CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. patent application Ser. No. 12/402,138, filed Mar. 11, 2009, the entire disclosure of which is hereby incorporated by reference.
FIELD OF INVENTION
The present invention relates generally to electric motors, and more particularly to systems and methods for cooling an electric motor.
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Electric motors generally include a stator and rotor mounted for rotation relative to the stator. An electromagnetic drive system including a plurality of magnets and/or electromagnets on the rotor and stator is used to drive rotation of the rotor relative to the stator. The rotor is connected to an output shaft so that as the drive system rotates the rotor the output shaft rotates. Operation of the motor, particularly under a load, generates heat. In some cases, one end of the motor (e.g., the driving end) reaches a higher temperature than the other due to this heat generation. The electromagnetic drive system also generates heat. Heat associated with operation of the motor can promote premature breakdown of lubricants (e.g., in the bearings), damage the electromagnetic drive system, and otherwise interfere with desired operation of the motor.
Some electric motors include passive cooling features, such as cooling fins and the like, to facilitate heat transfer out of the motor. Some electric motors include active cooling systems, such as a forced air ventilation systems. For example, a fan can be attached to the output shaft so rotation of the output shaft rotates the fan to generate air flow to cool the motor. Active cooling systems and passive cooling features such as cooling fins can be used in combination.
A motor's stator and rotor are commonly mounted in a housing. The housing provides a frame for anchoring the mounted rotor and stator and holding the stator fixed relative to the housing. The housing can also be a barrier preventing people (or other objects) from contacting parts of the motor inside the housing. In some cases the stator and rotor are totally enclosed by and sealed within the housing in order to limit the potential for dust and other debris to interact with the rotor or stator and thereby interfere with operation of the motor. A fan can be used to cool a totally enclosed motor (e.g., by directing air over the housing), in which case the motor may be referred to as Totally Enclosed Fan-Cooled (TEFC). The drive end of a TEFC motor is typically hotter than the opposite end because the fan is installed opposite the drive end. Sometimes, an internal air circuit is used to improve heat distribution in the motor by interchanging air from one end of the motor to the other. For example, in one conventional TEFC motor, a fan pumps air from one end of the housing to the other through passages in the rotor. Air is returned to the first end of the housing through passages in the stator and/or housing.
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In one embodiment, an electric motor includes a housing and a stator mounted in the housing. A rotor is mounted in the housing for rotational movement relative to the stator about a central axis. The rotor has first and second opposite ends and a plurality of fluid flow passages through the rotor between the first and second ends. An electro-magnetic drive system is adapted to drive rotation of the rotor relative to the stator. A fluid circulation system is adapted to produce fluid flow in the housing. The fluid flow includes fluid flow from the first end of the rotor to the second end of the rotor through at least one of the fluid flow passages and fluid flow from the second end of the rotor to the first end of the rotor through at least one other of the fluid flow passages.
Another aspect of the invention is a rotor assembly for an electric motor. The rotor assembly includes a rotor having a central axis and first and second opposite ends. The rotor defines at least in part a plurality of openings at each end and a plurality of fluid flow passages between the first and second ends. Each of said fluid flow passages extends between at least one of said openings at the first end and at least one of said openings at the second end. A hub is fixedly secured to the rotor adjacent one of the first and second ends. The hub includes an outward-facing surface having one or more outward-facing channels and an inward-facing surface defining at least in part one or more conduits through the hub. The conduits and outward-facing channels are aligned with and adjacent a respective one of said openings. The assembly has an impeller having a peripheral edge margin, an inlet radially inward from the peripheral edge margin, and an outlet radially outward from the inlet. The impeller is fixedly secured to at least one of the hub and the rotor and adapted to propel a fluid radially outward from the inlet to the outlet when the rotor assembly is rotated about said central axis. The impeller is positioned relative to the hub so the outward-facing channel of the hub is adjacent the impeller inlet and the inward-facing surface of the conduit substantially prevents fluid flow directly to the impeller inlet from the opening that is aligned with the conduit.
Another aspect of the invention is a method of cooling an electric motor having a housing, a stator in the housing, a rotor having first and second opposite ends mounted in the housing for rotational movement relative to the stator, and an electro-magnetic drive system adapted to drive rotation of the rotor relative to the stator. A fluid is pumped from the first end of the rotor through a first fluid flow passage through the rotor to the second end of the rotor. The fluid is pumped from the second end of the rotor through a second fluid flow passage in the rotor to the first end of the rotor.
