EP3141755A1

EP3141755A1 - Rotary compressor

Info

Publication number: EP3141755A1
Application number: EP16186351.9A
Authority: EP
Inventors: Makoto Ogawa; Hajime Sato; Shigeki Miura; Ikuo Esaki; Masanari Uno; Hirofumi SHIMAYA; Yuichi Muroi
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2015-09-09
Filing date: 2016-08-30
Publication date: 2017-03-15
Also published as: JP2017053263A

Abstract

The present invention provides a rotary compressor having increased efficiency while ensuring reliability of sliding bearings between eccentric shaft portions and rotors. This is achieved by reducing the axial width and the diameter of the eccentric shaft portions and thereby reducing oil film shear loss between the eccentric shaft portions and the rotors. Provided is a rotary compressor in which a drive shaft 14 includes eccentric shaft portions 15, 16, and rotors 25, 26 rotationally movably fitted to the eccentric shaft portions 15, 16, respectively, are configured to eccentrically rotationally move along the inner peripheral surfaces of the cylinder chambers 17, 18 to thereby compress refrigerant gas or other gases, and further in which bearing rings 33, 34 are provided between the eccentric shaft portions 15, 16 and the rotors 25, 26, and the axial widths of the eccentric shaft portions 15, 16 and bearing rings 33, 34 are smaller than the axial widths of the rotors 25, 26.

Description

{Technical Field}

The present invention relates to a rotary compressor in which bearing rings are provided between eccentric shaft portions of the drive shaft and respective rotors fitted to the eccentric shaft portions to rotationally move within cylinder chambers.

{Background Art}

Rotary compressors include an eccentric shaft portion at the drive shaft and are configured to compress a refrigerant gas or other gases by eccentrically rotationally moving a rotor, fitted to the eccentric shaft portion in a rotationally movable manner, along the inner peripheral surface of a cylinder chamber. In such rotary compressors, a sliding bearing is formed between the eccentric shaft portion of the drive shaft and the inner peripheral surface of the rotor, which is rotationally movably fitted to the eccentric shaft portion. Rotation of the drive shaft causes oil film shear loss due to shearing of the lubricating oil film formed between the sliding bearing surfaces, which results in a decrease in efficiency by an amount corresponding to associated power loss (mechanical loss).
Such oil film shear loss can be reduced by reducing the axial width and the diameter of the eccentric shaft portion so that the shear loss can be reduced (the shear loss decreases in proportion to the sliding bearing surface area). However, the lubricating oil film becomes thinner and the probability of solid-to-solid contact increases, which promotes wear and refrigerant leakage and will lead to decreased reliability.
PTL 1 discloses a rotary compressor as follows. The rotary compressor includes a dual rotor structure having an annular inner rotor provided between an eccentric shaft portion and a rotor so that the number of revolutions of the outer rotor can be reduced. With this configuration, the oil retention ability of the contact portion between the outer rotor and a blade (vane) can be increased. In addition, an edge notch is provided between the inner rotor and the outer rotor to form an intermediate pressure chamber so that the pressure difference can be reduced. As a result, refrigerant leakage can be reduced and therefore an improvement in compression efficiency can be achieved.
PTL 2 discloses a 2-cylinder rotary compressor including upper and lower cylinder bodies with a separator plate therebetween partitioning them. In this rotary compressor, in order to minimize refrigerant leakage through seal portions between the separator plate and the rotor edges, the upper eccentric shaft portion is configured to have a large outside diameter and the lower eccentric shaft portion is configured to have a small outside diameter relative to the diameter of the through hole formed in the separator plate. With this configuration, the drive shaft can be passed through the separator plate to be assembled, eliminating the need for a structure with separate drive shafts.

