Centrifugal oil pump for a variable speed hermetic compressor

Details Centrifugal oil pump for a variable speed hermetic compressor Centrifugal oil pump for a variable speed hermetic compressor

1996-04-18

1998-01-13

Freay, Charles G.

Pumps

Motor driven

Electric or magnetic motor

4174241, 418 94, F04B 3504, F01C 2104

Patent

active

057072205

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention refers to an oil pump for variable speed hermetic compressors of the reciprocating type, particularly those having a vertical shaft and used in refrigerators and freezers.


BACKGROUND OF THE INVENTION

These appliances require that their respective hermetic compressors supply the exact refrigerating capacity necessary to remove the internal heat from the medium to be refrigerated. As the refrigerating capacity is proportional to the flow of the refrigerant mass pumped by the compressor, a variation of the refrigerating capacity is related to a variation of the mass flow pumped by the compressor. A technique of continuously obtaining said variation in the refrigerant mass flow is by varying the motor speed.
There are studies indicating that the variable speed compressors need an operative range from 15Hz to 100Hz, i.e., speeds between 900 and 6000 rpm, in order to achieve a good refrigerating performance. Such speed variation affects the mechanical operation of the compressor, especially the operation of the oil pump, which conducts the oil to the bearings of the compressor mechanism and other regions in need of lubrication, such as the connecting rod and piston.
Centrifugal pumps are the oil pumping mechanisms most used in hermetic compressors, both for their relatively low cost and adequate operation in 3000 rpm up to 3600 rpm rotation range, which result from the frequency of the electrical network. Nevertheless, such mechanisms become inoperative at low rotation speeds.
Conventional oil pumps of the centrifugal type, such as the one illustrated in FIG. 1 and presently in use, are not capable of pumping the oil to the bearings when the compressor needs to operate at low speeds.
The operative limitations of the centrifugal pump are related to the difference between its larger radius (R) and its smaller radius (r), as shown in the equation below, which governs the behavior of the centrifugal pump: bearings; g is the gravitational constant; R is the larger radius of the pump; r is the smaller radius; and .omega. is the angular speed (rd/sec). The search for an increase in the oil pumping efficiency in such compressors by simply increasing the larger radius (R) of the pump is unfeasible, because such increase, which is necessarily substantial to achieve the desired pumping, also affects the external diameter of the compressor shaft and, consequently, all of the manufacturing processes of the compressor and the performance thereof, since it causes greater losses due to friction. It should be observed that small diameter alterations are not enough to achieve the necessary degree of centrifugal pumping at rotational speeds close to or lower than 900 rpm.
Conventional centrifugal pumps which have a vertical or a horizontal shaft are widely used in hermetic compressors, as evidenced by the patent documents U.S. Pat. No. 4,478,559; U.S. Pat. No. 4,569,639; DT 209,877 and FR 2,492,471. Nevertheless, said centrifugal pumps do not work, or work inefficiently, at rotational speeds lower than about 900 rpm.
In another solution, described in a copending patent application of the same applicant, the increase in the pumping efficiency is achieved through a pump rotor having ascending helical grooves which are provided along a portion of the outer surface of the longitudinal extension of said rotor. This solution, though presenting an efficient lubrication at rotational speeds (600 rpm) lower than those reached with conventional oil pumps, achieves its pumping effect by mechanically moving the oil along the helical grooves of the pump rotor.


OBJECT OF THE INVENTION

Thus, it is an object of the present invention to provide a centrifugal type oil pump for variable speed reciprocating hermetic compressors having a vertical shaft, in which the pumping performance is similar to that obtained with pumps using mechanical movement of the oil at low rotational speeds, e.g., about 600 rpm.
A second object of the present invention is to provide an oil pump as mentioned above, whose pu

REFERENCES:
patent: 3184157 (1965-05-01), Galin
patent: 4792296 (1988-12-01), Kobayashi et al.
patent: 5007808 (1991-04-01), Fraser et al.
patent: 5176506 (1993-01-01), Siebel
patent: 5377781 (1995-01-01), Yun

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