JPH10141220A - Muffler structure of double end piston-type compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a muffler structure of a double end pistontype compressor having a structure in which discharge gas from one compression chamber and discharge gas from the other compression chamber are smoothly joined to each other in a muffler space. SOLUTION: Respective gas passage 46, 47 connect respective compression chambers 23, 24 faced to each other to a muffler chamber 42 through discharge chambers 32, 33. Respective gas passages 46, 47 are composed of linear first passages 46a, 47a and second passages 46b, 47b. The center axes S2 of the second passages 46b, 47b are parallel deviated from the center axes S1 of the first passages 46a, 47a outward from cylinder blocks 11a, 11b, and the shapes of respective gas passages 46, 47 are formed into crank shapes as a whole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-headed piston type compressor applied to, for example, a vehicle air conditioning system, and more particularly to a muffler structure of the compressor.

[0002]

2. Description of the Related Art In a double-headed piston type compressor, a cylinder bore is formed in a cylinder block constituting a part of a housing, and a double-headed piston is accommodated in the cylinder bore. The front-side compression chamber is formed so as to be surrounded by a front-side piston end surface and a cylinder bore. The rear compression chamber is formed so as to be surrounded by a rear piston end surface and a cylinder bore. And
By the reciprocating motion of the piston, refrigerant gas is sucked into each compression chamber, compressed, and discharged.

Here, due to the compression operation of the compressor described above, vibration and noise are generated due to the pressure pulsation of the discharge gas. For this reason, conventionally, various compressors provided with a muffler have been proposed. For example, according to the present applicant,
In the technology disclosed in JP-A-152077, a muffler space is formed in an outer portion of a cylinder block. The discharge gas from the front compression chamber flows into the muffler space via the front gas passage. The discharge gas from the rear compression chamber flows into the muffler space via the rear gas passage. Therefore, the two discharge gases are merged in the muffler space, and the pressure pulsation is attenuated by the expansion type muffler function of the muffler space.

[0004]

However, in the above-mentioned prior art, the opening of the front gas passage and the opening of the rear gas passage are arranged to face each other in the muffler space. The shape of each gas passage is a straight line with the same central axis as the gas passage facing each other. Therefore, the inflow direction line of the discharge gas flowing from the front compression chamber and the inflow direction line of the discharge gas flowing from the rear compression chamber overlap in the muffler space, and the two discharge gases collide in front. I couldn't make a smooth merge. If the two discharge gases are not merged smoothly in the muffler space, the muffler effect by the muffler space is not effectively exerted, and the pressure loss of the discharge gas in the muffler space is increased.

The present invention has been made in view of the problems existing in the above prior art, and an object of the present invention is to provide a method in which a discharge gas from one compression chamber and a discharge gas from the other compression chamber are muffled. An object of the present invention is to provide a muffler structure of a double-headed piston type compressor that is configured to smoothly merge in a space.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, a muffler space is formed in a housing, and a compression chamber formed by being surrounded by one piston end surface and a cylinder bore, and the other. Each of the compression chambers formed by being surrounded by the piston end face and the cylinder bore is connected to the muffler space via a gas passage, and the inflow direction line of the discharge gas flowing into the muffler space from one compression chamber is connected to the other. A muffler structure in which the shape of the gas passage is set so as to be inclined with respect to the inflow direction line of the discharge gas flowing from the compression chamber and to intersect both inflow direction lines in the muffler space.

According to the second aspect of the present invention, a large-capacity portion is provided in the muffler space between the intersection of the two inflow direction lines and the outlet of the muffler space to increase the cross-sectional area of the combined discharge gases. It is a thing.

According to the third aspect of the present invention, a crank chamber for accommodating a mechanism for reciprocating a piston is formed in the housing, and the muffler space is disposed on an outer peripheral side of the crank chamber. The gas passage is opened to the muffler space at a position shifted to the outside of the housing as compared with a portion on the compression chamber side.

According to a fourth aspect of the present invention, the shape of the gas passage near the opening to the muffler space is formed in a crank shape. In the invention of claim 5, the shape near the opening to the muffler space in the two gas passages is linear, and the center axis of the same straight portion in one gas passage is relative to the center axis of the straight portion in the other gas passage. And both center axes intersect in the muffler space.

