EP1975413A1

EP1975413A1 - Multi stage rotary compressor

Info

Publication number: EP1975413A1
Application number: EP08251003A
Authority: EP
Inventors: Naoya Morozumi; Kenshi Ueda
Original assignee: Fujitsu General Ltd
Current assignee: Fujitsu General Ltd
Priority date: 2007-03-28
Filing date: 2008-03-20
Publication date: 2008-10-01
Also published as: US20080240954A1; CN101275562A; JP2008240667A

Abstract

There is provided a two-stage compression rotary compressor in which the balancer mass of a rotor can be made as small as possible, and the moments that tilt the whole of a shaft can be balanced. The axial length L2 of a high-stage side crankshaft 72 corresponding to a high-stage compressing section 32 is longer than the axial length L1 of a low-stage side crankshaft 73 corresponding to a low-stage compressing section 31 (L2 > L1).

Description

TECHNICAL FIELD

The present invention relates to a rotary compressor having two-stage compressing sections including a low-stage compressing section and a high-stage compressing section. More particularly, it relates to a technique for preventing a deflection occurring on a shaft connecting a motor and the compressing section to each other to enhance the reliability.

BACKGROUND ART

Generally, in a rotary compressor, in order to reduce a loss of refrigerant caused by the leakage by sealing the gap of a compression chamber and to lubricate sliding portions such as bearings, a compressing section is arranged in the lower part of a closed vessel in which lubricating oil accumulates.
Also, in a two-stage compression rotary compressor, in order to make better the balance of compressive load torques produced in two compressing sections and the balance of centrifugal forces acting on the off-center parts corresponding to the two compressing sections, that is, turning pistons and the off-center parts of a shaft engaging with the pistons, the compression phases of a low-stage compressing section and a high-stage compressing section are shifted through 180 degrees.
By the centrifugal forces acting on the two off-center parts of the shaft and the two turning pistons, a moment that tends to tilt the whole of the shaft is produced. Therefore, a balancer is attached to above and below a rotor of a motor to cancel the moment that tends to tilt the whole of the shaft.
In the two-stage compression rotary compressor, in terms of the compression characteristics thereof, the volume of the high-stage compressing section must be smaller than the volume of the low-stage compressing section. As means for decreasing the volume of compression chamber, there are available a method in which the thickness of compression chamber, that is, the thickness of a cylinder is decreased and a method in which the turning radius of the piston is decreased. In both of these methods, the centrifugal forces acting on the off-center parts of the shaft and the pistons are smaller in the high-stage compressing section having a smaller volume than in the low-stage compressing section having a larger volume.
Therefore, as described in Japanese Patent Application Publication No. H11-230073 , there is known means for decreasing the mass of the balancer by arranging the low-stage compressing section, on which a larger centrifugal force acts, on the side close to the rotor to which the balancer is attached, that is, by arranging the low-stage compressing section above the high-stage compressing section.
However, in the case where the low-stage compressing section is arranged above the high-stage compressing section, there arises a problem described below. Depending on the operation pressure condition and the rotational speed condition of the compressor, the oil level of lubricating oil lowers from the compressing section arranged on the upper side in the closed vessel, and the compressing section on the upper side is exposed to refrigerant gas. Therefore, the refrigerant leaks into a suction chamber and the compression chamber passing through a gap between a vane and a vane groove, whereby a leakage loss is created.
If the low-stage compressing section is arranged on the upper side, since the interior of closed vessel has the discharge pressure of the high-stage compressing section, the difference in pressure between the suction chamber and the compression chamber is large as compared with the case where the high-stage compressing section is arranged on the upper side, so that the quantity of refrigerant leaking into the suction chamber and the compression chamber through the gap increases, which presents a problem of further decreased efficiency of compressor.
Accordingly, an object of the present invention is to provide a rotary compressor in which the mass of a balancer can be decreased, and thereby the deflection of a shaft is reduced, so that the seizure in bearing parts and the contact of a rotor with a stator can be prevented.

