JP2012021411A - Control apparatus of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent sulfur from locally remaining and a catalyst from deteriorating, by a simple method, when making the sulfur accumulated in an NOx catalyst desorb, concerning a control apparatus of an internal combustion engine.SOLUTION: The control apparatus of the internal combustion engine includes: a reducing agent supplier for supplying a reducing agent to an exhaust gas on the upstream of the NOx catalyst in order to make the sulfur accumulated in the NOx catalyst desorb; a variable valve system in which valve timing of one or both of an intake valve and an exhaust valve is variable; and a desorption portion controller for controlling a portion which becomes a desorption temperature of the sulfur or more in the NOx catalyst to move along with time by changing the valve timing in stages with the variable valve system such that one or both of an amount and temperature of the exhaust gas discharged from the internal combustion engine varies along with time during supply of the reducing agent.

Description

  The present invention relates to a control device for an internal combustion engine.

  In internal combustion engines that are operated at an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio, such as diesel engines and lean-burn engines, NOx storage reduction catalysts that can purify NOx in exhaust gas are widely used. In the exhaust gas, sulfur components such as sulfur oxide (SOx) are contained by burning sulfur contained in the fuel and engine oil. This sulfur component is absorbed and deposited on the NOx catalyst. When sulfur accumulates on the NOx catalyst, the NOx absorption performance of the NOx catalyst is reduced. For this reason, it is sometimes necessary to carry out sulfur poisoning regeneration to remove sulfur accumulated on the NOx catalyst. In order to desorb sulfur from the NOx catalyst, a reducing agent such as HC is supplied into the exhaust gas to make the air-fuel ratio stoichiometric or rich, and the catalyst bed temperature is set to a predetermined temperature (such as heat of oxidation reaction of the reducing agent). For example, about 600 to 700 ° C.) or higher is required.

  Japanese Patent Laid-Open No. 2001-263109 discloses that when the sulfur poisoning regeneration is performed, the exhaust temperature is increased by advancing the valve opening timing of the exhaust valve by a variable valve device in order to increase the bed temperature of the NOx catalyst. Techniques to do this are disclosed.

JP 2001-263109 A JP 2005-90276 A Japanese Patent Laid-Open No. 2004-52597 JP 2008-38634 A

  Conventionally, when sulfur poisoning regeneration is performed, it is generally aimed to raise the temperature of the entire NOx catalyst to a temperature higher than the temperature at which sulfur is desorbed. However, in practice, it is difficult to raise the temperature of the entire NOx catalyst uniformly, and therefore a portion where the temperature does not rise sufficiently and a portion where the temperature rises excessively occur. FIG. 13 is a diagram showing an example of the distribution of catalyst bed temperature during execution of conventional sulfur poisoning regeneration. FIG. 13 shows the case of an apparatus in which an oxidation catalyst is arranged on the front side of the NOx catalyst. In the example shown in this figure, the reductant is not sufficiently oxidized at the site close to the front end of the NOx catalyst (boundary with the oxidation catalyst), so the bed temperature does not reach the temperature required for sulfur desorption (in the figure). A portion indicated by A), sulfur cannot be eliminated. On the other hand, at a portion near the rear end of the NOx catalyst, the bed temperature rises excessively (portion indicated by B in the figure), leading to catalyst deterioration.

  On the other hand, in Patent Document 4 described above, the degree of activity of an oxidation catalyst provided upstream of an exhaust purification device such as a NOx catalyst is changed to increase the temperature of the predetermined portion of the exhaust purification device. A technique for reproducing the performance of the above is disclosed. However, in this technique, an electric heater is used to change the degree of activity of the oxidation catalyst, which increases the cost.

  The present invention has been made in view of the above points, and when desorbing sulfur deposited on a NOx catalyst, sulfur can remain locally or the catalyst can be deteriorated by a simple method. An object of the present invention is to provide a control device for an internal combustion engine that can be suppressed.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
A NOx catalyst disposed in the exhaust passage of the internal combustion engine;
Reducing agent supply means for supplying a reducing agent to exhaust gas upstream of the NOx catalyst in order to desorb sulfur accumulated on the NOx catalyst;
A variable valve gear that varies the valve timing of one or both of the intake valve and the exhaust valve;
By changing the valve timing stepwise by the variable valve device such that one or both of the amount and temperature of the exhaust gas discharged from the internal combustion engine change with time during the supply of the reducing agent, A desorption site control means for controlling the site where the sulfur desorption temperature or higher in the NOx catalyst is moved over time;
It is characterized by providing.

The second invention is the first invention, wherein
The variable valve operating device has a function of changing an open period of the intake valve,
The desorption site control means changes the opening period of the intake valve stepwise by the variable valve device so that the amount of exhaust gas discharged from the internal combustion engine changes with time.

The third invention is the first or second invention, wherein
The variable valve operating device has a function of changing the opening timing of the exhaust valve,
The desorption site control means is characterized in that the opening timing of the exhaust valve is changed stepwise by the variable valve device so that the temperature of the exhaust gas discharged from the internal combustion engine changes with time.

According to a fourth invention, in any one of the first to third inventions,
Sulfur deposition amount estimation means for estimating a sulfur deposition amount that is the amount of sulfur deposited for each part when the NOx catalyst is divided into a plurality of parts from the upstream side toward the downstream side,
Each part of the NOx catalyst corresponds to a part that becomes equal to or higher than the sulfur desorption temperature at each stage when the desorption part control means changes the valve timing stepwise.
When the valve timing is changed stepwise, the desorption site control means determines the sulfur deposition amount for each site of the NOx catalyst before the supply of the reducing agent according to the estimated value of the sulfur deposition amount for each site. The valve timing holding time for each is changed.

