Improvement in the lubricating system for a hermetically sealed reciprocating compressor

Abstract: The compressor comprises a hermetically sealed casing (7) in which a piston (8) is operable by a rotating shaft (9) an end portion of which rotatably drives pumping means adapted to supply a lubrication system of the compressor with lubricant oil from an oil bath (13) contained in the casing. The pumping means comprise a helical-screw rotor (14) which is coupled by snap-fitting to said rotating means (9) and combines with an adjacent coaxial stator (15) to define a pumping chamber (16) dipped in said oil bath (13).

Description: The present invention refers to a hermetically sealed compressor, in particular a compressor of the reciprocating type used to equip household and similar refrigerating apparatuses, provided with a improved type of lubrication system. The operation of the compressors of the above cited kind is largely known to be made possible by the presence, inside a hermetically sealed casing containing the main operational elements of the compressor, of a certain amount of lubricant oil which is circulated in a system provided for the lubrication of moving parts. Furthermore, the lubricant oil promotes cooling down of those parts of the compressor which are subject to intense heating due to the presence of compressed gas. Various arrangements are known in the art which are adapted to cause the lubricant oil to circulate, usually owing to a centrifugal effect, in the lubrication systems of hermetically sealed compressors. Generally, such arrangements comprise a hollow tapered tube which is mounted coaxially at an end portion of the crankshaft operating a piston with a reciprocating motion. The free end portion of said tapered tube is perforated and dipped in a bath of lubricant oil. The structure is such that, when the crankshaft rotates at a speed which is not lower than approx. 2700 to 3000 rpm, a pressure system is created that is adapted to take in the oil and circulate it in the lubrication system. In some cases, inside the tapered tube there are provided appropriately coaxial inserts that are adapted to boost the flow rate and the head in the lubrication system. Although simple and satisfactory at high rotational speeds of the crankshaft, ie. high operating speeds, all such solutions are however substantially ineffective when such an operating speed is relatively low, for instance lower than the above cited value of approx. 2700 to 3000 rpm. Quite to the contrary, in view of minimizing friction, turbulent flow and, in general, in view of substantially reducing energy losses, it would be desirable that, in modern hermetically sealed compressors, the crankshaft, or driving shaft, be able to rotate at substantially reduced speeds, ie. below 2700 rpm. WO 93/22557, which is the basis for the introductory clause of claim 1, discloses a reciprocating compressor with oil pumping means including a helical-screw rotor which is driven by a rotating shaft and combines with an adjacent coaxial stator to define a pumping chamber dipped in a lubricant oil bath. The stator is mounted by means of support means in a roughly articulated manner that undesirably does not ensure accurate location of the stator in an axial alignment with the rotor, thereby affecting operation of the compressor. It is therefore a main purpose of the present invention to provide a hermetically sealed reciprocating compressor provided with a simply structured lubrication system which is particularly effective also at substantially reduced rotational speeds of the crankshaft or driving shaft. It is a further purpose of the present invention to provide a hermetically sealed compressor of the above cited kind, which comprises a lubrication system provided with particularly simple, low-cost and readily assemblable pumping means. According to the present invention, such aims are reached in a hermetically sealed reciprocating compressor provided with a lubrication system including the features as recited in the appended claims. The characteristics and the advantages of the present invention will be better understood from the description which is given below by way of non-limiting example with reference to the accompanying drawings in which: Figure 1 is a cut-away view of a partially cross-sectioned hermetically sealed reciprocating compressor according to the present invention; Figure 2 is an enlarged view of a detail of the compressor illustrated in Figure 1; Figure 3 is a side view of a detail of the illustration appearing in Figure 2, as rotated about its axis by approx. 