JP2548499Y2 - Exhaust gas purification device for internal combustion engine - Google Patents

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 for an internal combustion engine, and more particularly to a technique for controlling an exhaust gas purifying catalyst to an optimum temperature.

[0002]

2. Description of the Related Art Conventionally, purification has been carried out from problems of three components (CO, HC, NOx) discharged from an internal combustion engine and environmental pollution, and various measures have been taken. For example, a three-way catalyst system for a gasoline vehicle uses a three-way catalyst for purifying three components (CO, HC, NOx) in exhaust gas into N ₂ , CO ₂ , and H ₂ O. Since the three-way catalyst works most effectively on the exhaust gas when the is burned near the stoichiometric air-fuel ratio, the state (the stoichiometric air-fuel ratio)
The engine is controlled by the air-fuel ratio feedback system.

[0003] In recent years, exhaust gas purifiers using catalysts have also been used in diesel engines in order to reduce unburned substances such as particulates in exhaust gas (see Japanese Patent Application Laid-Open No. 254251/1990).

[0004]

By the way, in the catalyst in the exhaust gas purifying apparatus for a diesel engine as described above, the purifying action of the exhaust gas changes depending on the temperature of the exhaust gas. For example, if the exhaust gas temperature is low, unburned substances cannot be purified, and if it is too high, the SO ₂ in the exhaust gas
As a result, the amount of sulfate increases.

[0005] Figure 8 is a characteristic diagram showing the relationship between exhaust gas temperature and the purification performance and sulfates of the catalyst inlet, it can not be purified in the purification starting temperature T ₁ of less, by the sulphate product temperature T ₂ above, sulphates amount It can be seen that increases. Heretofore, as a regenerating device for a particulate trap, there has been known a device for heating exhaust gas using a heating means such as a burner or a heater (Japanese Utility Model Application Laid-Open No. 62-184).
No. 126, etc.).

Therefore, it is conceivable to heat the exhaust gas at a low temperature of the exhaust gas by using the heating device in the above-mentioned purifying apparatus. However, since a burner or a heater is used, an energy source is required. However, there is a drawback that the driving fuel efficiency is also deteriorated. Further, when the exhaust gas is at a high temperature, the exhaust gas cannot be cooled.

In view of the above-mentioned conventional problems, the present invention has a simple structure in which a heat exchanger made of a low melting point metal as a heat storage material is interposed in an exhaust passage, so that the exhaust gas purifying action of the catalyst can be improved. An object of the present invention is to maintain exhaust gas at an optimum temperature which is good and has a small amount of sulfate.

[0008]

SUMMARY OF THE INVENTION Therefore, the present invention provides an exhaust gas purifying apparatus for an internal combustion engine having a catalyst for purifying exhaust gas in an exhaust passage. Is provided with a low melting point metal as a regenerator for cooling and solidifying at a predetermined low temperature to heat the exhaust gas, and the mutual heat exchange action between the low melting point metal and the exhaust gas to heat the exhaust gas. A configuration in which a heat exchanger for selectively performing cooling is interposed on a catalyst upstream side of an exhaust passage, wherein the low-melting-point metal is filled in a case provided in a main body of the heat exchanger, When a predetermined space is formed in the case in the charged state, the exhaust gas purification start temperature is T ₁ , the sulfate generation temperature is T ₂ , and the melting point of the low melting point metal is T _mp ,
T ₁ <was the relationship of T _mp <T _2.

[0009]

