JPH09317524A - Nitrogen oxide cleaning apparatus for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrogen oxide cleaning apparatus for internal combustion engines having excelent cleanability and a simple structure. SOLUTION: This nitrogen oxide cleaning apparatus 1 is provided with fuel injection means 11 to 14, a fuel injection control means (ECU) 40, a plurality of catalyst units 21, 22, catalyst temperature judging means (exhaust gas sensor) 24 to 26, and operating condition detecting means. The first and second catalyst units 21 and 22 are disposed on upstream and downstream sides of an exhaust path in series each other. Cylinders are comprised of a first cylinder group connected to the upstream of the first catalyst unit 21 and a second cylinder group connected to the exhaust path between the catalyst units 21 and 22. The fuel injection control means outputs main fuel injection command and post fuel injection command to the respective cylinders, causing the quantity of fuel injection to be prescribed according to the temperature of the catalysts 21 and 22.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas purification device for purifying nitrogen oxides contained in exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art Nitrogen oxides (NOx) emitted from an internal combustion engine such as a diesel engine are purified by using a catalyst device using a metal-supported zeolite or the like. The purification rate of the catalyst device is, as shown by a curve 51 in FIG. 2, a specific temperature range (T1 to T3 in FIG.
It shows a high purification rate only at (~ 300 ° C). In addition, it is known that the reaction of this catalyst for nitrogen oxides is promoted by adding an HC (hydrocarbon) component such as fuel. Therefore, a method has been proposed in which a reducing agent such as light oil is supplied from the upstream of the catalyst device and mixed with the exhaust gas to promote purification of nitrogen oxides.

From the above viewpoint alone, it is sufficient to supply a large amount of HC, which is a reducing agent, in order to increase the purification rate of nitrogen oxides. However, when the supply of HC is increased, the temperature of the catalyst device rises due to the heat of reaction of HC, which exceeds the temperature range in which the purification rate is good in the vicinity of T2 shown in FIG. Therefore, it is necessary to add an appropriate amount of HC according to the state and maintain the catalyst device in a state of high purification rate.

Therefore, in Japanese Unexamined Patent Publication No. 4-214919, a plurality of units each having a catalyst and an HC supply device are provided, and the HC supply device is operated only for units within a predetermined temperature range to prevent the catalyst from overheating. A purifying device has been proposed which prevents the nitrogen oxides and improves the purification rate of nitrogen oxides.

[0005]

However, Japanese Patent Application Laid-Open No.
The nitrogen oxide purifying device disclosed in Japanese Patent No. 214919 has a problem in that HC supply devices are required for the number of catalyst devices, the structure of the device is complicated, and the device is large and costly. The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide an excellent nitrogen oxide purification device capable of increasing the purification rate of nitrogen oxides with a simpler configuration. .

[0006]

In a nitrogen oxide purifying device according to the invention of claim 1, a catalyst device is arranged in series on the downstream side of the first catalyst device and the first catalyst device where the catalyst device is arranged on the upstream side of the exhaust passage. A second catalyst device, and all cylinders are connected to a first cylinder group connected upstream of the first catalyst device and an exhaust passage between the first catalyst device and the second catalyst device. And a second cylinder group.

Further, the fuel injection control means issues a main fuel injection command for generating engine output and a post fuel injection command for supplying hydrocarbons for each cylinder or each cylinder group. Then, the fuel injection control means adjusts the amount of post-fuel injection in accordance with the temperatures of the first catalyst device and the second catalyst device determined by the catalyst temperature determination means, and suppresses overheating of each catalyst device while performing nitrogen oxidation. Maximize the purification rate of objects.

Due to the above-mentioned structure, the exhaust gas discharged from the first cylinder group flows into the first catalyst device, while the second catalyst device receives from the second cylinder group. The exhaust gas discharged and the exhaust gas purified by the first catalyst device flow in. Since the post-fuel injection amount can be set for each cylinder or each cylinder group, the HC supplied to the first catalyst device can be set.
The amount of reducing agent, that is, the amount of post-fuel injection, and the amount of HC reducing agent supplied to the second catalytic device, that is, the amount of post-fuel injection, can be set separately.

Therefore, the HC appropriate for the temperature conditions of the first and second catalyst devices determined by the catalyst temperature determination means is used.
A reducing agent can be supplied to each catalytic device. That is, it is possible to supply an appropriate amount of HC (post fuel) to the catalyst device without supplying wasteful HC (post fuel) to the catalyst device and control the catalyst device to a state where the purification rate is as high as possible. Since the post fuel injection is injected during the expansion stroke or the exhaust stroke, H that is suitable for the reduction of nitrogen oxides due to the heat in the cylinder is used.
It also has the effect that it can be changed to C.

For example, as described in claim 2, a low temperature first temperature zone (T1 or less in FIG. 2) in which the purification rate of nitrogen oxides of the catalyst device changes at an extremely low level, and purification of nitrogen oxides A second temperature zone (T1 to T2 in FIG. 2) in which the rate increases with temperature, a third temperature zone (T2 to T3 in FIG. 2) in which the purification rate of nitrogen oxides decreases with temperature, and nitrogen oxides The temperature zone is divided into a high temperature fourth temperature zone (T3 or higher in FIG. 2) in which the purification rate of the engine changes at an extremely low level, and the amount of post fuel injection amount for each cylinder or each cylinder group is large for each temperature zone. By changing the thickness and the distribution ratio, it is possible to achieve effective purification of nitrogen oxides (see the embodiment example described later).

This is because the increasing / decreasing tendency of the purification rate with respect to temperature is completely different depending on the temperature zones.
This is because the purification rate cannot be maximized unless the fuel injection is controlled after the characteristics are met. For example,
In the relationship between the second temperature zone and the third temperature zone,
As described in claim 3, in the third temperature zone,
A post-fuel injection amount smaller than the post-fuel injection amount in the second temperature zone is set for the cylinders belonging to the first cylinder group, and a cylinder in the second temperature zone is set for the cylinders belonging to the second cylinder group. It is preferable to set a post fuel injection amount that is larger than the post fuel injection amount.