(Operation) In the first aspect of the present invention, the suction, compression and discharge of the refrigerant gas in each compression chamber are performed by the reciprocating motion of the double-headed piston. And
The discharge gas from each compression chamber flows into the muffler space via the gas passage.

Here, by suitably setting the shape of the gas passage, the flow direction line of the discharge gas flowing from one compression chamber into the muffler space is changed to the flow direction of the discharge gas flowing from the other compression chamber. While being inclined with respect to the direction line, both inflow direction lines intersect in the muffler space. Therefore, the discharge gas from one compression chamber and the discharge gas from the other compression chamber merge smoothly at an angle in the muffler space. The pressure pulsation of the combined discharge gases is attenuated by the muffler action of the muffler space.

According to the second aspect of the present invention, by providing the large-capacity portion in the muffler space and expanding the passage cross-sectional area of the merged discharge gas, the discontinuity of the passage cross-section in the muffler space is reduced. The enhanced and inflatable muffler effect is effectively achieved.

According to the third aspect of the present invention, the gas passage is opened to the muffler space at a position shifted to the outside of the housing as compared with a portion on the compression chamber side. Therefore, for example, it is possible to increase the volume of the crank chamber by the same amount.

According to the fourth aspect of the present invention, the shape of the gas passage near the opening to the muffler space is formed in a crank shape. Discharge gas from each compression chamber tends to flow in the same gas passage in the shortest distance, and as a result, the inflow direction line of one discharge gas is inclined with respect to the inflow direction line of the other discharge gas, Both inflow direction lines intersect in the muffler space. Therefore, the discharge gas from one compression chamber and the discharge gas from the other compression chamber merge smoothly at an angle in the muffler space.

According to the fifth aspect of the present invention, the discharge gas from each compression chamber flows through the gas passages along the straight gas passages and flows into the muffler space. But,
In both gas passages, the center axis of the straight portion in one gas passage is inclined with respect to the center axis of the straight portion in the other gas passage, and both center axes intersect in the muffler space. Therefore, the discharge gas from one compression chamber and the discharge gas from the other compression chamber merge smoothly at an angle in the muffler space.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, first and second embodiments of the present invention will be described. In the second embodiment, the same or equivalent members as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

(First Embodiment) As shown in FIG. 1, a pair of cylinder blocks 11A and 11B are joined to each other at opposing edges. The front housing 12
It is joined to the front end surface of the front cylinder block 11A via a front valve body 13. The rear housing 14 is joined to the rear end face of the rear cylinder block 11B via a rear valve forming body 15. In the present embodiment, the cylinder blocks 11A and 11B, the front housing 12, and the rear housing 14 each constitute a housing structure.

A plurality of bolt insertion holes 16 (only one is shown in the drawing) are formed in the rear housing 14 from the front housing 12 through the cylinder blocks 11A and 11B. The same number of through bolts 17 are inserted into the bolt insertion holes 16 from the front housing 12 side, and are screwed into the screw holes 16a formed by the bolt insertion holes 16 of the rear housing 14 with screw portions 17a formed at the distal ends thereof. Have been combined. The front housing 12 and the rear housing 14 are fastened and fixed to the end surfaces of the corresponding cylinder blocks 11A and 11B by the through bolts 17.

The drive shaft 18 is connected to the cylinder block 11.
A, 11B and the center of the front housing 12 are rotatably supported via a pair of radial bearings 19. The lip seal 20 is interposed between the outer periphery of the front end of the drive shaft 18 and the front housing 12. The drive shaft 18 is operatively connected to an external drive source such as a vehicle engine via a clutch mechanism (not shown). When the clutch mechanism is connected, the driving force of the external drive source is transmitted and the drive shaft 18 is rotated.

A plurality of cylinder bores 21 are provided on the drive shaft 1.
8, each cylinder block 11A,
It penetrates and is formed at predetermined intervals on the same circumference between both ends of 11B. The same number of double-headed pistons 22 are reciprocally fitted and supported in the respective cylinder bores 21, and compression chambers 23 (front side) are provided in the respective cylinder bores 21 between both end faces thereof and the valve forming bodies 13 and 15. ) And 24 (rear side).

