JP2012136967A - Two-stage compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To downsize a two-stage compressor to the extent possible, regarding the two-stage compressor which is provided in an air conditioner capable of switching between cooling and heating and is connected to a cooling medium circuit for performing a two-stage compression freezing cycle.SOLUTION: A low stage supercharging unit (1) for supercharging the cooling medium sucked into the inlet of a low stage cylinder chamber (55) during cooling operation of the cooling medium circuit (60) is provided in the two-stage compressor (10).

Description

  The present invention relates to a two-stage compressor connected to a two-stage compression refrigeration cycle.

  Conventionally, a two-stage compressor in which compression chambers for compressing fluid are arranged in two upper and lower stages is known (see, for example, Patent Document 1). Some of these two-stage compressors are connected to a refrigerant circuit that performs a two-stage compression economizer cycle.

  By the way, when this refrigerant circuit is provided in an air conditioner capable of switching between cooling and heating, the volume of the compression chamber of the two-stage compressor is determined based on the rated capacity of heating operation or cooling operation in the air conditioner.

  In general, comparing the volume of the compression chamber determined based on the heating standard and the volume of the compression chamber determined based on the cooling standard, the volume of the compression chamber based on the cooling standard is smaller. For this reason, when the volume of the compression chamber is determined based on the cooling standard, an efficient operation is possible during the cooling operation, but the capacity becomes insufficient during the heating operation. Conversely, if the compression chamber volume is determined based on the heating standard, efficient operation is possible during heating operation, but cooling capacity is excessive during cooling operation, and efficient operation cannot be expected. Usually, it is preferable to determine the volume of the compression chamber based on the heating standard in order to prevent a lack of capacity in both the heating operation and the cooling operation.

  Here, in the case of the two-stage compressor, the intermediate pressure refrigerant in the refrigerant circuit is injected into a connection line that connects the discharge port of the low-stage compression chamber and the suction port of the high-stage compression chamber, thereby increasing the heating capacity. ing. For this reason, when determining the volume of the compression chamber based on the heating standard, it is necessary to consider the contribution ratio of the injection effect to the heating capacity. The larger the contribution ratio is set, the smaller the volume of the compression chamber can be made.

JP 2006-152931 A

  However, if the volume of the compression chamber is too small, the cooling capacity may be insufficient during the cooling operation. For this reason, the volume of the compression chamber could be reduced only within a range in which insufficient capacity during cooling operation does not occur.

  The present invention has been made in view of the above points, and an object thereof is to be connected to a refrigerant circuit that is provided in an air conditioner capable of switching between a cooling operation and a heating operation and performs a two-stage compression refrigeration cycle. In a two-stage compressor, the size of the two-stage compressor is made as small as possible without causing excess or deficiency in the cooling operation and heating operation.

In the first invention, both the high-stage compression chamber (36) and the low-stage compression chamber (37) for sucking and compressing fluid while increasing and decreasing the volume periodically extend from the low-stage compression chamber (37). A compression mechanism (12) having a low-stage suction path (1a) and a low-stage discharge path (5), and a high-stage suction path (2a) and a high-stage discharge path (6) both extending from the high-stage compression chamber (36). ) And an electric motor (13) that drives the compression mechanism (12), and the low-pressure refrigerant of the refrigerant circuit (60) that performs the two-stage compression refrigeration cycle flows through the low-stage suction passage (1a). The low-pressure line (81, 80) communicates, and the high-stage discharge path (6) communicates with the high-pressure line (80, 81) through which the high-pressure refrigerant of the refrigerant circuit (60) flows, and the low-stage discharge path ( The intermediate pressure line (82) through which the intermediate pressure refrigerant of the refrigerant circuit (60) flows is communicated with the connection line (7) that communicates the high pressure suction passage (2a) with 5),
Use of the heat source side heat exchanger (61) of the refrigerant circuit (60) that can be switched between a cooling operation (cooling operation in the case of an air conditioner) and a heating operation (heating operation in the case of an air conditioner) The premise is a two-stage compressor provided between the side heat exchanger (62).

  The two-stage compressor is connected to the low-pressure line (81, 80) through the low-stage suction passage (1a) during the cooling operation of the refrigerant circuit (60) for cooling the use-side heat exchanger (62). A low-stage supercharging section (1) for supercharging the refrigerant sucked into the low-stage compression chamber (37) is provided.

  In the first invention, the maximum amount of refrigerant sucked into the low-stage compression chamber (37) during the cooling operation by the low-stage supercharger (1) does not provide the low-stage supercharger (1). It becomes larger than the case. Accordingly, the maximum cooling capacity of the use side heat exchanger (62) during the cooling operation is increased.

In a second aspect based on the first aspect, the low-stage supercharging section (1) is opened and closed at a cycle corresponding to the operating frequency of the electric motor (13) and is low in the low-pressure line (81, 80). The low-stage suction path (1a) communicating through the stage buffer space (3b),
The sound speed of the refrigerant during the cooling operation of the refrigerant circuit (60) is c1 [m / s], the maximum operating frequency of the electric motor (13) is fmax [Hz], and the volume of the low-stage compression chamber (37) is V1 [ m3], where the passage area of the low-stage suction passage (1a) is M1 [m2], the length L1 of the low-stage suction passage (1a) is 0.9 × Lm1 ≦ L1 ≦ 1.1 × It is characterized by satisfying the relationship of Lm1 (where Lm1 = (c1 / (4 × fmax) − (V1 / M1))).

  In the second aspect of the invention, the low-stage suction passage (1a) is set to a length L1 that causes the suction refrigerant in the low-stage compression chamber (37) to be supercharged during the cooling operation. When the electric motor (13) is at the maximum operating frequency, the refrigerant sucked into the low-stage compression chamber (37) is supercharged. This increases the maximum amount of refrigerant sucked into the low-stage compression chamber (37).

  According to a third invention, in the first or second invention, during the heating operation of the refrigerant circuit (60) for heating the use side heat exchanger (62), the connection line is connected through the high-stage suction passage (2a). A high-stage supercharging section (2) for supercharging the refrigerant sucked from (7) into the high-stage compression chamber (36) is provided.

  In the third invention, the maximum amount of refrigerant sucked into the high-stage compression chamber (36) during the heating operation by the high-stage supercharger (2) is provided in the high-stage supercharger (2). It becomes larger than the case without it. Along with this, the maximum heating capacity of the use side heat exchanger (62) during the heating operation increases.

