JP2653483B2 - Exhaust structure of engine with exhaust turbocharger - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust structure of an engine with an exhaust turbocharger.

(Prior Art) In an exhaust turbocharged engine, two-parallel two turbochargers are arranged in parallel with each other, as is called a sequential turbocharger.
At the time of low speed, only one exhaust turbocharger is operated to be in the first state where the supercharging capacity is small, and at the time of high speed, two exhaust turbochargers are operated to supercharge. It is proposed that the second state be large in supply capacity. That is, responsiveness is ensured by reducing the size of the exhaust turbocharger (hereinafter referred to as a primary-side turbocharger) operated at a low speed. On the other hand, at high speeds, a large supercharging capacity can be obtained by operating the remaining exhaust turbochargers (hereinafter, secondary turbochargers). Such a sequential turbo is, for example,
No. 60-178329.

The switching between the operation and the non-operation of the secondary-side turbocharger is performed by opening and closing an exhaust cut valve provided upstream of (the turbine of) the secondary-side turbocharger. This is performed by switching the supply and cutoff of exhaust gas to the engine. In order to minimize the leakage of exhaust gas from the exhaust cut valve when the valve is closed, the exhaust cut valve is back-pressure type, that is, the valve is pressed in the valve closing direction by receiving the exhaust gas pressure on the upstream side when the valve is closed. It is proposed that the valve be opened against the exhaust gas pressure when the valve is opened.

(Problems to be Solved by the Invention) In the case of the above-described sequential turbo, if the exhaust cut valve is of a back pressure type, it is necessary to open the exhaust cut valve against the exhaust gas pressure on the upstream side, so that a considerable amount of time is required when the valve is opened. A large force is required, and how to reduce the valve opening force becomes a problem.

For this reason, it is conceivable to reduce the effective opening area of the exhaust passage as much as possible to reduce the valve opening force caused by the differential pressure between the upstream side and the downstream side of the exhaust cut valve. However, in order to efficiently exhaust the exhaust gas from the engine, it is desired that the effective opening area of the exhaust passage is large. Therefore, it is difficult to simply reduce the effective opening area of the exhaust passage. .

Therefore, the object of the present invention is to assume that the supply and cutoff of the exhaust gas to the secondary side turbocharger is switched by a back pressure type exhaust cut valve, and the force required to open the exhaust cut valve is reduced. An object of the present invention is to provide an exhaust structure of an engine with an exhaust turbocharger which can be reduced as much as possible.

(Means and Actions for Solving the Problems) In order to achieve the above object, the present invention has the following configuration. That is, an exhaust passage of the engine has a first exhaust passage and a second exhaust passage which are at least partially parallel to each other, and a primary exhaust turbocharger constantly operated with respect to the first exhaust passage is provided. A secondary-side exhaust turbocharger, a valve installed upstream of the secondary-side exhaust turbocharger and opened against the exhaust pressure on the upstream side with respect to the second exhaust passage; A pressure-type exhaust cut valve is provided; a first portion of the effective opening area of the second exhaust passage that serves as an exhaust inlet of the secondary-side exhaust turbocharger; and a second portion in which the exhaust cut valve is installed. The part and the third part upstream of the exhaust cut valve by a predetermined distance are set so that the first part and the second part are substantially equal, and the third part is larger than the first part and the second part. It is set as follows.

With such a configuration, the exhaust cut valve installation portion becomes a portion having a substantially minimum effective opening area in the exhaust passage, and the force required for opening the valve can be reduced. In other words, in order to operate the exhaust turbocharger efficiently, the effective opening area of the exhaust passage is reduced near the exhaust turbocharger in order to increase the flow rate of the exhaust gas. In this case, the process for increasing the flow rate of the exhaust gas is performed from the exhaust port of the engine to the portion where the exhaust cut valve is installed. Of course, the effective opening area near the exhaust port of the engine is ensured to be large, so that the exhaust gas exhaust efficiency from the engine can be made different from the conventional one.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Overall System In FIG. 1, an exhaust passage 2 for exhausting exhaust gas of an engine 1 has two branch exhaust passages 2a and 2b extending independently of the engine 1. Further, the intake passage 3 through which the intake air of the engine 1 flows has two branch intake passages 3a and 3b which are branched on the downstream side of the air flow meter 4 for detecting the intake air amount. 3b joins on the upstream side of the intercooler 5. In the intake passage 3 on the downstream side of the intercooler 5, a throttle valve 6,
A surge tank 7 and a fuel injection valve 8 are provided.

