Patent Application
20100102647
The present disclosure generally relates to a stator case for an electrical machine, and more specifically to a cooling stator case with a continuous spiral groove.
Electric machines such as, for example, motors and generators may be used to generate mechanical power in response to an electrical input or to generate electrical power in response to a mechanical input. Magnetic, resistive, and mechanical losses within the motors and generators during mechanical and electrical power generation cause a build up of heat, which may be dissipated to avoid malfunction and/or failure of the device. One of the limitations on the power output of the electric generators may be the capacity to dissipate this heat.
Cooling stator cases or jackets provide an excellent means for cooling electric motors and generators, such as brushless permanent magnet motors operating at high speeds and driven by fuel-powered engines to generate electrical power. Electric motors and generators generate considerable heat and require an efficient cooling system. Motors and generators are often equipped with a means for cooling, formed of a cooling jacket provided with grooves or passages built into the motor/generator housing. Circulating oil or water, or even air through the grooves or passages provides cooling to the motors and generators.
It is common practice in machining applications to machine spiral grooves into a metal part. Machined spiral grooves into a housing have been shown to work well to remove the necessary heat from these components, however machined spiral grooves are expensive to cut in a production environment.
In a patent application to Burjes et al. (2007/0268464 A1), a method of making a motor/generator cooling jacket is disclosed. A hollow cylindrical housing is cast with an outer peripheral surface and an annular axially facing end surface, a plurality of grooves formed in the outer peripheral surface and a radial lip at one end. The Burjes et al. patent application also teaches inlet and outlet ports drilled through the end surface to communicate with the grooves, and sealing recesses and o-ring seals integrated for sealing. However, the prior art process does not provide mechanisms to protect from pressure drop across the channels.
Further, the Burjes invention teaches a non-continuous flow path, which may require the cooling fluid to make 180-degree turns and flow in opposite directions. This non-continuous circulation path may further contribute to inconsistent and inefficient means for equally cooling the stator, and may lead to a less efficient system potentially causing a higher than desired pressure drop across the entire path of the fluid.
The present disclosure is directed to overcoming one or more of the issues set forth above.
The present disclosure, in one form, provides an electric motor/generator low hydraulic resistance cooling mechanism including a hollow cooling stator case having an inner and outer coaxial surface. The inner surface defines a generally cylindric cavity for receiving a stator in heat transference contact with the inner surface. The outer surface has integrated spiral groove cooling passages that have filleted rectangular cross sections.
Other novel features of the present disclosure will be in part apparent and in part pointed out hereinafter.
The present disclosure provides an apparatus for cooling an electric drive motor or generator that overcomes the limitations of the prior art. In the detailed description that follows, like numerals are used to denote like elements appearing in one or more of the figures.
The cooling stator case 20 of the present disclosure has inner 32 and outer 34 coaxial surfaces. The inner surface 32 defines a generally cylindric cavity for receiving a stator, for example.
The cooling stator case 20 of the present disclosure may be fabricated through a casting process or through machining. Within the context of this disclosure, casting should be understood to mean any manufacturing process by which a molten material such as metal or plastic is introduced into a mold, allowed to solidify within the mold, and then ejected or broken out to make a fabricated part. Casting is often used for making parts of complex shape that would be difficult or uneconomical to make by other methods, such as cutting from solid material. Types of casting known in the art include sand casting, die casting, permanent mold casting, centrifugal casting, continuous casting, and the like.
Turning now to
The spiral groove section 40 of the present disclosure circulates the fluid in a continuous direction and does not require the fluid to make any 180 degree turns (i.e., the fluid is not required to reverse travel flow direction and go back toward an opposite direction), which may keep pressure drop to a minimum. This continuous circulation of cooling fluid may further help to provide a consistent and efficient means of equally cooling the stator (as no interruptions to the spiral groove section 40 means equal cooling all around).