In such a configuration, the exhaust gas discharged from the internal combustion engine is discharged to the outside through the exhaust passage, and when passing through the exhaust passage, contacts the heat exchanger and the catalyst in this order.
Here, the heat storage body filled in the heat exchanger case is made of a low melting point metal that melts at a predetermined temperature to cool the exhaust gas and solidifies at a predetermined temperature to heat the exhaust gas. When the temperature of the exhaust gas increases, the low melting point metal dissolves, and the heat of melting at that time is taken from the exhaust gas. For this reason,
The temperature of the exhaust gas decreases. On the other hand, when the temperature of the exhaust gas decreases, the low melting point metal solidifies, and the heat of solidification at that time is released to the exhaust gas. Therefore, the temperature of the exhaust gas increases.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompanying drawings. In FIG. 1, an exhaust pipe 2 constituting an exhaust passage of an internal combustion engine 1 is provided with a catalyst device 4 filled with a catalyst 3 for purifying exhaust gas. On the upstream side of the catalyst device 4 of the exhaust pipe 2, a low-melting metal as a heat storage body that melts at a predetermined high temperature to cool the exhaust gas and solidifies at a predetermined low temperature to heat the exhaust gas is provided. A heat exchanger 9 for selectively heating and cooling the exhaust gas by a mutual heat exchange action between the low-melting metal and the exhaust gas; A heat exchanger 6 for selectively heating and cooling the exhaust gas is interposed by the exchange action.

Here, the heat storage body has a melting point of 150 to 300.
° C low melting point metal 10, such as tin with a melting point of 232 ° C, indium at 156 ° C, selenium at 217 ° C,
It consists of bismuth at 71 ° C and lithium at 180 ° C.
As shown in FIG. 1, the low-melting metal 10 is filled in a case 11 in advance, and is disposed in a housing 12 as a main body of a heat exchanger 9 which is interposed in the exhaust pipe 2 on the upstream side of the catalyst 3. I do.

In this case, as shown in FIGS. 3 to 5, a large number of pipes 13 are arranged along a central axis direction in a case 11, which is formed in a cylindrical, rectangular or elliptical cylindrical shape. Each tube 13
Are supported on both end walls of the case 11 and are opened at the both end surfaces. The case 11 is disposed in the housing 12 such that one end face of the case 11 faces the exhaust gas inlet 12a of the housing 12 and the other end face faces the exhaust gas outlet 12b of the housing 12. And hold it.

As shown in the figure, a predetermined space 14 is formed in the case 11 in a state where the low melting point metal 10 is filled in the case 11. The space 14 is evacuated or filled with a gas such as air or nitrogen. A heat insulating material 15 is mounted on the outer peripheral surface of the case 11. Next, the operation of such a configuration will be described.

Exhaust gas discharged from the internal combustion engine 1 is discharged to the outside via an exhaust pipe 2, and when passing through the exhaust pipe 2, contacts the low melting point metal 10 and the catalyst 3 in this order. When the exhaust gas passes through the heat exchanger 9, the exhaust gas flows from the exhaust gas inlet 12 a of the housing 12 into the respective pipes 13 through the openings of the respective pipes 13 at the front end face of the case 11, and the respective pipes at the rear end face of the case 11. Exhaust gas outlet 1 of housing 12 from opening 13
2b.

Here, when the temperature of the exhaust gas increases, the low melting point metal 10 is melted, and the heat of melting at that time is taken from the exhaust gas. For this reason, the temperature of the exhaust gas decreases. on the other hand,
When the temperature of the exhaust gas decreases, the low melting point metal 10 solidifies, and the heat of solidification at that time is released to the exhaust gas. Therefore, the temperature of the exhaust gas increases. Therefore, by repeating such an operation, the temperature of the exhaust gas is reduced to a temperature near the melting point _Tmp of the low melting point metal 10 (for example, 232 ° for tin).
C), and can always be maintained at an optimum temperature for the catalyst 3, that is, a temperature at which the purifying action of the catalyst 3 is high and the amount of sulfate is small.

[0016] Figure 6 is a characteristic diagram showing the transition of the exhaust gas catalyst 3 inlet over time during actual running of the vehicle, in the conventional purification starting temperature T ₁ of less and sulfate product that can not purify the unburnt Although resulting in temperature T ₂ more temperature shifts, according to the present invention, the temperature of the catalyst 3 inlet T ₁ and T ₂
It is clear that the temperature of the exhaust gas can always be maintained at the optimum temperature for the catalyst 3, so that T ₁ <T _mp <T ₂ .
By selecting the low melting point metal 10, the optimal control of the temperature of the exhaust gas can be performed more reliably.

