with the SCR reducing agent. It is characterized by controlling it so that it is reduced.

The invention according to claim 5 is the engine control device according to claim 4.
The engine further comprises a pair of NOx sensors provided in the exhaust passage on the upstream side and the downstream side of the SCR catalyst to measure the concentration of NOx.
The NOx catalyst regeneration control unit is
The consumption of NH ₃ in the SCR catalyst was calculated based on the difference in NOx concentration between the upstream side and the downstream side of the SCR catalyst detected by the pair of NOx sensors.
Based on the consumption amount of NH ₃ and the supply amount of the reducing agent for SCR, the adsorption amount of NH ₃ in the SCR catalyst was calculated.
It is characterized in that the degree of setting the injection timing of the additional injection in the rich step to the advance angle side as the adsorption amount of NH ₃ in the SCR catalyst increases is suppressed.

The invention according to claim 6 is the engine control device according to any one of claims 1 to 5.
Further provided with a NOx catalyst rich purge control unit for performing NOx catalyst rich purge control, which reduces NOx occluded from the NOx catalyst by setting the air-fuel ratio to the rich state.
The PM filter regeneration control unit is characterized in that the PM filter regeneration control is subsequently started after the end of the NOx catalyst rich purge control.

Further, another aspect of the present invention according to claim 7 is.
In a lean state where the air-fuel ratio of the exhaust gas is leaner than the theoretical air-fuel ratio, which is provided in the exhaust passage of the engine and is provided integrally with the oxidation catalyst that can oxidize the unburned fuel in the exhaust or on the downstream side thereof. A NOx catalyst that absorbs NOx in the exhaust gas and reduces the stored NOx when the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, and fine particles in the exhaust gas provided on the downstream side of the oxidation catalyst. It is an engine control method equipped with a PM filter capable of collecting state substances and a fuel injection valve for introducing fuel into the cylinder of the engine.
A rich step in which the air-fuel ratio of the exhaust gas introduced into the NOx catalyst is set to a rich state where the air-fuel ratio is richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, and a lean air-fuel ratio and unburned fuel from the stoichiometric air-fuel ratio are the oxidation catalysts. A NOx catalyst regeneration step for removing the sulfur component occluded in the NOx catalyst by repeating a rich lean cycle including a lean step for setting the lean state to be introduced into the NOx catalyst in a plurality of cycles.
The air-fuel ratio of the exhaust gas introduced into the PM filter is set to be leaner than the stoichiometric air-fuel ratio and the unburned fuel is introduced into the oxidation catalyst, and the collected fine particle-like substance is transferred from the PM filter. PM filter regeneration step to remove and
Have,
In the NOx catalyst regeneration step, at least during the rich step, the main injection for injecting fuel for obtaining engine torque into the cylinder and the fuel being injected into the cylinder at a time retarded from the main injection. Additional injection is carried out,
In the NOx catalyst regeneration step, the fuel injection valve is controlled so that the injection timing of the additional injection is on the advance side in the cycle in which the execution time is earlier than in the cycle in which the execution time is later. It is characterized by that.

With the above configuration, according to the invention of each claim of the present application, the following effects can be obtained.

First, according to the invention of claim 1, among the plurality of cycles of NOx catalyst regeneration control, the cycle in which the execution time is early is the injection timing of the additional injection (appropriately, the additional injection timing is higher than the cycle in which the implementation time is late. The fuel injection valve is controlled so that (also referred to as) is closer to the advance side. Here, the amount of sulfur component desorbed from the NOx catalyst by controlling the regeneration of the NOx catalyst can be expected to increase as the amount of sulfur component adsorbed on the NOx catalyst increases. Further, in the NOx catalyst regeneration control, by setting the additional injection timing to the advance angle side, the combustion of the additional injection in the cylinder is promoted, and as a result, the exhaust temperature rises. Further, the higher the temperature, the more efficient the desorption of the sulfur component from the NOx catalyst, and by setting the additional injection timing to the advance angle side, a large amount of the sulfur component desorbed from the NOx catalyst can be expected.

That is, among the multiple cycles of NOx catalyst regeneration control, the sulfur component occluded in the NOx catalyst is the largest, and therefore, in the cycle in which the amount of desorption of the sulfur component can be expected to be large and the implementation time is early, the additional injection timing in the rich step is set. By setting the lead angle side, the amount of the sulfur component desorbed from the NOx catalyst can be efficiently increased.

Further, since the PM filter can be regenerated in the lean state in the NOx catalyst regeneration control, the regeneration of the PM filter and the regeneration of the NOx catalyst can be performed at the same time. This is advantageous for fuel economy.

Further, according to the invention of claim 2, since the additional injection timing in the rich step of NOx catalyst regeneration control is not set to the advance angle side for a long period of time, the additional injection timing is set to the advance angle side. The increase in smoke due to this is suppressed.

Further, according to the invention of claim 3, in the initial stage of NOx catalyst regeneration control in which the accumulated amount of the sulfur component in the NOx catalyst is relatively large, the additional injection timing in the rich step is set to the advance side. This promotes the desorption of the sulfur component from the NOx catalyst. On the other hand, after the initial stage of NOx catalyst regeneration control, the amount of sulfur component deposited decreases relatively, so by setting the additional injection timing to a constant value on the retard side from the initial stage, the increase in smoke is suppressed. Will be done. That is, the increase in smoke is suppressed while efficiently desorbing the sulfur component from the NOx catalyst.

Further, according to the invention of claim 4, in the NOx catalyst regeneration control, the supply amount of the reducing agent for SCR is controlled so that the additional injection timing in the rich step is set to the advance angle side. There is. Here, in the rich step of NOx catalyst regeneration control, desorption of the nitrogen component in addition to the sulfur component from the NOx catalyst is also promoted, and NH ₃ may be generated from the desorbed nitrogen component. At this time, if the additional injection timing in the rich step is set to the advance angle side, the amount of desorption of the nitrogen component also increases, and the amount of NH ₃ generated also increases.

In this case, when NH ₃ is supplied to the SCR catalyst in a normal supply amount from the reducing agent supply means for SCR, NH ₃ generated from the NOx catalyst is additionally supplied, so that NH ₃ is excessive in the SCR catalyst. Will be supplied to. However, according to this configuration, in the NOx catalyst regeneration control, the more the additional injection timing in the rich step is set to the advance side, that is, the larger the amount of NH ₃ produced from the NOx catalyst, the more the reducing agent for SCR is supplied. Since the amount is controlled to be small, the excessive supply of NH ₃ to the SCR catalyst is suppressed.

Further, according to the invention of claim 5, the larger the adsorption amount of NH ₃ in the SCR catalyst, the more the degree to which the additional injection timing in the rich step of the NOx catalyst regeneration control is set to the advance side is suppressed. As a result, the amount of NH ₃ released from the NOx catalyst is reduced, so that excessive supply of NH ₃ to the SCR catalyst is suppressed.

Further, according to the invention of claim 6, in the NOx catalyst rich purge control, the temperature of the PM filter disposed on the downstream side is maintained at a high temperature by the heat generated by the oxidation of the unburned fuel in the oxidation catalyst. To. Therefore, if the PM filter regeneration control is subsequently performed after the NOx catalyst rich purge control is completed, it is easy to raise the temperature of the PM filter to a temperature at which fine particle substances can be removed at an early stage, and it is necessary to raise the temperature of the PM filter. The amount of unburned fuel supplied can be reduced.

Further, according to the invention of claim 7, the effect of claim 1 is realized in the engine control method.

That is, according to the engine control device and control method according to the present invention, the S poisoning of the NOx catalyst can be eliminated more efficiently.

It is a schematic block diagram of the engine system to which the control device of the engine which concerns on embodiment of this invention is applied. It is a figure which shows DPF schematically. It is a figure which conceptually shows the adsorption of NOx and SOx in a NOx catalyst. It is a block diagram which shows the control system of an engine system. It is a figure which showed the control map of the passive DeNOx control and the active DeNOx control. It is a flowchart which showed the flow of DeNOx control, DPF control, and DeSOx control. It is a flowchart which showed the flow of DeSOx control. It is explanatory drawing which shows typically the aggregation of the sulfur component in a NOx catalyst. It is a time chart which shows the time change of each parameter when DeSOx control or the like is performed. It is a graph which shows the relationship between the adsorption amount of _NH3 in an SCR catalyst, and the post-injection timing in a rich step of DeSOx control.

Hereinafter, the engine control device according to the embodiment of the present invention will be described with reference to the drawings.

(1) Overall Configuration FIG. 1 is a schematic configuration diagram of an engine system 100 to which the engine control device of the present embodiment is applied.

The engine system 100 includes a 4-stroke engine main body 1, an intake passage 20 for introducing air (intake) into the engine main body 1, an exhaust passage 40 for exhausting exhaust gas from the engine main body 1 to the outside, and a first. It includes a turbocharger 51 and a second turbocharger 52. The engine system 100 is provided in the vehicle, and the engine body 1 is used as a drive source for the vehicle. The engine body 1 is, for example, a diesel engine and has four cylinders 2 arranged in a direction orthogonal to the paper surface of FIG.

The engine body 1 has a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 provided on the upper surface of the cylinder block 3, and a piston 5 inserted into the cylinder 2 so as to be reciprocally slidable. There is. A combustion chamber 6 is formed above the piston 5.

The piston 5 is connected to the crank shaft 7, and the crank shaft 7 rotates around its central axis according to the reciprocating motion of the piston 5.

The cylinder head 4 includes an injector 10 for injecting fuel into the combustion chamber 6 (inside the cylinder 2) and a glow plug 11 for raising the temperature of the fuel-air mixture in the combustion chamber 6 in each cylinder 2. There is one set for each.

In the example shown in FIG. 1, the injector 10 is provided in the center of the ceiling surface of the combustion chamber 6 so as to face the combustion chamber 6 from above. Further, the glow plug 11 has a heat generating portion at its tip that generates heat when energized, and this heat generating portion is attached to the ceiling surface of the combustion chamber 6 so as to be located near the tip portion of the injector 10. ing. For example, the injector 10 is provided with a plurality of nozzles at its tip, and the glow plug 11 is such that the heat generating portion is located between the plurality of sprays from the plurality of jets of the injector 10 so as not to come into direct contact with the fuel spray. , Have been placed.

