JPH07180540A - Exhaust emission control device for diesel engine - Google Patents

Abstract

PURPOSE:To effectively purify nitrogen oxide in exhaust gas through simple constitution without worsening fuel consumption and increasing smoke. CONSTITUTION:An exhaust emission control device for a diesel engine comprises a fuel feed means consisting of a purifying catalyst 2 for a nitrogen oxide capable of purifying nitrogen oxide in exhaust gas in a region wherein an excess air factor exceeds 1; and an electronic control type fuel injection nozzle 4, and is constituted such a manner that pilot injection is effected in prior to main injection effected by a fuel feed means. The exhaust purifying device for a diesel engine is caused to control an activation factor detecting means 12 to detect the activation factor of a purifying catalyst 2 and a pilot injection timing according to the detecting value of the activation factor detecting means 12. A fuel injection control means 11 to adjust an interval between a pilot injection timing and a main injection timing through control of the pilot injection timing is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device for a diesel engine equipped with a purification catalyst capable of purifying nitrogen oxides in exhaust gas in a region where the excess air ratio is larger than 1, that is, in a lean region. is there.

[0002]

2. Description of the Related Art Conventionally, as a purification catalyst for purifying NOx (nitrogen oxide) emitted from a diesel engine,
For example, as disclosed in JP-A-4-334526, it is preferable to use a catalyst in which a noble metal such as platinum or a transition metal is supported on a carrier made of alumina, silica, titania, zirconia, aluminum phosphate, aluminum nitrate or the like. However, this purifying catalyst is capable of purifying nitrogen oxides in a region where the excess air ratio is greater than 1, and is active when there is a large amount of unburned fuel in the exhaust gas and the temperature is high to some extent. It is known to change.

Further, as disclosed in Japanese Patent Laid-Open No. 3-68516, in a diesel engine in which a nitrogen oxide purifying catalyst is provided in an exhaust system, a communication passage having a relief valve is provided in the middle of a fuel supply passage, A part of the fuel supplied to the cylinder during the fuel injection period is relieved to the cylinder in the exhaust stroke through the communication passage, thermally decomposed, and then discharged to activate the purification catalyst. ing.

Further, by retarding the injection timing of the fuel injected into each cylinder when the engine with low activity of the above-mentioned purification catalyst is cold, the unburned component of the fuel led to the exhaust system is increased. It is known that the purifying catalyst is activated thereby to effectively purify nitrogen oxides.

[0005]

In the conventional device having the above structure, a part of the fuel that is originally burned in the engine is led to the exhaust system, so that the fuel efficiency of the engine is lowered and the fuel consumption is deteriorated. Inevitably, there is a problem that the combustibility of the engine is reduced and the amount of smoke (black smoke) in the exhaust gas discharged is increased.

The present invention has been made to solve the above problems, and is a diesel engine that can effectively purify exhaust gas with a simple structure without causing deterioration of fuel consumption and increase of smoke. An object is to provide an exhaust emission control device for an engine.

[0007]

The invention according to claim 1 is
A nitrogen oxide purifying catalyst capable of purifying nitrogen oxides in the exhaust gas in a region where the excess air ratio is larger than 1 and an electronically controlled fuel supply means are provided, and before the main injection by the fuel supply means. In an exhaust gas purification device for a diesel engine configured to perform a pilot injection, an activation rate detection unit that detects an activation rate of the purification catalyst, and the pilot injection according to a detection value of the activation rate detection unit Fuel injection control means for adjusting the interval between the pilot injection timing and the main injection timing by controlling the timing is provided.

According to a second aspect of the present invention, in the exhaust gas purification apparatus for a diesel engine according to the first aspect, the pilot injection timing and the main injection timing are changed as the nitrogen oxide purification catalyst is activated. It is configured to shorten the interval.

According to a third aspect of the present invention, in the exhaust emission control system for a diesel engine according to the first or second aspect, cold state detecting means for detecting whether or not the engine is in a cold state is provided. , When it is confirmed by the cold state detecting means that the engine is in the cold state,
The injection timing control for adjusting the interval between the pilot injection timing and the main injection timing is executed.

According to a fourth aspect of the present invention, in the diesel engine exhaust emission control device according to any one of the first to third aspects, the fuel injection control means sets the advance amount of the pilot injection start timing with respect to the main injection start timing. By controlling, the pilot injection timing, the main injection timing, and the interval are adjusted.