{Citation List}

{Patent Literature}

{PTL 1} Japanese Unexamined Utility Model Application, Publication No. S60-92791
{PTL 2} Japanese Domestic Re-publication of PCT International Publication No. WO2013/057946

{Summary of Invention}

{Technical Problem}

The rotary compressor disclosed in PTL 1 includes a dual rotor structure having inner and outer rotors to reduce the number of revolutions of the outer rotor compared with the case of using a single rotor (N ≥ Ni > No, where N is the number of revolutions of the single rotor, Ni is the number of revolutions of the inner rotor, and No is the number of revolutions of the outer rotor), to thereby reduce the amount of refrigerant leakage. However, this compressor is not of the type in which the efficiency is increased by reducing the shear loss due to the oil film formed between the eccentric shaft portion of the drive shaft and the rotor and therefore reducing associated power loss (mechanical loss).
The compressor disclosed in PTL 2 is designed to minimize refrigerant leakage through seal portions between the separator plate and the rotor edges by reducing the diameter of the lower eccentric shaft portion. However, PTL 2 does not suggest increasing the efficiency by reducing the shear loss due to the oil film formed between the sliding bearing surfaces of the eccentric shaft portion and the rotor and therefore reducing associated power loss (mechanical loss) by reducing the diameter of the eccentric shaft portion.
The present invention has been made in view of the above-described circumstances. Accordingly, an object of the present invention is to provide a rotary compressor in which the efficiency is increased by reducing the axial width and the diameter of the eccentric shaft portion and thereby reducing oil film shear loss between the eccentric shaft portion and the rotor while ensuring reliability of the sliding bearing between the eccentric shaft portion and the rotor.

{Solution to Problem}

In order to solve the aforementioned problems, a rotary compressor of the present invention employs the following means. A rotary compressor according to one aspect of the present invention includes: a drive shaft including an eccentric shaft portion at a predetermined axial location; a cylinder body forming a cylinder chamber corresponding to the eccentric shaft portion; an upper bearing mounted on an upper surface of the cylinder body and a lower bearing mounted on a lower surface of the cylinder body, the upper and lower bearings defining the cylinder chamber and rotatably supporting the drive shaft; a rotor fitted to the eccentric shaft portion to rotationally move within the cylinder chamber; and a bearing ring between the eccentric shaft portion and the rotor, wherein axial widths of the eccentric shaft portion and the bearing ring are smaller than an axial width of the rotor.
In this aspect, the rotary compressor is configured such that the drive shaft includes an eccentric shaft portion, and a rotor rotationally movably fitted to the eccentric shaft portion is eccentrically rotationally moved along the inner peripheral surface of the cylinder chamber to thereby compress a refrigerant gas or other gases, and further that a bearing ring is provided between the eccentric shaft portion and the rotor. Furthermore, the axial widths of the eccentric shaft portion and the bearing ring are reduced relative to the axial width of the rotor. The sufficiently reduced axial widths of the bearing ring and the eccentric shaft portion result in a reduced sliding bearing surface area between them and the rotor, so that the oil film shear loss is proportionately reduced. Moreover, as a result of interposing the bearing ring between the eccentric shaft portion and the rotor, the bearing ring and the rotor each have an angular velocity that is lower than that of a rotor in the case where the rotor is directly rotatably fitted to the eccentric shaft portion. Thus, the use of the bearing ring reduces the sliding area of the sliding bearing surfaces to reduce the oil film shear loss and consequently improves the efficiency. Although the contact pressure P applied to the eccentric shaft portion increases by an amount corresponding to the reduction in the sliding area of the sliding bearing surfaces, the use of the bearing ring reduces the sliding velocity V between the rotor and the eccentric shaft portion to thereby maintain a constant PV value, so that reliability of lubrication is ensured while achieving a reduction in oil film shear loss.
In the first aspect described above, the rotary compressor is preferably configured such that: the drive shaft is provided as two eccentric shaft portions at upper and lower locations with a predetermined spacing therebetween; two upper and lower compression mechanisms are provided with a separator plate therebetween, each of the compression mechanisms including a cylinder body forming a cylinder chamber corresponding to one of the eccentric shaft portions and a rotor fitted to the corresponding eccentric shaft portion to rotationally move within the corresponding cylinder chamber; and a bearing ring is provided between each eccentric shaft portion and each rotor.
In this aspect, the 2-cylinder rotary compressor is configured such that the two compression mechanisms are provided at upper and lower locations with a separator plate therebetween and that the bearing ring is provided between the eccentric shaft portion and the rotor in each of the compression mechanisms. Two-cylinder rotary compressors are generally able to provide high performance due to, for example, reduced vibration, reduced noise, and higher speed operation, compared with single-cylinder rotary compressors. In such a 2-cylinder rotary compressor according to this aspect, the axial widths of the bearing rings and eccentric shaft portions of the two compression mechanisms are sufficiently reduced to reduce the sliding bearing surface areas between the eccentric shaft portions and the rotors and thereby reduce the oil film shear loss. Furthermore, the use of the bearing ring reduces the sliding velocity V between the rotor and the eccentric shaft portion so that the PV value, which is the product of the sliding velocity and the contact pressure P applied to the eccentric shaft portion, is maintained constant and therefore reliability of lubrication is ensured. Consequently, increased efficiency due to reduced oil film shear loss and ensured reliability of lubrication are both achieved and therefore even higher performance for the 2-cylinder rotary compressors are provided.
In the first aspect, the rotary compressor is preferably configured such that the eccentric shaft portion at the lower location has a diameter smaller than a diameter of the eccentric shaft portion at the upper location, the eccentric shaft portion at the lower location being positioned farther from an electric motor coupled to one end of the drive shaft, the eccentric shaft portion at the upper location being positioned closer to the electric motor.
In this aspect, the diameter of the eccentric shaft portion at the lower location, which is positioned farther from the electric motor coupled to one end of the drive shaft, is smaller than the diameter of the eccentric shaft portion at the upper location, which is closer to the electric motor. Thus, the eccentric shaft portion at the lower location has not only a reduced axial width but also a reduced diameter, and this reduces the oil film shear loss more effectively (the shear loss decreases in proportion to the sliding bearing surface area). Consequently, power loss due to oil film shear loss is further reduced to achieve increased efficiency. Furthermore, the use of the bearing ring reduces the sliding velocity V between the rotor and the eccentric shaft portion so that the PV value, which is the product of the sliding velocity and the contact pressure P applied to the eccentric shaft portion, is maintained constant and therefore reliability of lubrication is ensured. Moreover, the reduced diameter of the eccentric shaft portion at the lower location makes it possible to reduce, by a corresponding amount, the inside diameter of the through hole formed in the separator plate for passing the eccentric shaft portion at the lower location therethrough for assembling. As a result, the lengths of the seal portions between the separator plate and the rotor of each of the compression mechanisms are increased, and compression efficiency can also be increased by inhibiting refrigerant leakage through the seal portions.