The injector 10 is an injection mainly performed to obtain engine torque, and is a main injection that injects fuel that burns near the compression top dead point into the combustion chamber 6 and a combustion that is on the retard side of the main injection. Even so, it is possible to carry out post-injection (additional injection) in which fuel is injected into the combustion chamber 6 at a time when the combustion energy hardly contributes to the engine torque.

The cylinder head 4 has an intake port for introducing air supplied from the intake passage 20 into the combustion chamber 6 of each cylinder 2, an intake valve 12 for opening and closing the intake port, and a combustion chamber 6 of each cylinder 2. An exhaust port for leading the exhausted exhaust to the exhaust passage 40 and an exhaust valve 13 for opening and closing the exhaust port are provided.

In the intake passage 20, in order from the upstream side, the air cleaner 21, the compressor 51a of the first turbocharger 51 (hereinafter, appropriately referred to as the first compressor 51a), and the compressor 52a of the second turbocharger 52 (hereinafter, appropriately referred to as appropriate). , The second compressor 52a), the intercooler 22, the throttle valve 23, and the surge tank 24 are provided. Further, the intake passage 20 is provided with an intake-side bypass passage 25 that bypasses the second compressor 52a and an intake-side bypass valve 26 that opens and closes the intake-side bypass passage 25. The intake side bypass valve 26 is switched between a fully closed state and a fully open state by a drive device (not shown).

In the exhaust passage 40, in order from the upstream side, the turbine 52b of the second turbocharger 52, the turbine 51b of the first turbocharger 51, the first catalyst 43, and the particulate matter (PM: Particulate Matter) in the exhaust gas. A DPF (Diesel Particulate Filter) 44, a urea injector (reducing agent supplying means for SCR) 45, an SCR (Selective Catalytic Reduction) catalyst 46, and a slip catalyst 47 are provided.

The SCR catalyst 46 hydrolyzes the urea injected from the urea injector 45 to generate ammonia, and reacts (reduces) this ammonia with NOx in the exhaust to purify it.

DPF44 collects particulate matter (PM: Particulate Matter) in the exhaust. FIG. 2 is a cross-sectional view taken along an exhaust flow path schematically showing the DPF 44. In the DPF 44, a large number of passages are formed in a grid pattern with porous ceramics or the like, and the plurality of passages are a passage 44a in which the exhaust upstream side is open and the exhaust downstream side is closed, and a passage 44a in which the exhaust upstream side is closed and the exhaust is exhausted. The passages 44b opened on the downstream side are alternately arranged in a staggered manner. The exhaust gas that has entered the passage 44a passes through the partition wall 44c that separates the passages and exits to the passage 44b. At this time, the partition wall 44c functions as a filter for preventing the fine particle substance from coming out to the passage 44b, and the fine particle substance is collected in the partition wall 44c.

Further, the partition wall 44c of the DPF 44 is coated with the oxidation catalyst layer 44d. Hydrocarbons (HC), that is, unburned fuel, carbon monoxide (CO), and the like are adsorbed on the oxidation catalyst layer 44d, and these are oxidized to water and carbon dioxide by oxygen in the exhaust gas. This oxidation reaction occurring in the oxidation catalyst layer 44d is an exothermic reaction, and when the oxidation reaction occurs in the oxidation catalyst layer 44d, the temperature of the exhaust gas is raised.

The PM collected in the DPF44 is burned by being exposed to a high temperature and being supplied with oxygen, and is removed from the DPF44. The temperature at which PM is efficiently burned and removed from DPF44 is relatively high, about 600 ° C. Therefore, in order to burn PM and remove it from DPF44, it is necessary to raise the temperature of DPF44 to a relatively high temperature.

The first catalyst 43 includes a NOx catalyst 41 for purifying NOx and an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 42.

The oxidation catalyst 42 uses oxygen in the exhaust gas to oxidize hydrocarbons (HC), that is, unburned fuel, carbon monoxide (CO), and the like to change them into water and carbon dioxide. Here, this oxidation reaction generated in the oxidation catalyst 42 is an exothermic reaction, and when the oxidation reaction occurs in the oxidation catalyst 42, the temperature of the exhaust gas is raised.

As conceptually shown in FIG. 3 (a), the catalyst metal 41a is supported on the NOx catalyst 41, and as the catalyst metal 41a, for example, a noble metal such as platinum (Pt) or rhodium (Rh) is adopted. Will be done. Further, the storage agent 41b is carried on the NOx catalyst 41, and as the storage agent 41b, for example, an alkaline earth metal, an alkali metal, or a rare earth is adopted. More specifically, as the occlusion agent 41b, for example, barium (Ba), strontium (Sr), magnesium (Mg) and the like are adopted, and the air-fuel ratio of the exhaust is leaner than the theoretical air-fuel ratio (air). When the excess ratio λ> 1), NOx in the exhaust is oxidized by the catalyst metal 41a and stored in the occlusion agent 41b. Further, as shown in FIG. 3B, in the NOx catalyst 41, when the air-fuel ratio of the exhaust gas is in the lean state, the SOx in the exhaust gas is also oxidized by the catalyst metal 41a and stored in the occlusion agent 41b.

The NOx and SOx occluded in the NOx catalyst have a state in which the air-fuel ratio of the exhaust is close to the stoichiometric air-fuel ratio (λ≈1) or a rich state (λ <1) smaller than the stoichiometric air-fuel ratio, that is, the NOx catalyst 41. The passing exhaust gas is released and reduced in a reducing atmosphere containing a large amount of unburned HC. Therefore, the NOx catalyst 41 is a NOx storage-reducing catalyst (NSC: NOx Storage Catalyst).

Specifically, the NOx catalyst 41 is configured to be able to occlude oxygen contained in the exhaust gas in a lean state in which the excess air ratio λ of the exhaust gas is larger than 1. For example, the NOx catalyst 41 contains ceria and the like having an oxygen occlusion ability. Then, the NOx catalyst 41 oxidizes NO in the exhaust gas using the oxygen contained in the exhaust gas and the stored oxygen (referred to as NO ₂ ), and stores the NO.

Further, the NOx catalyst 41 is adapted to generate and release NH3 (ammonia) when reducing the stored NOx. Specifically, at the time of NOx reduction, "N" in NOx stored in the NOx catalyst 41 and NOx passing through the NOx catalyst 41 are bound to H or the like which is a reducing agent introduced into the NOx catalyst 41. Then, NH3 is generated.

The first catalyst 43 is formed, for example, by coating the surface of the catalyst material layer of DOC with the catalyst material of NSC.

In this embodiment, the exhaust passage is not provided with a separate device for supplying air or fuel, and the air-fuel ratio of the exhaust corresponds to the air-fuel ratio of the air-fuel mixture in the combustion chamber 6. That is, when the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is leaner than the stoichiometric air-fuel ratio, the air-fuel ratio of the exhaust is also lean, and the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is close to the stoichiometric air-fuel ratio (λ). When ≈1) or a rich state smaller than the theoretical air-fuel ratio (λ <1), the air-fuel ratio of the exhaust is also near the theoretical air-fuel ratio (λ≈1) or a rich state smaller than the theoretical air-fuel ratio (λ). It becomes <1).

As shown in FIG. 1, the urea injector 45 injects urea into the exhaust passage 40 on the downstream side of the DPF 44. The urea injector 45 is connected to the urea tank 45c via the urea supply path 45a and the urea delivery pump 45b, and the urea pumped from the urea tank 45c by the urea delivery pump 45b is injected into the exhaust passage 40. In this embodiment, a heater 45d is provided to prevent the urea from freezing. The urea injected from the urea injector 45 is introduced into the SCR catalyst 46.

The SCR catalyst 46 purifies NH3 (ammonia) by reacting (reducing) it with NOx in the exhaust gas. The SCR catalyst 46 hydrolyzes urea injected from the urea injector 45 to generate NH3 (CO (NH2) 2 + H2O → CO2 + 2NH3), and reacts (reduces) the generated NH3 with NOx in the exhaust gas to produce NOx. Purify.

As described above, in the present embodiment, the urea injected (supplied) into the exhaust passage 40 by the urea injector 45 functions as the NH3 raw material and the reducing agent for SCR in the claims.

Specifically, in the SCR catalyst 46, the introduced NH3 is adsorbed, and NOx is reduced by the reaction between the adsorbed NH3 and NOx. Further, as described above, when NOx is reduced in the NOx catalyst 41, NH3 is also released from the NOx catalyst 41, and the SCR catalyst 46 is exhausting the NH3 released from the NOx catalyst 41. NOx is also purified by reacting (reducing) with NOx.

For example, in the SCR catalyst 46, a catalyst metal (Fe, Ti, Ce, W, etc.) having a function of reducing NOx by NH3 is supported on a zeolite having a function of trapping NH3 to serve as a catalyst component, and this catalyst component is used as a catalyst component. It is made by supporting it on the cell wall of a honeycomb carrier.

Both the SCR catalyst 46 and the NOx catalyst 41 can purify NOx, but they have different temperatures at which the purification rate (NOx storage rate) becomes high, and the NOx purification rate (NOx storage rate) of the SCR catalyst 46 is different. ) Increases when the exhaust temperature is relatively high, and the NOx purification rate of the NOx catalyst 41 increases when the exhaust temperature is relatively low.

That is, in the present embodiment, NOx is purified by using both the NOx catalyst 41 and the SCR catalyst 46. Specifically, the temperature of the SCR catalyst 46 is lower than the first temperature, and the SCR catalyst 46
When the NOx purification rate is low, NOx purification is performed only by the NOx catalyst 41.
The temperature of the SCR catalyst 46 is equal to or higher than the second temperature (the second temperature is higher than the first temperature) and the SCR
When the NOx purification rate by the catalyst 46 is high, NOx purification is performed only by the SCR catalyst 46. Then, when the temperature of the SCR catalyst 46 is between the first temperature and the second temperature, NOx
NOx purification is performed by both the catalyst 41 and the SCR catalyst 46. Further, even when the exhaust gas flow rate is large and the NOx purification rate by the SCR catalyst 46 is low, the NOx catalyst 41 and the SCR
NOx purification is performed with both the catalyst 46 and the catalyst 46.

