JPH0541215Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an exhaust gas purification device installed in the exhaust system of an internal combustion engine for automobiles, and is particularly applicable to exhaust gases of the type in which the catalytic converter is placed directly downstream of the exhaust manifold. Regarding gas purification equipment.

[Prior art] As a prior art related to the present invention,
Publication No. 163624 and Japanese Utility Model Application Publication No. 59-137318 are known.

In the exhaust purification device disclosed in the above-mentioned Japanese Utility Model Publication No. 58-163624, an expansion chamber is provided in the center of the exhaust manifold, and curved passages of the exhaust manifold are opened on the left and right sides. An oxygen sensor is installed in this expansion chamber, and the wall surface on the side where the oxygen sensor is installed is convex to the extension line of the curved passage into the expansion chamber. The lower end of the convex portion facing the upper surface of the catalyst is recessed so that a space for exhaust gas diffusion is formed between the convex portion and the upper surface of the catalyst.

With such a device, it is possible to improve the spread of exhaust gas flowing into the catalytic converter without impairing the exhaust gas contact with the oxygen sensor, and it is possible to effectively utilize the catalyst over the entire cross section. Become.

In the exhaust purification device disclosed in Japanese Utility Model Application Publication No. 59-137318, an adapter is interposed between an exhaust manifold and an exhaust pipe, and a catalytic converter having a monolith catalyst carrier inside is attached to the adapter.
The adapter has a gas inlet from the exhaust manifold and a gas outlet to the exhaust pipe which are separated from each other, and an outlet from the gas inlet and an outlet to the gas outlet in the middle. It has an opening with the gas inlet facing the same direction. on the other hand,
A catalytic converter having a monolithic catalyst carrier inside is installed in the opening of the adapter, and the catalytic converter has an inlet for exhaust gas from a gas inlet of the adapter at one end and a delivery of exhaust gas to a gas outlet of the adapter at one end. and an air chamber at the other end for inverting the exhaust gas that has passed through a portion of the monolithic catalyst carrier to the remaining portion of the monolithic catalyst carrier.

In such an exhaust purification device, one side of the monolithic catalyst carrier is used as a surface for both exhaust gas inflow from the adapter side and exhaust gas delivery to the adapter side, so that the gas flow to the monolithic catalyst carrier of the adapter is The area of the outlet does not need to be particularly widened, and the non-uniform distribution of exhaust gas flow caused by widening the inlet flow path to the monolithic catalyst carrier as in conventional devices is avoided.

In addition, the monolithic catalyst carrier is used by dividing the two parts corresponding to the inlet for exhaust gas from the adapter and the outlet for exhaust gas to the adapter into the forward and return paths of the exhaust gas, so that the exhaust gas and the catalyst are separated into two parts. The contact time with the exhaust gas is increased, improving the exhaust gas purification performance, and by reducing the cross-sectional area of the flow path, non-uniformity in the flow distribution of the exhaust gas passing therethrough can be suppressed. By equalizing the flow of these exhaust gases and using the monolithic catalyst carrier back and forth, the entire monolithic catalyst carrier can be used effectively.

[Problem to be solved by the invention] In order to improve the warm-up characteristics of the catalytic converter, it is advantageous to have the catalytic converter located immediately downstream of the exhaust manifold as described above. However, this structure shortens the distance between the catalytic converter and the combustion chamber, so the temperature of the catalyst becomes too high at high speeds.
To prevent thermal degradation of the catalyst, the following measures are required:

In other words, it is necessary to make the air-fuel ratio rich at high speeds to prevent the catalyst temperature from exceeding a certain value, or it is necessary to increase the exhaust manifold branch length or increase the volume of the exhaust manifold. Measures such as lowering the gas temperature are required. Therefore, problems arise in that the high-speed fuel ratio deteriorates due to the enrichment of the air-fuel ratio, and the weight of the vehicle increases as the weight of the exhaust manifold increases.

Additionally, the above structure has another problem. In other words, an oxygen sensor is installed in the exhaust manifold, but if the cross-sectional area of the flow path downstream of the exhaust manifold where the oxygen sensor is installed is simply ensured to be large, the flow velocity of exhaust gas will decrease and the feedback frequency will decrease. . When the flow rate of exhaust gas reaching the oxygen sensor decreases, feedback response becomes slow, exhaust gas purification cannot be well controlled, and it becomes difficult to reduce the level of harmful substances discharged.

