JPH10288067A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent fuel post-injected for supplying hydrocarbon to NOx catalyst from adhering to cylinder walls and mixing into lubricating oil. SOLUTION: A temperature and pressure in a cylinder are estimated with engine operating conditions and post-injection timing and, based on the estimated results, the lower and upper limit set values of the post-injected amount are calculated (step 106, 107). When the post-injected amount Y1 for each cylinder calculated with the engine operating conditions and catalyst temperature is smaller than the lower limit set value, the post-injection is stopped, and the post-injected amount for several cycles is accumulated. When the accumulated value X reaches the lower limit set value or higher, the number of cylinders to be post-injected is calculated based on the supplied amount of light oil Z for each unit time and engine speed, and the post-injected amount Y for each cylinder (for each stroke) is calculated (steps 108 to 110). Then, when the post- injected amount Y is higher than the upper limit set value, the post-injected amount Y is corrected to the upper limit set value and the post-injection is performed (steps 111, 112, and 113).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine for reducing and purifying nitrogen oxides contained in exhaust gas of an internal combustion engine with a catalyst.

[0002]

2. Description of the Related Art In order to purify nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine in which fuel is burned under an excessive amount of oxygen such as a diesel engine, a NO.
x catalyst is installed, and hydrocarbon (fuel) is used as a reducing agent and NO
A technique for reducing and purifying NOx by supplying it to an x catalyst has been proposed. As shown in FIG. 4, the NOx purification characteristics of this catalyst are determined in a predetermined activation temperature range (for example, from 200 ° C. to 400 ° C.).
° C), the NOx purification rate is high, and NO
It is known that the NOx purification rate changes according to the amount of hydrocarbon supplied to the x catalyst.

[0003] Since the exhaust gas of a normal internal combustion engine hardly contains hydrocarbons, NOx is generated by a NOx catalyst.
In order to reduce and purify the exhaust gas, it is necessary to add a hydrocarbon as a reducing agent to the exhaust gas. To do this, a small amount of fuel is post-injected from the fuel injection valve in the expansion or exhaust stroke after fuel injection (main injection) from the fuel injection valve, and the uninjected fuel (hydrocarbon) is reduced by this post-injection. Some agents are supplied to a NOx catalyst.

However, in this method, when the amount of post-injected fuel is large or the post-injection pressure is high, a part of the post-injected fuel reaches the cylinder wall and adheres to the lubricating oil. Thus, the viscosity of the lubricating oil may be reduced to deteriorate the lubricating oil, or in the worst case, the piston may be seized. In addition, if a part of the post-injected fuel adheres to the cylinder wall, the amount of post-injected fuel supplied to the NOx catalyst is insufficient, and the NOx purification rate is reduced.

Therefore, in Japanese Patent Application Laid-Open No. 8-74561, after the exhaust valve and the intake valve are both opened and the air flow in the cylinder is strong, the post-injection is performed to prevent the post-injected fuel from adhering to the cylinder wall. Propose to avoid.

[0006]

However, as described in the above-mentioned publication, if the amount of fuel to be post-injected is large or the pressure of fuel to be post-injected is high only by utilizing the air flow in the cylinder, Again, a part of the post-injected fuel may adhere to the cylinder wall. Further, the fuel injection valve is designed to operate accurately within the adjustment range of the injection amount at the time of main injection, and is not originally good at adjusting a small amount of fuel injection as at the time of post-injection. Therefore, when the amount of fuel to be post-injected is small, the post-injection amount is likely to fluctuate due to the influence of individual differences (variation) and aging of the fuel injection valve, and the actual post-injection amount is deviated from the target value. As a result, the optimum amount of hydrocarbons cannot be supplied to the NOx catalyst.

Accordingly, a first object of the present invention is to prevent the post-injected fuel from adhering to the cylinder wall, and a second object is to provide a post-injection amount when the post-injection amount is small. Is to solve the problem of variation in

[0008]

According to claim 1 of the present invention,
The operating state of the internal combustion engine is detected by the operating state detecting means, and the active state of the catalyst is detected by the catalyst active state detecting means, and the injection control means detects the detected value of the operating state detecting means and the catalyst active state detecting means. The amount of hydrocarbon supplied to the catalyst based on the detected value (hereinafter referred to as "target post-injection amount")
And the post-injection timing is set. Further, the number of cylinders to be post-injected and the post-injection amount per cylinder are calculated based on the target post-injection amount and the detection value of the operating state detecting means. In response, a post-injection command is output to the fuel injection means.