The slip catalyst 47 oxidizes and purifies unreacted NH3 discharged from the SCR catalyst 46.

The exhaust passage 40 includes an exhaust side bypass passage 48 that bypasses the second turbine 52b, an exhaust side bypass valve 49 that opens and closes the exhaust passage, a wastegate passage 53 that bypasses the first turbine 51b, and a wastegate that opens and closes the wastegate passage 53. A valve 54 is provided. The exhaust side bypass valve 49 and the wastegate valve 54 are switched to a fully closed state and a fully open state by a drive device (not shown), respectively, and are changed to an arbitrary opening degree between them.

The engine system 100 according to the present embodiment includes an EGR device 55 that recirculates a part of the exhaust gas to the intake air. The EGR device 55 connects the portion of the exhaust passage 40 upstream of the upstream end of the exhaust side bypass passage 48 and the portion of the intake passage 20 between the throttle valve 23 and the surge tank 24. A first EGR valve 57 that opens and closes the valve, and an EGR cooler 58 that cools the exhaust gas passing through the EGR passage 56. Further, the EGR device 55 has an EGR cooler bypass passage 59 that bypasses the EGR cooler 58, and a second EGR valve 60 that opens and closes the EGR cooler bypass passage 59.

(2) Control system The control system of the engine system will be described with reference to FIG. The vehicle is mainly provided with a DCU (Dosing Control Unit) 300 for controlling the urea injector 45 and a PCM (Power-train Control Module) 200 for controlling other parts. The PCM200 and the DCU300 are microprocessors composed of a CPU, a ROM, a RAM, an I / F, and the like, respectively. In the present embodiment, the PCM 200 and the DCU 300 constitute the control device according to the claim. Further, the PCM 200 has a NOx catalyst rich purge control unit 201 that implements DeNOx control (NOx catalyst rich purge control), DeSOx control (NOx catalyst regeneration control), and DPF regeneration control (PM filter regeneration control), which will be described later. , NOx catalyst regeneration control unit 202 and PM filter regeneration control unit 203.

Information from various sensors is input to the PCM 200. For example, the PCM 200 detects the amount of intake air, which is the amount of fresh air (air) flowing through the intake passage 20 provided in the vicinity of the rotation speed sensor SN1 for detecting the rotation speed of the crank shaft 7, that is, the engine rotation speed, and the air cleaner 21. Airflow sensor SN2, intake pressure sensor SN3, exhaust passage 40 that detects the pressure of intake air in the surge tank 24 after being supercharged by the turbochargers 51 and 52 provided in the surge tank 24, that is, the boost pressure. Of these, it is electrically connected to the exhaust O2 sensor SN4 or the like that detects the oxygen concentration in the portion between the first turbocharger 51 and the first catalyst 43, and receives input signals from these sensors SN1 to SN4. .. Further, the vehicle is provided with an accelerator opening sensor SN5 for detecting the accelerator opening, which is the opening of the accelerator pedal (not shown) operated by the driver, a vehicle speed sensor SN6 for detecting the vehicle speed, and the like. The detection signals from these sensors SN5 and SN6 are also input to the PCM200. The PCM 200 controls the injector 10 and the like by executing various operations and the like based on the input signals from the sensors (SN1 to SN6 and the like).

The DCU300 and the PCM200 are connected so as to be able to communicate in both directions. The DCU 300 calculates the amount of urea to be injected into the exhaust passage 40 by the urea injector 45 using the calculation result of the PCM 200 and the like, and controls the urea injector 45. The DCU300 also controls the urea delivery pump 45b and the heater 45d.

(2-1) Normal control In the normal control performed during normal operation in which DeNOx control, DeSOx control and DPF regeneration control are not performed, the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 (hereinafter, simply mixed) is performed in order to improve fuel efficiency. The air-fuel ratio of Qi) is made leaner (λ> 1) than the theoretical air-fuel ratio. For example, in normal control, the excess air ratio λ of the air-fuel mixture is about λ = 1.7. Further, in the normal control, the post injection is stopped and only the main injection is performed. Further, in normal control, the operation of the glow plug 11 is stopped. Further, in normal control, the first EGR valve 57, the second EGR valve 60, the intake side bypass valve 26, the exhaust side bypass valve 49, and the wastegate valve 54 are the operating states of the engine body 1, for example, the engine rotation speed and the engine, respectively. The EGR rate and the boost pressure are controlled to be appropriate values according to the load and the like.

(2-2) DeNOx Control Control for releasing (desorbing) NOx stored in the NOx catalyst 41 (hereinafter, appropriately referred to as storage NOx) from the NOx catalyst 41, which is carried out by the NOx catalyst rich purge control unit 201. DeNOx control (NOx catalyst rich purge control) is described.

As described above, in the NOx catalyst 41, in a state where the air-fuel ratio of the exhaust gas and thus the air-fuel ratio of the air-fuel mixture is close to the stoichiometric air-fuel ratio (λ≈1) or in a rich state (λ <1) smaller than the stoichiometric air-fuel ratio. The storage NOx is reduced. Therefore, in order to reduce the storage NOx, it is necessary to reduce the air-fuel ratio of the exhaust gas and the air-fuel ratio of the air-fuel mixture as compared with those during the normal operation (when the normal control is performed).

As one method of reducing the excess air ratio λ of the air-fuel mixture (the excess air ratio λ of the exhaust gas), it is conceivable to reduce the amount of fresh air (air) introduced into the combustion chamber 6. However, if the amount of fresh air is simply reduced, the engine torque may not be obtained properly. In particular, if the amount of fresh air is reduced during acceleration, acceleration may deteriorate. Further, when adjusting the amount of fresh air, it is relatively difficult to accurately control the excess air ratio λ of the air-fuel mixture.

Therefore, in the present embodiment, post-injection is performed in order to reduce the air-fuel ratio of the air-fuel mixture without reducing the amount of fresh air or while suppressing the reduction amount of the amount of fresh air to a small amount. That is, the PCM200 (NOx catalyst rich purge control unit 201) reduces the air-fuel ratio of the exhaust gas by causing the injector 10 to perform post injection in addition to main injection. For example, in DeNOx control, the excess air ratio λ of the air-fuel mixture and the exhaust gas is set to about λ = 0.94 to 1.06.

In the present embodiment, DeNOx control for carrying out post-injection in order to reduce the occluded NOx is carried out only in the first region R1 and the second region R2 shown in FIG. In the first region R1, the engine speed is equal to or higher than the preset first reference speed N1 and the preset second reference speed N2 or less, and the engine load is equal to or higher than the preset first reference load Tq1 and in advance. It is a region of the set second reference load Tq2 or less. The second region R2 is a region where the engine load is higher than that of the first region R1 and the engine load is equal to or higher than the preset third reference load Tq3.

Further, the PCM200 (NOx catalyst rich purge control unit 201) performs active DeNOx control in the first region R1 to perform post-injection at the timing when the post-injected fuel burns in the combustion chamber 6. The injection timing of the post injection is set in advance, for example, in the first half of the expansion stroke, which is set between 30 and 70 ° CA after the compression top dead center. In the present embodiment, in active DeNOx control, the glow plug 11 is energized to heat the air-fuel mixture in order to promote the combustion of the post-injected fuel.

Further, in the active DeNOx control, the opening degree of the first EGR valve 57 and the second EGR valve 60 is smaller (closed side) than in the normal operation while introducing the EGR gas into the combustion chamber 6, that is, the active DeNOx control is tentatively performed. Make it smaller than the opening when it was not done. In the present embodiment, in the active DeNOx control, the first EGR valve 57 is fully closed and the second EGR valve 60 is opened, but the opening degree thereof is smaller than in the normal operation.

This is to reduce the amount of soot produced by this combustion while promoting the combustion of the post-injected fuel. Specifically, when the post-injected fuel is burned, the post-combustion gas generated by the main injection is present in the combustion chamber 6 in addition to the EGR gas. Therefore, if a large amount of EGR gas is introduced, the post-injected fuel and air may be insufficiently mixed and a large amount of soot may be generated. On the other hand, since the post injection is performed at the timing when the temperature and pressure in the combustion chamber 6 are relatively low, the combustion stability tends to deteriorate. Therefore, as described above, in the active DeNOx control, the first EGR valve 57 is closed, the introduction of the low temperature EGR gas that has passed through the EGR cooler 58 is stopped, the second EGR valve 60 is opened, and the high temperature EGR gas is opened. Is introduced to promote the combustion of the post-injected fuel and improve the combustion stability, while making the opening degree of the second EGR valve 60 smaller than that during normal operation to reduce the amount of soot generated.

Specifically, the PCM200 includes the opening degree of the first EGR valve 57 and the opening degree of the second EGR valve 60 during active DeNOx control, and the opening degree of the first EGR valve 57 and the opening degree of the second EGR valve 60 during normal operation. However, it is stored in a map of engine speed, engine load, etc., and the PCM200 (NOx catalyst rich purge control unit 201) extracts a value from the map corresponding to the control being executed and the first EGR valve 57. And the opening degree of the second EGR valve 60 is set. At the same engine speed and engine load, the value of the map for active DeNOx control is set smaller than the value of the map for normal control.

On the other hand, in the second region R2, the PCM200 (NOx catalyst rich purge control unit 201) determines that the post-injected fuel does not burn in the combustion chamber 6 (the latter half of the expansion stroke, for example, 100 ° CA after the compression top dead center). Passive DeNOx control is performed to perform post-injection at ~ 120 ° CA). Further, in the passive DeNOx control, the first EGR valve 57 and the second EGR valve 60 are fully closed in order to prevent the EGR cooler 58 and the like from being blocked by the deposit caused by the post-injected unburned fuel.

As described above, the control content of the DeNOx control is changed between the first region R1 and the second region R2 for the following reason.

In a region where the engine load is low or the engine load is relatively high but the engine speed is low, the temperature of the NOx catalyst 41 tends to be lower than the temperature at which the storage NOx can be reduced as the exhaust temperature is low. Therefore, in the present embodiment, DeNOx control is stopped in this region.

