JP4556367B2 - Engine exhaust purification device and method for judging purification - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an engine exhaust purification device and a purification performance determination method thereof.
[0002]
[Prior art]
The exhaust gas discharged from the combustion chamber of an automobile engine into the exhaust passage contains air pollutants such as NOx (nitrogen oxide), HC (hydrocarbon), CO (carbon monoxide), and PM (airborne matter). In order to purify these air pollutants, an exhaust gas purification device using an exhaust gas purification catalyst is provided in the exhaust passage. Then, using such an exhaust gas purification catalyst, HC, CO, and PM are purified by oxidation, and NOx is purified by reduction. In addition, in order to reduce NOx, a reducing component (reducing agent) that deprives oxygen from NOx. However, in an automobile engine, HC in exhaust gas is used as a reducing component.
[0003]
By the way, in general, the exhaust gas purification catalyst gradually deteriorates due to heat or poisoning, and its activity is lowered. Therefore, in an automobile engine, it is necessary to appropriately grasp the purification performance or degree of deterioration of the exhaust gas purification catalyst. Thus, JP-A-8-284648 discloses O 2 provided downstream of the exhaust gas purification catalyst.₂A catalyst deterioration diagnosis device that detects a decrease in the low-temperature activity of the exhaust gas purification catalyst based on the degree of activation delay after engine start of the sensor output, and performs the deterioration diagnosis of the exhaust gas purification catalyst based on this detection Is disclosed.
[0004]
[Problems to be solved by the invention]
However, a conventional catalyst deterioration diagnosis device as disclosed in, for example, Japanese Patent Laid-Open No. 8-284648 has a problem that it is difficult to accurately determine the purification performance or the degree of deterioration of the exhaust gas purification catalyst. The present invention has been made to solve the above-described conventional problems, and provides a means for easily and accurately determining the purification performance or the degree of deterioration of an exhaust gas purification catalyst at a low temperature. It should be a challenge.
[0005]
[Means for Solving the Problems]
  An engine exhaust gas purification apparatus according to the present invention, which has been made to solve the above-described problems, includes: (i) a catalyst (three-way catalyst, four-way catalyst, or NOx trap catalyst) disposed in an exhaust passage of an engine and having oxidation performance. Noble metal catalyst including NOx reduction catalyst) and (ii) O in exhaust gas upstream of the catalyst₂Upstream O to detect (or estimate) concentration₂Concentration detection means; and (iii) O in exhaust gas downstream of the catalyst₂Downstream O to detect (or estimate) concentration₂Concentration detection means, and (iv) upstream O₂Upstream O detected by the concentration detection means₂Concentration and downstream O₂The downstream O detected by the concentration detection means₂And (v) a catalyst temperature detecting means for detecting (or estimating) the catalyst temperature in an engine exhaust purification apparatus comprising a purification performance determining means for determining a catalyst purification performance (or degree of deterioration) based on the concentration, (Vi) Exhaust gas composition changing means (O) for changing the reducing component (reducing agent) concentration in the exhaust gas upstream of the catalyst so as to shift between the high concentration state and the low concentration state.₂(Vii) the purifying performance determining means is a catalyst in the case where the reducing component concentration is changed by the exhaust gas composition changing means. A predetermined temperature range in which the oxidation performance of the catalyst is not more than a predetermined level (for example, a predetermined temperature range lower than the catalyst temperature (light-off temperature) at which the reduction component purification rate of the catalyst is a predetermined value)OutsideUpstream O detected when₂Concentration and downstream O₂Based on the concentration (deviation, change degree deviation, etc.), the purification performance (or deterioration degree) of the catalyst is determined.
[0006]
In general, this type of catalyst having oxidation performance is in an inactive state when its temperature (catalyst temperature) is low. Then, activation starts when the catalyst temperature rises to a certain temperature (hereinafter, this temperature is referred to as “activation start temperature”). Further, when the catalyst temperature rises, the degree of activation increases accordingly, and when the catalyst temperature rises above a certain temperature, the catalyst is completely activated (hereinafter, this temperature is referred to as “activation completion temperature”). However, the activation start temperature and the activation completion temperature are not so different (for example, 20 ° C.). The catalyst temperature at which the degree of activation or the purification rate of the catalyst reaches a predetermined value (for example, 50%) is called “light-off temperature”. Here, the activation start temperature, the activation completion temperature, and the light-off temperature become higher as the catalyst deteriorates (however, there is an upper limit).
[0007]
On the other hand, when the reducing component concentration upstream of the catalyst is changed from the high concentration state to the low concentration state or from the low concentration state to the high concentration state, the reducing component O₂As consumption changes, upstream O₂Concentration and downstream O₂Each concentration varies. For example, in the case of a zeolitic catalyst, the upstream O is around the light-off temperature.₂Concentration change and downstream O₂Difference from density change (hereinafter referred to as “O₂This is called “density difference”. ) Becomes larger, and both the low temperature side and the high temperature side are O₂The difference in density change is reduced. That is, O₂The catalyst temperature when the difference in concentration change is the largest indicates the light-off temperature of the catalyst.
In the case of an alumina-based catalyst, in the temperature range close to the light-off temperature, the greater the degree of activation of the catalyst, the more O₂The difference in density change increases. That is, O₂The catalyst temperature at which the concentration variation difference is a specific value almost indicates the light-off temperature of the catalyst.
At this time, whether it is a zeolite-based catalyst or an alumina-based catalyst, as the catalyst is activated, the upstream O₂For the absolute value of concentration, downstream O₂The absolute value of the concentration naturally decreases on average.
[0008]
Therefore, in this exhaust purification device, the predetermined temperature range in which the purification performance of the catalyst should be determined is, for example, slightly higher than the light-off temperature of the undegraded catalyst, and slightly higher than the light-off temperature of the completely deteriorated catalyst. If set to the range up to the temperature, O₂Based on the difference in concentration variation, the light-off temperature of the catalyst can be easily and accurately grasped. For example, in the case of a zeolitic catalyst, O₂The catalyst temperature at which the difference in concentration change is maximum is almost the light-off temperature. In the case of an alumina catalyst, O₂The catalyst temperature at which the difference in concentration change becomes the specific value is almost the light-off temperature. From this light-off temperature, it is possible to easily and accurately determine the purification performance or the degree of deterioration of the catalyst at a low temperature. Therefore, according to this exhaust gas purification apparatus, the purification performance or deterioration degree of the catalyst can be easily and accurately determined.
[0009]
  In the exhaust emission control device, the purification performance determination means includes the upstream O when the reducing component concentration is in the low concentration state.₂Typical values of concentration (for example, peak value, average value, etc.) and upstream O when in a high concentration state₂The first representative value difference, which is the difference from the representative value of the concentration, and the downstream O when the reducing component concentration is in the low concentration state.₂Typical value of concentration and downstream O when in high concentration state₂It is preferable to determine the purification performance of the catalyst based on the second representative value difference that is the difference from the representative value of the concentration. In this way, the determination performance of the catalyst purification performance or the degree of deterioration is improved.