According to a fifth invention, in any one of the first to fourth inventions,
A sulfur deposition amount estimating means for estimating a sulfur deposition amount that is an amount of sulfur deposited for each portion when the NOx catalyst is divided into a plurality of portions from the upstream side toward the downstream side;
A sulfur desorption amount estimating means for estimating a sulfur desorption amount, which is an amount of sulfur desorbed, for each part of the NOx catalyst during the supply of the reducing agent;
Remaining for each part of the NOx catalyst based on the estimated value of the sulfur deposition amount before the supply of the reducing agent and the estimated value of the sulfur desorption amount during the supply of the reducing agent A sulfur residual amount estimating means for estimating a sulfur residual amount that is an amount of sulfur;
With
Each part of the NOx catalyst corresponds to a part that becomes equal to or higher than the sulfur desorption temperature at each stage when the desorption part control means changes the valve timing stepwise.
When the valve timing is changed step by step, the desorption site control means changes the valve timing when the estimated value of the remaining amount of sulfur at the site where sulfur is being desorbed falls below a predetermined value. It is characterized by changing to the stage.

  According to the first invention, when sulfur accumulated on the NOx catalyst is desorbed, only a part of the NOx catalyst is set to the sulfur desorption temperature or higher, and the portion that is equal to or higher than the sulfur desorption temperature is moved with time. be able to. For this reason, it is possible to avoid an excessive increase in the catalyst bed temperature and to suppress deterioration of the catalyst. Moreover, sulfur can be reliably desorbed from the entire NOx catalyst. Furthermore, according to the first aspect of the invention, the above effect can be achieved by controlling the variable valve operating apparatus, and no dedicated equipment is required. For this reason, it can be realized at a low cost with a simple configuration.

  According to the second invention, when sulfur accumulated on the NOx catalyst is desorbed, the sulfur desorption site can be accurately controlled by changing the opening period of the intake valve.

  According to the third aspect of the present invention, when sulfur accumulated on the NOx catalyst is desorbed, the sulfur desorption site can be accurately controlled by changing the opening timing of the exhaust valve.

  According to the fourth aspect of the present invention, when sulfur accumulated on the NOx catalyst is desorbed, the sulfur desorption time at each part can be changed based on the sulfur accumulation amount at each part of the NOx catalyst. For this reason, it can suppress that sulfur desorption time of each site | part is too short, and sulfur remains, or sulfur desorption time is too long and a reducing agent is consumed wastefully.

  According to the fifth aspect, when the sulfur deposited on the NOx catalyst is desorbed, the sulfur desorption time at each part can be changed based on the amount of sulfur deposited at each part of the NOx catalyst. For this reason, it can suppress that sulfur desorption time of each site | part is too short, and sulfur remains, or sulfur desorption time is too long and a reducing agent is consumed wastefully.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows distribution of the bed temperature of an oxidation catalyst and a NOx catalyst at the time of sulfur poisoning reproduction | regeneration. It is a figure which shows distribution of the bed temperature of an oxidation catalyst and a NOx catalyst at the time of sulfur poisoning reproduction | regeneration. It is a figure for demonstrating control of the open period of the intake valve at the time of sulfur poisoning reproduction | regeneration in Embodiment 1 of this invention. It is a figure for demonstrating control of the opening timing of the exhaust valve at the time of sulfur poisoning reproduction | regeneration in Embodiment 1 of this invention. It is a map of the absorption rate coefficient of sulfur. It is a map of the absorption rate coefficient of sulfur. It is a map of the absorption rate coefficient of sulfur. It is a map of the desorption rate coefficient of sulfur. It is a map of the desorption rate coefficient of sulfur. It is a map of the desorption rate coefficient of sulfur. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows the example of distribution of the catalyst bed temperature at the time of execution of the conventional sulfur poisoning reproduction | regeneration.

Embodiment 1 FIG.
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes an engine 10 mounted on a vehicle or the like. In the present embodiment, the engine 10 is described as a diesel engine (compression ignition internal combustion engine), but the present invention is also applicable to a spark ignition internal combustion engine that performs lean combustion. In the present invention, the number of cylinders and the cylinder arrangement of the engine 10 are not particularly limited. FIG. 1 shows a cross section of one cylinder of the engine 10.

  The engine 10 includes a cylinder block 4 and a cylinder head 6 assembled to the cylinder block 4. A piston 8 is inserted in the cylinder. An intake port 12 and an exhaust port 14 are formed in the cylinder head 6. An intake passage 22 for introducing fresh air into the cylinder is connected to the intake port 12, and an exhaust passage 24 for discharging exhaust gas is connected to the exhaust port 14.

  Each cylinder is provided with a fuel injector 30, an intake valve 32, and an exhaust valve 34 for directly injecting fuel into the cylinder. The fuel injector 30 is connected to a common rail (not shown), and is supplied with high-pressure fuel from the common rail. The common rail always stores high-pressure fuel compressed by the supply pump. The fuel injector 30 can inject fuel at an arbitrary timing a plurality of times during one cycle.

  A NOx catalyst 28 is disposed in the exhaust passage 24. The NOx catalyst 28 captures and stores NOx (nitrogen oxide) in the exhaust gas when the inflowing exhaust gas is leaner than stoichiometric (theoretical air-fuel ratio), and stores it when the inflowing exhaust gas is stoichiometric or rich. This is a NOx storage reduction catalyst having a function of reducing and purifying the NOx that has been reduced. An oxidation catalyst 27 is disposed on the upstream side of the NOx catalyst 28. In the illustrated configuration, the oxidation catalyst 27 and the NOx catalyst 28 are installed in a common casing. In this specification, when describing the sites in the oxidation catalyst 27 and the NOx catalyst 28, the upstream side is also referred to as “front” and the downstream side is also referred to as “rear”.

  An intake throttle valve 36 is provided in the intake passage 22. An EGR passage 26 is connected to the intake passage 22 downstream of the intake throttle valve 36. The opposite end of the EGR passage 26 is connected to the exhaust passage 24. Through this EGR passage 26, external EGR (Exhaust Gas Recirculation) in which a part of the exhaust gas in the exhaust passage 24 is recirculated to the intake passage 22 can be performed. In the middle of the EGR passage 26, an EGR valve 38 for controlling the EGR amount is provided.