Further, as described above, post-injection is performed in DeNOx control, but if the post-injected fuel is discharged to the exhaust passage 40 as it is without burning, the EGR cooler 58 or the like is generated by the deposit caused by this unburned fuel. There is a risk of blockage. Therefore, it is preferable to burn the post-injected fuel in the combustion chamber 6. However, in a region where the engine load is high or the engine load is relatively low but the engine speed is high, combustion occurs due to the high temperature in the combustion chamber 6 or the short time per crank angle. It is difficult to sufficiently mix the post-injected fuel and air until the gas in the chamber 6 is exhausted, and the post-injected fuel may not be sufficiently burned in the combustion chamber 6. be. Insufficient mixing may increase soot. Therefore, DeNOx control is basically stopped in such a region.

However, in the second region R2 where the engine load is very high, the air-fuel ratio of the air-fuel mixture is kept small even during normal operation due to the large injection amount of the main injection (hereinafter, appropriately referred to as the main injection amount). Be done. Therefore, in the second region R2, the injection amount of the post injection required for reducing the storage NOx (hereinafter, appropriately referred to as the post injection amount) is reduced, and the unburned fuel is discharged to the exhaust passage 40. The influence can be suppressed to a small extent.

Therefore, in the present embodiment, in the first region R1 where neither the engine load nor the engine rotation speed is too low and not too high, active DeNOx control is performed in which the post-injected fuel is burned in the combustion chamber 6. In the second region R2, passive DeNOx control is performed so that the post-injected fuel is not burned in the combustion chamber 6. The second region R2 is a region where the exhaust temperature is sufficiently high and the oxidation catalyst 42 is sufficiently activated. Therefore, the unburned fuel discharged to the exhaust passage 40 is purified by the oxidation catalyst 42. Further, by permitting DeNOx control only in the load range during medium rotation in this way, it is possible to secure the combustion stability of the post injection when the DeNOx control is executed and suppress the deterioration of the exhaust performance.

In the active DeNOx control and the passive DeNOx control, the temperature of the SCR catalyst 46 is lower than the predetermined temperature, the temperature of the NOx catalyst 41 is equal to or higher than the predetermined temperature, and the NOx storage amount is the amount of NOx stored in the NOx catalyst 41, respectively. Is more than the prescribed amount, the implementation is permitted. However, as described above, the active DeNOx control is performed only when the engine body 1 is operated in the first region R1, and the passive DeNOx control is performed when the engine body 1 is operated in the second region R2. It is carried out only in. Further, in the present embodiment, the minimum value of the NOx storage amount permitted to be carried out is set to a value smaller in the passive DeNOx control than in the active DeNOx control.

In the present embodiment, as will be described later, the active DeNOx control is performed before the implementation of the DPF regeneration control when the DPF regeneration control is started in the state where the engine main body 1 is being operated in the first region R1. Instead of this, active DeNOx control may be performed when the NOx storage amount is very high, regardless of whether or not the DPF regeneration control is performed. However, even in this case, active DeNOx control is performed while the engine body 1 is being operated in the first region R1. Also in the above case, when the temperature of the SCR catalyst 46 is raised to a temperature at which the NOx can be purified by the SCR catalyst 46, the NOx can be purified by the SCR catalyst 46, so active DeNOx control is not performed. Further, even in the above case, if the temperature of the NOx catalyst 41 is not raised to a temperature at which the stored NOx can be reduced, the active DeNOx control is not performed.

The temperature of the NOx catalyst 41 is estimated based on, for example, the temperature detected by the temperature sensor provided immediately upstream of the NOx catalyst 41. The temperature of the SCR catalyst 46 is estimated based on, for example, the temperature detected by the temperature sensor provided immediately upstream of the SCR catalyst 46. The NOx storage amount is estimated by, for example, integrating the amount of NOx in the exhaust gas estimated based on the operating state of the engine body 1, the flow rate of the exhaust gas, the temperature, and the like.

(2-3) DPF regeneration control In the present embodiment, the PM filter regeneration control unit 203 is a control for removing the PM collected in the DPF 44 and regenerating the purification capacity of the DPF 44 (PM filter). Playback control) is carried out.

In the DPF regeneration control, the oxidation catalyst 42 reaches a predetermined temperature to enable an oxidation reaction, and the amount of PM collected in the DPF 44 (hereinafter, simply referred to as PM deposition amount) is set in advance to start regeneration. It starts when the amount of deposit is exceeded. The PM deposit amount is calculated from, for example, the front-rear differential pressure of the DPF 44 (difference between the pressure on the upstream side and the pressure on the downstream side of the DPF 44) calculated from the pressure sensors provided on the upstream side and the downstream side of the DPF 44. To. Further, the regeneration start deposit amount is set to a value smaller than the maximum amount of PM deposits that can be collected by DPF44.

As described above, PM collected in DPF44 can be burned off at a high temperature. On the other hand, if HC or the like, that is, unburned fuel is oxidized in the oxidation catalyst 42 contained in the first catalyst 43 provided on the upstream side of the DPF 44, the temperature of the exhaust gas flowing into the DPF 44 and thus the temperature of the DPF 44 are increased. be able to. Furthermore, the temperature of the DPF 44 can be raised by causing the unburned fuel to undergo an oxidation reaction also in the oxidation catalyst layer 44d of the DPF 44.

Therefore, in the present embodiment, as DPF regeneration control, post-injection is performed while making the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio, and air and unburned fuel are made to flow into the oxidation catalyst 42 to make them an oxidation catalyst. Control to oxidize at 42 is carried out. Specifically, in the DPF regeneration control, the post-injected fuel is posted at the timing when it does not burn in the combustion chamber 6 (in the latter half of the expansion stroke, for example, 100 ° CA to 120 ° CA after the compression top dead center). Carry out the injection. For example, in the DPF regeneration control, the excess air ratio λ of the air-fuel mixture and the exhaust gas is set to about λ = 1.2 to 1.4.

Further, in the DPF regeneration control, the first EGR valve 57 and the second EGR valve 60 are fully closed in order to prevent unburned fuel from flowing into the EGR passage 56 and the EGR cooler 58 and blocking them. Further, in the DPF regeneration control, since it is not necessary to burn the post injection, the energization to the glow plug 11 is stopped.

(2-4) DeSOx control DeSOx, which is a control carried out by the NOx catalyst regeneration control unit 202 to reduce and remove SOx (sulfur component, hereinafter appropriately referred to as occluded SOx) stored in the NOx catalyst 41. The control (NOx catalyst regeneration control) will be described below.

As described above, in the NOx catalyst 41, the occluded SOx is reduced in a state where the air-fuel ratio of the exhaust is close to the stoichiometric air-fuel ratio (λ≈1) or in a rich state (λ <1) smaller than the stoichiometric air-fuel ratio. .. Along with this, even with DeSOx control, in addition to the main injection, in order to make the air-fuel ratio of the air-fuel mixture close to the stoichiometric air-fuel ratio (λ≈1) or richer than the stoichiometric air-fuel ratio (λ <1). Perform post injection.

However, since SOx has a stronger binding force than NOx, in order to reduce the occluded SOx, the temperature of the NOx catalyst 41 and the temperature of the exhaust gas passing through the NOx catalyst 41 are set to a higher temperature (about 600 ° C.) than during DeNOx control. There is a need to. On the other hand, as described above, if the unburned fuel is oxidized in the oxidation catalyst 42, the temperature of the exhaust gas passing through the first catalyst 43 and the NOx catalyst 41 can be increased.

Therefore, in the present embodiment, as DeSOx control, post-injection is performed in the same manner as in DeNOx control to make the air-fuel ratio of the exhaust richer than in normal operation and to be near or smaller than the theoretical air-fuel ratio (hereinafter, as appropriate, simply). The rich step (to make it rich) and post-injection while making the air-fuel ratio of the exhaust leaner than the theoretical air-fuel ratio (hereinafter, simply referred to as lean) are performed to feed air and unburned fuel to the oxidation catalyst 42. A plurality of rich lean cycles are performed, including a lean step of feeding and oxidizing them with the oxidation catalyst 42.

In the rich step, similar to the active DeNOx control, the post-injected fuel is post-injected at the timing of combustion in the combustion chamber 6 (the first half of the expansion stroke, for example, 30 to 70 ° CA after the compression top dead center). To carry out.

Specifically, the post injection timing (additional injection timing) in the rich step is set to the initial post injection timing on the most advanced angle side in the first rich lean cycle, and the post injection timing is set in the subsequent rich lean cycle. After being set to the retard side, it is finally maintained constant at the final post injection timing. For example, the initial post injection timing is set to 40 ° CA after compression top dead center, the final post injection timing is set to 70 ° CA after compression top dead center, and two rich lean cycles are set during this period. If so, the post-injection timing during this period is set to 50 ° CA and 60 ° CA after the compression top dead center so as to be gradually delayed from the initial post-injection timing to the final post-injection timing, respectively.

Then, in the rich step, the air-fuel ratio of the air-fuel mixture and the exhaust is set to be close to the stoichiometric air-fuel ratio by setting the excess air ratio λ of the air-fuel mixture and the exhaust to about 1.0. For example, in the rich step, the excess air ratio λ of the air-fuel mixture and the exhaust gas is set to about λ = 0.94 to 1.06.

Further, in the rich step, as in the case of active DeNOx control, the first EGR valve 57 is fully closed while the second EGR valve is fully closed in order to improve the stability of this combustion while suppressing the soot associated with the combustion of the post-injected fuel. The valve 60 is opened and the opening degree of the second EGR valve 60 is made smaller than in normal operation. Further, the PCM200 (NOx catalyst regeneration control unit 202) sets the throttle valve 23, the exhaust side bypass valve 49 and the wastegate valve 54 so that the air-fuel ratio of the air-fuel mixture is low, respectively, when the intake air amount is smaller than that during normal operation. Is also controlled to decrease.

On the other hand, in the lean step, post-injection is performed at a timing when the post-injected fuel does not burn in the combustion chamber 6 (in the latter half of the expansion stroke, for example, 100 ° CA to 120 ° CA after the compression top dead center). .. Then, the air-fuel ratio of the air-fuel mixture and the exhaust is made leaner than the stoichiometric air-fuel ratio by setting the excess air ratio λ of the air-fuel mixture and the exhaust to 1 or more. For example, in the lean step, the excess air ratio λ of the air-fuel mixture and the exhaust gas is set to about λ = 1.2 to 1.4. Further, in the lean step, the first EGR valve 57 and the second EGR valve 60 are fully closed in order to prevent the EGR cooler and the like from being blocked by the deposit caused by the unburned fuel.