In one of the two branch exhaust passages 2a and 2b, a turbine TP that is rotationally driven by exhaust gas is disposed in one branch exhaust passage 2a, and the turbine TP is disposed in one branch intake passage 3a. The blower Cp is connected via a rotation axis LP. The primary turbine supercharger 9 is constituted by using the turbine TP, the rotating shaft LP, and the blower Cp as main elements. Similarly, a turbine TS driven by exhaust gas is disposed in the other branch exhaust passage 2b, and a blower CS is disposed in the other branch intake passage 3b. These turbines TP and blower CS Is the rotation axis LS
To form a secondary turbocharger 10.

The passage portions on the upstream side of the blowers Cp and CS of the branch intake passages 3a and 3b are formed so as to face each other at a branch portion branched from the intake passage 3 so as to be linear with each other. The generated pressure wave is applied to the other branch intake passage.
The structure is such that it is easy to propagate to the 3a side, easy to propagate to the air flow meter 4 side, and difficult to propagate to the air flow meter 4 side.

An exhaust cut valve 11 is disposed in the secondary branch exhaust passage 2b on the upstream side of the turbine TS. The exhaust cut valve 11 closes the branch exhaust passage 2b in a low rotation range to cut off the supply of exhaust gas to the turbine TS of the secondary turbocharger 10, and shuts off only the primary turbocharger 9. It is provided for operation.

The upstream portion of the exhaust cut valve 11 in the secondary branch exhaust passage 2b is connected to the turbine branch TP upstream of the primary branch exhaust passage 2a via the communication passage 12. The communication passage 12 is connected to a bypass passage 18 in which a waste gate valve 17 is disposed, with respect to the exhaust passage 2 downstream of the turbines TP and TS.
Connected through. The upstream portion of the wastegate valve 17 in the bypass passage 18 is connected between the turbine TS and the exhaust cut valve 11 in the branch exhaust passage 2b through a leakage passage 14 in which the exhaust leakage valve 13 is provided. Have been.

The exhaust leakage valve 13 is operated by a diaphragm type actuator 16, and a pressure chamber of the actuator 16 is connected to a downstream side of a blower Cp of the primary turbocharger 9 via a control pressure conduit 15. The side is open to the branch intake passage 3a. This leak valve 13 is opened when the supercharging pressure P1 on the downstream side of the blower Cp becomes equal to or higher than a predetermined value (for example, 500 mmHg) in the process of increasing the engine speed,
Thus, a small amount of exhaust gas is supplied to the turbine TS through the bypass passage 14 when the exhaust cut valve 11 is closed. Accordingly, the turbine TS starts rotating before the exhaust cut valve 11 opens, thereby improving the supercharging responsiveness when the exhaust cut valve 11 is opened and reducing the torque shock. The differential pressure between the upstream side and the downstream side of the valve 11 becomes smaller, and the force for opening the exhaust cut valve 11 can be further reduced.

Reference numerals 19 and 20 denote diaphragm actuators for operating the exhaust cut valve 11 and the waste gate valve 17, respectively. The operation of these actuators will be described later.

On the other hand, an intake cut valve 21 is provided in the secondary branch intake passage 3b downstream of the blower Cp. Further, a passage 22 for bypassing the blower CS is provided, and a relief valve 23 is provided in the bypass passage 22. The intake cut valve 21 is operated by a diaphragm type actuator 24 as described later. Also, the above relief valve
Reference numeral 23 denotes a valve that opens the bypass passage 22 slightly before the intake cut valve 21 and the exhaust cut valve 1 are opened in the process of increasing the engine speed, and the exhaust leakage valve 13 when the exhaust cut valve 11 is closed. Blower CS based on opening operation
This prevents the pressure in the branch intake passage 3b between the blower CS and the intake cut valve 21 from rising due to the rotation of the blower CS, and is provided so that the blower CS can rotate easily. Such a relief valve 23 is operated by a diaphragm type actuator 25.