The entire spiral groove section 40 is designed to optimize the cooling performance of the coolant. In other words, the individual cooling passages or channels 42 area and length can vary and be designed to allow the coolant to extract the ideal amount of heat from the hot stator. A longer cooling groove path, will allow the coolant more time in contact with the cooling stator case. A shorter path shorter means the coolant will spend less time against the cooling stator case. Similarly, you can adjust the coolant fluid velocity by adjusting the area of the cast cooling passage 42. These features allow correctly designed fluid dynamics for the particular cooling system. To lessen pressure head losses and provide low hydraulic resistance, the cooling channels include several novel features. Head losses are known to include frictional losses, contraction, expansion, and directional change losses. Relief radii (R) and variations in pitch may play significant roles in reducing losses associated with spiral cooling.
Turning now to
The cooling passages 42 may have at least four and one half helical turns, following the geometry of the helical core 50. The channels have a pitch and overall axial length. Further, the pitch may be variable. The helical core 50 includes at least two continuously interconnecting outer tabs 52, which reside outside of the casting and bridge the core prints. These tabs 52 will locate the helical core 50 and also provide ridigity to the core structure.
The cooling passages 42 not only allow the fluid to circulate without interruptions, but also help in reducing costs. It is very expensive to machine a cooling stator case 20 with groove sections, and the time to machine is extremely long. Casting the passages 42 into the part 20 eliminates the large amount of machining and associated time required, and still provides the advantageous continuous path. Following casting, the cooling stator case outer surface 34 may be machined into a smooth uniform diameter.
The stator case 20 is sealed with the outer case (not shown) to prevent the cooling fluid from escaping. The outer case may include a flange on one of its two opposing ends for bolting, at least inlet port, an outlet port, and a port for venting. The cooling stator case 20 may slip into the outer case until the last millimeters of travel of the stator case. Next, the stator case 20 may pilot into the outer case for a slight press fit at the opposing ends of the case. The cooling groove area 40 maintains a clearance fit (or slip fit tolerance) relative to the outer case, and the pilots are slight presses as would be understood in the art. Bolts may keep the outer case connected to the cooling stator case 20, and the bolts may provide for annular alignment and allow one way bolting. Optionally, the cooling jacket or case 20 may be cast into the outer case that the electric motor or generator stator presses into. The outer case may be comprised of a material with a relatively high thermal conductivity such as a metal. Advantageously, a metal outer case allows for effective heat transference.
Casting the groove as the part is designed fits most cast processes that would already be used to make traditional prior art stator cooling jackets without the cast grooves. Therefore, no exotic tooling need be designed or created to cast the parts disclosed herein, and a larger pool of suppliers that may not have special machines that can turn a large spiral groove may be utilized.
The electric motor/generator cooling mechanism described herein can be used for cooling jackets for the motors and generators of any applicable system requiring a closed cooling environment, and where air cooling is not sufficient. In use, coolant flows through the one or more inlet ports of the outer case and is directed along the path previously described before exiting the stator case through the outlet port. Optionally, in one embodiment, there may be two inlets located at the opposing ends of the outer case. The inlet and outlet ports may be within close proximity of each other. The cooling fluid may simultaneously flow from one of the inlet ports in a first radial direction and from the other inlet port in a second radial direction to the center of the cooling groove area 40 and exit out of the outlet port. The outlet port may be located between two of the inlet ports.
The vent for purging air may be located in the middle of the cooling grooves area 40, 180 degrees away from the outlet port. As the coolant flows along these paths, it contacts the stator housing or cooling stator case 20 and the outer case and removes heat, thereby cooling the stator. The removal of heat is particularily efficient due to the aforementioned cooling passages 42.
While the present disclosure has been described in conjunction with a specific embodiment of an electric machine, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description.
For example, the cooling jacket could be modified to have different numbers and arrangement of grooves, fins and walls to provide for different flow paths through the jacket, or could have more or less parallel passages than the number shown. Further, the inlet and outlet points could be varied to vary the number of flow paths. The particular arrangement used for a given application will depend on size, heat transfer requirements, and possible other factors. Accordingly, the disclosure is intended to embrace all such alternative, modifications and variations, which fall within the spirit and scope of the appended claims.