  The engine 10 includes an intake variable valve operating device 42 that makes the valve timing of the intake valve 32 variable, and an exhaust variable valve operating device 44 that makes the valve timing of the exhaust valve 34 variable.

  The intake variable valve operating system 42 shortens or lengthens the opening period (working angle) of the intake valve 32 continuously or stepwise by changing one or both of the opening timing and closing timing of the intake valve 32. It has at least a function that can be performed. The specific mechanism of the intake variable valve operating device 42 is not particularly limited. For example, the above function can be achieved by interposing a mechanical mechanism such as a swing cam between the intake cam shaft and the intake valve 32. It may be realized, or a mechanism such as an electromagnetically driven valve that can open and close the intake valve 32 at an arbitrary time may be used.

  The exhaust variable valve device 44 has at least a function capable of increasing or decreasing the opening timing of the exhaust valve 34 continuously or stepwise. The specific mechanism of the exhaust variable valve device 44 is not particularly limited. For example, the above function may be realized by providing an actuator that rotates the exhaust camshaft relative to the timing gear. Alternatively, a mechanism such as an electromagnetically driven valve that can open and close the exhaust valve 34 at an arbitrary time may be used.

  A fuel addition valve 46 capable of injecting fuel into the exhaust gas is installed in the exhaust passage 24 at a position upstream of the oxidation catalyst 27 and the NOx catalyst 28. The fuel addition valve 46 may be installed in the cylinder head 6 (exhaust port 14).

  The system of this embodiment includes an ECU (Electronic Control Unit) 50. The ECU 50 includes various actuators such as a fuel injector 30, an intake throttle valve 36, an EGR valve 38, an intake variable valve operating device 42, an exhaust variable valve operating device 44, a fuel addition valve 46, and the rotation angle (crank angle) of the crankshaft 16. ), And an accelerator position sensor 58 for detecting the accelerator pedal position of the driver's seat of the vehicle are electrically connected.

When performing NOx reduction for reducing and purifying NOx occluded in the NOx catalyst 28, or when performing sulfur poisoning regeneration for desorbing sulfur accumulated in the form of sulfur oxide or the like on the NOx catalyst 28 It is necessary to supply a reducing agent such as HC, CO or H ₂ into the exhaust gas. In the present embodiment, the reducing agent can be supplied by injecting fuel from the fuel addition valve 46. However, the method for supplying the reducing agent is not limited to this, and any method may be used. For example, the reducing agent may be supplied by performing post injection for injecting fuel from the fuel injector 30 in the expansion stroke, or the reducing agent may be supplied by combining these plural methods.

  2 and 3 are diagrams showing the distribution of the bed temperature of the oxidation catalyst 27 and the NOx catalyst 28 during the sulfur poisoning regeneration. The horizontal axis of the graph represents the distance from the front end of the oxidation catalyst 27 and corresponds to the positions of the oxidation catalyst 27 and the NOx catalyst 28 illustrated on the graph. Below, with reference to FIG. 2, the relationship between the catalyst bed temperature distribution and the exhaust gas amount (flow rate) at the time of sulfur poisoning regeneration will be described first.

  In FIG. 2, curve A represents the distribution of catalyst bed temperature when the amount of exhaust gas is relatively small, and curve B represents the distribution of catalyst bed temperature when the amount of exhaust gas is relatively large. Further, the temperature indicated by the broken line indicates the lowest temperature necessary for sulfur desorption from the NOx catalyst 28 (hereinafter referred to as “sulfur desorption temperature”). The sulfur desorption temperature is, for example, about 600 to 700 ° C. When the amount of exhaust gas is small, the exhaust gas flow rate in the catalyst becomes slow. That is, the exhaust gas passes through the catalyst relatively slowly. For this reason, there is sufficient time for the reducing agent to undergo an oxidation reaction before reaching the front part of the NOx catalyst 28, so that the temperature of the front part of the NOx catalyst 28 increases as curve A shows. Exceeds sulfur desorption temperature. On the other hand, since the reducing agent is consumed up to the front part of the NOx catalyst 28, the temperature is lowered at the rear part of the NOx catalyst 28 and is lower than the sulfur desorption temperature.

  On the other hand, when the amount of exhaust gas is large, the exhaust gas flow rate in the catalyst increases. That is, the exhaust gas passes through the catalyst in a short time. For this reason, there is no time for the reducing agent to sufficiently oxidize before reaching the front part of the NOx catalyst 28, and many reducing agents undergo oxidation reaction at the rear part of the NOx catalyst 28. As a result, as indicated by curve B, the temperature at the front part of the NOx catalyst 28 does not rise sufficiently and does not reach the sulfur desorption temperature, but the temperature at the rear part of the NOx catalyst 28 does not reach the sulfur desorption temperature. Over temperature.

  Next, with reference to FIG. 3, the relationship between the distribution of the catalyst bed temperature during the sulfur poisoning regeneration and the temperature of the inflowing exhaust gas will be described. In FIG. 3, curve C represents the distribution of the catalyst bed temperature when the temperature of the exhaust gas flowing into the oxidation catalyst 27 (hereinafter referred to as “catalyst-containing gas temperature”) is relatively high, and curve D represents The distribution of the catalyst bed temperature when the gas temperature with catalyst is relatively low is shown. When the catalyst-containing gas temperature is high, the reaction rate of the reducing agent is increased. For this reason, the reducing agent sufficiently oxidizes until reaching the front part of the NOx catalyst 28, and as shown by the curve C, the temperature of the front part of the NOx catalyst 28 rises and sulfur desorption occurs. Exceeds the separation temperature. On the other hand, since the reducing agent is consumed up to the front part of the NOx catalyst 28, the temperature is lowered at the rear part of the NOx catalyst 28 and is lower than the sulfur desorption temperature.

