JP4647579B2 - Exhaust gas purification system - Google Patents

Description

  The present invention relates to an exhaust gas purification system that purifies nitrogen oxides (NOx) contained in exhaust gas.

  In the exhaust gas purification system, a NOx absorption reduction catalyst for purifying NOx is provided in the exhaust system of the internal combustion engine. Here, the NOx absorption reduction catalyst absorbs NOx in the exhaust gas discharged from the internal combustion engine, and when the amount of absorbed NOx exceeds a predetermined amount, controls the exhaust gas to a reduced state by increasing the amount of fuel, etc. Reduce absorbed NOx. In this way, the NOx absorption / reduction catalyst purifies NOx and restores the absorption ability of the absorbent that absorbs NOx by absorption and reduction of NOx.

The NOx absorption reduction catalyst is poisoned by sulfur oxides contained in the exhaust gas. Here, in the exhaust gas purification system, generally, the NOx absorption reduction catalyst is heated to a high temperature and the atmosphere is rich, that is, the air-fuel ratio is controlled to be smaller than the ideal air-fuel ratio (stoichiometry). The poisoned sulfur oxide is purified (for example, refer to Patent Document 1).
JP 2000-170525 A

  Here, in the exhaust gas purification system, in order to remove sulfur poisoning, it is necessary to raise the temperature of the NOx absorption reduction catalyst to a predetermined temperature. If the NOx absorption reduction catalyst is in such a high temperature state, the NOx purification catalyst is purified. Can not do.

  That is, when the sulfur poisoning is being removed, the temperature of the NOx absorption reduction catalyst is high, so NOx purification cannot be performed, and the NOx contained in the exhaust gas deteriorates to the engine exhaust gas level. There's a problem.

  Further, if NOx is deteriorated while sulfur poisoning is being removed, even if NOx is reduced during normal driving, NOx obtained by weighted averaging deteriorates as a result, which is a problem.

  The present invention has been made to solve such a problem. A three-way catalyst (Three Way Catalyst) is installed between the internal combustion engine and the NOx absorption reduction catalyst, and during sulfur poisoning control, Since the atmosphere of both the NOx reduction absorption catalyst and the three-way catalyst is controlled to be rich, the sulfur removal control is being performed by purifying NOx with the three-way catalyst and performing the sulfur removal control with the NOx absorption reduction catalyst. An object of the present invention is to provide an exhaust gas purification system that can prevent the deterioration of NOx.

  In order to solve the above problems, an exhaust gas purification system according to the present invention is an exhaust gas purification system provided in an exhaust gas system of an internal combustion engine that can be driven by self-ignition, and has an NOx capturing / purifying function and an SOx capturing function. -At least one of the first purification unit and the second purification unit that also have a purification function, and the first purification unit and the second purification unit, up to a temperature at which SOx trapped in the purification unit is released Temperature adjustment means for raising the temperature, and air-fuel ratio control means for adjusting the air-fuel ratio of the exhaust gas supplied to the first purification section and the second purification section, and at a predetermined timing, Either the first purification unit or the second purification unit is heated by the temperature adjusting unit to a temperature at which SOx is released, and the purification unit is not heated by the temperature adjusting unit And controlling the air-fuel ratio of the exhaust gas to the rich side by the air-fuel ratio control means for.

  In the present invention, at a predetermined timing, either the first purification unit or the second purification unit is heated up to the temperature at which SOx is released by the temperature adjusting unit, and the temperature is adjusted by the temperature adjusting unit. Since the air-fuel ratio of the exhaust gas is controlled to the rich side by the air-fuel ratio control means with respect to the non-purifying part, it is possible to perform sulfur removal control in the other purifying part while purifying NOx in one purifying part, NOx deterioration during removal control can be prevented.

  In the exhaust gas purification system according to the present invention, the first purification unit and the second purification unit are arranged in series on the flow path of the exhaust gas output from the internal combustion engine, and the first purification unit Preferably, the part is a three-way catalyst, and the second purification part is a NOx reduction / absorption catalyst.

  In the present invention, it is possible to perform sulfur removal control in the second purification section in the subsequent stage while purifying NOx in the first purification section in the front stage, and to prevent deterioration of NOx during the control of sulfur removal. .

  Further, in the exhaust gas purification system, from the relationship between the air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas supplied to the first purification unit and the second purification unit, and the torque and the rotational speed of the internal combustion engine And a first storage means for storing a table for determining a target air-fuel ratio that is equal to or lower than the theoretical air-fuel ratio, and the air-fuel ratio control means is configured to detect the torque and the rotational speed detected from the internal combustion engine. Based on this, the target air-fuel ratio is obtained from the table stored in the first storage means, and the internal combustion engine is controlled so that the air-fuel ratio detected by the air-fuel ratio detection means becomes the obtained target air-fuel ratio. It is preferable to do.

  In the present invention, the target air-fuel ratio is obtained from the table stored in the first storage means based on the torque and rotational speed detected from the internal combustion engine, and the air-fuel ratio detected by the air-fuel ratio detection means is obtained. Since the internal combustion engine is controlled to achieve the target air-fuel ratio, the air-fuel ratio can be controlled to match the characteristics of the internal combustion engine.

  Further, in the exhaust gas purification system, temperature detection means for detecting the temperature of the first purification unit or the second purification unit, and a correction coefficient corresponding to the temperature of the first purification unit or the second purification unit Correction coefficient calculation for calculating a correction coefficient from the correction coefficient table stored in the second storage means based on the second storage means in which the table is stored and the temperature detected by the temperature detection means And the air-fuel ratio control means corrects the determined target air-fuel ratio based on the correction coefficient calculated by the correction coefficient calculation means, and detects the air-fuel ratio detected by the air-fuel ratio detection means. It is preferable to control the internal combustion engine so that becomes the corrected target air-fuel ratio.

  In the present invention, the target air-fuel ratio is obtained from the table stored in the first storage means based on the torque and the rotational speed detected from the internal combustion engine, and further the correction coefficient table stored in the second storage means. The target air-fuel ratio obtained is corrected based on the correction coefficient of the engine, and the internal combustion engine is controlled so that the air-fuel ratio detected by the air-fuel ratio detection means becomes the corrected target air-fuel ratio. The air-fuel ratio can be controlled to match the temperature of the part.

  Further, in the exhaust gas purification system, the correction coefficient table stored in the second storage means indicates that the temperature of the first purification section or the second purification section detected by the temperature detection means is within a predetermined range. When the temperature is within (for example, 500 ° C. to 700 ° C.), the target air-fuel ratio is corrected to the lean side, and the temperature of the first purification unit or the second purification unit detected by the temperature detection unit Is lower than a lower limit value (eg, 500 ° C.) within a predetermined range, it is preferable that the correction is made up of a correction coefficient for correcting the target air-fuel ratio to the rich side. In addition, 500 degreeC-700 degreeC shown as a predetermined range is an illustration, Comprising: It is not restricted to this. The temperature of the first purification unit and the second purification unit changes depending on the vehicle type, the configuration of the engine, the layout, and the like, and the predetermined range also changes appropriately.