A control pressure conduit 26 of an actuator 24 that operates the intake cut valve 21 is connected to an output port of a three-way valve 27 formed of an electromagnetic solenoid valve. Further, a control pressure conduit 28 of the actuator 19 that operates the exhaust cut valve 11 is connected to an output port of a three-way valve 29 similarly formed of an electromagnetic solenoid valve. Actuator that further operates the relief valve 23
Twenty-five control pressure conduits 30 are connected to the output ports of a three-way valve 31 similar to that described above. The control pressure conduit 32 of the actuator 20 that operates the wastegate valve 17 is connected to the output port of a three-way valve 33 composed of an electromagnetic solenoid valve. Three-way valves 27, 29, 31 comprising these electromagnetic solenoid valves and
33 is controlled by a control circuit 35 configured using a microcomputer. The control circuit 35 controls each electromagnetic solenoid valve based on detected values such as the engine speed Ne, the intake air amount Q, the throttle opening TVO, and the lower pressure P1 on the downstream side of the blower Cp of the primary turbocharger 9. Control.

Of the four electromagnetic solenoid valves, one input port of the three-way valve 29 is open to the atmosphere, and the other input port is connected to the negative pressure tank 43 via the conduit 36.
An intake negative pressure Pn downstream of the throttle valve 6 is introduced into the negative pressure tank 43 via a check valve 37. The three-way valve 27 has one input port connected to the negative pressure tank 43 via a conduit 36, and the other input port connected to an output port of a differential pressure detection valve 39 via a conduit 38. I have.

As shown in FIG. 2, the casing 51 of the differential pressure detecting valve 39 is divided into three chambers 54, 55, 56 by two diaphragms 52, 53, and the chamber 54 has an input port 54a and a chamber 54. Five
5, an input port 55a is opened, and an output port 57 and an atmosphere opening port 58 are connected to the chamber 56. The port 54a is connected to the downstream side of the intake cut valve 21 via the conduit 41 so as to introduce the supercharging pressure P1 downstream of the primary side blower Cp. Port 55a is connected to conduit 42
Is connected upstream of the intake cut valve 21 to introduce a pressure P2 upstream of the intake cut valve 21 when the intake cut valve 21 is closed. When the pressure difference between the pressures P1 and P2 is large, the differential pressure detection valve 39 opens the port 47 with the valve body 59 connected to the two diaphragms 52 and 53 to introduce the atmosphere into the conduit 38. However, when the differential pressure P2-P1 falls within a predetermined value ± ΔP, the port 57 is closed by the spring 59. Therefore, with the three-way valve 27 communicating the conduit 26 with the conduit 38, the differential pressure P2
When −P1 becomes larger than the predetermined value ± ΔP, the air is introduced into the actuator 24, and the intake cut valve 21 is opened.
Also, when the three-way valve 27 allows the conduit 26 to communicate with the conduit 36,
A negative pressure is supplied to the actuator 24, and the intake cut valve 21 is closed.

On the other hand, when the three-way valve 29 connects the conduit 28 to the conduit 36,
The negative pressure is supplied to the actuator 19, and the exhaust cut valve 11 is closed. At this time, only the primary side turbocharger 9 is operated. When the three-way valve 29 releases the conduit 28 to the atmosphere, the exhaust cut valve 11 is opened, and the secondary turbocharger 10 is operated.

FIG. 3 is a control map showing the open / closed state of the intake cut valve 21 and the exhaust cut valve 11 together with the open / closed state of the exhaust leak valve 13, the wastegate valve 17 and the relief valve 23. Is stored.

Here, one input port of the three-way valve 31 is also open to the atmosphere, and the other input port is connected to the negative pressure tank 43.When the engine is running at a low speed, the intake negative pressure Pn is introduced into the conduit 30. Although the relief valve 25 opens the bypass passage 22, the three-way valve is opened before the intake cut valve 21 and the exhaust cut valve 11 are opened, as shown in FIG. 31 is switched to the atmosphere side by a signal from the control circuit 35, whereby the relief valve 25 closes the bypass passage 22.

