JPH0374513A - Exhaust gas purification device for diesel engine - Google Patents

Abstract

PURPOSE:To prolong the service life of a NOx purifying catalyst by providing a particulate removing device on the upstream side of the NOx purifying cata lyst, and a catalyst protecting means operated when exhaust gas temperature exceeds a specified valve and air-fuel ratio becomes richer than a specified value. CONSTITUTION:A catalyst 20 to purify NOx in exhaust gas is placed on the way of an exhaust pipe 18 of a diesel engine. A particulate filter 21 for trapping particulates in exhaust gas is placed on the upstream side of the catalyst 20. A particulate remover 23 is constituted with both components 21, 22 so that particulates adhering to the filter 21 can be burned with the burner 22. A secon dary air passage 38 is connected to an exhaust pipe 18 located between the filter 21 and the catalyst 20, and a secondary air pump 36 is connected via a secondary air control valve 40 to the upstream side of the pipe 38 to constitute a catalyst protecting device 46. The valve 40 is opened when air-fuel ratio exceeds a specified value with exhaust gas temperature above a specified value so that the exhaust gas temperature is lowered for preventing the catalyst 20 from deteriorating.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in an exhaust gas purification device for a diesel engine.

(Prior art) Diesel engines are operated with a lean air-fuel ratio, so unlike gasoline engines, 1 (C and C) in the exhaust gas is
Although there is not much O, NOx in the exhaust gas becomes a problem because it causes acid rain. For this reason, in diesel engines, it is strongly desired to purify NOx in exhaust gas.

On the other hand, the N)13 catalytic reduction method is known as a method for purifying NOx in exhaust gas, but this NH3 catalytic reduction method has a complicated system and high cost, and the combustion gas temperature is high. There are many unresolved problems in applying it to automobiles because it sometimes causes secondary pollution due to NH3 being emitted.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 63-100919, a NOx purification catalyst containing CU has been proposed as a catalyst capable of purifying NOx in the presence of HC in an oxidizing atmosphere.

(Problem to be Solved by the Invention) However, although this NOx purification catalyst containing Cu can effectively purify NOx when the air-fuel ratio of the exhaust gas is lean, the exhaust gas temperature is high and the exhaust gas When the air-fuel ratio is rich, there is a problem that the copper ions of the NOx purification catalyst are reduced to metallic copper and lose their activity.

Further, as shown in FIG. 6, the NOx purification catalyst described above has the following characteristics:
There is also the problem that the purification performance varies depending on the exhaust gas temperature, and the purification performance peaks when the exhaust gas temperature is around 500° C., and the purification performance decreases above or below this temperature.

In view of the above, an object of the present invention is to prevent the NOx purification catalyst from deteriorating even when the exhaust gas temperature is high and the air-fuel ratio is rich.

(Means for solving the problem) In order to achieve the above object, the invention of claim (1)
The temperature and air-fuel ratio of the exhaust gas upstream of the Ox purification catalyst are detected, and when the exhaust gas is in an atmosphere that degrades the NOx purification catalyst, the atmosphere of the NOx purification catalyst is made to be an atmosphere that does not deteriorate.

Specifically, the solution taken by the invention of claim (1) is based on an exhaust gas purification device for a diesel engine equipped with a NOx purification catalyst containing Cu in the exhaust system, and is provided upstream of the NOx catalyst. , a particulate removal device that collects and burns particulates in exhaust gas, a catalyst protection means that makes the atmosphere of the NOx purification catalyst an atmosphere that does not deteriorate;
an exhaust gas temperature sensor that detects the temperature of exhaust gas flowing into the Ox purification catalyst; an air-fuel ratio detection means that detects the air-fuel ratio of the exhaust gas upstream of the NOx purification catalyst; and the exhaust gas temperature sensor and air-fuel ratio detection means. receives the output signal from
The apparatus further includes a control means for operating the catalyst protection means when the temperature of the exhaust gas becomes higher than a predetermined value and the air-fuel ratio becomes richer than a predetermined value.

In addition, in the invention of claim (2), in order to prevent deterioration of the NOx purification catalyst and improve the purification performance of the NOx purification catalyst, the catalyst protection means is provided as a secondary air purifier for supplying secondary air upstream of the NOx purification catalyst. This is an air supply device.