  In the present invention, if the correction table for correcting the target air-fuel ratio obtained from the table stored in the first storage means corrects the target air-fuel ratio to the lean side if the temperature of the purification unit is within a predetermined range, the purification is performed. When the temperature of the part is lower than the lower limit value within the predetermined range, the target air-fuel ratio is configured with a correction coefficient that corrects the target air-fuel ratio to the rich side. be able to.

  In the exhaust gas purification system, the air-fuel ratio control means is configured to increase the post-injection amount when the air-fuel ratio detected by the air-fuel ratio detection means is leaner than the target air-fuel ratio. It is preferable to control the internal combustion engine so as to reduce the post-injection amount when the engine is controlled and is richer than the target air-fuel ratio.

  In the present invention, since the increase / decrease in the post-injection amount is controlled based on the air / fuel ratio detected by the air / fuel ratio detection means, the internal combustion engine can be controlled to the target air / fuel ratio without complicated control.

  According to the present invention, a three-way catalyst (Three Way Catalyst) is installed between the internal combustion engine and the NOx absorption reduction catalyst, and the atmosphere of both the NOx reduction absorption catalyst and the three-way catalyst is controlled during the control of sulfur poisoning. Since the control is performed so as to be rich, NOx deterioration during control of sulfur removal can be prevented by performing sulfur removal control with the NOx absorption reduction catalyst while purifying NOx with the three-way catalyst.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an exhaust gas purification system 1 to which the present invention is applied together with an internal combustion engine (hereinafter referred to as “engine”) 3. The engine 3 is, for example, a four-cylinder (only one shown) diesel engine mounted on a vehicle (not shown).

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

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

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

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

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

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

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

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

  Here, according to a preferred embodiment of the present invention, the amount of intake air in the air-fuel mixture without throttling is changed by changing the opening of the variable vane 8c without operating the throttle valve 12. Decrease. More specifically, according to the control of the ECU 2 according to the operation of an accelerator pedal (not shown), the variable vane 8c is opened without the operation of the throttle valve 12, thereby reducing the intake air amount. The exhaust gas is purified by setting the air-fuel ratio A / F of the exhaust gas in the vicinity of the ideal air-fuel ratio (hereinafter referred to as “stoichiometric”) or rich.

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

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

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

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

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

  The EGR device 14 is provided with an EGR cooling device 15 for cooling the EGR gas. The EGR cooling device 15 includes a bypass passage 15a, an EGR passage switching valve 15b, and an EGR cooler 15c. The bypass passage 15a is provided on the downstream side of the EGR control valve 14b of the EGR pipe 14a so as to bypass the EGR pipe 14a, and the EGR passage switching valve 15b is attached to a branch portion of the bypass passage 15a, 15c is provided in the middle of the bypass passage 15a. The EGR passage switching valve 15b selectively switches the downstream portion of the EGR passage switching valve 15b between the EGR pipe 14a side and the bypass passage 15a side under the control of the ECU 2.

  As described above, when the EGR passage switching valve 15b is switched to the bypass passage 15a side, the EGR gas is passed through the bypass passage 15a, cooled by the EGR cooler 15c, and then returned to the intake pipe 4. On the other hand, when switched to the opposite side, the EGR gas recirculates to the intake pipe 4 through the EGR pipe 14a alone without being cooled.

  Here, according to a preferred embodiment of the present invention, throttling is performed by changing the exhaust gas recirculation rate (EGR rate) by controlling the EGR control valve 14b without operating the throttle valve 12. Without it, the amount of intake air in the mixture is reduced. More specifically, the intake air amount is decreased by increasing the exhaust gas recirculation rate (EGR rate) by opening the EGR control valve 14b according to the control of the ECU 2 according to the operation of an accelerator pedal (not shown). The exhaust gas is purified by setting the air-fuel ratio A / F of the exhaust gas in the vicinity of the stoichiometric or rich state.

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

  Further, a first A / F sensor 33 and a second A / F sensor 34 are respectively provided immediately upstream and downstream of the three-way catalyst 16 in the exhaust pipe 5. The first and second A / F sensors 33 and 34 linearly detect oxygen concentrations A / F1 and A / F2 in the exhaust gas in a wide range of air-fuel ratios from the rich region to the lean region, respectively. Based on the oxygen concentration A / F1 detected by the first A / F sensor 33, the ECU 2 calculates an actual air-fuel ratio A / FACT representing the air-fuel ratio of the actual gas burned in the combustion chamber 3c. Further, the ECU 2 outputs a detection signal indicating an operation amount (hereinafter referred to as “accelerator opening”) AP of an accelerator pedal (not shown) from the accelerator opening sensor 35.

  The ECU 2 is composed of a microcomputer including an I / O interface, CPU, RAM, ROM, and the like. The detection signals from the various sensors 30 to 36 described above are each input to the CPU after A / D conversion and shaping by the I / O interface.

  In accordance with these input signals, the CPU determines the operating state of the engine 3 according to a control program stored in the ROM, and includes control of the fuel injection amount and the intake air amount according to the determined operating state. Control of the engine 3 is executed.

<Configuration of NOx catalyst 17>
The NOx catalyst 17 is a monolithic structure type catalyst composed of a carrier coated with two or more different catalyst layers, and includes a first catalyst layer including a solid acid catalyst having ammonia adsorption ability, a noble metal and a cerium oxide-based material. And a second catalyst layer containing at least a NOx purification catalyst. The NOx purification catalyst will be described below.

<First catalyst layer>
<Constituents>
The first catalyst layer is preferably used as the outermost surface layer in direct contact with the exhaust gas in the NOx purification catalyst. Moreover, it is preferable not to contain a platinum component substantially, and it is more preferable not to contain the noble metal component in general.

  The first catalyst layer includes a solid acid catalyst having ammonia adsorption ability. As the solid acid catalyst, a zeolite catalyst is preferably used. Moreover, it is preferable that an iron element is added to a zeolitic catalyst, and it is preferable that a cerium element is further added.

  The reason why the exhaust gas purification performance, particularly NOx purification performance, is improved by adding iron element or cerium element to the zeolitic catalyst is not clear, but for iron element, NOx and reducing components are adsorbed, As for cerium element, NOx is adsorbed by the ability to store and release oxygen, and it is expected that the poisoning of the catalyst by the reducing component is suppressed by the ability to store and release oxygen. Thus, by using both components together, it is considered that these effects are synergistic and a more excellent effect as a catalyst is exhibited.

<Second catalyst layer>
<Constituents>
A precious metal such as platinum and a cerium oxide-based material are added to the second catalyst layer. This is because the NOx purification ability is improved by the synergistic action of the noble metal of the cerium oxide material and platinum. The reason why the NOx purification performance is improved in this way is not clear, but it is thought that the poisoning of platinum by the reducing component is prevented and the NOx adsorption action may be the cause.

  The second catalyst layer includes a noble metal as a catalytically active species and a cerium oxide-based material, preferably a cerium oxide-based material supporting a noble metal and a zirconium oxide-based material supporting a noble metal. As the noble metal, platinum is an essential component, and gold, palladium, and rhodium can be used as necessary. However, it is preferable to use platinum as a main component because of its high activity.