  In this case, the purification performance determination means has a predetermined range of deviation between the first representative value difference and the second representative value difference.OutsideMore preferably, it is determined that the catalyst has deteriorated when the catalyst temperature exceeds the predetermined temperature.
[0010]
  In the exhaust purification apparatus,The purification performance judging means judges the purification performance of the catalyst when the catalyst temperature is in a predetermined temperature range where the oxidation performance of the catalyst is not more than a predetermined degree.It is preferable to be.
[0011]
In the exhaust emission control device, the exhaust gas composition changing means has a predetermined period (for example, in a transition period) in which the catalyst temperature transitions between a state where the catalyst temperature is lower than the predetermined temperature and a state where the catalyst temperature is higher than the predetermined temperature (for example, during transition). 1 to 10 s) It is preferable that the reducing component concentration is increased or decreased (for example, by a difference of 1000 ppm). In this way, the purification performance or the degree of deterioration of the catalyst can be determined more accurately and reliably.
[0012]
In the exhaust gas purification apparatus, the exhaust gas composition changing means starts the acceleration when the catalyst temperature is lower than the predetermined temperature, and then reduces the reducing component concentration over a predetermined period (for example, until the catalyst is activated). It is preferable to increase or decrease. In this way, the purification performance or the degree of deterioration of the catalyst can be determined more accurately and reliably. In addition, although the exhaust gas temperature is relatively low in a diesel engine, the exhaust gas temperature rises during acceleration, so that the purification performance or the degree of deterioration of the catalyst can be reliably determined.
[0013]
In the exhaust purification apparatus, the upstream side O is within the transition period.₂O to reduce concentration₂Concentration reducing means (for example, post injection, ignition retard) is preferably provided. In this way, the purification performance or the degree of deterioration of the catalyst can be determined with higher accuracy.
[0014]
  The method for determining the purification performance of the engine exhaust purification system according to the present invention includes: (i) a catalyst that is disposed in the exhaust passage of the engine and has oxidation performance; and O in the exhaust gas upstream of the catalyst.₂Upstream O to detect concentration₂Sensor and O in exhaust gas downstream of catalyst₂Downstream side O to detect concentration₂Engine exhaust purification device equipped with sensor (ii) upstream O₂Upstream O detected by sensor₂Concentration and downstream O₂Downstream side O detected by the sensor₂And (iii) reducing component concentration in the exhaust gas upstream of the catalyst between a high concentration state and a low concentration state. On the other hand, (iv) when the reducing component concentration is changed, the catalyst temperature is within a predetermined temperature range in which the oxidation performance of the catalyst is not more than a predetermined levelOutsideO₂Concentration and downstream O₂The purification performance of the catalyst is determined based on the concentration.
  According to this purification performance determination method, it is possible to easily and accurately determine the purification performance or the degree of deterioration of the catalyst for the same reason as in the case of the exhaust purification apparatus.
[0015]
  Another engine exhaust purification device (control device) according to the present invention includes (i) a catalyst that is disposed in the exhaust passage of the engine and has oxidation performance, and (ii) O in exhaust gas upstream of the catalyst.₂Upstream O to detect concentration₂Concentration detection means; and (iii) O in exhaust gas downstream of the catalyst₂Downstream side O to detect concentration₂Concentration detection means, and (iv) upstream O₂Upstream O detected by the concentration detection means₂Concentration and downstream O₂The downstream O detected by the concentration detection means₂In an engine exhaust purification device (control device) comprising a control state change means for changing the control state of the engine based on the concentration, (v) catalyst temperature detection means for detecting the catalyst temperature, and (vi) upstream of the catalyst Exhaust gas composition changing means for changing the concentration of the reducing component in the exhaust gas so as to shift between a high concentration state and a low concentration state, and (vii) the control state changing means includes the exhaust gas composition When the reducing component concentration is changed by the changing means, the catalyst temperature is within a predetermined temperature range in which the oxidation performance of the catalyst is not more than a predetermined degree.OutsideUpstream O detected when₂Concentration and downstream O₂The control state of the engine is changed based on the concentration.
[0016]
According to this exhaust gas purification device, O, for the same reason as in the case of the exhaust gas purification device,₂Based on the concentration variation difference, the light-off temperature of the catalyst, and hence the purification performance or degree of deterioration of the catalyst can be easily and accurately grasped, and the control state of the engine can be preferably changed accordingly. For this reason, the controllability of the engine can be improved and the emission performance can be improved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described.
As shown in FIG. 1, in each cylinder (only one is shown) of an automobile multi-cylinder diesel engine 1 (hereinafter referred to as “engine 1”), the intake passage 2 enters the combustion chamber 3 in the intake stroke. Air for fuel combustion is inhaled. The air in the combustion chamber 3 is compressed by the piston 4 in the compression stroke, and is in a high temperature / high pressure state. In the vicinity of the top dead center of the compression stroke or the expansion stroke, fuel (light oil or the like) is injected from the fuel injection valve 5 into the high-temperature and high-pressure air in the combustion chamber 3, and this fuel self-ignites and burns. As will be described later, the fuel injection is divided into two parts, basic injection (main injection) and post injection. The combustion gas generated by the combustion of the fuel, that is, the exhaust gas, is discharged to the exhaust passage 6 in the exhaust stroke. Such a stroke is repeated and the piston 4 reciprocates, and the reciprocating motion of the piston 4 is converted into the rotational motion of the crankshaft 7.
[0018]
The fuel injection valve 5 is arranged so that the injection port faces the combustion chamber 3, and injects fuel directly into the combustion chamber 3. Here, the fuel injection valve 5 is connected to the fuel supply passage 8. A high pressure fuel pump 9 driven by the crankshaft 7 and a fuel distributor 10 for distributing fuel to each cylinder are interposed in the fuel supply passage 8. The high pressure fuel pump 9 operates so that the fuel pressure in the fuel supply passage 8 is maintained at a predetermined value or more.
[0019]
The intake passage 2 is provided with an adjustment valve 11 (open / close valve) that adjusts the flow of air from the intake passage 2 to the combustion chamber 3. Although not shown, the intake passage 2 is provided with an air cleaner for removing dust in the air and an air flow sensor for detecting the air flow rate in order from the upstream side in the air flow direction. . The engine 1 is provided with a water temperature sensor 18 for detecting the engine water temperature (engine temperature).
[0020]
In the exhaust passage 6, in order to purify HC, CO, NOx, etc. in the exhaust gas, a zeolite-based catalyst (hereinafter simply referred to as “catalyst”) having oxidation performance (oxidation promotion function) and reduction performance (reduction promotion function). The exhaust gas purification device 12 (catalytic converter) using the catalyst temperature sensor is interposed, and the exhaust gas purification device 12 is provided with a catalyst temperature sensor 13 for detecting the catalyst temperature. The upstream and downstream sides of the exhaust purification device 12 (catalyst) are respectively O 2 in the exhaust gas in the exhaust passage 6.₂Upstream O to detect concentration₂Sensor 14 (Linear O₂Sensor) and downstream O₂Sensor 15 (Linear O₂Sensor).