  On the other hand, when the catalyst-containing gas temperature is low, the reaction rate of the reducing agent becomes slow. For this reason, the reducing agent does not sufficiently oxidize until reaching the front part of the NOx catalyst 28, and many reducing agents undergo oxidation reaction at the rear part of the NOx catalyst 28. As a result, as indicated by curve D, the temperature at the front part of the NOx catalyst 28 does not rise sufficiently and does not reach the sulfur desorption temperature, but the temperature at the rear part of the NOx catalyst 28 does not reach the sulfur desorption temperature. Over temperature.

  In the present embodiment, when the sulfur poisoning regeneration is performed, in order to avoid the excessive increase in the catalyst bed temperature and to reliably desorb sulfur from the entire NOx catalyst 28, the above-described principle is used to eliminate NOx. In the catalyst 28, control was performed so that a portion that is equal to or higher than the sulfur desorption temperature moves with time. In this embodiment, the NOx catalyst 28 is divided into three parts, a front part, a middle part, and a rear part, and sulfur is desorbed for each part.

  FIG. 4 is a diagram for explaining the control of the opening period of the intake valve 32 at the time of sulfur poisoning regeneration in the present embodiment. Hereinafter, with reference to FIG. 4, control of the opening period of the intake valve 32 (hereinafter referred to as “intake valve opening period”) during the sulfur poisoning regeneration of the present embodiment will be described.

  The amount (flow rate) of the exhaust gas discharged from the engine 10 changes according to the intake valve opening period. If the intake valve opening period is lengthened, the amount of air sucked into the cylinder increases, so the amount of exhaust gas increases. On the other hand, if the intake valve opening period is shortened, the amount of air sucked into the cylinder is reduced, so that the amount of exhaust gas is reduced.

  In the first stage, the control is performed so that the distribution of the catalyst bed temperature becomes a curve indicated by (1) in FIG. For this purpose, the amount of exhaust gas may be relatively reduced, and the value is set to V1. In order to set the exhaust gas amount to V1, the intake valve opening period may be set to a relatively short L1. By controlling in this way, the catalyst bed temperature peaks at the front part of the NOx catalyst 28 and exceeds the sulfur desorption temperature. For this reason, sulfur can be desorbed from the front portion of the NOx catalyst 28. At this time, in the middle and rear portions of the NOx catalyst 28, the bed temperature does not rise excessively, and the catalyst does not deteriorate.

  In the second stage, the control is performed so that the distribution of the catalyst bed temperature becomes a curve indicated by (2) in FIG. For that purpose, the exhaust gas amount may be set to a medium level, and the value is set to V2. In order to set the exhaust gas amount to V2, the intake valve opening period may be set to a medium length L2. By controlling in this way, the catalyst bed temperature peaks at the middle part of the NOx catalyst 28 and exceeds the sulfur desorption temperature. For this reason, sulfur can be desorbed from the middle part of the NOx catalyst 28. At this time, the bed temperature is not excessively increased at the front and rear portions of the NOx catalyst 28, and the catalyst does not deteriorate.

  In the third stage, the control is performed so that the distribution of the catalyst bed temperature becomes a curve indicated by (3) in FIG. For this purpose, the amount of exhaust gas may be made relatively large, and the value is set to V3. In order to set the exhaust gas amount to V3, the intake valve opening period may be set to a relatively long L3. By controlling in this way, the catalyst bed temperature reaches a peak at the rear part of the NOx catalyst 28 and exceeds the sulfur desorption temperature. For this reason, sulfur can be desorbed from the rear portion of the NOx catalyst 28. At this time, the bed temperature does not excessively increase at the front and middle portions of the NOx catalyst 28, and the catalyst does not deteriorate.

  In the present embodiment, in the sulfur poisoning regeneration control, the intake variable valve operating apparatus 42 is controlled so that the intake valve opening period becomes longer in steps of L1, L2, and L3. As a result, the first to third stages of sulfur desorption proceed as described above, and sulfur can be desorbed sequentially from the front portion to the rear portion of the NOx catalyst 28. For this reason, it is possible to reliably desorb the NOx catalyst 28 without leaving any sulfur.

  In addition, since the catalyst bed temperature does not rise uniformly from the front to the rear, when the entire NOx catalyst 28 is heated at a temperature higher than the sulfur desorption temperature at once, a portion where the bed temperature rises excessively is generated. Cause deterioration. On the other hand, according to the present embodiment, since only a part of the NOx catalyst 28 is set to the sulfur desorption temperature or more at each stage, it is possible to prevent the bed temperature from excessively increasing at other portions. For this reason, deterioration of the NOx catalyst 28 can be reliably suppressed.

  As described above, it is preferable that sulfur is desorbed from the upstream portion toward the downstream portion as the order of desorbing sulfur from each portion of the NOx catalyst 28. If the sulfur at the downstream site is desorbed first, then when the sulfur is subsequently desorbed from the upstream site, the desorbed sulfur may reattach to the downstream site where regeneration has been completed. Because there is. On the other hand, if sulfur is desorbed from the upstream site toward the downstream site, re-adhesion as described above can be prevented, so that sulfur in the entire NOx catalyst 28 can be more reliably removed. Can do.

  FIG. 5 is a diagram for explaining the control of the opening timing of the exhaust valve 34 during the sulfur poisoning regeneration in the present embodiment. Hereinafter, the control of the opening timing of the exhaust valve 34 (hereinafter referred to as “exhaust valve opening timing”) during the sulfur poisoning regeneration of the present embodiment will be described with reference to FIG.

  If the exhaust valve opening timing is advanced, exhaust gas that is still hot during expansion in the cylinder is exhausted from the engine 10, so that the gas temperature containing the catalyst also increases. On the other hand, if the exhaust valve opening timing is delayed, exhaust gas that has sufficiently expanded in the cylinder and lowered in temperature is exhausted from the engine 10, so that the temperature of the gas containing the catalyst also decreases.