SUMMARY OF THE INVENTION

To achieve the above object, the present invention has some features described below. A rotary compressor having a two-stage compressing section including a low-stage compressing section and a high-stage compressing section provided in a closed shell, and a motor for driving the two-stage compressing section, the high-stage compressing section being arranged on the motor side, is characterized in that when the axial length of the off-center part of shaft corresponding to the low-stage compressing section, that is, a low-stage side crankshaft, is taken as L1, and the axial length of the off-center part of shaft corresponding to the high-stage compressing section, that is, a high-stage side crankshaft, is taken as L2, L2 is longer than L1.
According to this configuration, the mass of a balancer attached to a rotor can be made small by making the axial length of the high-stage side crankshaft longer than that of the low-stage side crankshaft. Thereby, the deflection of the whole of the shaft is reduced, so that seizure caused by a local excessive load of a bearing part and the contact of the rotor with a stator can be prevented.
As a preferable mode, the rotary compressor is characterized in that the rotational speed of the compressing section is variable. According to this configuration, in the rotary compressor in which the rotational speed is variable, when the rotational speed is high, the centrifugal forces acting on an upper balancer and a lower balancer increase, by which the deflection of the shaft is increased, and therefore the effect of the present invention is further increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a rotary compressor in accordance with one embodiment of the present invention;
FIG. 2 is a transverse sectional view of a compressing section of the rotary compressor shown in FIG. 1;
FIG. 3 is a schematic view showing rotating parts of the rotary compressor shown in FIG. 1 and centrifugal forces acting thereon; and
FIG. 4 is a schematic view showing a deflected state of a shaft formed by centrifugal forces of the rotary compressor shown in FIG. 1.