[0021]
Here, porous MFI (zeolite) is used for the catalyst carrier (base material). And this MFI carries Pt (platinum), Rh (rhodium), Pd (palladium), etc. as a catalyst noble metal. As the catalyst carrier, porous β-type zeolite or porous Y-type zeolite may be used instead of MFI. Zeolite such as MFI, β-zeolite, and Y-type zeolite has the property of trapping (adsorbing) HC at a predetermined temperature (for example, 200 to 240 ° C.) or less and releasing the HC when the temperature exceeds a predetermined temperature. Have.
[0022]
Further, the engine 1 is provided with an EGR passage 16 that recirculates a part of the exhaust gas in the exhaust passage 6 to the intake passage 2 as EGR gas. An EGR control valve 17 for controlling the EGR gas flow rate is interposed in the EGR passage 16. Thereby, a part of the exhaust gas in the exhaust passage 6 can be recirculated to the intake passage 2 while the flow rate is adjusted by the EGR control valve 17. Accordingly, air (fresh air) introduced from the outside of the engine and EGR gas (exhaust gas) passing through the EGR control valve 17 are sucked into the combustion chamber 3.
[0023]
Further, the engine 1 is provided with a control unit 20 for performing various engine controls and for determining the purification performance or the degree of deterioration (monitor control) of the exhaust purification device 12 (catalyst). The control unit 20 includes a purification performance determining means, an exhaust gas composition changing means, an O₂A comprehensive control device for the engine 1 including a concentration reduction unit, a control state change unit, and the like, and performs various controls such as monitor control and fuel control, which will be described later, based on various control information. . Hereinafter, a specific control method of monitor control and fuel control executed by the control unit 20 will be described with reference to flowcharts shown in FIGS.
[0024]
First, a control method for monitor control will be described with reference to the flowcharts shown in FIGS.
In this monitor control, the catalyst temperature Tcat detected by the catalyst temperature sensor 13 in step S1, the upstream O₂Upstream side O detected by sensor 14₂Concentration Oxup (n), downstream O₂Downstream side O detected by sensor 15₂Various control information (data) such as density Oxdn (n) is input.
[0025]
  Next, in step S2, the catalyst temperature Tcat is changed to the first catalyst temperature Tcat._TenHigher and second catalyst temperature Tcat₂₀Lower (Tcat_Ten<Tcat <Tcat₂₀) Or not.
FThe Resh catalyst (a catalyst that has not deteriorated at all) is in an inactive state when the catalyst temperature Tcat is lower than the activation start temperature (for example, 200 ° C.), and the HC purification rate is almost 0, but the catalyst temperature Tcat is active. When the temperature becomes higher than the catalyst start temperature, the catalyst activity or the HC purification rate increases as the catalyst temperature Tcat increases. The catalyst is completely activated when the catalyst temperature Tcat is equal to or higher than the activation completion temperature (for example, 220 ° C.), and the HC purification rate is almost 100%. Note that the light-off temperature at which the HC purification rate reaches a predetermined value (for example, 50%) is between the activation start temperature and the activation completion temperature (for example, 210 ° C.).
[0026]
When the catalyst deteriorates, the activation start temperature, activation completion temperature, and light-off temperature increase as the degree of deterioration increases. For example, in a completely deteriorated catalyst, the activation start temperature, the activation completion temperature, and the light-off temperature are several tens of degrees C. (for example, 40.degree. C.) higher than the fresh catalyst. In the case of a deteriorated catalyst, the HC purification rate does not reach 100% even when the catalyst temperature is equal to or higher than the activation completion temperature.
Here, the first catalyst temperature Tcat_TenIs set to a temperature slightly lower than the light-off temperature of the fresh catalyst, and the second catalyst temperature Tcat_{2 0}Is set to a light-off temperature of the catalyst that is almost completely deteriorated or slightly higher.
[0027]
In step S2, Tcat_Ten<Tcat <Tcat_{2 0}(YES), in steps S3 to S14, O₂Density change amount difference ΔOx is a predetermined threshold value ΔOxav₀Data processing is performed such as storing the catalyst temperature Tcat (n) in the case of exceeding.
First, in steps S3 to S6, the first reference time t after the monitor control is started.₁₀Upstream O in the period until the elapse of time (period in which the HC concentration is in a high concentration state)₂Concentration average value Oxup₁av and downstream O₂Concentration average value Oxdn₁av is calculated.
[0028]
  Figure12As shown in (a), when the monitor control is being performed, the HC addition control signal is turned on / off at a predetermined cycle, and accordingly, the HC concentration upstream of the catalyst is in a high concentration state and a low concentration state. Are changed at predetermined intervals. Here, the time width during which the HC addition control signal is turned on and the HC concentration upstream of the catalyst is in a high concentration state is expressed as τ₁(For example, 0.5 to 5 s), and the time width during which the HC addition control signal is turned off and the HC concentration upstream of the catalyst is in the low concentration state is τ₂(For example, 0.5 to 5 s), the first reference time t₁₀Is the time width τ₁Corresponding to The second reference time t described later₂₀Is the time width (τ₁+ Τ₂).
[0029]
Specifically, in step S3, the elapsed time t after the start of monitor control is the first reference time t.₁₀It is determined whether or not it is less than the first reference time t₁₀If less than (YES), the first reference time t₁₀Repeatedly in step S4 until O reaches₂Concentration Oxup (n) and downstream O₂The density Oxdn (n) is stored.
[0030]
In step S5, the elapsed time t is changed to the first reference time t.₁₀Whether the first reference time t is reached or not is determined.₁₀(YES), in step S6, the period (0 to t₁₀) That is, upstream O during the period when the HC concentration is in a high concentration state₂Concentration average value Oxup₁av and downstream O₂Concentration average value Oxdn₁av is calculated (averaged).
[0031]
Next, in steps S7 to S10, the first reference time t₁₀After the elapse of the second reference time t₂₀Upstream O in a period until lapse of time (period in which the HC concentration is in a low concentration state)₂Concentration average value Oxup₂av and downstream O₂Concentration average value Oxdn₂av is calculated.
Specifically, in step S7, the elapsed time t after the start of monitor control is the first reference time t.₁₀And the second reference time t₂₀Is less than (t₁₀<T <t₂₀) Or not, and t₁₀<T <t₂₀If (YES), the second reference time t₂₀Until it reaches the upstream O in step S8₂Concentration Oxup (n) and downstream O₂The density Oxdn (n) is stored.
[0032]
In step S9, the elapsed time t is changed to the second reference time t.₂₀Whether or not the second reference time t is reached.₂₀(YES), in step S10, the period (t₁₀~ T₂₀) That is, upstream O during the period when the HC concentration is in a low concentration state₂Concentration average value Oxup₂av and downstream O₂Concentration average value Oxdn₂av is calculated (averaged).