{Advantageous Effects of Invention}

With the present invention, the sufficiently reduced axial widths of the bearing rings and eccentric shaft portions result in reduced sliding bearing surface areas between them and the rotors, which proportionately reduces the oil film shear loss. Moreover, as a result of interposing the bearing rings between the eccentric shaft portions and the rotors, the bearing rings and the rotors each have an angular velocity that is lower than that of rotors in the case where the rotors are directly rotatably fitted to the eccentric shaft portions. Thus, the use of the bearing rings improves the efficiency by reducing the sliding bearing surface areas and thereby reducing oil film shear loss. Although the contact pressure P applied to the eccentric shaft portion increases by an amount corresponding to the reduction in the sliding area of the sliding bearing surfaces, the use of the bearing ring reduces the sliding velocity V between the rotor and the eccentric shaft portion to thereby maintain a constant PV value, so that reliability of lubrication is ensured while achieving a reduction in oil film shear loss.

{Brief Description of Drawings}

{Fig. 1} FIG. 1 is a longitudinal cross-sectional view of a rotary compressor according to a first embodiment of the present invention;
{Fig. 2} FIG. 2A is an enlarged cross-sectional view of a compression mechanism portion of the rotary compressor, FIG. 2B is a transverse cross-sectional view of its upper cylinder body, and FIG. 2C is a transverse cross-sectional view of its lower cylinder body;
{Fig. 3} FIG. 3 is a longitudinal cross-sectional view of a rotary compressor according to a second embodiment of the present invention; and
{Fig. 4} FIG. 4A is an enlarged cross-sectional view of a compression mechanism portion of the rotary compressor, FIG. 4B is a transverse cross-sectional view of its upper cylinder body, and FIG. 4C is a transverse cross-sectional view of its lower cylinder body.