As described above, in DeSOx control, it is necessary to make the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 lean. Therefore, it is difficult to perform DeSOx control in the second region R2 where the engine load is high and the air-fuel ratio of the air-fuel mixture cannot be sufficiently lean. On the other hand, as described above, the control for burning the post injection is preferably performed in the first region R1. Therefore, in the present embodiment, DeSOx control is performed only when the engine main body 1 is operated in the first region (specific operation region) R1.

The PCM200 calculates the fuel injection amount corresponding to the required torque calculated from the accelerator opening and the like as the main injection amount. Next, the PCM200 has an exhaust oxygen concentration detected by the exhaust O2 sensor SN4 provided on the upstream side of the first catalyst 43 (NOx catalyst 41), an intake air amount detected by the airflow sensor SN2, and a combustion chamber. The oxygen concentration (oxygen concentration before combustion) in the combustion chamber 6 is estimated based on the amount of EGR gas introduced into 6. Then, the basic value of the post injection amount is calculated based on the estimated oxygen concentration in the combustion chamber 6, that is, the oxygen concentration of the intake air. The amount of EGR gas is estimated from the operating state of the engine, the front-rear differential pressure of the EGR valves 57 and 60, and the like. Next, the PCM 200 feedback-corrects this basic post-injection amount based on the oxygen concentration of the exhaust gas detected by the exhaust O2 sensor SN4, the amount of the main injection, and the like. That is, the PCM 200 feedback-controls the post injection amount so that the air-fuel ratio of the exhaust corresponding to the detected oxygen concentration of the exhaust becomes the target air-fuel ratio, thereby making the air-fuel ratio of the exhaust an appropriate value. As described above, in the present embodiment, the excess air ratio λ of the exhaust gas is changed by changing the injection amount of the post injection.

Here, as described above, if the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is leaner than the stoichiometric air-fuel ratio and the post-injection is performed without burning the fuel, PM can be burned and removed. , PM combustion can be removed when the lean step is performed. Then, in the present embodiment, the air-fuel ratio of the air-fuel mixture in the lean step is set to the same value as the air-fuel ratio in the DPF regeneration control as described above so that the combustion of PM can be removed when the lean step is performed. (So that the air-fuel ratio λ is λ = 1.2 to 1.4).

(2-5) Injection Control of Urea Water Next, the injection control of the urea injector 45 will be described. Hereinafter, the amount of urea injected from the urea injector 45 is appropriately referred to as a urea injection amount. As described above, the injection control of the urea injector 45 is carried out by the DCU 300 while obtaining the information from the PCM 200.

For NOx reduction, that is, DeNOx control or DeSOx control, NH ₃ is released from the NOx catalyst 41 and introduced into the SCR catalyst 46. Therefore, if the urea injection amount when DeNOx control or DeSOx control is performed is the same as the urea injection amount when these controls are not performed, the amount of NH ₃ supplied to the SCR catalyst 46 becomes excessive. There is a risk that NH ₃ will slip on the downstream side of the SCR catalyst 46. Therefore, when DeNOx is controlled and when DeSOx is controlled, the urea injection amount is smaller than when these controls are not performed.

However, if the urea injection amount during DeNOx control and DeSOx control is controlled to a predetermined amount that is smaller than that when these controls are simply not performed regardless of the operating conditions, the urea injection amount is supplied to the SCR catalyst 46. It has been found that the amount of NH ₃ may be excessive or insufficient, and a large amount of NH ₃ may slip through the downstream side of the SCR catalyst 46 or NOx may not be properly purified in the SCR catalyst 46. Therefore, in the present embodiment, the DCU300 estimates the amount of NH _{3 released from the NOx catalyst 41 for DeNOx control and DeSOx control, and the larger the estimated NH 3 amount} , the smaller the urea injection amount. The injector 45 is controlled.

The procedure for estimating the amount of _NH3 released from the NOx catalyst 41 will be described below.

In the present embodiment, the DCU 300 is functionally provided with a first estimation unit 301 and a second estimation unit 302.

The first estimation unit 301 is NH ₃ generated by binding NOx stored in the NOx catalyst 41 with H or the like as a reducing agent during DeNOx control and DeSOx control (hereinafter, appropriately, the first NH). ₃ ) is estimated.

In the second estimation unit 302, NOx (hereinafter, appropriately, RawNOx) generated in the engine body 1 and flowing into the NOx catalyst 41 and H or the like as a reducing agent are combined by the NOx catalyst 41 during DeNOx control and DeSOx control. The amount of NH ₃ produced by this (hereinafter, appropriately referred to as the second NH ₃ ) is estimated.

The first estimation unit 301 first estimates the current NOx storage amount of the NOx catalyst 41. Next, the first estimation unit 301 multiplies the estimated value of the NOx storage amount by the first temperature coefficient β1, the first flow coefficient β2, the first A / F coefficient β3, and the first thermal deterioration coefficient β4, respectively. Then, the amount of the first NH ₃ is calculated.

The first temperature coefficient β1 is set according to the temperature of the NOx catalyst 41. Specifically, the temperature coefficient β1 is set to a smaller value as the temperature of the NOx catalyst 41 increases. That is, it is known that the higher the temperature of the NOx catalyst 41, the more the reaction in which the NOx occluded in the NOx catalyst 41 is converted into HN ₃ is promoted, and the higher the temperature of the NOx catalyst 41, the first NH ₃ The first temperature coefficient β1 is set so that the amount is calculated to be large.

The first flow coefficient β2 is set according to the exhaust flow rate. Specifically, the first flow coefficient β2 is set to a larger value as the exhaust flow rate increases. That is, as the exhaust flow rate increases _, the amount of the reducing material flowing into the NOx catalyst 41 increases and the amount of HN ₃ released from the NOx catalyst 41 increases. The first flow coefficient β2 is set so that the amount is calculated to be large.

The first A / F coefficient β3 is set according to the air-fuel ratio (A / F) of the exhaust gas. Specifically, the A / F coefficient β3 is set to a larger value as the air-fuel ratio of the exhaust gas is smaller (richer). That is, the richer the air-fuel ratio of the exhaust gas, the larger the amount of the reducing material flowing into the NOx catalyst 41 and the larger the amount of NH ₃ released from the NOx catalyst 41. The first A / F coefficient β3 is set so that the first _NH3 amount is calculated to be larger.

The first thermal deterioration coefficient β4 is a coefficient set according to the degree of deterioration of the NOx catalyst 41. The PCM200 estimates the degree of deterioration of the NOx catalyst 41 based on the traveling time of the vehicle, the number of times DeNOx control is performed, and the like, and the thermal deterioration coefficient β4 increases as the estimated degree of deterioration increases (deterioration progresses). Approximately), it is considered to be a large value. That is, it is known that the higher the degree of deterioration of the NOx catalyst 41 is, the more the reaction in which the NOx occluded in the NOx catalyst 41 is converted into NH ₃ is promoted, and the higher the degree of deterioration is correspondingly. The thermal deterioration coefficient β4 is set so that the amount of the first NH ₃ is calculated to be large.

The second estimation unit 302 first estimates the amount (flow rate) of RawNOx discharged from the engine body 1. In the present embodiment, the flow rate of RawNOx is estimated from the exhaust flow rate, the excess air ratio λ of the air-fuel mixture, and the like. Next, the second estimation unit 302 calculates the amount of the second NH ₃ by multiplying the estimated value of the storage NOx amount by the second flow coefficient β22 and the second A / F coefficient β23, respectively.

The second flow coefficient β22 is set according to the exhaust flow rate. Specifically, the second flow coefficient β22, like the first flow coefficient β2, has a larger value as the exhaust flow rate increases. However, unlike NOx stored in the NOx catalyst 41, the effect of the temperature of the NOx catalyst 41 on RawNOx becomes equivalent when the temperature of the NOx catalyst 41 becomes a predetermined temperature or higher, and the second flow rate coefficient β22 is the NOx catalyst 41. When the temperature of is above a predetermined temperature, it is a constant value.

The second A / F coefficient β23 is set according to the air-fuel ratio (A / F) of the exhaust gas. Specifically, the second A / F coefficient β23 is set to a larger value as the air-fuel ratio of the exhaust gas is smaller (rich), similarly to the second A / F coefficient β3. However, unlike NOx stored in the NOx catalyst 41, the effect of the air-fuel ratio of the exhaust gas on RawNOx is equivalent when the air-fuel ratio of the exhaust is equal to or less than a predetermined value, and the second A / F coefficient β23 is that of the exhaust gas. When the air-fuel ratio is equal to or higher than a predetermined value, it is a constant value.

In this way, in this embodiment, the amount of the first NH ₃ and the amount of the second NH ₃ are estimated.
Then, the DCU300 sets the total amount of the first NH ₃ and the second NH ₃ to D.
It is calculated as NH ₃ released from the NOx catalyst 41 during eNOx control and DeSOx control.

The DCU300 estimates the amount of NH ₃ released from the NOx catalyst 41 during DeNOx control and with DeSOx control, subtracts this from the urea injection amount when these controls are not performed, and finally the value is obtained. The urea injector 45 is controlled as a urea injection amount.

(2-6) Control Flow Next, the flow of active DeNOx control, DPF regeneration control, and DeSOx control will be described with reference to the flowchart of FIG.

In step S1, the PCM 200 determines whether or not the DPF regeneration permission flag is 1. If this determination is NO, the process proceeds to step S20, the PCM200 performs normal control, and then ends the process (returns to step S1). On the other hand, if the determination in step S1 is YES, the process proceeds to step S2. The DPF regeneration permission flag is a flag that becomes 1 when the regeneration of the DPF 44 is permitted and becomes 0 when the regeneration of the DPF is prohibited. In the present embodiment, the DPF regeneration permission flag is set to 1 when the PM accumulation amount of the DPF44 is equal to or greater than the regeneration start accumulation amount, and is set to 0 when the PM accumulation amount is equal to or less than the regeneration end accumulation amount. The regeneration end deposit amount is a PM deposit amount reduced to such an extent that it is no longer necessary to remove PM from the DPF44, and is set to a value near 0, for example.

