Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-03-26
2004-03-02
Le, Dang (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S256000
Reexamination Certificate
active
06700284
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fan assemblies and, more particularly, to a fan assembly including a switched reluctance fan motor with a segmented stator.
BACKGROUND OF THE INVENTION
Fan assemblies are commonly used for moving air and generally include a fan housing, a fan, and a fan motor. There are two main types of fan assemblies. Centrifugal fan assemblies blow air perpendicular to an axis of rotation of the fan and the fan motor. Axial fan assemblies blow air parallel to the axis of rotation of the fan and the fan motor. Axial and centrifugal fan assemblies are typically used in beating, ventilating and air conditioning (HVAC) systems in residential, commercial, and/or industrial applications.
The axial fan assembly typically includes a fan bracket that positions the fan motor relative to the housing. The fan is connected to a shaft of the fan motor. The fan draws air into an inlet of the housing and propels it in an axial direction through the outlet of the fan housing. Because the fan motor is located in the inlet, the size of the fan motor reduces the area of the inlet and the airflow that is provided by the axial fan.
The centrifugal fan assembly includes a fan bracket that mounts the fan in an inlet of the housing. A radial hub connects a shaft of the fan motor to a squirrel cage fan. The centrifugal fan directs the air in a direction that is perpendicular to the axis of the motor. As with the axial fan assembly, the fan motor is located in the inlet, which reduces the area of the inlet and the airflow that is provided by the centrifugal fan.
The fan motors of both types of fan assemblies typically include a rotor with plurality of rotor poles and a stator that includes a plurality of stator poles. The rotor is connected to and rotates with a shaft that is supported by motor bearings. The stationary stator is typically mounted on a radially inner surface of a housing of the fan motor. A drive circuit generates a set of stator currents in winding wire that is wound around the stator poles. The set of stator currents set up a magnetic field that causes the rotor, the shaft and the fan to rotate.
As the fan rotates, it draws air into the inlets that are located on opposite sides of the fan housing. The amount of airflow that can be delivered by the fan assembly is related to the effective area of the inlet and to the speed that the fan rotates. The effective area of the inlet is determined in part by the size of the fan motor. In other words, because the fan motor is mounted in the inlet of both types of fans, the fan motor adversely impacts airflow.
Reluctance motors are conventionally used as fan motors. Reluctance motors produce torque as a result of the rotor tending to rotate to maximize the inductance of an energized winding of the stator. As the energized winding is electrically rotated, the rotor also rotates in an attempt to maximize the inductance of the energized winding of the stator. In synchronous reluctance motors, the windings are energized at a controlled frequency. In switched reluctance motors, control circuitry and/or transducers are provided for detecting the angular position of the rotor. A drive circuit energizes the stator windings as a function of the sensed rotor position. The design and operation of switched reluctance fan motors is known in the art and is discussed in T. J. E. Miller, “Switched Reluctance Electric Motors and Their Control”, Magna Physics publishing and Clarendon Press, Oxford, 1993, which is hereby incorporated by reference.
In switched reluctance motors, there are two distinct approaches for detecting the angular rotor position. In a “sensed” approach, an external physical sensor senses the angular position of the rotor. For example, a rotor position tranducer (RPT) with a hall effect sensor or an optical sensor physically senses the angular position of the rotor. In a “sensorless” approach, electronics that are associated with the drive circuit derive the angular rotor position without an external physical sensor. Angular rotor position can be derived by measuring the back electromotive force (EMF) or inductance in unenergized windings, by introducing diagnostic pulses into energized andlor unenergized windings and sensing the resulting electrical response, or by sensing other electrical parameters and deriving rotor angular position.
The stator of conventional switched reluctance motors generally includes a solid stator core or a laminated stator with a plurality of circular stator plates. The stator plates are punched from a magnetically conducting material and that are stacked together. The solid core or the stack of stator plates define salient stator poles that project radially inward and inter-polar slots that are located between the adjacent stator poles. Winding wire is wound around the stator poles. Increasing the number of winding turns and the slot fill increases the torque density of the electric machine. The stator poles of switched reluctance motors typically have parallel sides that do not inherently hold the winding wire in position. Tangs on radially inner ends of the stator poles have been provided to help maintain the winding wire on the stator poles with some limited success. Tangs limit an area between radially inner ends of the stator poles, which may cause problems during the winding process.
In switched reluctance fan motors using the “sensed” approach, a rotor position transducer (“RPT”) is used to detect the angular position of the rotor with respect to the stator. The RPT provides an angular position signal to the drive circuit that energizes the windings of the switched reluctance fan motor. The RPT typically includes a sensor board with one or more sensors and a shutter that is coupled to and rotates with the shaft of the rotor. The shutter includes a plurality of shutter teeth that pass through optical sensors as the rotor rotates.
Because rotor position information is critical to proper operation of a switched reluctance motor, sophisticated alignment techniques are used to ensure that the sensor board of the RPT is properly positioned with respect to the housing and the stator. Misalignment of the sensor board is known to degrade the performance of the electric motor. Unfortunately, utilization of these complex alignment techniques increases the manufacturing costs for switched reluctance motors equipped with RPTs.
The RPTs also increase the overall size of the switched reluctance motor, which can adversely impact motor and product packaging requirements. The costs of the RPTs and their related manufacturing costs often place switched reluctance motors at a competitive disadvantage in applications that are suitable for open-loop induction electric motors that do not require RPTs.
Another drawback with RPTs involves field servicing of the switched reluctance motors. Specifically, wear elements, such as the bearings, located within the enclosed rotor housing may need to be repaired or replaced. To reach the wear elements, an end shield must be removed from the housing. Because alignment of the sensor board is critical, replacement of the end shield often requires the use of complex realignment techniques. When the service technician improperly performs the alignment techniques, the motor's performance is adversely impacted.
In an effort to eliminate the RPTs and to reduce manufacturing costs and misalignment problems, the “sensorless” approach for sensing rotor position is used. The various methods of performing the “sensorless” approach have drawbacks that are attributable, in part, to variations in the inductance and resistance of the stator windings due to assembly and tolerance variations.
Fan assemblies incorporating switched reluctance motors can be improved in several important areas. Specifically, it is desirable to improve the torque density of switched reluctance motors that are used in fan assemblies. By increasing the torque density of the fan motor, the size of the fan motor can be reduced for a given torque density and/or the size can be maintained with an
Randall Steven P.
Wallace Craig E.
Williams Donald J.
Harness & Dickey & Pierce P.L.C.
Le Dang
LandOfFree
Fan assembly including a segmented stator switched... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fan assembly including a segmented stator switched..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fan assembly including a segmented stator switched... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3292500