That is, in the third temperature zone, it is necessary to suppress the excessive temperature rise of the upstream first catalyst device whose temperature is higher than the maximum temperature of the purification rate, while the second temperature is relatively low.
In order to raise the temperature of the catalytic converter of
This is because supplying C to improve the purification rate is an appropriate control.

The structure based on the technical idea of claims 1 to 3 is not effective only when the number of catalyst devices is two, and when three or more catalyst devices exceeding two are provided. Is also applicable. That is, the number of catalyst devices is N as described in claim 4, the cylinder is divided into a group of N cylinders, and the amount of post-fuel injection is adjusted according to the temperature of each catalyst device. Maximize the purification rate of nitrogen oxides while suppressing overheating of the catalyst device.

With the above configuration, the exhaust gas discharged from the I-th cylinder group flows into the I-th catalyst device, while the (I + 1) -th catalyst device has the ( The exhaust gas discharged from the (I + 1) th cylinder group and the exhaust gas purified by the I-th catalyst device flow in. Since the post-fuel injection amount can be set for each cylinder or each cylinder group, the amount of HC reducing agent supplied to the I-th catalyst device, that is, the post-fuel injection amount and the (I + 1) -th catalyst device are supplied. The amount of HC reducing agent, that is, the amount of post-fuel injection can be set separately.

Therefore, it is possible to supply an appropriate HC reducing agent to each catalyst device in accordance with the temperature states of the I-th and (I + 1) -th catalyst devices judged by the catalyst temperature judging means.
That is, it is possible to supply an appropriate amount of HC (post fuel) to the catalyst device without supplying wasteful HC (post fuel) to the catalyst device and control the catalyst device to a state where the purification rate is as high as possible. Also, when the number of catalyst devices is three or more, claims 5 and 6
According to the described invention, it is possible to achieve the same operational effects as those of the second or third aspect.

Further, in each of the above-mentioned constitutions 1 to 6, the nitrogen oxide purifying temperature range of the catalyst device arranged on the upstream side is arranged on the downstream side as described in claim 7. It is preferable that the temperature is lower than the temperature range in which the nitrogen oxides of the catalyst device can be purified. With such a configuration, it becomes possible to quickly raise the temperature of the upstream catalytic device, which can be easily heated at the time of starting, etc., and activate it at a lower temperature quickly.

Further, as described in claim 8, the total amount of post-fuel injection in the cylinder group is set, and all the post-fuel injection in the cylinder group is concentrated and injected into a part of the cylinders in the cylinder group. It is preferable to do so. Because, compared to the case where the post fuel injection amount is set uniformly in each cylinder,
By concentrating the post-fuel injection in some of the cylinders, the injection amount of the post-fuel injection in the cylinders to be injected can be made relatively large, and the fuel injection means has a relatively high operating performance (for example, the response speed of the valve or This is because it is possible to use a low operable minimum operation amount.

Further, as described in claim 9, by further adjusting the amount of main fuel injection for each cylinder group in addition to the post fuel injection amount, overheating of each catalyst device can be suppressed more appropriately. It is possible to maximize the purification rate of nitrogen oxides. That is, by adjusting the total main fuel injection amount in a cylinder group, the amount of exhaust gas flowing into the catalyst device connected to that cylinder group is changed, thereby controlling the heating rate and cooling rate of the catalyst device. It is possible to do so.

For example, when there are two catalyst devices as claimed in claim 11, in the first temperature zone, the main fuel injection is concentrated in the first cylinder group so that the first catalyst device is It is preferable to accelerate the temperature rise and to concentrate the main fuel injection in the first cylinder group in the fourth temperature zone of the second aspect to promote cooling of the second catalyst device.

That is, in the first temperature zone, the main fuel injection is concentrated in the first cylinder group so that the inflow of exhaust gas is concentrated in the first catalyst device and the temperature rise of the first catalyst device is promoted. Thus, the purification rate of the first catalyst device can be rapidly increased. Further, in the fourth temperature zone, the main fuel injection is concentrated in the first cylinder group, the inflow of exhaust gas is concentrated in the first catalyst device, the second catalyst device is cooled, and the second catalyst device is purified. This is because it becomes possible to shift to a region of higher temperature and lower temperature. In the latter case, the nitrogen oxides in all the exhaust gas are purified by the second catalyst device which maintains a high purification rate.

When the number of catalyst devices is N and is generalized, the temperature of the I-th catalyst device located on the upstream side is set to the first temperature zone as described in claim 10. , The main fuel injection is concentrated in the I-th cylinder group to accelerate the temperature rise of the I-th catalyst device, and in the fourth temperature zone, the main fuel injection is performed in the I-th cylinder group. The same effect can be obtained by concentrating the groups to promote cooling of the downstream (I + 1) th catalytic devices.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment As shown in FIG. 1, the first embodiment includes solenoid valve injectors 11 to 11 as fuel injection means provided for each of the cylinders 81 to 84.
14 and fuel injection means (solenoid valve injectors 11 to 1)
4), an electronic control unit (ECU) 40 as a fuel injection control unit, a plurality of catalyst devices 21 and 22 arranged in the exhaust passages 35 and 34 for reducing and purifying nitrogen oxides, and the catalyst devices 21 and 22. Exhaust temperature sensors 24 to 26 as catalyst temperature determining means for measuring the temperature of the engine, and an engine rotation sensor 28 and an accelerator sensor 29 as operating state detecting means capable of detecting at least stroke positions of the cylinders 81 to 84. It is a nitrogen oxide purifying apparatus 1 for an internal combustion engine that has.

The catalyst devices 21 and 22 have exhaust passages 34 to 3 respectively.
7, a first catalytic device 21 arranged upstream of the first catalytic device 21 and the first catalytic device 21.
The cylinders 81 to 84 are composed of a second catalyst device 22 arranged in series on the downstream side of the catalyst device 21, and the cylinders 81 to 84 are first cylinders 81 to 83 connected to the upstream side of the first catalyst device 21. It comprises a second group of cylinders 84 connected to the exhaust passage 36 between the first catalytic device 21 and the second catalytic device 22 (that is, corresponding to N = 2 in claim 4).

