Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-11-19
2003-03-04
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C336S107000
Reexamination Certificate
active
06528913
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention pertains to an apparatus employed in grounding the stator and end plates of a dynamoelectric device. In particular, the invention pertains to a terminal block constructed of an electrically insulating material and a ground connector constructed of a electrically conductive material that is installed in the terminal block, where the ground connector has a plug projecting from the terminal block at one end and a tab with a fastener hole at its opposite end. Attachment of the terminal block to the stator of the device simultaneously positions the tab of the ground connector with the tab hole aligned with fastener holes of the stator and at least one end plate of the device where assembling the stator and end plate together by a threaded fastener also secures the tab of the ground connector between the stator and end plate.
(2) Description of the Related Art
A dynamoelectric device is often constructed with a ground system that directs electrical energy away from the device in the case of an electric malfunction in the device that could shock a person touching the device or its supporting equipment. In a typical electrical device the ground is attached to an external frame or housing of the device. This insures that in the event of a power supply wire making contact directly or indirectly with the frame or housing of the device that is accessible to a person using the device, the electric energy can be directed away from the housing of the device. By directing the electric energy to a ground a “short circuit” condition is created where the electric energy is directed away from the device along the path of least resistance, thus preventing any person contacting the device from receiving an electrical shock. The high current flow through the ground in situations such as this will often cause self-actuating protective switches in the device to open the circuit and stop electrical current flow to the device. This protects both the device from a high current surge and also protects people who may otherwise contact the malfunctioning device and receive a shock.
In electrical devices such as electric motors installed in household appliances, the external frame of the device is required to be provided with a ground connection to protect persons using the appliance if an electrical malfunction occurs. The ground connection is often directed to a water pipe of the home or the ground pole in a three prong plug electrical socket. Because the electric motor is typically mounted directly to the metallic structure of the appliance, the ground connection is directly to the frame of the motor. In the event of an electric malfunction in the motor, the electric current is directed to the grounding system and people using the appliance are protected from receiving an electrical shock. Grounding of electrical devices in this manner is common. For the purpose of explaining the subject matter of the invention, the example of a small electric motor is used. However, it should be understood that the example is illustrative only and that the grounding system of the invention may be employed in many different types of electrical devices and is not intended to be limited to use with only electric motors.
FIG. 1
is a side elevation view of a typical electric motor
10
. The motor is basically comprised of a stator assembly
12
, a pair of end plates
14
,
16
secured to opposite end surfaces of the stator assembly
12
, and a rotor (not shown) mounted on a rotor shaft
18
which in turn is mounted for rotation in a pair of bearings (not shown) mounted in the two end plates
14
,
16
. A terminal block
20
constructed of an insulating material is mounted on the stator assembly
12
. The terminal block
20
has a series of electrical plugs
22
projecting from the block that are connected to the wiring of the stator assembly
12
and provide external connections to the circuitry of the appliance or other device with which the motor is used. The motor also comprises a ground connector
24
that is easily accessible for connection to a conductor used to connect the motor to an external ground, such as the earlier example of the water pipe. The ground connector
24
is secured and grounded to both the stator assembly
12
and one of the two end plates
14
of the motor by the bolt
26
and nut
28
threaded fasteners that secure the end plates
14
,
16
to the opposite end surfaces of the stator assembly
12
.
FIG. 2
shows the stator
30
removed from the stator assembly
12
of the motor shown in FIG.
1
. The stator
30
in this example is comprised of a stack of laminate plates that each have the same, generally square peripheral edge
32
. The peripheral edges
32
of each of the plates in the stator stack forms a portion of the motor frame or exterior surface of the motor. The stator has a generally cylindrical center bore
34
surrounded by a plurality of stator poles
36
. Four fastener holes
38
pass entirely through the stator stack adjacent the four corners of the stator. The stator fastener holes
38
are positioned on the stator so that they will align with four fastener holes
40
in each of the end plates
14
,
16
when the end plates are positioned on the opposite end surfaces of the stator. The stator also has two pairs of terminal block mounting post holes
42
adjacent opposite ends of the stator. The mounting post holes
42
are provided in pairs on opposite sides of the stator to enable a single terminal block to be mounted on either side of the stator or a pair of terminal blocks mounted on the opposite sides of the stator if needed. The mounting post holes
42
are dimensioned to receive mounting posts
44
of the terminal block
20
and to hold the terminal block securely against one of the end surfaces of the stator adjacent the post holes. Typically, the ground connector
24
is also mounted on the end surface of the stator adjacent the terminal block
20
. This provides all of the electrical connections to the motor on one side of the motor. As seen in
FIG. 2
, the ground connector
24
has a plug
46
at one end that projects from a grounding tab
48
. The tab
48
has a hole
50
therethrough that is dimensioned to be the same size as the stator fastener holes
38
and the end plate fastener holes
40
.
Generally describing the assembly of a motor such as that shown in FIG.
1
and the attachment of the prior art ground connector
24
to the motor, after the stator poles
36
are wound, the winding connections from the stator poles and other circuitry of the motor are made to the conductor plugs
22
of the terminal block
20
. The terminal block
20
is then mounted on the end surface of the stator assembly
12
by inserting its posts
44
into the mounting post holes
42
of the stator. The rotor assembly is then inserted into the stator bore. The rotor is supported in the stator bore by inserting the opposite ends of the rotor shaft
18
into bearing assemblies mounted into the two end plates
14
,
16
as the end plates are assembled over the opposite end surfaces of the stator assembly
12
.
In assembling the end plates
14
,
16
to the opposite end surfaces of the stator assembly
12
, the stator fastener holes
38
are aligned with end plate fastener holes
40
provided in each of the end plates. The end plates
14
,
16
are secured to the opposite end surfaces of the stator assembly
12
by bolts
26
inserted through the aligned fastener holes of the stator and the end plates and by the nuts
28
screw threaded on the projecting ends of the bolts. However, before the bolts
26
are inserted through the aligned holes of the end plates and the stator assembly, the ground connector
24
is first positioned between the stator assembly and one of the end plates in its position shown in FIG.
1
. The ground connector tab
48
is inserted between the stator
12
and the one end plate
14
with its tab hole
50
aligned with a fastener hole
38
of the stator and a fastener hole
40
of the end plat
Emerson Electric Co.
Nguyen Tran
Perez Guillermo
Thompson & Coburn LLP
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