Scroll compressor with unitary crankshaft, upper bearing and counterweight

Abstract: A scroll-type compressor (10) or other rotating machine employs a crankshaft (36) having an integral counterweight (50) to compensate for the off-axis orbiting motion of the device's orbiting scroll (26). The crankshaft (36) is unitarily formed with a generally cylindrical crank portion (42) at an upper end of the shaft (36), and with the counterweight (50) formed immediately adjacent the crank (36). The counterweight (50) is preferably in the form of a segment of a cylinder of smaller radius than that is disposed within the radius of the cylindrical passage of the stator (40). This permits the rotor and shaft assembly (36), with counterweight (50), to be assembled from below after installation of the stator (40).

Description: The present invention relates to a scroll compressor. In particular, the invention relates to rotating pumps or compressors of the scroll type, and is more particularly directed to an improved construction involving an integral shaft and counterweight. Scroll type compressors have been known, in principle, for several decades. In general, a scroll-type compressor or similar machine comprises a pair of mating scrolls, each of which has an involute spiral wrap of similar shape, mounted on respective base plates. Normally, one scroll is held fixed, and the other is orbited to revolve, but not rotate, being held by an Oldham ring or other anti-rotating structure. The walls of the two involute wraps define crescent-shaped volumes which become smaller and smaller and move from the outside to the center of the mating scrolls as the orbiting scroll revolves. A compressible fluid, such as a refrigerant gas, can be introduced at the periphery of the spiral wraps, and is compressed as it is moved under the orbiting motion of the device. The compressed fluid is then discharged at the center. By introducing a compressed fluid at the center and permitting its expansion to drive the device, the scroll machine can be used as a motor. However, the orbiting motion of the moving scroll is unbalanced and off axis. Consequently, a moment is involved, which must be appropriately balanced by a suitable counterweight. Current designs for scroll-type compressors or other scroll-type rotating machines are rotationally supported on the rotor shaft between the position of the rotor and the eccentric drive for the orbiting scroll. This requires that the counterweight be positioned a considerable axial distance away from the orbiting scroll that is intended to counterbalance. Often, the counterweight is attached onto the rotor, and a bearing for the shaft has to be designed to accommodate the rotor-mounted counterweight. EP-A-165714 discloses a scroll compressor in which the shaft is rotationally supported in a support frame with an upper bearing portion of the shaft. A counterweight integrally formed with the shaft is disposed between the support frame and the crank. In JP-A-1 170 779 there is described a scroll compressor according to the preamble of claim 1. Specifically, JP-A-1 170 779 describes a scroll compressor of the type including a shell which contains a fixed scroll and an orbiting scroll which is disposed off the axis of the fixed scroll for revolving about the axis of the fixed scroll, rotation-preventing means for holding the orbiting scroll against rotation but permitting it to revolve in an orbiting motion, an electric motor stator mounted within said shell and having a cylindrical passage therethrough of a predetermined radius, and an electric motor rotor assembly rotatably journalled within the shell for driving said orbiting scroll in its orbiting motion. The rotor assembly includes a crankshaft assembly and a generally cylindrical rotor mounted on the crankshaft assembly and fitting in the generally cylindrical passage of the stator. The crankshaft assembly has an elongated shaft, a crank situated at an upper end of the shaft and that it journalled in a journal housing member beneath the orbiting scroll, and a counterweight which balances the off-axis orbiting motion of the orbiting scroll, the counterweight being formed immediately adjacent the position of the crank, the rotor assembly being the single structure within the predetermined radius between the motor stator and the journal housing member. The crank includes eccentric mounting means for driving the orbiting scroll and imparting the orbiting motion thereto. A lower bearing rotatably journals a lower end of the shaft, the lower bearing being disposed below the rotor assembly. Where the counterweight is a separate part that must be attached to the rotor or shaft, an additional assembly step is required. Also, the counterweight can possibly become loose under severe use or after prolonged operation, thus limiting the reliability of the compressor. It is an object of the invention to provide a scroll compressor providing