{Description of Embodiments}

Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment

Now the first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a longitudinal cross-sectional view of a rotary compressor according to a first embodiment of the present invention. FIG. 2A is an enlarged cross-sectional view of its compression mechanism portion, FIG. 2B is a transverse cross-sectional view of its upper cylinder body, and FIG. 2C is a transverse cross-sectional view of its lower cylinder body. Although in the illustrated example a rotary compressor 1 of the present embodiment is a 2-cylinder rotary compressor, the present invention is not limited to this and may be applied to a single-cylinder rotary compressor as will be appreciated.
The rotary compressor 1 is an electric compressor of a sealed structure including a cylindrical sealed housing 2 sealed at the upper and lower ends by covers 3, 4 with an electric motor 5 provided in an upper region in the housing and compression mechanisms 6 (rotary compression mechanisms) to be driven by the electric motor 5 provided in a lower region therein. A plurality of mounting feet 7 are provided at the lower outer periphery of the sealed housing 2. An outlet pipe 8 is provided in an upper region of the sealed housing 2 so as to pass through the upper cover 3. High pressure refrigerant gas compressed by a compression mechanism 6 and discharged into the sealed housing 2 can be released to the outside of the compressor (refrigeration cycle) through the outlet pipe 8.
An accumulator 9 is integrally attached to the outer periphery of the sealed housing 2 to separate the liquid fraction such as oil and liquid refrigerant contained in the low pressure refrigerant gas returned from the refrigeration cycle so that only the gas fraction can be sucked into the compression mechanism 6 through inlet pipes 10, 11. The separated oil is returned to the compressor from the bottom of the accumulator 9 in small increments through small openings formed in the inlet pipes 10, 11.
The electric motor 5 includes a stator 12 and a rotor 13, and the stator 12 is secured to the inner peripheral surface of the sealed housing 2 by shrink fitting, press fitting, or other means. A drive shaft 14 is integrally coupled to the rotor 13 so that the rotational driving force can be transmitted to the compression mechanism 6 via the drive shaft 14. In lower regions of the drive shaft 14 are provided an upper eccentric shaft portion 15 and a lower eccentric shaft portion 16 with a phase difference of 180 degrees, at two upper and lower locations with a predetermined axial spacing therebetween. The upper eccentric shaft portion 15 and lower eccentric shaft portion 16 correspond to an upper rotary compression mechanism 6A and a lower rotary compression mechanism 6B of the compression mechanism 6 described below, respectively.
The compression mechanism (rotary compression mechanism) 6 is a 2-cylinder rotary compression mechanism including the upper rotary compression mechanism 6A and the lower rotary compression mechanism 6B. The upper rotary compression mechanism 6A and the lower rotary compression mechanism 6B respectively include an upper cylinder body 19 and a lower cylinder body 20 that respectively form an upper cylinder chamber 17 and a lower cylinder chamber 18 and are secured within the sealed housing 2 to respectively correspond to the upper eccentric shaft portion 15 and lower eccentric shaft portion 16 of the drive shaft 14.
The upper rotary compression mechanism 6A and the lower rotary compression mechanism 6B include: a separator plate 21 interposed between the upper cylinder body 19 and the lower cylinder body 20 to define the upper cylinder chamber 17 and the lower cylinder chamber 18, the separator plate 21 having a through hole 22 through which the lower eccentric shaft portion 16 can be passed; an upper bearing 23 mounted on the upper surface of the upper cylinder body 19 to define the upper cylinder chamber 17 and support the drive shaft 14 in a manner to allow it to rotate; and a lower bearing 24 mounted on the lower surface of the lower cylinder body 20 to define the lower cylinder chamber 18 and support the drive shaft 14 in a manner to allow it to rotate.
The upper rotary compression mechanism 6A and the lower rotary compression mechanism 6B include: an upper rotor 25 and a lower rotor 26 rotationally movably fitted to the upper eccentric shaft portion 15 and lower eccentric shaft portion 16, respectively, to be eccentrically rotationally moved within the upper cylinder chamber 17 and the lower cylinder chamber 18; and vanes 27, 28 (see FIG. 2) slidably fitted in vane grooves (not illustrated) formed in the upper cylinder body 19 and the lower cylinder body 20 to respectively partition the upper cylinder chamber 17 and the lower cylinder chamber 18 into the inlet side and the outlet side.