In step S2, the PCM 200 determines whether or not the engine body 1 is being operated in the first region R1. If this determination is NO, the process proceeds to step S20, the PCM200 performs normal control, and then ends the process (returns to step S1). On the other hand, if the determination in step S2 is YES, the process proceeds to step S3.

In step S3, the PCM 200 (NOx catalyst rich purge control unit 201) carries out active DeNOx control.

After step S3, the process proceeds to step S4. In step S4, the PCM200 (NOx catalyst rich purge control unit 201) determines whether or not the storage NOx amount is equal to or less than the preset DeNOx end determination amount, that is, the storage NOx amount is DeNOx as the active DeNOx control is performed. It is determined whether or not the amount has dropped to the end determination amount or less. If this determination is NO, the process returns to step S2. On the other hand, if this determination is YES, the process proceeds to step S5. That is, the PCM200 (NOx catalyst rich purge control unit 201) continues the active DeNOx control until the storage NOx amount is equal to or less than the DeNOx end determination amount and the determination in step S4 is YES. The DeNOx end determination amount is set to a value near 0, for example.

During the DeNOx control, the DCU 300 estimates the amount of NH ₃ released from the NOx catalyst 41, and controls the urea injector 45 so that the larger the estimated amount, the smaller the urea injection amount.

Then, when the determination in step S4 is YES, the PCM200 (NOx catalyst rich purge control unit 201) proceeds to step S5. In step S5, the PCM 200 stops the active DeNOx control and implements (starts) the DPF regeneration control. Following step S5, the process proceeds to step S6.

In step S6, the PCM 200 (PM filter regeneration control unit 203) determines whether or not the PM deposit amount is equal to or less than the preset DeSOx start deposit amount (reference amount). If this determination is NO, the PCM 200 (PM filter reproduction control unit 203) returns to step S5. That is, the PCM200 (PM filter regeneration control unit 203) continues the DPF regeneration control until the PM deposition amount drops below the DeSOx start deposition amount. The DeSOx start deposit amount is set to an amount of 10% or more and 20% or less of the regeneration start deposit amount, and in this embodiment, it is set to 10% of the regeneration start deposit amount.

Then, when the PM deposit amount decreases to the DeSOx start deposit amount or less and the determination in step S6 becomes YES, the PCM 200 proceeds to step S7. In step S7, the PCM 200 determines whether or not the engine body 1 is being operated in the first region R1. If this determination is NO, the process proceeds to step S20, the PCM200 performs normal control, and then ends the process (returns to step S1).

On the other hand, if the determination in step S7 is YES, the process proceeds to step S100, and the PCM200 (NOx catalyst regeneration control unit 202) starts DeSOx control. That is, when the PM deposition amount drops below the DeSOx start deposition amount, the control is switched to DeSOx control. Exposure to is suppressed.

Here, the inventor of the present application has found that when the NOx catalyst 41 is exposed to the DPF regeneration condition for a long time, it becomes difficult to desorb the occluded SOx even by the DeSOx control. It is considered that the reason why it is difficult to desorb the occlusion SOx even by the DeSOx control is as follows. As schematically shown in FIG. 7, the occluded SOx is occluded on the NOx catalyst 41, for example, in the occluded agent 41b. As shown in FIG. 7A, when the NOx catalyst 41 is exposed to the DPF regeneration condition, the occlusion agent 41b tends to aggregate.

Further, when the NOx catalyst 41 is exposed to a higher temperature or a longer time under the DPF regeneration conditions, the aggregation of the occlusal agent 41b is further promoted as shown in FIG. 7 (b), and the occlusal SOx is less likely to react with the catalyst metal 41a. turn into. Since the regeneration of the DPF 44 generally takes a long time, the NOx catalyst 41 is easily exposed to the DPF regeneration conditions for a long time. As a result, the occluded SOx is difficult to be desorbed from the NOx catalyst 41 even by the DeSOx control.

On the other hand, in the present embodiment, as described above, when the PM deposition amount drops below the DeSOx start deposition amount, the DeSOx control is started, so that the NOx catalyst 41 is exposed to the DPF regeneration condition for a long time. It is suppressed. As a result, the aggregation of the occlusion agent 41b in the NOx catalyst 41 is suppressed, so that SOx can be easily desorbed from the NOx catalyst 41 by the subsequent DeSOx control.

DeSOx control according to step S100 will be described with reference to FIG. The PCM200 (NOx catalyst regeneration control unit 202) determines in step S101 whether or not the DeSOx cycle number n is 1. Here, the DeSOx cycle number n indicates the number of times the next rich lean cycle is executed in the DeSOx control. That is, if the DeSOx cycle number n is 1, it means that the DPF regeneration control is switched to the DeSOx control and the cycle is the first rich lean cycle.

If the determination in step S101 is YES, that is, the first rich lean cycle, the PCM 200 (NOx catalyst regeneration control unit 202) proceeds to step S103 and sets the post injection timing of the rich step to the initial post injection timing. In the present embodiment, the initial post-injection timing is set to 40 ° CA after the compression top dead center, and this post-injection timing is set to the most advanced side in all rich lean cycles.

If the determination in step S101 is NO, the PCM200 (NOx catalyst regeneration control unit 202) proceeds to step S102 and determines whether or not the DeSOx cycle number n is less than the predetermined cycle number n0. Here, the predetermined number of cycles n0 means the number of cycles in which the post injection timing in the rich step is set to the advance angle side from the final post injection timing.

If the determination in step S102 is YES, the post injection timing in the rich step is set to the retard side from the post injection timing in the rich step of the rich lean cycle one time before. If the determination in step S102 is NO, the post injection timing in the rich step is set to the final post injection timing.

In this embodiment, the predetermined number of cycles n0 is set to 3. That is, in the DeSOx control, the post injection timing in the rich step is set to the retard side stepwise until the third rich lean cycle, and is maintained constant at the final post injection timing after the fourth injection. For example, the post-injection timing in the rich step is initially set to 40 ° CA after compression top dead center, which is the most advanced injection timing, and then after compression top dead center as the number of rich lean cycles increases. It gradually increases to 50 ° CA and 60 ° CA, and is maintained constant at 70 ° CA after the compression top dead center after the fourth time.

After steps S103 to S105, the process proceeds to step S106. In step S106, the rich step is executed for a predetermined time, and then the process proceeds to step S107. In step S107, a lean step is performed for a predetermined time, and then the process proceeds to step S108. In step S108, the number of DeSOx cycles n is counted up to n + 1, that is, the number of DeSOx cycles is increased by one.

After step S108, the process proceeds to step S8. As described above, in DeSOx control, a plurality of rich lean cycles including a rich step and a lean step are carried out, the occluded SOx is desorbed in the rich step, and the temperature of the NOx catalyst is maintained high in the lean step. PM is burned off from DPF44. That is, the occluded SOx decreases in the rich step, and the PM decreases in the lean step.

Further, during the implementation of DeSOx control, the DCU 300 estimates the amount of NH ₃ released from the NOx catalyst 41, and controls the urea injector 45 so that the larger the estimated amount, the smaller the urea injection amount.

Here, in the present embodiment, during DeSOx control, the post injection timing of the rich step in the first rich lean cycle is set to the initial post injection timing, which is the injection timing on the most advanced side, and as a result, the post injection is performed. Since the fuel is easily burned in the cylinder and the exhaust temperature rises, the amount of NH ₃ released from the NOx catalyst 41 tends to increase. In the subsequent rich lean cycle, the post-injection timing of the rich step is gradually delayed, so that the amount of NH3 released from the NOx catalyst 41 is gradually reduced. Therefore, the DCU 300 controls the urea injector 45 so that the urea injection amount decreases as the post injection timing in the rich step is set to the advance angle side.

In step S9, it is determined whether or not the PM deposit amount is equal to or less than the preset regeneration end deposit amount. If this determination is NO, the PCM200 (NOx catalyst regeneration control unit 202) returns to step S7. That is, the PCM200 (NOx catalyst regeneration control unit 202) continues DeSOx control until the PM deposition amount drops below the regeneration end deposition amount, that is, repeats the rich lean cycle. On the other hand, if this determination is YES, the PCM200 (NOx catalyst regeneration control unit 202) proceeds to step S20, and the PCM200 performs normal control and then ends the process.

FIG. 9 is a diagram schematically showing the time change of each parameter when the above control is performed.

When the DPF regeneration permission flag changes from 0 to 1 at time t1, active DeNOx control is executed. Specifically, the air-fuel ratio of the exhaust is made richer than the stoichiometric air-fuel ratio, and post-injection is performed. At this time, the injection timing of the post injection is relatively advanced (first half of the expansion stroke) so that the post-injected fuel burns in the combustion chamber 6. Further, the first EGR valve 57 is fully closed, and the opening degree of the second EGR valve 60 is smaller than the opening degree during normal operation, that is, immediately before time t1 (to the closed side), but to the open side rather than the fully closed side. Will be done.

With the implementation of active DeNOx control, the NOx storage amount gradually decreases after time t1. Further, as the post-injected fuel burns in the combustion chamber 6 and the temperature of the exhaust gas increases, the temperature of the DPF 44 gradually increases after the time t1. Although not shown, the temperature of the oxidation catalyst 42 also gradually increases.

Further, although not shown, the urea injector 45 releases NH ₃ from the NOx catalyst 41 by implementing DeNOx control, and the urea injection amount is smaller than that in the case where DeNOx control is not performed. Be controlled.

When the amount of occluded NOx becomes equal to or less than the amount of DeNOx end determination at time t2, the active DeN
The Ox control is stopped, and then the DPF regeneration control is started (PM filter regeneration step).

Specifically, at time t2, the air-fuel ratio of the exhaust gas is switched to leaner than the stoichiometric air-fuel ratio. Further, the post injection is carried out after the time t2, but the injection timing of this post injection is set to the timing on the retard side (the latter half of the expansion stroke), and the post-injected fuel is exhausted without being burned in the combustion chamber 6. It is discharged to the passage 40. Further, the second EGR valve 60 is fully closed in addition to the first EGR valve 57.

By this control, the temperature of the exhaust gas rises due to the oxidation reaction in the oxidation catalyst 42 and the oxidation catalyst layer 44d, which further increases the temperature of the DPF 44.

