Scroll member for scroll type fluid displacement apparatus

Abstract: A scroll type fluid displacement apparatus is disclosed in which a pair of scrolls (18, 19) interfit at an angular and radial offset, each scroll including a circular end plate (181, 19) and a spiral element (182, 192). A steplike rebate portion (185) is provided at an outer peripheral edge portion of at least one of the plates. It extends from the outer end of the corresponding spiral element (182, 192), has an inner wall ℓ' following the path of an extension of the involute curve ℓ defining the inner wall surface of the spiral element (182, 192) and its surface is left unfinished. Accordingly, the time for manufacturing each spiral element can be reduced and waste of material, which is produced by turning the scroll elements to finish them, is decreased.

Description: The present invention relates to scroll type fluid displacement apparatus, and more particularly, to the outer configuration of a scroll member for scroll type fluid displacement apparatus. Scroll type fluid displacement apparatus is well known in the prior art. For example, US-A-4494914 discloses a fluid displacement apparatus which includes a pair of interfitting scroll members. Each scroll member has a circular end plate and a spiral element extending from one end surface of the end plate. These scroll members are maintained angularly and radially offset so that they interfit and make a plurality of line contracts between their spiral curved surfaces and, as a result, the volume of the fluid pocket changes. Since the volume of the fluid pockets increases or decreases according to the direction of the orbital motion, such scroll type displacement apparatus is applicable to compress, expand or pump fluids. To achieve the smoother operation of such scroll type displacement apparatus, the inner and outer wall surfaces of the spiral elements and the axial end surfaces of the end plates may be provided with a finishing process over their entire surfaces, by turning in conventional manner. However, this takes a long time, and since the entire surfaces of the scrolls are finished by turning, much material of the scrolls will be wasted. See also JP-A-59-37289 A primary object of this invention is to provide scrolls for a scroll type fluid displacement apparatus which can be manufactured in a shorter time, and another object of this invention to provide scrolls which can be manufactured at low cost. According to the invention, apparatus of the above mentioned type is characterized in that at least one of the circular end plates of the scroll members is provided with either an unfinished steplike rebate portion at an outer peripheral edge portion thereof, the rebate portion extending from the outer end of the corresponding spiral element, and having an inner wall ℓ following the path of an extension of the involute curve ℓ' defining the inner wall surface of the spiral element, or with an unfinished portion at the same position. An example of apparatus according with the present invention will now be described with reference to the accompanying drawings, in which:- Fig. 1 is a cross-sectional view of a first scroll type compressor containing a scroll member; Figs. 2a-2d are schematic views illustrating the relative movement of interfitting spiral elements; Fig. 3 is a front view of a scroll member in accordance with this invention; Fig. 4 is a perspective view of a part of the scroll of Figure 3; and, Fig. 5 is a enlarged perspective view of part of Figure 4. Referring to Fig. 1, a scroll type fluid displacement apparatus is shown which consists of a scroll type compressor. The compressor includes a compressor housing 10 having a front end plate 11 and a cup-shaped casing 12 which is attached to an end surface of the front end plate 11. An opening 111 is formed in the centre of the front end plate 11 for a drive shaft 13. The casing 12 is fixed to the inside surface of the front end plate 11 by fastening devices, for example bolts and nuts (not shown), so that the open end of the casing 12 is covered by the front end plate 11. The front end plate 11 has an annular sleeve 15 projecting from its front end surface, the sleeve 15 surrounding the drive shaft 13 to define a shaft seal cavity. A shaft seal assembly 16 is assembled on the drive shaft 13 within the shaft seal cavity. The drive shaft 13 is formed with a disk-shaped rotor 131, at its inner end, rotatably supported by the front end plate 11 through a bearing 14 located within the opening 111. The drive shaft 13 is also rotatably supported by the sleeve 15 through a bearing 17. The outer end of the drive shaft 13 which extends from the sleeve 15 is connected to a rotation transmitting device, for example, an electromagnetic clutch which may be disposed on the outer peripheral surface of the sleeve 15 for transmitting rotary movement to the drive shaft 13. Thus, the drive shaft 13 is driven by an external power source, for example, the engine of a vehicle, through the rotating transmitting device. A number of elements are located within the inner chamber of cup-shaped casing 12, including a fixed scroll 18, an orbiting scroll 19, a driving mechanism for the orbiting scroll 19 and a rotation preventing/thrust bearing device 20 for the orbiting scroll 19, formed between the inner wall of the casing 12 and the rear end surface of the front end plate 11. The fixed scroll 18 includes a circular end plate 181, a spiral element 182 affixed to and extending from one end surface of the circular end plate 181 and a plurality of internally threaded bosses 183 axially projecting from the outer end surface of the end plate 181. The axial end surface of each boss 183 is seated on the inner surface of an end plate 121 of the casing 12 and fixed therewithin by bolts 21. The circular end plate 181 partitions the inner chamber of the casing 12 into two chambers: a discharge chamber 22 and a suction chamber 23. A seal ring 24 is located between the outer peripheral surface of the end plate 181 and the inner wall of the casing 12 to seal off and define the two chambers. A discharge port 184, which interconnects the centre portions of the scrolls with the discharge chamber 22, is formed through the end plate 181. The orbiting scroll 19 also includes a circular end plate 191 and a spiral element 192 affixed to and extending from one side surface of the end plate 191. The spiral element 192 of the orbiting scroll 19 and the spiral element 182 of the fixed scroll interfit at an angular offset of 180° and a predetermined radial offset. At least a pair of sealed off fluid pockets are thereby defined between the spiral elements 182,192. Each scroll, which comprises a spiral element and circular end plate integrally formed with one another, is initially formed by casting, and this initially formed scroll is finished by turning to obtain an accurate surface to ensure sealing of the interfitting scrolls. The orbiting scroll 19, which is connected to the driving mechanism and to the rotation preventing/thrust bearing device 20, is driven in an orbital motion at a circular radius by rotation of the drive shaft 13 thereby to compress fluid passing through the compressor unit, according to the general principles described above. Referring to Fig. 2, the compression cycle of fluid in one fluid pocket will be described. Fig. 2 shows the relationship of fluid in the fluid pocket to crank angle, and shows that one compression cycle is completed in this case at a crank angle of 360°. Two spiral elements 182, 192 are angularly offset and interfit with one another. As shown in Figure 2a, the orbiting spiral element 192 and fixed spiral element 182 make four line contacts A-D. A pair of fluid pockets A₁, A₂ are defined between line contacts D-C and line contacts A-B, as shown by the dotted regions. The fluid pockets A₁, A₂ are defined not only by the wall of spiral elements 182, 192 but also by the end plates. When orbiting the spiral element 182 so that the centre of the orbiting spiral element 192 revolves around the centre of the fixed spiral element 182, the fluid pockets A₁, A₂ shift angularly and radially towards the centre of the interfitted spiral elements with the volume of each fluid pockets A₁, A₂ being gradually reduced, as shown in Figs. 2a-2d. Therefore, the fluid in each pocket is compressed. As clearly shown in Figs. 2a-2d, the outer wall surfaces of the spiral elements 182, 192, from the outer terminal end of the respective spiral element to the points A,D which first contact with the outer terminal end of the opposed spiral element to form the sealed off fluid pockets, do not serve in the compression cycle. Referring to Figs. 3 and 4, a fixed scroll 18 in accordance with a further embodiment of this invention is shown. The circular end plate 181 of the fixed scroll 18 is provided with a stepped rebate 185 at its outer peripheral edge portion, extending over 180° from the outer terminal end of the spiral element 181. The rebate portion 185 of the end plate 181 is formed on the outerside of an imaginary line ℓ which is an extension of the involute curve defines the inner wall surface of the spiral element 182. The inner wall surface line ℓ' of the rebate portion 185 may be shifted inwardly of the involute curve ℓ whilst still securing effective compression. The rebate portion 185 is initially formed by casting so that its height from the other end surface of the end plate 181 is less than the height of the other portion of the end plate 181 which is subsequently finished by turning. Referring to Fig. 5, an enlarged view illustrating the outer end portion of the spiral element 182 is shown. An arc-shaped shaped slant surface 186 is formed between the spiral element 182 and the end plate 181 to reinforce the base of the spiral element 182. The arc-shaped slant surface 186 is defined with an axial height h from the surface of the rebate portion 185. The axial height h can be small until the position in which the spiral element 182 may not be broken down. The arc-shaped slant surface 186 is formed by casting, and is not finished by turning. The present application is a divisional of application no. 87303700.6 filed 27 April 1987.