Low pressure refrigerant gas can be sucked into the upper cylinder chamber 17 of the upper rotary compression mechanism 6A and the lower cylinder chamber 18 of the lower rotary compression mechanism 6B from the inlet pipes 10, 11 through inlet ports 29, 30. The refrigerant can be compressed by rotational movement of the upper rotor 25 and lower rotor 26 to be discharged into outlet chambers 31, 32 through outlet ports and outlet valves (not illustrated), and after being discharged from there into the sealed housing 2, the refrigerant is directed to the upper end of the sealed housing 2 so that it can be discharged to the refrigeration cycle through the outlet pipe 8.
In the 2-cylinder rotary compression mechanism 6, any one of the upper bearing 23, the upper cylinder body 19, and the lower cylinder body 20 is secured to the inner peripheral surface of the sealed housing 2 by plug welding, swaging, or other means. The other components are integrally fastened and secured to any one of the secured upper bearing 23, upper cylinder body 19, and lower cylinder body 20 via bolts or other means. A predetermined amount of lubricating oil is stored at a bottom portion within the sealed housing 2 and thus sliding regions within the compression mechanism 6 can be supplied with the lubricating oil via oil feed holes formed in the drive shaft 14 as is well known.
The above-described configuration is a typical configuration for the 2-cylinder rotary compressor 1. The present embodiment further employs the following configuration in order to reduce oil film shear loss that occurs as a result of shearing of the lubricant films formed between the sliding bearing surfaces of the upper eccentric shaft portion 15 and the upper rotor 25 fitted to the eccentric shaft portion 15 and between the sliding bearing surfaces of the lower eccentric shaft portion 16 and the lower rotor 26 fitted to the eccentric shaft portion 16. FIGS. 2A, 2B, and 2C are enlarged views of the principal portion.
The upper eccentric shaft portion 15 and the lower eccentric shaft portion 16 located in lower regions of the drive shaft 14, at upper and lower locations with a predetermined axial spacing therebetween, are provided with a phase difference of 180 degrees relative to each other. Annular bearing rings 33, 34 are rotatably fitted to the outer peripheries of the upper eccentric shaft portion 15 and the lower eccentric shaft portion 16, respectively. The upper rotor 25 and the lower rotor 26 are rotatably fitted to the outer peripheries of the bearing rings 33, 34, respectively. That is, the bearing ring 33 is interposed between the upper eccentric shaft portion 15 and the upper rotor 25 with the bearing ring 33 being rotatable relative to each of them and the bearing ring 34 is interposed between the lower eccentric shaft portion 16 and the lower rotor 26 with the bearing ring 34 being rotatable relative to each of them.
Accordingly, the following relationship is satisfied: $ω_{1} = ω 2 + ω 3$
where ω1 is the angular velocity of rotors in the case where the rotors are alone directly fitted to the eccentric shaft portions; and ω2 is the angular velocity of the bearing rings 33, 34 and ω3 is the angular velocity of the rotors 25, 26, in the case where the rotors 25, 26 are fitted to the eccentric shaft portions with the bearing rings 33, 34 interposed therebetween. Thus, the following relationships hold: $ω 1 \geq ω 2, ω 1 \geq ω 3 (whereinω 1 \geq ω 2 > ω 3) .$
The axial widths of the upper eccentric shaft portion 15 and lower eccentric shaft portion 16 are each h1, and the axial widths of the bearing rings 33, 34 fitted to their outer peripheries have the same widths h1. On the other hand, the upper rotor 25 and the lower rotor 26, which are rotationally movable within the upper cylinder chamber 17 and the lower cylinder chamber 18, have a width h2, which is slightly smaller than the axial widths of the upper cylinder chamber 17 and the lower cylinder chamber 18. The width h2 is determined depending on the axial widths of the upper cylinder body 19 and lower cylinder body 20, and the width h1 of the upper eccentric shaft portion 15, lower eccentric shaft portion 16, and bearing rings 33, 34 are set to be sufficiently small relative to the width h2 (h1 < h2).
With the configurations described above, the present embodiment provides the following functions and advantages. In the rotary compressor (sealed type electric compressor) 1 described above, once the compression mechanism 6 is actuated by rotation of the electric motor 5, low pressure refrigerant gas is sucked into the upper cylinder chamber 17 of the upper rotary compression mechanism 6A and the lower cylinder chamber 18 of the lower rotary compression mechanism 6B from the accumulator 9 through the inlet pipes 10, 11 and the inlet ports 29, 30. The refrigerant gas is compressed by eccentric rotational movement of the upper rotor 25 and the lower rotor 26 and then is discharged into the outlet chambers 31, 32 through the outlet ports and the outlet valves (not illustrated).