According to a fifth aspect of the present invention, in the exhaust gas purification device for a diesel engine according to the first aspect, there is provided a first temperature sensor for detecting a temperature of exhaust gas introduced into a nitrogen oxide purification catalyst, and the above-mentioned first temperature sensor. A second temperature sensor for detecting the temperature of the exhaust gas derived from the purification catalyst is provided, and the activation rate of the catalyst is detected based on the difference between the detection values of the two temperature sensors.

[0012]

According to the invention described in claim 1, the advance amount of the pilot injection timing with respect to the main injection timing is set according to the activation rate of the purification catalyst detected by the activation rate detecting means, and the activation is performed. The lower the rate, the longer the interval between the pilot injection timing and the main injection timing, and the pilot injection timing is controlled by the fuel injection control means, so that the unburned fuel amount led to the catalyst installation portion is increased. Will increase.

According to the second aspect of the invention, the pilot injection timing is controlled by the fuel injection control means and the purification catalyst is activated, so that the pilot injection timing and the main injection timing are changed. The interval is controlled to be short, which reduces the amount of unburned fuel that is led to the installation portion of the purification catalyst.

According to the third aspect of the present invention, when it is confirmed by the cold state detecting means that the engine is in the cold state, the pilot injection timing corresponding to the activation rate of the purification catalyst is set. When the control is executed and it is confirmed that the engine is not in the cold state, the normal injection control is executed without controlling the pilot injection timing.

According to the fourth aspect of the present invention, the advance amount of the pilot injection start timing with respect to the main injection start timing is set according to the activation rate of the catalyst, so that the purification catalyst is led to the installation portion. The amount of unburned fuel that is consumed is controlled.

According to the invention described in claim 5, the nitrogen oxide and the unburned fuel are passed through the purifying catalyst according to the difference between the detection value of the first temperature sensor output means and the detection value of the second temperature sensor. The amount of heat generated due to the promotion of the reaction with is detected, and the activation rate of the purification catalyst is detected based on this detected value. Then, the injection timing control for adjusting the interval between the pilot injection timing and the main injection timing is executed based on the detected value of the activation rate.

[0017]

FIG. 1 shows an embodiment of an exhaust emission control device for a diesel engine according to the present invention. This exhaust purification device includes a nitrogen oxide purification catalyst 2 provided in an exhaust pipe 1,
An electronically controlled fuel injection nozzle 4 provided in each cylinder of the engine body 3 and an electronically controlled fuel injection pump 5 for supplying fuel to each cylinder through the fuel injection nozzle 4.
And a controller 6 for outputting a control signal to the electronically controlled fuel supply means composed of the fuel injection nozzle 4 and the fuel injection pump 5 to control the injection timing, injection pressure and injection amount of the fuel.

The purifying catalyst 2 is a catalyst capable of purifying nitrogen oxides in exhaust gas in a region where the excess air ratio is larger than 1, and a noble metal such as platinum or a transition metal is
It is supported on a carrier made of alumina, silica, titania, zirconia, aluminum phosphate, aluminum nitrate or the like.

The engine body 1 is provided with a cooling water temperature sensor 7 for detecting the temperature of the cooling water and a crank angle sensor 8 for detecting the crank angle, and the exhaust pipe 1 is also provided.
A first temperature sensor 9 and a second temperature sensor 10 that detect the exhaust gas temperature at the upstream and downstream portions of the purification catalyst 2 are provided in the.

The controller 6 includes fuel injection control means 11 for controlling the injection timing of the fuel injected from the fuel injection nozzle 4 into each cylinder, the first and second temperature sensors 9,
An activation rate detecting means 12 for detecting the activation rate of the purification catalyst 2 in accordance with the output signal of 10, and the cooling water temperature sensor 7
And a cold state detecting means 13 for detecting whether or not the engine is in a cold state according to the output signal of

As shown in FIG. 2, the fuel injection control means 11 performs main injection of a required amount of fuel at an appropriate time corresponding to the operating condition of the engine, and pilot injection of a small amount of fuel before the main injection. This control signal is output to the fuel injection nozzle 4 and the fuel injection pump 5, and the pilot injection start timing is controlled in accordance with the detection value of the activation rate detection means 12, whereby the pilot injection start timing and It is configured to adjust the interval Pt from the main injection start timing.