  According to a fourth invention, in the third invention, the high-stage supercharging section (2) is opened and closed at a cycle corresponding to the operating frequency of the electric motor (13) and is connected to the high-pressure line (80, 81). The high-stage suction passage (2a) communicated via the stage buffer space (4b), and the sound speed of the refrigerant during the heating operation of the refrigerant circuit (60) is c2 [m / s], and the electric motor (13) When the maximum operating frequency is fmax [Hz], the volume of the high stage compression chamber (36) is V2 [m3], and the passage area of the high stage suction path (2a) is M2 [m2], the high stage The length L2 of the suction passage (2a) satisfies the relationship of 0.9 × Lm2 ≦ L2 ≦ 1.1 × Lm2 (where Lm2 = (c2 / (4 × fmax) − (V2 / M2)). It is characterized by that.

  In the fourth aspect of the invention, the high stage communication passage portion (2a) is set to a length L2 that makes the suction refrigerant in the high stage compression chamber (36) supercharged during the heating operation. When the electric motor (13) is at the maximum operating frequency, the refrigerant sucked into the high-stage compression chamber (36) is supercharged. This increases the maximum amount of refrigerant sucked into the high-stage compression chamber (36).

  In a fifth aspect based on the second aspect, the high-stage suction path (2a) is configured so that the high-stage suction path is in a heating operation of the refrigerant circuit (60) for heating the use side heat exchanger (62). (2a) is a high-stage supercharger (2) that supercharges the refrigerant sucked from the connection line (7) into the high-stage compression chamber (36) through the connection line (7), and has an operating frequency of the electric motor (13). The refrigerant circuit (60) is configured to communicate with the high-pressure line (80, 81) via the high-stage buffer space (4b), and is configured to open and close at a corresponding cycle. c2 [m / s], the maximum operating frequency of the motor (13) is fmax [Hz], the volume of the high-stage compression chamber (36) is V2 [m3], and the passage area of the high-stage suction path (2a) is When M2 [m2] is set, the length L2 of the high-stage suction passage (2a) is 0.9 × Lm2 ≦ L2 ≦ 1.1 × Lm2 (only While satisfying the relationship of Lm2 = (c2 / (4 × fmax) − (V2 / M2)), the length L2 of the high stage suction path (2a) is the length of the low stage suction path (1a). It is characterized by being set shorter than L1.

  In the fifth aspect of the present invention, during the heating operation, the pressure loss of the refrigerant passing through the high stage suction path (2a) is smaller than the pressure loss of the refrigerant passing through the low stage suction path (1a). This makes it easier for more refrigerant to be drawn into the high-stage compression chamber (36) than in the low-stage compression chamber (37).

  Here, when the intermediate pressure refrigerant of the refrigerant circuit (60) is injected into the two-stage compressor (10) to increase the capacity of the heating operation, more than the low-stage compression chamber (37). If the refrigerant is sucked in, the amount of the refrigerant from the low-stage compression chamber (37) toward the high-stage compression chamber (36) increases. If the amount of the refrigerant increases excessively, it may become difficult to inject into the two-stage compressor (10), and the amount of refrigerant discharged from the high-stage compression chamber (36) may not increase.

  In the fifth aspect of the invention, more refrigerant is more easily sucked into the high-stage compression chamber (36) than in the low-stage compression chamber (37), so that the refrigerant is discharged from the high-stage compression chamber (36). The amount of refrigerant tends to increase.

In a sixth aspect based on the second aspect, the high-stage suction passage (2a) is configured so that the high-stage suction passage is in a heating operation of the refrigerant circuit (60) for heating the use-side heat exchanger (62). (2a) is a high-stage supercharger (2) that supercharges the refrigerant sucked from the connection line (7) into the high-stage compression chamber (36) through the connection line (7), and has an operating frequency of the electric motor (13). The refrigerant circuit (60) is configured to communicate with the high-pressure line (80, 81) via the high-stage buffer space (4b), and is configured to open and close at a corresponding cycle. c2 [m / s], the maximum operating frequency of the motor (13) is fmax [Hz], the volume of the high-stage compression chamber (36) is V2 [m3], and the passage area of the high-stage suction path (2a) is When M2 [m2] is set, the length L2 of the high-stage suction passage (2a) is
While satisfying the relationship of 0.9 × Lm2 ≦ L2 ≦ 1.1 × Lm2 (where Lm2 = (c2 / (4 × fmax) − (V2 / M2))), the passage area of the low-stage suction passage (1a) M1 is set to be larger than the passage area M2 of the high-stage suction passage (2a).

  In the sixth aspect of the invention, during the cooling operation, the pressure loss of the refrigerant passing through the low stage suction path (1a) is smaller than the pressure loss of the refrigerant passing through the high stage suction path (2a). This makes it easier for more refrigerant to be drawn into the low-stage compression chamber (37) than in the high-stage compression chamber (36). As a result, the amount of refrigerant discharged from the low-stage compression chamber (37) is likely to increase.

  According to the present invention, the maximum cooling capacity of the use side heat exchanger (62) during the cooling operation can be increased by the low stage supercharging section (1). As the maximum cooling capacity is increased, the volume of the low-stage compression chamber (37) can be reduced, and the size of the two-stage compressor can be reduced.

  According to the second aspect of the invention, the maximum refrigerant suction amount of the low-stage compression chamber (37) during the cooling operation is increased by setting the low-stage suction path (1a) to a predetermined length L1. Therefore, the volume of the low-stage compression chamber (37) can be reduced by an amount corresponding to the increase in the maximum refrigerant suction amount. Thus, the volume of the low-stage compression chamber (37) can be reduced by a relatively easy means.

  In the electric motor (13), when the operating frequency is lower than the maximum operating frequency, in other words, even if the refrigerant is supercharged at the minimum operating frequency, the maximum of the low-stage compression chamber (37) is It is difficult to increase the refrigerant suction amount. For this reason, in the second aspect of the invention, the refrigerant is supercharged when the electric motor (13) is at the maximum operating frequency for the purpose of reliably increasing the maximum refrigerant suction amount of the low-stage compression chamber (37). The length of the low-stage suction passage (1a) is set so as to be in a state.

  Moreover, according to the said 3rd invention, the maximum heating capability of the utilization side heat exchanger (62) at the time of the said heating operation can be enlarged by the said high stage supercharging part (2). As the maximum heating capacity is increased, the volume of the high-stage compression chamber (36) can be further reduced, and the size of the two-stage compressor can be further reduced.

  According to the fourth aspect of the present invention, the maximum refrigerant suction amount of the high stage compression chamber (36) during the heating operation is increased by setting the high stage suction path (2a) to a predetermined length L2. Therefore, the volume of the high-stage compression chamber (36) can be reduced by an amount corresponding to the increase in the maximum refrigerant suction amount. Thus, the volume of the high stage compression chamber (36) can be reduced by a relatively easy means.

