FLUID COMPRESSOR

Abstract: A fluid compressor includes a closed case (10) and a cylinder (20) which is arranged in the case and has two opposite ends. A columnar rotating rod (34) is located in the cylinder to be eccentric thereto, and rotatable along with the cylinder. The rod has a spiral groove on the outer circumferential surface thereof, and a spiral blade (42) is fitted in the groove to divide the space between the rod and the cylinder into a plu­ rality of operating chambers. The ends of the cylinder are rotatably supported by first and second bearings (22, 26). The first bearing is secured to the casing. A drive unit (12) for rotating the cylinder and rod includes a rotor fixed to the cylinder. The rotor has the center of gravity which is apart from the middle of the cylinder in its axial direction toward the first bearing.

Description: The present invention relates to a fluid compressor, and more particularly, to a compressor for compressing refrigerant gas in a refrigeration cycle, for example. An example of a fluid compressor is shown in U.S. Patent No. 4,875,842 corresponding to DE 38 30 746 A1 by the applicant of the present application. This type of compressor comprises a closed casing, and a compressor unit and,a motor unit both housed in the closed casing. The motor unit has a stator fixed to the inner surface of the casing, and a rotor arranged within the stator coaxially therewith. The compressor unit has a cylinder fixed coaxially within the rotor and rotated integrally with the rotor. A piston is rotatably arranged within the cylinder such that the piston is eccentric in respect to the axis of the cylinder. A spiral groove is formed on the outer circumferential surface of the piston, extending from one end of the piston to the other end thereof. The pitches of the spiral groove are gradually reduced with distance from the suction side of the cylinder towards the discharge side thereof. A spiral blade having a suitable elasticity is fitted in the spiral groove. The space defined between the cylinder and the piston is divided into a plurality of operating chambers by means of the aforementioned blade. The capacities of the operating chambers are gradually reduced with distance from the suction side of the cylinder towards the discharge side thereof. When the cylinder and the piston are rotated by the motor unit in synchronism with each other, refrigerant gas in the refrigeration cycle is introduced into the operating chambers through the suction end of the cylinder. The sucked gas is gradually compressed while being transferred to the discharge end of the cylinder. The highly pressurized gas is discharged from the discharge end of the cylinder into the closed casing. The suction-side end portion of the cylinder is rotatably supported by a main bearing secured to the inner surface of the casing. The discharge-side end portion of the cylinder is engaged with a sub-bearing. The sub-bearing is arranged to be movable in the radial direction of the cylinder in relation to the casing. Namely, the cylinder is substantially cantilevered by the main bearing. The rotor of the motor unit is secured to the outer circumferential surface of the cylinder. The center of gravity of this rotor is situated on the center axis of the cylinder and is apart from the middle of the cylinder in its axial direction toward the main bearing. However, in such known compressor said rotor is secured to the cylinder in such a way that the contact portion between cylinder and rotor does not overlap with said main bearing in the axial direction. This known structure, in which the weight of the rotor is supported by the end edge of the main bearing might cause deformation of the cylinder due to the weight of the rotor. As has been stated above, in the compressor having the cylinder supported substantially at its one end, the rotational movement characteristics are greatly influenced by the state of the supported cylinder, rotor, etc. When the respective members are not precisely aligned, for instance, when a deviation appears between the axis of the rotor and that of the cylinder or between the axis of the rotor and that of the stator, the cylinder and the rotor may whirl, with respect to an intersection between the fixed surface of the main bearing and the center axis of the cylinder. In particular, when the center of gravity of the rotor is greatly separated from the secured surface of the main bearing, as in the case of the above-described compressor, such whirling of the cylinder and rotor is worsened. As a result, vibration and noise of the compressor increases, and the frictional loss at the sliding portion of the bearing is considerably abraded, thereby lowing the operation efficiency of the compressor. Furthermore, the rotor and the stator may contact and damage each other. The present invention has been made in consideration of the above problems, and its object is to provide a fluid compressor wherein vibration and noise is reduced, a frictional loss of a bearing section is small, and high reliability and durability can be ensured. This object is solved by a compressor as claimed in claim 1. With this structure, the rotor is arranged such that the center of gravity of the rotor is situated within the main bearing and on the center axis of the cylinder. With this structure, the whirling of the rotational body can be reduced. