Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-05-25
2001-07-03
Hofsass, Jeffery (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S679000
Reexamination Certificate
active
06255955
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to electric motors and, more particularly, to a brush warning indicator in an electric motor.
Electric motors typically are devices which convert electric energy into mechanical energy through the utilization of magnetic fields. Direct current electric motors utilize carbon brushes to transfer an electrical current between an external source and rotating commutators mounted on an armature of a rotor mounted in the motor.
The armature includes armature coils connected to two commutator bars. The electrical current flows through the carbon brushes into the contacting commutators and armature coils. The electrical current induces a magnetic field in the armature. Magnets in the frame of the motor generate magnetic fields which repel/attract fields in the armature. The direction of the current flowing through the armature is constantly changing, resulting in a constantly changing magnetic field. This change of current flow causes the rotor to rotate and produce mechanical energy.
The brushes are held in contact with the commutator using mechanical springs. As brushes wear beyond a point of minimum brush spring force, the springs may no longer maintain the brushes in contact with the commutator. It is known to utilize brush wear indicators to signal the need for brush replacement. Typically, such indicators include limit switches or leads inserted into the brush, to signal when the brush is worn beyond a predetermined point of wear and should be replaced. A voltage equal to the armature voltage can then be detected at an output terminal of a limit switch or lead, to indicate that the brush should be replaced.
These known brush wear indicators increase the cost and complexity of electric motors. Further, the utilization of switches activated by brush spring movement may fail or malfunction due to the complexity of these indicators. In addition, indicators that utilize leads inserted into the brush are typically metallic and may contact the commutator and result in metal on metal structural damage.
Accordingly, it would be desirable to decrease the cost of a brush warning indicator. Additionally, it would be desirable to decrease the complexity of the brush warning indicator.
BRIEF SUMMARY OF THE INVENTION
In an exemplary embodiment of the invention, a brush warning indicator includes four contact springs and four brushes. Each contact spring is in contact with a respective brush in a brush holder attached to a brush yoke. When the brush moves beyond a predetermined point, each contact spring contacts a respective brush holder rivet. Contact with the rivet generates a voltage in the contact spring which is equal to the brush voltage. A terminal, connected to the contact spring, relays the voltage to a remote location which indicates that the brush is worn out and should be replaced.
The contact spring allows for an increased reliability of the brush warning indicator. Each contact spring is attached to the existing brush yoke with the terminal. In addition, each contact spring is inserted through respective openings in the brush yoke to provide contact with the respective brushes.
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Armstrong Teasdale LLP
General Electric Company
Hofsass Jeffery
Horton Esq. Carl B.
Tang Son
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