Further, a boost pressure P1 is introduced into one input port of the three-way valve 33 through the control pressure conduit 15 of the actuator 16, so that the engine speed Ne and the throttle opening TVO are equal to or higher than predetermined values and are excessive. When the supply pressure P1 exceeds a predetermined value, the control circuit 35 opens the two-way valve 33 and introduces the supercharge pressure P1 to the actuator 20, whereby the wastegate valve
17 opens the bypass passage 18. Further, the other input port of the three-way valve 33 is open to the atmosphere, and when the atmosphere is supplied to the actuator 20, the wastegate valve 17 is closed.

Flowcharts (FIGS. 4A and 4B) FIGS. 4A and 4B show flowcharts for performing control in accordance with the map of FIG. 3 (S is a step, and the exhaust leakage valve 13, the wastegate valve Except for 17). In this flowchart, the flow of the processing changes depending on the flag in one of the ranges from 1 to 6, and the meaning of this flag is as shown in FIG.
That is, since the valves 11, 21, and 23 are each provided with a hysteresis for opening and closing, two characteristic lines are set for each of the valves 11, 21, and 23, and a total of six characteristic lines are set. Having. Then, the flag is changed every time the characteristic line is crossed, and when the operating state is displaced in a direction approaching the region on the right side in FIG. 3 (region on the high rotation and high load side), the flag is set to “2”, It is changed by an even number such as “4” or “6”. Conversely, when the operating state changes to the left area in FIG. 3, the flag is changed with an odd number such as "5", "3", or "1". Of course, at the start of the operation, the flag is set to "1" in the low rotation and low load region (initialization).

Based on the above, the flowchart will be briefly described.

First, the system is initialized at S1 in FIG. 4A, and the flag is set to 1 at this time. Next, in S2, after the engine speed R and the intake air amount Q are inputted, the Q1 to Q6 which determine the above-mentioned six characteristic lines are inputted.
(Intake air amount) and R1 to 16 (engine speed) are read from the map.

After S3, in S4, it is determined whether or not the changing speed of the intake air amount Q is larger than the set value A. In this determination of S4
If YES, in S5, Q1-Q6 read out in S3 above
For each of R1 and R1 to R6, a predetermined amount of decrease correction (ΔQ1
To ΔQ6 and subtraction of ΔR1 to ΔR6), and then the process proceeds to S6. If the determination in S4 is NO, the process proceeds to S6 without going through S5. The process in S5 corresponds to a process for expanding the operating region of the secondary turbocharger 10 to a lower load and a lower rotation speed during acceleration. In S6, it is determined whether the flag F is 1 or not.
Initially, the flag F is initialized to 1, so this determination is YES. At this time, if the determination of S7 or S8 is YES, after the flag F is set to 2 in S9, the relief valve 23 is closed in S10 (negative pressure supply to the actuator 25). If the determinations in S7 and S8 are both NO, the process returns.

If the determination in S6 is NO, in S11, it is determined whether or not the flag F is twice the integer m, that is, whether it is 2, 4, or 6. If the determination in S11 is YES, it is determined in S12 whether the flag F is 2. If the determination in S12 is YES, and if the determination in S13 or S14 is YES, the flag F is set to 4 in S15, and then the exhaust cut valve 11 is opened in S16 (the air is cut off to the actuator 19). Supply). When both the determinations of S13 and S14 are NO, the determinations of S17 and S18 are both YES.
, After the flag is set to 1 in S19, S
At 20, the relief valve 23 is opened (negative pressure is supplied to the actuator 25). If the determination in S17 or S18 is NO, the process is returned.

If the determination in S12 is NO, it is determined whether or not the flag F is 4 in S21. If the determination in S21 is YES,
This is when the flag F is set to 6 or 3, or the process is returned as it is. That is, in either of S22 and S23,
If YES, after the flag F is set to 6 in S24, the intake cut valve 21 is opened in S25 (the actuator 24 is connected to the conduit 38). Further, when both the determinations of S22 and S23 are NO, when the determinations of S26 and S27 are both YES, the flag F is set to 3, and then the exhaust cut valve 11 is closed in S29 (to the actuator 19). Negative pressure supply).
If the determination in any of S26 and S27 is NO, the process returns.

When the determination in S21 is NO, the current flag F is 6. This is the time when the flag F is set to 5 or the process returns. That is, S30 and S
If both of the determinations 31 are YES, the flag F is set to 5 in S32, and then the intake cut valve 21 is closed in S33 (a negative pressure is supplied to the actuator 24). If NO in either of S30 and S31, the process returns.

