MOTOR-OPERATED COMPRESSOR

Abstract

An electric compressor includes a first scroll and a second scroll engaged with the first scroll and making an orbiting motion to form a pair of two compression chambers with the first scroll. A rotary shaft is eccentrically coupled to the second scroll and is rotatably supported by a bearing member. A frame is fixed to an opposite side of the first scroll from the second scroll with the second scroll being interposed between the frame and the first scroll. The frame includes a bearing support portion, and the bearing member is inserted into and fixed to the bearing support member with an interference fit.

Claims

1. An electric compressor comprising: a first scroll; a second scroll engaged with the first scroll on a first side of the first scroll, the second scroll being configured to make an orbiting motion relative to the first scroll to form a pair of two compression chambers with the first scroll; a rotary shaft eccentrically coupled to the second scroll; a bearing member rotatably supporting the rotary shaft; and a frame fixed to an opposite, second side of the first scroll with the second scroll interposed between the frame and the first scroll, the frame including a bearing support portion, and the bearing member being inserted into the bearing support portion and fixed to the bearing support portion, wherein an inner diameter of the bearing support portion is smaller than an outer diameter of the bearing member before the bearing member is inserted into the bearing support portion.

2. The electric compressor of claim 1, wherein the inner diameter of the bearing support portion is 0.08% to 0.13% smaller than the outer diameter of the bearing member before the bearing member is inserted into the bearing support portion.

3. The electric compressor of claim 2, wherein the frame comprises a material having a thermal strain temperature lower than a thermal strain temperature of the bearing member or a thermal strain temperature of the rotary shaft.

4. The electric compressor of claim 3, wherein the bearing support portion includes a guide surface, and an inner diameter of the guide surface of the bearing support portion increases in a direction in which the bearing member is inserted into the bearing support portion.

5. The electric compressor of claim 4, wherein an axial length of the guide surface is or less of an entire axial length of the bearing support portion.

6. The electric compressor of claim 1, wherein a pressure of a refrigerant discharged from at least one of the pair of compression chambers is 100 bar or greater during operation of the electric compressor.

7. The electric compressor of claim 6, wherein the frame comprises aluminum material.

8. An electric compressor comprising: a first scroll; a second scroll engaged with the first scroll on a first side of the first scroll, the second scroll being configured to orbit relative to the first scroll to form a pair of two compression chambers with the first scroll; a rotary shaft eccentrically coupled to the second scroll; a frame fixed to an opposite, second side of the first scroll with the second scroll interposed between the frame and the first scroll and the rotary shaft penetrating through a portion of the second scroll; a bearing support portion formed in the frame; and a bearing member inserted into the bearing support portion and disposed between the frame and the rotary shaft or between the second scroll and the rotary shaft and rotatably supporting the rotary shaft, wherein an outer diameter of the bearing member is 0.08% to 0.13% greater than an inner diameter of the bearing support portion before the bearing member is inserted into the bearing support portion.

9. The electric compressor of claim 8, wherein a shaft hole through which the rotary shaft penetrates is formed in the frame on one side of the bearing support portion, and a sealing member is disposed in the shaft hole to seal a gap between an inner circumferential surface of the shaft hole and an outer circumferential surface of the rotary shaft.

10. The electric compressor of claim 9, wherein the sealing member is formed of a material having a coefficient of thermal expansion that is larger than with a coefficient of thermal expansion of the frame.

11. The electric compressor of claim 8, wherein the frame comprises aluminum and the bearing member comprises steel.

12. The electric compressor of claim 11, wherein in a state in which the bearing member is press-fit into the bearing support portion, an inner diameter at a corner of the bearing support portion is the same along a circumferential direction.

13. The electric compressor of claim 11, wherein in a state in which the bearing member is press-fit into the bearing support portion, an inner diameter at a corner of the bearing support portion is the same as an outer diameter of the bearing member along the circumferential direction.

14. The electric compressor of claim 8, wherein a pressure of a fluid discharged from at least one of the pair of compression chambers is 100 bar or greater during orbiting motion of the second scroll relative to the first scroll.