Claims: A scroll type fluid displacement apparatus including a housing (12), a pair of scroll members (18), (19), one (18) of the scroll members being fixedly disposed relative to the housing and having a circular end plate (181) from which a first spiral element (182) extends into the interior of the housing, and the other scroll member (19) being movably disposed for non-rotative orbital movement within the interior of the housing and having an end plate (191) from which a second spiral element (192) extends, the first and second spiral elements interfitting at an angular and radial offset to make a plurality of line contacts (A-D) to define at least one pair of sealed off fluid pockets (A₁, A₂) and drive means (13) operatively connected to the other scroll member (19) to effect its orbital motion and that of the line contacts, whereby the fluid pockets (A₁, A₂) move inwardly and change in volume, each scroll member initially being formed roughly approximate to its finished shape and being finished to obtain an accurate surface to ensure sealing of the fluid pockets, characterized in that at least one of the circular end plates (181, 191) of the scroll members is provided with an unfinished steplike rebate portion (185) at an outer peripheral edge portion thereof, the rebate portion (185) extending from the outer end of the corresponding spiral element (182, 192) and having an inner wall ℓ' following the path of an extension of the involute curve ℓ defining the inner wall surface of the spiral element (182, 192). Apparatus according to claim 1, wherein an arc-shaped portion (186) is formed as a base portion to the spiral element (182) adjacent the rebate portion (185).

Inventors: FUKUHARA SEIICHI, FUKUSHIMA EIJI, FUKUHARA, SEIICHI, FUKUSHIMA, EIJI
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1987
Main classification: F01C1
IPC codes: F01C1