  According to the fifth aspect of the invention, by setting the length L2 of the high stage suction passage (2a) to be shorter than the length L1 of the low stage suction passage (1a), the low stage compression chamber ( Compared to 37), more refrigerant is easily sucked into the high-stage compression chamber (36). As a result, the amount of refrigerant discharged from the high-stage compression chamber (36) is likely to increase compared to the case where the high-stage suction path (2a) and the low-stage suction path (1a) have the same length. It is possible to easily improve the capacity during heating operation.

  According to the sixth aspect of the present invention, the passage area M1 of the lower suction path (1a) is set larger than the passage area M2 of the higher stage suction path (2a), whereby the higher stage compression chamber ( Compared to 36), more refrigerant is easily sucked into the low-stage compression chamber (37). As a result, the amount of refrigerant discharged from the low-stage compression chamber (37) is likely to increase compared to the case where the high-stage suction path (2a) and the low-stage suction path (1a) have the same area. It is possible to easily improve the capacity during the cooling operation.

It is a longitudinal cross-sectional view of the two-stage compressor with a muffler concerning this embodiment. It is a longitudinal cross-sectional view near the compression mechanism of the two-stage compressor with a muffler which concerns on this embodiment. It is a transverse cross section of the compression mechanism of the two-stage compressor with a muffler concerning this embodiment. It is a refrigerant circuit figure of the air harmony device concerning this embodiment. It is a longitudinal cross-sectional view of the compression mechanism vicinity of the two-stage compressor with a muffler which concerns on the modification 1 of this embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, after describing the configuration of a two-stage compressor with a muffler (hereinafter referred to as a compressor) (10) according to an embodiment of the present invention, a refrigerant circuit (60) to which the compressor (10) is connected is provided. The air conditioner will be described.

<Two-stage compressor with muffler>
FIG. 1 is a longitudinal sectional view showing a configuration of a compressor (10) according to the present embodiment. As shown in FIG. 1, the compressor (10) with a muffler includes a compressor main body (10a) and a muffler (3,4).

-Compressor body-
The said compressor main-body part (10a) is provided with the casing (11), the compression mechanism (12), and the electric motor (13), as shown in FIG.

(casing)
The casing (11) is composed of a vertically long cylindrical sealed container with both ends closed, and a cylindrical body (14a) and an upper end plate (14b) for closing the upper end side of the body (14a) A lower end plate (14c) for closing the lower end side of the body (14a). First to third inlet tubes (15a, 15b, 15c) are attached to the body part (14a) through the lower part of the body part (14a). A discharge pipe (17) is attached through the upper part of the upper body (14a). The electric motor (13) and the compression mechanism (12) are accommodated in the casing (11).

  A terminal terminal (9) is attached to the top of the upper end plate (14b) through the top. An inverter (not shown) is connected to the terminal terminal (9) via electric wiring. The inverter is configured to supply current to the electric motor (13) through the electric wiring and to adjust the frequency of the current within a predetermined range. That is, the operating capacity of the compressor (10) can be freely changed within a predetermined range by the inverter.

  An oil sump is formed at the bottom of the lower end plate (14c). Lubricating oil for lubricating the sliding portion of the compression mechanism (12) is stored in the oil reservoir.

(Electric motor)
The electric motor (13) includes a stator (18a) and a rotor (18b) both formed in a cylindrical shape. The stator (18a) is fixed to the body (14a) of the casing (11). The rotor (18b) is disposed in the hollow portion of the stator (18a). A rotating shaft (20) is fixed in the hollow portion of the rotor (18b) so as to penetrate the rotor (18b), and the rotor (18b) and the rotating shaft (20) rotate integrally. ing.

  The rotating shaft (20) has a main shaft portion (21) extending vertically, and two eccentric portions (22, 23) are integrally formed near the lower end of the main shaft portion (21). These eccentric parts (22, 23) are a low-stage eccentric part (22) and a high-stage eccentric part (23) above the low-stage eccentric part (22), both of which are main shaft parts (21 ). The shaft centers of the low-stage eccentric part (22) and the high-stage eccentric part (23) are eccentric by a predetermined distance with respect to the axis of the main shaft part (21), and the low-stage eccentric part (22) and the high-stage eccentric part (22) The eccentric directions of the step side eccentric portions (23) are shifted from each other by 180 degrees.

  A centrifugal pump (24) is provided at the lower end of the main shaft (21). The centrifugal pump (24) is immersed in the lubricating oil in the oil reservoir, and the lubricating oil is supplied to an oil supply path (not shown) in the rotating shaft (20) as the rotating shaft (20) rotates. After pumping up, it supplies to each sliding part of a compression mechanism (12) and an electric motor (13).

(Compression mechanism)
As shown in FIG. 2, the compression mechanism (12) includes a front head (30), a high-stage cylinder (31), a middle plate (32), a low-stage cylinder (33), and from the upper side to the lower side. The rear heads (34) are stacked in this order, and these members (30, 31, 32, 33, 34) are fastened by a plurality of bolts (35). The portion consisting of the front head (30), the high stage cylinder (31) and the middle plate (32) constitutes the high stage compression section (12a), and the middle plate (32), the low stage cylinder (33) and the rear head. The portion consisting of (34) constitutes the low-stage compression section (12b).

  Moreover, the through-hole part in which the rotating shaft (20) mentioned above is inserted is provided in the center part of these members (30, 31, 32, 33, 34). The inner peripheral surfaces of the through hole portions in the front head (30) and the rear head (34) constitute a sliding bearing portion that rotatably supports the main shaft portion (21) of the rotating shaft (20). Further, the through hole portions of the high stage cylinder (31) and the low stage cylinder (33) are formed to have larger diameters than the through hole portions of the front head (30), the middle plate (32) and the rear head (34). Yes.

  In the high stage cylinder (31), the upper end opening surface of the high stage cylinder (31) is closed by the front head (30), and the lower end opening face of the high stage cylinder (31) is closed by the middle plate (32). As a result, the portion of the through hole in the high-stage cylinder (31) becomes a closed space. This closed space constitutes a high-stage cylinder chamber. A high-stage eccentric part (23) of the rotary shaft (20) is located in the high-stage cylinder chamber, and a high-stage piston (38) is fitted on the high-stage eccentric part (23). On the outer peripheral surface of the high-stage piston (38), a high-stage blade that extends radially outward from the outer peripheral surface is integrally formed.