Other objects and features will be in part apparent and in part pointed out hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
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FIG. 1 is a perspective illustrating one embodiment of a motor of the present invention in cross section;
FIG. 2 is an elevation of the motor in cross section;
FIG. 3 is a perspective of a rotor assembly of the motor with parts removed to illustrate bi-directional fluid flow through the rotor;
FIG. 4 is a perspective of the rotor assembly sectioned along planes including the lines 4-4 on FIG. 6 and illustrating one of multiple possible paths for fluid flow back and forth through the rotor;
FIG. 5 is a side elevation of the rotor assembly with an end plate removed to show blades of an impeller and fluid flow passages through the rotor;
FIG. 6 is a side elevation similar to FIG. 5, but including the end plate;
FIG. 7 is an exploded perspective of the rotor assembly;
FIG. 8 is an exploded perspective of components of a fluid circulation system of the rotor assembly;
FIG. 9 is a side elevation of a hub of the fluid circulation system; and
FIG. 10 is a perspective of another embodiment of a rotor assembly.
Corresponding reference characters indicate corresponding parts throughout the drawings.
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Referring to the drawings, first to FIGS. 1 and 2 in particular, one embodiment of an electric motor of the present invention, generally designated 101, is depicted as a totally enclosed fan-cooled (TEFC) electric motor. The motor 101 includes a housing 103, a stator 105 mounted in the housing, and a rotor assembly 109 mounted in the housing for rotation relative to the stator. In this embodiment, the rotor assembly 109 includes a rotor 111 and components of a fluid circulation system 115 for cooling at least some parts of the motor 101 as described in more detail below.
The motor 101 has an electromagnetic drive system 119 operable to drive rotation of the rotor 111. Generally, the electromagnetic drive system includes a plurality of magnets and/or electromagnets on or in the rotor 111 and stator 105 and arranged so electromagnetic forces can be produced by the drive system to drive rotation of the rotor relative to the stator. Various electromagnetic drive systems can be used within the scope of the invention. In the illustrated embodiment, for example, the rotor assembly 109 is received in a generally cylindrical cavity 135 in the stator 105 so the stator substantially surrounds the circumference of the generally cylindrical rotor assembly. The stator 105 includes a plurality of electromagnets 123 spaced circumferentially around the cavity 135. The rotor 111 includes a plurality of laminated disks 139 stacked together and collectively extending generally between first and second opposite axial ends 141, 143 of the rotor. Electromagnets 121 (FIG. 3) are spaced circumferentially around the rotor 111 at an outer cylindrical surface 131 of the rotor opposing the inner cylindrical cavity-defining surface 133 of the stator 105. The electromagnets 121, 123 are energized at appropriate times to interact in a way that drives rotation of the rotor 111. This electromagnetic drive system 119 is well-known in the art and will not be discussed in further detail herein.
The rotor 111 is connected to an output shaft 151 so the output shaft rotates as the drive system 119 drives the rotor. In the illustrated embodiment, the output shaft 151 is received in a central opening 153 defined by an inner generally cylindrical surface 155 of the rotor 111. The output shaft 151 is fixedly secured to the rotor 111. Various techniques and structures that are well-known in the art are suitable for fixedly securing the output shaft 151 to the rotor 111. Thus, the connection of the output shaft to the rotor will not be discussed in any further detail herein.
The housing 103 is suitably a conventional motor housing. The housing 103 can be constructed of plastic, metal, or any other suitable material. In the embodiment shown in the drawings, the stator 105 and rotor assembly 109 are totally enclosed by and sealed in the housing 103. Thus, the housing 103 limits the potential for ambient dust and debris outside the housing to interact with the rotor 111, stator 105, or any other parts of the motor 101 inside the housing. Accordingly, the motor 101 of the illustrated embodiment is resistant to the effects of dust and debris in the environment. However, it is possible that the housing only partially encloses or does not enclose the rotor assembly 109 and stator 105 therein within the scope of the invention. The stator 105 is secured to the housing 103 in a manner that limits rotation of the stator relative to the housing. The rotor assembly 109 is mounted in a manner that allows the rotor 111 to rotate relative to the stator 105 (and the housing 103) on a central axis 161 of the rotor. Various techniques and structures that are well known in the art can be used to mount the rotor assembly 109 and stator 105 in the housing 103. Thus, these techniques and structures will not be described in any further detail.