A scroll type fluid displacement apparatus

Abstract: A scroll type compressor has a crank pin (142) eccentrically extending from an inner end of a drive shaft (14). A bushing (27) swingable about the crank pin connects the crank pin to an orbiting scroll (21). First (202) and second (212) spiral elements are urged together in response to the reaction force of gas compression which is exerted on the central axis (Oc) of the bushing. A control mechanism, consisting either of an enlarged diameter region (143b) in the hole in which the crank pin is mounted (Fig.2) or a supportive elastic member (51), allows the position of the axis (Od) of the crank pin to be altered so that the force between the spiral elements does not become excessive when an abnormally large reaction force of gas compression is exerted on the central axis of the bushing. This provides excellent sealing of the fluid pockets and reduces wearing of the spiral element surfaces with a simple construction.

Description: This invention relates to a scroll type fluid displacement apparatus, and more particularly, to fluid compressor units. Scroll type apparatuses have been well known in the prior art. For example, US-A-4,824,346 discloses a device including two scrolls each having an end plate and a spiral wrap. The scrolls are maintained angularly offset so that both spiral elements interfit at a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. One of the scrolls is an orbiting scroll and the other one is a fixed scroll. The relative orbital motion of these scrolls shifts the line contact along the spiral curved surfaces, and therefore, changes the volume of the fluid pockets. Accordingly, it is desirable that sealing force at the line contact be sufficiently maintained in a scroll type compressor, because the fluid pockets are defined by the line contacts between two spiral elements which are interfitted together, and the line contacts shift along the surface of the spiral elements toward the center of spiral elements by the orbital motion of the scroll, to thereby move the fluid pockets to the center of the spiral elements with consequent reduction of volume, and compression of the fluid in the pockets. On the other hand, if the contact force between the spiral elements becomes too large in maintainng the sealing line contact, wear of spiral elements surfaces increases. The contact force of both spiral elements thus must be suitably maintained. With reference to FIGS. 5(a) and 5(b), the operation of this type of compressor is described below. Center Os of disk-shaped rotor 31 integrally formed with a drive shaft, center Oc of axial bushing 23, and center Od of crank pin 45 are respectively placed. The distance between Os and Oc is the radius Ro of orbital motion. When crank pin 45 is fitted into eccentric hole 231 of bushing 23, center Od of crank pin 45 is placed, with respect to Os, on the opposite side of a line L1, which is through Oc and perpendicular to line L2 through Oc and Os, and also beyond the line through Oc and Os in direction of arrow A of rotor 31. This relationship between centres Os, Oc & Od holds true in all rotative positions of rotor 31. Od, at this particular point of motion, is located in the upper left hand quadrant defined by the lines L1 and L2. When rotor 31 rotates, drive force Fd is exerted et Od to the left and reaction force Fr of gas compression appears at Oc to the right, with both forces being parallel to line L1. Therefore, the arm Od-Oc can swing outward by the creation of the moment generated by forces Fd and Fr so that, a spiral element of an orbiting scroll, which is rotatably disposed on bushing 23 through a needle bearing, is forced toward the spiral element of a fixed scroll and the orbiting scroll orbits with the radius Ro around center Os of rotor 31. The rotation of the orbiting scroll is prevented by a rotation preventing mechanism, described in the above patent, whereby the orbiting scroll orbits and keeps its relative angular relationship. The fluid pockets move because of the orbital motion of the orbiting scroll, to thereby compress the fluid. When fluid is compressed by orbital motion of the orbiting scroll, reaction force Fr, caused by the compression of the fluid, acts on the spiral element. This reaction force Fr acts in a direction tangential to the circle of orbiting motion. This reaction force, which is shown as Fr, in the final analysis, acts on center Oc of bushing 23. Since bushing 23 is rotatably supported by crank pin 45, bushing 23 is subject to a rotating moment generated by Fd and Fr with radius E2 around center Od of crank pin 45. This moment is defined as Fd(E2)(sinϑ), where ϑ is the angle between the line Od-Oc and L1, because Fd=Fr . The orbiting scroll which is supported by bushing 23, is also subject to the rotating moment with radius F2 around center Od of crank pin 45 and, hence, the rotating moment is also transfered to the spiral element of the orbiting scroll. This moment urges the spiral element against the spiral element of the fixed scroll with an urging force, i.e., a seal force Fp. Fp acts through a moment arm E3=E2cosϑ . Since the moments