Internally loaded universal motor

Details Internally loaded universal motor Internally loaded universal motor

2000-08-11

2002-06-25

Tamai, Karl (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S077000, C310S093000, C310S051000

Reexamination Certificate

active

06411004

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a universal motor. More specifically, the present invention discloses a universal motor that has an internal load for preventing excessive rotation of the motor when the motor has a light external load.
2. Description of the Prior Art
Universal motors are electric motors that, because of their ability to accept both AC and DC power sources, can be found quite readily in the market place, such as in cordless powered screwdrivers, blenders, etc. Universal motors are also in wide use in industry, as they have a simple, reliable design.
Please refer to FIG.
1
.
FIG. 1
is an exploded view diagram of a prior art universal motor
10
. The universal motor
10
comprises a stator
20
, a rotor
30
and end brackets
50
and
70
. The rotor
30
has a shaft
32
onto which are mounted a commutator
34
and a rotor core
36
. The rotor core
36
is wound with copper wire to form many individual groups of windings
38
. Each of these windings
38
is electrically connected to a corresponding surface
35
on the commutator
34
. The ends of the shaft
32
are rotatably fixed in bushings
52
and
72
of the end brackets
50
and
70
, respectively. The end brackets
50
and
70
are firmly mounted onto the stator
20
. Hence, the rotor core
36
rotates within the stator
20
, and the commutator
34
rotates with the rotor core
36
. The stator
20
also has many windings
22
, which have leads
24
for delivering electrical power to the windings
22
. The end bracket
50
comprises brush holders
60
for elastically holding brushes
62
in contact with the commutator
34
. Electrical power is delivered by the brushes
62
to the commutator
34
, and hence to the appropriate windings on the rotor core
36
. Each brush holder
60
comprises a socket
61
into which a brush
62
is slidably disposed, a spring
64
for elastically pushing the brush
62
towards the commutator
34
, and an external contact
66
. The external contact
66
is electrically connected to the brush
62
, and is used to deliver electrical power to the brush
62
. Wires
68
lead off from the external contacts
66
to a power source (not shown).
When operating under a proper external load, the universal motor
10
will spin at a given RPM (revolutions per minute) with a given torque. Please refer to
FIG. 2
, which is a graph of torque versus RPM for the universal motor
10
. Generally speaking, the relationship of torque versus RPM for the universal motor
10
is a linear one. Hence, when the universal motor
10
has a light external load, its rotational speed will increase dramatically. This rapid rotation of the universal motor
10
is a significant source of unwanted noise.
SUMMARY OF THE INVENTION
It is therefore a primary objective of this invention to provide a universal motor that has an internal load to prevent excessive rotation when the motor has a light external load.
The present invention, briefly summarized, discloses an internally loaded universal motor that has a stator, a rotor, brushes and a loading device for generating an internal load on the universal motor. The shaft has a commutator, and a rotor core adjacent to the commutator. The rotor core is electrically connected to the commutator and rotates within the stator. The brushes deliver electrical power to the commutator. The loading device prevents excessive rotation of the rotor when the universal motor has a low external load.
It is an advantage of the present invention that the internal load insures that the universal motor always has at least a slight load when there is a very low, or no, external load. By always providing a load on the universal motor, the rotational speed of the motor is kept down, which helps to reduce the noise emanating from the motor.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.


REFERENCES:
patent: 2482840 (1949-09-01), Collins et al.
patent: 4185214 (1980-01-01), Gerber et al.
patent: 5497039 (1996-03-01), Blaettner
patent: 8-266008 (1996-10-01), None

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