ROTARY COMPRESSOR

Abstract: A rotary compressor which essentially includes a shaft (4), a compression mechanism (2) including a cylinder (11) and a rotary piston (12) provided on the shaft (4) to suck, compress and discharge refrigerant gas by rotating the rotary piston (12) eccentrically in the interior of the cylinder (11), a motor (3) to drive the shaft (4), a journal bearing (13, 14) to freely rotatably support the shaft (4), and an axial direction oil groove (42, 44, 51-55, 57) being formed along with about the axial direction of the shaft (4) at a position corresponding to a low pressure area of an oil film of the lubricating oil (L) caused by a deflection of the shaft (4) due to the eccentric rotation of the rotary piston (12).

Description: The present invention relates to rotary compressors and, in particular, to rotary compressors employing journal bearings for supporting its revolving parts. Rotary compressors which serve to suck, compress and discharge gases and a drive motor connected together with a single shaft and located in a housing are known. Conventionally, rotary compressors have been widely used for refrigerators, air conditioners, etc., because it is relatively easy to minimise their size, and also easy to control their compression capacity by variable speed control of the drive motor. In recent years, rotary compressors have been used with a higher speed rotation of the drive motor to increase the compression capacity. To perform a higher speed operation of rotary compressors, mechanical vibration in the bearing section of the compressor must be reduced sufficiently and also the durability of the bearing section must be increased. To bring about reduction in vibration, a balancer has been positioned on the revolving shaft so as to compensate for rotation unbalance of the revolving part due to a rotary piston eccentrically provided on the revolving part. Furthermore, to increase the durability of the bearing section, journal bearings have been used instead of ball bearings. A journal bearing is designed to interpose an oil film in a gap between a journal on the shaft and the journal bearing. The oil film serves as a lubricant and reduces mechanical friction between the shaft and the journal bearing. A rotary compressor is known from JP-A-58-158393 in which an oil groove is defined on the inner surface of each of the two journal bearings. Lubricating oil is introduced to the oil grooves and then spreads to the whole bearing surface for producing the oil film. Furthermore, US-A-3622212 discloses a bearing for a journal lubricated by oil under pressure in which two helical grooves are formed ahead of the load zone of the bearing. One groove has a relatively small pitch angle while the other groove is of greater width and a greater pitch angle. However, another problem still remains in that the shaft deflects in a direction perpendicular to its longitudinal axis during rotation. This is because the shaft receives centrifugal forces of the piston and the balancer which are both eccentrically mounted on the shaft at its different axial positions. The deflection of the shaft increases with the rotation speed of the shaft so that the shaft makes contact with the journal bearing against the oil film. It is difficult to avoid contact between the journal bearing and the journal on the shaft in a conventional compressor and, for this reason, the operating efficiency is lowered, the durability also deteriorates and, in the worst case, it provokes damage to the bearing section. An object of the present invention is to provide a rotary compressor in which these difficulties are overcome. According to the present invention, a rotary compressor comprises a rotatable shaft, a compression mechanism including a cylinder, and a rotary piston provided on said shaft to suck, compress and discharge refrigerant gas by rotating said rotary piston eccentrically in the interior of said cylinder; a motor connected to drive said shaft; a pair of spaced-apart journal bearings, each arranged to rotatably support said shaft, the bearing surface of each bearing and the corresponding bearing surface of the shaft being separated by a gap containing a film of lubricating oil and a groove extending from one end to the other of the bearing surface of the bearing or the shaft to supply oil to said gap; characterised in that the opposite ends of the groove are positioned at regions of the gap corresponding to low oil film pressure allowed by lateral deflection of the shaft as it rotates. In a rotary compressor, it is impossible to completely get rid of deflection of the revolving shaft in the interior of the journal bearing in terms of its construction. The deflection mode of the revolving shaft is determined by the relative position of the rotary piston, the bearing sections and the revolving shaft as described above and, further, when a balancer is provided, the relative relation in terms of the positions of these three parts is determined and, on the one hand, it is considered that the deflection mode in the rotation surface of a revolving shaft is influenced by the progrsess of the rotating angle of the revolving shaft and takes a specific pattern. Therefore, the revolving shaft comes nearer to a bearing