If the determination in S11 is NO, the process shifts to S41 in FIG. 4B. In this S41, it is determined whether or not the flag F is 3. When the determination is YES, the flag F is set to 1 or 4, or the process returns. That is, when both the determinations of S42 and S43 are YES, the flag F is set to 1 in S44, and then the relief valve 23 is opened in S45 (a negative pressure is supplied to the actuator 25). Further, if any of the determinations of S42 and S43 is NO, S46 and S47
Is YES, the flag F is set in S48.
Is set to 4, the exhaust cut valve 11 is opened in S49 (atmospheric supply to the actuator 19). And S4
Returned when both determinations of 6, S47 are NO.

If the determination in S41 is NO, the current flag F is 5. At this time, the flag F is set to 3 or 6, or the process returns. That is, when both the determinations of S50 and S51 are YES, after the flag F is set to 3 in S52, the exhaust cut valve 11 is closed in S53 (a negative pressure is supplied to the actuator 19). If one of the determinations is NO, S54, S55
When either of the determinations is YES, the flag F is set in S56.
Is set to 6, the intake cut valve 21 is opened in S57 (the actuator 24 is connected to the conduit 38). Then, when both the determinations of S54 and S55 are NO, the process is returned.

Next, the setting of the effective opening area of the branch exhaust passage 2b will be described in detail below, together with a supplementary explanation of the exhaust cut valve 11.

First, the exhaust cut valve 11 is a back pressure type that is swung about a swing support point 11a and is pressed in the valve closing direction by exhaust gas pressure on the upstream side when the valve is closed. Therefore, when opening the exhaust cut valve 11, it is necessary to open the exhaust cut valve 11 against the exhaust gas pressure on the upstream side, but the effective opening area of the portion where the exhaust cut valve 11 is installed is reduced. The smaller the force, the smaller the force required to open the valve.

In FIG. 1 again, in the branch exhaust passage 2b, an inlet portion (water drain portion) of the (second turbine TS) of the secondary side turbocharger 10 downstream of the exhaust cut valve 11 is shown as a first portion A1, and the exhaust gas is cut. The installation portion of the valve 11 is shown as a second portion A12, and a portion upstream of the exhaust cut valve 11 by a predetermined distance is a third portion.
Shown as A3. The effective opening area of the third portion A3 is substantially equal to the effective opening area of the exhaust port of the engine 1.

The setting of the effective opening area of the three parts A1 to A3 is the first
The part A1 and the second part A2 are made substantially equal, and the third part
A3 is larger than both the first and second portions A1 and A2. And, from the third part A3 to the second part A2,
The nozzle is shaped so that the effective opening area gradually decreases toward the downstream, so that the exhaust gas flows smoothly from the third portion A3 to the second portion A2 and the flow velocity gradually increases.

In the above configuration, since the effective opening area of the third portion A3 is large, the exhaust gas is efficiently discharged from the engine 1 without having a large resistance. In addition, since the flow rate of the exhaust gas is increased between the third portion A3 and the second portion A2, the secondary turbocharger 10 operates efficiently. The second portion where the exhaust cut valve 11 is installed is located at a position where the effective opening area is sufficiently small in terms of the operating efficiency of the secondary turbocharger, similarly to the first portion. The force required to open the exhaust cut valve 11 is small.

FIG. 5 shows that when the engine 1 is an in-line six-cylinder engine, the engine 1 is divided into two cylinder groups for every three cylinders whose intake strokes are not continuous with each other, and the exhaust gas from one cylinder group (passes through the branch exhaust passage 2a). The primary-side turbocharger 9 is operated, and the secondary-side turbocharger 10 is operated by exhaust gas (passing through the branch exhaust passage 2b) from another cylinder group. Therefore, the upstream portion of each branch exhaust passage 2a or 2b is substantially constituted by the exhaust manifold 61P or 61S.

In the case of FIG. 5, the third part A3 is an exhaust manifold.
It is set as a collection part of 61S. The effective opening area of each exhaust port portion (connection portion to the exhaust manifolds 61S and 61P) A4 of the engine 1 is slightly smaller or equal to the effective opening area of the third portion A3. It is made larger than the two parts A1 and A2.