DETAILED DESCRIPTION

An embodiment of the present invention is explained with reference to FIG. 1. The present invention is not limited to this embodiment. A rotary compressor 1 includes a cylindrical closed vessel 2 arranged in the vertical direction, a motor 4 provided in an upper part in the closed vessel 2, and a compressing section 3 in a lower part therein.
The closed vessel 2 consists of a cylindrical main shell 21, a dome-shaped top shell 22 that closes the upper end part of the main shell 21, and a dome-shaped bottom shell 23 that closes the lower end part of the main shell 21. The top shell 22 and the bottom shell 23 are fixed to the main shell 21 by welding.
The top shell 22 is provided with a refrigerant discharge pipe 24 for discharging the refrigerant having been discharged into the closed vessel 2 from the compressing section 3 to the outside of the closed vessel 2.
A stator 41 of the motor 4 is shrinkage fitted to the main shell 21. A rotor 42 of the motor 4 is shrinkage fitted onto a shaft 7 mechanically connecting the motor 4 to the compressing section 3. Above and below the rotor 42, an upper balancer 43 and a lower balancer 44 are attached, respectively, to balance the centrifugal forces of the whole of rotating parts.
The compressing section 3 is provided with a high-stage compressing section 32 in the upper part thereof and a low-stage compressing section 31 in the lower part thereof. The discharge side of the low-stage compressing section 31 and the suction side of the high-stage compressing section 32 are connected to each other by an intermediate connection pipe 26 on the outside of the closed vessel 2, by which a two-stage compressing section is formed.
Next, the configuration of each section of the compressing section 3 is explained with reference to FIG. 2. FIG. 2 shows the transverse cross section of the low-stage compressing section 31 shown in FIG. 1. The configuration of the high-stage compressing section 32 is the same as that of the low-stage compressing section 31 except that the pistons are 180° out-of-phase.
Each of the compressing sections 31 and 32 has a cylinder 200, 400 and a cylindrical piston 220, 420 accommodated in a cylindrical cylinder bore 200a, 400a formed on the inside of the cylinder 200, 400. Between the internal wall of the cylinder bore 200a, 400a and the outer peripheral surface of the piston 220, 420, a working space for refrigerant is formed.
The cylinder 200, 400 is provided with a cylinder groove 200b, 400b directed from the cylinder bore 200a, 400a toward the outer periphery direction, and has a flat plate shaped vane 230, 430 in the cylinder groove 200b, 400b.
Between the vane 230, 430 and the internal wall of the closed vessel 2, a spring 240, 440 is provided. By the urging force of the spring 240, 440, the tip end of the vane 230, 430 is brought into sliding contact with the outer wall of the piston 220, 420, by which the working space is divided into a suction chamber V1, V2 and a compression chamber C1, C2.
In order to make the working space volume of the high-stage compressing section 32 smaller than that of low-stage compressing section 31, each of the cylinder 200, the piston 220, and the vane 230 on the high-stage side has a smaller thickness in the axial direction than each of the cylinder 400, the piston 420, and the vane 430 on the low-stage side.
Next, referring again to FIG. 1, the whole of the compressor 1 is explained. The compressor 1 has a main frame 100 above the high-stage side cylinder 200, an intermediate partition plate 300 between the high-stage side cylinder 200 and the low-stage side cylinder 400, and a sub-frame 500 below the low-stage side cylinder 400, and the upside and the downside of each of the two working spaces are closed by the main frame 100, the intermediate partition plate 300, and the sub-frame 500, whereby each of the two working spaces is formed into a closed space.
Above the main frame 100, a high-stage side discharge muffler cover 130 is provided, and a high-stage side discharge muffler chamber M2 for reducing the pressure pulsation of discharged refrigerant is formed. Below the sub-frame 500, a low-stage side discharge muffler cover 510 is provided, and a low-stage side discharge muffler chamber M1 for reducing the pressure pulsation of discharged refrigerant is formed.
The high-stage side discharge muffler cover 130, the main frame 100, the high-stage side cylinder 200, the intermediate partition plate 300, the low-stage side cylinder 400, the sub-frame 500, and the low-stage side discharge muffler cover 510 are fixed integrally with bolts (not shown), and further the outer peripheral part of the main frame 100 is fixed to the main shell 21 by spot welding.
The main frame 100 and the sub-frame 500 have bearing parts 110 and 502, respectively, so that the shaft 7 is fitted in the bearing parts 110 and 502 so as to be rotatably supported.
The shaft 7 has two crankshafts 72 and 73 that are off-centered in the 180 different direction. One crankshaft 72 engages with the piston 220 of the high-stage compressing section 32, and the other crankshaft 73 engages with the piston 420 of the low-stage compressing section 31.
Along with the rotation of the shaft 7, the pistons 220 and 420 turn while slidingly contacting with the inside walls of the respective cylinder bores 200a and 400a, and following this turning motion of the pistons 220 and 420, the vanes 230 and 430 reciprocate, by which the volumes of the suction chambers V1 and V2 and the compression chambers C1 and C2 are changed continuously. Thus, the compressing section 3 repeats the suction and compression of refrigerant.
The suction chamber V1 of the low-stage compressing section 31 is connected to a refrigerant suction pipe 64 via a low-stage side suction hole 410 provided in the cylinder 400. The compression chamber C1 of the low-stage compressing section 31 is connected to the intermediate connection pipe 26 via a low-stage side discharge hole 520 provided in the sub-frame 500 and the low-stage side discharge muffler chamber M1.
More specifically, the low-stage side discharge hole 520 is provided with a check valve 540. Also, the refrigerant suction pipe 64 is connected to the low-stage side suction hole 410 via a low-stage side suction connection pipe 411, and the intermediate connection pipe 26 is connected to the low-stage side discharge muffler chamber M1 via an intermediate discharge connection pipe 521.
The suction chamber V2 of the high-stage compressing section 32 is connected to the intermediate connection pipe 26 via a high-stage side suction hole 210 provided in the cylinder 200. The compression chamber C2 of the high-stage compressing section 32 is open to the interior of the closed vessel 2 via a high-stage side discharge hole 120 provided in the main frame 100 and the high-stage side discharge muffler chamber M2.
More specifically, the high-stage side discharge hole 120 is provided with a check valve 140. Also, the intermediate connection pipe 26 is connected to the high-stage side suction hole 210 via an intermediate suction connection pipe 211.
At the side of the body of the compressor 1, an accumulator 6 consisting of an independent closed vessel 61 is provided. Above the accumulator 6, a refrigerant return pipe 62 is provided, the refrigerant return pipe 62 being connected to a heat pump system, not shown. Below the accumulator 6, there is provided the refrigerant suction pipe 64 one end having an L shape of which is extended to the upper part in the accumulator 6 and the other end of which is connected to the suction chamber V1 of the low-stage compressing section 31 from the side surface of the compressor 1.
Next, the flow of refrigerant in the above-described configuration is explained with reference to FIGS. 1 and 2. The refrigerant flowing from the heat pump system side into the accumulator 6 passing through the refrigerant return pipe 62 is separated so that a liquid refrigerant lies in the lower part of the accumulator 6 and a gas refrigerant lies in the upper part thereof.
When the low-stage side piston 420 is turned to increase the volume of the low-stage side suction chamber V1, the gas refrigerant in the accumulator 6 is sucked into the low-stage side suction chamber V1 of the compressor body 1 through the refrigerant suction pipe 64.
After one turn of the piston 420, the low-stage side suction chamber V1 comes to a position isolated from the low-stage side suction hole 410, and is turned to the low-stage side compression chamber C1 as it is, by which the refrigerant is compressed.
When the pressure of the compressed refrigerant reaches the pressure in the low-stage side discharge muffler chamber M1 on the outside of the check valve 540 provided in the low-stage side discharge hole 520, that is, an intermediate pressure, the check valve 540 is opened, by which the compressed refrigerant is discharged into the low-stage side discharge muffler chamber M1.
After the pressure pulsation of refrigerant, which may cause noise, has been reduced in the low-stage side discharge muffler chamber M1, the refrigerant is guided into the suction chamber V2 of the high-stage compressing section 32 through the intermediate connection pipe 26.
The refrigerant guided into the suction chamber V2 of the high-stage compressing section 32 is sucked, compressed, and discharged in the high-stage compressing section 32 on the same principle as that of the low-stage compressing section 31. After the pressure pulsation of refrigerant has been reduced in the high-stage side discharge muffler chamber M2, the refrigerant is discharged into the closed vessel 2.
The refrigerant is further guided to a portion above the motor 4 after passing through a core notch (not shown) in the stator 41 of the motor 4 and a gap between a core and a coil, and is discharged to the system side through the discharge pipe 24.
Next, the centrifugal forces acting on the rotating parts in the compressor configured as described above are explained with reference to FIG. 3. FIG. 3 is a schematic view extractingly showing the rotating parts in the compressor.
As the centrifugal forces acting on the rotating parts, there are generated a centrifugal force (F1) acting on the low-stage side crankshaft 73 and the low-stage side piston 420 engaging therewith, a centrifugal force (F2) acting on the high-stage side crankshaft 72 and the high-stage side piston 220 engaging therewith, a centrifugal force (F4) acting on the upper balancer 43 attached to above the rotor 42, and a centrifugal force (F3) acting on the lower balancer 44 attached to below the rotor 42. To balance these centrifugal forces in the horizontal direction, the following equation holds. $F 1 + F 4 = F 2 + F 3$
To balance moments that tend to tilt the whole of shaft, Equation (2) is obtained from the moment around the application point of F3. $F 1 \times (Lx - Ly) = F 2 \times Ly + F 4 \times Lz$