surface in the specific area of the rotation surface during every rotation and is cleared from the bearing surface in other areas. In the area where the revolving shaft comes close to the bearing surface, if the oil film pressure is not high, it results in both parts coming into contact. On the contrary, as attention has not been conventionally paid to the position of the oil groove, there may be a case that the oil groove is positioned in the area where the revolving shaft comes nearer to the bearing surface. Due to the fact that the oil film pressure is low in the oil groove, contact between both parts occur. Such problems occur, in particular, at the ends of the bearing surface. In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a longitudinal section of an embodiment of a rotary compressor according to the present invention; Figure 2 is a horizontal section of part of the compression mechanism of the rotary compressor according to the present invention; Figures 3 and 4 are cut-away perspective views of the journal bearings of the rotary compressor according to the present invention; Figures 5a and 5b are drawings illustrating the axial deflection mode of the shaft of the rotary compressor according to the present invention; Figure 6 illustrates the locus of the revolving shaft of the rotary compressor according to the present invention; Figures 7 and 8 are cut-away perspective views of the journal bearings of the rotary compressor according to another embodiment of the present invention; and Figures 9 to 11 are perspective views showing, respectively, different embodiments of the shaft of the rotary compressor according to the present invention. Referring to Figure 1, a rotary compressor comprises a compression mechanism 2, a driver motor 3 and a rotatable shaft 4, all located in a cylindrical closed housing 1. The motor drives the compression mechanism 2 by way of the shaft 4. Compression mechanism 2 includes a cylinder 11 defining a central opening, an annular rotary piston 12 mounted on an eccentric section 4a of the shaft 4 at a position in the cylinder 11 and a pair of lower and upper journal bearings, respectively. Journal bearings have respective flange sections 13a, 14a and bearing sections 13b, 14b. Flange sections 13a, 14a close off the upper and lower ends of cylinder 11 so as to define a chamber 15. Bearing sections 13b and 14b support journals on the shaft 4 at opposite ends of eccentric section 4a. Chamber 15 is divided, as shown in Figure 2, into two parts by rotary piston 12 and a blade 16 which is slidably mounted in cylinder 11 and is urged into contact with the external circumference surface of rotary piston 12. Motor 3 comprises a stator 21 fixed to the inner wall of housing 1 and a rotor 22 supported on shaft 4. A suction pipe 23 penetrates through the housing 1 and the cylinder 11 to introduce refrigerant gases into chamber 15 from a piping system (not shown). A discharge opening 24 and a delivery valve 25 are installed in flange section 14a of Journal bearing 14 to discharge the gases compressed in chamber 15 into the housing 1. A delivery Pipe 26 extending through housing 1 to discharge the compressed gases is positioned adjacent motor 3 to the piping system as well. Suction pipe 23 and discharge opening 24 are located, as shown in Figure 2, in positions at the rotational direction side of rotary piston 12 and at its opposite side, respectively, with reference to blade 16. The revolving part of the rotary compressor has balancers 27 and 28 positioned on opposite sides of the compression mechanism 2. Balancer 27 is fixed to the lower end of shaft 4, while balancer 28 is fixed to the lower end of rotor 22 of motor 3. Balancers 27 and 28 compensate rotational unbalance of the revolving part due to the eccentric rotation of eccentric section 4a of shaft 4 and rotary piston 12. Shaft 4 has a central bore 32 which extends to an oil sump defined at the bottom end of housing 1 through a suction hole 31 formed in balancer 27. Bore 32 is enlarged in diameter at its lower end corresponding to compression mechanism 2. In the enlarged bore, a spiral blade 33 is located. Spiral blade 33 is formed by twisting a strip-shaped body through 180 degrees in the rotational direction of shaft 4 so that it scrapes up lubricating oil L contained in the oil sump of housing 1 into the bore when the shaft rotates. Shaft 4 has, furthermore, two radial lubricating holes 34, 35 in positions which, respectively correspond to lower and upper journal bearings 13, 14 so as to guide lubricating oil L into gaps between lower and upper journal bearings 13, 14 and the corresponding journal portions of shaft 4. Lower journal bearing 13 is formed with a circumferential oil groove 41 and an axial direction oil groove 42 on its inner surface Q as a bearing surface, as shown in Figure 3. Circumferential oil groove 41 is formed at one end of lower journal bearing 13 adjacent to compression mechanism 2, while axial direction oil groove 42 is formed spirally along the axis of lower journal bearing 13. The position of oil groove 42 on bearing surface Q with reference to blade 16 is described below. That is, the upper and lower ends of oil groove 42 are defined, as shown in Figure 3, at respective positions in