JPH08210130A - Exhaust manifold for internal combustion engine - Google Patents

Abstract

PURPOSE: To provide an exhaust manifold having an outer circumferential wall section where a tensile stress is generated at least when the engine is in operation, wherein the outer circumferential wall is precluded from crack generation despite eventual generation of tensile stress by furnishing a compressive stress applying means which gives compressive stress to the wall periodically. CONSTITUTION: When engine operation is started, the temp. of an exhaust manifold 1 heightens, but the temps. of bosses 6, 8, 10 rise slowly compared with the temp. of the manifold 1, and the temps. of bridging members 11, 12 rise still more slowly. Accordingly the temps. of the bridging members 11, 12 remain less high even though the temp. of the manifold 1 heightens, and the amount of thermal expansion becomes smaller than that of the manifold 1. This causes generation of a compressive stress in the manifold 1 to result in a rise of the temps. of the bridging members 11, 12, so that a tensile stress is again generated in the exhaust manifold 1. Thus micro-cracks generated when tensile stress is applied are corrected by this compressive stress, and the outer circumferential wall of the manifold 1 is precluded from crack initiation.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an exhaust manifold for an internal combustion engine.

[0002]

2. Description of the Related Art An exhaust manifold comprises a plurality of branch pipes fixed to an engine body and a branch pipe collecting portion where the branch pipes are assembled with each other. In such an exhaust manifold, there are a high temperature portion and a low temperature portion, so that a considerable difference occurs in the thermal expansion amount in the exhaust manifold. If there is a difference in the amount of thermal expansion as described above, a large compressive thermal stress or tensile thermal stress is locally generated in the wall surface of the exhaust manifold, which causes cracks. In this case, the region where the compressive thermal stress occurs or the region where the tensile thermal stress occurs varies depending on the structure of the exhaust manifold.

Therefore, in order to reduce such compressive thermal stress or tensile thermal stress, the thickness of the pipe wall of the exhaust manifold is gradually increased from the exhaust gas inlet side toward the exhaust gas outlet side. Is known (see Japanese Utility Model Laid-Open No. 62-98720).

[0004]

By the way, recently, the exhaust gas temperature has been gradually increased with the increase in the output of the engine, and accordingly, the temperature of the exhaust manifold has been gradually increased. However, when the temperature of the exhaust manifold becomes higher, cracks are much more likely to occur when tensile strain is generated by tensile thermal stress than when compressive strain is generated by compressive thermal stress. That is, when compressive strain occurs, a part of the crystal structure is broken and destroyed, but in this case, it takes a considerable time to grow into a crack. On the other hand, when tensile strain occurs, a large number of microcracks are generated inside, and when the temperature of the exhaust manifold is high, these microcracks grow into cracks in a relatively short time. Therefore, when the temperature of the exhaust manifold is high, the occurrence of tensile strain has a greater effect on the occurrence of cracks than the occurrence of compression strain,
Therefore, it is necessary to intensively prevent the occurrence of cracks due to tensile strain in the exhaust manifold having a high temperature.

The occurrence of cracks due to this tensile strain cannot be prevented by merely thickening the tube wall of the exhaust manifold, as in the known exhaust manifold described above.
That is, if the pipe wall of the exhaust manifold is made thicker, the tensile stress locally generated in the pipe wall becomes smaller, but if the exhaust manifold becomes hot, a large number of microcracks are generated, and as long as the tensile stress acts, Since these microcracks gradually grow to cracks, there is no change in the occurrence of cracks at a relatively early stage.

[0006]

According to the first aspect of the present invention for solving the above problems, an exhaust manifold having an outer peripheral wall portion in which a tensile stress is generated at the time of engine operation has an outer periphery in which a tensile stress is generated. It is provided with a compressive stress applying means for applying a compressive stress to the wall portion periodically.