The compressed gas is discharged from the outlet chambers 31, 32 into the sealed housing 2 for a time and then is directed to an upper space within the sealed housing 2 through, for example, a refrigerant passage formed between the sealed housing 2 and the electric motor 5, and from there, the compressed gas is discharged to the outside of the compressor (refrigeration cycle) through the outlet pipe 8.
During the compression operation, lubricating oil is supplied to the sliding regions of the upper and lower rotary compression mechanisms 6A, 6B to provide lubrication, for example, between the drive shaft 14 and the upper bearing 23 and between the drive shaft 14 and the lower bearing 24, between the upper eccentric shaft portion 15 and the bearing ring 33 and between the lower eccentric shaft portion 16 and the bearing ring 34, between the bearing ring 33 and the upper rotor 25 and between the bearing ring 34 and the lower rotor 26, between the upper rotor 25 and the inner peripheral surface of the upper cylinder chamber 17 and between the lower rotor 26 and the inner peripheral surface of the lower cylinder chamber 18, between the vane 27 and the outer peripheral surface of the upper rotor 25 and between the vane 28 and the outer peripheral surface of the lower rotor 26, between the vanes 27, 28 and the respective vane grooves, between the upper rotor 25 and the upper bearing 23, between the lower rotor 26 and the lower bearing 24, and between the rotors 25, 26 and the separator plate 21.
In ordinary rotary compressors, a sliding bearing is formed between the eccentric shaft portion of the drive shaft and the inner peripheral surface of the rotor that is rotationally movably fitted to the eccentric shaft portion. Rotation of the drive shaft causes oil film shear loss due to shearing of the lubricating oil film formed between the sliding bearing surfaces and the efficiency decreases by a corresponding amount. Such oil film shear loss can be reduced by reducing the axial width and the diameter of the eccentric shaft portion (the shear loss decreases in proportion to the sliding bearing surface area). However, the contact pressure applied to the eccentric shaft portion increases and therefore the lubricating oil film becomes thinner, which results in increased probability of solid-to-solid contact to promote wear and refrigerant leakage and consequently lead to decreased reliability.
The present embodiment employs the configuration in which the bearing ring 33 is interposed between the upper eccentric shaft portion 15 and the upper rotor 25 with the bearing ring 33 being rotatable relative to each of them and the bearing ring 34 is interposed between the lower eccentric shaft portion 16 and the lower rotor 26 with the bearing ring 34 being rotatable relative to each of them. Furthermore, the axial width h1 of the bearing rings 33, 34, the upper eccentric shaft portion 15, and the lower eccentric shaft portion 16 is sufficiently small with respect to the axial width h2 of the upper rotor 25 and the lower rotor 26 (h1 < h2).
Thus, the sufficiently small axial width h1 of the bearing rings 33, 34, the upper eccentric shaft portion 15, and the lower eccentric shaft portion 16 reduces the sliding bearing surface areas between them and the upper and lower rotors 25, 26, so that the oil film shear loss is proportionately reduced. Moreover, the bearing ring 33 is interposed between the upper eccentric shaft portion 15 and the upper rotor 25 and the bearing ring 34 is interposed between the lower eccentric shaft portion 16 and the lower rotor 26. As a result, the angular velocities ω2 of the bearing rings 33, 34 and ω3 of the upper rotor 25 and the lower rotor 26 are each lower than the angular velocity ω1 of rotors in the case where the rotors are alone directly rotatably fitted to the eccentric shaft portions, as described above.
Consequently, an improvement in the efficiency is achieved by the reduced oil film shear loss, which is accomplished by sufficiently reducing the axial width h1 of the bearing rings 33, 34, the upper eccentric shaft portion 15, and the lower eccentric shaft portion 16 and thereby reducing the sliding areas of the sliding bearing surfaces. The reduction in the sliding areas of the sliding bearing surfaces increases, by a corresponding amount, the contact pressure P applied to the eccentric shaft portions. The use of the bearing rings 33, 34 reduces the sliding velocity V between the eccentric shaft portions 15, 16 with the bearing rings 33, 34 and the upper and lower rotors 25, 26, so that the PV value is maintained constant and reliability of lubrication is ensured. As a result, increased efficiency due to reduced oil film shear loss and ensured reliability of lubrication are both achieved.