15. An electric compressor comprising: a frame; a fixed scroll fixed to the frame; an orbiting scroll engaged with the fixed scroll, the orbiting scroll being configured to make an orbiting motion relative to the fixed scroll to form a pair of two compression chambers with the fixed scroll; a rotary shaft eccentrically coupled to the orbiting scroll; and a bearing member rotatably supporting the rotary shaft, wherein the orbiting scroll is interposed between the frame and the fixed scroll, the frame includes a bearing support portion, the bearing member is inserted into the bearing support portion and fixed to the bearing support portion, an inner diameter of the bearing support portion is smaller than an outer diameter of the bearing member before the bearing member is inserted into the bearing support portion, and the bearing support portion includes a guide surface along a portion of the inner diameter of the bearing support portion with an inner diameter of the guide surface increasing in a direction in which the bearing member is inserted into the bearing support portion.

16. The electric compressor of claim 15, wherein the inner diameter of the bearing support portion is 0.08% to 0.13% smaller than the outer diameter of the bearing member before the bearing member is inserted into the bearing support portion.

17. The electric compressor of claim 16, wherein the frame comprises a material having a thermal strain temperature lower than a thermal strain temperature of the bearing member or a thermal strain temperature of the rotary shaft.

18. The electric compressor of claim 17, wherein the bearing support portion includes a guide surface, and an inner diameter of the guide surface of the bearing support portion increases in a direction in which the bearing member is inserted into the bearing support portion.

19. The electric compressor of claim 18, wherein an axial length of the guide surface is or less of an entire axial length of the bearing support portion.

20. The electric compressor of claim 15, wherein a pressure of a fluid discharged from at least one of the pair of compression chambers during operation of the electric compressor is 100 bar or greater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and together with the description serve to explain the principles of the invention.

[0040] In the drawings:

[0041] FIG. 1 is a cross-sectional view of an electric compressor according to the present disclosure;

[0042] FIG. 2 is a cross-sectional view illustrating a compression unit in the electric compressor according to FIG. 1;

[0043] FIG. 3 is a cross-sectional view taken along line VI-VI in FIG. 2;

[0044] FIG. 4 is a cross-sectional view illustrating a main frame and a main bearing which are separated from each other according to the embodiment of the present disclosure;

[0045] FIG. 5 is a cross-sectional view of a main frame and a main bearing which are combined with each other according to an embodiment of the present disclosure;

[0046] FIG. 6 is a graph illustrating the amount of interference between a main bearing and a bearing support portion in an electric compressor according to the present embodiment; and

[0047] FIG. 7 is a cross-sectional view illustrating another embodiment of a bearing support portion of a main frame in an electric compressor according to the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

[0048] Description will now be given in detail of the exemplary embodiments, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components will be provided with the same reference numbers, and description thereof will not be repeated.

[0049] Hereinafter, an electric compressor according to the present disclosure will be described in detail with reference to an embodiment shown in the accompanying drawings.

[0050] The electric compressor according to the present disclosure may be a scroll compressor in which two scrolls are engaged to compress a refrigerant. The electric compressor according to the present disclosure may be a component of a refrigerating cycle apparatus that sucks and compresses a refrigerant as a working fluid. In this embodiment, a high-temperature, high-pressure electric scroll compressor which uses carbon dioxide (CO.sub.2) as a working fluid and has a discharge pressure of 100 bar, more precisely, about 130 bar and a discharge temperature of about 170 C. will be described as an example. FIG. 1 is a cross-sectional view illustrating an electric compressor according to the present disclosure.

[0051] Referring to FIG. 1, the electric compressor 100 according to an embodiment of the present disclosure includes a casing 101, a frame 102, a driving unit 103, and a compression unit 104. The frame 102 may include a main frame 121 and a sub-frame 125. Referring to an overall positional relationship, for example, the main frame 121 is fixed to the middle of an inner wall of the casing 101 and the driving unit 103 for generating a driving force is installed on one side (front side) of the main frame 121. The compression unit 104 for receiving a driving force of the driving unit 103 and compressing the refrigerant may be provided on the other side (rear side) of the main frame 121.