[0033]
Next, in step S11, the upstream O when the HC concentration is in a low concentration state is obtained by the following equations 1 and 2.₂Concentration average value Oxup₂upstream O when in a high concentration state with av₂Concentration average value Oxup₁Difference ΔOxup from av (hereinafter referred to as “upstream O₂This is called “density difference ΔOxup”. ) And downstream O when the HC concentration is in a low concentration state₂Concentration average value Oxdn₂Downstream O when in a high concentration state with av₂Concentration average value Oxdn₁ΔOxdn (hereinafter referred to as “downstream O₂Density difference ΔOxdn ”).
ΔOxup ← Oxup₂av− Oxup₁av …………………………………… Formula 1
ΔOxdn ← Oxdn₂av− Oxdn₁av …………………………………… Formula 2
[0034]
Subsequently, in step S12, the upstream O₂Concentration difference ΔOxup and downstream O₂Based on the concentration difference ΔOxdn, O₂A density change amount difference ΔOx is calculated.
ΔOx ← ΔOxup−ΔOxdn ………………………………………… Formula 3
[0035]
In step S13, O₂Density change amount difference ΔOx is a predetermined threshold value ΔOxav₀If it exceeds (YES), the current catalyst temperature Tcat (n) is stored in step S14. O₂Density change difference ΔOx is the threshold ΔOxav₀If it is below, step S14 is skipped and the process returns to step S1.
Thus, in steps S2 to S14, Tcat₁₀~ Tcat₂₀Within the range of O₂Density change difference ΔOx is the threshold ΔOxav₀The catalyst temperature Tcat (n) in the case of exceeding is continuously memorized.
[0036]
In step S2, the catalyst temperature Tcat is changed to the first catalyst temperature Tcat._TenOr the second catalyst temperature Tcat_{2 0}When it is determined as above (NO), it is determined in steps S15 to S21 whether or not the catalyst is deteriorated.
Specifically, in step S15, O₂After the density change amount difference ΔOx is reset, the previous time is Tcat in step S16._Ten<Tcat <Tcat_{2 0}It is determined whether or not. And last time Tcat_Ten<Tcat <Tcat_{2 0}If it is (YES), in steps S17 to S21, it is determined whether or not the catalyst has deteriorated. The previous Tcat_Ten<Tcat <Tcat_{2 0}If not (NO), the process returns to step S1.
[0037]
In step S17, each catalyst temperature Tcat (n) stored in step S14 is read. Subsequently, in step S18, these catalyst temperatures Tcat (n) are averaged to calculate a catalyst temperature average value Tcat (n) av. In step S19, the catalyst temperature average value Tcat (n) av is set to a predetermined threshold value Tcat (n) av.₀It is determined whether it is greater than Tcat (n) av> Tcat (n) av₀If so (YES), it is determined in step S20 that the catalyst has deteriorated. On the other hand, Tcat (n) av ≦ Tcat (n) av₀If (NO), it is determined in step S21 that the catalyst is normal. Note that after the determination of the purification performance or the degree of deterioration of the catalyst is made in this way, the monitor control ends. That is, this determination is performed only once in one run. This is because the catalyst does not deteriorate so rapidly.
[0038]
Thus, in this monitor control, O₂Density change difference ΔOx is the threshold ΔOxav₀When the catalyst temperature average value Tcat (n) av in the case of exceeding is high, it is determined that the catalyst is deteriorated, and when it is low, it is determined that the catalyst is normal. The reason is as follows.
That is, as described above, when the catalyst deteriorates, the light-off temperature (the activation start temperature and the activation completion temperature also) increases according to the degree of deterioration. Therefore, it can be determined whether the catalyst is degraded or normal depending on whether the light-off temperature is higher than a predetermined threshold.
[0039]
On the other hand, in the case of a zeolitic catalyst, O near the light-off temperature.₂The concentration change difference ΔOx becomes large, and both the low temperature side and the high temperature side are O.₂The density change amount difference ΔOx becomes small. Therefore, O₂The catalyst temperature when the concentration change amount difference ΔOx is the largest indicates the light-off temperature of the catalyst.
[0040]
  Figure10(A) to (c)TheFor the Olite fresh catalyst, the concentration of HC upstream of the catalyst is shown.12The upstream O at around 160 ° C., around 200 ° C., and around 240 ° C. when increased or decreased in a pattern as shown in (a).₂Concentration Oxup and downstream O₂The change characteristic with respect to time of density Oxdn is shown.
  Figure10(A)-(c), figure11(A) to (c) are upstream O₂Concentration and downstream O₂Concentration and O₂Relative comparisons are made with reference to the low concentration state. That is, when the light is off or activated, the catalyst is activated.₂Downstream O against concentration₂Average density O₂Since the absolute value of the concentration decreases on average, the data is processed so that it can be corrected and ΔOx can be easily determined.
ThisThis fresh catalyst is in an inactive state at around 160 ° C., is almost in a light-off state at around 200 ° C., and is completely active at around 240 ° C. Figure10As is clear from (a) to (c), in this fresh catalyst, near the light-off temperature (around 200 ° C.), O₂The density change amount difference ΔOx (= ΔOxup−ΔOxdn) is very large. Further, in the vicinity of 160 ° C. on the low temperature side and 240 ° C. on the high temperature side, both are O₂The density change amount difference ΔOx is small.
[0041]
  Also figure11(A) to (c)TheFor Olite-based deteriorated catalysts, the HC concentration upstream of the catalyst is plotted.12The upstream O at around 200 ° C., around 240 ° C., and around 280 ° C. when increased or decreased in a pattern as shown in (a).₂Concentration Oxup and downstream O₂Shows the change characteristics of concentration Oxdn with time. ThisThe deteriorated catalyst is in an inactive state near 200 ° C., is almost in a light-off state near 240 ° C., and is in a completely active state near 280 ° C. Figure11As is clear from (a) to (c), thisdeteriorationIn the case of a catalyst, near the light-off temperature (around 240 ° C.), O₂The density change amount difference ΔOx (= ΔOxup−ΔOxdn) is very large. Further, in the vicinity of 200 ° C. on the lower temperature side and 280 ° C. on the higher temperature side, both are O₂The density change amount difference ΔOx is small.
[0042]
  Figure15In (a) and (b), when a zeolite-based catalyst is used, the upstream O in the case where the HC concentration upstream of the catalyst is repeatedly increased or decreased in a predetermined cycle.₂Concentration and downstream O₂The change characteristic of density is shown. Figure15(A), (b), (d) are upstream and downstream O₂Each concentration is a relative comparison using the values at the time of HC increase as a reference. Where15(A) is at the time of light-off.15(B) is when activated.
  Also figure15(C) shows a case where the catalyst temperature is raised while repeatedly increasing / decreasing the HC concentration upstream of the zeolite catalyst in a predetermined cycle.₂The change characteristics with respect to time of the density change amount difference ΔOx are shown.
[0043]
  Figure15As is clear from (a) to (c), in the zeolitic catalyst, O₂The density change difference ΔOx is the largest near the light-off temperature, and both the low temperature side and the high temperature side are O₂The density change amount difference ΔOx is small. Thus, O₂Although it is not necessarily clear that the density change amount difference ΔOx becomes the maximum near the light-off temperature, it is considered to be due to the following reason. That is, at the time of light-off, the catalytic metal (noble metal) is not completely activated, and the HC temporarily taken in on the zeolite does not burn when the amount of HC is increased. After this, O cut by HC cut₂As the concentration increases, the accumulated HC becomes O at once.₂React with. As much as the accumulated HC burns, O₂Decreases in response.