That is, as the activation rate of the purification catalyst 2 decreases, the interval Pt increases in advance so that the purification catalyst 2
The interval Pt adapted to the activation rate of the purification catalyst 2 is read from the control table set to the optimum value in accordance with the type of the engine, the type of engine, etc., and the pilot injection start corresponding to the main injection start timing is read out accordingly. The amount of advance of the time is set. Then, a control signal for injecting pilot fuel at a predetermined timing determined based on the detected value of the crank angle sensor 8 and the set value of the advance angle amount is sent from the controller 6 to each injection nozzle 4 and fuel injection pump. 5 will be output.

The activation rate detecting means 12 detects the temperature of the exhaust gas introduced into the purification catalyst 2 detected by the first temperature sensor 9 and the exhaust gas from the purification catalyst 2 detected by the second temperature sensor 10. The amount of heat generated by the nitrogen oxide coming into contact with the purification catalyst 2 and being reduced to nitrogen gas is detected based on the difference with the temperature of the exhaust gas. The larger the difference in the detected temperature values, the higher the activation rate of the purification catalyst 2 is detected by the activity detecting means 12.

The cold state detecting means 13 compares the temperature of the cooling water detected by the cooling water temperature sensor 7 with a preset reference value to determine whether or not the engine is in the cold state. Is to detect. When the cold state detecting means 13 confirms that the engine is in the cold state, the fuel injection control means 11 adjusts the interval Pt between the pilot injection start timing and the main injection start timing. When the control is executed and it is confirmed that the engine is not in the cold state, a control signal for stopping the injection timing control is output to the fuel injection control means 11 via the activation rate detection means 12. It is configured.

In the above construction, when the cold state detecting means 13 detects that the engine is in the cold state, the activation rate of the purification catalyst 2 is detected by the activation rate detecting means 12. The detection signal is output to the fuel injection control means 11. Then, the advance amount of the pilot injection start timing obtained from the control table is corrected according to the detection value of the activation rate detecting means 12, so that the pilot injection timing is feedback-controlled.

As a result, when the activation rate of the purification catalyst 2 is low, the pilot injection start timing is controlled so that the advance amount of the pilot injection start timing with respect to the main injection start timing becomes large, and the pilot injection start is performed. The interval Pt between the timing and the main injection start timing is adjusted to be long. Further, as the purification catalyst 2 is activated, the pilot injection start timing is controlled so that the advance amount of the pilot injection start timing with respect to the main injection start timing becomes smaller, and the pilot injection start timing and the main injection start timing are controlled. Will be adjusted so that the interval Pt between and becomes short.

As described above, as the activation rate of the purification catalyst 2 is lower, pilot injection is performed at an earlier timing, and a part of the pilot fuel injected before the cylinder pressure sufficiently rises to the wall surface of the piston or the like. Because it will adhere
The amount of unburned fuel led to the exhaust pipe 1 increases. For example, as shown in FIG. 3A, when the interval Pt between the pilot injection start timing and the main injection start timing, that is, the advance amount of the pilot injection start timing is set in the range of 10 to 40 ° As the amount of advance increases, the amount of unburned fuel such as HC gas supplied to the purification catalyst increases.

By advancing the pilot injection start timing, the retard control for delaying the main fuel injection timing is executed as in the conventional apparatus [see FIG. 3B]. In addition, the amount of unburned fuel (HC emission amount) led to the exhaust pipe 1 can be increased. Further, by advancing the pilot injection start timing or delaying the main injection timing as described above, as shown in (A) and (B) of FIG. The temperature will rise.

Since the purification catalyst 2 is activated in accordance with the increase of the unburned fuel supplied to the purification catalyst 2 and the rise of the exhaust gas temperature, as shown in FIG.
By executing the control for increasing the advance amount, the purification rate of nitrogen oxides (NOx) can be increased.

That is, the effect of activating the purification catalyst 2 by increasing the amount of unburned fuel introduced into the installation portion of the purification catalyst 2 and the effect of internal EGR by the pilot injection are combined. It is possible to effectively purify nitrogen oxides (NOx). As a result, FIG. 5B
As shown in, the nitrogen oxide purification rate can be increased to the same extent as in the case where the main injection timing is delayed. Therefore, the nitrogen oxide in the exhaust gas can be effectively reduced by setting the advance amount of the pilot injection start timing to an appropriate value in accordance with the activation rate of the purification catalyst 2.