  On the other hand, in the low-stage cylinder (33), the upper end opening surface of the low-stage cylinder (33) is closed by the middle plate (32), and the lower end opening face of the low-stage cylinder (33) is closed by the rear head (34). As a result, the portion of the through hole in the low-stage cylinder (33) becomes a closed space. This closed space constitutes the low-stage cylinder chamber (55). In the low-stage cylinder chamber (55), the low-stage eccentric part (22) of the rotating shaft (20) is located, and the low-stage piston (39) is fitted on the low-stage eccentric part (22). Yes. A low-stage blade (41) extending radially outward from the outer peripheral surface is integrally formed on the outer peripheral surface of the low-stage piston (39).

  Next, each cylinder (31, 33) will be described. Since each cylinder (31, 33) has the same configuration, the low-stage cylinder (33) will be described, and the description of the high-stage cylinder (31) will be partially omitted.

  As shown in FIG. 3, the low-stage cylinder (33) is formed with a circular groove (42) that partially opens into the low-stage cylinder chamber (55) in plan view. The circular groove (42) is a bush groove (42), and the lower blade (41) is positioned in the bush groove (42).

  In each bush groove (42), a pair of bushes (43) formed in a half-moon shape in plan view is fitted in a state of sandwiching the low-stage blade (41). The arc surface of the bush (43) can be slidably contacted with the inner peripheral surface of the bush groove (42), and the flat surface of the bush (43) is in contact with the side surface of the lower blade (41). Can be slid in contact.

  The low-stage cylinder (33) is formed with a low-stage low-stage suction passage (44) that penetrates radially between the inner peripheral surface and the outer peripheral surface of the low-stage cylinder (33). ing. The opening end (44a) on the inner peripheral surface side of the low-stage suction through passage (44) is opened and closed by the outer peripheral surface of the low-stage piston (39) that moves eccentrically. Each time the low-stage piston (39) makes one revolution, the open end (44a) of the low-stage suction through passage (44) opens for a predetermined time. The end of the first inlet tube (15a) is inserted and fixed in the low-stage suction through passage (44).

  In addition, the high-stage suction through-passage (54) of the high-stage cylinder (31) is also similar to the low-stage suction through-passage (44) each time the high-stage piston (38) rotates once. The high suction passage (54) opens for a predetermined time. The end of the second inlet tube (15b) is inserted and fixed in the high-stage suction through passage (54).

  The low-stage cylinder chamber (55) is partitioned into two spaces by the low-stage blade (41). One is a space on the suction side communicating with the first inlet tube (15a), and the other is a space on the discharge side where a low-stage discharge hole (45) formed in the rear head (34) is opened. . The suction-side and discharge-side space portions constitute a low-stage compression chamber (37). The suction-side space in the high-stage cylinder chamber communicates with the second inlet tube (15b), and the discharge-side space in the high-stage cylinder chamber is formed in the front head (30). The high-stage discharge hole (8b) is open. The suction-side and discharge-side space portions in the high-stage cylinder chamber constitute a high-stage compression chamber (36).

  A muffler cover (46) is provided on the upper surface of the front head (30) to cover the high-stage discharge hole. A high-stage discharge chamber (47) is formed inside the muffler cover (46). The muffler cover (46) is formed with a through hole that penetrates the muffler cover (46) and communicates the high-stage discharge chamber (47) with the internal space of the casing (11). The refrigerant flow path from the high-stage discharge hole (8b) to the discharge pipe (17) through the high-stage discharge chamber (47) and the internal space of the casing (11) is high. A stage discharge path (6) is formed.

  The rear head (34) has a thick annular main body (34a) and a thick annular closure plate (34b). The main shaft portion (21) of the rotating shaft (20) is located in the hollow portions of the main body portion (34a) and the closing plate (34b).

  The main body (34a) has a substantially annular recess (48) formed in the thick part of the main body (34a). This recessed part (48) is opened in the lower surface of the said main-body part (34a). When the closing plate (34b) closes the opening surface of the recessed portion (48), the recessed portion becomes a closed space. This closed space constitutes the low-stage discharge chamber (49).

  The main body (34a) has a communication hole (45) that passes through the main body (34a) in the vertical direction and communicates the low-stage discharge chamber (49) and the low-stage compression chamber (37). Is formed. The communication hole (45) constitutes the low-stage discharge hole (45) described above. The main body (34a) communicates between the low-stage discharge chamber (49) and the outside of the main body (34a) through the thick part of the main body (34a) in the radial direction. A communication hole (51) is formed. The end of the third inlet tube (15c) is inserted and fixed in the communication hole (50). The refrigerant flow path from the low-stage discharge hole (45) through the low-stage discharge chamber (49) and the communication hole (51) to the third inlet tube (15c) A discharge passage (5) is formed.

-Muffler part-
The muffler part (3,4) is composed of a low-stage suction muffler (3) and a high-stage suction muffler (4). Each of these mufflers (3, 4) is a vertically long cylindrical sealed container with both ends closed. By providing these mufflers (3, 4) in the middle of the refrigerant passage, the pulsation of the refrigerant generated in the refrigerant passage downstream of the muffler (3, 4) is more upstream than the muffler (3, 4). It is possible to suppress transmission to the refrigerant flowing through the refrigerant passage on the side.

  As shown in FIG. 1, the refrigerant inflow pipe joints (3a, 4a) are attached to the upper ends of the mufflers (3,4) so as to penetrate the upper ends. A low-stage suction pipe is attached to the lower end of the low-stage suction muffler (3) through the lower end. One end of the low-stage suction pipe is connected to the first inlet tube (15a) of the casing (11), and the other end is a muffler space (low-stage buffer space) (3b) of the low-stage suction muffler (3). ) Is open at the top.

  Here, the passage from the low-stage compression chamber (37) to the low-stage muffler space (3b) of the low-stage side suction muffler (3) is the low-stage suction path (1a). The low-stage suction passage (1a) includes the low-stage suction through-passage (44), and opens and closes as the low-stage suction through-passage (44) opens and closes.

  The length L1 of the low-stage suction path (1a) is such that the sound speed of the refrigerant during the cooling operation of the refrigerant circuit (60) is c1 [m / s], and the maximum operating frequency of the electric motor (13) is fmax [Hz]. When the volume of the low-stage compression chamber (37) is V1 [m3] and the passage area of the low-stage suction passage (1a) is M1 [m2], the relationship of Formula 1 is satisfied.

L1 = c1 / (4 × fmax) − (V1 / M1) (Formula 1)
A high-stage suction pipe is attached to the lower end of the high-side suction muffler (4) so as to penetrate the lower end. One end of the high-stage suction pipe is connected to the second inlet tube (15b) of the casing (11), and the other end is a muffler space (high-stage buffer space) (4b) of the high-stage suction muffler (4). ) Is open at the top.