An electronic control unit (ECU) 40 as fuel injection control means receives the output signals of the catalyst temperature determination means and the operation status detection means, and is a main engine for generating engine output near the compression top dead center. A fuel injection command and a post-fuel injection command for supplying hydrocarbons in the expansion stroke or exhaust stroke are sent to the fuel injection means for each cylinder 81-.
Emitted every 84, the first catalytic device 21 or the second catalytic device 2
Cylinder 81-84 or cylinder 81-corresponding to the temperature of 2
The amount of the post fuel injection for the 83 group and the cylinder 84 group (waveforms b1 to b4, FIGS. 3 to 6) is adjusted, and each catalyst device 21,
The purification rate of nitrogen oxides is maximized while suppressing overheating of No. 22.

That is, fuel injection control means (ECU 40)
Is a low temperature first temperature zone (T <T1 in FIG. 2) in which the purification rate of nitrogen oxides of the first catalyst device 21 changes at an extremely low level, and the nitrogen oxides of the first catalyst device 21. The second temperature zone where the purification rate increases with the temperature T (T in FIG. 2).
1 <T <T2), and the third temperature zone in which the purification rate of nitrogen oxides in the first catalyst device 21 decreases with the temperature T (see FIG. 2).
Of T2 <T <T3) and the fourth temperature zone of high temperature (T> T3 of FIG. 2) where the purification rate of nitrogen oxides of the first catalyst device 21 changes at an extremely low level. Then, as shown in FIGS. 3 to 6, each cylinder 8 is provided for each temperature zone.
The magnitude and distribution ratio of the post fuel injection amount (waveforms b1 to b4) for the groups 1 to 83 and the group of cylinders 84 are changed.

For example, as shown in FIG. 5, in the third temperature zone, the cylinders 81 to 83 belonging to the first cylinder group are included.
4 is set to a post-fuel injection amount (waveforms b1 to b3) smaller than the post-fuel injection amount (waveforms b1 to b3) in the second temperature zone shown in FIG.
For No. 4, a post fuel injection amount (waveform b4) larger than the post fuel injection amount (waveform b4) in the second temperature zone shown in FIG. 4 is set.

The following is a supplementary explanation of each.
As shown in FIG. 1, the internal combustion engine of this example is a diesel engine 8, and fuel is supplied from a fuel pump 89 to each of the solenoid valve injectors 11-14. In the figure, reference numeral 88 is a fuel pipe in which the fuel is constantly accumulated in a high pressure state. Then, the cylinders 81 to 83 of the first cylinder group
The exhaust pipes 31 to 33 are integrated into one exhaust pipe 35,
It is connected to the first catalyst device 21. The exhaust pipe 34 of the cylinder 84 belonging to the second cylinder group is connected to the exhaust pipe 36 that connects the first catalyst device 21 and the second catalyst device 22.

On the other hand, FIG. 2 shows the purification characteristics of the catalyst devices 21 and 22. The curve indicated by the reference numeral 51 indicates the purification characteristics of nitrogen oxides, and the curve indicated by the reference numeral 52 indicates the purification characteristics of hydrocarbons. Is shown. That is, when the temperature T of the catalyst is lower than T1, neither nitrogen oxide nor HC is purified, and the temperature T of the catalyst is T.
Only when it becomes 1 or more, the purification of nitrogen oxides and HC is substantially started. And the purification rate of nitrogen oxides increases,
When the temperature exceeds the temperature T2 at which the purification rate of nitrogen oxides becomes maximum, the purification rate of nitrogen oxides decreases and the catalyst temperature T rises to T3.
Above, the purification rate of nitrogen oxides is almost zero.

As described above, substantial purification of nitrogen oxides is performed only when the temperature of the catalyst is within the predetermined temperature range T1 to T3. For example, in a catalyst in which Pt is supported on zeolite, the above T1 is about 200 ° C. and T2 is about 25
0 ° C and T3 are about 300 ° C. Further, for example, in a catalyst in which Cu is supported or ion-exchanged on zeolite, T1 is about 300 ° C, T2 is about 400 ° C, and T3 is about 500 ° C. Then, as described above, H of fuel etc.
Although the purifying reaction of nitrogen oxides can be promoted by adding a C (hydrocarbon) component, on the other hand, the addition of HC increases the reaction on the upstream side of the catalytic device, and the catalytic device 21, 22 There is a problem that the purification rate decreases due to the temperature rise.

Next, the mode of operation of the nitrogen oxide purifying apparatus 1 of this embodiment will be described with reference to FIGS. In the figure, the horizontal axis represents the crank angle and the vertical axis represents the fuel injection rate per unit time. FIG. 3 shows a waveform of the fuel injection of the solenoid valve injectors 11 to 14 based on the fuel injection command of the ECU 40 when the temperature of the first catalyst device 21 is lower than T1, that is, in the first temperature zone. .
That is, a1 to a4 indicate the waveforms of the main fuel injection amounts of the cylinders 81 to 84, and b1 to b4 indicate the cylinders 81 to 8 respectively.
4 shows the waveform of the post fuel injection amount. Further, in the figure, UD indicates the timing of the top dead center of the cylinder, LD indicates the timing of the bottom dead center, and the subscripts 1 to 4 of the cylinder correspond to the cylinders 81 to 84.

FIG. 4 also shows that the first catalyst device 21
Shows the waveform of the fuel injection of the solenoid valve injectors 11 to 14 when the temperature is above T1 and below T2, that is, in the second temperature zone. Further, FIG. 5 shows a waveform of fuel injection of the solenoid valve injectors 11 to 14 when the temperature of the first catalyst device 21 is in the range of T2 to less than T3, that is, the third temperature zone, and FIG. The temperature of the device 21 is T
The waveform of the fuel injection of the solenoid valve type injectors 11-14 in the case of being in the range of 3 or more, that is, in the fourth temperature zone is shown.