The present invention focuses on the above problems and aims to provide an exhaust gas purification device that can improve fuel efficiency at high speeds, increase the feedback frequency, and improve exhaust gas purification performance. shall be.

[Means for solving the problem] The exhaust gas purification device of the present invention that meets this purpose has the following features:
In an exhaust gas purification device, a catalytic converter is disposed immediately downstream of an exhaust manifold, an oxygen sensor is disposed upstream of the catalytic converter, and the exhaust gas purification is controlled based on a feedback signal from the oxygen sensor. , the cross-sectional area of the flow path becomes smaller as it goes downstream, and a constriction part is formed that allows the exhaust gas flowing into the exhaust manifold to reach the oxygen sensor without reducing the flow velocity, and a catalytic converter is installed downstream of the constriction part. The cross-sectional area of the flow path gradually increases as it approaches the center.

[Function] In the exhaust gas purification device configured as described above, since the exhaust manifold is formed with a constriction part,
The exhaust gas that has flowed into the exhaust manifold reaches the oxygen sensor without reducing its flow rate. Therefore, the feedback frequency is higher than in the conventional structure in which the oxygen sensor is provided at a portion with a large cross section of the flow path, and the feedback response is accelerated.
Therefore, the controllability of the exhaust gas purification device is improved, and it becomes possible to reduce the emission level of harmful substances.

Furthermore, on the downstream side of the throttle part, an enlarged diameter part is formed where the cross-sectional area of the flow path gradually increases as it approaches the catalytic converter, so the flow velocity of exhaust gas slows down after the throttle part. , it becomes possible to lower the temperature of the exhaust gas flowing into the catalytic converter. Therefore, thermal deterioration of the catalyst at high speeds is suppressed, and deterioration of high speed fuel efficiency due to enrichment of the air-fuel ratio is prevented. That is, it becomes possible to make the air-fuel ratio leaner, and it is possible to improve fuel efficiency.

[Embodiments] Hereinafter, preferred embodiments of the exhaust gas purification device of the present invention will be described with reference to the drawings.

First Embodiment FIGS. 1 to 6 show a first embodiment of the present invention. In Figures 1 to 3, 1
1 shows an exhaust manifold attached to the cylinder head 10. This exhaust manifold 11
is for a four-cylinder engine, and has four branches 11a, each of which has an exhaust gas inlet 11b formed at its upstream end. A flange portion 11c for fixing the exhaust manifold 11 to the cylinder head 10 is formed at the upstream end of the branch 11a. In this embodiment, one flange portion 11c is provided for two branches 11a.
is formed. The downstream of each branch 11a is collected by a collection part 11d, and the exhaust gases flowing in from the exhaust gas inlet 11b are joined here.

On the downstream side of the gathering portion 11d, it extends downward, and a catalytic converter 12 is disposed at the end thereof. Inside the catalytic converter 12, a catalyst carrier 14 carrying a noble metal as a catalyst is housed. Gathering part 11 of exhaust manifold 11
d, the flow path cross-sectional area becomes smaller as it goes downstream, and the exhaust gas inlet 11 of the exhaust manifold 11
A constriction portion 11e is formed to guide the exhaust gas flowing into the portion b without reducing its flow velocity. Further, downstream of the constricted portion 11e, an enlarged diameter portion 11f is formed in which the cross-sectional area of the flow passage gradually increases as it approaches the catalytic converter 12. That is, the upper and downstream portions of the constricted portion 11e are formed in a cone shape (truncated cone shape), and the cross-sectional shape of the flow path in this portion is smoothly changed.

The throttle portion 11e is provided with an oxygen sensor 13 connected to an electronic control device (not shown).
The oxygen sensor 13 detects the oxygen concentration in the exhaust gas flowing through the exhaust manifold 11, and feeds back an electric signal corresponding to the concentration to the electronic control device. As described above, the exhaust gas that has flowed into the exhaust manifold reaches the oxygen sensor 13 without reducing the flow velocity.