  Here, the passage from the high stage compression chamber (36) to the muffler space (4b) of the high stage side suction muffler (4) is the high stage suction path (2a). The high stage suction path (2a) includes the high stage suction through path (54), and opens and closes as the high stage suction through path (54) opens and closes.

  The length L2 of the high-stage suction passage (2a) is such that the sound speed of the refrigerant during the heating operation of the refrigerant circuit (60) is c2 [m / s], and the maximum operation frequency of the electric motor (13) is fmax [Hz]. When the volume of the high-stage compression chamber (36) is V2 [m3] and the passage area of the high-stage suction passage (2a) is M2 [m2], the relationship of Expression 2 is satisfied.

L2 = c2 / (4 × fmax) − (V2 / M2) (Formula 2)
The length L2 of the high stage suction path (2a) is shorter than the length L1 of the low stage suction path (1a).

<Refrigerant circuit>
Next, the refrigerant circuit (60) to which the compressor (10) is connected will be described. This refrigerant circuit (60) is provided in an air conditioner capable of switching between cooling and heating. The refrigerant circuit (60) is configured to perform a two-stage compression economizer cycle, and carbon dioxide is sealed as a refrigerant in the refrigerant circuit (60).

   In addition to the compressor (10), the refrigerant circuit (60) includes a four-way switching valve (71), an outdoor heat exchanger (heat source side heat exchanger) (61), an indoor heat exchanger (use side heat). An exchanger (62), a supercooling heat exchanger (63), a cooling expansion valve (64), a heating expansion valve (72), and a pressure reducing valve (65) are connected.

  The four-way selector valve (71) has four ports. The first port (P1) and the second port (P2) communicate with each other, and the third port (P3) and the fourth port (P4) communicate with each other. The cooling position (state shown by the solid line in FIG. 4), the heating position where the first port (P1) and the third port (P3) communicate, and the second port (P2) and the fourth port (P4) communicate (Figure 4 (state indicated by a broken line in FIG. 4). A ninth refrigerant pipe (18) extending from the discharge pipe (17) of the compressor (10) is connected to the first port (P1) of the four-way switching valve (71), and the fourth port (P4). The first refrigerant pipe (70a) extending from the refrigerant inflow pipe joint (3a) of the low-stage suction muffler (3) is connected to the first refrigerant pipe (70a).

  The outdoor heat exchanger (61) exchanges heat between outdoor air taken in by an outdoor fan (not shown) provided in the vicinity of the outdoor heat exchanger (61) and the refrigerant in the refrigerant circuit (60). It is a cross fin type fin-and-tube heat exchanger. A second refrigerant pipe (70b) extending from the second port (P2) of the four-way switching valve (71) is connected to one end of the outdoor heat exchanger (61). And the 3rd refrigerant | coolant piping (66) extended from the other end of the said outdoor heat exchanger (61) branches, and one is connected to the end of the high temperature side channel | path (63a) of the said supercooling heat exchanger (63), The other is connected to one end of the pressure reducing valve (65). A heating expansion valve (72) is connected to a portion of the third refrigerant pipe (66) before branching.

  The supercooling heat exchanger (63) is provided with a low temperature side passage (63b) in addition to the high temperature side passage (63a), and the refrigerant passing through the high temperature side passage (63a) and the low temperature side passage (63b) The refrigerant passing through is configured to exchange heat. And the 4th refrigerant | coolant piping (69a) extended from the other end of the said high temperature side channel | path (63a) is connected to the inlet_port | entrance part of the said expansion valve for cooling (64).

  The pressure reducing valve (65) is configured to reduce the refrigerant to a predetermined pressure by adjusting the valve opening degree of the pressure reducing valve (65). The decompression amount of the refrigerant is set to be smaller than the decompression amounts of the cooling expansion valve (64) and the heating expansion valve (72). The fifth refrigerant pipe (67a) extending from the pressure reducing valve (65) is connected to one end of the low temperature side passage (63b) of the supercooling heat exchanger (63). A sixth refrigerant pipe (67b) extending from the other end of the low-temperature side passage (63b) extends from the third inlet tube (15c) of the compressor (10), and is connected to the high-stage suction muffler (4). It communicates in the middle of the connecting pipe (7) connected to the refrigerant inflow pipe joint (4a).

  The heating expansion valve (72) reduces the refrigerant to a predetermined pressure by adjusting the valve opening of the heating expansion valve (72) when the four-way switching valve (71) is in the heating position. On the other hand, when the four-way switching valve (71) is in the cooling position, the opening degree of the heating expansion valve (72) is set to the fully open position.

  When the four-way switching valve (71) is in the cooling position, the cooling expansion valve (64) adjusts the valve opening of the cooling expansion valve (72) to reduce the refrigerant to a predetermined pressure. On the other hand, when the four-way switching valve (71) is in the heating position, the opening degree of the cooling expansion valve (72) is set to the fully open position. A seventh refrigerant pipe (69b) extending from the other end of the cooling expansion valve (64) is connected to one end of the indoor heat exchanger (62).

  The indoor heat exchanger (62) exchanges heat between indoor air taken in by an indoor fan (not shown) provided in the vicinity of the indoor heat exchanger (62) and the refrigerant in the refrigerant circuit (60). It is a cross fin type fin-and-tube heat exchanger. The eighth refrigerant pipe (70) extending from the other end of the indoor heat exchanger (62) is connected to the refrigerant inflow pipe joint (3a) of the low-stage suction muffler (3).

  When the four-way switching valve (22) is set to the cooling position, the outdoor heat exchanger (61) serves as a radiator and the indoor heat exchanger (62) serves as an evaporator to perform a cooling operation. . On the other hand, when the four-way selector valve (22) is set to the heating position, the outdoor heat exchanger (61) serves as an evaporator and the indoor heat exchanger (62) serves as a radiator to perform heating operation. .

-Driving action-
After describing the operation of the compressor (10), the operation of the refrigerant circuit (60) will be described in detail.

<Two-stage compressor with muffler>
In the compressor (10), when the rotating shaft (20) of the electric motor (13) rotates, pistons (38, 39) attached to the eccentric portions (22, 23) of the rotating shaft (20) are cylinders. The chamber (36,37) rotates eccentrically. As a result, the volume of the compression chamber formed between each piston (38, 39) and each cylinder chamber (36, 37) periodically fluctuates, and refrigerant suction operation, compression operation and discharge are performed in the compression chamber. The operation is performed continuously.

  The refrigerant that has passed through the low-stage suction muffler (3) and the low-stage suction passage (1a) is sucked into the low-stage compression chamber (37) of the compression mechanism (12). Here, since the low-stage suction passage (1a) opens and closes at a predetermined interval, the speed of the refrigerant sucked into the low-stage compression chamber (37) tends to be uneven, and the low-stage suction passage ( The refrigerant flowing through 1a) is pulsating.