simplicity of assembly and increasing the reliability of the compressor, while achieving optimal balancing. To achieve this, the scroll compressor of the invention is characterized by the features set forth in the characterizing portion of claim 1. Basically, according to the invention, the counterweight is integrally formed with the shaft and is disposed below the crank on the shaft, the radial extent of the counterweight being no greater than the radius of the stator passage and the gas discharge path being located separate from the crank. Advantageous embodiments of the invention are claimed in the subclaims. In accordance with an aspect of the present invention, a scroll-type compressor is provided with a rotor shaft that is fabricated so as to have an integral upper bearing and an integral counterweight. The scroll compressor has a fixed scroll mounted in the housing and an orbiting scroll which is disposed off the axis of the fixed scroll to revolve about the axis of the fixed scroll. A rotation-preventing mechanism holds the orbiting scroll against rotation but permits it to revolve in an orbiting motion. An electric motor drive for the compressor has a stator armature that is mounted within the housing. The stator has a cylindrical passage through it of a predetermined radius to accommodate a rotor assembly that is rotationally journaled within the housing. A generally cylindrical rotor is mounted on the shaft and fits into the generally cylindrical passage of the stator, leaving a small annular gap. There is a generally cylindrical upper bearing formed on an upper end of the shaft. The bearing serves as a crank and has an off-axis void on its upper surface into which fits a stem of the orbiting scroll. A radial compliance device can favorably be employed here. Immediately adjacent the bearing on the shaft is the counterweight which is in the form of a segment of a cylinder and which is disposed radially opposite the offset represented by the orbiting scroll. The counterweight is disposed entirely within a radius equal to the predetermined radius of the stator passage. This permits the rotor assembly to be installed from below by inserting it through the stator. A rotor counterweight, in the form of a half ring, is mounted onto the lower end of the rotor, radially opposite to the position of the main, integral counterweight. The lower end of the shaft is supported in a lower bearing. With this integral shaft design, inventories are reduced because fewer parts are required, and an assembly step is eliminated in production, as the counterweight does not require a mounting step to attach either to the shaft or to the rotor. Because the shaft and counterweight are all one piece, there is no possibility of the counterweight coming off or becoming loose. Fig. 1 is a longitudinal sectional view of a scroll-type compressor according to one preferred embodiment of this invention. Fig. 2 is a side elevation of a rotor crankshaft according to this embodiment of the invention. Fig. 3 is a top plan view of the shaft and rotor assembly. Fig. 4 is a bottom plan view of the shaft and rotor assembly. With reference to the Drawing, Fig. 1 shows a scroll compressor assembly 10 of the type which can be used with a refrigeration or air conditioning system. The assembly 10 has a generally cylindrical shell or housing 12, which is closed off at its lower end with a lower cap 14 and is closed off at its upper end with an upper cap 16. A pressure dome 18 in the cap 16 holds gas that is compressed in the compressor and conducts it to a high pressure outlet 20 from the center of a fixed scroll 22 that is rigidly mounted within the housing 12. The fixed scroll 22 has an involute or spiral wrap 24. The assembly 10 also has an orbiting scroll 26 with a similar involute wrap 28 that interleaves with the wrap 24 of the fixed scroll 22. A male stub 30 depends from the orbiting scroll 26 at the center or axis thereof. An anti-rotation device, such as an Oldham's ring 32 is associated with the orbiting scroll 26 to prevent rotation of the orbiting scroll, but while permitting it to revolve without rotation around the axis of the fixed scroll 22. A crankcase 34 and bearing are situated with the housing 12 just below the orbiting scroll 26. A one-piece crankshaft assembly 36 as shown in Fig. 2 can be unitarily cast of ductile iron or an equivalent material. A generally cylindrical electrical rotor 38 is press fit onto the shaft 36 and fits into a cylindrical passage in an electric motor stator armature 40 that is affixed in place onto the interior of the housing 12. The passage has a predetermined radius, so that a small gap remains between the rotor 38 and the stator 40. The rotor 38 and stator 40 constitute an electric motor for the compressor assembly 10. A generally cylindrical crank 42 which is unitarily formed on an upper end of the shaft 36 is journaled within the crankcase 34. At the top surface