Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-08-22
2003-12-23
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S233000, C310S237000, C310S236000
Reexamination Certificate
active
06667564
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a mechanically-commutated DC motor. In particular, it relates to a mechanically-commutated DC motor in which the stator assembly comprises the windings and the rotor assembly comprises the permanent magnet.
BACKGROUND OF THE INVENTION
A conventional DC brush motor
100
, shown in
FIG. 7
, gets its name from the brush commutation system, which includes stationary brushes and rotating commutator bars. In a permanent magnet DC brush motor, the stator assembly comprises the permanent magnet and the rotor assembly comprises the windings. The stator
110
of a permanent magnet DC motor will have two or more permanent magnet pole pieces
110
a
and
110
b
. The opposite polarities of the energized winding
102
and the stator magnets attract, causing the rotor to rotate until it is aligned with the stator
110
. Just as the rotor reaches alignment, the brushes
114
move across the commutator bars
112
and energize the next winding. The commutator bars
112
and brushes
114
result in the reversal of current being made automatically, so the rotor continues to turn in the same direction. The integrated commutation system results in permanent magnet DC brush motors being cost effective and easy to control.
A conventional DC brushless motor
100
′ is shown in FIG.
8
. Compared to a DC brush motor, a conventional DC brushless motor has an “inside-out” configuration. In other words, the permanent magnet
110
′ becomes the rotating part and the windings
102
′ are placed on the stator poles
110
′. Unlike a conventional DC brush motor, a DC brushless motor
100
′ cannot be driven by simply connecting it to a source of direct current. An electronic amplifier or driver
112
′ is used to perform the commutation electronically in response to low-level signals from an optical or hall-effect sensor
114
′. The current in the external circuit must be reversed at defined rotor positions. Hence, the DC brushless motor
100
′ is actually being driven by an alternating current through an electronic amplifier or driver
116
′, which is connected directly to a direct current source.
The “inside-out” configuration commonly used in DC brushless motors improves motor thermal characteristics and has better flux distribution, resulting in a better torque-to-mass ratio.
BRIEF SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide a mechanically-commutated DC motor having the cost effectiveness and ease of control of conventional DC brush motors and the improved motor thermal characteristics, flux distribution, and torque-to-mass ratio characteristics of conventional DC brushless motors.
This and other objects of the invention are achieved by the provision of a DC motor having a mechanical commutation system and an “inside-out” configuration, in which the stator assembly comprises the windings and the rotor assembly comprises the permanent magnet. The mechanically commutated DC motor comprises a rotor assembly, a stator assembly, a plurality of terminating conductive pads, and first and second stationary power supply terminals (one of which is positive and one of which is negative). The stator assembly includes a plurality of lamination stacks positioned around a central aperture, a plurality of coil bobbins each being positioned on a corresponding lamination stack, and a plurality of copper coils, each coil being wound on a corresponding bobbin. The rotor assembly includes a rotor body with a permanent magnet ring, a non-conductive timing cam integrated into one face of the rotor body, and a shaft. The rotor body is housed in the aperture of the stator assembly. The permanent magnet ring is radially magnetized in an alternating polarity pattern with at least one pair of poles.
The mechanical commutation system comprises the timing cam, the power supply terminals, and the conductive pads. In general, if there are c stator coils, there are a corresponding number c of conductive pads. Each conductive pad has first and second flexible, inwardly-extending contacts selectively movable into and out of electrical contact with the positive and negative power supply terminals, respectively, in response to the action of the timing cam.
In one aspect of the invention, the stator assembly has three coils connected in a delta configuration, and the rotor body has two magnetized pole pairs.
In another aspect of the invention, the two power supply terminals are concentric, centered on the rotational axis of the rotor assembly, and positioned facing the timing cam. The conductive pads are positioned circumferentially around the outer of the two power supply terminals, with the flexible contacts extending into the aperture of the stator body and being interposed between the timing cam and the power supply terminals. Adjacent ends of adjacent coils terminate on a common conductive pad, so that the ends of each coil terminate on two different conductive pads, and each conductive pad receives the ends of two different coils.
REFERENCES:
patent: 3426223 (1969-02-01), Vaughan
patent: 3566851 (1971-03-01), Pfrommer
patent: 4782255 (1988-11-01), Oosaka et al.
patent: 5283405 (1994-02-01), Nolte
patent: 5753990 (1998-05-01), Flynn et al.
patent: 5770902 (1998-06-01), Batten
“Brushless Motors”,Technology Handbook, Parker Automation Electromechanical Division, pp. A17-A19 (no date).
Bui Tanh M.
Du Bruce Q.
Mobley Jeffrey D.
Buehler Motor, Inc.
Jacobson & Holman PLLC
Mohandesi Iraj A.
Ramirez Nestor
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