  On the other hand, the low-stage suction path (1a) is a length capable of causing the refrigerant supercharging effect using the inertia force generated by the pulsation, that is, a length calculated based on the above-described equation 1. L1 is set.

  As a result, when the operating frequency during the cooling operation of the electric motor (13) becomes close to the maximum value, the refrigerant is supercharged and the amount of refrigerant sucked into the low-stage compression chamber (37) increases. Due to the increase in the refrigerant intake amount, the cooling capacity of the air conditioner increases.

  The refrigerant compressed and discharged in the low-stage compression chamber (37) joins the refrigerant flowing from the sixth refrigerant pipe (67b) while passing through the connection pipe (7). The merged refrigerant passes through the high stage suction muffler (4) and the high stage suction passage (2a) and is sucked into the high stage compression chamber (36) of the compression mechanism (12). Here, the high-stage suction path (2a) opens and closes at a predetermined interval in the same manner as the low-stage suction path (1a). For this reason, the speed of the refrigerant sucked into the high stage compression chamber (36) is likely to be uneven, and the refrigerant flowing through the high stage suction passage (2a) is pulsating.

  On the other hand, the high-stage suction path (2a) is a length capable of causing the refrigerant supercharging effect using the inertia force generated by this pulsation, that is, a length calculated based on the above-described equation (2). L2 is set.

  Thereby, when the operation frequency at the time of heating operation in the electric motor (13) becomes near the maximum value, the refrigerant is supercharged, and the amount of refrigerant sucked into the high stage compression chamber (36) is increased. The increase in the refrigerant intake amount increases the heating capacity of the air conditioner.

  Then, the refrigerant compressed to a pressure exceeding the critical pressure in the high-stage compression chamber (36) is discharged into the casing (11) of the compressor body (10a) and then passed through the discharge pipe (17). , Discharged to the outside of the casing (11).

<Refrigerant circuit>
Next, the operation of the refrigerant circuit (60) in the air conditioner will be described.

-Cooling operation-
During the cooling operation of the air conditioner, the four-way switching valve (71) is set to the cooling position. The opening degree of the cooling expansion valve (64) is adjusted as necessary, and the opening degree of the heating expansion valve (72) is set to fully open.

  As a result, the ninth refrigerant pipe (18), the second refrigerant pipe (70b), and the third refrigerant pipe (66) become a high-pressure line (80), and the fourth refrigerant pipe (69a) and the eighth refrigerant. The pipe (70) and the first refrigerant pipe (70a) serve as a low pressure line (81). The fifth refrigerant pipe (67a) and the sixth refrigerant pipe (67b) serve as an intermediate pressure line (82) regardless of the switching operation of the four-way switching valve (71). And a refrigerant | coolant circulates in the continuous line direction shown in FIG. 4, and a vapor compression type refrigeration cycle is performed in the said refrigerant circuit (60).

  The high-pressure refrigerant discharged from the compressor (10) flows into the outdoor heat exchanger (61). The high-pressure refrigerant flowing into the outdoor heat exchanger (61) radiates heat to the outdoor air sent from the outdoor fan, and then flows out of the outdoor heat exchanger (61). This high-pressure refrigerant is diverted after passing through the fully opened heating expansion valve (72), and part of it flows into the high temperature side passage (63a) of the supercooling heat exchanger (63), and the rest The pressure is reduced to a predetermined pressure by the pressure reducing valve (65) to become an intermediate pressure refrigerant, and then flows into the low temperature side passage (63b) of the supercooling heat exchanger (63).

  In the supercooling heat exchanger (63), the high pressure refrigerant in the high temperature side passage (63a) and the intermediate pressure refrigerant in the low temperature side passage (63b) exchange heat. The high-pressure refrigerant dissipates heat to the intermediate-pressure refrigerant and is cooled, and then flows out of the high-temperature side passage (63a). On the other hand, the intermediate pressure refrigerant absorbs heat from the high pressure refrigerant and is heated, and then flows out of the low temperature side passage (63b).

  On the other hand, the high-pressure refrigerant that has flowed out of the high-temperature side passage (63a) flows into the cooling expansion valve (64) and is reduced to a predetermined pressure. After the decompression, the high-pressure refrigerant turns into a two-phase low-pressure refrigerant, and then flows out of the cooling expansion valve (64). The low-pressure refrigerant that has flowed out of the cooling expansion valve (64) flows into the indoor heat exchanger (62). In the indoor heat exchanger (62), the low-pressure refrigerant absorbs heat from the indoor air of an indoor fan disposed in the vicinity of the indoor heat exchanger (62) and evaporates to become a low-pressure gas refrigerant. Outflow through heat exchanger (62). At this time, the room air is cooled by the low-pressure refrigerant, and the cooled air is sent into the room. Thereby, the room is cooled.

  The low-pressure gas refrigerant that has flowed out of the indoor heat exchanger (62) is sucked into the low-stage compression chamber (37) of the compressor (10) through the low-stage suction muffler (3). When the electric motor (13) is at the maximum operating frequency, as described above, the low-pressure gas refrigerant to be sucked into the low-stage compression chamber (37) is supercharged.

  The low-pressure gas refrigerant sucked into the low-stage cylinder chamber (55) is discharged after being compressed in the low-stage compression chamber (37). The refrigerant discharged from the low-stage compression chamber (37) merges with the intermediate-pressure refrigerant that has flowed out of the low-temperature side passage (63b) of the supercooling heat exchanger (63), and the refrigerant after merging is combined with the high-stage refrigerant. It is sucked into the upper and higher compression chambers (36) through the side suction muffler (4). The refrigerant is compressed in the high-stage compression chamber (36) to become a high-pressure refrigerant, and then discharged through the casing (11) to the outdoor heat exchanger (61). As the refrigerant circulates in this manner, the cooling operation of the air conditioner is performed.

-Heating operation-
During the heating operation of the air conditioner, the four-way switching valve (71) is set to the heating position. The opening degree of the heating expansion valve (72) is adjusted as necessary, and the opening degree of the cooling expansion valve (64) is set to fully open.

  As a result, the fourth refrigerant pipe (69a), the eighth refrigerant pipe (70), and the first refrigerant pipe (70a) become a high-pressure line (80), and the ninth refrigerant pipe (18) and the second refrigerant pipe. The pipe (70b) and the third refrigerant pipe (66) serve as a low pressure line (81). Then, the refrigerant circulates in the direction of the broken line shown in FIG. 5, whereby a vapor compression refrigeration cycle is performed in the refrigerant circuit (60).