Second Embodiment

Next the second embodiment of the present invention will be described with reference to FIGS. 3 and 4. The present embodiment differs from the first embodiment in that the diameter of the lower eccentric shaft portion 16A is smaller than the diameter of the upper eccentric shaft portion 15. The other features are the same as those of the first embodiment and therefore a description thereof is not repeated.
The present embodiment employs a configuration in which, of upper and lower eccentric shaft portions of the drive shaft 14 disposed with a predetermined axial spacing therebetween, a lower eccentric shaft portion 16A, which is the lower one of them, has a diameter d2 that is smaller than a diameter d1 of the upper eccentric shaft portion 15 (d1 > d2) in addition to having the axial width h1, which is smaller than the axial width h2 of the upper and lower rotors 25, 26.
As will be appreciated, as a result of reducing the diameter d2 of the lower eccentric shaft portion 16A relative to the diameter d1 of the upper eccentric shaft portion 15, the inside diameter of a bearing ring 34A, which is rotatably fitted to the lower eccentric shaft portion 16A, is correspondingly reduced. As for the angular velocities ω4 of the bearing ring 34A and ω5 of the rotor 26, the relationship ω1 = ω4 + ω5 holds as in the first embodiment and the aforementioned conditions are satisfied in this embodiment as well. In this configuration, the diameter of an axis end portion 14A, which extends downwardly from the lower end of the lower eccentric shaft portion 16A and is supported by the lower bearing 24, is also reduced. However, this does not cause a particular problem because the lower bearing 24 is employed as an auxiliary bearing in contrast to the main upper bearing 23.
In this embodiment, not only the axial width h1 of the lower eccentric shaft portion 16A and bearing ring 34A is reduced but also the diameter d2 of the lower eccentric shaft portion 16A is reduced, and therefore the lower eccentric shaft portion 16A has the reduced axial width h1 and reduced diameter d2 in combination, which reduces oil film shear loss more effectively (the shear loss decreases in proportion to the sliding bearing surface areas).
Therefore, a further reduction in power loss due to oil film shear loss is achieved, so that the efficiency is increased. In addition, the use of the bearing rings 33, 34A reduces the sliding velocities V between the rotors 25, 26 and the eccentric shaft portions 15, 16A to thereby maintain the PV values, which are the products of the sliding velocities and the contact pressures P applied to the eccentric shaft portions 15, 16A, to be constant, so that suitable oil films are formed to ensure reliability of lubrication and prevent wear and refrigerant leakage due to oil film depletion. As a result, increased efficiency and reliability of lubrication are both achieved.
Moreover, the reduced diameter d2 of the lower eccentric shaft portion 16A makes it possible to reduce, by a corresponding amount, the inside diameter of the through hole 22, which is formed in the separator plate 21 to allow the eccentric shaft portion 16A to be passed therethrough for assembling. As a result, the lengths of the seal portions formed between the separator plate 21 and the upper and lower rotors 25, 26 are increased, and by minimizing refrigerant leakage through the seal portions, the compression efficiency can also be increased.
The present invention is not limited to the embodiments described above but may be suitably modified without departing from the scope of the invention. For example, in the above embodiments, descriptions have been given of examples in which the present invention is applied to 2-cylinder rotary compressors 1, but it is apparent that the same advantages can also be obtained when the invention is applied to a single-cylinder rotary compressor having a single cylinder chamber and therefore, as will be appreciated, the present invention encompasses single-cylinder rotary compressors.
Also, as will be understood, the present invention is not limited to single-stage rotary compressors but similarly applicable to 2-stage compressors having two cylinders with one of the cylinder chambers disposed on the downstream side and the cylinder chamber of the other cylinder disposed on the upstream side.