  In the first stage, the control is performed so that the distribution of the catalyst bed temperature becomes a curve indicated by (1) in FIG. For that purpose, the temperature of the gas containing the catalyst may be made relatively high, and the value is set to T1. In order to set the catalyst-containing gas temperature to T1, the exhaust valve opening timing may be set to relatively early E1. By controlling in this way, the catalyst bed temperature peaks at the front part of the NOx catalyst 28 and exceeds the sulfur desorption temperature. For this reason, sulfur can be desorbed from the front portion of the NOx catalyst 28. At this time, in the middle and rear portions of the NOx catalyst 28, the bed temperature does not rise excessively, and the catalyst does not deteriorate.

  In the second stage, the control is performed so that the distribution of the catalyst bed temperature becomes a curve indicated by (2) in FIG. For that purpose, the catalyst-containing gas temperature may be set to an intermediate level, and the value is set to T2. In order to set the temperature of the gas containing the catalyst to T2, the exhaust valve opening timing may be set to a moderate E2 that is neither early nor late. By controlling in this way, the catalyst bed temperature peaks at the middle part of the NOx catalyst 28 and exceeds the sulfur desorption temperature. For this reason, sulfur can be desorbed from the middle part of the NOx catalyst 28. At this time, the bed temperature is not excessively increased at the front and rear portions of the NOx catalyst 28, and the catalyst does not deteriorate.

  In the third stage, the control is performed so that the distribution of the catalyst bed temperature becomes a curve indicated by (3) in FIG. For this purpose, the temperature of the gas containing the catalyst may be made relatively low, and the value is set to T3. In order to set the catalyst-containing gas temperature to T3, the exhaust valve opening timing may be set to E3 that is relatively late. By controlling in this way, the catalyst bed temperature reaches a peak at the rear part of the NOx catalyst 28 and exceeds the sulfur desorption temperature. For this reason, sulfur can be desorbed from the rear portion of the NOx catalyst 28. At this time, the bed temperature does not excessively increase at the front and middle portions of the NOx catalyst 28, and the catalyst does not deteriorate.

  In the present embodiment, in the sulfur poisoning regeneration control, the exhaust variable valve operating apparatus 44 is controlled so that the exhaust valve opening timing is delayed in steps of E1, E2, and E3. Thereby, the sulfur desorption of the 1st-3rd step mentioned above advances, and the effect similar to the control demonstrated based on FIG. 4 is acquired.

  In the present invention, the above-described effects can be obtained by executing either the exhaust gas amount control as described with reference to FIG. 4 or the exhaust gas temperature control as described with reference to FIG. However, the control of the exhaust gas amount as described based on FIG. 4 and the control of the exhaust gas temperature as described based on FIG. 5 may be executed in combination.

  As described above, in the present embodiment, in the sulfur poisoning regeneration control, the valve timings of the intake valve 32 and the exhaust valve 34 are sequentially changed to the first to third stages, so that the NOx catalyst 28 approaches the front and the middle. Then, sulfur is sequentially desorbed from each rear part. At this time, in order to desorb all sulfur from each site and reduce the amount of reducing agent used as much as possible, the valve timing is set to the next stage at the timing when sulfur has just desorbed from the target site. It is ideal to change to

  In order to realize such an ideal, the amount of accumulated sulfur (hereinafter referred to as “sulfur deposition amount”) is estimated for each part of the NOx catalyst 28, and before sulfur poisoning regeneration (reducing agent). The larger the amount of accumulated sulfur at that part in (before supply), the longer the valve timing holding time at the stage where that part is targeted. Thereby, according to the sulfur deposition amount for every site | part, the sulfur desorption time of the site | part can be changed. Therefore, it is possible to suppress the sulfur desorption time at each site from being too short and the sulfur from remaining, or the sulfur desorption time from being too long to waste the reducing agent.

  Further, during the sulfur poisoning regeneration, the amount of sulfur to be desorbed (hereinafter referred to as “sulfur desorption amount”) is estimated for each site of the NOx catalyst 28, and the sulfur desorption is performed for the site where sulfur is desorbed. The valve timing may be changed to the next stage when the value obtained by subtracting the sulfur desorption amount during sulfur poisoning regeneration from the sulfur accumulation amount before poison regeneration becomes equal to or less than a predetermined reference value. In this case, as the amount of sulfur deposition before sulfur poisoning regeneration increases, the time until the value obtained by subtracting the sulfur desorption amount from the sulfur deposition amount becomes equal to or less than the reference value becomes longer. For this reason, also in this case, the retention time (sulfur desorption time) of the valve timing at the stage where the relevant part is targeted changes in accordance with the amount of sulfur deposition in each part.

Hereinafter, an example of a method for estimating the sulfur accumulation amount and the sulfur desorption amount for each part of the NOx catalyst 28 will be described.
(Calculation of sulfur deposit in the front part)
Assuming that the sulfur concentration in the exhaust gas flowing into the front portion of the NOx catalyst 28 is C1, this C1 is equal to the sulfur concentration in the exhaust gas exhausted from the engine 10, and is calculated as follows. Can do. The sulfur contained in the exhaust gas discharged from the engine 10 is the sum of the sulfur contained in the burned fuel and the sulfur contained in the burned engine oil. Therefore, the sum of the value obtained by multiplying the sulfur concentration in the fuel by the fuel consumption amount and the value obtained by multiplying the sulfur concentration in the engine oil by the engine oil consumption amount is divided by the exhaust gas amount to be discharged from the engine 10. The exhaust gas sulfur concentration, that is, the sulfur concentration C1 of the exhaust gas flowing into the front part can be calculated. In this calculation, the values of the sulfur concentration in the fuel and the sulfur concentration in the engine oil can be stored in the ECU 50 in advance by examining the values of the fuel and engine oil used in the country or region where the vehicle is used. Good. As the fuel consumption amount, the value of the fuel injection amount from the fuel injector 30 may be used. The engine oil consumption may be calculated on the basis of an empirically calculated map representing the relationship between the operating state of the engine 10 and the engine oil consumption in the ECU 50 in advance. The exhaust gas amount can be calculated based on the intake air amount.