the angles of 240 degrees and 270 degrees in the system of angular co-ordinates wherein the position of blade 16 is the standard axis and the rotating direction (arrowhead of bold lines in the drawing) of shaft 4 is positive. Upper journal bearing 14 is also formed with a circumferential oil groove 43 and an axial direction oil groove 44 on its inner surface R as a bearing surface, as shown in Figure 4. Circumferential oil groove 43 is formed at one end of lower journal bearing 14 adjacent to compression mechanism 2, while axial direction oil groove 44 is formed spirally along the axis of upper journal bearing 14. The position of oil groove 44 on bearing surface R with reference to blade 16 is described below. That is, the lower and upper ends of oil groove 44 are defined, as shown in Figure 4, at respective positions in the angles of 280 degrees and 60 degrees in the above-mentioned angular co-ordinates system. The operation of the rotary compressor is as follows: when motor 3 is driven, compression mechanism 2 sucks refrigerant gas P from suction pipe 23 to the interior of chamber 15, refrigerant gas P is compressed according to the eccentric rotary motion of rotary piston 12 in chamber 15. Refrigerant gas P thus compressed is discharged to the interior of housing 1 through discharge opening 24 and delivery valve 25. Then, refrigerant gas P is exhausted from housing 1 of the rotary compressor to the exterior piping system (not shown) through delivery pipe 26. The lubrication between journal bearings 13, 14 and shaft 4 is as follows: lubricating oil L contained in the bottom oil sump of housing 1 is introduced into bore 32 of shaft 4 through suction hole 31 of balancer 27. Lubricating oil L thus introduced turns, accompanied by the rotation of spiral blade 33, and is fed to circumferential oil grooves 41, 43 of journal bearings 13, 14 through lubricating holes 34, 35 with its centrifugal force. In journal bearings 13, 14, since oil grooves 42, 44 are provided and shaft 4 rotates in the drive direction, lubricating oil L is fed to circumferential oil grooves 41, 43. Lubricating oil L moves in the direction that, in oil grooves 42, 44, it moves away from chamber 15, respectively, by the relative motion between shaft 4 and journal bearings 13, 14. Now the centres of gravity of the pair of balancers 27, 28, rotary piston 12 and eccentric section 4a of shaft 4 have relative positions, as diagrammatically shown in Figure 5a. In Figures 5a and 5b, as described later, the illustrated position referred by 4a is assumed to represent the centre of gravity of a combination of rotary piston 12 and eccentric section 4a of shaft 4. When shaft 4 rotates at a high speed, it shows most likely a deflection mode, as shown in Figure 5b, due to the eccentricity of the above respective elements, i.e. balancers 27, 28, rotary piston 12 and eccentric section 4a of shaft 4. In Figure 5b, two loops, denoted by Su and Sl, respectively, show deflection loci of the shaft 4 at its upper and lower ends. Shaft 4 further receives pressure influences by blade 16 and refrigerant gas P in chamber 15. Therefore, each section of shaft 4 takes a deflection locus of a particular pattern. If the deflection is taken at the position corresponding to the upper end of lower journal bearing 13, it has a locus S of an elliptical pattern, as shown in Figure 6. In Figure 6, a circle denoted by Q represents the inner surface or bearing surface Q of lower journal bearing 13 and the system of angular co-ordinates described before, i.e. the co-ordinates wherein the position of blade 16 is the standard axis and the rotating direction of shaft 4 is positive, is also shown. Now an effect of the deflection of shaft 4 taking the particular pattern, e.g. the elliptical pattern locus S will be described. Pressure of shaft 4 against bearing surface Q increases at a position where the shaft 4 deflects nearer to bearing surface Q, while the pressure decreases at a position where shaft 4 deflects away from bearing surface Q. Therefore, the oil film is required to be so hard as to resist against the pressure in particular at the position where shaft 4 deflects nearer to bearing surface Q. Pressure or the resisting force of an oil film becomes weak at a position where the gap between shaft 4 and bearing surface Q is relatively wide. Especially, the pressure of the oil film is extremely weak at the position where an axial direction oil groove is defined. On the other hand, the pressure of the oil film increases at a position just prior to the position of shaft 4. The area where the oil film must be hard and the other area where it is allowed to be weak are able to be specified on the bearing surface of the journal bearing in reference to the position of blade 16. For example, the latter area, i.e. the low pressure area of the oil film at the upper end of lower journal bearing 13 is roughly specified in the range of 205 degrees to 295 degrees on the angular co-ordinates system, shown in Figure 6. Therefore, the position of the upper end of axial direction oil groove 42 of lower journal bearing 13, i.e. 240 degrees, as described before, is, of course, set on the low pressure area of the oil film. Likewise, low pressure areas at bearing surface R of upper journal