JPH03281929A - Exhaust system of engine - Google Patents

Abstract

PURPOSE:To control temperature of a catalyst in all driving ranges and improve scavenge efficiency by connecting cylinders of an engine with a catalyst device through plural exhaust passages in various length in parallel, for example, guiding exhaust gas into a short exhaust passage in a small intake air amount range. CONSTITUTION:Exhaust passages 3 are connected to respective cylinders 1 formed in respective banks L, R respectively, and there are provided catalysts 4 in the exhaust passages 3 as a catalyst device in an engine. With this constitution, there are provided the first exhaust passages 6 and the second exhaust passages 7 whose one end is connected to a collecting exhaust passage 5 and the other end is connected to the catalyst 4 in the exhaust passages 3. Besides, the first exhaust passages 6 are set short in a straight shape, and the second exhaust passages 7 are set into long in a U-shape. Moreover, collecting parts of collecting exhaust passages 5, the first exhaust passages 6, and the second exhaust passages 7 are provided with switch valves 9. Then the switch valves 9 are operated so that exhaust gas may be guided into the first short exhaust passages 6 in a small intake air amount range, and exhaust gas may be guided into the second long exhaust passages 7 in a large intake air amount range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in an exhaust system for an engine equipped with a catalyst device in an exhaust passage.

(Prior Art) Conventionally, as an engine exhaust system, for example, the
As disclosed in Japanese Patent No. 10052, there is known an engine in which an exhaust passage is connected to an exhaust port of an engine cylinder, and a catalyst device is provided in this exhaust passage, so that the catalyst device purifies exhaust gas. .

(Problem to be solved by the invention) In such an engine, the flow rate of exhaust gas is small in the low intake air amount range, so the temperature of the catalyst device does not rise sufficiently and activation is insufficient, resulting in exhaust gas There is a dislike that purification cannot be carried out properly. On the other hand, in a high intake air amount region, the flow rate of exhaust gas is large, so the catalyst device becomes a resistance, reducing the scavenging efficiency of the engine, and the temperature of the catalyst device increases too much, which tends to cause its deterioration.

The present invention has been made with attention to these points,
The purpose is to make the length of the exhaust passage variable to improve temperature control of the catalyst device and scavenging efficiency over the entire operating range of the engine.

(Means for Solving the Problems) In order to achieve the above object, the solving means of the present invention connects the cylinders of the engine and the catalyst device in parallel through a plurality of exhaust passages having different lengths. In this case, the exhaust gas is guided to a short exhaust passage, and in the case of a high intake air installation, a switching means is provided to guide the exhaust gas to a long exhaust passage.

(Function) With the above configuration, in the present invention, exhaust gas from the cylinder is guided to the catalyst device through a short exhaust passage in a low intake air amount region, so that the temperature of the exhaust gas from the cylinder is not significantly reduced. The exhaust gas enters the catalyst device, and the temperature of the catalyst device rises sufficiently to be fully activated, thereby effectively purifying the exhaust gas.

On the other hand, in a high intake air amount region, the exhaust gas from the cylinder is guided to the catalyst device via a long exhaust passage, so the catalyst device is used as a volume chamber to create a resonance effect according to the length of the exhaust passage, and scavenge the engine. Increased efficiency. Furthermore, since the distance from the cylinder to the catalyst device is long and the temperature of the exhaust gas decreases during this distance, the temperature rise of the catalyst device is suppressed and its deterioration is prevented.

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

1 to 3 show a six-cylinder engine equipped with an exhaust system according to an eleventh embodiment of the present invention. As shown in FIG. 1, this engine has a left bank L and a right bank R.
Three cylinder cores are formed in each bank L and H, respectively. An intake passage 2 is provided between banks L and R. The intake passage 2 has one end open to the atmosphere and the other end connected to each cylinder 1 to supply fresh air to each cylinder 1.

Further, an exhaust passage 3 is connected to each cylinder 1 for each bank. A catalyst 4 as a catalyst device is provided in the exhaust passage 3 to purify the exhaust gas.

The exhaust passage 3 includes a collective exhaust passage 5 whose one end is connected to each cylinder 1 and whose other end is collected into one, and a first exhaust passage 5 whose one end is connected to the collective exhaust passage 5 and the other end is connected to the catalyst 4. It consists of an exhaust passage 6, a second exhaust passage 7, and a downstream exhaust passage 8 whose one end is connected to the catalyst 4 and whose other end is gathered at left and right banks. And the first exhaust passage 6
is set in a short straight line, and the second exhaust passage 7 is set in a long U-shape. Specifically, the catalyst 4 is used as a volume chamber, and the tuned rotational speed of the resonance effect obtained by the collective exhaust passage 5 and the second exhaust passage 7 is set as N1,
Let N2 be the tuned rotation speed of the resonance effect obtained by the collective exhaust passage 5 and the first exhaust passage 6, and let N2 be the maximum allowable rotation speed.
max, Nmax< (3/2)N1. It is set so that Nmax<N2 is satisfied. Further, the catalyst side gathering portion of the first exhaust passage 6 and the second exhaust passage 7 is formed in a volume chamber having a predetermined volume.