In the illustrated example, the temperature of DPF44 has not yet reached the temperature at which PM can be burned at time t2, and when this temperature is reached at time t3, the PM deposition amount begins to decrease. Further, in the illustrated example, when the temperature of the DPF 44 reaches a temperature at which PM can be burned, the post injection amount is reduced.

When the PM deposition amount drops below the DeSOx start deposit amount at time t4, that is, 10% lower than the regeneration start deposit amount, DeSOx control is started (NOx catalyst regeneration step). Specifically, the rich step is first carried out at time t4, and the post injection is carried out in which the injection timing is relatively advanced and the injected fuel is set to burn in the combustion chamber 6. At the same time, the air-fuel ratio of the exhaust is made richer than the theoretical air-fuel ratio. Further, the second EGR valve 60 is opened. However, similarly to the active DeNOx control, the opening degree of the second EGR valve 60 is made smaller (closed side) than the opening degree during normal operation, that is, the opening degree immediately before time t1 even in the rich step. In the present embodiment, the opening degree of the second EGR valve 60 is substantially the same between the rich step and the active DeNOx control. The first EGR valve 57 is kept fully closed.

Next, a lean step is carried out at time t5, and post-injection is carried out in which the injection timing is relatively retarded and the injected fuel is set so as not to burn in the combustion chamber 6. The air-fuel ratio of the exhaust is leaner than the theoretical air-fuel ratio. Further, the second EGR valve 60 is fully closed again. Also at this time, the first EGR valve 57 is kept fully closed.

Then, the rich step and the lean step are repeated, and as a result, the amount of occluded SOx decreases after the time t4. Specifically, the amount of occluded SOx decreases with the implementation of the rich step. In addition, the amount of PM deposited will decrease due to the implementation of the lean step.

At this time, in the first rich lean cycle, the post injection timing in the rich step is set to the initial post injection timing with the most advanced angle. In the subsequent rich lean cycle, the post injection timing in the rich step is set to the retard side stepwise, and is set to be constant at the final post injection timing in the fourth and subsequent rich lean cycles having a predetermined number of cycles n0. ..

Although not shown, the urea injector 45 releases NH ₃ from the NOx catalyst 41 by implementing DeSOx control, and the urea injection amount is smaller than that when DeSOx control is not performed. Be controlled.

Here, in the present embodiment, at the time of DeSOx control, the post injection timing of the rich step in the first rich lean cycle is set to the initial post injection timing which is the most advanced side, and as a result, the fuel by the post injection is used in the cylinder. Since it is easy to burn inside and the exhaust temperature rises, the amount of NH ₃ released from the NOx catalyst 41 tends to increase. In the subsequent rich lean cycle, the post-injection timing of the rich step is gradually delayed, so that the amount of NH ₃ released from the NOx catalyst 41 is gradually reduced. Therefore, the amount of NH ₃ released from the NOx catalyst 41 decreases stepwise as the number of rich lean cycles progresses, so that the amount of urea injected by the urea injector 45 increases stepwise.

Then, at time t6, the SOx occlusion amount decreases to an amount that no longer requires DeSOx control (for example, near zero), but the PM accumulation amount is still larger than the regeneration end accumulation amount, so the DeSOx control is continued.

After that, as the PM deposit amount decreases to the regeneration end deposit amount or less at time t7, the DeSOx control is terminated and the control is switched to the normal control. Specifically, the post injection amount is set to 0 and the post injection is stopped. Further, the first EGR valve 57 is opened, and the opening degree of the second EGR valve 60 is made larger (open side) than during the DeNOx control and the DeSOx control rich step. Further, the DPF regeneration flag is set to 0.

In the present embodiment, in the DeSOx control, the occluded SOx is reduced from the NOx catalyst in the rich step, and PM is burned and removed from the DPF44 in the lean step. In this case, the PM deposition amount is reduced to the regeneration end deposition amount. The capacities of the NOx catalyst 41 and the DPF 44 are appropriately set so that the S poisoning is eliminated before. Further, the NOx catalyst 41 detects the amount of NOx slipping from the NOx catalyst 41 by a NOx sensor provided on the upstream side of the SCR catalyst 46, and the NOx catalyst 41 is poisoned by S based on the amount of NOx slipping through. It is configured so that it can be indirectly detected whether the NOx storage amount has decreased to a problematic state.

(3) Action, etc. As described above, in the first rich lean cycle, the post injection timing of the rich step is set to the initial post injection timing on the most advanced angle side in the present embodiment. Here, the amount of SOx desorbed from the NOx catalyst 41 by DeSOx control can be expected to increase as the amount of SOx adsorbed on the NOx catalyst 41 increases. Further, in the DeSOx control, by setting the post injection timing of the rich step to the advance angle side, the fuel produced by the post injection can be easily burned in the cylinder, which raises the exhaust temperature. A large amount of SOx desorption can be expected.

That is, at the start of DeSOx control in which the amount of SOx occluded in the NOx catalyst 41 is the largest and therefore the amount of SOx desorption can be expected to be large, the post injection timing of the rich step is set to the initial post injection timing which is the most advanced side. By doing so, the amount of SOx desorbed from the NOx catalyst 41 can be efficiently increased.

Further, by delaying the post injection timing of the rich step stepwise, the post injection timing of the rich step in DeSOx control is not set to the advance angle side for a long period of time, so that the post injection timing is set to the advance angle side. The increase in smoke due to this is suppressed.

Further, since the post-injection timing of the rich step is maintained constant at the final post-injection timing after the predetermined number of cycles n0, in the initial stage of DeSOx control in which the amount of SOx deposited in the NOx catalyst 41 is relatively large. By setting the post injection timing of the rich step to the advance angle side, the desorption of SOx from the NOx catalyst 41 is promoted. On the other hand, since the amount of SOx deposited decreases relatively after the initial stage of DeSOx control, the increase in smoke is suppressed by keeping the post injection timing of the rich step constant at the final post injection timing later than the initial stage. Will be done. That is, the increase in smoke is suppressed while efficiently desorbing SOx from the NOx catalyst 41.

Further, in the DeSOx control, the urea injector 45 reduces the urea injection amount as the post injection timing of the rich step is set to the advance side, that is, as the amount of NH ₃ released from the NOx catalyst 41 increases. Since it is controlled, it is suppressed that NH ₃ is excessively supplied to the SCR catalyst 46 and slips through the slip catalyst 47.

Since the DeSOx control is started when the PM deposition amount drops below the DeSOx start deposition amount, that is, at a relatively early timing after the start of the DPF regeneration control, the time during which the NOx catalyst 41 is exposed to the DPF regeneration condition is limited. To. As a result, the aggregation of the occlusion agent 41b in the NOx catalyst 41 is suppressed, so that it is suppressed that SOx does not easily react with the catalyst metal 41a. Therefore, in the NOx catalyst regeneration control, the occluded SOx can be easily desorbed from the NOx catalyst 41, and the NOx catalyst 41 can be efficiently recovered from S poisoning.

Further, since the DeSOx control is performed after the PM deposited on the DPF44 is removed to some extent, the temperature of the DPF44 in the DeSOx control is suppressed from being excessively raised.

This is because, in the rich state in the NOx catalyst regeneration control, the unburned fuel tends to adhere to the DPF44, and the unburned fuel reacts with the oxygen supplied in the lean state, and the temperature of the DPF44 tends to rise. At this time, if a large amount of PM is deposited on the DPF 44, the combustion of the PM is promoted in a chain reaction as the temperature of the DPF 44 rises, which may cause the temperature of the DPF 44 to rise excessively. However, according to the present invention, since the DeSOx control is performed after the PM deposit amount in the DPF44 is reduced to some extent, the DeSOx control suppresses the excessive increase in the temperature of the DPPF44.

Further, during the active DeNOx control, the post-injected fuel is burned in the combustion chamber 6, and the DPF regeneration control is continuously performed after the active DeNOx control.

Therefore, the temperature of the exhaust gas can be raised during active DeNOx control, thereby activating the oxidation catalyst 42 and raising the temperature of the DPF 44, and the PM collected in the DPF 44 can be further increased during the subsequent DPF regeneration control. It can be burned from an early timing. Therefore, it is possible to shorten the time from the start of the DPF regeneration control until the temperature of the DPF 44 reaches the temperature at which the PM burns, as compared with the case where the active DeNOx control and the DPF regeneration control are performed at different timings. Therefore, the amount of unburned fuel that must be supplied to the oxidation catalyst 42 due to this temperature rise can be suppressed to a small amount, and the fuel efficiency can be improved.

Further, since the NOx occluded in the NOx catalyst 41 is reduced before the implementation of the DPF regeneration control, even if the temperature of the NOx catalyst 41 rises due to the implementation of the DPF regeneration control, the NOx catalyst accompanies this temperature rise. Since it is possible to prevent a large amount of NOx from leaving 41, the exhaust performance can be improved.

Further, in the present embodiment, since the post-injected fuel is configured to burn in the combustion chamber 6 during active DeNOx control, the post-injection is performed on the retard side where the fuel does not burn in the combustion chamber 6. Compared to the case where the post-injected fuel leaks from the combustion chamber 6 to the crankcase side, the amount mixed in the engine oil can be suppressed to a small amount, and the fuel is exhausted by the deposit caused by the unburned fuel. It is possible to prevent various devices provided in the passage from being blocked.

Further, in the present embodiment, when the PM deposition amount is reduced to the DeSOx start deposition amount or less after the DPF regeneration control is started, the DeSOx control including the lean step is started. Therefore, by implementing DeSOx control, PM of DPF44 can be burned and removed while reducing and removing SOx occluded in the NOx catalyst, and the purification performance of NOx catalyst 41 and DPF44 is efficiently returned to a high state. be able to. That is, compared to the case where the DPF regeneration control and the DeSOx control are individually performed, the time required for the regeneration control of the DPF44 can be shortened, and the amount of fuel required for combustion of the PM of the DPF44 can be suppressed to a small amount to achieve fuel efficiency. Can be further enhanced.

Further, in the present embodiment, when the DeSOx control rich step is performed, the opening degree of the EGR valves 57 and 60 is set to the opening side on the closed side as compared with the normal operation (that is, when DeSOx control is not performed). In addition to controlling, the EGR valve 60 is controlled to be fully closed (that is, the opening on the closed side further than when the DeSOx control is performed) in the DPF regeneration control.