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figs. 1 to 4 show a fluid compressor according to an embodiment of the present invention, in which: Fig. 1 is a longitudinal-sectional view showing the overall structure of the compressor; Fig. 2 is an enlarged sectional view of the part including a main bearing; Fig. 3 is a side view of a rotating rod; and Fig. 4 is a side view of a blade. An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. In the embodiment shown in Fig. 1, the present invention is applied to a closed type compressor for compressing refrigerant gas in a refrigeration cycle. The compressor comprises a closed casing 10, an electric motor unit 12, and a compressor unit 14 driven by the motor unit 12, which are arranged within the casing 10. The casing 10 has cup-shaped large-diameter portion 10a and small-diameter portion 10b, the opening edges of which are coupled with each other. As shown in Figs. 1 and 2, the motor unit 12 comprises an annular stator 16 fixed to the inner surface of the large-diameter portion 10a of the casing 10, and an annular rotor 18 coaxially arranged within the stator 16. The location of the motor unit 12 is apart from the middle in the axis of casing 10 towards the bottom wall of the large-diameter portion 10a. The rotor 18 is formed such that the center C of gravity thereof is situated at the middle in the center axis of the rotor. The compressor unit 14 includes a cylinder 20 having a suction end portion and a discharge portion. The rotor 18 is coaxially fitted on the outer circumferential surface of the suction end portion of cylinder 20. The suction end portion (the right end portion in the figure) of the cylinder 20 is rotatably supported and hermetically sealed by a main bearing 22 secured to the inner surface of the large-diameter portion 10a of the casing 10. The bearing 22 has a cylindrical insertion portion 24 slidably inserted into the cylinder 20, a proximal end surface 22a secured to the bottom wall of the large-diameter portion 10a, and a distal end surface 22b situated within the cylinder 20 and opposite to the proximal end surface 22a. A sub-bearing 26 is fitted into the discharge end portion (the left end portion in the figure) of the cylinder 20. The bearing 26 has a cylindrical insertion portion 28 slidably inserted into the discharge end portion of the cylinder 20. The insertion portion 28 hermetically seals the discharge end portion of the cylinder 20. The bearing 26 is supported on the casing 10 by means of an elastic support member 30 or a plate spring, so that it can move in the radial direction of the cylinder 10. Specifically, the support member 30 is engaged with an engage member 32, fixed to the bottom surface of the small-diameter portion 10b of the casing 10, so that the support member 30 can move in the radial direction of the cylinder 20. The support member 30 is engaged with the proximal-end surface of the bearing 26, thereby urging the bearing 26 towards the discharge end of the cylinder 20 and restricting the rotation of bearing 26 relative to the cylinder 20. As has been stated above, the cylinder 20 and the rotor 18 are supported on one side thereof by means of the main bearing 22, and also they are supported by means of the bearings 22 and 26 coaxially with the stator 16. The positional relationship between the rotor 18, cylinder 20, and main bearing 22 will now be described. As shown in Figs. 1 and 2, the rotor 18 is secured on the suction end portion of the cylinder 20. The center C of gravity of the rotor 18 is apart from the middle G in the axis of the cylinder 20 towards the main bearing 22 and is situated within the main bearing 22, that is, on the center axis B of the cylinder 20 between the proximal end surface 22a and the distal end surface 22b of the bearing 22. Suppose that an intersection between the center axis B of the cylinder 20 and the proximal end surface 22a of the main bearing 22 is set as a reference position O, and an intersection between the center axis B and the distal end surface 22b of main bearing 22 is set as a position P. In this case, the distance E between the reference position O and the center C of gravity of the rotor 18 is smaller than the distance F between the reference position O and the position P (E<F). As shown in Figs. 1 and 3, a rotating rod 34 serving as a rotating body is contained in the cylinder 20, extending in the axial direction of the cylinder 20. The rod 34 comprises a columnar rod body 35 having a diameter smaller than the inner diameter of the cylinder 20, and a pair of journal portions 36a and 36b extending coaxially from both ends of the body 35. The center axis A of the rod 34 is situated at eccentricity e from the center axis B of the cylinder 20, and part of the outer circumferential surface of the body 35 is in contact with the inner circumferential surface of the cylinder. The journal portions 36a and 36b are rotatably inserted in support holes 22c and 26a formed in the bearings 22 and 26, whereby the rotating rod 34 is rotatably supported by the bearings 22 and 26. As shown