Then, FIG. 7 shows a flowchart of the operation of the apparatus 1. That is, first, in step 601, the ECU 40 reads the output signals of the accelerator sensor 29, the rotation sensor 28, and the exhaust temperature sensors 24-26. Then, in step 602, the main fuel injection amount for obtaining the engine output is calculated from the signals of the accelerator sensor 29 and the rotation sensor 28. Next, at step 603, the catalyst temperatures of the first catalyst device 21 and the second catalyst device 22 are estimated based on the output signals of the exhaust temperature sensors 24-26.

As a method of estimating the catalyst temperature of the first catalyst device 21, for example, as a simple method, there is a method of using the exhaust temperature of the exhaust temperature sensor 25 at the downstream side, and the exhaust temperature sensor 24 at the upstream side and the downstream side. , 25, whichever is higher. There is also a method of using a weighted average value of the outputs of the upstream and downstream exhaust gas temperature sensors 24 and 25.

Similarly, as a method of determining the catalyst temperature of the second catalyst device 22, for example, a method of using the exhaust temperature of the exhaust temperature sensor 26 downstream thereof as a simple method,
There is a method of adopting the higher one of the upstream and downstream exhaust gas temperature sensors 25 and 26. There is also a method of using a weighted average value of the outputs of the upstream and downstream exhaust gas temperature sensors 25 and 26.

Then, in step 604, the first boundary temperature or first set temperature T1, the second boundary temperature or first set temperature T2 and the third boundary temperature or first set temperature T3 shown in FIG. 2 are read. . Then, in step 605, it is determined whether or not the catalyst temperature T of the first catalyst device 21 is lower than the first set temperature T1, and if so, the process proceeds to step 606,
If not, the process proceeds to step 607.

When the process proceeds to step 606, that is, the catalyst temperature of the first catalyst device 21 is the catalyst activation start temperature T1.
If the number of cylinders has not reached 80, the cylinders belonging to the first cylinder group 81
The post-fuel injection amount of ~ 83 is set to zero. Further, the post fuel injection amount for the second cylinder group (cylinder 84) is determined by the second catalyst device 2
The value is set to a value corresponding to the catalyst temperature Ts of 2.

That is, the catalyst temperature of the downstream second catalyst device 22 is usually lower than the temperature of the first catalyst device 21. The reason is that the temperature of the exhaust gas lowers due to heat dissipation before reaching the downstream second catalyst device 22. Therefore,
In the normal case, as shown in FIG. 3, the amount of the post fuel injection b4 of the second catalyst device 22 is set to zero.

However, due to the heat capacity of the catalyst device 22, that is, thermal inertia, the temperature of the second catalyst device 22 is the first.
It may be higher than that of the catalyst device 21, and in this case, considering the curve 51 of FIG. 2 according to the temperature Ts, the second cylinder group is set to the post fuel injection amount for keeping the purification rate of nitrogen oxides high. The value of (cylinder 84) is set. And step 62
In step 0, the ECU 40 commands the solenoid valve injectors 11-14 to perform main fuel injection and post-fuel injection at the set amount and the timing shown in FIG.

As an example of a concrete set amount in FIG. 3, for example, the amount of a1 to a4 (integrated value, the same applies hereinafter) is 50 mm3 /
It is a stroke, and the amount of b1 to b4 is zero. That is,
The total amount of post-injection of cylinders 81 to 84 is 0 mm3 / engine 2
Therefore, the deterioration rate of fuel efficiency due to the post fuel injection with respect to the main fuel injection amount is 0%. As a result, when the catalyst devices 21 and 22 are inactive, wasteful post-injection is not performed and deterioration of fuel efficiency is avoided.

On the other hand, when the result of step 605 is negative, the process proceeds to step 607, and in step 607,
It is determined whether the catalyst temperature T of the first catalyst device 21 is lower than the second set temperature T2. If yes, the process proceeds to step 608, and if not, the process proceeds to step 609. When the process proceeds to step 608, that is, when the catalyst temperature of the first catalyst device 21 has reached the catalyst activation start temperature T1 but is lower than the maximum temperature T2 (in the second temperature zone), as shown in FIG. As shown in, the amount of the post fuel injection b1 to b3 of the cylinders 81 to 83 belonging to the first cylinder group is set to a relatively small amount A1.

The reason is that by increasing the HC concentration of the exhaust gas flowing into the first catalyst device 21, the purification rate of nitrogen oxides is directly increased, and at the same time, the reaction heat of the HC causes the first catalyst device 21 to react. Is to raise the purification rate as an indirect effect. At this time, normally, not all of the supplied HC reacts in the upstream catalyst device 21, and unreacted HC flows into the downstream second catalyst device 22. Therefore, in the second catalyst device 22 as well, the temperature rise of the catalyst device 22 occurs due to the reaction of the residual HC.

The post-fuel injection amount of the second catalyst device 22 is a value A2 corresponding to the catalyst temperature Ts of the second catalyst device 22.
Set to. That is, the post fuel injection amount of the second cylinder group (cylinder 84) is set to such an amount that the catalyst temperature of the downstream second catalyst device 22 does not excessively rise. Then, proceeding to step 620, the ECU 40 commands the solenoid valve injectors 11-14 to perform main fuel injection and post-fuel injection at the set amount and the timing shown in FIG.

As an example of a specific set amount in FIG. 4, for example, the amount of the main fuel injections a1 to a4 is 50 mm3 / stroke, and the amount A1 of the post fuel injection b1 to b3 of the first cylinder group.
Is 1 mm3 / stroke corresponding to 2% of the main fuel injection amount, and the amount A2 of the rear fuel injection b4 of the second cylinder group is 1 mm3 / stroke corresponding to 2% of the main fuel injection amount. That is, the total amount of post-injection of the cylinders 81 to 84 is 4 mm3 / 2 revolutions of the engine, and therefore the deterioration rate of fuel efficiency due to post-fuel injection is 2% with respect to the main fuel injection amount.

In this case, the exhaust gas flowing into the second catalyst device 22 is the exhaust gas flowing from the exhaust pipe 34 (the cylinder 84
Exhaust gas) and the exhaust gas exhausted by the first catalyst device 21, and the HC concentration of the exhaust gas of the cylinder 84 is diluted by the exhaust gas exhausted by the first catalyst device 21 and having a low HC concentration. Therefore, the HC concentration of the exhaust gas of the second catalyst device 22 becomes lower than the HC concentration of the exhaust gas of the first catalyst device 21.