Here, if the flow path cross-sectional area of the exhaust gas inlet 11b at the upstream end of each branch in the exhaust manifold 11 is A, and the flow path cross-sectional area of the throttle part 11e is B, the ratio of both surfaces is A:B=1: 1 to 1:2.5, that is, B/A is set to 1 to 2.5.

Further, the ratio of the flow passage cross-sectional area B of the throttle portion to the flow passage cross-sectional area C of the catalytic converter 12 is set to B:C=1:4 to 1:8, that is, C/B=4 to 8.

Next, the operation in the first embodiment will be explained.

Exhaust gas flowing out from the combustion chamber of each cylinder of the engine passes through each exhaust port in the cylinder head to each exhaust gas inlet 11b of the exhaust manifold 11.
and flows into each branch 11a. The exhaust gases that have flowed into each branch 11a join together at a collecting portion 11d and are guided to the catalytic converter 12. A constriction part 11e is formed in the gathering part 11d, and the cross-sectional area of the flow path becomes smaller as it goes downstream.Since the oxygen sensor 13 is provided in this constriction part 11e, each exhaust gas inlet The exhaust gas flowing into the oxygen sensor 13 passes through the oxygen sensor 13 without reducing the flow velocity.
is guided to the part where it is installed. In other words,
The ratio of the flow passage cross-sectional area A of the exhaust gas inlet 11b to the flow passage cross-sectional area B of the throttle part 11e is B/A=1 to
2.5, the gas flow velocity up to the constriction part 11e becomes faster, and the feedback frequency F becomes the fourth
It can be made large as shown in the figure.

As can be seen from Fig. 4, in the engine of this example, the B/A ratio starts to decrease from around 2.5, and by setting the B/A ratio within 1 to 2.5, the feedback frequency F can be greatly increased. is maintained, and a decrease in feedback responsiveness is prevented.

Figure 5 shows the relationship between the B/A ratio and the back pressure D. The smaller the B/A ratio, the higher the back pressure D, but when the ratio is around 2 to 3, the back pressure D decreases. However, the change in back pressure with respect to the change in B/A ratio is also reduced.

FIG. 6 shows the relationship between the ratio C/B of the flow passage cross-sectional area B of the throttle portion and the flow passage cross-sectional area C of the catalytic converter and the temperature drop of the exhaust gas. here,
Since the C/B ratio is between 4 and 8, the aperture section 11
In the process of flowing into the catalytic converter 12 from e,
The exhaust gas expands in proportion to the cross-sectional area of the flow path, and C/B
When the ratio value is around 8, the exhaust gas temperature T decreases significantly. Therefore, the temperature of the exhaust gas flowing into the catalytic converter 12 does not reach the level of thermal deterioration of the catalyst even at high speeds, and there is no need to reduce the temperature of the exhaust gas by enriching the air-fuel ratio. Fuel efficiency is improved.

Second Embodiment FIGS. 7 and 8 show a second embodiment of the present invention. The difference between the second embodiment and the first embodiment is the arrangement position of the catalytic converter, and other parts are similar to the first embodiment, so a description of the similar parts will be omitted and only the different parts will be described. The same applies to other embodiments to be described later.

7 and 8, a cylinder block 21 is located below the cylinder head 10, and an oil pan 22 is attached to the lower surface of the cylinder block 21. As shown in FIGS. A deep bottom portion 22a of the oil pump 22 is located directly below the auxiliary machinery 23 of the engine. In the vicinity of the shallow bottom part 22b of the oil pan 22, utilizing the dead space,
A catalytic converter 24 is provided. The catalytic converter 24 is a mixed flow type catalytic converter with a large gas inflow area, and is mounted horizontally so that the exhaust gas flows horizontally.

An oxygen sensor 13 is provided in a constricted portion 11e of the exhaust manifold 11, and a catalytic converter 24 is provided downstream of the constricted portion 11e, as in the first embodiment.
It forms a cone-shaped enlarged diameter portion 11f in which the flow passage cross-sectional area increases as it approaches. The catalytic converter 24 is held by a stay 25 fixed to the cylinder block 21. An exhaust pipe 26 is connected to the downstream end of the catalytic converter 24, and the exhaust pipe 26 passes under the shallow bottom portion 22b of the oil pan 22 and extends toward the rear of the vehicle.