According to a second aspect of the invention, in the first aspect of the invention, the compressive stress imparting means extends at a distance from the exhaust manifold outer peripheral wall surface so as to straddle the exhaust manifold outer peripheral wall portion where tensile stress is generated, and both ends of the exhaust manifold outer peripheral wall surface. The portion is composed of a bridging member connected to the outer peripheral wall surface of the exhaust manifold. Also, 3
According to the first aspect of the present invention, in the first aspect, the compressive stress applying means comprises a support device that directly or indirectly supports the exhaust manifold by the engine body, and the support device attaches to the exhaust manifold outer peripheral wall portion where tensile stress is generated. A compressive stress is periodically applied.

[0008]

[Function] Even if a large tensile stress is locally generated in the pipe wall of the exhaust manifold when the exhaust manifold is at a high temperature and a large number of micro cracks are generated, these micro cracks are generated when the temperature of the exhaust manifold is high. When a compressive stress is generated in the region where these are present, these microcracks disappear and return to their original state. That is, the microcracks are repaired. When a compressive stress is periodically generated in a region where a large tensile stress is generated in this manner, the microcracks are not repaired each time, and therefore the microcracks do not grow to cracks, and thus cracks are generated. It will not occur.

Therefore, in the first aspect of the present invention, in order to prevent the microcracks from growing to cracks, compressive stress is periodically applied to the outer peripheral wall portion of the exhaust manifold where tensile stress is generated by the compressive stress applying means. In the second aspect of the invention, the temperature of the exhaust manifold gradually rises when the operation of the engine is started, but at this time, the temperature of the bridging member rises slowly after the temperature rise of the exhaust manifold. During this time, since the thermal expansion amount of the bridging member is smaller than the thermal expansion amount of the exhaust manifold outer peripheral wall portion, compressive stress is generated in the exhaust manifold outer peripheral wall portion between both ends of the bridging member.

In the third aspect of the invention, compressive stress is periodically applied to the outer peripheral wall portion of the exhaust manifold where tensile stress is generated by the supporting device.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an exhaust manifold 1 provided for three cylinders in one bank of a V-6 engine. This exhaust manifold 1 has three branch pipes 2,
A mounting flange 3 for fixing to the engine body is fixed to the tip of each branch pipe 2. These branch pipes 2 are assembled in a manifold collecting portion 4, and a mounting flange 5 is also fixed to the exhaust gas outlet of the manifold collecting portion 4. For example, a catalytic converter is attached to this attachment flange 5.

Exhaust manifold 1 is on the exhaust manifold 1.
Of the four outwardly projecting pillars for supporting the heat insulator, that is, the boss 6 and the outward projecting EGR gas extraction hole 7 for taking out the recirculated exhaust gas (hereinafter referred to as EGR gas). A columnar body, that is, a boss 8 and an outwardly protruding columnar body, that is, a boss 10 in which an insertion hole 9 for inserting an oxygen concentration sensor is formed are integrally formed.
One of the four heat insulator bosses 6 is formed on the manifold collecting portion 4, and the remaining three heat insulator bosses 6 are formed on the branch pipe 2. Further, the EGR gas boss 8 and the sensor boss 10 are formed on the manifold collecting portion 4, and in the embodiment shown in FIG. 1, the EGR gas boss 8 is the heat insulator boss 6 and the sensor on the manifold collecting portion 4. It is arranged between these bosses 6 and 10 at a distance from the boss 10.

By the way, when these bosses 6, 8, 10 are provided, these bosses 6, 8, 10 serve as a kind of cooling fin, that is, these bosses 6, 8,
Since the heat radiation surface area is large in the portion where the bosses 6, 8 and 10 are formed, the temperature becomes lower than the wall surface portion of the exhaust manifold 1 where the bosses 6, 8 and 10 are not formed. Therefore, the amount of thermal expansion of the portion where these bosses 6, 8, 10 are formed is smaller than the amount of thermal expansion of the portion where these bosses 6, 8, 10 are not formed. Tensile stress will be generated in the wall surface of the surrounding exhaust manifold 1. This tensile stress is generated in the wall surface of the exhaust manifold 1 between the bosses 6, 8 and 10, that is, between the heat insulator boss 6 and the EGR gas boss 8 of the manifold collecting portion 4, and between the EGR gas boss 8 and the sensor. It becomes the largest in the wall surface of the exhaust manifold 1 between the boss 10.