[0052] In addition, a control unit for controlling an operation of the compressor may be provided outside the casing 101. The control unit may be located on the opposite side of the compression unit 104 with respect to the driving unit 103.

[0053] As illustrated in FIG. 1, the casing 101 may include a shell 111, a front cover 112, and a rear cover 113. The shell 111 is formed in a cylindrical shape with both end portions (front and rear) opened, and a suction space S1 may be formed therein. Inside the shell 111, the driving unit 103, the frame, and the compression unit 104 may be accommodated.

[0054] The front cover 112 may be coupled to close a front end portion of the shell 111, and the control unit, a power supply unit, or the like, may be connected to the outside of the front cover 112. The rear cover 113 may be coupled to seal a rear end portion of the shell 111. As will be described later, the rear cover 113 may form a part of the discharge space S2 and may include an oil separation portion 116.

[0055] The front cover 112 may be provided with an intake port 114 to which a suction pipe is connected to allow the refrigerant to flow into the suction space S1. The intake port 114 may be formed so as to be positioned at the front end portion of the driving unit 103 which is opposite to the compression unit 104 with respect to the driving unit 103. Accordingly, the refrigerant may flow into the inside of the casing 101 through the intake port 114 and may be sucked into the compression unit 104 after passing through the driving unit 103 from the front side to the rear side.

[0056] In addition, the rear cover 113 may include an exhaust port 115 to which the discharge pipe is connected to guide the refrigerant compressed by the compression unit 104 to the refrigerating cycle. A rear space of the compression unit 104 closed by the rear cover 113 may be the discharge space S2 communicating with the exhaust port 115. An oil separator 116 separating oil from a mixture of the discharged refrigerant and oil may be formed at a path from the discharge space S2 to the exhaust port 115. FIG. 1 shows an embodiment in which the oil separator 116 communicating with the discharge space S2 separates the refrigerant and oil from each other by a centrifugal force. The oil separated from the refrigerant may be accumulated in a recovery space 116a formed on the bottom surface of the oil separator 116.

[0057] The driving unit 103 includes a stator 131 and a rotor 132, and generates a rotational force for driving the rotary shaft 135. In this embodiment, the stator 131 is fixed to an inner circumferential surface of the shell 111 and may have an annular shape to form a cylindrical space therein. The rotor 132 may be disposed in the inner space of the stator 131 so as to be spaced apart from the stator 131. The rotor 132 may have a substantially cylindrical shape, and a rotary shaft 135 may be coupled to the center thereof. When power is supplied to the driving unit 103, the rotor 132 and the rotary shaft 135 may rotate together by an interaction between the stator 131 and the rotor 132.

[0058] The rotary shaft 135 may be received in the shell 111 and may be rotatably supported on the frame 120. The rear side of the rotary shaft 135 may be supported in a radial direction by the main bearing 161 mounted on the main frame 121. The inner ring of the main bearing 161 is formed of a deep recess ball bearing which is coupled to the rotary shaft and the outer ring of the inner ring is coupled to the main frame 121. The main bearing 161 is configured as a deep recess ball bearing in which an inner face is coupled to the rotary shaft and an outer face is coupled to the main frame 121, and is press-fit to the bearing support portion 123 of the main frame 121. A mounting structure of the main bearing will be described in detail later.

[0059] The front end portion of the rotary shaft 135 may be supported in a radial direction by a sub-bearing 162 mounted on the sub-frame 125 formed on the inner surface of the front cover 112. A portion of the outer circumferential surface of the rotary shaft 135 may be coupled to the rotor 132 to receive a rotational force generated by the driving unit 103.

[0060] The compression unit 104 may include a first scroll 140 that is a fixed scroll and a second scroll 150 that is an orbiting scroll. The second scroll 150 is eccentrically coupled to the rotary shaft 135 coupled to the rotor 132 of the driving unit 103 and rotates relative to the first scroll 140 to form a pair of compression chambers P each including a suction chamber, an intermediate pressure chamber, and a discharge chamber.