On the other hand, when the result of step 607 is negative, the procedure proceeds to step 609, and in step 609,
It is determined whether the catalyst temperature T of the first catalyst device 21 is lower than the third set temperature T3. If yes, the process proceeds to step 610, and if not, the process proceeds to step 611. When the process proceeds to step 610, that is, when the catalyst temperature of the first catalyst device 21 is equal to or higher than the purification rate maximum temperature T2 and lower than the purification stop temperature T3 (in the third temperature zone), the first cylinder group The post-fuel injection amount of the cylinders 81 to 83 belonging to A3 is set to A3, which is smaller than A1.

The reason is to prevent excessive temperature rise of the first catalyst device 21. That is, the upstream first catalyst device 2
In the case of 1, almost all the HC reacts, but since the post injection amount A3 is small, it is possible to suppress the excessive temperature rise. Then, the temperature of the exhaust gas flowing out of the first catalytic device 21 and flowing into the second catalytic device 22 is lowered by heat radiation. Therefore, the second catalyst device 22 can be adjusted to a state where the purification rate of nitrogen oxides is higher. That is, normally, by setting the post fuel injection amount for the second cylinder group (cylinder 84) to A4 which is larger than A2, the purification rate of the second catalyst device 22 can be maintained at a high level.

Then, the process proceeds to step 620 and the ECU 4
0 instructs the solenoid valve injectors 11 to 14 to perform main fuel injection and post-fuel injection at the set amount and the timing shown in FIG. As an example of a specific set amount in FIG. 5, for example, the amount of the main fuel injections a1 to a4 is 50 mm3 / stroke, and the amount A3 of the post fuel injection b1 to b3 of the first cylinder group is A3.
Is 0.5 mm3 / stroke corresponding to 1% of the main fuel injection amount, and the amount A4 of the rear fuel injection b4 of the second cylinder group is 2.5 mm3 / stroke corresponding to 5% of the main fuel injection amount. That is, the total amount of post injection of the cylinders 81 to 84 is 4 mm3.
Since the engine is rotated twice, the deterioration rate of fuel efficiency due to the post fuel injection with respect to the main fuel injection amount is 2%.

On the other hand, when the routine proceeds to step 611, that is, when the catalyst temperature of the first catalyst device 21 is equal to or higher than the purification stop temperature T3 (in the fourth temperature zone), the first cylinder group (cylinders 81 to 81). The post fuel injection amount for 83) is set to zero.
On the other hand, the temperature of the exhaust gas flowing into the second catalyst device 22 is
Due to the heat radiation, it becomes lower than the exhaust gas flowing out of the first catalyst device 21. Therefore, there are cases where the second catalyst device 22 can be in a state where nitrogen oxides can be purified, that is, the third temperature zone, and the amount of post fuel injection to the second cylinder group (cylinder 84) is The temperature is set to a value corresponding to the catalyst temperature Ts of the two-catalyst device 22.

Then, the process proceeds to step 620 and the ECU 4
0 commands the solenoid valve injectors 11 to 14 for main fuel injection and post-fuel injection at the set amount and the timing shown in FIG. As an example of the specific set amount in FIG. 6, for example, the amount of the main fuel injection a1 to a4 is 50 mm3 / stroke, the amount of the post fuel injection b1 to b3 of the first cylinder group is zero,
The amount A5 of the post fuel injection b4 of the second cylinder group is 1 mm3 / stroke, which corresponds to 2% of the main fuel injection amount. That is,
The total amount of post-injection of cylinders 81 to 84 is 1 mm3 / engine 2
Therefore, the deterioration rate of fuel efficiency due to the post fuel injection with respect to the main fuel injection amount is 0.5%.

FIG. 8 shows the effect of the nitrogen oxide purifying apparatus 1 of this example in comparison with the case where the post-fuel injection is uniformly set to a constant amount without performing the control as in this example. The horizontal axis shows the temperature of the exhaust gas flowing into the catalyst device, and the vertical axis shows the purification rate of nitrogen oxides in%. Reference numeral 54 in FIG.
The curves indicated by are the first catalyst device 21 and the second catalyst device 22.
Is a purification characteristic when the post fuel injection amount for the cylinders 81 to 84 is set to a small value, for example, 0.5 mm3 / stroke regardless of the catalyst temperatures T and Ts. The curve indicated by the reference numeral 55 is obtained when the post-fuel injection amount for the cylinders 81 to 84 is set to a relatively large value, for example, 1 mm3 / stroke, regardless of the catalyst temperatures T and Ts of the first catalyst device 21 and the second catalyst device 22. The purification characteristics of.

Compared to the former characteristic (reference numeral 54), the latter characteristic (reference numeral 55) has a large amount of HC, so that the catalyst heats up due to the reaction heat of the HC on the low temperature side of the inflowing exhaust gas and the purification rate is improved. The value of the maximum purification rate increases as the amount of HC increases as the exhaust gas temperature at which the maximum purification rate is improved decreases. However, on the hot exhaust gas side, HC
The reaction device heats up the catalyst device excessively and the purification rate decreases.

On the other hand, in the case of the nitrogen oxide purifying apparatus 1 of this example, that is, when the temperature of the first catalyst device 21 is low (second temperature zone), the post injection amounts of all the cylinders 81 to 84 are compared. When the temperature of the first catalyst device 21 is higher (third temperature zone), the post-injection amount of the first cylinder group (cylinders 81 to 83) is set to a small value (for example, 1 mm3 / stroke). 0.5 mm3 / stroke and a large post-injection amount of the second cylinder group (cylinder 84) (for example, 2.5 m
The characteristic when m3 / stroke) is indicated by reference numeral 56. As can be seen from the figure, the nitrogen oxide purification device 1 of the present example shows a high purification rate of nitrogen oxides in a wide range of exhaust gas temperature range.

As described above, according to this example, when the temperature of the catalyst is low, the temperature rise is promoted, and when the temperature of the catalyst is high,
It is possible to suppress excessive temperature rise and achieve a high nitrogen oxide purification rate over a wide range. Further, according to this example, the device does not become large-sized or significantly complicated.