Here, the radius of curvature R ₁ of the gathering part of the exhaust manifold 11 when viewed from the front (FIG. 7) direction is composed of a single or multiple circular arcs, and the radius is
It is 150-300mm. Also, the side (Fig. 8)
The radius of curvature R ₂ of the gathering portion of the exhaust manifold 11 when viewed from the direction is similarly 150 to 300 mm. Then, the exhaust gas inlet 11 of the exhaust manifold 11
The length l from b to the upstream end of the catalytic converter 24 is 500 to 700 mm.

In the second embodiment configured in this way,
The relationship between the length l of the exhaust manifold and the temperature of the exhaust gas flowing into the catalytic converter 24 is shown in FIG. In other words, as the length l of the exhaust manifold 11 increases, the temperature of the exhaust gas flowing into the catalytic converter 24 also decreases, but it is desirable that the temperature of the exhaust gas is in the range G between t ₁ and t ₂ °C. . Therefore, the length of the exhaust manifold 11 is
By setting it within 500 to 700 mm, the inlet temperature of exhaust gas can be kept low even under normal usage conditions, and thermal deterioration of the catalyst can be prevented.

Furthermore, since the exhaust manifold 11 has a smooth arc shape, flow path resistance is reduced and engine output is improved. Furthermore, by arranging the catalytic converter 24 as shown in FIG. 1, it is also possible to expand the degree of freedom in mounting auxiliary machinery. Other operations are similar to those in the first embodiment.

Third Embodiment FIG. 10 shows a third embodiment of the present invention. The configuration of this embodiment is substantially similar to the second embodiment, and the exhaust manifold 11 is formed almost symmetrically with the exhaust manifold 11 shown in FIG. In this case as well, the radius of curvature R ₃ of the gathering portion 11d of the exhaust manifold 11 when viewed from the front direction (FIG. 10) is composed of a single or multiple circular arcs as in FIG. 7, and the radius is 150~ It is 300mm. The radius of curvature when viewed from the side is also the same as in FIG. The operation of this embodiment is similar to that of the second embodiment, but
By making the shape of the exhaust manifold 11 symmetrical with respect to the second embodiment, the degree of freedom in the layout of auxiliary equipment and the like is further expanded.

Fourth Embodiment FIGS. 11 and 12 show a fourth embodiment of the present invention. This embodiment has almost the same structure as the second embodiment, and only the structure of the catalytic converter is different. In the second embodiment, the catalytic converter was of a mixed flow type, and the exhaust gas that entered from the upstream side of one catalyst carrier was discharged from the downstream side as it was, but in this embodiment, the exhaust gas was directly discharged from the downstream side. The exhaust gas is then discharged into the exhaust pipe.

That is, as shown in FIGS. 11 and 12, the catalytic converter 31 houses two catalyst carriers 32 and 33 made of, for example, a metal carrier, and each catalyst carrier 32 and 33 is separated by a partition. wall 30
It is divided by. The exhaust gas inflow surface of the catalyst carrier 32 and the exhaust gas discharge surface of the catalyst carrier 33 are located on the same plane.
The upstream side of is connected to the exhaust manifold 11. The downstream side of the catalyst carrier 32 and the upstream side of the catalyst carrier 33 are communicated with each other by an exhaust gas return section 34 . The downstream side of the catalyst carrier 33 is connected to an exhaust pipe 26 passing under the shallow bottom portion 22b of the oil pan 22. In other words, the exhaust gas that has flowed into the catalytic converter 31 is
2. The exhaust gas flows through the exhaust gas return section 34 and the catalyst carrier 33 in this order, and is discharged into the exhaust pipe 26. In this embodiment, the characteristics of the metal carrier are utilized to form a chamber in which the metal carrier is housed in a semicylindrical shape.

In the fourth embodiment configured in this way,
It becomes possible to locate the exhaust gas inflow portion and the exhaust gas outflow portion of the catalytic converter 31 at the same location, resulting in an advantageous structure in terms of space. Other operations are similar to those in the first embodiment.