Further, the tensile stress generated between the bosses 6, 8 and 10 is further increased when the temperature of the exhaust manifold 1 is increased after the engine is started. That is, since the bosses 6, 8 and 10 have a large heat capacity, the temperature of the bosses 6, 8 and 10 rises at a slower speed than the temperature of the exhaust manifold 1 after the engine is started.
The temperature difference between the wall surface of the exhaust manifold 1 in which the bosses 10, 8 and 10 are not formed becomes large. Therefore, during this time, a large tensile stress is generated between the bosses 6, 8 and 10. Anyway, such a boss 6,
When 8 and 10 are formed on the exhaust manifold 1, a tensile stress is generated in the wall surface of the exhaust manifold 1 between the bosses 6, 8 and 10 every time the engine is operated, and finally, A crack will occur between the bosses 6, 8 and 10.

Therefore, in the embodiment according to the present invention, FIG.
As shown in (B) and (B), a bridge extending between the outer end portion of the side wall surface of the heat insulator boss 6 and the outer end portion of the side wall surface of the EGR gas boss 8 at a distance from the outer peripheral wall surface of the exhaust manifold 1. The outer end of the side wall surface of the EGR gas boss 8 and the outer end of the side wall surface of the sensor boss 10 are connected to each other by a member 11 by a bridging member 12 extending from the outer peripheral wall surface of the exhaust manifold 1 at a distance. I am trying to do it.

When the operation of the engine is started, the temperature of the outer peripheral wall of the exhaust manifold 1 gradually rises. At this time, the bosses 6, 8 and 10 slowly rise as the temperature of the exhaust manifold 1 rises as described above. At this time, bridge member 1
Nos. 1 and 12 rise more slowly as the temperature of the exhaust manifold 1 rises. Therefore, even if the temperature of the exhaust manifold 1 becomes considerably high, the temperature of the bridging members 11, 12 does not rise so much, and thus the thermal expansion amount of the bridging members 11, 12 is the amount of exhaust gas between the bosses 6, 8, 10. It is considerably smaller than the thermal expansion amount of the outer peripheral wall of the manifold 1. As a result, each boss 6, 8,
Compressive stress will be generated in the outer peripheral wall of the exhaust manifold 1 between 10. Then, after a while, the bridge member 11,
Since the temperature of 12 rises, tensile stress is again generated in the outer peripheral wall of the exhaust manifold 1 between the bosses 6, 8 and 10.

As described above, in this embodiment, the outer peripheral wall of the exhaust manifold 1 between the bosses 6, 8 and 10 is restarted every time the engine is started, that is, in a state where the temperature of the exhaust manifold 1 is relatively high. Compressive stress is generated inside. As a result, the micro-cracks generated when tensile stress acts on the outer peripheral wall of the exhaust manifold 1 between the bosses 6, 8 and 10 are repaired by the cyclically generated compressive stress, and thus the bosses. It is possible to prevent the outer peripheral wall of the exhaust manifold 1 between 6, 8 and 10 from being cracked.

In the embodiment shown in FIGS. 2A and 2B, the bridging members 11 and 12 are cast at the same time when the exhaust manifold 1 is cast. That is, in this embodiment, the bridging members 11 and 12 are integrally formed with the corresponding bosses 6, 8 and 10 when the exhaust manifold 1 is cast. 2 in FIG.
The modification of the Example shown to (A) and (B) is shown. In addition, in FIG. 3, 13 indicates a heat insulator, and 14 indicates an EGR gas conduit. In this modification, the mounting flange 15 fixed to the tip of the EGR conduit 14 is formed large so as to cover the top surface of the heat insulator boss 6. This mounting flange 1
5 is fastened to the top of the EGR gas boss 8 using, for example, a nut, and the end of the mounting flange 15 is fastened to the top of the heat insulator boss 6 together with the heat insulator 13 by, for example, a bolt. Therefore, in this modified example, the mounting flange 15 of the EGR gas conduit 14 constitutes a bridging member.