  On the other hand, when activated, the catalytic metal is also fully activated, and less HC accumulates on the zeolite when the amount of HC is increased.₂It is considered that there is no significant difference in density.
[0044]
  Figure15In (d), at the time of light-off, after changing the HC concentration upstream of the zeolite catalyst from the low concentration state to the high concentration state, the upstream O in the case where the high concentration state is continued.₂Concentration and downstream O₂A relative comparison of the concentration change characteristics is shown. Figure15As is clear from (d), O₂Immediately after setting the concentration to a high concentration state, for a while, downstream O₂The concentration is greatly reduced. This is O₂This is because immediately after the concentration is made high, rapid combustion occurs due to the release of HC adhering to the surface of the zeolite catalyst. However, after this, the downstream O₂Concentration rises and eventually upstream O₂Concentration and downstream O₂The difference in density is almost eliminated. This is because the HC adhering to the zeolite catalyst gradually disappears, and O₂This is because consumption is reduced.
  Therefore, it can be said that it is necessary or effective to repeatedly increase or decrease the HC concentration upstream of the catalyst also in the monitor control of the zeolite catalyst.
[0045]
Thus, in the case of a zeolitic catalyst, in the vicinity of the light-off temperature, regardless of the presence or absence or degree of deterioration, O₂The density change amount difference ΔOx increases. Therefore, regardless of the presence or degree of deterioration, O₂The catalyst temperature Tcat when the concentration change amount difference ΔOx becomes large substantially indicates the light-off temperature.
In other words, the catalyst temperature average value Tcat (n) av in the monitor control of the engine 1 using the zeolite catalyst almost indicates the light-off temperature of the catalyst. Therefore, according to this monitor control, the light-off temperature of the catalyst can be easily and accurately grasped, and the purification performance or the degree of deterioration can be easily and accurately determined.
[0046]
Hereinafter, the control method of fuel control will be described with reference to the flowcharts shown in FIGS.
In this fuel control, first, in step S31, the catalyst temperature Tcat detected by the catalyst temperature sensor 13, the upstream side O₂Upstream side O detected by sensor 14₂Concentration Oxup (n), downstream O₂Downstream side O detected by sensor 15₂Various control information (data) such as the concentration Oxdn (n) and the engine water temperature Tw detected by the water temperature sensor 18 are input.
[0047]
Next, in step S32, the fuel basic injection amount Qmb (main injection amount) and the basic injection timing Imb (main injection timing) are calculated (set) according to the accelerator opening (load) and the engine speed. The Subsequently, in step S33, the fuel post injection amount Qpb and the post injection timing Ipb are calculated (set). The basic fuel injection and the post-injection are executed with a pause interval of 0.05 to 1.0 ms. The post injection is performed as follow-up injection for reducing the generation of smoke at the time of high load and high rotation, or for supplying HC for NOx reduction to the NOx reduction catalyst. The fuel may be injected in multiple stages, or post injection may not be performed (single stage injection).
[0048]
In step S34, it is determined whether or not the monitor control (light-off monitor) is finished. If the monitor control is not finished (NO), the catalyst temperature Tcat is changed to the first catalyst temperature Tcat in step S35._TenHigher and second catalyst temperature Tcat_{2 0}Lower (Tcat_Ten<Tcat <Tcat_{2 0}) Or not. And Tcat_Ten<Tcat <Tcat_{2 0}If so (YES), fuel control for assisting monitor control (hereinafter referred to as “monitor auxiliary fuel control”) is performed. That is, in the current travel (operation of the engine 1), the monitor auxiliary fuel control is performed only when the monitor control is not yet finished and the steps S1 to S14 are repeatedly executed in the monitor control. In other cases, normal fuel injection is performed based on the fuel injection amount and fuel injection timing set in steps S32 to S33.
[0049]
When the monitor auxiliary fuel control is performed, first, in step S36, the previous catalyst temperature Tcat is the first catalyst temperature Tcat._TenIt is determined whether or not: The previous catalyst temperature Tcat is the first catalyst temperature Tcat._TenIf it is below (YES), that is, if the monitor auxiliary fuel control has not been performed previously, 1 is set in the flag Fcatin in step S37, and then the monitor auxiliary fuel control is executed in steps S39 to S49. Is done. The flag Fcatin is a flag that is set to 1 when the monitor auxiliary fuel control is being performed.
[0050]
In step S36, the previous catalyst temperature Tcat is changed to the first catalyst temperature Tcat._TenIf it exceeds (NO), it is determined in step S38 whether or not the flag Fcatin is 1. If the flag Fcatin is 1, monitor auxiliary fuel control is executed in steps S39 to S49.
[0051]
When the monitor auxiliary fuel control is performed, first, in steps S39 and S40, the accelerator opening change amount Δα is set to a predetermined value Δα.₀₁And the accelerator opening α is a predetermined value α.₀₁It is determined whether or not the value exceeds. Where Δα ≦ Δα₀₁And α ≦ α₀₁(NO in both steps S39 and S40), that is, in the steady state (non-accelerated state) and in the middle / low load state, the rate of temperature rise of the catalyst is small. Is increased by the predetermined value Qpcq, or the basic injection timing Imb is retarded by the predetermined value Imcq, and the temperature rise of the exhaust gas or the catalyst is promoted. In this case, the predetermined value Qpcq is equal to O in the exhaust gas.₂It is preferably set so that the concentration decreases.
[0052]
Here, instead of changing the post injection amount Qpb or the basic injection timing Imb, the basic injection amount Qmb is increased by a predetermined value Qmcq, or the post injection timing Ipb is delayed by a predetermined value Ipcq in the direction in which the exhaust gas temperature rises. The angle may be advanced or the angle may be advanced (retard if Ipb is advanced from ATDC 15 ° CA, advance if it is retarded from ATDC 15 ° CA). In this case, the predetermined value Qmcq is equal to O in the exhaust gas.₂It is preferably set so that the concentration decreases. If the post injection is a follow-up injection, the post injection timing Ipb is also retarded in accordance with the delay of the basic injection timing Imb.
The catalyst temperature rise may be promoted by increasing the EGR amount or opening the adjustment valve 11 (throttle valve).
[0053]
On the other hand, Δα> Δα in step S39.₀₁(Yes), or α> α in step S40₀₁If it is determined that the exhaust gas temperature or the catalyst temperature naturally rises (YES), that is, in the acceleration state or the high load state, step S41 is skipped.