(Function) According to the configuration of the invention of claim (1), since the particulate removal device is disposed upstream of the NOx catalyst, particulates in the exhaust gas are collected before reaching the NOx purification catalyst, and NOx
It does not reach the purification catalyst.

In addition, the engine is equipped with a control means that activates the catalyst protection means when the exhaust gas temperature rises above a predetermined value and the air-fuel ratio becomes richer than a predetermined value. When the particulates collected by the removal device burn, and the temperature of the exhaust gas upstream of the NOx purification catalyst becomes higher than a predetermined value, and the air-fuel ratio exceeds the set value by 1 Rusoti, that is, the NOx purification catalyst deteriorates. In this range, the catalyst protection means is activated to make the atmosphere around the NOx purification catalyst an atmosphere that does not deteriorate.

Further, according to the configuration of the invention of claim (2), when the temperature of the exhaust gas on the upstream side of the NOx purification catalyst becomes higher than a predetermined value (and the air-fuel ratio becomes richer than the set value), the secondary air supply device Since secondary air is supplied upstream of the exhaust gas, the air-fuel ratio of the exhaust gas tends to be lean, preventing deterioration of the NOx purification catalyst, and the temperature of the exhaust gas decreases, reducing the NOx purification catalyst.
x The purification performance of the purification catalyst is improved.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows a body structure when the exhaust gas purification device for a diesel engine according to the first embodiment of the present invention is applied to a diesel engine 10. Intake pipe for
14 is an intake manifold that distributes air to each cylinder of the diesel engine 10; 15 is a fuel injection pump that injects and supplies fuel to each cylinder; 16 is an exhaust manifold that collects exhaust gas discharged from each cylinder; 18 is an exhaust manifold that collects exhaust gas discharged from each cylinder; This is an exhaust pipe that discharges exhaust gas.

Further, in the same figure, 20 is a NOx purification catalyst that reduces NOx in exhaust gas, and is manufactured as follows. In other words, mordenite, a type of zeolite [
Na20-Al! 03 ・Na of n5t02 is replaced with H, and the molar ratio of 5i02/A1:Oi is 10 or more,
A material with a pore diameter of approximately 7 angstroms is prepared, and is impregnated with an aqueous solution of organic acid steel to cause ion exchange and support Cu. In this case, the higher the copper ion exchange rate, the higher the NOx purification rate, and 5tO=/A1
2(The higher the molar ratio of h, the higher the catalytic activity.

Further, this NOx purification catalyst 20 has 2Cu +NO-
2Cu2"+N0-=2Cu" +N2 +02 It decomposes NO into 02 along with N, and as mentioned above, it has a high purification rate for NO at around 500℃ and also , has significantly higher No decomposition performance than other catalysts.

In addition, in the same figure, 21 is a DPF (diesel particulate filter) disposed in the exhaust pipe 18 upstream of the NOx purification catalyst 20 to collect and filter particulates in the exhaust gas, and 22 is a DPF 21 upstream of the DPF 21. This burner is disposed on the wall of the exhaust pipe 18 and burns particulates adhering to the DPF 21.The DPF 21 and burner 22 collect particulates in the exhaust gas and burn the collected particulates. Particulate removal device 23 to remove
is configured.

In this way, the upstream side 1:DP of the NOx purification catalyst 20
Since F21 is installed, fine particles in the exhaust gas are
Since it is collected by the PF 21 and does not reach the NOx purification catalyst 20, deterioration in the purification performance of the NOx purification catalyst 20 is prevented.

Further, since the burner 22 is disposed upstream of the DPF 21, when a large number of particles adhere to the DPF 21 and the exhaust gas flow condition deteriorates, the burner 22 can burn and remove the particles.

Incidentally, the means for burning the attached particulates is the burner 2.
2, a heater disposed in the DPF 21 or a high frequency induction heating means may be used.

Further, in the above case, in order to make it easier to burn the particulates attached to the DPF 21, the filter of the DPF 21 can be coated with a catalyst to lower the combustion temperature of the particulates.

