Lubrication – Systems – Vertical shaft
Patent
1997-03-24
1998-06-09
Denion, Thomas E.
Lubrication
Systems
Vertical shaft
184 616, 184 12, 184 63, 310 54, 310 90, F01M 100
Patent
active
057621640
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
1. Field of the Invention
The present invention refers to an oil pump for variable speed hermetic compressors of the reciprocating type, and more particularly, those having a vertical shaft and used in refrigerators and freezers.
2. Background of the Invention
Refrigeration 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 refrigerant mass pumped by the compressor, the refrigerating capacity is varied by changing the mass flow pumped by the compressor. A common technique of continuously obtaining variations in mass flow employs varying the compressor motor speed.
There are studies indicating that variable speed compressors require an operative range from 15 Hz to 100 Hz, i.e., between 900 and 6000 rpm, in order to achieve good refrigerating performance. Such speed variations affect the mechanical operation of the compressor, specially the operation of the oil pump, which conducts oil to the bearings of the compressor mechanism and other regions requiring lubrication, such as the connecting rod and piston.
Centrifugal pumps are the most common oil pumping mechanisms used in hermetic compressors, both for their low cost and adequate operation in the range of from 3000 to 3600 rpm, which results from the frequency of the electrical network. Nevertheless, such mechanisms become inoperative at low rotational 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 operates 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 can be seen 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 "" is the angular speed (rad/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 an increase, which must be substantial to achieve the desired pumping characteristics, also affects the external diameter of the compressor shaft and, consequently, the manufacturing process for the compressor and the performance thereof caused by greater losses due to friction. It should be observed that small diameter alterations are not sufficient to achieve the necessary degree of centrifugal pumping at rotational speeds close to or less than 900 rpm.
Conventional centrifugal pumps which utilize a vertical or horizontal shaft and are widely used in hermetic compressors, are disclosed in U.S. Pat. No. 4,478,559 and U.S. Pat. No. 4,569,639; and DT 209,877 pumps are inoperable, or work inefficiently, at rotational speeds less than about 900 rpm.
U.S. Pat. No. 4,097,185 describes a centrifugal pump, which operates in stages and through which the whirl of oil at the bottom of the compressor sump can be reduced. A lower cavity in the pump allows the oil intake to the pump and its smaller radius (r) as a function of the desired oil flow. As this smaller radius (r) increases, the performance of the pump is reduced.
Other forms of centrifugal pumps are described in patent documents DT 209,936 and DT 2,502,567. These pump configurations use a blade that is press fitted into the pump shaft and function as an impeller for the oil.
The patent FR 2,204,233 describes a conventional centrifugal pump, which is mounted to an eccentric shaft of a compressor. The pump mechanism is disposed at the lower part of the compressor body, and the motor is disposed at the upper part. This configuration allows the oil to be pumped at a slightly lower rotation speed, due to a reduction in the required pumping height. Nevertheless, the minimum rotation speed still remains much higher than the desired mini
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Krueger Manfred
Lilie Dietmar Erich Bernhard
Denion Thomas E.
Empresa Brasileira de Compressores S/A - Embraco
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