The crank chamber 25 is defined in the middle of the cylinder blocks 11A and 11B. The swash plate 26 is fitted and fixed to the drive shaft 18 in the crank chamber 25, and its outer peripheral portion is
2 moored in the middle. And the piston 22
Is reciprocated via the swash plate 26 by the rotation of the drive shaft 18. A pair of thrust bearings 28 are interposed between both end surfaces of the swash plate 26 and inner end surfaces of the cylinder blocks 11A and 11B. The swash plate 26 is interposed between the two cylinder blocks 11A and 11B via the thrust bearing 28. It is clamped and held. The crank chamber 25 is connected to an external refrigerant circuit (not shown) and forms a suction pressure region.

The front suction chamber 29 and the rear suction chamber 3
Numeral 0 is formed at the center of the front housing 12 and the rear housing 14. The suction passage 31 is provided between the two cylinder blocks 11A, 11B and the valve body 13,
The front suction chamber 29 and the rear suction chamber 30 are connected to the crank chamber 25.
The front-side discharge chamber 32 and the rear-side discharge chamber 33 are formed in an annular shape at the outer peripheral portions in the front housing 12 and the rear housing 14. Both discharge chambers 32, 33
Are equal.

A plurality of suction holes 34 are provided in each cylinder bore 21.
Corresponding to the valve forming members 13 and 15. The suction valve 35 is formed in each of the valve forming bodies 13 and 15, and opens and closes each of the suction holes 34. Then, as the piston 22 moves from the top dead center position to the bottom dead center position, the suction valve 35 is opened, and the corresponding compression chambers 23,
The refrigerant gas is sucked into 24.

A plurality of discharge holes 36 are provided in the respective valve forming bodies 13 and 15 so as to correspond to the respective cylinder bores 21. The discharge valve 37 is formed in each of the valve forming bodies 13 and 15, and opens and closes each of the discharge holes 36. As the piston 22 moves from the bottom dead center position to the top dead center position, the discharge valve 37 moves.
, The refrigerant gas in each of the compression chambers 23 and 24 is compressed to a predetermined pressure and discharged to the corresponding discharge chambers 32 and 33. In addition, the opening degree of the discharge valve 37 depends on each valve forming body 1.
3 and 15 are defined by the retainer 38 provided.

Next, the muffler structure of the double-headed piston type compressor having the above configuration will be described. Front muffler 41
A is formed integrally with the outer portion of the front cylinder block 11A, and the rear muffler portion 41B is formed integrally with the outer portion of the rear cylinder block 11B. Both muffler part 41
The inner spaces of A and 41B are the muffler portions 41 facing each other.
B, 41A. Both muffler part 41
A, 41B has an inner space of both cylinder blocks 11B, 1B.
The two muffler portions 41A, 41 are integrated by joining 1A.
A muffler space 42 straddling B is formed.

The front gas passage 46 is formed from the front valve body 13 to the front cylinder block 11A, and connects the front compression chamber 23 to the muffler space 42 via the front discharge chamber 32. . The rear gas passage 47 extends from the rear valve body 15 to the rear cylinder block 11 </ b> B.
4 is connected to a muffler space 42 via a rear discharge chamber 33.

The first and second gas passages 46 and 47 will be described in detail.
Each of the valve forming bodies 13 and 15 is formed in a straight line from the outer peripheral portion to the cylinder block 11A or 11B so as to open at the outermost peripheral portion thereof. The second passages 46b and 47b are opened inside the muffler space 42 at the lower part of the front wall surface or the rear wall surface, respectively.
It is drilled in each cylinder block 11A, 11B.
The second passages 46b and 47b correspond to the corresponding first passages 4.
6a and 47a are connected at the back. The first passage 46a, the first passage 47a, and the second passage 46b
The center axes S1 and S2 of the and the second passage 47b coincide with each other, and the passage length and the inner diameter are equal. In the present embodiment, the center axis S2 of the second passages 46b and 47b is aligned with the center axis S2 of the first passages 46a and 47a.
1, the gas passages 46 and 47 have a crank shape as a whole, and are shifted in parallel to the outside of the cylinder blocks 11A and 11B (upper side in the drawing).