Further, a switching valve 9 is provided at a meeting point of the collective exhaust passage 5, the first exhaust passage 6, and the second exhaust passage 7. This switching valve 9 is controlled by a control unit (not shown). Data such as intake air flow rate and engine speed are input to this control unit.
The switching valve 9 is operated so as to guide the exhaust gas to the exhaust passage 6, and in the high intake air amount region, to guide the exhaust gas to the long second exhaust passage 7 as shown in FIG.

Therefore, in the above embodiment, in the low intake air amount region, the exhaust gas from the cylinder 1 is guided to the catalyst 4 via the short first exhaust passage 6, so the temperature of the exhaust gas from the cylinder 1 is not much lowered and Therefore, the temperature of the catalyst 4 rises sufficiently and becomes sufficiently activated, and the exhaust gas is effectively purified.

On the other hand, in a high intake air amount region, the exhaust gas from the cylinder 1 is guided to the catalyst 4 via the long second exhaust passage 7, so that the catalyst 4 is used as a volume chamber and a resonance effect corresponding to the length of the exhaust passage is obtained. This improves engine scavenging efficiency. In addition, the distance from the cylinder to the catalyst 4 is long, and the temperature of the exhaust gas decreases during this time, so the temperature rise of the catalyst 4 is suppressed and its deterioration can be prevented.

(Second Embodiment) FIG. 4 shows a second embodiment. In this second embodiment, a long second exhaust passage 7 is connected to the catalysts 4 of the other banks L and R. This makes it possible to reduce the bending of the second exhaust passage 7 and reduce exhaust resistance.

(Third Embodiment) FIG. 5 shows a third embodiment. In this third embodiment, the second exhaust passages configured as in the second embodiment are communicated with each other by a communication passage 20 at a midway portion thereof, and an on-off valve 21 is provided in this communication passage 20. That is, by opening the on-off valve 21, the tuned rotational speed of the resonance effect changes, and the scavenging effect can be brought out even more effectively in accordance with the engine rotational speed.

(Fourth Embodiment) FIGS. 6 to 8 show a fourth embodiment. In this fourth embodiment, in an exhaust system configured as in the second embodiment,
The first exhaust passage 6 and the switching valve 9 of the right bank R are not provided,
The right bank R is always connected to the catalyst 4 via the long second exhaust passage 7. That is, in the low intake air amount region and during cold conditions, the switching valve 9 is closed as shown in FIG.
By opening the first exhaust passage 6 of the left bank L and closing the second exhaust passage 7, exhaust gas from all cylinders 1 is guided to the catalyst 4 of the left bank L.
As shown in the figure, by closing the first exhaust passage 6 of the left bank L and opening the second exhaust passage 7 using the switching valve 9, exhaust gas from each bank L and R is directed to the catalyst 4 of each bank L and R. I am trying to guide each of them.

Therefore, in this fourth embodiment, in the low intake air amount range and during cold conditions, the exhaust gas from all cylinders 1 is concentrated and guided to the catalyst 4 in the left bank L, so that the temperature of the catalyst 4 is maintained at a sufficient temperature. It rises and becomes fully activated, and exhaust gas purification is performed well.

On the other hand, in the high intake air amount region, the exhaust gas is dispersed to the two catalysts 4 and guided to the catalyst 4 via the long second exhaust passage 7, so that the engine scavenging efficiency is improved due to the resonance effect and the catalyst deteriorates. Prevention and effectiveness can be increased.

Furthermore, in this fourth embodiment, 02 sensors 22 are provided at three locations to detect the oxygen concentration in the exhaust gas and to detect the air-fuel ratio. One is upstream of the catalyst 4 in the left bank L, and the other is downstream of the gathering part in the downstream exhaust passage 8. With this arrangement, the air-fuel ratio can be detected with high accuracy in either the low intake air amount region or the high intake air amount region.

