JPS61112715A - Exhaust purifying apparatus for diesel engine - Google Patents

Abstract

PURPOSE:To burn articulates and remove NOX by disposing NOX reducing catalyst in an exhaust path of an engine and providing a catalyst temperature raising means for maintaining said catalyst at temperature of about 300 deg.C-400 deg.C. CONSTITUTION:In an exhaust path of an engine are provided at least one of Co, Fe and Ni, rate earth elements and a filter 10 coated with NOX recuding catalyst comprising platinum group metal. A catalyst temperature raising means is provided to maintain the reducing catalyst temperature at about 300 deg.C-400 deg.C. The first catalyst temperature raising means controls a throttle valve 25 such that an electromagnetic change-over valve 26 is changed over to control the opening of the throttle valve 25 according to the rotational frequency and load of the engine. The second catalyst temperature raising means controls a heater and when the temperature cannot be raised only by the throttle control, current is supplied to an electric heater 22.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an exhaust purification device for a diesel engine.

BACKGROUND OF THE INVENTION Since diesel engines are operated with excess air, there is a high concentration of oxygen in the exhaust gas of diesel engines, so the reduction catalyst or three-way catalyst used for gasoline engines is However, it is not possible to reduce NOx in the exhaust gas of a diesel engine. Therefore, conventionally, catalysts have not been used to reduce NOx in exhaust gas, and the current situation is to try to reduce NOx by recirculating the exhaust gas or adjusting the fuel injection time.

In addition, a diesel engine that captures particulates contained in the exhaust gas of a diesel engine with a filter and throttles a throttle valve installed in the intake passage in order to burn and remove the particulates captured by the filter has been disclosed in Japanese Patent Publication. It is described in Publication No. 59-150921. In this diesel engine, the exhaust gas temperature is raised by throttling a throttle valve provided in the intake passage to burn particulates captured by the filter, and NOx cannot be removed.

Problems to be Solved by the Invention As described above, in conventional diesel engines, NOx is not removed using a catalyst, and even if NOx is removed using recirculated exhaust gas, etc., NOx is not sufficiently removed. It is not possible.

Means for Solving the Problems In order to solve the above problems, according to the present invention, the engine exhaust passage is equipped with a NOx reducing material made of at least one metal selected from Co, Fe, and Ni, a rare earth element, and a platinum group metal. The catalyst is provided with catalyst temperature increasing means for maintaining the temperature of the reduction catalyst at approximately 300 to 400 degrees.

Embodiment Referring to FIG. 1, 1 is an engine main body, 2 is an intake manifold, 3 is an intake duct connected to a gathering part of the intake manifold 2, 4 is an exhaust duct connected to an exhaust manifold (not shown), 5 is an exhaust turbocharger connected to the outlet of the exhaust duct 4; 6 is an exhaust pipe connected to the outlet of the exhaust turbocharger 5; and 7 is another exhaust pipe connected to the exhaust pipe 6. The exhaust pipe 6 includes a main passage 8 and a bypass passage 9 that bypasses the main passage 8. A cylindrical filter 10 is disposed within the main passage 8. On the other hand, a bypass valve 12 operated by a negative pressure diaphragm actuator 11 is inserted into the bypass passage 9, and this bypass valve 12 is normally kept in a closed state.

Therefore, the exhaust gas is normally filtered through the filter 10 as shown by arrow A.
It passes through the interior and is discharged to the atmosphere through the exhaust pipe 7. The actuator 11 has a negative pressure chamber therein, and fully opens the bypass valve 12 when negative pressure is applied to the negative pressure chamber, and closes the bypass valve 12 when atmospheric pressure acts within the negative pressure chamber. This negative pressure chamber is selectively connected to a negative pressure source or to the atmosphere via an electromagnetic switching valve 14 controlled by an output signal of an electronic control unit 13.

The electronic control unit 13 consists of a digital computer, with RAM interconnected by a bidirectional bus 15.
(Random access memory) 16, ROM (IJ-only memory) 17, CPU (ficro processor) 1
8, an input port 19 and an output port 20.

The electromagnetic switching valve 14 is connected to the output port 20 via the drive circuit 21.
connected to.

