Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-05-24
2002-07-09
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S085000, C310S089000, C310S090000, C310S233000, C310S088000
Reexamination Certificate
active
06417595
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of permanent magnet motors, wound field motors, and other mechanically commutated motor devices. In particular, this invention relates to direct current and universal motors having close tolerance seals for the suppression of sparks and leakage current losses within the motors.
BACKGROUND OF THE INVENTION
Various permanent magnet motors and wound field motors must be operable in volatile environments. Examples of permanent magnet and wound field motors include direct current (“DC”) and universal motors. DC and universal motors produce sparks by the contact of a conductive brush and a commutator. In a volatile environment, the sparks produced by the conductive brush and commutator may produce flammable activity.
Additionally, a DC or universal motor that is totally sealed for controlling sparks from being released into ambient air does not have forced air flowing through the internal components of the motor. A motor that is cooled by forced airflow through the motor is normally smaller and manufactured with less materials than a similar motor that is designed to be totally enclosed.
Further, in a totally sealed DC or universal motor, the shaft and bearing of an electric motor are normally grounded, and the commutator and conductive brushes are at a high potential. The conductive brushes are in contact with the commutator of the electric motor and carbon dust from the brushes coat the surface between the bearing and the brushes. In turn, the carbon brush dust causes a leakage current loss within the system.
A DC motor is generally a lower speed motor that includes various components such as an armature, a commutator or collector and conductive brushes that are well known in the art of electric motors. The armature of a DC motor includes a cylindrical iron core that carries the active conductors embedded in slots of the iron core and connected to segments of the commutator. Direct current is carried to and from the armature by stationary conductive brushes. The rotating commutator automatically switches or distributes current to the conductors so that the magnetic flux and subsequent torque of a motor is steady and in one direction. Further, a DC motor includes a permanent magnet that is utilized for the stationary magnetic field, but there is a minimal space between the permanent magnet and the armature. Due to the minimal space, there is a negligible amount of cooling in the interior of the DC motor. Thus, in order to cool the interior of a DC motor in an aggressive manner, air must be brought into the motor, and then expelled from the motor.
A universal motor is a relatively high speed motor in which the speed can be varied. A universal motor is designed to operate on direct or alternating current. Further, a universal motor includes a laminated magnetic circuit to minimize eddy-current and hysteresis losses. Similar to a DC motor, the universal motor has minimal space in the interior of the motor. Thus, it is preferred to cool the interior of the motor by having air brought into the motor and then expelled from the motor.
An example of an industry that utilizes DC and universal motors in the pump assembly is the consumer, professional and industrial painting industry. In the painting industry, liquid paint is pumped via a DC or universal motor from its holding source. Upon the paint being pumped by the motor, the paint flows through a fluid filter and is released through a nozzle onto the working surface.
A major component of the paint spraying system is the pump that is powered by a DC or universal motor. Although induction alternating current motors and gasoline powered engines are utilized, DC and universal motors are preferred in the industrial paint spraying system because these types of motors are less bulky, lighter, more efficient, and less noisy than a gasoline powered engine. Further, DC or universal motors have higher starting torques, higher acceleration rates, and can be speed controlled more easily then alternating current motors.
A problem exists when a paint spraying system is utilized in a chemically volatile environment. DC and universal motors produce sparks by the electrical and mechanical contact of the conductive brushes and commutator. In a volatile environment, the sparks produced by the contact of the conductive brushes and commutator may produce flammable activity. In such a situation, a fully enclosed electric motor may be necessary to prohibit the sparking within the electric motor from producing flammable activity.
In prior art electric motors, a solution was to provide a motor casing for enclosing the entire motor assembly. The prior motors provided a labyrinth seal to isolate sparks produced within the cavity from ambient atmosphere surrounding the motor housing. The prior motors also provided an enclosed motor assembly that cooled the motor assembly by an internal fan within the housing.
The prior art electric motors do not disclose a separately shielded or enclosed compartment for sealing the commutator and conductive brushes while effectively cooling the other components of the motor assembly. Additionally, such known devices have heretofore not provided a simple, efficient and cost effective motor configuration that provides adequate spark protection while maintaining proper cooling of the motor assembly. The totally enclosed motor housing configurations are relatively expensive to produce. Further, a simple cost-effective approach has heretofore not been devised for adequately enclosing the commutator and conductive brush assemblies where sparking is initiated within the motor.
A further problem exists within the sealed or enclosed compartment for sealing the commutator and conductive brushes. As previously disclosed, the electric motor includes a commutator, conductive brushes and a bearing for shaft rotation. As the conductive brushes begin to wear, a byproduct of carbon dust is released within the sealed and enclosed commutator assembly. The carbon dust deposits within the sealed commutator assembly. After an extended period of time, the carbon dust eventually provides a leakage current path between, the energized conductive brushes and commutator surface, and the grounded metal shaft and bearing. As a result, leakage current losses are present in the system.
Prior art motors do not disclose a single component close tolerance seal between, the grounded bearing and shaft and the energized conductive brushes and commutator. Accordingly, the carbon dust formed within commutator assembly induces a leakage current path within the system.
Therefore, a need exists for a simple, but yet effective spark suppression motor apparatus that is relatively inexpensive to manufacture. Additionally, a need exists for an electric motor that is effective in preventing sparking within the motor assembly, but yet provides the required cooling of the motor assembly. Further, there is a need for a close fitting shield around the conductive brushes and commutator that minimizes the internal volume of the commutator assembly in order to keep internal flammable activity to a minimum. A need also exists for a close tolerance fit between the commutator seal and the commutator in order to prevent the spread of any spark or flame to the external atmosphere. Moreover, a need exists for a close tolerance seal that alleviates leakage current losses within the electric motor.
SUMMARY OF THE INVENTION
In one aspect of the present invention, an electric motor is provided. A component of the electric motor, the commutator assembly, includes a commutator and a brush assembly. The brush assembly encloses conductive brushes that are in contact with the commutator. A shaft is rotatably mounted about an axis, and a bearing is disposed around the shaft. The commutator is connected to the shaft. Additionally, a seal surrounds the commutator, wherein the seal substantially isolates the commutator assembly from the internal ambient atmosphere of the electric motor.
In another aspect of the present invention,
McMillan Electric Company
Merchant & Gould P.C.
Mullins Burton S.
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