In this way, when the target post-injection amount is large, the number of post-injection cylinders can be increased to make the post-injection amount per cylinder within an appropriate range. Adhesion of post-injection fuel can be prevented. As a result, even when the target post-injection amount is large, mixing of post-injection fuel into the lubricating oil can be prevented, and the life of the lubricating oil can be extended, and
The post-injection amount required for NOx reduction purification can be accurately controlled in accordance with the target value, and the NOx purification rate can be improved.

Further, in the present invention, the post-injection timing is set based on the detected value of the operating state detecting means (the operating state of the internal combustion engine) and the detected value of the catalyst active state detecting means. Since the temperature in the cylinder and the strength of the air flow in the cylinder vary depending on the post-injection timing, the optimal post-injection timing is set according to the operating state of the internal combustion engine and the activation state of the catalyst, so that the post-injection fuel And the effect of preventing post-injection fuel from adhering to the cylinder wall can be further enhanced.

The lower limit value and the upper limit value of the post-injection amount per cylinder are set and calculated.
The post-injection command may be output only when the post-injection amount per cylinder is within the range between the lower limit set value and the upper limit set value.
With this configuration, the post-injection is not performed unless the calculated post-injection amount per cylinder does not exceed the lower limit set value (that is, the lower limit of the injection amount at which the fuel injection means can perform the injection operation with high accuracy). Variation can be prevented, and the amount of hydrocarbon supplied to the catalyst can be controlled to a target value. Moreover, when the post-injection amount per cylinder exceeds the upper limit set value (that is, the upper limit value of the post-injection amount where the post-injection fuel does not adhere to the cylinder wall), the post-injection is not performed. Adhesion can be reliably prevented.

In this case, if the post-injection amount per cylinder is smaller than the lower limit set value, the post-injection is stopped and the post-injection amount for several cycles is integrated, and the integrated value is calculated. A post-injection command is output when the post-injection amount is equal to or greater than the lower limit set value. If the post-injection amount per cylinder exceeds the upper limit set value, 1 is output.
It is preferable that the post-injection command is output after correcting the post-injection amount per cylinder to the upper limit set value. In this way, it is possible to accurately control the post-injection amount required for NOx reduction purification in accordance with the target value while preventing the post-injection amount from fluctuating and the post-injection fuel from adhering to the cylinder wall. The NOx purification rate can be improved.

Further, the lower limit of the post-injection amount per cylinder is set to 1 to 8 mm ³ / stroke per liter of displacement of one cylinder of the internal combustion engine (one injection operation).
And the upper limit set value is preferably set within a range of 8 to 20 mm ³ / stroke. According to the experimental results of the present inventor, when the post-injection amount per liter of displacement of one cylinder is smaller than 1 mm ³ / stroke, the post-injection amount varies significantly, so the lower limit set value is set to 1 mm.
Must be set to ³ / stroke or more. Also, if the post-injection amount per liter of displacement per cylinder exceeds 20 mm ³ / stroke, the post-injection fuel adheres to the cylinder wall remarkably, so the upper limit set value must be 20 mm ³ / stroke or less. There is. Since the lower limit set value and the upper limit set value change depending on the individual difference (variation) of the fuel injection means, aging, the operating state, and the like, the lower limit set value is set to 1
~8mm ³ / in the range of the stroke, the upper limit set value 8-2
By appropriately setting the value within the range of 0 mm ³ / stroke, it is possible to prevent the post-injection amount from scattering and the post-injection fuel from adhering to the cylinder wall.

In this case, the in-cylinder state of each cylinder is estimated based on the detected value of the operating state detecting means and the post-injection timing, and based on the estimated in-cylinder state of each cylinder. The lower limit set value and the upper limit set value may be set. That is, since the behavior and the reforming degree of the fuel post-injected into the cylinder differ depending on the in-cylinder state of each cylinder, if the lower limit set value and the upper limit set value are set based on the in-cylinder state of each cylinder, a wide range is obtained. Variations in the post-injection amount and adhesion of post-injection fuel to the cylinder wall under operating conditions can be prevented.

Further, as the in-cylinder pressure or the in-cylinder temperature of each cylinder estimated based on the detected value of the operating state detecting means and the after-injection timing increases, the lower limit set value and the lower limit value of the cylinder may be increased. The upper limit set value may be set large. In other words, the higher the in-cylinder pressure temperature of each cylinder,
The better the thermal reforming of the post-injected fuel and the higher the in-cylinder pressure, the stronger the flow of air flowing in the cylinder, and the less likely the post-injected fuel adheres to the cylinder wall. Therefore, if the in-cylinder pressure or in-cylinder temperature of each cylinder increases, the lower limit set value and the upper limit set value are set to be larger, so that an optimal set value according to the in-cylinder pressure or in-cylinder temperature of each cylinder is obtained. Obtainable.