(Fifth Example) FIGS. 9 and 10 show a fifth example. In this fifth embodiment, in the exhaust system configured as in the second embodiment, the first exhaust passage 6 and the switching valve 9 of the left bank L are not provided, and the long second exhaust passage 7 is always provided for the left bank. It is connected to the catalyst 4 via. Furthermore, a third exhaust passage 7 is located directly upstream of the catalyst in the left bank L.
An exhaust passage 23 is connected thereto, and the third exhaust passage 23 is connected to the downstream side of the gathering portion of the downstream exhaust passage 8 . This downstream exhaust passage 8 and the third exhaust passage 2
A second switching valve 24 is provided at the connection portion with 3. That is, in the low intake air amount region and during cold conditions, as shown in FIG.
4 closes the downstream side of the collecting part in the downstream exhaust passage 8 and opens the third exhaust passage 23, so that exhaust gas from all cylinders 1 is first guided to the catalyst 4 in the right bank R and then to the left bank L. In the high intake air amount region, as shown in FIG. 10, the switching valve 9 closes the first exhaust passage 6 of the right bank R and opens the second exhaust passage 7, and the second switching valve 24 opens the downstream side of the collecting part in the downstream side exhaust passage 8 and closes the third exhaust passage 23, thereby transferring exhaust gas from each bank L and H to each bank L.
, R's Catalyst 4.

This fifth embodiment also provides the same functions and effects as the fourth embodiment.

(Sixth Embodiment) FIGS. 11 to 13 show a sixth embodiment. In this sixth embodiment, in the exhaust system configured as in the fourth embodiment, a resonance container 25 is provided at a position corresponding to the catalyst 4 in the right bank R, and further downstream of the gathering part in the downstream exhaust passage 8. Catalyst 4 is installed in That is, in each of the previous embodiments, the catalyst 4 was made to function as a volume chamber, and the pressure wave of the exhaust gas was reversed by the catalyst 4, but in this sixth embodiment, the resonance vessel 2
5 inverts the exhaust pressure wave. With this configuration, in the low intake air amount range and during cold conditions, as shown in FIG. 12, the exhaust gas from all cylinders 1 is guided to the catalyst 4 in the left bank L, as in the fourth embodiment In the high intake air amount region, as shown in FIG. I am trying to lead to Catalyst 4.

This sixth embodiment also provides the same functions and effects as those of the fourth embodiment. Moreover, in the high intake air amount range, the exhaust gas in the left bank L is far away from the cylinder
Since the exhaust gas temperature is lowered, the effect of preventing deterioration of the catalyst 4 is increased.

In this sixth embodiment, 02 sensors 22 are provided in the exhaust passages upstream of each catalyst.

(Seventh Embodiment) FIG. 4 shows a seventh embodiment. In this seventh embodiment, in the exhaust system configured as in the first embodiment, the first exhaust passage 6 of the left bank L, the switching valve 9 and the catalyst 4 are not provided, and the collecting part in the downstream exhaust passage 8 is A catalyst 4 is also provided on the downstream side, and the second exhaust passage 7 of the right bank R is connected to the downstream exhaust passage 8 of the left bank L. In this case, for the right bank R, the same operation and effect as in the first embodiment can be obtained.

(Eighth Example) FIG. 15 shows an eighth example. In this eighth embodiment, compared to the exhaust system configured as in the first embodiment, both the left and right banks L and R are not provided with the first exhaust passage 6 and the switching valve 9, and the left bank L is equipped with a catalyst 4. is not provided,
A catalyst 4 is provided downstream of the gathering portion in the downstream exhaust passage 8. That is, the exhaust gas from cylinder 1 of left bank L passes through two catalysts 4,
Exhaust gas from the cylinder 1 of the right bank R passes through one catalyst 4. In that case, the distance from the cylinder 1 to the upstream catalyst 4 in the left bank L is set shorter than the distance from the cylinder 1 to the catalyst 4 in the right bank R. Furthermore, the distance from the cylinder 1 to the downstream catalyst 4 is set to be the same for the left and right banks L and R. Furthermore, in the left bank ■7 near the catalyst 4, the air-fuel ratio is set rich at high speed and high load to protect the catalysts 1-4.

In the eighth embodiment, while obtaining the same functions and effects as in the eighth embodiment, unlike the fixed structural member, the switching valve 9, which is vulnerable to heat loads, is not provided, so even if the heat load is applied, the exhaust gas is removed. Equipment reliability is maintained high.

(Ninth Embodiment) FIGS. 16 to 18 show a ninth embodiment. This ninth embodiment is characterized by the control of the control unit. In other words, the map shown in FIG. 16 is a basic control map, and the first exhaust passage 6 is connected to the lower load side of the line connecting low speed, high load and high speed, low load as a boundary, and the map shown in FIG. The second exhaust passage 7 is controlled to communicate with the second exhaust passage 7 on the side.