Assuming that the amount of sulfur absorbed per unit time (hereinafter referred to as “sulfur absorption amount”) at the front portion of the NOx catalyst 28 is A1, A1 can be calculated by the following equation.
A1 = C1, α, β, γ (1)
Here, α, β, and γ are absorption rate coefficients represented by maps shown in FIGS.

  The sulfur absorption amount A1 at the front part of the NOx catalyst 28 increases as the sulfur concentration C1 of the exhaust gas flowing into the front part increases. For this reason, A1 is proportional to C1. However, if the amount of sulfur already deposited is large, sulfur becomes difficult to be absorbed. The absorption rate coefficient α shown in FIG. 6 is a coefficient for correcting the point. Further, when the catalyst bed temperature is low, such as immediately after the engine is started, sulfur is hardly absorbed. The absorption rate coefficient β shown in FIG. 7 is a coefficient for correcting the point. Further, when the amount of exhaust gas is large, the flow rate of exhaust gas passing through the NOx catalyst 28 is increased, so that the amount of sulfur that passes through without being absorbed increases. The absorption rate coefficient γ shown in FIG. 9 is a coefficient for correcting the point.

The ECU 50 can calculate the sulfur accumulation amount D1 of the front portion of the NOx catalyst 28 by integrating the value of A1 calculated by the above equation (1). That is, in the ECU 50, when the calculation interval is Δt, D1 may be updated by performing the following calculation every time.
D1 = D1 + A1 · Δt (2)

  In the above calculation, the value of D1 calculated last time may be used as the sulfur deposition amount used for calculating the absorption rate coefficient α. Further, the catalyst bed temperature used for calculating the absorption rate coefficient β may be detected by a temperature sensor or estimated by a known method.

(Calculation of sulfur deposition in the middle part)
The sulfur concentration C2 in the exhaust gas flowing into the middle part of the NOx catalyst 28 is obtained by subtracting the sulfur absorbed in the front part from the sulfur concentration C1 of the exhaust gas flowing into the front part. Since it is obtained, it can be calculated by the following equation.
C2 = C1 · (1−α · β · γ) (3)

The sulfur absorption amount A2 per unit time in the middle part of the NOx catalyst 28 can be calculated by the following equation.
A2 = C2, α2, β2, γ2 (4)
However, α2, β2, and γ2 are absorption rate coefficients for the middle part and are the same as the absorption rate coefficients α, β, and γ for the front part described above, and are not shown in the figure.

The ECU 50 can calculate the sulfur accumulation amount D2 of the middle part of the NOx catalyst 28 by integrating the value of A2 calculated by the above equation (4). That is, the ECU 50 may update D2 by performing the following calculation every time.
D2 = D2 + A2 · Δt (5)

  In the above calculation, the previously calculated value of D2 may be used as the sulfur deposition amount used for calculating the absorption rate coefficient α2.

(Calculation of sulfur accumulation in the rear part)
The sulfur concentration C3 in the exhaust gas flowing into the rear portion of the NOx catalyst 28 is obtained by subtracting the sulfur absorbed in the middle portion from the sulfur concentration C2 of the exhaust gas flowing into the middle portion. Since it is obtained, it can be calculated by the following equation.
C3 = C2 · (1−α2 · β2 · γ2) (6)

The sulfur absorption amount A3 per unit time at the rear portion of the NOx catalyst 28 can be calculated by the following equation.
A3 = C3 · α3 · β3 · γ3 (7)
However, α3, β3, and γ3 are absorption rate coefficients for the rear part, and are the same as the absorption rate coefficients α, β, and γ for the front part, and are not shown.

The ECU 50 can calculate the sulfur accumulation amount D3 of the rear portion of the NOx catalyst 28 by integrating the value of A3 calculated by the above equation (7). That is, the ECU 50 may update D3 by calculating the following formula every time.
D3 = D3 + A3 · Δt (8)

  In the above calculation, the value of D3 calculated last time may be used as the sulfur deposition amount used for calculating the absorption rate coefficient α3.

(Calculation of sulfur desorption at each site)
When the sulfur desorption amount per unit time of each part of the NOx catalyst 28 during sulfur poisoning regeneration is G, the standard desorption rate H is desorption rate coefficients ε, θ, μ, the sulfur desorption amount G is It can be calculated by the following formula.
G = H · ε · θ · μ (9)

  However, the reference desorption rate H is a sulfur desorption amount per unit time determined empirically under a predetermined sulfur deposition amount, catalyst bed temperature, and air-fuel ratio A / F. The desorption rate coefficients ε, θ, and μ are represented by maps shown in FIGS. 9 to 11, respectively. The sulfur desorption amount increases as the sulfur deposition amount increases. The desorption rate coefficient ε shown in FIG. 9 is a coefficient for correcting the point. Further, sulfur is more easily desorbed when the catalyst bed temperature is higher, and is not desorbed unless a predetermined sulfur desorption temperature is exceeded. The desorption rate coefficient θ shown in FIG. 10 is a coefficient for correcting the point. Further, sulfur is not desorbed unless the air-fuel ratio A / F is less than stoichiometric (theoretical air-fuel ratio). A desorption rate coefficient μ shown in FIG. 11 is a coefficient for correcting the point.

  During the sulfur poisoning regeneration, the ECU 50 calculates the sulfur desorption amount G per unit time for each part by performing the calculation of the above equation (9) for each part of the NOx catalyst 28. Then, by integrating the sulfur desorption amount G per unit time for each part, the sulfur desorption amount can be calculated for each part of the NOx catalyst 28.