[0016]

[Embodiment (1)] Hereinafter, an embodiment (1) in which the present invention is applied to, for example, a 4-cylinder diesel engine will be described with reference to FIGS.
1 will be described. First, the configuration of the entire engine control system will be described with reference to FIG. To each cylinder of the diesel engine 10 which is an internal combustion engine, intake air taken in through an intake pipe 11 is taken in through an intake manifold 13. Each cylinder of the diesel engine 10 is provided with a pressure-accumulation type fuel injection valve 14 as a fuel injection means. To each fuel injection valve 14, fuel stored at a high pressure from a high-pressure fuel pump 15 is distributed through a common rail 16. . The common rail 16 is provided with a fuel pressure sensor 12 (fuel pressure detecting means) for detecting the pressure of fuel (common rail fuel pressure) distributed to each fuel injection valve 14.

The exhaust gas discharged from each cylinder of the diesel engine 10 is supplied to an exhaust manifold 17 (exhaust passage).
The exhaust gas is discharged to one exhaust pipe 18 (exhaust passage). A catalyst for reducing and purifying NOx in the exhaust gas, that is, a NOx catalyst 19 is provided in the exhaust pipe 18. The base material of the NOx catalyst 19 has a large number of flow paths formed by a honeycomb lattice made of a porous member such as a ceramic. A coating layer such as zeolite or silica is provided on the surface of the porous member. Further, a noble metal such as Pt, a transition metal such as Cu, or an alkali metal or an alkaline earth metal is supported on the surface.

An exhaust gas temperature sensor 20 is provided downstream of the NOx catalyst 19. This exhaust temperature sensor 20
Functions as a catalyst active state detecting means for detecting the exhaust gas temperature at the outlet of the NOx catalyst 19 and estimating the catalyst temperature (catalytic active state) from the exhaust gas temperature. Diesel engine 1
0, the engine electronic control circuit (hereinafter referred to as “ECU”).
25) controls the fuel injection valve 14 of each cylinder. The ECU 25 reads signals output from an accelerator sensor 26 and an engine speed sensor 27 (both of which correspond to operating state detecting means) to detect the operating state of the diesel engine 10 and to output the output of the exhaust temperature sensor 20. The signal is read and the NOx catalyst 19
Estimate the temperature of

The ECU 25 is mainly composed of a microcomputer, and has a built-in ROM (storage medium).
Stores a main injection control program (not shown), a post-injection control program shown in FIG. 2, map data shown in FIGS. 3 to 7, and the like. The ECU 25 executes the main injection control program to execute the fuel injection valve 14 of each cylinder.
The main injection command for generating the engine output is output to the engine, and the post-injection control program shown in FIG. 2 is executed to calculate the number of post-injection cylinders and the post-injection amount per cylinder. Accordingly, the fuel injection valve 14 of each cylinder functions as an injection control unit that outputs a post-injection command for supplying hydrocarbons to the NOx catalyst 19.

Hereinafter, the processing contents of the post-injection control program executed by the ECU 25 will be described with reference to the flowchart of FIG. This program is executed immediately before the post injection. When the program is started, first, in step 101, the post-injection amount integrated value X is initialized and X = 0.
In the next step 102, the engine speed sensor 2
7. The signals of the engine speed, the accelerator opening, and the exhaust temperature output from the accelerator sensor 26 and the exhaust temperature sensor 20 are read. Thereafter, in step 103, the amount of NOx emitted from the engine 10 is calculated from the map data shown in FIG. 3 based on the engine speed and the accelerator opening.

Thereafter, in step 104, based on the exhaust gas temperature read in step 102 and the NOx emission amount calculated in step 103, the light oil supply amount Z per unit time to be supplied to the NOx catalyst 19 by post-injection. (Corresponding to the target post-injection amount) is calculated from the map data shown in FIG.
The post-injection amount Y1 per stroke (one injection operation) of the fuel injection valve 14 when the light oil supply amount Z per unit time is post-injected by one cylinder is based on the engine speed read in step 102. calculate.

Thereafter, in step 105, the post-injection timing is calculated from the map data shown in FIG. 5 based on the engine load and the exhaust gas temperature, and in the next step 106, the engine operating conditions (engine speed, accelerator opening The in-cylinder state (in-cylinder temperature and in-cylinder pressure) is estimated from the map data stored in the ROM of the ECU 25 based on the temperature and the post-injection timing. Then, in the next step 107, the above step 10
Based on the in-cylinder temperature and the in-cylinder pressure estimated from 5, the lower limit set value and the upper limit set value of the post-injection amount are calculated from the map data shown in FIG.

