The present invention relates generally to a stator assembly and more specifically to a system for cooling the stator assembly.
Electric devices such as motors and generators having a stator secured within a housing of the motor/generator are well known. A rotor mounted on a shaft is coaxially positioned within the stator and is rotatable relative to the stator about the longitudinal axis of the shaft. The passage of current through the stator creates a magnetic field tending to rotate the rotor and shaft. It is also well known that it is necessary to maintain the stator within a predefined temperature range and to keep the stator free of contaminants in order to ensure optimal performance and reliability of the motor/generator.
Two primary changes can be made to the stator that will increase the torque density or the torque per unit weight of the motor/generator. One primary change is to increase the number of stator windings. The greater the slot fill factor, or percent of the motor/generator's volume that is occupied by windings, the greater the motor's torque will be. Increasing a motor/generator's slot fill factor will also increase the efficiency of the device. This method for improving torque, however, is physically limited by the shape and size of the stator. The other primary change employed to increase the motor's torque density involves increasing the amount of current that flows through the stator windings. Increases in current flowing through the stator windings cause increases in stator heating due to resistive or ohmic heating.
One application of the electric motor/generator described hereinabove is the hybrid electric vehicle. Hybrid electric vehicles offer potential improvements in fuel economy and reductions in tailpipe emissions. A hybrid electric vehicle incorporates a traditional internal combustion engine combined with an electromechanical hybrid transmission having one or more electric motor/generators arranged in series or parallel and gearing arrangements such as planetary gear sets. The electric motor/generators assist in propulsion or energy absorption (storage) depending on the mode of operation. As with any energy conversion device, the motor/generators are less than 100 percent efficient, and reject some energy as heat. Efficient removal of this waste heat is required in order to achieve a highly efficient operating mode of the hybrid electric vehicle.
A stator assembly is provided having a generally annular stator core including a plurality of radially inwardly extending stator teeth. A stator wire is wound around each of the plurality of stator teeth to form a plurality of stator coils. Each of the plurality of stator coils are spaced apart to at least partially define a plurality of generally axially extending cooling channels through which a cooling medium, such as oil, flows. Additionally, the plurality of stator teeth each include a respective flanged end portion each adapted to retain an axially extending strip member. The strip member at least partially defines the cooling channel. The cooling medium operates to cool the plurality of stator coils. In the preferred embodiment, at least a portion of the flow of the cooling medium within the cooling channel is turbulent.
A first and second end ring may be disposed on opposite axial ends of the stator assembly. The first end ring defines a first chamber operable to communicate the cooling medium to each of the plurality of cooling channels and the second end ring defines a second chamber operable to receive the cooling medium from each of the plurality of cooling channels. An oil transfer plate may be provided to communicate the cooling medium to at least one bore defined by the first end ring. The at least one bore is configured to communicate cooling medium to the first chamber at points radially coincident with each of the cooling channels and may be selectively configured to communicate cooling medium to the first chamber in one of a generally radial and a generally axial orientation or any orientation therebetween. Additionally, a motor assembly and an electromechanical hybrid transmission are disclosed with the stator assembly provided.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
Referring to the drawings wherein like reference numbers represent the same or similar components throughout the several figures, there is shown in
Referring to
With continued reference to
The epoxy resin 30 has good thermal conduction properties and therefore enhances the thermal conductivity between the stator coils 28 and the oil 40. Accordingly, the thermal conduction of the epoxy resin 30 facilitates the process of transferring heat from the stator coils 28 to cool the electric motor 10 (shown in
Referring now to
An oil transfer plate 54 is mounted within the transmission housing 44 and operates to communicate cooling fluid or oil 40, indicated by arrows 40, to the first end ring 46 of the stator 14. The oil 40 is introduced to the first chamber 50 through one of twelve holes or bores 56 defined by the first end ring 46. Each of the twelve bores 56 are preferably radially aligned with a respective cooling channel 38. The oil 40 is communicated to each of the respective bores 56 through an annular groove 58 defined by the oil transfer plate 54. The specific targeting of oil 40 within the first chamber 50 will be discussed in greater detail hereinbelow with reference to
Referring to
In sum, the invention herein described provides for an efficient and closed system for cooling the stator 14. By providing a closed cooling system, losses due to drag caused by oil impinging on the spinning rotor 18 are reduced or eliminated. Additionally, the stator 14 is cooled more uniformly, thereby eliminating potential for localized “hot spots” due to stagnant oil 40 that may reduce the peak power and reliability of the motor 10. Furthermore, present system for cooling the stator 14 may significantly increase the continuous power rating of the motor 10 thereby increasing the power density of the motor 10.
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of ZCL-3-32060-02 awarded by NREL/DOE.
Number | Name | Date | Kind |
---|---|---|---|
4415822 | Aiba | Nov 1983 | A |
6617717 | Okawa | Sep 2003 | B2 |
6762520 | Ehrhart et al. | Jul 2004 | B1 |
6933633 | Kaneko et al. | Aug 2005 | B2 |
20020047485 | Okawa | Apr 2002 | A1 |
20020074871 | Kikuchi et al. | Jun 2002 | A1 |
20030062780 | Kaneko et al. | Apr 2003 | A1 |
20030132673 | Zhou et al. | Jul 2003 | A1 |
20040100154 | Rahman et al. | May 2004 | A1 |
20050206251 | Foster | Sep 2005 | A1 |
20050236920 | Kusase et al. | Oct 2005 | A1 |
Number | Date | Country | |
---|---|---|---|
20070200441 A1 | Aug 2007 | US |