Although not clear why the purification of NOx in the exhaust gas is promoted by the use of platinum oxidizes NO occupying most of the exhaust gas by platinum NO _2, this NO _2, used in the present invention It is considered that the reaction with the reducing component is promoted by adsorbing to the cerium component of the catalyst to be promoted.

  The catalytically active noble metal is used by being supported on a cerium oxide-based material or a heat-resistant inorganic oxide other than the cerium oxide-based material (also simply referred to as a heat-resistant inorganic oxide). The noble metal can be supported on the cerium oxide-based material or the heat-resistant inorganic oxide constituting the catalyst layer, but may be supported on a specific inorganic oxide. The specific inorganic oxide preferably includes a cerium oxide-based material having a high specific surface area value and excellent heat resistance. Such a cerium oxide-based material contains a very small amount in the crystal to improve heat resistance. Those in which rare earth elements such as lanthanum (La) and praseodymium (Pr) are incorporated are preferred. Moreover, as another heat resistant inorganic oxide, (gamma) -alumina is preferable.

<Laminated form of first catalyst layer and second catalyst layer>
In the present invention, the NOx purification catalyst constituting the NOx catalyst 17 has an arrangement relationship between the first catalyst layer and the second catalyst layer. That is, it is preferable that the second catalyst layer and the first catalyst layer are sequentially laminated on the support, and the first catalyst layer is the uppermost layer. The lower second catalyst layer is preferably configured such that the noble metal content decreases sequentially or stepwise from the first catalyst layer side toward the carrier side. This means that the lower layer is not necessarily a single layer, and may be formed of multiple layers so that the noble metal content decreases sequentially or stepwise.

<Arrangement of NOx purification device>
As shown in FIG. 1, the NOx catalyst 17 is connected to the exhaust pipe 5 from the engine 3, but the temperature of the NOx catalyst 17 can be adjusted to 400 ° C. or lower, preferably 300 ° C. or lower, not shown. Adjustment means may be provided.

  Further, the exhaust pipe 5 from the engine 3 preferably has a configuration in which the three-way catalyst 16 and the NOx catalyst 17 are sequentially arranged along the exhaust direction. In this case, it is preferable that the NOx catalyst 17 be disposed at a position where it is not substantially affected by the heat from the engine 3. The NOx catalyst 17 is characterized by having a sufficient NOx purification capacity in an operating region at a low temperature. Therefore, a sufficient NOx removal effect can be obtained even if they are arranged away from the position where they are not substantially affected by the heat from the engine 3. Specifically, the NOx catalyst 17 may be disposed, for example, under the floor of a vehicle, and the NOx catalyst 17 in the present invention is characterized by a high degree of freedom in layout.

<First embodiment>
Here, the temperature range in which the NOx catalyst 17 for diesel acts is about 250 ° C. to 400 ° C., and the sulfur oxide (hereinafter referred to as “poisoning”) trapped by the NOx catalyst 17 (hereinafter referred to as “poisoning”). , Referred to as “SOx”) is about 600 ° C. Therefore, during the SOx removal control (that is, when the temperature is about 600 ° C.), the NOx processing capacity decreases, and the NOx increases by about 90% compared to when the NOx catalyst 17 is operating. .

  In the exhaust gas purification system 1 according to the present invention, the NOx catalyst 17 is brought into a high temperature (about 500 ° C. to 700 ° C.) at which SOx can be removed, and the three-way catalyst 16 disposed upstream of the NOx catalyst 17. By controlling the air-fuel ratio A / F of the inflowing exhaust gas to stoichiometric (14.7) or less, it becomes possible to simultaneously purify NOx and remove SOx. Hereinafter, control for simultaneously performing NOx purification and SOx removal will be described with reference to FIG. 3, which is a simplified diagram of FIG. In the following, the same names and numbers are assigned to the same components as those in FIG.

  As shown in FIG. 3, the exhaust gas purification system 1 includes a first A / F sensor 33 (air-fuel ratio detection means) and a three-way catalyst 16 (first catalyst) through an exhaust pipe 5 through which exhaust gas discharged from the engine 3 passes. And a NOx catalyst 17 (second purification unit), and various controls are performed by the ECU 2.

  The three-way catalyst 16 is provided with a three-way catalyst temperature sensor 40 (temperature detection means) that detects the temperature of the three-way catalyst 16. The three-way catalyst temperature sensor 40 outputs a detection signal to the ECU 2.

  As shown in FIG. 3, the ECU 2 includes a first ROM 41 (first storage means) and an A / F control unit 42 (air-fuel ratio control means, control means).

  The first ROM 41 stores a table for determining a target air-fuel ratio that is equal to or lower than the stoichiometry from the relationship between the torque of the engine 3 and the rotational speed. Further, in the table, for example, as shown in FIG. 4, the target air-fuel ratio is determined from the relationship between the torque (0, 50, 100, 150, 200) and the rotational speed (0, 1000, 2000, 3000). ing. In the table shown in FIG. 4, the target air-fuel ratio is determined based on the case where the three-way catalyst 16 is 600 ° C. Note that the table shown in FIG. 4 is an example, and the target air-fuel ratio is not particularly limited as long as the target air-fuel ratio is equal to or less than stoichiometric (A / F = 14.7).

  Further, the A / F control unit 42 obtains the target air-fuel ratio from the table stored in the first ROM 41 based on the torque and the rotational speed detected from the engine 3, and the first A / F sensor 33 The engine 3 is controlled so that the supplied oxygen concentration A / F1 becomes the target air-fuel ratio.

  The ECU 2 more preferably includes a second ROM 43 (second storage unit) and a correction coefficient calculation unit 44 (correction coefficient calculation unit) in order to purify NOx in the three-way catalyst 16. Based on the temperature of the original catalyst 16, the target air-fuel ratio is corrected.

  The second ROM 43 stores a correction coefficient table corresponding to the temperature of the three-way catalyst 16. Further, the correction coefficient table corrects the target air-fuel ratio to the lean side when the temperature of the three-way catalyst 16 detected by the three-way catalyst temperature sensor 40 is higher than 600 ° C., and the three-way catalyst temperature. When the temperature of the three-way catalyst 16 detected by the sensor 40 is lower than 600 ° C., the three-way catalyst 16 includes a correction coefficient for correcting the target air-fuel ratio to the rich side. For example, as shown in FIG. Correction coefficients (0.99, 1, 1.01, 1.02) corresponding to the temperature of the catalyst 16 (500 ° C., 600 ° C., 700 ° C., 800 ° C.) are determined. Note that the correction coefficient table shown in FIG. 5 is an example, and is not limited to this.

  In addition, the correction coefficient calculation unit 44 calculates a correction coefficient from a correction coefficient table stored in the second ROM 43 based on the temperature detected by the three-way catalyst temperature sensor 40, and the calculated correction coefficient is A / Output to the F control unit 42.

  The A / F control unit 42 corrects the target air-fuel ratio obtained from the first ROM 41 based on the correction coefficient supplied from the correction coefficient calculation unit 44, and supplies oxygen supplied by the first A / F sensor 33. The engine 3 is controlled so that the concentration A / F1 becomes the corrected target air-fuel ratio.