  The high-pressure refrigerant discharged from the compressor (10) flows into the indoor heat exchanger (62) through the four-way switching valve (71).

  In the indoor heat exchanger (62), the high-pressure refrigerant radiates heat to the indoor air of an indoor fan disposed in the vicinity of the indoor heat exchanger (62), and then flows out of the indoor heat exchanger (62). At this time, the room air is heated by the low-pressure refrigerant, and the heated air is sent into the room. Thereby, the room is heated.

  The high-pressure refrigerant that has flowed out of the indoor heat exchanger (62) passes through the fully-opened cooling expansion valve (64) and the high-temperature side passage (63a) of the supercooling heat exchanger (63). A part branches and flows to the pressure reducing valve (65), and the rest flows to the heating expansion valve (72).

  The high-pressure refrigerant flowing into the pressure reducing valve (65) is decompressed to a predetermined pressure by the pressure reducing valve (65) to become an intermediate pressure refrigerant, and then the low-temperature side passage (63b) of the supercooling heat exchanger (63) Flow into.

  In the supercooling heat exchanger (63), the high pressure refrigerant in the high temperature side passage (63a) and the intermediate pressure refrigerant in the low temperature side passage (63b) exchange heat. The high-pressure refrigerant dissipates heat to the intermediate-pressure refrigerant and is cooled, and the intermediate-pressure refrigerant absorbs heat from the high-pressure refrigerant and is heated.

  The high-pressure refrigerant sucked into the heating expansion valve (72) is depressurized to a predetermined pressure by the pressure reducing valve (65) to become a low-pressure refrigerant, and then flows into the outdoor heat exchanger (61). The low-pressure refrigerant flowing into the outdoor heat exchanger (61) is cooled by outdoor air sent from the outdoor fan and evaporated, and then flows out of the outdoor heat exchanger (61).

  The low-pressure refrigerant flowing out of the outdoor heat exchanger (61) is sucked into the low-stage compression chamber (37) of the compressor (10) through the low-stage suction muffler (3). The low-pressure gas refrigerant sucked into the low-stage compression chamber (37) is discharged after being compressed in the low-stage compression chamber (37). The refrigerant discharged from the low-stage compression chamber (37) merges with the intermediate-pressure refrigerant that has flowed out of the low-temperature side passage (63b) of the supercooling heat exchanger (63), and the refrigerant after merging is combined with the high-stage refrigerant. It is sucked into the high pressure compression chamber (36) through the side suction muffler (4).

  When the electric motor (13) is at the maximum operating frequency, the intermediate pressure refrigerant to be sucked into the high-stage compression chamber (36) is supercharged as described above. The intermediate-pressure refrigerant is compressed in the high-stage compression chamber (36) to become a high-pressure refrigerant, and is then discharged from the discharge interval (17) through the casing (11). Thus, the refrigerant | coolant circulates and the heating operation of an air conditioning apparatus is performed.

-Effect of the embodiment-
According to the present embodiment, the low-stage suction path (1a) is set to a length L1 that makes the refrigerant sucked in the low-stage compression chamber (37) supercharged during the cooling operation. When the electric motor (13) is at the maximum operating frequency, the refrigerant sucked into the low-stage compression chamber (37) is supercharged. When the refrigerant is supercharged, the maximum amount of refrigerant sucked into the low-stage compression chamber (37) is increased, and the volume of the low-stage compression chamber (37) is reduced by the increase in the maximum refrigerant intake amount. can do. Thereby, the size of the compressor (10) can be reduced.

  Further, according to the present embodiment, the high-stage suction passage (2a) is set to a length L2 that makes the suction refrigerant in the high-stage compression chamber (36) supercharged. When the electric motor (13) is at the maximum operating frequency, the refrigerant sucked into the high-stage compression chamber (36) is supercharged. When the refrigerant is supercharged, the maximum amount of refrigerant sucked into the high-stage compression chamber (36) increases, and the volume of the high-stage compression chamber (36) is further increased by the increase in the maximum refrigerant suction amount. Can be small. Thereby, the size of the compressor (10) can be further reduced.

  Further, according to the present embodiment, by setting the length L2 of the high-stage suction passage (2a) shorter than the length L1 of the low-stage suction passage (1a), the low-stage compression chamber (37) Compared to the above, more refrigerant is easily sucked into the high-stage compression chamber (36). As a result, the amount of refrigerant discharged from the high-stage compression chamber (36) is likely to increase compared to the case where the high-stage suction path (2a) and the low-stage suction path (1a) have the same length. It is possible to easily improve the capacity during heating operation.

-Modification of Embodiment 1-
In the compressor of the first modification shown in FIG. 5, unlike the above embodiment, the passage area M2 of the high stage suction passage (2a) is set smaller than the passage area M1 of the low stage suction passage (1a). ing.

  In this case, during the cooling operation, the pressure loss of the refrigerant passing through the low stage suction path (1a) is smaller than the pressure loss of the refrigerant passing through the high stage suction path (2a). This makes it easier for more refrigerant to be drawn into the low-stage compression chamber (37) than in the high-stage compression chamber (36). As a result, the amount of refrigerant discharged from the low-stage compression chamber (37) is likely to increase. As a result, it is possible to easily improve the performance during the cooling operation.

<< Other Embodiments >>
About the said embodiment, it is good also as the following structures.

  In the present embodiment, the low-stage muffler space (3b) of the low-stage suction muffler (3) constitutes a low-stage buffer space, and the muffler space (4b) of the high-stage suction muffler (4) is high. Although the stage buffer space is configured, the present invention is not limited to this. For example, the low-stage buffer space may be constituted by an accumulator. In this case, it is necessary that a space having a predetermined capacity capable of suppressing the pulsation of the refrigerant flowing into the accumulator is formed in the accumulator.

  In the present embodiment, the compression mechanism (12) is a so-called swing type compression mechanism. However, the compression mechanism (12) is not limited to this, and the volumes such as a rotary type, a scroll type, and a reciprocating type may be used. You may be comprised with the compression mechanism of the type | mold.

  In the present embodiment, the length L1 of the low-stage suction passage (1a) is set so as to satisfy the expression 1, but is not limited thereto, and is not limited to 0.9 × Lm1 ≦ L1 ≦ 1. 1 × Lm1 (where Lm1 = (c1 / (4 × fmax) − (V1 / M1)) is satisfied) The range of the length L1 is the low-stage suction path (1a). However, it is determined based on the characteristic that the supercharging effect of the refrigerant becomes maximum when the length L1 of the present embodiment is long, and the supercharging effect of the refrigerant becomes smaller as the length becomes longer or shorter than the length L1.