Here, the discharge gas flowing from the discharge chambers 32 and 33 into the gas passages 46 and 47 flows into the gas passages 4 and 47, respectively.
It is intended to flow in the shortest distance within 6,47. That is,
The flow path of the discharge gas in each of the gas passages 46 and 47 is such that the shape of the gas passages 46 and 47 is a crank shape.
The first and second passages 46a, 46b, 47a, 47b are defined to be inclined toward the discharge chambers 32, 33 with respect to the central axes S1, S2. Therefore, as shown in FIG. 2, the flow direction line L1 of the discharge gas from the front discharge chamber 32 flowing into the muffler space 42 is different from the flow direction line L2 of the discharge gas from the rear discharge chamber 33. The two inflow direction lines L1 and L2 intersect in the muffler space 42.

A discharge port 48 as an outlet of the muffler space 42
Is bored in the rear muffler portion 41B. The muffler space 42 is connected to an external refrigerant circuit via the discharge port 48. The concave portion 41a is recessed in the upper part of the front wall surface and the rear wall surface inside the muffler space 42, and by providing the concave portion 41a, a large capacity portion 42a is formed in the muffler space 42. ). The large-capacity portion 42a is located at the intersection K of the two inflow direction lines L1 and L2.
The discharge gas existing between the discharge gas and the discharge port 48 has a larger passage cross-sectional area in the muffler space 42 of the combined discharge gas, thereby increasing the discontinuity of the passage cross-section.

Next, the operation of the double-headed piston type compressor having the above configuration will be described. When the driving force is transmitted from the external drive source such as a vehicle engine to the drive shaft 18 by the connection of the clutch mechanism, the reciprocating motion of the piston 22 starts in conjunction with the rotation of the swash plate 26. When the reciprocation of the piston 22 starts, the compression chambers 23 and 24
Of the refrigerant gas from the suction chambers 29 and 30, the compression in the compression chambers 23 and 24, and the discharge chamber 32 and
A cycle of discharging to 33 is started.

As shown by the arrows in FIG. 2, the discharge gas discharged into the front and rear discharge chambers 32 and 33 passes through the gas passages 46 and 47, respectively, to form the muffler space 4.
It flows into 2. At this time, as described above, the flow direction line L1 of the discharge gas from the front discharge chamber 32 flowing into the muffler space 42 is inclined with respect to the flow direction line L2 of the discharge gas from the rear discharge chamber 33. And intersect in the muffler space 42. Therefore, the front side discharge chamber 32
And the gas discharged from the rear-side discharge chamber 33 are smoothly merged at an angle in the muffler space 42. Then, the combined discharge gas is discharged from the discharge port 4.
During the period 8, the pressure pulsation is attenuated to a small value due to the effective inflatable muffler effect particularly by the large capacity portion 42 a. As a result, vibration and noise caused by the pressure pulsation of the discharge gas are reduced.

The present embodiment having the above configuration has the following effects. (1) By forming the gas passages 46 and 47 in the shape of a crank, the inflow direction line L1 of the discharge gas from the front discharge chamber 32 flowing into the muffler space 42 is transferred from the rear discharge chamber 33. It is inclined with respect to the inflow direction line L2 of the discharge gas, and both inflow direction lines L1 and L2 intersect in the muffler space 42. Therefore, the two discharge gases smoothly merge at an angle in the muffler space 42. As a result, the muffler action by the muffler space 42 is effectively exerted, and the pressure loss due to collision between the two discharge gases in the muffler space 42 can be reduced.

(2) The large-capacity section 42a is
Between the intersection K of the two inflow direction lines L1 and L2 and the discharge port 48, and enlarges the cross-sectional area of the merged discharge gases in the muffler space 42. Accordingly, the discontinuity of the passage cross-sectional area of the discharge gas in the muffler space 42 is increased, and the expansion-type muffler function of the muffler space 42 is more effectively achieved.

(3) For example, the first passages 46a, 47a
Is directly extended toward the crank chamber 25 and connected to the muffler space 42. In this case, the first passage 4
6a and 47a are thin portions 11 of the cylinder blocks 11A and 11B for shielding the crank chamber 25 and the muffler space 42.
a. In other words, when such a configuration is adopted, the thin portion 11a must be displaced toward the crank chamber 25 side, and the volume of the crank chamber 25 becomes small. For example, the crank chamber 25 constitutes a passage of the suction gas as described above, and also serves as a muffler for attenuating the pressure pulsation of the suction gas. Therefore, the volume of the crank chamber 25, which is the expansion space for the intake gas, is desired to be as large as possible.