  Further, the A / F control unit 42 specifically sets the post injection amount when the oxygen concentration A / F1 supplied by the first A / F sensor 33 is leaner than the target air-fuel ratio. The engine 3 is controlled to increase, and when the oxygen concentration A / F1 is richer than the target air-fuel ratio, the engine 3 is controlled to decrease the post-injection amount.

  In this way, the ECU 2 reaches either the three-way catalyst 16 or the NOx catalyst 17 to a temperature at which SOx is released at a predetermined timing based on the oxygen concentration A / F1 of the first A / F sensor 33. While raising the temperature, the air-fuel ratio of the exhaust gas is controlled to the rich side with respect to the catalyst that has not been heated. For example, the ECU 2 controls the temperature raising unit 45 to raise the temperature of the NOx catalyst 17 (see FIG. 3).

  Next, a specific control procedure of the exhaust gas purification system 1 will be described with reference to a flowchart shown in FIG. In the following, the ECU 2 estimates the SOx poisoning amount of the NOx catalyst 17 based on the travel distance or the fuel consumption amount, and based on the estimation result, it is determined that the SOx removal of the NOx catalyst 17 is necessary. The description will be made on the assumption that the SOx removal control is requested.

  In step S1, the A / F control unit 42 determines whether or not the temperature (bed temperature) of the NOx catalyst 17 has reached a temperature at which SOx can be removed. Specifically, the A / F control unit 42 determines whether the temperature of the NOx catalyst 17 is within a predetermined range (for example, 500 ° C. to 600 ° C.) based on the TLNC supplied from the NOx catalyst temperature sensor 36. to decide. The lower limit temperature at which SOx can be removed varies in the range of about 500 ° C. to 600 ° C. depending on the regeneration time and the frequency of SOx removal. Further, the higher the temperature, the more efficiently the SOx removal can be performed, but a lower one is desirable in order to prevent the catalyst from being deteriorated, and the temperature varies depending on EM (exhaust gas) by normal control. In the present embodiment, the temperature at which SOx can be removed is about 600 ° C., and in the process of step S 1, the temperature obtained by the difference between the temperature when removing SOx from the 600 ° C. and the lower limit temperature (for example, 100 ° C.) is subtracted from the temperature (for example, 500 ° C.). In addition, 500 degreeC-600 degreeC shown as a predetermined range is an illustration, Comprising: It is not restricted to this. The temperature of the NOx catalyst 17 varies depending on the vehicle type, engine configuration, layout, and the like, and the predetermined range also varies as appropriate.

  If the temperature of the NOx catalyst 17 is not a temperature at which SOx can be removed (NO), the process proceeds to step S2, and if the temperature of the NOx catalyst 17 is a temperature at which the SOx can be removed (YES), the process proceeds to step S3.

  In step S2, the A / F control unit 42 performs control to raise the temperature of the NOx catalyst 17 to a predetermined temperature. Specifically, the A / F control unit 42 increases the post injection amount or increases the intake air amount so that the temperature of the NOx catalyst 17 exceeds a predetermined range (for example, 500 ° C. to 600 ° C.). Control to be. Note that the combustion rich and post rich settings are set so that the three-way catalyst 16 is 600 ° C. or higher, and therefore the A / F control unit 42 is set to 500 ° C., which is the lowest temperature at which SOx can be removed. Control to raise the temperature.

  In step S3, the A / F control unit 42 determines whether the air-fuel ratio A / F of the exhaust gas flowing into the three-way catalyst 16 is the same as the target air-fuel ratio. Specifically, the A / F control unit 42 determines the table (see FIG. 4) stored in the first ROM 41 based on the current running state (obtained from the torque detected from the engine 3 and the rotational speed). The target air-fuel ratio is obtained from the reference.

  In the table shown in FIG. 4, as described above, the target air-fuel ratio is determined based on when the temperature of the three-way catalyst 16 is within a predetermined range (for example, 600 ° C. to 900 ° C.). Correction is performed according to the temperature of the catalyst 16. Specifically, the A / F control unit 42 corrects the target air-fuel ratio based on the correction coefficient supplied from the correction coefficient calculation unit 44. In addition, 600 to 900 degreeC shown as a predetermined range is an illustration, Comprising: It is not restricted to this. The temperature of the three-way catalyst 16 varies depending on the vehicle type, engine configuration, layout, and the like, and the predetermined range also varies as appropriate.

  Here, when the temperature of the three-way catalyst 16 is within a predetermined range (for example, 600 ° C. to 900 ° C.), the reactivity of the supplied CO is increased, so that the supply amount of CO can be reduced. Correct the fuel ratio to the lean side. Further, when the temperature of the three-way catalyst 16 is lower than a lower limit value (for example, 600 ° C.) within a predetermined range (for example, 600 ° C. to 900 ° C.), the reactivity of the reducing agent is deteriorated. In order to increase the supply amount, the target air-fuel ratio is corrected to the rich side.

  The A / F control unit 42 determines whether or not the oxygen concentration A / F1 detected by the first A / F sensor 33 provided on the upstream side of the three-way catalyst 16 is the same as the corrected target air-fuel ratio. to decide. If they are the same (YES), the process proceeds to step S4. If they are not the same (NO), the process proceeds to step S5.

  In step S <b> 4, the exhaust gas purification system 1 performs NOx purification with the three-way catalyst 16 while removing the SOx with the NOx catalyst 17.

  In step S5, the A / F control unit 42 determines whether the air-fuel ratio A / F of the exhaust gas flowing into the three-way catalyst 16 is smaller than the target air-fuel ratio. When the air-fuel ratio A / F of the exhaust gas flowing into the three-way catalyst 16 is smaller than the target air-fuel ratio (YES), the process proceeds to step S6, and the air-fuel ratio A / F of the exhaust gas flowing into the three-way catalyst 16 is If it is not smaller than the target air-fuel ratio (NO), the process proceeds to step S7.

  In step S6, the A / F control unit 42 performs control so as to decrease the post injection amount, and corrects the air-fuel ratio A / F to the lean side.

  In step S7, the A / F control unit 42 performs control to increase the post injection amount and corrects the air-fuel ratio A / F to the rich side.

  In this way, the exhaust gas purification system 1 reduces the post injection amount when correcting to the lean side to adjust the supplied CO, and post correction amount when correcting to the rich side. Increase the amount. The exhaust gas purification system 1 controls the air-fuel ratio A / F to be the corrected target air-fuel ratio by increasing / decreasing the main injection amount in the combustion rich region where the post-injection amount is not used. .

  Accordingly, in the exhaust gas purification system 1, the atmosphere (A / F) of both the three-way catalyst 16 and the NOx catalyst 17 on the downstream side of the three-way catalyst 16 is stoichiometric (14.7) or less. While purifying NOx with the original catalyst 16, it is possible to remove SOx with the NOx catalyst 17. Therefore, the exhaust gas purification system 1 can reduce NOx, which has been deteriorated by 90% in the conventional SOx removal, by almost 100%, and the exhaust gas (EM) during the SOx removal control is equivalent to that during normal driving. It becomes possible to reduce to the extent.