Further, since the amount of unburned fuel led to the exhaust pipe 1 is increased by advancing the pilot injection start timing as described above, the combustion efficiency of the fuel is optimized. The purification catalyst 2 can be effectively activated without affecting the main injection set to. Therefore, as shown in (A) of FIG. 6 and (A) of FIG. 7, it is possible to improve the function of purifying the nitrogen oxides by the purifying catalyst 2 without significantly reducing the fuel consumption of the engine, and to exhaust gas. The amount of smoke discharged from the pipe 1 can be reduced.

That is, by delaying the timing of the main injection, the combustion efficiency is lowered as in the case where a part of the fuel that is originally burned in the engine is led to the exhaust pipe. It is possible to effectively prevent a large decrease in fuel consumption as shown in FIG. 6 (B), or a large amount of smoke caused by ignition delay as shown in FIG. 7 (B). can do.

Further, by executing the injection timing control for adjusting the interval Pt between the pilot injection start timing and the main injection start timing according to the activation rate of the purification catalyst 2,
When the activation rate detecting means 12 detects that the purification catalyst 2 is activated, the interval Pt is shortened accordingly.
Since the amount of unburned fuel in the pilot injection that is derived to (1) can be reduced, the fuel efficiency of the engine can be improved more effectively.

In the above embodiment, the cold state detecting means 13 detects whether or not the engine is in the cold state according to the temperature of the cooling water detected by the temperature sensor 7, and the engine is in the cold state. When it is confirmed that the above-mentioned injection timing control for adjusting the interval Pt between the pilot injection start timing and the main injection start timing is executed, When the engine is cold, the purification catalyst 2 can be activated to effectively reduce the nitrogen oxides in the exhaust gas, and the injection timing control is unnecessarily executed to reduce the fuel efficiency of the engine. Can be reliably prevented.

Moreover, since the pilot injection is performed when the engine is cold, ignition delay can be prevented.
It is possible to effectively suppress combustion noise that is likely to occur when the engine is cold due to the ignition delay or the like.

The amount of unburned fuel led to the exhaust pipe 1 can be controlled by adjusting the interval between the peak of the pilot injection pressure and the peak of the main injection pressure. However, if the interval Pt between the pilot injection start timing and the main injection start timing is adjusted by changing the pilot injection start timing as described above, it is easy to set the injection timing. Therefore, the emission control of the unburned fuel can be executed easily and accurately.

The temperature of the exhaust gas supplied to the nitrogen oxide purifying catalyst 2 and the temperature of the purifying catalyst 2 from the first and second temperature sensors 9 and 10 provided in the exhaust pipe 1 as described above. Detects the temperature of exhaust gas discharged and
When the activation rate detecting means 12 detects the activation rate of the purification catalyst 2 based on the difference between the detected values, an inexpensive temperature sensor is used to activate the activation rate of the purification catalyst 2. Can be accurately detected.

Further, in the above embodiment, the fuel supply device is composed of the electronically controlled fuel injection nozzle 4 for controlling the fuel injection timing and the electronic fuel injection pump 5 for controlling the fuel injection amount and injection pressure. I explained the example of
Instead of this configuration, a unit injector type fuel supply device capable of controlling the injection timing, injection amount and injection pressure of the fuel may be provided.

[0039]

As described above, in the invention according to claim 1, the interval between the pilot injection timing and the main injection timing is adjusted according to the activation rate of the purification catalyst detected by the activation rate detecting means. With this configuration, a part of the pilot fuel is led to the installation portion of the purification catalyst in an unburned state, so that the purification catalyst can be properly treated without deteriorating the fuel consumption and increasing the smoke amount. There is an advantage that nitrogen oxides in the exhaust gas can be reduced by activating the state.

According to the second aspect of the present invention, the pilot injection timing and the main injection timing are changed as the pilot injection timing control by the fuel injection control means is executed and the nitrogen oxide purification catalyst is activated. Since the interval is shortened, it is possible to prevent the unburned fuel amount led to the installation portion of the purification catalyst from becoming unnecessarily large, and it is possible to more effectively suppress deterioration of fuel consumption.