bearing 14 are also specified. That is, the low pressure area of the oil film at the lower end of lower journal bearing 13 is roughly specified in the range from 180 degrees to 360 degrees. The low pressure area of the oil film at the lower end of upper journal bearing 14 is roughly specified in the range from 225 degrees to 315 degrees, and the low pressure area of the oil film at the upper end of upper journal bearing 14 is roughly specified in the range from 45 degrees to 225 degrees. In accordance with the above, respective positions of the upper end of axial direction oil groove 42 of lower journal beariong 13 and the lower and upper ends of axial direction oil groove 44 of upper journal bearing 1A, i.e. 270 degrees, 280 degrees and 60 degrees, as described before in reference to Figures 3 and 4, are also set in the low pressure areas of the oil films. Therefore, other areas of the bearing surfaces, where the contact of shaft 4 with lower and upper journal bearings 13, 14 are likely to occur in particular, are left in high pressure states of the oil films so that the contact of shaft 4 with journal bearings 13, 14 can be prevented. Further, the oil film pressures at the areas where axial direction oil grooves 42, 44 exist become almost negative while shaft 4 is rotating. This means that the inducing of lubricating oil L into axial direction oil grooves 42, 44 from bore 32 of shaft 4 can be smoothly made. Moreover, the lubrication performance can be improved by further providing respective journal bearings 13, 14 with circumferential oil grooves other than 41, 42 at respective positions corresponding to lubricating holes 34, 35 of shaft 4. However, this invention is not limited to the embodiments described above. Figures 7 and 8 show another embodiment in that oil grooves 51, 52 formed in journal bearings 13, 14 extend through more than one turn. Even in this case, as the positions of the ends of oil grooves 51 and 52 are specified in the same positions as in the previous embodiment, the effect of the present invention can be taken. In this case, the oil supplying function of axial direction oil grooves 51, 52 can be further strengthened. The present invention shall not be limited to the case of forming axial direction oil grooves in the journal bearings and, for example as shown in Figure 9, it may be good to form axial direction oil grooves 53, 54 in the outer surface of shaft 4. Where the deflection mode of shaft 4 is the same as that shown in Figure 5, it is desirable to set the positions of both respective ends of axial direction oil grooves 53, 54 as follows: when making the direction from the centre of shaft 4 to the centre of the eccentric section 4a as a reference and considering the system of angular co-ordinates that the direction to turn the revolving shaft (arrowhead in bold line as illustratd) is made as positive, it is desirable as the ranges of 0 degrees to 180 degrees, -25 degrees to 75 degrees, 0 degrees to 90 degrees, and -15 degrees to 165 degrees in the order from the end of the lower end of shaft 4 become the low pressure areas. In the embodiment shown in Figure 1, they are of 60 degrees, 60 degrees, 80 degrees and 10 degrees, respectively, which fulfil the conditions and the effect of the present invention can be taken. In this case, there is no need to form circumferential oil grooves in journal bearings 13, 14. Further, also in this case, the performance of the oil suplying function can be improved by extending axial direction oil groove 55 through more than one turn, as shown in Figure 10. Moreover, lubricating hole 56 of shaft 4 may be opened in the intermediate part of axial direction oil groove 57, as shown in Figure 11. In this case a circumferential oil groove 58 is defined at a position corresponding to the opening of lubricating hole 56 and respective ends of axial direction oil groove 57 are inclined away from the rotating direction of shaft 4, so that the oil supplying function from circumferential oil groove 58 to the respective ends of axial direction oil groove 57 can be smoothly made and effected. In addition to these, the present invention can be carried out by modifying it in various ways in accordance with the deflection mode of the revolving shaft of the rotary compressor. The positions of the axial direction oil groove can be specified only for a particularly required end of the journal bearing and also in the case the effect of this invention can be taken. According to the present invention, since the axial direction oil grooves are not positioned in the high pressure areas of oil film formed in the gap between the shaft and journal bearing, there is no way to decrease the oil film pressure in the part where the shaft and the journal bearing are most near, which can cause lowering of the bearing load capacity. Furthermore, according to the present invention, since the axial direction oil grooves are positioned in the areas where the pressure of oil film is allowed to be low, the oil supplying function is accelerated so that the lubricating oil can be smoothly fed to the bearing surface. Therefore, according to the present invention, the operational efficiency of the rotary compressor and the durability of the bearing section can be improved.