<Second embodiment>
Here, the NOx catalyst is poisoned by SOx contained in the exhaust gas. The exhaust gas purification system generally includes a removing means for removing SOx poisoned by the NOx catalyst, and the SOx poisoned by the NOx catalyst based on a certain travel distance and fuel consumption. The NOx catalyst is poisoned and removed by driving the removal means according to the estimation result.

  By the way, in the case of an exhaust gas purification system in which a three-way catalyst is provided between the engine and the NOx catalyst, SOx is also poisoned by the three-way catalyst. Poisoning may occur and the NOx catalyst may not be poisoned by SOx.

  The exhaust gas purification system 1 according to the present invention estimates the SOx poisoning amount of the entire system in consideration of the SOx poisoning amount of the three-way catalyst 16, and determines the frequency (timing) of SOx poisoning removal by the NOx catalyst. By optimizing, it is possible to reduce fuel consumption. Hereinafter, control for optimizing the frequency (timing) of SOx poisoning removal by the NOx catalyst will be described with reference to FIG. 7 which is a simplified diagram of FIG. In the following, the same names and numbers are assigned to the same constituent elements as those in FIGS.

  As shown in FIG. 7, the exhaust gas purification system 1 includes a first A / F sensor 33 (air-fuel ratio detection means) and a three-way catalyst 16 (first catalyst) through an exhaust pipe 5 through which exhaust gas discharged from the engine 3 passes. And a NOx catalyst 17 (second purification unit), and various controls are performed by the ECU 2.

  The three-way catalyst 16 is provided with a three-way catalyst temperature sensor 40 (temperature detection means) that detects the temperature of the three-way catalyst 16. The three-way catalyst temperature sensor 40 outputs a detection signal to the ECU 2.

  As shown in FIG. 7, the ECU 2 includes a three-way catalyst temperature adjustment unit 50 (temperature adjustment unit), a NOx catalyst temperature adjustment unit 51 (temperature adjustment unit), and a control unit 52 (capture estimation amount calculation unit, operation control unit). , A discharge amount calculation means).

  The three-way catalyst temperature adjustment unit 50 adjusts the temperature of the three-way catalyst 16 in accordance with a signal supplied from the control unit 52.

  The NOx catalyst temperature adjustment unit 51 adjusts the temperature of the NOx catalyst 17 in accordance with a signal supplied from the control unit 52.

  The control unit 52 calculates an estimated poisoning amount of SOx poisoned by the three-way catalyst 16 and the NOx catalyst 17 based on the travel distance or the fuel consumption amount. Further, the control unit 52 corrects the estimated SOx poisoning amount of the NOx catalyst 17 based on the calculated estimated SOx poisoning amount of the three-way catalyst 16, and based on the corrected poisoning estimated amount, The operation of the NOx catalyst temperature adjusting unit 51 is controlled so as to release SOx poisoned by the NOx catalyst 17.

  Here, the configuration of the control unit 52 will be described. The control unit 52 counts an estimated amount of SOx poisoned by the three-way catalyst 16, a counter 52B for counting an estimated amount of SOx poisoned by the NOx catalyst 17, A counter control unit 52C that controls the counter 52A and the counter 52B is provided.

  The counter 52A supplies a predetermined signal to the three-way catalyst temperature adjusting unit 50 when the count value is controlled to be added, subtracted or stopped by the counter control unit 52C, and when the count value reaches a predetermined value. The three-way catalyst temperature adjustment unit 50 adjusts the temperature of the three-way catalyst 16 according to the signal supplied from the counter 52A.

  The counter 52B is supplied with a predetermined signal to the NOx catalyst temperature adjusting unit 51 when the count value is controlled to be added, subtracted or stopped by the counter control unit 52C and the count value reaches a predetermined value. The NOx catalyst temperature adjustment unit 51 adjusts the temperature of the NOx catalyst 17 in accordance with the signal supplied from the counter 52B.

  The counter control unit 52C calculates the estimated poisoning amount of SOx poisoned by the NOx catalyst 17 based on the travel distance or the fuel consumption amount, controls the counter 52A according to the calculation result, and travels. Based on the distance or the fuel consumption amount, the estimated poisoning amount of SOx poisoned by the NOx catalyst 17 is calculated, and the counter 52B is controlled according to the calculation result.

  Specifically, when the counter control unit 52C determines that the three-way catalyst 16 is poisoned by SOx based on the travel distance or the fuel consumption, the NOx catalyst 17 is poisoned by SOx. In order to correct the estimated amount, the counter 52B is controlled to stop.

  Thus, the exhaust gas purification system 1 corrects the estimated SOx poisoning amount of the NOx catalyst 17 according to the estimated SOx poisoning amount of the three-way catalyst 16 by the counter control unit 52C. The estimated poison amount can be accurately estimated, and the start timing of the SOx poisoning removal of the NOx catalyst 17 can be optimized according to the count value of the counter 52B.

  Here, the operation in the case where the control unit 52 calculates the estimated amount of SOx poisoned by the three-way catalyst 16 and the NOx catalyst 17 based on the fuel consumption amount of the engine 3 will be described.

  When the control unit 52 determines that the three-way catalyst 16 is poisoned by SOx based on the fuel consumption, the control unit 52 performs stop control on the counter 52B that estimates the SOx poisoning estimation amount of the NOx catalyst 17. Then, the estimated poisoning amount of SOx poisoned by the NOx catalyst 17 is corrected. The control unit 52 controls the operation of the NOx catalyst temperature adjustment unit 51 so as to release SOx poisoned by the NOx catalyst 17 based on the corrected estimated amount of poisoning. Further, the control unit 52 calculates the SOx poisoning estimation amount based on the fuel consumption amount from the start of measurement, for example, by setting the sulfur content contained in the fuel to 10 ppm. For example, when 25 L of fuel is consumed, the SOx Is estimated to be 0.0005 g.

  Next, the operation when the control unit 52 calculates the estimated amount of SOx poisoned by the three-way catalyst 16 and the NOx catalyst 17 based on the travel distance will be described.

  When the control unit 52 determines that the three-way catalyst 16 is poisoned by SOx based on the travel distance, the control unit 52 adds a counter 52B for estimating the SOx poisoning estimation amount of the NOx catalyst 17 according to the travel distance. No, that is, by controlling the stop of the counter 52B, the estimated poisoning amount of SOx poisoned by the NOx catalyst 17 is corrected. The control unit 52 controls the operation of the NOx catalyst temperature adjustment unit 51 so as to release SOx poisoned by the NOx catalyst 17 based on the corrected estimated amount of poisoning. For example, the control unit 52 calculates the estimated poisoning amount based on whether the travel distance has reached 400 km from the start of measurement. For example, if the travel distance has reached 400 km, the control unit 52 calculates the estimated SOx poisoning amount. Calculated to be 0.0005 g.

  In addition, the ECU 2 includes a third ROM 53 (storage means) in order to calculate the estimated amount of SOx poisoned by the three-way catalyst 16 more preferably.