FIG. 6 more specifically shows the setting of the effective opening area of the exhaust passage from the exhaust manifold 61S to the secondary turbocharger 10 in the one shown in FIG. FIG. 7 shows the setting of the effective opening area of the exhaust passage from the exhaust manifold 61P to the primary turbocharger 9 more specifically. The primary-side turbocharger 9 has the same effective opening area as the secondary-side turbocharger 10 except that the primary-side turbocharger 9 does not have the exhaust cut valve 11 (first example). See also figure). 6 and 7
In the drawings, the exhaust port is indicated by reference numeral 81.

(Effects of the Invention) As apparent from the above description, the present invention optimally sets the effective opening area of the second exhaust passage for the secondary-side turbocharger to reduce the exhaust gas exhaust efficiency from the engine and the secondary The force required to open the exhaust cut valve can be reduced without sacrificing the operation efficiency of the side turbocharger.

Further, by adopting the configuration as described in claim 2, the differential pressure between the upstream side and the downstream side of the exhaust cut valve is reduced, and the force when the exhaust cut valve is opened is further reduced. It is possible to improve the supercharging response and reduce the torque shock by the secondary exhaust turbocharger when the exhaust cut valve is opened due to the pre-rotation of the secondary exhaust turbocharger. Obtainable.

With the configuration as described in claim 3, the flow of the exhaust gas from the third portion to the second portion is made smooth, and the exhaust gas is directed toward the secondary-side exhaust turbocharger. This is preferable in terms of improving the supercharging performance of the secondary-side exhaust turbocharger by increasing the flow velocity of the exhaust gas.

By adopting the configuration as described in claim 4, the configuration can be simplified by using the collection portion of the exhaust manifold as the third portion.

[Brief description of the drawings]

FIG. 1 is an overall system diagram showing one embodiment of the present invention. FIG. 2 is a sectional view of the voltage detection valve shown in FIG. FIG. 3 is a characteristic diagram showing switching characteristics of each valve. 4A and 4B are flowcharts when performing control according to the characteristic diagram of FIG. FIG. 5 is a main part system diagram showing another embodiment of the present invention. 6 and 7 are partial cross-sectional side views specifically showing a state of an exhaust passage to a turbocharger in the one shown in FIG. 1: Engine 2: Exhaust passage 2a, 2b: Branch exhaust passage 9: Primary turbocharger 10: Secondary turbocharger Tp: Turbine (primary side) Ts: Turbine (secondary side) 11: Exhaust cut valve 11a: Swing fulcrum A1: First part A2: Second part A3: Third part

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Tajima 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (56) References JP-A-59-145327 (JP, A) JP-A-1 JP-A-1-300017 (JP, A) JP-A-60-178329 (JP, U) JP-A-63-171624 (JP, U)

Claims (4)

(57) [Claims] An exhaust passage of an engine has a first exhaust passage and a second exhaust passage which are at least partially parallel to each other, and a primary exhaust turbocharger constantly operated with respect to the first exhaust passage. A secondary exhaust turbocharger and a valve installed upstream of the secondary exhaust turbocharger against the exhaust pressure on the upstream side with respect to the second exhaust passage. A back pressure type exhaust cut valve is provided, a first portion of the effective opening area of the second exhaust passage serving as an exhaust inlet of the secondary exhaust turbocharger, and the exhaust cut valve are installed. The second portion and the third portion upstream of the exhaust cut valve by a predetermined distance are set so that the first portion and the second portion are substantially equal, and the third portion is the first portion and the second portion. Engine with an exhaust turbocharger, which is set larger than Exhaust structure 2. The exhaust system according to claim 1, wherein the exhaust gas is exhausted between the secondary exhaust turbocharger and the exhaust cut valve in the second exhaust passage when the exhaust cut valve is closed. An exhaust structure for an engine with an exhaust turbocharger, wherein a leakage passage for supplying gas to pre-rotate the secondary exhaust turbocharger is connected. 3. The first exhaust passage according to claim 1, wherein the second exhaust passage is formed in a nozzle shape such that an effective opening area gradually decreases from the third portion to the second portion. An exhaust structure of an engine with an exhaust turbocharger, characterized in that: 4. The engine with an exhaust turbocharger according to claim 1, wherein the third portion is constituted by a collection portion of an exhaust manifold connected to a plurality of cylinders. Exhaust structure.