JPH0650126A - Exhaust emission control device of diesel engine - Google Patents

Abstract

PURPOSE:To prevent increase of growth of sulphate at the time when exhaust gas temperature is high with an oxidization catalyzer to purify exhaust gas of a diesel engine. CONSTITUTION:This exhaust emission control device 1 has a first case 10 enclosing an oxidization catalyzer 20 and a second case 30 covering the first case 10, and between the first case 10 and the second case 30, a by-pass passage 46 is formed. An entrance 40 of exhaust gas is branched into a first passage communicating through to the by-pass passage 46, and a first change-over valve 70 and a second change-over valve 72 are respectively provided in each of the passages. A controller 60 opens and closes the change-over valves in accordance with information of a sensor 64 to detect temperature of exhaust gas G and when temperature is lower than a set value, it flows exhaust gas to a flow passage F1 and when it becomes higher than the set value, it flows exhaust gas to a flow passage F2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus using an oxidation catalyst in a diesel engine.

[0002]

2. Description of the Related Art One of measures for reducing particulate matter (particulate material) emitted from a diesel engine
An exhaust gas purifying apparatus using an oxidation catalyst has been proposed as one means. This exhaust gas purifying apparatus uses SOF (Solub) contained in particulate matter together with CO and HC in exhaust gas.
It has the function of oxidizing le Organic Fraction) with a catalyst to convert it into CO ₂ and H ₂ O for purification. As this oxidation catalyst, a catalyst in which a noble metal such as Pt, Pd, or Rh is supported by using a ceramic or metal material as a carrier substrate is used. FIG. 2 is a graph showing an experimental result in which the horizontal axis represents the catalyst inlet temperature of exhaust gas and the vertical axis represents the purification rate of exhaust gas. A curve B represents changes in the purification rate of SOF, and curves A ₁ and A ₂ indicates the amount of particulate matter of the two types of catalysts. Also, FIG. 3 is a graph showing the experimental results in which the horizontal axis represents the catalyst inlet temperature of exhaust gas and the vertical axis represents the change rate of exhaust gas. Curves C ₁ and C ₂ show the purification rates of two types of catalysts. A curve D shows the generation rate of sulfate. As is clear from both graphs, the purification performance of this type of oxidation catalyst improves as the temperature of the exhaust gas increases. However, with this catalyst, when the exhaust gas temperature increases, the amount of SO ₂ in the exhaust gas that oxidizes to SO ₃ (sulfate, sulfuric acid mist) also increases. Since this sulfate or the like is counted as a particulate matter, even if the SOF is reduced, the sulfate will increase and the particulate matter will increase as a whole. That is, if the purification efficiency of SOF is improved, the production amount of sulfate increases, and conversely, if the production amount of sulfate is suppressed, the purification ability of SOF also decreases.

[0003]

SUMMARY OF THE INVENTION For example, Japanese Patent Laid-Open No. 4-5
Japanese Patent No. 4211 discloses an apparatus that includes two types of catalysts in parallel, switches the passage of the exhaust gas according to the temperature of the exhaust gas, and passes the exhaust gas to either one of the catalysts. Also,
Japanese Utility Model Laid-Open No. 63-128219 discloses a device for heating the catalyst to an active temperature by returning exhaust gas passing through the catalyst to the catalyst again when the temperature of the exhaust gas is low when the engine is warmed up and the catalyst is inactive. It is disclosed. However,
In the former publication, since the two catalysts are used in parallel, the device becomes large and the weight space also increases. Further, there is a problem that the temperature of the catalyst on the side where the exhaust gas does not pass decreases, and the purification efficiency in the initial state where the exhaust gas is introduced next decreases. The latter publication relates to a catalyst heating means at the time of warming up, and is not a purifying device that takes measures against the high temperature exhaust gas of a diesel engine. The present invention provides a purification device that effectively utilizes an oxidation catalyst according to the temperature of exhaust gas of a diesel engine.

[0004]

The purifying apparatus of the present invention has a first case containing an oxidation catalyst and a second case covering the outside of the first case. A bypass passage is formed between the cases. The exhaust gas inlet is branched into a first passage communicating with the first case and a second passage communicating with the bypass passage, and the first passage is provided in the first and second passages.
And a second switching valve is provided. It has a sensor that detects the temperature of exhaust gas and a controller that operates a switching valve according to the temperature.

[0005]

When the temperature of the exhaust gas is equal to or lower than the set value, the exhaust gas is flowed to the catalyst side for purification by oxidation, and when the exhaust gas temperature is high, the catalyst is bypassed to suppress the increase in sulfate production. Even in this state, the catalyst is kept warm by the exhaust gas and kept activated.