  The third ROM 53 stores a table for determining the amount of SOx released by the three-way catalyst 16 from the relationship between the temperature of the three-way catalyst 16 and the air-fuel ratio A / F of the exhaust gas. Further, for example, as shown in FIG. 8, the table shows the air-fuel ratio A / F (14.7, 14.5, 14.3, 14.1, 13.9) and the temperature of the three-way catalyst 16 (300 The amount of SOx released by the three-way catalyst 16 is determined from the relationship between the three-way catalyst 16. The unit of SOx release is g / sec. The table shown in FIG. 8 is an example, and the present invention is not limited to this.

  The control unit 52 calculates, for example, an estimated amount of poisoning of SOx poisoned by the three-way catalyst 16 based on the fuel consumption (hereinafter referred to as “first calculated value”), and three. Based on the temperature detected by the original catalyst temperature sensor 40 and the oxygen concentration A / F1 detected by the first A / F sensor 33, the three-way catalyst 16 is obtained from the table stored in the third ROM 53. The amount of released SOx is calculated (hereinafter referred to as “second calculated value”). The controller 52 subtracts the second calculated value from the first calculated value to calculate the estimated poisoning amount of SOx poisoned by the final three-way catalyst 16.

  Here, a specific example of the procedure for correcting the estimated SOx poisoning amount will be described with reference to the flowchart shown in FIG. In the following description, the counter 52A and the counter 52B assume that the sulfur content is 10 ppm, and integrate (count up) the values calculated from the fuel consumption.

  In step S10, the control unit 52 determines whether or not the temperature (bed temperature) of the three-way catalyst 16 is a temperature at which SOx is poisoned. Specifically, the control unit 52 determines whether the temperature of the three-way catalyst 16 is about 200 ° C. to 400 ° C. based on the detection value supplied from the three-way catalyst temperature sensor 40. If the temperature of the three-way catalyst 16 is the SOx poisoning temperature (YES), the process proceeds to step S11. If the temperature of the three-way catalyst 16 is not the SOx poisoning temperature (NO), the process proceeds to step S14. .

  In step S11, the controller 52 determines that the temperature (bed temperature) of the three-way catalyst 16 is the SOx release temperature, and the air-fuel ratio A / F of the exhaust gas is the air-fuel ratio A at which the three-way catalyst 16 can release SOx. It is determined whether it is smaller than / F. Specifically, the control unit 52 refers to the table stored in the third ROM 53, and the temperature of the three-way catalyst 16 is released from the SOx based on the detection value supplied from the three-way catalyst temperature sensor 40. Based on the oxygen concentration A / F1 supplied from the first A / F sensor 33, the air-fuel ratio A / F of the exhaust gas is the air-fuel ratio A / F at which the three-way catalyst 16 can release SOx. To determine if it is smaller than.

  When the temperature (bed temperature) of the three-way catalyst 16 is the SOx release temperature and the air-fuel ratio A / F of the exhaust gas is smaller than the air-fuel ratio A / F at which the three-way catalyst 16 can release SOx (YES) In step S12, the temperature (bed temperature) of the three-way catalyst 16 is not the SOx release temperature, or the air-fuel ratio A / F of the exhaust gas is the air-fuel ratio A / F at which the three-way catalyst 16 can release SOx. If not smaller (NO), the process proceeds to step S13.

  In step S <b> 12, the control unit 52 performs subtraction control on the counter 52 </ b> A that counts the estimated SOx poisoning amount of the three-way catalyst 16 based on the table stored in the third ROM 53, and sets the SOx of the NOx catalyst 17. The counter 52B that counts the estimated poisoning amount is added and controlled.

  In step S <b> 13, the control unit 52 adds and controls the counter 52 </ b> A that counts the estimated SOx poisoning amount of the three-way catalyst 16 based on the table stored in the third ROM 53, and sets the SOx of the NOx catalyst 17. A counter 52B that counts the estimated poisoning amount is controlled to stop.

  In step S14, the controller 52 determines that the temperature (bed temperature) of the three-way catalyst 16 is the SOx release temperature, and the air-fuel ratio A / F of the exhaust gas is the air-fuel ratio A at which the three-way catalyst 16 can release SOx. It is determined whether it is smaller than / F. Specifically, the control unit 52 refers to the table stored in the third ROM 53, and the temperature of the three-way catalyst 16 is released from the SOx based on the detection value supplied from the three-way catalyst temperature sensor 40. Based on the oxygen concentration A / F1 supplied from the first A / F sensor 33, the air-fuel ratio A / F of the exhaust gas is the air-fuel ratio A / F at which the three-way catalyst 16 can release SOx. To determine if it is smaller than.

  When the temperature (bed temperature) of the three-way catalyst 16 is the SOx release temperature and the air-fuel ratio A / F of the exhaust gas is smaller than the air-fuel ratio A / F at which the three-way catalyst 16 can release SOx (YES) In step S15, the temperature (bed temperature) of the three-way catalyst 16 is not the SOx release temperature, or the air-fuel ratio A / F of the exhaust gas is the air-fuel ratio A / F at which the three-way catalyst 16 can release SOx. If not smaller (NO), the process proceeds to step S16.

  In step S <b> 15, the control unit 52 performs subtraction control on the counter 52 </ b> A that counts the estimated SOx poisoning amount of the three-way catalyst 16 based on the table stored in the third ROM 53, and sets the SOx of the NOx catalyst 17. The counter 52B that counts the estimated poisoning amount is added and controlled.

  In step S <b> 16, the control unit 52 controls the stop of the counter 52 </ b> A that counts the estimated SOx poisoning amount of the three-way catalyst 16 based on the table stored in the third ROM 53, and sets the SOx of the NOx catalyst 17. The counter 52B that counts the estimated poisoning amount is added and controlled. Note that the process of step S16 corresponds to the case where the temperature of the three-way catalyst 16 is not the temperature at which SOx can be poisoned and is not the temperature at which SOx is released. In this pattern, the estimated SOx poisoning amount calculated from the consumption amount is added to the counter 52B as it is.

  Further, regarding the operations of the counter 52A and the counter 52B that change according to the control of the counter control unit 52C, the change in the vehicle speed, the change in the estimated amount of poisoning of SOx calculated from the fuel consumption, and the three-way catalyst 16 FIG. 10 shows a time chart when compared with each temperature change.

  Further, as shown in FIG. 10A, the speed of the vehicle travels constant at the first speed for a predetermined time, then increases to the second speed, and then increases to the second speed for a predetermined time. It changes so that it may drive constant.

  Further, the estimated SOx poisoning amount calculated from the fuel consumption amount changes in accordance with a change in the vehicle speed, as shown in FIG.

  Further, as shown in FIG. 10C, the temperature of the three-way catalyst 16 is kept constant within the temperature at which SOx can be poisoned when the vehicle speed is running at the first speed. When the vehicle speed increases to the second speed, the temperature rises with the increase, and when the vehicle speed travels constant at the second speed, the increased temperature gradually decreases. Change. Further, in FIG. 10, when the temperature of the three-way catalyst 16 remains constant within the range where SOx can be poisoned, the region 1 is defined, and the temperature of the three-way catalyst 16 increases within the poisonable range. When the temperature of the three-way catalyst 16 exceeds the range that can be poisoned, the region 3 is set.