F3 and F4, that is, the mass of the upper balancer 43 of the rotor 42 and the mass of the lower balancer 44 thereof are determined so as to satisfy Equation (2).
Rearranging Equation (2) gives $F 1 = (F 1 \times (Lx - Ly) - F 2 \times Ly) / Lz$
From Equation (3), it can be seen that F4 can be decreased as F1 is decreased or F2 is increased.
That is to say, the upper balancer 43 of the rotor 42 can be made smaller as the mass of the low-stage side crankshaft 73 is decreased or the mass of the high-stage side crankshaft 72 is increased.
Hereunder, the state in which the shaft 7 is deflected by the centrifugal forces acting on the shaft 7 is explained with reference to FIG. 4. FIG. 4 is a schematic view extractingly showing the shaft 7 and the bearing part 110 supporting the shaft 7.
If the deflection of the whole of the shaft 7 increases, especially in the bearing part 110 of the main frame 100, the shaft 7 deforms exceeding the gap between the shaft 7 and the bearing part 110, and comes locally into contact with the bearing part 110 at the upper or lower part of the bearing part 110, which may cause seizure.
To solve this problem, the axial length of the high-stage side crankshaft 72 is made longer than the axial length of the low-stage side crankshaft 73. Thereby, the upper balancer 43 of the rotor 42 can be made small, so that the deflection of the whole of the shaft 7 is reduced, whereby seizure caused by a local excessive load of the bearing part 110 and the contact of the rotor 42 with the stator 41 can be prevented.
On the other hand, the effect described below can be achieved. In the compressor used for a heat pump for an air conditioner, a water heater, and the like, the suction pressure Ps and the discharge pressure Pd of the compressor change mainly depending on the outside air temperature condition. This fact means that the compression ratio φ (= Pd/Ps) as the whole of compressor is not constant, so that it is necessary to respond to a wide range.
Taking the suction volume of the low-stage compressing section 31 as V1, the suction volume of the high-stage compressing section 32 as V2, and the specific heat of compressed gas as κ, in the case where losses in the compressing sections 31 and 32 are neglected, the compression ratio φ 1 of the low-stage compressing section 31 is expressed as φ 1 = (V1/V2)^κ. That is to say, the compression ratio φ 1 of the low-stage compressing section 31 is determined by the suction volumes of the two cylinders without depending on the outside air temperature condition.
Therefore, under the condition in which the total compression ratio φ is high, for example, in a cooling operation under a condition in which the outside air temperature is especially high or in a heating operation under a condition in which the outside air temperature is especially low, the compression ratio φ 2 of the high-stage compressing section 32 is high necessarily.
That is to say, under such a condition, the load torque of the high-stage compressing section 32 is higher than that of the low-stage compressing section 31. To support this load, the length of crankshaft not shorter than a predetermined length is necessary. However, the increase in length of crankshaft achieved than necessary is unfavorable because it may cause an increase in slide loss in a crank part.
Therefore, as described above, the axial length L2 of the high-stage side crankshaft is made longer than the axial length L1 of the low-stage side crankshaft (L2 > L1). Thereby, both of the improvement in reliability in the crankshaft bearing parts and the improvement in efficiency due to the reduction in slide loss can be achieved.
In this embodiment, the rotary compressor 1 configured so that in the compressor provided with the two-stage compression type compressing section having the low-stage compressing section 31 and the high-stage compressing section 32, the working space volume of the high-stage compressing section 32 is made smaller than that of the low-stage compressing section 31 by making the axial length of the high-stage compressing section 32 shorter than that of the low-stage compressing section 31 has been shown typically as a preferred mode. However the configuration of the rotary compressor 1 may be such that the working space volume of the high-stage compressing section 32 is made smaller by making the axial lengths of the low-stage compressing section 31 and the high-stage compressing section 32 equal to each other and by making the turning radius of the high-stage side piston 220 smaller than that of the low-stage side piston 420.
Also, the rotary compressor 1 may be a two-stage compression rotary compressor configured so that a gas injection cycle is used as the refrigerating cycle, and an injection refrigerant is allowed to flow into an intermediate compressing section between the low-stage compressing section 31 and the high-stage compressing section 32.
Also, the compressing mechanism of the compressing section 3 is not limited to the compressing mechanism shown in this embodiment if the compressor is configured so that the change in volumes of the suction chamber V1, V2 and the compression chamber C1, C2 caused by the turning motion of the piston 220, 420 imparted by the crankshaft 72, 73 is utilized.

