CN113048079A

CN113048079A - Air supercharging device with back-to-back type impellers

Info

Publication number: CN113048079A
Application number: CN202110279427.XA
Authority: CN
Inventors: 彭学院; 陈钦隆; 李佐良; 陈志凯; 史婷; 冯健美
Original assignee: Sichuan Dachuan Compressor Co ltd; Xian Jiaotong University
Current assignee: Sichuan Dachuan Compressor Co ltd; Xian Jiaotong University
Priority date: 2021-03-16
Filing date: 2021-03-16
Publication date: 2021-06-29

Abstract

The application discloses air supercharging device with back-to-back impeller relates to fuel cell air pressure charge system technical field. The air supercharging device comprises a volute, wherein a back-to-back impeller is arranged in the volute, and the back-to-back impeller comprises a first impeller and a second impeller which are connected into a whole through a connecting table; a rotating shaft is arranged in the first impeller and is respectively connected with the back-to-back impeller and an output shaft of the driving motor; a diffuser is arranged between the volute and the connecting platform of the back-to-back impeller, and divides the inner cavity of the volute into a first cavity and a second cavity; a first air port and a second air port are arranged on the side wall of the first cavity, the center line of the first air port is overlapped with the axis of the first impeller, and the center line of the second air port is perpendicular to the axis of the first impeller and faces the first impeller; and a third air port and a fourth air port are arranged on the side wall of the second cavity, the central line of the third air port is superposed with the axis of the second impeller, and the central line of the fourth air port is vertical to the axis of the second impeller and faces the second impeller.

Description

Air supercharging device with back-to-back type impellers

Technical Field

The present application relates to the field of fuel cell air supercharging systems, and more particularly, to an air supercharging device having back-to-back impellers.

Background

The air compressor is an important part of a cathode air supply system of the vehicle fuel cell system, and plays roles of improving the power density and efficiency of the fuel cell, reducing the size of the fuel cell, facilitating water heat management and the like by pressurizing inlet air of the fuel cell stack.

The electrochemical reaction of the fuel cell has more strict requirements on the parameters of air such as temperature, humidity, pressure, flow and the like compared with the traditional air compressor. Therefore, a compressor having superior performance and good matching with the fuel cell system is important for the fuel cell system. When the centrifugal compressor works, the impeller rotates to apply work to the gas working medium, the gas is thrown into the fixed element behind the impeller, a vacuum area is formed in the impeller to suck external fresh working medium, and continuous rotation of the impeller can ensure continuous movement of the gas working medium. Therefore, compared with the conventional circulating pump such as a sliding vane type circulating pump, a scroll type circulating pump, a screw type circulating pump, etc., the circulating pump has the advantages of small volume, light weight, low noise, etc., and is considered as the most promising air pressurization mode.

The centrifugal air compressors of the prior art are inefficient because they are typically driven by a conventional electric motor through a gearbox.

In order to solve the technical problem, Chinese patent ' a high-speed direct-drive centrifugal two-stage air compressor ' (publication number: CN110374892A) ' discloses a high-speed direct-drive centrifugal two-stage air compressor, which comprises a high-speed permanent magnet motor, a spline shaft, a first-stage centrifugal compressor, a second-stage compressor, a middle box body, a rotor system and an air inlet structure, wherein the middle box body is arranged between the first-stage centrifugal compressor and the second-stage compressor, a stator part of the high-speed permanent magnet motor is connected with the high-speed permanent magnet motor through the air inlet structure, air inlet of the first-stage compressor enters through the air inlet structure, compressed air at the outlet of the first-stage compressor enters a cooler through a pipeline to be cooled and then enters the inlet of the second-stage compressor. The disadvantages of this structure are: the first-stage compressor and the second-stage compressor play a role in balancing or fixing the impeller through the middle box body, the size of the whole compressor is large, and the arrangement mode is complex.

Disclosure of Invention

The embodiment of the application provides an air supercharging device with back-to-back impeller, under the prerequisite that can effectively improve the operating efficiency of compressor, can also balance axial load, shortens axial length, has compact structure's advantage.

