Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-03-17
2001-01-23
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C384S471000, C384S479000, C384S486000
Reexamination Certificate
active
06177744
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of electric motors and seals for such motors. More particularly, the invention relates to a novel arrangement for maintaining lubricant, such as oil mist, within a bearing cavity to supply continuous lubrication to rotor bearings during operation of the motor, and for enhancing sealing of regions within which the rotor bearings are disposed.
2. Description of the Related Art
A wide variety of electric motors are available and are currently in use throughout a range of industrial applications. In general, such motors include a stator provided in a motor housing, and a rotor surrounded at least partially by the stator and supported for rotation within the housing. The stator and rotor may be mechanically and electrically configured in various manners, depending upon the application, the power available to drive the motor, and so forth. In general, however, electric power is applied to the stator and the rotor is thereby driven in rotation to produce rotary motion and transmit mechanical power via an output shaft which may be coupled to a driven load.
In conventional electric motors the rotor and output shaft are most often supported by anti-friction bearings on either end of the motor housing. Depending upon the size of the motor and the anticipated loading, the rotor and shaft support bearings may be journal bearings, needle bearings, roller bearings, ball bearings, and so forth. To prolong the useful life of the rotor bearings, it is commonplace to equip the motor with a means for lubricating the bearing elements during operation. For example, the bearings may be provided with a synthetic or mineral grease or oil which coats surfaces of the bearing elements and which may preclude the ingress of contaminants, such as dirt, debris, moisture, and so forth into the bearing. In other applications, a pressurized oil mist may be circulated through a bearing cavity to provide continuous lubrication of the bearing and to similarly prevent the ingress of contaminants, while flushing the bearing cavity of contaminants and moisture.
A difficulty which arises in oil mist-lubricated motor bearings involves the escape of oil mist into the motor housing and outwardly into the atmosphere surrounding the motor. In particular, in totally-enclosed, fan-cooled motors, a negative pressure may be created within the motor housing due to the circulation of air through the housing under the influence of a fan mounted on the rotor shaft. In many applications no seal is used to retain the oil mist within the bearing cavity. Even where seals are employed these are typically provided for preventing the ingress of contaminants and moisture into the bearing cavity, often inadvertently facilitating the conveyance of oil mist from the bearing cavity into the motor enclosure.
Other difficulties in sealing anti-friction bearings installed on electric motor shafts arise from the relative speeds between the sealing elements and the rotating elements, typically the shaft itself. In particular, while certain sealing arrangements may be employed to isolate inner bearing cavities from ambient air and from the inner volume of the electric motor housings, the use of such seals is typically limited by the relative surface velocity of the rotating and non-rotating elements. In particular, seals designed to ride on rotating shafts or other rotating elements secured to the shafts may require certain relative velocities in order to maintain an adequate seal. In certain applications, the motor shaft must be increased in size to provide sufficient velocity to maintain the desired seal, despite the fact that the oversized dimensions of the shaft are not necessary for transmitting anticipated torque levels. However, where such velocities become excessive, the seal life may be significantly reduced due to heating caused by friction between the seal and the rotating member. Moreover, depending upon the motor design and its rated speed, the same sealing arrangements may not be applicable due to the increased speed of the motor (e.g., two-pole speeds of 3600 rpm in 60 Hertz electrical supply systems).
There is a need, therefore, for an improved technique for providing a seal adjacent to a motor bearing which is effective at maintaining an oil mist or similar lubricant within the environment of the bearing, while also inhibiting the ingress of contamination and moisture into the vicinity of the bearing. In particular, there is a need for a sealing technique for motor bearings which can be both installed on new motors as well as retrofitted on existing motors in which such lubricant systems are employed. There is also a particular need for a sealing technique for motor bearings which provides an enhanced sealing capability despite the particular speed of the rotor shaft, and that avoids or reduces the tendency of the shaft seal to overheat due to high relative surface speeds during operation.
SUMMARY OF THE INVENTION
The invention provides a novel technique for sealing a lubricant within a region of an electric motor designed to respond to these needs. The invention is particularly well suited for use in motors, such as totally-enclosed, fan-cooled motors, wherein an air-born lubricant in the vicinity of a bearing may be drawn or sucked into the motor enclosure during operation. The technique employs seals which may be retrofitted to existing motors to enhance their performance, or which may be designed into new machines. The seals may have a relaxed fit about the rotor shaft as compared to existing shaft seals, reducing the tendency to wear either the shaft or the seal during operation. The sealing force exerted by the seal is enhanced by the pressure of the lubricant system, providing improved sealing, even at a range of shaft speeds.
Thus, in accordance with a first aspect of the invention, a seal assembly is provided for isolating a rotor bearing lubricated by a pressurized lubricating medium. The seal assembly isolates the bearing from an ambient region. The rotor bearing is disposed between a stationary member and a rotating member. The pressurized lubricating medium is provided to the bearing at a first pressure higher than a second pressure in the ambient region. The seal assembly includes a support portion and a riding portion. The support portion is adapted to be secured to the stationary member. The riding portion extends from the support portion towards the bearing. The riding portion is configured to ride against the rotating member during rotation of the rotating member and to apply sealing force against the rotating member. The riding portion includes a pressure application region configured to be exposed to the first pressure during operation. The sealing force is produced at least partially by application of the first pressure against the pressure application region. The sealing force is thus enhanced by the pressure of the lubricating medium. In accordance with a particularly preferred configuration, the lubricating medium continuously flows through the cavity in which the bearing is supported.
In accordance with another aspect of the invention, a seal arrangement is provided for an electric motor bearing. Electric motor includes a stationary housing and a rotor rotatably supported within the housing by the bearing. The bearing is disposed in a bearing cavity defined at least partially by the housing and the rotor. The housing includes a fluid path for continuously circulating a lubricant through the bearing cavity at an internal pressure higher than ambient pressure. The seal arrangement includes first and second seals disposed about the rotor shaft. The first seal has a first support portion and a first riding portion. The first support portion is supported in the housing and the first riding portion extends from the first support portion to contact a first region of the rotor. The first riding portion thus exerts a sealing force against a first region to seal the bearing cavity. The second seal has a second
Paschall T. Wayne
Subler William L.
Trickel Harvey A.
Dinh Le Dang
Gerasimow A. M.
Horn John J.
Ramirez Nestor
Reliance Electric Technologies LLC
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