Claims: A rotary compressor comprising a rotatable shaft (4), a compression mechanism (2) including a cylinder (11), and a rotary piston (12) provided on said shaft to suck, compress and discharge refrigerant gas by rotating said rotary piston (12) eccentrically in the interior of said cylinder (11); a motor (3) connected to drive said shaft (4); a pair of spaced-apart journal bearings (13, 14), each arranged to rotatably support said shaft, the bearing surface of each bearing and the corresponding bearing surface of the shaft being separated by a gap containing a film of lubricating oil and a groove extending from one end to the other of the bearing surface of the bearing or the shaft to supply oil to said gap; characterised in that the opposite ends of the groove are positioned at regions of the gap corresponding to low oil film pressure allowed by lateral deflection of the shaft as it rotates. Rotary compressor according to claim 1, wherein said shaft (4) is formed with an axial bore (32), and a lubricating hole (34, 35) passing through said shaft (4) to couple said bore (32) with an outer surface of said shaft (4) to feed said lubricating oil (L) from said bore to said gap between said journal bearing (13, 14) and said shaft (4). Rotary compressor according to claim 2, wherein said journal bearing (13, 14) has a circumferential oil groove (41, 43, 56) formed at its inner surface (Q, R) in the position corresponding to said lubricating hole (34, 35, 56). Rotary compressor according to any preceding claim, wherein said shaft (4) is provided with a balancer (27, 28) to compensate the eccentricity of said rotary piston (12). Rotary compressor according to claim 4, wherein a balancer (27, 28) is provided on said shaft (4) at each side of said compression mechanism (2) in the axial direction of said shaft (4). Rotary compressor according to claim 4 or 5, wherein said journal bearing (13), which supports said shaft (4) at the side of said compression mechanism (2) away from said motor (3), has the end of its groove furthest from the compression mechanism set in the range from 180 degrees to 360 degrees in the direction that said shaft (4) rotates with reference to the position of a blade (16) slidably provided in said cylinder (11) and urged into contact with said rotary piston (12). Rotary compressor according to claim 4, 5 or 6, wherein said journal bearing (13), which supports said shaft (4) at the side of said compression mechanism (2) away from said motor (3), has the end of its groove nearest to the compression mechanism set in the range from 205 degrees to 295 degrees in the direction that said shaft (4) rotates with reference to the position of a blade (16) slidably provided in said cylinder (11) and urged into contact with said rotary piston (12). Rotary compressor according to claim 4, 5, 6 or 7, wherein said journal bearing (14), which supports said shaft (4) at the position between said compression mechanism (2) and said motor (3), has the end of its groove adjacent to said compression mechanism (2) set in the range from 225 degrees to 315 degrees in the direction that said shaft (4) rotates with reference to the position of a blade (16) slidably provided in said cylinder (11) and urged into contact with said rotary piston (12). Rotary compressor according to any of claims 4 to 8, wherein said journal bearing (14), which supports said shaft (4) at the position between said compression mechanism (2) and said motor (3), has the end of its groove adjacent to said motor (3) set in the range from 45 degrees to 225 degrees in the direction that said shaft (4) rotates with reference to the position of a blade (16) slidably provided in said cylinder (11) and urged into contact with said rotary piston (12). Rotary compressor according to claim 1, wherein each oil groove (51-55, 57) is on the outer surface of the shaft (4). Rotary compressor according to claim 10, wherein said journal bearing (13) supports said shaft (4) at the side of said compression mechanisn (2) away from said motor (3) and said position of the oil groove (53, 54, 55, 57) at its end