[0061] The first scroll 140 is provided with a fixed side disk plate portion 141 in a circular plate shape, and a fixed side wall portion 142 protruding toward the main frame 121 may be formed on one side of the fixed side end plate portion 141.

[0062] A fixed wrap 143 to be engaged with the orbiting wrap 152 (to be described later) and forming a pair of two compression chambers P protrudes from the center of the fixed side disk plate portion 141. A suction opening (hot shown) communicating with the suction space S1 of the casing 101 may be formed at the center of the fixed side disk plate portion 141. A discharge port 144 connected from a final compression chamber to the discharge space S2 of the casing 101 may be formed at the center of the fixed side disk plate portion 141.

[0063] In the second scroll 150, an orbiting side disk plate portion 151 having a disk shape is formed, an orbiting wrap 152 protruding toward the fixed side disk plate portion 141 and engaged with the fixed wrap 143 is formed on one side of the orbiting side disk plate portion 151. A boss recess 153 is formed in the other side surface of the orbiting side disk plate portion 151 so that an eccentric bearing 163 for supporting the rotary shaft 135 is inserted and fixed.

[0064] The main frame 121 is formed in a substantially disc shape and may be coupled to the fixed side wall portion 142 of the first scroll 140 and the inner surface of the casing 101 so as to be supported.

[0065] A back pressure space 122 is formed at the center of the main frame 121 to form a back pressure space S3 for supporting the second scroll 150 toward the first scroll 140, and a balance weight 136, which is coupled to the rotary shaft 135 and compensates for imbalance according to an eccentric movement of the second scroll 150, may be rotatably received in the back pressure space portion 122.

[0066] Since a gap between the back pressure space portion 122 of the main frame 121 and the second scroll 150 in contact therewith and a gap between the main frame 121 and the rotary shaft 135 are sealed, the back pressure space portion 122 is sealed to form the back pressure space S3 described above. For example, a first sealing member 171 is provided on a lower surface of the second scroll 150 in contact with the main frame 121 to seal a thrust bearing surface between the main frame 121 and the second scroll 150, and a second sealing member 172 is provided between an inner circumferential surface of a shaft hole 124 of the main frame 121 and an outer circumferential surface of the rotary shaft 135 to seal a radial bearing surface between the main frame 121 and the rotary shaft 135.

[0067] The first sealing member 171 and the second sealing member 172 may be formed in a ring shape having a rectangular cross-section or a V or U cross-section and may be formed of a material such as rubber, Teflon, or engineer plastic. The first sealing member 171 and the second sealing member 172 may be formed of a material having a lower friction coefficient than the main frame 121 or the second scroll 150 in consideration of friction loss.

[0068] Meanwhile, a back pressure passage F connecting the discharge space S2 and the back pressure space S3 may be formed in the fixed side disk plate portion 151 of the first scroll 150 and the main frame 121. This causes the oil separated in the discharge space S2 to move to the back pressure space S3 through the back pressure passage F to form the back pressure in the back pressure space S3.

[0069] The electric compressor according to the present disclosure operates as follows.

[0070] First, when power is applied to the driving unit 103, the rotary shaft 135 rotates together with the rotor 132 of the driving unit 103 to transmit rotational force to the second scroll 150. The second scroll 150 eccentrically connected to the rotary shaft 135 is pivoted by an eccentric distance by an anti-rotation member 180 so that the compression chamber P is continuously moved toward the radial center side of the rotary shaft 135 and the volume is reduced.

[0071] Accordingly, the refrigerant flows into the suction space S1 through the intake port 114 and is sucked into the compression chamber P. At this time, the refrigerant may cool the stator 131 and the rotor 132 while passing through the stator 131.

[0072] Thereafter, the refrigerant sucked into the compression chamber P is compressed while being moved toward the center side along the movement path of the compression chamber P, and the refrigerant is discharged to the discharge space S2 formed between the first scroll 140 and the rear cover 113.