30°; Figure 4 is a view of the section taken along the IV-IV line in Figure 3; Figure 5 is a view of the section taken along the V-V line in Figure 3; and Figure 6 is a view of the longitudinal section of the detail illustrated in Figure 3, in which a screw-like coaxial portion has been removed. With particular reference to Figures 1 and 2, the compressor is shown to mainly comprise a hermetically sealed casing 7 which houses at least a piston 8 adapted to slide with a reciprocating movement within a corresponding cylinder provided in a body 12 suspended with spring means within the casing 7. Said piston 8 is operated, through a connecting rod 10, by a substantially vertical crankshaft 9 provided with an inner axial cavity 11. The hermetically sealed compressor is provided with a system for ensuring appropriate lubrication to its moving parts, said system comprising an array of channels of a per sè known type, which are not shown in the drawing for reasons of greater simplicity of this description. Said lubrication system is supplied, through pumping means that will be described with greater detail farther on, from a bath of lubricant oil 13 collected on the bottom of the casing 7. According to a feature of the present invention, said pumping means comprise mainly a helical-screw rotor 14 which combines with an adjacent coaxial stator 15 to define a pumping chamber 16 drawing from said lubricant oil bath 13. More precisely, said stator 15 comprises substantially a bush having a cylindrical cavity in which the rotor 14 is inserted. The latter has an outside diameter that substantially corresponds to the diameter of the afore cited cylindrical cavity, which defines the pumping chamber 16 with the helical thread of the rotor 14. The lower end portion of the stator 15 and the rotor 14 is dipped in the lubricant oil bath 13. Referring now also to Figures 3 through to 6, the rotor 14 can be seen to be rotatably integral with the shaft 9. In a preferred manner, said rotor 14 extends axially upwards with a stem 17 that is connected to a surrounding cylindrical bush 18 by means of radial spokes 19. In a preferred manner, the rotor 14, the stem 17, the spokes 19 and the bush 18 are made as a single-piece construction of plastic material. Furthermore, the upper end portion of the bush 18 is preferably provided with grooves 20, such as for instance L-shaped grooves, which define two curvilinear, diametrically opposed elastic reeds 21. On the outer surface of each said reed 21 there is provided a stud or projection 22. The lower end portion of the bush 18 comprises an enlarged axial portion 23 which has a larger diameter both inside and outside. In particular, the inside diameter of said enlarged portion 23 is slightly larger than the outside diameter of the stator 15, while on its inner surface there is provided a female or similar thread 24, the winding direction of which is similar to the one of the rotor 14. The thread 24 combines with the outer wall of the stator 15 to form a corresponding channel substantially in the shape of a spiral. The rotor 14 can be readily and easily mounted on to the shaft 9 by inserting the bush 18 axially in the cavity 11 of the same shaft until the free end portion of the latter strikes against the enlarged portion 23 of the rotor. Furthermore, the mutual angular locking effect between the rotor 14 and the shaft 9 is created by the coupling of shapes between the studs 22 of the elastic reeds 21 and corresponding notches 25 provided in the inner surface of the crankshaft. The stator 15 is integrally provided with an outer collar 26 having a preferably curvilinear lower surface against which the correspondingly shaped edge 27 of an opening 28 provided in an appropriately shaped attachment bracket 29 abuts. The opposite ends of said bracket 29 are attached to the body 12 of the compressor by means of bolts 30 or similar fastening means. The stator 15 is inserted in a slack manner in the opening 28 of the bracket 29, by which it is supported axially in place in an articulated manner. As a result, the axis of the stator 15 can advantageously incline with respect to the vertical, so as to be able to make up for possible displacements or deviations of the suspended body 12 of the compressor and, as a result, to keep a precise alignment with the rotor 14 and the shaft 9. The angular locking of the stator 15 is ensured by outer radial ribs 31, or similar means, which get inserted axially, in a freely slidable manner, into corresponding notches provided on the edge 27 of the opening 28 of the support bracket. In practical operation, when the rotor 14 rotates together with the shaft 9, the lubricant oil bath 13 is drawn in by the helical-screw pumping means 14, 15 and is sent under pressure into the lubrication system of the compressor passing through the helical