In this case, the lower limit set value and the upper limit set value are set larger as the in-cylinder temperature and the in-cylinder pressure increase. Lower limit setting values, the fuel injection valve 14 is the lower limit of the accuracy injection operation can injection amount, specifically 1 cylinder exhaust amount per liter of the engine 1 to 8 mm ³ / stroke (preferably 2 to 6 mm ³ / Stroke), and the upper limit set value is the upper limit value of the post-injection amount at which the post-injection fuel does not adhere to the cylinder wall, and specifically, 8 to 20 mm per liter of displacement of one cylinder of the engine. ³ / stroke (preferably 8 to 12 mm ³ / stroke). For example, in a 4-cylinder engine with a displacement of 2 liters,
The lower limit set value is set within a range of 0.5 to ⁴ mm ³ / stroke, and the upper limit set value is set within a range of 4 to 10 mm ³ / stroke. For an eight-cylinder engine with a displacement of 12 liters, the lower limit set value is 1.5. ~12mm ³ / stroke, the upper limit set value is set in the range of 12~30mm ³ / stroke.

In the next step 108, the post-injection amount Y1 calculated in step 104 is integrated with the previous post-injection amount integrated value X (X = 0 at the time of the first processing) to obtain the post-injection amount integrated value X. Update. Thereafter, in step 109, the post-injection amount integrated value X is compared with the lower limit set value set in step 107, and if the post-injection amount integrated value X is smaller than the lower limit set value, the process returns to step 102, and The processing up to step 109 is repeated.

If the post-injection amount Y1 per cylinder is smaller than the lower limit set value, the post-injection is stopped and the post-injection amount for several cycles is integrated, and the integrated value X is set to the lower limit value. When it becomes equal to or more than the value, the process proceeds from step 109 to step 110, and based on the light oil supply amount Z per unit time and the engine speed calculated in step 104, the number of cylinders to be post-injected is shown in the map data shown in FIG. It is calculated from: That is, the number of post-injection cylinders increases as the light oil supply amount Z increases, and the number of post-injection cylinders increases as the engine speed decreases. Then, the post-injection amount Y per cylinder (per stroke) is calculated based on the number of post-injection cylinders thus calculated, the light oil supply amount Z per unit time, and the engine speed. At this time, if the calculated post-injection amount Y per cylinder becomes smaller than the lower limit set value, the number of post-injection cylinders is decreased by 1 until the post-injection amount Y per cylinder becomes equal to or more than the lower limit set value. The post-injection amount Y per cylinder is calculated again.

Thereafter, at step 111, the post-injection amount Y per cylinder is compared with the upper limit set value set at step 107, and if the post-injection amount Y per cylinder is larger than the upper limit set value, the routine proceeds to step 111. Proceeding to 112, the post-injection amount Y per cylinder is corrected to the upper limit set value, and proceeding to step 113. If the post-injection amount Y per cylinder is equal to or less than the upper limit set value in step 111, the process proceeds to step 113 without correcting the post-injection amount Y per cylinder. This step 1
In step 13, a post-injection command is output to the fuel injection valve 14 in accordance with the post-injection amount Y per cylinder, post-injection timing, and post-injection cylinder number calculated by the above-described processing, post-injection is executed, and the present program ends. .

When executing the post-injection, the post-injection cylinder is changed as needed so that the post-injection cylinder is not biased to some of the cylinders. For example, when post-injection is performed with N cylinders smaller than the total number of cylinders of the engine, post-injection is performed so that post-injection is performed in all combinations in consideration of a combination of selecting N cylinders from all cylinders. The combination of cylinders is changed every one or several cycles.

For example, the order of post-injection in the case of post-injection with two cylinders in a four-cylinder engine will be described with reference to FIGS. 8 to 11. As shown in FIG. After the post-injection for one or several cycles in the injection cylinder group, as shown in FIG. 9, for one or several cycles in the post-injection cylinder group consisting of the second cylinder and the third cylinder as another cylinder group,
After injection. Thereafter, as shown in FIG. 10, in the post-injection cylinder group including the third cylinder and the fourth cylinder, for one or several cycles,
After the post-injection, post-injection is performed for one or several cycles in a post-injection cylinder group including the first cylinder and the fourth cylinder as shown in FIG. Note that the order of switching the post-injection cylinder group is not limited to the above order, and may be changed as appropriate.