  Further, the length L2 of the high-stage suction passage (2a) is also set so as to satisfy Equation 2, but is not limited to this, and 0.9 × Lm2 ≦ L2 ≦ 1.1 × Lm2 (however, Lm2 = (c2 / (4 × fmax) − (V2 / M2)) The range of the length L2 is also determined based on the above-described characteristics.

  In addition, the above embodiment is an essentially preferable illustration, Comprising: It does not intend restrict | limiting the range of this invention, its application thing, or its use.

  As described above, the present invention is useful for a two-stage compressor connected to a two-stage compression refrigeration cycle.

1a Low stage suction path (Low stage supercharging part)
2a High stage suction path (High stage supercharging part)
3 Lower suction muffler
3b Lower muffler space (Lower buffer space)
4 High-stage suction muffler
4b High muffler space (High buffer space)
10 Compressor
11 Casing
12 Compression mechanism
13 Electric motor
36 High-stage compression chamber
37 Low-stage compression chamber
38 High piston
39 Low stage piston

Claims (6)

Both the high-stage compression chamber (36) and the low-stage compression chamber (37) that suck in and compress the fluid while periodically increasing and decreasing the volume, and the low-stage suction passage (1a) both extending from the low-stage compression chamber (37) ) And a low-stage discharge path (5), a compression mechanism (12) having both a high-stage suction path (2a) and a high-stage discharge path (6) extending from the high-stage compression chamber (36), and the compression mechanism An electric motor (13) for driving (12),
A low-pressure line (81, 80) through which a low-pressure refrigerant flows in a refrigerant circuit (60) that performs a two-stage compression refrigeration cycle communicates with the low-stage suction path (1a), and the high-stage discharge path (6) Is connected to the high-pressure line (80, 81) through which the high-pressure refrigerant of the refrigerant circuit (60) flows, and the connection line (7) connects the low-stage discharge path (5) and the high-stage suction path (2a). Is connected to an intermediate pressure line (82) through which the intermediate pressure refrigerant of the refrigerant circuit (60) flows,
A two-stage compressor provided between a heat source side heat exchanger (61) and a use side heat exchanger (62) of the refrigerant circuit (60) capable of switching between a cooling operation and a heating operation,
During the cooling operation of the refrigerant circuit (60) for cooling the use-side heat exchanger (62), the low-pressure line (81,80) to the low-stage compression chamber (37) through the low-stage suction passage (1a). A two-stage compressor comprising a low-stage supercharging unit (1) for supercharging the sucked refrigerant. In claim 1,
The low stage supercharger (1) is opened and closed at a cycle corresponding to the operating frequency of the electric motor (13) and communicates with the low pressure line (81, 80) via the low stage buffer space (3b). The lower suction passage (1a),
The sound speed of the refrigerant during the cooling operation of the refrigerant circuit (60) is c1 [m / s], the maximum operating frequency of the electric motor (13) is fmax [Hz], and the volume of the low-stage compression chamber (37) is V1 [ m3], when the passage area of the lower suction path (1a) is M1 [m2],
The length L1 of the lower suction path (1a) is
A two-stage compressor characterized by satisfying a relationship of 0.9 × Lm1 ≦ L1 ≦ 1.1 × Lm1 (where Lm1 = (c1 / (4 × fmax) − (V1 / M1))). In claim 1 or 2,
During the heating operation of the refrigerant circuit (60) for heating the use side heat exchanger (62), the refrigerant is sucked from the connection line (7) into the high stage compression chamber (36) through the high stage suction passage (2a). A two-stage compressor comprising a high-stage supercharging section (2) for supercharging the refrigerant to be supercharged. In claim 3,
The high-stage supercharging section (2) is opened and closed at a cycle corresponding to the operating frequency of the electric motor (13) and communicates with the high-pressure line (80, 81) via the high-stage buffer space section (4b). The above-described high suction passage (2a),
The sound speed of the refrigerant during the heating operation of the refrigerant circuit (60) is c2 [m / s], the maximum operating frequency of the electric motor (13) is fmax [Hz], and the volume of the high-stage compression chamber (36) is V2 [ m3], when the passage area of the high suction passage (2a) is M2 [m2],
The length L2 of the high suction path (2a) is
A two-stage compressor satisfying a relationship of 0.9 × Lm2 ≦ L2 ≦ 1.1 × Lm2 (where Lm2 = (c2 / (4 × fmax) − (V2 / M2))). In claim 2,
The high-stage suction path (2a) is connected to the connection line (7) through the high-stage suction path (2a) during the heating operation of the refrigerant circuit (60) for heating the use-side heat exchanger (62). A high-stage supercharging unit (2) for supercharging the refrigerant sucked into the high-stage compression chamber (36), which is opened and closed at a cycle corresponding to the operating frequency of the electric motor (13) and the high-pressure line ( 80, 81) to communicate with the higher buffer space (4b),
The sound speed of the refrigerant during the heating operation of the refrigerant circuit (60) is c2 [m / s], the maximum operating frequency of the electric motor (13) is fmax [Hz], and the volume of the high-stage compression chamber (36) is V2 [ m3], when the passage area of the high suction passage (2a) is M2 [m2],
The length L2 of the high suction path (2a) is
While satisfying the relationship of 0.9 × Lm2 ≦ L2 ≦ 1.1 × Lm2 (where Lm2 = (c2 / (4 × fmax) − (V2 / M2)),
The two-stage compressor characterized in that a length L2 of the high stage suction path (2a) is set shorter than a length L1 of the low stage suction path (1a). In claim 2,
The high-stage suction path (2a) is connected to the connection line (7) through the high-stage suction path (2a) during the heating operation of the refrigerant circuit (60) for heating the use-side heat exchanger (62). A high-stage supercharging unit (2) for supercharging the refrigerant sucked into the high-stage compression chamber (36), which is opened and closed at a cycle corresponding to the operating frequency of the electric motor (13) and the high-pressure line ( 80, 81) to communicate with the higher buffer space (4b),
The sound speed of the refrigerant during the heating operation of the refrigerant circuit (60) is c2 [m / s], the maximum operating frequency of the electric motor (13) is fmax [Hz], and the volume of the high-stage compression chamber (36) is V2 [ m3], when the passage area of the high suction passage (2a) is M2 [m2],
The length L2 of the high suction path (2a) is
While satisfying the relationship of 0.9 × Lm2 ≦ L2 ≦ 1.1 × Lm2 (where Lm2 = (c2 / (4 × fmax) − (V2 / M2)),
A two-stage compressor characterized in that a passage area M1 of the low-stage suction passage (1a) is set larger than a passage area M2 of the high-stage suction passage (2a).

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