pumping chamber 16 via the hollow space comprised between the bush 18 and the stem 17, as well as along the cavity 11 of the shaft 9. The rotary motion of the rotor 14 creates a suction effect that causes the stator 15 to be lifted upwards, so that its upper end portion tends to abut against the inner top portion of the enlarged portion 23. As a result, any possible axial clearance existing between the stator 15 and the rotor 14 are hereby substantially eliminated automatically. In any case, possible lubricant oil seeping through into the thin hollow space comprised between the outer surface of the stator 15 and the inner wall of the enlarged portion 23 of the rotor is dynamically compensated by the thread 24 which, when the rotor 14 is rotating, gives rise to an hydraulic upward thrust in the above cited hollow space. In conclusion, any seepage of lubricant oil; which could lead to pressure losses in the lubrication system of the compressor, is thereby automatically avoided. As a result, the efficiency level of the pumping means 14, 15 is particularly high, so that the whole lubrication system of the compressor is particularly effective even at relatively low rotational speeds of the shaft 9. In fact, as it has been demonstrated also experimentally, the hermetically sealed reciprocating compressor according to the present invention is effectively lubricated even at rotational speeds of the shaft 9 situated in a range of approx. 1,000 to 1,200 rpm. Furthermore, the substantial simplicity of construction and assembly of the hermetically sealed reciprocating compressor according to the present invention can be clearly inferred from the above given description. It will be appreciated the the above described hermetically sealed compressor may be subject to a number of modifications without departing from the scope of the present invention.

Claims: Hermetically sealed reciprocating compressor comprising a hermetically sealed casing in which at least a piston is operable by a rotating shaft, an end portion of which rotatably drives pumping means adapted to supply a lubrication system of the compressor with lubricant oil from a lubricant oil bath contained in the casing, said pumping means including a helical-screw rotor (14) which is driven by said rotating shaft (9) and combines with an adjacent coaxial stator (15) to define a pumping chamber (16) dipped in said lubricant oil bath (13), the stator (15) being mounted in an articulated manner by means of support means (29), the stator (15) comprising a substantially cylindrical bush, characterized in that this bush is provided with an outer collar (26) having a curvilinear lower surface against which a correspondingly shaped edge (27) of an opening (28) provided in a support bracket (29) attached to the body (12) of the compressor abuts, said stator (15) being additionally provided with at least a radial rib (31) that gets inserted in an axially slidable manner in a corresponding notch provided in said shaped edge (27). Hermetically sealed reciprocating compressor according to claim 1, characterized in that said rotor (14) extends axially upwards with a stem (17) that is connected to a surrounding cylindrical bush (18) by means of spokes (19), the upper end portion of said bush (18) being snap-fitted to said end portion of the rotating shaft (9). Hermetically sealed reciprocating compressor according to claim 2, wherein the rotating shaft comprises an inner axial cavity, characterized in that the upper end portion of the bush (18) is inserted axially in said cavity (11) of the shaft (9) and comprises curvilinear elastic reeds (21) on the outer surface of which there are provided respective studs or similar projections (22) which get locked by the coupling of shapes into corresponding notches (25) provided in the inner surface of the rotating shaft (9). Hermetically sealed reciprocating compressor according to claim 2, characterized in that the lower end portion of the bush (18) comprises an enlarged axial portion (23) having a larger diameter both inside and outside, in the inner surface of which there is provided a female or similar thread (24) having the same winding direction as the helical-screw rotor (14) and combining with the outer wall of the stator (15) to form a corresponding spiral-shaped channel. Hermetically sealed reciprocating compressor according to claim 4, characterized in that said rotor (14), the stem (17), the spokes (19), the reeds (21) and said enlarged portion (23) are made in the form of a single-piece construction.

Inventors: RAFFIN LUCA, RAFFIN, LUCA
Applicants: ZANUSSI ELETTROMECC, ZANUSSI ELETTROMECCANICA S.P.A.
Application year: 1996
Main classification: F04B39
IPC codes: F04B39