Therefore, when the DPF regeneration control is performed, it is possible to prevent the various devices provided in the exhaust passage 40 such as the EGR cooler 58 from being blocked by the deposit caused by the unburned fuel discharged in the exhaust passage 40, and the DeSOx control. During the implementation of the rich step, the amount of soot produced by the combustion of the post-injected fuel can be suppressed while improving the combustion stability of the post-injected fuel.

Similarly, in the present embodiment, when the active DeNOx control is performed, the opening degree of the EGR valves 57 and 60 is set to the opening on the closed side as compared with the normal operation (that is, when the active DeNOx control is not performed). I'm in control. Therefore, when the DeNOx control is performed, the amount of soot generated by the combustion of the post-injected fuel can be suppressed to a small amount while improving the combustion stability of the post-injected fuel.

Further, in the present embodiment, since DeSOx control is performed every time the DPF regeneration control is performed, it is easy to maintain the SOx deposition amount in a small state, SOx is suppressed from being taken in by aggregation, and high NOx purification efficiency is achieved. Can be secured.

(4) Modification Example In addition to the above embodiment, the post injection timing of the rich step in DeSOx control may be adjusted based on the adsorption amount of NH ₃ in the SCR catalyst 46. Specifically, when the amount of NH ₃ adsorbed by the SCR catalyst 46 is large, the post injection timing in the rich step during DeSOx control is advanced so as to suppress the amount of NH ₃ released from the NOx catalyst 41. The degree of setting on the side may be suppressed.

That is, as shown in FIG. 10, the larger the adsorption amount of NH ₃ in the SCR catalyst 46, the more the degree of setting the post injection timing in the rich step during DeSOx control to the advance angle side may be suppressed, and the predetermined number of cycles n0. After that, it may be maintained constant at the final post injection timing. Thereby, SOx can be desorbed while suppressing the amount of NH ₃ released from the NOx catalyst 41 in the rich step, and PM can be burned in the lean step to be removed from the regeneration 44 of the DPF.

Here, the adsorption amount of NH ₃ in the SCR catalyst 46 is obtained by adding the amount of NOx released from the NOx catalyst 41 calculated by the above estimation to the amount of urea injected to the SCR catalyst 46 by the injector 45. From now on, the consumption of NH ₃ in the SCR catalyst 46 may be reduced. For the consumption of NH ₃ in the SCR catalyst 46, the purification amount of NOx in the SCR catalyst 46 is calculated based on a pair of NOx sensors provided on the immediately upstream side and the immediately downstream side of the SCR catalyst 46, and the NOx in that amount is calculated. It is calculated as the amount of NH ₃ required for purification.

In the above embodiment, in the first rich lean cycle, the post injection timing of the rich step is set to the initial post injection timing on the most advanced angle side, and in the subsequent cycle, the post injection timing is gradually set to the retarded angle side, and the predetermined cycle. In the cycle after the number n0, the final post injection timing is set to be constant. However, the post-injection timing of the rich step in the cycle in which the implementation time is early may be on the advance side of the post-injection timing of the rich step in the cycle in which the implementation timing is late. The post-injection timing of the It is not necessary to set it on the advance side. For example, in the cycle up to a predetermined number of cycles n0, the post injection timing of the rich step in the second rich lean cycle may be set to the advance side more than the post injection timing of the rich step in the first rich lean cycle. .. Further, the predetermined number of cycles n0 does not have to be plural, and may be 1. In this case, only in the first rich lean cycle, the post injection timing of the rich step is set to the advance angle side with respect to the post injection timing of the rich step in the subsequent rich lean cycle.

Further, in the above-described embodiment, the case where the active DeNOx control and the subsequent DPF regeneration control and DeSOx control are performed while the engine main body 1 is being operated in the first region R1 has been described. , May be carried out in a region other than the first region R1.

Further, in the above embodiment, the case where the second EGR valve 60 is fully closed during the DPF regeneration control has been described, but the second EGR valve 60 may be opened during the DPF regeneration control. However, even in this case, since the post-injected fuel does not burn in the DPF regeneration control, the opening degree of the second EGR valve 60 during the DPF regeneration control is set to normal operation in order to prevent the EGR cooler and the like from being blocked. It is preferable that the time is smaller than that of the active DeSOx control and the DeNOx control rich step. Further, the opening degree of the second EGR valve 60 may be different between the time of DeNOx control and the time of DeSOx control.

1 Engine body (engine)
2 cylinders 6 combustion chamber 10 injectors (fuel injection device)
40 Exhaust passage 41 NOx catalyst 42 Oxidation catalyst 44 DPF (PM filter)
200 PCM (control means)
201 NOx catalyst rich purge control unit 202 NOx catalyst regeneration control unit 203 PM filter regeneration control unit

Claims (7)

In a lean state where the air-fuel ratio of the exhaust gas is leaner than the theoretical air-fuel ratio, which is provided in the exhaust passage of the engine and is provided integrally with the oxidation catalyst that can oxidize the unburned fuel in the exhaust or on the downstream side thereof. A NOx catalyst that absorbs NOx in the exhaust gas and reduces the stored NOx when the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, and fine particles in the exhaust gas provided on the downstream side of the oxidation catalyst. An engine control device equipped with a PM filter capable of collecting state substances and a fuel injection valve for introducing fuel into the cylinder of the engine.
A rich step in which the air-fuel ratio of the exhaust gas introduced into the NOx catalyst is set to a rich state where the air-fuel ratio is richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, and a lean air-fuel ratio and unburned fuel from the stoichiometric air-fuel ratio are the oxidation catalysts. A NOx catalyst regeneration control unit that performs NOx catalyst regeneration control for removing the sulfur component stored in the NOx catalyst by repeating a rich lean cycle including a lean step for setting the lean state to be introduced into the NOx catalyst.
The air-fuel ratio of the exhaust gas introduced into the PM filter is set to be leaner than the stoichiometric air-fuel ratio and the unburned fuel is introduced into the oxidation catalyst, and the collected fine particle-like substance is transferred from the PM filter. The PM filter regeneration control unit that implements the PM filter regeneration control to be removed,
Equipped with
In the NOx catalyst regeneration control, at least during the rich step, the main injection for injecting fuel for obtaining engine torque into the cylinder and the fuel being injected into the cylinder at a time retarded from the main injection. Additional injection is carried out,
The NOx catalyst regeneration control unit controls the fuel injection valve so that the injection timing of the additional injection is on the advance side in the cycle in which the execution time is earlier than in the cycle in which the execution time is later among the plurality of cycles. , Engine control device. Among the plurality of cycles, the NOx catalyst regeneration control unit has the fuel injection valve so that the cycle in which the execution time is earlier is gradually advanced to the injection timing of the additional injection than the cycle in which the execution time is later. To control,
The engine control device according to claim 1. The NOx catalyst regeneration control unit controls the fuel injection valve so that the injection timing of the additional injection in the rich step becomes constant after repeating the rich lean cycle for a predetermined number of cycles.
The engine control device according to claim 1 or 2. The engine supplies an SCR catalyst provided on the downstream side of the NOx catalyst to the exhaust passage, and an SCR reducing agent composed of a raw material of NH ₃ or NH ₃ between the NOx catalyst and the SCR catalyst. Further equipped with a reducing agent supply means for SCR,
In the control device, the more the injection timing of the additional injection in the rich step is set to the advance side in the NOx catalyst regeneration control, the more the SCR reducing agent supply means is supplied with the SCR reducing agent. Control to reduce,
The engine control device according to any one of claims 1 to 3. The engine further comprises a pair of NOx sensors provided in the exhaust passage on the upstream side and the downstream side of the SCR catalyst to measure the concentration of NOx.
The NOx catalyst regeneration control unit is
The consumption of NH ₃ in the SCR catalyst was calculated based on the difference in NOx concentration between the upstream side and the downstream side of the SCR catalyst detected by the pair of NOx sensors.
Based on the consumption amount of NH ₃ and the supply amount of the reducing agent for SCR, the adsorption amount of NH ₃ in the SCR catalyst was calculated.
The degree to which the injection timing of the additional injection in the rich step is set to the advance angle side as the adsorption amount of NH ₃ in the SCR catalyst increases is suppressed.
The engine control device according to claim 4. Further provided with a NOx catalyst rich purge control unit for performing NOx catalyst rich purge control, which reduces NOx occluded from the NOx catalyst by setting the air-fuel ratio to the rich state.
The PM filter regeneration control unit starts the PM filter regeneration control after the end of the NOx catalyst rich purge control.
The engine control device according to any one of claims 1 to 5. In a lean state where the air-fuel ratio of the exhaust gas is leaner than the theoretical air-fuel ratio, which is provided in the exhaust passage of the engine and is provided integrally with the oxidation catalyst that can oxidize the unburned fuel in the exhaust or on the downstream side thereof. A NOx catalyst that absorbs NOx in the exhaust gas and reduces the stored NOx when the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, and fine particles in the exhaust gas provided on the downstream side of the oxidation catalyst. It is an engine control method equipped with a PM filter capable of collecting state substances and a fuel injection valve for introducing fuel into the cylinder of the engine.
A rich step in which the air-fuel ratio of the exhaust gas introduced into the NOx catalyst is set to a rich state where the air-fuel ratio is richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio, and a lean air-fuel ratio and unburned fuel from the stoichiometric air-fuel ratio are the oxidation catalysts. A NOx catalyst regeneration step for removing the sulfur component occluded in the NOx catalyst by repeating a rich lean cycle including a lean step for setting the lean state to be introduced into the NOx catalyst in a plurality of cycles.
The air-fuel ratio of the exhaust gas introduced into the PM filter is set to be leaner than the stoichiometric air-fuel ratio and the unburned fuel is introduced into the oxidation catalyst, and the collected fine particle-like substance is transferred from the PM filter. PM filter regeneration step to remove and
Have,
In the NOx catalyst regeneration step, at least during the rich step, the main injection for injecting fuel for obtaining engine torque into the cylinder and the fuel being injected into the cylinder at a time retarded from the main injection. Additional injection is carried out,
In the NOx catalyst regeneration step, the fuel injection valve is controlled so that the injection timing of the additional injection is on the advance side in the cycle in which the execution time is earlier than in the cycle in which the execution time is later. , How to control the engine.

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