Bearing shaft seal

Details Bearing shaft seal Bearing shaft seal

1999-05-19

2001-06-19

Mah, Chuck Y. (Department: 3626)

Seal for a joint or juncture

Seal between relatively movable parts

Close proximity seal

C277S421000

Reexamination Certificate

active

06247702

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a sealing assembly for inhibiting passage of particles or liquids between a shaft and an aperture through which the shaft extends. More particularly, the present invention relates to electric motors incorporating a sealing assembly to inhibit passage of external contaminants between a rotatably mounted shaft and a bore in an end frame of the motor through which the shaft extends. Even more particularly, the present invention relates to a labyrinthine bearing shaft seal assembly adapted to seal a passageway between a rotatably mounted shaft and a bore in an end frame of an electric motor in order to prevent passage of external contaminants through the passageway which contaminants could cause damage to motor bearings used to support the shaft or other internal components of the motor.
BACKGROUND OF THE INVENTION
Electric motors typically include a housing and a pair of end frames mounted on the respective ends of the housing. Each end frame includes a bearing for supporting a rotor shaft for rotation about an axis. It is generally desirable to provide a seal for the rotating shaft to prevent contaminants in the surrounding environment from working themselves into contact with the bearings and/or lubricant for the bearings. An important factor that contributes to the operating life of an electric motor is the operating life of the bearings used to support the rotor shaft. If contaminants such as, for example, water, dirt, debris, dust, etc., enter the bearing cavity or other internal cavities of the motor, the operation of the bearings could be adversely affected leading to premature failure of the bearings or of the motor itself. Bearing failures generally require costly repairs to an electric motor or may require replacement of the motor with an entirely new motor.
Electric motors contemplated for use according to the present invention are typically operable in outdoor environments wherein the outer components of the motor are subject to exposure to moisture, dirt, various contaminants or the like. In those situations, it is known to provide various sealing mechanisms between the rotating shaft and the end frame of the motor to prevent external contaminants, particularly water or other liquids, from moving axially along the shaft through the space between the rotating shaft and the end frame and into the interior of the motor housing.
This is also a significant problem for electric motors in pumps used for such things as swimming pools, hot tubs, waste water treatment facilities or other aquatic or fluid transporting/separating apparatuses. In these environments, there is typically provided a sealing device between the pump and the electric motor driving an impeller. On the impeller side of the sealing device, there is typically a fluid, such as water in a swimming pool, under pressure. If the sealing device fails or leaks, the pressurized fluid may be forced through the sealing device and splashed against an exposed outer wall or end frame of the motor through which the motor shaft normally extends. As a result, it is also desirable to have shaft seals in electric motors of this type.
There are several prior mechanisms for sealing an area between a shaft and an end frame of a motor through which the shaft passes. These prior sealing mechanisms include, for example: (1) maintaining a tight tolerance between the end frame and the rotating shaft; (2) positioning a single, generally flat, slinger washer on the rotating shaft near an outer surface of the end frame where the shaft extends through the end frame; or (3) utilizing a standard shaft lip seal assembly.
However, these prior sealing mechanisms either fail to provide adequate protection or, fail to extend motor operating life at a cost that is acceptable to the ultimate consumer.
SUMMARY OF THE INVENTION
Many problems exist with the prior sealing mechanisms. For example, it is difficult to manufacture and maintain a tight tolerance between the end frame and the rotating shaft extending therethrough. The clearance space between the rotating shaft and the stationary end frame must be small enough to prevent the penetration of contaminants, but large enough so that the rotating shaft does not contact the stationary end frame during operation. In addition, manufacturing and/or assembling a motor having such precise tolerance limitations is extremely expensive. This type of sealing mechanism is particularly unsatisfactory in preventing liquid contaminants from contaminating the internal workings of an electric motor.
In an effort to improve upon the mentioned tight tolerance sealing assembly, it is known to mount a single, generally flat, slinger washer on the rotating shaft near an outer surface of the end frame through which the shaft extends. Typically, such slingers are made of rubber. These single slingers may take on any number of different sizes or shapes depending on a manufacturer's preferred method of construction or assembly. Although this solution eliminates the necessity for maintaining a tight tolerance between the shaft and the end frame as required by the tight tolerance sealing method, it has been found that external contaminants, particularly liquid contaminants such as water, are able to easily pass over the outermost periphery of the slinger, travel down a surface of the slinger exposed between the slinger and the end frame and migrate axially along the rotating shaft through the space between the rotating shaft and the end frame, thereby contaminating various internal components of the motor. Stated differently, the prior single slinger seal design does not provide a complex labyrinthine path for the external contaminants to travel. Once the external contaminants pass over or around the outermost edge of the slinger, the travel path of the contaminants does not appreciably change before the contaminants are allowed to gain access to the inside of the motor along the axially extending shaft.
In the other type of known seal, a low-friction lip seal made of a rubber-type material, a thermo plastic material, or even a silicon or graphite-type material is fixed to the end frame of a motor around the rotor shaft such that at least a portion of the lip seal rubs or comes into contact with the outer surface of the rotating shaft. The rubbing action between the lip seal and the shaft eliminates the clearance space between the shaft and the end frame; however, the lip seal also creates a frictional drag on the rotating shaft. In order to prevent external contamination, the lip seal must be of sufficient strength and rigidity to keep the gap closed between the shaft and the end frame. The greater the seal, the greater the motor strength that is needed to overcome the frictional drag created between the shaft and the lip seal. Also, the greater the frictional drag, the greater the overall efficiency of the motor will be undesirably affected.
Accordingly, the invention provides a bearing shaft seal or sealing assembly for an apparatus which includes a shaft extending through a hole in the apparatus, such as, for example, an electric motor. The bearing shaft seal is positioned around a shaft of the motor adjacent to an end frame of the motor through which the shaft extends so as to seal off a clearance space created between the shaft and the end frame. In this way, the sealing assembly according to the present invention effectively closes the clearance space or passageway between the shaft and the end frame to protect the internal cavities of the motor, particularly, a bearing cavity, from undesirable contamination from external influences such as dirt, dust, debris, liquid, etc.
According to one embodiment, the sealing assembly includes a first sealing member or slinger washer, a second sealing member or an expansion plug and, preferably, a third sealing member or a second slinger washer all of which are properly positioned within or near an end frame of, e.g., a motor. In a preferred embodiment, a weep hole or drainage slot is appropriately located

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