in Fig. 1, an engaging groove is formed in the outer circumferential surface of the suction end portion of the rod body 35. A drive pin 38 projecting from the inner surface of the cylinder 20 is inserted into the engaging groove so as to be movable in the radial direction of the cylinder 20. Accordingly, when the motor unit 12 is energized to rotate the cylinder 20 integral with the rotor 18, the rotational force of the cylinder 20 is transmitted to the rotating rod 34 through the pin 38. Consequently, the rod 34 is rotated within the cylinder 20 while the outer circumferential surface of the rod 34 is partially in contact with the inner surface of the cylinder 20. As is shown in Figs. 1 and 3, a spiral groove 40 is formed on the outer circumferential surface of the rod body 35, and extends between both ends of the rod body 35. The pitches of the groove 40 gradually become narrower with distance from the suction end of the cylinder 20 towards the discharge end thereof. The depth and width of the groove 40 is substantially constant for the entire length of the groove. In Fig. 3, the pitches of the turns of the groove 40 are denoted by a to e , from the discharge end of the cylinder 20 to the suction end thereof. A spiral blade 42, shown in Fig. 4, is fitted in the groove 40. Each part of the blade 42 is movable in the radial direction of the rod 34 along the groove 40. The outer circumferential surface of the blade 42 is brought into close contact with the inner surface of the cylinder 20. The thickness of the blade 42 is substantially equivalent to the width of the groove 40 over the entire length. The width of each part of the blade 42 in the radial direction is substantially equal to the depth of the groove 40. The blade 42 is formed, in advance, such that the pitches thereof gradually decrease with distance from one end of the blade to the other end thereof, before the blade 24 is to be fitted in the groove 40. The pitches of the blade 42 and the shape of the side surfaces 40a of the blade correspond to those of the groove 40. Namely, the pitches a to e of the turns of the blade 40 from the left end to the right end are substantially equal to the pitches of the turns of the groove 40 from the discharge end to the suction end thereof. Further, the angle and shape of each part of the blade 42 correspond to those of the corresponding part of the groove 40. The blade 42 is formed, for example, by means of injection molding, with use of a mold having the same shape as the rotational rod with the spiral groove. As is shown in Fig. 1, the space defined between the inner surface of cylinder 20 and the outer circumferential surface of the rod body 35 is divided by the blade 42 into a plurality of operating chambers 44, which are aligned in the axial direction of the cylinder 20. Each operating chamber 44, which is defined by two adjacent turns of the blade 42, is substantially in the form of a crescent extending along the blade from a contact portion between the rod body 35 and the inner surface of the cylinder to the next contact portion. The capacities of the operating chambers 44 are reduced gradually with distance from the suction end of the cylinder 20 toward the discharge end thereof. A suction hole 46 is formed in the bearing 22 supporting the suction end portion of the cylinder 20. The suction hole 46 extends in the axial direction of the cylinder 20. One end of the suction hole 46 is open into the suction end portion of the cylinder 20, and the other end thereof is connected to a suction tube 48 of the refrigeration cycle. The bearing 26 supporting the discharge end portion of the cylinder 20 has a discharge hole 50. One end of the hole 50 is open into the discharge end portion of cylinder 20, and the other end thereof is open to the inside of the casing 10 via the support member 30. The discharge hole 50 may be formed in the cylinder 20. A lubrication oil is stored in the bottom of the casing 10. In Fig. 1, reference numeral 52 denotes a discharge tube which communicates with the inside of the casing 10. The operation of the compressor having the above-described structure will be described. When the motor unit 12 is energized, the rotor 18 along with the cylinder 20 rotates, and at the same time the rotating rod 34 rotates while its outer circumferential surface is partially in contact with the inner surface of the cylinder 20. Since the blade 42 rotates with its outer circumferential surface put in contact with the inner surface of the cylinder 20, the respective portions of the blade 42 gradually are pushed into the groove 40 as they approach the contact portion between the outer circumferential surface of the rod body 35 and the inner surface of the cylinder 20, and emerge from the groove 40 as they go away the contact portion. When the compressor unit 14 is operated, refrigerant gas is sucked into the cylinder 20 through the suction tube 48 and the suction hole 46. In accordance with the rotation of the rotating rod 34, the sucked gas is conveyed from the suction end of the cylinder 20 to the discharge end thereof through the operating chambers 44. As has been described above, the capacities of the operating chambers 44 decrease gradually with distance from