On the other hand, radially arranged electric heaters 22 are arranged in the artificial part of the filter 10, and the electric heaters 22 are connected to the output port 20 via a drive circuit 23. Furthermore, a temperature sensor 24 is inserted into the filter 10 to detect the temperature of the filter 10, and this temperature sensor 24 is connected to the input port 19 via an AD converter 25.

On the other hand, a throttle valve 25 whose opening and closing are controlled by a negative pressure diaphragm actuator 24 is disposed within the intake duct 3 . The actuator 24 has a negative pressure chamber and an atmospheric pressure chamber separated by a diaphragm, and the negative pressure chamber is selectively connected to a negative pressure source or the atmosphere via an electromagnetic switching valve 26. The diaphragm of the actuator 24 is linked via a control rod 27 to a valve shaft 28 of a throttle valve 25 . When negative pressure is applied within the negative pressure chamber of the actuator 24, the throttle valve 25 is rotated in the valve closing direction, and when atmospheric pressure is applied within the negative pressure chamber of the actuator 24, the throttle valve 25 is rotated in the valve opening direction. The electromagnetic switching valve 26 is connected to the output port 20 via a drive circuit 29. A throttle valve opening sensor 30 that detects the opening of the throttle valve 25 is attached to the valve shaft 28 of the throttle valve 25, and this throttle valve opening sensor 30 is connected to the AD converter 3.
1 to the input port 19. In addition, a load sensor that detects the engine load, for example, a load sensor 32 that detects the rack position of a fuel injection pump, is connected to the input port 19 via an AD converter 33, and the load sensor 32 detects the rack position of the fuel injection pump. A number sensor 33 is connected to input port 19 . Inside the CPU 18, the rotation speed sensor 33
The engine speed is calculated from the output pulse.

The filter 10 is made of cordierite with a three-dimensional network structure.
- It is coated with alumina, and the particulate high boiling point HC in the exhaust gas is removed from the filter 1.
While flowing through the mesh structure, it is captured by the mesh structure and deposited inside the mesh structure. Note that this filter 10
Since it is sufficient to capture the particulate high boiling point 11c without increasing the exhaust pressure so much, the internal shape of the filter IO may be any shape such as a honeycomb shape, a monolith shape, or a pellet shape.

According to the present invention, at least one metal selected from Co, Fe, and Ni and rare earth IN (La) are coated on a support made of cordierite coated with γ-alumina.

Th, Ce, etc.) and platinum group metals (Pt, Rh, Ru.

A catalyst consisting of three components (Pd, Os, Ir, etc.) is supported. It has been found that these catalysts have strong reducing properties against NOx in the presence of excess oxygen, and this strong reducing property is exhibited within a certain temperature range as will be described later.

Next, a method for producing a carrier supporting such a catalyst and N
Ox purification performance will be explained.

As described above, cordierite having a three-dimensional network structure coated with T-alumina is used as the carrier.

First, a carrier is immersed in a mixed solution of cobalt nitrate and lanthanum nitrate to impregnate Co and La onto the carrier. Then, it is dried by blowing warm air at 60° C. for a predetermined period of time.

Next, the carrier is immersed in an acidic nitric acid solution of PT to adsorb Pt onto the carrier. Next, warm air at 60℃.

Spray on it for a specified period of time and let it dry.

The carrier was then exposed to 20°C saturated steam of 10% ammonia aqueous solution for 10 minutes, and then exposed to 400°C hydrogen atmosphere for 4 minutes.
H2 reduction is performed by exposing for 0 minutes, and single Co is deposited on the carrier.
form.

Note that C is the first NOx reduction catalyst.

It has been found that it is preferable to first deposit La and La on the carrier and then deposit pt on the carrier.

FIG. 4 shows the results of testing the NOx purification performance of the carrier thus obtained by placing it in an exhaust passage. The carrier has a volume of about 2000 cn and is coated with about 360 g of alumina, and the amounts of co, La+pt are about 8.8 g, 4.0 g, and 1.2 g, respectively.