In FIGS. 1 and 2, 24 communicates the exhaust pipe 18 upstream of the DPF 21 and downstream of the NOx purification catalyst 20 with the intake pipe 12, and directs the exhaust gas from the exhaust pipe 18 to the intake pipe 12. and EGR passages, 26A, 26B that recirculate
is interposed in the EGR passage 24 near the communication part with the exhaust pipe 18, and is used to vary the amount of exhaust gas recirculated through the EGR passage 24.
GR pulp, 28A, 28B is a negative pressure introduction passage that communicates the vacuum pump 29 attached to the alternator with the EGR valves 26A, 26B, and introduces negative pressure into the EGR pulp 26A, 26B; 30A, 30B are negative pressure introduction passages. 28A,
This is an EGR solenoid valve that is installed in EGR valve 28B and adjusts the opening degree of EGR valves 26A and 26B by duty control.

The EGR passage 24 and EGR valves 26A and 2 explained above
6B, negative pressure introduction passages 28A, 28B, vacuum pump 29, and EGR solenoid valve 30A0B.
A GR device 32 is configured, and as a result of this EGR device 32, exhaust gas is recirculated to the intake system and the heat capacity of the combustion chamber is increased, NOx discharged into the exhaust gas is reduced.

In this case, when the engine is under low load, exhaust gas is extracted from the upstream side of the DPF 21, and when the engine is under high load, NOx
EG so as to extract exhaust gas from the downstream side of the purification catalyst 20.
Each of the R soli solenoid pulps 30A0B is controlled.

In this way, when the engine is under low load, DPF2
By extracting exhaust gas from the upstream side of engine 1, high-temperature exhaust gas is obtained, improving the combustibility of the engine. In addition, when the engine is under high load, exhaust gas is
By passing through the exhaust gas, NOx is decomposed into 02 and N2, and the exhaust gas with high specific heat is returned to the intake system, so the combustion temperature is lowered and the amount of NOx emissions is reduced.

Further, in this embodiment, the EGR passage 2 in the intake pipe 12
An intake throttle valve 12a is disposed on the upstream side of the communication portion with 4. The reason for this is that in diesel engines, the difference between intake pressure and exhaust pressure is small, so exhaust gas is
4 into the intake pipe 12. Therefore, when the exhaust gas is recirculated, the intake throttle valve 12a is throttled to a predetermined intake pressure to facilitate the recirculation of the exhaust gas. However, even in this case, the amount of exhaust gas recirculation can be adjusted by adjusting the opening degrees of the EGR valves 26A and 26B: J8!
I do it.

Further, in FIG. 1, 36 is an air pump which is a supply source of secondary air, 38 is an air pump 36, DPF 21 and N
a secondary air passage 4 for communicating with the exhaust pipe 18 between the Ox purification catalyst 20 and supplying secondary air to the exhaust pipe 18;
0 is a secondary air adjustment valve that varies the amount of secondary air flowing through the secondary air passage 36; 42 is a secondary air adjustment valve that communicates with the vacuum pump 29 and the secondary air adjustment valve 40; The negative pressure introduction passage 44 that supplies pressure is a secondary air solenoid valve that is interposed in the negative pressure introduction passage 42 and adjusts the opening degree of the secondary air adjustment valve 40 by duty control. Secondary air pump 36, secondary air passage 38, secondary air adjustment valve 40, negative pressure introduction passage 4
2 and secondary air solenoid valve 44, NO.
A secondary air supply device 46 is configured to supply secondary air upstream of the x purification catalyst 20. This secondary air supply bag rrt46 constitutes a catalyst protection means for preventing deterioration of the NOx purification catalyst 20, and when secondary air is supplied into the exhaust gas by the secondary air supply device 46, NOx purification is performed. As the temperature of the exhaust gas flowing into the catalyst 20 decreases, the air-fuel ratio tends to lean.

In this way, the exhaust gas becomes rich and high temperature because the diesel engine 10 is in a high load state, or the exhaust gas becomes high temperature due to the heat generated when particulates attached to the DPF 21 are burned by the burner 22 or the like. Also, by supplying secondary air, the air-fuel ratio of the exhaust gas tends to be lean, and the temperature of the exhaust gas can be lowered.

Therefore, when the exhaust gas is rich and high temperature, NO
Since it is possible to prevent the copper ions of the x purification catalyst 20 from being reduced to metallic copper and losing activity and the NOx purification catalyst 120 deteriorating, the NOx purification catalyst 20 is protected. In addition, as the temperature of the exhaust gas decreases, the NOx purification catalyst 2
0 purification performance can also be improved.