[0054]
Next, in step S42, the count value of the elapsed time t after the start of the monitor control is incremented by 1 (t ← t + 1). Subsequently, in step S43, the elapsed time t is changed to the first reference time t.₁₀It is determined whether or not the value exceeds. The elapsed time t is the first reference time t₁₀If it does not exceed (NO), in step S46, the set value α is set to the post injection increase value Qpobd to increase the HC concentration in the exhaust gas upstream of the catalyst, or the set value is set to the basic injection timing retard value Imobd. γ is set. Instead of using the post injection increase value Qpobd or the basic injection timing retard value Imobd, set the set value β to the basic injection increase value Qmobd or set the set value δ to the post injection timing retard value Ipobd. Also good. As a result, the HC concentration in the exhaust gas upstream of the catalyst is set to a high concentration state.
[0055]
In step S43, the elapsed time t is the first reference time t.₁₀(YES), in step S44, the elapsed time t is the second reference time t.₂₀It is determined whether or not. The elapsed time t is the second reference time t₂₀If not (NO), in step S47, the post-injection increase value Qpobd is set to 0 or the basic injection timing retard value Imobd is set to 0 in order to bring the HC concentration in the exhaust gas upstream of the catalyst into a low concentration state. Set. When the basic injection increase value Qmobd or the post injection timing retard value Ipobd is used instead of the post injection increase value Qpobd or the basic injection timing retard value Imobd, 0 is set to them.
In step S44, the elapsed time t is changed to the second reference time t.₂₀If it is determined that there is, the elapsed time t is reset to 0 in step S45 (t ← 0).
[0056]
Next, in step S48, the final basic injection amount Qmt, the final basic injection timing Imt, the final post injection amount Qpt, and the final post injection timing Ipt are set by the following equations 4 to 7. Thereafter, in step S49, the basic injection is executed at the final basic injection amount Qmt and the final basic injection timing Imt, and the post injection is executed at the final post injection amount Qpt and the final post injection timing Ipt.
Qmt ← Qmb + Qmobd ……………………………………………… Formula 4
Qpt ← Qpb + Qpobd ………………………………………………… Formula 5
Imt ← Imb ＋ Imobd ………………………………………………… Formula 6
Ipt ← Ipb + Ipobd …………………………………………………… Formula 7
[0057]
By the way, when it is determined in step S38 that the flag Fcatin is not 1 (NO), in step S50, the previous catalyst temperature Tcat is the second catalyst temperature Tcat._{2 0}It is determined whether or not this is the case. The previous catalyst temperature Tcat is the second catalyst temperature Tcat._{2 0}If this is the case (YES), that is, the catalyst temperature Tcat is the second reference temperature Tcat before the previous time_{2 0}After the above, the second reference temperature Tcat again_{2 0}If it is less, the flag Fcatde is set to 1 in step S51, and then the fuel injection amount or the fuel injection timing is corrected so that the exhaust gas temperature or the catalyst temperature decreases in steps S53 to S55. The flag Fcatde is a flag that is set to 1 when such correction is performed.
[0058]
In step S50, the previous catalyst temperature Tcat is changed to the second catalyst temperature Tcat._{2 0}If it is less than (NO), it is determined in step S52 whether the flag Fcatde is 1 or not. If the flag Fcatde is 1, the fuel injection amount or the fuel injection timing is corrected in steps S53 to S55 so that the exhaust gas temperature or the catalyst temperature decreases.
[0059]
When the fuel injection amount or the fuel injection timing is corrected so that the exhaust gas temperature or the catalyst temperature is lowered, first, in steps S53 and S54, the accelerator opening change amount Δα is set to a predetermined value Δα, respectively.₀₂Whether the accelerator opening α is smaller than (negative value) or not and the predetermined value α₀₂It is determined whether or not it is smaller. Where Δα ≧ Δα₀₂And α ≧ α₀₂(NO in both steps S53 and S54), that is, in the non-decelerating state and in the middle / high load state, the temperature decrease rate of the catalyst is small, so that the post injection amount Qpb is a predetermined value Qpcq ′ in step S55. Or the basic injection timing Imb is advanced by a predetermined value Imcq ′ to promote a decrease in the catalyst temperature.
[0060]
Here, instead of changing the post injection amount Qpb or the basic injection timing Imb, the basic injection amount Qmb is decreased by a predetermined value Qmcq ′, or the post injection timing Ipb is decreased to a predetermined value Ipcq ′ in a direction in which the exhaust gas temperature decreases. Only the retarded angle or the advanced angle may be set.
In addition, you may accelerate | stimulate the fall of a catalyst temperature by supplying or increasing secondary air.
[0061]
In step S53, Δα <Δα₀₂Is determined (YES) or α <α in step S54₀₂If it is determined (YES), that is, if the vehicle is in a deceleration state or a low load state, the exhaust gas temperature or the catalyst temperature naturally decreases, so step S55 is skipped.
If it is determined in step S52 that the flag Fcatde is not 1 (NO), the flag Fcatin is reset to 0 in step S56, and steps S53 to S55 are skipped.
[0062]
By the way, in the monitor control and the fuel control shown in FIGS. 2 to 6, the purification performance or the deterioration degree of the catalyst is determined. However, instead of this determination or in addition to this determination, the control state of the engine 1 may be changed based on the state of the catalyst ascertained by the monitor control.
For example, as shown in FIG. 7, steps T1 to T3 are inserted between step S33 and step S34 of the flowchart shown in FIG. 4, and when the engine 1 is cold, based on the catalyst temperature average value Tcat (n) av. You may perform control which promotes the raise of a catalyst temperature.
[0063]
In this case, at step T1, the engine water temperature Tw is a predetermined value Tw.₀Whether or not is less than Tw <Tw₀If (YES), that is, if the engine is cold, it is determined in step T2 whether or not the catalyst temperature Tcat exceeds a value obtained by adding a predetermined value ΔTcat to the catalyst temperature average value Tcat (n) av. If Tcat ≦ Tcat (n) av + ΔTcat (NO), the post injection amount Qpb is increased by the predetermined value Qpbcold in step T3, or the basic injection timing Imb is retarded by the predetermined value Imbcold, and the exhaust gas temperature and thus the catalyst Increase in temperature is promoted. Note that the basic injection amount Qmb may be increased by a predetermined value Qmbcold to promote an increase in the exhaust gas temperature and thus the catalyst temperature.
[0064]
Here, when only the control state of the engine 1 is changed and the determination of the catalyst purification performance or the degree of deterioration is not performed, the monitor control steps S19 to S22 shown in FIG. 2 may be deleted (both are performed). In this case, steps S19 to S22 are left).
[0065]
In the above-described embodiment, a zeolite-based catalyst is used in the exhaust purification device 12. However, when an alumina-based catalyst is used, the control method of monitor control is slightly different from the case where a zeolite-based catalyst is used. Therefore, hereinafter, monitor control in the case of using an alumina catalyst will be described.
[0066]
As described above, in the case of a zeolitic catalyst, O is near the light-off temperature regardless of the presence or absence or degree of deterioration.₂The density change amount difference ΔOx increases. Therefore, regardless of the presence or degree of deterioration, O₂The catalyst temperature Tcat when the concentration change amount difference ΔOx becomes large substantially indicates the light-off temperature.
