Patent Application
20120280580
1. Field of the Invention
The present invention relates to electric motors and more particularly to electric motors having cooling apparatus.
2. Background Art
Consumer product satisfaction is driven at a particular product price point by product safety, product reliability, and product longevity. This is particularly so in the field of consumer paper shredders, where a shredder can endure excessive or rough wear despite the non-industrial focus of the shredder product specifications. Such excessive or rough wear can, over time, degrade the reliability and longevity of the shredder product causing the consumer to become dissatisfied with the product. In some cases, repeated stresses on the moving parts of the shredder may cause part failure, leading to the expense of product repair or replacement, a further decrease in satisfaction, or even loss of goodwill for the respective consumer in the paper shredder brand. Even marginally stressful moments of operation may in the aggregate take their toll on the operating machinery of the shredder.
One shredder part which can be vulnerable to mechanical and thermal stresses is the shredder electric motor, which can arise from, for example, frequent starting, overloading, jamming, and continuous, beyond-rating use. Over time, the cumulative stresses faced by a shredder motor may lead to premature failure or poor performance. A common thread with these stressors is the heating effects of motor current (I2R losses). Many sophisticated electronic controllers have been devised to reduce the effects of I2R losses upon motors. Complex mechanical cooling systems have been advanced for large motors, as well. However, in the sphere of fractional-horsepower electric motors, as used in light- to medium-duty paper shredders, sophisticated electronic controllers and complex mechanical coolers can add prohibitive premiums to the motor cost, and to the cost to consumers, reducing a manufacturer's market share. An inexpensive cooling apparatus for fractional-horsepower motors is needed.
The foregoing need is met by cooling apparatus and methods for a fractional-horsepower motor. In one embodiment, the motor cooling apparatus includes a heat shoe, a heat diffuser, and a heat pipe coupled therebetween. The heat shoe can be configured to at least partially cover a portion of, and to receive motor thermal energy from, the motor. The heat pipe can be coupled to the heat shoe, and can be configured to convey the motor thermal energy from the heat shoe. The heat diffuser can be coupled to receive motor thermal energy from the heat pipe. It also can be configured to diffuse at least a portion of the motor thermal energy into an ambient atmosphere apart from the motor. In an embodiment, a thermal sensor can be coupled to the motor and configured to sense a motor thermal condition; and a fan can be coupled to the thermal sensor through a controller. The controller is configured to control the speed of the fan relative to the motor thermal condition sensed by the thermal sensor. In another embodiment, the controller is configured to control the speed of the fan relative to motor thermal condition or a motor condition other than the motor thermal condition. In another embodiment, the cooling apparatus is a heat shoe thermally integrated with the heat diffuser.
The method can include conductively receiving motor thermal energy from portion of a fractional-horsepower motor by a heat shoe; conductively receiving motor thermal energy by a heat pipe coupled to the heat shoe; conveying motor thermal energy by the heat pipe to a heat diffuser; receiving motor thermal energy by the heat diffuser from the heat pipe; and releasing the motor thermal energy from the heat diffuser causing the motor to be cooled.
Embodiments of the present invention disclosed herein are illustrated by way of example, and are not limited by the accompanying figures, in which like references indicate similar elements, and in which:
Skilled artisans can appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention. In the figures, like numbers correspond to like elements.
Embodiments of the present invention can assist in reducing overheating in a motor. In particular, selected embodiments can be used with a fractional horsepower (FHP) motor, as may be used without limitation, to power a home or office paper shredder. Some embodiments are passive devices, while some are active.
Heat shoe 110 can be a device typically formed from conductive material in a manner that contacts at least a portion of a FHP motor casing (not shown). In some embodiments, a heat shoe can be formed to contactingly surround an outer casing of an FHP. A thermally conductive adhesive may be interposed between the FHP casing and heat shoe 110 to improve thermal conduction from the motor into the heat shoe. The heat shoe 110 can be thermally coupled to an end of at least one heat pipe 120a, 120b.
Additional cooling may be achieved on the way to, and at, the cool end, by thermally coupling the thermoconductor 120a, 120b to a radiative heat diffuser 130, or heat sink, such as pin diffuser 130. A pin diffuser may be formed from numerous slim, densely populated radiative fins, often formed on a solid, radiative, heat-spreading metal base. The plural fins assist with radiative, convective, and conductive cooling by the diffuser. In selected embodiments, thermoconductor 120a, 120b may be heat pipes 120a, 120b. A heat pipe, such as heat pipes 120a, 120b, is a passive, highly conductive two-phase heat transfer device, which absorbs heat on one end (“heated end”) and releases heat on the other end (“cooled end”). In this case, the “heated end” is thermally coupled to the FHP motor.
A heat pipe can be characterized by a vacuum tight, sealed containment shell or vessel, a working fluid or coolant, and a capillary wick structure in contact with the containment shell. In general, a coolant in the heat pipe changes from a liquid phase in the cool end to a vapor phase in the heated end. The coolant vapor is drawn back through the wick via capillary action to the cool end, dissipating heat along the way. At the cool end, the coolant returns to a liquid phase, returning again to the heated end to continue the cycle. Heat pipes also are well-known in the arts, such as, without limitation, an HP-1 heat pipe from Thermacore Inc., Lancaster, Pa., USA. In some embodiments plural heat pipes thermally couple the heat shoe and the heat diffuser, further enhancing heat conduction.
Thus, by coupling a heat pipe 120a, 120b to a heat diffuser 130, a substantial amount of heat may be drawn away from the heated end of the heat tube, as may be the case when thermally coupled to a heat shoe 110 fitted around, and thermally linked to, an FHP motor (Not shown). Materials for a heat shoe and a heat diffuser are ubiquitous and are well-known in the thermal engineering arts, and typically include a metal such as aluminum, copper, or an Al—Cu alloy, although other thermally-conductive metals may be used. A thermally-conductive, electrically insulative thermal interface material, such as mica or one of well-known ceramic-based materials, may be interposed in contacts between the heat shoe and the motor.
The fan 250 can operate continuously or, as depicted in
Although the controller 340 and fan 350 can be responsive to a thermal condition of the motor element 325, the controller 340 also may increase fan 350 speed in response to a sensed change 390 in a mechanical condition, such as decreased motor speed or an increased motor torque or an ambient condition. FIG. 3A illustrates active cooling with separate heat shoe and heat diffuser linked with heat pipes. On the other hand,
Fan unit 450 may be coupled to a controller, such as controller 340 in
The embodiments of the present invention disclosed herein are intended to be illustrative only, and are not intended to limit the scope of the invention. It should be understood by those skilled in the art that various modifications and adaptations of the prevent invention as well as alternative embodiments of the prevent invention may be contemplated or foreseeable. It is to be understood that the present invention is not limited to the sole embodiments described above, but encompasses any and all embodiments within the scope of the following claims.