Further, in FIG. 1, 50 is a cooling water temperature sensor that detects the engine cooling water temperature, 51 is an intake air temperature sensor that detects the engine intake air temperature, 52 is an intake pressure sensor that detects the engine intake pressure, and 54 is NOx Exhaust gas temperature sensor 55 that detects the temperature of exhaust gas upstream of the purification catalyst 22
02 sensor is an air-fuel ratio detection means for detecting the air-fuel ratio of exhaust gas flowing into the NOx purification catalyst, and 56 is a pressure sensor for detecting the pressure of the exhaust gas. It can detect when there is too much adhesion and the filter is clogged. In FIG. 1, 60 is a control unit with a built-in CPU, which receives an engine cooling water temperature signal from the cooling water temperature sensor 50, an engine intake air temperature signal from the intake air temperature sensor 51, and an engine intake air temperature signal from the intake pressure sensor 52. Barometric pressure signal, exhaust gas temperature signal from the exhaust gas temperature sensor 54, exhaust gas air-fuel ratio signal from the 02 sensor 55, exhaust gas pressure signal from the pressure sensor 56, engine speed signal and engine load signal from the fuel injection pump 15. etc., it is determined whether or not to operate the EGR device 232 based on the engine rotation speed signal and the engine load signal, and duty control is performed on the EGR solenoid valve 30 and the secondary air solenoid valve 44 based on the exhaust gas temperature signal. Then, combustion in the burner 22 is controlled based on the exhaust gas pressure signal from the pressure sensor 56. The control unit 60 constitutes a control means that operates the secondary air supply device 46 as a catalyst protection means when the temperature of the exhaust gas becomes higher than a predetermined value and the air-fuel ratio becomes richer than a predetermined value. .

Next, duty control for the secondary air adjustment valve 40 will be explained based on the flowchart in FIG.

First, in step SAI, the opening/closing duty value MA of the secondary air solenoid valve 44 is set to 0 to fully close the secondary air adjustment valve 40, and in step SA2
Then, the O sensor 55 detects the oxygen concentration in the exhaust gas and measures the air-fuel ratio (A/F).

In step SA3, it is determined whether the air-fuel ratio is rich or not. If it is not rich, the process returns to step SAI since there is no risk of deterioration of the NOx purification catalyst 20. If it is rich, the exhaust gas temperature sensor 54 The exhaust gas temperature T1 is detected.

Next, in step SA5, the exhaust gas temperature T1 and the NOx
Set exhaust gas 2 set as the lower limit temperature of the region where the purification catalyst 20 deteriorates! i degrees T, compared with 'r+ <
It is determined whether T2 or not, and if T<T, there is no risk of deterioration of the NOx purification catalyst 20, so step SA is performed.
6, the opening/closing duty (11i MA) of the secondary air solenoid valve 44 is left as is.

On the other hand, if T1≧T2 in step SA5, NOx
In order to prevent the purification catalyst 20 from deteriorating, step S
At A7, input MA+Ml) ((!!, MD constant duty value) as the opening/closing duty value MA of the secondary air solenoid valve 44 to make the air-fuel ratio of the exhaust gas lean.

In this way, when the air-fuel ratio of the exhaust gas is rich and the temperature is high, secondary air is supplied to the upstream side of the NOx purification catalyst 20, so the air-fuel ratio of the exhaust gas tends to be lean and the exhaust gas Temperature decreases.

FIG. 4 shows an exhaust gas purification device for a diesel engine according to a second embodiment of the present invention.
Instead of the EGR system r1t32 and the secondary air supply device 46 being provided, an exhaust gas bypass passage 62 that bypasses the exhaust gas to the outer peripheral side of the NOx purification catalyst 20, and an N
Disposed upstream of the Ox purification catalyst 20, the NOx purification catalyst 2
Bypass valve 64 for opening and closing the inlet of 0
The exhaust gas bypass passage 62 and the bypass valve 64 constitute a catalyst protection means 66 that prevents the NOx purification catalyst 22 from deteriorating.