Furthermore, the map shown in FIG. 17 is a control map that takes cold times into consideration, and with respect to the above-mentioned basic control map, the boundary line is set closer to the high speed and high load side during cold times than during warm times. As a result, the temperature of the catalyst 4 rises sufficiently during cold periods when the exhaust gas temperature is low, and the catalyst 4 is sufficiently activated.
Exhaust gas is effectively purified.

Furthermore, the map shown in FIG. 18 does not selectively connect the first exhaust passage 6 and the second exhaust passage 7 as in the previous embodiments, but rather an operating region in which no resonance effect of exhaust gas is expected. (For example, in a medium speed and medium load region), both the first exhaust passage 6 and the second exhaust passage 7 are communicated with each other to reduce exhaust resistance.

(Tenth embodiment) Figures 19 and 20 show a tenth embodiment. This 10th
The embodiment is characterized by the connection structure between the first exhaust passage 6 and the second exhaust passage 7 to the catalyst 4. That is, the 19th
As shown in the figure, the shape of the connecting end of the first exhaust passage 6 is formed to be wider and smoother than the shape of the connecting end of the second exhaust passage 7. As a result, the exhaust gas is diffused throughout the catalyst when the first exhaust passage 6 is in communication, and the exhaust gas purification function is enhanced. FIG. 20 shows a modification thereof and has the same operation and effect.

(Eleventh Embodiment) FIGS. 21 to 22 show an eleventh embodiment. This 11th
In the embodiment, only the first exhaust passage 6 is covered with a heat insulating cover 26. As a result, the exhaust gas is kept at a high temperature when the first exhaust passage 6 is in communication, and the purification function of the exhaust gas is enhanced. FIG. 21 shows an example of application to the first embodiment, and FIG. 22 shows an example of application to the second embodiment.

(Effects of the Invention) As explained above, according to the engine exhaust system of the present invention, the engine cylinder and the catalyst device are connected in parallel through a plurality of exhaust passages having different lengths, and in the low intake air amount region, the engine cylinder and the catalyst device are connected in parallel. We have provided a switching means to guide exhaust gas to a short exhaust passage, and to guide exhaust gas to a long exhaust passage in a high intake air volume range, so that the temperature of the catalyst device can be sufficiently raised in a low intake air volume range to improve exhaust gas purification performance. In addition, it is possible to improve engine scavenging efficiency and prevent deterioration of the catalyst device due to the resonance effect in a high intake air amount region.

[Brief explanation of the drawing]

Figures 1 to 3 show a first embodiment of the present invention, with Figure 1 being a general schematic diagram, Figure 2 being an explanatory diagram of operation in a low intake air amount region, and Figure 3 being a high intake air amount. FIG. FIG. 4 is a diagram corresponding to FIG. 1 showing a second embodiment of the present invention. FIG. 5 is a diagram corresponding to FIG. 1 showing a third embodiment of the present invention. 6 to 8 show a fourth embodiment of the present invention, FIG. 6 is a general schematic diagram, FIG. 7 is an explanatory diagram of operation in a low intake air amount region, and FIG. 8 is a high intake air amount. FIG. 9 and 10 show a fifth embodiment of the present invention, FIG. 9 is an explanatory diagram of the operation in a low intake air amount region, and FIG. 10 is an explanatory diagram of the operation in a high intake air amount region. 11 to 13 show a sixth embodiment of the present invention, in which FIG. 11 is a general schematic diagram, FIG. 12 is an explanatory diagram of operation in a low intake air amount region, and FIG.
The figure is an explanatory diagram of operation in a high intake air amount region. FIG. 14 is a diagram corresponding to FIG. 1 showing a seventh embodiment of the present invention. 15th
The figure is a diagram corresponding to FIG. 1 showing an eighth embodiment of the present invention. 16 to 18 are map diagrams showing a ninth embodiment of the present invention. 19 and 20 are enlarged sectional views of essential parts showing a tenth embodiment of the present invention. Figures 21 and 22
The figure is a diagram corresponding to FIG. 1 showing an eleventh embodiment of the present invention. 3...Exhaust passage 4...Catalyst 6...First exhaust passage 7...Second exhaust passage 9...Switching valve Fig. 4 Fig. 10 Fig. 9 Fig. 8 Fig. 6 Figure Figure Figure 13 Figure 11 Figure 12 Figure \L *14fi! ff 15th Artwork〉Science〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉〉Fig.

Claims (1)

[Claims] (1) Engine cylinders and catalytic converters are connected in parallel through multiple exhaust passages of different lengths, and in low intake air volume ranges, exhaust gas is led to short exhaust passages, and in high intake air volume ranges, exhaust gas is guided to long exhaust passages. An engine exhaust system characterized by being provided with a switching means leading to an exhaust passage.