of this crank 42 there is an offset female receptacle or socket 48. The socket 48 serves as a receptacle for the make stub 30 of the orbiting scroll 26. A counterweight 50 is also unitarily formed on the shaft 36, in this embodiment adjacent crank 42. Preferably, the counterweight 50 is arcuate in form, in the shape of a segment of a cylinder, and here subtending an arc of approximately 160°. The counterweight 50 is disposed to the side opposite the radial position of the offset of the orbiting scroll 26. The counterweight 50 lies at or within the radius of the cylindrical passage in the stator 40. This feature permits the crank and rotor assembly to be installed from below after the stator 40 has been affixed into the housing 12. The counterweight 50 extends axially downwards to the position of an upper ring 52 on the rotor 38. There is also a lower ring 54 on the rotor 38. A generally semi-circular or half-ring rotor counterweight 56 is affixed onto the lower ring 54 in the position radially opposite that of the counterweight 50. Then, a lower bearing 58 journals a lower end 60 of the shaft 36. Also shown in Fig. 1 is an electrical connector 62 which connects electrical power to the stator 40. It should be apparent from the above description that this unitary crankshaft 36, with integral crank 42 and counterweight 50, not only provides simplicity of assembly, but increases the reliability of the compressor. With this assembly, the counterweight 50 is rigidly and permanently situated on the crankshaft 36, and is situated as close as possible to the axial position of the orbiting scroll 26, thereby providing optimal balancing. Placing the counterweight 50 at the upper end of the crankshaft 36, rather than directly on the rotor 38, minimizes the effect of destructive transient torques, and thereby further increases the reliability of the compressor 10.

Claims: A scroll compressor (10) of the type including a shell (12) which contains a fixed scroll (22) and an orbiting scroll (26) which is disposed off the axis of the fixed scroll (22) for revolving about the axis of the fixed scroll (22), rotation-preventing means (32) for holding the orbiting scroll (26) against rotation but permitting it to revolve in an orbiting motion, an electric motor stator (40) mounted within said shell (12) and having a cylindrical passage therethrough of a predetermined radius, an electric motor rotor assembly (38) rotatably journalled within the shell (12)for driving said orbiting scroll (26) in its orbiting motion, the rotor assembly (38) including a crankshaft assembly (36,42,50) and a generally cylindrical rotor (38) mounted on said crankshaft assembly and fitting in said generally cylindrical passage of said stator (40), said crankshaft assembly (36, 42, 50) having an elongated shaft (36), a crank (42) situated at an upper end of said shaft (36) and that is journalled in a journal housing member (34) beneath said orbiting scroll (26), and a counterweight (50) which balances the off-axis orbiting motion of said orbiting scroll (12), said counterweight (50)being formed immediately adjacent the position of said crank (42), said rotor assembly (38) being the single structure within said predetermined radius between said motor stator (40) and said journal housing member (34), said crank (42) including eccentric mounting means (48) for driving said orbiting scroll (12) and imparting said orbiting motion thereto, and a lower bearing (58) rotatably journaling a lower end of said shaft (36), said lower bearing (58) being disposed below said rotor assembly (38), characterized by said counterweight (50) being integrally formed with said shaft (36) and being disposed below said crank (42), the gas discharge path being located separate from said crank (42), and the radial extend of said counterweight (50) on said shaft (36) being no greater than said predetermined radius so as to permit the shaft with counterweight to pass through said stator passage upon installation. The scroll compressor of claim 1, characterized in that said shaft (36) and said counterweight (50) are unitarily cast of iron. The scroll compressor of claim 1, characterized in that said crank (42) is a generally cylindrical crank member unitarily formed at said upper end of said shaft (36). The scroll compressor of claim 1, characterized in that said counterweight (50) is generally a cylindrical segment, and subtends an arc of about 160°. The scroll compressor of claim 1, characterized in further comprising a rotor counterweight (56) mounted on said rotor (38) on an end remote from the first mentioned counterweight (50) and disposed radially opposite the position of the first-mentioned counterweight (50).

Inventors: BARITO THOMAS ROBERT, FRASER HOWARD HENRY JR, BARITO, THOMAS ROBERT, FRASER, HOWARD HENRY, JR.
Applicants: CARRIER CORP, CARRIER CORPORATION
Application year: 1990
Main classification: F04C29
IPC codes: F04C18, F04C23, F04C29