[0073] Oil of the refrigerant discharged to the discharge space S2 is separated in the discharge space S2 or the oil component is separated as the refrigerant passes through the oil separator 116, and the refrigerant is discharged to the refrigerating cycle through the exhaust port 115. Meanwhile, the separated oil may remain in the recovery space 116a of the oil separator 116 and be recovered.

[0074] Meanwhile, in the electric compressor as described above, a discharge pressure and discharge temperature differ depending on the type of refrigerant as described above. For example, in the case of R134a refrigerant, a discharge pressure is approximately 30 bar and a discharge temperature is approximately 120 C. However, in the case of CO.sub.2 refrigerant, a discharge pressure is about 100 bar or greater, specifically, 130 bar or greater, and a discharge temperature is about 150 C., specifically, about 170 C. Therefore, compared with the conventional R134a refrigerant, when the CO.sub.2 refrigerant is used, the compressor operates under much higher pressure and high temperature conditions.

[0075] In this case, if a coefficient of thermal expansion of the support member for inserting and fixing the bearing is higher than the coefficient of thermal expansion of the bearing, the support member is thermally expanded more than the bearing during operation and the bearing may not be firmly fixed. As a result, the bearing is detached from the support member to weaken durability of the bearing, shortening the service life and reducing reliability of the compressor. In particular, in the case of a low-pressure type in which the inside of the casing is filled with a suction pressure, the rotary shaft moves in the axial direction and the behavior of the second scroll coupled to the rotary shaft may become unstable. Then, the compression chamber may not be tightly sealed, so that the refrigerant may leak from the compression chamber, and the rotary shaft may move in the axial direction and the circumferential direction to increase compressor noise and friction loss.

[0076] However, if the bearing support member is made of a material having a low coefficient of thermal expansion such as iron or steel, the weight of the bearing support member is increased. Then, when it is applied to a vehicle, the weight of the vehicle increases, which may be disadvantageous. In the field of electric compressors, which are automotive compressors, parts made of a lightweight aluminum material are used even though the coefficient of thermal expansion is somewhat high. This is the same with the bearing support members.

[0077] Accordingly, in the present disclosure, in an electric compressor using a lightweight component, such as aluminum, even though the coefficient of thermal expansion thereof is high, the bearing supporting the rotary shaft may be easily and firmly coupled to the bearing support member. In particular, the main frame disposed adjacent to the back pressure space among the frames supporting the bearing is in a condition of a relatively high temperature and a high pressure, and thus, the main frame is highly likely to be thermally expanded during an operation of the compressor.

[0078] If the inner diameter of the bearing support increases due to thermal expansion of the main frame, the main bearing coupled to the main frame is easily separated from the bearing support. As a result, the life of the bearing as well as the efficiency and reliability of the compressor may be significantly reduced. This is the same with an eccentric bearing fixed to the second scroll formed of an aluminum material. Hereinafter, a structure for easily and firmly fixing the main bearing to the main frame will be described. However, the same may be applied to the second scroll and the eccentric bearing.

[0079] FIG. 2 is a cross-sectional view illustrating a compression unit in the electric compressor according to FIG. 1, FIG. 3 is a cross-sectional view taken along line VI-VI in FIG. 2, FIG. 4 is a cross-sectional view illustrating a main frame and a main bearing which are separated from each other according to the embodiment of the present disclosure, and FIG. 5 is a cross-sectional view of a main frame and a main bearing which are combined with each other according to an embodiment of the present disclosure;

[0080] As illustrated, in the electric compressor according to the present embodiment, the main frame 121 is formed with the back pressure space portion 122 described above at the center of a thrust surface where the second scroll 150 is opposed, a bearing support portion 123 to which the main bearing 161 is inserted and fixed is formed at the center of the bottom of the back pressure space portion 122, and a shaft hole 124 to which the rotary shaft 135 penetrates to be coupled may be formed at the center of the bottom of the bearing support portion 123. A sealing recess 124a into which a second sealing member 172 is inserted and supported may be formed to be stepped on the bearing support portion 123 in an inner circumferential surface of the shaft hole 124. Thus, the main frame 121 may be formed to be stepped through at least three stages opposite to the thrust surfaces.