In contrast, in the case of an alumina-based catalyst (a catalyst in which a noble metal catalyst such as Pt, Rh, or Pd is supported on an alumina carrier), the degree of activation of the catalyst increases as the degree of activation of the catalyst increases near the light-off temperature.₂The density change amount difference ΔOx increases. That is, O₂The catalyst temperature when the concentration change amount difference ΔOx is a specific value (range) corresponding to the light-off temperature substantially indicates the light-off temperature of the catalyst.
[0067]
Therefore, in the monitor control when an alumina catalyst is used, O₂Density change difference ΔOx is set value ΔOx₁Larger and set value ΔOx₂What is necessary is just to memorize | store the catalyst temperature when it is smaller. Set value ΔOx₁Or set value ΔOx₂Corresponds to the light-off temperature of the fresh catalyst.
Specifically, as shown in FIG. 9, in the flowchart of the monitor control when the alumina catalyst is used, step S12 of the flowchart shown in FIG. 2 is changed to “ΔOx ← ΔOxdn−ΔOxup”, and step S13 is changed. , O₂Density change difference ΔOx is set value ΔOx₁Larger and set value ΔOx₂This is replaced with step T21 for determining whether or not it is smaller.
[0068]
  Figure12In (a) to (c), when the HC concentration upstream of the alumina catalyst is increased or decreased in a predetermined cycle, the downstream O when the catalyst temperature is 200 ° C., 220 ° C., and 250 ° C.₂The time course of concentration and HC concentration is shown. These figures are also figure10The figure11As in the case of, data is processed and shown so that ΔOx can be easily compared relatively. Figure12As is clear from (a) to (c), the downstream side O of the alumina catalyst₂The concentration change characteristics10Or figure11This is very different from the change characteristics of the zeolite-based catalyst.
[0069]
  Figure13In the case of using an alumina catalyst in (a) to (c), the upstream O in the case where the HC concentration upstream of the catalyst is repeatedly increased or decreased at a predetermined cycle₂Concentration and downstream O₂The change characteristic of density is shown. Figure13(A)-(c), figure14(B) is upstream O₂Concentration and downstream O₂Concentration, O at the time of HC cut₂Relative comparisons are made using density values as a reference. Also figure13(A) is when inactive,13(B) is at the time of light-off.13(C) is when activated.
  Also figure14In (a), O in the case where the HC concentration upstream of the catalyst is repeatedly increased or decreased at a predetermined cycle.₂The change characteristic with respect to the catalyst temperature of the concentration variation difference ΔOx is shown.
[0070]
  Figure13(A)-(c) and figure14As apparent from (a), in the temperature range close to the light-off temperature, the higher the catalyst temperature, the more O₂The density change amount difference ΔOx is large. Figure14Catalyst temperature T in (a)₁~ T₂Is the light-off temperature range, and the set value ΔOx₁And set value ΔOx₂Respectively, T₁And T₂Is a value corresponding to. The reason for this is not clear, but unlike zeolite, HC in the exhaust gas is in direct contact with alumina, which has a poor ability to temporarily incorporate HC into the surface. And O₂Reacts directly with O₂On the other hand, when activated, the catalytic metal oxidizability further increases and more O₂It is thought that this is because of the decrease.
[0071]
  Figure14(B) In the light-off state, when the HC concentration upstream of the alumina catalyst is changed from the low concentration state to the high concentration state and then the high concentration state is continued, the upstream O₂Concentration and downstream O₂The change characteristic of density is shown. Figure14As is clear from (b), the downstream side O for a while immediately after the HC concentration was changed to a high concentration state.₂The concentration is greatly reduced. This is because immediately after the HC concentration is brought to a high concentration state, rapid combustion occurs (ignitions) due to a rapid increase in HC.
[0072]
However, after this, the downstream O₂Concentration rises and eventually (approximately 60 seconds) upstream O₂Concentration and downstream O₂The difference in density is almost eliminated. This is because the oxidation reaction gradually becomes an equilibrium state, and O₂This is because consumption is reduced.
Therefore, in this monitor control, it can be said that it is necessary or effective to repeatedly increase or decrease the HC concentration upstream of the catalyst.
[0073]
In addition, as shown in FIG. 8, when the catalyst used in the exhaust purification device 12 is a NOx trap catalyst (a noble metal, an alkaline earth metal such as Ba, or a catalyst in which an alkali metal is supported on alumina), FIG. Steps T11 to T18 may be inserted between step S33 and step S34 in the flowchart shown.
In this case, first, at step T11, it is determined whether or not the catalyst temperature Tcat exceeds a value obtained by adding a predetermined value ΔTcat to the catalyst temperature average value Tcat (n) av. If Tcat ≦ Tcat (n) av + ΔTcat (NO), NOx trap control is performed in steps T12 to T18.
[0074]
That is, first, at step T12, the NOx trap amount NO of the NOx trap catalyst is estimated. Subsequently, in step T13, the estimated NOx trap amount NO is changed to a predetermined threshold NO.₀It is determined whether or not the value exceeds. Where NO> NO₀If so (YES), the counter T in step T14_NOxCounting starts or continues. Counter T_NOxIs a counter for counting a period during which the fuel injection amount should be increased when NOx is released by the NOx trap catalyst.
In step T13, NO ≦ NO₀(NO), in step T15, the counter T_NOxIs being counted. If counting is in progress (YES), steps T14 to T18 are executed.
[0075]
Next, at step T16, the counter T_NOxCount value is set value T_NOx0It is determined whether or not the value exceeds. Where counter T_NOxCount value is set value T_NOx0If it does not exceed (NO), in step T17, the basic injection amount Qmb (or the post injection amount Qpb) is increased (becomes rich) in order to purify the NOx trap catalyst by releasing NOx.
[0076]
On the other hand, in step T16, the counter T_NOxCount value is set value T_NOx0If it exceeds (YES), in step T18 the counter T_NOxAnd the NOx trap amount NO (estimated value) is reset to zero.
[0077]
【The invention's effect】
As described above, according to the present invention, it is possible to easily and accurately determine the purification performance or the degree of deterioration of the exhaust gas purification catalyst.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of a diesel engine equipped with an exhaust emission control device according to the present invention.
FIG. 2 is a flowchart showing a control method of monitor control of an exhaust purification device using a zeolite catalyst.
FIG. 3 is a flowchart showing a control method of monitor control of an exhaust purification device using a zeolite catalyst.
FIG. 4 is a flowchart showing a control method of fuel control.
FIG. 5 is a flowchart showing a control method of fuel control.
FIG. 6 is a flowchart showing a control method of fuel control.
FIG. 7 is a flowchart showing a modification of the control method of fuel control.
FIG. 8 is a flowchart showing a modification of the control method of fuel control.
FIG. 9 is a flowchart showing a control method of monitor control of an exhaust purification apparatus using an alumina-based catalyst.
FIGS. 10 (a) to 10 (c) respectively show upstream O in the inactive state, light-off state, and active state when a zeolite-based fresh catalyst is used.₂Concentration and downstream O₂It is a graph which shows the change characteristic of density with respect to time.
FIGS. 11A to 11C are diagrams showing upstream side O, in an inactive state, a light-off state, and an active state, respectively, when a zeolite-based deterioration catalyst is used.₂Concentration and downstream O₂It is a graph which shows the change characteristic of density with respect to time.