are equal, FpE2cosϑ =FdE2 sinϑ . Thus, urging force Fp is expressed by the following formula. Fp=Fdtanϑ Accordingly, urging force Fp can be determined suitably by relevantly predetermining the angle ϑ. However, when the abnormal compression conditions, e.g., suction of liquid refrigerant or compression of liquid refrigerant, occur, reaction force Fr increases greater than the normal, and urging force Fp becomes very large. When urging force Fp becomes too large, the contact force between both scroll elements also becomes too large. Thus, abnormal abrasion occurs between the wall surfaces of the scroll elements, and causes deformation of the scroll elements and damage thereto. Particularly, when the range of the rotational speed of a compressor is very wide, such as for an automotive air conditioning system, and when the angle is predetermined to be sufficient to accomplish the urging force Fp, the urging force Fp becomes excessive under the range of high rotational speed even though the above-mentioned abnormal compression conditions to not occur. Thus, the above problems may occur. JP-A-2-115588 discloses a scroll compressor with a bushing and an eccentrically located driving pin whereby a moment around the driving pin on the bushing is generated by the compression gas force in the fluid pockets in the direction for reducing the radius of orbit of the orbiting scroll. JP-A-2-86976 discloses a scroll machine having an orbiting scroll member with a central boss wherein a crankshaft is fitted with the interposition of a resilient sleeve. According to the present invention, a scroll type fluid displacement apparatus comprising a housing having a fluid inlet port and a fluid outlet port; a fixed scroll fixedly disposed in the housing having a first end plate from which a first wrap extends; an orbiting scroll having a second end plate from which a second wrap extends, the first and second wraps interfitting at an angular offset to make a plurality of line contacts to define at least one pair of sealed-off fluid pockets; a driving mechanism including a drive shaft rotatably supported by the housing and a crank pin eccentrically extending from an inner end of the drive shaft; a bushing including a central axis offset from the central axes of the drive shaft and the crank pin for drivingly connecting the crank pin to the orbiting scroll, the bushing being swingable about the crank pin, the orbiting scroll being moved by the bushing, in orbital motion with line contact between the first and second wraps, by the movement about the central axis of the crank pin in response to the reaction force of compression gas exerted on the central axis of the bushing; rotation preventing means for preventing the rotation of the orbiting scroll during its orbital motion; a mechanism for changing the angle between a first line which crosses, perpendicularly, a line passing through the central axes of the drive shaft and the bushing and which passes through the central axis of the bushing, and a second line which passes through the central axes of the crank pin and the bushing, (as described in US-A-4824346); is characterised in that the mechanism is a control mechanism for reducing the angle when an abnormally large reaction force of compression is exerted on the central axis of the bushing; the control mechanism being formed by a rotor fixed to the inner end of the drive shaft adjacent the bushing, the rotor having a first hole in which one end of the crank pin is securely connected, the hole having a region of relatively greater diameter adjacent the bushing, and the other end of the crank pin having a curved profile and fitting into a second hole in the bushing, whereby the reduction in angle between the first and second lines is provided by elastic bending of the crank pin and its inclination to the axis of the bushing. In the accompanying drawings: Fig. 1 is a cross-sectional view of a scroll type compressor in accordance with one embodiment of the present invention. Fig. 2 is a main portion of a driving mechanism of a scroll type compressor as shown in FIG. 1. FIGS. 3(a) and 3(b) are diagrams of the motion of the bushing in the embodiment of FIG. 1. FIG. 4 is a graph illustrating the relationship between urging force Fp and driving force Fd. FIGS. 5(a) and 5(b) are diagrams of the motion of the bushing of a conventional scroll type compressor. Referring to FIG. 1, a fluid displacement apparatus in accordance with one embodiment of the present invention, in particular a scroll type refrigerant compressor is shown. The compressor includes housing 10 comprising front end plate 11 and cup-shaped casing 12 fastened to an end surface of front end plate 11. Opening 111 is formed in the center of front end plate 11 for supporting drive shaft 14. The center of drive shaft 14 is thus aligned or concentric with the center line of housing 10. Annular projection 112, concentric with opening 111, is formed on the rear end surface of front end plate 11 and faces cup-shaped casing 12. Annular projection 112 contacts an inner wall of the opening of cup-shaped casing 12. Cup-shaped casing 12 is attached to the rear end