  FIG. 12 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to perform sulfur poisoning regeneration of the NOx catalyst 28. Hereinafter, with reference to FIG. 12, when the control of the intake valve opening period described based on FIG. 4 and the control of the exhaust valve opening timing described above based on FIG. 5 are executed in combination. Control will be described. In the control shown in FIG. 12, for each part of the NOx catalyst 28, a value obtained by subtracting the sulfur desorption amount during sulfur poisoning regeneration from the sulfur deposition amount before sulfur poisoning regeneration (hereinafter referred to as “sulphur residual amount”). The valve timing is switched at a timing at which “)” becomes equal to or lower than a predetermined reference value, and the process proceeds to sulfur desorption at the next site. In FIG. 12, sulfur is abbreviated as “S”, the intake valve is abbreviated as “IN valve”, and the exhaust valve is abbreviated as “EX valve”.

  According to the routine shown in FIG. 12, first, it is determined whether or not the total sulfur deposition amount obtained by adding up the sulfur deposition amounts for the respective portions of the NOx catalyst 28 is equal to or greater than a predetermined value (step 100). This predetermined value is a value set in advance to determine whether or not it is necessary to perform sulfur poisoning regeneration. That is, when the amount of accumulated sulfur in the entire NOx catalyst 28 exceeds this predetermined value, it is considered that sulfur poisoning regeneration needs to be performed, and sulfur poisoning regeneration control is started.

  In the sulfur poisoning regeneration control, first, sulfur poisoning regeneration of the front portion of the NOx catalyst 28 is started (step 102). In order to perform sulfur poisoning regeneration at the front portion of the NOx catalyst 28, as described above, the amount of exhaust gas is relatively small and the temperature of the gas containing the catalyst is relatively high. The ECU 50 includes an operating state such as an engine speed and an engine load, and an exhaust gas amount and a catalyst-containing gas temperature necessary for performing sulfur poisoning regeneration at a front portion of the NOx catalyst 28 under the operating state. A map that defines the relationship is stored in advance. Based on the map, the target exhaust gas amount and the target catalyst-containing gas temperature are respectively calculated (steps 104 and 106). Subsequently, based on the calculated target exhaust gas amount and target catalyst-containing gas temperature, a target intake valve opening period and a target exhaust valve opening timing are respectively calculated (steps 108 and 110). Then, the opening timing and closing timing of the intake valve 32 are controlled by the intake variable valve operating apparatus 42 so that the calculated target intake valve opening period is realized (step 112). Further, the exhaust variable valve gear 44 controls the closing timing of the exhaust valve 34 so that the calculated target exhaust valve opening timing is realized (step 114).

  After the valve timing is controlled by the above processing, the reducing agent is supplied (step 116). The supply amount of the reducing agent is such that the catalyst bed temperature at the peak portion becomes equal to or higher than the sulfur desorption temperature as shown in the catalyst bed temperature distribution shown in FIGS. 4 and 5, and the deterioration of the catalyst is promoted. It is controlled so that it does not become such an excessively high temperature.

  While the sulfur poisoning regeneration of the front part of the NOx catalyst 28 is being performed, the ECU 50 determines the sulfur desorption during the sulfur poisoning regeneration from the sulfur deposition amount before the sulfur poisoning regeneration of the front part of the NOx catalyst 28. The amount of sulfur remaining after subtracting the amount is sequentially calculated. Then, it is determined whether or not the amount of remaining sulfur at the front portion has become a predetermined reference value or less (step 118). This reference value is a value set in advance to determine whether or not the sulfur accumulated in the front portion has been desorbed. Therefore, while the sulfur remaining amount at the front part exceeds the reference value, the valve timing is maintained and the sulfur poisoning regeneration at the front part is continued. If the amount of residual sulfur in the front part falls below the above reference value, the sulfur poisoning regeneration in the front part is terminated, the valve timing is switched, and the sulfur poisoning regeneration in the middle part is performed. Is started (step 120).

  In order to perform sulfur poisoning regeneration in the middle part of the NOx catalyst 28, as described above, the exhaust gas amount may be set to a medium level and the catalyst-containing gas temperature may be set to a medium level. The ECU 50 includes an operating state such as an engine speed and an engine load, and an exhaust gas amount and a catalyst-containing gas temperature necessary for performing sulfur poisoning regeneration of the middle part of the NOx catalyst 28 under the operating state. A map that defines the relationship is stored in advance. Based on the map, the target exhaust gas amount and the target catalyst-containing gas temperature are respectively calculated (steps 122 and 124). Subsequently, a target intake valve opening period and a target exhaust valve opening timing are calculated based on the calculated target exhaust gas amount and target catalyst-containing gas temperature (steps 126 and 128), respectively. Then, the opening timing and closing timing of the intake valve 32 are controlled by the intake variable valve operating apparatus 42 so that the calculated target intake valve opening period is realized (step 130). Further, the exhaust variable valve gear 44 controls the closing timing of the exhaust valve 34 so that the calculated target exhaust valve opening timing is realized (step 132).

  While the sulfur poisoning regeneration of the middle part of the NOx catalyst 28 is being performed, the ECU 50 determines the sulfur desorption during the sulfur poisoning regeneration from the sulfur deposition amount before the sulfur poisoning regeneration of the middle part of the NOx catalyst 28. The amount of sulfur remaining after subtracting the amount is sequentially calculated. Then, it is determined whether or not the amount of remaining sulfur in the middle part is equal to or lower than a predetermined reference value (step 134). This reference value is a value set in advance to determine whether or not the sulfur accumulated in the middle part has been desorbed. Therefore, while the sulfur remaining amount at the middle part exceeds the reference value, the valve timing is maintained and the sulfur poisoning regeneration at the middle part is continued. When the sulfur remaining amount at the middle part is below the above reference value, the sulfur poisoning regeneration at the middle part is terminated, the valve timing is switched, and the sulfur poisoning regeneration at the rear part is performed. Is started (step 136).