To achieve the above object, embodiments of the present application provide an air supercharging device having back-to-back impellers, including a volute; the back-to-back impeller is arranged in the volute and comprises a first impeller and a second impeller, and the first impeller and the second impeller are arranged back-to-back and are connected into a whole through a connecting table; the first end of the rotating shaft is fixedly connected with the back-to-back impeller, and the second end of the rotating shaft is used for connecting an output shaft of a driving motor; the diffuser is arranged between the volute and the connecting platform of the back-to-back impeller and divides an inner cavity of the volute into a first cavity and a second cavity; a first air port and a second air port are arranged on the side wall of the first cavity, the center line of the first air port is overlapped with the axis of the first impeller, and the center line of the second air port is perpendicular to the axis of the first impeller and arranged towards the first impeller; and a third air port and a fourth air port are arranged on the side wall of the second cavity, the central line of the third air port coincides with the axis of the second impeller, and the central line of the fourth air port is perpendicular to the axis of the second impeller and faces the second impeller.

Further, the volute includes a first annular duct portion and a second annular duct portion disposed in an axial direction, the first annular duct portion being disposed away from the drive motor; the first air port is arranged on one side, away from the second annular pipe part, of the first annular pipe part, and the second air port is arranged on the side wall of the first annular pipe part; the third gas port is arranged on one side, far away from the first annular pipe part, of the second annular pipe part, and the fourth gas port is arranged on the side wall of the second annular pipe part.

Furthermore, a connecting part is arranged on one side, away from the first annular pipe part, of the second annular pipe part, a taper hole is arranged in the connecting part, and the size of one end, away from the second annular pipe part, of the taper hole is smaller than that of one end, close to the second annular pipe part, of the taper hole; an intermediate body is arranged in the taper hole, the intermediate body is in a circular truncated cone shape, and the outer conical surface of the intermediate body is matched with the inner wall surface of the taper hole; a second through hole is formed in the intermediate body, and a second end of the rotating shaft extends out of the second through hole and then is connected with an output shaft of the driving motor; the end of the intermediate body is connected with the shell of the driving motor.

Furthermore, a first air pipeline is arranged on one side, away from the second annular pipe part, of the first annular pipe part, and an inner cavity of the first air pipeline forms the first air port; a second air pipeline is arranged at the mouth part of the second air port; a third air port is formed between the second through hole and the rotating shaft, and a third air pipeline communicated with the third air port is arranged on the side wall of the connecting part; and a fourth air pipeline is arranged at the mouth part of the fourth air port.

Further, the volute comprises a first sub-volute and a second sub-volute which are symmetrically arranged along the axis of the back-to-back impeller; the first sub-volute and the second sub-volute are connected by a bolt.

Further, the diffuser includes along first sub-diffuser and the sub-diffuser of second of back of the body formula impeller's axis symmetry setting, first sub-diffuser with first sub-volute integrated into one piece, the sub-diffuser of second with second sub-volute is integrated into one piece.

Furthermore, a first through hole which penetrates through the back-to-back impeller along the axial direction is formed in the back-to-back impeller; the rotating shaft is a stepped shaft, and the diameter of the first end of the rotating shaft is smaller than that of the second end of the rotating shaft; the first end of the rotating shaft is provided with external threads, the first end of the rotating shaft extends out of the first through hole and then is fastened with the nut, and the back-to-back impeller is clamped between the nut and the second end of the rotating shaft.

Further, the first air port is a first air inlet, and the second air port is a first air outlet; the third air port is a second exhaust port, and the fourth air port is a second air inlet port.

Further, the first air port is a first air inlet, and the second air port is a first air outlet; the third air port is a second air inlet, and the fourth air port is a second air outlet.

Further, the first exhaust port communicates with the second intake port.

Compared with the prior art, the application has the following beneficial effects:

1. this application is through the back-to-back formula impeller and the integral type casing that adopt the integral type, under the prerequisite that can effectively improve the operating efficiency of compressor, can also balance axial load, shortens axial length, has compact structure's advantage.