  Here, in the area 1, as shown in FIG. 10D, the counter 52A is controlled to be added (counted up) by the counter control unit 52C at the first ratio, and the counter 52B is controlled by the counter control. The stop control is performed by the unit 52C.

  In the area 2, as shown in FIG. 10D, the counter 52A is controlled to be added (counted up) by the counter control unit 52C at the second rate, and the counter 52B is controlled by the counter control unit 52C. Is controlled to stop.

  In the area 3, as shown in FIG. 10D, the counter 52A is controlled to be stopped by the counter control unit 52C, and the counter 52B is controlled to be added at a constant rate by the counter control unit 52C. .

  Next, the procedure for correcting the start timing of SOx poisoning removal according to the travel distance will be described with reference to the flowchart shown in FIG. The ECU 2 is assumed to include a fourth ROM 54. The fourth ROM 54 is a table that determines a correction distance based on the estimated SOx poisoning amount of the three-way catalyst 16. The correction distance table corresponds to the estimated SOx poisoning amount (0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005) of the three-way catalyst 16, for example, as shown in FIG. The accumulated distance (0, 80, 160, 240, 320, 400) to be performed is determined. The correction distance table shown in FIG. 12 is an example, and is not limited to this.

  In step S20, the control unit 52 determines whether or not the temperature (bed temperature) of the three-way catalyst 16 is a temperature at which SOx is poisoned. Specifically, the control unit 52 determines whether the temperature of the three-way catalyst 16 is about 200 ° C. to 400 ° C. based on the detection value supplied from the three-way catalyst temperature sensor 40. If the temperature of the three-way catalyst 16 is the SOx poisoning temperature (YES), the process proceeds to step S21. If the temperature of the three-way catalyst 16 is not the SOx poisoning temperature (NO), the process proceeds to step S24. .

  In step S21, the controller 52 determines that the temperature (bed temperature) of the three-way catalyst 16 is the SOx release temperature, and the air-fuel ratio A / F of the exhaust gas is the air-fuel ratio A at which the three-way catalyst 16 can release SOx. It is determined whether it is smaller than / F. Specifically, the control unit 52 refers to the table stored in the third ROM 53, and the temperature of the three-way catalyst 16 is released from the SOx based on the detection value supplied from the three-way catalyst temperature sensor 40. Based on the oxygen concentration A / F1 supplied from the first A / F sensor 33 at a temperature (300 ° C. or higher), the air-fuel ratio A / F of the exhaust gas can release SOx of the three-way catalyst 16 It is determined whether or not the air-fuel ratio A / F is smaller than stoichiometric (14.7).

  The temperature (bed temperature) of the three-way catalyst 16 is the SOx release temperature (300 ° C. or higher), and the air-fuel ratio A / F of the exhaust gas is the air-fuel ratio A / F (14 7), the process proceeds to step S22, where the temperature (bed temperature) of the three-way catalyst 16 is not the SOx release temperature (300 ° C. or higher) or the air-fuel ratio A / F of the exhaust gas. Is not smaller than the air-fuel ratio A / F (14.7) at which the three-way catalyst 16 can release SOx, the process proceeds to step S23.

  In step S22, the control unit 52 performs subtraction control on the counter 52A that counts the SOx poisoning estimation amount of the three-way catalyst 16 based on the table stored in the third ROM 53, and calculates the poisoning estimation amount. To do. And the control part 52 calculates | requires integrated distance (beta) from the calculated poisoning estimated quantity based on the correction distance table stored in 4th ROM54, and subtracts it from the reference | standard start determination distance. In this way, the start timing of SOx poisoning removal is corrected based on the travel distance.

  In step S23, the control unit 52 adds and controls the counter 52A that counts the SOx poisoning estimation amount of the three-way catalyst 16 based on the table stored in the third ROM 53, and calculates the poisoning estimation amount. To do. And the control part 52 calculates | requires integrated distance (alpha) from the calculated poisoning estimated quantity based on the correction distance table stored in 4th ROM54, and adds it to the reference | standard start determination distance. In this way, the start timing of SOx poisoning removal is corrected based on the travel distance.

  Further, in step S24, the controller 52 determines that the temperature (bed temperature) of the three-way catalyst 16 is the SOx release temperature, and the air-fuel ratio A / F of the exhaust gas is an empty space where the three-way catalyst 16 can release SOx. It is determined whether the fuel ratio is smaller than the fuel ratio A / F. Specifically, the control unit 52 refers to the table stored in the third ROM 53, and the temperature of the three-way catalyst 16 is released from the SOx based on the detection value supplied from the three-way catalyst temperature sensor 40. Based on the oxygen concentration A / F1 supplied from the first A / F sensor 33, the air-fuel ratio A / F of the exhaust gas is the air-fuel ratio A / F at which the three-way catalyst 16 can release SOx. To determine if it is smaller than.

  When the temperature (bed temperature) of the three-way catalyst 16 is the SOx release temperature and the air-fuel ratio A / F of the exhaust gas is smaller than the air-fuel ratio A / F at which the three-way catalyst 16 can release SOx (YES) In step S25, the temperature (bed temperature) of the three-way catalyst 16 is not the SOx release temperature, or the air-fuel ratio A / F of the exhaust gas is the air-fuel ratio A / F at which the three-way catalyst 16 can release SOx. If not smaller (NO), the process proceeds to step S26.

  In step S25, the control unit 52 performs subtraction control on the counter 52A that counts the SOx poisoning estimation amount of the three-way catalyst 16 based on the table stored in the third ROM 53, and calculates the poisoning estimation amount. To do. Then, the control unit 52 obtains the integrated distance γ from the calculated poisoning estimation amount based on the correction distance table stored in the fourth ROM 54, and subtracts it from the reference start determination distance. In this way, the start timing of SOx poisoning removal is corrected based on the travel distance.

  In step S <b> 26, the control unit 52 controls to stop the counter 52 </ b> A that counts the estimated SOx poisoning amount of the three-way catalyst 16 based on the table stored in the third ROM 53. Note that the process of step S26 corresponds to the case where the temperature of the three-way catalyst 16 is not the temperature at which SOx can be poisoned and is not the temperature at which SOx is released. In this pattern, the estimated SOx poisoning amount calculated from the consumption amount is added to the counter 52B as it is, and SOx poisoning removal is started based on the reference start determination distance.

  In this way, the exhaust gas purification system 1 corrects the estimated SOx poisoning amount of the NOx catalyst 17 in accordance with the estimated SOx poisoning amount of the three-way catalyst 16, so that the estimated SOx poisoning of the NOx catalyst 17 is estimated. The amount can be calculated accurately. Further, since the exhaust gas purification system 1 determines the timing of the start of SOx poisoning removal of the NOx catalyst 17 based on the accurately calculated estimated amount of SOx poisoning of the NOx catalyst 17, the timing should be optimized. Thus, the fuel consumption can be reduced. Further, since the exhaust gas purification system 1 performs NOx purification with the three-way catalyst 16 and performs SOx poisoning removal with the NOx catalyst 17, the above-described A according to the timing of performing poisoning removal of the NOx catalyst 17. The air-fuel ratio of the exhaust gas is made rich by the control operation by the / F control unit 42 (air-fuel ratio control means).