the suction end of the cylinder 20, thus, the refrigerant gas is gradually compressed as it is conveyed toward the discharge end of the cylinder. The compressed refrigerant gas is discharged into the inside of the casing 10 through the discharge hole 50 formed in the bearing 26. Further, the gas is returned to the refrigeration cycle through the discharge tube 52. According to the fluid compressor having the above-described structure, the rotor 18 of the motor unit 12 is secured to the cylinder 20 such that the center of gravity of the rotor 18 is apart from the middle in the axis of the cylinder 20 toward the main bearing 22. In particular, in this embodiment, the center C of gravity of the rotor 18 is situated within the main bearing 22. Thus, the center C of gravity of the rotor 18 is close to the reference point O on the proximal end surface 22a of the main bearing 22, and the angular moment acting about the reference point O upon the rotor 18, cylinder 20 and main bearing 22 is remarkably reduced. Accordingly, with the compressor, the whirling of the rotor, cylinder and main bearing can be reduced, which occurs owing to the characteristic frequency of the rotor 18, the displacement between the axes of the rotor 18 and the cylinder 20, the displacement between the axes of the rotor and the main bearing 22, the displacement between the axes of the rotor and the stator 16, etc. As a result, the vibration of the compressor in operation and the noise due to the vibration can be reduced. In addition, frictional loss due to the whirling of the rotor, cylinder and main bearing is decreased between the cylinder and the main bearing and between the rotating rod and the main bearing. Therefore, the operation efficiency and reliability of the compressor can be improved. According to this embodiment, before the blade 42 is fitted in the spiral groove 40 of the rotating rod 34, the blade 42 is previously formed so as to have the same shape and pitches as those of the groove 40. The advantages attained by this feature will be stated. In a conventional compressor, the blade is formed in a shape which is relatively easily obtained (e.g. with equal pitches), and then the blade is fitted into a spiral groove in the rotating rod. More specifically, the blade, having the pitches and shape different from those of the spiral groove, is extended in its axial direction and elastically deformed so as to accord with the pitches of the spiral groove and, in this state, the blade is fitted in the spiral groove of the rotating rod. However, if the blade is elastically deformed in its axial direction to a considerable degree, the shape of the respective portions of the blade do not accord with the corresponding portions of the spiral groove. Thus, the respective portions of the blade are not allowed to move in the groove smoothly. As a result, it is conventionally necessary to employ the material of the blade, which is relatively soft and has sufficient elasticity. When the blade is formed of an excessively soft material, it deforms freely and largely in accordance with the pressure acting on each turn and with the wall shape of the groove. Thus, the blade easily moves in the circumferential direction of the spiral groove. There is a concern that the end of the blade abuts against the end of the groove or the blade is removed from the groove. In such a case, either or both of the blade and groove are deformed or damaged, and the reliability and durability of the compressor are deteriorated. Further, it is very difficult to select a suitable material for the blade in consideration of the above problems. By contrast, according to the present embodiment, the blade 42 is previously formed to have the same shape and pitches as those of the spiral groove 40 of the rotating rod 34, as has been stated above. Therefore, it is not necessary to elastically deform the blade in its axial direction, and the blade can easily fitted in the spiral groove. In addition, compared to the conventional compressor, the material for the blade can be selected relatively freely, and a relatively hard material having less elasticity may be employed. Thus, the blade is prevented from largely deforming in accordance with the shape of the groove, and also the blade is prevented from moving in the circumferential direction of the groove. The end of the blade is prevented from contacting the end of the groove, and the blade is not removed from the groove. The deformation and damage of the groove and blade can be prevented. Therefore, the reliability and the durability of the compressor can be improved. The present invention is not limited to the above-described embodiment, and various modifications may be made within the scope of the subject matter of the present invention as it is defined by the claims.. For instance, the present invention can be applied not only to compressors for a refrigeration cycle, but also to compressors for other purposes. In the above embodiment, the proximal end surface of the main bearing is secured directly to the inner surface of the casing; however, it is possible to provide an intermediate member such as a seat between the proximal end surface of the bearing and the inner surface of the casing.