2. Two back of body back formula impellers in this application are compression wheel and expansion pulley respectively, have both solved the problem of tail gas energy utilization on fuel cell air charging system, have simplified the arrangement of air compressor machine complete machine again simultaneously, have overcome the problem that the air compressor machine size is too big, axial load can't be balanced after adding the expansion pulley and carrying out tail gas recovery.

3. Two back of body back formula impellers in this application are the compression wheel of different stages, have balanced the axial force promptly, have realized multistage compression again, have simplified the arrangement of air compressor machine complete machine simultaneously.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a cross-sectional view of an air charging system having back-to-back impellers according to an embodiment of the present application;

FIG. 2 is a schematic perspective view of an air supercharger with back-to-back impellers according to an embodiment of the present disclosure;

fig. 3 is a schematic perspective view of a back-to-back impeller according to an embodiment of the present disclosure;

fig. 4 is a schematic perspective view of a first sub-volute and first sub-diffuser integrated piece according to an embodiment of the present application;

FIG. 5 is a schematic perspective view of a second sub-volute and second sub-diffuser integrated member according to an embodiment of the present application;

FIG. 6 is a schematic perspective view of an intermediate in an embodiment of the present application;

FIG. 7 is a cross-sectional view of an intermediate body in an embodiment of the present application;

fig. 8 is a schematic perspective view of a rotating shaft in an embodiment of the present application.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

In the description of the present application, it is to be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present application and simplifying the description, but do not indicate or imply that the referred device or element must have a particular orientation, be constructed in a particular orientation, and be operated, and thus should not be construed as limiting the present application.

In the description of the present application, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; the specific meaning of the above terms in the present application can be understood in a specific case by those of ordinary skill in the art.

The terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless otherwise specified.

Referring to fig. 1 to 3, an embodiment of the present application provides an air supercharging apparatus having a back-to-back impeller, including a volute 1, a back-to-back impeller 2, a rotating shaft 3, and a diffuser 4. Back-to-back impellers 2 are arranged in a volute 1. The back-to-back impeller 2 comprises a first impeller 21 and a second impeller 22, wherein the first impeller 21 and the second impeller 22 are arranged back-to-back and are connected into a whole through a connecting platform 23. The first end of the rotating shaft 3 is fixedly connected with the back-to-back impeller 2, and the second end of the rotating shaft 3 is used for connecting an output shaft of a driving motor (not shown). The diffuser 4 is arranged between the volute 1 and the connecting platform 23 of the back-to-back impeller 2, and divides the inner cavity of the volute 1 into a first cavity 7 and a second cavity 8. The side wall of the first cavity 7 is provided with a first air port 11 and a second air port 12, the first air port 11 coincides with the axis of the first impeller 21, and the second air port 12 is perpendicular to the axis of the first impeller 21 and faces the first impeller 21. The side wall of the second cavity 8 is provided with a third air port 13 and a fourth air port 14, the axis of the third air port 13 coincides with the axis of the second impeller 22, and the fourth air port 14 is perpendicular to the axis of the second impeller 22 and is arranged towards the second impeller 22.

With continued reference to fig. 1 and 2, in some embodiments, the volute 1 includes axially disposed first and second

annular duct portions

15, 16, the first annular duct portion 15 being disposed remotely from the drive motor. The first gas port 11 is provided on a side of the first annular pipe portion 15 away from the second annular pipe portion 16, and the second gas port 12 is provided on a side wall of the first annular pipe portion 15. The third gas port 13 is provided on the side of the second annular pipe portion 16 away from the first annular pipe portion 15, and the fourth gas port 14 is provided on the side wall of the second annular pipe portion 16.