FIG. 4 and FIG. 5 (A) show still another embodiment. In this embodiment, the same components as those in FIG. 1 are designated by the same reference numerals. As shown in FIGS. 4 and 5 (A), in this embodiment, the exhaust manifold 1 is for a four-cylinder internal combustion engine, and a catalytic converter 16 is attached to a mounting flange 5 formed in the manifold collecting portion 4. ing. The catalytic converter 16 is supported by the engine body by stays 17. Thus, when the exhaust manifold 1 and the catalytic converter 16 are curved and extend as a whole when viewed from the mounting flange 3 of the branch pipe 2, the largest tensile stress is exerted on a portion having the smallest cross-sectional area outside the curved structure. Is likely to occur. In the embodiment shown in FIGS. 4 and 5 (A), the greatest tensile stress is generated in the outer portion indicated by X of the manifold collecting portion 4.

Therefore, in this embodiment, the bridging member 18 is provided so as to straddle the outer side portion X of the manifold collecting portion 4 where the largest tensile stress is generated. This bridging member 18
Are cast at the same time when the exhaust manifold 1 is cast so as to be spaced from the outer peripheral wall surface of the exhaust manifold 1. Also in this embodiment, the bridging member 1 is provided for a while after the engine is started.
Since the temperature of 8 does not rise so much, the amount of thermal expansion of the bridging member 18 is small. Therefore, during this time, the manifold collecting portion 4 can be maintained even when the temperature of the outer peripheral wall of the exhaust manifold 1 is relatively high.
A compressive stress is generated in the outer portion X of the. Therefore, also in this embodiment, the microcracks are repaired by this compressive stress, and thus the generation of cracks can be prevented.

FIG. 5B shows a modification of FIGS. 4 and 5A. In this modification, bosses 19 are formed on the outer peripheral wall surfaces of the exhaust manifold 1 on both sides of the outer side X of the manifold assembly 4 where the largest tensile stress is generated, and the tops of these bosses 19 are connected to each other by the bridging member 20. There is. FIG. 6 shows still another embodiment. In this embodiment, the same components as those in FIGS. 5A and 5B are designated by the same reference numerals. In this embodiment, the catalytic converter 1
6 is supported by a further supporting device 21 in addition to the stay 17. The support device 21 includes an actuator 22 formed of a hydraulic cylinder supported by the engine body 1. A hydraulic piston 23 of the actuator 22 is connected to the catalytic converter 16 via a link member 24. The hydraulic chamber 25 in the actuator 22 is connected to the discharge port of the hydraulic pump via the opening / closing valve 26 controlled by the output signal of the electronic control unit 30, and the oil in the hydraulic chamber 25 is returned to the oil sump via the throttle 27. To be done.

When the on-off valve 26 is opened, the on-off valve 2
Pressurized oil is supplied into the hydraulic chamber 25 via 6. When pressurized oil is supplied into the hydraulic chamber 25, the hydraulic piston 2
3 causes the catalytic converter 16 to rotate clockwise about the pivot 28, thus causing a compressive stress in the outer portion X of the manifold collecting portion 4. The electronic control unit 30 comprises a digital computer,
A ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36 are connected to each other by a bidirectional bus 31. A signal corresponding to the output signal of the air flow meter 40 indicating the intake air amount and an output signal of the exhaust temperature sensor 43 indicating the exhaust gas temperature in the exhaust manifold 1 correspond to the input port 35, respectively.
An input pulse is input through the D converter 37, and an output pulse of the rotation speed sensor 41 representing the engine rotation speed is input to the input port 35.
The output pulse of the vehicle speed sensor 42 indicating the vehicle speed and the ON / OFF signal of the ignition switch 44 are input.
On the other hand, the output port 36 is connected to the open / close valve 2 via the drive circuit 38.
6 is connected.

FIG. 7 shows a routine for controlling the actuator 22. This routine is executed, for example, by interruption at regular time intervals. Referring to FIG. 7, first, at step 50, it is judged if the driving condition of the actuator 22 is satisfied. When the driving condition of the actuator 22 is satisfied, the routine proceeds to step 51, where, for example, the temperature T of the exhaust gas flowing in the exhaust manifold 1
It is determined whether or not e is higher than a preset temperature, for example, 800 ° C. When Te> 800 ° C., the routine proceeds to step 52, where the actuator 22 is driven for a fixed time. That is, in the embodiment shown in FIG.
6 is opened and pressurized oil is supplied into the hydraulic chamber 25, whereby compressive stress is generated in the outer portion X of the manifold collecting portion 4.