  Further, when the exhaust gas purification system 1 determines the start timing of SOx poisoning removal according to the travel distance, for example, when the total travel distance reaches 400 km, the SOx poison removal removal is performed. Start control. Here, when the three-way catalyst 16 is poisoned with SOx, the NOx catalyst 17 disposed on the downstream side of the three-way catalyst 16 is not poisoned with SOx. There is no need to perform SOx poisoning removal control.

  Therefore, the exhaust gas purification system 1 according to the present invention corrects the determination distance 400 km for starting SOx poisoning removal according to the estimated SOx poisoning amount of the three-way catalyst 16, so that wasteful SOx poisoning removal control is performed. Can be eliminated. Further, as described above, in the exhaust gas purification system 1 according to the present invention, the three-way catalyst 16 is SOx poisoned by adding the distance calculated based on the correction distance table shown in FIG. 12 to the start determination distance. Accordingly, the start determination distance is corrected to be longer, and when SOx is released from the three-way catalyst 16, the start determination distance is corrected to be shorter. Therefore, the three-way catalyst 16 is poisoned by SOx. The start timing of SOx poisoning removal of the NOx catalyst 17 is extended, and the fuel consumption can be improved by about 1 to 2 percent.

  The present invention is not limited to the embodiment described above, and can be implemented in various modes. Furthermore, the present invention is not limited to an engine mounted on a vehicle, but can be applied to various industrial internal combustion engines including an engine for a marine propulsion device such as an outboard motor having a crankshaft arranged in a vertical direction. Of course. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

1 is a diagram schematically showing an exhaust gas purification system to which the present invention is applied together with an internal combustion engine. It is a figure which shows a part of exhaust gas purification apparatus. FIG. 2 is a first diagram showing a simplified diagram of the exhaust gas purification system shown in FIG. 1. It is a schematic diagram which shows the table for determining a target air fuel ratio. It is a schematic diagram which shows the table in which the correction coefficient corresponding to the temperature of a three-way catalyst is defined. It is a flowchart with which it uses for description which controls so that air-fuel ratio A / F becomes the target air-fuel ratio after correction | amendment. FIG. 3 is a second diagram showing a simplified diagram of the exhaust gas purification system shown in FIG. 1. It is a schematic diagram which shows the table for determining the discharge amount of SOx by a three-way catalyst. It is a flowchart with which it uses for description about the procedure which correct | amends the poisoning estimated amount of SOx. It is a figure where it uses for description of the specific operation | movement of a counter. It is a flowchart with which it uses for description about the procedure which correct | amends the start timing of the poisoning removal of SOx by a travel distance. It is a schematic diagram which shows the table which determines the correction distance based on the poisoning amount of SOx of a three-way catalyst.

Explanation of symbols

  1 exhaust gas purification system, 2 ECU, 3 engine, 4 intake pipe, 5 exhaust pipe, 6 injector, 8 supercharger, 8c variable vane, 12 throttle valve, 13a swirl valve, 14b EGR control valve, 16 three-way catalyst, 17 NOx catalyst, 30 crank angle sensor, 31 air flow sensor, 33 first A / F sensor, 36 NOx catalyst temperature sensor, 40 three-way catalyst temperature sensor, 41 first ROM, 42 A / F control unit, 43 second ROM, 44 correction coefficient calculation unit, 50 three-way catalyst temperature adjustment unit, 51 NOx catalyst temperature adjustment unit, 52 control unit, 52A, 52B counter, 52C counter control unit, 53 third ROM

Claims (3)

A three-way catalyst and a NOx reduction / absorption catalyst that are arranged in series on the exhaust gas flow path of the internal combustion engine that can be driven by self-ignition, and that have a NOx trapping / purifying function and also a SOx trapping / purifying function;
Temperature adjustment means for raising the temperature of the NOx reduction / absorption catalyst to a temperature at which SOx trapped by the NOx reduction / absorption catalyst is released;
Air-fuel ratio control means for adjusting the air-fuel ratio of the exhaust gas supplied to the three-way catalyst and the NOx reduction absorption catalyst,
At a predetermined timing, after the heating by the temperature control unit the NOx reduction absorbent catalyst to a temperature at which SOx is released, the theoretical air-fuel ratio of the exhaust gas by the air-fuel ratio control means to said three-way catalyst An exhaust gas purification system that removes SOx from the NOx reduction and absorption catalyst while purifying NOx by the three-way catalyst by controlling to a richer side than the air-fuel ratio,
The exhaust gas purification system includes air-fuel ratio detection means for detecting an air-fuel ratio of exhaust gas supplied to the three-way catalyst,
Temperature detecting means for detecting the temperature of the three-way catalyst;
A target air-fuel ratio table for determining a target air-fuel ratio that is lower than the stoichiometric air-fuel ratio from the relationship between the torque of the internal combustion engine and the rotational speed, and a correction coefficient table corresponding to the temperature of the three-way catalyst are stored. Storage means;
Correction coefficient calculation means for calculating a correction coefficient from the correction coefficient table based on the temperature detected by the temperature detection means;
The air-fuel ratio control means is stored in the storage means based on the torque and the rotational speed detected from the internal combustion engine after the NOx reduction and absorption catalyst has been heated to a temperature at which SOx is released . The target air-fuel ratio is obtained from the target air-fuel ratio table, and the target air-fuel ratio obtained from the target air-fuel ratio table is corrected based on the correction coefficient calculated by the correction coefficient calculating means and detected by the air-fuel ratio detecting means. By controlling the internal combustion engine so that the corrected air / fuel ratio becomes the corrected target air / fuel ratio, the NOx is removed by the three-way catalyst while removing NOx from the NOx reduction catalyst,
The correction coefficient table corrects the target air-fuel ratio obtained from the target air-fuel ratio table to the lean side when the temperature of the three-way catalyst detected by the temperature detecting means is within a predetermined range, When the temperature of the three-way catalyst detected by the temperature detecting means is lower than a lower limit value within a predetermined range, the three-way catalyst is constituted by a correction coefficient for correcting the target air-fuel ratio obtained from the target air-fuel ratio table to the rich side. An exhaust gas purification system characterized by   The air-fuel ratio control means controls the internal combustion engine to increase the post-injection amount when the air-fuel ratio detected by the air-fuel ratio detection means is leaner than the target air-fuel ratio, and the target 2. The exhaust gas purification system according to claim 1, wherein the internal combustion engine is controlled so as to reduce a post-injection amount when richer than an air-fuel ratio. In the exhaust gas flow path, the three-way catalyst and the NOx reduction / absorption catalyst are provided in this order from the upstream side toward the downstream side,
The exhaust gas purification system according to claim 1 or 2, wherein the NOx reduction / absorption catalyst is provided under a floor of a vehicle.

Images