{Reference Signs List}

1 rotary compressor
5 electric motor
6 compression mechanism (rotary compression mechanism)
6A upper rotary compression mechanism
6B lower rotary compression mechanism
14 drive shaft
15 upper eccentric shaft portion
16, 16A lower eccentric shaft portion
17 upper cylinder chamber
18 lower cylinder chamber
19 upper cylinder body
20 lower cylinder body
21 separator plate
23 upper bearing
24 lower bearing
25 upper rotor
26 lower rotor
33, 34, 34A bearing ring
h1 axial width of upper and lower eccentric shaft portions and bearing rings
h2 axial width of upper and lower rotors
d1 diameter of upper eccentric shaft portion
d2 diameter of lower eccentric shaft portion

Claims

A rotary compressor (1) comprising:
a drive shaft (14) comprising an eccentric shaft portion (15, 16) at a predetermined axial location;

a cylinder body (19, 20) forming a cylinder chamber (17, 18) corresponding to the eccentric shaft portion (15, 16);

an upper bearing (23) mounted on an upper surface of the cylinder body (19, 20) and a lower bearing (24) mounted on a lower surface of the cylinder body (19, 20), the upper and lower bearings (23, 24) defining the cylinder chamber (17, 18) and rotatably supporting the drive shaft (14);

a rotor (25, 26) fitted to the eccentric shaft portion (15, 16) to rotationally move within the cylinder chamber (17, 18); and

a bearing ring (33, 34) between the eccentric shaft portion (15, 16) and the rotor (25, 26),

wherein axial widths of the eccentric shaft portion (15, 16) and the bearing ring (33, 34) are smaller than an axial width of the rotor (25, 26).
The rotary compressor (1) according to claim 1,
wherein the drive shaft (14) comprises two eccentric shaft portions at upper and lower locations with a predetermined spacing therebetween,
wherein two upper and lower compression mechanisms (6A, 6B) are provided with a separator plate (21) therebetween, each of the compression mechanisms (6A, 6B) comprising a cylinder body (19, 20) forming a cylinder chamber (17, 18) corresponding to one of the eccentric shaft portions (15, 16) and a rotor (25, 26) fitted to the corresponding eccentric shaft portion (15, 16) to rotationally move within the corresponding cylinder chamber (17, 18), and
wherein a bearing ring (33, 34) is provided between each eccentric shaft portion (15, 16) and each rotor (25, 26).
The rotary compressor (1) according to claim 2,
wherein the eccentric shaft portion (16) at the lower location has a diameter smaller than a diameter of the eccentric shaft portion (15) at the upper location, the eccentric shaft portion (16) at the lower location being positioned farther from an electric motor (5) coupled to one end of the drive shaft (14), the eccentric shaft portion (15) at the upper location being positioned closer to the electric motor (5).