Referring to fig. 1, in some embodiments, the side of the second annular pipe portion 16 remote from the first annular pipe portion 15 is provided with a connection portion 17, and a tapered hole 173 is provided in the connection portion 17, the dimension of the end of the tapered hole 173 remote from the second annular pipe portion 16 being smaller than the dimension of the end near the second annular pipe portion 16. The intermediate body 5 is arranged in the taper hole 173. Referring to fig. 6 and 7, the intermediate body 5 has a truncated cone shape, and the outer tapered surface of the intermediate body 5 is fitted to the inner wall surface of the tapered hole 173. The middle body 5 is internally provided with a second through hole 51, the second end of the rotating shaft 3 extends out of the second through hole 51 and then is connected with an output shaft of the driving motor, and the end part of the middle body 5 is connected with a shell of the driving motor, so that the middle body 5 cannot slip off from the volute 1 along with the working vibration of the compressor.

With continued reference to fig. 6 and 7, in some embodiments, the small end of the central body 5 is provided with a cylindrical projection 53 on which threads or the like may be machined to effect coupling of the central body 5 to the drive mechanism housing.

Referring to fig. 1 and 2, in some embodiments, a side of the first annular tube portion 15 remote from the second annular tube portion 16 is provided with a first gas conduit 151, an inner cavity of the first gas conduit 151 forming the first gas port 11. The second air duct 152 is disposed at the mouth of the second air port 12, the third air port 13 is formed between the second through hole 51 and the rotating shaft 3, and the third air duct 171 communicated with the third air port 13 is disposed on the side wall of the connecting portion 17. The mouth of the fourth port 14 is provided with a fourth air conduit 161. Specifically, a third through hole 172 is provided on a side wall of the connecting portion 17, referring to fig. 6, a fourth through hole 52 is provided on a side wall of the intermediate body 5, and the third air duct 171 is communicated with the third air port 13 through the third through hole 172 and the fourth through hole 52.

Referring to fig. 4 and 5, in some embodiments, to facilitate disassembly, volute 1 includes first and second sub-volutes 18, 19 symmetrically disposed along its axis. The first sub-volute 18 and the second sub-volute 19 are connected by bolts (not shown). Specifically, a plurality of first connection holes 181 arranged side by side in the axial direction are formed in the side wall of the first sub-volute 18, a plurality of second connection holes 191 arranged side by side in the axial direction are formed in the side wall of the second sub-volute 19, after the first sub-volute 18 is in butt joint with the second sub-volute 19, the positions of the first connection holes 181 correspond to the positions of the second connection holes 191, and bolts sequentially penetrate through the first connection holes 181 and the second connection holes 191 and then are fastened with nuts.

When the solution in which the scroll casing 1 includes the first sub-scroll casing 18 and the second sub-scroll casing 19 is adopted, in some embodiments, for convenience of processing, the diffuser 4 includes the second sub-diffuser 42 and the second sub-diffuser 42 symmetrically disposed along the axis of the back-to-back impeller 2. In order to prevent the diffuser 4 from loosening during operation of the embodiment of the present application, the second sub-diffuser 42 and the second sub-diffuser 42 are both semi-annular, the second sub-diffuser 42 and the first sub-volute 18 are integrally formed, and the second sub-diffuser 42 and the second sub-volute 19 are integrally formed. Specifically, the second sub-diffuser 42 is integrally cast with the first sub-volute 18, and the second sub-diffuser 42 is integrally cast with the second sub-volute 19.

With continued reference to fig. 4 and 5, to facilitate alignment during installation, in some embodiments, the abutting surface of the first sub-diffuser is provided with a first positioning protrusion 43 and a first positioning groove 44, and the first positioning protrusion 43 and the first positioning groove 44 are respectively located on two sides of the axis of the back-to-back impeller 2. The abutting surface of the second sub diffuser 42 is provided with a second positioning protrusion 45 matched with the first positioning groove 44 and a second positioning groove 46 matched with the first positioning protrusion 43, after the second sub diffuser 42 is abutted with the second sub diffuser 42, the first positioning protrusion 43 is embedded into the second positioning groove 46, and the second positioning protrusion 45 is embedded into the first positioning groove 44.