In this embodiment, the gas passages 46, 4
The center axis S2 of the second passages 46b and 47b constituting the seventh member 7 is shifted to the outside of the cylinder blocks 11A and 11B with respect to the center axis S1 of the first passages 46a and 47a. That is, instead of shifting the thin portion 11a to the crank chamber 25 side, the gas passages 46 and 47 (the first passage 46) are used.
a, 47a) is compared with a portion (second passages 46b, 47b) on the compression chambers 23, 24 side, and the cylinder block 11A,
An opening was made in the muffler space 42 at a position shifted outward from 11B. Therefore, the capacity of the crank chamber 25 can be increased, and, for example, the effect of attenuating the pressure pulsation of the intake gas becomes large.

(4) For example, if the compressor of this embodiment is 10
Assuming that each cylinder is a cylinder (five cylinders on one side), each discharge chamber 32, 3
The pressure pulsation of the discharge gas discharged into 3 has a rotation fifth-order component whose phase is shifted by 180 ° from each other as main components.
Here, the attenuation rate of the pressure pulsation until the discharge gas discharged to the front discharge chamber 32 reaches the muffler space 42 and the pressure pulsation until the discharge gas discharged to the rear discharge chamber 33 reaches the muffler space 42. Is different, the pressure pulsation of the discharged gas merged in the muffler space 42 is mainly composed of two rotation fifth-order components having different peaks. Therefore, the muffler effect by the muffler space 42 is not effectively exerted.

However, in the present embodiment, the discharge chambers 32 and 33 have the same volume, and the passage cross-sectional areas and the passage lengths (degrees of throttle) of the gas passages 46 and 47 are the same. That is, the attenuation rate of the pressure pulsation until the discharge gas discharged to the front side discharge chamber 32 reaches the muffler space 42 and the pressure pulsation until the discharge gas discharged to the rear side discharge chamber 33 reaches the muffler space 42. The attenuation rate is set to be substantially the same. Therefore, in the muffler space 42, the peaks of the two rotation fifth-order components coincide, and one rotation tenth-order component becomes the main component of the pressure pulsation of the discharge gas. As a result, the muffler action by the muffler space 42 is effectively performed, and further reduction in vibration and noise can be achieved.

(5) The muffler space 42 is sealed simultaneously with the joining of the two cylinder blocks 11B and 11A. Accordingly, the muffler space 42 is not required to be a separate member from the cylinder blocks 11B and 11A, and the number of components constituting the compressor can be reduced. As a result, the number of steps of assembling the compressor can be reduced, and the manufacturing cost can be reduced.

(Second Embodiment) FIG. 3 shows a second embodiment. In the present embodiment, the portions of the front gas passage 51 and the rear gas passage 52 located on the opening side to the muffler space 42 are linear, and one of the linear portions 51
The central axis I1 of a (which may be considered the inflow direction line L1) is
The center axis I2 of the other straight portion 52a (the inflow direction line L2
To the discharge chambers 32 and 33 respectively. The central axes I1 and I2 of the straight portions 51a and 52a intersect in the muffler space 42. The discharge gas from the front compression chamber 32 and the discharge gas from the rear compression chamber 33 are separated in the muffler space 42. At a smooth angle. Therefore, a muffler effect similar to that of the first embodiment is exerted, and the pressure pulsation of the discharge gas is attenuated.

In this embodiment, the same effects as those of the first embodiment are obtained. For example, the present invention can be implemented in the following modes without departing from the spirit of the present invention. (1) In the first embodiment, the second passages 46b, 4
The gas passages 46, 47 are formed in a crank shape by shifting the center axis S2 of 7b relative to the center axis S1 of the first passages 46b, 47b in the circumferential direction of the cylinder blocks 11A, 11B.

(2) In the first embodiment, the central axis S2 of the second passages 46b, 47b is aligned with the first passages 46b, 4
7b with respect to the center axis S1 of the cylinder block 11A,
Each gas passage is formed in a crank shape by being shifted inward of 11B.

(3) Contrary to the second embodiment, the linear portions 51a, 52a of the gas passages 51, 52 are inclined toward the muffler space 42. (4) Between the front housing 12 and the front cylinder block 11A, or the rear cylinder block 1
Muffler space 42 is formed between 1B and rear housing 14.

