Patent Application
20200144882
The is disclosure relates to electric machines, and more specifically to electric machines that include a compressible layer between a stator core and a housing to facilitate an interference fit between the housing and the stator core.
Vehicles such as battery-electric vehicles and hybrid-electric vehicles contain a traction-battery assembly to act as an energy source for the vehicle. The traction battery may include components and systems to assist in managing vehicle performance and operations. The traction battery may also include high-voltage components, and an air or liquid thermal-management system to control the temperature of the battery. The traction battery is electrically connected to an electric machine that provides torque to driven wheels. Electric machines typically include a stator and a rotor that cooperate to convert electrical energy into mechanical motion or vice versa.
According to one embodiment, an electric machine includes a stator core, a cylindrical housing circumscribing the core, and an annular compressible layer. The annular compressible layer is received on the core and has an outer surface disposed against the housing. A diameter of the outer surface is larger than a diameter of an inner surface of the core to form an interference fit between the housing and the compressible layer.
According to another embodiment, an electric machine includes a stator core and a cylindrical housing circumscribing the core. The housing defines an inner circumferential surface. An annular sleeve is interposed between the core and the housing. The sleeve is received on the core and has an outer circumferential surface disposed against the inner surface. A diameter of the outer surface is larger than a diameter of the inner surface to form an interference fit between the housing and the sleeve.
According to yet another embodiment, an electric machine includes a stator core, a cylindrical housing circumscribing the core, and an annular sleeve interposed between the core and the housing. The sleeve includes arcuate segments circumferentially arranged around the stator core in a spaced relationship. An outer diameter of the sleeve is larger than an inner diameter of the housing to form an interference fit between the housing and the sleeve.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
Referring to
The electric machine 20 may be powered by a traction battery of the vehicle. The traction battery may provide a high-voltage direct current (DC) output from one or more battery-cell arrays, sometimes referred to as battery-cell stacks, within the traction battery. The battery-cell arrays may include one or more battery cells that convert stored chemical energy to electrical energy. The cells may include a housing, a positive electrode (cathode), and a negative electrode (anode). An electrolyte allows ions to move between the anode and cathode during discharge, and then return during recharge. Terminals allow current to flow out of the cells for use by the vehicle.
The traction battery may be electrically connected to one or more power electronics modules. The power electronics modules may be electrically connected to the electric machines 20 and may provide the ability to bi-directionally transfer electrical energy between the traction battery and the electric machine 20. For example, a typical traction battery may provide a DC voltage while the electric machine 20 may require a three-phase (AC) voltage. The power electronics module may include an inverter that converts the DC voltage to a three-phase AC voltage as required by the electric machine 20. In a regenerative mode, the power electronics module may convert the three-phase AC voltage from the electric machine 20 acting as a generator to the DC voltage required by the traction battery. While the electric machine 20 is described as a traction motor for a vehicle, this disclosure is not limited to any particular application. The electric machine 20, for example, may also be used in industrial equipment, electrical generation, and the like.
Referring to
The core 26 defines a plurality of teeth 35 extending radially inward. Adjacent teeth 35 cooperate to define slots 36 circumferentially arranged around the core 26. The slots 36 may be equally spaced around the circumference and extend axially from a first end 38 of the core 26 to a second end 39. A plurality of coil windings 40 are wrapped around the stator core 26 and are disposed within the slots 36. Portions of the wires generally extend in an axial direction through the slots 36. At the stator core ends 38, 39, the windings 40 bend to extend circumferentially around the top or bottom of the stator core 26 forming the end windings 42.
The housing 21 may be secured to the stator core 26 by an interference fit (press fit). The interference fit may be supplemented by fasteners or other joining means. An interference fit can be formed by inserting an inner component into an outer component having an inner diameter that is smaller than an outer diameter of the inner component. The tightness of an interference fit is based on the amount of interference (size difference between the inner and outer diameters). The electric machine 20 may interference fit the housing 21 to the stator 22. Interference fitting the housing directly onto the core, however, is problematic when the housing and the stator core are formed of different materials that have different coefficients of thermal expansion (CTE).