When the temperature of the exhaust manifold 1 is high and a tensile stress acts on the outer portion X of the manifold collecting portion 4 for a long period of time, microcracks are generated in the outer portion X of the manifold collecting portion 4, and at this time, the exhaust manifold is opened. The microcracks can be repaired by generating a compressive stress in the outer portion X of the manifold assembly 4 for a very short time while the temperature of 1 is high. Therefore, in the routine shown in FIG.
It is determined whether or not an appropriate period has elapsed after the compressive stress is generated in the outer portion X of the drive unit, and it is determined that the driving condition is satisfied when the appropriate period has elapsed.

For example, at step 50, the number of times the engine is operated is counted from the ON / OFF signal of the ignition switch 44, and when the engine is operated several tens of times, it is judged that the driving condition is satisfied. In this case, the actuator 22 is driven only once every time the engine is operated several tens of times. In step 50, the cumulative value of the traveling distance is calculated based on the output signal of the vehicle speed sensor 42, or the cumulative value of the engine speed is calculated.
It is also possible to determine that the driving condition is satisfied when these accumulated values exceed a certain value. It is also possible to count the number of times the exhaust gas temperature Te has exceeded 800 ° C. in step 50, and determine that the driving condition has been satisfied when this number exceeds a certain value.

On the other hand, in step 51 of FIG. 7, it is judged based on the output signal of the exhaust gas temperature sensor 43 whether the exhaust gas temperature Te has reached 800 ° C. or higher. Further, instead of providing such an exhaust temperature sensor 43, the relationship between the exhaust gas Te, the engine speed, the intake air amount, and the ignition advance value is RO in advance.
The exhaust gas temperature Te can be obtained from the relationship stored in M32.

In the embodiment shown in FIG. 6, a hydraulic cylinder is used as the actuator 22. However, it is also possible to use a piezoelectric element or a solenoid as the actuator 22.

[0028]

Since the generation of cracks in the exhaust manifold can be prevented, the life of the exhaust manifold can be extended.

[Brief description of drawings]

FIG. 1 is a front view of an exhaust manifold.

FIG. 2 is a view showing a part of an exhaust manifold according to the present invention, (A) showing a front view and (B) showing a side view of (A).

FIG. 3 is a side view of a part of an exhaust manifold showing a modification example of FIGS. 2A and 2B.

FIG. 4 is a front view of an exhaust manifold showing still another embodiment.

5A and 5B are side views of the exhaust manifold, in which FIG. 5A is a side view of the exhaust manifold shown in FIG. 4, and FIG. 5B is a side view showing a modified example of FIG.

FIG. 6 is a side view of an exhaust manifold showing still another embodiment.

FIG. 7 is a flowchart for controlling an actuator.

[Explanation of symbols]

 1 ... Exhaust manifold 2 ... Branch pipe 4 ... Manifold collecting part 6, 8, 10 ... Boss 11, 12 ... Bridge member

Claims (3)

[Claims] 1. An exhaust manifold having an outer peripheral wall portion in which a tensile stress is generated at least during engine operation, and an internal combustion engine provided with a compressive stress applying means for periodically applying a compressive stress to the outer peripheral wall portion in which a tensile stress is generated. Exhaust manifold. 2. A bridge bridge in which the compressive stress applying means extends at a distance from the exhaust manifold outer peripheral wall surface so as to extend over the exhaust manifold outer peripheral wall portion where tensile stress is generated, and both ends are connected to the exhaust manifold outer peripheral wall surface. The exhaust manifold for an internal combustion engine according to claim 1, wherein the exhaust manifold comprises a member. 3. The compression stress applying means comprises a support device for directly or indirectly supporting the exhaust manifold by the engine body, and the compression stress is periodically applied to the exhaust manifold outer peripheral wall portion where tensile stress is generated by the support device. An exhaust manifold for an internal combustion engine according to claim 1, wherein the exhaust manifold is provided.