In the embodiment (1) described above, the number of cylinders to be post-injected based on the light oil supply amount Z (target post-injection amount) per unit time and the engine speed calculated from the catalyst activation state and engine operating conditions. Is calculated, and the post-injection amount Y per cylinder is calculated.
When the number of cylinders is large, the number of cylinders to be post-injected is increased to make the post-injection amount Y per cylinder within an appropriate range, and the post-injection fuel can be prevented from adhering to the cylinder wall. This allows
Even when the light oil supply amount Z is large, it is possible to prevent the post-injection fuel from being mixed into the lubricating oil, prolong the life of the lubricating oil, and adjust the post-injection amount necessary for NOx reduction purification to the target value. The control can be performed with high accuracy, and the NOx purification rate can be improved.

Further, in the above embodiment (1), taking into account that the temperature in the cylinder and the strength of the air flow in the cylinder vary depending on the post-injection timing, the post-injection is performed based on the engine load and the exhaust gas temperature. Since the timing is calculated, the optimal post-injection timing can be set according to the engine operating state and the catalyst activation state, thereby improving the post-injection fuel and preventing the post-injection fuel from adhering to the cylinder wall. Effect can be enhanced.
Furthermore, taking into account that the behavior and the reforming degree of the fuel post-injected into the cylinder vary depending on the cylinder temperature and the cylinder pressure, the cylinder temperature and the cylinder pressure are determined based on the engine operating conditions and the post-injection timing. The lower limit value and upper limit value of the post-injection amount are calculated based on the estimation result, so that the post-injection amount varies and the post-injection fuel adheres to the cylinder wall under a wide range of operating conditions. Can be prevented.

Further, since the post-injection cylinders are changed at any time so that the post-injection cylinders are not biased to some of the cylinders, the post-injection is performed by using the fuel injection valves 14 of all the cylinders almost equally. The fuel injection valve 14 can be prevented from deteriorating at an early stage due to uneven post-injection in a specific cylinder, and durability can be improved. In this embodiment (1),
The number of cylinders to be post-injected was calculated from the two-dimensional map of FIG. 7 using the light oil supply amount Z per unit time and the engine speed as parameters, and the fuel pressure detected by the fuel pressure sensor 12 and the light oil per unit time were calculated. The number of cylinders to be post-injected may be calculated from a three-dimensional map using the supply amount Z and the engine speed as parameters. For example, when the fuel pressure at the time of post-injection is high, the number of cylinders to be post-injected is increased to reduce the post-injection amount per cylinder. Thus, even when the fuel pressure during the post-injection is high, it is possible to prevent the post-injection fuel from adhering to the cylinder wall. [Embodiment (2)] In the embodiment (1), the number of cylinders to be post-injected is calculated from the map data in FIG. 7 based on the light oil supply amount Z per unit time and the engine speed.
In the embodiment (2) shown in FIG. 12, the post-injection amount integrated value X and the exhaust gas temperature Tg at the outlet of the NOx catalyst 19 indicating the catalyst activation state.
Based on the (catalyst temperature), the number of post-injection cylinders and the post-injection amount per cylinder are calculated, and the post-injection fuel of a reforming degree suitable for the catalyst activation state is supplied to the NOx catalyst 19. Hereinafter, the processing content of the post-injection control program of FIG. 12 executed in the embodiment (2) will be described.

In the post-injection control program of FIG. 12, the same processing as in steps 101 to 109 of FIG. 2 is performed to calculate the light oil supply amount Z per unit time to be supplied to the NOx catalyst 19 by post-injection. First, the post-injection amount Y1 per cylinder (per stroke) is calculated, and the post-injection amount Y is integrated until the integrated value X of the post-injection amount Y1 exceeds the lower limit set value (step 120). Then, if the post-injection amount integrated value X is equal to or larger than the lower limit set value, step 121 is executed.
To the NOx catalyst 19 detected by the exhaust gas temperature sensor 20.
The outlet exhaust temperature Tg (catalyst temperature) is compared with the set temperature T1. Here, the set temperature T1 is set to a catalyst temperature (preferably 240 ° C. to 270 ° C.) showing the maximum NOx purification rate.

In step 121, if the exhaust gas temperature Tg is higher than the set temperature T1, the routine proceeds to step 122, where the number of post-injection cylinders is increased by one from the previous cylinder, and the routine proceeds to step 124. On the other hand, if the exhaust gas temperature Tg is equal to or lower than the set temperature T1, the routine proceeds to step 123, where the number of post-injection cylinders is reduced by one from the previous cylinder, and the routine proceeds to step 124.
Proceed to.