In this second embodiment, under conditions where the NOx purification catalyst 20 deteriorates, that is, when the air-fuel ratio of the exhaust gas is rich and the temperature is high, the bypass valve 64 is closed.
Exhaust gas is released from the exhaust gas bypass passage 62. In this way, exhaust gas under conditions that degrade the NOx purification catalyst 20 does not flow through the NOx purification catalyst 20, so deterioration of the NOx purification catalyst 20 is prevented.

As described above, when the exhaust gas bypass path 62 is provided on the outer peripheral side of the NOx purification catalyst 20, when the exhaust gas is bypassed, N
A rapid temperature drop of the Ox purification catalyst 20 can be prevented, and a deterioration in purification performance when the exhaust gas returns to flow through the NOx purification catalyst 20 can be prevented.

In addition, in the second embodiment, the control unit 60 controls the air-fuel ratio (A/F ) is in the rich operating region, the opening/closing of the bypass valve 64 is controlled in response to a bypass valve position signal etc. from the bypass valve 64.

Note that the control for the bypass valve 64 may be 2fJI type control of fully open and fully closed, or the bypass valve 64 may be controlled according to the conditions that cause the NOx purification catalyst 20 to deteriorate.
The opening degree of No. 4 may be controlled to be adjusted.

In addition, as for the structure of the exhaust gas bypass passage 62, instead of the second embodiment, as shown in FIG. 62 may be provided.

(Effects of the Invention) As explained above, according to the diesel engine exhaust gas purification device according to the invention of claim (1), the particulate removal device for collecting particulates in the exhaust gas is provided upstream of the NOx purification catalyst. NO due to particulates in the exhaust gas.
x The deterioration of the purification performance of the purification catalyst is prevented. Further, since the particulate removal means includes a catalyst protection means and a control means that operates the catalyst protection means when the temperature of the exhaust gas becomes higher than a predetermined value and the air-fuel ratio becomes richer than a predetermined value, the particulate removal means Exhaust gas is reduced to NO by burning
Even if the atmosphere is such that the NOx purification catalyst deteriorates, the catalyst protection means can reliably prevent deterioration of the NOx purification catalyst.

Further, according to the engine exhaust gas purification device according to the claimed invention, since the catalyst protection means is a secondary air supply device that supplies secondary air upstream of the NOx purification catalyst, NOx
x When the temperature of the exhaust gas upstream of the purification catalyst becomes higher than a predetermined value and the air-fuel ratio becomes richer than a predetermined value, secondary air is supplied upstream of the NOx purification device, thereby preventing deterioration of the NOx purification catalyst. At the same time, the purification performance of the NOx purification catalyst is improved.

[Brief explanation of drawings]

1 to 3 show a first embodiment of the present invention, and FIG. 1 is an overall configuration diagram of an exhaust gas purification device for a diesel engine;
FIG. 2 is a sectional view of the EGR device, FIG. 3 is a flowchart showing a method of controlling the secondary air supply device, and FIG. 4 is the overall configuration of an exhaust gas purification device for a diesel engine according to a second embodiment of the present invention. 5 is an overall configuration diagram showing a modification of the second embodiment, and FIG. 6 is a diagram showing the relationship between exhaust gas temperature and NOx purification performance in the NOx purification catalyst. 0...Diesel engine 2...Intake pipe 8...Exhaust pipe 0...NOx purification catalyst 1...DPF 2...Burner 3 Figure 4 Figure port

Claims (2)

[Claims] (1) In an exhaust gas purification device for a diesel engine equipped with an NO_x purification catalyst containing Cu in the exhaust system, a particulate removal device is disposed upstream of the NO_x catalyst and collects and burns particulates in the exhaust gas. And said NO_
a catalyst protection means for creating an atmosphere around the x purification catalyst that does not deteriorate; an exhaust gas temperature sensor that detects the temperature of the exhaust gas upstream of the NO_x purification catalyst; and an air-fuel ratio of the exhaust gas flowing into the NO_x purification catalyst. receiving output signals from the exhaust gas temperature sensor and the air-fuel ratio detection means, and when the temperature of the exhaust gas becomes higher than a predetermined value and the air-fuel ratio becomes richer than a predetermined value, the catalyst protection means is activated. 1. An exhaust gas purification device for a diesel engine, comprising a control means for operating the device. (2) The exhaust gas purification device for a diesel engine according to claim (1), wherein the catalyst protection means is a secondary air supply device that supplies secondary air upstream of the NO_x purification catalyst.