FIGS. 12 (a) to (c) show the downstream O in the inactive state, light-off state, and active state, respectively, when using an alumina-based catalyst.₂It is a graph which shows the change characteristic with respect to time of a density | concentration and downstream HC density | concentration.
FIGS. 13A to 13C are diagrams showing upstream side O, in an inactive state, a light-off state, and an active state, respectively, when an alumina-based catalyst is used.₂Concentration and downstream O₂It is a graph which shows the change characteristic of density with respect to time.
FIG. 14 (a) shows O in an alumina catalyst.₂6 is a graph showing a change characteristic of the concentration change amount difference ΔOx with respect to the catalyst temperature, and (b) shows the upstream O in the light-off state when the HC concentration is not repeatedly increased or decreased.₂Concentration and downstream O₂It is a graph which shows the change characteristic of density with respect to time.
FIGS. 15A to 15B are diagrams showing upstream O in a light-off state and an active state when a zeolite catalyst is used, respectively.₂Concentration and downstream O₂It is a graph which shows the change characteristic of a density | concentration with respect to time, (c) is O in a zeolitic catalyst.₂6 is a graph showing a change characteristic with respect to time of a concentration change amount difference ΔOx, and FIG. 6D is an upstream side O in a light-off state when the HC concentration is not repeatedly increased or decreased.₂Concentration and downstream O₂It is a graph which shows the change characteristic of density with respect to time.
[Explanation of symbols]
  DESCRIPTION OF SYMBOLS 1 ... Engine (diesel engine), 2 ... Intake passage, 3 ... Combustion chamber, 4 ... Piston, 5 ... Fuel injection valve, 6 ... Exhaust passage, 7 ... Crankshaft, 8 ... Fuel supply passage, 9 ... High-pressure fuel pump, DESCRIPTION OF SYMBOLS 10 ... Fuel distributor, 11 ... Regulating valve, 12 ... Exhaust gas purification device, 13 ... Catalyst temperature sensor, 14 ... Upstream O₂Sensor, 15 ... downstream O₂Sensor, 16 ... EGR passage, 17 ... EGR control valve, 18 ... Water temperature sensor, 20 ... Control unit.

Claims (9)

A catalyst that is disposed in the exhaust passage of the engine and has oxidation performance;
Upstream O ₂ concentration detection means for detecting O ₂ concentration in the exhaust gas upstream of the catalyst;
Downstream O ₂ concentration detection means for detecting the O ₂ concentration in the exhaust gas downstream of the catalyst;
The upstream O ₂ concentration detected by the upstream O ₂ concentration detector, and determining purification performance determining means for purifying performance of the catalyst on the basis of the downstream O ₂ concentration downstream O ₂ concentration detected by the detection means In an exhaust emission control device for an engine equipped with
Catalyst temperature detecting means for detecting the catalyst temperature;
Exhaust gas composition changing means for changing the reducing component concentration in the exhaust gas upstream of the catalyst so as to shift between a high concentration state and a low concentration state is provided,
The purification performance determination means is detected when the catalyst temperature is outside a predetermined temperature range where the oxidation performance of the catalyst is not more than a predetermined degree when the reducing component concentration is changed by the exhaust gas composition changing means. An engine exhaust purification system characterized in that the purification performance of a catalyst is determined based on an upstream O ₂ concentration and a downstream O ₂ concentration. The purifying performance determining means, first the reducing component concentration is the difference between the representative value of the upstream O ₂ concentration when a high concentration and a representative value of the upstream O ₂ concentration when the low concentration state 1 a representative value difference, a second representative value which is a difference between the representative value of the downstream O ₂ concentration at the reduction component concentration is high concentration and a representative value of the downstream O ₂ concentration when the low concentration state 2. The engine exhaust gas purification apparatus according to claim 1, wherein the purification performance of the catalyst is determined based on the difference. The catalyst is deteriorated when the catalyst temperature when the deviation between the first representative value difference and the second representative value difference is outside the predetermined range exceeds the predetermined temperature when the purification performance determination means The engine exhaust gas purification apparatus according to claim 2, wherein the engine exhaust gas purification device is determined. The purification performance determination means determines the purification performance of the catalyst when the catalyst temperature is in a predetermined temperature range in which the oxidation performance of the catalyst is not more than a predetermined degree. The exhaust emission control device for an engine according to any one of the above.   The exhaust gas composition changing means increases or decreases the reducing component concentration in a predetermined cycle within a transition period in which the catalyst temperature shifts between a state lower than a predetermined temperature and a state higher than the predetermined temperature. The exhaust emission control device for an engine according to claim 1.   The exhaust gas composition changing means increases or decreases the reducing component concentration over a predetermined period after acceleration is started when the catalyst temperature is lower than the predetermined temperature. 5. An exhaust emission control device for an engine according to 5. 6. The engine exhaust gas purification apparatus according to claim 5, wherein an O ₂ concentration reducing means for reducing the upstream O ₂ concentration is provided during the transition period. A catalyst that is disposed in the exhaust passage of the engine and has oxidation performance, an upstream O ₂ sensor that detects the O ₂ concentration in the exhaust gas upstream of the catalyst, and a downstream O that detects the O ₂ concentration in the exhaust gas downstream of the catalyst exhaust purification device for an engine and a _second sensor, the upstream O ₂ concentration detected by the upstream O ₂ sensor, on the basis of the downstream O ₂ concentration detected by the downstream O ₂ sensor purifying catalyst In the purification performance determination method for determining performance,
While the reducing component concentration in the exhaust gas upstream of the catalyst is changed to shift between a high concentration state and a low concentration state,
When the reducing component concentration is changed, when the catalyst temperature is outside a predetermined temperature range in which the oxidation performance of the catalyst is not more than a predetermined level, the catalyst is based on the upstream O ₂ concentration and the downstream O ₂ concentration. A purification performance determination method characterized in that the purification performance of the water is determined. A catalyst that is disposed in the exhaust passage of the engine and has oxidation performance;
Upstream O ₂ concentration detection means for detecting O ₂ concentration in the exhaust gas upstream of the catalyst;
Downstream O ₂ concentration detection means for detecting the O ₂ concentration in the exhaust gas downstream of the catalyst;
The upstream O ₂ concentration detected by the upstream O ₂ concentration detector, a control state changing means for changing a control state of the engine based on the downstream O ₂ concentration detected by the downstream O ₂ concentration detector In an exhaust emission control device for an engine equipped with
Catalyst temperature detecting means for detecting the catalyst temperature;
Exhaust gas composition changing means for changing the reducing component concentration in the exhaust gas upstream of the catalyst so as to shift between a high concentration state and a low concentration state is provided,
The control state change means is detected when the catalyst temperature is outside a predetermined temperature range where the oxidation performance of the catalyst is not more than a predetermined degree when the reducing component concentration is changed by the exhaust gas composition changing means. An engine exhaust purification system that changes a control state of an engine based on an upstream O ₂ concentration and a downstream O ₂ concentration.

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