In Figure 4, the broken line indicates the engine speed is 2000 r, p.
, m, and the solid line indicates when the engine speed is 300O
The cases of r, p, and m are shown. Further, in FIG. 4, the vertical axis C shows the NOx purification rate, and the horizontal axis T shows the temperature of the carrier. It can be seen from FIG. 4 that the NOx purification rate reaches its peak when the carrier temperature is around 350°C.

In addition, in FIG. 4, the section T, that is, the temperature of the carrier is about 3
The purification rate is quite high between 00℃ and 400℃,
If the temperature of the carrier is maintained within this temperature range T, the NO
It can be seen that x purification rate can be obtained.

As mentioned above, the bypass valve 12 shown in FIG.
and is discharged into the outside air through the main passage 8. The filter 10 has a three-dimensional network structure of cordierite coated with γ-alumina as a carrier, and a catalyst made of three components of at least one metal selected from Co, Fe, and Ni, a rare earth element, and a platinum group metal on the carrier. It consists of what it carries. Therefore, in order to obtain high NOx purification efficiency using this filter 10, it is necessary to maintain the filter 10 at a temperature between 300°C and 400°C, preferably around 350°C.

Next, referring to the flowchart shown in Fig. 2, filter 1 is
A method for maintaining the temperature at about 350°C will be explained. Referring to FIG. 2, first, in step 40, the temperature t of the filter 10 is detected from the output signal of the temperature sensor 24. Next, in step 41, it is determined whether a flag that is set when the filter salt t has been in a low temperature state for a certain period of time has been set. Normally this flag will be reset, so step 42 is reached. In step 42, it is determined whether the filter salt t is below 340°C, and if t<340°C, the process proceeds to step knob 43. In step 43, it is determined whether or not the timer is set, and if the timer is not set, the timer is set in step 44. This timer is reset after a certain period of time. Next, in step 45, it is determined whether a certain period of time determined by a timer has elapsed. This time is, for example, 30 seconds. If a certain period of time has not elapsed, proceed to the steering knob 46 and close the throttle valve 2.
5 aperture control is performed.

Throttling the throttle valve 25 reduces the amount of excess air supplied into the engine cylinder, resulting in an increase in the temperature of the exhaust gas.

However, if the throttle valve 25 is throttled too much, combustion will deteriorate. It is known to what extent the exhaust gas temperature will be the highest without deteriorating combustion, and it is also known from the beginning how much throttle the throttle will worsen combustion. The relationship between the opening degree of the throttle valve 25 at which the exhaust gas temperature is highest within a range that does not deteriorate combustion, the engine speed, and the engine load is stored in advance in the ROM 17, and in step 46, the throttle valve 25 is opened according to this relationship. The opening degree is controlled. That is, if the throttle valve opening is larger than the throttle valve opening determined by the engine speed and load, the electromagnetic switching valve 26 is switched to communicate the negative pressure chamber of the actuator 24 with the negative pressure source, thereby reducing the throttle valve 25 opening.
When the opening degree of the throttle valve becomes smaller than the opening degree determined by the engine speed and load, the opening degree of the throttle valve 25 is increased by switching the electromagnetic switching valve 26 and opening the negative pressure chamber of the actuator 24 to the atmosphere. In this way, the opening degree of the throttle valve 25 is maintained at a constant opening degree determined by the engine speed and engine load, and thus the exhaust gas temperature is raised.

Next, if the temperature t of the filter 10 becomes higher than 340°C, the process proceeds to step 47, where it is determined whether the filter salt t is higher than 360°C, and if t≦360°C, the aperture control continues. Ru. When the temperature reaches t>360° C., the process proceeds to step 48, where the throttle valve control is stopped and the throttle valve 25 is kept fully open. Therefore, the temperature of the filter 10 is 340℃
to 360°C, NO in the exhaust gas is
x will be well purified.

On the other hand, if a certain period of time has elapsed in step 45, that is, if the state of t<340°C has elapsed for a certain period of time, the process proceeds to step 49 and a flag is set.

Therefore, the process proceeds from step 41 to step 50. In step 50, it is determined whether the temperature t of the filter 10 is smaller than 340°C, and if t<340°C, the electric heater 22 is activated in step 51.