surface in front end plate 11 by a fastening device, such as bolts and nuts (not shown), so that the opening of cup-shaped casing 12 is covered by front end plate 11. O-ring 18 is placed between the outer peripheral surface of annular projection 112 and the inner wall of the opening of cup-shaped casing 12 to seal the mating surfaces between front end plate 11 and cup-shaped casing 12. Drive shaft 14 is forms with disk-shaped rotor 141 at its inner end portion. Disk-shaped rotor 141 is rotatably supported by front end plate 11 through bearing 13 located within opening 111. Front end plate 11 has annular sleeve 15 projecting from its front end surface. Sleeve 15 surrounds drive shaft 14 to define a shaft seal cavity. Shaft seal assembly 16 is assembled on drive shaft 14 within the shaft seal cavity. O-ring 19 is placed between the front end surface of front end plate 11 and sleeve 15 to seal the mating surfaces between front end plate 11 and sleeve 15. As shown in FIG. 1, sleeve 15 is formed separately from front end plate 11 and is attached to the front end surface of front end plate 11 by screws (not shown). Alternatively, sleeve 15 may be formed integral with front end plate 11. Electromagnetic clutch 17 is supported on the outer surface sleeve 15 and is connected to the outer end portion of drive shaft 14. A number of elements are located within the inner chamber of cup-shaped casing 12 including fixed scroll 20, orbiting scroll 21, a driving mechanism for orbiting scroll 21, and a rotation preventing/thrust bearing device 22 for orbiting scroll 21. The inner chamber of cup-shaped casing 12 is formed between the inner wall of cup-shaped casing 12 and the rear end surface of front end plate 11. Fixed scroll 20 includes circular end plate 201, wrap or spiral element (spiroidal wall) 202 affixed to or extending from one end surface of circular end plate 201, and a plurality of internal bosses 203. The end surface of each boss 203 is seated on an inner end surface of end plate portion 121 of cup-shaped casing 12 and is fixed on end plate portion 121 by a plurality of bolts 122, one of which is shown in FIG. 1. Circular end plate 201 of fixed scroll 20 partitions the inner chamber of cup-shaped casing 12 into discharge chamber 26 having bosses 203, and suction chamber 25, in which spiral element 202 of fixed scroll 20 is located. Sealing member 24 is placed within circumferential groove 205 in circular end plate 201 to form a seal between the inner wall of cup-shaped casing 12 and outer peripheral surface of circular end plate 201. Hole or discharge port 204 is formed through circular end plate 201 at a position near the center of the spiral elements to communicate between discharge chamber 26 and the spiral element center. Orbiting scroll 21, which is disposed in suction chamber 25, includes circular end plate 211 and wrap or spiral element (spiroidal wall) 212 affixed to or extending from one end surface of circular end plate 211. Both spiral elements 202,212 interfit at an angular offset of 180° and a predetermined radial offset to make a plurality of line contacts. The spiral elements define at least one pair of fluid pockets between their interfitting surfaces. Orbiting scroll 21 is connected to the driving mechanism and rotation preventing/thrust bearing device to effect orbital motion of orbiting scroll 21 at a circular radius Ror by the rotation of drive shaft 14 and thereby compressing fluid passing through the compressor. Referring to FIG. 2, the driving mechanism of orbiting scroll 21 will be described in greater detail. Drive shaft 14 is formed with disk-shaped rotor 141 at its inner end portion and is rotatably supported by front end plate 11 through bearing 13 located within opening 111 of front end plate 11. Circular end plate 211 of orbiting scroll 21 has tubular boss 213 axially projecting from the end surface opposite from which spiral element 212 extends. Axial bushing 27 fits into boss 213, and is rotatably supported therein by a bearing, such as needle bearing 28. Bushing 27 has balance weight 271 (not shown in FIG. 2) which is shaped as a portion of a disk and extends radially from bushing 27 along a front end surface thereof. Eccentric hole 272 is formed in bushing 27 at a position radially offset from the center of bushing 27. Crank pin or drive pin 142 fits into axial bore 143 which is formed through disk-shaped rotor 141 and is radially offset from the center of drive shaft 14. Axial bore 143 comprises small diameter portion 143a and large diameter portion 143b. The diameter of crank pin 142 is equal to that of small diameter portion 143a and is less than that of large diameter portion 143b. One end of crank pin 142 is securedly connected with disk-shaped rotor 141 at small diameter portion 143a of axial bore 143 and extends through its large diameter portion 143b with a gap between the inner surface of large diameter portion 143b and the outer surface of disk-shaped rotor 141. The other end of crank pin 142 is formed in spherical shape at its outer surface and fits into the eccentrically disposed hole 272. Bushing 27 is therefore driven in an orbital path by