Claims: A fluid compressor comprising: a closed casing (10); a cylinder (20) arranged within the casing and having a suction end and a discharge end; a columnar rotating body (34) located in the cylinder to extend in the axial direction of the cylinder and be eccentric thereto, and rotatable synchronously with the cylinder while part of the rotating body is in contact with the inner surface of the cylinder, said rotating body having a spiral groove on the outer circumferential surface thereof, said groove having pitches gradually narrowing with distance from the suction end of the cylinder; a spiral blade (42) fitted in said groove to be slidable, substantially in the radial direction of the cylinder, said blade having an outer circumferential surface closely in contact with the inner surface of the cylinder, and dividing the space defined between the inner surface of the cylinder and the outer circumferential surface of the rotating body into a plurality of operating chambers; first and second bearings (22, 26) for rotatably supporting both ends of the cylinder and also rotatably supporting the opposite ends of the rotating body, said first bearing being secured to said closed casing; and drive means (12) for synchronously rotating said cylinder and said rotating body so as to successively transport a fluid introduced from the suction end of the cylinder into the cylinder toward the discharge end of the cylinder through the operating chambers, and discharging the fluid to the outside from the discharge end of the cylinder; said drive means (12) including a rotor (18) secured to the outer circumferential surface of said cylinder (20) and rotating integrally with the cylinder, said rotor having the center of gravity being situated on the center axis of the cylinder and being apart from the middle of the cylinder in its axial direction toward said first bearing (22), characterized in that: said rotor (18) is arranged so that the center of gravity of said rotor (18) is situated within the first bearing (22) and on the center axis of the cylinder (20). A fluid compressor according to claim 1, characterized in that said first bearing (22) has an insertion portion (24) inserted in the end portion of the cylinder (20), a secured surface (22a) secured to the casing (10), and a distal end surface (22b) located inwards of the cylinder, said center of gravity of the rotor being situated between said secured surface and said distal end surface of the bearing and on the center axis of the cylinder. A fluid compressor according to claim 1, characterized in that said second bearing (26) is movable in the radial direction of the cylinder (20), in relation to the closed casing (10). A fluid compressor according to claim 1, characterized in that said drive means (12) includes a stator (16) secured to the inner surface of the closed casing (10) and arranged coaxially with said rotor (18) on the outside of the rotor, said stator and said rotor constituting a motor unit.

Inventors: AIKAWA, EIICHI, FUJIWARA, TAKAYOSHI, HONMA, HISANORI, SONE, YOSHINORI, AIKAWA, EIICHI, C/O INTELLECTUAL PROPERTY DIVISION, FUJIWARA, TAKAYOSHI, C/O INTELLECTUAL PROPERTY DIV, HONMA, HISANORI, C/O INTELLECTUAL PROPERTY DIV., SONE, YOSHINORI, C/O INTELLECTUAL PROPERTY DIV.
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1990
Main classification: F04C18
IPC codes: F04C29, F04C18