away from said compression mechanism (2) is set in the range from 0 degrees to 180 degrees in the direction that said shaft (4) rotates with reference to an eccentric position of said rotary piston (12). Rotary compressor according to claim 10 or 11, wherein said journal bearing (13) supports said shaft (4) at the side of said compression mechanism (2) away from said motor (3) and the position of the oil groove (53, 54, 55, 57) at the end adjacent to said compression mechanism (2) is set in the range from -25 degrees to 75 degrees in the direction that said shaft (4) rotates with reference to an eccentric position of said rotary piston (12). Rotary compressor according to claim 10, wherein said journal bearing (14) supports said shaft (4) at the position between said compression mechanism (2) and said motor (3) and the position of said oil groove (53, 54, 55, 57) at the end adjacent to said compression mechanism (2) is set in the range from 0 degrees to 90 degrees in the direction that said shaft (4) rotates with reference to an eccentric position of said rotary piston (12). Rotary compressor according to claim 10 or 13, wherein said journal bearing (14) supports said shaft (4) at the position between said compression mechanism (2) and said motor (3) and the position of said oil groove (53, 54, 55, 57) at the end adjacent to said compression mechanism (2) is set in the range from -15 degrees to 165 degrees in the direction that said shaft (4) rotates with reference to an eccentric position of said rotary piston (12). Rotary compressor according to claim 4, wherein said balancer (27, 28) is provided at both sides of said motor (3). Rotary compressor according to claim 4 or 15, wherein said journal bearing (13, 14) supports said shaft (4) at the position between said compression mechanism (2) and said motor (3) and the position of said axial direction oil groove (42, 44, 51-55, 57) in the end adjacent to said compression mechanism (2) is set in the range from -80 degrees to 10 degrees in the direction that said shaft (4) rotates with reference to a position that a blade (16) urged into contact with said rotary piston (12) is slidably provided in said cylinder (11). Rotary compressor according to claim 4 or 15, wherein said journal bearing (13, 14) supports said shaft (4) at the position between said compression mechanism (2) and said motor (3) and the position of said axial direction oil groove (42, 44, 51-55, 57) at the end adjacent to said motor (3) is set in the range from 10 degrees to 190 degrees in the direction that said shaft (4) rotates with reference to a position that a blade (16) urged into contact with said rotary piston (12) is slidably provided in said cylinder (11). Rotary compressor according to claim 4 or 5, wherein said journal bearing (13, 14) supports said shaft (4) at the position between said compression mechanism (2) and said motor (3) and the position of said axial direction oil groove (42, 44, 51-55, 57) in the end adjacent to said compression mechanism (2) is set in the range from -45 degrees to 135 degrees in the direction that said shaft (4) rotates with reference to a position that a blade (16) urged into contact with said rotary piston (12) is slidably provided in said cylinder (11). Rotary compressor according to claim 4 or 5, wherein said journal bearing (13, 14) supports said shaft (4) at the position between said compression mechanism (2) and said motor (3) and the position of said axial direction oil groove (42, 44, 51-55, 57) at the end adjacent to said motor (3) is set in the range from 180 degrees 360 degrees in the direction that said shaft (4) rotates with reference to a position that a blade (16) urged into contact with said rotary piston (12) is slidably provided in said cylinder (11). Rotary compressor according to any preceding claim, wherein said axial direction oil groove (42, 44, 51-55, 57) consists of more than one turn in said journal bearing (13, 14).

Inventors: KUBO, MASAHIRO C/O PATENT DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1986
Main classification: F04C29
IPC codes: F04C23, F04C29, F04C18