the revolution of crank pin 142 and can rotate within needle bearing 28. In the above construction, since crank pin 142 is disposed in axial bore 143 with a gap at its large diameter portion 143b, crank pin 142 can he elastic to the axis of axial bore 143. In addition, since crank pin 142 has the spherical-shaped outer surface in eccentric hole 272 of bushing 27, crank pin 142 can he inclined to the axis of bushing 27. Referring to FIGS. 3(a) and 3(b), the operation of the driving mechanism as shown in FIG. 2 will he described below. Center Os of disk-shaped rotor 141 connected to drive shaft 14, center Oc of bushing 27, and center Od of crank pin 142 are respectively placed. The distance between Os and Oc is the radius Ro of orbital motion. When crank pin 142 is fitted into eccentric hole 272 of bushing 27, center Od of crank pin 142 is placed, with respect to Os, on the opposite side of a line L1, which is through Oc and perpendicular to line L2 through Oc and Os, and also beyond the line through Oc and Os in direction of arrow A of rotor 141. This relationship centers Os, Oc and Od holds true in all rotative positions of rotor 141. Od, at this particular point of motion, is located in the upper left hand quadrant defined by lines L1 and L2. When orbiting element 212 operates under the normal air conditioning load, crank pin 142 orbits with radius r around center Os of rotor 141. On the other band, when orbiting element 212 compresses liquid fluid or operates under the condition of high air conditioning load, reaction force Fr of high gas compression is exerted at center Oc of bushing 27 to the right. Since the radius Ro of orbital motion is not changed, crank pin 142 orbits with the radius r₋Δr around center Os of rotor 141. Accordingly, crank pin 142 is inclined toward center Os of rotor 141, and center Od of crank pin 142 moves from the position as shown in FIG. 3(a) to the position as shown in FIG. 3(b). Thus, angle ϑ between line t through Od and Oc, and line L1 changes to angle ϑ 1, less than angle ϑ. Since angle ϑ becomes small, urging force Fp also becomes small as understood from the above formula. Thus, as shown in FIG. 4, even though abnormal large reaction force Fr acts on the scroll element, urging force Fp of orbiting element 212 does not become large in excess. As shown in the above embodiment, it is accomplished to maintain urging force F p suitably by reducing the angle between line L1 and line t through Oc and Od. Accordingly, many mechanisms to accomplish the above effectiveness can be thought out.

Claims: A scroll type fluid displacement apparatus comprising a housing (11,12) having a fluid inlet port and a fluid outlet port; a fixed scroll (20) fixedly disposed in the housing (11,12) and having a first end plate (201) from which a first wrap (202) extends; an orbiting scroll (21) having a second end plate (211) from which a second wrap (212) extends, the first (202) and second (212) wraps interfitting at an angular offset to make a plurality of line contacts to define at least one pair of sealed-off fluid pockets; a driving mechanism including a drive shaft (14) rotatably supported by the housing (11) and a crank pin (142) eccentrically extending from an inner end of the drive shaft; a bushing (27) including a central axis offset from the central axes of the drive shaft and the crank pin for drivingly connecting the crank pin to the orbiting scroll (21), the bushing being swingable about the crank pin, the orbiting scroll being moved by the bushing, in orbital motion with line contact between the first (202) and second (212) wraps, by the movement about the central axis of the crank pin in response to the reaction force of compression gas exerted on the central axis of the bushing; rotation preventing means for preventing the rotation of the orbiting scroll (21) during its orbital motion; a mechanism for changing the angle between a first line (L1) which crosses, perpendicularly, a line (L2) passing through the central axes (Os,Oc) of the drive shaft and the bushing and which passes through the central axis (Oc) of the bushing (27), and a second line (t) which passes through the central axes (Od,Oc) of the crank pin (142) and the bushing; characterised in that the mechanism is a control mechanism for reducing the angle when an abnormally large reaction force of compression is exerted on the central axis of the bushing; the control mechanism being formed by a rotor (141) fixed to the inner end of the drive shaft adjacent the bushing (27), the rotor having a first hole (143) in which one end of the crank pin (142) is securely connected, the hole having a region (143b) of relatively greater diameter adjacent the bushing (27), and the other end of the crank pin having a curved profile and fitting into a second hole (272) in the bushing, whereby the reduction in angle between the first (L1) and second (t) lines is provided by elastic bending of the crank pin (142) and its inclination to the axis of the bushing.

Inventors: TERAUCHI KIYOSHI, TERAUCHI, KIYOSHI
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1991
Main classification: F04C18
IPC codes: F04C29, F04C18