  In order to perform sulfur poisoning regeneration at the rear portion of the NOx catalyst 28, as described above, the amount of exhaust gas is relatively large and the temperature of the gas containing the catalyst is relatively low. The ECU 50 includes an operating state such as an engine speed and an engine load, and an exhaust gas amount and a catalyst-containing gas temperature necessary for performing sulfur poisoning regeneration at a rear portion of the NOx catalyst 28 under the operating state. A map that defines the relationship is stored in advance. Based on the map, the target exhaust gas amount and the target catalyst-containing gas temperature are respectively calculated (steps 138 and 140). Subsequently, based on the calculated target exhaust gas amount and target catalyst-containing gas temperature, a target intake valve opening period and a target exhaust valve opening timing are respectively calculated (steps 142 and 144). Then, the opening timing and closing timing of the intake valve 32 are controlled by the intake variable valve operating apparatus 42 so that the calculated target intake valve opening period is realized (step 146). Further, the closing timing of the exhaust valve 34 is controlled by the variable exhaust valve device 44 so that the calculated target exhaust valve opening timing is realized (step 148).

  While the sulfur poisoning regeneration of the rear part of the NOx catalyst 28 is being performed, the ECU 50 desorbs sulfur during the sulfur poisoning regeneration from the sulfur deposition amount before the sulfur poisoning regeneration of the rear part of the NOx catalyst 28. The amount of sulfur remaining after subtracting the amount is sequentially calculated. Then, it is determined whether or not the amount of remaining sulfur in the rear portion has become equal to or less than a predetermined reference value (step 150). This reference value is a value set in advance to determine whether or not sulfur accumulated in the rear part has been desorbed. Therefore, while the remaining amount of sulfur in the rear part exceeds the reference value, the valve timing is maintained and the sulfur poisoning regeneration in the rear part is continued. When the sulfur remaining amount in the rear part is below the above reference value, it can be determined that the sulfur poisoning regeneration in the rear part has been completed, so the supply of the reducing agent is stopped and the sulfur poisoning is stopped. The reproduction control ends (step 152).

  According to the routine processing of FIG. 12 described above, the value obtained by subtracting the sulfur desorption amount during sulfur poisoning regeneration from the sulfur deposition amount before sulfur poisoning regeneration is equal to or less than the reference value for the site during sulfur desorption. At this time, the sulfur poisoning regeneration of the part is finished. For this reason, the sulfur poisoning regeneration can be completed by accurately determining the timing at which the sulfur at the site has just been desorbed. Therefore, it is possible to more reliably suppress sulfur remaining at each portion because the sulfur is left too short or sulfur is left too long and the reducing agent is consumed wastefully.

  In the first embodiment described above, the case where the NOx catalyst 28 is divided into three parts from the upstream side to the downstream side to perform sulfur poisoning regeneration has been described. However, two parts, or four or more parts are used. The sulfur poisoning regeneration may be performed separately.

  In the first embodiment described above, the “desorption site control means” in the first, fourth and fifth inventions is realized by the ECU 50 executing the routine shown in FIG.

10 Engine 22 Intake passage 24 Exhaust passage 27 Oxidation catalyst 28 NOx catalyst 30 Fuel injector 32 Intake valve 34 Exhaust valve 42 Intake variable valve operating device 44 Exhaust variable valve operating device 46 Fuel addition valve 50 ECU

Claims (5)

A NOx catalyst disposed in the exhaust passage of the internal combustion engine;
Reducing agent supply means for supplying a reducing agent to exhaust gas upstream of the NOx catalyst in order to desorb sulfur accumulated on the NOx catalyst;
A variable valve gear that varies the valve timing of one or both of the intake valve and the exhaust valve;
By changing the valve timing stepwise by the variable valve device such that one or both of the amount and temperature of the exhaust gas discharged from the internal combustion engine change with time during the supply of the reducing agent, A desorption site control means for controlling the site where the sulfur desorption temperature or higher in the NOx catalyst is moved over time;
A control device for an internal combustion engine, comprising: The variable valve operating device has a function of changing an open period of the intake valve,
The desorption site control means changes the opening period of the intake valve stepwise by the variable valve device so that the amount of exhaust gas discharged from the internal combustion engine changes with time. Item 2. A control device for an internal combustion engine according to Item 1. The variable valve operating device has a function of changing the opening timing of the exhaust valve,
The desorption site control means changes the opening timing of the exhaust valve stepwise by the variable valve device so that the temperature of the exhaust gas discharged from the internal combustion engine changes with time. Item 3. The control device for an internal combustion engine according to Item 1 or 2. Sulfur deposition amount estimation means for estimating a sulfur deposition amount that is the amount of sulfur deposited for each part when the NOx catalyst is divided into a plurality of parts from the upstream side toward the downstream side,
Each part of the NOx catalyst corresponds to a part that becomes equal to or higher than the sulfur desorption temperature at each stage when the desorption part control means changes the valve timing stepwise.
When the valve timing is changed stepwise, the desorption site control means determines the sulfur deposition amount for each site of the NOx catalyst before the supply of the reducing agent according to the estimated value of the sulfur deposition amount for each site. The control device for an internal combustion engine according to any one of claims 1 to 3, wherein the valve timing holding time for each is changed. A sulfur deposition amount estimating means for estimating a sulfur deposition amount that is an amount of sulfur deposited for each portion when the NOx catalyst is divided into a plurality of portions from the upstream side toward the downstream side;
A sulfur desorption amount estimating means for estimating a sulfur desorption amount, which is an amount of sulfur desorbed, for each part of the NOx catalyst during the supply of the reducing agent;
Remaining for each part of the NOx catalyst based on the estimated value of the sulfur deposition amount before the supply of the reducing agent and the estimated value of the sulfur desorption amount during the supply of the reducing agent A sulfur residual amount estimating means for estimating a sulfur residual amount that is an amount of sulfur;
With
Each part of the NOx catalyst corresponds to a part that becomes equal to or higher than the sulfur desorption temperature at each stage when the desorption part control means changes the valve timing stepwise.
When the valve timing is changed step by step, the desorption site control means changes the valve timing when the estimated value of the remaining amount of sulfur at the site where sulfur is being desorbed falls below a predetermined value. The control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the control is performed in the following steps.

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