Patent Application
20070132330
The present invention relates generally to fan assemblies employing line-start permanent magnet (LSPM) motors, and LSPM motors that more readily achieve synchronous speeds, including when the motors are coupled to loads.
Various types of fan assemblies are known in the art for moving air including, for example, condenser fans for air conditioning systems, oscillating and non-oscillating fans for comfort or exhaust purposes, etc. Many of these fan assemblies have conventionally employed induction motors for driving rotation of fan blades to move air. More recently, permanent magnet motors and, in particular, brushless DC (BLDC) motors, have been incorporated into fan assemblies. BLDC motors are generally more efficient and less noisy than comparable induction motors. These BLDC motors require electronic variable frequency controllers to control energization of the BLDC motors.
As recognized by the present inventor, the controllers for BLDC motors are expensive and increase the overall cost of fan assemblies in which they are used. The present inventor has therefore recognized a need for an alternative to BLDC motors for use in fan assemblies.
In order to solve these and other needs in the art, the present inventor has designed fan assemblies which employ line-start permanent magnet (LSPM) motors. LSPM motors do not require expensive electronic controllers, and are generally more efficient than comparable induction motors. Additionally, the present inventor has designed LSPM motors that more readily achieve synchronous speed, including when the motor is coupled to a load. These improved LSPM motors can be used in a variety of applications including fan assemblies, fluid pumps, etc.
According to one aspect of the present invention, a fan assembly includes at least one fan blade for moving air and a line-start permanent magnet motor having a shaft. The fan blade is coupled to the shaft of the line-start permanent magnet motor such that rotation of the shaft causes rotation of the fan blade for moving air.
According to another aspect of the present invention, a line-start permanent magnet (LSPM) motor includes a shaft and a squirrel cage rotor having a plurality of embedded magnets. The LSPM motor is configured to permit limited rotation of the squirrel cage rotor relative to the shaft as a speed of the motor approaches a synchronous speed.
According to yet another aspect of the invention, a line-start permanent magnet (LSPM) motor includes a shaft, a rotor assembly including a squirrel cage rotor having a plurality of embedded permanent magnets, and a coupling finger extending from the shaft and positioned within a notch defined by the rotor assembly to allow limited rotation of the rotor assembly relative to the shaft as the LSPM motor approaches a synchronous speed.
Further aspects of the present invention will be in part apparent and in part pointed out below. It should be understood that various aspects of the invention may be implemented individually or in combination with one another. It should also be understood that the detailed description and drawings, while indicating certain exemplary embodiments of the invention, are intended for purposes of illustration only and should not be construed as limiting the scope of the invention.
Like reference symbols indicate like elements or features throughout the drawings.
A fan assembly according to a first embodiment of the present invention is shown in
The fan assembly 100 of
In some preferred embodiments, the LSPM motor 104 is an eight pole motor. However, LSPM motors have more or less than eight poles can also be employed. Further, the LSPM motor 104 can employ a single-phase or multi-phase (e.g., 3-phase) design.
In certain applications and under certain conditions, an LSPM motor can have difficulty achieving synchronous speed, particularly when a load is coupled to the motor shaft during starting. To address this issue, an LSPM motor according to another embodiment of the present invention includes a shaft and a squirrel cage rotor having several embedded permanent magnets. The LSPM motor is configured to permit limited rotation of the squirrel cage rotor relative to the shaft as a speed of the motor approaches a synchronous speed. As further explained below, permitting limited rotation of the rotor relative to the shaft assists the LSPM motor in achieving synchronization, including when a load is coupled to the shaft. Two specific constructions of such an LSPM motor will now be described with reference to
As shown in
Rather than fixedly coupling the rotor assembly 204 to the shaft 206 in a conventional manner, a slippery interface is provided between the rotor assembly 204 and the shaft 206 so as to permit the rotor to rotate freely relative to the shaft 206, except as limited by interaction between the notch 212 and the coupling finger 214.
When the LSPM motor 200 is energized with the coupling finger 214 generally centered within the notch 212, the rotor assembly 204 is essentially starting under a no-load condition. Once the rotor assembly 204 has rotated a limited distance such that one side of the notch 212 engages the finger 214, the motor may have already established its synchronous torque. In that event, the motor has achieved its synchronous torque which may pull the shaft 206, and any load coupled to the shaft 206, up to synchronous speed within a short time period. If the synchronous torque is insufficient to pull the shaft 206 and load up to synchronous speed quickly, the motor will run at an asynchronous speed that is lower than the synchronous speed. In this case, the torque provided by the permanent magnets 210a-h is pulsating. This pulsating torque causes the rotor assembly 204 to vibrate back and forth on the shaft 206, typically beginning at about 80% of the synchronous speed, to the extent permitted by the notch 212 and the coupling finger 214. This back and forth vibration will last only a short period of time, until the rotor assembly 204 is pulled up to synchronous speed. Once the rotor assembly 204 is synchronized, the synchronous torque is established. Shortly thereafter, one side of the notch 212 will engage the coupling finger 214 and the synchronous torque will pull the shaft 206 and load up to synchronous speed.
In other words, because the rotor assembly 204 is permitted to rotate a limited distance relative to the shaft 206, the rotor assembly 204 can be synchronized during a short essentially no-load condition, or synchronized shortly after vibrating back and forth about the shaft 206 in response to the pulsating asynchronous torque. Therefore, as compared to a rotor fixedly coupled to the shaft 206, the LSPM motor 200 of this embodiment can be synchronized more readily. Similarly, if the LSPM motor 200 loses synchronization for some reason, the limited ability of the rotor to rotate relative to the shaft 206 will assist the motor in pulling the rotor assembly 204, the shaft 206 and the load back to synchronization.
As just one example, a single-phase LSPM motor having a rotor fixedly coupled to the shaft was unable to synchronize at 250 volts, while a comparable LSPM motor constructed according to the present embodiment (and having the same load coupled to the shaft) achieved synchronous speed at only 187 volts.
In the embodiment of
Referring again to
The LSPM motor 200 described above with reference to
As should be apparent, the LSPM motor 200 described above with reference to
Those skilled in the art will recognize that various changes can be made to the exemplary embodiments and implementations described above without departing from the scope of the present invention. Accordingly, all matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense.