The stator core 26 is typically formed from steel whereas the housing 21 is typically formed of a lighter weight material such as aluminum. The CTE of aluminum is roughly double that of steel. This CTE difference causes the amount of interference between the steel core and the aluminum housing to change based on temperature. At high temperatures, the amount of interference is reduced due to the expansion of the housing relative to the core, and, at low temperatures, the amount of interference is increased due to the contraction of the aluminum housing relative the steel core.
Testing and simulation by Applicant has determined that a loss of interference can occur at the upper temperature range of a traction motor leading to release of the stator core from the housing, and excessive interference can occur at the lower temperature range of the traction motor leading to stator or housing damage. For example, the aluminum housing may crack due to excessive interference at lower temperatures.
This disclosure proposes to add a compressible layer 48 between the stator core 26 and the housing 21 so that a proper interference fit is maintained over the operating temperature range of the electric machine 20. The compressible layer 48 allows an initially tighter interference fit at room temperature so that proper interference is maintained at the upper temperatures of the operating range, and is compressible to prevent damage to the housing 21 or the stator core 26 at lower temperatures of the operating range. The compressible layer 48 may be formed of a material having a lower elastic modulus than the housing and/or the stator core. The compressible layer may be formed of a material having an elastic modulus between 0.1 to 6.5 gigapascals (GPA). Example materials include magnesium or polymers. The materials chosen for the compressible layer 48 may depend upon the materials of the stator core 26 and the housing 21. One suitable combination is to use a magnesium or polymer compressible layer with a steel core and an aluminum housing.
The compressible layer 48 may be annular to encircle the stator core 26. The compressible layer 48 may be formed of a single component or may include multiple pieces that are circumferentially arranged around the outer surface 29 of the stator core. The compressible layer 48 includes an inner circumferential surface 49 having an inner diameter 50 disposed on the outer diameter 29 of the stator core and an outer circumferential surface 52 that engages with an inner surface 44 of the housing 21. The outer surface 52 has an outer diameter that is larger than the inner diameter of surface 44 to form an interference fit between the housing 21 and the compressible layer 48. In one embodiment, the compressible layer 48 is a sleeve. The sleeve may be a single piece as shown in
Referring to
In the illustrated embodiment, the sleeve 60 has smooth inner and outer surfaces, however, in other embodiments, the sleeve 60 may include connection features for interconnecting with the housing or the stator core. For example, one of the core and the sleeve includes a projection and the other of the core and the sleeve includes a receptacle that receives the projection therein. In some embodiments, multiple projections and receptacles may be used to secure the sleeve and core. The connection features aid in retaining the sleeve to the core during installation of the housing as well as retain the sleeve in place during the contraction and expansion of the housing and the core due to temperature changes. In some embodiments, the connection features may be between the housing and the sleeve rather than between the sleeve and the core.
Referring to
In the illustrated embodiment, the connection features are teeth 100 defined on the outer surface 98 of the stator core 84 and teeth 102 defined on the inner surfaces 90 of the segments 88. The teeth 100 and 102 mesh with each other to secure the segments 88 onto the stator core 84. In other embodiments, the meshing teeth may be replaced with projections and receptacles. While illustrated in conjunction with connection features, the multi-segment sleeve 82 may be used in electric machines that do not include connection features.
Referring to
A resting outer diameter 119 of the corrugated spring 112 (measured between diametrically opposing outer contacts 118) is larger than the inner diameter of the housing 120 so that the corrugated spring 112 is compressed when installed. The compression of the spring 112 creates sufficient friction between the inner and outer contacts 116, 118 and the stator core 114 and the housing 120, respectively, to secure the housing 120 to the stator core 114 similar to the interference fit of the above-described embodiments. The spring 112 is configured to expand to maintain frictional engagement when the housing expands relative to the stator core 114 at higher temperatures, and is configured to contract to prevent damage when the housing 120 contracts relative to the stator core 114 at lower temperatures.
The spring 112 may be tubular to axially extend along a substantial portion of the stator core 114. In some embodiments, the corrugated spring 112 may be as long as the stator core 114. Alternatively, multiple, shorter springs may be used.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.