According to the third aspect of the invention, when the cold state detecting means confirms that the engine is in the cold state, the fuel injection control means controls the pilot injection timing. Therefore, during the cold period when the activation rate of the purification catalyst is low, the purification catalyst can be activated to effectively reduce the nitrogen oxides in the exhaust gas, and the injection timing control is executed unnecessarily. It is possible to reliably prevent the occurrence of a situation where the fuel efficiency of the engine is deteriorated. Further, since the ignition delay can be prevented by performing the pilot injection when the engine is cold, there is an advantage that combustion noise that is likely to occur when the engine is cold due to the ignition delay can be effectively suppressed. .

According to the fourth aspect of the invention, the interval between the pilot injection timing and the main injection timing is changed by changing the advance amount of the pilot injection start timing with respect to the main injection start timing according to the activation rate of the catalyst. Therefore, it is possible to easily and accurately control the amount of unburned fuel led to the installation portion of the purification catalyst to appropriately control the activation rate of the purification catalyst.

According to the fifth aspect of the invention, the reaction between the nitrogen oxides and the unburned fuel by the purifying catalyst is caused by the difference between the detected value of the first temperature sensor output means and the detected value of the second temperature sensor. The amount of heat generated by the acceleration is detected, and the activation rate of the purification catalyst is detected based on this detection value, so the activation rate of the catalyst can be detected easily and properly using an inexpensive sensor. There is an advantage that can be done.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram showing an embodiment of an exhaust emission control device for a diesel engine according to the present invention.

FIG. 2 is a graph showing a fuel injection state.

FIG. 3 shows a change state of an unburned fuel (HC gas) discharge amount, (A) is a graph of an example of the present invention, and (B) is a graph of a comparative example.

4A and 4B show changes in exhaust gas temperature, where FIG. 4A is a graph of an example of the present invention, and FIG. 4B is a graph of a comparative example.

FIG. 5 shows changes in the purification rate of nitrogen oxides (NOx), (A) is a graph of the example of the present invention, and (B) is a graph of a comparative example.

6A and 6B show changes in fuel consumption, where FIG. 6A is a graph of an example of the present invention, and FIG. 6B is a graph of a comparative example.

7A and 7B are graphs showing an example of the present invention, and FIG. 7B is a graph showing a comparative example, showing a state of change in smoke amount.

[Explanation of reference numerals] 2 purification catalyst 4 fuel injection nozzle (fuel supply device) 5 fuel injection pump (fuel supply device) 9 first temperature sensor 10 second temperature sensor 11 fuel injection control device 12 purification rate detection means 13 cold state Detection means

Claims (5)

[Claims] 1. A nitrogen oxide purifying catalyst capable of purifying nitrogen oxides in exhaust gas in a region where the excess air ratio is greater than 1, and an electronically controlled fuel supply means. In the exhaust gas purification device of a diesel engine configured to perform pilot injection before the main injection by, the activation rate detection means for detecting the activation rate of the purification catalyst, and the detection value of the activation rate detection means An exhaust emission control device for a diesel engine, comprising fuel injection control means for adjusting the interval between the pilot injection timing and the main injection timing by controlling the pilot injection timing accordingly. 2. The diesel engine according to claim 1, characterized in that the interval between the pilot injection timing and the main injection timing is shortened as the nitrogen oxide purification catalyst is activated. Exhaust purification device. 3. Cold injection detecting means for detecting whether or not the engine is in a cold state is provided, and when the cold state detecting means confirms that the engine is in a cold state, pilot injection is performed. The exhaust emission control device for a diesel engine according to claim 1 or 2, characterized in that it is configured to execute injection timing control for adjusting an interval between the timing and the main injection timing. 4. The fuel injection control means controls the advance amount of the pilot injection start timing with respect to the main injection start timing to adjust the interval between the pilot injection timing and the main injection timing. The exhaust emission control device for a diesel engine according to any one of claims 1 to 3. 5. A first temperature sensor for detecting the temperature of the exhaust gas introduced into the nitrogen oxide purification catalyst, and a second temperature sensor for detecting the temperature of the exhaust gas derived from the purification catalyst are provided. The exhaust emission control device for a diesel engine according to claim 1, characterized in that the activation rate of the catalyst is detected based on the difference between the detection values of the two temperature sensors.