13 and 14 show a modification of FIG. 12. In FIG. 12, two catalyst carriers are housed in one catalytic converter, but in this modification (FIG. 13), two catalytic converters 35,
36 is used, and each catalytic converter 35, 3
Catalyst carriers 37 and 38 made of ceramic as a base material, for example, are housed in the catalyst carriers 6, respectively. 14th
In the illustrated catalytic converter 45, one catalyst carrier 39 made of ceramic as a base material is mounted on the partition wall 40.
The structure is divided by Therefore,
A first passage 41 and a second passage 42 are formed in the catalyst carrier 39, and the exhaust gas that has passed through the first passage 41 flows into the second passage 42 via the exhaust gas return section 34. It is becoming more and more common.

[Effects of the invention] As explained above, when using the exhaust gas purification device of the invention, the cross-sectional area of the flow path becomes smaller as it goes downstream in the exhaust manifold, and the flow velocity of the exhaust gas flowing into the exhaust manifold is reduced. Since a constriction portion is formed that allows the oxygen to reach the oxygen sensor without deterioration, the feedback frequency can be increased compared to the conventional structure, and the feedback response is accelerated. Therefore, the controllability of the exhaust gas purification device is improved, and the emission level of harmful substances can be reduced. Moreover, this also makes it possible to reduce the amount of noble metal supported on the carrier of the catalytic converter, thereby realizing cost reduction of the catalytic converter.

In addition, an enlarged diameter section is formed downstream of the throttle section, where the cross-sectional area of the flow path gradually increases as it approaches the catalytic converter, so the flow velocity of exhaust gas slows down after the throttle section. , the temperature of the exhaust gas flowing into the catalytic converter can be reduced. As a result, thermal deterioration of the catalyst at high speeds is suppressed, preventing deterioration of high speed fuel efficiency due to enrichment of the air-fuel ratio, and improving fuel efficiency.

Further, by gradually increasing the flow passage cross-sectional area of the enlarged diameter portion, rapid expansion of exhaust gas can be suppressed, and noise caused by this can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a front view of an exhaust gas purification device according to a first embodiment of the present invention, FIG. 2 is a sectional view taken along line - in FIG. 1, and FIG. 3 is a sectional view taken along line - line in FIG. Fig. 4 is a characteristic diagram showing the relationship between the ratio of the exhaust gas flow passage cross-sectional area and the feedback frequency in the apparatus shown in Fig. 1, and Fig. 5 is a characteristic diagram showing the relationship between the ratio of the exhaust gas flow passage cross-sectional area and the feedback frequency in the apparatus shown in Fig. 1. A characteristic diagram showing the relationship between
FIG. 6 is a characteristic diagram showing the relationship between the exhaust gas flow path area ratio and exhaust gas temperature in the device shown in FIG. 1, and FIG. 7 is a front view of the exhaust gas purification device according to the second embodiment of the present invention. , Fig. 8 is a side view of the device shown in Fig. 7, Fig. 9 is a characteristic diagram showing the relationship between the length of the exhaust manifold and the temperature of the exhaust gas flowing into the catalytic converter in the device shown in Fig. 7, and Fig. 10. is the third part of this invention
Front view of the exhaust gas purification device according to the example, No. 11
The figure is a front view of an exhaust gas purification device according to the fourth embodiment of the present invention, FIG. 12 is a cross-sectional view taken along the - line in FIG. 11, and FIGS. 13 and 14 show each modification of FIG. FIG. 10... Cylinder head, 11... Exhaust manifold, 11a... Branch, 11b... Exhaust gas inlet, 11d... Collection part, 11e... Throttle part,
11f... Expanded diameter part, 12, 24, 35, 36, 4
5...Catalytic converter, 13...Oxygen sensor, A
...Cross-sectional area of the exhaust gas inlet, B...Cross-sectional area of the throttle, C...Cross-sectional area of the catalytic converter.

Claims (1)

[Scope of utility model registration request] In an exhaust gas purification device, a catalytic converter is disposed immediately downstream of an exhaust manifold, an oxygen sensor is disposed upstream of the catalytic converter, and the exhaust gas purification is controlled based on a feedback signal from the oxygen sensor. , the cross-sectional area of the flow path becomes smaller as it goes downstream, and a constriction part is formed that allows the exhaust gas flowing into the exhaust manifold to reach the oxygen sensor without reducing the flow velocity, and a catalytic converter is installed downstream of the constriction part. 1. An exhaust gas purification device characterized by forming an enlarged diameter portion in which the cross-sectional area of the passage gradually increases as it approaches the exhaust gas purifier.