Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-03-09
2001-10-09
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S071000, C310S0400MM, C310S089000, C310S06800R, C310S239000, C310S072000
Reexamination Certificate
active
06300696
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to small electric motors and in particular, to the end cap assembly for an electric motor of a direct current permanent magnet stator type.
RELATED ART
It is often desired to reduce the amount of electrical noise generated by an electric motor. This is done by adding a capacitor or other electronic components to the motor circuit. Typically, a capacitor is connected between the motor terminals and because of their size, the capacitor is mounted on the outside of the motor where it is subject to physical damage. With the advent of chip-type capacitors, it has been possible to fit the capacitor to the inside of the motor end cap. One such arrangement is shown in EP 0607032 A1 where a chip capacitor is pressed into contact with a motor terminal by a conductive spring bearing against the other terminal, like a battery in a torch. While this is very simple, it does require the assembly of the chip and the spring into a slot in the end cap.
SUMMARY OF THE INVENTION
The present invention aims to simplify assembly even further by eliminating the need for the separate spring. Certain embodiments build upon the compact nature of the end cap by incorporating further noise suppression or motor protection devices such as chokes, surge suppressors and overcurrent/overtemperature protection devices.
Accordingly, the present invention provides a miniature electric motor comprising a housing having an open end; a permanent magnet stator fitted to the housing; a rotor having an armature and a commutator; an end cap engaging the open end of the housing; two brush assemblies supported by the end cap and including brushes in sliding contact with the commutator; two motor terminals connected to the brush assemblies and supported by the end cap; bearings supporting the rotor for rotation in the housing; and a chip capacitor supported by the end cap; wherein resilient contact means integral with the motor terminals directly engage respective side portions of terminal ends of the chip capacitor.
Preferably, the chip capacitor is disposed in a groove in the end cap. The use of a groove helps to locate the capacitor during assembly.
Preferably, the resilient contact means are fingers. The use of fingers extending from the motor terminals and engaging a side of the respective terminal ends of the chip capacitor has the advantage of being less sensitive to variations in the length of the chip as while the thickness of the chip is controlled, the length can vary significantly due to manufacturing tolerances.
Preferably, the fingers of the motor terminals engage an outer longitudinal edge of the terminal ends of the chip capacitor. If the capacitor is disposed in a groove in the end cap this will cause the chip capacitor to pivot within the groove and partially blocking the groove thereby making resilient contact with the capacitor and retaining it within the groove.
Preferably, the end cap assembly includes a choke connected between one brush terminal and one motor terminal.
Preferably, the end cap assembly includes a positive temperature coefficient thermistor connected between one motor terminal and one brush assembly.
Preferably, the motor terminals are female terminals supported by respective terminal posts integral with the end cap. Female terminals make for a more compact motor but add considerably to the space constraints within the end cap.
Preferably, the terminal posts are substantially triangular in section. This arrangement allows the contact portion of the motor terminal a wide range of resilient movement while supporting it against excessive movement which would deform the terminal.
Preferably, the motor housing and end cap have two flat sides connected by two arcuate sides and the motor terminals are located along one of the flat sides. Alternatively, the motor terminals may be located along one of the arcuate sides of the end cap assembly.
REFERENCES:
patent: 4613781 (1986-09-01), Sanders
patent: 5196750 (1993-03-01), Strobl
patent: 5281876 (1994-01-01), Sato
patent: 5563462 (1996-10-01), Strobl et al.
patent: 5598045 (1997-01-01), Ohtake et al.
patent: 5600193 (1997-02-01), Matsushima et al.
patent: 5633542 (1997-05-01), Yuhi et al.
patent: 5942819 (1999-08-01), Burgess et al.
patent: 4430225A (1995-06-01), None
patent: 0509683A (1992-10-01), None
patent: 0607032A (1994-07-01), None
patent: 0607032A1 (1994-07-01), None
patent: 2330954A (1999-05-01), None
patent: A8-0064405 (1996-03-01), None
Johnson Electric S.A.
Mullins Burton S.
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