Next, the process proceeds to step 46. When t≧340°C, the process proceeds to step 52, where it is determined whether the filter salt t is smaller than 360°C. If t≦360°C, the process proceeds to step 51.
The heater 22 continues to operate. The process then proceeds to step 46. Therefore, it can be seen that the aperture control is also being performed while the heater 22 is being operated. t>3
When the temperature reaches 60° C., the operation of the heater 22 is stopped in step 53, and the flag is then reset in step 54, so that only the throttle control by the throttle valve 25 continues to be performed again.

As described above, according to the present invention, if filter salt t can be maintained within the range of 340°C to 360°C only by throttling control, filter salt t is controlled only by throttling control, and filter salt t is maintained at 340°C or higher only by throttling control. When this is not possible, heater control is also performed at the same time. Therefore, in the former case, the throttle control constitutes the catalyst temperature raising means, and in the latter case, the throttle control and the heater control constitute the catalyst temperature raising means.

Furthermore, particulate high boiling point HC is captured within the mesh structure of the filter IO. When it is time for the filter 10 to regenerate, that is, when the integrated value of the engine rotational speed exceeds a certain value (in this case, a non-volatile RAM is provided) or when the back pressure upstream of the filter 10 becomes above a certain value. (In this case, a pressure sensor is installed inside the exhaust pipe 6.) The electromagnetic switching valve 14 is operated to open the bypass valve 12, and then the heater 22 is operated to open the filter 1.
The particulate high boiling point HC deposited on the 0 is burned. Since such regeneration processing is well known, it will not be described in detail here. However, one feature of the embodiment shown in FIG. 1 is that the filter 10 for capturing particulates is also used for reducing NOx. In this case, the particulate high boiling point HC captured in the filter 10 is N
It is particularly effective because it acts as a reducing agent for Ox.

Another embodiment is shown in FIG. In this embodiment, a catalytic converter 61 containing a monolithic catalyst 60 is connected to the exhaust pipe 4. Similar to the filter 10 shown in FIG. 1, this monolithic catalyst 6o uses cordierite coated with T--alumina as a carrier, and on this carrier, at least one metal selected from Co, Fe, and Ni and a rare earth metal are added. It supports platinum group metals. However, this monolith catalyst 6
゜ has a large number of holes extending straight in the flow direction of exhaust gas, so it does not have much ability to capture particulates. In this embodiment as well, the throttle valve 25 and heater 22 are controlled in the same manner as in the embodiment shown in FIG.

Note that when the throttle valve 25 is throttled while the vehicle is running, the exhaust gas temperature increases as described above, but at the same time, HC and Go act as reducing agents for NOx in the exhaust gas.

Particulates and 5OF in particulates (
/ffl-like hydrocarbons), and these can also promote NOx purification. Note that if the fuel injection timing is delayed, afterburning occurs and the exhaust gas temperature rises, and the amount of reducing agent in the exhaust gas mentioned above also increases, so in addition to throttle control and heater control, the fuel injection timing is further controlled. You can also do that.

Effects of the Invention By using a catalyst that can reduce NOx even in the presence of excess oxygen and controlling the temperature of the catalyst carrier so that the catalyst has the highest purification performance, NOx in the exhaust gas of a diesel engine can be effectively reduced. Can be purified. .

[Brief explanation of the drawing]

Fig. 1 is an overall diagram of a diesel engine, Fig. 2 is a flowchart, Fig. 3 is an overall diagram showing another embodiment of the diesel engine, and Fig. 4 is a diagram showing the relationship between carrier temperature and NOx purification rate. be. 1... Engine body, 3... Intake duct, 4.6.7.
...Exhaust pipe, 8...Main passage, 9...Bypass passage,
10...filter, work 2...bypass valve, 13...
・Electronic control unit, 22... Electric heater, 25...
- Throttle valve.

Claims (1)

[Claims] A NOx reduction catalyst made of at least one metal selected from Co, Fe, and Ni, a rare earth element, and a platinum group metal is arranged in the engine exhaust passage, and the temperature of the reduction catalyst is increased from approximately 300°C to 4°C.
An exhaust purification device for a diesel engine equipped with a catalyst temperature raising means to maintain the temperature at 00°C.