In step 124, step 1
The post-injection amount Y (per stroke) per cylinder is calculated based on the number of post-injection cylinders set in 22 or 123, the light oil supply amount Z per unit time, and the engine speed. Thereafter, in step 125, the post-injection amount Y per cylinder is compared with the lower limit set value. If the post-injection amount Y per cylinder is equal to or greater than the lower limit set value, the process proceeds to step 126, but the process proceeds to step 126. If the post-injection amount Y is smaller than the lower limit set value, step 1
Returning to 23, the number of post-injection cylinders is reduced by one cylinder, and the post-injection amount Y per cylinder is calculated again (step 124).

When the post-injection amount Y per cylinder is equal to or greater than the lower limit set value, the routine proceeds to step 126, where the post-injection amount Y per cylinder is compared with the upper limit set value, and the post-injection amount per cylinder is determined. If the injection amount Y is larger than the upper limit set value, the routine proceeds to step 127, where the post-injection amount Y per cylinder is corrected to the upper limit set value, and the routine proceeds to step 128. If it is determined in step 126 that the post-injection amount Y per cylinder is equal to or less than the upper limit set value, the process proceeds to step 128 without correcting the post-injection amount Y per cylinder. In step 128, the post-injection amount Y per cylinder calculated by the above-described processing, the post-injection timing,
A post-injection command is output to the fuel injection valve 14 according to the number of post-injection cylinders, post-injection is executed, and this program ends. When performing the post-injection, the same as in the embodiment (1),
The post-injection cylinder is changed as needed so that the post-injection cylinder is not biased to some of the cylinders.

In the embodiment (2) described above, the exhaust gas temperature Tg at the outlet of the NOx catalyst 19 detected by the exhaust gas temperature sensor 20 is detected as substitute data of the catalyst temperature, and the exhaust gas temperature Tg is detected.
When g is below the set temperature T1, the number of post-injection cylinders is increased,
By reducing the amount of post-injection per cylinder, the amount of heat per unit volume received by the post-injected fuel from within the cylinder is increased to promote reforming of the post-injected fuel. As a result, the fuel in which the proportion of low-boiling hydrocarbons is increased is supplied to the NOx catalyst 19,
x Increase purification rate.

When the exhaust gas temperature Tg is higher than the set temperature T1, the number of post-injection cylinders is reduced to increase the post-injection amount per cylinder, so that the post-injection fuel per unit volume received from within the cylinders. Is supplied to the NOx catalyst 19 with a relatively small amount of heat and a reduced proportion of low boiling point hydrocarbons. This prevents the post-injection fuel from burning in the NOx catalyst 19, thereby preventing a reduction in the NOx purification rate. [Embodiment (3)] In the embodiment (3), by executing the post-injection control program of FIG.
The number of cylinders to be post-injected and the post-injection amount Y per cylinder are calculated in consideration of the fuel pressure in the common rail 16 detected in Step 2. Hereinafter, the processing content of the post-injection control program in FIG. 13 will be described. When this program is started, first, in step 131, the post-injection amount integrated value X is initialized to X = 0, and in the next step 132, the engine speed sensor 2
7. Read signals of the engine speed, accelerator opening, exhaust temperature, and fuel pressure output from the accelerator sensor 26, the exhaust temperature sensor 20, and the fuel pressure sensor 12. After this,
In step 133, the amount of NOx emitted from the engine 10 is calculated from the map data shown in FIG. 3 based on the engine speed and the accelerator opening.

Thereafter, in step 134, based on the exhaust gas temperature read in step 132 and the NOx emission amount calculated in step 133, the light oil supply amount Z per unit time to be supplied to the NOx catalyst 19 by post-injection. (Corresponding to the target post-injection amount) is calculated from the map data shown in FIG.
The post-injection amount Y1 per one stroke (one injection operation) of the fuel injection valve 14 when the light oil supply amount Z per unit time is post-injected by one cylinder is based on the engine speed read in step 132. calculate.

Thereafter, in step 135, the post-injection timing is calculated from the map data shown in FIG. 5 based on the engine load and the exhaust gas temperature. In the next step 136, the post-injection amount Y1 calculated in step 134 is calculated. Is added to the previous post-injection amount integrated value X to update the post-injection amount integrated value X. Thereafter, in step 137, the post-injection amount integrated value X is compared with a preset lower limit set value. If the post-injection amount integrated value X is smaller than the lower limit set value, the process returns to step 132, and steps 132 to 137 are performed. The process up to is repeated. Here, the lower limit set value, the first cylinder exhaust amount per liter of the engine fuel injection valve 14 which is the lower limit of the accuracy injection operation can injection amount 1 to 8 mm ³ / stroke (preferably 2 to 6 mm ³ / stroke ) Is set within the range.