[0006]

1 is an explanatory view showing an exhaust gas purifying apparatus for a diesel engine of the present invention. The exhaust gas purifying apparatus generally designated by reference numeral 1 has a first case 10 in which an oxidation catalyst 20 is arranged, and the oxidation catalyst 20 is provided with a seal member 15 provided on the outer peripheral portion of the first case 10. Positioned inside. A second case 30 is provided on the outer peripheral portion of the first case 10, and a bypass passage 46 is formed on the outer side of the first case 10 and the inner side of the second case 30.
Inside the inlet portion 40 for the exhaust gas G, the first passage 42 and the second passage 42 are provided.
It branches into the passage 44. The first passage 42 communicates with the first case 10 and guides the exhaust gas G to the catalyst 20. First
A first switching valve 70 is provided in the passage 42.

A first outlet 40 for the exhaust gas purified by the catalyst 20 is formed on the downstream side of the catalyst 20 in the first case 10. A second switching valve 72 is arranged in the second passage 44 of the exhaust gas G, and the second passage 44 communicates with the bypass passage 46. The bypass passage is the second case 3
It leads to the 2nd exit 50 of exhaust gas formed in the end of 0. A temperature sensor 64 is provided in the exhaust gas inlet 40 of the purifier and detects the temperature of the exhaust gas G introduced. The temperature signal of the exhaust gas G is sent to the controller 60 via the line 65. The controller 60 is driven by the battery 62, and the output signals are lines 66 and 67.
Via the first switching valve 70 and the second switching valve 72
Be transmitted to. The first switching valve 70 and the second switching valve 72 are alternately opened and closed. First switching valve 70
Is opened and the second switching valve 72 is closed, the exhaust gas G is guided along the flow path F ₁ passing through the catalyst 20. When the first switching valve is closed and the second switching valve 72 is opened, the exhaust gas G is guided along the flow path F ₂ .

The exhaust gas purifying apparatus of the present invention is constructed as described above, and the controller 60 includes the temperature sensor 64.
When the temperature of the exhaust gas G detected by the exhaust gas reaches a set temperature at which the production of sulfate is remarkable, the switching valves 70 and 72 are opened and closed so that the exhaust gas flows along the _second flow path F ₂ .
When the temperature of the exhaust gas G is equal to or lower than the set temperature, the controller 60 opens / closes the switching valves 70 and 72 so that the exhaust gas G flows along the _first flow path F ₁ . Therefore, the exhaust gas G of the diesel engine is purified by the oxidation catalyst when the temperature is below the set value. In particular, SOF is effectively purified

When the temperature of the exhaust gas rises above a set value, if it passes through the oxidation catalyst, the amount of sulfate produced increases, and the overall purification efficiency rather decreases. Therefore, bypassing the oxidation catalyst causes the purification efficiency to decrease. To avoid. Even during this period, the oxidation catalyst is heated by the heat of the exhaust gas passing through the bypass passage and is kept activated. Therefore, even when the temperature of the exhaust gas is lowered and the exhaust gas is introduced along the first flow path F ₁ , efficient purification is achieved by the activated oxidation catalyst.

[0010]

As described above, the present invention provides an exhaust gas purifying apparatus for a diesel engine, wherein an oxidation catalyst having a high purifying efficiency is disposed in the first case when the temperature of the exhaust gas is a set value or less, The first case is wrapped with the second case to form a bypass passage therebetween. A downstream side of the exhaust gas inlet is branched into a first passage communicating with the oxidation catalyst and a second passage communicating with the bypass, and a switching valve is provided in each passage. The controller opens and closes the switching valve according to the temperature of the exhaust gas, and the exhaust gas passes through the catalyst to the bypass. With this configuration, the oxidation catalyst that is affected by the exhaust gas temperature is effectively used to achieve optimum purification. By flowing the exhaust gas to the bypass formed around the oxidation catalyst, the catalyst is always activated, and efficient purification is performed when the exhaust gas passage is switched.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention.

FIG. 2 is a graph showing the action of an oxidation catalyst.

FIG. 3 is a graph showing the action of an oxidation catalyst.

[Explanation of symbols]

 1 Exhaust Gas Purification Device 10 First Case 20 Oxidation Catalyst 30 Second Case 40 Exhaust Gas Inlet 42 First Passage 44 Second Passage 46 Bypass Passage 48 First Outlet 50 Second Outlet 60 Controller 64 Temperature Sensor 70th 1 switching valve 72 2nd switching valve

Claims (1)

[Claims] 1. An exhaust gas purifying apparatus mounted on an exhaust system of a diesel engine, comprising: a first case having an oxidation catalyst therein, and an outer side of the first case, the first case being surrounded by the first case. Provided in a second case forming a bypass passage, a first passage communicating the exhaust gas inlet with the first case, a second passage communicating the exhaust gas inlet with the bypass passage, and the first passage First to be
Switching valve, a second switching valve provided in the second passage, a temperature sensor for detecting the temperature of the exhaust gas, and the control data of the first and second switching valves using the exhaust gas temperature data as input information. The controller for introducing the exhaust gas into the first case when the exhaust gas temperature is equal to or lower than the set value, and the exhaust gas into the bypass passage when the exhaust gas temperature is equal to or higher than the set value. Exhaust gas purification device for diesel engines that controls valves.