[0081] The bearing support portion 123 is formed to be stepped to have an inner diameter D2 smaller than an inner diameter D1 of the back pressure space portion 122 at the bottom surface (front surface in the drawing) 122a of the back pressure space portion 122 forming the back pressure space S3, and a shaft hole 124 having an inner diameter D3 smaller than the inner diameter D2 of the bearing support portion 123 may be formed to be stepped on a bottom surface (front surface in the drawing) 124a of the bearing support portion 123. Accordingly, the bearing support portion 123 is opened at a first end portion toward the second scroll 150, and the main bearing 161 may be press-fit into the bearing support portion 123 through the first end portion.

[0082] As described above, a sealing recess 124a may be formed on one side of the bearing support portion 123, and a second sealing member 172 may be inserted into the sealing recess 124a. The sealing recess 124a may communicate with the back pressure space portion 122 constituting the back pressure space S3 through the main bearing 161 formed of a deep groove ball bearing. Accordingly, the back pressure space S3 may be sealed at one end by the second sealing member 172.

[0083] The second sealing member 172 may be formed in a rectangular cross-sectional shape or may be formed in a V-shaped cross-section or a U-shaped cross-sectional shape as described above and may be formed of a material having a coefficient of thermal expansion larger than that of the main frame, such as rubber or Teflon. Thus, when the main bearing 161 is press-fit to the main frame 121, a warm shrink fitting method of heating the main frame 121 and subsequently inserting the main bearing 161 may not be applied. That is, since the sealing recess 124a into which the second sealing member 172 is inserted is opened toward the bearing support portion 123 into which the main bearing 161 is inserted, the main bearing 161 must be inserted into the main frame 121 in a state in which the second sealing member 172 is first coupled. However, as described above, since the second sealing member 172 is formed of a material having a coefficient of thermal expansion larger than that of the main frame 121, if the second sealing member 172 is heated in a state where the second sealing member 172 is inserted into the main frame 121, the second sealing member 172 may be excessively thermally deformed or damaged. Thus, the main bearing 161 is press-fit into the bearing support portion 123 in a state where the second sealing member 172 is inserted into the main frame 121.

[0084] When the compressor is operated in a state where the main bearing 161 is press-fit into the bearing support portion 123, the compressor discharges a high temperature, high pressure refrigerant compressed to 150 to 170 C. and 100 to 130 bar with respect to a discharge pressure to the discharge space S2. The high-temperature and high-pressure refrigerant is separated into oil and refrigerant in the discharge space S2, and the oil is reduced to a certain degree through the back-pressure passage F to move to the back-pressure space S3. Therefore, although the temperature and pressure in the back pressure space S3 are lower than the temperature and pressure of the refrigerant in the discharge space, the temperature and pressure may be considerably higher than those of a case of applying the R134a refrigerant. When the main frame 121 is brought into contact with the high-temperature and high-pressure oil, the bearing support portion 123 of the main frame 121 made of aluminum is thermally expanded more than the main bearing 161 made of a steel material. Then, the inner circumferential surface 123a of the bearing support portion 123 and the outer circumferential surface 161a of the main bearing 161 are separated and the main bearing 161 is released from the bearing support portion 123, and thus, the amount of shaking of the main bearing 161 may be significantly increased.

[0085] Considering this, in this embodiment, as illustrated in FIGS. 4 and 5, the inner diameter D2 of the bearing support portion 123 may be formed to be smaller than the outer diameter D4 of the main bearing 161 (more precisely, the outer diameter of the outer race). Then, when the main bearing 161 is press-fit into the bearing support portion 123, an inner part of the bearing support portion 123 is pressed and compressed by the main bearing 161 and the outer circumferential surface 161a of the main bearing 161 may be tightly brought into close contact with the inner circumferential surface 123a of the bearing support portion 123. Thus, even though the main frame 121 thermally expands more than the main bearing 161 by the oil of high temperature and high pressure, the main bearing 161 may be prevented from being easily released. In the figure, the shaded area A is the pressed part of the bearing support portion.