If the post-injection amount Y1 per cylinder is smaller than the lower limit set value, the post-injection is stopped and the post-injection amount for several cycles is integrated, and the integrated value X is set to the lower limit value. When the value becomes equal to or more than the value, the process proceeds from step 137 to step 138, and based on the light oil supply amount Z per unit time and the fuel pressure calculated in step 134, the number of cylinders to be post-injected is calculated from the map data shown in FIG. calculate. That is, the number of post-injection cylinders increases as the light oil supply amount Z increases, and the number of post-injection cylinders increases as the fuel pressure increases. Then, the post-injection amount Y per cylinder (per stroke) is calculated based on the number of post-injection cylinders thus calculated, the light oil supply amount Z per unit time, and the engine speed. At this time, if the calculated post-injection amount Y per cylinder becomes smaller than the lower limit set value, the number of post-injection cylinders is decreased by 1 until the post-injection amount Y per cylinder becomes equal to or more than the lower limit set value. The post-injection amount Y per cylinder is calculated again.

Thereafter, in step 139, the post-injection amount Y per cylinder is compared with a preset upper limit set value. If the post-injection amount Y per cylinder is larger than the upper limit set value, the routine proceeds to step 140. Then, the post-injection amount Y per cylinder is corrected to the upper limit set value, and the routine proceeds to step 141. Here, the upper limit set value is 8 to 20 mm ³ / stroke (preferably 8 to 12 mm) per liter of displacement of one cylinder of the engine, which is the upper limit of the post-injection amount at which the post-injection fuel does not adhere to the cylinder wall.
mm ³ / stroke).

If it is determined in step 139 that the post-injection amount Y per cylinder is equal to or less than the upper limit set value, the process proceeds to step 141 without correcting the post-injection amount Y per cylinder. In step 141, a post-injection command is output to the fuel injection valve 14 in accordance with the post-injection amount Y per cylinder, the post-injection timing, and the number of post-injection cylinders calculated by the above-described processing, and the post-injection is executed. finish. When performing the post-injection, the post-injection cylinder is changed as needed so that the post-injection cylinder is not biased to some of the cylinders, as in the first embodiment.

In the above-described embodiment (3), when the fuel pressure at the time of post-injection is high, the number of cylinders to be post-injected is increased and the post-injection amount per cylinder is reduced to thereby reduce the cylinder wall. Adhesion of post-injected fuel to the fuel cell can be prevented. Thereby, even when the fuel pressure at the time of post-injection is high, mixing of post-injection fuel into the lubricating oil can be prevented, the life of the lubricating oil can be extended, and the supply amount of hydrocarbons to the NOx catalyst 19 can be reduced. It is possible to control accurately with the target value, and N
Ox purification rate can be improved.

In this embodiment (3), the lower limit set value and the upper limit set value are set in advance, but may be calculated from the map data shown in FIG. 6 as in the embodiment (1). At this time, the lower limit set value and the upper limit set value may be calculated in consideration of the fuel pressure. Further, in the present embodiment (3), the number of cylinders to be post-injected is determined by the light oil supply amount Z per unit time.
The fuel oil pressure is calculated from the two-dimensional map shown in FIG. 14 using parameters as parameters, but after the three-dimensional map using the light oil supply amount Z per unit time, the fuel pressure, and the engine operating state (engine speed, etc.) as parameters. The number of cylinders to be injected may be calculated.

In the example of the system configuration shown in FIG.
An exhaust temperature sensor 20 is installed downstream of the catalyst 19, and NO
The exhaust temperature downstream of the x catalyst 19 is detected as a substitute for the catalyst temperature.
It may be inside or upstream of the NOx catalyst 19. Even in this case, the detected exhaust gas temperature can be used as the catalyst temperature.

In each of the above embodiments, the present invention is applied to a four-cylinder diesel engine. However, it is needless to say that the number of cylinders is not limited to four and may be other. No. The internal combustion engine to which the present invention can be applied is not limited to a diesel engine, but can also be applied to a direct injection (direct injection) gasoline engine.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an entire engine control system showing an embodiment (1) of the present invention.

FIG. 2 is a flowchart showing a flow of processing of a post-injection control program in an embodiment (1).

FIG. 3 is a diagram conceptually illustrating an example of map data for obtaining a NOx emission amount from an engine speed and an accelerator opening.