In the above example, the case of a total of two catalyst devices 21 and 22 has been described, but in the case of four cylinders, it is possible to use a maximum of four catalyst devices. In this case, if the number of catalyst devices is increased, the structure becomes more complicated, but the purification rate of nitrogen oxides is improved.

Further, the first catalytic device 21 and the second catalytic device 2
The catalysts 2 and 1 may have the same characteristics, but may be catalyst devices 21 and 22 having different characteristics. In the latter case, in particular, a catalyst (for example, Pt / zeolite catalyst) capable of purifying nitrogen oxides in a low temperature region by the first catalyst device 21 arranged upstream is used, and the second catalyst device 22 on the downstream side is used. A catalyst that is activated in a high temperature range by
u / zeolite catalyst), the temperature range in which nitrogen oxides can be purified can be widened, and the temperature of the upstream catalyst device 21 rises faster due to the heat of the exhaust gas. There is an advantage that the catalyst device 21 can be activated.

Conventionally, when a catalyst device which is activated at a lower temperature and a catalyst device which is activated at a higher temperature are arranged in series, a catalyst device which is activated at a higher temperature on the upstream side is provided for the following reason. The method of arranging was adopted. That is, the reason is that, when HC is supplied from the upstream side of the catalyst device, if a catalyst that is activated at low temperature is arranged on the upstream side,
This is because there is a risk that all HC will react in the upstream catalyst device and HC will not be able to be supplied to the downstream catalyst.

When such a system is adopted, in the case of accelerating from idling, it is desired to promptly activate the catalyst device on the upstream side, which can easily raise the temperature, to purify the nitrogen oxides. The catalyst on the upstream side does not activate until it reaches a high temperature, resulting in a low purification rate in mode running. However, in this example, since HC can be supplied to each of the upstream catalyst device 21 and the downstream catalyst device 22, no trouble occurs due to the above reason, and therefore, the catalyst device 2 that is activated upstream at low temperature is used.
By disposing 1, the catalyst device can be started up quickly without any problems.

Second Embodiment In this embodiment, as shown in FIG. 9, in the first embodiment, the post fuel injection in the first cylinder group (cylinders 81 to 83) is performed in one cylinder 81 (or 82, 83). This is another embodiment example in which injection is performed collectively and the other cylinders 82 and 83 are not subjected to post injection. FIG. 9 shows a fuel injection waveform in a state (second temperature zone) corresponding to FIG. 4 of the first embodiment. Further, in this example, the number of cylinders in the second cylinder group is one. However, if the second cylinder group is composed of a plurality of cylinders, only one cylinder belonging to the second cylinder group will perform the post-injection. carry out.

For example, the amount of main fuel injection a1 to a4 is 50 m
m3 / stroke), and the post-fuel injection amount of the first cylinder group is 6% of the main fuel injection amount by the post-injection b1 of the cylinder 81.
Is set to 3 mm3 / stroke, and the amounts of post injection b2, b3 of the cylinders 82, 83 are set to zero. The amount of post fuel injection b4 of the second cylinder group is 1 mm3 / stroke, which corresponds to 2% of the main fuel injection amount. That is, the cylinders 81 to 84
The total amount of post-injection is 4 mm3 / 2 engine revolutions, so the fuel consumption deterioration rate due to post-fuel injection is 2% with respect to the main fuel injection amount.

According to this example, the solenoid valve injector 11
Among the above, the first and fourth solenoid valve injectors 11 and 14 are the only solenoid valve injectors with high sensitivity and high speed response. Therefore, the injector can be downsized and the cost can be reduced, and the second and third solenoid valve injectors 1 can be used.
The number of operations of Nos. 2 and 13 is halved and durability is also improved. Others are the same as those in the first embodiment.

Third Embodiment As shown in FIGS. 10 and 11, this embodiment is different from the first embodiment in that the main fuel injection amount is different between the first cylinder group and the second cylinder group. 3 is an example of one embodiment. That is, the main fuel injection amount is made different depending on the engine operating condition and the temperatures of the catalyst devices 21 and 22.

FIG. 10 shows a waveform of fuel injection of the solenoid valve injectors 11 to 14 when the catalyst temperature of the first catalyst device 21 is lower than T1 (first temperature zone). 3 corresponds to FIG. The main fuel injection amount of each cylinder of the first cylinder group (cylinders 81 to 83) is the same amount (for example, 67 mm3 / stroke), and the main fuel injection amount of the cylinder 84 of the second cylinder group is zero. That is, the total amount of main fuel is the same as in FIG. 3 of the first embodiment, and only the distribution is changed. Then, since the main fuel injection in the second cylinder group is zero, the cylinder 84 functions as an air pump.

As described above, since the main fuel is shared only by the first cylinder group, the temperature of the exhaust gas flowing into the first catalyst device 21 becomes high, the temperature rise is promoted, and the nitrogen oxides are purified. The rate will rise quickly. The amount of post-injection is set to a small value (for example, 1 mm3 / stroke) in the cylinders 81 to 83 of the first cylinder group, and zero in the second cylinder 84. The reason why the post fuel injection is performed on the first cylinder group is that the main catalyst injection causes the first catalyst device 21 to rapidly rise in temperature, and the nitrogen oxides can be rapidly purified by the first catalyst device 21. Is.

As a result, the total amount of post-injection in the case of the above values is 3 mm3 / 2 engine revolutions, and the deterioration of fuel efficiency due to post-injection with respect to the main fuel injection amount is 1.5% on average. Further, the post-injection of the second cylinder group is set to zero because the cylinder 84 of the first cylinder group serves as an air pump and the second catalyst device 22.
This is because the temperature of is decreased and the purification effect of nitrogen oxides cannot be expected.

On the other hand, FIG. 11 shows a waveform of fuel injection of the solenoid valve injectors 11 to 14 when the catalyst temperature of the first catalyst device 21 is T3 or higher (fourth temperature zone). This corresponds to FIG. 6 of Example 1. The main fuel injection amount of each cylinder of the first cylinder group (cylinders 81 to 83) is the same amount (for example, 67 mm3 / stroke), and the main fuel injection amount of the cylinder 84 of the second cylinder group is zero. That is, the total amount of main fuel is the same as in FIG. 6 of the first embodiment, and only the distribution is changed. Since the main fuel injection of the second cylinder group is zero, the cylinder 84 of the second cylinder group acts as an air pump.