[0086] However, when the inner diameter D2 of the bearing support portion 123 is too small as compared with the outer diameter D4 of the main bearing 161, the outer circumferential surface 161a of the main bearing 161 and the inner circumferential surface of the bearing support portion 123 are excessively adhered to each other to increase a bearing load excessively, and resultantly, friction loss in the main bearing 161 at the time of rotation of the rotary shaft 135 may increase.

[0087] Thus, it is important to set the inner diameter of the bearing support portion 123 such that the main bearing 161 is not released to be shaken due to thermal expansion of the bearing support portion 123, while the outer circumferential surface 161a of the main bearing 161 and the inner circumferential surface 123a of the bearing support portion 123 are not excessively brought into close contact with each other.

[0088] FIG. 6 is a graph illustrating the amount of interference between the main bearing and the bearing support portion the electric compressor according to the present embodiment. This is a graph based on the data obtained by experiencing many trials and errors of the researchers belonging to the present applicant.

[0089] As shown in the figure, an X axis is set to designate the amount of interference (%), a first Y axis is set to designate the amount of shaking of the rotary shaft, and a second Y axis is set to designate a bearing load, and results of comparing an optimal relationship between the shaking amount of the rotary shaft over the amount of interference and a bearing load are as follows.

[0090] That is, as the amount of interference decreases, the amount of shaking of the rotary shaft increases while the bearing load decreases. Conversely, as the amount of interference increases, the amount of shaking of the rotary shaft decreases while the bearing load increases.

[0091] However, such a phenomenon shows that the amount of shaking of the rotary shaft and a fluctuation range of the bearing load are significantly improved in the range of 0.08 to 0.13% of the amount of interference compared with the other ranges. Accordingly, when the amount of interference is set to be in the range of 0.08 to 0.13%, the rotary shaft may be stably supported and the load of the bearing may be appropriately maintained, thereby improving the reliability and efficiency of the compressor.

[0092] An example of an actual experiment is as follows. A main frame used in the experiment is aluminum, and the main bearing is made of steel. Therefore, the coefficient of thermal expansion of the main frame is 0.000023 and that of the main bearing is 0.000012, so that the coefficient of thermal expansion of the main frame is about twice that of the main bearing.

[0093] Also, the experiment was conducted in an environment in which an assembly temperature was 25 C., which is room temperature, and a driving temperature was about 100 C. Here, in the case of the CO.sub.2 refrigerant, the discharge temperature is 150 C. or higher, but the temperature is lowered as the discharged refrigerant moves to the back pressure space, so the temperature of the actual back pressure space is set at 100 C. lower than the discharge temperature. However, considering the discharge temperature of CO.sub.2 refrigerant, the amount of interference was conservatively defined.

[0094] Also, a machining error was set to be managed to 10 m or less.

[0095] Based on the above conditions, the inner diameter of the main frame and the outer diameter of the main bearing at the assembly temperature of 25 C. are as follows.

TABLE-US-00001 TABLE 1 Minimum Average Maximum Inner diameter of main frame (mm) 46.935 46.945 46.955 Outer diameter of main bearing (mm) 46.989 46.955 47

[0096] Thus, the amount of interference is as follows.

TABLE-US-00002 TABLE 2 Amount of interference Minimum Average Maximum 0.034 0.0495 0.065

[0097] That is, the amount of interference is 0.034 to 0.065 mm before the main bearing is assembled to the main frame.

[0098] The inner diameter of the main frame and the outer diameter of the main bearing at a driving temperature of 100 C. are as follows.

TABLE-US-00003 TABLE 3 Minimum Average Maximum Inner diameter of main frame (mm) 47.008 47.018 47.028 Outer diameter of main bearing (mm) 47.034 47.040 47.045

[0099] Thus, the amount of interference is calculated as follows.