(5) The muffler space 42 extends from the front housing 12 to the rear cylinder block 11B or from the front cylinder block 11A to the rear housing 14.

(6) A muffler space 42 is formed to extend from the front housing 12 to the rear housing 14. To describe the technical idea that can be grasped from the above-described embodiment, the muffler portions 41A, 41A,
By integrally providing 41B, both muffler portions 41A, 41
The muffler space 42 is formed between B.
5. The muffler structure according to any one of 5.

In this manner, the muffler space 42 is not required to be provided separately from the housing components 11A and 11B, and the number of components constituting the compressor can be reduced. As a result, the number of compressor assembly steps is reduced,
Manufacturing costs can be reduced.

[0046]

According to the first, fourth and fifth aspects of the present invention, by suitably setting the shape of the gas passage,
The inflow direction line of the discharge gas flowing into the muffler space from one compression chamber is inclined with respect to the inflow direction line of the discharge gas flowing from the other compression chamber, and both the inflow direction lines are within the muffler space. Intersect. Therefore, the discharge gas from one compression chamber and the discharge gas from the other compression chamber merge smoothly at an angle in the muffler space.
As a result, the muffler action by the muffler space is effectively exerted, and the pressure loss due to collision between the two discharge gases in the muffler space can be reduced.

According to the second aspect of the present invention, by providing the large-capacity portion in the muffler space, the discontinuity of the passage cross section of the merged discharge gas in the muffler space is increased, and the expansion type muffler function is provided. Is effectively performed. As a result, vibration and noise due to the pressure pulsation of the discharge gas are effectively reduced.

According to the third aspect of the present invention, the gas passage is opened to the muffler space at a position shifted to the outside of the housing as compared with the part on the compression chamber side. So, for example,
It is possible to increase the volume of the crank chamber by the same amount. For example, if the crank chamber is a passage for the suction gas, the effect of attenuating the pressure pulsation of the suction gas becomes large.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a double-headed piston type compressor.

FIG. 2 is a diagram illustrating the operation of a muffler structure.

FIG. 3 is an enlarged sectional view of a main part showing a muffler structure according to a second embodiment.

[Explanation of symbols]

11A, 11B: Cylinder block as a housing component, 12: Front housing, 14: Rear housing, 21: Cylinder bore, 22: Piston, 23: Front compression chamber, 24: Rear compression chamber, 4
2 muffler space, 46 front gas passage, 47 rear gas passage, L1 inflow direction line, L2 inflow direction line.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Ito 2-1-1 Toyota-cho, Kariya-shi, Aichi Prefecture Inside Toyota Industries Corporation

Claims (5)

[Claims] 1. A cylinder bore formed in a housing formed by joining a plurality of housing components, and a double-headed piston accommodated in the cylinder bore, and suction of refrigerant gas and the like by reciprocation of the piston. In the double-headed piston compressor that performs compression and discharge, a muffler space is formed in the housing, and a compression chamber formed by being surrounded by one piston end surface and a cylinder bore, and being surrounded by the other piston end surface and a cylinder bore. Connected to the muffler space via gas passages, and the flow direction of the discharge gas flowing into the muffler space from one compression chamber is changed to the discharge gas flowing from the other compression chamber. And the shape of the gas passage was set such that both the inflow direction lines intersect in the muffler space. Hula structure. 2. A large-capacity section in the muffler space between the intersection of both inflow direction lines and the outlet of the muffler space, the large-capacity portion increasing the passage cross-sectional area of both merged discharge gases. The described muffler structure. 3. A crank chamber for housing a mechanism for reciprocating a piston is formed in the housing,
The muffler space is provided on an outer peripheral side of the crank chamber, and the gas passage is opened to the muffler space at a position shifted to the outside of the housing as compared with a part on the compression chamber side. 3. The muffler structure according to 2. 4. The muffler structure according to claim 1, wherein a shape of the gas passage near an opening to the muffler space is formed in a crank shape. 5. The shape of the two gas passages near the opening to the muffler space is linear, and the center axis of the straight portion in one gas passage is inclined with respect to the center axis of the straight portion in the other gas passage. The muffler structure according to any one of claims 1 to 3, wherein both central axes intersect in the muffler space.