FIG. 4 is a diagram conceptually showing an example of map data for obtaining a light oil supply amount per unit time from an exhaust gas temperature and a NOx emission amount.

FIG. 5 is a diagram conceptually illustrating an example of map data for obtaining a post-injection timing from an engine load and an exhaust gas temperature.

FIG. 6 is a diagram conceptually showing an example of map data for obtaining a lower limit set value and an upper limit set value from in-cylinder pressure and in-cylinder temperature.

FIG. 7 is a diagram conceptually showing an example of map data for obtaining the number of cylinders to be post-injected from an engine speed and a light oil supply amount Z;

FIG. 8 is a time chart showing an example of the order of cylinders for post-injection (part 1).

FIG. 9 is a time chart showing an example of the order of cylinders to be post-injected (part 2);

FIG. 10 is a time chart showing an example of the order of cylinders to be post-injected (part 3);

FIG. 11 is a time chart showing an example of the order of cylinders subjected to post-injection (part 4).

FIG. 12 is a flowchart showing the flow of processing of a post-injection control program according to the embodiment (2).

FIG. 13 is a flowchart showing the flow of processing of a post-injection control program in the embodiment (3).

FIG. 14 is a diagram conceptually showing an example of map data for obtaining the number of cylinders to be post-injected from a fuel pressure and a light oil supply amount Z;

[Explanation of symbols]

 Reference Signs List 10 diesel engine (internal combustion engine) 11 intake pipe 12 fuel pressure sensor (fuel pressure detecting means) 13 intake manifold 14 fuel injection valve (fuel injection means) 17 exhaust manifold (exhaust passage) 18 exhaust pipe (exhaust passage) 19 NOx catalyst ( Catalyst) 20 Exhaust temperature sensor (catalyst activation state detecting means) 25 ECU (injection control means) 26 Accelerator sensor (operating state detecting means) 27 Engine speed sensor (operating state detecting means).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/34 F02D 41/34 H ZAB ZAB (72) Inventor Kenji Nakamura 1-1-1, Showa-cho, Kariya-shi, Aichi Pref. Inside DENSO

Claims (6)

[Claims] A fuel injection means is provided for each cylinder of the internal combustion engine, a catalyst for reducing and purifying nitrogen oxides in exhaust gas is provided in an exhaust passage of the internal combustion engine, and engine output is provided to the fuel injection means of each cylinder. An exhaust gas purification apparatus for an internal combustion engine, comprising: an injection control unit that outputs a main injection command for generation and outputs a post-injection command for supplying hydrocarbons to the catalyst to a fuel injection unit of at least one cylinder. Operating state detecting means for detecting an operating state of the internal combustion engine; and catalyst active state detecting means for detecting an active state of the catalyst, wherein the injection control means includes a detection value of the operating state detecting means and the catalyst activity. The amount of hydrocarbon supplied to the catalyst based on the detection value of the state detection means (hereinafter, referred to as “target post-injection amount”)
And the post-injection timing is set. Further, the number of cylinders to be post-injected and the post-injection amount per cylinder are calculated based on the target post-injection amount and the detection value of the operating state detecting means. And outputting a post-injection command to the fuel injection means in response to the command. 2. The post-injection control means sets a lower limit value and an upper limit value of the post-injection amount per cylinder, and the calculated post-injection amount per cylinder falls within a range between the lower limit value and the upper limit value. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a post-injection command is output only in the case of (i). 3. When the post-injection amount per cylinder is smaller than the lower limit set value, the injection control means stops post-injection and integrates the post-injection amount for several cycles. When the post-injection amount is equal to or more than the set value, the post-injection command is output. When the post-injection amount per cylinder exceeds the upper limit set value, the post-injection amount per cylinder is corrected to the upper limit set value and the post-injection command is output. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the exhaust gas is output. 4. The lower limit set value is set within a range of 1 to 8 mm ³ / stroke per liter of displacement of one cylinder of the internal combustion engine, and the upper limit set value is set per liter of displacement of one cylinder of the internal combustion engine. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the value is set within a range of 8 to 20 mm ³ / stroke. 5. The injection control unit estimates an in-cylinder state of each cylinder based on a detection value of the operating state detection unit and the post-injection timing, and based on the estimated in-cylinder state of each cylinder. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 2 to 4, wherein a lower limit set value and the upper limit set value are set. 6. The injection control means sets the lower limit setting value and the upper limit setting as the in-cylinder pressure or in-cylinder temperature of each cylinder estimated based on the detected value of the operating state detecting means and the post-injection timing increases. The exhaust gas purifying apparatus for an internal combustion engine according to claim 5, wherein the value is set to a large value.