TABLE-US-00004 TABLE 4 Amount of interference Minimum Average Maximum 0.006 0.022 0.037

[0100] That is, even when the compressor is driven, the bearing support portion 123 of the main frame 121 and the main bearing 161 secure an appropriate amount of interference, so that the main bearing 161 may be prevented from being separated from the bearing support portion 123. In this case, as for the ratio of the inner diameter D2 of the bearing support portion 123 to the outer diameter D4 of the main bearing D4, the inner diameter D2 of the main frame may be smaller by 0.07 to 0.14% than the outer diameter D4 of the main bearing. However, the ratio may be conservatively defined to about 0.08 to 0.13% in consideration of the fact that the oil moving to the back pressure space S3 is decompressed as described above.

[0101] Meanwhile, when the amount of interference is applied, the load applied to the main bearing is as follows.

TABLE-US-00005 TABLE 5 Amount of interference 0.034 0.065 Bearing tangential stress (Mpa) 80.83 154.24 Frame tangential stress (Mpa) 66.54 127.26 Bearing & frame circumferential 14.9 28.45 stress (Mpa)

[0102] This is because, when the inner diameter D2 of the bearing support portion and the outer diameter D4 of the main bearing are designed to satisfy the above amount of interference, the stress is less than plastic deformation in the tangential and circumferential directions, and thus, the bearing load is not excessively increased to degrade compressor efficiency.

[0103] Therefore, when the amount of interference before assembling the main bearing 161 to the main frame 121 is limited to 0.08 to 0.13% as described above, even when the compressor is driven, the main bearing 161 is not released from the bearing support portion 123 of the main frame 121, ensuring reliability, and since the load of the main bearing 161 is not excessively increased to degrade compressor efficiency, the compressor efficiency may be increased.

[0104] Meanwhile, another embodiment of the electric compressor according to the present disclosure is as follows.

[0105] That is, in the above-described embodiment, the inner circumferential surface of the bearing support portion of the main frame is formed to have the same inner diameter, but in this embodiment, the corner of the inner circumferential surface of the bearing support portion is inclined to easily press-fit the main bearing.

[0106] FIG. 7 is a cross-sectional view illustrating another embodiment of a bearing support portion of a main frame in an electric compressor according to the present disclosure.

[0107] As shown in the figure, an angled or curved guide surface 123b may be formed at an edge of the first end portion opened in the inner circumferential surface of the bearing support portion 123 so as to be enlarged toward the first end direction.

[0108] The axial length L2 of the guide surface 123b is smaller than of the entire axial length L1 of the bearing support portion 123 and, in a maximum width of the guide surface 123b, the outer diameter D5 of the guide surface may be smaller than or equal to the outer diameter D4 of the main bearing. Accordingly, although the guide surface 123b is formed, the main bearing 161 and the bearing support portion 123 may be kept in close contact with each other, so that the fixing force to the main bearing may be secured.

[0109] The outer edge of the outer race forming the main bearing 161 is chamfered so that the outer ring edge 161b of the main bearing 161 slides on the guide surface 123b of the bearing support portion 123 so as to be smoothly press-fit when the main bearing 161 is press-fit.

[0110] The structure for press-fitting the main bearing 161 into the bearing support portion 123 of the electric compressor according to the present embodiment is the same as that of the above-described embodiment. In this embodiment, since the guide surface 123b is formed at the corner of the bearing support portion 123, bearing power between the bearing support portion 123 and the main bearing 161 may be slightly reduced in the portion where the guide surface 123b is formed, as compared with the aforementioned embodiment. However, in a portion where the guide surface is not formed, the amount of interference is secured as 0.08-0.13% as in the above-described embodiment, so that the bearing power supporting the main bearing 161 may be secured sufficiently.

[0111] The foregoing embodiments and advantages are merely exemplary and are not to be considered as limiting the present disclosure. The present teachings may be readily applied to other types of apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments.

[0112] As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be considered broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.