The amount of post-injection is the same as that of the cylinder 8 of the first cylinder group.
1 to 83 are zero, and the cylinder 84 of the second cylinder has a large value (for example, 4 mm3 / stroke). Therefore, the total amount of post-injection is 4 mm3 / 2 engine revolutions, and the deterioration of fuel efficiency due to post-injection with respect to the main fuel injection amount is 2.0 on average.
%. As described above, since the cylinder 84 of the second cylinder group is operated as an air pump, the second catalyst device 2 on the downstream side is operated.
The temperature of No. 2 is lowered, and it is possible to maintain the temperature at which nitrogen oxides can be purified.

The reason why the post-injection of the first cylinder group is set to zero is that the first catalyst device 21 cannot perform the purifying action at a high temperature. Further, the post-injection amount of the cylinder 84 of the second cylinder group is made larger because the exhaust gas of all the cylinders 81 to 84 does not purify the nitrogen oxides but the second catalyst device 22.
This is because a large amount of HC is added to increase the purification rate of nitrogen oxides. As described above, according to this example, even when the first catalytic device 21 is in the first and fourth temperature zones, control that promotes purification of the catalytic device can be performed. Others are the same as those in the first embodiment.

Embodiment 4 As shown in FIG. 12, this embodiment is the same as Embodiment 3 except that
This is another embodiment example in which the number of cylinders belonging to the first cylinder group is two and the number of cylinders belonging to the second cylinder group is two. By doing so, when the first catalyst device 21 is in the first and fourth temperature zones, the catalyst device 21 or the catalyst device 22 can exert the nitrogen oxide purifying action in a wider temperature range. It will be possible.

That is, when in the first temperature zone, the main fuel is concentrated in the two cylinders 81 and 83 of the first cylinder group,
1st rather than Embodiment 3 which concentrated on one cylinder 81-83
The temperature of the catalyst device 21 can be raised more quickly. Also,
Even if it is in the fourth temperature zone, the two cylinders belonging to the second cylinder group
Since the two cylinders 82 and 84 function as the air pump, the cooling of the second catalyst device 22 is strengthened more than the case of the third embodiment in which one cylinder functions as the air pump, and the first catalyst device 21 is cooled. Second in a wider temperature range of
The purifying action of the catalyst device 22 can be maintained. Others are the same as the third embodiment.

Embodiment 5 As shown in FIG. 13, this embodiment is different from Embodiment 1 in that engine cylinders 81 to 86 and solenoid valve injector 11 are used.
The number of 16 to 16 is 6, and the cylinders 81 to 8 belonging to the first cylinder group
In this example, there are five cylinders and one cylinder 86 belonging to the second cylinder group. Others are the same as those in the first embodiment.

In the above, the catalyst devices 21, 22
Is not limited to two, but may be three or more. Further, the number of cylinders in the first cylinder group may be four, and the number of cylinders in the second cylinder group may be two. The concept of each embodiment can be similarly applied to the three-cylinder engine and the eight-cylinder engine.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of a nitrogen oxide purifying apparatus according to a first embodiment.

FIG. 2 is a diagram showing a relationship between a catalyst temperature and a purification rate of the nitrogen oxide purifying apparatus according to the first embodiment.

FIG. 3 is a diagram showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus according to the first embodiment (first temperature zone).

FIG. 4 is a diagram showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus of the first embodiment (second temperature zone).

FIG. 5 is a diagram showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus of the first embodiment (third temperature zone).

FIG. 6 is a diagram showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus of the first embodiment (fourth temperature zone).

FIG. 7 shows a case where the purification characteristics (reference numeral 56) of the nitrogen oxide purifying apparatus according to the first embodiment are simply controlled (reference numerals 54 and 5).
The figure displayed together with 5).

FIG. 8 is a flowchart showing a control procedure of the nitrogen oxide purifying apparatus according to the first embodiment.

FIG. 9 is a diagram showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus of the second embodiment (second temperature zone).

FIG. 10 is a diagram showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus of the third embodiment (first temperature zone).

FIG. 11 is a diagram showing a waveform of fuel injection for each cylinder in the nitrogen oxide purifying apparatus of the third embodiment (fourth temperature zone).

FIG. 12 is a system configuration diagram of a nitrogen oxide purifying apparatus according to a fourth embodiment.

FIG. 13 is a system configuration diagram of a nitrogen oxide purifying apparatus according to a fifth embodiment.

[Explanation of symbols]

1. . . Nitrogen oxide purifier, 11-14. . . Solenoid valve injection (fuel injection means), 21, 22. . . Catalyst device, 24-26. . . Exhaust temperature sensor, 40. . . ECU (fuel injection control means),

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location F01N 3/28 301 F01N 3/28 301G F02D 41/22 380 F02D 41/22 380D 385 385D 41/38 41/38 B 41/40 9523-3G 41/40 C 45/00 301 45/00 301C 312 312R (72) Inventor Hajime Suguro 1-1c Showa-cho, Kariya city, Aichi Prefecture NIPPON DENSO CORPORATION

Claims (11)

