Rotary expansible chamber devices – Heat exchange or non-working fluid lubricating or sealing – Non-working fluid passage in inner working or reacting member
Reexamination Certificate
1999-04-19
2001-02-20
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Heat exchange or non-working fluid lubricating or sealing
Non-working fluid passage in inner working or reacting member
C418S088000, C418S097000, C418S098000, C418S060000, C418S188000
Reexamination Certificate
active
06190149
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to vacuum pumps having integrally mounted oil pumps for supplying oil for lubricating shaft bearings and sealing the pump piston(s).
BACKGROUND OF THE INVENTION
Vacuum pumps are widely used across a broad spectrum of industrial applications including, for example, the manufacture of vacuum coated automotive products, the environmental testing of spacecraft, chemical manufacturing process applications and biological and medical research.
Typical mechanical vacuum pumps have some form of piston which reciprocates or rotates within a cylinder to effect the removal of gas from a chamber or vessel to which the pump intake is connected. Large capacity pumps may have multiple piston-cylinder combinations. The piston or pistons are commonly driven by a shaft mounted on bearings within the vacuum pump. The bearings and pistons must constantly be kept lubricated to avoid problems caused by excessive friction between moving parts such as excessive wear, piston overheating leading to piston seizure and bearing overheating leading to bearing failure. Lubricating oil is commonly used to lubricate the moving parts of the vacuum pump. The lubricating oil also serves a second function in that it forms the necessary gas tight seal between the piston and cylinder ensuring that the gas displaced by the vacuum pump piston(s) does not leak back across the piston-cylinder interface from the high pressure side to the low pressure side of the pump.
A known method for supplying sealing/lubricating oil to shaft bearings and the piston and cylinder is by a combination of gravity feed, centrifugal force and differential pressure. An oil reservoir from which oil flows under gravity is positioned immediately above the pump. Oil lines connect the reservoir to the end caps of the vacuum pump where oil flows into the cylinders through two paths: (1) through the bearings and thence through metering rings; and (2) through oil feed ducts in the vacuum pump side covers. Where a center shaft bearing is provided, oil to one of the end caps is also conducted through a longitudinal axial passage in the shaft connected to an extended port opening onto the bearing.
The natural oil flow from the reservoir is augmented by maintaining the reservoir at atmospheric pressure and conducting the oil into the cylinder of the pump when it is under vacuum and after the oil has lubricated the bearings or other moving parts. Thus, the oil tends to flow through the pump under gravity, the centrifugal force of the rotating shaft and is also forced through the pump by a pressure differential between the reservoir and the pump cylinder. The oil is expelled from the cylinder along with the gas displaced by the vacuum pump piston(s). The gas/oil mixture passes through a separator where the oil is separated from the gas and the oil is returned to the reservoir while the gas is expelled to the atmosphere.
Although this oil distribution system has proved practical under many circumstances, there are conditions wherein the gravity/differential pressure system of lubrication does not supply sufficient oil to effectively lubricate the bearings and seal the piston(s) of the vacuum pump.
As an example, when a vacuum pump is evacuating a relatively large vessel, such as a large vacuum chamber capable of holding a spacecraft for vacuum testing, oil distribution can be a problem. During an initial period of operation of the pump, there will be almost no pressure difference between the cylinder pressure and the atmospheric pressure in the reservoir, thus, there will be no pressure differential augmenting the oil flow from the reservoir. This situation is due to the relatively small volume of the cylinder compared with the much larger chamber volume. Each stroke or rotation of the piston removes a relatively small volume of gas from the chamber, and it may take several minutes, depending upon the chamber size, before any appreciable pressure differential is realized within the chamber and the cylinder. During this initial phase of vacuum pump operation, the oil flows only under gravity and not by any pressure differential. Adequate oil for lubrication and piston/cylinder sealing may not be obtainable under gravity flow alone, leading to increased wear of pump parts and shorter pump life. Catastrophic pump failure could also result in the form of a piston seizure or bearing failure.
Another example is when pressure in the reservoir is reduced by an auxiliary vacuum pump to remove volatile process materials that collect in the oil. If not removed from the oil in the reservoir, the volatile materials re-expand in the cylinders, increasing cylinder pressure above the desired level. The volatiles may also adversely affect the lubricating qualities of the oil. Reduction of reservoir pressure, however, removes the differential pressure component that induces oil flow.
One method of supplying adequate sealing and lubricating oil to vacuum pump pistons and bearings is to use an auxiliary oil pump. Such oil distribution systems are effected by mounting an oil pump on the outside of the vacuum pump housing to pump oil from the reservoir to the bearings and pistons. Such oil pump configurations typically require complicated plumbing, valving and manifolds which drive up the purchase cost of the vacuum pump, as well as the maintenance and operating costs.
SUMMARY AND OBJECTS OF THE INVENTION
The invention concerns an oil distribution system having an integral oil pump for distributing sealing and lubricating oil to pistons, bearings and other components within a vacuum pump or other machine. The invention comprises a shaft rotatably mounted on a bearing, which is preferably the main drive shaft of a vacuum pump. The shaft has a longitudinal passage which extends from one end at least to a point adjacent to a bearing. A port extends from the passage and exits the shaft adjacent to the bearing. An oil pump is positioned within the vacuum pump adjacent to the end of the shaft from which the passage extends. The oil pump is operatively connected to the shaft by means which permit the shaft to drive the oil pump when the shaft rotates. The oil pump has an inlet for admitting oil and an outlet which is connected to the passage within the shaft. When the shaft turns, it drives the oil pump which pumps the oil supplied to the inlet into the passage of the shaft. The oil travels down the shaft and exits through the port, contacting and thereby lubricating the adjacent bearing. The oil then passes through a metering ring arranged adjacent to the bearing between the bearing and the cylinder and enters the cylinder where it performs its sealing function. A parallel oil feed duct is also provided which communicates between the port and the cylinder. Oil exiting the port is also conducted through the oil feed duct directly into the cylinder to ensure that an adequate supply of oil is provided for sealing the piston/cylinder interface and lubricating the pistons.
In one embodiment of the invention, the oil pump is a vane-type pump having a housing which forms a chamber having a cylindrical sidewall. The oil inlet is disposed in the housing. An eccentric rotor is connected to the shaft and rotates within the housing chamber. The rotor has a sliding vane which extends from the rotor in sealing contact with the chamber sidewall. The outlet is arranged concentrically within the rotor and communicates between the chamber and the shaft passage. Oil supplied to the inlet is drawn into the chamber as the rotor turns and forced out through the outlet into the passage. The oil travels through the passage and exits the port to lubricate the bearing and seal the piston, as described above.
In the presently preferred embodiment, a gerotortype oil pump is used. The gerotor pump has a housing forming a chamber and is mounted adjacent to the end of the shaft from which the passage extends. The oil inlet is disposed within the housing and communicates with the chamber. An outer rotor is mounted within the chamber for rotational motion about an axis
Denion Thomas
Stokes Vacuum Inc.
Synnestvedt & Lechner LLP
Trieu Theresa
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