In the above configuration, when the case 11 is filled with the low melting point metal 10,
Since a predetermined space portion 14 is formed in 1,
The case 11 can be prevented from being damaged by expansion due to a rise in temperature of the low melting point metal 10, and leakage of the low melting point metal 10 to the outside can be effectively prevented. FIG. 7 shows another embodiment in which the low-melting point metal 10 is employed as a heat storage body. A heat transfer fin 16 for promoting a heat effect is provided on a part of the outer peripheral surface of the exhaust pipe 2. A case 17 surrounding a part of the outer peripheral surface of the provided exhaust pipe 2 through a space is provided.
7 is filled with a low melting point metal 10. In this case, Case 1
7 is filled with the low melting point metal 10 so that a predetermined space 18 is formed in the case 17 and the space 18 is evacuated or filled with a gas such as air or nitrogen. deep. Further, a heat insulating material 19 is mounted on the outer peripheral surface of the case 17.

Also in this embodiment, the temperature of the exhaust gas can be maintained at a temperature near the melting point _Tmp of the low-melting metal 10, and the temperature of the catalyst 3 can always be maintained at an optimum temperature. As described above, the present invention has been described with reference to the specific embodiments. However, the present invention is not limited to the embodiments, and may be implemented by a person skilled in the technical field attached to the present invention. It should be noted that various changes and modifications can be made without departing from the scope of the claims.

[0019]

As described above, the present invention provides a heat exchanger for selectively heating and cooling the exhaust gas by the mutual heat exchange between the low melting point metal as the heat storage element and the exhaust gas. , Because it is interposed on the upstream side of the catalyst in the exhaust passage,
The temperature of the exhaust gas can be constantly maintained at the optimum temperature for the catalyst, the amount of sulfate can be kept small, and the action of purifying the unburned substances can be improved. There is an advantage that does not occur, in particular, according to the present invention, it is possible to maintain the temperature of the catalyst inlet exhaust gas purification starting temperature T ₁ of the temperature in the region of the sulfate product temperature T _2, the temperature of the exhaust gas It is clear that the optimum temperature for the catalyst can be maintained at all times, and by selecting the low melting point metal so that T ₁ <T _mp <T ₂ , the optimum control of the exhaust gas temperature can be more reliably performed. There is an advantage that the predetermined space can be formed in the case of the heat exchanger when the low melting point metal is filled in the case. The case can be prevented from being damaged by the tension, and leakage of the low melting point metal to the outside can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of an exhaust gas purification device for an internal combustion engine according to the present invention.

FIG. 2 is a cross-sectional view of the heat exchanger in the embodiment.

FIG. 3 is a sectional view taken along the line AA in FIG. 2;

FIG. 4 is a sectional view taken along the line AA in FIG. 2;

FIG. 5 is a sectional view taken along the line AA in FIG. 2;

FIG. 6 is a characteristic diagram showing a change in exhaust gas at a catalyst inlet with time.

FIG. 7 is a cross-sectional view of a heat exchanger according to still another embodiment.

FIG. 8 is a characteristic diagram showing the relationship between the exhaust gas temperature at the catalyst inlet, the purification performance, and the amount of sulfate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust pipe 3 Catalyst 9 Heat exchanger 10 Low melting metal 11 Case 12 Housing

Claims (1)

(57) [Scope of request for utility model registration] In an exhaust gas purifying apparatus for an internal combustion engine having a catalyst for purifying exhaust gas in an exhaust passage, the exhaust gas is cooled at a predetermined high temperature to cool the exhaust gas and a predetermined low temperature.
Low melting as heat storage material that solidifies at temperature and heats exhaust gas
It includes a point metal, by mutual heat exchange action between the low melting point metal with the exhaust gas, a heat exchanger for cooling and heating of the exhaust gas selectively, and interposed in the catalyst upstream of the exhaust passage structure so
There, the low melting point metal is disposed within the body of the heat exchanger
The case is filled, and a predetermined empty space is filled in the case in the filled state.
While the gap is formed, the exhaust gas purification start temperature is set to T ₁ , and the sulfate formation temperature is set to
T _2, when the melting point of the low melting metal was T _mp, T ₁ <T _mp
<Exhaust gas purification device for an internal combustion engine, characterized in that a relation of T _2.