[Claims] 1. A fuel injection means provided for each cylinder, a fuel injection control means for controlling the fuel injection means, a plurality of catalyst devices arranged in an exhaust passage for reducing and purifying nitrogen oxides, and the catalyst device. A nitrogen oxide purifying apparatus for an internal combustion engine, comprising: a catalyst temperature determining means for measuring or estimating the temperature of the exhaust gas; and an operating condition detecting means capable of detecting at least the stroke position of the cylinder. Of the first catalyst device and a second catalyst device arranged in series downstream of the first catalyst device, and the cylinder is connected to the upstream side of the first catalyst device. The fuel injection control means includes a first cylinder group and a second cylinder group connected to an exhaust passage between the first catalyst device and the second catalyst device. Output signal of detection means Accordingly, a main fuel injection command for generating an engine output near the compression top dead center and a post fuel injection command for hydrocarbon supply in the expansion stroke or the exhaust stroke are supplied to the fuel injection means for each cylinder. The post-fuel injection amount for each cylinder or group of cylinders is adjusted in accordance with the temperature of the first catalyst device or the second catalyst device to suppress the overheating of each catalyst device while maximizing the purification rate of nitrogen oxides. A nitrogen oxide purifying device for an internal combustion engine, which is characterized in that 2. The low temperature first temperature zone in which the purification rate of nitrogen oxides in the first catalyst device changes at an extremely low level, and the first catalyst device in the fuel injection control means according to claim 1. Second temperature zone in which the purification rate of nitrogen oxides in the first catalytic device increases with temperature, a third temperature zone in which the purification rate of nitrogen oxides in the first catalytic device decreases with temperature, and nitrogen in the first catalytic device The temperature zone is divided into a high temperature fourth temperature zone where the purification rate of oxides changes at an extremely low level,
A nitrogen oxide purifying apparatus for an internal combustion engine, wherein the size and distribution ratio of the post fuel injection amount for each cylinder or each cylinder group is changed for each temperature zone. 3. The fuel injection control means according to claim 2, wherein, in the third temperature zone, the post-fuel injection amount is set for cylinders belonging to the first cylinder group in the second temperature zone. Internal combustion engine characterized by setting a post fuel injection amount that is smaller than the post fuel injection amount set in the second temperature zone for cylinders belonging to the second cylinder group. Nitrogen oxide purification equipment for engines. 4. A fuel injection means provided for each cylinder, a fuel injection control means for controlling the fuel injection means, a plurality of catalyst devices arranged in an exhaust passage for reducing and purifying nitrogen oxides, and the catalyst device. A nitrogen oxide purifying apparatus for an internal combustion engine, comprising: a catalyst temperature determining means for measuring or estimating the temperature of the cylinder; and an operating state detecting means capable of detecting at least the stroke position of the cylinder. To the first catalytic device, the second catalytic device, ..., And the N-th catalytic device in the order of N catalytic devices arranged in series in the exhaust passage, while the entire cylinder has a single or a plurality of catalytic devices. The first cylinder group is connected upstream of the first catalyst device, and the I-th cylinder group with a natural number I exceeding 1 is the (I-1) th cylinder group. ) Catalytic device and No. I catalyst device Is connected to an exhaust passage between the fuel injection control means and the fuel injection control means, and the fuel injection control means receives the output signals of the catalyst temperature determination means and the operation status detection means and receives the output signals of the engine near the compression top dead center. An injection command and a post-fuel injection command for supplying hydrocarbons in the expansion stroke or exhaust stroke are issued to the fuel injection means for each cylinder, and the cylinders or the cylinders corresponding to the temperatures of the N catalyst devices are output. An apparatus for purifying nitrogen oxides in an internal combustion engine, wherein the amount of post-fuel injection for a cylinder group is adjusted to suppress overheating of each catalyst device while maximizing the purification rate of nitrogen oxides. 5. The fuel injection control means according to claim 4, wherein the low temperature first temperature zone in which the purification rate of nitrogen oxides in each catalyst device changes at an extremely low level, and the nitrogen oxides in each catalyst device Temperature zone in which the purification rate of NOx increases with temperature, a third temperature zone in which the purification rate of nitrogen oxides of each catalytic device decreases with temperature, and the purification rate of nitrogen oxides of each catalytic device is extremely low. It is characterized in that the temperature zone is divided into a high temperature fourth temperature zone which changes with the level, and the size and distribution ratio of the post fuel injection amount for each cylinder or each cylinder group is changed for each temperature zone. Nitrogen oxide purification device for internal combustion engine. 6. The fuel injection control means according to claim 5, wherein when the temperature of the I-th catalyst device is in the third temperature zone, the fuel injection control means controls the cylinders belonging to the I-th cylinder group. Set a post fuel injection amount smaller than the post fuel injection amount set in the second temperature zone,
1) A nitrogen oxide purifying apparatus for an internal combustion engine, characterized in that a post fuel injection amount larger than a post fuel injection amount set in the second temperature zone is set for cylinders belonging to the first and subsequent cylinder groups. 7. The characteristic of the catalyst device according to any one of claims 1 to 6, wherein the catalyst device arranged upstream has a nitrogen oxide purifiable temperature range arranged downstream. A nitrogen oxide purifying apparatus for an internal combustion engine, which is at a temperature lower than a temperature range in which the catalytic device can purify nitrogen oxides. 8. The fuel injection control means according to claim 1, wherein the fuel injection control means sets a total post fuel injection amount in a cylinder group, and sets the post fuel injection in that cylinder group as the cylinder group. A nitrogen oxide purifying device for an internal combustion engine, characterized in that the fuel is concentrated and injected into a part of the cylinders. 9. The fuel injection control means according to claim 1, wherein the fuel injection control means further adjusts a main fuel injection amount for each cylinder group in addition to the post fuel injection amount. An apparatus for purifying nitrogen oxides in an internal combustion engine, which maximizes a rate of purifying nitrogen oxides while suppressing overheating of the catalyst device. 10. The temperature of the I-th catalytic device located on the upstream side according to claim 9,
When in the first temperature zone described, the main fuel injection is concentrated in the I-th cylinder group to accelerate the temperature rise of the I-th catalyst device. In the case of being in the temperature zone of No. 4, the main fuel injection is concentrated in the I-th cylinder group to promote the cooling of the (I + 1) th and subsequent downstream catalytic devices, and the nitrogen oxide of the internal combustion engine Purification device. 11. The catalyst device according to claim 9, wherein the catalyst device comprises first and second catalyst devices, and the fuel injection control means comprises:
In the first temperature zone of claim 2, the main fuel injection is concentrated in the first cylinder group to promote the temperature rise of the first catalyst device, and in the fourth temperature zone of claim 2, A nitrogen oxide purifying apparatus for an internal combustion engine, characterized in that main fuel injection is concentrated in a first cylinder group to promote cooling of a second catalyst device.