Claims

A rotary compressor comprising:
a closed vessel;

a low-stage compressing section and a high-stage compressing section provided in the closed vessel;

a shaft provided with a low-stage side off-center part and a high-stage side off-center part corresponding to the low-stage compressing section and the high-stage compressing section, respectively;

a motor connected mechanically to the shaft to drive the low-stage compressing section and the high-stage compressing section,

each of the low-stage compressing section and the high-stage compressing section having a cylinder; a piston turning in the cylinder while engaging with the off-center part of the shaft; and a vane the tip end of which comes into sliding contact with the piston while the vane reciprocates in a vane groove in the cylinder to form a suction chamber and a compression chamber for refrigerant together with the cylinder and the piston, and
further comprising:
an intermediate partition plate held between the low-stage compressing section and the high-stage compressing section to close one end surface of the suction chamber and the compression chamber; and

a main frame and a sub-frame each of which is provided with a bearing part for rotatably supporting the shaft and closes one end surface of the suction chamber and the compression chamber, in which

means for allowing the discharge side of the low-stage compressing section and the suction side of the high-stage compressing section to communicate with each other is provided, whereby a two-stage compressing section is formed, wherein
when the axial length of the off-center part of shaft corresponding to the low-stage compressing section is taken as L1, and the axial length of the off-center part of shaft corresponding to the high-stage compressing section is taken as L2, L2 is longer than L 1.
The rotary compressor according to claim 1, wherein the rotational speed of the compressing section is variable.