Referring to fig. 1, 3 and 8, the back-to-back impeller 2 is provided with a first through hole 24 penetrating in the axial direction inside. The rotating shaft 3 is a stepped shaft, the diameter of the first end of the rotating shaft 3 is smaller than that of the second end of the rotating shaft 3, the first end of the rotating shaft 3 is provided with an external thread 31, the first end of the rotating shaft 3 extends out of the first through hole 24 and then is fastened with a nut, and the back-to-back impeller 2 is clamped between the nut and the second end of the rotating shaft 3. The second end of the rotating shaft 3 is hermetically connected with the first through hole 24. For more firm installation, the inner wall of the first through hole 24 and the outer circle of the rotating shaft 3 can be bonded or in interference fit.

For the convenience of installation, in some embodiments, the outer diameter of the external thread 31 is smaller than the diameter of the smooth section of the rotating shaft 3, and the first through hole 24 is a stepped hole having a smaller diameter near one end of the external thread 31 than at the other end.

Referring to fig. 1 and 2, in order to simultaneously solve the problem of exhaust gas energy utilization in the air supercharging system of the fuel cell, the second impeller 22 is an expansion wheel, the first impeller 21 is a compression wheel, the first air inlet 11 is a first air inlet, the second air outlet 12 is a first air outlet, the third air outlet 13 is a second air outlet, and the fourth air outlet 14 is a second air inlet.

Therefore, the gas to be compressed by the compression wheel enters from the first air port 11, is compressed by the first impeller 21, is expanded by the diffuser 4, and then sequentially flows through the first annular pipe portion 15, the second air port 12 and the second air pipe 152 to be collected.

The tail gas which needs to be recovered by the expansion wheel enters from the fourth air port 14, flows through the second annular pipe part 16, is expanded by the diffuser 4, pushes the second impeller 22 to rotate, and is discharged into the air through the third air pipe 171 after flowing through the third air port 13, the fourth through hole 52 and the third through hole 172 in sequence, so that the synchronous operation of expansion and compression can be realized, and the energy of driving the first impeller 21 to rotate by the driving motor is saved.

With continued reference to fig. 1 and 2, in order to increase the intake air flow rate, the first impeller 21 and the second impeller 22 are both compression wheels, and the first impeller 21 and the second impeller 22 are the same stage, the first air port 11 is a first air inlet, the second air port 12 is a first air outlet, the third air port 13 is a second air inlet, and the fourth air port 14 is a second air outlet.

Therefore, the gas to be compressed by the first impeller 21 enters from the first air port 11, is compressed by the first impeller 21, is expanded by the diffuser 4, and then flows through the first annular pipe portion 15, the second air port 12, and the second air pipe 152 in sequence to be collected. Similarly, the tail gas to be compressed by the second impeller 22 enters the third air pipe 171, flows through the third through hole 172, the fourth through hole 52 and the third air port 13 in sequence, is compressed by the second impeller 22, is expanded by the diffuser 4, and then flows through the second annular pipe portion 16, the fourth air port 14 and the fourth air pipe 161 in sequence, and is collected.

With continued reference to fig. 1 and 2, in order to increase the compression ratio of the compressor, the first impeller 21 and the second impeller 22 are both compression wheels, the first air inlet 11 is a first air inlet, the second air outlet 12 is a first air outlet, the third air outlet 13 is a second air inlet, and the fourth air outlet 14 is a second air outlet, and the first air outlet is communicated with the second air inlet.

Therefore, the gas to be compressed by the first impeller 21 and the second impeller 22 enters from the first air port 11, is compressed by the first impeller 21, is expanded by the diffuser 4, sequentially flows through the first annular tube portion 15, the second air port 12 and the second air duct 152, enters the third air duct 171, sequentially flows through the third through hole 172, the fourth through hole 52 and the third air port 13, is compressed by the second impeller 22, is expanded by the diffuser 4, sequentially flows through the second annular tube portion 16, the fourth air port 14 and the fourth air duct 161, and is collected. Thus, multi-stage compression can be realized, and the compression ratio of the supercharger can be improved.

The above is only an embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions within the technical scope of the present disclosure should be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. An air charging device having back-to-back impellers, comprising:

a volute;

the back-to-back impeller is arranged in the volute and comprises a first impeller and a second impeller, and the first impeller and the second impeller are arranged back-to-back and are connected into a whole through a connecting table;

the first end of the rotating shaft is fixedly connected with the back-to-back impeller, and the second end of the rotating shaft is used for connecting an output shaft of a driving motor;

the diffuser is arranged between the volute and the connecting platform of the back-to-back impeller and divides an inner cavity of the volute into a first cavity and a second cavity;

a first air port and a second air port are arranged on the side wall of the first cavity, the center line of the first air port is overlapped with the axis of the first impeller, and the center line of the second air port is perpendicular to the axis of the first impeller and arranged towards the first impeller; and a third air port and a fourth air port are arranged on the side wall of the second cavity, the central line of the third air port coincides with the axis of the second impeller, and the central line of the fourth air port is perpendicular to the axis of the second impeller and faces the second impeller.

2. The air supercharging device having back-to-back impellers of claim 1,

the volute comprises a first annular pipe part and a second annular pipe part which are arranged along the axial direction, and the first annular pipe part is arranged far away from the driving motor;

the first air port is arranged on one side, away from the second annular pipe part, of the first annular pipe part, and the second air port is arranged on the side wall of the first annular pipe part;

the third gas port is arranged on one side, far away from the first annular pipe part, of the second annular pipe part, and the fourth gas port is arranged on the side wall of the second annular pipe part.

3. The air supercharging device having back-to-back impellers of claim 2,

a connecting part is arranged on one side, away from the first annular pipe part, of the second annular pipe part, a taper hole is arranged in the connecting part, and the size of one end, away from the second annular pipe part, of the taper hole is smaller than that of one end, close to the second annular pipe part, of the taper hole; an intermediate body is arranged in the taper hole, the intermediate body is in a circular truncated cone shape, and the outer conical surface of the intermediate body is matched with the inner wall surface of the taper hole; a second through hole is formed in the intermediate body, and a second end of the rotating shaft extends out of the second through hole and then is connected with an output shaft of the driving motor; the end of the intermediate body is connected with the shell of the driving motor.

4. The air supercharging device with back-to-back impellers of claim 3, wherein a side of the first annular duct portion remote from the second annular duct portion is provided with a first air duct, an inner cavity of the first air duct forming the first air port; a second air pipeline is arranged at the mouth part of the second air port;

a third air port is formed between the second through hole and the rotating shaft, and a third air pipeline communicated with the third air port is arranged on the side wall of the connecting part; and a fourth air pipeline is arranged at the mouth part of the fourth air port.

5. The air supercharging device having a back-to-back impeller of claim 1, wherein the volute includes a first sub-volute and a second sub-volute symmetrically disposed along an axis of the back-to-back impeller; the first sub-volute and the second sub-volute are connected by a bolt.

6. The air booster device with the back-to-back impeller of claim 5, wherein the diffuser includes a first sub-diffuser and a second sub-diffuser symmetrically disposed along an axis of the back-to-back impeller, the first sub-diffuser is integrally formed with the first sub-volute, and the second sub-diffuser is integrally formed with the second sub-volute.

7. The air supercharging apparatus having a back-to-back impeller according to claim 1, wherein the back-to-back impeller is provided inside with a first through hole that penetrates in an axial direction; the rotating shaft is a stepped shaft, and the diameter of the first end of the rotating shaft is smaller than that of the second end of the rotating shaft; the first end of the rotating shaft is provided with external threads, the first end of the rotating shaft extends out of the first through hole and then is fastened with the nut, and the back-to-back impeller is clamped between the nut and the second end of the rotating shaft.

8. The air supercharger having back-to-back impellers of any one of claims 1-7,

the first air port is a first air inlet, and the second air port is a first air outlet; the third air port is a second exhaust port, and the fourth air port is a second air inlet port.

9. The air supercharging device having back-to-back impellers of claim 1,

the first air port is a first air inlet, and the second air port is a first air outlet; the third air port is a second air inlet, and the fourth air port is a second air outlet.

10. The air booster device with back-to-back impellers of claim 9, characterized in that the first exhaust port is in communication with the second intake port.